Histology - Exam 3

Question 1

Describe ameloblasts.

Answer 1

Ameloblasts

• Form enamel which covers only the tooth crown.
• Enamel is the hardest substance in the body.
• Enamel is 96% inorganic salts, about 90% of which is calcium phosphate in the form of apatite crystals and 4% organic matter and water.
• Enamel is laid down in prisms.
• Each prism is formed by one ameloblast.
• Secreting apical domains = Tomes’ processes.
• Increment lines of Retzius are periods of rhythmic growth.

Question 2

Describe arterioles.

Answer 2

Arterioles

• Small arteries
• Tunica media consists of 1-3 layers of smooth muscle cells.
• Mean arterial pressure depends on proper tone of smooth muscles in arterioles (peripheral resistance arterioles).
  
  • Thickness of smooth muscle layer decreases as diameter becomes smaller.
• Give rise to metarterioles which have a discontinuous layer of smooth muscle tissue.

Question 3

Describe B cell development.

Answer 3

B Cells - Development

• Maturation of B cells involves the appearance of certain cell surface receptors:
  
  • IgM and IgD
  • MHC class II proteins
  • Complement receptors
  • Ig Fc receptors

Question 4

Describe bile.

Answer 4

Bile

• Hepatic bile is produced and secreted by the liver.
• Bile from the gallbladder is hepatic bile that has been stored and concentrated.
• Components:
  
  • Bile acids:
    
    • Cholic and chenodeoxycholic acids (synthesized in hepatocytes).
    • Deoxycholic acid and lithocholic acid (converted by bacteria).
  • Water and electrolytes.
  • Cholesterol and phospholipids (esp. lecithin).
  • Pigments and organic molecules:
    
    • Major pigment is bilirubin.

Question 5

Describe bilinogen.

Answer 5

Billinogen

• Oxidized into excreted products OR:
• Reabsorbed into the blood and carried back to the liver TO BE:
• Re-excreted by the liver OR:
• Excreted in the urine.

Question 6

Describe bilirubin formation.

Answer 6

Bilirubin Formation

• Hemoglobin is released from damaged RBCs.
• Hemoglobin is phagocytized by macrophages.
• Split into globin and heme.
• Heme ring is opened to free iron.
• Heme is transported in the blood by transferrin.
• Straight chain of pyrole nuclei is formed.
• Heme is converted by heme oxygenase into biliverdin.
• Biliverdin -> free (unconjugated) bilirubin.
• Free bilirubin is transported attached to plasma albumin to liver hepatocytes.
• Free bilirubin is released from plasma albumin within the liver cells and conjugated:
  
  • With glucuronic acid -> bilirubin glucoronids (80%).
  • With sulfate -> bilirubin sulfate (10%).
  • With a variety of other substances (10%).
• Conjugated bilirubin is secreted (active transport) into the intestine.
• Conjugated bilirubin in the intestine is converted by bacterial action into urobilinogen.

Question 7

Describe Clara cells.

Answer 7

Clara Cells

• These cells are found only in bronchioles.
• Number of Clara cells increases as ciliated columnar cells decrease.
• Histologically, these cells can be identified by an apical surface that bulges into the lumen of the airway.
• Secrete surface-active lipoprotein that prevents collapse of terminal bronchioles during exhalation.
• Contain abundant SER.

Question 8

Describe dermal papillae.

Answer 8

Integument - Dermal Papillae

• Upward projections from each secondary dermal ridge.

Question 9

Describe dust cells.

Answer 9

Dust Cells

• Macrophages, derived from monocytes.
• Phagocytize particles such as pollutants, bacteria, and surfactant that are not trapped in the mucous and expectorated.
• Relation to CHF:
  
  • In CHF, fluid containing the breakdown products of hemoglobin (iron-containing hemosiderin) leak into alveolar spaces and are phagocytized by the dust cells.
  • The iron-containing dust cells are referred to as heart failure cells.

Question 10

Describe elastic arteries.

Answer 10

Elastic Arteries

• Conducting arteries.
• Stretch during systole and recoil during diastole.
• Tunica media consists of layers of elastic fibers organized into elastic laminae:
  
  • 40 layers in newborn to 70 layers in older adult.
  • CT is interspersed between the elastic laminae.
• Include:
  
  • Aorta
  • Pulmonary trunk
  • Large branches of aorta.

Question 11

Describe endothelium.

Answer 11

Endothelium

Question 12

Describe ethanol metabolism.

Answer 12

Ethanol Metabolism

Question 13

Describe GALT.

Answer 13

Gut-Associated Lymphoid Tissue

• The bulk of the body’s immune defenses is centered in GALT.
• Components:
  
  • Transitory aggregations of lymphocytes, neutrophils, eosinophils.
  • Permanent structures:
    
    • Appendix
    • Peyer’s patches
    • Mesenteric lymph nodes

Question 14

Describe gastric glands.

Answer 14

Gastric Glands

• Simple branched tubular glands.
• Narrow isthmus opens into bottom of a gastric pit.
• Fundus (base) of the gland extends into the lamina propria.
• Cells of the gastric glands:
  
  • Mucous neck cells secrete soluble mucous.
  • Stem cells in neck replace other cells of the gastric pit.
  • Chief cells (zymogenic cells).
    
    • Secrete pepsinogen.
  • Parietal cells (oxyntic cells):
    
    • Manufacture HCl.
    • Secrete intrinsic factor.
  • Enteroendocrine cells (Amine Precursor Uptake and Decarboxylation - APUD cells):
    
    • Diffuse neuroendocrine cells that secrete hormones.

Question 15

Describe hair follicles.

Answer 15

Hair Follicles

• Develop from epidermis as elastic, keratinized threads.
• Components of follicle:
  
  • Root sheaths (external and internal)
  • Hair shaft
  • Hair bulb
• Sebaceous glands and arrector pili muscles are associated with hair follicles.
• Hair bulb:
  
  • Expanded lower part of hair follicle.
  • Matrix
  • Vascularized dermal papilla.
• External root sheath:
  
  • Down growth of epidermis.
• Internal root sheath:
  
  • Generated by bulb matrix.
  • Layers:
    
    • Henle’s layer (outermost).
    • Huxley’s layer
    • Cuticle
      
      • Interlocks with cuticle of hair shaft.
• Hair shaft:
  
  • Layers:
    
    • Medulla (innermost)
    • Cortex
    • Cuticle

Question 16

Describe interpapillary peg.

Answer 16

Integument - Interpapillary Peg

• Downward growth of epidermis along crest.

Question 17

Describe keratinization.

Answer 17

Epidermis - Keratinization

Question 18

Describe keratinocyte stem cells.

Answer 18

Keratinocyte Stem Cells

• These cells can reestablish epidermis in severely burned patients.
• Migration pathways:
  
  • Bulb-epidermis stem cell pathway.
  • Bulb-sebaceous gland stem cell pathway.
  • Bulb-hair stem cell pathway.

Question 19

Describe Kupffer cells.

Answer 19

Liver - Kupffer Cells

• Phagocytic cell.
• Derived from monocytes.
• Lines hepatic sinusoids.

Question 20

Describe langerhans cells.

Answer 20

Langerhans Cells

• Dendritic cells.
• From monocytes.
• Antigen-presenting cells.
• Primarily in stratum spinosum.
• Migrate from epidermis to lymph nodes.
• Birbeck granules.

Question 21

Describe lymph node histology.

Answer 21

Lymph Node - Histology

• 1-25mm in diameter.
• Hilus - entry and exit point for vessels:
  
  • Efferent lymphatic vessels as well as arteries and veins enter/leave through the hilus.
  • Afferent lymphatic vessels enter the convex side of the node.
• Capsule - dense collagen fibers, some elastic fibers and smooth muscle fibers.
• Trabeculae
• Cortex:
  
  • Outer:
    
    • Contains lymph follicles (nodules).
  • Follicles:
    
    • Contain B cells, follicular dendritic cells, and migrating dendritic cells.
    • Secondary follicles:
      
      • Mantle (dark stained)
      • Germinal center (lighter stained)
    • Primary:
      
      • Lack mantle and germinal center.
    • Deep (inner):
      
      • Contains T_H cells, macrophages
      • High endothelial venules (HEVs)
        
        • Port of entry for circulating differentiated lymphocytes to seed lymph node.
  • Medulla:
    
    • Irregular arrangement of loose medullary sinuses and dense medullary cords:
      
      • Sinuses are lined with macrophages.
      • Cords consist of blood vessels, lymphoblasts and plasma cells.
    • Site of lymphocyte reentry into lymph stream.
    • Thymic-dependent areas in subcortical and deeper medullary regions.

Question 22

Describe lymphoid tissue.

Answer 22

Lymphoid Tissue

• Appears in body as a gradient from diffuse lymphoid tissue to lymphoid organs.
• Lymphoid organs:
  
  • Primary - where precursor cells mature into immunocompetent cells, and are programmed to recognize a specific antigen.
    
    • Thymus and bone marrow.
  • Secondary - trapped antigens stimulate clonal expansion of mature T & B cells.
    
    • Lymph nodes, spleen, tonsils.
• Lymphocytes mature in primary lymphoid organs and then take up residence in secondary lymphoid organs.
• Lymphoid follicle (nodule)
  
  • Primary vs. secondary (with germinal center).

Question 23

Describe melanocytes.

Answer 23

Melanocytes

• Derived from melanoblasts.
• Do not form desmosome attachments in epidermis.
• Inject melanin granules into keratinocytes.
• Pathway for melanin formation:
  
  • Tyrosine -> 3,4-dihydroxyphenylalanine (DOPA) -> dopaquinone -> melanin
  • Requires tyrosinase.

Question 24

Describe Merkel cells.

Answer 24

Merkel Cells

• Mechanoreceptors
• May also act as diffuse neuroendocrine cells.
• Usually in stratum germinativum.
• Contains catecholamine-like granules.

Question 25

Describe mesangial cells.

Answer 25

Mesangial Cells

• Contractile: utilize cytoskeletal contractile proteins to modify blood flow through glomerular capillaries.
• Phagocytic: take up worn out glomerular basal lamina for recycling and also phagocytose immunoglobulins trapped in the basal lamina.
• Proliferative
• Synthesize matrix and collagen.
• Secrete prostaglandins and endothelins.
• Respond to angiotensin II.
• Provide mechanical support and regulate blood flow.

Question 26

Describe muscular arteries.

Answer 26

Muscular Arteries

• Distributing arteries.
• Tunica media consists of smooth muscle that responds to autonomic stimulation and hormones:
  
  • Thickness of smooth muscle layer decreases as diameter becomes smaller.
  • Gradual transition from elastic artery to muscular artery.
• Include:
  
  • All named arteries of body except elastic arteries.

Question 27

Describe nephrons.

Answer 27

Nephrons

• Cortical nephrons:
  
  • The renal corpuscles of these nephrons are located in the cortex.
  • Their glomeruli empty into peritubular capillary networks that surround the proximal and distal convoluted tubules of their own nephrons and those of surrounding nephrons.
  • They have short loops of Henle that do not extend deeply into the medulla.
• Juxtamedullary nephrons:
  
  • The renal corpuscles of these nephrons are located in the cortex next to the cortical-medullary junction.
  • Their glomeruli empty into vasa recta consisting of long, straight arterioles and venules that run parallel to the loops of Henle and collecting ducts.
  • They have long loops of Henle that extend deeply into the medulla.

Question 28

Describe odontoblasts

Answer 28

Odontoblasts

• Form the dentin matrix throughout the life of the tooth.
• Form single layer of cells lining pulp cavity.
• Tomes’ dentinal fibers (odontoblastic processes):
  
  • Cytoplasmic extensions of the odontoblasts continuing through the predentin and dentinal layers to the dentin-enamel junction;
  • They occupy a space in the dentin matrix known as dentinal tubules.
• Incremental lines (of Ebner and Owen)

Question 29

Describe Peyer’s patches.

Answer 29

Peyer’s Patches

• Dome-shaped lymphoid structures under the mucosal surface.
• Contain B- and T-cell dependent areas.
• Possess high endothelial venules (HEVs), which facilitate entrace of lymphocytes into lymphoid organs from the bloodstream.
• The mucosal covering of the dome of the Peyer’s patches includes specialized M (microfold) cells:
  
  • Sample particulate antigen and present it to antigen-presenting cells in the underlying lamina propria.
• The antigen-presenting cells (APCs) and macrophages phagocytize the antigen and present it to helper and cytotoxic T cells as well as B lymphocytes.

Question 30

Describe pneumocytes.

Answer 30

Pneumocytes

• Type I:
  
  • Very thin cytoplasm.
  • Cover about 95% of the alveolar surface.
  • Tight junctions connect with other type I cells.
  • Basal lamina may be fused with basal lamina of nearby capillaries.
• Type II pneumocytes:
  
  • Rounded cells that bulge into the alveolar lumen.
  • Cover about 5% of the alveolar surface.
  • Can divide and replace Type I pneumocytes.
  • Produce phospholipid-protein surfactant that coats alveolar walls.

Question 31

Describe primary lymphoid follicles.

Answer 31

Lymphoid Follicles - Primary

• Spherical, tightly packed accumulations of virgin B cells and dendritic reticular cells that have not been exposed to antigens.

Question 32

Describe Purkinje cells.

Answer 32

Purkinje Cells

• Large specialized cardiac muscle cells.
• Carry impulses to ordinary cardiomyocytes.

Question 33

Describe sebaceous glands.

Answer 33

Sebaceous Glands

• Holocrine glands.
• Branched acinar glands with short ducts.
• Found everywhere except palms and soles.
• Continuously produce sebum - released into hair follicle.
• Growth is stimulated at puberty by sex hormones.

Question 34

Describe secondary dermal ridges.

Answer 34

Integument - Secondary Dermal Ridges

• Occur in double rows, branched.
• Thin collagenous, reticular, and elastic fibers.

Question 35

Describe secondary lymphoid follicles.

Answer 35

Lymphoid Follicles - Secondary

• Derived from primary follicles that have been exposed to non-self antigens.
• Not present at birth.
• Structure:
  
  • Corona (cortex):
    
    • Darker peripheral region.
    • Composed of densely packed B lymphocytes.
  • Germinal center:
    
    • Central, lighter stained region.
    • Composed of B lymphocytes, memory B cells, plasma cells, dendritic reticular cells which function as antigen-presenting cells.
• Vascular supply:
  
  • Arteriole and venule supply the cortex.
  • Another arteriole and venule supply the center.
  • Lymph capillaries are not present.

Question 36

Describe some of the genetic causes of deafness and balance.

Answer 36

Question 37

Describe surfactant.

Answer 37

Surfactant

• Secreted by Clara cells and Type II alveolar cells.
• Type II alveolar cells contain numerous lamellar bodies:
  
  • Distinctive under EM.
  • Contain dipalmitoylphosphatidylcholine (lecithin).
    
    • Secreted from apical domain of cells.
    • Combine with proteins from Clara cells.
• Surfactant reduces surface tension on alveolar surface.
• Type II alveolar cells phagocytize old surfactant.

Question 38

Describe sweat glands.

Answer 38

Sudoriferous Glands

• Both merocrine and apocrine glands.
• Merocrine glands:
  
  • Coiled, simple tubular secretory portions:
    
    • Lined by simple epithelium.
    • Apical dark secretory cells secrete glycoproteins.
    • Basal clear cells secrete water and electrolytes.
    • Myoepithelial cells.
  • Duct system consists of stratified cuboidal epithelium except in epidermis.
  • Cholinergic endings.
• Apocrine glands:
  
  • Found in labia majora, areola, and axillary and anal regions.
  • Secretions are thicker and more viscous than merocrine types.
  • Excretory duct opens into hair follicle.
  • Adrenergic innervation.
  • Inactive until puberty.
  • Special types:
    
    • Ceruminous glands
    • Glands of Moll

Question 39

Describe T cell-mediated immunity.

Answer 39

Immunity - T Cell-Mediated

• Macrophage phagocytizes foreign material.
• Foreign proteins are broken down into fragments, some of which have antigenic properties (epitopes).
• Antigens are expressed on surface of macrophage bound to MHC II.
• MHC II/antigen complex is presented to activated helper T cell.
• Activated T cell undergoes mitosis:
  
  • Some daughter cells become memory cells.
  • Some daughter cells secrete interleukins.
• T cells attract B cells.
• B cells have access to free antigens.
• B cells undergo mitosis:
  
  • Some daughter cells become plasma cells
    
    • Secrete appropriate antibodies.
  • Some daughter cells become memory cells.

Question 40

Describe T cells.

Answer 40

T Cells

• Pre-T cells develop in bone marrow, travel to thymus to complete maturation.
• CD4+ T cells:
  
  • Recognize antigens bound to MHC II.
  • Helper cells:
    
    • Assist CD8+ cell differentiation.
    • Assist B cell differentiation.
• CD8+ T cells:
  
  • Cytolytic T cells.
  • Blind to an antigen presenting cell.
  • Undergo mitosis.
  • Release:
    
    • Perforins
    • Fas ligand
  • Recognize antigens bound to MHC I
  • Mediators of cellular immunity.

Question 41

Describe taste sensation.

Answer 41

Taste Sensation

• Except for bitter taste, taste sensations utilize various signal transduction pathways that result in depolarization of the taste cell.
  
  • Salt and sour utilize ionic transport as a signal transduction mechanism.
  • Sour involves hydrogen ion blockage of potassium ion channels to cause depolarization.
• Bitter taste involves a hypopolarized state similar to retinal cell signal transduction; sweet taste involves a hyperpolarized state.
  
  • Involves gustucin ( a homologue of retinal transducin).
  • Involves activation of G_alpha subunit, decrease in cGMP, and closure of Na⁺ channels and hypopolarization of the taste cell.

Question 42

Describe the acinus structure of the glands of the pancreas.

Answer 42

Pancreas - Acinus Structure of Glands

• Acini are serous.
• Acinar cells are pyramidal serous cells:
  
  • Basal zone is basophilic and contains nucleus and RER.
  • Apical zone with zymogen granules.
    
    • Precursors of the enzymes in pancreatic juice.
    • Trypsin, chymotrypsin, amylase, and lipase.
    • Specific receptors for cholecystokinin.
• Centroacinar cells:
  
  • Form a truncated cuboidal epithelium within the lumen of acini.
  • Continuous with the epithelium of the intercalated duct.
  • Unique to pancreas.
• No striated ducts.
• No myoepithelial cells.
• Release of digestive enzymes from serous acinar cells is stimulated by CCK.
• Bicarbonate-rich, alkaline fluid is released by ductal epithelial cells in response to secretin.

Question 43

Describe the activation sequence of the complement cascade.

Answer 43

Complement System - Activation

• C1 is made up of three subcomponents: C1q, C1r, C1s.
• Immunoglobulins bind to surface of pathogen.
• C1q binds to Fc region of Ig -> activates C1r -> activates C1s -> initiates complement cascade.
• C1s -> C4 -> C4a+C4b
• C4b binds to surface of pathogen.
• C1s -> C2 -> C2a+C2b
• C2b binds to C4b -> C4b-2b complex (C3 convertase)
• C4b-2b complex (C3 convertase) -> C3 -> C3a & C3b (C3b is most important opsonin).
• Multiple C3b bind to C3 convertase -> C4b-2b-3b complex (C5 convertase)
• C5 binds to C3b -> C5a + C5b
• When C6, C7, C8, and C9 are added to the complex they form pores in the membrane of the pathogen.

Question 44

Describe the alveolar ducts.

Answer 44

Alveolar Ducts

• Continuations of respiratory bronchioles.
• Cone-shaped.
• Squamous epithelium.
• Wall consists of smooth muscle with FECT.

Question 45

Describe the alveoli.

Answer 45

Alveoli

• Grouped in the alveolar sacs, separated by alveolar septa.
• Walls of alveoli and septa are thin and composed of:
  
  • Type I alveolar cells (Type I pneumocytes):
    
    • Less numerous than type II pneumocytes.
    • Cover largest surface area.
  • Type II alveolar cells (Type II pneumocytes):
    
    • Cuboidal or rounded.
    • Serve as stem cells for Type I and Type II pneumocytes
  • Macrophages (dust cells)
• Pores of Kohn:
  
  • Openings between adjacent alveoli.

Question 46

Describe the anal canal.

Answer 46

Anal Canal

• Epithelium of anus returns to stratified squamous epithelium.
• Skeletal muscle returns as external anal sphincter.

Question 47

Describe the appendix.

Answer 47

Appendix

Question 48

Describe the auditory meatus.

Answer 48

Ear - Auditory Meatus

• Outer 1/3 of the ear canal is composed of elastic cartilage.
• Inner 2/3 is composed of bone.
• Lining of the ear canal is stratified squamous epithelium with sebaceous glands and ceruminous glands (modified sebaceous glands).

Question 49

Describe the auditory organ of the inner ear.

Answer 49

Inner Ear - Auditory Organ

• Consists of:
  
  • Cochlear duct (scala media) divides the bony cochlea into:
    
    • Scala vestibuli
    • Scala tympani
  • Vestibular membrane - forms the roof of the duct
  • Basilar membrane - forms the floor of the duct.
  • Stria vascularis - forms the lateral aspect of the duct. Participates in the formation of the endolymph.
  • Organ of Corti - lies on the basilar membrane.

Question 50

Describe the auditory ossicles.

Answer 50

Middle Ear - Auditory Ossicles

• Malleus (hammer):
  
  • Malleus attaches to the tympanic membrane.
  • Named because it articulates with the “anvil.”
• Incus (anvil):
  
  • Intermediate bone between the stapes and the malleus.
  • “Incus” refers to an anvil, on which the hammer strikes.
• Stapes:
  
  • 3rd bone in series.
  • So-named because it is shaped like a stirrup due to the opening for the stapedial artery.
  • Inserts onto the oval window.

Question 51

Describe the auricle of the ear.

Answer 51

Ear - Auricle

• This is the pinna of the ear and the auditory canal.
• Integument overlying elastic cartilage:
  
  • Thin keratinized, stratified squamous epithelium.
  • Hair follicles can be observed in the dermis.

Question 52

Describe the bile canaliculus.

Answer 52

Liver - Bile Canaliculus

• Extracellular canal located between two rows of hepatocytes.
  
  • Receives bile from hepatocytes.
• Canal of Hering (cholangiole):
  
  • Receives bile from canaliculus.
  • Carries bile to bile ductule.

Question 53

Describe the bile canaliculus.

Answer 53

Bile Canaliculus

Question 54

Describe the “blind sac” origin of lymphatic capillaries.

Answer 54

Lymphatic Characteristics

• Single layer of endothelial cells.
• Basal lamina may be abscent.
• Anchoring filaments.
• Valves in larger lymphatics.

Question 55

Describe the blood, lymphatic, and nerve supply to the small intestine.

Answer 55

Small Intestine - Blood, Lymphatic, and Nerve Supply

Question 56

Describe the blood-air barrier in the lung.

Answer 56

Blood-Air Barrier

• Consists of:
  
  • Thin capillary endothelium (continuous).
  • Thin epithelium of pneumocyte.
  • Intervening basal lamina produced by both cell types.
• Permits gas exchange but does not allow fluids or cells to enter alveoli (normally).

Question 57

Describe the blood-thymic barrier.

Answer 57

Thymus - Blood-Thymic Barrier

• Located in thymic cortex.
• Prevents antigens in the blood from reaching developing T cells in thymic cortex.
• Leaky during fetal life to allow for development of immunologic tolerance to self-antigen.
• Components:
  
  • Endothelium
  • Endothelial basal lamina
  • Perivascular space
  • Basal lamina of reticular cells
  • Reticular cells
  • Thymic parenchymal cells

Question 58

Describe the bony labyrinth of the inner ear.

Answer 58

Inner Ear - Bony Labyrinth

• Complex system of canals and chambers embedded in the petrous portion of the temporal bone.
• Filled with high-sodium content perilymph.
• Consists of:
  
  • Semicircular canals
  • Cochlea
  • Scala vestibuli
  • Scala tympani

Question 59

Describe the bronchi.

Answer 59

Lung - Bronchi

• Trachea divides into 2 primary bronchi.
  
  • These bronchi lie outside the lung and are referred to as extrapulmonary.
  • Except for a smaller diameter, these bronchi resemble the trachea.
  • The cartilage rings that reinforce these bronchi are circular rather than horseshoe-shaped.
• Each primary bronchus divides into three (to right) and two (to left) secondary bronchi, also refered to as lobar bronchi.
  
  • Lobar bronchi are mostly intrapulmonary.
  • These bronchi are reinforced by circular rings of hyaline cartilage that transition to irregular plates.
• As the bronchi become smallier there is a decrease in height of the epithelium, a decrease in cartilage and glands, and an increase in the proportion of elastic fibers and smooth muscles.

Question 60

Describe the bronchioles.

Answer 60

Bronchioles

• Absence of cartilage.
• Absence of glands.
• Sparse goblet cells, especially in terminal bronchioles.
• Large amount of smooth muscle tissue.
• Diameter ranges from 0.3mm - 1mm.
• Epithelium transistions from ciliated columnar with a few goblet cells to ciliated cuboidal with no goblet cells (terminal bronchioles).
• Smallest bronchioles are the terminal bronchioles.
• Each terminal bronchiole branches to form two or more respiratory bronchioles.

Question 61

Describe the capsule of the thymus.

Answer 61

Thymus - Capsule

• Contains:
  
  • Blood vessels.
  • Efferent lymphatics are present.
  • Afferent lymphatics are not present, therefore, lymph does not circulate through thymus.
  • Extends trabeculae (septa) into the parenchyma.

Question 62

Describe the cardiac skeleton.

Answer 62

Histology of Heart - Cardiac Skeleton

• Dense collagenous CT
• Myocardial fibers originate and insert into the cardiac skeleton.

Question 63

Describe the cell types in the respiratory mucosa.

Answer 63

Respiratory Mucosa - Cell Types

• Ciliated columnar cells.
• Nonciliated columnar cells:
  
  • Have microvilli but no cilia.
• Stem cells:
  
  • Basal cells of pseudostratified epithelium.
  • Replace themselves.
• Goblet cells:
  
  • Mucous secreting cells.
  • Also stem cells; can replace other cells of epithelium.
• Neuroendocrine cells (small granule cells):
  
  • May be associated with sensory reception and are more prevalent in infants.
  • Release catecholamines.

Question 64

Describe the cell types of the glands of the large intestine.

Answer 64

Large Intestine - Gland Cell Types

Question 65

Describe the characteristics of the proximal convoluted tubule.

Answer 65

Proximal Convoluted Tubule - Characteristics

• Extends from the urinary pole of the renal corpuscle to the beginning of the loop of Henle.
• Simple cuboidal epithelium made up of truncated pyramidal cells.
• Apical tight junctions and brush border.
• Basolateral infoldings and interdigitations.
• Basal striations with abundant mitochondria (for active transport across basal membrane)
• Large, pale-staining nuclei.
• Eosinophilic cytoplasm.

Question 66

Describe the characteristics of the respiratory system.

Answer 66

Respiratory System - Characteristics

• The respiratory system consists of a conducting portion and a gas exchange portion.
• Respiratory mucosa lines the respiratory passageway and consists of:
  
  • Pseudostratified ciliated columnar epithelium:
    
    • AKA respiratory epithelium.
    • Lines most of the conducting structures.
  • Lamina propria:
    
    • Thin layer of loose CT.
  • Submucosa:
    
    • Dense irregular CT.

Question 67

Describe the cheek.

Answer 67

Oral Cavity - Cheek

• Structure is similar to the lip.
• One exception is the abundant elastic fibers present in the submucosa:
  
  • These are continuous with the fibers surrounding the striated muscle and the lamina propria.
  • This arrangement gives a maximum of distensibility to the oral mucous membrane.

Question 68

Describe the chief cells of the gastric gland.

Answer 68

Cells of the Gastric Gland - Chief Cells

• Secretes pepsinogen.

Question 69

Describe the cochlea.

Answer 69

Inner Ear - Cochlea

Question 70

Describe the collecting duct.

Answer 70

Collecting Duct

• Has a different embryological origin than that of the nephron.
• Wall consists of simple cuboidal epithelium.
• 2 major specialized cell types are associated with the collecting duct:
  
  • Principal cells:
    
    • Reabsorb Na⁺ and water and secrete K⁺ via ATPase pump.
  • Intercalated cells:
    
    • Secrete either H⁺ or bicarbonate ion.

Question 71

Describe the complement system.

Answer 71

Complement System

• An array of about 20 serum proteins which are synthesized in the liver and found in the blood.
  
  • Classic pathway:
    
    • Cascade is activated by antibody binding to a pathogen.
  • Alternate pathway:
    
    • Cascade is directly activated by the pathogen.
• Facilitates inflammatory responses.
• Involves coating the pathogen with complement initiating the cascade.
• Complement cascade results in:
  
  • Activation of the membrane attack complex (MAC) on the pathogen leading to perforations and lysis.
  • Production of opsonins, which are coatings that make the antigens more palatable to phagocytes.
  • Release of chemotactic agents (chemokines) which attract phagocytes (chemotaxis) to the areas of infection or inflammation.

Question 72

Describe the components of the respiratory system.

Answer 72

Respiratory System - Components

• Nose and olfactory mucosa.
• Paranasal sinuses
• Pharynx
• Larynx
• Trachea
• Lung

Question 73

Describe the cornified cell envelope.

Answer 73

Epidermis - Cornified Cell Envelope

• Extracellular:
  
  • Multi-lamellar lipid layer covalently linked to involucrine.
• Intracellular:
  
  • Involucrine
  • Small proline-rich proteins
  • Loricrin
  • Fillagrin and keratin complexes

Question 74

Describe the cristae ampullares of semicircular ducts.

Answer 74

Inner Ear - Cristae Ampullares of Semicircular Ducts

• Epithelium:
  
  • Columnar supporting cells.
  • Hair cells:
    
    • Similar to those of maculae.
• Cupula:
  
  • This is a gelatinous layer similar to the otolithic membrane but without the otoliths.
  • Movement of the head creates shear forces between the semicircular canals and the contained fluid.
  • Movement of the fluid displaces the cupula and causes the stereocilia to bend.

Question 75

Describe the crypt-villus system as one of the orders of folding observed in the gut tube.

Answer 75

Gut Tube - Crypt-Villus System

• Each villus contains a core of lamina propria.
• The crypts extend down between the villi below the bases of the villi.
• Crypts and villi constitute glands of the small intestine.
• Wall of villus is composed of a simple columnar epithelium with goblet cells.
• Each villus contains a capillary plexus.
• Each villus contains a blind-ending lymphatic referred to as a lacteal.

Question 76

Describe the crypts of Lieberkuhn.

Answer 76

Crypts of Lieberkuhn

• Simple tubular glands within the intestinal mucosa:
  
  • Open between adjacent villi and extend to muscularis mucosa.
  • Cells of the crypts:
    
    • Goblet cells
    • Enterocytes:
    • Paneth cells
    • Enteroendocrine cells

Question 77

Describe the development of the ear.

Answer 77

Ear - Development

Question 78

Describe the development of the integument.

Answer 78

Integument - Development

• Epidermis starts as a single layer of ectodermal cells.
  
  • Divide during sixth week to form:
    
    • Periderm - sloughs off to form vernix caseosa.
    • Inner cuboidal germinal layer:
      
      • Continues to proliferate to form adult layers of the epidermis and derivatives:
        
        • 10 weeks: fingernails
        • 12 weeks: hair buds and toenails
• Dermis is derived from mesoderm.

Question 79

Describe the development of the teeth.

Answer 79

Teeth - Development

• Dental primordium is formed from basal cells of the oral ectoderm.
• The labiodental lamina is an epithelial shelf that grows from the thickened primordium into the mesenchym as a bifid structure.
• The external limb splits later to form a grove that deepens to separate the lip and the remainder of the mouth.
• The internal limb is the dental lamina.
• Cells proliferate to form the tooth buds (germs) in each half-jaw.
• Later a second set of tooth-buds develops on the lingual side of each developing deciduous tooth plus three more posteriorly in each half-jaw.
• Epithelial bud becomes the:
  
  • Enamel organ:
    
    • Forms enamel
    • Caps the:
  • Dental papilla:
    
    • Condensation of mesenchyme that gives rise to dentin and pulp.
  • Dental sac (follicle)
    
    • CT sac surrounds the enamel organ and dental papilla and forms cementum and the periodontal membrane.

Question 80

Describe the development of the thymus.

Answer 80

Thymus - Development

Question 81

Describe the differentiation of T cells.

Answer 81

T Cell Differentiation

• Double negative T cells:
  
  • Lack cell surface molecules typical of mature T cells.
  • Enter cortex from blood vessels.
  • Proliferate in subcapsular area.
• Double positive T cells move to outer cortex:
  
  • Confronted with epithelial cells with the cell surface MHC classes I and II for clonal selection.
  • Express both CD4 and CD8 coreceptors and TCR receptors.
• Single positive T cells move to inner cortex:
  
  • Express TCR receptors and either CD4 or CD8 coreceptors.
• Clonal deletion is completed in medulla.

Question 82

Describe the distal convoluted tubule.

Answer 82

Distal Convoluted Tubule

• Lined with simple cuboidal epithelium with smaller cells than those of the PCT.
• Lumen is larger than that of the PCT and there is no brush border.
• Cytoplasm is less eosinophilic than that of the PCT.
• DCT is impermeable to water except in the presence of ADH.
  
  • Derived from the posterior pituitary.
  • Functions to reduce water loss.

Question 83

Describe the duct system of salivary glands.

Answer 83

Salivary Glands - Ducts

Question 84

Describe the ducts of the pancreas.

Answer 84

Pancreas - Ducts

• Duct of Wirsung is the main excretory duct.
• Duct of Santorini is the smaller accessory duct.
• Interlobular ducts:
  
  • Lined with simple columnar epithelium and goblet cells.
• Intercalated ducts:
  
  • Lined with low cuboidal cells.
  • Cells with receptors for secretin.
  • Cells secrete water and bicarbonate ion.

Question 85

Describe the endocardium.

Answer 85

Histology of Heart - Endocardium

• Innermost layer, lining the atria and the ventricles.
• Components:
  
  • Endothelium
  • Subendothelial CT
• Continuous with the tunica intima of the blood vessels entering and leaving the heart.
• Subendocardium is a layer located between the endocardium and the myocardium:
  
  • Contains nerves and Purkinje fibers (subendocardial fibers).

Question 86

Describe the endoplasmic reticulum in hepatocytes.

Answer 86

Liver - Hepatocyte ER

Question 87

Describe the enterocytes of the crypts of Lieberkuhn.

Answer 87

Crypts of Lieberkuhn - Enterocytes

• Columnar epithelial cells with the following characteristics:
• Basal nucleus, perinuclear Golgi, apical brush border.
• Produces disaccharidases.
• Involved in absorption of proteins, carbohydrates, lipids.
• Enzymes present on apical brush border are important in carbohydrate digestion.
• Produce enteropeptidase (enterokinase) which is necessary for the activation of pancreatic zymogens and proenzymes.

Question 88

Describe the enteroendocrine cell of the gastric gland.

Answer 88

Cells of the Gastric Gland - Enteroendocrine Cell

• Small cells with secretory vesicles polarized toward basal surface in proximity to blood vessels.
• Produce peptide hormones and serotonin.

Question 89

Describe the enteroendocrine cells of the crypts of Lieberkuhn.

Answer 89

Crypts of Lieberkuhn - Enteroendocrine Cells

• Stain with chromium (chromaffin).
• Agyrophilic (respond to silver stains).
• Produce peptide hormones and serotonin.
• May produce paracrine or autocrine secretions.
• Analogous to unicellular goblet cells.
• Formed from endodermal stem cells in all regions of the GI tract.

Question 90

Describe the epicardium.

Answer 90

Histology of Heart - Epicardium

• External surface is covered by simple squamous epithelium (mesothelium).
• Mesothelium overlies fibroelastic connective tissue containing adipose cells, nerves, and coronary vessels.

Question 91

Describe the excretory passages of the renal system.

Answer 91

Renal System - Excretory Passages

• Renal pelvis, ureter, and urinary bladder:
  
  • Layers:
    
    • Mucosa
    • Submucosa (not clearly demarcated)
    • Muscularis
    • Adventitia (FECT external to muscularis; serosa over superior surface of bladder.
  • Mucosa:
    
    • Transitional epithelium (urothelium), basement membrane, lamina propria of FECT; some loose lymphoid tissue and a few smooth muscle cells.
  • Muscularis:
    
    • Inner longitudinal and outer circular smooth muscle coat in ureter.
    • Lower third of ureter has a third external longitudinal coat.
    • Layers of smooth muscle in urinary bladder from detrusor muscle.

Question 92

Describe the exocrine secretions of the pancreas.

Answer 92

Pancreas - Exocrine Secretions

• Digestive enzymes:
  
  • Concentrated and stored in vesicles by Golgi:
    
    • Referred to as zymogen granules.
  • Synthesis and secretion is controlled by peptides secreted by duodenal enteroendocrine cells.
  • Synthesized as inactive proenzymes on RER of acinar cells.
• Bicarbonate ions:
  
  • Secretion is regulated by secretin:
    
    • Secreted by duodenal enteroendocrine cells when stimulated by food entering small intestine.
  • Synthesis of bicarbonate ions:
    
    • CO₂ diffuses into intercalated ducts fro blood.
    • CO₂ + H₂O -> H₂CO₃ (requires carbonic anhydrase).
    • H₂CO₃ -> HCO₃^- + H⁺
    • HCO₃^- is actively transported to lumen of intercalated duct.
    • Na⁺ and H⁺ are exchanged with Na⁺ flowing into the duct lumen and H⁺ flowing into blood.

Question 93

Describe the female urethra.

Answer 93

Female Urethra

• Mucosa is lined primarily with stratified or pseudostratified columnar epithelium with intraepithelial nests of mucous glands.
• Lamina propria is highly vascularized with veins with an abundance of elastic tissue.
• Submucosa is not discernible.
• Muscularis has an inner longitudinal and an outer circular layer of smooth muscle cells but is not well defined.
• Adventitia is not discernible.

Question 94

Describe the formation of atherosclerotic plaque.

Answer 94

Atherosclerotic Plaque

Question 95

Describe the functions of the integument.

Answer 95

Integument - Functions

• Protection from:
  
  • Mechanical injury.
  • Desication.
  • Foreign substances and microorganisms.
  • UV radiation.
• Thermoregulation.
• Regulation of BP (via dermal capillary network).
• Excretion of metabolic waste products.
• Synthesis of provitamin D.

Question 96

Describe the functions of the loop of Henle.

Answer 96

Loop of Henle - Functions

• Descending thin limb is permeable to water, Na⁺, and Cl^-.
• Ascending limb is impermeable to water and actively pumps Cl^- out of the tubule, allowing Na⁺ to flow.
• Major function of the loop of Henle is to establish the counter-current exchange system which creates the osmotic conditions necessary to pull water out of the DCT and collecting duct in the presence of ADH.

Question 97

Describe the functions of the organ of corti.

Answer 97

Inner Ear - Functions of Organ of Corti

Question 98

Describe the functions of the proximal convoluted tubule.

Answer 98

Proximal Convoluted Tubule - Functions

• Reabsorbs most of the filtrate, including water.
• Removes essentially all the glucose and amino acids from the filtrate.
• Reabsorbs most of the sodium and chloride ions.
• Characterized by a complex set of transporters, co-transporters, channels, and exchangers.

Question 99

Describe the functions of the spleen.

Answer 99

Spleen - Function

• Blood filtering functions:
  
  • Only lymphatic organ specialized to filter blood.
  • Stores and removes worn-out RBCs.
  • Recycles Fe.
  • Converts HGB to billirubin.
  • Blood formation in the fetus.
• Immunologic functions:
  
  • Screens foreign material in the blood.
  • Produces lymphocytes and plasma cells.
  • Removal leads to overwhelming bacterial infections in infants, children, and young adults.

Question 100

Describe the functions and structural specializations of the esophagus.

Answer 100

Esophagus - Function and Structure

• Functions:
  
  • Digestion (initiated in the mouth)
  • Addition of mucous to food bolus.
• Structural specializations:
  
  • Mucosa:
    
    • Stratified squamous nonkeratinized epithelium.
    • Mucous glands are found in the lamina propria and sub mucosa.
  • Muscularis externa:
    
    • Undergoes transition from skeletal muscle in the upper 1/3 to a mixture of skeletal and smooth muscle in the middle 1/3 to smooth muscle only in the lower 1/3.

Question 101

Describe the general histology of the intrapulmonary bronchi.

Answer 101

Intrapulmonary Bronchi

• Mucosa:
  
  • Similar to trachea and extrapulmonary bronchi.
  • Mucosal folds may be present due to smooth muscles.
  • Elastic fibers are prominent.
• Submucosa:
  
  • Characterized by loose CT and lymphatic tissue.
  • Contains mixed glands and mucous glands.
• Adventitia:
  
  • Contains hyaline cartilage plates surrounded by dense FECT.

Question 102

Describe the general histology of the thymus.

Answer 102

Thymus - Histology

• Most developed at puberty (10-15 grams at birth, 30-40 grams at puberty).
• Involutes during adolescence.
• No lymph follicles (nodules)
• No afferent lymph vessels.
• No lymph sinuses.
• Consists of:
  
  • Capsule
  • Trabeculae (septa)
  • Lobules

Question 103

Describe the general orgnaization of the integument.

Answer 103

Integument - General Organization

• Epidermis
• Basement membrane
• Dermis
  
  • Corresponds to lamina propria of a mucous membrane.
  • 0.5-3mm thick.
• Subcutaneous tissue (SubQ, superfiscial fascia, hypodermis).

Question 104

Describe the glands of Brunner.

Answer 104

Glands of Brunner

• Found in submucosa of duodenum.
• Responsible for:
  
  • Formation of bicarbonate and mucus.
    
    • Supplements bicarbonate from the pancreas.
    • Necessary to neutralize gastric acid.

Question 105

Describe the gut-associated lymphoid tissue (GALT).

Answer 105

Gut-Associated Lymphoid Tissue (GALT)

• IgA is the first line of defense and is found coating the luminal surface of the mucosal epithelium.
• Isolated lymph follicles are found in the lamina propria:
  
  • Specialized squamous epithelial cells (M cells) in the gut lumen serve to transport food antigens to the lymph follicles.
  • Antigen-stimulated B cells in the follicle secrete IgA.
• Diffuse lymphoid tissue in the lamina propria includes lymphocytes, macrophages, and IgA-secreting plasma cells.
• Aggregated lymphoid follicles form the tonsils of the oropharynx (Waldeyer’s ring) and Peyer’s patches in the submucosa of the ileum.

Question 106

Describe the hepatic lobules.

Answer 106

Liver - Hepatic Lobules

• Classic:
  
  • Central venule is in the center of the lobule.
  • Portal triads are at the angles.
• Portal:
  
  • Three central venules of adjacent lobules form a triangle.
  • Portions of the bile canaliculi of the three lobules drain into the same bile duct.
• Liver acinus:
  
  • Includes three zones defined by hepatic tissue receiving blood from a branch of the hepatic artery conducting blood to opposite central veins.
  • Metabolic gradient extends from hepatic triad to central vein.

Question 107

Describe the hepatic sinusoids.

Answer 107

Liver - Hepatic Sinusoids

• Lining:
  
  • Fenestrated endothelial cells.
  • Discontinuous basal lamina.
• Perisinusoidal cells:
  
  • Located in space of Disse.
  • Store vitamin A.
  • Produce collagen fibers and extracellular matrix components.
  • During cirrhosis:
    
    • Transform into myofibroblasts.
    • Become the main collagen type I producing cells.
      
      • Stimulated by cytokines from hepatocytes, Kupffer cells and lymphocytes.
• Subendothelial space of Disse:
  
  • Space between basal lamina and hepatocytes.
  • Contains microvilli of basolateral domain of hepatocytes.
  • Contains interstitial fluid that drains into the space of Mall that drains into lymphatics.

Question 108

Describe the hepatocyte.

Answer 108

Liver - Hepatocyte

• Polyhedral in form.
• Central nucleus with one or more nucleoli.
• Cytoplasm may contain glycogen, fat droplets, and pigments granules.
• Basolateral domain:
  
  • Microvilli
  • Faces space of Disse.
  • Involved in:
    
    • Absorption of blood-borne substances
    • Secretion of plasma proteins.
• Apical domain:
  
  • Borders bile canaliculus.

Question 109

Describe the histologic characteristics of the duodenum.

Answer 109

Duodenum - Histologic Characteristics

• Villi with wide spatulae or “leaflike” distal shape.
• Deep crypts of Lieberkuhn.
• Brunner’s glands with excretory ducts in submucosa.

Question 110

Describe the histologic characteristics of the ileum.

Answer 110

Ileum - Histologic Characteristics

• Villi narrow and shorter than in jejunum.
• Crypts of Lieberkuhn present.
• No glands in submucosa.

Question 111

Describe the histologic characteristics of the jejunum.

Answer 111

Jejunum - Histologic Characteristics

• Villi longer and narrow.
• Crypts of Lieberkuhn present.
• No glands in submucosa.

Question 112

Describe the histology of the larynx.

Answer 112

Larynx - Histology

• Epiglottis:
  
  • Lingual surface:
    
    • Covered with stratified squamous epithelium.
    • Lamina propria with loose CT and elastic fibers.
  • Pharyngeal surface:
    
    • Covered with pseudostratified ciliated epithelium.
    • Lamina propria with tubuloacinar seromucous glands.
  • Core of epiglottis consists of elastic cartilage.
• False vocal cords (vestibular folds):
  
  • Covered with pseudostratified ciliated epithelium.
  • Tip is covered by stratified squamous epithelium.
  • Lamina with seromucous glands.
• True vocal cords:
  
  • Covered with stratified squamous epithelium.
  • Lack seromucous glands.
• Remainder of larynx is covered with pseudostratified ciliated epithelium.

Question 113

Describe the histology of the larynx.

Answer 113

Larynx - Histology

• Epithelium:
  
  • Respiratory epithelium (pseudostratified ciliated columnar).
  • Stratified squamous epithelium.
• Cartilage:
  
  • Hyaline cartilages:
    
    • Thyroid, cricoid, arytenoids.
  • Elastic cartilages:
    
    • Corniculates, cuneiforms, tips of arytenoids, epiglottis.
• Muscle:
  
  • Skeletal muscle.

Question 114

Describe the histology of the nasopharynx.

Answer 114

Nasopharynx

• Mucosa:
  
  • Respiratory epithelium.
  • Lamina propria with FECT, mucous glands, serous and mixed glands, and diffuse lymphatic tissue.
• Submucosa:
  
  • Loose CT.
  • MALT (mucosa-associated lymphoid tissue).
• Waldeyer’s ring:
  
  • Ring of lymphoid tissue around nasopharynx.
  • Includes tonsils and adenoids.

Question 115

Describe the IgA secretion by GALT.

Answer 115

GALT - IgA Secretion

• Primary immunoglobulin produced by GALT.
  
  • Synthesized and secreted by plasma cells in the lamina propria of the gut.
  • Picked up at the basal surface of enterocytes and transported across the cell.
• While in the cell, sigA is linked to a protein called secretory component that inhibits degradation of the sigA by proteolytic enzymes in the GI lumen.
• Secretory IgA, unlike IgG, does not stimulate the complement system, but functions by coating microorganisms, thus inhibiting microorganism binding to the epithelium.

Question 116

Describe the immune surveillance system.

Answer 116

Immune Sureveillance Sytem

• Toll-like receptors are found on the surface of enterocytes.
  
  • Type of pattern recognition receptor.
  • Recognize structurally conserved molecules broadly shared by pathogens but distiguishable from host molecules (pathogen associated molecular patterns (PAMPs)).

Question 117

Describe the innervation of the gut wall.

Answer 117

Digestive Tube - Innervation

• Sympathetic:
  
  • Sympathetic postganglionic fibers pass through gut wall to glands and smooth muscle.
• Parasympathetic:
  
  • Preganglionic fibers synapse with postganglionic fibers in ganglia within the gut wall itself.
  • Meissner’s plexus:
    
    • Regulates local secretions, blood flow, and absorption.
  • ​Auerbach’s plexus:
    
    • Coordinates muscular activity of gut wall.

Question 118

Describe the intestinal tight junction barrier.

Answer 118

Intestine - Tight Junction Barrier

• Know why these junctions are especially important with regard to the GI tract epithelium.

Question 119

Describe the islets of Langerhans.

Answer 119

Pamncreas - Islets of Langerhans

• These are endodermal-derived cell aggregations which are interspersed irregularly among the acini.
• Cell types include:
  
  • A-cells (alpha cells):
    
    • Have fine cytoplasmic granules and are presumed to form glucagon.
  • B-cells (beta cells):
    
    • Have coarse cytoplasmic granules; they are more numerous than alpha cells and produce insulin.
  • D-cells (delta cells):
    
    • Secrete somatostatin, which helps to control levels of insulin and glucagon.

Question 120

Describe the juxtaglomerular apparatus.

Answer 120

Juxtaglomerular Apparatus

• Components:
  
  • Macula densa
    
    • Formed by elongated, densly packed cells in the wall of the convoluted tubule. Polarity of these cells is reversed.
    • Responds to changes in sodium and chloride concentration in the urine or hypotension.
    • Signals renin release from juxtaglomerular cells.
    • Involved in regulation of fluid-electrolyte balance and blood pressure regulation.
  • Extraglomerular mesangial cells
  • Juxtaglomerular cells
    
    • Modified smooth muscle cells associated with macula densa and afferent arteriole.
    • Secrete renin into the blood when stimulated by the macula densa.
    • Innervated by sympathetic nerve endings which increase renin release.

Question 121

Describe the large intestine.

Answer 121

Large Intestine

• Epithelium:
  
  • Simple columnar epithelium.
  • Crypts but no villi.
• Functions:
  
  • Secretion of mucus for lubrication.
  • Goblet cell is the prominent cell of the large intestine.
  • Absorption of fluid.
  • Formation of fecal mass.
  • Continuation of digestion initiated in small intestine.

Question 122

Describe the lingual pappilae.

Answer 122

Tongue - Lingual Papillae

• Filiform papillae:
  
  • Most numerous of all the papillae with a conical appearance.
  • Evenly distributed over the entire oral upper portion.
  • Lack taste buds.
• Fungiform papillae:
  
  • Relatively few in number.
  • Interspersed singly among the parallel rows of filliform papillae.
  • Have a mushroom appearance.
  • Taste buds are present only on the oral surface of the epithelium in contradistinction to the position of the taste buds on the circumvallate papillae whose taste buds are primarilly located on the lateral walls.
• Foliate papillae:
  
  • Rudimentary in humans, but well developed in lower animals.
  • The pharyngeal portion is free of papillae but contains the lingual tonsils.
• Circumvallete papillae:
  
  • Located along the sulcus terminalis as projections surrounded by a moat (circular flow).
  • Taste buds are present on the lateral walls.
  • Ducts of von Ebner’s glands (serous) open into the moat.

Question 123

Describe the lip.

Answer 123

Oral Cavity - Lip

• The oral cavity is lined with a mucous membrane lying on a vascular FECT layer; this mucosa consists of:
  
  • Stratified squamous epithelium.
  • Basement membrane.
  • Lamina propria.
• The lip is composed of a core of skeletal muscle (obicularis oris) cells embedded in FECT and covered externally by skin.
• An internal poorly keratinized, modified, stratified squamous epithelium lies on a lamina propria with high papillae.
• Within the lamina propria are mixed and mucous glands.
• Dermis has a rich plexus of capillaries which are prominent at the free margin of the lip.

Question 124

Describe the lobules of the thymus.

Answer 124

Thymus - Lobules

• Each lobule is composed of an outer, darker staining cortex and an inner, lighter staining medulla.
• Cortex (dark staining):
  
  • Stained densely with basic dyes such as H&E.
  • Cell population:
    
    • Epithelial reticular cells - secrete thymosin.
    • T cells in various stages of differentiation.
  • Thymocytes migrate from cortical areas to medullary areas.
  • Blood vessels surrounded by continuous epithelial barrier.
    
    • Allows thymus to maintain lymphopoiesis while segregated from antigens.
• Medula (light staining):
  
  • Specialized to allow entry channel into blood stream of mature lymphocytes.
  • Capillary beds are not sheathed by epithelial cells.
  • Hassall’s corpuscles:
    
    • Whorls of highly keritanized medullary epithelial cells:
      
      • Produce cytokine thymic stromal lymphopoietin:
        
        • Stimulates thymic dendritic cells needed for the maturation of single positive T-cells.

Question 125

Describe the characteristics of the loop of Henle.

Answer 125

Loop of Henle - Characteristics

• Extends from the PCT to DCT.
• Made up of descending limb and ascending limb.
• Each limb has a thin and a thick portion:
  
  • Thick segments of the loop of Henle are composed of simple low cuboidal epithelium.
  • Thin segments of the loop of Henle are composed of simple squamous epithelium.
  • Cells of thick ascending limb have no brush border and more basal vertical striations.
• Ascending limb is impermeable to water.

Question 126

Describe the maculae of saccule and utricle.

Answer 126

Inner Ear - Maculae of Saccule and Utricle

• Epithelium:
  
  • Columnar supporting cells.
  • Vestibular hair cells:
    
    • Numerous stereocilia.
    • Single kinocilium.
• Hair cells are in contact with afferent nerve endings.
• Otolithic membrane:
  
  • This is actually a gelatinous layer containing calcium carbonate crystals called otoliths that overlies the epithelium.
  • Stereocilia of the vestibular hair cells are embedded in this gelatinous layer.
  • Movements of the head displaces the otolithic membrane and causes a sensory impulse.

Question 127

Describe the male urethra.

Answer 127

Male Urethra

• Prostatic urethra:
  
  • Section of urethra passing through prostate gland.
  • Mucosa lined with transitional epithelium.
  • Highly vascularized with veins with abundant elastic tissue.
• Membranous urethra:
  
  • Tall pseudostratified columnar cells but variable.
  • Extends through urogenital diaphragm and receives striated muscle cells forming the external sphincter of the bladder.
• Cavernous urethra:
  
  • Lined with pseudostratified epithelium with patches of stratified squamous epithlelium.
• Glands:
  
  • Lacunae of Morgagni are invaginations of mucous membrane containing single or groups of intraepithelial mucous cells.
  • Glands of Littre are branched tubular glands opening into the lacunae of Morgagni.

Question 128

Describe the marginal zone of the Spleen.

Answer 128

Spleen - Marginal Zone

• Forms sinusoidal interface between red pulp and white pulp.
• Has an abundance of antigen-presenting cells.
• Lymphocytes first encounter antigens here.
• Activated T-helper cells activated B cells here.

Question 129

Describe the medullary ray.

Answer 129

Medullary Ray

Question 130

Describe the medullary region of the kidney.

Answer 130

Kidney - Medullary Region

Question 131

Describe the membranous labyrinth of the inner ear.

Answer 131

Inner Ear - Membranous Labyrinth

• Complex system of membranous structures embedded within the chambers of the bony labyrinth.
• Filled with high-potassium content endolymph.

Question 132

Describe the mesangium.

Answer 132

Mesangium

• Part of the glomerulus.
• Formed by mesangial cells embedded in a mesangial matrix.
• Intraglomerular mesangial cells are located between nearby capillaries in the glomerulus and cover endothelium not covered by podocytes.
• Extraglomerular mesangial cells are located between the afferent and efferent arterioles at the vascular pole and are associated with the juxtaglomerular apparatus.

Question 133

Describe the metabolism of bilirubin.

Answer 133

Bilirubin Metabolism

Question 134

Describe the microvasculature of the gut tube.

Answer 134

Digestive Tube - Microvasculature

Question 135

Describe the morphology of the spleen.

Answer 135

Spleen - Morphology

• 5.6” x 4”
• No lymph sinuses.
• No afferent lymph vessels.
• Covered by peritoneum except at hilus.
• Mesothelium-lined CT capsule contains some smooth muscle fibers and sends trabeculae into parenchyma.
• Blood vessels enter and leave hilus.
• Divided into red pulp and white pulp.

Question 136

Describe the mucosa of the digestive tube.

Answer 136

Digestive Tube - Mucosa

• Epithelium:
  
  • Stratified squamous transitioning to simple columnar.
  • May have secretory, absorptive, and/or protective functions.
• Lamina propria:
  
  • Loose areolar CT associated with epithelium.
  • Contains various glands and GALT.
• Muscularis mucosa:
  
  • Made up of 1-3 layers of smooth muscle.

Question 137

Describe the mucosal layer of the large intestine.

Answer 137

Large Intestine - Mucosal Layer

• Coats intestinal epithelial luminal surface with mucous.
  
  • Secreted by goblet cells.
  • Made up of 2 layers:
    
    • Outer layer contains microorganisms.
    • Inner layer contains antimicrobial proteins (from Paneth cells, enterocytes, and goblet cells) that resist microbial penetration.

Question 138

Describe the muscles of the middle ear.

Answer 138

Middle Ear - Muscles

• Tensor tympani:
  
  • Inserts on the malleus.
• Stapedius:
  
  • Inserts on the stapes.
• Muscles contract reflexively in response to loud sounds in order to dampen the vibrations of the auditory ossicles.

Question 139

Describe the muscularis externa of the digestive tube.

Answer 139

Digestive Tube - Muscularis Externa

• Inner circular layer of smooth muscle.
• Outer longitudinal layer of smooth muscle.
• Myenteric (Auerbach’s) nerve plexus lies between the 2 layers of muscle tissue.
• Functions:
  
  • Regulates the size of the lumen (circular layer of smooth muscle).
  • Regulates rhythmic movement of the GI tract (longitudinal layer of smooth muscle).

Question 140

Describe the myocardium.

Answer 140

Histology of Heart - Myocardium

• Consists of cardiac muscle cells.

Question 141

Describe the nose.

Answer 141

Respiratory System - Nose

• Epithelium:
  
  • Nares:
    
    • Stratified squamous epithelium continuous with epidermis.
    • Contains sebaceous glands, sudoriferous glands, and hair follicles.
  • Mucosa begins at level of nasal septum; includes:
    
    • Respiratory epithelium (pseudostratified ciliated columnar epithelium).
    • Basement membrane.
    • Lamina propria (blends with underlying bone or cartilage).
    • Depending on location, mucosa may be called mucoperiosteum, mucoperichondrium, or the Schneiderian membrane.

Question 142

Describe the olfactory epithelium.

Answer 142

Nose - Olfactory Epithelium

• Located in nasal cavity roof.
• Pseudostratified columnar epithelium without goblet cells.
• No distinct basment membrane.
• Sustentacular cells (support cells) with pigment granules.
• Basal cells with pigment granules:
  
  • Stem cells - give rise to immature olfactory cells.
• Olfactory cells:
  
  • Bipolar neurons
  • Apical end projects into nasal cavity as a knoblike ending with nonmotile cilia.
  • Cilia possess G-protein-linked oder-specific receptors.
  • Basal end of the cell extends as an unmyelinated axon, bundled with other similar axons, through the ethmoid plate to mitral cells located in the olfactory bulb.
  • Olfactory cells senesce and are replaced from basal cells.
• Olfactory glands of Bowman:
  
  • Located in the lamina propria.
  • Secrete odorant-binding protein.
  • Odorant-binding protein binds to oderant molecule in nasal cavity.

Question 143

Describe the openings of the middle ear.

Answer 143

Middle Ear - Openings

• Oval window:
  
  • Stapes attaches to the membrane covering the oval window.
  • Oval window opens into the scala vestibuli.
• Round window:
  
  • This membrane-covered region is at the end of the scala tympani.

Question 144

Describe the organ of Corti.

Answer 144

Inner Ear - Organ of Corti

Question 145

Describe the organization of hair bundles in the inner ear.

Answer 145

Question 146

Describe the organization of the liver.

Answer 146

Liver - Organization

• Epithelial parenchyma is composed of hepatic cells irregularly arranged as plates seen on edge as cell cords and radially arranged around the central vein.
• Space of Disse:
  
  • Separates hepatic cells from endothelial cells.
  • Active in transfer between blood and parenchyma.
• Space of Mall continuous with space of Disse:
  
  • Drains into lymphatics.
• Glisson’s thin capsule of FECT covers the surface except at the diaphragmatic attachment.
• CT septa extend from the capsule to form lobes and lobules (hepatic lobules).

Question 147

Describe the pancreas.

Answer 147

Pancreas - Generalizations

• Lobulated, compound, tubulo-alveolar gland with both an exocrine and an endocrine secretory function.
• CT support:
  
  • No organized capsule.
  • Thin layer of loose CT from which septa pass internally dividing the gland into many small lobules.
  • The delicate CT contains blood vessels, lymphatics, nerves, and excretory ducts.

Question 148

Describe the paneth cells of the crypts of Lieberkuhn.

Answer 148

Crypts of Lieberkuhn - Paneth Cells

• Basal crypt cells.
• Prominent eosinophilic granules.
• Produce lysozyme to control intestinal flora.

Question 149

Describe the paneth cells of the large intestine.

Answer 149

Large Intestine - Paneth Cells

• Found in bases of mucosal glands.
• Characteristics:
  
  • Basophilic basal cytoplasm.
  • Supranuclear Golgi complex.
  • Large, intensely acidophilic apical secretory granules.
• Secrete:
  
  • Lysozyme to increase permeability of bacteria by degrading peptidoglycan coat.
  • Defensins to increase membrane permeability of target organisms.
  • Tumor necrosis factor-alpha (proinflammatory cytokine).
  • May phagocytize some microorganisms and help regulate intestinal flora.

Question 150

Describe the parietal cells of the gastric gland.

Answer 150

Cells of the Gastric Gland - Parietal Cells

• Unique cell of the gastric gland.
• Large pyramidal shaped, eosinophilic cell.
• Produce HCl and gastric intrinsic factor.
  
  • Gastric intrinsic factor is necessary for absorption of vitamin B₁₂ by the terminal ileum.
• Generates H⁺ from carbonic acid, similar to osteoclast.
• Prominent intracellular canaliculi lined by microvilli.
• Tubulovesicle pools are part of exocytosis-endocytosis function.

Question 151

Describe the periodontal membrane.

Answer 151

Periodontal Membrane

• CT formed from dental sac with fibroblasts, osteoblasts, cementoblasts, collagen fibers, blood vessels, and nerve fibers.
• Highly metabolically active tissue.
• Binds cementum to bony socket.
• Sharpey’s fibers extend from cementum to alveolar wall via the membrane.
• Allows limited movement.
• Absorbs pressures of mastication and prevents this pressure from damaging alveolar bone.
• Affected by diseases such as diabetes and scurvy.

Question 152

Describe the plicae as one of the orders of folding observed in the gut tube.

Answer 152

Gut Tube - Plicae

• These are folds of the mucosa, each with a submucosal core.

Question 153

Describe the microvilli as one of the orders of folding observed in the gut tube.

Answer 153

Gut Tube - Microvilli

• Covered with glycoprotein and glycocalyx (glycolipid coat):
  
  • Glycocalyx contains an array of brush-border enzymes:
    
    • Maltase, sucrase, isomaltase, lactase, lipase, peptidases.
    • Produced by small intestinal epithelial cells.
• Bundles of actin filaments within microvillus is covered by a formin cap.
• Supported by core of actin microfillaments:
  
  • Actin filaments are tied to terminal web intermediate filaments (cytokeratins) via spectrin fibrils.
  • Actin filaments are bound to plasma membrane covering villus via membrane-linking proteins:
    
    • Myosin I and calmodulin.
  • Acrtin filaments are bound to each other via actin cross-linking proteins:
    
    • Villin and fimbrin.

Question 154

Describe the portal triad.

Answer 154

Liver - Portal Triad

• Location:
  
  • Found at angles (corners) of classic lobule.
• Components:
  
  • Branch of hepatic artery (arteriole).
  • Branch of portal vein (venule).
  • Bile duct (ductule).

Question 155

Describe the primary dermal ridge.

Answer 155

Integument - Primary Dermal Ridge

• Related to fingerprints.
• Found everywhere except forehead, external ear, perineum, and scrotum.
• Formed during months 3-4 of fetal life.
• Subdivided into two secondary dermal ridges by interpapillary peg.

Question 156

Describe the pulp of the teeth.

Answer 156

Teeth - Pulp

• Originates from the dental papilla containing condensed mesenchym.
• Consists of fibroblasts, macrophages, peripheral odontoblasts, reticular fibers, nerve fibers, and blood vessels that pass via the apical foramen.

Question 157

Describe the rapid cell turnover of the intestine.

Answer 157

Rapid Cell Turnover

• A protective mechanism used by the GI epithelium:
  
  • True of most of GI tract:
    
    • Particularly true of stomach and small intestine.
    • Lining replaced every 5 days in humans.
  • In esophagus and anus:
    
    • New cells are formed in basal layer of stratified epithelium and migrate through sub-basal levels to be sloughed off into the lumen.
  • In small intestine:
    
    • New cells are formed in the crypts from undifferentiated cells.
  • In large intestine:
    
    • There are no villi, so proliferative compartment is found at the base of the crypts.
  • In stomach:
    
    • Stem cells are found in the neck of the gastric glands.
    • Differentiated into:
      
      • Surface and neck mucus cells (turn over most rapidly)
      • Enteroendocrine cells
      • Parietal cells
      • Chief cells

Question 158

Describe the red pulp of the spleen.

Answer 158

Spleen - Red Pulp

• Surrounds white pulp and makes up about 80% of the spleen.
• Functions to filter blood.
• Contains large numbers of RBCs and other blood elements.
• Billroth cords form red pulp parenchyma:
  
  • Contain various blood cells, plasma cells, and antigen presenting cells.
  • Terminal capillaries open directly into substance of cords (open circulation).
  • Macrophages destroy worn-out or defective RBCs.
• Venous sinusoids:
  
  • Endothelial-lined sinusoids with a discontinuous basement membrane.
  • Storage sites for healthy RBCs.

Question 159

Describe the regions of the kidney.

Answer 159

Kidney

• Sagittal section reveals:
  
  • Outer capsule surrounding the entire kidney, except the hilum.
  • Outer cortical area beneath the capsule which has a cuplike form with the open side of the cup shape facing the hilum.
  • Juxtamedullary cortex deep to the outer cortical area.
  • Medullary area made up of triangular-shaped renal pyramids and divided into:
    
    • Outer medullary area deep to the juxtamedullary cortex.
    • Inner medullary area deep to the outer medullary area.
  • The renal pelvis into which the renal pyramids empty.
• Each kidney fed by a large renal artery branching directly off the abdominal aorta.

Question 160

Describe the regions of the stomach.

Answer 160

Stomach - Regions

• Cardia
  
  • Contains mostly mucous glands.
• Fundus:
  
  • Contains gastric glands:
    
    • Long tubular glands extending down to the muscularis mucosae.
    • Composed of mucous neck cells, parietal cells, chief cells, stem cells, and enteroendocrine cells.
• Body:
  
  • Contains gastric glands.
• Pylorus:
  
  • Contains mucous glands and hormone-secreting enteroendocrine cells.

Question 161

Describe the relationship between blood pressure and vascular anatomy.

Answer 161

Blood Pressure vs. Vascular Anatomy

• Note pressure drops as arteries leave the heart and become progressively smaller.
• The structure of the tunic, especially the tunica media changes from that of an elastic tunic to that of a muscular tunic.
• The more elastic arteries are conducting arteries.
• The more muscular arteries are distributing arteries.

Question 162

Describe the renal corpuscle.

Answer 162

Renal Corpuscle

• Glomerulus:
  
  • Afferent arteriole:
    
    • Juxtaglomerular cells:
      
      • Circular smooth muscle cells at vascular pole.
      • Secrete renin (hypertensive factor).
  • Glomerular formation of capillaries.
  • Efferent arteriole.
• Bowman’s capsule:
  
  • Double-layered, cup-shaped dilation of the nephron; consists of an inner and outer layer:
    
    • Parietal layer:
      
      • Outer layer of simple squamous epithelium.
      • Epithlelium is continuous with the simple cuboidal epithelium of the proximal convoluted tubule.
    • Visceral layer:
      
      • Inner layer of podocytes in contact with the endothelium of the glomerular capillaries.
  • Bowman’s space is located between the parietal and visceral layers and is continuous with the lumen of the proximal convoluted tubule.
• Involved in producing a filtrate of blood.
• The rest of the nephron, including the convoluted portions and the loop of Henle, as well as the collecting tubules, is involved in modifying the filtrate.
• Formation of urine involves three processes:
  
  • Filtration
  • Reabsorption
  • Secretion
• Whatever is filtered and secreted but not reabsorbed forms the excretory product of the kidneys - urine.

Question 163

Describe the renal filtration barrier.

Answer 163

Renal Filtration Barrier

• Components:
  
  • Fenestrated endothelium of glomerular capillaries.
  • Fused basal laminae of endothelial cells and podocytes.
  • Filtration barrier components:
    
    • Fenestrated endothelium of capillaries.
    • Basal Lamina:
      
      • Contains type IV collagen, fibronectin, laminin, heparin sulfate.
    • Filtration slits created by adjacent pedicels of podocytes:
      
      • Covered by filtration slit diaphragm.
      • Pedicels are attached to basal lamina via integrins.
• Selectivity:
  
  • Water, glucose, and most ions pass through filter into Bowman’s space.
  • Proteins are typically excluded from passing across the filter.
  • Molecules with a large negative charge are excluded.

Question 164

Describe the respiratory bronchioles.

Answer 164

Respiratory Bronchioles

• Diameter < 0.5 mm.
• Epithelium of low columnar to low cuboidal.
• Cilia present only in larger respiratory bronchioles.
• Goblet cells absent.
• Wall consists of smooth muscle within FECT.
• May have a few alveolar outpocketings:
  
  • Because gas exchange may occur here for the first time in the respiratory tree.

Question 165

Describe the segmentation of intrapulmonary bronchial tree.

Answer 165

Segmentation of Intrapulmonary Bronchial Tree

Question 166

Describe the serosa and adventitia (outermost layer) of the digestive tube.

Answer 166

Digestive Tube - Serosa and Adventitia (Outermost Layer)

• Serosa:
  
  • Composed of dense irregular CT.
  • Consists of a mesothelial lining and a layer of submesothelial connective tissue.
  • Forms visceral peritoneum.
  • Covers intraperitoneal portions of abdominal organs.
• Adventitia:
  
  • Dense irregular CT with adipose tissue.
  • Covers retroperitoneal portions of digestive system.

Question 167

Describe the stratum basale.

Answer 167

Epidermis - Stratum Basale (Germinativum)

• Deepest
• Columnar to high cuboidal keratinocytes.
• Keratins 5 & 14 (low-molecular weight keratins)
• Single layer of cells:
  
  • Held together by desmosomes.
  • Hemidesmosomes hold layer to basal lamina.
• High mitotic activity:
  
  • Mitotic activity produces stem cells differentiating keratinocytes.
  • Affected by chemotherapeutic and radiation treatments.
  • Keratinocytes are the major type of cell in the epidermis and are the cells that arise from the stratum basale and undergo keratinization.

Question 168

Describe the stratum corneum.

Answer 168

Epidermis - Stratum Corneum

• Multilayered (5-50 layers)
• Thicker in thick skin.
• Enucleated, flattened, dead keratinocytes.
• Cytoplasm replaced by keratin.
• Cytoplasm contains:
  
  • Keratin cross-linked with filaggrin -> cornified cell envelope.

Question 169

Describe the stratum granulosum.

Answer 169

Epidermis - Stratum Granulosum

• Multilayered
• Keratins 2e & 9
• Flattened nucleated keratinocytes.
• Keratohyalin aggregates:
  
  • Fillagrin induces cross-linkage of keratin filaments by disulfide bonds.
  • No limiting membrane.
• Membrane-coating granules (lamellar bodies)
  
  • Acylglucosylceramide -> intercellular spaces.
• Tonofilaments

Question 170

Describe the stratum lucidum.

Answer 170

Epidermis - Stratum Lucidum

• Flat keratinocytes lacking nuclei and organelles.
• Only found in thick skin.
• Contains eleiden.

Question 171

Describe the stratum spinosum.

Answer 171

Epidermis - Stratum Spinosum

• Polyhedral-shaped cells (prickle cells).
• Keratins 1 & 10 (high-molecular weight keratins).
• Keratohyalin granules develop.
• Membrane-coating granules first appear:
  
  • Lamellar bodies:
    
    • Contain lipid, carbohydrate, and hydrolytic enzymes.
• Tonofibrils:
  
  • Form intercellular bridges.

Question 172

Describe the structure of an antibody.

Answer 172

Antibodies - Structure

• Light and heavy chains.
• Highly variable regions:
  
  • Fab fragment - recognizes antigen.
• Less variable regions:
  
  • Fc fragment - binds antibody to cells.

Question 173

Describe the structure of capillaries.

Answer 173

Capillaries - Structure

Question 174

Describe the structure of the gallbladder.

Answer 174

Gallbladder - Structure

• Fundus
• Body
• Neck
  
  • Mucosal folds form the spiral valve of Heister.
• Wall:
  
  • Mucosa:
    
    • Epithlium is tall columnar with a striated border.
    • Lamina propria of CT has extensive vascular plexuses and may contain a few smooth muscle cells.
    • Rokitansky-Aschoff sinuses are small diverticula of the mucosa which extend into the muscular and perimuscular layers and may indicate pathological change.
  • Muscularis externa:
    
    • Layers of smooth muscle separated by layers of CT.
  • Serosa:
    
    • Has a broad perimuscular CT coat, rich in blood, lymphatic vessels and elastic fibers.

Question 175

Describe the structure of the stomach.

Answer 175

Stomach - Structure

• Epithelial lining:
  
  • Gastric mucosa consists of a simple columnar epithelium with mucous columnar cells.
  • Surface mucous cells secrete a protective insoluble mucous.
  • Rugae are longitudinal mucosal folds that are most prominent in an empty stomach.
• Gastric glands:
  
  • Gastric glands open into gastric pits.
• Muscularis externa:
  
  • Has 3 layers of smooth muscles.
  • 3rd layer is an inner oblique layer.

Question 176

Describe the structure of the trachea.

Answer 176

Trachea - Structure

• Mucosa:
  
  • Respiratory epithelium with thick basement membrane.
  • Lamina propria with delicate FECT (fibroelastic CT) and lymphatic tisse.
• Submucosa:
  
  • Many sero-mucous glands.
• Adventitia:
  
  • 16-20 horseshoe shaped cartilages interconnected by FECT.
  • Opening between arms of horseshoe-shaped cartilages closed by:
    
    • FECT, mucous membrane, and smooth muscles (trachealis muscles).
  • Mixed glands and capillaries.

Question 177

Describe the submucosa of the digestive tube.

Answer 177

Digestive Tube - Submucosa

• Dense, irregular CT.
• Vascularized
• Contains a nerve plexus: Meissner’s plexus (submucosal plexus).

Question 178

Describe the taste buds.

Answer 178

Tongue - Taste Buds

• Contain 2 types of cells derived from a single stem cell:
  
  • Sustentacular cells:
    
    • Spindle-shaped support cells and arranged like barrel-staves to surround the inner taste pore at the base.
  • Taste cells:
    
    • Each cell is long and slender with an elongated central nucleus and terminates as a short taste hair which projects into the external opening called the outer taste pore.
    • Possess apical microvilli with taste receptors.
    • Basal part of cell releases neurotransmitters.
    • Taste cells are dsitributed between the supporting cells.

Question 179

What are the three orders of folding in the gut tube.

Answer 179

Gut Tube - Three Orders of Folding

• Plicae
• Crypt-villus system
• Microvilli

Question 180

Describe the tongue.

Answer 180

Tongue

• Composed primarily of a core of skeletal muscle and glands, and is covered by a mucous membrane.
• Anterior 2/3 of the upper oral portion is separated from the posterior 1/3 by the sulcus terminalis.
• Lingual papillae appear on the oral portion as surface projections; they are formed of a central core of CT lamina propria covered by stratified squamous epithelium.

Question 181

Describe the trabeculae of the thymus.

Answer 181

Thymus - Trabeculae (Septa)

• Delicate CT
• Divides the thymus into incomplete lobules.

Question 182

Describe the transport of bile into the bile canaliculus.

Answer 182

Transport of Bile into the Bile Canaliculus

Question 183

Describe the tunica adventitia.

Answer 183

Vascular Tunics - Tunica Adventitia

• Outermost layer:
  
  • Lacking in arterioles.
• Consists of loose areolar tissue.
• Contains irregular fibroelastic tissue with adipocytes.
• Has small vessels (vasa vasorum) and nerves (nervi vasorum)

Question 184

Describe the tunica intima.

Answer 184

Vascular Tunics - Tunica Intima

• Components:
  
  • Endothelium and its basal lamina.
    
    • Found in all arteries and arterioles.
    • Endothelial cells produce von Willebrand’s factor VIII.
  • Subendothelial CT:
    
    • Found in all elastic and muscular arteries and some arterioles.
  • Internal elastic membrane:
    
    • Incomplete in elastic arteries but thick and complete in muscular arteries.

Question 185

Describe the tunica media.

Answer 185

Vascular Tunics - Tunica Media

• Made up of circular smooth muscle tissue and fibroblasts.
• Contains collagen and elastic fibers.

Question 186

Describe the tympanic membrane.

Answer 186

Ear - Tympanic Membrane

• The tympanic membrane (eardrum) separates the external auditory canal from the middle ear.
• Core is formed from vascularized, innervated connective tissue.
• External surface is covered by thin skin.
• Internal surface is covered by simple cuboidal epithelium.

Question 187

Describe the urinary bladder.

Answer 187

Urinary Bladder

Question 188

Describe the uriniferous tubule.

Answer 188

Uriniferous (Renal) Tubule

• Simple squamous epithelium of Bowman’s capsule becomes continuous with the simple cuboidal epithelium of the proximal convoluted tubule. The proximal convoluted tubule is the first part of the renal tubule.
• Parts:
  
  • Proximal convoluted tubule.
  • Descending limb of Henle (with thick and thin portions).
  • Loop of Henle.
  • Ascending limb of Henle (with thick and thin portions).
  • Distal convoluted tubule.
• Distal convoluted tubule is continuous with the collecting duct.

Question 189

Describe the vascular supply of the liver.

Answer 189

Liver - Vascular Supply

• Afferent blood vessels (give off interlobular branches):
  
  • Portal vein
  • Hepatic artery
• Branches from the portal vein enter the lobule and empty into the hepatic sinusoids:
  
  • Converge toward the center to empty into the:
• Central vein, an efferent vessel.
• Central veins unite to form a sublobular vein - tributary of the hepatic vein.
• Hepatic artery follows the branching of the portal vein through the interlobular CT; interlobular arterioles empty into the hepatic sinusoids, which drain to the central vein.

Question 190

Describe the vascularization of the spleen.

Answer 190

Spleen - Vascularization

• Arteries:
  
  • Splenic artery enters hilus.
  • Trabecular arteries branch off.
  • Central arteries:
    
    • Adventitia capillaries form, supplying white pulp, central arteries loose their white pulp investment and enter red pulp to form penicillus.
  • Penicillus - composed of pulp arteriole, sheathed arteriole, and terminal capillary.
  • Terminal capillary - drains into intercellular spaces (open system) or venous sinuses lined with reticuloendothelial cells (closed system).
• Veins:
  
  • Venous sinuses are lined with reticuloendothelial cells.
    
    • Drain into:
      
      • Pulp veins which united with trabecular veins forming splenic vein, which exits at hilus.

Question 191

Describe the vestibular organs of the inner ear.

Answer 191

Inner Ear - Vestibular Organs

• Patches of sensory structures that respond to changes in position.
• Consist of:
  
  • Maculae of the saccule and utricle.
  • Cristae ampullaris of the semicircular canals.

Question 192

Describe the white pulp of the spleen.

Answer 192

Spleen - White Pulp

• Elongated, branched strands always associated with arteries.
• Zones of diffuse lymphoid tissue and germinal centers.
• Site of clonal expansion of antigen-stimulated lymphocytes.
• B cell area contains secondary follicles in which central arteriole is off center.
• T cells are found in the areas surrounding the central artery near the center of the white pulp.
  
  • Forms the periarterial lymphatic sheath (PALS)
• Reticular fibers area associated with fixed macrophages and support splenic pulp.

Question 193

Describe thick vs. thin skin.

Answer 193

Integument - Thick vs. Thin

• Thick skin:
  
  • Occurs only on palms and soles - hairless.
  • Epidermis varies from 0.4-0.6 mm thick.
  • Displays all five epidermal layers.
• Thin skin:
  
  • Occurs over rest of body.
  • Epidermis varies from 75-100 micrometers thick.
  • Thinnest on eyelids.
  • Thickest on back.
  • Thicker on extensor surfaces than flexor surfaces.
  • Epidermal layers less distinct and lacking stratum lucidum.

Question 194

Describe veins.

Answer 194

Veins

• Comparison with arteries:
  
  • Larger lumen.
  • Thinner wall.
  • Valves are present in many veins.
• Larger veins have a layer of longitudinal smooth muscle in the inner aspect of the tunica adventitia.

Question 195

What are pericytes?

Answer 195

Pericytes

• Undifferentiated mesenchymal cells.
• May be contractile.
• May serve as stem cells to differentiate into fibroblasts, etc.

Question 196

What are the 2 layers of the dermis?

Answer 196

Dermis - Layers

• Papillary layer (closest to epidermis).
  
  • Loose CT.
  • Separated from epidermis by basal lamina.
  • Network of fine elastic fibers and abundant capillaries.
• Reticular layer:
  
  • Dense irregular CT.
  • Includes fibrocytes, macrophages, and adipocytes.

Question 197

What are the 3 sections of the small intestine?

Answer 197

Small Intestine - Sections

• Duodenum
• Jejunum
• Ileum

Question 198

What are the 3 types of capillaries?

Answer 198

Capillaries - 3 Types

• Be able to give examples of where each kind of capillary is found.

Question 199

What are the 4 layers of the digestive tube?

Answer 199

Digestive Tube - Layes

• Mucosa (innermost)
• Submucosa
• Muscularis externa
• Outermost layer:
  
  • Serosa
  • Adventitia

Question 200

What are the 4 regions of the inner ear?

Answer 200

Inner Ear - Regions

• Bony labyrinth
• Membranous labyrinth
• Vestibular organ
• Auditory organ

Question 201

What are the 5 classes of antibodies?

Answer 201

Antibodies - Classes

• IgA
• IgD
• IgG
• IgM
• IgE

Question 202

What are the 6 types of immunity?

Answer 202

Immunity - Types

• Innate
• Acquired
• Passive
• Active
• Cell-mediated
• Humoral

Question 203

What are the cardiac tunics?

Answer 203

Histology of Heart - Cardiac Tunics

• Endocardium
• Myocardium
• Epicardium

Question 204

What are the cells involved in tooth development?

Answer 204

Tooth Development - Cells

• Odonotoblasts
• Ameoblasts

Question 205

What are the characteristics of the dermis?

Answer 205

Dermis - Charateristics

• Dense fibrous irregular CT layer beneath epidermis.
• Derived from embryonic mesoderm.
• Induces development of epidermis and epidermal derivatives.
• Supports epidermis.

Question 206

What are the characteristics of the hypodermis?

Answer 206

Hypodermis - Characteristics

• Loose CT that underlies dermis.
• Corresponds to superficial fascia of gross anatomy.
• Technically not part of skin.
• May contain fat cells that can form a thick layer called the panniculus adiposus.

Question 207

What are the functions of the liver?

Answer 207

Liver - Function

• Removal of bile pigments from the blood and secretion of these pigments into the bile.
• Storing of glycogen.
• Converting fats and perhaps proteins to carbohydrates (gluconeogenesis).
• Maintaining constancy of blood glucose level.
• Chief site of amino acid deamination with urea as a by-product.
• Metabolizing fat and storing in liver.
• Synthesizing plasma proteins such as fibrinogen, prothrombin, and albumin.
• Storing of essential vitamins: A, D, B2, B3, B4, B12, and K.
• Serving as an embryonic hematopoietic organ.
• Ethanol metabolism.
• Detoxification of drugs, steroids, vitamins A and D, fatty acids, and carcinogens.

Question 208

What are the layers of the epidermis?

Answer 208

Epidermis - Layers

• Stratum basale (germinativum) - deepest
• Stratum spinosum
• Stratum granulosum - only a few cells in thin skin
• Stratum lucidum - absent in thin skin
• Stratum corneum - most superficial

Question 209

What are the layers of the intestinal wall?

Answer 209

Small Intestine - Layers

• Mucosa with lamina propria and muscularis mucosa.
• Submucosa
• Muscularis layers
• Serosa

Question 210

What are the major ducts of the liver and describe them.

Answer 210

Liver - Ducts

• Major ducts:
  
  • Cystic duct
  • Hepatic duct
  • Common bile duct.
• Mucosa:
  
  • Ducts are lined with columnar epithelium with goblet cells.
• Muscularis externa:
  
  • No definite pattern.

Question 211

What are the three vascular tunics?

Answer 211

Vascular Tunics

• All blood vessels except capillaries have 3 layers:
  
  • Tunica intima
  • Tunica media
  • Tunica adventicia

Question 212

What are the two divisions of the respiratory system?

Answer 212

Respiratory System

• 2 divisions:
  
  • Air-conducting portion.
  • Respiratory portion.

Question 213

What are lymphoid follicles.

Answer 213

Lympoid Follicles

• Lymph follicles (nodules):
  
  • Not enclosed within a capsule.
  • Occur singly or in aggregates.
  • Sites of B cell localization and proliferation.
  • Transient.
• Two types:
  
  • Primary follicles.
  • Secondary follicles.

Question 214

What is a major histocompatibility complex?

Answer 214

Major Histocompatibility Complex

• Main function of MHC gene products is the presentation of antigenic peptides to T cells.
• 2 classes:
  
  • MHC I - expressed on the surface of all cells except trophoblast and RBCs.
  • MHC II - expressed on the surface of B cells and antigen-presenting cells.
• CD8+ T cells recognized peptide fragments of foreign proteins bound to MHC I on the surface of cells.
  
  • CD8 is a member of the Ig superfamily.
    
    • Both CD8 and the T cells antigens receptor are required for binding of MHC I protein fragments.
• CD4+ T cells recognize peptide fragments of foreign proteins bound to MHC II proteins on surface of APCs.

Question 215

What is acquired immunity?

Answer 215

Acquired Immunity

• Develops in response to antigens.
• More powerful than innate immunity.
• Takes longer to develop.
• Displays specificity and memory.

Question 216

What is active immunity?

Answer 216

Active Immunity

• Long-lasting/permanent immunity due to self exposure to antigen resulting in memory T cells and B cells specific for antigen.

Question 217

What is an alveolar sac?

Answer 217

Alveolar Sac

• Composed of several alveoli.

Question 218

What is cementum?

Answer 218

Cementum

• Cells of the dental sac differentiate into cementoblasts which deposit cementum on the dentin of the root from neck to apex. Cementum has coarse collagen fibers (Sharpey’s) in a bone-like calcified matrix.

Question 219

What is IgA?

Answer 219

Antibodies - IgA

• Found in saliva, milk, GU and respiratory tracts.

Question 220

What is IgD?

Answer 220

Antibodies - IgD

• Found on surface of B cells travelling to lymphoid organs.

Question 221

What is IgE?

Answer 221

Antibodies - IgE

• Associated with allergic responses.

Question 222

What is IgG?

Answer 222

Antibodies - IgG

• Major Ig in blood.
• Responsible for most antibody activity.

Question 223

What is IgM?

Answer 223

Antibodies - IgM

• First antibody class expressed by developing B cells.

Question 224

What is innate immunity?

Answer 224

Innate Immunity

• Lacks immune specificity and memory.
• Response = inflammation.
• Neutrophils are the first responders.

Question 225

What is lymphopoiesis?

Answer 225

Lymphopoiesis

• All immune system cells originate in bone marrow.
• Immature T cells travel to thymus.
• B-cells travel to specific regions in lymphoid tissue.

Question 226

What is parenchyma?

Answer 226

Parenchyma

• Consists of the cells that typically pack areas of the lymphoid organ (mostly lymphocytes).

Question 227

What is passive immunity?

Answer 227

Passive Immunity

• Temporary immunity due to donated antibodies (i.e., transplacental passing of maternal antibodies to fetus).

Question 228

What is stroma?

Answer 228

Stroma

• Consists mostly of reticular fibers and cells, including undifferentiatted cells and fixed and free macrophages.

Question 229

What is the difference between diffuse and aggregated lymphatic tissue?

Answer 229

Lymphatic Tissue - Diffuse vs. Aggregated

• Diffuse:
  
  • Made up of scattered clusters of plasma cells, macrophages, and lymphocytes located in the connective tissue stroma and various other sites.
  • Subcutaneous-associated lymphoid tissue is found in the papillary layer of the dermis.
  • Lamina propria-associated lymphoid tissue includes:
    
    • MALT - mucosal-associated lymphoid tissue.
    • BALT - bronchial-associated lymphoid tissue.
    • GALT - gut-associated lymphoid tissue.
• Aggregated:
  
  • Lymphoid tissue is beneath and in contact with the epithelium.
  • Includes various tonsils and Peyer’s patches in the ileum.

Question 230

What is the epidermis derived from?

Answer 230

Embryonic ectoderm.

Question 231

What tissues form the teeth.

Answer 231

Teeth - Ebryonic Tissues

• 3 embryonic tissues interact in the development of teeth:
  
  • Ectoderm forms the enamel organ:
    
    • Consists of cells committed to formation of enamel.
    • Formed from the ectoderm under influence of mesoderm and neural crest.
  • Neural crest and mesoderm give rise to dental papilla.
    
    • Forms dentin, cementum, and pulp as well as surrounding connective tissue and periodontal pulp.