Chapter 4 Histology Flashcards
Histology
Study of normal structures of tissues
Tissues
Group of structurally and functionally related cells and their external environment, together perform common functions)
2 Components of Tissues
- Discrete population of cells; related in structure and function
- Extracellular matrix (ECM) - surrounding material
4 Primary tissue types
- Epithelial tissue
- Connective tissue
- Muscle tissue
- Nervous tissue
Epithelial Tissue
-Cover and line all body surfaces and cavities.
-Tightly packed sheets of cells with no visible ECM
-Form glands that manufacture secretions
Connective Tissue
-Connect all other tissues to one another
-ECM is very prominent
-Cells are scattered out
-Bind, support, protect and allow for transportation of substances
Muscle Tissue
-Capable of generating force by contracting
-Little ECM between cells
Nervous Tissue
-Capable of generating, sending, and receiving messages
-Within unique ECM
Extracellular Matrix (ECM)
Substance in liquid, thick gel, or solid form that surround cells of tissue
2 Components:
1. Ground substance
2. Protein Fibers
Functions of ECM
–Provides tissue with strength to resist tensile (stretching) and compressive forces
–Directs cells to proper positions within tissue and holds those cells in place
–Regulates development, mitotic activity, and survival of cells in a tissue
Ground Substance
- Most of ECM
-Extracellular fluid (ECF or interstitial fluid) with water, nutrients, ions, and three families of macromolecules:
- Glycosaminoglycans (GACS)
- Proteoglycans
- Cell- adhesion molecules (CAMs)
Glycosaminoglycans (GACS)
chondroitin sulfate (small) and hyaluronic acid (enormous):
Negative charges of sugars in GAG attract positively charged ions in ECF
Ions create concentration gradient within ECF; draw water out of cells and blood vessels by osmosis
Effectively “trap” water in ECM; help ECM to resist compression; GradientsCore Principle
Proteoglycans
GAGs bound to protein core (resembles bottle brush):
Thousands of proteoglycans bind to very long GAG (such as hyaluronic acid); form huge proteoglycan “aggregates”
Make ECM firmer, more solid, and resistant to compression
Form barrier to diffusion of substances through ECM; protect underlying tissue from invading microorganisms
Cell adhesion molecules (CAMs)
Different types of glycoproteins:
Adhere to cell and cells to surroundings; hold everything in place within ECM
CAMs bind to cell surface proteins as well as protein fibers and proteoglycans; maintain normal tissue architecture
Protein Fibers
Embedded within ground substance; long molecules composed of multiple fibrous subunits with rope like structure; enormous tensile strength.
- Collagen fibers
- Elastic fibers
- Reticular fibers
Collagen Fibers
- Make up 20–25% of all proteins in body
- Composed of multiple repeating subunits
- Form white fibrous protein
- Resistant to tension (pulling and stretching forces) and pressure
Elastic Fibers
- Composed of protein elastin surrounded by glycoproteins
- Extensibility allows fibers to stretch up to one and a half times resting length without breaking. once stretched, fibers return to resting length (elasticity)
Reticular Fibers
- Thin, short collagen fibers; form meshwork or scaffold that supports cells and ground substance of many tissues
- Form weblike structure in organs such as spleen that helps trap foreign cells
Marfan Syndrome
Results from defects in gene that codes for glycoprotein fibrillin-I
Fibrillin
Component of ECM required for normal deposition of elastic fibers
Characteristics and symptoms of Marfan Syndrome
*Tall stature with long limbs and fingers; multiple skeletal abnormalities, recurrent joint dislocations, heart valve and lens (eye) abnormalities, and dilation of aorta
*Aortic dissection (rupture) – most lethal complication; layers of aortic wall separate and blood flows between them; leads to aortic rupture; ensuing blood loss is nearly always fatal if not caught and treated immediately
Cell Junctions
Another way cells bind to one another; neighboring cell’s plasma membranes are linked by integral proteins:
*Tight junctions *Desmosomes
*Gap junctions
Tight Junctions
(occluding junctions)
Holds cells closely together, space between is impermeable to movement of macromolecules
–Integral proteins of adjacent cell’s plasma membranes are locked together; form seal around apical perimeter of cell
–Seal may not be complete, allowing for leakage in some tissues
Example – between cells in blood vessels; prevent blood cells from exiting vessels
Desmosomes
Linking integral proteins; allow for materials in extracellular fluid to pass through space between cells
–Increase strength of tissue by holding cells together; mechanical stress is more evenly distributed
–Integral “linker” proteins are attached to intermediate filaments of cytoskeleton for structural reinforcement
–In tissues subjected to great deal of mechanical stress (epithelia of skin)
Gap Junctions
small pores formed by protein channels between adjacent cells; allow small substances to flow freely between each cell’s cytoplasm
–In between cells that communicate with electrical signals (cardiac muscle cells)
–Gap junctions illustrate Cell–Cell Communication Core Principle
Epithelial Tissues
On every internal and external body surface. It is the barrier between body and external environment (line organs and fluid filled cavities)
Functions of Epithelial Tissues
- Protection
- Immune defenses
- Secretion
- Transport into other tissues
- Sensation
Protection
Shield underlying tissues from mechanical and thermal injury
Immune defense
Form physical barriers; prevent invasion by microorganisms; specialized cells of immune system are scattered throughout epithelial tissues to protect underlying tissues
Secretion
Form glands that produce substances like hormones and oils; secreted into blood or through ducts respectively
Transport into other tissues
Selective permeable membranes; substances are able to cross these barriers by passive or active transport and enter other tissues
Sensation
Associated with rich nerve supply, detect changes in internal and external environments
Ex: tastebuds
Esophagus
Tubular organ that transports food from mouth to stomach.
Identifying a cell
Any structure that contains dark purple nucleus
Identifying Ground substance
Looks clear or has a slight tinge of color
Identifying protein fibers
Look like wavy or straight lines
Identifying Collagen fibers
Form bundles that resemble certain cell types.
- If bundles lack nuclei then it is most likely a collagen fiber
Sublingual gland
Salivary gland that produces saliva under tongue
-Contains clusters of small, light red round discs that lack nuclei
Discs
Red blood cells (erythrocytes), located in blood vessels
Classification of Epithelial Tissues
Consist of tightly packed cells linked together by tight junctions and desmosomes.
-Make sheets of cells impermeable and resistant to physical stresses and mechanical injury
Avascular
(Epithelial tissues are avascular)
-Lack blood vessels, must obtain oxygen and nutrients by diffusion from deeper tissues
ECM Location
Found beneath cells in think Basement Membrane
Basement Membrane
Two components/layers :
- Basal lamina
- Reticular lamina
-These two layers “glue” and provide barrier to epithelial tissue to underlying connective tissue, anchor underlying blood vessels in place.
Basal Lamina
ECM synthesized by epithelial cells
-Consist of collagen fibers and ground substance
Reticular Lamina
Synthesized by underlying connective tissue
- Consist of reticular fibers and ground substance
Epithelial Tissues, classified by
Number of cells layers and shape of cells
Simple epithelia
Single cell layer, adapted for transportation of substances between different tissues
-Some have microvilli
-Some have cilia
Stratified epithelia
More than one cell layer
Squamous Cells
Flattened
Cuboidal Cells
Short
Columnar Cells
Tall and elongated
Microvilli
Increased surface area
Cilia
Move substances through hollow organs
4 Types of Simple Epithelia
- Simple squamous Epithelium
- Simple Cuboidal Epithelium
- Simple Columnar Epithelium
- Pseudostratified Columnar Epithelium
Simple Squamous Epithelium
-Very thin single layer of cells; “fried egg” appearance
- Adapted for rapid diffusion of substances (oxygen, carbon dioxide, fluids, and ions)
- In air sacs of lung, specific segments of kidney tubules, and lining blood vessel
Simple Cuboidal Epithelium
- Single layer of cube-shaped cells with large central nucleus
- Thin enough for rapid substance diffusion
- In segments of renal tubules, respiratory passages, ducts of many glands, and thyroid gland
Simple Columnar Epithelium
- Single layer of rectangular-shaped cells with nuclei in basal portion of cell
- Often microvilli (small intestine) or cilia
- (uterine tubes and segments of respiratory tract) on apical plasma membrane
Pseudostratisfied Columnar Epithelium
- Appears layered because nuclei are at various heights
- Only one cell-layer thick with basal plasma membranes firmly in contact with basement membrane
- In segments of respiratory tract and nasal cavity; ciliated
Transports across simple epithelia
- Paracellular transportation
- Transcellular transportation
Paracellular transportation
Substances leak between cells in epithelial membrane; limited due to tight junctions that make spaces between cells nearly impermeable
Transcellular transportation
Substance enters cell by crossing plasma membrane; diffuses across cytosol; exits cell through plasma membrane at opposite side
Stratified epithelium
More than one layer of cells; best as protective barriers where subjected to high degrees of mechanical stress
Types of Stratified Epithelium
- Keratinized stratified squamous epithelium
- Non-keratinized stratified squamous epithelium
- Stratified cuboidal epithelium
- Stratified columnar epithelium
- Transitional epithelium
Keratinized stratified squamous epithelium
-Apical cellular layers are dead
-lack nuclei
-filled with protein keratin
-makes tissue tough and resistant to friction
-well adapted for outer layers of skin
Non-keratinized stratified squamous epithelium
-apical cellular layers retain nuclei
-still alive
-in regions subjected to mechanical stress where surface must remain moist
-mouth, throat, esophagus, anus, and vagina
Stratified cuboidal epithelium
-rare in humans
-two cell layers
-lines ducts of sweat glands
Stratified columnar epithelium
-rare in humans
-few layers
-apical layer is columnar and basal cell layer is cuboidal
-in male urethra, cornea of eye, and ducts of certain glands such as salivary gland
Transitional epithelium
-only in urinary system
-lines interior of kidney, ureters, urinary bladder, and urethra
-cuboidal basal cell layers and dome-shaped apical cell layers in relaxed tissue
-ability of apical cells to flatten allows tissues to stretch
Gland
Structure of epithelial origin; synthesizes and secretes product from designated secretory cells.
-Classified by shape or how products are released:
1. Endocrine
2. Exocrine
Endocrine glands
Secrete products, usually hormones, directly into bloodstream without use of ducts:
Allow products to have systemic effects (on distant cells)
Exocrine Glands
-Multicellular glands that release products onto apical surfaces of epithelium (external surface of body) or lining hollow organ (opens to outside of body):
-Glands vary in complexity from single cells to large multicellular glands with branching ducts and many secretory units
Goblet cells
Most common unicellular exocrine gland; in digestive and respiratory tracts; secrete mucus- thick sticky liquid that protects underlying epithelium
Exocrine glands classification
Structure of duct and shape of clusters of secretory cells
Duct structure
-Simple glands - ducts dont branch
-Compound glands - branched ducts
Tubular
Long and straight or coiled configuration
Acinar
Spherical configuration
Tubuloacinar
Both tubular and acinar configurations
Methods of product secretion by exocrine glands
- Merocrine
- Holocrine
- Apocrine
Merocrine
Used by majority of exocrine glands, including salivary and sweat glands
-products packaged in secretory vesicles for release by exocytosis into ducts
Holocrine
Used by sebaceous glands in skin to secrete sebum; secretory cells accumulate product in cytosol; only release product when cell ruptures and dies; cells replaced by mitosis at gland base
Apocrine
Rare type of secretion; portions of cytoplasm are pinched off with product being secreted; observed during lipid droplet secretion in lactating mammary glands of many mammal species
Carcinogens
Agents that induce DNA changes (injury); can lead to cancer
Carcinoma
Term for epithelial cancer; common examples:
–Lung adenocarcinoma
–Ductal and papillary carcinoma – cancer of breast
–Basal cell carcinoma – cancer of skin
Connective Tissues
2 groups:
-Connective tissue proper
-Specialized connective tissue
Connective tissue functions
*Connecting and binding – anchor tissue layers in organs and link organs together
*Support – bone and cartilage support weight of body
*Protection – bone tissue protects internal organs; cartilage and fat provide shock absorption; components of immune system are throughout connective tissues
*Transport – blood is fluid connective tissue; main transport medium in bod
Connective tissue proper
(General connective tissue)
*Widely distributed in body
*Connect tissues and organs to one another
*Components of internal architecture of some organ
Cells of connective tissue proper
Resident cells permanently inhabit tissue; migrant cells migrate to areas of body depending on situation:
-Fibroblasts
–Adipocytes
–Mast cells
–Phagocytes
–Other immune system cells
Fibroblasts
Most common resident cell
Mature cells with properties of immature “blast” cell
Make protein fibers and ground substance (components of ECM); continually produce collagen proteins
Adipocytes (fat cells)
In many different connective tissues; cytoplasm filled with a single large lipid inclusion
Mast cells
largest resident cell
Immune system cells filled with cytosolic inclusions (granules) of inflammatory mediators (histamine)
Release mediators (degranulate) when stimulated, causing inflammation(protective response that activates immune system)
Phagocytes
-Immune system cells
-Ingest foreign substances, microorganisms, and dead or damaged cells by phagocytosis
- Include macrophages (resident or migrant) and neutrophils (migrant cells)
Other immune system cells
Migrate in and out of connective tissues depending on body’s needs
Types of connective tissue proper
–Loose connective tissue
–Dense connective tissue
–Reticular tissue
–Adipose tissue
Loose connective tissue
(Areolar tissue)
Mostly ground substance; contains all three types of protein fibers, fibroblasts, and occasionally adipocytes, suspended in ground substance
Beneath epithelium of skin, in membranes lining body cavities, and within walls of hollow organs
Contains and supports blood vessels vital to avascular epithelial tissues; houses immune system cells
Dense Connective tissue
(Fibrous connective tissue)
Mostly protein fibers. Three classes:
- Dense irregular connective tissue
- Dense regular connective tissue
- Dense regular elastic connective tissue
Dense irregular connective tissue
Predominantly disorganized collagen bundles:
–Strong; resists tension in all three planes of movement
–In high tension areas such as dermis (deep to skin) and surrounding organs and joints
Dense regular connective tissue
–Organized into parallel collagen bundles
–In tendons and ligaments; subject to tension in one plane of movement
Dense regular elastic connective tissue
(Elastic tissue)
–Mostly parallel-oriented elastic fibers with randomly oriented collagen fibers
–In walls of organs that must stretch to function (large blood vessels and certain ligaments)
Reticular Tissue
Mostly reticular fibers produced by fibroblasts.
Forms fine networks that support small structures such as blood and lymphatic vessels
Also in lymph nodes and spleen; forms weblike nets that trap old and foreign cells
Forms part of basement membrane; supports all epithelia and internal structure of liver and bone marrow
Adipose Tissue
(Fat tissue)
Fat-storing adipocytes and surrounding fibroblasts and ECM, adipocytes can increase in size to a point where fibroblasts and ECM are scarcely visible
Functions:
Fat storage (major energy reserve of body)
Insulation (retains warmth)
Shock absorption and protection
White Adipose tissue
Predominant fat tissue
- Appears white
- Adipocytes with one large lipid inclusion in cytosol
- Deep to skin as subcutaneous fat
- Abdomen, breasts, hips, buttocks, and thighs
-Visceral fat surrounds heart and abdominal organs
Brown adipose tissue
Less common
-Has brown appearance due to numerous mitochondria in cytoplasm and vast blood supply
-Contains multiple lipid inclusions
-More readily converted to energy to produce heat in cold temperatures
Obesity
Condition of excess adipose tissue in proportion to lean body mass; two forms:
Hypertrophic
Hypercellular
Hypertrophic Obesity
Lipid inclusions accumulate fatty acids
- Increase in size up to 4x normal
- Number of adipocytes remains unchanged
Hypercellular Obesity
Generally severe; number of adipocytes increases
- Correlates with development of obesity in infancy or early childhood (not adulthood)
- Adult adipocytes lack ability to divide to form new cells
Specialized Connective Tissue
Include three types of tissue:
- Cartilage
- Bone tissue (Osseous tissue)
- Blood
Cartilage
In joints between bones, ear, nose, and segments of respiratory tract.
- tough, flexible tissue; absorbs shock and resists tension, compression, and shearing forces; ECM consists of collagen and elastic fibers, proteoglycans, and glycosaminoglycans.
Bone Tissue (osseous tissue)
Supports body; protects vital organs; provides attachments for muscles that allow for movement; stores calcium; and houses bone marrow (produces blood cells and stores fat)
Blood
Unique connective tissue with liquid ECM (plasma); consists of mostly water, dissolved solutes, and protein
Cartilage: 2 cell types
- Chondroblasts
- Chondrocytes
Chondroblasts
Immature cells; divide by mitosis and make most of ECM
Chondrocytes
ECM to become mature and largely inactive
Cartilage: three classes
- Hyaline Cartilage
- Fibrocartilage
- Elastic Cartilage
Hyaline Cartilage
Most abundant cartilage:
–ECM mostly ground substance made of small bundles of fine collagen; gives tissue glossy bluish-gray appearance
–On ends of bones in joints (articular cartilage), linking sternum to ribs, framing sections of respiratory tract, and in nose
–Most of fetal skeleton is hyaline cartilage; replaced with bone during development
Fibrocartilage
Filled with bundles of collagen fibers; little room for ground substance in ECM
–Fibroblasts reside in tissue; also chondroblasts and chondrocytes; fill ECM with collagen and some elastic fibers
–Tissue has great tensile strength with some degree of elasticity
–In between bones of fibrous joints; forms articular discs that improve fit of bones in joints
Elastic Cartilage
Mostly elastic fibers in ECM:
–Allows tissue to vibrate
–In limited number of structures; external ear assists with detection of sound in air; larynx assists with production of sound
Bone
One of the hardest substances in the body.
-35% organic components and 65% inorganic calcium phosphate crystals.
-Dynamic tissue capable of remodeling
Osteoblast (bone)
“Bone-builders” on outer surface of bones; closely associated with dense irregular collagenous connective tissue covering (periosteum)
Carry out process of bone deposition; synthesize and secrete organic ECM and chemicals involved in trapping calcium in ECM
Osteocytes (bones)
Osteoblasts that have surrounded themselves with ECM in lacunae
- mature cells
-mostly inactive
-continue to make and secrete substances important for bone maintenance
Osteoclasts (bone)
large, multinucleated bone destroyers
-carry out process of bone resorption
-secrete hydrogen ions and enzymes that break down both inorganic and organic ECM
Blood
Unique , ECM is fluid:
-Plasma proteins
-Erythrocytes
-Leukocytes
-Platelets
Plasma Protein
Not like fibers found in other connective tissues; smaller with a variety of functions, including transport of substances and blood clotting
Erythrocytes
(red blood cells) bind to and transport oxygen throughout body
Leukocytes
(white blood cells) function in immunity
Platelets
cell fragments; major role in blood clotting
Osteoarthritis
Caused by age, joint trauma, genetic disorders, and infection
–Develops as hyaline cartilage lining joints degenerates
–Leads to destruction of proteoglycan and collagen fibers; may continue until bone is exposed
–Bones grind painfully together as motion occurs
Does glucosamine slow osteoarthritis degeneration of joints?
Muscle Tissue
Specialized for contraction
-Turn chemical energy of ATP into mechanical energy of movement
Main component of muscle tissue
Muscle Cell (myocyte)- excitable
Two forms of muscle cell
They are based on arrangement of myofilaments (protein bundles) in cytoplasm:
- Striated
- Smooth
Striated
Myofilaments arranged in alternating light and dark regions; appear striped (striated) under microscope
Ex: Skeletal and cardiac muscle tissue
Smooth
Myofilaments arranged in irregular bundles instead of repeating light and dark regions
Endomysium
Small amount of ECM that surrounds muscle tissue; helps hold muscle cells together in tissue
Three types of muscle tissue
- Skeletal muscle
- Cardiac muscle
- Smooth muscle
Skeletal muscle tissue
Mostly attached to skeleton; contraction produces body movement
-Must be stimulated by nervous system to contract; under voluntary (conscious) control
-Are long, extending to almost entire length of whole muscle
-Forms by fusion of embryonic myoblasts
Cardiac Muscle Tissue
Only in heart; composed of cardiac muscle cells; striated like skeletal muscle cells
Cardiac muscle tissue
-Involuntary – brain does not have conscious control over contraction
–Cells are short, branched; usually only on nucleus (uninucleate)
–Intercalated disc – dark line separating individual cardiac muscle cells; not in skeletal muscle; contains gap junctions and modified tight junctions; allows heart muscle to contract as uni
Smooth Muscle Tissue
Consists of smooth muscle cells; contractions are involuntary like cardiac muscle:
–In walls of nearly every hollow organ, blood vessels, eyes, skin, and ducts of certain glands
–Flattened cells with one centrally located ovoid nucleus
–In most smooth muscle tissue, plasma membranes of neighboring cells are linked together by gap junctions
Nervous tissue
Makes up majority of brain, spinal cord, and nerves; two main cell types and their surrounding ECM:
-Neurons
-Neurological cells
Neurons
Capable of sending and receiving message
-excitable (like muscle cells); once mature, no longer divide by mitosis; three main components
Neurological cells
Perform various functions; support neuron activities
Nervous tissue ECM
-ECM is unique
-Ground substance with unique proteoglycans not found in other tissues
-Contains very few protein fibers
Neurons main components
- Cell Body (soma)
- Solitary Axon
- Dendrites
Cell Body (Soma)
Biosynthetic center of neuron; location of nucleus and most organelles
Solitary Axon
Extends from one end of soma
-responsible for moving nerve impulse from soma to target cell (another neuron, muscle cell, or gland
Dendrites
Other extensions protruding from soma
-typically short with multiple branches
-receive impulses from axons of neighboring neurons
-deliver impulses to soma
Neuroglial Cells
Diverse group of smaller cells; support activity of neurons:
–Functions:
Anchoring neurons and blood vessels in place
Monitoring composition of extracellular fluid
Speeding up rate of nerve impulse transmission
Circulating fluid surrounding brain and spinal cord–Able to divide by mitosis (unlike neurons)
Organ
Two or more tissues that combine structurally and functional
Membranes
Thin sheets of one or more tissues; line body surface or cavity:
*Most consist of superficial epithelial layer resting on connective tissue layer; sometimes contain smooth muscle
Functions of Membrane
-Anchor organs in place,
-Serve as barriers
-Function in immunity, and secrete various substances
True Membranes
- Serous
- Synovial
- Fit above structural and functional definitions
- Do not open outside of body
Membrane like structures
Mucous and cutaneous membranes
-Don’t fit above structural and functional definitions
-Perform many of same functions
Serous Membranes or Serosae
Line pericardial, peritoneal, and pleural body cavities:
–Consist of mesothelium
- Fold over themselves; appearance of two layers; outer parietal layer lines body wall; inner visceral layer covers organ within body cavity
Mesothelium
Thin layer of simple squamous epithelium, associated basement membrane, and layer of connective tissue
Synovial Membranes
Line cavities surrounding freely moveable joints (knee or shoulder); two connective tissue layers without layer of epithelial cell
Outer layer of Synovial Membranes
Usually composed of mixture of loose and dense irregular connective tissue
Inner layer of Synovial Membranes
Synoviocytes (modified fibroblasts) secrete synovial fluid; watery, slippery fluid; primarily functions to lubricate joint
Mucous membranes
(mucosae)
Line all passages opening to outside of body; respiratory passages, mouth, nasal cavity, digestive tract, and male and female reproductive tracts:
–Layer of epithelium and basement membrane (connective tissue called lamina propria) and occasionally thin layer of smooth muscle
–Contain glands with goblet cells; produce and secrete mucus; serve several functions, primarily protection
Cutaneous Membrane
Refers to skin; largest organ of body; consists of
–Outer layer of keratinized stratified squamous epithelium (epidermis); tough, continuous protective surface; protects structures deep to it
Dermis
Layer of loose connective tissue beneath epidermis plus deeper layer of dense irregular connective tissue
Home to many blood vessels; provides means for oxygen and nutrients to diffuse into avascular epidermis
Friction rub
Results in grating sound; can be heard with stethoscope
*Causes chest pain; worsens with inhalation, body movement, and swallowing
*Usually resolves with treatment of underlying condition
