Weeks 1, 2 and 3 Flashcards
Does the lymphatic system return leaked fluid to the blood, also helps in transporting absorbed lipids from the gut?
Yes
What are lacteals?
Specialised lymph capillaries present in intestinal mucosa.
Do lymphatic trunks, which are formed by union of largest collecting vessels, drain large areas of the body?
Yes
Are lymphatic vessels named for regions of the body they drain?
Yes.
Are some of the names for lymphatic vessels the following:
- Paired lumbar
- Paired bronchomediastinal
- Paired subclavian
- Paired jugular trunks
- Single intestinal trunks
Yes.
What is lymphangitis?
A condition in which lymphatic vessels appear as painful red lines under the skin.
Is lymphangitis caused by inflammation of larger lymphatic vessels that contain vaso
vasora?
Yes.
In lymphangitis, do the vaso vasora become congested with blood?
Yes.
Do larger lymphatics, like blood vessels, receive their nutrients from branching vasa vasorum?
Yes.
Is the lymph system a low-pressure system like venous system?
Yes.
Is lymph propelled by:
– Milking action of skeletal muscle
Pressure changes in thorax during breathing
– Valves to prevent backflow
– Pulsations of nearby arteries
– Contractions of smooth muscle in walls of lymphatics
Yes.
Physical activity increases flow of lymph;
Immobilization of area keeps needed inflammatory material in area
for faster healing
Yes.
Lymphedema: severe localized oedema
Yes.
Caused by anything that prevents normal return of lymph to blood
– Examples: tumours blocking lymphatics or removal of lymphatics during cancer
surgery
– Lymphedema may improve if some lymphatic pathways remain and enlarge
Yes.
• Immune system cells
– T cells: attack and destroy infected cells
– B cells: produce plasma cells, which secrete antibodies
Yes.
Other lymphoid immune cells
– Macrophages
– Dendritic cells
Yes.
Supporting lymphoid cell
– Reticular cells produce reticular fibers called stroma in lymphoid organs
Yes.
Lymphoid Tissue
Houses and provides proliferation sites for lymphocytes
– Offer surveillance
Yes.
Lymphoid Tissue
Largely composed of reticular connective tissue, a type of loose
connective tissue
Yes.
Are there two main types of lymphoid tissues?
Yes.
Diffuse lymphoid tissue: loose arrangement of lymphoid cells and
some reticular fibers
– Found in virtually every body organ
– Larger collections in lamina propria of mucous membranes
Yes.
Lymphoid follicles (nodules): solid, spherical bodies consisting of tightly
packed lymphoid cells and reticular fibers
– Contain germinal centers of proliferating B cells
– May form part of larger lymphoid organs (nodes)
– Isolated aggregations in Peyer’s patches and in appendix
Yes.
Are lymph nodes the principal secondary lymphoid organs of body?
Yes.
Are the two main functions of lymph nodes:
1. Cleansing the lymph: act as lymph “filters”
2. Immune system activation: offer a place for lymphocytes to become
activated and mount an attack against antigens
Yes.
Do lymph nodes vary in shape and size, but most are bean shaped?
Yes.
Are lymph nodes small, less than 2.5 cm (~1 inch)?
Yes.
Are lymph nodes surrounded by external fibrous capsule?
Yes.
Lymph nodes: Do capsule fibers extend inward as trabeculae that divide node into
compartments
Yes.
Two histologically distinct regions of lymph node:
– Cortex
– Medulla
Yes.
Spleen functions
– Site of lymphocyte proliferation
– Cleanses blood of aged cells removes debris
– Stores breakdown products of RBCs (e.g., iron) for later reuse
– Stores blood platelets and monocytes for release into blood when needed
– May be site of foetal erythrocyte production
Yes.
• Spleen is encased by fibrous capsule and also has trabeculae
Yes.
• Histologically, consists of two components
– White pulp
– Red pulp
Yes.
Clinical homeostatic imbalance:
The spleen has a thin capsule, so direct blow or severe infection may
cause it to rupture, spilling blood into peritoneal cavity
Yes.
Splenectomy: surgical removal of ruptured spleen
Yes.
If spleen must be removed, liver and bone marrow take over most of its
functions
Yes.
Splenectomy: in children younger than 12, spleen will regenerate if a small part is left
Yes
Mucosa-associated lymphoid tissue (MALT)
– Lymphoid tissues in mucous membranes throughout body
Yes.
MALT: Protects from pathogens trying to enter body
Yes.
Malt: found in mucosa of respiratory tract, genitourinary organs, and
digestive tract; largest collections of MALT found in
– Tonsils
– Peyer’s patches
– Appendix
Yes.
Tonsils: Simplest lymphoid organs
Yes.
Tonsils: Form ring of lymphatic tissue around pharynx; appear as swellings of
mucosa
Yes.
Tonsils:Named according to location
– Palatine tonsils, Lingual tonsil, Pharyngeal tonsil, Tubal tonsils
Yes.
• Tonsil function - gather and remove pathogens
Yes.
Appendix: An offshoot of first part of large intestine
Yes.
Appendix: Contains a large number of lymphoid follicles
Yes.
Appendix: Location aids in functions (like Peyer’s patches)
Yes.
Appendix:
- Destroy bacteria, preventing them from breaching intestinal wall
- Generate “memory” lymphocytes
Yes.
Thymus: A bilobed lymphoid organ found in inferior neck
Yes.
Thymus: Functions as lymphoid organ where T cells mature
Yes.
Thymus is broken into lobules that contain outer Cortex and inner
Medulla
Yes
Thymus differs from other lymphoid organs
– Has no follicles
– Does not directly fight antigens
– Stroma is made up of epithelial cells, not reticular fibers
Yes.
The lymphatic vessels form a one-way system in which lymph flows only
toward the heart
– Returning leaked fluid back to the circulation
– Transporting absorbed nutrients (lipids) from the gut
Yes.
• The lymphoid organs and tissues provide the structural basis of the
immune system
– Lymph nodes, spleen, thymus, MALT and tonsils
– Lymphoid cells are housed and mature here
– Some lymphoid organs perform additional functions
Yes.
Immune system: Innate (nonspecific) defense system • Always prepared • Responding within minutes • Two lines of defenses • Inflammation
Yes.
Immune system: Adaptive (specific) defense system • Takes longer to react than innate • Third line of defense
Yes
Innate defenses Surface barriers • Skin • Mucous membranes
Yes.
Innate defenses Internal defenses • Phagocytes • Natural killer cells • Inflammation • Antimicrobial proteins • Fever
Yes.
Adaptive
defenses
Humoral immunity
• B cells
Yes.
Adaptive
defenses
Cellular immunity
• T cells
Yes.
First Line of Defense
Physical barriers
– Keratinized epithelial membrane and intact mucosae
– Hairs inside the nose
– Cilia in the upper respiratory tract
– Sticky mucus in digestive and respiratory tract
Yes.
First Line of Defense
Chemicals & enyzmes
– Acid mentle inhibits bacterial growth (skin, vagina,stomach)
– Lysozyme of saliva, respiratory mucus, and lacrimal fluid, Enzymes in stomach
– Defensins control bacterial and fungal colonization
– Sebum and dermicidin in sweat are toxic to some bacteria
Yes.
Second Line of Defense: Cells and Chemicals
Phagocytes
• Natural killer (NK) cells
• Antimicrobial proteins (interferons and complement)
• Inflammatory response (macrophages, WBCs, mast celles, and
inflammatory chemicals)
• Fever
Yes.
Phagocytosis
Opsonization: immune system uses antibodies or complement proteins
as opsonins that coat pathogens
• Cytoplasmic extensions (pseudopods) bind to and engulf particle in
vesicle called phagosome
• Phagosome fuses with lysosome, forming phagolysosome
• Phagolysosome is acidified, and lysosomal enzymes digest particles
• Indigestible and residual waste is exocytosed from phagocyte
Yes.
Inflammation: Tissue Response to Injury Inflammation is triggered whenever body tissues are injured • Trauma, heat, irritating chemicals, or infections by microorganisms • Benefits of inflammation: • Localize the damage and set a reparation of affected tissue • Alert the adaptive immune system • Cardinal signs of acute inflammation: • Redness • Heat • Swelling • Pain • Impairment of function
Yes.
Inflammation’s benefits It prevents the spread of damaging agents to nearby tissue It desposes of cell debris and pathogens It alerts the adaptive immune system It sets the stage for repair
Yes.
Inflammation: Tissue Response to Injury
Stages of inflammation
– Chemical ALARM
• Histamine released by mast cells
• Macrophages and epithelial cells of respiratory tissues, intestine have Toll-like
receptors (TLRs) CYTOKINES
• Kinins, prostaglandins (PGs), and complement
– Vasodilation and increased vascular permeability
• Role of OEDEMA Translocation of foreign material into lymphatics
• Role of FIBRIN MASH Isolate injured area
– Phagocyte mobilization
• Neutrophils flood area first; macrophages follow
Yes.
Antimicrobial Proteins
Antimicrobial proteins enhance innate defense
– Attacking microorganisms directly
– Hindering microorganisms’ ability to reproduce
• Most important antimicrobial proteins
– Interferons
– Complement proteins
• Complement system can be activated by three different pathways:
– Classical pathway
– Lectin pathway
– Alternative pathway
Yes.
Complement
• Inactive plasma proteins
• Major mechanism for destroying foreign substances
• Amplify inflammatory process
• Promote phagocytosis
• Lyses and kill certain bacteria (Membrane attack complex)
Yes.
Fever
• Abnormally high body temperature that systemic response to invading
microorganisms
• Leukocytes and macrophages exposed to foreign substances secrete
pyrogens
• Pyrogens act on body’s thermostat in hypothalamus, raising body
temperature
• Benefits of moderate fever
– Causes liver and spleen to sequester iron and zinc (needed by microorganisms)
– Increases metabolic rate, which increases rate
of repair
Yes.
Non-self substances, INTRUDERS, that can mobilize Antigens
adaptive defenses
and provoke an immune response
• Targets of all adaptive immune responses
• Most are large, complex molecules not normally found in body
• PROTEINS, POLYSACCHARIDES, LIPIDS, NUCLEIC ACIDS
Yes.
Do both B and T lymphocyte precursors originate in
red bone marrow?
Yes.
Role of Antigen-Presenting Cells (APCs) • Engulf and present fragments of Ag to T cells for recognition • Major types – Dendritic cells – Macrophages • Role of MHC proteins
Yes.
Activation and Differentiation of B Cells
• B cells are activated when antigens bind to surface receptors, crosslinking adjacent receptor
• Clonal selection, follows proliferation and differentiation of B cell into
effector cells
• Most clone cells become plasma cells, antibody-secreting effector cells
• Clone cells that do not become plasma cells become memory cells
– Provide immunological memory
– Mount an immediate response to future exposures to same antigen
Yes.
Immunological Memory
• Primary immune response: cell proliferation and differentiation upon
exposure to antigen for the first time (3-6 days after Ag encounter)
• Secondary immune response
- Re-exposure to same antigen gives faster, more prolonged, more
effective response
– Sensitized memory cells provide immunological memory
Yes.
Immunization by Injection of Antigens
• Immunization has been used for many years to produce acquired
immunity against specific diseases
• A person can be immunized by
– Injecting dead organisms that are no longer capable of causing disease but that still have
some antigens
– Toxins that have been treated with chemicals to destroy their toxic nature even though
their antigens for causing immunity are still intact
– And, finally, a person can be immunized by being infected with live organisms that have
been “attenuated”
Yes.
Antibodies
• Antibodies, called Immunoglobulins (Igs)—are proteins secreted by
plasma cells
- Gamma globulin portion of blood proteins
• Bind specifically with Ag detected by B cells
• Five Immunoglobulin (Ig) classes
Yes
In Summary…
• B Cells are activated (similar to T Cells) by Antigen Presenting Cells
• B Cells, upon activation, become Plasma Cells which are giant factories
of Antibody production
• Memory cells are also formed
• Secondary response is quicker and longer lasting than the primary
response
• Antibodies are of various types, each having its specific function
Yes.
Cellular Immune Response
• T cells provide defense against intracellular antigens
• T cell are best suited for cell to cell interaction
- For example: cells infected with viruses or bacteria, cancerous or abnormal cells,
foreign (transplanted) cells
• Some T cells directly kill cells; others release chemicals that regulate
immune response
Yes.
MHC Proteins and Antigen Presentation
• T cells respond only to processed fragments of antigens displayed on
surfaces of cells by major histocompatibility complex (MHC) proteins
• Antigen presentation is vital for activation of naive T cells and normal
functioning of effector T cells
• Two classes of MHC proteins:
• Class I MHC proteins: displayed by all cells except RBCs
• Class II MHC proteins: displayed by APCs (dendritic cells, macrophages, and B
cells)
Yes.
MHC Proteins and Antigen Presentation
• Class I MHC proteins
- Located on the surface of virtually all body cells
- Class I MHC crucial for CD8 cell activation
– Act as antigen holders; form “self” part that T cells recognize
– Inform cytotoxic T cells of microorganisms hiding in cells (cytotoxic T cells ignore
displayed self-antigens)
Yes.
MHC Proteins and Antigen Presentation
• Class II MHC proteins
- Less widespread than class I
- Bind with longer fragments (14–17 amino acids) of exogenous (extracellular)
antigens that have been engulfed and broken down in a phagolysosome by
antigen-presenting cell
- Class II MHC proteins recognized by naive CD4 and helper T cells
– Signal CD4 cells that help is required
Yes.
Activation and Differentiation of T cells
• Cytokines
- IL-2 is a key growth factor, acting on same cells that release it and other T cells
• Encourages activated T cells to divide rapidly
- Other cytokines amplify and regulate innate and adaptive responses
• Example: gamma interferon enhances killing power of macrophages
Yes.
Cellular Immune Response
• Helper T (TH
) cells
- Play central role in adaptive immune response
- Activate both humoral and cellular arms
- Once primed by APC presentation of antigen, helper T cells:
• Help activate B cells and other T cells
• Induce T and B cell proliferation
• Secrete cytokines that recruit other immune cells
• Without TH
, there is no immune response
Yes.
Cellular Immune Response
- Activation of CD8 cells
– CD8 cells require TH
cell to become activated into destructive cytotoxic T cells
– Cause dendritic cells to express co-stimulatory molecules required for CD8 cell
activation
– Cytotoxic T cells attack infected and cancerous cells
Yes.
Regulatory T (TReg) cells
- Diminish immune response by direct contact or by secreting inhibitory cytokines
such as IL-10 and transforming growth factor beta (TGF- )
- Important in preventing autoimmune reactions
– Suppress self-reactive lymphocytes in periphery (outside lymphoid organs)
– Research into using them to induce tolerance to transplanted tissue and alleviate
the severity of autoimmune diseases
Yes.
In Summary…
• T cells are responsible for “cell-mediated immunity”
• They are activated when APCs present antigen in association with MHC
proteins
• T-cells sensitive to the antigen are activated upon contact (clonal
expansion)
• T cells attack the antigen (cytotoxic T cells) and stimulate B cells (helper
T cells)
• Memory cells are also formed
Yes.
Immune disorders
• Autoimmune disorders
– Immune response mistakenly targets normal cells
• Immunodeficiency diseases
– Immune system does not develop properly or is blocked
Yes.
Autoimmune disorders
• Immune response mistakenly targets normal cells
• Failure of the Tolerance Mechanism Causes Autoimmune Disease
– Diseases like rheumatic fever, myasthenia gravis, lupus erythematosus
• Treatment of autoimmune diseases may include immunomodulatory
drugs. These drugs suppress immune system and make host susceptible
to develop infections!
Yes.
Immunodeficiency diseases
• An immunocompromised host is a patient with defects in host defenses
that predispose to infection.
• Risk factors include neutropenia, immune system defects (from disease
or immunosuppressive drug therapy), compromise of natural host
defenses, environmental contamination, and changes in normal flora of
the host.
• Immunocompromised patients are at high risk for a variety of bacterial,
fungal, viral, and protozoal infections.
Yes.
Hypersensitivity (Allergy) • Inappropriate or excessive immune response to allergens… – Immediate hypersensitivity (type I) – Cytotoxic reactions (type II) – Immune complex disorders (type III) – Delayed hypersensitivity (type IV) • Anaphylaxis – Circulating allergen affects mast cells throughout body
Yes.
Skin: Consists of two distinct regions 1. Epidermis—superficial region • Epithelial tissue 2. Dermis—underlies epidermis • Mostly fibrous connective tissue
Yes.
Hypodermis (superficial fascia)
- Subcutaneous layer deep to skin
- Not part of skin but shares some functions
- Mostly adipose tissue that absorbs shock & insulates
- Anchors skin to underlying structures – mostly muscles
Yes
EPIDERMIS Keratinized stratified squamous epithelium Four (or five) distinct layers 1. Stratum basale 2. Stratum spinosum 3. Stratum granulosum 4. Stratum lucidum (only in thick skin) 5. Stratum corneum
Yes
Four cell types
- Keratinocytes
- Melanocytes
- Dendritic (Langerhans) cells
- Tactile (Merkel) cells
Yes
EPIDERMIS 4 CELL TYPES Keratinocytes – Produce fibrous protein keratin – Most cells of epidermis – Tightly connected by desmosomes
Yes
EPIDERMIS 4 CELL TYPES
Melanocytes
– 10–25% of cells in deepest epidermis
– Produce pigment melanin – packaged into melanosomes
• Protect apical surface of keratinocyte nucleus from UVdamage
• Absorbs UV rays and dissipates the energy as heat
Yes.
EPIDERMIS 4 CELL TYPES
Dendritic (Langerhans) cells
– Macrophages – key activators of immune system (APC)
Yes
EPIDERMIS 4 CELL TYPES
4. Tactile (Merkel) cells
– Sensory touch receptors
Yes.
CELL DIFFERENTIATION IN EPIDERMIS
• Cells change from stratum basale to stratum corneum
Accomplished by specialized form ofapoptosis
– Controlled cellular suicide
• Cells slough off as dandruff and dander
• Shed ~ 50,000 cells every minute
• ~18Kgs/lifetime
– Support microscopic organism:
– House dust mite (type of dermatophagoids)
– House dust allergy: allergy to inhaled feaces of mites
Yes
DERMIS Strong, flexible connective tissue • Cells – Fibroblasts, macrophages, and occasionally mast cells and white blood cells • Fibers in matrix bind body together • Contains nerve fibers; blood and lymphatic vessels • Contains epidermal hair follicles; oil and sweat glands • Twolayers 1. Papillary 2. Reticular
Yes.
DERMIS: PAPILLARY LAYER
Areolar connective tissue with collagenand elastic fibres and bloodvessels
• Loosetissue
– Phagocytes can patrol for microorganisms
• Dermal papillae
– Superficial peg like projections
• Most contain capillary loops
• Some contain Meissner’s corpuscles (touch receptors)
• Some contain free nerve endings (pain receptors)
• Thick skin that lies atop dermal ridges, causes epidermal ridges
• Collectively ridges called friction ridges
• Enhance grippingability
• Contribute to sense of touch
• Pattern isfingerprints
Yes.
DERMIS: RETICULAR LAYER • ~80% of dermal thickness • Dense fibrous connective tissue 1. Elastic fibers – Provide stretch-recoil properties 2. Collagen fibers – Provide strength and resiliency – Bind water • Cleavage lines: most collagen fibers parallel to skin surface • Externally invisible • Important tosurgeons • Incisions parallel to cleavage lines gap less and heal more readily
Yes.
THE EVOLUTION OF SKINCOLOUR
UV light: 2 adverseeffects
– Causes skin cancer
– Breaks down folic acid (a vitamin B) needed:
• Cell division, fertility, fetal development
_ UV Bone deformities
• UV light desirable effect
– Stimulates keratynocytes to synthesize vitamin D
• Needed for absorption of
dietary Calcium, bone growth
Yes.
SKIN COLOUR Three pigments contribute to skincolour 1. Melanin (tyrosine polymer) • Only pigment made in skin 2. Carotene • Accumulates in stratum corneum and in fatty tissues of hypodermis 3. Haemoglobin • Oxygenated pigment in red blood cells Distribution is notrandom – Near equator AND Higher altitude: greater protection required from sun
Yes.
HOMEOSTATIC IMBALANCES
Excessive sun exposure
elastic fibers clump»_space;leathery skin depressed immune system
altered DNA of skin cells»_space; skin cancer
2. UV radiation destroys body’s folic acid stores (DNA synth.)
pregnancy: impair embryo CNS development
3. Chemical induced photosensitivity- skin rash antibiotics,
antihistamines, perfumes, detergents
4. Sunspots (tinea versicolour) are fungal infection;
not related to melanin
Yes.
SKIN COLOUR IN DIAGNOSIS
• Cyanosis
– Blue skin color - low oxygenation of hemoglobin
– Heart failure, severe respiratory disorders
– Dark skinned: masking of melatonin
• Where red cast can be observed, so can blue
• Nail beds
• Erythema (or redness)
– Fever, hypertension, inflammation, allergy
– Blushing
• Pallor (or blanching): pale
– Emotional stress (fear, anger)
– Anemia, low blood pressure
Yes.
SKIN COLOUR IN DIAGNOSIS
• Jaundice (yellow cast)
– Liver disorder
– Yellow bile pigments (bilirubin) accumulate in the blood
• Bronzing
– Inadequate steroid hormones in Addison’sdisease
– Pituitary gland tumor: inappropriate secretion of
melanocyte-stimulating hormone
• Bruises
– Clotted blood beneath skin
Yes.
APPENDAGES OF THE SKIN • Derivatives of theepidermis – Hairs and hair follicles • Dead keratinized cells of hard keratin – More durable than soft keratin of skin • Hair bulb – Hair follicle receptor (root hair plexus) – Sensory nerve endings - touch receptors – Hair matrix • Actively dividingarea – Nails – Sweat glands – Sebaceous (oil) glands
Yes
THE HAIR CYCLE
Average 2.25 mm growth per week
• Lose 90 scalp hairs daily
Yes.
FUNCTIONS OF THE HAIR
Trunk, limbs
• Warn of insects on skin, parasites crawling (lice, fleas)
Scalp:
• Physical trauma
• Minimize heat loss
– Brain: rich warm blood supply, scalp lacks insulatingfat
– Heat is easily conducted through the bones of theskull
– Wind
• Sunlight
–These may be the reasons why we still have hair
Eyebrow
• Non-verbal communication, enhance expressiveness
• Apes uses them: greetings, dominance
Yes.
NAILS Scalelike modifications of epidermis • Protective cover for distal, dorsal surfaceof fingers and toes – Useful tool: scratch an itch • Contain hard keratin (<>skin: softkeratin) • Nail matrix – Nail growth – Cells produced are keratinized – Slides distally
Yes.
SWEAT GLANDS Also called sudoriferous glands • All skin surfaces except nipples and parts of external genitalia • ~3 million per person • Two main types 1. Eccrine (merocrine) sweat glands 2. Apocrine sweat glands • Contain myoepithelial cells – Contract upon autonomic nervous system stimulation to force sweat into ducts
Yes.
SWEAT GLANDS Eccrine Sweat Glands • Most numerous • Abundant on palms, soles, andforehead • Ducts connect topores • Function in thermoregulation – Regulated by sympathetic nervous system • Their secretion issweat • Confined to axillary and anogenital areas • Sweat + fatty substances +proteins – Viscous; milky or yellowish – Odourless until bacterial interaction body odour
Yes.
SEBACEOUS (OIL) GLANDS • Widely distributed – Not in thick skin of palms and soles • Most develop from hair follicles and secrete into hair follicles • Relatively inactive until puberty – Stimulated by hormones, especially androgens • Secrete sebum – Oily holocrine secretion – Bactericidal – Softens hair and skin
Yes.
Digestive Process in the stomach
Mainly catabolic action – little absorption
• Proteins denatured (unravelled) by HCl
• Pepsin carries out enzymatic digestion of proteins.
Milk protein (casein) is denatured and partially
broken down by by rennin in infants
• Very little absorption: lipid-soluble alcohol
and aspirin are absorbed into blood
• Only stomach function essential to life is secretion
of intrinsic factor for vitamin B12 absorption
Yes.
Neural & hormonal control of gastric secretion
Gastric mucosa up to 3 L gastricjuice/day
• Neural mechanisms (short and long reflexes)
– Local enteric stimulation secretion
– Vagus nerve stimulation secretion
– Sympathetic stimulation secretion
• Hormonal control mainly gastrin from stomach mucosa
– Enzyme and HCl secretion
– Other local gastric “hormones” involved (eg histamine for HCl
synthesis)
– Some Gastrin released by small intestine (short term)
– Small intestine secretes Gastrin antagonists (Secretin, CCK)
“Enterogastrones”
Yes.
HCl Formation Carbonic acid (H2CO3 ) breaks down in Parietal cells • Produces H+ and HCO3 - − H+ pumped into stomach lumen − K+ moves into parietal cells from stomach lumen to balancecharge • HCO3 - from carbonic acid breakdown actively exchanged for plasma Cl– • HCO3 - flows into blood (via Cl– and HCO3 – antiporter) • Blood leaving stomach more alkaline Alkaline tide • Cl– then moves across Parietal cell into lumen • Combination of H+ and Cl–→ HCl in the lumen
Yes.
Intestinal phase
Begins with a brief stimulatory component followed
by inhibition
– Stimulatory component-partially digested food
– Inhibitory effects of 2 factors
Yes.
Response of the Stomach toFilling
Stomach stretches to accommodate incoming
food
– Pressure constant until 1.5 L food ingested
1. Receptive relaxation (Reflex-mediated)
• Anticipation and response to food send signal
• Coordinated by swallowing center of brain stem
2. Gastric accommodation
• Plasticity (stress-relaxation response) of smooth muscle
Yes.
Gastric Contractile Activity Peristaltic waves – begins at gastroesophageal sphincter • Gentle (thin stomach wall) – move toward pylorus at rate of 3/minute • More powerful (stronger wall) • Control- Enteric pacemaker cells
Yes.
Small Intestine: Gross Anatomy Major organ of digestion and absorption • 6-7 m long • From pyloric sphincter to ileocecal valve − Sphincters control entry and exit • Subdivisions – Duodenum – Jejunum – Ileum
Yes.
Duodenum Curves around head of pancreas • Shortest part of small intestine ≈ 25 cm long • Receives secretions from liver/gall bladder and pancreas – Separate ducts join at hepatopancreatic ampulla – Enter duodenum at major duodenal papilla – Entry controlled by hepatopancreatic sphincter • Most digestion takes place in duodenum
Yes.
Jejunum and Ileum Jejunum – Extends from duodenum to ileum – About 2.5 m long – most absorption of breakdown products occurs here • Ileum – Joins large intestine at ileocecal valve – About 3.6 m long
Yes.
Blood and Nerve supply to Small Intestine
Innervation: (from the “involuntary” nervous sytem)
• Parasympathetic: Excitatory
• Sympathetic: Inhibitory
Blood circulation: extensive arterial and venous supply
• Superior mesenteric artery brings blood supply to the
Small Intestine – picks up nutrients
• Veins (carrying nutrient-rich blood) drain into superior
mesenteric veins hepatic portal vein liver
Yes.
Structural Modifications of Small Intestine
Increase surface area of proximal part for
nutrient absorption
1. Circular folds (mucosa and sub-mucosa)
2. Villi (mucosa)
3. Microvilli (mucosa)
4. Intestinal Crypts (mucosa)
Yes.
Structural Modifications
Circular folds
– Permanent folds of mucosa and submucosa (~1 cm
deep) that force chyme to slowly spiral through lumen
more nutrient absorption
Yes.
Structural Modifications
Villi
– Fingerlike extensions (~1 mm high) of mucosa with
capillary bed and lymphatic lacteal for absorption
– Epithelial cells of the villi are called absorptive
cells (enterocytes)
Yes.
Structural Modifications
• Microvilli (brush border of villi themselves)
– Contain enzymes for carbohydrate, protein and some lipid
breakdown to complete digestion in small intestine
Yes.
Intestinal Crypts Contain a range of cells 1. Enterocytes -intestinal juices 2. Goblet cells - mucus 3. Enteroendocrine cells – Enterogastrones – CCK & Secretin, etc 4. Paneth Cells – defensins & lysozyme 5. Stem cells divide to produce crypt cells
Yes.
Microvilli
Contain many digestive enzymes on their brush border
Yes.
Other specialised intestinal cells
• Mucosa associated lymphoid tissue (MALT)
− Protect against bacteria etc
− Peyer’s patches – macrophages & lymphocytes
• Duodenal (Brunner’s) glands
− secrete alkaline mucus to neutralize acidic chyme
Yes.
Intestinal Juice (mainly in duodenum)
− 1-2 L secreted daily from a variety of glands
− Slightly alkaline; isotonic with blood plasma
− Largely water; contains mucus, enzyme-poor
(enzymes of small intestine only in brush border);
Yes.
Accessory organs of Duodenum Liver, Gallbladder & Pancreas 1. Liver - Many vital functions • Digestion: produces bile to aid in fat absorption from small intestine • “Non–digestive”: metabolism, detoxification, storage, phagocytic protection, synthesis (globin, angiotensin), breakdown (bilirubin, some hormones) 2. Gallbladder- bile storage 3. Pancreas – Pancreatic Juice - enzyme rich
Yes.
Liver Largest internal gland – Four lobes—right, left, caudate, and quadrate – Well supplied with blood vessels – Basis cell type is the hepatocyte – Many functions including producing bile – Important in health and disease
Yes.
Bile
Produced by the liver
• 900 ml/day, some stored in gall bladder
• Contains Bile Salts – cholesterol derivatives
− Act like detergent to aid digestion of lipids (micelles)
− Reabsorbed in ileum → liver
• Also contain Bilirubin – from the breakdown of
heme
− Provides much of the green/yellow colour of bile
− Further breakdown provides pigments which give
urine and feces their colour
Yes.
The Gallbladder
Thin-walled muscular sac on ventral surface of
liver
1. Stores and concentrates bile from liver
(produced/recirculated)
2. Muscular contractions release bile via cystic
duct, which flows into bile duct
Homeostatic imbalance
Gallstones
Yes.
Pancreatic Juice – Exocrine (vs Endocrine) 1200 – 1500 ml/day • Watery alkaline solution (pH 8) neutralizeschyme • Electrolytes (primarily HCO3 –) • Enzyme rich • Amylase, lipases, nucleases o active form secreted o require ions or bile for optimal activity • Proteases o inactive form secreted o Activated by membrane bound peptidase
Yes.
Digestion in the Small Intestine Chyme (acidic) from stomach contains – Partially digested carbohydrates and proteins – Undigested fats • 3–6 hours in small intestine – Most water absorbed – ~ All nutrients absorbed • Intestinal digestion relies on: − Secretion of Intestinal Juice, Bile & Pancreatic Juice − Motility of the small intestine − Opening/closing of pyloric sphincter for entry and also ileocecal valve for exit
Yes.
Large Intestine Main Regions • Cecum • Appendix • Colon • Rectum • Anal canal
Yes.
Large Intestine: Microscopic Anatomy
• Thicker mucosa of simple columnar epithelium
except in anal canal
– stratified squamous to withstand abrasion in anus
• No circular folds, villi or digestive secretions
• Abundant deep crypts with goblet cells
– Secreting mucus to help movement
• Mucosal MALT cells help provide protection
against microorganisms
Yes.
Digestive Processes in the Large Intestine
• Residue remains in large intestine 12–24 hours
• No food breakdown except by enteric bacteria
• Vitamins (B & K made by bacterial flora), water,
and electrolytes (especially Na+ Cl–) reclaimed
• Major functions:
– propulsion of feces to anus
– defecation
• Colon is not essential for life
– Ileostomy (ileum to abdominal wall)
– Ileoanal juncture (ileum-anal canal)
Yes.
Bacterial Flora
• Enter from small intestine or anus
1. Colonize colon
2. Synthesize some B complex vitamins and
vitamin K
3. Metabolize some host-derived molecules
(mucin, heparin, hyaluronic acid)
4. Ferment indigestible carbohydrates
5. Release irritating acids and gases (~500 ml/day)
Yes.
Intestinal Flora
• Viruses and protozoans
• Bacteria prevented from breaching mucosal
barrier
– Epithelial cells recruit dendritic cells to mucosa
sample microbial antigens present to T
cells of MALT IgA antibody-mediated
response restricts microbes
Yes.
Always wanted to know…but never asked • Flatulence or intestinal gas • Large intestine contains: 7-10Lgas • Average expelled amount: 500ml/day – Swallowed air + bacterial flora production – Mainly from intestines (70%) • Main gases − N2 , CO2 , H2 , CH4 , – H2S, amines: indole, skatole – H2 \: flammable • Explosion in surgery (500-600 in US/year)
Yes.
Defecation
• Mass movements force feces toward rectum
• Distension initiates spinal defecation reflex
• Parasympathetic signals
– Stimulate contraction of sigmoid colon and rectum
– Relax internal anal sphincter
• Conscious control allows relaxation of external
anal sphincter
Yes.
Defecation
• Mass movements force feces toward rectum
• Distension initiates spinal defecation reflex
• Parasympathetic signals
– Stimulate contraction of sigmoid colon and rectum
– Relax internal anal sphincter
• Conscious control allows relaxation of external
anal sphincter
Yes.
Digestion and Absorption
• Digestion
– Catabolic process for the break down of
macromolecules smaller molecules for
absorption
− Most breakdown of food is by hydrolysis
o Water reacts with food to break bonds
− Enzymes required
o Intrinsic and accessory gland enzymes speed up
the breakdown of food (“catalysts”)
Yes.
Absorption: Vitamins, minerals water
Vitamins: essential, not produced by the body, small amounts
• Fat Soluble Vitamins – A,D, E, K
• Absorbed along with fats in small intestine
• Water soluble Vitamins – C and B Vitamins
− Mainly absorbed with water in the small intestine
− B12 is a large molecule and requires Intrinsic Factor (from stomach)
− B12 absorbed in the ileum through exocytosis
Minerals/electrolytes
• Most minerals actively absorbed along length of small intestine
• Fe++ and Ca++ in duodenum
− Fe++ bound to ferritin in mucosa/released as needed (heme)
− Ca++ absorption linked to parathyroid activity/Vitamin D
Water
• ≈ 9L enters GI daily
• 95% reabsorbed in small intestine; rest in large intestine
• Most movement is osmosis
Yes.
Jejunum and Ileum (slide 17- typo) • Jejunum – Extends from duodenum to ileum – About 2.5 m long – most absorption of breakdown products occurs here • Ileum – Joins large intestine at ileocecal valve – About 3.6 m long
Yes.
