301 Anatomy & Physiology Flashcards
What is the lymphatic system?
An open-ended, one-direction network of vessels and nodes that convey lymph
Returns plasma-derived interstitial fluids to bloodstream
What is lymph?
Clear-to-white fluid of WBCs (mainly lymphocytes) that attack bacteria and foreign bodies in blood
When dietary fat enters lymphatic vessels, the recovered fluid is lymph
Functions of lymphatic system
- Defends body against pathogens (bacteria, viruses and fungi)
- Develop body immunity (produce lymphocytes that produce antibodies)
- Remove excess fluids from body
- Absorption & transport fats to bloodstream
- Immune cell production (lymphocytes and antibody producing cells)
What are lymphatic vessels?
Start as lymphatic capillaries
Made of overlapping endothelial cells
What happens when fluid accumulates in tissue?
Interstitial pressure increases
Pushing flaps inwards,
Opening gaps between cells,
Allowing fluid in
Why are lymphatic capillaries different from blood capillaries?
Lymphatic are so large they allow bacteria, immune cells (macrophages) to enter
Useful for large particles to reach bloodstream
Used for dietary fat absorption in intestine
What is lymph flow?
Enabled by same forces in blood flow in veins
From lymphatic capillaries to vessels and eventually drains into bloodstream via subclavian veins
Lymph flow path through the lymph node
- Afferent lymphatics carry lymph to lymph node from peripheral tissue
Afferent lymphatics penetrate capsule of lymph node on opposite side to hilum - Afferent vessels deliver to subcapsular space (reticular fibres, macrophages, dendritic cell meshwork)
Dendritic cells involved in immune initiation response - Lymph flows into outer cortex (contains B cells within germinal centres resembling lymphoid nodules)
- Lymph flows through lymph sinuses in deep cortex (dominated by T cells)
- Lymph goes into medullary sinus, region contains B & plasma cells
- Efferent lymphatics leave node at hilum, collect lymph from medullary sinus & carry to venous circulation
What are lymph nodes?
Bean-shaped structures scattered throughout lymphatic network
Most prominent in areas where vessels converge (armpits, neck, inner elbows and groin)
Contain lymphocytes (T and B cells for adaptive immunity)
Innate vs adaptive immunity
I: Body’s first line of defence against pathogens
A: Specialised response targeting specific germs, “remembering” them
What does the adaptive immune response do in lymph nodes?
Produces activated lymphocytes and antibodies specific to the invading pathogen
Then carried by lymph to bloodstream for whenever they are needed
What are the primary lymphoid organs and functions?
Thymus and bone marrow
Where immune cells develop
Sites of lymphocyte production, maturation and selection (self and non-self)
Mature lymphocytes leave primary for secondary organs
What are the secondary lymphoid organs and functions?
Lymph nodes, spleen and MALT
Lymph nodes and spleen most organised
When they encounter pathogens and become activated
All have T and B cell activity and develop lymphoid follicles
Haematopoietic stem cells in bone marrow
(Blood-forming cells) reside in bone marrow during foetal gestation
Bone marrow remains site of haematopoiesis (creating RBCs, WBCs and platelets) in adults
Where do T lymphocytes complete maturation?
Thymus
What do stem cells require to self-renew and differentiate?
Stem cell niches
Why is a bone marrow transplant used?
Treat leukaemia, lymphoma, neuroblastoma and myeloma
What are HLAs?
Human leukocyte antigens
Markers on cell surface which siblings and parents can match or need to find a donor from national bone marrow donation registry for transplant
Thymus in lymphatic system
T-cell development not complete until selection in thymus
Pass through defined developmental stages in specific thymic micro-environments to generate antigen receptors
Selected on reactivity to self MHC-peptide complexes (expressed on stromal cells)
Most T cells die here
Where do T-cell pre-cursors go from and to via what in lymphatics?
From bone marrow to thymus via blood
What are MALTs?
(Mucosa-associated lymphoid tissue)
Tonsils, Peyer’s patches (lymphoid follicles in SI, part of GALT (gut)), appendix, lymphoid follicles in mucous membranes
Important features of spleen in lymphatic system
Organises immune response against blood-borne pathogens
Supplied with antigens by splenic artery
Red pulp - RBCs destroyed
White pulp - PALS with T cells and B cells
Marginal zone - trap for antigens
What does PALS stand for?
Peri-arteriolar lymphoid sheath
Lymph node main functions
Committed to regulating immune response and 1st organised structure to face antigens
What are lymph nodes consisted of and connected with?
Packed with lymphocytes, macrophages and dendritic cells
Connected with blood and lymph vessels
4 distinct regions of lymph nodes
- Cortex - contains B lymphocytes, macrophages and follicular dendritic cells
- Follicle - microenvironment to support B cell development
- Para-cortex - T lymphocytes and dendritic cells (migrated from tissue)
Medulla - lymphocyte exit
MALT functions
Organises response to antigen entering mucosal tissues
Where are T and B cell zones and lymphoid follicles found?
Mucosal membranes
What is GALT?
Barely organised cluster of lymphoid cells
What are M-cells?
Specialised epithelial cells of MALTs that transport antigen across epithelium
What is tertiary lymphoid tissue?
Site of infection
What happens in tertiary lymphoid tissue?
Lymphocytes activate by antigen in SALT (skin associated lymph tissue) can return to lung and liver
Generate defined microenvironments organising returning lymphoid cells
What are toll-like receptors (TLRs)?
Help detect pathogens and other threats
What does TLR activation help with?
Activation in epithelia and activated macrophages help with inflammation
What do macrophages do in inflammation?
Secrete cytokines including chemokines that attract neutrophils
What happens when the body is invaded by a foreign body?
- Macrophages recognise invaders, engulf & destroy & keep markers so other cells recognise
- Macrophages release cytokines when engulfing
- Cytokines bind receptors on other macrophages to inform cells
- Macrophages can’t destroy all so travel to lymph nodes & bring info to lymphocytes
- T cells divide & help macrophages, can recognise damaged invader antigens then bind them & activate
- When activated, T cells (killer or helper) divide & increasing numbers to inflammation site so rest of invaders engulfed by macrophages
- B cells shoot out Ig’s
- B cells divide & increase in lymph nodes before moving to inflammation site
- Swollen lymph node as result of activated T & B cells
How quickly is an inflammatory response initiated?
Within hours of infection or wounding, characterised by swelling, heat, redness and pain
What 4 changes occur to local blood vessels when swelling, heat, redness and pain occur?
- Heat and redness during inflammation due to vascular diameter increase so slower blood flow
- Increased vascular permeability, endothelial cells of vessels have gaps now so fluid from blood exits accumulating in local tissue so oedema and pain
- Endothelial cells of vessels activated, cell-adhesion molecules promoting lymphocyte binding
- Microvessel clotting at infection site, pathogens stop spread to blood
In inflammation, fluid leaves blood and accumulates in local tissue, what does the fluid contain?
Plasma proteins like complement proteins and mannose binding lectin (helps defend against pathogens)
What is extravasation?
Leukocytes leaving bloodstream
They attach to endothelium and migrate into tissues where they attack pathogens
Purpose of inflammatory response
- Allow body to defend itself from invaders
- Induce local blood clotting as physical barrier
- Promote injured tissue repair
What triggers an inflammatory response?
Tissues are physically damaged or when pathogens are recognised by macrophages or later by other WBCs
After an inflammatory response occurs, what is induced?
Release of inflammatory mediators which cause response
What do macrophages and neutrophils secrete in inflammatory response?
Secrete prostaglandins, leukotrienes and platelet-activating factor (PAF) - (lipid mediators)
Why are prostaglandins, leukotrienes and PAF produced rapidly in inflammatory response?
Made from degraded membrane phospholipids
What do macrophages secrete and example?
Cytokines which are released by immune cells
Chemokines act as chemoattractants (attract cell to certain location)
What do chemokines cause?
Directed chemotaxis (movement of cells in direction with gradient of increasing/decreasing conc.)
Chemokines direct phagocytes towards chemokine source
2 cytokines which are important in inflammatory response and why?
- C5a - stimulates respiratory (oxidative burst), attracting neutrophils & monocytes
- TNF-α - produced rapidly by macrophages upon pathogen detection & activator of endothelial cells
What is oxidative burst?
What do local mast cells release in inflammatory response?
Granules containing histamines and TNF-α
Cytokines produced macrophages like TNF-α cause what?
Endothelial cells to rapidly externalise granules (Weibel-Palade bodies) containing P-selectin within minutes of pathogen detection by macrophages and P-selectin appear on local endothelial surfaces
What are important for leukocyte recruitment?
Selectins with others being intercellular adhesion molecule (ICAMs) and leukocyte integrins
Mechanism of P-selectin
Once appeared on local endothelial surface, RNA encoding E-selectin is synthesised
Both selectins interact with sulphated sialyl-Lewis X (present on neutrophil surface)
What makes up first wave of cells to cross blood vessel wall in inflammatory response and followed by what?
Neutrophils enter inflamed tissue (followed by monocytes and differentiate into tissue macrophages)
What crosses blood vessel wall later in inflammatory response?
Other leukocytes like eosinophils and lymphocytes
Where do lymphocytes like to travel and why is this a problem?
Centre of small blood vessels where blood flows fastest
Inflamed tissue has slower flow allowing leukocytes to interact with endothelial cells lining blood vessels
What 2 enzyme cascades are triggered by blood vessel injury?
Kinin (inflammatory mediator (bradykinin) production)
Coagulation (leads to fibrin clot formation)
What is bradykinin?
Vasoactive peptide that increases vascular permeability and causes pain
What are prostaglandins?
Physiologically active lipids, found in nearly all tissue (derived from arachidonic acid)
What is a lymphatic malformation?
Lymphatic system doesn’t form correctly causing parts of body to swell
Is congenital or primary condition as occurs before birth
What are other terms for lymphatic malformations?
Cystic hygroma or lymphangioma (outdated as these refer to cancer)
Cystic lymphatic malformations
Lymph piles up forming bubbles (cysts)
Microcystic (appear as small blisters near skin - blebs) or macrocystic (may tint skin blue and be painful, putting pressure on other body parts) or mixed
What are CCLAs (central conducting lymphatic anomalies)?
When central lymphatics transport chyle from intestines is malformed
Body tries to relieve pressure by finding new routes, pools & can leak into chest or abdomen
What cannot reach their destinations when CCLAs occur
Fats, proteins, immune cells and other passengers
Causing health problems
In CCLAs, what can be caused in chest and abdomen?
C: chylothorax causes cough, discomfort in chest and breathing difficulty
A: Chylous ascites, abdomen becomes large, full and painful
What is PID?
Infection of upper reproductive system including uterus, fallopian tubes and ovaries
Serious complication of PID
Infertility
Why does PID typically develop?
Bacterial infection in vagina or cervix causing inflammation of mucosal layer
60% of the time changing bacterial flora composition called bacterial vaginosis
Why does bacterial vaginosis occur?
Cervical mucus (barrier preventing bacteria entering uterus) becomes less effective
When normal balance of vaginal flora is altered and anaerobic bacteria proliferate and degrade cervical mucus
What can contribute to PID?
Retrograde menstruation (when menstrual blood flows back through fallopian tubes and into pelvic cavity)
Sexual intercourse
What is salpingitis and salpingo-oophoritis?
When PID reaches fallopian tubes
When PID also affects ovaries
What happens in PID?
Infection triggers response which sends neutrophils, plasma cells & lymphocytes into fallopian tubes
Damages tubal epithelium, tubes fill with pus
What happens when scar tissue forms to repair PID damage?
Areas with damaged epithelium tend to stick to one another, creating closed-off pockets and dead-end pouches in fallopian tubes
Scarring leads to PID complications
PID: what happens when pus builds up in tube and ovary?
Can turn into tubo-ovarian abscess which can be life-threatening if ruptured
PID: what happens when fluid builds up in a pocket?
Pocket created by scar tissue in tubes called hydrosalpinx
Can cause affected area to become swollen
Structural damage of fallopian tubes tends to cause difficulty getting pregnant, risk of ectopic pregnancy and chronic pelvic pain
Complication (syndrome) of PID
Fitz-Hugh-Curtis syndrome
Inflammation from PID spreads to peritoneum and to Glisson’s capsule which surrounds liver
Results in “violin string” adhesions of scar tissue attaching liver to peritoneum
Bacteria associated with PID
Neisseria gonorrhoeae
Chlamydia trachomatis
Bacteria involved in reproductive tract by surgery, abortion or normal vaginal birth
Can PID be single type of bacteria or multiple?
Mostly single but 30-40% can become polymicrobial
Symptoms of PID
Few or none
Pelvic pain, tenderness around ovaries and fallopian tubes, fever and abdominal vaginal discharge
PID diagnosis
Pelvic pain and cervical motion tenderness (mobilise cervix in vaginal exam causing pain)
PID: How do we know if Fitz-Hugh-Curtis syndrome is present?
Tenderness in right upper quadrant
PID testing
Vaginal discharge for BV
Nucleic acid amplification test look for chlamydia and gonorrhoea DNA
Laparoscopy of fallopian tubes
Ultrasound shows fluid in fallopian tubes
What can an ultrasound tell us in PID?
Whether a tubo-ovarian abscess or hydrosalpinx is present
PID treatment
Ceftriaxone injection
Cefotetan followed by 14 days oral doxycycline and metronidazole
Acetaminophen to manage pain
Surgery to remove adhesions with Fitz-Hugh-Curtis
Acute phase response to inflammatory disease
Intrinsic defence
Increase/decrease of blood protein production (acute phase proteins)
Liver –> fibrinogen, haptoglobin, serum amyloid protein & C-reactive protein
Innate vs adaptive immune systems
I: activated by chemical characterisation of antigen
A: antigen specific immune response
What is rheumatoid arthritis?
Autoimmune disease
Chronic inflammation of joints
What can rheumatoid arthritis affect?
Haematologic, cardiovascular and respiratory systems
What happens in rheumatoid arthritis?
Produce antibodies react with FC region of IgG
IgM-IgG complexes deposit in joints
Complexes activate complement cascade
Type III hypersensitivity
How many litres of plasma flow out tiny pores and how much returns to bloodstream?
20 out and 17 back so 3 still roams around body tissues
How does lymphatic system work?
Tissues soak up nutrients leaving waste
Plasma pick up waste and return to bloodstream
Tiny lymphatic capillaries pick up remaining fluid tissues
Plasma becomes lymph
Capillaries move lymph to lymphatic vessels
Vessels keep moving until they reach 1 of 2 ducts
What are the 2 major ducts in the lymphatic system (located in the neck)?
Right lymphatic duct and thoracic duct
Where do the lymphatic ducts merge and what happens?
Into large veins called subclavian veins and empty lymph into them
Lymph re-enters bloodstream and can flow through body again
What is lymph and its function
Collection of extra fluid drains from cells & tissues in body & isn’t reabsorbed into capillaries
Contains proteins, minerals, fats, damaged cells, cancer cells and germs
Transports lymphocytes
What do lymphatic vessels do?
Pulsing nearby arteries and squeezing of nearby muscles help move fluid through lymphatic vessels
Vessels contain one-way valves that keep lymph moving right way
What are tonsils and adenoids and what do they do?
Trap pathogens from food and air you take in
Part of body’s 1st line of defence against invaders
Adenoids are active during childhood
Swollen lymph nodes (lymphadenopathy)
Causes: infection, inflammation, cancer, strep throat, mononucleosis (glandular fever), HIV and infected skin wounds
What is lymphadenitis?
Lymphadenopathy caused by infection or inflammatory condition
Swelling or accumulation of fluid (lymphedema)
Blockage in system due to scar tissue from damaged lymph vessels/nodes can cause it
Fluid commonly builds up in arms or legs
At risk of deep skin infections
Cancer of lymphatic system
Lymphoma is cancer of lymph nodes that occur when lymphocytes multiply uncontrollably
Hodgkin’s and non-Hodgkin’s
Cancerous tumours also block lymphatic ducts or be near lymph nodes and interfere with lymph flow through node
What is lymphangitis?
Lymph vessel inflammation
What is lymphangioma?
Born with it
Presence of non-cancerous, fluid-filled bumps (cysts) under skin due to overgrown lymph vessels
What is intestinal lymphangiectasia?
Loss of lymph tissue in SI leads to loss of protein, gamma globulins, albumin and lymphocytes
What is lymphocytosis?
Higher than normal amount of lymphocytes
What is lymphatic filariasis?
Parasitic infection causing lymphatic system to malfunction
What is Castleman’s disease?
Overgrowth of cells in lymphatic system
What is lymphangioleiomyomatosis?
Rare disease where abnormal muscle-like cells begin to grow out of control in lymph nodes, lungs and kidneys
What is autoimmune lymphoproliferative syndrome?
Rare genetic disorder with high number of lymphocytes in lymph nodes, liver and spleen
Tests for lymphatic health
Imaging tests - computed tomography (CT) or magnetic resonance imaging (MRI)
How to keep the lymphatic system healthy?
Avoid exposure to toxic chemicals like pesticides and cleaning products (can build up in system so harder to filter waste)
Drink fluid so lymph can move around body
Healthy lifestyle
Call healthcare provider for suspected lymphatic disorders when…
Fatigue
Swollen lymph nodes (strep throat, HIV or cancer)
Unexplained swelling lasting >few weeks or interferes with daily activities
What is the GI tract?
Long tube open at both ends for food transit
Main portions: oesophagus, stomach, SI, large intestine and rectum
What are accessory structures and what do they include?
Not part of GI tract but contribute to food processing
Teeth, tongue, salivary glands, liver, gallbladder and pancreas
4 layers of GI
- Mucosa
- Sub mucosa
- Muscularis propria
- Adventita
What is the muscularis propria?
Smooth muscle of 2 layers (inner circular muscle and outer longitudinal layer)
What is the function of the muscularis propria?
Peristalsis: contraction producing rhythmic waves for food movement down gut
What systems are involved in the neural innervation of the gut?
Enteric NS - submucosal & myenteric plexus
Autonomic NS - parasympathetic & sympathetic
What are the eruption ages of the teeth?
Primary (deciduous) teeth
Central incisors 6-12mths
Lateral incisors 9-16mths
Canines 16-23mths
1st molars 12-16mths
2nd molars 24-32mths
Permanent (secondary) teeth
Central incisors 7-8yrs
Lateral incisors 8-9yrs
Canines 11-12yrs
1st/2nd premolars 10-12yrs
1st molars 6-7yrs
2nd molars 11-13yrs
3rd molars (wisdom) 17-21yrs
Structure of a tooth
Enamel: hard outer layer protects from wear
Dentin: calcified tissue
Pulp cavity: nerves and blood vessels
Root canal: extension of pulp
Cementum: attaches root to periodontal ligament
Periodontal ligament: anchors tooth to jawbone
Apical foramen: opening at root base for nerves/blood vessels
Gingiva (gums): base of teeth
Crown, neck, root: major tooth regions
What is mechanical digestion?
Chewing mixes food with saliva and forms bolus which is easily swallowed
What is chemical digestion?
Salivary amylase converts polysaccharides to disaccharides (starch to maltose)
What are the phases of deglutition (swallowing)?
Oral phase, pharyngeal phase and oesophageal phase
What happens in the oral phase of deglutition?
Food “prepared” into pellets (food bolus) into oropharynx
Bolus moved by back of tongue and other muscles to pharynx, requires voluntary elevation of soft palate preventing entry to nose
Cranial nerves include trigeminal, facial and hypoglossal
What cranial nerves are involved in deglutition?
Trigeminal, facial and hypoglossal
What is the pharyngeal phase of deglutition?
As bolus reaches pharynx, special sensory receptors activate involuntary swallowing
Reflex mediated by swallowing centre in medulla, food pushed back to pharynx & oesophagus
Prevent food going to trachea & lungs through involuntary larynx closure by epiglottis & vocal cords OR temporary breathing inhibition
Process protects lungs from injury as food can lead to severe infections & aspiration pneumonia
What is aspiration pneumonia?
Irritation of lung tissue
What is the oesophageal phase of deglutition?
Food leaves pharynx, enters oesophagus, tube of muscular structure moves food into stomach due to rhythmic contractions
Oesophagus has the upper and lower oesophageal sphincters, prevent food & saliva being vomited towards mouth
Sphincters serve as physical barrier to vomiting food
What are the 2 sphincters in the oesophagus and what is their function?
Upper and lower oesophageal
Prevent food & saliva being vomited towards mouth, acts as a physical barrier to food vomit
Stomach anatomy and functions
Oesophagus: connects stomach to lower oesophageal sphincter
Fundus: upper rounded part of stomach
Cardia: oesophagus meets stomach
Body: main central region
Pylorus: lower section connecting to SI
Pyloric sphincter: controls food passage to duodenum
Rugae of mucosa: folds allow stomach expansion
Curvatures: > and <curves of stomach
Muscle layers: longitudinal, circular and oblique
Duodenum: 1st part of SI
What is the histology of the stomach?
Mucosa: glands with mucus, acid & enzyme-secreting cells
Submucosa: connective tissue with blood vessels & nerves
Muscularis externa: 3 smooth muscle layers for churning
Serosa: outer protective layer
What are the key cells in stomach’s histology?
Parietal: produce acid
Chief: release pepsinogen
Mucous: protect lining
Enteroendocrine: release hormones
What are the functions of the stomach?
- Mix saliva, food & gastric juice forming chyme
- Reservoir for food before SI release
- Secretes gastric juice containing HCl, pepsin, intrinsic factor & gastric lipase
- Secretes gastrin into blood
What is the purpose of HCl, pepsin, intrinsic factor and gastric lipase in the stomach?
Kills bacteria & denatures proteins
Starts protein digestion
Aids B12 absorption
Aids triglyceride digestion
What is gastrin?
Hormone released by G cells in stomach duodenum and pancreas
Stimulates stomach to release HCl and convert pepsinogen to pepsin (active form), to break down proteins
What are the stimulatory factors in HCl secretion & regulation of stomach?
Gastrin: released by G cells
Histamine: released by enterochromaffin-like cells, binds H2 receptor on parietal cells
ACh: from vagus nerve, binds muscarinic receptors
ALL stimulating HCl production
What is the inhibitory factor in HCl secretion & regulation of stomach?
Somatostatin: inhibits gastrin release
What are the key neurotransmitters in HCl secretion?
Histamine, ACh & somatostatin
What do circular folds do in the SI?
Increase SA for digestion and absorption
What is the histology of the SI?
Mucosa: villi & microvilli (brush border) to increase SA for absorption
Submucosa: blood vessels, nerves and Brunner’s glands (in duodenum) secrete alkaline mucus
Muscularis externa: circular & longitudinal muscle layers for peristalsis
Serosa: Outer protective layer
What are the important cells in the SI mucosa layer?
Enterocytes: absorptive cells with microvilli
Goblet cells: secrete mucus for lubrication
Crypts of Lieberkühn: glands with Paneth cells (antimicrobial) & stem cells
What does the intestinal juice do in the SI?
Facilitates absorption of substances from chyme when they come in contact with villi
Where are brush border enzymes located and what do they do in the SI?
Surface microvilli of absorptive cells
Break down food products
Structure of the exocrine part of the pancreas
Acinar cells: produce digestive enzymes (amylase, lipase & protease)
Ductal cells: secrete bicarbonate to neutralise stomach acid in duodenum
Pancreatic duct: transports enzymes & bicarbonate to duodenum
Structure of the endocrine part of the pancreas
Islets of Langerhans
Alpha: secrete glucagon to raise blood glucose
Beta: secrete insulin to lower blood glucose
Delta: secrete somatostatin which regulates other hormones
Where is the location of the pancreas?
Posterior to stomach
Functions of the pancreas
Produces enzymes to digest carbs, proteins, fats & nucleic acids
Produces sodium bicarbonate which buffers stomach acid (alkaline)
Drains contents into duodenum
Structure of the liver lobules
Hepatocytes: main liver cells for metabolism, detoxification & bile production
Sinusoids: capillary spaces allowing blood flow between hepatocytes, lined with macrophages
Central vein: drains blood from each lobule
Structure of the gallbladder
Mucosa: simple columnar epithelium with folds (rugae) to expand bile storage
Muscularis: smooth muscle layer contracts to release bile
Perimuscular layer: connective tissue surrounding muscle
Serosa: outer layer (if exposed to abdominal cavity) or adventitia (if attached to liver)
Function of the liver
Makes bile, important for emulsification of fats
Function of the gallbladder
Stores bile until needed
What is the portal triad in the liver?
Located at each lobule corner, contain
Hepatic artery: supplies oxygenated blood
Portal vein: delivers nutrient-rich blood from intestines
Bile duct: collects bile from hepatocytes for digestion
What is the histology of the colon?
Mucosa: absorptive cells & many goblet cells for water absorption & lubrication
Submucosa: connective tissue with blood vessels
Muscularis externa: inner circular layer & outer teniae coli (longitudinal bands)
Serosa/adventitia: outer layer
Function of the colon
- Haustral churning, peristalsis & mass peristalsis drive colon contents to rectum
- Bacteria in LI convert proteins to amino acids, break them down & produce B vitamins and vitamin K
- Absorption of some water, ions & vitamins
- Formation of faeces
- Defecation
Glands in the colon
Crypts of Lieberkühn - simply tubular glands in mucosa for secretion & cell renewal
Cell types in the colon
Absorptive: reabsorb water & electrolytes
Goblet: abundant, secrete mucus for faecal lubrication
Stem: found in crypts, regenerate epithelial cells
Enteroendocrine: release hormones to regulate digestion (less common)
What happens in the chemical digestion of the colon?
Last stage of digestion through bacterial action
Substances further broken down by bacteria
Some vitamins synthesised by bacterial action
What does the colon absorb?
Water, electrolytes & some vitamins
What do faeces consist of?
Water, inorganic salts, sloughed-off epithelial cells, bacteria, bacterial decomposition products and undigested food portions
What happens in liver processing?
Hepatocytes metabolise & store nutrients
Detoxification of harmful substances
Bile production, by-products from metabolism used
Processed blood exits liver via hepatic veins to re-join systemic circulation
Nutrient movement in the hepatic portal vein
Blood rich in nutrients from GI to vein
Vein transports blood to liver
What is the defecation reflex?
- Rectal wall swells
- Stretch receptors send sensory nerve impulses to sacral spinal cord
- Motor impulses travel back to descending colon, sigmoid colon, rectum & anus
- Longitudinal rectal muscles contract & internal anal sphincter opens
If external sphincter relaxes defecation occurs
What are the phases of digestion?
- Cephalic - stimulates gastric secretion & motility
- Gastric - neural & hormonal mechanisms
- Intestinal - neural & hormonal mechanisms
What is the gastric phase of digestion?
Trigger, key actions and function
T: food in stomach
KA: gastrin: stimulates acid production
HCl & pepsinogen: aid in protein digestion
ACh: enhances digestive secretions
F: prepares stomach for protein digestion
What are the source, substrates & products of these digestive enzymes:
Salivary amylase
Lingual lipase
- Salivary glands
S: Starches (polysaccharides)
P: Maltose (disaccharide, maltotriose (trisaccharide) and α-dextrins - Lingual glands in tongue
S: triglycerides (fats & oils) & other lipids
P: fatty acids & diglycerides
What are the source, substrates & products of these digestive enzymes in the gastric juice:
Pepsin (activated from pepsinogen by pepsin and HCl)
Gastric lipase
- Stomach chief cells
S: Proteins
P: Peptides - Stomach chief cells
S: Proteins
P: Fatty acids & monoglycerides
What are the source, substrates & products of these digestive enzymes in the pancreatic juice:
Pancreatic amylase
Trypsin
Chymotrypsin
- Pancreatic acinar cells
S: Starches (polysaccharides)
P: Maltose (disaccharide, maltotriose (trisaccharide) and α-dextrins - Pancreatic acinar cells
S: Proteins
P: Peptides - Pancreatic acinar cells
S: Proteins
P: Peptides
How is trypsin activated?
From trypsinogen by enterokinase
How is chymotrypsin activated?
From chymotrypsinogen by trypsin
How is elastase activated?
From proelastase by trypsin
How is carboxypeptidase activated?
From procarboxypeptidase by trypsin
What are the source, substrates & products of these digestive enzymes in the pancreatic juice:
Elastase
Carboxypeptidase
Pancreatic lipase
- Pancreatic acinar cells
S: Proteins
P: Peptides - Pancreatic acinar cells
S: Amino acid at carboxyl end of peptides
P: Amino acids & peptides - Pancreatic acinar cells
S: Triglycerides (fats & oils) that have been emulsified by bile salts
P: Fatty acids & monoglycerides
What are the source, substrates & products of these digestive enzymes in the nucleases:
Ribonuclease
Deoxyribonuclease
- Pancreatic acinar cells
S: Ribonucleic acid
P: Nucleotides - Pancreatic acinar cells
S: Deoxyribonucleic acid
P: Nucleotides
What are the source, substrates & products of these digestive enzymes in the brush-border enzymes in microvilli plasma membrane:
α-dextrinase
Maltase
Sucrase
Lactase
Enterokinase
(All have SI source)
1. S: α-dextrins P: Glucose
2. S: Maltose P: Glucose
3. S: Sucrose P: Glucose & fructose
4. S: Lactose P: Glucose & galactose
5. S: Trypsiogen P: Trypsin
What are the source, substrates & products of these digestive enzymes in peptidases:
Aminopeptidase
Dipeptidase
Nucleosidases & phosphatases
(All have SI source)
1. S: Amino acid at amino end of peptides P: Amino acids & peptides
2. S: Dipeptides P: Amino acids
3. S: Nucleotides P: Nitrogenous bases, pentoses & phosphates
What are the activities and results of digestive activities in these structures:
Cheeks and lips
Salivary glands
- A: Keep food between teeth
R: Foods uniformly chewed during mastication - A: Secrete saliva
R: Lining of mouth & pharynx moistened & lubricated, softens, moistens and dissolves food and cleanses mouth & teeth, splits starch into smaller fragments
What are the activities and results of digestive activities in these structures:
Extrinsic tongue muscles
Intrinsic tongue muscles
- A: Move tongue side to side & in & out
R: Food manoeuvred for mastication, shaped into bolus & manoeuvred swallowing - A: Alter shape of tongue
R: Swallowing & speech
What are the activities and results of digestive activities in these structures:
Taste buds
Lingual glands
Teeth
- A: Serve as receptors for gustation & presence of food in mouth
R: Secretion of saliva stimulated by nerve impulses from taste buds to brainstem to salivary glands - A: Secrete lingual lipase
R: Triglycerides broken down into fatty acids & diglycerides - A: Cut, tear & pulverise food
R: Solid foods reduced to smaller particles
What are the activities and results of digestive activities in these structures:
Surface mucous cells & mucous neck cells
Parietal
Chief
- A: Secrete mucus & absorption R: forms protective barrier that prevents digestion of stomach wall & small quantity of water, ions, short-chain fatty acids & some drugs enter bloodstream
- A: Secrete intrinsic factor & secrete HCl R: Absorption of B12 & kill microbes in food, denatures proteins, converts pepsinogen to pepsin
- A: Secrete pepsinogen & gastric lipase R: Pepsin breaks down proteins to peptides & splits triglycerides to monoglycerides & fatty acids
What are the activities and results of digestive activities in these structures:
G cells
Muscularis
Pyloric sphincter
- A: Secrete gastrin R: stimulates parietal cells to secrete HCl & chief cells to secrete pepsinogen, contracts lower oesophageal sphincter, increases stomach motility & releases pyloric sphincter
- A: Gentle peristaltic movements R: Churns & breaks down food, mixing with gastric juice, forming chyme, forces chyme through pyloric sphincter
- A: Opens to permit chyme passage to duodenum R: Regulates chyme passage from stomach to duodenum, prevent chyme backflow to stomach
Activity in:
Pancreas
Liver
- Delivers pancreatic juice into duodenum via pancreatic duct to assist absorption
- Produces bile (bile salts) necessary for emulsification & absorption of lipids
Activity in:
Gallbladder
Small intestine
- Stores, concentrates & delivers bile into duodenum via common bile duct
- Major site of digestion & absorption of nutrients & water in GI tract
Activity in:
Mucosa/submucosa intestinal glands
Absorptive cells
Goblet cells
- Secrete intestinal juice to assist absorption
- Digest & absorb nutrients
- Secrete mucus
Activity in:
Enteroendocrine cells (S, CCK, K)
Paneth cells
Duodenal (Brunner’s) glands
- Secrete secretin, cholecystokinin & glucose-dependent insulinotropic peptide
- Secrete lysozyme (bacterial enzyme) & phagocytosis
- Secrete alkaline fluid to buffer stomach acids & mucus for protection & lubrication
Activity in:
Circular folds
Villi
Microvilli
- Folds of mucosa & submucosa increase SA for digestion & absorption
- Projections of mucosa are absorption sites of digested food & increase SA for digestion & absorption
- Membrane covered projections of absorptive epithelial cells containing brush-border enzymes and increase SA for digestion & absorption
Activity in:
Segmentation
Migrating motility complex (MMC)
- Type of peristalsis alternate circular smooth muscle fibre contractions produce segmentation & resegmentation of SI sections, mixes chyme with digestive juices & brings food into contact with mucosa for absorption
- Type of peristalsis waves of circular & longitudinal smooth muscle fibre contraction & relaxation passing length of SI, moves chime towards ileocecal sphincter
Activity and functions in:
Lumen
A: Bacterial
F: Breaks down undigested carbs, proteins & amino acids into products expelled in faeces or absorbed/detoxified by liver, synthesises B and K vitamins
Activity and functions in:
Mucosa
A: Secretes mucus & absorption
F: Lubricates colon, protects mucosa
Water absorption solidifies faeces and contributes to body’s water balance, solutes absorbed are ions & vitamins
Activities and functions in:
Muscularis
A: Haustral churning, peristalsis, mass peristalsis, defecation reflex
F: Moves contents from haustrum to haustrum by muscular contraction, moves contents along colon by circular and longitudinal muscle contraction, forces contents into sigmoid colon & rectum, eliminates faeces by contractions in sigmoid colon & rectum
Stimulus and site of secretion & major and minor effects:
Gastrin
S: Distension of stomach, partially digested proteins and caffeine in stomach & high pH of chyme stimulates gastrin secretion by enteroendocrine G cells
Maj: Promotes gastric juice secretion, increase motility & growth of gastric mucus
Min: Constricts lower oesophageal sphincter, relaxing pyloric sphincter
Stimulus and site of secretion & major and minor effects:
Secretin
S: Acidic (high H+) chyme enters SI stimulates secretin secretion by enteroendocrine S cells in mucosa or duodenum
Maj: Stimulates pancreatic juice & bile rich in HCO3-
Min: Inhibits gastric juice secretion, promotes growth & maintenance of pancreas, enhances CCK effects
Stimulus and site of secretion & major and minor effects:
Cholecystokinin (CKK)
S: Partially digested proteins, triglycerides & fatty acids enter SI stimulate CCK secretion by enteroendocrine CCK cells in mucosa of SI, CCK released in brain
Maj: Stimulates pancreatic juice secretion rich in digestive enzymes, causes bile ejection from gallbladder & sphincter to open in hepatopancreatic ampulla
Min: Inhibits gastric emptying, promotes growth & maintenance of pancreas, enhances secretin effects
