GI Flashcards
Name the connecting peritoneum of the abdominal cavity. (OLMF)
Roisin’s Gooch
Describe the greater omentum.
The GO originates from the greater curvature of the stomach. It folds back on itself to form the omentum bursa, entry is gained via the epiploic foramen. The GO then finds the parietal parietal peritoneum of the body wall. It folds back as the lesser omentum which fuses with the stomachs lesser curvature.
How does the saliva of ruminants and non-ruminants differ between low and high flow rates?
Non-rum - hypotonic to isotonic Rum - PO42- to HCO3- At low flow rates ions are reabsorbed from saliva before reaching the epithelial surface.
What is the function of mucous and serous salivary glands?
Mucous lubricate food and serous produce amylase which aid digestion.
What substances make up saliva?
Mucin and water = mucous Amylase Bicarbonate Phosphate Lysozymes Antibodies Tannins, Urea - ruminants
Name the main salivary glands of the dog and whether they are mucous or serous.
Mucous - parotid Mixed - mandibular, buccal, sublingual Zygomatic
What are the phases of digestion? (X3)
Cephalic - sight, smell and taste = brain activation and presecretions Gastric - lumen stretch/ contents Intestinal - metabolites/ chyme in duodenum
What fundus adaptations do horses and pigs have to allow amylase function to continue in the stomach?
Horse - Margo plicatus (separates regions of the stomach). Fundus in non-glandular as it arises from the oesophageal regions Pigs - Only mucous glands - develops from cardiac regions. Very extensive fundus.
Which structures arise from the fore, mid and hindgut?
Fore - up to mid duodenum and accessory organs Mid - mid duodenum to transverse colon Hind - descending colon and rectum
How does the stomach rotate during development?
Left and right - cranial extremity left, caudal extremity right Cranial and caudal - oesophageal region cranially, pylorus caudally
Name the different regions of the stomach.
Oesophageal, cardia, fundus, corpus, pylorus, pyloric Antrum
How does the embryonic development of the fundus differ between the dog, pig and horse?
In the dog the fundus develops from the primitive fundus region whereas in the pig it develops from the cardiac region (making it a mucous glandular area) and in the horse it develops from the oesophageal region (making it a non-glandular region of the stomach)
This specialized band in the equine stomach separates the fundus and corpus. Why is its presence significant?
Margo plicatus This band separates the glandular and non-glandular regions of the stomach - prevents self digestion.
Why do carnivores have no non-glandular region in the stomach?
They have no need since they do not use salivary amylase
Transverse abdominis
O - Medial surface of ventral ribs and deep lumbodorsal fascia. I - linea alba
External abdominal oblique
O - lateral, caudal ribs and lumbodorsal fascia I - linea alba and prepubic tendon
Fibres run caudoventrally
Internal abdominal oblique
O - tuber coxae and lumbodorsal fascia I - linea alba and caudal rib cartilages Fibres run cranioventrally
Rectus abdominis
O - sterna, ribs/ sternum I - prepubic tendon/ ventral pubis
What does the hepatic portal triad consist of? Describe the histology of each.
Hepatic artery - thick walled, filled with RBC Hepatic portal vein - thin walled Bile duct - cuboidal epithelia +/- lymph vessels
Describe the sinusoids of the hepatic lobule.
Sinusoids are lined with Fenstrated epithelium and hepatocytes. Space between Fenstrated epithelium and hepatocytes is called space of disse.
What are the specialized macrophages of the liver sinusoids also known as?
Kupfer cells
Draw a hepatic lobule. Describe the flow of blood from the hepatic portal vein back to the heart.
Central vein, hepatic portal triad etc etc Hepatic portal vein drains into the liver sinusoids which drains into the central vein of the lobule. This drains into the hepatic vein which empties into the caudal vena cava
What epithelial lining is found in the fore stomachs of the ruminant GI tract?
R,R,O - stratified squamous - derived from oesophageal region Abomasum - glandular - derived from stomach
How is the epithelium of the ruminant forestomachs (fermentation chambers) specialized?
Lamina epithelialis mucosae has a parakeratotic stratified squamous epithelium (protective against shearing forces)
What histological features of the lamina muscularis mucosae differ between the reticulum, rumen and omasum?
Reticulum - isolated smooth muscle mass Rumen - not present Omasum - LMM forms a double layer which follows papillae, inner muscularis interdigitates between the double layer.
Describe the gross folds of the ruminant forestomach
Reticulum - honey comb shaped with primary and secondary folds and tertiary papillae Rumen - conical papillae Omasum - sheet layers of folds with primary folds and smaller papillae
How does the linea alba alter down the abdomen?
In the dog the connection becomes thinner cranially to caudal since the load on the ventral abdominal wall decreases. The the horse and ox this width remains thick due to the large gut contents.
This GI hormone is released in response ACh and peptides/ amino acid from the caudal stomach. What does its release cause?
Gastrin causes HCl released and mucosal growth
This GI hormone is released from the duodenum and causes HCO3- release. What stimulates its release?
Secretin is released in response to HCl in the duodenum
CCK is short for what?
From which part of the GI tract is it released, what causes its release and what is its effect?
Cholecytokinin is released from the duodenum in response to fatty acids, peptides and amino acids and monoglycerides.
It causes release of pancreatic enzymes and contraction of the gall bladder releasing bile.
What effect does Gastric inhibitory peptide have on the GI tract, where is it released from?
GIP is released from the cranial small intestine in response to presence of fat, glucose and amino acids. It inhibits the release of HCl and insulin production.
What is the difference between the long and short reflex arcs of the GI tract?
Short reflex arcs are contained within the enteric nervous system (sensory +/- interneuron and motor neurone) whereas long reflex arcs communicate with the autonomic nervous system.
Which branch of the autonomic nervous system is inhibitory of enteric nervous system? What GI actions does it inhibit?
Sympathetic, inhibits GI secretion, motility and blood supply.
What stimulates the activation of the ENS and what does it stimulate?
Sensory fibres detect lumen contents and wall stretch and motor fibres stimulate motility of smooth muscle and epithelial cell secretion (juices and hormones)
Name the four types of GI tract contraction and the function of each type.
Segmental - mixing and chemical breakdown
Peristaltic - gradual aboral movement - progressive contraction from cranial to caudal, in bands
Anti-peristaltic - oral direction
Mass movement - empties entire sections of the GI tract
Which modulating signals stimulate the appetite and satiety centres of the brain?
Glucose (glucostat), CCK, Fat levels (lipostat), Smell, vision
What is the main neurotransmitter of the ENS?
Acetylcholine
Where does the SNS post-ganglionic fibres terminate in the GI tract? What is their effect?
They terminate either on post-ganglionic parasympathetic fibres with an inhibitory effect or directly onto smooth muscle of GI blood vessels causing vasoconstriction.
Describe the process of deglutation.
1) Voluntary controls - mechanical digestion and moulding of the food bolus and forcing to the back of the oral cavity.
2) Involuntary controls - Sensitive afferent cell stimulated which stimulates the swallowing reflex via the medulla.
3) Epiglottis closes, upper oesophageal sphincter is closed behind the bolus, peristaltic contraction down the oesophagus, lower oesophageal sphincter opens.
What is a physiological spincter? Name one.
It acts as a sphincter but there is no obvious difference in the tissue. The lower oesophageal sphincter.
Describe the relationship between the oesophagus and diaphragm.
The oesophagus enters the stomach obliquely through the diaphragm. When the stomach expands the opening closes, this physiological sphincter is known as the lower oesphageal sphincter. It is extremely pronounced in the horse, hence why they cannot vomit.
Name the histological layers of the GI tract.
(x4)
- Mucosa
- Lamina epithelialis mucosae - glands + folds
- Lamina propria mucosae - connective tissue
- Lamina muscularis mucosae - local motility and gland expression
- Submucosa - Loose connective tissue (larger nerves, blood vessels, nerve plexuses, ganglia, glands)
- Muscularis (smooth or skeletal) - Inner circular and outer longitudinal
- Serosa - Mesothelium & connective tissue (vessels, nerves, ganglia, adipose)
What function do folds in the mucosa of the GI tract play?
Increased surface area for secretion/ absorption
Describe the histological features of the oesophagus.
- Mucosa
- Lamina epithelialis = stratified squamous
- Lamina propria = typical
- Lamina muscularis variable according to species, scattered muscle bundles but absent in cervical region of dogs
- Submucosa - Contains many branched tubulo-alveolar glands secreting mucus
- Muscularis - Skeletal or smooth muscle depending on species. In dogs / ruminants = entirely skeletal. In horses / cats = skeletal to midway then smooth
- Serosa = typical
Label this histological slide.
- Lamina propria
- Mucous glands
- Muscularis (inner circular)
- Muscularis (outer longitudinal
- Muscularis mucosae
- Keratinized stratified squamous epithelium
- Submucosa
Describe the mucosal histology of the stomach.
How is the carnivores specialised?
- Mucosa
- Lamina epithelia contains gastric pits, these contain glands which secrete mucus, acid and pepsin
- Lamina propria contains many immune cells
- Lamina muscularis fairly extensive
Carnivores have a layer of dense connective tissue existing between lamina propria and lamina muscularis - stratum compactum.
What cell types are present in the gastric pits?
What is the function of each?
- Parietal (oxyntic) cells - secretes hydrochloric acid
- Mucous cells - secretes mucus
- Chief cells - secretes pepsinogen and gasstric lipase
- Endocrine cells
How do the glandular secretions of the stomach differ between the different regions?
- Oesophagus - stratified squamous, non-gland
- Cardiac and pyloric - Columnar epithelium, branched tubular coiled glands secreting mucus and entero-endocrine cells secreting hormones
- Fundic - Columnar epithelium, long branched tubular coiled glands
- Mucus neck cells
- Chief (peptic) cells
- Parietal (oxyntic) cells
Describe the morphology of the cells of the gastric pits.
- Mucus neck cells - pale staining, secrete protective mucu
- Chief (peptic) cells – pyramid shaped with basal nucleus. Contain zymogen granules along apical border which secrete pepsinogen. Leakage of granules in fixing often makes them look ‘foamy’.
- Parietal (oxyntic) cells – spherical or pyramidal in shape with central nucleus, acidophilic cytoplasm – secrete HCl.
What cell types are found in the villi and crypts of the small intestine?
- Villi
- Columnar microvilli – absorptive
- Goblet cells – secrete mucus
- Entero-endocrine cells
- M cells – cover GALT
- Crypts of Lieberkuhn
- Simple branched tubular invaginations
- Cell types as villus but also Paneth cells (acidophilic granule cells) – pyramid shaped with basal nuclei – secrete lysozyme (suggest phagocytic function).
How does the number of goblet cells alter down the length of the small intestine?
Increases
How do the glands of the submucosa of the small intestine differ between the core species?
Submucosa can contain intestinal submucosal glands = simple branched tubulo-acinar glands opening into crypts
- mucous (ruminants, dogs),
- mixed (cats)
- serous (horses, pigs).
How does the histology of the small intestine differ between the separate regions?
- Duodenum - Extensive villi, extensive intestinal submucosal glands = Brunner’s glands
- Jejunum - Villi usually smaller and less dense
- Ileum - Villi usually club-shaped, increased number of goblet cells and lymph nodules
Label this duodenal villi histological slide.
- Central lacteal
- Goblet cell
- Enterocyte
- Brush (striated) border = microvilli
- Surface mucous cells
Label the Brunner’s Gland in this slide.
What is the function of these glands?
2
Secretes mucus-rich alkaline secretion (containing bicarbonate) - neutralise contents of stomach
Which region of the small intestine would this histological slide be found?
How can you tell?
Illeum - club shaped villi
True or false
There are both villi and crypts present in the large intestine.
False
Crypts only are present
Which cells are found in abundance in the large intestine?
Mucous cells
What are the two functions of the pancreas?
- Exocrine = main cell type - secrete pancreatic juice for digestion
- Endocrine = isolated aggregates of cells (= islets of Langerhans) – secrete hormones involved in metabolism
What are the three cell types of the endocrine pancreas and what do they secrete?
- Alpha cells secrete glucagon
- Beta cells (majority) secrete insulin
- Delta cells secrete somatostatin
Describe the histological features of the exocrine pancreas.
- Acini of exocrine cells arranged around an extensive duct system
- Glands separated by dense collagenous capsule
- Intralobular (intercalated) ducts lined by squamous / cuboidal epithelium
- Interlobular ducts lined by columnar epithelium
Draw and name the regions of the stomach.
What are the fuctions of the stomach?
- Digestion - Starch and protein
- Protection - Acid kills microbes
- Storage - Delivers food the intestine in a controlled manner
- Mechanical - forms semi-liquid chyme
Describe the motility of the stomach.
(x5 stages)
- Receptive relaxation - prepares the stomach to recieve a meal
- Fundic contraction -
- Corpus contraction
- Pyloric sphincter opens
- Pyloric contraction & sphincter closes
Remember backflow causes remixing of the chyme.
Describe starch degradation in the stomach.
Starch is degraded by amylase which breaks down a1,4 and a1,6 bonds.
- amylose helix - 1,4
- amylopectin branches - 1,4 and 1,6
Remember amylase ONLY works on alpha-glycocidic bonds
Describe carbohydrate digestion in the oesophagus and stomach.
How does carbohydrate digestion differ between herbivores, carnivores and omnivores?
In the oral cavity salivary amylase begins digestion of starch to maltose, it works only at pH At the stomach the bolus is projected into the centre of the stomach allowing digestion to continue before the acid pH breaks down the enzyme.
- Omnivores - Extensive, non-glandular fundus allows lots of starch digestion
- Carnivores - No salivary amylase, low starch digestion
- Herbivores - None glandular fundus - depends on work load
Order these groups as to how much salivary amylase they possess.
Herbivore, carnivore, omnivore.
Omnivore, herbivore, carnivore.
Remember carnivores have NO salivary amylase.
How is emptying of the stomach stimulated and inhibited?
- Emptying - by stretch receptors in the stomach and release of gastrin leading to smooth muscle contraction.
- Inhibition of emptying - duodenal factors (pH, peptide and fat content - duodenal sensory cells stimulate SNS & inhibit PNS. Secretin/CCK/GIP all decrease emptying.
Gastrin stimulates the release of which hormone from ECL cells? What effect does this have?
How else can gastrin act to stimulate this and which other chemical also causes this?
Histamine, binds to histamine receptors stimulating H+ release into the gastric lumen (in exchange for K+).
Gastrin can act on gastrin receptors to cause this as can ACh on muscarinic receptors (acts via release of Ca2+)
Describe how the gastric juices degrade proteins in the stomach.
- HCl - stimulates cleavage and unfolding of pepsinogen. (also causes non-specific degradation of proteins)
- Pepsinogen - activated to pepsin, breaks down peptide links between amino acids
Name and describe the cell types present in the small intestine.
Enterocytes, entero-endocrine, paneth, goblet
- What are the characteristics of SI contraction?
- Name the different types of intestinal contraction.
- Describe pacemaker potentials in the SI.
- Contractions slow at the distal colon. MMC (migrating myoelectrical contraction) - as peristaltic contraction meets the ileum a new one starts at the duodenum.
- Segmental, peristaltic, mass movement
- Generated by cajal cells control slow-wave potentials which decrease in frequency down the SI (reduce strength of contraction)
Outline how carbohydrates (starch - maltose, sucrose, lactose) are digested and absorbted in the small intestine.
Name the transporters needed and their function.
- Maltose - glucose x2
- Sucrose - glucose and fructose
- Lactose - glucose and galactose
Transporters - GLUT5, SGLT2, GLUT2
How can lactose intolerance in older animals can lead to diarrhoea and abdominal pain?
- Build up of lactose (due to lack of lactase) increases osmotic force (water in) = diarrhoea
- Lactose fermentation = lactic acid. Decreased pH upsets microbes, VFAs are not absorbed and gas is produced = pain.
How does carbohydrate absorption differ between the major species (and neonates)?
- Neonates - lots of lactase
- Omnivores - SGLT1 is found throughout the gut
- Horses - SGLT1 is adaptable (throughout gut and upregulated
- Ruminants - fermented so SGLT1 levels are low
Describe digestion of protein within the small intestine.
How does this differ in the neonate?
Neonates need to be able to absorb intact proteins, ie globulins.
To enable absorption of these proteins the neonatal gut is adapted as follows:
- Epithelial cells are permeable to intact protein
- Stomach produces low HCl
- Pancreatic enzyme secretion is low
- Colostrum contains trypsin inhibitors (trypsin = protease)
How is fat digested in the small intestine?
What is a micelle?
ADD PICTURE
Micelle -
Aggregation of bile salts which absorb monoglycerides and FFA’s, allowing them to be absorbed by enterocytes.
Describe the absorption of water and minerals in the small intestine.
Minerals - Fe, Ca2+, Na+, K+, Cu
How do mineral channels differ throughout the SI?
- Water
- Paracellular (between tight junctions)
- Transcellular via aquaporins/ Na+/glucose cot
- Minerals
- Fe -
- Ca2+ - upregulated abs by calcitrol (active & passive)
- Na+ - 2nd transport of other molecules
- K+ simple diffusion
- Cu - Mb affects this
How is iron absorption regulated in the SI? What happens to the iron once it has been absorbed (high and low iron in blood)?
- Secondary active transport coupled with H+ via divalent metal transporter 1 (DMT-1)
- Low iron (unsat transferrin) - Fe2+ transferred to blood where it binds with transferrin for circulation round body
- High iron (sat transferrin) - Fe2+ remains in cell bound with apoferritin to form ferritin (intra-cellular storage of iron)
- Fe3+ poorly absorbed
- Reduced to Fe2+ by vitamin C or brush border enzyme ferri-reductase
Describe the anatomical position of the caecum in the dog compared with the horse.
In the dog the caecum is on the right side of the abdomen. It has no direct connection to the ileum. It is short and held in a spiral shape against the ileum by the ileocaecal fold.
In the horse the ileum opens into the caecum at the ileal papilla and the caecum opens onto the colon via the caecal colic valve.
Name the three parts of the large instestine of the dog.
What cell types are present in the LI?
What are the main functions of the LI?
- Ascending, transverse, descending
- Colonocytes (absorption w/o villi), goblet cells (mucous and bicarbonate)
- Microbial fermentation (caecum), water and ion absorption, glandular secretions (mucous and bicarb)
How is defacation from the rectum stimulated?
What occurs on stimulation?
Pressure sensors in the rectum sense faecal material and stimulate the defacation reflex.
The inner anal spincter relaxes leading to the outer anal sphincter which is under conscious control in the dog and unconscious control in the horse and bird.
Can you describe how each of these products are absorbed in the large intestine? (HINT: receptor types)
- VFA
- Na+
- Cl-
- Water
- VFAs - SCFA / HCO3- exchanger
- Na+ - sodium channels & NHE transporter, enhanced by aldosterone
- Cl- - Absorbed by bicarbonate / hydroxyl exchange
- Water - Osmotic pressure, hydrostatic pressure, solvent drag
Explain the physiology of constipation and diarrhoea.
- Constipation - reduced motility caused by excessive absorption of water making passage difficult
- Diarrhoea - Increased secretion (+poor reabsorption) or decreased absorption
- Nutritional overload, infection hypersecretion, stress PNS stimulation
Outline the differences between the absorptive and post-absorptive states
Abs = intestinally absorbed nutrients
Postabs = nutrients from bodilly stores
What is the fate of dietry carbohydrates in the absorptive state?
Broken down to glucose for absorption. Can be used in cells, converted to glycogen in the liver for storage, in the liver for storage or glycerol/TG and stored in adipose tissue.
What effects do insulin and glucagon have on the protein–> amino acid reaction?
Insulin = inhibits protein breakdown & stimulates aa–>protein
Glucagon = stimulates protein catabolism for release into plasma
FFA are converted to acetyl CoA by ________, this process takes place in the ______. The acetyl CoA can be used in the _____ or converted to _______ ______ which can be used by the brain.
- Beta oxidation
- liver
- TCA cycle
- Ketone bodies
What is the fate of A) Lipids, B) Proteins in the absoptive fate?
Lipids: Need to be made water soluble, done by binding to proteins: Albumin, Apoproteins (chylomicrons, VLDL, LDL, HDL)
Proteins: 75% protein synthesis (globulins, albumin) / keto acids (liver energy, lipid synthesis). 25% systemic circulation, protein synthesis, energy, fat/glycogen storage.
Fe2+ absorption in the small intestine.
Describe how.
How does iron transport differ at high and low blood iron levels?
Secondary active transport coupled with H+ via divalent metal transporter 1 (DMT-1)
Iron low (transferrin unsaturated) • Fe2+ transferred to blood & binds with transferrin for circulation round body
Iron high (transferrin saturated) • Fe2+ remains in cell bound with apoferritin forms ferritin (intra-cellular Fe)
Fe3+ poorly absorbed - Reduced to Fe2+ by vitamin C or brush border enzyme ferri-reductase
Ca2+ absorption in the small intestine.
Which vitamin affects absorption and how? In which physiological conditions may this be important?
Absorbed according to body requirements
Occurs both by active & passive transport - High dietary Ca2+ increases rate of passive
Low Ca2+ or requirement high (e.g. growth / lactation) active transport stimulated by calcitrol (vitD3) - Increases synthesis of calcium-binding proteins (calbindin)
Ca2+ pumped out of cell by Ca2+ ATPase
How does the equine gut differ from the general monogastric gut?
(x3 points)
- The ileum runs directly into the caecum through the ileo-colic valve
- The caecum runs dirctly into the ventral colon through the caecal-colic valve
- The pelvic flexure (narrowing of the colon) connects the ventral and dorsal portions of the ascending colon
- Note the taenial bands and haustrations found along the colon
Draw the equine gut.
Label
Describe the motility of the equine caecum and colon.
Caecum - segmental contraction mixes, mass movement (every 3-5mins) evacuates the contents through the caecal-colic valve
Colonic - Antiperistalsis and peristalsis, motility slows at the pelvic flexure. Large antiperistaltic turns allow further digestion
Which of the rectal quadrants would the small intestine, spleen and small colon?
Left dorsal
In which rectal quadrant would the pelvic flexure be found?
Left ventral
Which rectal quadrant would the caecum be found?
Right dorsal/ventral
Describe three abnormal gut sounds which can be found in the horse.
- Decreased - due to obstruction/ ileus
- Increased - due to enteritis/ spasmodic colic
- Tympanic - gut distension
Is amino acid absorption better in the horse or ruminant?
BUT how is protein utilisation better in the ruminant?
Horse
In the horse microbial protein is mostly lost due to their hind-gut fermentation chamber.
How is urea utilised in the hind-gut fermentation vat of the horse?
Secreted into the lumen and used as non-protein-nitrogen by microbes
What are the products of fermentation and what is there function?
- Acetate - ATP, acetyl CoA
- Butyrate - energy, cellular, homeostasis
- Propionate - gluconeogenesis
Which microbes would be found in the fermentation vat of the horse?
- Amylolytic - less than in cows since less hCHO enters the vat
- Lactate producers
- Methogenic
- Protozoa
- Fungi - mechanically split lignin
Ruminant forestomachs anatomy
- Reticulum - honey comb, muscled
- Rumen - smooth muscle, rigid papillae
- Omasum - omasal canal, leaves and papillae (large surface area)
- Abomasum - true stomach, glandular
Outline the process of primary ruminant cotraction.
(x4)
- Biphasic Reticular
- Forces coarse material to central/dorsal rumen
- Liquid > cranial blind sac to omasum
- Cranial blind sac & pillar
- Partially ferm > dorsal sac
- Well ferm > reticulum
- Dorsal sac
- Circular contraction
- Ventral sac
- Circular movement, well ferm to cranial blind sac (pillar contracted)
Outline the process of secondary ruminant contractions.
A failure in this type of contraction can lead to what clinical condition?
- Biphasic reticular
- Cranial sac and pillar
- Dorsal Sac
- Ventral sac
- Cranial pillar contracted, ingesta to dorsal sac
- Dorsal Sac
- Gas in dorsal sac moves to cardia = eructated
- Ventral sac
- Cranial Pillar contracted, ingesta to cardia
Failure = bloat
How do ruminantion contractions differ from primary contractions?
How does cudd reach the mouth?
An extra “pre-biphasic” reticular contraction forces material from the reticulum towards the cardia
Thoracic and oesophageal expansion forces food into the oesophagus. + antiperistalsis
When material is reswallowed it enters the dorsal sac.
How much gas can a high yielding dairy cow eructate in one day?
2000-4000 l/ day
Eructation contractions occur every 2-3 primary contraction
How does the oesophageal muscle differ between the core species?
The quicker you bolt your food the more skeletal muscle you have. ie,
- Bird = entirely smooth muscle
- Horse/ primate - mostly skeletal with some smooth
- Cat - Majority skeletal
- Dog/ pig - all skeletal
- Rumninant - half and half skeletal and smooth
Which nerves provide sympathetic and parasympathetic innervation to the oesophagus?
- Sympathetic - cervical sympathetic nerve trunk
- Parasympathetic - all supplied via the vagus nerve (cranial neck via teh RLN)
Describe peristaltic contraction down the GI tract.
Gradually pushes chyme in an aboral direction.
Behind the chyme: Stimulatory signals to circular muscle whilst longitudinal muscle is inhibited. This pushes chyme forwards.
Infront of the chyme: Circular muscle is relaxed whilst longitudinal is contracting allowing expansion and shortening of the gut in preparation for the chyme.
Describe the breakdown of RBCs by the liver
Initially RBCs are phagocytosed by siderophages into haem, globin and iron. The haem is converted to biliverdin (bile pigment) and transported to the liver via albumin as bilirubin. This compound is conjugated in the liver with glucoronic acid and excreted as stercobilin (or purely as urobilinogen).
What are the main componants of Bile?
What are the main functions of Bile?
Components: Water, ions, bicarbonate, proteins, pigments, Cholesterol, PLs, bile acids
- Acts as a detergent - allows pancreatic lipases to act
- Lipid absorption in GI tract - improves solubility
- Exit of waste & drugs
What is the primary precursor of bile salts?
What process does this compound undergo to produce primary bile salts? And secondary salts?
Cholesterol
Converted to cholic acid/ chenodeoxycholic acid, it is then made hydrophic by conjugation with either glycine or taurine.
Secondary bile salts are produced by bacterial deconjugation in the gut of the primary salts.
Describe the circular route of bile in the body.
(x2 stages)
- Secretion - Into bile canaliculi via active transport (BSEP), into canals which empty into duodenum via the major duodenal papilla (SoO)
- Recycling - Bile acids are absorbed from the ileum via active transport, reach the liver via the HPV, captured from blood stream via NTCPs. Enterohepatic circulation
Describe two mechanisms of cholestasis.
- Intrahepatic - Decreased bile flow & back flow of constituents (infections)
- Extrahepatic - due to obstruction of the bile duct (tumour etc)
What are the two major function of the pancreas?
Describe the histological features of each of these componants.
- Exocrine - digestion - Groups of acini surrounding suple excretory ducts which empty into the pancreatic and accessory ducts.
- Endocrine - metabolism - Isolated clumps called islets which surround capillaries.
- Islets contain alpha, beta and delta cells which secrete glucagon, insulin and somatostatin respectively
Insulin.
How is it produced?
Describe regulatory systems relating to its secretion and its activity in the body.
- Produced from prepro and proinsulin via cleavage by Cpeptide
- Secreted in response to increased blood glucose, GIP and parasympathetic stimulation.
- TKR
- Increases digestive enzymes = >metabolism, lipid synth and gluconeogenesis. Increased glucose uptake via GLUT4 (peripheral) and GLUT2 (liver). Increased protein production due to increased amino acid uptake.
Glucagon
Production
How does glucagon cause a decrease in blood glucose? It is released in response to what signals?
- Similar to insulin (prepro and proglucagon) and cleaved within the liver and kidneys.
- Released in response to decreased plasma glucose and amino acids and SNS stimulation
- Causes activation of adenyl cyclase (cAMP production), stimulating glycogenolysis and gluconeogenesis
Describe the differences in pancreatic enzyme production between horses, carnivores and pigs and ruminants. How does this relate to their feeding habits?
- Horse - Grazing = continuous juice secretion, meal feeding = increases after meals >> LOADS produced - compensates for low bicarbonate, also secreted in the ileum
- Carn/ pig - meal feeding = intermittent juice production
- Ruminant - Grazing = always secreting due to continuous flow of rumenal contents
Describe the enzymatic composition of the pancreatic juices.
Why are proteases secreted as zymogens and how are they activated?
- Proteins - (chymo)trypsin, elastase, carboxypeptidase. Lipase, phospholipase, amylase, (deoxy)ribonucleases
- Secreted as zymogens to prevent autodigestion
- They are activated by enteropeptidase in the intestinal lumen or via auto-catalyis
Describe how the stimuli of the ionic and enzymatic exocrine pancreas differ.
- Enzymatic - Fat/protein metabolites iin duodenum (CCK), vagus/gastrin stimulation in carnivores
- Ionic - Vagus/gastrin stimulation in herbivores, H+ in duodenum (secretin)
How do CCK and secretin differ in their feedback mechanisms?
- CCK = +ve feedback
- Secretin = -ve feedback
How does the pH of pancreatic juices differ at normal and high flow rates? Explain.
Normal - neutral - Bicarbonate is absorbed into acinar cells
High - alkaline - Bicarbonate is not absorbed in time
Describe the falciform ligament.
Attaches the liver to the ventral body wall. It is fat filled and within it can be felt the round ligament (remnant of the umbilical vein)
What structures border the epiploic foramen?
The hepatic portal vein, liver and caudal vena cava
Describe the GI blood supply.
Aorta has three main branches:
- Celiac - Left gastric, splenic, hepatic
- Cranial Mesenteric - Colic, ileal, jejunal
- Caudal Mesenteric - Left colic, cranial rectal
Describe the branching of the celiac artery.
- Splenic - Left gastroepiploic,
- Left gastric
- Hepatic - Right gastric, hepatic proper, right gastroepiploic, cranial pancreatoduodenal
Describe the branching of the cranial mesenteric artery.
- Jejunal - caudal pancreaticduodenal
- Colic - right and middle
- Ileocolic
- Mesenteric ileal
- Antimesenteric
Describe the branching of the caudal mesenteric artery.
- Cranial rectal
- Left colic
There is no celiac vein.
How does the body drain the cranial abdomen?
Via the hepatic portal vein.
Hepatic veins drain into caudal vena cava NOT hepatic portal (therefore main branch into hepatic portal is gastro-duodenal).
Left gastric drains into splenic NOT hepatic portal
Name the three venous anomalies of the abdomen.
- No celiac vein
- Cranial / caudal mesenterics are terminal veins of hepatic portal vein
- Left testicular vein drains into left renal vein NOT caudal vena cava
