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Gastrointestinal
| Question | Answer |
|---|---|
| What is motility? | movement of food through the GI tract |
| What is prehension? | bringing food into the mouth |
| What is egestion? | removal of undigested waste from GI tract |
| What does parotid mean? | serous/watery |
| What are the components of mucus? | mucin + water |
| Ruminant saliva | more serous bicarbonate to act as a buffer in the rumen no amylase phosphate and urea secretion always isotonic - at low flow conc of phosphate increases and at high flow conc of bicarb increases some antibodies |
| What are tannins/tannic acid? | polyphenolic compound in leaves and buds which reduce digestibility - ruminants eat these, so have proteins that bind to tannins to inactivate them |
| Non-ruminant saliva | more mucosal to lubricate passage of food low flow is hypotonic, high flow is isotonic lysozymes/antibodies amylase (in some species that eat a lot of starch) |
| How is saliva secretion controlled? | autonomic nervous system + basal secretion for oral hygiene |
| What are the reflex pathways for saliva secretion? | congenital - instinctive (salivary centre in medulla oblongata) conditioned - learned (initiated in cerebral cortex then travels to salivary centre) |
| Why are digestive juices mostly reabsored? | there is a lot of water and useful enzymes and proteins that can be recycled - prevents dehydration and saves energy |
| What are the 3 layers that make up the abdominal wall? | skin, subcutaneous fascia, muscles |
| What are the different types of subcutaneous fascia? | superficial: contains adipose for warmth and cutaneous trunci muscle for twitching deep: tough fibrous elastic sheet called the yellow abdominal tunic (ox & horse) |
| What are the different muscles in the abdominal wall? | laterally: internal and external abdominal oblique, transverse abdominal (IAO,EAO,TA) ventrally: rectus abdominis (RA) |
| What is the linea alba? | a long tendon that runs down the middle of the rectus abdominis - slightly different in different species |
| What is the innervation of the abdominal muscles? | spinal nerves from the last thoracic and first 5 lumbar vertebrae branch dorsally, ventrally and medially |
| What is the inguinal canal? | the potential space between the gap in IAO and a slit in the EAO - male urinary tract |
| Which embryological regions do the different parts of the GI tract evolve from? | endoderm: epithelial lining and exocrine glands mesoderm: muscle and connective tissue |
| What is the first stage of the formation of the GI tract in the embryo? | yolk sac is taken into the body to become the gut later separates to foregut, midgut and hindgut, each with its own arterial supply |
| In embryology, what does the foregut evolve into and which artery supplies it? | supplied by celiac artery enlargement of tube becomes stomach, which then turns sideways oesophagus develops between pharynx and stomach |
| In embryology, what does the midgut evolve into and which artery supplies it? | supplied by cranial mesenteric artery the huge liver pushes the midgut out into the umbilical cord the elongated tube rotates & twists to increase surface area later is inserted back into foetus as it grows |
| In embryology, what does the hindgut evolve into and which artery supplies it? | supplied by caudal mesenteric artery rotation of midgut pushes hindgut to the left differentiates into colon & rectum bud in ventral section becomes the allantois - later the lower urogenital tract |
| What is the endodermal diverticulum? | the junction between the foregut and midgut becomes the liver and pancreas |
| What are the 3 kinds of peritoneum? | parietal, visceral and connecting |
| Parietal peritoneum | lines the abdominal cavity |
| Visceral peritoneum | surrounds organs (shiny) |
| Connecting peritoneum types | mesentery (bowel to body wall) omentum (stomach to something) fold (bowel to bowel) ligament (non-bowel to something) |
| What are the names of the different openings in the diaphragm? | aortic hiatus oesophageal hiatus caval foramen (caudal vena cava) |
| Liver | 4 lobes: left and right (each separated into lateral and medial) quadrate and caudate gall bladder is storage unit for bile attachments: coronary ligament, triangular ligaments, round ligament (umbilical vein!) - very tightly bound |
| Stomach | 3 areas: fundus, corpus, pylorus attachments: greater & lesser omentum, gastro-splenic ligament |
| Spleen | blood storage attachment: gastro-splenic ligament |
| Duodenum | major papilla: bile and pancreatic ducts minor papilla: accessory duct attachments: mesoduodenum, hepato-duodenal ligament, duodenal-colic fold (the end of this signifies start of jejunum) |
| Pancreas | right and left lobes attachments: right in mesoduodenum, left in greater omentum |
| Jejunum | longest section attachments: under greater omentum and attached to body wall by mesentery - mesojejunum |
| Ileum | before caecum attachments: ilo-caecal fold, mesoileum |
| Caecum | beginning of large intestine attachments: ilo-caecal and caeco-colic folds in dogs often fills with gas and so easily visible on radiograph |
| Colon | ascending, transverse, descending attachment: mesocolon |
| How is the GI tract regulated? | pathways between sensory cells and CNS - combination of hormonal and neural regulation |
| What do sensory cells in the GI tract detect? | pH, wall stretch, nutrient concentration, osmolarity, irritation, metabolite concentration |
| What are the different reflex arcs in the GI tract? | short reflex arcs: enteric nervous system (ENS) long reflex arcs: from GI to CNS - autonomic nervous system |
| What are the different types of short reflex arc? | simple reflex: 1 afferent and 1 efferent neuron complex reflex: multiple simple reflexes connected by interneurons |
| What is the main transmitter in the ENS? | acetylcholine (mostly stimulatory but can be inhibitory) |
| What does the hormone gastrin do? | stimulates ECL cells to produce histamine - mainly effects parietal cells (HCL) released in stomach |
| What does the hormone secretin do? | stimulates the release of pancreatic fluid released in duodenum |
| What does the hormone cholecystokinin (CCK) do? | causes gall bladder and pancreas to secrete juices released in duodenum |
| What does gastric inhibitory peptide (GIP) do? | inhibits further secretion of HCL and stimulates insulin release released in cranial small intestine |
| What are the 3 phases of regulation in the GI tract? | cephalic: anticipating food (includes emotion) gastric: distension of stomach and presence of peptides intestinal: distension and lumen contents |
| What controls appetite? | The hypothalamus and satiety centre: cause direct effects on animal behaviour |
| What are the 3 theories for the inhibition of appetite? | glucostat CCK lipostat |
| What are the 4 types of motility in the GI tract? | segmental peristalsis anti-peristalsis mass movement |
| How do the pacemaker cells in the GI tract cause contractions? | repetitive and spontaneous oscillations in groups of cells connected by gap junctions between circular and longitudinal smooth muscle - these oscillations are beneath the threshold, when there is a stimulus the waves move up and above the threshold |
| What is deglutition? | swallowing |
| What happens in the process of deglutition? | 1. food is molded into bolus by tongue and pushed upwards and backwards to the pharynx 2. the soft palatte is forced upwards to seal nasal cavity 3. pressure-sensitive sensory cells are stimulated, alert the swallowing centre in the medulla to start ref |
| What are some disorders that can affect swallowing? | cleft palate epiglottis failure phyrangeal paralysis botulism (bacterial toxins block ACh release) myaesthenia gravis (antibodies formed against ACh receptors anaesthesia (inhalational pneumonia: choking on vomit) |
| What are the layers of the oesophageal wall? | mucosal submucosal muscular: striated/smooth, depends on species serosal/adventitia (real serosal) |
| What is the innervation of the oesophagus? | autonomic sympathetic: cervical chain parasympathetic: recurrent laryngeal (top) & vagus (the rest) |
| What is the name of the junction between oesophagus and stomach? | lower oesophageal or cardiac sphincter oblique angle - more physiological than anatomical always closed except during swallowing to prevent acid reflux |
| What is emesis? | vomiting sharp deep breath followed by forceful contraction of abdominal muscles to increase intra abdominal pressure via diaphragm |
| How is emesis controlled? | vomiting centre in medulla stimulated by phyrangeal/gastric distension or irritation vomiting normal in cats and dogs ruminants regurgitate some animals (like horses) can't vomit |
| What is gastric torsion/volvulus? | rotation of the stomach, seals off cardiac sphincter, preventing vomiting and swallowing stomach fills with gas and swells, can rupture blood supply can be compromised - hypoxia and necrosis, impaired venous return to heart will cause circulatory shock |
| What are the 4 functions of the stomach? | digestion protection storage mechanical breakdown/mixing |
| What does the hormone histamine do in the GI tract? | directly stimulates chief, parietal, and mucin cells in the stomach |
| Different cell types in the stomach wall | goblet cells parietal/oxyntic cells chief/peptic cells entero-endocrine cells |
| What are ECL cells? | Enterochromaffin-like cells that control acid secretion using histamine |
| How do the intestines undergo selective absorption? | concentration gradients secondary active transport (specific transporter proteins) |
| What are the different kinds of enzymes that can be found in the small intestine? | luminal: secreted by salivary glands/pancreas (need to be reabsorbed/digested to recycle) membrane-bound: attached to epithelia (easily reused) |
| What are the different cell types in the small intestine? | goblet cells: mucus enteroendocrine cells: sensory/hormone release paneth cells: prevent microbial penetration enterocytes: absorption - microvilli |
| What are the different types of peristaltic contractions in the small intestine? | irregular moderate: short distance then die out regular strong: long distance once wave of contraction reaches ileum, new waves starts at duodenum |
| SGLT1 | absorbs glucose and galactose from lumen into enterocyte sodium glucose co-transporter - conc gradient of sodium maintained by sodium/potassium ion ATPase pumps |
| GLUT2 | absorbs all monosaccharides from enterocytes to bloodstream |
| GLUT5 | fructose absorbed via facilitated transporter (passive due to conc gradient low in body) |
| Neonate special adaptations | high levels of lactase and lactose transporters epithelium in intestine permeable to intact proteins (antibodies) stomach produces very little HCL pancreatic enzyme secretion low colostrum has trypsin inhibitors (stops antibodies from being digested) |
| What do segmental contractions in the small intestine do? | mix contents in the lumen |
| What kinds of lipids are found in meat? | cholesterol esters phospholipids |
| What kinds of lipids are found in plants? | galactoglycerides phospholipids |
| What are tricglycerides broken down into? | monoglycerides + free fatty acids |
| How does bile help digestion? | contains bicarb to neutralise stomach acids and make suitable environment for enzymes contains bile salts that split up large fat droplets to smaller ones the water-soluble and fat-soluble components of bile keep fat droplets separated bile salts aggr |
| What are chylomicrons made of? | triglycerides + cholesterol + phospholipids made in golgi apparatus and transported in lymph |
| Where does 80% of water absorption take place? | the small intestine |
| Where does paracellular water absorption occur? | tight junctions between epithelial cells |
| Where does transcellular water absorption occur? | cell membrane via transporter proteins like aquaporins mostly osmosis via other transporters |
| What is solvent drag? | a solute (like an ion) moving across a membrane with water molecules |
| How are sodium ions absorbed in the small intestine? | secondary active transport via transporter proteins |
| How are potassium and chlorine ions absorbed in the small intestine? | diffusion |
| How are bicarbonate ions absorbed in the small intestine? | chloride counter transporter proteins |
| How is iron absorbed in the small intestine? | according to the body's needs: using transferrin if transferrin is saturated: Fe II stays in cell bound to apoferritin if transferrin is unsaturated: Fe II is transferred to the blood and bound to transferrin |
| How are calcium ions absorbed in the small intestine? | according to the body's needs active and passive transport active is stimulated by calcitrol (Vit D) transported out of cell by calcium/ATPase |
| What does calcitrol do? | Increases vitamin D-dependant synthesis of calcium-binding proteins (calbindin) |
| What 2 types of cells are found in the large intestine wall? | colonocytes: microvilli, absorb at luminal surface goblet cells: in crypts, release mucous for microbes |
| What may inhibit emptying of the stomach? (detected in duodenum) | high conc of peptides high pressure high osmolarity low pH high fat levels |
| What may stimulate emptying of the stomach? | dilatation of stomach peptides in stomach |
| How is water transported in the intestines? | paracellular: between cells via tight junctions transcellular: across cell membrane via transport proteins (aquaporins) |
| What can cause diarrhoea? | nutritional imbalance infections stress |
| How would you treat extreme dehydration caused by diarrhoea? | IV drip containing ions and water |
| How would you treat moderate dehydration caused by diarrhoea? | oral water solution with salts and glucose |
| How are the exocrine cells in the pancreas arranged? | acini - cells arranged around a duct that leads to gall bladder/duodenum stain darker nuclei pushed to outer edge of acinus, granular zymogens at base |
| How are the endocrine cells in the pancreas arranged? | islets of Langerhans - arranged around capillaries stain lighter |
| What is in pancreatic juice? | bicarbonate (at low flow rates it is reabsorbed, at high flow rates no time so higher conc and very alkaline) enzymes (proproteases stored as zymogens in pancreas) |
| What types of endocrine cells are there in the pancreas? | alpha: secrete glucagon beta: secrete insulin delta: secrete somatostatin HORMONES ALWAYS RELEASED TO BLOODSTREAM NEVER GI TRACT --> go to liver |
| What is secretion of insulin stimulated by? | increased glucose levels parasympathetic |
| Which transporter protein does insulin activate? | GLUT4 - present in nearly all tissues |
| What does insulin stimulate? | uptake of glucose into cells & glycogenesis uptake of amino acids (& protein synthesis) uptake of FFAs & glycerol formation for triglyceride storage |
| Which animals do not have gall bladders? | equids and rodents |
| What is the purpose of lobes in the liver? | allows flexibility - diaphragm always moving above it if not lobulated = not touching diaphragm (cows) |
| What is the structure of the liver? | capsule of connective tissue lobes & lobules - separated by septae (connective tissue) hepatocytes arranged into acini space of Disse (between hepatocyte and sinusoid) canaliculi between hepatocytes |
| What does the space of Disse do? | protect hepatocytes from toxins & pathogens |
| What is the name of the resident macrophages of the liver? | Kupffer cells - also breakdown red blood cells |
| What are the blood vessels present in the liver? | hepatic artery: from heart hepatic portal vein: from gut hepatic vein: drains to vena cava |
| What is the movement of blood in the liver? | portal vein + hepatic artery mix in sinusoids sinusoids drain into central veins central veins drain into hepatic vein hepatic vein drains into caudal vena cava |
| What is the sphincter of Oddi | where the cystic and hepatic bile ducts meet the duodenum inactive in animals without gall bladders |
| What does coenzyme cytochrome P450 do? | breaks down haem to bilirubin (red --> green --> yellow) transported to liver with albumin conjugated with glucuronic acid in the liver released into urine or bile |
| How is stercobilin formed? | metabolised bilirubin in the gut --> turns brown |
| What are some functions of the liver? | synthesis plasma proteins breakdown erythrocytes remove bacteria detoxification stores iron, glycogen, copper & vitamins macromolecule metabolism synthesis cholesterol and bile produce clotting factors |
| What are the components of bile? | water electrolytes biliary proteins pigments phospholipids bile acids (cholic & chenodeoxycholic acid) |
| How are primary bile acids made? | synthesised in the liver from cholesterol |
| How are bile acids made water soluble? | conjugated with amino acids |
| What are secondary bile acids? | converted from primary acids by bacteria in ileum produce deoxycholic and lithocholic acid |
| What is enterohepatic circulation? | pathway that bile salts take from the liver to the intestines then back to the liver, bypassing systemic circulation captured from blood by NTCP in ileum (very efficient) |
| NTCP | sodium-dependent taurocholate co-transporting polypeptide |
| What is polyuria plydipsia | excess urination and drinking |
| What is jaundice/icterus caused by? | increased bilirubin in blood |
| What is ascites? | excess fluid in abdominal cavity |
| What is hepatomegaly? | enlarged liver |
| What is microhepatica? | small liver |
| What can you test for in cats and dogs to diagnose liver disease? | enzymes ALT and AST |
| What can you test for in horses and ruminants to diagnose liver disease? | enzymes GGT and ALP |
| What are porto-systemic shunts? | connection between portal vein and caudal vena cava can be congenital (one shunt) or acquired (multiple small shunts) blood bypasses liver |
| How are lipids transported in the blood even though they are hydrophobic? | FFAs are bound to albumin all other lipids are bound to apoproteins |
| What does adipose tissue do to glucose? | converts to glycerol for triglyceride synthesis, any excess is converted to FFAs |
| VLDL | very low density lipoprotein synthesised in liver transports tryglycerides |
| LDL | low density lipoprotein transports cholesterol to cells made from VLDL remnants in liver |
| HDL | high density lipoprotein synthesised in liver removes cholesterol from cells and delivers to the liver |
| How is pyruvate made? | from lactate, glycerol, amino acids or glycolysis |
| Cori Cycle | skeletal muscle can't complete glycogenolysis as it can't dephosphorylate, so sends it back to the liver to receive glucose again |
| What does the liver do with FFAs? | converted to Acetyl CoA to use as energy source excess converted to ketone bodies |
| How do ruminants make ketone bodies? | can be synthesised from butyrate (prevents it from inhibiting gluconeogenesis from pyruvate) brain can't switch from glucose as energy source |
| How do monogastric animals make ketone bodies? | only synthesised in the liver brain can switch energy source from glucose to ketone bodies |
| What are the hormones that regulate metabolism? | insulin glucagon adrenaline glucocorticoids (starvation) |
| What is the oesophageal groove? | lips that form a tube, allowing food/milk to bypass the rumen and go straight to the omasum all young ruminants have it, stops functioning after weaning browsers will maintain function |
| What are the names of the four stomachs in a ruminant? | reticulum rumen omasum abomasum |
| How is the rumen divided? | Pillars/grooves; dorsal sac, ventral sac, and 2 caudal sacs |
| What kind of epithelium lines the rumen? | keratinised stratified squamous |
| What adaptation does the rumen GI tract have for absorption? | leaves and papillae - increases surface area |
| What is the reticulo-omasal orifice? | junction between omasum and rumen |
| Abomasum | HCl and pepsin secreted like in normal stomach young ruminants have rennin - enzyme that aids digestion of milk pH is slightly higher than normal stomach as rumen fluid tends to be more alkaline |
| What are primary contractions in the rumen and what do they do? | contractions of the smooth muscle around the rumen to mix contents and move some of it to the omasum (along with some microbes) |
| What are secondary contractions in the rumen and what do they do? | extra reticular contraction before primary contractions, cause eructation to expel gas |
| What is rumination? | regurgitation (anti-peristalsis), immediately reswallowing liquid, remastication and reswallowing the bolus anti-peristalsis caused by negative pressure in oesophagus, causing the lower oesophageal spincter to open - passive |
| How is rumen motility regulated? | autonomic long vago-vagal reflex control centre: dorsal vagal nuclei in medulla (made up of 2 nerve clusters that regulate frequency and strength of contractions) stimulated by tension receptors inhibited by mechano B receptors |
| What do mechano B receptors in the rumen detect? | stretch pH osmolarity VFAs |
| What stimulates the oesophageal groove to form a tube? | warm milk & sucking stimulates chemoreceptors in pharynx can also be stimulated by certain salt solutions (medical) |
| Why is milk entering the rumen a problem? | microbes digest lactose into lactate, amylolytic enzymes proliferate at expense of lactate-utilisers, so pH drops rapidly lactate harder to absorb than VFAs |
| How is an anaerobic environment maintained in the rumen? | facultative anaerobes use oxygen and adhere to luminal surface, use up all oxygen in the rumen this ensures that VFAs are formed and not carbon dioxide + water |
| What do amylolytic bacteria in the rumen digest? | alpha glycosidic bonds starch to simple sugars |
| What do cellulolytic bacteria in the rumen digest? | beta glycosidic bonds cellulose |
| What does fungi in the rumen break down? | lignin mechanically |
| What do proteolytic bacteria in the rumen digest? | peptide bonds proteins |
| What do methanogenic bacteria in the rumen do? | convert carbon dioxide to methane regenerates NAD for glycolysis |
| What do lactate utilisers in the rumen do? | convert lactate to propionate |
| What do protozoa in the rumen do? | produce VFAs, lactate, carbon dioxide and hydrogen store glucose as glycogen (can be retrieved in intestines) increase rate of fermentation |
| Rumen acidosis | high starch diet leads to rapid increased production of VFAs, decreasing pH amylolytic bacteria can handle low pH, so they proliferate at expense of other microbes - vicious cycle pH continues to drop, damaging rumen lining water enters by osmosis caus |
| How could you treat rumen acidosis? | IV alkaline fluids |
| Why can ruminants tolerate higher levels of toxins? | microbes degrade many toxins before they enter intestines/bloodstream |
| What kinds of lipids do microbes in the rumen hydrolyse to VFAs? | long chain fatty acids: FFAs, triglycerides, galactolipids |
| What do rumen microbes need to proliferate? | protein and energy |
| What can rumen microbes use for protein synthesis? | inorganic nitrogen: gas, nitrate, nitrite, and ammonium non-protein & organic nitrogen: amides, amines, peptides, amino acids, urea, nitrates, ammonium |
| When might a cow's protein demands increase? | early lactation can be met by increasing urea/insoluble protein in diet, increasing starch in diet |
| What happens to lactic acid in the liver? | converted to glucose |
| How is the equine large intestine divided? | areas: caecum, ventral colon, dorsal colon physiological valves: ileo-caecal & caeco-colic junctions, narrow pelvic flexure, narrowing transverse colon |
| What kind of muscle causes contractions in the equine colon? | longitudinal discontinuous muscle - separated into taenial bands that form pockets mixes contents and delays transit time |
| How are VFAs absorbed in horse colon? | large intestine mucosa (some lost in faeces) SCFA/bicarbonate exchanger protein |
| Why is fermentation slower in the horse than ruminants? | lower levels of amylolytic bacteria since starch is digested and absorbed in small intestine |
| How do microbes in the horse colon get nitrogen for protein synthesis? | urea secreted in ileum and large intestine |
| Why is a horse more efficient on abundant low quality forage than a cow? | can decrease gut transit time & eat more |
| What is special about the horse caecum? | used as fermentation chamber stops retrograde flow from colon to small intestine - protects microbial environment |
| What kinds of contractions occur in the horse colon? | segmental anti-peristalsis mass movement (caecum to colon, colon to rectum) |
| What is the epiploic foramen? | Opening into the omental bursa, between the greater and lesser omenta |
| What is the sigmoid flexure? | start of descending duodenum at junction with stomach, curves downwards/caudally |
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