The Digestive System - GI Lecture #1 W25 (1).pptx PDF

The Digestive System Learning Objectives List the functions of the digestive system. Describe the epithelial and muscle layers of the gastrointestinal tract. List the structures of the oral cavity. List and give the locations of the salivary glands. Name the types of teeth found in c...

The Digestive System Learning Objectives List the functions of the digestive system. Describe the epithelial and muscle layers of the gastrointestinal tract. List the structures of the oral cavity. List and give the locations of the salivary glands. Name the types of teeth found in carnivores and herbivores Differentiate between mechanical and chemical digestion. List the structures that make up the monogastric stomach and describe the function of each area. List the segments of the small and large intestine and describe the general functions of each segment. Explain the process of peristalsis. Describe the structure and functions of the rumen, reticulum, omasum, and abomasum. Differentiate between fermentative and nonfermentative digestion, with focus on hindgut fermenters (equine, lapine). Describe the structure and function of the parts of the avian digestive system. The Digestive System Tubing - Digestive tract, gastrointestinal tract (GIT),gastroenteric tract, alimentary canal, gut PLUS Organs not directly part of the tubing but attached by ducts The Digestive System Tubing PLUS Organs Salivary glands Liver pancreas Digestive System Functions 1. Prehension (grasping) of food with the lips or teeth Horse prehending food 2. Mastication - mechanical grinding and breaking down of food (chewing) 3. Chemical and physical digestion of food 4. Absorption of nutrients and water 5. Elimination of wastes Assumptions on my part Herbivore Carnivore Omnivore Monogastric animal Biochemistry sheet (under resources) Oral cavity - borders Aka buccal cavity (buck-all) Lips – skeletal or smooth muscle? Philtrum – cleft divides upper lip Cheeks – muscle?, lined with? Palate Horse grazing Palate Hard palate Soft palate Palatine, maxillary, Separates the incisive bones of pharynx into the skull oropharynx and nasopharynx Elongated soft palate – brachycephalic dogs and cats Oral cavity contents: teeth rostral to caudal – incisor, canine, premolar, molar Oral cavity contents: tongue What kind of muscle? Root attached to hyoid apparatus, sides of mandible Papillae specialized for grooming, moving food caudally taste buds Sensory and motor nerves – (Cranial Nerves VII and IX for sensory and XII for motor) Superficial blood vessels – in Cow tongue movements dogs – used for ? Tongue – adaptations  Salivary Glands Salivary glands - produce saliva; usually four pairs with ducts that carry the saliva to the oral cavity 1. Parotid salivary glands - ventral to the ear canals (half) 2. Mandibular salivary glands - ventral to the parotid glands at the caudal angle of the mandible 3. Sublingual salivary glands - medial to the shafts of the mandible just under the base of the tongue 4. Buccal salivary glands (aka zygomatic in dog and cat) What is in saliva? Water Proteins Electrolytes Antibodies Glycoproteins Bicarbonate – increases pH Enzymes – lysozyme – kills germs and in some species amylase (slide 16) – digests starch Nervous system control over salivation Parasympathetic (CN X) creates larger volume of more watery saliva Sympathetic stim’n produces smaller volume more mucoid saliva Conditioned responses? Species variation Ruminants – more saliva, more bicarbonate Amylase – important in amylase humans, pigs and rats lacking in dogs, cats, ruminants Horses have some  Food has been chewed and mixed with saliva – now where does it go? Bolus Pharynx – shared with what other body system Cartilage flap preventing food from going down the trachea = ? Deglutition CN responsible for swallowing (mostly XII – hypoglossal n.) Stages of swallowing pg 391 Esophagus First and 2nd sphincters encountered – upper esophageal sphincter, lower esophageal sphincter (aka cardiac sphincter) Inner muscle layer – circular (act as sphincter when reach stomach) Outer muscle layer – longitudinal Peristalsis only Mucus producing glands Endoscopy Removal of Swallowed Soc k from Puppy's Stomach Species differences – esophagus muscle layers Dogs and ruminants – skeletal muscle for entire esophagus Horse – cranial 2/3 is skeletal (diff from text) Pigs – cranial 1/3 skeletal http://vhc.missouri.edu/small-animal-hospital/small-animal-internal- medicine/diseases-and-treatments/esophagostomy-tube- information-and-care/ Primates and cats – distal esophagus is smooth muscle Birds and alligators – all smooth muscle  Esophagus issues https://youtu.be/nS kKNbedhNQ fluoroscopy Barium swallow in a dog Horse choking (above) Food stuck in Equine esophagus (below) Stomach - location Stomach - canine Stomach in radiographs – barium swallow outlines GIT, gas is dark Why would he eat that??? Stomach functions Storage of food (fundus expands) Mechanical breakdown of food Chemical breakdown of food chyme [kyme] Cardiac sphincter (aka LES) Stomach functions Cardia – makes alkaline mucus Canine, porcine stomach – all glandular Equine stomach – fundus non- glandular (margo plicatus) Bovine stomach – first 3 chambers non-glandular  Equine stomach – margo plicatus fundus Equine stomach view with endoscope Equine stomach specimen Comparing the equine and porcine stomachs – non-glandular area (called fundus by some and not by others) is not protected from stomach acid. Dividing line in the equine stomach between glandular and non-glandu regions is called the margo plicatus. Gastric Pits – in cardia, fundus & pylorus of dogs Parietal cells - produce hydrochloric acid Chief cells - produce the enzyme precursor pepsinogen Mucous (neck/progenitor) cells - produce the protective mucus Digestive enzyme precursors (proenzymes) – why? Pepsinogen  pepsin in presence of HCl Pepsin digests proteins Glands in the pyloric region – more branched than in body/fundus Mucus secreting cells G cells – secrete gastrin – hormone goes into bloodstream Plus the others already mentioned Recall… Recall also…. Stimulation of secretions Release of Parasympath Anticipate Release of Increased HCl, etic NS meal Ach flow of saliva pepsinogen, stimulated gastrin Gastrin comes back via Food enters Local reflexes and More Ach bloodstream to stomach vagal reflexes released stimulate more HCl release Stomach contractions and stomach emptying Gastric contractions: Stomach emptying: Distension of Balance between stomach causes gastrin signaling peristalsis in fundus and body pylorus and relax duodenum saying Distension causes “whoa” Gastrin increases peristalsis in pyloric smooth muscle region contraction at pylorus AND relaxes pyloric sphincter SI – duodenum, jejunum, ileum Canine digestive system laid out  A) Duodenum Most of it runs down the right side of the abdomen Spoons with pancreas Mesoduodenum Chemical digestion Sends signals to stomach depending on pH, osmolarity of chyme Cholecystokinin (CCK) and secretin – hormones! Enteropeptidase (enzyme for protein digestion) v/d canine radiograph with barium in stomach Duodenum secretions - hormones CCK – hormone, Secretin – hormone, inhibits stomach decreases acid emptying, tells production in pancreas to secrete stomach, increases pro-enzymes and bicarb from bicarbonate, pancreas stimulates gall bladder contraction, stimulates duod. Why is bicarbonate mucosa to release so important at this enteropeptidase point? (converts trypsinogen  Piglet duodenum with pancreas B) Jejunum – the “guts” Suspended from body wall by mesentery Chemical digestion and absorption of nutrients C) Ileum I Peyer’s patches here – part of immune system Ce Absorption here Ends at colon in dog and cat Co (ileocecocolic junction) Surface area of small intestine – microvilli  villi  plicae Histology of jejunum wall Electron micrograph of vil in the jejunum Movements in SI Peristalsis Segmentation Large Intestine – cecum, colon (ascending, transverse, descending in dogs and cats), rectum, anus Microbial digestion Water absorption Electrolytes (ions) absorption Species variations in gross anatomy (pg 444) Above – canine Segmentation, lateral radiograph peristalsis, of abdomen antiperistalsis, mass LI = large int. movement Rectum/anus When feces enters rectum  sensory receptors Defecation reflex – internal anal Rectal palpation on a horse – palpating pelvic flexure in large colon sphincter relaxes Brain sent message External anal sphincter relaxes? Pacemaker cells in the GIT??? Stomach, SI and colon Specialized smooth muscle cells Between submucosa and inner circular muscle layer Also between circular and longitudinal muscle layers Slow fluctuations in resting potential – if stimulated to reach threshold then end up with pattern of contraction Alternating periods of activity and rest Blood supply of GIT Celiac a. – stomach, pancreas, liver, spleen, proximal duodenum Cranial mesenteric a. – rest of duodenum, jejunum, ileum, cecum, large intestine (part) Canine dissection video - showing bra nches off the aorta - just focus on the Caudal mesenteric 3 main branches, but review parts of t