GIT.Combined.pdf

The Gastrointestinal System (GIT) NSCI 5720 Vertebrate Anatomy and Physiology  Objectives Explain the function of the gastrointestinal tract What is mechanical digestion and what is it’s function What is chemical digestion and what is it’s function Explain how diet type can be r...

The Gastrointestinal System (GIT) NSCI 5720 Vertebrate Anatomy and Physiology  Objectives Explain the function of the gastrointestinal tract What is mechanical digestion and what is it’s function What is chemical digestion and what is it’s function Explain how diet type can be relates to the anatomy of dentition and gastrointestinal tract Briefly discuss the anatomy and function of the stomach and small intestine of carnivores, ruminants and hindgut fermenters  Terms Mastication – chewing Deglutition – swallowing Eructation – burping Emesis – vomiting Sphincter – a circular ring of muscle that controls entry/exit from an organ For interest only: Ptyalism – salivation Regurgitation vs vomiting (emesis) Gastrointestinal Tract – Gastrointestinal Tract: continuous tube running from the mouth to Overview the anus Divided into stomach, small intestine and large intestine – based on function We will be discussing them in three parts for our lectures 1. Mouth, oesophagus, stomach 2. Small and large intestine 3. Accessory organs (liver and pancreas) Terms Functions of the Gastrointestinal System Digestion - physical and chemical breakdown of foods (ingesta) Absorption of nutrients, electrolytes and water Expulsion of waste materials  Function Digestion = process of breaking down complex nutrients into simple molecules Two types of digestion: Mechanical digestion – reduces size of food to enable it to pass through the GIT and increases surface area available to digestive enzymes Mastication (chewing) and mixing contractions in stomach Chemical digestion – splitting apart chemical bonds between food particles by enzymes Function Absorption Once mechanical/chemical digestion has taken place Process of transporting the simple molecules across the intestinal wall into the circulation for distribution Explusion Defecation = discharge of faeces from the body Faeces = waste matter remaining after digestion of food (excrement) Ingesta (food taken in) Food is made up of: Carbohydrates Proteins Fats Other essential nutrients we ingest include: Water Minerals Vitamins  Ingesta – Building blocks of food During digestion complex molecules are broken down into their building blocks so they an be absorbed & utilised by the body Food type Building blocks Protein Amino acids Carbohydrates Simple sugars eg. Glucose, fructose Fats Triglycerides and fatty acid chains  Types of Gastrointestinal Systems There are two ways to classify an animal’s gastrointestinal system: By food type Omnivore Carnivore Herbivore By anatomy Monogastric Ruminant/Foregut Fermenter Hindgut Fermenter Gastrointestinal System Type – Food Type Omnivore Consume plant and animal material Concentrated, easily digestable diet so they do not need to consume a large amount of food  small simple stomach Pig, rat, human  Gastrointestinal System Type – Food Type Carnivore An animal that consumes animal material (meat) Obligate carnivore – can only digest meat, so depend on eating meat for survival eg. All cats Concentrated, easily digestable diet, so do not need to consume much  small simple stomach Cat, dog  Gastrointestinal System Type – Food Type Herbivore Diet consists of plant material, which is of low nutritive value of food Mammals cannot digest cellulose, therefore it needs to be broken down in the gut by bacteria – takes a longer time so requires a storage area Herbivores often tend to consume a large amount of food at once for digestion later – also requires storage There are two locations where storage takes place Foregut – eg. rumen (complicated stomach) in ruminants Hindgut – eg. caecum and colon in rabbits and horses  Monogastric Simple stomach Digestion occurs in a simple (single chambered) stomach and absorption of nutrients occurs in small intestine Pig, rat, dog Foregut/Ruminant Gastrointestinal System Type – Digestion occurs in a multi chambered stomach (rumen) and absorption of nutrients occurs in small intestine and Anatomy Type some in large intestine (particularly caecum) Sheep, cow, giraffe, buffalo Hindgut Digestion occurs in simple (single chambered) stomach and absorption of nutrients mainly occurs in large intestine (particularly caecum) Rabbit, horse, elephant, hippo, rhino  Comparison of Gastrointestinal Tracts Cow – herbivore/ruminant Horse – herbivore/hindgut fermenter Dog – carnivore/monogastric  Ngā pātai? Any questions?  Oral Cavity Takes in food (ingesta) Some species have a prehensile lips & tongue – cow, horse, sheep Mastication = the act of chewing Mechanical breakdown of ingesta into small particles  increases surface area for chemical digestion Involves the teeth & tongue Saliva – mixed in with ingesta, sometimes contains digestive enzymes  Tongue and Lips Function of the tongue: Ingestion of food Taste Form a food bolus to swallow Grooming (especially cats) Thermoregulation – licking fur can cool an animal through evaporation of saliva Contains skeletal muscle – voluntary control  Prehensile tongue/lips Different use for each species Used to consume/grasp food Giraffe - https://www.youtube.com/watch?v=lSVRbSqxRVc Cows - https://www.youtube.com/watch?v=ZwdyMufH--4 Cats and dogs https://www.youtube.com/watch?v=295bNJiTA20 When “pilling” an animal Base of tongue for pilling an animal  Teeth Mandible – lower jaw Maxilla – upper jaw  Teeth Mechanically break food particles into small pieces for swallowing and also increases surface area for contact with digestive enzymes later Carnivore – sharp, cutting, ripping, scissor like action, gripping Herbivore – flat, grinding, large surface area Omnivore – hybrid of both Dental Pad  Salivary Glands Saliva lubricates food  allows it to be swallowed Antibacterial enzymes Omnivores – mild digestive enzymes (not in carnivores) Fun fact - cows may secrete 100-200L saliva daily Saliva composition differs between species based on diet, but salivary gland anatomy is the same  Salivary Glands Parotid gland “beside the ear” Mandibular Sublingual + some smaller glands Each gland has a duct that runs from the gland into the mouth  Oesophagus Muscular tube that carries (masticated, lubricated) food from the mouth to the stomach Oesophagus passes from the oropharynx, down the neck into the thorax, passes through the diaphragm into the abdomen where it joins the stomach Upper and lower oesophageal  the stomach Similar between species  Movement of Food Through the Oesophagus The passage of ingesta into the stomach  active process Peristalsis = rhythmic contraction of longitudinal muscles propagating a wave down a tube ie. the oesophageal muscles squeeze in waves, which push the food along the GIT Stomach – Monogastric & Hindgut Fermenters “Simple Stomach” Stomach is abdominal and sits caudal to the liver (which sits behind the diaphragm) – if very full may extend beyond the ribs Stomach function Storage Chemical digestion – enzymes Mechanical mixing – muscular contractions  Chemical Digestion Chemical Digestion Hydrochloric acid (HCl) is secreted making stomach contents acidic: Kills microbes etc Denatures (unfolds) proteins making them easier to digest Mucous secretion – cells secrete mucus to protect gastric mucosa from stomach acid (so it doesn’t digest itself) Mechanical Digestion Stomach lining = gastric mucosa Muscular layers produce rhythmic Segmental Contractions = a churning motion Mixes digesta with digestive enzymes Folds in mucosa = Rugae  Hindgut fermenters Simple stomach equivalent to the monogastric stomach but they also consume the high volume/low-quality food that ruminants do Their microbial digestion/absorption takes place in the large intestine  this will be covered in the next lecture  Ruminant Stomach (interest only) Cellulose makes up the structure of plant material Cellulose is not digestible by mammals, they lack the enzymes to break down the cellulose cell wall Bacteria in the rumen break cellulose down into volatile fatty acids – the ruminant can then use this for energy “chewing the cud”  regurgitation of digesta so that the animal can chew the food again, breaking it down into smaller particles  increases surface area for bacterial contact and digestion Ruminant Stomach (interest only) Four-chambered stomach: often collectively termed “the rumen” Rumen Reticulum Omasum AbomasumFour-chambered (interest only)  (interest only) Reticulum Omasum Rumen Abomasum Ngā Pātai? Any Questions? The Digestive System – Small & Large Intestine NSCI 5720 Vertebrate Anatomy and Physiology  Quick Recap Food ingested in the mouth Masticated and lubricated with saliva Swallowed into the oesophagus and peristalsis moves food bolus through the sphincters into the stomach Digesta is mixed (segmental contractions) and undergoes chemical digestion in the stomach Hindgut fermenters have a simple stomach – digestion mainly occurs in the hindgut which is what we will be covering now Fluoroscopy of GIT (for interest) Food then passes from the stomach to the small intestine...  The Small Intestine Extends from stomach to caecum (large intestine) Ileocaecocolic junction (Q in your lab books) The major site of chemical digestion and nutrient absorption  amino acids, glucose, glycerol and fatty acids etc Three segments – duodenum, jejunum, ileum Enteric/Enteral – pertaining to the intestines Enteral nutrition Enteritis Enterotomy  Small Intestine - Anatomy All segments - small diameter, smooth, muscular tube Duodenum – extends from the stomach, forms a loop, pancreas sits in the loop Jejunum – longest, narrowest part, because it is so long - needs to be folded to fit within the abdomen Ileum – short, straight-ish section of small intestine that connects the jejunum with the caecum (large intestine)  Peritoneum Very thin serous connective tissue lining of the abdomen – firmly attached to body wall Helps provide lubrication and smooth movement of organs within the abdomen Peritonitis – inflammation/infection in the peritoneum Very serious disease, often life threatening  Mesentery Fold of peritoneum – a thin layer of serous connective tissue with lacelike deposits of fat (adipose tissue) Connects intestines to the dorsal body wall Functions: Fat storage and a passage for blood vessels, lymphatics, and nerves to supply the intestines Lubrication for contractions, body movements Helps to wall off areas of infection Omentum (not examinable) Cranial Caudal  Small Intestine – Digestion (Secretions) Digesta leaving the stomach and entering the small intestine triggers the release of digestive enzymes from the pancreas and gall bladder Gall bladder & pancreas empty into the duodenum via ducts: Bile duct releases bile from the gall bladder  mostly fat digestion Pancreatic duct - digestive enzymes produced in the pancreas are secreted into the duodenum for digestion of protein, carbohydrates etc Intestinal enzymes – mostly carbohydrates We will discuss the liver and pancreas further in the next lecture…. Small Intestinal Lining - Mucosa Once food is chemically digested, the small intestine then needs to absorb the nutrients – passive diffusion To maximise absorption – need a large intestinal surface area to maximise mucosal contact with nutrients for absorption Adaptations to increase surface area Villi – folds/projections of mucosa (villus = singular) Microvilli – fingerlike projections on the epithelial cells lining the villi Nutrients are absorbed into veins draining intestines Small Intestine – Passage of Digesta Two types of contraction in the small intestine Peristalsis – co-ordinated contractions to propel digesta along GIT from one section to the next Segmental contractions - to mix digesta, increasing contact of digesta with digestive enzymes Ngā Pātai? Any Questions?  The Large Intestine Larger diameter than small intestine - extends from the ileocaecal valve (junction of small and large intestine) to the anus Three segments - caecum, colon and rectum No villi, almost no enyzymes Large Intestine - Functions Caecum – storage vat and area for bacterial fermentation (digestion) of cellulose, particularly important for hindgut fermenters Colon – water and electrolyte absorption Rectum – Storage of faeces ready for explusion Large Intestine - Caecum Caecum – blind ended sac Stores digesta and allows for bacterial fermentation (digestion) of cellulose Small in monogastric animals (diet has limited cellulose) Moderate-sized in ruminants Very large in hindgut fermenters Large Intestine – Position in Abdomen  Caecum- Hindgut Fermenter Major site of storage and bacterial digestion (fermentation) of cellulose Very large Horse caecum Rabbit caecum Caecum – Hindgut Fermenter Caecum has sac-like pouches (sacculations) with many small ridges that are designed to slow the passage of food Ensures the microbes have adequate time to ferment the digesta  Colon Material entering the colon is very liquid  water and electrolytes are absorbed, becomes semi-solid by the descending colon Absorption of water is important for water balance Goblet cells in mucosa produce mucous for lubrication  sometimes will see mucus on faeces (along with small amounts of fresh blood) with colitis  Rectum Storage of faeces prior to expulsion through the anus Does not perform much in the way of digestion Faeces consists of water, mucous, inorganic salts, epithelial cells, bacteria & undigested food  Anal sacs Dogs and cats Small sac on either side of anus – ventrolateral “Evil-smelling” fluid is secreted into the sacs – drains into the anus through a single duct on each side The sac is compressed during defecation, expelling contents  territorial marker Anal sacs – not glands (the lining of the sacs contains the glands) Can become obstructed/infected and uncomfortable for an animal  Ngā Pātai? Any Questions? The Digestive System – Accessory GIT organs NSCI 5720 Vertebrate Anatomy and Physiology  Objectives Be able to name and describe the function of the accessory gastrointestinal organs Be able to identify the accessory gastrointestinal organs and know their location within the rest of the GIT Accessory GIT Organs Liver Gall bladder Pancreas  Position in the body Liver is in the cranial abdomen, caudal to the diaphragm Gall bladder is a small green sack that lives within the lobes of the liver Pancreas – lies next to the duodenum  Liver Dark red, red-brown, lobulated organ in the cranial abdomen Very dense texture Sharp edges = normal Smooth, shiny  Function of the Liver Production of bile Process nutrients Storage of fat-soluble vitamins (A, E, D, K) - DEAK Detoxification of medications & breakdown of hormones for elimination  Portal Circulation The nutrients absorbed by the intestines are drained into the veins All these veins converge to form one vein called the portal vein This travels to the liver  takes nutrients, medications, toxins etc to the liver to metabolise/distribute to organs that need them After the blood has been “filtered” it then goes into the caudal vena cava to be returned to the heart Gall Bladder Stores and concentrates bile to be secreted into the small intestine Does not produce bile – liver does Not present in horse and rat Bile Important role in fat breakdown – breaks down fats in GIT allowing them to be absorbed Secreted into small intestine via bile duct Usually green/yellow pigment  The Pancreas Two parts (types of cells) to the gland: Exocrine pancreas – secretes digestive enzymes into the GIT. Exocrine = A gland that makes substances such as sweat, tears, saliva, milk, and digestive juices, and releases them through a duct or opening to a body surface eg. Digestive enzymes Endocrine pancreas – secretes hormones (insulin) into the blood Endocrine = The glands and organs that make hormones and release them directly into the blood so they can travel to tissues and organs all over the body eg. insulin  Exocrine pancreas Secretes digestive enzymes in their inactive form into the intestine Enzymes within the duodenum activate these enzymes so they Pancreas start digestion Protects the pancreas from digesting itself Pale cream/pale pink lobulated organ that is connected to the duodenum (right cranial abdomen) Secretes enzymes into the duodenum through the pancreatic duct  Ngā Pātai? Any Questions? How does the GIT sit in the body...? (important to know this for your physical exam) https://vetmed.illinois.edu/imaging_anatomy/index.html https://vetmed.illinois.edu/imaging_anatomy/canine/ab/ex03/c0313_Canv as.html Intestinal obstruction – gas pattern (interest only) Obstructive gas pattern Normal abdomen Chicken GIT (interest only) Reptile GIT – very varied Any Pātai? Any Questions?