NSCI 5720 Gastrointestinal System PDF

The Gastrointestinal System (GIT) NSCI 5720 Vertebrate Anatomy and Physiology  Objectiv es 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...

The Gastrointestinal System (GIT) NSCI 5720 Vertebrate Anatomy and Physiology  Objectiv es 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 Gastrointestinal Tract: continuous tube running Tract – from the mouth to the anus Overview 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  Terms Ingestion – Taking food into the body through the mouth Digestion – Breaking food down into building blocks for absorption. Occurs in the stomach and small intestine (SI) Absorption – These building blocks are taken up into the blood and transported to the liver for processing. Occurs in the small intestine (SI) Metabolism – Chemical reactions converting the building blocks in food into energy for cells. Mostly takes place in the liver. Excretion – Removal of indigestible material 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 Carbohydra Simple sugars tes 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 Gastrointesti small intestine Pig, rat, dog nal System Foregut/Ruminant Type – Anatomy Digestion occurs in a multi chambered stomach (rumen) and absorption of nutrients occurs in Type small intestine and 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/monogast ric  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=lSVRb SqxRVc Cows - https://www.youtube.com/watch?v=Zwdy MufH--4 Cats and dogs https://www.youtube.com/watch?v=295b NJiTA20 When “pilling” an animal Base of tongue for pilling an animal  Teeth Mandible – lower jaw Maxilla – upper jaw Incisors – small teeth at the front Canines – large single-root teeth Premolars – multi-root teeth, majority of cheek teeth, variable size and shape Molars – single and multi-root teeth, caudal most teeth, flatter surface  Teet h 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) Reticulu Omasu mRume m Abomasu n m Ngā Pātai? 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