Small Intestine PDF

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 Hind...

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 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 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  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