Animal Digestion Name, locate and describe the functions of the parts of the digestive system.

Introduction Digestion is defined as the breakdown of nutrients We consume: Proteins Carbohydrates Fats Nucleic acids These are broken down into their simplest forms

And that’s not all… We also consume: Water – is not digested Hydrates body’s cells Enables transport and exchange of materials to and from the cells Gases Nutrients Waste Regulates body temperature Vitamins / Minerals (living source) / (non-living source) *These are needed in trace amounts to assist reactions in the cells

From Beginning to End Mouth Esophagus Stomach Small intestine Large intestine Anus

https://www.teachingchannel.org/videos/biology-digestion-lesson-video

Mouth Point at which ingestion takes place and where food is chewed. Site that begins mechanical and chemical digestion of food Mechanical digestion = chewing Chemical digestion = secretion of saliva

Teeth provide mechanical digestion of food by breaking, cutting, and tearing. The increased surface area : aids in the swallowing process. Allows more efficient digestion by chemicals.

Salivary Glands Secrete saliva which: Saliva contains the enzymes: moistens the food (makes it slippery) stimulates taste Begins chemical digestion Saliva contains the enzymes: salivary amylase salivary maltase *Enzymes are organic catalysts that speed up chemical reactions without being altered by the reaction.

Saliva includes: Water: moistens consumed feed and aids in the taste mechanisms. Mucin: lubrication aid for swallowing. Bicarbonate Salts: acts as a buffer to regulate pH of the stomach. Enzymes: salivary amylase/maltase initiates carbohydrate breakdown.

Structures Beyond the Mouth… Esophagus: hollow, muscular tube that transports “bolus” from the mouth to the stomach; Ingested material is moved by a series of muscular contractions referred to as peristaltic waves. Cardiac Sphincter: valve at the junction of the stomach and esophagus. Stomach: hollow, pear shaped, muscular digestive organ

Functions of Stomach (Site of Digestion) Muscular movements cause physical breakdown by grinding food between folds (called rugae). Secretes digestive juices for chemical breakdown: 1) Hydrochloric Acid 2) Pepsin 3) Rennin

Parts of the stomach: Cardiac sphincter- prevents backflow Esophageal region: non-glandular area surrounding the cardiac sphincter Cardiac gland region: contains cells that produce primarily mucus (protects stomach lining)

Fundic gland region: contains cells that provide the gastric secretions needed for the initial stages of digestion. Parietal cells: produce hydrochloric acid. Chief cells: produce enzymes or precursors of enzymes Pyloric gland region: contains cells that produce mucus and some proteolytic (protein digesting) enzymes. Pylorus sphincter: at the beginning of the small intestine which controls passage of material (chyme) out of the stomach

Stomach contents approximately a pH of 2 (kills bacteria). Material arriving at the stomach is called the bolus Material leaving the stomach is called chyme.

Chemical > Mechanical Just a Reminder… Both types of digestion are occurring in the stomach: Mechanical and Chemical The churning of the stomach is considered mechanical digestion The enzyme activity is considered chemical digestion Chemical > Mechanical

Small Intestine - 3 sections Duodenum (first section) Receives secretions from: Pancreas: acts on proteins, carbohydrates and lipids Liver: bile (stored in the gallbladder) breaks down fat. Active site of digestion Jejunum: (middle section) active in nutrient absorption Ileum: (last section) active in nutrient absorption

Pancreas Endocrine Exocrine Insulin glucagon Enzymes (acini) Bicarbonate (ducts)

Small Intestine Walls of the S.I. are lined with a series of fingerlike projections called villi, which in turn have minute projections called microvilli that increase the nutrient absorption area.

Small intestine cont’d… Each nutrient has a specific absorption site. Each villus contains an arteriole and venule, together with a drainage tube of the lymphatic system, a lacteal. The venules ultimately drain into the portal blood system, which goes directly to the liver. The lymph system empties via the thoracic duct into the vena cava.

S.I. contents are approximately pH 6 to 7. Sight of digestion and absorption. Passive absorption = results from diffusion or movement from high concentrations to low concentrations. Active absorption = transport of molecules across the intestinal lining. (villi) engulf the molecules and then actively transport these molecules to either the bloodstream or the lymph. Nutrients are carried to the liver where it is detoxified.

Large Intestine – 3 sections 1. Cecum (first sections) size varies considerably in different species; Non-functional in humans (appendix) Horses contain an active flora of bacteria similar to the microbial population in rumen compartment of ruminants. Bacterial breakdown of cellulose and other carbohydrate material so the horse can utilize fibrous feeds. Site of bacterial synthesis of water-soluble vitamins and protein.

2. Colon (middle section): largest part of the large intestine Primary area of water restoration from intestinal contents. 3. Rectum (last section) the end of the digestive tract before the unabsorbed material (feces) is excreted out the anus. 4. Anus: external opening where unabsorbed materials (feces) are expelled from the body.

Functions of the L.I. Site of water restoration Secretion of some mineral elements calcium Storage reservoir of undigested GI contents. Bacterial fermentation: Synthesis of some water-soluble vitamins and vitamin K. Some bacterial breakdown of fibrous ingredients. Synthesis of some protein Limited absorption of feedstuff from the L.I.

Cross-section of Digestive Tract

Defecation Reflex: mass movement  rectal distension internal sphincter (invol)  external sphincter (vol)

Bulk flow of liquid in gut Input Ingestion ~ 2 litres per day Secretion (gut) ~ 7 litres/day Output Faeces ~100 ml/day Conclude ~ 9 litres/day absorbed Small intestine reabsorbs  7.5 L/day of water Large Intestine reabsorbs 1.4 L/day

Digestive Health: Protection & Problems Immune defense: M-cells, Peyer's patches, lymphocytes Irritable bowel disease – chronic inflammation Diarrhea: leads to dehydration (4 million deaths/yr) Vomiting (emesis) can lead to alkalosis Ulcers- H. pylori "heart-burn"  acid reflux disease

Summary Processes of digestion: ingestion, digestion, absorption, secretion, motility, reabsorption & defecation Anatomy of digestion: mouth, esophagus, stomach, small & large intestines, rectum, anus (pancreas & liver) Enzyme hydrolysis of carbohydrates, proteins, lipids and nucleic acids provide the nutrients, absorbed & conducted to liver for storage and conversion

Some good websites http://kidshealth.org/kid/body/digest_noSW.html http://www.teachnet.ie/farmnet/Digestive.htm http://biology.clc.uc.edu/courses/bio105/digestiv.htm http://www.williamsclass.com/SeventhScienceWork/HumanBodySystemProject.htm