DR.SOURABH KANT , I.V.R.I. ,- IZATNAGAR, INDIA

What is Digestion

Digestion is the breakdown of food into smaller components that can be more easily absorbed and assimilated by the body

These smaller substances are absorbed through the small intestine into the blood stream

Digestion is a form of catabolism that is often divided into two processes based on how food is broken down:

1. Mechanical digestion2. Chemical digestion

Mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed by digestive enzymes.

chemical digestion, enzymes break down food into the small molecules the body can use

Monogastric animal different from Ruminant animal

I. A monogastric organism has a simple single-chambered stomach

II. In ruminantorganism, like a cow, goat, or sheep, which has a four-chambered complex stomach

III. Monogastrics cannot digest the fiber molecule cellulose as efficiently as ruminants

IV. No rumination like ruminant animal

V. A monogastric digestive system works as soon as the food enters the mouth

VI. Saliva moistens the food and begins the digestive process.

VII. After being swallowed, the food passes from the esophagus into the stomach, where stomach acid and enzymes help to break down the food

VIII. While in ruminant,it undergo degradation by means of microbe like protozoa,bacteria,fungus

IX. Bile salts stored in the gall bladder empty the contents of the stomach into the small intestines where most fats are broken down. The pancreas secretes enzymes and alkali to neutralize the stomach acid.

Consist of 6-main parts: 1. Mouth2. Esophagus3. Stomach4. Small Intestine (SI)5. Large Intestine (LI)6. Supportive organsa. Liverb. Pancreasc. gall bladder

Digestion in Mouth

1-Receive feed with the help of Lips, teeth and tongue help in prehension

2-Saliva secretion 3-paired saliva glands in the mouth

i. Parotids glandii. Submandibular (submaxillary) glandiii. Sublingual gland

4-Digestion- Mechanical (chewing)- Enzymatic (α-amylase → starch digestion)

Food taste5- tasted buds

Composition and Function of saliva(mouth)

Composition- 99% water

Mucus → lubrication aid for swallowingBicarbonate salts (Na) → buffer to regulate pH of stomachAmylase enzyme in some species Human-strong activityPigs- limitedHorses- not exist

Function of Saliva

1.Lubricant2. Protection of membranes in mouth3. Digestion (amylase)4. Thermoregulations (dogs-panting; cats-grooming

Factors affecting saliva production

1. Feed intakeas intake increase → saliva flow ↑

2. Feed moisture contentwet feed → ↓saliva

3. Diet composition (fiber) fiber increase chewing → saliva flow ↑

4. Health 5.Healing power

Esophagus

Hollow muscular tube lined with mucosal cells that transport ingesta from the mouth to stomachPeristaltic muscular contractionsCardiac valve (sphincter) at the end of esophagus prevent ingesta from moving back

Size and various enzyme in stomach

Size vary between species Human: 1.5 L (20% of human GI relative capacity) Pigs: 7.9 L (30% of pigs GI relative capacity) Horses: 18.2 L (9% of horses GI relative capacity)

Secretions in the stomach (gastric Juices)1.Hydrochloric acid (HCL)2. Pepsinogen3. Mucus

1.Hydrochloric acid (HCL)Lowers stomach pH = 1-3

Low pH cause: a. Initiate protein digestion (denaturation) b. Activate a protein digestive enzyme (pepsin) c. Kill pathogenic bacteria in ingested feeds

Contd….

2.Pepsinogen-inactive proteolytic enzyme- conversion to pepsin (active proteolytic enzyme) requires HCL (low pH condition)

3.Mucus- Protecting stomach wall from acid and pepsin- Malfunction → Ulcer - No absorption of nutrients in the stomach - Materials leaving the stomach called Chyme

Functions of Stomach

1. Storage of ingested feed (control flow)2. Reduce feed particle size through its muscular movements3. Initiate protein digestion4. Secretions of gastirc juices

Liver

1.Bile synthesis

2. Site for urea formation

3. Detoxification of harmful compounds

4. Storage of CHO (glycogen) and vitamins

5. Synthesis of glucose

6. Synthesis of cholesterol and triglycerides

7. Synthesis and degradation of amino acids

Bile

Bile Synthesis(Liver Function)

-Made in the liver- Stored in gallbladder -Secreted bile enters duodenum (small intestine) via duct (bile duct)

Bile Function(Liver Function)

a.Emulsification of fats to facilitate lipids b.digestion and absorption in small intestine Activate pancreatic lipase enzyme

Contd….Assist in CHO, proteins and lipids digestion in small intestinePancreatic secretions enter duodenum (small intestine) via duct

Pancreatic secretions: 1.Digestive enzymes: 2. Bicarbonate (buffer)3. Hormones

Digestive enzymes

a. Amylase → digest starchb. Trypsin c. Chymotrypsin d. Carboxypeptidasee. Neucleaseb - e → involve in proteins digestionf. Lipase → digest lipidsg. cholesterol esterase → digest cholesterol

Contd…

Bicarbonate (buffer)- Neutralize small intestine pH- Enzymes require pH > 6.5 to function in small intestine (duodenum)

- Pancreatic enzymes and bicarbonate are made in pancreas → released into duodenum (small intestine) via duct.

Hormonesa. Insulinb. Glucagon

- Released into blood- Regulate (maintain) blood glucose level

High blood glucose → insulin release →↑ glucose uptake by cells and also increase glycogen synthesis

Low blood glucose → ↑ glucagon release →a. breakdown glycogen to glucoseb. increase synthesis of glucose from AA

Contd…Different part of Small Intestine (SI) 1. Duodenum 2. Jejunum 3. ileumDuodenum- First section of SI ,Shortest section- Main site for CHO, protein and lipid digestion - pH = 6.0-6.5

- Digestion accomplished by secretions from: a. Pancreas (enzymes and buffer) b. Duodenal wall (enzymes) c. Liver (bile)Duodenal wall secretions-Enzymes1. Maltase 2. Sucrase 3. Lactase 4. Aminopeptidase 5. Dipeptidase help in protein digestin

Contd….

Jejunum and ileumJejunum = Middle sectionIleum = Last section

Jejunum & ileum are the main site for nutrients absorption (AA, glucose, FA, vit & minerals)

Walls of lower intestine are folded and lined with villi (fingerlike projections) → help in ↑ing surface area

Each villi has minute projections called microvilli → more ↑ in surface area

Absorption in SI1. Passive diffusion2. Facilitated diffusion 3. Active absorption

Passive diffusionfrom high to low concentration eg. minerals, water

Facilitated diffusion-from high to low concentration but use carrier proteins in intestinal surface- eg. Vitamins

Active absorption:-from low to high concentration- requires energy and specific carrier proteinseg. Glucose and amino acids

Contd….

Sections of LI1.Cecum2. Colon: 3. Rectum

Cecum-first section of LI- Contain active bacteria similar to rumen bacteria - Fermentation siteMonogastric animals however, don't benefit from these vitamins and bacterial protein

Colon:Storage sitewater absorption (also some minerals absorption)No absorption of amino acids and sugars

Contd…..

Rectum last section of LI functions 1. Fiber digestion- Digestion by bacteria inhabiting the cecum (very limited in monogastric animals except in horses) - End-products of fermentation (VFA, B-vits, bactereial protein) have little use.

2. Absorption- water (mainly)- very limited absorption of nutrients (feedstuff or microbial origin)- No AA or glucose absorption

Thanks