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Digestion is the breakdown of large, complex organic

molecules into smaller , more simple components

that can be absorbed and used by the body.

Molecules need to be small enough to diffuse across

plasma membranes of the cells lining the intestinal

wall through the process of absorption.

• Digestion includes all the processes that chemically

and mechanically break down food into nutrients

• Begins immediately after food is ingested

• Includes Mechanical and Chemical digestion

– Mechanical digestion is mechanical

– changes of the physical state of the food by ,• Mastication in the mouth– reducing the

food particle size through chewing, and

mixes food with saliva

• Deglutition

• Churning of the contents in the GI lumen

(stomach and intestinal movement so they

are well mixed with the GI juices

• Propelling food through the digestive tract

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Chemical digestion: changes in chemical composition of

food as it travels through the digestive tract; these changes

are the result of hydrolysis by Digestive enzymes

Digestive enzymes are characterized by

Extracellular, organic (protein) catalysts follows the Principles

of enzyme action which are

A.Specific in their action as proteinases hydrolysis

protein ,Lipases hydrolysis fat and saccaridase hydrolysis

disaccarides

B.Function optimally at a specific pH

C.Enzymes are continually being destroyed or eliminated from

the body and must continually be synthesized

Ingestion : is the consumption of or taking in of

nutrients

Mastication: chewing. Breaking down of food in the

mouth with the help of teeth

Deglutition: swallowing of solids or liquids

Digestion: breaking down of large nutrient molecules

into smaller ones so that they may be absorbed

Absorption: transfer of medium and small sized

nutrient molecules from GIT lumen into blood

Defecation: passage of stools/ faeces from the rectum

to the exterior

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Gastrointestinal (Gl) tract (Alimentary canal)

1. Mouth

2. Oral Cavity

3. Pharynx

4. Esophagus

5. Stomach

6. Small

intestine

7. Large

intestine

8. Anus

Accessory structures Not in tube path

1. Salivary gland

2. Liver

3. Gall bladder

4. Pancreas

Three pairs:1.PAROTID :on side of face (swell with the mumps) 2. SUBLINGUAL: (below tongue) and 3.SUBMANDIBULAR: both in lower jaw produce saliva

Functions of Salivary1.Lubrication : to facilitate mastication of food and make it slides easily through the 2.Saliva coats the oral cavity and esophagus 3.Solubilises dry food: in order to be tasted, the molecules in food must be disolved 4.Oral hygiene: The oral cavity is almost constantly flushed with saliva, which floats away food debris and keeps the mouth relatively clean

J-shaped pouch of the Located slightly left of center in the body with Capacity: about 1 litre has two openinga.Cardiac Sphincter:Muscle that surrounds the esophagus at its junction with the stomach , Opens to admit food into the stomachb. Pyloric sphincter : Muscle that surrounds the stomach at its junction with the small intestine: Opens to admit CHYME into the small intestine

Functions a.Storage area for ingested food (empties in 2-6 hours)b.Place for digestive enzymes (pepsin and salivary amylase) to workc.Main place for protein digestiond.Absorption of small molecules (e.g. H2O, ethanol)

3 meters or 10 feet in length, Walls highly convoluted to S.A.Interior folds covered with villi: tiny fingerlike projections that further S.A.Divided into 3 parts:Duodenum (first 25 cm): Produces digestive enzymes: lactase, peptidase, maltase, nuclease Jejunum Ileum

Functions: 1. Completes digestion

2.Absorption of nutrients

a.monosaccharides, amino acids, short peptides, fatty acids are transported into intestinal cells, and diffuse into bloodstream

b. Fats diffuse into intestinal cells and are deposited in the lacteal (lymph vessel in the villus)

Blood Supply For GBlood Supply For Gastrointestinalastrointestinal TractTract

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1. Synthesize and secerte bile that act as detergent – emulsifies fats thus facilitate fate digestion

2. Detoxifies/removes toxic substances as Drugs and Alcohol

3. Stores Gycolgen, Vitamins (A, D, E, K), Fe, other minerals and Cholesterol

4. Activates vitamin D 5. Formation of Fetal RBC 6. Formation of plasma protein: albumin, globulin and

fibrinogen7. Stimulate bone marrow to form RBCs in adult

through secretion of erythropoietin hormone8. Metabolizes absorbed food molecules

1. Carbohydrates2. Proteins3. Lipids

Has exocrine function through

Production of pancreatic

juice (digestive enzymes and

sodium bicarbonate to

neutralize acidic chyme)

Has Endoocrine functions

through Production of insulin,

a hormone that influences

the cells’ uptake of glucose

from the bloodstream ,

and Glucagon hormone that

share with insulin to adjust

blood sugar

5 partsAscending colonTransverse coloDescending colonRectum - stores fecesAnus- muscles close

the rectum until release of feces is appropriate

FunctionsReabsorption of waterFormation of feces Manufacture of some amino acids, growth factors, vitamins B's and K by E.coli)