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)
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