The digestive system breaks down food into simpler compounds that can be absorbed and used by the body. It includes the oral cavity, esophagus, stomach, small intestine, large intestine, and digestive glands. In the mouth, saliva containing the enzyme amylase begins breaking down carbohydrates. The stomach contains acids and enzymes that further break down food into a semi-solid mass called chyme. The small intestine completes digestion with enzymes from the pancreas and liver that break down proteins, carbohydrates, and lipids. The large intestine absorbs water from undigested food matter which is then excreted as feces.
2. Digestion :
Breakdown of food into simpler compounds , ready to be used by body ,
for energy purposes
Digestive system : many organs : food into energy
Disassembly process
5. Various systems involved in digestion
Endocrine : Glands : Secrete hormones for digestion
Nervous System : Contraction and relaxation of muscles in the
stomach ,
Lymphatic system/ Circulatory system : Absorption of food
Bile acids from Liver, Pancreatic juice , stomach acid, enzymes
6. Digestion in Oral Cavity
Selection of food: taste / smelled : aid of organs of sight and smell
Tongue : Sensory and Muscularly organ : Taste buds
Grinding / mastication : grinded by teeth : form bolus : easy passage through esophagus
Lubrication : saliva : Salivary Glands: (below tongue)
Saliva has mucus or water , an enzyme named AMYLASE
Digestion : Amylase starts digestion of carbohydrates
7. Amylase
Digestion of complex carbohydrates into simple ones
Starch to simple sugar molecules
8. Saliva : Bolus
Food moist and Lubricated
Chemicals ( sodium bicarbonate) antiseptic for killing germs
Bolus: Softened, partly digested, slimy food mass , rolled into oval lump
Pushed down through pharynx into esophagus :
Muscle contract to prevent backward flow
9. Swallowing
Beginning of swallowing : voluntary
Once reaches back of the mouth become involuntary
Peristalsis : Characteristic movement of digestive tract : involuntary( not
under our control)
Alternative contraction and relaxation of muscles
10. Continue from back of mouth , esophagus, stomach and along all
digestive tract
Antiperistalsis: Vomiting
Hunger pang: Peristaltic movement / Hunger contractions : initiated
due to low blood glucose levels
Movement of food aided by gravity
But peristaltic movement strong enough
Headstand/ astronauts
11.
12. Sphincters:
Muscle rings separating one organ from the other
Smooth muscle contraction : move food in one direction , no
flow back
At the junction of esophagus and stomach : Cardiac Sphincter
13. Digestion in Stomach
Cardiac sphincter opens on receiving peristalsis wave from esophagus
Stomach : Elastic muscular bag , stores food temporarily , digests food
Stomach : Muscular layer + Mucosal layer
Muscle layer : contraction and digestion : Mechanical grinding or
digestion of food
Three layers of smooth muscles
Different shapes of muscles
Longitudinal , circular , oblique
14.
15.
16. Stomach : Gastric Juice
Mucosa / inner wall of stomach : Gastric Glands : secret many hormones
nad chemical
Mucus :
Hydrochloric Acid
Enzyme : PEPSIN :
All these make up the gastric juice
Released on sight/ smell of food and quality
17. Mucus : Thick secretion : protects the inner wall from being
digested by the enzymes and from the HCl
HCl : maintains 2-3 pH of stomach
Proper action of PEPSIN
Softens food
Pepsin : Breakdown of Protein molecules
18. End of stomach
Food now called as chyme : Acid mixed food , semi
solid mass
Reaches Pyloric Sphincter
Opening and chyme pushed into Small intestine
19. Heart Burn/ GERD
Gastro Esophageal Reflex Disease
Burning sensation
Back flush of acidic chime into esophagus
Overeating / fatty food/ lying down immediately after food
Caffeine, smoking, alcohol consumption
20. Digestion in Small Intestine
Remaining sugars , proteins , fats digested in Small intestine
Digestion that started from oral cavity ending in SI.
Smooth muscle : contractions : Digest
Enzymes and bile juice ( form liver) Pancreatic juice ( pancreas)
pour into SI
21. Enzymes of Small Intestine
Firstly pH of the acidic chime changed by Alkaline secretions ( sodium
bicarbonate)
Pancreas: Pancreatic duct : Pancreatic juice : has all enzymes to digest all
components of food carbohydrates, proteins, lipids/ fats
23. Bile Juice
Produced in live and stored for some time in Gall Bladder
Through bile duct into SI
Green watery fluid
fats : Breakdown : Large globules to small globules ( Emulsification )
Small globules easily digested by LIPASE
24.
25. Types of digestion
Mechanical and Chemical
Mechanical : Contractions of Smooth muscles layers
along the digestive tract
Chemical : Through enzymes , chemical
Both digestion in all major organs
Figure 2.4
26. Large Intestine / colon
Material passed into large intestine from the Small intestine contains undigested food , large
amounts of water, dissolved salts.
Water and salts are absorbed into blood while undigested material rejected as feces.
Undigested food: Plant fibers, dead bacteria, undigested fats/ proteins
Water reabsorption is very important , if not absorbed due to any reason : Diarrhoea
Water absorbed excessively : Constipation
27. Rectum:
Last Part of intestine
Feces stored temporarily
Rejected through anus
Anus is controlled by sphincters
Sphincters give defecation reflex: Controlled by adults
28. Bacteria in Large Intestine
Make a few vitamins and Vitamin K
Very important for clotting