The human digestive system breaks down food through both mechanical and chemical digestion. Food is ingested and broken down mechanically by teeth and enzymes in the mouth, stomach, and small intestine. In the stomach and small intestine, chemicals like acids and enzymes produced by the liver, pancreas, and intestines themselves further break down food into small molecules that can be absorbed into the bloodstream. The digestive system includes the mouth, esophagus, stomach, small and large intestines, and accessory organs like the liver, gallbladder and pancreas that produce digestive juices to break down proteins, lipids, and carbohydrates.

1. PHYSIOLOGY OF HUMAN
DIGESTIVE SYSTEM
By: Sanjay Kumar
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2. Steps of Holozoic Nutrition
• Ingestion: Food taken into mouth
• Digestion: Food broken down by teeth and
digestive enzymes
• Absorption: into bloodstream
• Egestion: Undigested
material egested through anus

3. Digestion
• Types
• Mechanical (physical): increase surface area to
increase rate of enzyme action
• Chew
• Tear
• Grind
• Mash
• Mix
• Chemical: Enzymatic reactions to that change
• Carbohydrates into simple sugars
• Proteins into amino acids
• Lipids into fatty acids and glycerol

4. Overview of Digestion
Organs of the digestive system are either part of the
gastrointestinal tract (alimentary canal) or accessory
digestive organs.
a. Mouth
b. Pharynx
c. Esophagus
d. Stomach
e. Small bowel
f. Large bowel
2. Accessory Organs glands
e. Liver
f. pancreas
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5. The parts of the digestive system
• The mouth
• The oesophagus
• The stomach
• The small intestine
• The large intestine

6. The Mouth
• There two major processes which take place:
• • Mastication (Chewing):
• - Breaks down large food molecules.
• - Increases surface area of food particles.
• • Secretion of Saliva:
• - Contains salivary amylase (ptyalin) that
• digests starch to maltose.
• - Provides an alkaline medium.
• - Lubricants and moistens food.

7. Mouth and Associated Organs
• Food enters the GI tract at the mouth. It is chewed,
manipulated by the tongue, and moistened with saliva.
• Mouth has two parts:
1. vestibule – space between cheek and teeth.
2. oral cavity proper – space internal to the teeth.
• Tongue
- skeletal muscle
- mixes food with saliva into a compact mass known as
a BOLUS.
- LINGUAL FRENULUM attaches the tongue to the floor
of the mouth and prevents posterior movement of the
tongue.

8. Tooth Anatomy
• Enamel: hardest substance in the body
• Pulp Cavity: contains arteries, veins, and nerves.
• Alveolus: made of alveolar bone
• Root: made of dentin
• Gingiva: gum
• Periodontal membrane: periosteum found
around the tooth
• Cementum: material that holds the tooth in the
alveolus.

9. Types of Teeth
• INCISORS – chisel shaped for nipping food.
• CANINES – cone shaped for tearing
• PREMOLARS –
• MOLARS - grinding food
• 32 teeth in the Permanent Dentition
• 20 teeth in the Deciduous Dentition

10. Biting
and
Cutting
Incisor
Grasping
and
Tearing
Canine
Grinding
and
Crushing
Pre - Molar
Grinding
and
Crushing
Molar

11. Saliva
• saliva
• moistens the food
• contains enzymes (ptyalin or salivary amylase)
• begins digestion of starch into smaller polysaccharides.
Function:
• Mechanical digestion.
• increasing surface area for faster chemical
• The pH of the mouth is about 7.2 (slightly alkaline as 7
directly in the middle of the scale)

12. The Oesophagus
o a tube connecting the mouth to the
stomach
o running through the Thoracic cavity.
Location:
• lies behind windpipe (Trachea).
 The trachea has as an epiglottis
 preventing food from entering the
windpipe,
 moving the food to the esophagus while
swallowing.
Function:
to take food from mouth to stomach by
muscular action called peristalsis

13. Peristalsis – alternate waves of
muscular contraction and
relaxation in the primary
digestive organs. The end
result is to squeeze food
from one part of the system
to the next.
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14.  The stomach is a J shaped expanded bag, located
just left of the midline between the esophagus and
small intestine.
 It is divided into four main regions
 The first section is the cardiac which surrounds the
cardial orifice where the esophagus enters the
stomach.
 The fundus is the superior, dilated portion of the
stomach that has contact with the left dome of the
diaphragm.
 The body is the largest section between the fundus
and the curved portion of the J.
Stomach

15. Stomach
Function of stomach
• The short-term storage of ingested food.
• Mechanical breakdown of food by
churning and mixing motions.
• Chemical digestion of proteins by acids
and enzymes.
• Stomach acid kills bugs and germs.
• Some absorption of substances such as
alcohol.
• Most of these functions are achieved by
the secretion of stomach juices by
gastric glands in the body and fundus.
• Some cells are responsible for secreting
acid and others secrete enzymes to
break down proteins

18. THE ACCESSORY ORGANS:
• support the digestive system BUT are not part of the
digestive tract
• These organs secrete fluids into the digestive tract, and
are connect by ducts.
The accessory organs include
 liver
 gall bladder
 pancreas

19. LIVER
 largest of these organs
 mass of about 1.5 kg.
 liver produces bile
Bile
• greenish yellow pigment
• made up bile pigments and bile salts
• it breaks down old red blood cells.

20. Functions of the Liver
 Bile production: 600-1000 mL/day. Bile salts (bilirubin), cholesterol,
fats, fat-soluble hormones, lecithin
 Neutralizes and dilutes stomach acid
 Bile salts emulsify fats. Most are reabsorbed in the ileum.
 Secretin (from the duodenum) stimulates bile secretions,
increasing water and bicarbonate ion content of the bile
 Storage
 Glycogen, fat, vitamins, copper and iron. Hepatic portal blood
comes to liver from small intestine.
 Nutrient interconversion
 Amino acids to energy producing compounds
 Hydroxylation of vitamin D. Vitamin D then travels to kidney
where it is hydroxylated again into its active form
 Detoxification
 Hepatocytes remove ammonia and convert to urea
 Phagocytosis
 Kupffer cells phagocytize worn-out and dying red and white blood
cells, some bacteria
 Synthesis
 Albumins, fibrinogen, globulins, heparin, clotting factors

21. GALL BLADDER
oa storage sac.
o The bile is secreted into it
o The bile is stored here.
HOW IT WORKS
 food containing fat enters the digestive
tract
 salts are secreted into the small intestine
to digest fats.
 The bile emulsifies fats in partly digested
food
 thereby assisting their absorption

22. Composition of Bile
• A yellow-green, alkaline solution containing bile
salts, bile pigments, cholesterol, neutral fats,
phospholipids, and electrolytes
Bile salts are cholesterol derivatives that:
1. Emulsify fat
2. Facilitate fat and cholesterol absorption
3. Help solubilize cholesterol
• The chief bile pigment is bilirubin, a waste product
of heme

23. Regulation of
Bile Release
Figure 23.25

28. Small Intestine
• The small intestine performs the majority of digestion and
absorption of nutrients. Partly digested food from the stomach
is further broken down by enzymes from the pancreas and bile
salts from the liver and gallbladder.
• These secretions enter the duodenum at the Ampulla of Vater.
After further digestion, food constituents such as proteins, fats,
and carbohydrates are broken down to small building blocks
and absorbed into the body's blood stream.
• The lining of the small intestine is made numerous villi (folds
of mucosa) and each villus is covered by epithelium with
projecting microvilli (brush border). This increases the surface
area for absorption by a factor of several hundred. The mucosa
of the small intestine responsible for absorption, whilst others
secrete digestive enzymes and mucous to protect the intestinal
lining from digestive actions.

29. • The stomach is an enlarged segment of the digestive
tract.
• Present left side of the abdomen below the diaphragm.
• Typically J-shaped.

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33. Over All Digestion Process in Human