Human Digestive System: Unraveling the Intricacies of our Inner Factory Introduction Welcome to this comprehensive guide on the human digestive system! In this article, we will embark on a fascinating journey through the intricacies of our inner factory, exploring the processes and functions that allow our bodies to break down and absorb nutrients from the food we consume. Join us as we unravel the secrets of digestion, absorption, and elimination, shedding light on the marvelous mechanism that keeps us nourished and energized. The Human Digestive System: An Overview The human digestive system is a complex network of organs and processes that work together to facilitate the digestion and absorption of food. From the moment we take a bite to the final elimination of waste, this remarkable system ensures that our bodies receive the vital nutrients needed for growth, repair, and maintenance. The Mouth: Where It All Begins The journey of digestion commences in the mouth. As food enters our oral cavity, it undergoes the first stage of mechanical digestion through the process of chewing. The teeth break down the food into smaller pieces, increasing its surface area for efficient chemical digestion. The saliva, secreted by the salivary glands, also plays a crucial role by moistening the food and initiating the breakdown of complex carbohydrates with the enzyme amylase. The Esophagus: A Pathway to the Stomach Once food is sufficiently chewed and mixed with saliva, it travels down the esophagus, a muscular tube connecting the mouth to the stomach. Through rhythmic contractions known as peristalsis, the esophagus propels the food downward, allowing it to reach the stomach for further processing. The Stomach: A Gastric Playground The stomach serves as a temporary reservoir for food and facilitates both mechanical and chemical digestion. It churns and mixes the food with gastric juices, including hydrochloric acid and enzymes such as pepsin. This powerful combination breaks down proteins and kills harmful bacteria, preparing the food for the next phase of digestion. The Small Intestine: The Hub of Absorption The small intestine is where the magic of absorption truly takes place. Divided into three parts—the duodenum, jejunum, and ileum—it receives the partially digested food from the stomach. The walls of the small intestine are lined with finger-like projections called villi, which increase the surface area for nutrient absorption. Here, the nutrients are broken down into their smallest forms and are transported into the bloodstream for distribution to the body's cells. The Large Intestine: Processing Waste As the now-depleted food mass enters the large intestine, the focus shifts from digestion to waste processing. The large intestine absorbs water and electrolytes from the remaining undigested material, forming solid waste known as feces. The feces are then stored in the rectum until elimination through the anus occurs.

1. PHYSIOLOGY
OF
DIGESTION
By- Deepanshu Kumar Yadav
B.Sc B.Ed CBZ
VTH Semester

2. The digestive system is formed of
1. Alimentary canal
2. Digestive glands

4. Mucosa
Sub mucosa
Circular muscle layer
Longitudinal muscle layer
Serosa
Structure of
Alimentary canal

5. Mastication (Chewing)
•Mechanical breakdown of large
food particles into smaller ones in
the mouth.
•Increase exposed surface area to
enzymes and help swallowing.
Forming bolus.

6. Salivary Secretion
Saliva is secreted primarily by three pairs of glands:
1. the parotid glands: 20%
2. the submandibular: 75%.
3. the sublingual glands: 5%.
4. many small buccal glands in mouth cavity.

7. Salivary Secretion
Saliva (Water- 99.5%) (Solids-0.5%)
•800- 1500 ml/day with proteins & electrolytes
•pH→ 6- 7.0 ( 8.0 during active secretion)
•Hypotonic ( Na+& Cl- less , K+& HCO3 more than plasma
•Contains
IgA,
lysozyme,
lactoferrin,
mucin
prolin rich proteins

8. Functions of Saliva
Cooling hot foods.
Neutralizing acid.
Lysozyme attacks the walls of bacteria.
Antibodies (immune globulin IgA)
destroy oral pathogenic bacteria.

9. Digestive Functions Of Saliva
• Saliva has 3 digestive enzymes, namely salivary amylase, maltase and lingual
lipase.
Salivary Amylase – it is a carbohydrate – digestive enzyme. It acts on cooked
or boiled starch and converts into dextrin and maltose.
Optimum pH, necessary for the activation of salivary amylase is 6. salivary
amylase cannot act on cellulose.
Maltase – It is present only in traces in human saliva and it converts maltose
into glucose.
Lingual Lipase – lingual lipase is a lipid digesting (lipolytic) enzyme.
It is secreted from serous glands situated on the posterior aspect of the tongue.
It digests milk fats. It hydrolyses triglycerides into fatty acids and
diacylglycerol.

10. Swallowing (Deglutition)
Propelling of food from mouth to
stomach through pharynx and
oseophagus.

11. Stomach

12. Stomach is divided anatomically
Fundus
Body
Antrum
Pylorus

13. Secretory function of stomach
Gastric
gland

14. Functions of HCl
• Killing bacteria
• Dissolve food into chyme
• Activate pepsinogen
• Iron & calcium absorption
• Stimulate secretin hormone & bile flow

15. Acid secretion
1
2

16. Digestive Function
Pepsin – it is secreted as inactive pepsinogen. Pepsinogen is converted
Into pepsin by HCL. Optimum pH, for activation of pepsinogen pH
1.0-2.0 .
Action of Pepsin – it converts proteins into proteoses, peptones, and
polypeptides, pepsin also causes curdling and digestion of milk (Casein).
Gastric Lipase – it is a weak lipolytic enzyme when compared to pancreatic lipase. It
is active only when the pH, is between 4 and 5 and becomes inactive at pH, below
2.5.

17. Pancreas

18. Pancreatic secretion
The pancreas is involved in blood sugar control and
metabolism within the body.
Volume →1500 ml / day
• pH → 8-8.3, Alkaline ( HCO3)
• α alpha cells secrete glucagon (increase glucose in blood)
• β beta cells secrete insulin (decrease glucose in blood)
• δ delta cells secrete somatostatin (regulates/stops α and β cells)
• γ (gamma) cells, secrete pancreatic polypeptide.

19. Pancreatic Digestive Enzymes

20. Liver & Biliary system

21. Functions of the liver
Liver acts as a chemical factory, an excretory
system, an exocrine and an endocrine gland
1. Vascular Functions for Storage and Filtration of Blood:
store 200-400 ml. of blood Kupffer cells(remove 90% of bacteria in
the portal venous blood (the colon bacilli)

22. 2. Metabolic Functions:
Carbohydrate metabolism: (glucostat" ) Glycogenesis-
glycogenolysis- gluconeogenesis- Cori cycle (formation of glycogen
from lactic acid)
Lipid metabolism: oxidation of fatty acids - Formation of
lipoproteins - lipogenesis
Protein metabolism: Deamination of amino acids - Formation of
urea , plasma proteins, most of coagulation factors& non-essential amino
acids
Storage of vitamins: Such as vitamin A, D, E, K and B12. &
iron
Detoxification or excretion of drugs, hormones and other
substances

23. 3. Secretory and excretory
functions: Formation of bile:
• Bile is required for the digestion and
absorption of fats ( bile salts) and for the
excretion of water-insoluble substances
such as cholesterol and bilirubin
• Secretion is continuous through all the day
& is stored in gall bladder

24. Composition of bile
• 500-1500 ml/day
• Fresh bile is alkaline
• Becomes acidic during storage in gall
bladder to prevent precipitation of
calcium

25. Bile Salts
•
•
– Primary bile acids: cholic acid and
chenodeoxycholic acid.
•
– Secondary bile acids: In the colon, bacteria
convert cholic acid to deoxycholic acid and
chenodeoxycholic acid to lithocholic acid.
– Sodium and potassium salts of bile acids
conjugated to glycine or taurine ( glycocholic
& taurocholic acids)
– The bile acids are synthesized from
cholesterol.

26. 1.Digestion of fat
a. Activation of pancreatic lipase
b. Emulsification of fat preparatory to its
digestion and absorption by
- detergent action reduce surface →
tension between fat globules
- hydrotropic action
Function of bile salts

27. 2. Absorption of fat & fat soluble
vitamins-
form micelles, micelles are bile acid-lipid
water-soluble complexes that play an
important role in keeping lipids in
solution and transporting them to the
brush border of the intestinal epithelial
cells, where they are absorbed.

28. The Gallbladder
Functions of the Gallbladder:
Storage of Bile Concentration of
Bile
removal of sodium by the gallbladder mucosa
through an active transport mechanism, which
passively draws chloride, bicarbonate and water.
Prevention of marked rise in the Intrabiliary
pressure
Secretion of white bile Acidification of Bile:
(absorption of bicarbonate)

29. Control of Gallbladder Emptying
= Cholagogues
Cholecytokinin (CCK)
major stimulus for gallbladder contraction
and sphincter of Oddi relaxation.
Vagal stimulation
cephalic stage of digestion and vago-vagal
reflex during the gastric phase of digestion

31. PARTS
The small intestine is
divided into three
structural parts:
(I)The duodenum
(II)The jejunum
(III)The ileum

32. • The duodenum is a short structure ranging
from 20 cm to 25 cm in length, and shaped
like a "C".
• The jejunum is the midsection of the small
intestine, connecting the duodenum to the
ileum. It is about 2.5 m long.
• The ileum is the final section of the small
intestine. It is about 3 m long, and contains
villi similar to the jejunum.

33. FUNCTIONS
Digestion
• The small intestine is where most
chemical digestion takes place.
• Many of the digestive enzymes that act in the
small intestine are secreted by the pancreas
and liver and enter the small intestine via the
pancreatic duct.
• Digestion of proteins & carbohydrate

35. MCQ
QUESTION

36. 1. Chymosin is also known as ______.
a. Lipase
b. Amylase
c. Trypsin
d. Rennin

37. Answer : (d)Rennin

38. 2. Pancreatic juice is stimulated by the release
of
a. Secretin
b. Cholecystokinin
c. Enterokinase
d. Both (a) and (b)

39. Answer : (D) Both (a) and (b)
Secretin & Cholecystokinin

40. 3. Enterokinase helps in the conversion of
a. Lactose to Sucrose
b. Trypsinogen into trypsin
c. Pepsinogen into pepsin
d. Proteins into Polypeptide

41. Answer :
(b) Trypsinogen into trypsin

42. 4. In humans, lacteals are found in ______.
a. Ileum
b. Oesophagus
c. Ear
d. Rennin

43. Answer : (a) Ileum

44. 5. ______ is a characteristic feature of
epithelial cells of the intestine.
a. Glottis
b. Pilus
c. Bolus
d. Microvilli

45. Answer : (d) Microvilli

46. Thank You