Class 11 biology ch 16 Digestion and Absorption notes made through ncert book


Class 11 biology ch 16 Digestion and Absorption notes made through ncert book

Human Digestive System :


Digestion: The process of conversion of compless food substnces

into simple absorbable form is called digestion.

it include alimentry canal and digestive glands.


the alimentry cnal begins with the mouth and ends in anus. Mouth leads to oral cavity or buccal cavity.

it has number of teeth and a muscular tongue.

In human teeth is embeded in a socket of jaw bone.


Such type of teeth is called thecodent.

The most mammals like human beings are diphyodont because they form two set of teeth during their life i.e. a set of milk teeth and a set of permanent teeth.

The teeth in huma are also of different types, thus called heterodent.

the teeth are of 4 types:



3.Pre molars



Class 11 biology ch 16 Digestion and Absorption notes made through ncert book
Class 11 biology ch 16 Digestion and Absorption notes made through ncert book

Dental formula: The arrangement of teeth

in each half of the upper and lower jaw in

the order I,C,PM,M is called dental fromula. i.e. 2123/2123

Tongue: Muscular, freely movable structure attached to the floor of the oral cavity by frenulum.

The upper surface has small projection called paplliae, some of which beer taste buds.

Pharynx: A common passage for food and air. Both trachea and oesophagous opens into pharnyx.

the opening of the trachea or

wind pipe is called glottis.

Epiglottis: A cartilegenous flap called epiglottis that prevent the entry of food into glottis during swalloing of food.

Oesophgous: A thin long tube which wxtends posteriorly passing through the neck, thorax and diaphragm and leads to stomach.

Class 11 biology ch 16 Digestion and Absorption notes made through ncert book

Gstro oesphageal spincter muscles:

A muscular spincter that regulates the opening of oesophagous into the stomach.

Stomach: A J-shaped structure located into the upper left portion of abdominal cavity. It haas the four major parts:-

  1. Cardiac portion- Part into which oesophagous opens.
  2. Fundus portion- The small portion above cardiac portion which mostly contaion gases.
  3. Body- The main control part of stomach where food stores temporatily for digestion.
  4. Pyloric region- The lower most end that opens into small intestine

Pyloric spincter: It guard the entry of food from stomach to small intestine (duodenum).

Small intestine: It has distinguishable region:-

  1. Duodenum: C- shaped small portion
  2. Jejunum: Long coiled middle region.
  3. Ileum: Highly coiled ileum.

Large intestine: It is divided into 3 parts:

-Caecum: A small blind sac which hosts some suymbiotic micro- organisms. vermiform appendix which is a narrow finger like projection arises from caecum. It is a vastigeal organ in human.

Colon It is divided into
four parts

a. An ascending part

b. An transverse part

c. A desending part

d. A sigmoid part

3. Rectum: A small wide part which sotres stoal temporaly untill it fget released.

Anus: A small opening through which undigested waste released frim body.

Wall of Alimentary canal:- The wall of alimentary canal from oesophagous to rectum posses four layer-Serosa: The outermost layer, made up of a thin mesothelium with some connectie tissue.

Muscularis: It is composed of two layer of muscles

(a) Outer longitudinal muscles (b) Inner curcular muscles

Sub-mucosal layer: It is formed of loose connective tissue containing nerves, blood and lymph vessels. In the region of duodenum some unicellular glands are also present in this layer.

Mucosa: The inner most layer linning the lumen of alimentary canal. In the stomach it form some irregular folds called rugae. In the small intestine it forms many small projections called villi.

The cells present around the villi further produces many microscopic projections, which is called micro villi giving brush border appearance. increasing in large surface area to support absorption of digested food

The mucosal epithelium also contain goblet cells, that secrets mucous. it also forms gastric glads that secrates gastric juices.

In intestine, also forms crypts in between the bases of villi in the intestine called crypts of liberkubn. In general all the four layers of wall of alimentary cnal shows some kind of modification of different parts.

Class 11 biology ch 16 Digestion and Absorption notes made through ncert book

Digestive glands:-

  1. Salivary glands: Secretes saliva in the oral cavity. In human it is of 3 pairs-

(a) Parotid: Found in cheek region.

(b) Sublingual: Below the tongue.

(c) Submaxillary or submandibulary: lower jaw.

2.Liver: The largest gland of the body weight is 1.2 to 1.5 k.g in adult human.

It is situated in the abdominal cavity. Just below the diaphragm. It has two lobes. Hepatic lobules, covered by glissons capsule. They are the structural and functional unit of liver made up of hepatic cells.

The secreation of liver is stored and concentrated in gall bladder.

Bile duct and pancreatic duct open together

in duodenum by hepato-pancreatic duct. It is guarded by spincter of oddi.

3. Pancreas: It is a soft lobulated greyish pink gland which weight about 60 gm. consist of exocrine and endocrine portions.

The exocrine portion secreates alkaline pancreatic juices, that contain many digestive enzyme like trypsin, amylase, chymotrypsin, etc.

The endocrine portion secretes hormone like insulin and glycogen.

Digestion of food:-

In the byccal cavity:

Buccal cavity peerforms two major functions

  1. Mastication of food
  2. Facilitation of swallowing

The teeth and tongue with the help of saliva masticate and mix up the food.

The saliva composed of:-

  1. Electrolytes
  2. Enzyme ( salivary amylase or ptylin)
  3. lysozyme

About 30% of starch is hydrolyzed into disaccharide ( maltose) by salivary amylase in optimum pH 6.8.

Lysozyme acts as antibacterial agent preventing infections. Mucus un the saliva helps in luberication and adherning the masticated food particles into a bolus.

The bolus us then passed into oesophagous through pharnyx by swallowing or deglutition . By peristalisis the bolus from the oesophagous passed into the stomach.

In the stomach:-

The mucosa of stomach has gastric glands. Gastric glands have 3 major types of cells namely:

(i) Mucus neck cells- secreates mucus

(ii) Peptic or cheif or zymogen cells – secreates proenzyme pepsinogen.

(iii) Pariteal or oxyntic cells- secretes HCl and castless intrinsic factor ( factor essential for absorption for vitamin B12).

In the stomach stores the food for 4-5 hours. The food mixed with the acidic gastric juice and form chyme. Pepsinogen converted into active pepsin in presence of HCl. Active pepsin covert proteins into proteases and peptones ( peptides).

Mucus and bicarbonate ions play important role in lubrication and protection of mucosal epithelium form excoriation by HCl and active enzyme. HCl provides the acidic pH of stomach (1.8).

Renin is an enzyme present in gastric juice helps in digestion of milk proteins. Small amount of lipase are present in gastric juice helps in digestion of fats.

In the intestine:-

Important secretion added to the intestine during digestion:

(i) Bile juice (ii) Pancreatic juice (iii) Intestinal juice or succus entericus

The pancreatic juice contain following enzyme:

  1. Trypsinogen
  2. chymotrypsinogen
  3. Procarboxypeptidase
  4. Amylase
  5. lipase
  6. Nucleases

Trypsinogen is activated by an enzyme entero kinase secreated by intestinal mucosa into active trypsin.

Active trypsin activates other enzymes in the pancreatic juices in the intestine. The bile released into the duodenum contains:

  1. Bile pigments ( bilirubin and biliverdin)
  2. Bile salts
  3. cholesterol
  4. Phospholipids

Bile salts helps in emulsification of fats, i.e. breakdown of fats into small micelles. Bile also activates lipase. The intestinal mucosa contains goblet cells which secretes mucus.

The secretion of brush borders cells of intestinal mucosa and the goblet cells constitute the intestinal juice or succus entericus.

The intestinal juice contains variety of enzymes:-

  1. Disaccharides ( maltase, lactase and sucrose)
  2. Dipeptidases
  3. lipases
  4. Nucleosidases

Sub- mucosal glands ( Brunner’s gland ) also secretes alkaline fluid to counter act acidic chyme before secretion of bile and pancreatic juice.

Digestion in small intestine:-(in ncert book)

Functions of succus entericus:-( in ncert book)

How is Absorption of digested products:-

it is the process by which the end product of digestion passes through the intestinal mucosa into the blood or lymph.

it is carried out by passive, active or

facilitated transport mechanism.

Glucose, amino acid and electrolytes are absorbed by simple diffusion into the blood in the concentration gradient.

Fructose and some amino acids absorbed with the help of carrier ions like Na. This is called facilitated diffusion.

Active transport of digested food and electrolytes take place against the concentration gradient hence require energy.

Absorption of fatty acids and glycerol:-

Fatty acids and glycerol being insoluble cannot be absorbed into blood. They are transported into mucosal epithelium and triglycerides are formed.

Triglycerides are covered by a protein coat to form small fat globules called chylomicron,

which are incorporated into the lacteal in the villi.

These lymph vessels ultimately release the absorbed substance into the blood stream.

Assimilation and egestion:-

Absorbed substance finally reach tissues which utilize them for their activities, this process is called assimilation.

The digestive wastes, soidfied into coherent faeces in rectum removed to outside periodically by the process called defaecation. Vomiting: It is the ejection of stomach content through the mouth. these reflex action is controlled by the vomit center in the medulla.

Diarrhea: Frequent defection of liquid faeces is known as diarrhea. It reduces the absorption of food.

Constipation: In this the faeces are retained within the rectum as the bowel movement occur irregularly.

Indigestion: Incomplete digestion usually accompained by one or more of the following symptoms like pain, nausea, vomiting,

heartburn, acid regurgitation accumulation of gas and escape of gas from the stomach.

Protein-energy malnutrition:-

Protein deficiency /protein – energy malnutrition sometimes called protein – calorie malnutrition (PCM ) – is the most common nutritional dosorder in developing countries.

PEM is widely prevalent in infants and pre-school children kwashiorkor and marasmus are the two types of protein deficiency diseases.

Class 11 biology ch 16 Digestion and Absorption notes made through ncert book


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