14. HUMAN NUTRITION
Food is the basic requirement of all living beings. It Provides energy and organic materials for growth and repairing of
tissues. The major components of the food are carbohydrates.
Nutrition
It is the sum of all processes through which food is taken in and utilized to obtain energy. WHO (World Health
Organization) defines nutrition as the intake of food considered in relation to the body's dietary need.
Digestion
It is a catabolic process in which complex and large components of food are broken down into their respective simpler and
smaller forms with the help of various hydrolytic enzymes.
Human Digestive System
In human, digestion occurs through a complex system known as human digestive system. It comprises of alimentary canal
and associated digestive glands.
I. Alimentary canal
It is a long tubular structure starting from mouth and ending with anus. It is about 8-10 meters long.
Alimentary canal consists of different structures which are described below
1. Oral Cavity
(i) Incisors present at the front of the mouth and are used for cutting or clipping.
(iI) Canines are next to incisors and are used for puncturing or holding or tearing.
(iii) Premolars and molars are the innermost and are used
for crushing or grinding the food.
Dental Formula
The number and the kinds of teeth in mammals are represented by an equation called dental formula.
These are constant for every species.
Since, two halves of each jaw are identical, the teeth of only one side are recorded in this formula.
I C Pm M
For vertebrates, this formula looks like
I C Pm M
Here, I = Incisors, C = Canines, Pm = Premolars, M = Molars.
The total number of teeth in jaw = number of teeth in dental formula × 2.
The dental formula in human
2123 2102
(i) Human (Adult) = × 2 = 32 (ii) Human (Child) = × 2 = 20
2123 2102
, • Tongue is a muscular movable organ attached to the floor of the buccal cavity through an attachment called frenulum.
Small projections called papillae are present all over the surface of the tongue. Some of the papillae bears taste buds.
2. Pharynx
It is a small funnel-shaped chamber located behind the oral cavity. It serves as a common passage for both food and air,
i.e. it communicates with both esophagus (food pipe) and trachea (windpipe).
3. Oesophagus
It is the thin, long muscular tube that extends and leads into a J-shaped bag-like structure called stomach. A muscular
gastro-esophageal sphincter regulates the opening of esophagus into the stomach.
4. Stomach
it is the most dilated J-shaped part of the alimentary canal, which is situated between the esophagus and the small
intestine, below the diaphragm.
Stomach has three major parts as given below
(i) Cardiac stomach, the upper portion into which the esophagus opens.
(ii) Fundic stomach, the dome-shaped region above and left of cardiac.
(iii) Body stomach, the large central portion of stomach that stores the food.
(iv) Pyloric stomach, the lower portion, which opens into the first part of small intestine, i.e. duodenum. It contains
ring-like muscles called sphincter which regulates its opening.
5. Small Intestine
The longest part of the alimentary canal, i.e. small intestine is fitted in a compact space as extensively coiled structure in
our belly. It has three regions, i.e. ‘U’-shaped duodenum, middle jejunum and the highly coiled ileum, which opens into
the large intestine.
6. Large Intestine
It has a shorter length than the small intestine, but it is called large because it has a wider in diameter than the small
intestine.
• Caecum It is the small, blind sac which hosts symbiotic microorganisms. A vestigial organ, i.e. vermiform appendix
arises from it.
• Colon It is divided into 3 parts ascending, transverse and descending colon.
• Rectum It is the end portion of colon which opens into anus.
7. Anus
It is the end point of alimentary canal, which helps in the exit of waste materials by a process called egestion or
defaecation.
Histological Structure of Alimentary Canal
(1) Serosa It is the outermost layer. It is made up of a layer of squamous epithelium called mesothelium and inner
layer of connective tissue.
(2) Muscularis externa This layer is formed of smooth muscles, usually arranged in three concentric layers.
(3) Submucosa It is a loose connective tissue layer. It is richly supplied with blood and lymphatic vessels.
Duodenal submucosa shows presence of glands.
(4) Mucosa (Mucous membrane) It is the innermost layer lining the lumen of alimentary canal. It is named so
because it secretes mucus. This layer shows modifications in different regions.
Digestive Glands
The glands associated with the alimentary canal are as follows :
1. Salivary Glands
• Serous cells secrete a fluid containing digestive enzyme called salivary amylase.
• Mucous cells produce mucus that lubricates food and helps in swallowing.
Food is the basic requirement of all living beings. It Provides energy and organic materials for growth and repairing of
tissues. The major components of the food are carbohydrates.
Nutrition
It is the sum of all processes through which food is taken in and utilized to obtain energy. WHO (World Health
Organization) defines nutrition as the intake of food considered in relation to the body's dietary need.
Digestion
It is a catabolic process in which complex and large components of food are broken down into their respective simpler and
smaller forms with the help of various hydrolytic enzymes.
Human Digestive System
In human, digestion occurs through a complex system known as human digestive system. It comprises of alimentary canal
and associated digestive glands.
I. Alimentary canal
It is a long tubular structure starting from mouth and ending with anus. It is about 8-10 meters long.
Alimentary canal consists of different structures which are described below
1. Oral Cavity
(i) Incisors present at the front of the mouth and are used for cutting or clipping.
(iI) Canines are next to incisors and are used for puncturing or holding or tearing.
(iii) Premolars and molars are the innermost and are used
for crushing or grinding the food.
Dental Formula
The number and the kinds of teeth in mammals are represented by an equation called dental formula.
These are constant for every species.
Since, two halves of each jaw are identical, the teeth of only one side are recorded in this formula.
I C Pm M
For vertebrates, this formula looks like
I C Pm M
Here, I = Incisors, C = Canines, Pm = Premolars, M = Molars.
The total number of teeth in jaw = number of teeth in dental formula × 2.
The dental formula in human
2123 2102
(i) Human (Adult) = × 2 = 32 (ii) Human (Child) = × 2 = 20
2123 2102
, • Tongue is a muscular movable organ attached to the floor of the buccal cavity through an attachment called frenulum.
Small projections called papillae are present all over the surface of the tongue. Some of the papillae bears taste buds.
2. Pharynx
It is a small funnel-shaped chamber located behind the oral cavity. It serves as a common passage for both food and air,
i.e. it communicates with both esophagus (food pipe) and trachea (windpipe).
3. Oesophagus
It is the thin, long muscular tube that extends and leads into a J-shaped bag-like structure called stomach. A muscular
gastro-esophageal sphincter regulates the opening of esophagus into the stomach.
4. Stomach
it is the most dilated J-shaped part of the alimentary canal, which is situated between the esophagus and the small
intestine, below the diaphragm.
Stomach has three major parts as given below
(i) Cardiac stomach, the upper portion into which the esophagus opens.
(ii) Fundic stomach, the dome-shaped region above and left of cardiac.
(iii) Body stomach, the large central portion of stomach that stores the food.
(iv) Pyloric stomach, the lower portion, which opens into the first part of small intestine, i.e. duodenum. It contains
ring-like muscles called sphincter which regulates its opening.
5. Small Intestine
The longest part of the alimentary canal, i.e. small intestine is fitted in a compact space as extensively coiled structure in
our belly. It has three regions, i.e. ‘U’-shaped duodenum, middle jejunum and the highly coiled ileum, which opens into
the large intestine.
6. Large Intestine
It has a shorter length than the small intestine, but it is called large because it has a wider in diameter than the small
intestine.
• Caecum It is the small, blind sac which hosts symbiotic microorganisms. A vestigial organ, i.e. vermiform appendix
arises from it.
• Colon It is divided into 3 parts ascending, transverse and descending colon.
• Rectum It is the end portion of colon which opens into anus.
7. Anus
It is the end point of alimentary canal, which helps in the exit of waste materials by a process called egestion or
defaecation.
Histological Structure of Alimentary Canal
(1) Serosa It is the outermost layer. It is made up of a layer of squamous epithelium called mesothelium and inner
layer of connective tissue.
(2) Muscularis externa This layer is formed of smooth muscles, usually arranged in three concentric layers.
(3) Submucosa It is a loose connective tissue layer. It is richly supplied with blood and lymphatic vessels.
Duodenal submucosa shows presence of glands.
(4) Mucosa (Mucous membrane) It is the innermost layer lining the lumen of alimentary canal. It is named so
because it secretes mucus. This layer shows modifications in different regions.
Digestive Glands
The glands associated with the alimentary canal are as follows :
1. Salivary Glands
• Serous cells secrete a fluid containing digestive enzyme called salivary amylase.
• Mucous cells produce mucus that lubricates food and helps in swallowing.
