HUMAN DIGESTIVE SYSTEM-PART-3 TEXT

HUMAN DIGESTIVESYSTEM-PART-3

BIOLOGY

Stomach:

Stomach as a muscular bag it is present on the left side in the abdominal cavity, below the diaphragm. Part of the stomach into which oesophagus opens is called cardiac  stomach.

Part of the stomach that opens into duodenum is called pyloric stomach. Opening of the pyloric stomach into duodenum is protected by pyloric sphincter.

Muscles in the walls of the stomach are involuntary muscles. These are arranged longitudinally, diagonally and circularly. These muscles, contract in different directions. As a result food is churned in the stomach.

Stomach has three important roles:

1. it stores the food temporarily.

2. mixing of various components in the food thoroughly – this occurs due to contraction  and relaxation of muscles.

3. it brings about phusical and chemical changes in the food.

Internally stomach wall is lined by mucous membrane. A number of glands called gastric glands are present in this membrane. Each gastric gland opens by a small pore into the lumen of stomach. Gastric glands secrete gastric juice and mucin.

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Gastric juice is a thick, clear and straw coloured fluid. Gastric juice contains hydrochloric acid and enzymes. The food gets mixed with hydrochloric acid present in the gastric juice.

Hydrochloric acid kills bacteria present in food. It also destroys the structure of proteins, so that enzymes can digest them easily.  Mucous membrane protects stomach wall from the action of acid present in the gastric juice.

Pepsin and lipase are the enzymes present in the gastric juice. When pepsin is secreted, it is inactive and is called as pepsinogen. Acids converts inactive pepsinogen to pepsin which is the active form of the enzyme.

Pepsin breaks down proteins into peptones and proteases. Lipase converts fats into fatty acids and glycerol. In children, another enzyme called rennin is secreted into the stomach. It curdling of milk. This enzyme disappears as the child grows.

Food is retained in the stomach for two to four hours and is partially digested in the stomach. As the food is undergoing changes in stomach, the pyloric sphincter closes the opening of stomach into duodenum.

The pyloric sphincter allows only small quantities of food into duodenum at a time. The food that enters the duodenum is called chyme. This is acidic and very soft.

THANKYOU,

NANDITHA AKUNURI

HUMAN DIGESTIVE SYSTEM-PART 2

HUMAN DIGESTIVE SYSTEM-PART 2

BIOLOGY

Oesophagus is a narrow tube and connects pharynx and somach. It has both volume and involuntary muscles. These muscles are arranged circularly and longitudinally.

Internally, the wall of esophagus is lined with a mucous membrane which secretes mucous. Mucous acts as a lubricant and helps in the easy and smooth passage of food.

Swallowing means pushing food into oesophagus, is a voluntary act. Once food enters oesophages, swallowing becomes an involuntary act.

When food enters into oesophages, the muscles present in its wall contract and relax alternately producing wave like movements. These are called peristaltic movements.

They help in pushing the food down the oesophagus into the stomach. Peristaltic movements of oesophagus are involuntary. There are no digestive enzymes in oesophagus. Oesophagus is only a passage through which food enters into stomach.

Hence, food does not undergo any change in pharynx and oesophagus. However, amylase present in the saliva continues to act on the starch present in the food.

THANKYOU,
NANDITHA AKUNURI

HUMAN DIGESTIVE SYSTEM- PART-1

HUMAN DIGESTIVE SYSTEM- PART-1

BIOLOGY

Children we are going to learn about human digestive system and its function. Human digestive system starts from Mouth, buccal cavity, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus are the parts in the human digestive system.

Mouth, salivary glands and their functions Mouth is only an opening of the digestive system. Taking in of food digestive system. Taking in of food through mouth is called ingestion. The cavity or space in the mouth is called oral cavity or buccal cavity.

Digestion starts in buccal cavity. Teeth, tongue and openings of three pairs of salivary gland are present in baccual cavity.

Physical and chemical nature of the food changes when it is masticated with the help of teeth and mixed with saliva.

There are four types of teeth in man- incisors, canines, premolars and molars- each for a specific functions.

The arrangement of teeth is same on the upper and lower jaws.An adult human has thirty two teeth – 8 incisors, 4 canines, 8 premolars, and 12 molars.

Tongue is muscular and pushes the food on to the teeth during mastication. Taste buds on the tonge sense the taste of food.

Three pairs of salivary glands are present in the buccal cavity. They are parotid, sub-lingual and sub-maxillary glands .

Parotid glands are present near the ear. Secretion from these glands is sent into buccal cavity through ducts.

Other two pairs of glands open below the tongue through ducts. Saliva is released when food is present in buccal cavity. It is also released at the sight, smell and even thought of food. Saliva contains large amount of waste small amounts of salts and mucous.

Saliva is slightly alkaline in nature. It contains an enzymes called salivary. Amylase converts starch into dextrin and maltose sugar. As the food stays only for short time in the buccal cavity, starch is partly digested here.

Mucous present in the saliva makes the food sticky and helps its passage easy through pharynx. The food in buccal cavity undergoes mainly physical changes. Saliva is also useful as a solvent for dissolving the chemical substance present in food.

THANKYOU,
NANDITHA AKUNURI