Human Physiology




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1 (P6, P7)





need a continuous supply of nutrients to maintain the proper functioning and
structure of our body. Digestive system ensures that these nutrients are made
available for the body. These nutrients are derived from the food we eat. Food
comes from water, organic molecules such as fats, carbohydrates, proteins,
vitamins etc, and inorganic salts. Food provides fuel to the body in the form
of calories which are required by the body to carry out daily activities. These
calories mainly come from carbohydrates and fats. Proteins support the growth
and repair functions of the body. Inorganic salts are important to keep running
many of the body processes e.g. sodium, potassium, and chloride act as
electrolytes and maintain fluid balance and normal blood pressure.


digestive system consists of a group of organs which help in the ingestion,
breakdown, digestion, absorption, and egestion (excretion) of the food. These
organs make up the Digestive Tract
and the Accessory Structures that
lie outside the tract but are connected to it through tubes or ducts.


Digestive Tract is composed of the mouth, pharynx, oesophagus, stomach, and
small and large intestines. The accessory structures that lie outside the tract
are the salivary glands (parotid, submandibular, sublingual glands), pancreas,
liver, and gallbladder.


of blood also plays an important part in the digestive system. The circulation
involving stomach, small and large intestines, pancreas, and liver is called
the Splanchnic Circulation. Blood to
these organs is pumped by the heart through the arteries coming from the
abdominal aorta. The blood that leaves these organs then goes to the liver
through portal vein. This part is called Portal
Circulation. Flow of blood through the splanchnic circulation increases
when we eat a meal. This helps in taking up of the digestion products from the
digestive tract. This also supplies extra oxygen and other important nutrients
to meet the extra energy demands created by the processes which occur after a


are different sections of the digestive system each having a different




we eat, the food is broken down into smaller pieces by the act of chewing. This
chewing is aided by biting and grinding of teeth which helps in mechanical
digestion. Skeletal muscles of the jaws, lips, cheeks, and tongue aid in the
process of chewing. The food is reduced to particles of a size which is
convenient for swallowing. This constitutes mechanical digestion.

digestion is facilitated by the release of saliva by salivary glands, which
lubricates the food. The saliva contains an enzyme called Amylase which begins
the chemical digestion of starch.









is propelled along the Oesophagus into the stomach. Churning of the stomach
helps in mechanical digestion which further breaks the food into even smaller
pieces. This is aided by the water and mucous which is secreted by the glands
in the stomach lining. Hydrochloric acid is also secreted into the stomach
which kills microorganisms and makes the stomach environment acidic. The enzyme
Pepsin is activated in the acidic condition which begins the chemical digestion
of proteins.


Small Intestine:






portion of food which is mostly liquidised passes through the Pyloric Sphincter
into the Duodenum. The sphincter is a muscular constriction at the base of the
stomach. The mucus in the duodenum is mildly alkaline. Pancreatic juice is
secreted into the duodenum through a duct. It contains digestive enzymes which
help in the digestion of food. Bile is also released from the bile duct which
helps in the digestion of fats.



is the longest part of the digestive system. This is where most of the
nutrients from the food are absorbed into the blood stream. The internal lining
of the ileum consists tiny finger like projections called Villi which increase
the surface area for absorption.


Large Intestine:


this part of the digestive system, water is reabsorbed from the food so it
forms a semi solid mass called Faeces. This is composed of a mixture of
undigested material from the food, dead cells from gut lining, and bacteria
which is then excreted out of the body. Certain minerals and vitamins are also
absorbed here.


faeces is excreted from the rectum through the opening called Anus.

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