Hetrotrophic Nutrition (For Classes 7 and 10)
Complete Explanation  --- PART 3 ---

NCERT Page 99 Class 10 (Highlighted Points are discussed below)

Salivary amylase functions at or near neutral pH in human beings and pig. It is absent in herbivores. 

Role of Lysozyme

Saliva contains an antibacterial enzyme which is called  lysozyme which dissolves the cell wall of Gram positive bacteria and kills them. There is no digestion in Oesophagus. 

Alimentary Canal

Oesophagus conducts the food from mouth into stomach. Stomach is the chief site of protein digestion.

Showing Oesophagus

Chyme

Food mixed with gastric juice in the stomach is called Chyme. Chyme is the thick liquid made of partially digested food and stomach juices made in the stomach and moves into the small intestine for further digestion.

Enzyme secreting cells of fundic gland are are chief cells parietal cells, Goblet cells and are argentaffin cells. 

Curdling Of Milk

Besides pepsinogen peptic cells also secrete prorennin and a week enzyme gastric lipase . Pepsinogen is activated into pepsin by HCl. Rennin changes milksoluble protein casein into insoluble semifluid calcium paracaseinate. This is called curdling of milk . 

Amount of rennin decreases with age so absent in adult men. 

About HCl

HCl secreted from oxyntic cells make the gastric juice acidic that is pH is in between 2.0 -3.7. It is essential for  conversion of pepsinogen which is inactive protein digestive enzyme into to active pepsin. Pepsin is a protein splitting endopeptidase.

Functions of HCl

The most important functions of HCL is to activate both pepsinogen and prorennin and killing of microorganisms like bacteria ingested with food and drinks.

Achlorohydria 

The total achlorohydria means lack of HCl secreted in stomach. 

Role of Mucus

Mucus secreted by Goblet cell protects stomach wall against HCl action and protein digestive enzymes.

Chyle

Food in the small intestine is in the form of liquid emulsion called chyle. It is mixed with three digestive fluids namely bile, pancreatic juice and intestinal juice.

Imagine the inside walls of the 23 feet of your small intestine covered with these finger-like projections. 

Why? What's their purpose, and why is the small intestine so long? These projections absorb. Absorb what? Minerals and nutrients from food. 

And the length of the small intestine allows as much of these important substances to be absorbed as possible.

The small intestine is a narrow tube about 7 meters (23 feet) long in adults. 

It is the site of most chemical digestion and virtually all absorption. 

The small intestine consists of three parts: the duodenum, jejunum and ileum.

Micro Villi

Digestion in the Small Intestine

The duodenum is the first and shortest part of the small intestine. 

Most chemical digestion takes place here, and many digestive enzymes are active in the duodenum . Some are produced by the duodenum itself. Others are produced by the pancreas and secreted into the duodenum.

The jejunum is the second part of the small intestine, where most nutrients are absorbed into the blood. As shown in Figure below, the mucous membrane lining the jejunum is covered with millions of microscopic, fingerlike projections called villi (singular, villus).

           

Villi contain many capillaries, and nutrients pass from the villi into the bloodstream through the capillaries. Because there are so many villi, they greatly increase the surface area for absorption.

In fact, they make the inner surface of the small intestine as large as a tennis court!

Bile

Bile contains no digestive enzymes yet it play an important role in fat digestion and absorption. 

Pancreatic Juice

Pancreatic juice is alkaline that is 7.5 - 8.5 pH.It is colourless liquid having four types of enzymes that is proteolytic pro enzyme which contains trypsinogen,chymotrypsinogen and procarboxypeptidase.

Lactose Intolerence

Lactose intolerance is a condition caused by lack of enzyme called lactase which in turn causes the body to be unable to digest lactose sugar found in Milk products.

Dental caries

Dental caries or tooth decay causes gradual softening of enamel and dentine. It begins when bacteria acting on sugars produce acids that softens or demineralises the enamel. 

Masses of bacterial cells together with food particles stick to the teeth to form dental plaque. Saliva cannot reach the tooth surface to neutralise the acid as plaque covers the teeth.

Brushing the teeth after eating removes the plaque before the bacteria produce acids. If untreated, microorganisms may invade the pulp, causing inflammation and infection.

           Animation Picture For Clear Concept