Gastric glands have three major types of cells namely-
(i) mucus neck cells which secrete mucus
(ii) peptic or chief cells which secrete the proenzyme pepsinogen; and
(iii) parietal or oxyntic cells which secrete HCI and intrinsic factor (factor essential for absorption of vitamin B₁₂).

Excess dehydration leads to loss of salts from the body. This disturbs the electrolyte balance of the body.

The actual amount of energy from combustion of 1g of food is the physiological value of food.

The amount of heat liberated from complete combustion of 1g food in a bomb calorimeter is its gross calorific value or gross energy value.

Human beings get two sets of teeth during their life. This phenomenon is called diphyodont.

Parotid gland

The bile released into the duodenum contains bile pigments (bilirubin and biliverdin), bile salts, cholesterol and phospholipids but no enzymes.Bile helps in emulsification of fats, i.e,breaking down of the fats into very small micelles.Bile also activates lipases. Lipase carry out the digestion of fats.

The alimentary canal is composed of following basic layers:
1. Inner Mucosa Layer
2. Inner Circular Muscular Layer
3. Outer Longitudinal Muscular Layer

The mucosa is secreated by the goblet cells.It also mixes with the bicarbonates from the pancreas.These protect the intestinal mucosa from acid food.It also provides an alkaline medium(pH-7.8) for pancreatic enzyme activities.Submucosal glands(Brunner's glands) also help in this action.

Fats are broken down by lipases into di and monoglycerides in the duodenum of small intensine as
Fats\(\overset { Lipase }{ \longrightarrow } \) Diglycerides \(\longrightarrow \) Monoglycerides. 

Various causative factors for indigestion are
(i) Inadequate secretion of digestive enzymes and gastrointestinal hormones
(ii) Anxiety
(iii) Food poisoning
(iv) Overeating and spicy food

Pancreas contributes in following functions in the body
(i) It contributes to the digestion of different components of food.
(ii) The absorption of food breaken down products from the digestive tract start taking place here.
(iii) The metabolism of blood sugar is regulated. Hence, if any malfunctioning happens to pancreas, it fails to perform these functions properly.

Ileocaecal valve is present where an ileum of small intestine enters the cecum of the large intestine. It helps in preventing the backflow of fecal matter from caecum into ileum.

(i)Salivary amylase splits starch and glycogen first to dextrins and then into disaccharides like maltose, isomaltose and small dextrins called 'limit' dextrins.
starch\(\overset { salivary }{ \underset { amylase }{ \longrightarrow } } \) Maltose + Isomaltose + a-dextrins
(ii)Bicarbonate ions in saliva neutralise the acids present in food.The thiocyanate ions of saliva act as anti-microbial agent.Thses prevent infection by the microbes.

Starch is not digested in the stomach, because the enzyme ptyalin (salivary amylase) that is used in its digestion cannot survive in the acidic (low) pH of the stomach due to the presence of HCl.