Biology: NCERT Summary of Class 11 on Plant and Human Physiology

HUMAN PHYSIOLOGY-2 BY NIKHIL PURANIK

ABOUT MIE MY NAME IS NIKHIL PURANIK PURSUING B.E IN MECHANICAL ENGINEERING FROM RNSIT LIVE IN BENGALURU PROFILE https://unacademy.com/user/nikhilrpuranik

TOPICS COVERED DIGESTIVE GLANDS DIGESTION OF FOOD

DIGESTIVE GLANDS The digestive glands associated with the alimentary canal include the salivary glands, the liver and the pancreas. Saliva is mainly produced by three pairs of salivary glands, the parotids (cheek), the sub-maxillary/sub-mandibular (lower jaw) and the sublinguals (below the tongue). These glands situated just outside the buccal cavity secrete salivary juice into the buccal cavity. Liver is the largest gland of the body weighing about 1.2 to 1.5 kg in an adult human. It is situated in the abdominal cavity, just below the diaphragm and has two lobes. 4

The hepatic lobules are the structural and functional units of liver containing hepatic cells arranged in the form of cords. Each lobule is covered by a thin connective tissue sheath called the Glisson's capsule. The bile secreted by the hepatic cells passes through the hepatic ducts and is stored and concentrated in a thin muscular sac called the gall bladder. The duct of gall bladder (cystic duct) along with the hepatic duct from the liver forms the common bile duct

Gall bladder Duct from gall bladder Ducts from liver Common bile duct -Pancreas Pancreatic duct Duodenum- Hepato-pancreatic duct 6

The bile duct and the pancreatic duct open together into the duodenum as the common hepato-pancreatic duct which is guarded by a sphincter called the sphincter of Oddi. The pancreas is a compound (both exocrine and endocrine) elongated organ situated between the limbs of the 'U' shaped duodenum The exocrine portion secretes an alkaline pancreatic juice containing enzymes and the endocrine portion secretes hormones, insulin and glucagon. 7

DIGESTION OF FOOD The process of digestion is accomplished by mechanical and chemical processes. The BUCCAL CAVITY performs two major functions, mastication of food and facilitation of swallowing. The teeth and the tongue with the help of saliva masticate and mix up the food thoroughly Mucus in saliva helps in lubricating and adhering the masticated food particles into a bolus. The bolus is then conveyed into the pharynx and then into the oesophagus by swallowing or deglutition

The bolus further passes down through the oesophagus by successive waves of muscular contractions called peristalsis The gastro-oesophageal sphincter controls the passage of food into the stomach. The saliva secreted into the oral cavity contains electrolytes (Na+, K+, CH, HCO- and enzymes, salivary amylase and lysozyme. The chemical process of digestion is initiated in the oral cavity by the hydrolytic action of the carbohydrate splitting enzyme, the salivary amylase About 30 per cent of starch is hydrolysed here by this enzyme (optimum pH 6.8) into a disaccharide maltose. Salivary Amylase Maltose Starch pH 6.8 9

Lysozyme present in saliva acts as an antibacterial agent that prevents infections. The mucosa of STOMACH has gastric glands. 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; (ii) parietal or oxyntic cells which secrete HCl and intrinsic factor (factor essential for absorption of vitamin B12) The stomach stores the food for 4-5 hours. The food mixes thoroughly with the acidic gastric juice of the stomach by the churning movements of its muscular wall and is called the chyme. 10