Q.Name the three pairs of salivary glands found in humans.

Intestinal juice (succus entericus), secreted by glands in the small intestine's mucosa, contains several enzymes that complete the digestion of carbohydrates, proteins, and to a lesser extent, fats and nucleic acids.

Enzymes present in intestinal juice include:

• Enterokinase (enteropeptidase): activates pancreatic trypsinogen into active trypsin.
• Disaccharidases: maltase (breaks maltose into glucose), sucrase (breaks sucrose into glucose and fructose), and lactase (breaks lactose into glucose and galactose).
• Peptidases: aminopeptidase and dipeptidase, which break down peptides into free amino acids.
• Nucleosidases and nucleotidases: act on nucleic acid breakdown products.
• Intestinal lipase: assists in the final breakdown of fats (though most fat digestion is carried out by pancreatic lipase).

Together these enzymes act at the brush border and within the lumen of the small intestine, converting larger digested fragments (from gastric and pancreatic digestion) into the simple absorbable units — monosaccharides, amino acids, and fatty acids/glycerol.

The liver secretes bile and carries out storage, detoxification and metabolic regulation.

Main functions of the liver: (1) It secretes bile, which emulsifies fats and helps their digestion. (2) It stores excess glucose as glycogen and releases it when needed, thus regulating blood sugar. (3) It detoxifies harmful substances and converts toxic ammonia into urea. (4) It stores vitamins (A, D, B12) and iron. (5) It helps in metabolism of carbohydrates, proteins and fats, and produces plasma proteins. (6) In the foetus it forms blood cells.

The stomach and the small intestine (duodenum) are alimentary-canal organs whose own walls carry exocrine glands, secreting enzymes/mucus straight into the gut lumen.

Most 'digestive glands' people think of first — the liver and the pancreas — are accessory organs: they sit OUTSIDE the alimentary canal and pour their secretions in through ducts. But two organs that are THEMSELVES part of the canal also carry gland tissue built into their own walls, so they double as exocrine glands:

1. Stomach — its mucosa is packed with gastric glands made of three cell types: mucous neck cells (secrete mucus), peptic/chief cells (secrete pepsinogen), and oxyntic/parietal cells (secrete HCl and intrinsic factor). All of this is released straight into the stomach lumen — classic exocrine secretion.
2. Small intestine (duodenum) — Brunner's glands in the duodenal submucosa secrete alkaline mucus that protects the duodenal lining from acidic chyme entering from the stomach, and the crypts of Lieberkühn (found throughout the small intestine) secrete succus entericus (intestinal juice), which carries a battery of digestive enzymes (maltase, sucrase, lactase, peptidases, lipase, etc.).

So both organs do double duty — they are conduits/digestion sites of the alimentary canal AND exocrine secretory organs in their own right, unlike the liver/pancreas which are accessory (not part of the canal) though also exocrine.

Three pairs of salivary glands - parotid, sub-mandibular and sublingual - secrete saliva into the buccal cavity to aid digestion.

Human salivary glands are exocrine glands located around the buccal (oral) cavity. There are three pairs:

1. Parotid glands - the largest pair, located just below and in front of each ear, between the skin of the cheek and the masseter muscle. Their secretion (via Stensen's duct) opens near the second upper molar tooth.
2. Sub-mandibular (submaxillary) glands - located in the floor of the mouth, below the mandible (lower jaw), near the angle of the jaw. Their duct (Wharton's duct) opens near the base of the tongue.
3. Sublingual glands - the smallest pair, situated beneath the tongue, in the floor of the mouth. They open through several small ducts (of Rivinus) directly into the floor of the mouth.

Together these glands secrete saliva, which contains salivary amylase (ptyalin) and mucin, and initiates the digestion of starch.

The pancreas is a dual-function (heterocrine) gland: removing it would knock out both its exocrine digestive enzymes and its endocrine hormones (insulin/glucagon), causing severe malabsorption/malnutrition together with uncontrolled high blood sugar (diabetes mellitus).

The pancreas has two distinct functional components, and removing the whole organ affects both:

1. Exocrine (digestive) function: the pancreas normally secretes pancreatic juice containing enzymes such as trypsin (protein digestion), pancreatic amylase (starch digestion), and lipase (fat digestion) into the duodenum. Without the pancreas, these enzymes would be absent, so proteins, carbohydrates and especially fats would be very poorly digested and absorbed, leading to malnutrition, weight loss, and fatty, bulky stools (steatorrhea).
2. Endocrine function: the Islets of Langerhans in the pancreas secrete insulin (which lowers blood glucose by promoting its uptake and storage) and glucagon (which raises blood glucose by promoting glycogen breakdown). Without the pancreas, insulin would be completely absent, so blood glucose would rise uncontrollably — a severe form of diabetes mellitus — leading to symptoms like excessive thirst, urination, and, if untreated, life-threatening complications.

In practice, a person whose pancreas is removed can only survive with lifelong insulin injections and pancreatic enzyme replacement supplements taken with meals.

The liver is the largest gland in the human body, and correspondingly the largest gland attached to the alimentary canal, mainly known digestively for producing bile.

The liver, a large, reddish-brown organ located in the upper right abdomen, is the single largest gland in the human body by weight, performing hundreds of metabolic functions -- among its digestive roles, it continuously produces bile, which is stored and concentrated in the gall bladder before being released into the duodenum to emulsify dietary fats, aiding their digestion by lipase. The pancreas (option d) is also a major digestive gland (producing a wide range of enzymes) but is considerably smaller than the liver. The kidney (option a) and heart (option c) are not digestive glands at all. Note: this topic is taught in the Digestion and Absorption chapter, which is no longer part of the current syllabus, so this question is answered honestly as a legacy/out-of-syllabus item.