Digestive System Questions and Answers

Answer: C

The dog's permanent dental formula is \(\frac{3-1-4-2}{3-1-4-3}\).

A dental formula gives, for one side of the jaw, the number of incisors, canines, premolars and molars, upper over lower. The adult dog has 3 incisors, 1 canine, 4 premolars and 2 molars on each side above, and 3, 1, 4 and 3 below.

\[ 2 \times (3+1+4+2) + 2 \times (3+1+4+3) = 20 + 22 = 42 \]

So a dog has 42 permanent teeth. The other formulae give 32, 28 and 40 teeth and do not match the canine dentition; the lower jaw always has one more molar than the upper in the dog.

Answer: A

The salivary gland is the parotid gland.

The parotid is the largest salivary gland in most domestic animals, lying below the ear, and opens into the mouth by the parotid duct opposite the upper cheek teeth. With the mandibular and sublingual glands it produces saliva, which in ruminants buffers the rumen.

The adrenal, thyroid and parathyroid glands are endocrine glands: they have no ducts and release hormones into the blood, not saliva into the mouth.

Answer: B

The honeycomb pattern is seen in the reticulum.

The reticulum, the second compartment of the ruminant stomach, has a mucosa raised into ridges that form a network of four- to six-sided cells, like a honeycomb.

The rumen is lined by tongue-like papillae, the omasum by many parallel leaves (laminae), which is why it is called the 'book', and the jejunum is part of the small intestine, lined with villi.

Answer: B

Bile is secreted by the liver.

Liver cells (hepatocytes) secrete bile continuously. It is stored and concentrated in the gall bladder and released into the duodenum, where bile salts emulsify fats for digestion. Horses have no gall bladder, so their bile flows straight into the intestine.

Parietal cells of the stomach secrete hydrochloric acid, the pancreas secretes pancreatic juice and insulin, and endocrine glands secrete hormones into the blood.

Answer: B

The acidity is due to Hydrochloric acid.

The parietal cells of the gastric glands secrete hydrochloric acid, which gives gastric juice a pH of about 1.5 to 3.5. The acid kills many swallowed microbes and activates pepsinogen to pepsin for protein digestion.

Citric acid occurs in citrus fruits, acetic acid in vinegar, and carbolic acid (phenol) is a disinfectant. None is secreted by the stomach.

Answer: C

Hydrochloric acid is secreted by the Parietal cells.

The parietal (oxyntic) cells of the gastric glands secrete hydrochloric acid and also intrinsic factor, which is needed to absorb vitamin B12.

Chief cells secrete pepsinogen, the precursor of the enzyme pepsin. Enteroendocrine cells release hormones such as gastrin into the blood. Goblet cells produce mucus, and in the stomach mucus comes from surface mucous cells. None of them makes the acid.

Answer: C

The enzyme is rennin.

Rennin (chymosin) is secreted in the stomach of infants, especially of young calves. It converts the soluble milk protein caseinogen into casein, which combines with calcium to form a curd. Curdling keeps milk in the stomach longer, so protein-digesting enzymes have more time to act.

Pepsin digests proteins into peptides but is not the curdling enzyme. Gastrin is a hormone that stimulates gastric juice secretion, not an enzyme. Lipase digests fats.

Answer: B

The enzyme not found in pancreatic juice is pepsin.

Pepsin is secreted by the chief cells of the stomach as pepsinogen and is activated by hydrochloric acid. It works best at the strongly acidic pH of the stomach.

Pancreatic juice is alkaline and carries the enzymes for the small intestine: trypsin (secreted as trypsinogen) for proteins, pancreatic amylase for starch, and lipase for fats. So the other three options are all genuine pancreatic enzymes.

Answer: A

Mumps affects the salivary glands.

Mumps is an acute viral infection, caused by a paramyxovirus, whose characteristic sign is painful swelling of the parotid glands, the largest salivary glands, in front of and below the ears. Other salivary glands may also swell.

The virus can spread to other organs, causing orchitis, pancreatitis or meningitis, but the pituitary, thyroid and adrenal glands are not its typical targets. The MMR vaccine prevents it.

Answer: B

The hormone that stimulates HCl secretion is gastrin.

Gastrin is released by G cells in the antrum of the stomach when food, especially protein, enters it. It stimulates the parietal cells to secrete hydrochloric acid, both directly and by releasing histamine from nearby cells.

Somatostatin inhibits acid secretion. Secretin also inhibits gastric acid, and stimulates bicarbonate-rich pancreatic juice to neutralise acid entering the duodenum. Cholecystokinin causes gallbladder contraction and pancreatic enzyme secretion, and slows gastric emptying.