Chapter 16: The Digestive System

Question 1

calorific value

Answer 1

the calorific value of a food component is defined as the amount of energy gained on the complete digestion of that food item. It is expressed in terms of kilocalories or kilojoules available per gram of food item.

1g of fat = 37KJ (9kcal)
1g of carbohydrates = 17KJ (4kcal)
1g of proteins = 17KJ (4kcal)

Question 2

another name of the alimentary canal?

Answer 2

gastrointestinal tract (GIT)

Question 3

mouth (buccal cavity)

Answer 3

this is where the grinding and mixing of food with saliva takes place. it opens with the upper and lower lip. the upper portion of the buccal cavity is formed by the palate. the palate is of two types - hard and soft palate.

the hard palate has transverse ridges called rugae

the uvula hangs freely in the buccal cavity. it is composed of connective and muscular tissues and is responsible for closing the internal nares during swallowing food.

Question 4

teeth

Answer 4

teeth are hard structures used for the mastication of food.

Teeth are fixed in the cavity of the jaw known as the alveolus of the tooth socket. the tissue of the jaw that surrounds the teeth forms the gum. it is composed of a hard bone-like material called dentine. the tooth consists of three parts:

root: it lies below the gum line. it is not visible.
neck: it is surrounded by the gum.
crown: It lies above the gum line and is visible on opening the mouth. it is made up of hard white material called enamel.

each tooth has a central cavity known as the pulp cavity. the outer layer of the pulp cavity consists of odontoblasts that secrete dentine. the root has a root canal that communicates with the pulp cavity. the nerve endings and blood capillaries reach the pulp cavity through this opening

Question 5

teeth on the basis of arrangement?

Answer 5

thecodont: mammals have their teeth fixed in the cavity of the jaw.

Question 6

teeth on the basis of structure?

Answer 6

mammals have heterodont type structures with four types of teeth:

incisors: chisel-shaped used for cutting.
canines: pointed used for tearing.
premolars: flat used for crushing and grinding.
molars: lie behind premolars also used for crushing and grinding.

Question 7

teeth on the basis of how many sets?

Answer 7

diphyodont: mammals have two sets of teeth, milk teeth and permanent teeth.

Question 8

The dental formula of an adult?

Answer 8

2123/2123 * 2 = 32

Question 9

The dental formula of a child?

Answer 9

2102/2102 * 2 = 20

Question 10

tongue

Answer 10

it is a muscular organ that is attached to the floor of the buccal cavity through the mucous membrane called frenulum linguae, the tongue manipulates the food mixing it with saliva. it helps in speaking and cleaning the food debris. it also helps in swallowing.

Question 11

another name for swallowing?

Answer 11

deglutition

Question 12

saliva

Answer 12

it contains:

1. ptyalin (salivary amylase used for digestion of starch)
2. mucus
3. pathogen-killing enzymes.

Question 13

salivary glands

Answer 13

1. parotid gland: found front and below the ears.
2. submandibular gland: found in the lower and inner jaw
3. Sublingual gland: found below the tongue.

Question 14

pharynx

Answer 14

the buccal cavity opens into the pharynx in the throat which is divided into three parts:
nasopharynx: it is the upper portion of the pharynx that is attached to the internal nares. the pharyngeal tonsils are lymphatic tissues attached to its posterior wall.

oropharynx: it opens into the glottis. a flap covers the glottis known as the epiglottis and prevents from food going down the trachea while swallowing.
laryngopharynx: it opens into the gullet and continues as the oesophagus

Question 15

oesophagus

Answer 15

it is a long narrow tube that connects the pharynx to the stomach and is responsible for moving and mixing the food with the help of peristalsis.

Question 16

peristalsis?

Answer 16

it is antagonistic pair of the circular and longitudinal muscles of the oesophagus which involuntarily contract and relax to push the bolus forward.

Question 17

bolus?

Answer 17

It is the masticated food that travels from the oesophagus into the stomach.

Question 18

stomach

Answer 18

the stomach is a j-shaped bag-like structure that is responsible for churning the food. it is located below the diaphragm on the left side of the upper abdominal cavity. it can hold up to 2 to 3 litres of food.

Question 19

four regions of the stomach?

Answer 19

cardiac region: the oesophagus opens into the stomach. the oesophageal sphincter prevents food from going back into the oesophagus.

fundic region: upper curvature of the stomach.

body: the central region of the stomach
pylorus: the stomach opens into the small intestine. the pyloric sphincter prevents the food from going into the stomach from the small intestine.

Question 20

how is gastric juice secreted?

Answer 20

the mucosa of the stomach is highly folded and is known as rugae.

it contains the gastric glands which are made up of four types of cells:

oxyntic cells: secrete HCl
goblet cells: secrete mucus
peptic cells: secrete pepsinogen
argentaffin cells: secrete the hormone gastrin

Question 21

gastrin?

Answer 21

it is the hormone secreted by the argentaffin cells of the gastric gland and stimulates digestion

Question 22

gastric juice

Answer 22

1. HCl
2. Intrinsic factor ( for digestion of vitamin B12)
3. pepsinogen and prorenin
4. mucus

Question 23

chyme?

Answer 23

it is the food after it has been churned in the stomach.

Question 24

small intestine

Answer 24

the stomach opens into the small intestine which is the longest part of the digestive system. it is 7.5 m long and 2.5 cm in width. it is divided into three parts:

duodenum: it is the shortest part of the small intestine. the bile duct and the pancreatic duct open into the duodenum.
jejunum: it is 2 m long and has irregular folds.
ileum: it is 5 m long and has irregular folds. villi are attached to the wall of the ileum to increase its absorptive surface.

Question 25

villi

Answer 25

villi are finger-like projections on the wall of the ileum which increase the absorptive surface and make absorption more efficient. they are made up of a single layer of compound epithelium which are fimbriated from microvilli, arteries, vessels, interconnecting blood capillaries and lymphatic vessel- lacteal. the base of the villi has pores that secrete intestinal juice (succus entericus)

Question 26

large intestine

Answer 26

it is the last part of the alimentary canal and has three parts:

caecum: it is around a blind sac that has a vermiform appendix attached to its side. an inflamed appendix can lead to appendicitis.
colon: it moves up on the right side of the abdominal cavity and is known as the ascending colon. it turns left below the stomach - transverse colon and turns down to join the rectum- descending colon.
rectum: it is a short muscular tube that opens into the anus which opens during defecation.

it absorbs water and undigested food

Question 27

what is defecation?

Answer 27

it is the passing of faeces.

Question 28

histology of GIT

Answer 28

serosa: it is the outermost layer made up of squamous epithelial. it represents the visceral peritoneum

muscularis externa: it consists of two types of smooth muscles. the outer longitudinal and inner circular.

sub-mucosa: it is made up of dense fibrous tissue with plenty of blood vessels, a network of nerves and lymphatics.

mucosa: it is the innermost layer that is made up of a simple layer of columnar epithelium and a thin layer of connective tissue known as lamina propria. it is in direct contact with the food and secrete enzyme and absorb.

Question 29

liver

Answer 29

the liver is the largest gland in the body that is situated below the ribcage behind the diaphragm on the right side of the abdominal cavity. it is has a large right lobe and a small left lobe. the gall bladder stores and concentrates the bile juice and is present below the right lobe

Question 30

functions of the liver

Answer 30

1. it converts excess glucose into glycogen and makes it available when required thus regulating the blood sugar.
2. it produces fibrinogen for coagulation of blood.
3. it converts excess amino acid into urea
4. it stores excess water and regulated blood volume
5. it breaks down RBC with the help of bilirubin

Question 31

pancreas

Answer 31

it is located between the stomach and duodenum and secretes the pancreatic juice.

Question 32

glycogenesis

Answer 32

converts glucose into glycogen

Question 33

glycogenolysis

Answer 33

converts glycogen into glucose

Question 34

glyconeogenesis

Answer 34

converts amino acids, fatty acids and glycerol into glucose

Question 35

lipogenesis

Answer 35

converts glucose into fat. can cause fatty liver.

Question 36

absorption of carbohydrates

Answer 36

the end product of carbohydrates are monosaccharides- fructose, glucose and galactose. the body only digests d-isomers of these monosaccharides.

fructose is absorbed mainly by passive transport where the nutrients are absorbed along the concentration gradient.

glucose and galactose are absorbed with the help of sodium-glucose symport. it is a carrier protein-mediated process that requires energy. when the carrier protein carries sodium ion in the cell, it drags the glucose and galactose along with it

Question 37

absorption of amino acids

Answer 37

only l-isomers are absorbed. sodium-amino acid symport. it is a carrier protein-mediated process that requires energy. when the carrier protein carries sodium ion in the cell, it drags the amino acid along with it.

Question 38

absorption of lipids

Answer 38

the end product of lipids is fatty acid and glycerol. the short fatty acid chains combine with bile salts to form droplets of fat called micelles. once inside the intestinal cell, the bile salts separate, and the fatty acids combine to form triglycerides. they then combine with protein to form chylomicron which then leaves the cell and enter the lateral.