Digestive System

Question 1

Define digestion

Answer 1

The process that breaks down complex food substances into simple, soluble molecules that are small enough to be absorbed into the body cells

Question 2

Define physical digestion

Answer 2

Mechanical breakdown of food into smaller particles to provide large surface area to volume ratio for faster rate of chemical digestion by digestive enzymes

Question 3

Define chemical digestion

Answer 3

Breakdown of large food molecules into small soluble molecules catalysed by digestive enzymes through hydrolytic reactions.

Question 4

Describe digestion in mouth

Answer 4

Act of taking food into mouth is called ingestion. Chewing breaks down food into pieces to increase surface area to volume ratio for faster rate of chemical digestion by digestive enzymes. Saliva produced by salivary glands in mouth moistens and soften food. Contains salivary amylase which digests starch into maltose. Thoroughly chewed food rolled into bolus in preparation for swallowing. After swallowing, bolus enters oesophagus. Digestion of starch continues in oesophagus

Question 5

What is optimum pH of salivary amylase

Answer 5

6.5-7.5

Question 6

Define peristalsis

Answer 6

A rhythmic wave like muscular contraction of the wall (towards the stomach for oesophagus)

Question 7

In small intestine, which is longitudinal muscle and which is circular muscle

Answer 7

Inner muscle is circular muscle and outer muscle is longitudinal muscle

Question 8

Describe physical digestion in stomach

Answer 8

Stomach is elastic, muscular bag, with thick muscular walls
Food is churned and mixed with gastric juice by peristaltic contractions of stomach wall for hours. Partly digested food becomes liquefied, forming chyme which passes into duodenum in small amounts

Question 9

Describe chemical digestion in stomach

Answer 9

In presence of food, gastric glands contained in stomach secrete gastric juice, consisting mainly of hydrochloric acid and two enzymes, pepsin and rennin
Hydrochloric acid - acidic medium suitable for action of enzymes in stomach, kills bacteria, converts pepsinogen(inactive) to pepsin(active)
Pepsin(optimum pH - 2) - digests proteins to polypeptides by hydrolysis

Question 10

Describe liver, pancreas, gallbladder

Answer 10

Pancreas is gland lying below stomach which produces several digestive enzymes
Liver is largest gland that produces bile, alkaline liquid containing bile salts and bile pigments
Gall bladder stores bile

Question 11

Describe bile

Answer 11

Function is to emulsify fats, to physically break them down into tiny fat droplets to increase surface area to volume ratio for faster digestion by lipase
Does not contain digestive enzymes
Creates alkaline environment for enzymes action and reduces acidity of chyme

Question 12

Describe enzymes produced by pancreas and their action (in pancreatic juice)

Answer 12

Pancreatic amylase - starch to maltose
Trypsin - Protein to polypeptides
Pancreatic lipase - Emulsified fat to fatty acids + glycerol

Question 13

Describe enzymes produced by intestinal gland and their action (in intestinal juice)

Answer 13

Peptidase - Polypeptides to amino acids
Maltase - Maltose to glucose
Sucrase - Sucrose to glucose + fructose
Lactase - Lactose to glucose + galactose
Intestinal lipase - emulsified fat to fatty acids + glycerol

Question 14

What does the small intestine consist of

Answer 14

Duodenum, jejunum, highly coiled ileum

Question 15

Why is small intestine long

Answer 15

To provide sufficient time for absorption of food substances to take place

Question 16

Describe villi adaptation and function of small intestine

Answer 16

Inner walls of small intestine have many transverse folds bearing many finger-like projections called villi. Each villus possesses numerous microvilli
This increases surface area to volume ratio for faster absorption of digested food substances by diffusion

Question 17

Why epithelium of villus of small intestine one cell thick

Answer 17

To reduce the distance for digested products to diffuse into capillaries and lacteal

Question 18

Describe blood capillary adaptation of small intestine

Answer 18

Small intestine consists of dense network of blood capillaries and lacteal within the villi.
This continuous transport of digested food substances maintains a steep concentration gradient for absorption of digested products by diffusion

Question 19

Describe absorption of digested products in small intestine

Answer 19

Glucose and amino acids are absorbed by facilitated diffusion into blood capillaries of villi. They are absorbed by active transport when there is lower concentration in intestinal lumen than in blood capillaries. Fatty acids and glycerol diffuse into epithelial cells and recombined to form minute fat globules before diffusing into the lacteal. Most water and minerals absorbed in large intestine

Question 20

Describe transportation of digested products away from small intestine

Answer 20

Blood capillaries of small intestine join to form venules which join to form hepatic portal vein. Hepatic portal vein carries mainly glucose and amino acids to the liver to be processed. Fat globules are transported away from small intestine by lacteal

Question 21

Define assimilation

Answer 21

The utilisation of absorbed nutrients and how body deals with excess nutrients

Question 22

Describe assimilation of glucose

Answer 22

Glucose is substrate for respiration to release energy for cellular activities. Excess glucose is converted into glycogen by liver cells and stored. This stimulated by insulin produced by pancreas. Glycogen converted into glucose by liver cells when blood glucose level is low, stimulated by glucagon produced by pancreas

Question 23

Describe assimilation of amino acids

Answer 23

Required to make new cell materials that are used for growth and repair of worn-out parts of body. Required to make enzymes and hormones. Excess amino acids are deaminated in the liver. Amino group is removed and converted into urea to be excreted in the urine

Question 24

Describe assimilation of lipids

Answer 24

Required to maintain cell membranes
Required in production of steroids hormones.
Fats are required to protect vital organs such as heart and kidneys.
When there is inadequate supply of glucose, fats will be broken down in liver to provide energy
Excess fats stored in adipose tissues under skin. Fats droplets collect in cytoplasm and fat droplets increase in size and number to form one large globule of fat in middle of cell, pushing cytoplasm into thin layer and nucleus to one side.

Question 25

Describe absorption in the large intestine

Answer 25

After absorption of nutrients in small intestine, undigested and unabsorbed matter enters LI. Consists of mixture of water, bile pigments, cellulose from plant cells, dead bacteria. Movement of undigested materials along LI by peristalsis. Li absorbed most water & minerals into bloodstream. Absorption of water from undigested remains in LI results in formation of faeces. Walls of large intestine secretes mucus which helps to bind faeces along large intestine. Faeces temporarily stored in rectum and as they accumulate, pressure in rectum increases, causing “desire” to expel faeces through anus. When rectum is full, rectal wall muscles contract to egest faeces, egestion/defecation

Question 26

Functions of liver

Answer 26

Bile production
Regulation of blood glucose
Protein synthesis of proteins in blood
Deamination of excess amino acids
Breakdown of red blood cells
Detoxification

Question 27

Describe protein synthesis of proteins in blood

Answer 27

Ribosomes in liver cells synthesise plasma proteins from amino acids absorbed from diet

Question 28

Describe deamination of excess amino acids in liver + breakdown of RBC

Answer 28

Excess amino acids cannot be stored by body and must be deaminated. Amino groups are removed and converted to urea which will be removed by kidneys. Carbon residues of deaminated amino acids are converted into glucose

Liver breaks down haemoglobin in RBC and stores released iron

Question 29

Describe detoxification in liver

Answer 29

Liver cells convert harmful substances into harmless ones (detoxification). Alcohol broken down in liver and removed from body system. Liver cells produce alcohol dehydrogenase that breaks down alcohol to acetaldehyde, further broken down to glucose that can be used in respiration to provide energy for cellular activities
Hydrogen peroxide toxic by-product of cellular activities. Broken down into water and oxygen by enzyme catalase in liver cells

Question 30

Effects of excessive alcohol

Answer 30

Alcohol is depressant
Affects area of cerebrum which controls behaviour and speech, reduced self control
Depresses motor centre of brain, poor coordination and sluggish reflexes, longer reaction times
Stimulates acid secretion in stomach and increases risk of gastric ulcers
Cirrhosis of liver whereby liver cells are destroyed and replaced with fibrous scar tissue, liver less able to function, liver failure and death
Withdrawal symptoms (delirious state)
Mental retardation, stunted growth, damaged organ, birth defects of developing foetus
Social effects: neglect family, financial problems, STDs, crime rates