Digestive and Excretory Systems

Question 1

Define digestion

Answer 1

The mechanical and chemical breakdown of food to small molecules that can be absorbed into the body.

Question 2

Define digestive system

Answer 2

The system that breaks down the food taken into the body ready for absorption into the cells.

Question 3

Define the alimentary canal

Answer 3

The tube that runs from the mouth to the anus that food passes through

Question 4

Describe the difference between mechanical and chemical digestion

Answer 4

Mechanical - the muscular breakdown of food e.g. chewing, churning of the stomach
Chemical - the chemical breakdown of food through enzymes in the stomach acid and enzymes in saliva.

Question 5

Explain the small intestine and it’s role in digestion

Answer 5

• It has a pyloric sphincter connecting it to the large intestine
• It is made up of three sections; duodenum, jejunum and ileum.
• Digestion mostly occurs in the duodenum
• Small intestine secretes pancreatic juices, intestinal juices and bile.

Question 6

Explain the role of the pancreas in digestion

Answer 6

Pancreatic amylase - turns starch to disaccharides
Pancreatic lipase - turns lipids to fatty acids and glycerol
Pancreatic protease (trypsin) - turns proteins to amino acids
Deoxyribonuclease and ribonuclease - DNA & RNA

Question 7

What does bile do in the digestive system?

Answer 7

• It is made in the liver and stored in the gallbladder
• Contains bile salts
• Emulsifies lipids into fat droplets, making them easier to be broken down by lipase.

Question 8

What are the end products of digestion?

Answer 8

Carbohydrates are digested to monosaccharides
Proteins are digested to amino acids
Lipids are digested to fatty acids and glycerol

Question 9

What is absorbed in the small intestine?

Answer 9

• Amino acids
• Simple sugars
• Fatty acids and glycerol
• Nutrients
• Water

Question 10

How does the small intestine absorb?

Answer 10

Lymph capillary (lacteal): absorption of fatty acids and glycerol, fat soluble vitamins > carried to lymph nodes > blood
Blood capillaries: absorption of amino acids, simple sugars, water, water soluble vitamins > carried to liver
(Movement of small intestine, villi and mucosa lining promote absorption)

Question 11

How does digestion in the large intestine occur?

Answer 11

Mechanical digestion - bacteria break down organic compounds (vitamins and minerals).
Absorption: water, vitamins and minerals
Waste becomes semi-solid (faeces) which are stored then eliminated through anus (contain water, undigested food (cellulose), bacteria, bile salts (pigment).

Question 12

Define the excretory system

Answer 12

Removal of the wastes of metabolism from the body

Question 13

What organs does the excretory system include?

Answer 13

Skin - excretes urea, excess water and excess salts in sweat
Lungs - excretes carbon dioxide and excess water in expired air
Liver - excretes bile pigments in the faeces, via the intestines
Kidneys - excretes urea, excess water and excess salts in urine

Question 14

What is the role of the liver in the excretory system?

Answer 14

The liver breaks down excess amino acids and toxins in the blood.
The process of removing amino acids is deamination.
The liver also takes in ammonia and converts it to urea.

Question 15

What is the role of the skin in the excretory system?

Answer 15

The sweat glands in the skin secrete water. In the water is dissolved sodium chloride, lactic acid and urea which are excreted during sweating.

Question 16

What do the kidneys consist of?

Answer 16

Renal pelvis - funnels urine into the ureter
Cortex - outer part of kidney
Medulla - inner part of kidney
Renal artery - carries blood to kidney
Renal vein - carries blood away from kidney
Ureter - carries urine to bladder

Question 17

What does the nephron consist of?

Answer 17

It begins with the glomerular capsule that encloses the glomerulus. Leading away from the glomerular capsule is the renal tubule, which begins with the proximal convoluted tubule. Beyond the tubule is a straight portion known as the Loop of Henle. After this, is the distal convoluted tubule which then forms with other nephrons to make the collecting duct, which filters into the renal pelvis

Question 18

How do the nephrons remove waste from the blood and regulate blood composition?

Answer 18

The nephrons are well supplied with blood vessels. Blood enters the kidney through the renal artery, which upon entering the kidney, the artery divides into small arterioles. Each renal corpuscle is supplied by an arteriole known as the afferent arterioles which then forms the glomerulus. The capillaries then unite to form the efferent arteriole that passes out of the renal corpuscle.

Question 19

What is peritoneal dialysis?

Answer 19

• Occurs inside the body
• Catheter is placed through the wall of the abdomen and passes fluid containing glucose and other substances at concentrations similar to those found in the blood into the abdominal cavity. There are no wastes. Wastes then diffuse out of the blood and into the fluid. The catheter then drains the fluid and waste.

Question 20

What is haemodialysis?

Answer 20

Occurs through a dialysis machine that acts as an artificial kidney. The blood passes through thousands of fine tubes that are made of differentially permeable membrane and are immersed in a bath of fluid. The concentrations of substances in the fluid are similar to blood, except the fluid has no waste. Waste then diffuses into the fluid and out of the blood.

Question 21

What is glomerular filtration?

Answer 21

Blood is forced out of the glomerulus and into glomerular capsule due to a higher blood pressure in the afferent arterial than the efferent arterial. What enters the capsule is a substance called filtrate. It contains water, salts, amino acids, fatty acids, glucose, urea, uric acid, creatinine, hormones, toxins and ions.

Question 22

What is selective reabsorption?

Answer 22

Much of the filtrate is useful as the body needs it and therefore needs to be reabsorbed back into the blood. The renal tube is involved in the selection and the reabsorption. Water reabsorption is regulated and is sometimes called facultative reabsorption.

Question 23

What is tubular secretion?

Answer 23

Reabsorption removes substances whereas tubular secretion adds materials to the filtrate. The tubules secrete substances into eh filtrate so they can leave the body.