Excretion

Question 1

Define metabolism

Answer 1

The sum of all chemical reactions in the body

Question 2

Define excretion

Answer 2

Excretion is the removal of toxic materials and waste products of metabolism from organisms

Question 3

Define egestion

Answer 3

Egestion is the elimination of undigested materials from the alimentary canal

Question 4

What is a catabolic reaction

Answer 4

A catabolic reaction is a reaction that breaks up complex molecules into simpler molecules

Question 5

What is an anabolic reaction

Answer 5

An anabolic reaction is a reaction that builds up simpler molecules into complex molecules

Question 6

Why must metabolic waste products be removed from the body

Answer 6

Can be harmful and prevent homeostasis of body if accumulated

Question 7

What are some examples of excretory products

Answer 7

• CO2
• Excess water
• Excess minerals and salts
• Bile pigments

Question 8

What is the kidney

Answer 8

• Contains numerous nephrons
• Responsible for osmoregulation

Question 9

What is the ureter

Answer 9

Tube connecting kidney to bladder

Question 10

What is the bladder

Answer 10

Muscular bag that stores urine

Question 11

What does a nephron consist of

Answer 11

• Glomerulus
• Bowman’s capsule
• Proximal convoluted tubule
• Loop of Henle
• Distal convoluted tubule

Question 12

What is the urethra

Answer 12

Muscular tube for urine to flow from bladder to exterior

Question 13

Define ultrafiltration

Answer 13

Ultrafiltration is a non-selective filtering process which occurs at the glomerulus

Question 13

What are the processes involved in urine formation

Answer 13

• Ultrafiltration
• Selective reabsorption

Question 14

Describe the process of ultrafiltration

Answer 14

• Renal artery splits into numerous arterioles, and each arteriole splits into a glomerulus
• Lumen of afferent arteriole bringing blood towards glomerulus is larger than that of efferent arteriole bringing blood away from glomerulus
• Blood enters glomerulus more readily than it leaves, causing blood to build up and result in high blood pressure
• This provides the main force required for ultrafiltration
• Pressure forces blood plasma out of glomerular capillaries and into the Bowman’s capsule
• Blood plasma forced out contains water and small molecules, forming filtrate in Bowman’s capsule
• Blood cells, platelets, blood proteins and fats remain in the blood and leaves glomerulus via efferent arteriole

Question 14

What is the glomerulus

Answer 14

A network of blood capillaries

Question 15

What is the average composition of urine

Answer 15

• 96% water
• 2% urea
• 1.8% salts
• 0.2% nitrogenous substances

Question 15

Define selective reabsorption

Answer 15

Selective reabsorption is the transport of useful substances from the filtrate back into the bloodstream

Question 16

Describe the process of selective reabsorption

Answer 16

• Selective reabsorption is usually completed at the proximal convoluted tubule
• All glucose, amino acids and vitamins are reabsorbed
• 85% of sodium ions, chloride ions and water are reabsorbed at the proximal convoluted tubule
• Some water and ions are reabsorbed at the loop of Henle
• Water and smaller concentrations of ion are reabsorbed at the distal convoluted tubule
• Remaining water required is reabsorbed at collecting duct

Question 16

How are useful solutes reabsorbed back into blood during selective reabsorption

Answer 16

• Facilitated diffusion
• Active transport

Question 17

How can urine composition vary

Answer 17

• Protein-rich diet > more urea
• Water-rich diet > more urine
• Salty food > more salts
• Cold temperature > more urine
• Diabetes > glucose present

Question 18

Why is there glucose present in urine of a diabetic

Answer 18

• Diabetic patient unable to store excess glucose as glycogen in body
• Blood has high glucose concentration
• Glucose is all filtered at glomerulus
• Nephrons are unable to reabsorb glucose fast enough
• Glucose passes out in urine

Question 19

Define osmoregulation

Answer 19

Osmoregulation is the maintenance of a constant water potential in the body

Question 20

What controls volume of water in blood

Answer 20

Anti-diuretic hormone (ADH)

Question 21

What is ADH

Answer 21

- Produced by hypothalamus - Released by pituitary gland - Target organ in kidney

Question 22

What happens when water potential of blood increases beyond the norm

Answer 22

- Osmoreceptors in hypothalamus detect increase in blood water potential - Osmoreceptors send nerve impulses to hypothalamus - Hypothalamus sends nerve impulses to pituitary gland - Pituitary gland releases less ADH into bloodstream - Walls of distal convoluted tubule and collecting duct become less permeable to water so less water is reabsorbed back into blood - Negative feedback sent to hypothalamus via osmoreceptors once water potential of blood decreases back to the norm

Question 23

What happens when water potential of blood decreases below the norm

Answer 23

- Osmoreceptors in hypothalamus detect the decrease in blood water potential - Osmoreceptors send nerve impulses to hypothalamus - Hypothalamus sends nerve impulses to pituitary gland - Pituitary gland releases more ADH into the bloodstream - Walls of distal convoluted tubule and collecting duct become more permeable to water - More water is reabsorbed back into the blood - Negative feedback sent to hypothalamus via osmoreceptors once water potential of blood increases back to the norm

Question 24

What are the features of a dialyser

Answer 24

- Narrow tubing speeds up rate of diffusion between blood and dialysis fluid - Direction of dialysis fluid flow is opposite to direction of blood flow, maintaining concentration for removal of waste products

Question 25

Where is blood drawn from for haemodialysis

Answer 25

Fistula in patient's arm