Excretion

Question 1

what is excretion

Answer 1

process of removing metabolic waste products, toxic substances and excess substances from the body

Question 2

why is excretion necessary

Answer 2

so that harmful substances will not build up in the body to cause harm

Question 3

what are the 2 functions of kidney

Answer 3

1) excrete metabolic waste products such as urea, excess water and mineral salts

2) regulates water potential and solute concentration in the blood to maintain a constant water potential in the body

Question 4

what are ureters

Answer 4

narrow tubes connecting the kidneys to the urinary bladder

Question 5

what is the urinary bladder

Answer 5

elastic muscular bag that stores urine

Question 6

what is the urethra

Answer 6

duct which urine passes from the bladder to the outside of the body

Question 7

what are the 4 parts that make up a kidney nephron

Answer 7

1) Bowman’s capsule
2) proximal convoluted tubule
3) loop on Henlé
4) distal convoluted tubule

Question 8

describe the process of ultrafiltration

Answer 8

• afferent arteriole being wider than the efferent arteriole creates a high blood pressure in the glomerulus to ensure a pressure difference
• blood plasma is forced of the glomerular blood capillaries into the Bowman’s capsule
• filtered blood plasma (glomerular filtrate) contains small, soluble substances forced out into the Bowman’s capsule

Question 9

what are 3 adaptations of the glomerulus blood capillaries?

Answer 9

1) network of blood capillaries
- provides large surface area for ultrafiltration

2) one-cell thick walls with tiny pores
- shorter diffusion distance, allows small soluble substances to be filtered into the Bowman’s capsule

3) covered by a thin, partially permeable membrane (basement membrane)
- only allows very small, soluble molecules/ions to pass through
- impermeable to blood cells, platelets and large molecules (e.g. proteins)

Question 10

what happens at the proximal convoluted tubule during selective reabsorption

Answer 10

• most water reabsorbed by osmosis
• most mineral salts reabsorbed by diffusion and active transport
• all glucose and amino acids reabsorbed by active transport

Question 11

what happens at the loop of Henlé during selective reabsorption

Answer 11

• some water reabsorbed by osmosis
• some mineral salts reabsorbed by active transport

Question 12

what happens at the distal convoluted tubule during selective reabsorption

Answer 12

• some water reabsorbed by osmosis
• some mineral salts reabsorbed by active transport

Question 13

what happens at the collecting duct during selective reabsorption

Answer 13

• some water reabsorbed by osmosis

Question 14

what is osmoregulation

Answer 14

maintenance of constant body water potential by controlling the water potential and solute concentration in the blood

*controlled by antidiuretic hormone (ADH)
*secreted/produced by hypothalamus, released into bloodstream by pituitary gland

Question 15

what could happen if water potential in the blood is too high

Answer 15

water could enter the RBCs via osmosis and the RBCs would swell and may lyse

Question 16

what could happen if water potential in the blood is too low

Answer 16

water could leave the RBCs via osmosis and the RBCs would shrink and crenate

Question 17

what happens if the water potential in the blood is too high

Answer 17

• pituitary gland releases less antidiuretic hormone (ADH)
• cells in the walls of the collecting ducts become less permeable to water; less water reabsorbed from collecting ducts into blood capillaries
• larger volume, lower concentration of urine produced
• water potential of blood returns to normal

Question 18

what happens if the water potential in the blood is too low

Answer 18

• pituitary gland releases more antidiuretic hormone (ADH)
• cells in the walls of the collecting ducts become more permeable to water; more water reabsorbed from collecting ducts into blood capillaries
• smaller volume, higher concentration of urine produced
• water potential of blood returns to normal

Question 19

what are 3 causes for kidney failure

Answer 19

1) high blood pressure
2) diabetes
3) alcohol abuse

Question 20

what is the process of kidney dialysis

Answer 20

• blood drawn from vein in patient’s arm is pumped through tubing in dialysis machine
• tubing bathed in a specially-controlled dialysis machine, walls of tubing partially permeable
• small molecules diffuse out of the tubing into the dialysis fluid; blood cells, platelets and large molecules (e.g. proteins) remain in the blood

Question 21

what are 3 features of dialysis machines

Answer 21

1) dialysis tubing is narrow, long and coiled
- increases surface-area-to-volume ratio to speed up rate of exchange of substances between blood and dialysis fluid

2) blood flows in the opposite direction of dialysis fluid
- maintains concentration gradient for complete removal of urea from blood into dialysis fluid

3) dialysis fluid (37°C) has the same composition as blood but lacks nitrogenous waste
- prevents essential molecules (e.g. glucose and amino acids) from diffusing out of the blood into the dialysis fluid due to the lack of a concentration gradient
- absence of nitrogenous waste maximises concentration gradient for fast removal of such waste from blood via diffusion
- set at 37°C to prevent loss/gain of body heat