Excretion

Question 1

what is excretion

Answer 1

the removal from organisms of the waste products of metabolism and substances in excess of requirements

Question 2

what are examples of excretion

Answer 2

• CO2 produced in respiration is excreted by the lungs
• urea, excess water and excess ions are excreted by the kidneys

Question 3

what is urea

Answer 3

urea, produced in liver, needs to be excreted because at high concentrations it denatures enzymes

Question 4

what is the role of the kidney

Answer 4

• excretion of toxic waste products (eg. urea)
• osmoregulation: maintaining water and salt content of blood and body fluids

Question 5

what is the nephron

Answer 5

is the functional unit of the kidney. Each kidney contains thousands of nephrons. Nephron consists of a glomerulus with its renal capsule and renal tubule

Question 6

describe what happens in the nephron

Answer 6

1. ultrafiltration in the glomerulus= water, glucose, urea, ions are filtered out of the blood ( only plasma and small molecules can leak out of the capillary- not cells)
2. filtrate moves from renal capsule down the renal tubule. As it does so, the capillaries that surround the tube absorb back substance that are needed, i.e. all the glucose, most water, some ions. This is called selective reabsorption
3. The rest of the fluid with urea, excess ions, excess water continues down the renal tubule. It then enters the collecting duct and then the ureter. (now fluid called urine)

Question 7

what is in the renal system

Answer 7

renal vein, adrenal glands, renal artery, kidney, ureter, bladder, urethra

Question 8

renal artery

Answer 8

contains blood with high urea concentration

Question 9

renal vein

Answer 9

contains blood with lower urea concentration

Question 10

ureter

Answer 10

carries urine from kidney to bladder

Question 11

bladder

Answer 11

stores up to about 500 cm^3 of urine before expelling it from the body

Question 12

sphincter

Answer 12

ring of muscle which controls flow of urine from bladder to urethra

Question 13

urethra

Answer 13

carries urine from bladder to outside

Question 14

cortex

Answer 14

contains glomeruli which filter excess fluid and waste products out of the blood

Question 15

medulla

Answer 15

contains long regions of kidney tubules which can vary the amount and composition of the urine