Unit 3 - Homeostasis (2)

Question 1

Kidney structure

Answer 1

each kidney receives high pressure blood from the descending aorta via the renal artery
the solid portion of the kidney has an outer region (cortex) and an inner region (medulla)
there is an empty space called the pelvis in the centre of a kidney
each kidney contains about a million filter units called nephrons that remove wastes from the blood

Question 2

Roles of the kidneys

Answer 2

filtering wastes from your blood

maintaining the osmolarity of your blood (keeping you properly diluted by retaining or eliminating water)

Question 3

Nephron structure

Answer 3

the glomerulus, Bowman’s capsule, proximal convoluted tubule, and distal convoluted tubule are located in the renal cortex
the loop of Henle and collecting duct are located in the renal medulla

Question 4

Roles of the nephrons

Answer 4

crude filtration
selective reabsorption
osmoregulation
tubular secretion
fine tuning of filtrate concentration

Question 5

Crude filtration

Answer 5

the renal artery branches into smaller arterioles that diverge throughout the renal cortex
unfiltered blood is carried to a glomerulus via an afferent arteriole
the glomerulus is a particularly leaky ball of capillaries
blood pressure forces small solutes out, but cells, proteins, and large molecules stay in the blood

Question 6

Selective reabsorption

Answer 6

the filtered blood exits the glomerulus through the efferent arteriole
the filtrate is collected by the Bowman’s capsule
the desirable molecules in the filtrate (glucose, amino acids) are then reabsorbed by active transport in the proximal convoluted tubule

Question 7

Osmoregulation

Answer 7

after the proximal convoluted tubule, the filtrate passes through the loop of Henle
the loop of Henle passes deeply into the renal medulla
the loop of Henle uses active transport of sodium ions to establish a hypertonic environment in the medulla
a countercurrent multiplier accomplishes this

Question 8

Tubular secretion

Answer 8

the nephron tubule returns to the cortex
the distal convoluted tubule now uses active transport to remove waste molecules (uric acid, ammonia, penicillin) that could not be removed in the glomerulus

Question 9

Fine tuning of filtrate concentration

Answer 9

filtrate finally enters the collecting duct

the collecting duct passes through the medulla which was made hypertonic by the loop of Henle

Question 10

Homeostasis - dehydration

Answer 10

posterior pituitary releases ADH which makes your collecting ducts permeable to water
water diffuses into the renal medulla and is picked up by peritubular capillaries

Question 11

Homeostasis - too much water

Answer 11

there is no ADH, and your collecting ducts are impermeable to water
watery filtrate passes right through the collecting duct and enters the pelvis, making watery urine

Question 12

Urine after the nephrons

Answer 12

after accumulating in the renal pelvis, urine is carried down one of the ureters to the urinary bladder
it then leaves the body via the urethra

Question 13

The countercurrent multiplier

Answer 13

makes the renal medulla very hypertonic so that we can recapture much of the water from urine
the descending loop of Henle is permeable to both water and sodium, the ascending loop is impermeable to water and actively pumps out sodium
there is no pump in biology that can establish an ion gradient larger than 200 milliosmoles/Litre, so this process is more efficient

Question 14

Antidiuretic hormone

Answer 14

ADH is released by the posterior pituitary hormone
it decreases urine output by making the collecting duct permeable to water
opposite of a diuretic which increases urine output