Excretion - homeostatic control

Question 1

what is waste (give e.g)

Answer 1

a product of metabolic reactions. can be toxic if not excreted.

e.g. CO2 is a waste product of respiration, excreted by lungs.

e.g. urea (nitrogenous waste) is excess of amino acids
which is broken down in liver as ammonia
then as urea
excreted by kidneys

mammals produce urea
fish produce ammonia
birds produce uric acid

Question 2

liver structure

Answer 2

blood enters through hepatic artery
leaves through hepatic vein
hepatic portal vein supplies with blood from digestive system

hepatocytes have many mitochondria
large nuclei
prominent Golgi body
to ensure a high metabolic rate

blood from hepatic artery is highly oxygenated
mixes with blood from HPV in sinusoids

Kupffer cells in sinusoids protect against disease.
they’re macrophages that engulf pathogens in blood from HPV.

hepatocytes (canaliculi) secrete bile
passes through bile ducts
stored in gall bladder

Question 3

liver functions

Answer 3

hepatocytes in response to insulin can absorb excess glucose in blood and convert to glycogen.
hepatocytes, in response to glucagon, can convert glycogen into glucose to release into blood

detoxification - neutralises and breaks down unwanted chemicals produced in chemical reactions. enzymes break down toxins to non-toxic substances.

ornithine cycle converts ammonia to urea to be excreted by kidneys. excess proteins are delivered to liver to be deaminated (amine group removed from amino acids to become highly toxic ammonia). Then converted into urea (only toxic in high concs)

Question 4

What is osmoregulation?

Answer 4

Process of controlling water potential of blood

Question 5

Kidney structure

Answer 5

Renal artery supplies blood to be filtered
Renal vein takes away filtered blood

Cortex - outer layer that contains many capillary networks carrying blood from renal arteries to nephrons

Medulla - contains nephrons

Pelvis - where urine collects before travelling to ureter

Question 6

Where does ultrafiltration occur

Answer 6

Bowman’s capsule

Question 7

Where is glucose reabsorbed?

Answer 7

PCT

Question 8

What happens in the loop of Henle?

Answer 8

Na+ and Cl-ions are actively transported
Out of the ascending limb into medulla
To lower water potential

Question 9

Where does water move out of in ultrafiltration and how?

Answer 9

Descending limb, DCT, collecting duct
via osmosis
due to water potential gradient

Liquid remaining in the duct forms the urine.

Question 10

Ultrafiltration process

Answer 10

Blood enters afferent arteriole

Splits into glomerulus

Causing high hydrostatic pressure

Water and small molecules (glomerulus filtrate) are forced out the capillaries

Passes through basement membrane and podocytes (like a sieve)

Proteins and RBCs too big to pass through so stay in blood and leave via efferent arteriole

Question 11

why are there many mitochondria in the walls of the ascending limb?

Answer 11

to provide enough energy to actively transport Na+ and Cl- ions out of the ascending limb

Question 12

how is the water potential lowered in the Loop of Henle?

Answer 12

due to the accumulation of Na+ and Cl- outside nephron

so water leaves by osmosis into the interstitial space and is reabsorbed by blood capillaries

Question 13

what happens at the base of the loop of Henle?

Answer 13

some Na+ and Cl- ions diffuse out as there is a dilute solution due to the water osmosising out.

Question 14

which section of the medulla is very concentrated?

Answer 14

the filtrate in the DCT
so even more water diffuses out by osmosis
whatever remains is collected as urine

Question 15

features of the hypothalamus

Answer 15

contains osmoreceptors

produces ADH which is stored in the posterior pituitary gland. this travels to kidney via blood

Question 16

if water potential too high?

Answer 16

water enters the osmoreceptors by osmosis
causes lysis
so they stimulate hypothalamus to produce less ADH
DCT and collecting duct become less permeable to water
less water reabsorbed and more water lost in urine (dilute)

Question 17

if water potential too low?

Answer 17

water leaves osmoreceptors by osmosis
causes them to shrivel
so they stimulate hypothalamus to produce less ADH
DCT and collecting duct become more permeable to water
more water reabsorbed and less lost in urine (conc)

Question 18

how ADH works

Answer 18

ADH binds to complementary receptors on target cells in the DCT or collecting duct
activating adenyl cyclase to make cAMP
activating enzymes causing aquaporin vesicles to fuse w membrane

so membrane becomes more permeable to water
so more water leaves to be absorbed by the bloodstream

Question 19

testing urine for pregnancy

Answer 19

pregnancy tests use monoclonal antibodies to detect hCG, a hormone only pregnant women produce

absorbent end is urinated on
1st mobile antibody, complementary to hCG, has coloured dye attached
2nd immobilised antibody, complementary to antigen
3rd immobilised antibody, complementary to first antibody

Question 20

what can cause kidney failure?

Answer 20

infection
high blood pressure
genetic conditions
physical damage

damages anything in the Bowman’s capsule and can filter large molecules out

if it completely fails the improper filtration of the blood can lead to urea build-up and electrolyte imbalance

Question 21

haemodialysis

Answer 21

blood enters one side of dialysis machine
dialysis fluid enters other side of machine
both separated by partially permeable membrane

takes many hours multiple times a week
must have a careful diet to keep blood levels constant