topic 5.1.2: excretion

Question 1

define excretion

Answer 1

removal of toxic waste products of metabolic reactions

Question 2

what is the overall function of the liver?

Answer 2

-stores glycogen, detoxifies blood and stores urea

Question 3

give the name, function and structure of the 3 blood vessels into and out of the liver

Answer 3

HEPATIC ARTERY- supplies oxygenated blood (narrow)
HEPATIC PORTAL VEIN- supplies products of digestion (branched)
HEPATIC VEIN- carries blood away

Question 4

describe and explain the structure of hepatocytes

Answer 4

many mitochondria- more atp to maintain high metabolic rate
large nuclei- active dna transcription
prominent golgi apparatus- high level of protein processing

Question 5

describe and explain the structure of sinusoids

Answer 5

blood from hepatic artery and portal vein mixes
lined with hepatocytes- thin for short diffusion pathway
increased O content to supply hepatocytes
contain kupfer cells- act as macrophages

Question 6

describe and explain the structure of canaliculi

Answer 6

spaces where bile is gathered
bile is secreted from hepatocytes from breakdown of RBCs then passes through bile ducts into gallbladder

Question 7

what are the 3 main functions of the liver?

Answer 7

carb metabolism, deamination and detoxification

Question 8

describe carbohydrate metabolism in the liver

Answer 8

hepatocytes involved in homeostatic control of glucose
blood glucose rises- insulin stimulates glycogenesis
blood glucose falls- glucagon stimulates glycolysis

Question 9

describe deamination in the liver

Answer 9

removal of amine group from a molecule
excess diet protein cannot be stored so amine group removed and converted to ammonia
co2 added to ammonia to reduce toxicity to produce urea

Question 10

what is the ornithine cycle

Answer 10

production of urea from ammonia through a set of enzyme controlled reactions

Question 11

describe detoxification in the liver

Answer 11

the neutralisation and breakdown of unwanted chemicals such as alcohol
eg hydrogen peroxide is split into O2 and H2O by catalase
ethanol can be broken down by alcohol dehydrogenase into ethanal then ethanoate

Question 12

what is the main function of the kidney

Answer 12

responsible for excretion of nitrogenous waste and osmoregulation

Question 13

give the name and function of the 2 main blood vessels in the kidney

Answer 13

renal artery supplies blood
renal vein carries blood away

Question 14

what are the 3 distinct layers of the kidney

Answer 14

cortex- dark outer layer containing capillary networks carrying blood to nephrons
medulla- contains nephrons
pelvis- where urine collects before leaving for ureter

Question 15

describe the structure of a nephron

Answer 15

glomerulus- filters small solutes from blood (contained in bowman’s capsule)
proximal convoluted tubule- reabsorption
descending loop of henle- water passes out of filtrate
ascending loop of henle- reabsorption of ions from filtrate
distal convoluted tubule- selectively secretes and absorbs ions
collecting duct- reabsorbs solutes and water from filtrate

Question 16

where does ultrafiltration take place

Answer 16

glomerulus

Question 17

how does blood enter the glomerulus

Answer 17

afferent arterioles

Question 18

what are the 3 sieve membranes involved in ultrafiltration

Answer 18

CAPILLARIES- fenestrations allow filtrate through endothelial cells
BASEMENT MEMBRANE- made of network of collagen fibres, most plasma contents can pass through but RBCs and proteins are retained
PODOCYTES- in walls of bowmans capsule, extensions called pedicels that wrap around capillaries forming slits to filter fluid further

Question 19

how does blood leave the glomerulus

Answer 19

efferent arteriole (narrower diameter so higher pressure)

Question 20

what does the filtrate entering the capsule contain

Answer 20

glucose, salt, urea, and other substances in same conc as blood plasma

Question 21

why does selective reabsorption occur

Answer 21

filtrate is hypotonic to blood plasma so most filtered substances need to return

Question 22

what happens in the proximal convoluted tubule

Answer 22

all glucose, amino acids, vitamins and hormones actively transported into blood
most NA+ actively transported back, CL- and H2O follows
diffusion into capillary networks

Question 23

what happens in the descending limb of the loop henle

Answer 23

filtrate is isotonic with blood and tissue fluid
upper part is impermeable to water, lower part is permeable
water moves into tissue fluid in medulla through osmosis down conc gradient, then into blood
not permeable to NA+ and CL-
tissue fluid gains conc which sets up gradient

Question 24

what happens in the ascending limb of the loop of henle

Answer 24

lower section is permeable to ions and they move out through diffusion down conc gradient
in upper section ions are actively pumped out to set up conc gradient
impermeable to water
filtrate becomes more and more dilute, tissue fluid becomes more and more concentrated

Question 25

what happens in the distal convoluted tubule

Answer 25

permeability varies with adh levels
if body lacks salt, NA+ actively pumped out with CL- following down electrochemical gradient
water can also leave in presence of adh

Question 26

what happens in the collecting duct

Answer 26

passes down through medulla
water moves out through osmosis down conc gradient controlled by adh

Question 27

what is osmoregulation

Answer 27

the process of controlling the amount of water and ions in the blood

Question 28

what do osmoreceptors do

Answer 28

in hypothalamus
detect changes in water potential. when low, water leaves through osmosis down conc gradient, causing them to shrivel and stimulate posterior pituitary gland to produce more adh

Question 29

describe the mechanism of adh action

Answer 29

released from p gland, carried in blood to collecting duct
binds to receptors on cell membranes (1st messenger)
triggers formation of cyclic amp (2nd messenger) which relays the signal to molecules inside
vesicles containing aquaporins fuse with membrane which makes it permeable to water
negative feedback loop

Question 30

what can cause kidney failure

Answer 30

infection, high bp, genetics, physical damage

Question 31

what can kidney failure cause

Answer 31

large molecules filter out of blood into filtrate, build up of urea in blood

Question 32

how is kidney failure detected

Answer 32

glomerular filtration rate measured by testing creatine levels (breakdown product of muscles so high levels may indicate kidneys aren’t filtering properly)

Question 33

how does haemodialysis work

Answer 33

blood enters dialysis machine, dialysis fluid separated by partially permeable membrane. fluid contains no urea and normal plasma levels for glucose and mineral ions
multiple times a week, may require careful diet

Question 34

how does peritoneal dialysis work

Answer 34

utilises peritoneum in lining of abdomen
dialysis fluid introduced using catheter
fluid left for several hours then drained

Question 35

what are the drawbacks of a kidney transplant

Answer 35

immunosuppressants required, lack of donors

Question 36

how are monoclonal antibodies used in pregnancy tests

Answer 36

wick of test submerged in urine, immobilised antibodies in window bind to HCG/antibody complex, more immobilised antibodies bind to mobilised antibodies regardless of whether they are bound to HCG as a control