31 Kidney functions and malfunctions Flashcards
what are the functions of the kidneys?
filtering the blood of waste products
excretion of urea and waste products
maintaining water potential of the blood
how is urea formed?
ammonia formed from excess amino acids being deaminated
combined with CO(2) in ornithine cycle
converted to urea
what are the components of a nephron?
Bowman’s capsule
glomerulus
PCT
loop of Henle
DCT
collecting duct
what is ultrafiltration?
the filtering of the blood at a molecular level
what is selective reabsorption?
absorption of useful molecules back into the blood from the fluid in the nephron tubule
what is required for ultrafiltration?
high hydrostatic pressure in arterioles
filter (to retain molecules with Mr > 65000
outline the process of ultrafiltration
blood brought in via afferent arteriole
hydrostatic pressure in glomerulus ∴ small molecules in plasma forced into Bowman’s capsule
what are the layers of the Bowman’s capsule and their functions?
endothelium
- narrow fenestrations to allow transfer of plasma and solutes
basement membrane
- fine mesh of collagen and glycogen
- prevents passage of molecules with Mr > 65000
podocytes
- projections allow filtered fluid to enter lumen of Bowman’s capsule
where does selective reabsorption take place in?
PCT (90%)
LoH
DCT
outline some of the adaptations in cells of the PCT
microvilli - incr. SA for osmosis/facilitated diffusion and co-transporter proteins
basal membrane - incr. SA for transporter proteins
mitochondria - ATP synthesis
tight junctions - prevents substances from moving between cells, ensuring transcellular movement
how is water reabsorbed in the loop of Henle?
Na+ and Cl- actively pumped out ascending limb
w.p. decreases in medulla’s tissue fluid (ascending limb impermeable to water)
∴ water moves out of descending limb by osmosis
w.p. decreases in filtrate to tip of hair pin
Na+ and Cl- diffuse out of ascending limb ∴ w.p. increases
w.p.g. created between cortex and medulla
collecting duct permeable to water ∴ water moves out by osmosis into medulla
concentrated urine production
what is osmoregulation?
the regulation of the water potential of body fluids
what is ADH?
a hormone produced by specialised nerve cells known as neurosecretory cells
what is the function of osmoreceptors?
detecting changes in the w.p. of the blood flowing through the hypothalamus
how do osmoreceptors respond to low water potential?
ADH is secreted from the posterior pituitary gland into the blood plasma
what is the effect of ADH?
acts on the cells in the walls of the collecting duct
attaches to receptors on CSM
causes cyclic AMP concentration to increase
aquaporins stimulated to fuse with membrane
water passes through the channels ∴ w.p. of urine increases ∴ concentration of urine increases
when is EPO secreted?
when blood O(2) levels falls
when is renin secreted?
when blood volume falls
what is the effect of renin?
catalyses conversion of angiotensinogen
increases blood volume by constricting blood vessels
increases blood pressure
∴ ADH secreted to increase water reabsorption in kidneys
give two causes of acute kidney failure
bacterial infection
kidney stones
give two causes of chronic kidney failure
uncontrolled diabetes mellitus (type 1 or 2)
hypertension
how is kidney failure diagnosed?
reduction in urine volume
bloody/cloudy urine
oedema (accumulation of fluid in tissues)
high concentration of creatinine in urine
what are the consequences of untreated kidney failure?
accumulation of toxins –> death
increased renin production –> hypertension
less EPO produced
cardiovascular diseases
how is kidney failure treated by haemodialysis?
blood taken from artery and passed through dialysis machine (artificial filtering)
heparin added to prevent clotting
takes several hours, 3x a week
how is kidney failure treated by peritoneal dialysis?
peritoneum acts as dialysis membrane
takes minutes, several times a day
what are the conditions required for a successful kidney transplant?
compatibility of donor RBC antigens and haplotype
arteries, veins and ureter must be attached
immunosuppressant drugs must be administered to prevent an immune response
what is the future of kidney transplants?
growing kidneys from induced pluripotent stem cells
embryonic stem cells used for therapeutic cloning
