3.4 Homeostasis and the kidney

What do small gaps in capillaries do?

allow small molecules to pass out of capillaries but prevents larger molecules like proteins leaving - ultrafiltration

What does the basement membrane do?

provides further filtration, small pores allow small molecules to pass through in ultrafiltration

What are podocyte cells?

the final barrier for ultrafiltration, substances such as ions, urea, AA, hormones and water pass through by diffusion or active transport

where does osmoregulation occur?

in the loop of henle and the collecting duct

What happens in the ascending limb of the loop of henle?

sodium and chlorine ions are pumped into the tissue fluid causing its water potential to decrease

Why does the water move out of the descending limb into the tissue fluid?

the ions have reduced the water potential so water passes out by osmosis and then is absorbed into vasa recta

what parts of the brain control osmoregulation?

osmoreceptors in the hypothalamus detect low water potential of blood

posterior pituitary gland secretes antidiuretic hormone (ADH)

What effect does ADH have on the cells of the collecting duct walls?

ADH binds to receptors on the CD cells

causes vesicles containing aquaporins to fuse to cell membrane

H2O moves by osmosis into the blood from the filtrate, increasing water potential

What are the structural functions of the cells in the proximal convoluted tubule for selective reabsorption?

tight junction between cells prevents molecules diffusing back into the filtrate

have microvilli to increase the surface for an increased rate of selective reabsorption

mitochondria for active transport of substances into blood from filtrate

basal channel increases surface area

What substances are co transported into the PCT cell with Na+ in selective reabsorption

glucose or amino acids, they then pass out by facilitated diffusion into the capillary

what is the role of the sodium potassium pump in the PCT cell during reabsorption?

exchanges 3Na+ out of pct and 2K+ into the pct cell to maintain low Na+ conc gradient in the PCT wall

how does high protein cause kidney failure?

increases blood urea levels which can form kidney stones from uric acid

how does low protein cause kidney failure?

leads to accumulation of fluid in the tissues

lower blood pressure

reduction of kidney function

less plasma proteins which maintain osmotic pressure

How does high blood pressure cause kidney failure?

excessive filtration by glomerulus

causing loss of nutrients

damage to glomerulus which can cause cells and plasma proteins to be lost in urine

Why should K+ levels be controlled

to high levels of K+ can disrupt nerve impulses

drugs or diet can cause the rate of K+ reabsorption to increase

why should Ca2+ levels be controlled?

excessive loss can lead to less Ca in bones and brittle bone disease

reduces Ca can lead to hormonal production issues and ca salt deposition in tissues