B15 - The kidney Flashcards
Explain how blood passes through the heart to reach the kidneys. (6)
Oxygenated blood enters pulmonary vein. Blood pumped into left atrium, bicuspid valve, left ventricle. Heart contracts from apex. Semilunar valve opens. Blood travels through descending aorta, which branches off into renal artery to carry blood into kidney.
What are the filtering units of the kidneys called?
Nephrons
How is urine released from the kidneys? (3)
- Nephrons filter and produce sterile urine.
- urine passes out kidney down ureters (tubes)
- lead to bladder (muscular bag)
- when bladder is full, a sphincter muscle relaxes and urine passes out of body down the urethra.
In order, state the structures of the nephron. (5)
Bowman’s capsule
Proximal convoluted tube
Loop of henle
Distal convoluted tube
Collecting duct
What are the two main functions of the kidneys?
Excretion - filter nitrogenous waste out blood
Osmoregulation - maintain water balance and pH of blood and tissue fluid.
What are the three main functions of the nephron and where do they occur? (3)
- ultrafiltration - Bowman’s capsule
- selective reabsorption - proximal convoluted tube
- osmoregulation - distal convoluted tube and collecting duct
Explain the process of ultrafiltration in as much detail as possible.
- Blood enters glomerulus through afferent arteriole and leaves through efferent arteriole
- afferent wider than efferent/efferent narrower.
- this creates high hydrostatic pressure in glomerular capillaries.
- Glomerular blood vessels have fenestrations (acts as a seive).
- blood forced out glomerulus into the basement membrane (2nd seive)
- basement membrane restricts passage of large blood cells and plasma proteins
- epithelial cells of Bowman’s capsule have podocytes which act as an additional filter.
- podocytes have pedicels which wrap around capillaries of glomerulus, forming slits to ensure any large cells that manages to leave capillaries a blocked off.
Why is selective reabsorption needed? (2)
- some useful substances may end up in the filtrate.
- reuptake of useful substances from filtrate back into the blood.
Useful substances e.g. glucose, amino acids, hormones,
What are the adaptations of the proximal convoluted tube and how do they aid in selective reabsorption?
microvilli:
- increase SA for reabsorption
many mitochondria:
- provide ATP for Na+/K+ pump proteins
Tightly packed cells:
- no fluid passes in-between
Explain the process of selective reabsorption. (3)
- In proximal convoluted tube (extending from Bowman’s capsule).
- Na+K+ pump uses ATP from mitochondria to pump Na+ ions out of the proximal CT epithelial cells/wall and into the blood.
- Na+ passively diffuses down concentration gradient from filtrate into the epithelial cells.
- Uses a co-transport protein, which also brings glucose and amino acids back into the epithelial cells.
- solutes diffuse from epithelial cells into blood.
Explain how filtrate is moved through the loop of henle in order to establish a salt gradient.
- ascending limb is very permeable to Na+ and Cl-
- Na+ and Cl- diffuse out of lower section of ascending limb into medulla.
- Na+ and Cl- actively pumped out upper end of ascending limb.
- lowers water potential in medulla, becomes very salty
- increases water potential due to removal of solutes.
- ascending limb impermeable to water, so water cannot follow down a concentration gradient.
Descending limb:
- permeable to water
- lower water potential in medulla causes water to move out filtrate by osmosis into surrounding capillaries.
- water potential down the descending limb gradually decreases
- fluid at hairpin end of d.limb is hypertonic (more concentrated) than blood capillaries.
What is the purpose of the loop of henle? (2)
- establishes a salt gradient in medulla
- makes tissue fluid of the medulla hypertonic (more concentrated)
- allows mammals to produce urine more concentrated than the blood.
- acts as a countercurrent multiplier, using energy to produce concentration gradients for the movement of substances.
Why do desert animals have a longer loop of henle? (2)
- conserve more water
- more Na+ & Cl- pumped into medulla from ascending limb, so higher water potential gradient.
- more water reabsorbed/leaves from collecting duct
- smaller volume of concentrated urine produced.
What is a secondary messenger?
- molecule that relays signals received at cell surface receptor to molecules inside the cell
Describe the mechanism of ADH in the collecting duct. (4)
- ADH binds to cell membrane of collecting duct.
- cAMP inside cell causes a cascade of events
- vesicles in the cells lining the collecting duct fuse with the side of the membrane in contact with the tissue fluid of the medulla.
- These vesicles have aquaporins on their membrane.
- aquaporins make the cell surface membranes of the collecting duct more permeable to water.
- water moves into tissue fluid by osmosis (due to hypertonic medulla established by the loop of henle).
