Week 2.2 - structure & function (workbook) Flashcards
what does the kidney consist of microscopically?
outer cortex and inner medulla surrounding the renal pelvis
what does the renal pelvis connect?
kidney to ureters
what is the microscopic functional unit of the kidney?
the nephron
what is the nephron?
a long tube, lined with epithelial cells, with the glomerulus at one end, and a connection to the renal pelvis at the other
what is the filter of the nephron?
the glomerulus
where is the glomerulus located?
in the kidney cortex
where does filtrate formed by the glomerulus pass?
passes first through the proximal convoluted tubule (PCT) in the cortex
what happens after filtrate passes through the PCT?
the nephron then dips down into the medulla forming a hairpin loop ‘loop of Henle’
what comes after the loop of Henle?
as the nephron ascends it forms the distal convoluted tubule, in the cortex
what comes after the distal convoluted tubule?
finally, the nephron joins the collecting duct that passes through the medulla to the renal pelvis
what do specialised afferent and efferent arterioles do?
maintains the relatively high, constant filtration pressure in the capillaries at the glomerulus
why is the high constant filtration pressure in the capillaries at the glomerulus necessary?
drives water and small molecules out of the plasma at a rate of about 125ml/min (180L/day) - glomerular filtration rate (GFR)
what is the GFR?
180L/day or 125ml/min
what is the function of the proximal convoluted tubule?
specialised section of the nephron reabsorbs about 70-80% of most ions and water, plus most or all of the small organic molecules not destined for secretion (e.g. glucose, amino acids)
is reabsorption in the PCT regulated?
not tightly
how does the filtrate remain isotonic with ECF?
water follows the reabsorption of solute
how are the epithelial cells lining the nephron like?
polarised, with different properties on the membrane facing the filtrate (apical / luminal membrane) and that facing the extra-cellular space (basolateral membrane)
what is the reabsorption of many substances linked to in the PCT?
linked to the active movement of sodium ions
how are sodium ions moved?
by active transport across the basolateral membrane, so generating a concentration gradient between the intra-cellular fluid and filtrate
why is the concentration gradient between the intra-cellular fluid and filtrate important?
this then drives the reabsorption of most ions and small molecules, with water following passively by osmosis
what happens as filtrate passes through the loop of Henle?
solute is selectively reabsorbed
how is the fluid leaving the loop of Henle like? why?
there is overall less reabsorption of water, so the fluid leaving the loop is hypotonic
how does the fluid move through the loop of Henle?
first down the descending limb, then up the ascending limb
how does a hypertonic environment come about within the kidney medulla?
a process of counter current multiplication (as fluid moves through loop of Henle) generates a very hypertonic environment within the medulla
what happens in the distal tubule and collecting duct?
further reabsorption of both water and electrolytes from the ultra-filtrate in the distal nephron is now variable
what does the amount of solute or solvent reabsorbed in the distal tubule / collecting duct depend on?
the fluid and electrolyte balance of the body
what is diuresis?
when the body has too many of certain substances in the fluid that the kidneys filter
what happens in diuresis?
ions are reabsorbed, but not the water, producing a large volume of dilute urine (where there is need to excrete a lot of water)
what happens if water needs to be conserved?
water is absorbed with ions in the DCT, drawn out of the collecting duct into the hypertonic renal medulla - producing very small volumes of very concentrated urine
