m11 + 12 lecture - urinary system Flashcards
what organ does the urinary system include?
kidneys
- smaller than a fist
- covered in fat
what are the functions of the kidney?
- clean the blood of waste
maintain:
- BP (RAAS)
- O2 concentration in the blood (RBC production)
- pH and electrolyte balance (albumin, K+, Na+, Cl-, Ca++)
what is the nephron?
- functional unit of the kidneys
- responsible for urine formation
- mainly in cortex of kidney, a portion extends into the medullary region (loop of Henle)
what are the steps of urine formation by the nephron?
1) filtration
2) reabsorption
3) excretion/secretion
how many nephrons are in each kidney?
- 1 million per kidney
about how many nephrons are cortical and juxtamedullary ?
cortical nephron - 85%
juxtamedullary nephron - 15%
- long loop
- helps to concentrate urine
what are the parts of the nephron?
- renal corpuscle
- glomerulus (podocytes)
what is the renal corpuscle?
- made from the glomerulus and the bowman’s capsule
- this is the filtration unit of the kidneys
what is the glomerulus?
- a network of very porous fenestrated capillaries, held together by podocytes
- receives blood from the afferent arteriole and is drained by the efferent arteriole (only kind of capillary bed drained by an arteriole)
what is a podocyte?
- helps prevent rupture of the glomerulus
- reinforces the membrane and has filtration slits
what is the JG apparatus made of?
- macula densa cells of DCT
- juxtaglomerular cells (granular cells of afferent arteriole)
what do the juxtaglomerular cells do?
- monitor the BP and O2 content in the afferent arteriole
- release renin to increase BP (RAAS)
- produce EPO to increase RBCs and O2
what do the macula densa cells do?
- tubuloglomerular feedback mechanism (TGFM)
- cells of the DCT which lie close to the glomerulus
- these cells act as chemoreceptors that sense the concentration of the filtrate
- change the flow of blood thru the afferent arteriole and the filtration rate thru the glomerulus
what is filtrate formation?
- driven by hydrostatic pressure (BP)
- kidneys form 180L of filtrate per day
—-> we reabsorb 178.2L = 99%
—-> we only secrete 1.8L = 1% in our urine - filtrate is the same as plasma except without any protein/cells
- anything not reabsorbed = considered urine
equation for net filtration pressure (NFP)?
glomerular filtration pressure –> GFP
(+/-) colloid osmotic pressure –> COP
(+/-) capsular hydrostatic pressure –> CHP
= net filtration pressure –> NFP
why is filtrate formed?
- due to glomerular filtration pressure - this is the same as glomerular hydrostatic pressure
- pressure in the glomerulus is much higher than regular capillaries at 55mmHg (vs. 15mmHg normally)
- this pressure will force fluid and small particles out of the blood into the bowman’s capsule
two factors will oppose this:
- capillary osmotic pressure = around 30 mmHg
- capsular hydrostatic pressure = usually 15 mmHg
what is the glomerular filtration rate (GFR)?
- the rate at which filtrate forms
- 125mL/min
what factors affect filtrate formation?
- BP changes in the afferent arteriole
- hydration
- health of glomerular capillaries
- age
what happens when BP increases?
- filtrate formation increases
- reabsorption decreases
—> urine formation increases and becomes more dilute
—> nephron does not have time to reabsorb the fluid
* if greatly affected by how much water you take in per day*
through what mechanisms is regulation of GFR done?
intrinsic and extrinsic mechanisms
where does renal autoregulation, an intrinsic control of filtrate formation, occur?
it is myogenic, in the muscles
how does renal autoregulation occur?
- done by controlling the BF through the afferent and efferent arterioles
- reflex action monitors stretch in the afferent arteriole and will adjust to changes in pressure
—> maintains BF through the kidneys => maintains GFR if active/resting or in positional changes
what is tubuloglomerular feedback mechanism (TGFM)?
- the macula densa cells monitor the concentration (osmotic pressure) of the filtrate in the DCT (quality control)
–> the GFR influences the reabsorption rate and affects the amt. of materials we lose or reabsorb - the goal of TGFM is to maintain an even GFR to prevent a loss or excessive gain in electrolytes
what happens to reabsorption if filtration is low? (TGFM)
reabsorption is high, the concentration is low and the MD will increase BF - in the afferent arteriole