7. Renal Physiology - Production of URINE Flashcards
Kidney functions
- regulate BLOOD PRESSURE
- stimulate synthesis of RED BLOOD CELLS
- maintain body’s CALCIUM levels
- regulation of blood composition
KIDNEYS have 2 CAPILLARY BEDS:
(connect arteries and veins)
- GLOMERULUS
- PERITUBULAR CAPILLARIES
despite fluctuations in SYSTEMATIC BLOOD PRESSURE the kidneys maintain..
CONSTANT BLOOD FLOW
BLOOD flows into the GLOMERULUS THROUGH..
AFFERENT ARTERIOLE
BLOOD passes OUT the GLOMERULUS through
EFFERENT ARTERIOLE
what happens in the RENAL CORPUSCLE
production of FILTRATE (water, salts, glucose, amino acids..)
role of PROXIMAL CONVOLUTED TUBULE
(most) REABSORPTION of WATER, IONS and all ORGANIC NUTRIENTS including GLUCOSE
- ALL glucose reabsorbed
ROLE of LOOP OF HENLE
DESCENDING LIMB (thin) :
FURTHER REABSORPTION of WATER
ROLE of LOOP OF HENLE
ASCENDING LIMB (thick) :
REABSORPTION of SODIUM and CHLORIDE IONS
ROLE of DISTAL CONVOLUTED TUBULE
SECRETION of unwanted things eg EXCESS IONS, acids, drugs and toxins
VARIABLE REABSORPTION of WATER,SODIUM IONS and CALCIUM IONS (under HORMONAL CONTROL)
ROLE of COLLECTING DUCT
further VARIABLE REABSORPTION of WATER (under HORMONAL CONTROL)
and REABSORPTION or SECRETION of SODIUM, POTASSIUM, HYDROGEN and BICARBONATE IONS
what happens at the PAPILLARY DUCT (end of collecting duct)
delivery of URINE to MINOR CALYX
final destination
COMPOSITION of URINE (varies)
UREA (most)
POTASSIUM, SODIUM, CHLORIDE (EXCESS IONS)
CREATINE (By-product of cellular metabolism)
BICARBONATE IONS (buffer)
URIC ACID (dissolves and transports HYDROGEN IONS out)
average urine volume per day for an adult
1.4 L
URINARY EXCRETION calculation
EXCRETION =
FILTRATION - REABSORPTION + SECRETION
where does FILTRATION occur in the KIDNEY
in BOWMAN’S CAPSULE of Nephron (from GLOMERULUS)
approx how much FILTRATION SURFACE in each KIDNEY
6 m^2
FILTRATION BED of GLOMERULUS has 3 main LAYERS
CAPILLARY ENDOTHELIUM (flattened endothelial cells)
BASEMENT MEMBRANE - structural (prevents damage to endothelium)
PODOCYTES (foot-like processes) - wrap around vessels of glomerulus to generate pressure
- come together to create ‘sieve’
why does the FILTRATION BED of GLOMERULUS allow MOST SMALL MOLECULES to pass but NOT cells or large proteins
it is HIGHLY FENESTRATED
both CELLULAR LAYERS of FILTRATION BED of GLOMERULUS - CAPILLARY ENDOTHELIUM & PODOCYTES special feature
contain NEGATIVELY CHARGED GLYCOPROTEINS
- creates REPELLING FORCE to + ions
what is there between Pedicels
FILTRATION SLITS
what should NOT be removed from blood / found in filtrate or urine
RED BLOOD CELLS
PLASMA PROTEINS
Plasma components
what PASS through FILTRATION BED of GLOMERULUS and are found in FILTRATE (Bowman’s Capsule)
UNCHARGED MOLECULES (LESS than 30,000 DALTONS)
- SALTS/IONS (sodium, potassium, chloride)
- GLUCOSE
- SMALL PROTEINS
- WATER
what is the FILTRATION RATE in the RENAL CORPUSCLE
approx 125 ml / min
(180 litres / day)
what is REQUIRED for FILTRATION
PRESSURE
what INCREASES PRESSURE in the GLOMERULUS for FILTRATION
EFFERENT ARTERIOLE has a SMALL DIAMETER
(afferent wide) so difficult for blood to leave
INCREASES PRESSURE in GLOMERULUS
so MORE BLOOD FILTERED
3 TYPES of PRESSURE that add to the NET FILTRATION PRESSURE in the GLOMERULUS and what are their values
- GLOMERULAR HYDROSTATIC PRESSURE (HPg):
60mm Hg OUT
(pressure of blood trying to push/filter out) - BLOOD COLLOID OSMOTIC PRESSURE (OPg):
32mm Hg IN
(trying to retain the water) - CAPSULAR HYDROSTATIC PRESSURE (HPc):
18mm Hg IN
(structure pushing back In)
what is the value of the NET FILTRATION PRESSURE (NFP)
10 mm Hg OUT
(HPg = 60 out, OPg = 32 in, HPc = 18 in)
RENAL BLOOD FLOW (RBF) is
the VOLUME of BLOOD DELIVERED to the KIDNEYS per unit of time
1.2 L / MIN
how much of your RBF is your RENAL PLASMA FLOW
55% of RBF
PLASMA makes up 55% of BLOOD
RATE of RENAL PLASMA FLOW (RPF)
0.625 L / MIN
(625 mL / min)
what is GLOMERULAR FILTRATION RATE (GFR) and what is the value
measure of how much FLUID SQUEEZED THROUGH GLOMERULAR bed per unit time
0.125 L / MIN
(125 mL / min)
what is FILTRATION FRACTION (FF) and what is the value
PORTION of PLASMA that was DELIVERED TO KIDNEY that is PASSED THROUGH TO the BOWMAN’S CAPSULE
= 20%
= GFR / RPF x 100
GFR = 125 ml / min
RPF = 625 ml/min
what is RENAL PLASMA CLEARANCE (RPC)
VOLUME of PLASMA that is CLEARED OF A KNOWN SUBSTANCE per unit time
CRITERIA for when GFR and RENAL PLASMA CLEARANCE are the SAME
if the substance is:
- FILTERED FREELY
- NOT SECRETED OR REABSORBED
- NOT METABOLISED/BROKEN DOWN
- NOT TOXIC
CALCULATION for estimating GFR
U V / P
U = SOLUTE CONC in the URINE
V = VOLUME of URINE EXCRETED PER MIN
P = SOLUTE CONC IN PLASMA
RBF:
RPF:
GFR:
FF:
RBF: 1200 ml/min
RPF: 625 ml/min
GFR: 125 ml/min
FF: 20%
only substance where GFR and RPC are the SAME (meets all criteria)
INULIN
(not routinely used due to complexity, not naturally in blood)
use COCKROFT-GAULT (CG) formula instead
COCKROFT-GAULT formula estimates… and how is it compared to GFR ESTIMATE
CREATINE CLEARNACE (Ccr) instead of GFR
OVERESTIMATES GFR by 15-40%
(as also SECRETED by tubules)
negative CONSEQUENCES of LOW GFR
- STIMULATION of RAAS SYSTEM. ELEVATED BLOOD PRESSURE
- DECREASED EXCRETION H+ and DECREASED RETENTION of BICARBONATE causes METABOLIC ACIDOSIS
- DECREASED ELIMINATION of UREA and CREATINE
- DECREASED ELIMINATION of DRUG METABOLITES such as aminoglycoside antibiotics, leading to TOXIC levels in blood
relationship between BLOOD PRESSURE and GFR
INCREASE BP = INCREASE GFR
(more blood entering glomerulus, increased hydrostatic pressure so increased filtration)
MECHANISM to REDUCE (control) GFR from increased BP
- MYOGENIC AUTOREGULATION (RAPID response)
increased STRETCH of the AFFERENT ARTERIOLE (as a result of high BP) is sensed by GRANULAR CELLS sat around afferent arteriole
- CONSTRICT
- REDUCE amount of BLOOD FLOWING INTO GLOMERULUS
- REDUCES GFR
affect of INCREASED BLOOD PRESSURE on CARDIOVASCULAR SYSTEM to decrease it
INCREASED STRETCH of ATRIA of HEART
- INCREASED SECRETION of ANP
- BLOCKS RELEASE of RENIN
(renin causes reabsorption of water and salt and increases blood volume normally by RAAS system)
