- regulate BLOOD PRESSURE - stimulate synthesis of RED BLOOD CELLS - maintain body's CALCIUM levels - regulation of blood composition

7. Renal Physiology - Production of URINE Flashcards by Ibby Khan

Kidney functions

regulate BLOOD PRESSURE
stimulate synthesis of RED BLOOD CELLS
maintain body’s CALCIUM levels
regulation of blood composition

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KIDNEYS have 2 CAPILLARY BEDS:
(connect arteries and veins)

GLOMERULUS
PERITUBULAR CAPILLARIES

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despite fluctuations in SYSTEMATIC BLOOD PRESSURE the kidneys maintain..

CONSTANT BLOOD FLOW

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BLOOD flows into the GLOMERULUS THROUGH..

AFFERENT ARTERIOLE

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BLOOD passes OUT the GLOMERULUS through

EFFERENT ARTERIOLE

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what happens in the RENAL CORPUSCLE

production of FILTRATE (water, salts, glucose, amino acids..)

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role of PROXIMAL CONVOLUTED TUBULE

(most) REABSORPTION of WATER, IONS and all ORGANIC NUTRIENTS including GLUCOSE

ALL glucose reabsorbed

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ROLE of LOOP OF HENLE
DESCENDING LIMB (thin) :

FURTHER REABSORPTION of WATER

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ROLE of LOOP OF HENLE
ASCENDING LIMB (thick) :

REABSORPTION of SODIUM and CHLORIDE IONS

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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)

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ROLE of COLLECTING DUCT

further VARIABLE REABSORPTION of WATER (under HORMONAL CONTROL)

and REABSORPTION or SECRETION of SODIUM, POTASSIUM, HYDROGEN and BICARBONATE IONS

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what happens at the PAPILLARY DUCT (end of collecting duct)

delivery of URINE to MINOR CALYX

final destination

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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)

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average urine volume per day for an adult

1.4 L

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URINARY EXCRETION calculation

EXCRETION =

FILTRATION - REABSORPTION + SECRETION

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where does FILTRATION occur in the KIDNEY

in BOWMAN’S CAPSULE of Nephron (from GLOMERULUS)

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approx how much FILTRATION SURFACE in each KIDNEY

6 m^2

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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)