Physio Kidney

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What is the maximum concentration of urine?: 1200 mOsmolar or 4 TIMES that of the plasma.
Describe reabsorption in the proximal tubule.: Isosmotic.
Solutes and water are reabsorbed in equal proportions so no change in osmolarity and no osmotic concentration gradient is achieved.

Very water permeable.
Describg reabsorption in the descending limb of the loop of Henle.: Water permeable and salt impermeable.
Water gets reabsorbed by osmosis so the tubular fluid becomes hypertonic.
What are certain consequences of severe renal disease?: Hypertension
Osteoporosis
Anemia
Neuropathy
What are the endocrine functions of the kidney?: Secretion of renin
Secretion of erythropoietin
Activation of vitamin D
Inactivation of certain hormones like insulin
What are the general functions of kidneys?: Regulation of volume and composition of ECFs.
Regulation of blood pressure
Excretion of end products of metabolism (urea, ammonia, creatinine)
Excretion of foreidn substances like drugs.
The kidneys receive how much of the cardiac output?: About 20% = 1000 ml/min/2kidneys
What percentage of the plasma flowing through the kidney is filtered through the glomerulus into Bowman's Capsule?: 20%, also known as the average filtration fraction.
How much of protein free filtrate is formed?: 125 ml/min
How much filtrate leaves the kidney by way of urine?: Less than 2 ml/min
What is found in the CORTEX of the kidney?: Glomeruli, proximal tubules, distal tubules, cortical portion of collecting ducts. Also peritubular capillaries.
What is found in the outer medulla of the kidney?: Portions of the loop of Henle (important: TAL), medullary portion of blood vessels and collecting ducts.
What is found in the inner medulla (papilla) of the kidney?: Thin portions of loop of Henle, papillary portions of collecting ducts. The hairpin portion of loop of Henle and vasa recta.
Glomerular carpillaries are held together by what kinds of cells?: Mesangial cells
Which part of the microvasculature secretes renin?: Juxtaglomerular apparatus
The proximal tubule reabsorbs how much of the filtrate?: 2/3
Remember this is called obligatory reabsorption.
What are the 2 differnet nephron rypes?: Cortical nephrons: penetrate only into the outer zone of medulla.
Juxtamedullary nephrons 25%--lie near the medulla and have long loops that dip sometimes all the way to the renal papilla; are important in the production of a concentrated urine and salt retention.
What are the hydrostatic pressures in the glomerular capillaries vs. the peritubular capillaries?: glomerular = 60 mmHg - for rapid fluid filtration
Peritubular = 10-18 mmHg (book says 12)-for rapid fluid reabsorption
Extrinsic mechanisms of controlling renal blood flow: Neural (SNS)
Renin angiotensin system decreases renal blood flow.
Vasopressin decreases medullary blood flow.
Atrial natriuretic peptide vasodilates afferent and efferent arterioles.
Acetylcholine, dopamine, NO, prostaglandin are vasodilators whose action leads an increase in RBF.
Intrinsic mechanisms of controlling renal blood flow: Autoregulation.
RBF is independent of renal arterial pressure within the ranges of perfusion pressures of 70-190 mmHg
Myogenic Theory: Increased pressure in the afferent arteriole leads to smooth muscle distention. The smooth muscle contracts and increases its resistance so that blood flow is maintained constant.
Tubuloglomerular Feedback Mechanism: 2 components: juxtaglomerular cells (smooth muscle cells of afferent arterioles- contain renin and are in contact with macula densa cells) and macula densa (beginning of distal tubule).

Decreased macula densa sodium chloride causes dilation of afferent arterioles and increased renin release!
What is the mathematical equation for urinary excretion rate?: = filtration rate - reabsorption rate + secretion rate
Distribution of renal blood flow to the cortex vs. medulla: cortex = 90% (book says 98-99%)

Remember: flow to the renal medulla is supplied by the vasa recta.
What does angiotensin II do?: powerful vasoconstrictor-- constricts teh efferent arterioles.
Raises teh glomerular hydrostatic pressure and reduces renal blood flow.
What would an increase in arterial pressure do to glomerular hydrostatic pressure and GFR?: Increase it -- only a small effect due to autoregulation.
What would an increase in afferent arteriolar resistance do to glomerular hydrostatic pressure and GFR?: Reduces PG and decreases GFR.
What would an increase in efferent arteriolar resistance do to glomerular hydrostatic pressure and GFR?: Moderate increase: Raise PG and increase GFR slightly.

Severe increase: Will also reduce renal blood flow --> increased filtration fraction --> increase the glomerular colloid osmotic pressure --> decrease in GFR
What are the 3 layers of the filtering apparatus?: Endothelium - fenestrae; negative charge
Basement membrane - collagen and proteoglycan fibrilla (fibronectin) with large spaces; negative charge.
Epithelial cells (podocytes) - foot processes separated by slit pores/filtration slits; negative charge.
Which molecules are freely filterable?: water, sodium, glucose, inulin (up to a MW of 5000)
Which molecules do not pass through the filter?: Albumin = MW = 70,000
How do you calculate Net Filtration Pressure?: PG- PB - PiG + PiB
=60-18-32+0
=10 mmHg
What is the equation for filtration fraction?: GFR/renal plasma flow
Increase in afferent arteriolar tone does what to GFR?: reduces glomerular hydrostatic pressure and decreases GFR. Renal blood flow also decreases.
What is the equation for Plasma Clearance?: (Us x V)/(Ps) = excretion rate/plasma concentration of the substance
Equation for filtered load: GFR x Ps
Equation for excretion rate: Us x V
Equation for secretion rate: excretion rate - filtered load
=(Us x V) - (GFR x Ps)
Equation for rate of reabsorption.: Filtered load - excretion rate
=(GFR x Ps) - (Us x V)
Increase in arterial pressure does what to PERITUBULAR capillary hydrostatic pressure?: Raises this pressure and decreases reabsorption. (buffered thru autoregulation)
Increase in resistance of either afferent/efferent arterioles does what to PERITUBULAR capillary hydrostatic pressure?: Reduces the pressure and increases reabsorption.
Increasing the filtration rate does what to colloid osmotic pressure of PERITUBULAR capillaries?: the pressure increases, increasing reabsorption.
An increase in Kf does what to reabsorption?: Increases reabsorption.

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