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Flashcards in Day 1 5/12/15 Deck (28):

Main Physiological Function of the Kidney

-the maintenance of the composition and volume of the extracellular fluid


Total Intracellular Volume

27 L


Total Extracellular Volume

15 L


Liquid input is ________ urine output.

-equal to
-ECF volume over the course of a typical day does not change


Things the Renal System Regulates

-ECF volume
-ECF osmolarity
-EF electrolyte composition
-metabolic wastes
-foreign substances


Nephron Components

-1 million nephrons per kidney
-consists of glomerular and peritubular capillaries and the tubule


Nephron Functions

1. glomerular filtration
2. tubular reabsorption
3. excretion


Non-ECF Functions of the Kidney

1. produce erythropoetin from precursor synthesized in liver
2. regulate BP via angiotensin regulation
3. secrete renin which inc. BP by cleaving angiotensinogen to angiotensin (see above)


Molecular Cut Off Size for Filtration

-60,000 daltons (or smaller can be filtered)
-note that albumin is 67,000 daltons



-30 mm avg
-oncotic pressure
-on the blood side, the large dissolved proteins in the plasma (i.e. serum albumin, immunoglobulins) do not filter
-as water is extracted from the plasma by filtration, the protein concentration rises, resulting in a net negative osmotic pressure that opposes filtration.
-this is also called the colloid osmotic pressure or COP
-opposes glomerular filtration



-10 mm avg
-results from the fact that filtrate must flow in narrow confines of the tubule
-results in backpressure at bowman's capsule
-opposes glomerular filtration



-46mm avg
-filtration out of the capillary is driven by the value of the blood pressure where filtration occurs
-only significant driving force for filtration


Glomerular Filtration Rate (GFR) =

GFR = K (Pgc - Pt - pgc)
K = 1 for men and 0.8 for women


Net Filtration Pressure

The sum of the forces (Pgc - Pt - pgc) is called net filtration pressure or NFP
-6 mm avg



-works over BP range of 75 to 150
-ex. drop in MAP will cause afferent arterioles to dilate to restore Pgc, GFR and RBF to normal values
-responds to normal, rapid fluctuations in MAP within normal range
-only involves afferent arterioles
-mechanism of arteriolar changes: myogenic
-location of mechanism: intrinsic to kidney


Renal Solution to Chronic Hypovolemia

-mediated by external and renal baroreceptors
-responds to chronic, significant drops in MAP below normal due to hypovolemic events
-purpose: maintain GFR but reduce RBF during circulatory emergencies
-arterioles involved: afferent and efferent
-mechanism of arteriolar changes: baroreceptor mediated (direct neural + hormonal)
-location of mechanism: intrinsic + extrarenal


Glomerulotubular Balance

-refers to the ability of the obligatory reabsorption mechanisms in the proximal tubule to compensate for changes in filtered blood
-i.e. proximal tubule reabsorption readjusts to filtration changes so that a fixed proportion of the filtered load of water and NaCl is always reabsorbed. This proportion is 65%.


Tubuloglomerular Feedback

-directly regulates GFR of each nephron in response to changes in [NaCl] at a specialized group group of epithelial cells called the macula densa that can cause the arteriole to constrict or dilate


Reabsorption Range of Water and NaCl

-86 - 99.95% of water is reabsorbed
-98 - 99.99% of NaCl is reabsorbed
-most of the filtered water and salt is obligatorily reabsorbed, with only a small fraction under homeostatic control


Nearly all obligatory recapture of water and salt occurs in the:

-proximal segments (ie. proximal tubule and loop of Henle)


Homeostatically varied reabsorption primary takes place in:

-the fine tuning segments (ic. distal tubule and collecting duct)


Primary Energetic Event of Reabsorption

-when Na+ is actively extruded from interior of tubular epithelium by the basolateral Na/ ATPase pump
-reabsorption of Cl-, H2O and other solutes is coupled to the active reabsorption of Na+


Role of the Proximal Tubule

-reabsorbing most (65%) of the obligatorily reabsorbed load of water and NaCl
-recapture of important metabolites in filtrate


Role of the Loop of Henle (des. and asc. loop)

-descending loop: 15% of H2O reabsorption, H2O permeability is high but there is no permeability to NaCl
-ascending loop: 25% of NaCl reabsorption, water permeability in the ascending limb is quite low


Role of Distal Tubule & Collecting Duct

-8-10% of NaCl reabsorption
-6-20% of H2O reabsorption
-sensitive to aldosterone and ADH


Anti-Diuretic Hormone (ADH)

-also known as vasopressin
-increases water permeability of fine tuning segments
-in presence of ADH, small vesicles containing aquaporins are fused to apical membrane of epithelial cells



-upregulates basic pathway for Na reabsorption


Role of Diuretics

-inc. tubular flow and excretion in most substances