Day 1 5/12/15

Question 1

Main Physiological Function of the Kidney

Answer 1

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

Question 2

Total Intracellular Volume

Answer 2

27 L

Question 3

Total Extracellular Volume

Answer 3

15 L

Question 4

Liquid input is ________ urine output.

Answer 4

• equal to

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

Question 5

Things the Renal System Regulates

Answer 5

• ECF volume
• ECF osmolarity
• EF electrolyte composition
• ECF pH
• metabolic wastes
• foreign substances

Question 6

Nephron Components

Answer 6

• 1 million nephrons per kidney

- consists of glomerular and peritubular capillaries and the tubule

Question 7

Nephron Functions

Answer 7

1. glomerular filtration
2. tubular reabsorption
3. excretion

Question 8

Non-ECF Functions of the Kidney

Answer 8

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)

Question 9

Molecular Cut Off Size for Filtration

Answer 9

• 60,000 daltons (or smaller can be filtered)

- note that albumin is 67,000 daltons

Question 10

(pi)gc

Answer 10

• 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

Question 11

Pt

Answer 11

• 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

Question 12

Pgc

Answer 12

• 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

Question 13

Glomerular Filtration Rate (GFR) =

Answer 13

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

Question 14

Net Filtration Pressure

Answer 14

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

Question 15

Autoregulation

Answer 15

• 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

Question 16

Renal Solution to Chronic Hypovolemia

Answer 16

• 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

Question 17

Glomerulotubular Balance

Answer 17

• 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%.

Question 18

Tubuloglomerular Feedback

Answer 18

-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

Question 19

Reabsorption Range of Water and NaCl

Answer 19

• 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

Question 20

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

Answer 20

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

Question 21

Homeostatically varied reabsorption primary takes place in:

Answer 21

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

Question 22

Primary Energetic Event of Reabsorption

Answer 22

• 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+

Question 23

Role of the Proximal Tubule

Answer 23

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

Question 24

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

Answer 24

• 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

Question 25

Role of Distal Tubule & Collecting Duct

Answer 25

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

Question 26

Anti-Diuretic Hormone (ADH)

Answer 26

• 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

Question 27

Aldosterone

Answer 27

-upregulates basic pathway for Na reabsorption

Question 28

Role of Diuretics

Answer 28

-inc. tubular flow and excretion in most substances