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EXAM 4 PHYSIO: RENAL 1
EXAM 4 PHYSIO: RENAL 1
Major functions of the kidneys?
1. regulate water vol
2. regulate bal of iorganic ions
3. regulate body pH
4. excretion of metabolic wastes
5. produce hormones/enzymes
6. reg blood pressure
Normal osmolarity of body fluids:
300 mOsm
What hormones do the kidneys synthesize?
1. Erythropoietin
2. 1,25- Dydroxyvitamin D3 (Calcitrol)
3. Renin (not a hormone though)
1, 25-Dihydroxyvitamin D3
Increases absorption of Ca & PO4 from the GI tract.
Function of renin?
Hydrolyzes Angiotensinogen to Angiotensin I
Function of AII?
1. aldosterone secretion (Na retention in kidney)
2. Stimulates thirst (increased water ingestion)
What are the two kinds of nephrons?
1. cortical nephron
2. juxtamedullary nephron
What is the mOsm value in the deepest portion of medulla?
1200 mOsm
What are some commonalities between the cortex and medulla?
1. two arteriole (afferent, efferent)
2. two capillary beds (glomerular--filtration and peritubular/vasa recta)
Cortical Nephrons
1. peritubular capillaries (90% of renal blood flow).

Remove reabsorbed solutes and H2O.
Juxtamedullary nephrons
Vasa recta
10% renal blood flow

Helps maintain osmotic gradient.
Principles of the nephron
1. filters plasma
2. reabsorb the substances body needs.
3. secrete what body doesn't need.
4. excrete what is left (urine)
Area of nephron where filtration takes place?
Renal corpuscle
Reabsorption and secretion occurs where?
Rest of the tubule
Loop of Henle
Reabsorbs NaCl and thus separates Salt and H2O.
Distal tubule and CD
Fine tunes ion absorption
Amount excreted is equal to:
Amount filtered - Amount reabsorbed + Amount secreted.
Reabsorption value
~180L / day
Excretion value
1-2L per day
Renal blood flow
1L/min
Renal Plasma flow
625ml/min (900L/day)
GFR value
125ml/min (180 L/ day)
Pgc
Glomerular capillary BP
Conditions leading to decreased GFR:
1. constriction of afferent arteriole and normal efferent arteriole.
2. decreased Pgc

Condition 2
1. Normal AA
2. Dilated EA
3. Decreased Pgc
Conditions leading to increased GFR?
Case 1
1. Constricted EA
2. Inc Pgc

Case 2
1. Dilated AA
2. Increased Pgc
Extrarenal mechanism in the control of arteriolar resistance:
Neural and hormonal inputs to AA and EA alter the resistance of both in a similar way.
Two examples of Intra-renal mechanisms (autoregulation):
1. myogenic
2. tubuloglomerular feedback
Myogenic
AA respond to increased BP--> inc contraction of AA smooth muscles--> inc resistance--> dec Pgc--> dec GFR
Tubuloglomerular feedback
Paracrine inputs to AA alter its resistance so Pgc remains constant, therefore GFR remains constant.
Macula densa
Senses Na concentration in the distal tubule.

Senses increase in luminal salt load.

Release paracrines that act on smooth muscle cells of AA.
Inc arterial BP can lead to:
inc Pgc--> Inc GFR--> inc amount of salt load moved into tubule--> macula densa release paracrines to act on AA--> inc AA resistance--> dec Pgc--> dec GFR.