BIO215 Renal System

3 Basic Functions of the Renal System

1. Regulation of fluid and electrolyte balance
2. Regulation of plasma osmolarity
3. Excretion of metabolic waste products

3 Main Steps of fluid and electrolyte balance

1. Glomerular Filtration
2. Tubular Reabsorption
3. Tubular Secretion

Factors affecting Glomerular Filtration Rate (GFR)

-Net filtration pressure,
-Permeability of corpuscular membranes,
-Surface area available for filtration.

Glomerular Filtration pressure is the result of 4 Starling Forces:

1. hydrostatic pressure in the glomerular capillaries (PGC)
2. Osmotic pressure in the glomerular capillaries (�GC)
3. hydrostatic pressure in the Bowman's capsule (PBC)
4. Osmotic pressure in the Bowman's capsule (�BC).

Mechanisms to maintain GFR

1. Myogenic regulation
2. tuboglomerular feedback
3. Mesangial cell targeting

Order of Flow

Glomerulus->Bowman's Space->Proximal Convoluted Tube->Proximal straight tubule->descending limb->ascending limb->distal convoluted tubule->collecting duct

Glomerulus/Bowman's Capsule

Forms ultra filtrate of plasma

Proximal tubule

bulk reabsorption of solutes and water; recreation of solutes (except K+) and organic acids/bases

Loop of Henle

establishes medullary osmotic gradient

Ascending Limb

Reabsorption of NaCl

Descending limb

bulk reabsorption of water

Distal tubule and cortical collecting ducts

fine-tuning of the reabsorption/secretion of small quantity of solute remaining

Cortical and medullary collecting ducts

fine-tuning of water reabsorption, reabsorption of urea

Factors controlling Glomerulus/Bowman's capsule

Starling forces (P gc, P bs, pi gc)

Factors controlling Proximal tubule

active transport of solutes with passive water reabsorption; parathyroid hormone inhibits phosphate ion reabsorption

Factors controlling descending limb

passive water reabsorption

Factors controlling ascending limb

active transport

Factors controlling distal double and cortical collecting ducts

aldosterone stimulates Na+ reabsorption and K+ excretion; parathyroid hormone stimulates calcium ion reabsorption

Factors controlling cortical and medullary collecting ducts

vasopressin increases passive reabsorption of water

Renal Clearance:

the volume of plasma from which that substance is completely cleared by the kidneys per time.

Urea is formed...

in the liver during protein catabolism

only about _____of the urea stays in the tubules, critical in __________

40%, preventing massive H2O loss via the osmotic effect of urea on H2O

urea also prevents excessive H2O loss by

strengthening the medullary osmotic gradient.

the anatomical arrangement of the vasa recta (descending and ascending limbs)

prevents the erosion of the medullary osmotic gradient

ADH (anti diuretic hormone) is released by neurosecretory cells in response to what 4 things:

-high blood osmolarity
-low blood volume
-decreased blood pressure
-Angiotensin II

Effects of ADH on principle cells lining the distal DCT and CD:

1.ADH binds to receptors on the basolateral membrane.
2.Activation of a G-protein activates adenylate cyclase which catalyzes the formation of cAMP which
3.Activates protein kinase A which then
4.Stimulates insertion of new H2O channels
(AQP-2) into the a

In all tubular segments where Na+ is reabsorbed, it is actively transported across ___________ Because this active transport keeps the intracellular [Na+] low____________

the basolateral membrane by the Na+/K+ ATPase pump; Na+ passively enters the cell across the apical membrane

_______________are the most abundant anions in tubular fluid, they are most frequently reabsorbed with Na+.

Cl- and H2CO3-

________________are the cations most commonly secreted when Na+ is reabsorbed.

K+ and H+

Juxta-glomerular cells secrete the enzyme Renin in response to:

-Low blood pressure
-Sympathetic nerve stimulation
-Secretion of Prostaglandin by macula densa cells which sense Na+ concentration in distal convoluted tubule.

Renin catalyzes conversion of circulating Angiotensinogen (produced by the liver) into :

Angiotensin I.

Endothelial cells possess the membrane bound enzyme ACE (angiotensin converting enzyme) which converts Angiotensin I to:

Angiotensin II.

Angiotensin II which:

-Causes peripheral vasoconstriction of smooth muscles in arterioles
(increases resistance),
-Promotes secretion of ADH by posterior pituitary gland which increases H2O reabsorption in collecting duct which increases blood volume
-Stimulates to adrenal cor

aldosterone

?Acts on the principal cells in the distal part of the DCT and the CT to:
?Increase the number and activity of Na+/K+ ATPase pumps on the basolateral surface.
?Inserts K+ channels on the apical surface (increases secretion of K+).
-Inserts Na+ channels on

macula densa cells detect:

changes in [Na+] and [Cl-] as well as flow rate of tubular fluid.

When ___ decreases, renin secretion increases. Once renin is released into the bloodstream, initiates series of rxns that increase ______________ secretion by the adrenal cortex. Increases both __reabsorption and __ secretion.

[Na+],aldosterone,Na+, K+

Parathyroid hormone is a :

peptide hormone secreted by the parathyroid glands in response to a decrease in plasma [Ca++].

PTH has the following effects:

-Stimulates Ca++ reabsorption in the ascending limb of the loop of Henle and DT,
-Stimulates activation of 1,25 (OH)2D3 in the kidneys which stimulates Ca++ absorption in the digestive tract and Ca++ reabsorption in the kidneys, and
-Stimulates the resorp

Calcitonin is a a peptide hormone that is secreted from C cells of the thyroid gland and which acts...

to decrease plasma [Ca2+] by acting to increase the rate of bone deposition and to decrease the rate of Ca2+ reabsorption in the kidneys.

�Overall, in the DT and CD there are 2 primary effects of importance to pH regulation:

-Newly synthesized HCO3- are added to the plasma, and
-H+ is secreted into the tubular filtrate.