Ch 14 Part 2 -- Urinary System -- VTPP 435

Ch 14 Part 2 -- Urinary System -- VTPP 435

Glomerular Membrane

-where fluid in Bowman's capsule must go through; retains blood cells and plasma proteins, but allows water and solutes to filter through
-3 layers:
(1) Glomerular Capillary Wall
(2) Basement Membrane
(3) Inner Layer of Bowman's Capsule

Glomerular Capillary Wall

-single layer of flattened endothelial cells
-perforated by a lot of large pores to allow water and solutes to be permeate thru

Basement Membrane

-acellular gelatinous layer
-made of collagen for structural strength
-made of glycoproteins to prevent filtration of small plasma proteins
-plasma proteins are repelled by the negative charge of glycoproteins
-proximal tubule picks up proteins that do fit in by to return them to blood

Inner Layer of Bowman's Capsule

-made of Podocytes -- octopus like epithelial cells that encircle glomerular tuft
-has filtration slits for fluid to leave glomerular capillaries and enter lumen of Bowman's Capsule

Difference between Glomerular Capillaries and other and Capillaries

-Glomerular Capillaries are more permeable than capillaries, else where so more fluid is filtered
-Filtration for Glomerular occurs across entire length of the capillary

Glomerular Capillary Blood Pressure

-hydrostatic pressure exerted by blood within glomerular capillaries
-heart contraction produces energy for glomerular filtration, and resistance in afferent & efferent arterioles
-major force producing glomerular filtration

Plasma-Colloid Osmotic Pressure

-caused by uneven plasma protein distribution across glomerular membrane
-more water in bowman's capsule than glomerular capillaries, due to osmosis

Bowman's Capsule Hydrostatic Pressure

-pressure exerted by fluid pushes fluid out of Bowman's Capsule

Filtration Coefficient (Kf)

-how much glomerular surface area
-how permeable glomerular membrane is

Autoregulation to control GFR

-prevents spontaneous GFR changes to maintain constant blood flow
-alters afferent arteriole by constricting or dilating it

Myogenic Mechanism for Autoregulation

-responds to changes in pressure in nephron's vascular comonent
-afferent arteriole automatically constricts when stretched due to increased arterial driving pressure

TubuloGlomerular Feedback (TGF) for Autoregulation

-senses changes in salt level in fluid flowing thru nephron's tubular component
-Macula Densa detects changes in salt level and releases ATP and adenosine to constrict arteriole afferent when there is too much salt

Mesangial Cells

-hold tuft of glomerular capillaries that comes into contact with blood
-contraction closes off portion of filtering capillaries to reduce surface area

2 Major Control Mechanisms Control GFR

-regulate radius of afferent arterile
1) Autoregulation
2) Extrinsic Sympathetic Control -- regulates arterial blood pressure long-term