(2) Ch.19 Renal Exchange

Front 1

renal tubules

Back 1

In the kidneys, water and solutes are exchanged btwn plasma and fluid in the _____ _______ to regulate the composition of plasma.

Front 2

glomerular filtration

Back 2

___________ _________ is the bulk flow of protein-free plasma from the glomerular capillaries into Bowman's capsule.

Front 3

Reabsorption

Back 3

_________ is the selective transport of molecules from the lumen of the renal tubules to the interstitial fluid outside the tubules.

Front 4

diffusion

Back 4

Reabsorbed molecules eventually enter the peritubular capillaries by _________, and are then returned to the general circulation.

Front 5

Secretion
peritubular capillaries

Back 5

_________ is the selective transport of molecules from the peritubular fluid to the lumen of the renal tubules. These secreted molecules come from the plasma of the __________ __________.

Front 6

glomerular filtration

Back 6

Filtration at the renal corpuscle is driven by Starling (hydrostatic & osmotic pressure gradients) in walls of glomerular capillaries
Filtrate resembles plasma, except lack of most proteins in plasma.

Front 7

epithelial cells

Back 7

What are the Bowman's capsule and the wall of the renal tubule are composed of these cells?

Front 8

Bowman's capsule
basement membrane

Back 8

In the ________ ______, this epithelium folds upon itself to envelop the glomerular capillaries. Below the epithelium, there is a _________ ________ that acts as the primary filtration barrier for proteins.

Front 9

1. cap. endothelial cell layer
2. surrounding epithelial cell layer
3. basement membrane

glomerular membrane or filtration membrane

Back 9

What are the 3 barriers that the glomerular filtrate has to pass to get to the Bowman's capsule? What is the name of the layers combined?

Front 10

foot processes
podocytes

Back 10

The epithelial cells that cover the glomerular capillaries have special extensions or ____ ________, giving them their name _________.

Front 11

slit pores

Back 11

As fluid moves out of the glomerular capillaries, it passes through gaps btwn the podocytes, called ____ _____.

Front 12

slit diaphrams

Back 12

The sizes of the slit pores are regulated by ____ ________.

Front 13

bulk flow of protein-free fluid

Back 13

The presence of fenestrations (pores) in the capillary endothelium, the large number of slit pores in the surrounding capsule epithelium, and the large surface area of the filtration barrier combine to make the renal corpuscle favorable for the _____ _____ of _______-____ ______ btwn blood and the lumen of Bowman's capsule (bowman's space)

Front 14

glomerular filtration pressure

Back 14

The sum of the Starling forces in the renal corpuscle is called the ____________ _________ _________, which is analagous to the net filtration pressure.

Front 15

1. Glomerular capillary hydrostatic pressure
2. Bowman's capsule oncotic pressure
3. Bowman's capsule hydrostatic pressure
4. Glomerular oncotic pressure

Back 15

What are the 4 Starling forces?

Front 16

Glomerular capillary hydrostatic pressure

Back 16

favors filtration
equal to the blood pressure in the glomerular capillaries
Pressure is higher here than in most hydrostatic pressures in other caps, because of the high resistance to the efferent arteriole (located downstream from glo. caps.)
The presence of high resistance in any network of vessels tends to raise the pressure in vessels located upstream while lowering the pressure downstream.

Front 17

Bowman's capsule oncotic pressure

Back 17

favors filtration
due to presence of nonpermanent solutes
exerted by the presense of proteins
Proteins in the interstitial fluid tends to pull fluids out of caps and into capsule
Very little protein concentration in Bowman's capsule

Front 18

Bowman's Capsule hydrostatic pressure

Back 18

opposes filtration
pressure is higher than the hydrostatic pressure in interstitial fluid surrounding cap beds because the large volume of fluid that filters out of the glomerular caps is "funneled" into Bowman's capsule.

Front 19

Glomerular oncotic pressure

Back 19

opposes filtration
presence of proteins tend to draw filtrate back into glomerulus.
oncotic pressure is higher than other systemic capillaries, because the blood flows through these caps loses a substantial fraction of it water as a result of glomerular filtration, and causes plasma proteins to increase.

Front 20

glomerular filtration rate (GFR)

Back 20

The volume of the plasma filtered per unit time

Front 21

filtration fraction

Back 21

The fraction of the renal plasma volume that is filtered is called the ________ _______ and is equal to the glomerular filtration rate divided by the renal plasma flow rate.

Front 22

GFR

Back 22

Changes in the ___ do NOT cause a large increase or decrease in urine output, because the ___ is relatively constant by the instrinsic and extrinsic mechanisms.

Front 23

Intrinsic control of GFR

Back 23

If MAP ↑ it also ↑ the GFR, because it affects glomerular capillaries, which in turn influences GFR.
MAP ↓ then GFR ↓
Tends to ↑ or ↓ urine flow, which interferes w/ Kidneys' ability to regulate the V and composition of the plasma.
3 mechanisms:
myogenic regulation
tubuloglomerular feedback
mesangial cell contraction

Front 24

myogenic regulation

Back 24

afferent arteriolar smooth muscle

Front 25

tubuloglomerular feedback

Back 25

operate by changing of the afferent arteriole

Front 26

mesengial cells contraction

Back 26

acts by changing the permeability of the filtration barrier

Front 27

myogenic regulation
tubuloglomerular feedback
mesengial cells contraction

Back 27

What are the 3 intrinsic mechanisms to the GFR?

Front 28

myogenic regulation

Back 28

smooth muscle of afferent arteriole is sensitive to stretch and responds to stretch by contraction.

MAP ↑ leads to a pressure in afferent arteriole to ↑, which causes its wall to stretch. ↑ in glomerular capillaries leads to ↑ glomerular filtration pressure and GFR ↑.
Afferent arteriole stretch leads to constriction, which ↑ resistance to flow.
BP ↓ in blood vessels going downstream and in glomerular capillaries.
This ↓ in pressure counteracts the initial rise in pressure that triggered constriction of that afferent arteriole.
Negative feedback mechanisms tend to keep glomerular cap pressure and GFR at a relatively constant rate.

Front 29

stretch
chemical agents

Back 29

The smooth muscle of the afferent arteriole is sensitive not only to ________ but also to _________ _______ that are secreted by cells of the macula densa, which are located in the nearby distal tubule.

Front 30

tubuloglomerular feedback

Back 30

triggered by a chemical signals released frol cells in the macula densa
a change in GFR causes in the flow of tubular fluid past the macula densa, which alters the secretion of certain paracrines from the macula densa.
These paracrines then trigger contraction or relaxation of the afferent artiole, which causes a change in glomerular capillary pressure and GFR in the direction opposite to that of the original change.
The negative feedback control of GFR opposes the initial response of the change in flow that is triggered.

Front 31

tubuloglomerular feedback

Back 31

MAP ↑ -- afferent arteriolar pressure ↑ -- glomerular capillary pressure ↑ -- GFR -- flow at macula densa ↑ -- chemical signals -- constriction of afferent arteriole ↑ -- resistance of afferent arteriole ↑ -- glomerular capillary pressure ↓ ---- negative feedback to glomerular capillary pressure ↑

Front 32

tubuloglomerular feedback

Back 32

Triggered by chemical signals released from cells in the macula densa in response to increased GFR, prevents significant changes to GFR when MAP changes by affecting glomerular capillary pressure.

Front 33

mesengial cells contraction

Back 33

An increase in BP, which increases GFR, stretches mesangial cells. In response to the stretch, the mesengial cells contract, decreasing the surface area of capillaries available for filtration, which decreases the GFR back to normal.

Front 34

Mesangial cells

Back 34

_________ _____ are modified smooth muscle cells located around glomerular capillaries.

Front 35

Extrinsic control of Glomerular Filtration & Renal blood flow

Back 35

When MAP goes above or below the norm range, the GFR rises or falls, respectively, because intrinsic mechanisms are no longer able to prevent glomerular capillary pressure from changing.

When MAP ↓, GFR ↓ directly due to the lowered filtration pressure. ↓ MAP also triggers an ↑ in SNS activity via baroreceptor reflexes. ↑ sympathetic nerve activity, smooth muscle in afferent and efferent arteriole constrict and contract, which ↑ overall resistance of the renal vasculature and ↓ the GFR. The ↑ in renal vascular resistance acts to ↓ renal blood flow and raises the total peripheral resistance, which ↑ MAP. The ↓ in GFR also ↓ urine output, which help body conserve water. Minimizes reduction in BV, which in turn counteracts further ↓ in arterial pressure.

Front 36

GFR

Back 36

• The amount of filtrate produced at all the nephrons per minute. Equals about 125ml/min.
• 180 liters/day
o How? There are 3 processes. Filtration is just 1 of them.
• Urine volume – 1 to 1.5 liters/day
• Why is so much filtrate produced?
• A major nephron function is the removal of nitrogenous wasters, primarily urea from the plasma.
• Producing a large volume of filtrate will remove large amounts of urea.
• Must put most of water back into bloodstream by reabsorbing the water.
• Filtration process allows for the removal of large amounts of urea from the plasma & the concentration of that urea into small volume of water (urine).

Front 37

reabsorption

Back 37

• Since such a high volume of filtrate is produced per day most all of what was filtered must be put back into the bloodsteam.
• At the proximal convoluted tubule 100% of all the nutrient filtered are reabsorbed back into the bloodstream (via peritubular capillaries). Use active transport to move the nutrients.
• About 70% of all of the electrolytes & water are also reabsorbed from the proximal convoluted tubule. Is basically automatic so is called nonregulated reabsorption.
• A small (approximately) 20% of salts & water are reabsorbed from the loop of Henle.
o What we are cleaning is plasma, not RBCs
• At the distal convoluted tubule & collecting tubule the amount of salt & water reabsorption is controlled by the action of HORMONES. This is called regulated reabsorption because how much is actually happening can vary over time.
• Usually, most + ions are reabsorbed through active transport processes while most – ions & water are reabsorbed by passive processes (diffusion).

Front 38

secretion

Back 38

• Usually an active transport process that moves molecules from the peritubular capillaries into the nephron tubules usually at the distant convoluted tubules or collecting tubules.
o Ex. of molecules secreted at the distant convoluted tubules are H+ ions & K+ ions.
• Provides nephrons with a 2nd way to remove unwanted molecules from the plasma.
o What the 1st way? Filtration