Lecture 2 : Filtration at the Renal Corpuscle Flashcards by Brooke Routhier

Renal Corpuscle:

Glomerulus
Glomerular Capsule

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Glomerulus

Capillary bed

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Glomerular Capsule

cup surrounding glomerulus

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Renal Tubule:

Proximal Convoluted Tubule

Nephron Loop (Loop of Henle)

Distal Convoluted Tubule

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Proximal Convoluted Tubule

leads out of glomerular capsule

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Nephron Loop (Loop of Henle)

Descending limb into medulla

Ascending limb back to cortex

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Distal Convoluted Tubule

leads to collecting duct

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____ collects from many nephrons and completes modification of urine

Collecting duct

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The cortex contains:

renal corpuscles

proximal convoluted tubules

distal convoluted tubules

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The medulla contains the straight structures:

loops of Henle
collecting ducts
vasa recta blood vessels

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Renal cortex histology

Glomeruli stand out visually

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Renal medulla histology

Lots of tubes running in parallel

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Renal corpuscle histology:

squamous epithelium of parietal layer of glomerular capsule
glomerular capsular space
glomerulus

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Proximal convoluted tubule histology:

fuzzy lumen due to long microvilli

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Distal convoluted tubule histology:

clear lumen

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Two types of nephrons distinguished by location:

Cortical & Juxtamedullary nephrons

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Both types of nephrons filter ___ and process filtrate to make ____.

blood
urine

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Cortical nephrons

85% of all nephrons

Located primarily in the cortex; only part of the loop of Henle dips into medulla

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Juxtamedullary nephrons

Renal corpuscle located near the cortex-medulla junction

Loop of Henle dips deep into the medulla

Primary role is to establish osmotic gradient in kidney to make it possible to concentrate urine

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____ carries blood into the glomerulus

Afferent arteriole

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___ leads out of the glomerulus and drains into ____ capillary bed surrounding proximal and distal convoluted tubules

Efferent arteriole
peritubular

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In juxtamedullary nephrons, efferent arteriole drains into _____ associated with the nephron loop.

vasa recta

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Blood vessels of the Nephron

These are low pressure capillary beds which favor exchange of substances from interstitial spaces around tubules

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Urine formation and blood adjustment relies on:

FILTRATION, REABSORPTION
SECRETION

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Glomerular filtration

dumps cell-free and protein-free blood filtrate into the container (glomerular capsule or Bowman’s capsule)

Tubular reabsorption

reclaims what the body needs to keep (from tubule to the blood)

Tubular secretion

selectively adds to the filtrate (from blood to tubule)

Excretion

the term used to describe elimination of finished urine from body

The kidneys will process 180 L (47 gallons) of blood derived fluid (filtrate) a day, BUT, only ___ leaves the body as urine

1.5 L

Filtrate ≠ Urine

We only call it urine after ALL processing is complete

structure of typical capillary bed

Small holes within and between endothelial cells allow solutes and water to move across capillary wall

Blood moves from arteriole across the capillary bed to a ___

venule

Exchange with interstitial space occurs across the ___

capillary wall

Forces in Capillary Exchange:

Filtration Reabsorption

Filtration:

Water and small solutes squeezed out of the capillary into the interstitial fluid

Reabsorption:

Water drawn back into the capillary from the interstitial fluid

Filtration is driven by blood pressure _____

capillary hydrostatic pressure (CHP)

Reabsorption is pulled by ____ exerted by large plasma proteins trapped in blood

osmotic pressure

______ of arteriole increases blood flow into capillary bed = ___ filtration pressure

Vasodilation increases

_____ of arteriole decreases blood flow into capillary bed = ____ filtration pressure

Vasoconstriction Decreases

Glomerulus

A coiled capillary bed between two arterioles

The _____brings blood into the glomerulus

afferent arteriole

Capillaries of the glomerular tuft are ____, and capillary hydrostatic fluid pushes fluid and solutes out of the capillary

fenestrated

Blood leaves the capillary through the ______

efferent arteriole

Note that we can adjust ____ (and affect pressure) from either side of the glomerulus!

flow

The glomerular capsule has a ____ and a ______:

parietal layer visceral layer

Parietal layer

simple squamous epithelium outer part of capsule

Visceral layer

inner visceral layer special cells called PODOCYTES with “foot processes”

High pressure blood entering glomerular capillary bed is filtered a filtration membrane and the filtered material is collected in the _____

glomerular capsular space

The Filtration Membrane has three (3) layers:

1) Fenestrated endothelium of glomerular capillary 2) Basement Membrane 3)Filtration slits between the foot processes of podocytes (visceral layer of glomerular capsule)

Fenestrated endothelium of glomerular capillary

Allows passage of everything but blood cells

Basement Membrane

Repels negatively charged macromolecules (plasma proteins)

Filtration slits between foot processes of podocytes (visceral layer of glomerular capsule)

Slit diaphragm cover filtration slits adding a final barrier to macromolecules Glomerular mesangial cells phagocytize debris caught between layers

“Ultrafiltrate of Blood Plasma”

In healthy nephrons, filtrate contains anything that is in blood plasma, except cells and proteins

Anything smaller than 3nm easily passes through membrane:

water, glucose, amino acids, drugs

Anything larger than 5nm stays in the capillary :

maintains the osmotic pressure of blood, preventing loss of all water to capsular space

The presence of cells or proteins in the urine can indicate problems with the ______

filtration membrane

Two types of pressure affect fluid flow:

Hydrostatic pressure Osmotic (oncotic) pressure

Hydrostatic pressure

pressure of fluid against walls of a vessel Can be: blood in the capillary pushing toward the capsular space (HPgc) fluid in the capsular space pushing toward the blood vessel (HPcs)

Osmotic (oncotic) pressure

pressure exerted by particles (proteins) in the blood (or a fluid) which tend to “pull” water into the vessel or space (OPgc)

Pressures in the glomerular and capsular space can be pulling water in:

opposite directions and therefore oppose each other

The sum of all opposing forces determines the ___ pressure in a system.

NET

____ is the most important force determining net pressure in a healthy kidney, and can be regulated

Glomerular Capillary Hydrostatic pressure

Glomerular capillary hydrostatic pressure can be adjusted by altering ___

arteriole diameter

Efferent arteriole vasodilation

Modify the amount of blood LEAVING the glomerulus

Afferent arteriole vasoconstriction

Modify the amount of blood ENTERING the glomerulus

Osmolarity

the number of particles or solutes in a given volume of water

Blood plasma has a normal osmotic concentration of ___

~280-300mOsm

The goal of the kidneys is to keep the osmolarity of body fluids constant by regulating _____

urine concentration and volume

Maintaining constant osmolality of extracellular fluids is crucial for preventing cells, particularly in the brain, from :

shrinking or swelling from osmotic movement of water.

Filtrate is ___ with Blood

Isosmotic = same osmotic pressure

Osmolarity of blood entering kidney =

300

Osmolarity of blood in afferent arteriole =

300

Osmolarity of blood in efferent arteriole =

300

Osmolarity of filtrate =

300

Filtrate is a pre-urine, produced at the ___ by filtering blood through the filtration membrane

glomerulus

Filtrate contains waste products we want to eliminate from blood and :

water ions glucose amino acids

How do we prevent loss of water, ions and nutrients from body if we put it into the filtrate?

The long tubule system of the nephron