Renal Physiology Flashcards
Basic Function of the Kidney
1) Urine Production Via Filtration and Reabsorption 2) Regulation of blood and cleaning/filtering 3) Secretion of hormones in response to blood. Ex) Renin, Erythropoietin, VitD 99% of filtration gets reabsorbed by body
List and identify structure of nephron
List the vasculature associated with the nephron
1) Afferent arteriole => brings blood into the glomerulus for filtration.
2) Efferent arteriole => bring blood out that has reabsobed substances from nephron.
3) Peritubular capillaries => Tiny blood vessels of the efferent arterioles that surround the PCT and DCT and are crucial in reabsorption.
4) Vasa Recta => Extension of the peritubular capillaries that surround the loop of henle.
What are the two types of nephrons found in the kidney
1) Cortical
2) Juxtaglomerular
Function of juxtamedullary vs cortical nephron
Juxtamedullary => more responsible for the concentration of urine (minority of nephrons in kidney)
Cortial => Excretion of waste (Majority of nephrons in kidney)
Big take away from lecture was Juxtamedullary is the nephron that is mainly involved in urine production.
Structural differences between the cortial and juxtamedullary nephron
Cortical:
- Glomerulus in upper region of cortex
- Only a small part of the loop of Henle is in medullary
- Does NOT have a thin ascending tubule
Juxtaglomerular:
- Glomerulus is near the border of cortex and medulla
- Loop of Henle runs deep in medulla
- Contains both a thin and thick acending limb
Basement membrane of glomerulus
Bowman’s capsule
What are podocytes
Specialized cells of the glomerulus that wrap around capillaries and that neighbor cells of the Bowman’s capsule
An extension of the podocytes
Pedicels
What do pedicels form
Form filtration slits
Permeability of filtrate through the glomerulus is dependent upon
Size and charge
Filtrate that is less that 15 Angstroms are _____ where are substrate greater than 35 Angstroms are _____.
Freely filtered
Not filtered
At what range of size is filtration possible but limited
Between 15A - 35A
Closer to 15A => easier the filtering
Closer to 35A => harder the filtering
Explain how charge can play a role in filtration.
Pedicels (filtration slits) have a highly negative charge. Therefore, there is an electrostatic attraction between filtrate with a charged cation.
Charge has a larger affect on filtration rate than size.
Example) A 15A negatively charged particle will have a slower filtration rate than a 20A postiviely charged particle.
Although the 20A is bigger, b/c its relatively close to 15A and is positively charged makes it faster.
What is the the concentration of free filtered molecules relative to plasma and Bowman’s Space
Concentration of filtrate in PLASMA = Concentration of filtrate in Bowman’s Space
What is the the concentration of non-freely filtered molecules relative to plasma and Bowman’s Space.
Concentration of filtrate in PLASMA > Concentration of filtrate in Bowman’s Space
What are the 4 types of Starling forces
PGC => Hydrostatic Glomerular Capsule Pressure
πBS => Oncotic Bowman’s Space Pressure
PBS => Hydrostatic Bowman’s Space Pressure
πGC => Oncotic Glomerular Capsule Pressure
Hydrostatic Pressure can be described as
Pushing force
Oncotic Presssure can be described as
Sucking force
Express the starling forces and how they affect filtration/reabsorption
Filtrate goes from glomerulus into _____ and then into ____.
Bowman’s Space and Proximal Tubule
Net movements of filtrate can be expressed by what equation and define that equation:
Starling Equation:
What do we assume of the oncotic pressure in the Bowman’s Space (πBS)
πBS = 0 mmHg,
Because proteins are NOT filtered from the Glomerular Capsule into the Bowman’s Space.
If proteins end up being filtered, this is indicative of a physiological disorder.
Diseases/disorders that can cause protein in urine (proteinuria):
Ex) Nephrotic syndrome, Lupus, Goodpasture’s syndrome and Glomerulonephritis
Give an example of something that gives urinary tract obstruction
Kidney stone
What part of the kidney can be obstructed by a kidney stone and what net effect does this cause
Kidney stone => blockage of renal calyx
Blockage of renal calyx => filtrate cannot leave kidney into ureter
Backing up of filtrate in Bowman’s Space can occur => lead to forced reabsorption rather than filtration.
Explain Nephrotic Syndrome
Renal Disease in which the Glomerular capillaries are damaged. Damage causes proteins to enter into filtrate.
Why is proteinuria bad. We want proteins to be circulating in our bloodstream. By excreting proteins out of our body, our blood circulating CANNOT be sucking water out of intersitial spaces (onoctic pressure is eliminated).
People with Nephrotic Syndrome have a pooling of H20 in their interstitial spaces.
What is edema
Swelling caused by excess fluid trapped in your body’s tissues.
Rate at which the ultrafiltrate forms in Bowman’s space
Glomerular Filtration Rate (GFR)
Why is GFR so important
Indicative of patient health
Equation for GFR
Delta P => Derived from Starling equation
Kf => Filtration Coefficient and is invariant (typically from 10-15)
Explain how changes in plasma flow affect filtration rate:
Movement of solutes from glomerular capillaries to Bowman’s space
Filtration
Return most filtered solutes to circulation
Reabsorption
Transport of solutes from the peritubular capillaries and Vasa Recta into the tubular lumen.
Secretion
Solute in urine due to filtration, secretion, and reabsorption
Excretion
67% of reabsorption into the peritubular capillaries
At PCT (proximal convoluted tubules)
**REMEMBER: Peritubular capillaries are an extension of efferent arterioles.
Define Autoregulation
Maintain balanced GFR flow to mediate reabsorption
What happens if blood pressure falls below a normal range
Low blood pressure => low renal plasma blood flow => low GFR => hemorrhage/heart failure
*hemorrhage => ruptured blood vessel
What happens if blood pressure falls above a normal range
High blood pressure (hypertension) => High renal plasma blood flow => High GFR => tachycardia
Name the two ways in which autoregulation occurs:
1) Myogenic Response
2) Tubular Glomerular Feedback
Explain where filtration, reabsoprtion, secretion and excretion are occuring in the nephron
Why is it bad if GFR is too high
Filtration is too much and not enough reabsorption is occuring in the body. Patient is peeing out alot of necessary substances.
Why is it bad if GFR is way too low
Reabsorption is too much and not enough filtration is occuring in the body. Waste especially is reabsorbed.
Explain the kidney’s myogenic response to maintain homeostatic GFR
If there is high GFR in the afferent arteriole => stretch occurs.
Stretch receptors are activated and opening of Ca2+ channels occur. Ca2+ channels constrict the afferent arteriole to lower GFR
Explain the kidney’s Tubuloglomerular response to maintain homeostatic GFR
Involves Macula Densa Cells.
These cells sense GFR flow via NaCl content.
If there is severe change in GFR, Juxtaglomerular cells are signal a vasoactive response.
1) High GFR => High Filtration.
Kidney releases Adenosine. Adenosine => Constricts afferent arteriole => lowers GFR to normal
2) Low GFR = > Low Filtration
Kidney releases Renin. Renin catalyzes Angiotensinogen to Angiotensin-I. Then Angiotensin-1 is converted to Angiotensin-II by ACE.
Angiotensin-ll => Constrict efferent arteriole to elevate GFR back to normal.
In a health person, what is the relationship between Na+ intake and Na+ excretion
Na+ intake = Na+ excretion
A person who has more Na+ intake> Na+ excretion is said to have
High blood pressure and blood volume
A person who has more Na+ intake< Na+ excretion is said to have
low blood pressure and blood volume
What occurs at the early proximal convoluted tubule
30-35% Na+ reabsorption
Na+ draws H20 reabsorption
What occurs at the late proximal convoluted tubule
~35% Na+ reabsorption
Na+ draws H20 reabsorption
What occurs at the thick ascending limb
25% Na+ reabsorption
(No H2O)
What occurs at early distal tubule
5% Na+ reabsorption
Late Distal Tubule and Collecting Duct
3% Na+ Reabsorption
Explain how the RAAS system work and when it is activated
When there is LOW Na+ intake (and HIGH Na+ excretion) => LOW BLOOD PRESSURE
Sympathetic Response => RAAS:
Angiotensinogen => Angiotensin-I => Angiotensin-ll => Aldosterone
Aldosterone => increases Na+ and water reabsorption (acts on principal cells)
RAAS => raised blood pressure
Describe some of the actions of Angiotensin-ll
=> Stimulates aldosterone secretion
=> Constricts efferent arteriole
=> Stimulates thirst
=>Stimulates Na+ reabsorption at PCT
What is Atrial Natriuretic Peptide (ANP) and when is it released.
ANP is a hormone secreated by atria when there is a heavy intake of Na+ (increase in ECF volume and blood pressure).
ANP is secreted out from the heart in response to stretch and increases GFR. This encourages filtration and inhibits reabsorption of Na+.
It also inhibits aldosterone.
ANP => REDUCES B/P
What function do anti-diuretics serve
=> Urinary Retention
What is ADH
Anti-diuretic hormone (vasopressin). Its a hormone that works on Distal and Collecting duct to reabsorb water.
ADH binds to a G-Protein receptor and causes a release of cAMP in principal cells. => Aquaporin H20 channels are activated in the principal cells to stimulate water reabsorption.
How is ADH activated
1) By a 1 mOSm/L rise in plasma (more solutes and less water)
2) Hypovolemia => loss of blood volume
What actions does angiotensin II have that are not related to its ability to vasoconstrict? Angiotensin II:
Increases Na+ reabsorption by proximal tubule
