Week 8 - Renal Function - Optional Flashcards
hilum
entry/exit of blood vessels, veins and ureter
cortex
outer pale layer
contains nephrons
medulla
pinky central area
contains nephrons
nephrons
are a complex tubular structure that enables the refinement of the filtrate which will eventually be excreted based on what components the blood needs
What’s the nephron responsible for?
processing the blood
What are the three main areas of the nephron?
renal corpuscle
renal tubule
collecting ducts
What are the two different kinds of nephrons?
juxtamedullary and cortical
What is the functional unit of the kidney?
nephron
What allows the nephron to perform its function?
changes in the types of cells along the length of the nephron
What is the process of refining the filtrate?
1.
isosmotic fluid leaving the proximal convoluted tubule becomes progressively more concentrated in the descending limb
- removal of solutes in the thick ascending limb creates hyposmotic fluid
3.
permeability to water and solutes in the distal tubule and collecting ducts is regulated by hormones
4.
final urine osmolarity depends on reabsorption in the collecting ducts
Where does glomerular filtration occur?
renal corpuscle
where plasma moves from blood vessels of the glomerulus into the lumen of Bowmans capsule
What percent of the plasma moves into the Bowmans capsule?
20%
- most of this is reabsorbed further
What happens to the 80% in GF?
proceeds to the peritubular capillary (or vasa recta) where decoration of desired solutes into the nephron lumen occurs, ready for excretion.
What is the rate of filtration called?
glomerular filtration rate (GFR)
What percentage of volume is excreted in GF?
<1%
What is glomerular filtration rate?
it is the volume of plasma from which a given substance is removed by glomerular filtration
What are the factors effecting GFR?
hydrostatic pressure
colloid osmotic pressure
hydrostatic pressure
What is the GFR like?
relavtiely constant
What is GFR control by?
net filtration
- changes in renal blood flow and blood pressure
filtration coefficient
- changes in diameter of the afferent and efferent arterioles to alter the GFR
What are the three ways GFR can be controlled?
hormonal
- angiotensin ii
- prostaglandins
nervous
- sympathetic nerves release noradrenaline
-> arteriole constriction
Autoregulation
- myogenic réponse - response to pressure changes
- tubuloglomular feedback - release of hormones due to physical changes in afferent and efferent arterioles and ascending limb of loop of henle
Tubuloglomerular Feedback
- GFR increases
Clinical uses of GFR
evaluate kidney function
- assessment of filtering capabilities but not diagnose
What does GFR tell us?
estimates efficiency with which substrate are cleared from the blood by glomerular filtration
measure of nephron function
One method of GFR estimation
- can be performed using exogenous or endogenous substances
- clearance of substance by kidney can be measured if substance fits the following criteria
-> present at stable conc.
-> physiologically inert
-> freely filtered at the glomerulus
-> is not secreted, reabsorbed, synthesised or metabolised in the kidney
therefore
filtered s = excreted s in urine
GFR x [S]plasma = [s]urine x urinary flow rate (V excreted/unit time)
Method 2 of GFR estimation
- exogenous substances
- most accurate estimation
- can be radio isotopes or not
- example = inulin
Inulin
- plant product that is filtered but not reabsorbed
- if 100% goes in 100% must come out
What does creatine phosphate break down into?
creatinine
What is the production of creatinine like?
relatively constant depending on amount of muscle mass
Where does creatinine pass through?
the glomerulus into the filtrate during glomerular filtration
How much creatinine is excreted into the proximal convoluted tubule?
a small amount
How much creatinine is reabsorbed?
virtually nothing
GFR estimation - methods 2 - urinary clearance
- Timed urine collection throughout 24-h
- Large intra-individual day-to-day coefficient of variation for repeated measures of creatinine clearance
basic function of kidney
- Control of blood composition (fluid and electrolyte balance)
- regulation of osmolarity
- Maintenance of ion balance
- Homeostatic regulation of pH - Control of blood volume
- Control of blood pressure
4.Production of hormones: erythropoietin and calcitriol
- Excretion of waste: urea, urate, creatinine in urine
Changes in Blood Composition
- Osmolarity and volume can change independently
- Dehydration decreases blood volume/pressure, and increases
osmolarity
-> Compensation involves cardiovascular responses, Angiotensin II (ANG II), vasopressin, and thirst - pH changes:
-> H+ concentration is closely regulated
-> changes can alter three-dimensional structure of proteins
abnormal pH affects the nervous system
pH changes:
- Acidosis: neurons become less excitable; CNS depression
- Alkalosis: hyperexcitable
- pH disturbances (often associated with K+ disturbances
Controlling Fluid and Electrolyte Balance - ascending limb events
ascending limb pumps out Sodium, potassium and chloride ions and filtrate becomes hyposmatic
Controlling Fluid and Electrolyte Balance - What happens to blood in vasa recta?
vasa recta removed water leaving the loop of henle
Controlling Fluid and Electrolyte Balance - What happens to the filtrate entering the descending limb?
becomes progressively more concentrated as it loses water
Controlling Fluid and Electrolyte Balance - How is it achieved?
by countercurrent exchanger mechanism
Controlling Fluid and Electrolyte Balance - What controls the permeability to water of the ducts?
ADH
Controlling Fluid and Electrolyte Balance - What controls the permeability of descending limb of henle?
aldosterone
Products that change the acid-base balance - Acid
- organic acids
- ketoacids, metabolic organic acid production can increase
- production of CO2 -> H2 production
Products that change the acid-base balance - Base
few dietary or metabolic sources of bases
How is acid-base balance achieved?
- NHE secretes H+
- H+ in filtrate combines with filtered HCO3- to form CO2-
- CO2 diffuses into cell
- CO2 combines with water to form H+ and HCO3-
- H+ is secreted again
- HCO3- is reabsorbed with Na+
- Glutamine is metabolised to ammonium ion and HCO3-
- NH4+ is secreted and excreted
Principle of Blood Volume Control
if volume falls too low, GFR stops
volume loss can be replaced only by volume input from outside the body
volume gain - cab be offset by volume loss in urine
GFR can be adjusted and kidney recycles fluid
Regulated H2O reabsorption
= kidney conserves volume
When is erythropoietin produced?
production stimulated by decrease in PO2
What happens when is erythropoietin produced?
stimulates erythrocyte production through differentiation of CFU-E proerythroblast
Where is erythropoietin produced?
production in interstitial cells in kidney
What is calcitriol?
active form of vitamin D
Where is calcitriol produced?
produced by the enzyme C1-alpha-hydroxylase from stored calcifediol
What is the half life of calcitriol?
approx 14 days
Why is calcitriol important?
essential in maintenance of calcium uptake from the GI tract
What duration can kidney disease be?
can be acute or chronic
Acute Kidney disease
rapid metabolic disbalance
high mortality but commonly reversible with treatment
Chronic Kidney Disease
associated with a number of disorders such as
- diabetes
- hypertension
- glomerulonephritis
- polycystic kidney disease
