Renal Physiology 1 Flashcards
Give the basic functions of the kidney
- Volume, osmolarity & electrolytes regulation
- Control of arterial blood pressure
- excretion of metabolic wastes and bio active substances such as hormones, toxins, antigens and drugs
- Acid base balance
- Erythropitein production
- Activation of vitamin D for calcium balance
What is the functional unit of the kidney ?
Nephron
What is the flow through the kidney?
Renal —> segmental —> interlobar—> arcuate—> cortical radial (interlobular)—> afferent arterioles—> efferent arteriole —> peritubular capillaries
Contrast cortical and Juxtaglomerular nephrons
Cortical nephrons- 80-85% & short loops of Henle
Juxtaglomerular nephrons- 15-20% & having long loops of henle
Describe the juxtaglomerular apparatus
The structures present very close to the glomerulus make juxtaglomerular(JG) made up of three cell types:
- Granular cells(or juxtaglomerular cells) in afferent arteriole releases renin
- Extra Glomerular Mesangial cells(or lacis cells)
- Macula dense cells are modified epithelial cells of early DCT - sense NaCl load
JGA- auto regulates of the Glomerular filtration of the single nephron by tubuloglomerular feedback mechanism
What are the 3 basic functions of the nephron?
- Glomerular filtration- filtering of plasma in the Glomerular capillarie(1st step)
- Tubular Reabsorption- movement of substances from tubular fluid to blood
- Tubular secretion: movement of substances from the blood into the tubular fluid
What is remaining in the tubular fluid after three basic processes gets excreted in urine- renal excretion
How to calculate the amount of solute excreted?
Amount of solute excreted (E)= amount filtered(F)- amount reabsorbed(R)+ amount secreted (S)
What is renal blood flow?
1200 ml/min (RBF)
Describe Glomerular filtration & renal blood flow
- GF is the 1st step in formation of urine
- A portion of the blood as it flows through the Glomerular capillaries is filtered into Bowman’s space
- The filtrate is called ultrafiltrate & has all components of plasma except for plasma proteins & blood cells
- GFR( Glomerular filtrate rate) is expressed as mL per minute of liter per day
- Approximately 120-125 mL/min or 180 L/day plasma is filtered in an adult
The entire plasma of 3 liters is filtered 60 times a day
What is the Effective Renal Plasma Flow(ERPF)?
700 ml/min
The amount of plasma flowing to the parts of the kidney that have a function in the production of constituents of urine)
GFR= 120 ml/min (both kidneys) (Glomerular filtration rate)
Filtration fraction(GFR/ERPF) 15-25%
Describe Glomerular filtration process & the barrier
Filtration occurs through filtration barrier which has three layers:
- the endothelium of Glomerular capillary
- the basement membrane (has negative charges)
- epithelial cells(podocytes) surrounding the Glomerular capillary
What are the determinants of filter ability ?
- Suze less than 10,000 kilodaltons are freely filterable
- with larger molecules movement is restricted & ceases if more than 70,000 kilodaltons
-Charge
-If negatively charged & large filterability is restricted
- Positively charged molecules easily filtered
- Neutral charge is relatively easy to filter
Since serum proteins are negatively charged & large they cannot be filtered
-Shape affects the filtration
What is filterability?
Concentration ratio in ultra filtrate & plasma
How to calculate IF Filterability?
Means the concentration of solutes in plasma= concentration in Bowman’s space
What are the positive forces favoring filtration?
PGC= hydrostatic pressure in the glomerulus
piBS= is oncotic pressure in the Bowman’s capsule
What are the negative forces opposing filtration or forces favoring reaspbsorotion?
PBS= is the hydrostatic pressure
PiGC= Is the oncotic pressure in (Glomerular capillary )
What is net filtration pressure(NFP)?
Is the difference of these forces
NFP= (PGC+ PIBS)- (PBC+ PIGC)
Give an example of Glomerular filtration being determined
Forces favoring filtration (+)
PGC= 45 mm Hg(relatively constant )
PiBS= usuallly 0 mm Hg
Forces opposing filtration or forces favoring Reabsorption (-)
PBS- 10 mm Hg (relatively constant)
PiGC(on average)= 25 mm Hg (increases along capillary)
Net filtration pressure= the differences in these forces
NFP= (45-(10+ 25)= +10 mm Hg
How do starling forces change in afferent and efferent arterioles ?
PGC decreases slightly from afferent to efferent due to along the length of the capillary; PiGC increases from afferent to efferent due to filtration of fluid
How can GFR be determined by starling forces ?
GFR= Kf x (PGC-PBS- PiGC)
Where
Kf= filtration coefficient which is the product of:
- Water permeability of the filtration barrier - Total surface area of the filtration barrier
Kf= 10- 15 ml/min mmHg (normally)
So if you alter any of the above factors GFR is affected
What is the function of autoregulation ?
Autoregulation of blood flow in the kidneys maintains a nearly constant GFR when mean arterial blood pressure is between 80 and 180 mm Hg
Summarize autoregulation of blood flow in the kidneys
Below 80 mm Hg- reduced blood pressure and increased 180 mm Hg-severe hypertension
Myogenic
Tubuloglomerular feedback
Without autoregulation increase in BP can lead to dramatic increase in GFR which could lead to serious losses of NaCl & water frommECF
Summarize myogenic mechanism of autoregulation
- Increased blood pressure
- Increased Afferent arteriole stretch
- Non-specific cation channels open
- Depolarization
- Calcium channels open- increased intracellular calcium
- Afferent arteriole contracts
Summarize tubuloglomerular feedback
-Increase in GFR, Increase in NaCl delivery
Releases ATP from macula densa cells.
- This splits into adenosine AMP & ADP - Adenosine binds to its receptor in Afferent arteriole & vasoconstricts it
Construction of afferent:
- decreased renal plasma flow (RPF)
- Decreased GFR
This will maintain constant plasma flow. The mechanism fails with BP<80 or >180
Decreased delivery Na+ to macula densa dilates the arteriole & leads to increase in renal blood flow and GFR
