Kidney Function 1 Flashcards
What are the functions of the kidney?
- water and sodium homeostasis
- control of ion concentration
- acid base balance
- excretion of waste
- endocrine
- conserve or excrete water depending on conditions
What hormones are produced by the kidney?
EPO, renin, vitamin D3, PGI2
What are the two types of glomeruli?
superficial cortical glomeruli and juxtamedullary glomeruli
What percentage of glomeruli are superficial cortical glomeruli?
85%
What is the difference between SCG and JMG?
SCG have a short loop of Henle and are located in the outer cortex, JMG have a long loop and are located at the junction between cortex and medulla so their loop can penetrate deep into the medulla
What is the osmolarity of concentrated urine?
1200
What is the osmolarity of dilute urine?
300
What are the segments of the nephron?
- bowman’s capsule
- proximal tubule (convoluted tubule and pars recta)
- thin descending loop of Henle
- thin ascending loop of Henle
- thick ascending loop of Henle
- distal tubule
- collecting duct
Where is most of the reabsorption done?
in the proximal tubule
Which part of the nephron is responsible for diluting urine?
thick ascending limb of Henle
Is there one collecting duct for every nephron?
no - a number of distal tubules converge on one collecting duct
What is the rate of renal blood flow?
1L/min
What is the filtration fraction?
0.2 - the amount of plasma that is filtered
What is the rate of renal plasma flow?
600mL/min
What is the GFR?
180L/day - amount of plasma filtered per day
What is the most important force that affects GFR?
Hydrostatic pressure in the glomerular capillary - this is why you need pre and post glomerular arterioles
Why isn’t all of the GFR excreted in urine?
because the peritubular capillaries reabsorb most of the filtrate
What happens to GFR with age?
it decreases
What is the amount of solute excreted equal to?
the amount filtered - the amount reabsorbed + the amount secreted
What is auto regulation?
the ability of renal blood flow to remain constant across a range of blood pressures (MAP 80mHg - 180mmHg)
What controls auto regulation?
tubular glomerular feedback and myogenic reflex
What is tubular glomerular feedback?
the macula densa in the thick ascending limb of the loop of Henle detects the amount of sodium chloride and there is a paracrine signal from the macula densa to the afferent arteriole to constrict with an increase in sodium chloride
What mediators send the paracrine signal from the macula densa to the afferent arteriole?
adenosine and thromboxane (vasoconstrictors) and prostaglandins (vasodilator)
What is the myogenic reflex?
The ability of the afferent arteriole to constrict in response to stretch
What is the purpose of auto regulation?
to keep the pressure in the glomerulus constant so that the filtration pressure is always 50mmHg
What else is macula densa involved in?
renin release
What is the function of renin?
increase blood pressure and conserve salt
What causes renin release?
volume depletion and blood pressure decrease, sodium depletion (detected via macula densa), activation of sympathetic nervous system
Where is renin released from?
granular cells of afferent arteriole
What is the action of renin?
converts ANGI to ANGII
What is the action of ANGII
many ways to increase blood pressure
What is clearance?
the amount of plasma that is cleared of a solute per unit of time
How do you calculate clearance?
UV/P where U is equal to the concentration in urine, V is the volume of urine and P is the plasma concentration
What is creatinine clearance equal to?
GFR = 180L/day
What would happen if GFR decreased?
creatinine concentration in the plasma would rise
What is glucose clearance equal to?
0 - filtered freely but all is reabsorbed
What happens if plasma glucose concentration is too high?
it saturates the active transport maximum so can’t all be reabsorbed and there is glucose in the urine
What is penicillin clearance?
greater than GFR - because it is both filtered and secreted but not reabsorbed
What must filtration pass through?
fenestrations of capillary walls, the basal lamina and filtration slits in foot processes of podocytes
What are the limitations of what can be filtered?
size and charge - large molecules and negatively charged molecules are repelled
Which plasma protein is highly negatively charged and therefore repelled?
albumin
What does albumin in the urine indicate?
advanced diabetes - degeneration of basal lamina
What is the hydrostatic pressure in the glomerular capillary?
50mmHg
What is the hydrostatic pressure in Bowman’s capsule?
10mmHg
What is the oncotic pressure in the glomerular capillary?
25-40mmHg - increases as filtration occurs
What is the oncotic pressure in Bowman’s capsule?
0mmHg
What is the net filtration pressure?
15mmHg
What stops filtration from occurring at the end of the capsule?
the increase in oncotic pressure in the glomerular capillary
What happens to GFR with constriction of the afferent arteriole?
GFR will decrease - reduce the flow so reduce the pressure so reduce the GFR
What happens to GFR with constriction of the efferent arteriole?
GFR will increase - bank up blood will increase pressure so increase GFR
Which arteriole does angiotensin II preferentially constrict?
the efferent arteriole - therefore leads to an increase in GFR
What will constrict the afferent arteriole?
noradrenaline (sympathetic nervous system) - trying to maintain BP and will sacrifice blood flow to the kidney to ensure the blood flow to the brain is maintained - but will hopefully be balanced out by RAAS
What makes up the juxtaglomerular apparatus?
macula densa cells, granular cells and the mesangial cells
What is the function of mesangial cells?
provide structure and constrict the glomerular capillaries to alter glomerular filtration by altering capillary surface area
How is the pressure in Bowman’s capsule increased?
blocking the outflow e.g. kidney stones or benign prostatic hypertrophy - the result will be a decrease in GFR
