FUNCTIONS OF THE KIDNEY Flashcards
functions
-Removing metabolic waste from the extracellular fluid
(urea, acids)
-Controlling the volume of extracellular fluid (close link
to blood pressure)
-Maintaining optimal concentrations of vital solutes in
the extracellular fluid (Na, K, H, Ca, Mg, Cl, Phos)
How much of the cardiac output goes to the kidneys
20%
three basic processes of the nephron
glomerular filtration - filtering of blood into tubule forming the primitive urine (glomerular filtrate)
tubular reabsorption - selective absorption of substances from tubule to blood
tubular secretion - secretion of substances from blood to tubular fluid
what is the glomerular filtration barrier
A unique structure allowing extracellular fluid to be
filtered and to leave the body:
– Specialised capillary endothelium
– Glomerular basement membrane – collagen based
– Podocyte foot processes
Normal GFR approx
100ml/min = 144L per day
movement of solutes and water across membranes ..
diffusion
specific membrane channels
- energy dependent
- down a conc gradient
- down an electrical gradient
- down an osmotic gradient
controlled by systemic and local mediators
PCT cell features
basolateral membranes with infoldings for ATPase
apical membrane with microvillae and aquaporins .
cuboidal
how much sodium chloride is reabsorbed in PCT
approx 70%
nearly all amino acids and glucose is reabsorbed in PCT
what are the loop of henle rules
1. Thick ascending limb is impermeable to water, but actively transports sodium, potassium and chloride 2. Thick ascending limb provides the concentration gradient to promote water reabsorption from the thin DLH 3. Thin descending limb is freely permeable to salt and water 4. Vasa recta doesn’t wash away the gradient by using countercurrent exchange
what does the juxta-glomerular apparatus
maintains GFR in face of increases or decreases in blood flow to the kidney
macula densa senses tubular flow
what does the macula densa produce when there is an increase in tubular flow
adenosine which causes afferent arteriolar constriction
if there is a reduced tubular flow…
sensed by macula densa which causes granular cells to produce renin
reasons for reduced sensed volume
extracellular fluid depletion haemorrhage
vasodilation
pump failure
Kidney response to reduced sensed
volume
•Efferent glomerular arteriolar constriction preserves waste excretion • Avid tubular sodium and water re-absorption preserves extracellular fluid volume net effect - oliguria - concentrated urine - low urine Na concentration - high urine potassium secretion
what helps maintain extracellular fluid calcium concentration
sensing tissues - parathyroid gland
calciotropic hormones - parathyroid hormone , hydroxylated vitamen D
effector tissues - kidney , intestine and bone
equation for clearance
= number of particles in urine /concentration of particles in plasma
what is creatinine
normal product of muscle metabolism
plasma concentration is dependent on muscle mass and kidney function
incompletely filtered but some tubular secretion
creatinine clearance
= (urine volume x creatinine concentration in urine )/ conc of creatinine in plasma
effect of muscle ,mass on the serum creatinine levels leads to …
overestimation of function in women , elderly and other low muscle mass groups
what are the 3 concentric layers of connective tissue that protect and stabalise the kidnay?
fibrous capsule - layer of collagen fibres
adipose fat
renal fascia - dense fibrous outer layer that anchors the kidney into surrounding structures . the renal fascia also lines the renal sinus and internal cavity within the kidney
what is the hilum
is the entry of artery , renal nerves and exit of the vein and ureter
what is the difference between the cortical and juxtamedullary nephrons
85% Cortical nephrons & 15% Juxtamedullary nephrons
• Cortical nephrons are situated mainly in the cortex, they have a short loop that dips slightly into the medulla.
• Juxtamedullary nephrons have long nephron loops that extend deep into the medulla. The long loop plays a key role in water conservation and the formation of concentrated urine
the walls of the glomerular capillaries are covered in what?
podocytes which are specialised cells that create slits
what is the glomerular filtration barrier
endothelial cells
glomerular basement membrane
podocytes
what is autoregulation
is the process by which the afferent arterioles respond to changes in pressure in the glomerulus by dilating or constricting (myogenic reflexes). This maintains the local pressure constant between 60-70mmHg.
juxtaglomerular apparatus is made up of
macula dense (specialised part of the DCT ) juxtaglomerular cells (produce renin ) mesengial cells
RAAS system
when blood volume falls
juxtaglomerlar cells secrete renin into blood stream
renin converts angiotensin I
ACE from lungs converts angiotensin I to II
ANG II causes sytemic vasoconstriction . increasing BP . Acts on the adrenal glad to produce aldosterone
what is atrial natriuretic peptide ANP
hormone released from the atria when blood volume is high . the increased venous return stretches the walls of the atria and releases ANP
causes dilation of the afferent arterioles and constriction of efferent , thus increasing GFR.
there is decreased reabsorption of sodium in the tubules
where is the majority of bicarbonate absorbed
PCT
characteristics of the thin descending loop
permeable to water but impermeable to sodium and other salts
characteristics of the thick ascending loop
actively pumps out sodium and chlorine but is impermeable to water
what is the osmolarity of the loop
The osmolarity of the loop and the surrounding interstitial renal space increases deeper into the medulla. Therefore, the deeper medullary parts of the kidneys are saltier. The base of the loop has an osmolarity of 1200 mOsm/L • Countercurrent
what is an overview of the counter current multiplication
- Sodium and chloride are pumped out of the thick ascending limb and into the interstitial fluid.
- This pumping action raises the osmotic concentration in the interstitial fluid around the thin descending limb.
- This results in an osmotic flow of water out of the thin descending limb and into the peritubular fluid. This loss of water increases the solute concentration in the thin descending limb.
- The arrival of the highly concentrated solution in the thick ascending limb speeds up the transport of sodium and chloride ions into the interstitial fluid of the medulla.
what does a NK2CL co transport do?
located on the apical membrane of the thick ascending limb . it transports 2 chloride ions , 1 sodium ion and one potassium ion by active transport .
the potassium can be recycled as it passively moves back down the conc gradient to the tubular lumen. the positive charge created by the potassium drives other ions to pass through the intracellular gaps.
this is targeted by loop diuretics like furosemide
how much of the primary filtrate reaches the DCT
15-20%
what is an ENaC
epithelial sodium channel is unique protein that sits within the apical membrane of the principal cell and has affinity for sodium . sodium moves through the ENaC alone . the entry of sodium from the lumen creates a lumen negative voltage which stimulates the secretion of potassium ions into the lumen via apical channel
things to look out for in urinalysis
frothy urine - protein present concentrated urine - dehydration fishy smell - infection sweat smell - ketones (DKA) blood - visible haematuria and or non visible
what are the different types of calculi?
calcium oxalate (60%) calcium phosphate (15%) uric acid (10%)
symptoms of renal stones
continuous dull ache in loins
symptoms of ureteric stones
cause classic renal colic due to increase in peristalsis in ureters in response to passage of small stone - pain usually radiated from loin to groin