Kidney Flashcards
What does renal mean
Something related to the kidney
What are the main functions of the kidney
Maintain extracellular fluid composition and volume
Maintain mass balance/clearance
Filtration followed by reabsorption
Secretion of some waste product
Produces some hormones (erythropoietin)
what are the main components of a nephron
Renal corpuscle
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
Where is majjority of the volume reabsorbed?
70% almost immediately reabsorbed in the proximal convoluted tubule
Fine tunin in the remaining sections
Describe the general anatomy of the renal corpuscle
Has Bowman’s capsule surrounding the glomerulus.
The glomerular filter is formed of 3 layers; endothelium, glomerular basement membrane and podocytes
What is the glomerulus
It is like a ball of wool and a tangle of porous capillaries, whos function is to allow for material to leave the blood stream into the bowmans capsule
What is the bowmans capsule
Surrounds the glomerulus, and absorbs filtrate from glomerulus
What is the function of podocytes
They form a filtration barrier which is wrapped around glomerular capillaries to ensure large proteins dont leave the capillary
What goes through the renal corpuscle
Small molecules (<3 nm)
water, glucose, amino acids
urea, small ions like Na+, K+
What doesn’t go through the renal corpuscle?.
Large proteins
Blood cells (red and white)
What are some common tests to measure glomerular filtration
Inulin and Creatinine. These substances aren’t reabsorbed by the kidney. Thus, we see the concentration of the substance in urine x urine flow rate, divided by concentration of substance in blood, to give us to glomerular filtration rate. It shows how much has been absorbed into the kidney through the glomerulus
Function of the proximal convoluted tubule
It is lined with cells covered in microvilli, and is the main site of reabsorption of most solutes (glucose, Na+, amino acids, vitamins and bicarbonate) (70% of solutes reabsorbed). Also allows for reabsorption of water
Main part is seen in ability for reabsorption of glucose into the bloodstream
Active transport ensures maximum reabsorption of glucose
What is the loop of henle
It has a thin descending limb and a thick ascending limb. It assists in decreasing the water content of urine by reabsorbing water and electrolytes, thereby regulating concentration of urine
It is split into the descending and ascending limb
Explain the descending limb and its function
Descending limb is permeable to water but not to ions like Na+ and Cl-. As filtrate flows down the limb, water moves out of the tubule into interstitial fluid through osmosis. The movement of water concentrates the filtrate, increasing its solute concentration as it descends deeper.
Explain the ascending limb and its function
The ascending limb is impermeable to water. Instead it actively transports ions, particularly Na+ and Cl- ions into surrounding interstitial fluid. Active transport through specialised ion channels and co transporters.
Active transport creates concentration gradient in interstitial fluid, with higher concentrations of ions deeper in the medulla
This active transport is important as high difference in solute concentration will put walls under stress
Explain the interstitial osmolarity as we go down the loop of henle
As we go down the loop of henle, the interstitial osmolarity increases. This is because descending is permeable to water –> initial water in interstitial fluid increases, thus osmolarity is low, however as water keeps getting out, it reaches a point where water can’t go out anymore and due to active transport of ions out of the ascending limb, there is increased osmolarity but no water –> interstiail fluid decreases. Increased osmolarity going down the loop of henle
What is the role of the kidney in hormonal control
It produces aldosterone, which is in response to low blood pressure, ultimately increasing the retention of Na+ in the distal convoluted tubule and collecting duct
It also responds to the hormone Anti-diuretic hormone (ADH) which is produced by hypothallamus in response to high solute concentration in blood. This increases reabsoroption of water in nephron collecting duct by increasing insertion of aquaporins into collecting duct walls
What is the role of the distal convoluted tubule
Similar to proximal convoluted tubule but shorter with fewer microvilli. Excess K+ is actively secreted into nephron here, under control of aldosterone. Excess H+ secreted here to maintain pH. Mainly less permeable to water compared to proximal, and mainly regulates reabsorption of specific ions such as Na+, Ca2+, Cl- etc.
What is the function of collecting ducts?
Collects urine produced by nephrons and delivers it to the renal pelvis
Involved in water balance, as it is permeable to water. It reabsorbs water under influence of ADH. ADH increases permeability of collecting duct to water via aquaporins
How are solutes moved from nephrons
Nephrons are surrounded by capillaries. Substances leaving nephron are reabsorbed into bloodstream straight away due to capillaries surrounding the nephron
What is the renal threshold
Concentration of a substance in blood, above which the kidney removes it in the urine
What is the renal threshold of glucose
10mmols/L
What is the main composition of urine
95% water, 2.5% urea, Na+ largest component after urea, and urachrome
Describe the mechanism of reabsorption of glucose
Na+ is actively pumped out of the tubule, glucose is then co transported with Na+ via a transmembrane protein. This is active transport and ensures maximum reabsorption of glucose
