Kidney Structure + Function Flashcards
What is the functional unit of the kidney?
The nephron.
How many nephrons are there in each kidney?
Around 1 million.
What are the two main types of nephrons?
Cortical nephrons (80–85%) and juxtamedullary nephrons (15–20%).
What is the glomerulus?
A tuft of capillaries where blood is filtered under pressure.
Where is the glomerulus located?
In the renal cortex, within the Bowman’s capsule.
What kind of filtration occurs in the glomerulus?
Ultrafiltration – movement of water and small solutes into Bowman’s space.
What molecules are typically filtered through the glomerulus?
Water, glucose, salts, urea, amino acids.
What structures prevent large molecules like proteins from being filtered?
The glomerular basement membrane and podocyte filtration slits.
What pressure drives glomerular filtration?
Glomerular hydrostatic pressure (~60 mmHg).
What is the glomerular filtration rate (GFR)?
The volume of filtrate formed per minute (~125 mL/min in adults).
Where is the PCT located?
In the renal cortex, right after the Bowman’s capsule.
What are the main functions of the PCT?
Reabsorption of nutrients, water, and electrolytes; secretion of H+ and organic acids.
What percentage of filtered substances is reabsorbed in the PCT?
About 65–70%.
What substances are actively reabsorbed in the PCT?
Glucose, amino acids, Na+, Cl−.
What helps increase surface area in the PCT for reabsorption?
Microvilli (forming a brush border).
How is glucose reabsorbed in the PCT?
Via sodium-glucose co-transporters (SGLTs).
Is water reabsorption in the PCT dependent on hormones?
No, it is passive and follows solute reabsorption (isosmotic).
What is the main function of the loop of Henle?
To concentrate urine by creating a salt gradient in the medulla.
What are the two limbs of the loop of Henle?
Descending limb and ascending limb.
What is the descending limb permeable to?
Water (but not salts).
What is the ascending limb permeable to?
Salts (Na+, K+, Cl−), but impermeable to water.
How does the loop of Henle concentrate urine?
Through the countercurrent multiplier system.
Where is the loop of Henle longer, in cortical or juxtamedullary nephrons?
Juxtamedullary nephrons – important for urine concentration.
Where is the DCT located?
In the renal cortex, after the loop of Henle.
What is reabsorbed in the DCT?
Sodium, chloride, calcium.
Which hormone regulates calcium reabsorption in the DCT?
Parathyroid hormone (PTH).
hich hormone acts on the DCT to increase sodium reabsorption?
Aldosterone.
Does the DCT participate in acid-base balance?
Yes – secretes H+ and reabsorbs bicarbonate.
Is water reabsorption in the DCT hormone-dependent?
Yes – depends on antidiuretic hormone (ADH) in the late DCT/collecting duct.
What comes after the DCT in the nephron?
The collecting duct.
Which hormone increases water reabsorption in the collecting duct?
Antidiuretic hormone (ADH/vasopressin).
What is the juxtaglomerular apparatus (JGA)?
A structure that regulates blood pressure and GFR.
What cells release renin?
Juxtaglomerular cells in the afferent arteriole.
What stimulates renin release?
Low blood pressure, sympathetic stimulation, or low Na+ in the DCT (detected by macula densa).
What is the glomerulus?
The glomerulus is a network of capillaries located at the beginning of a nephron in the kidney, responsible for filtering blood to form urine.
What process occurs in the glomerulus?
Ultrafiltration, where blood is filtered under pressure into the Bowman’s capsule.
What structures comprise the filtration barrier in the glomerulus?
The filtration barrier consists of three components: the endothelial cells of glomerular capillaries, the glomerular basement membrane, and podocytes of the Bowman’s capsule.
What is the function of the podocytes in the glomerulus?
Podocytes are specialized cells in the Bowman’s capsule that wrap around capillaries of the glomerulus, forming filtration slits that prevent large molecules from passing into the urine.
What is the function of the fenestrae in the endothelial cells of the glomerular capillaries?
The fenestrae are pores about 70nm in diameter that prevent the filtration of blood cells while allowing other components to pass through
How does the glycocalyx of the endothelial cells contribute to the filtration process?
The glycocalyx consists of negatively charged glycosaminoglycans that hinder the diffusion of negatively charged molecules by repelling them due to like charges.
What are the three layers of the glomerular basement membrane?
The lamina rara interna (inner thin layer), the lamina densa (thick layer), and the lamina rara externa (outer dense layer).
What role do heparan sulfate proteoglycans play in the glomerular basement membrane?
They help restrict the movement of negatively charged molecules across the basement membrane.
How do podocyte foot processes contribute to the filtration process?
The foot processes interdigitate to form filtration slits, which are bridged by a thin diaphragm with small pores that prevent large molecules, such as proteins, from crossing.
What is the main job of the proximal convoluted tubule (PCT)?
It reabsorbs most of the water, salts, glucose, and amino acids from the urine.
How much of the filtered substances does the PCT reabsorb?
About 65% of water and salts, and 100% of glucose and amino acids.
What kind of cells line the PCT?
Cuboidal cells with tiny finger-like projections called microvilli (brush border).
Why does the PCT have microvilli?
To increase surface area for better reabsorption.
How does glucose get reabsorbed in the PCT?
It’s pulled in together with sodium through special transport proteins.
What pump helps move sodium out of the PCT cells?
The sodium-potassium pump.
What is the primary function of the Loop of Henle in the nephron?
The primary function is to aid in the reabsorption of sodium and water, contributing to the maintenance of plasma volume, blood pressure, and urine production.
What percentage of filtered sodium is absorbed by the Loop of Henle?
Approximately 25% of filtered sodium is absorbed by the Loop of Henle.
What is the primary site of sodium reabsorption in the Loop of Henle?
The primary site of sodium reabsorption is the thick ascending limb (TAL).
How does water move in the thin descending limb of the Loop of Henle?
Water moves passively through aquaporin-1 (AQP1) channels in the thin descending limb.
How is sodium reabsorbed in the thin ascending limb?
Sodium is reabsorbed passively through epithelial sodium (eNaC) channels, and chloride is reabsorbed via chloride (Cl-) channels.
What drives sodium reabsorption in the thick ascending limb (TAL)?
Sodium reabsorption in the TAL is driven by the Na+/K+ ATPase on the basolateral membrane, which pumps 3 Na+ ions out and 2 K+ ions into the cell, creating an electrochemical gradient.
What is the function of the NKCC2 transporter in the TAL?
The NKCC2 transporter moves one Na+ ion, one K+ ion, and two Cl- ions across the apical membrane in the TAL.
How are potassium ions handled in the TAL?
Potassium ions are transported back into the tubule by renal outer medullary potassium (ROMK) channels to prevent toxic buildup within the cell.
How is the early DCT different from the late DCT?
The early DCT is mainly involved in the absorption of sodium, chloride, and calcium and is impermeable to water.
The late DCT and CD involve sodium reabsorption, potassium secretion, and acid-base control.
What is the role of the macula densa in the early DCT?
The macula densa is sensory epithelium involved in tubuloglomerular feedback, which regulates glomerular filtration rate (GFR) and blood flow within the nephron.
What is the mechanism of sodium absorption in the early DCT?
Sodium is absorbed via the NCC symporter (sodium-chloride cotransporter), which uses the sodium gradient created by the Na+/K+-ATPase transporter.
How do thiazide diuretics affect the early DCT?
Thiazide diuretics inhibit the NCC symporter, reducing sodium reabsorption and increasing sodium excretion.
What role does parathyroid hormone (PTH) play in calcium absorption in the early DCT?
PTH increases calcium reabsorption by promoting the insertion of more calcium channels in the cells of the early DCT.
What are the two main cell types in the late DCT and CD?
The two main cell types are principal cells and intercalated cells.
What is the function of principal cells in the late DCT and CD?
Principal cells are responsible for sodium reabsorption and potassium secretion.
Sodium is reabsorbed through ENaC channels, and potassium is secreted through a potassium uniporter.
How do intercalated cells contribute to acid-base balance?
Type A intercalated cells secrete H+ into the lumen and reabsorb HCO3- to correct acidosis, while type B intercalated cells secrete HCO3- and reabsorb H+ to correct alkalosis.
What transporters are involved in hydrogen ion secretion by type A intercalated cells?
Type A intercalated cells use hydrogen-ATPase and H+/K+-ATPase transporters to secrete H+ into the lumen.
How do type A intercalated cells prevent H+ reabsorption after secretion?
Hydrogen ions react with phosphate or ammonia in the lumen, forming charged compounds (NH4+ and H2PO4–), which cannot be reabsorbed.
What role do K+/Cl– symporters play in intercalated cells?
K+/Cl– symporters prevent the accumulation of chloride and potassium ions within the intercalated cells by allowing leakage back into the extracellular fluid.
What is the main role of the collecting duct?
The main role of the collecting duct is water reabsorption, which is regulated by anti-diuretic hormone (ADH) and aquaporins.
How does ADH regulate water reabsorption in the collecting duct?
ADH binds to V2 receptors on tubular cells, increasing the number of aquaporin-2 channels in the apical membrane, which increases the permeability to water.
What is the effect of increasing aquaporin-2 channels in the collecting duct?
Increasing aquaporin-2 channels allows more water to be reabsorbed from the filtrate, resulting in more concentrated urine.
How does ADH affect urea reabsorption in the medullary collecting duct?
ADH promotes urea reabsorption, which increases osmolarity in the interstitium and helps reabsorb more water.
What is urea recycling, and how does it assist in water reabsorption?
Urea recycling involves the movement of urea from the interstitium back into the thick ascending limb, where it acts as an osmole, enhancing water reabsorption in the nephron.
