Renal 1 Flashcards
(22 cards)
What are the main functions of the kidney?
Filter metabolic waste, regulate blood pH, control body fluid volume and ion concentration, excrete drugs, produce erythropoietin for RBC production, and maintain bone health through calcium/phosphate balance.
Describe the organs in the renal system
Kidneys
Ureters
Bladder
Urethra
Describe the blood supply path through the kidney.
Renal artery → afferent arteriole → glomerular capillaries → efferent arteriole → peritubular capillaries/vasa recta → renal venules → renal vein.
Describe the structure of the kidney
The cortex and the medulla
What are cortical and juxtamedullary nephrons?
Cortical: short loop of Henle, bowmans capusule in cortex.
Juxtamedullary: long loop of Henle extending bowmans into medulla, important for urine concentration, associated with vasa recta. Has peritubular capillaries
Describe the different structures in the nephron
1) Afferent artery
2) Glomerulas capillary
3)Bowmans capsule
4)Efferent artery
5)Proximal convoluted tubule
6)Descending limb
7)Loop of Henle
8)Ascending limb
9) Distal convoluted tubule
10) Collecting duct
What drives glomerular filtration?
Net hydrostatic pressure: blood hydrostatic pressure (55 mmHg) minus capsular hydrostatic pressure and oncotic pressure (~45 mmHg combined).
What are the 2 pathways to regulate GFR
Intrinsic Pathways: Myogenic response and tubuloglomerular feedback.
Extrinsic Pathways: Neural and hormonal responses (e.g., RAAS, ANP).
Describe the intrinsic myogenic response in GFR regulation.
Increased BP stretches afferent arteriole → activates Na+ channels → depolarisation → Ca2+ influx → smooth muscle contraction → vasoconstriction → protects glomerulus.
Explain tubuloglomerular feedback (TGF).
High NaCl sensed by macula densa → NKCC2-mediated uptake → ATP release → converted to adenosine → binds A1 receptor → Ca2+ influx in mesangial cells → afferent arteriole constriction → reduces GFR.
What is the effect of caffeine on TGF?
Caffeine antagonises A1 adenosine receptors → prevents afferent arteriole constriction → increases GFR → promotes diuresis.
Describe the extrinsic neural regulation of GFR.
Low BP activates sympathetic nervous system → norepinephrine → constricts afferent/efferent arterioles → reduces filtration to conserve fluid and maintain perfusion.
Describe the RAAS pathway.
Low perfusion/GFR due to bleeding or dehydration → renin from JG cells → converts angiotensinogen to angiotensin I → ACE converts to angiotensin II → vasoconstriction + aldosterone from adrenal cortex → increased Na+/water reabsorption due to it affecting the sodium receptors of the epithelial cells in the collecting duct.
Describe the ANP pathway in GFR regulation.
High BP → atrial stretch → ANP release inhibits renin → vasodilation of afferent arterioles + mesangial relaxation → increased GFR → more Na+/water excretion.
What does the cockroft gault equation show and why is it important
It indicates creatinine clearance and if creatine is high can indicate acute kidney injury
What are the 3 stages of urine formation?
- Glomerular filtration
, 2. Tubular reabsorption, - Tubular secretion.
Reabsorption mechanisms in the proximal tubule.
1)Sodium (Na⁺) enters tubular cells from urine using:
Sodium-glucose co-transporters (SGLT1/SGLT2)
Sodium-phosphate (NaPi) cotransporters
Sodium-anion cotransporters (e.g. NaS1)
2)Glucose and phosphate enter the cells with sodium.
3)Water (H₂O) follows sodium via osmosis.
4)Sodium is pumped into the blood via Na⁺/K⁺ ATPase.
5)Glucose exits into blood via GLUT1/GLUT2 transporters.
6)Anions (Cl⁻, SO₄²⁻, etc.) follow passively due to electrical gradients.
7)Excess sodium or anions that don’t get reabsorbed are excreted.
Reabsorption in the Loop of Henle.
Same process as in the proximal tubule but with an extra transporter the NKCC2 transporter which reabsorbs more sodium, potassium and chloride
Sodium (Na⁺), potassium (K⁺), and chloride (Cl⁻) enter cells via NKCC2 transporter using active transport (thick ascending limb).
Water is not reabsorbed in the thick ascending limb — it is impermeable to water. (this makes the conc gradients elsewhere)
Sodium is pumped into the blood using Na⁺/K⁺ ATPase.
Potassium is recycled back into urine via ROMK channels to maintain NKCC2 function.
Chloride diffuses into the blood passively or via Cl⁻ channels.
Reabsorption in the distal convoluted tubule (DCT).
NCC (Na+-Cl- cotransporter), Na+/K+ ATPase, H+ secretion, K+ secretion, Cl- passive diffusion.
Reabsorption in the collecting duct.
Aldosterone stimulates ENaC channels to reabsorb sodium from urine.
Sodium is pumped into the blood via Na⁺/K⁺ ATPase.
Water reabsorption occurs through aquaporins (AQP2, AQP3, AQP4), which are regulated by antidiuretic hormone (ADH). More ADH more aquaporins
Potassium is secreted into urine in exchange for sodium.
Mechanism of aldosterone action.
Binds intracellular Mineralocorticoids Receptors in urothelial cells → translocates to nucleus → increases transcription of ENaC and Na+/K+ ATPase → increases Na+ and water reabsorption.
Ends with increased salt and water retention and increased potassium excretion
Now describe the whole process in one go (I’m being mean I know)
- Glomerulus – Filtration
Blood enters the glomerulus via the afferent arteriole.
Filtration occurs through fenestrated capillaries and the glomerular basement membrane.
Small molecules (water, electrolytes, glucose, amino acids, urea, some drugs) pass into Bowman’s capsule to form glomerular filtrate.
Large molecules and cells (e.g. proteins, RBCs, lipids, protein-bound drugs) do not pass the barrier and remain in the blood.
Filtrate enters the proximal tubule as tubular fluid.
- Proximal Tubule – Reabsorption & Secretion
Reabsorption:
Na⁺ is reabsorbed via Na⁺/K⁺ ATPase (on basolateral side), creating a gradient.
Water follows Na⁺ by osmosis (via aquaporins and paracellular transport).
Glucose, amino acids, phosphate, sulphate, and bicarbonate are co-transported with Na⁺ (SGLT, NaPi, NaS1).
~65% of Na⁺ and water are reabsorbed here.
Small filtered proteins are taken up by pinocytosis, degraded in lysosomes, and amino acids returned to blood.
Secretion:
Organic anions and cations, protein-bound drugs, and metabolites (e.g. penicillin, uric acid, creatinine) are secreted into the tubule via specific transporters.
H⁺ and NH₄⁺ are also secreted based on acid-base status.
- Loop of Henle – Water & Electrolyte Reabsorption
Descending Limb:
Permeable to water, but not to solutes.
Water is reabsorbed into the hypertonic medullary interstitium (created by Na⁺ from ascending limb).
Ascending Limb (Thick segment):
Impermeable to water.
Na⁺, K⁺, and Cl⁻ are actively reabsorbed via the NKCC2 cotransporter.
Creates medullary concentration gradient for urine concentration.
- Distal Convoluted Tubule – Selective Reabsorption
Na⁺ and Cl⁻ reabsorbed via NCC (Na⁺-Cl⁻ cotransporter).
Na⁺/K⁺ exchange:
Principal cells reabsorb Na⁺ via ENaC.
K⁺ is secreted into urine.
Na⁺/H⁺ exchange:
Intercalated cells secrete H⁺ to regulate blood pH.
This site is influenced by aldosterone, which increases ENaC and Na⁺/K⁺ ATPase expression.
- Collecting Duct – Hormonal Regulation
Na⁺ reabsorption continues via ENaC under aldosterone control.
Water reabsorption occurs under the influence of ADH:
ADH stimulates insertion of aquaporin-2 (AQP2) channels into the apical membrane.
Water exits into blood via AQP3/4 (basolateral).
In the absence of ADH, water is not reabsorbed → dilute urine.
H⁺ and K⁺ secretion are fine-tuned here.
