01: Normal Kidney Structure & Function Flashcards
Adult kidney size
10-12cm
Functions of kindeys
- Waste disposal (dz: waste accumulation, uremia)
- Regulate water/mineral balance (dz: vol overload, hyperkalemia, hyperphosphatemia)
- Regulate acid/base balance (dz: acidosis)
- Synthesize erythropoeitin (dz: anemia)
- Vitamin D3 1-hydroxylation (dz: hypocalcemia, metabolic bone dz)
- Insulin metabolism (dz: hypoglycemia)
Major kidney compartments
- Glomerulus (affected by immune-mediated dz)
- Tubules (affected by ischemic or toxic dz)
- Interstitium (affected by inflammatory dz)
- Blood vessels (affected by HTN or vasculitis)
Cellular components of glomerulus
- Glomerular endothelial cell
- Mesangial cell
- Viseral epithelial cell (podocyte)
- Parietal epithelial cell
Glomerular Filtration
GFR = K x A x (ΔP - Δπ)
Glom cap. hydrostatic pressure = 40-50 mmHg
Glom cap. oncotic pressure = 15-25 mmHg
Bowman’s space hydrostatic pressure = 10-15 mmHg
EFP = 10-15 mmHg
Rete mirable
Peritubular interstitial capillaries in renal cortex allowing for easy reabsorption into capillary bed
Mesangial cells
Support the ramifying glomerular capillary network.
Glomerular capillary is not completely encircled by basement membrane, but is open at the mesangial interface.
Contracts in response to angiotensin II, vasopressin, norepinephrine, PAF, PGF2α.
Relaxes in response to ANP, dopamine, PGE2.
Glomerular basement membrane (GBM)
- Lamina rara externa
- Lamina densa
- Lamina rara interna
- 320nm in thickness
- Type IV collagen in all three layers
- Laminin in all three layers
- Heparin sulfate in rara layers
- Rara are negative charge sites
- GBM restricts proteins based on size and charge (negatively charged proteins more restricted)
Filtration slit diaphragm
- Zipper-like configuration
- Lateral pores highly size restrictive (about the size of albumin; 40 angstroms)
- Nephrin molecules extend into center of slit from adjacent foot processes to form the slit diaphragm; overlapping regions form central bar with lateral pores
Proximal tubule
- Bulk transport of water and solutes (isotonic)
- Reabsorbs ~60% of filtered NaCl and water, and ~90% of filtered bicarbonate
- Reabsorbs nutrients such as glucose and amino acids
- Secretes a number of organic anions
Loop of Henle
- Descending thin limb highly water permeable
- Ascending limb impermeable to water
- Thick asecnding limb (TALH) reabsorbs 15-25% of filtered NaCl; important for generation of medullary gradient; site of action of loop diuretics (e.g., furosemide)
Distal convoluted tubule
- Reabsorbs ~5% of filtered NaCl load
- Site of macula densa which senses NaCl; located in proximity to juxtaglomerular apparatus, responsible for renin release
- DCT is the site of action of thiazide diuretics
Role of juxtaglomerular apparatus in BP control
- **JG cells **activated by a) ↓[NaCl], b) ↓perfusion pressure in afferent arteriole, or c) sympathetic stimulation.
- JG cells secrete renin, which converts **angiotensinogen **to angiotensin I
- Angiotensin I converted into angiotensin II
- Angiotensin II causes a) vasoconstriction, and b) ↑aldosterone –> Na+ retention
- ↑Blood pressure, which has a feedback loop onto JG cells
Cortical collecting duct
- Determines final composition of urine, based on homeostatic needs
- Comprised of principle cells (PC) and intercalated cells (IC)
- PCs can reabsorb last 2-5% of NaCl; site of action of aldosterone, vasopressin, atrial natriuretic peptide (ANP); site of action of K-sparing diuretics
- ICs mediate acid secretion
Glomerular Filtration Rate (GFR)
- Measure of kidney function
- Volume of plasma filtered by kidney per unit of time (mL/min or Liters/24hrs)
- nl ~ 90-150 mL/min (200 L/day)
- Estimated by measuring serum creatinine (byproduct of muscle metabolism generated at constant rate and freely filtered without reabsorption)
- Serum creatinine levels are inversely related to kidney function
GFR = (U[creat] x Volume24hrs)/P[creat]
