Renal physiology Flashcards
Kidney functions
Excretion of metabolic waste products and foreign chemicals
Regulation of water and electrolyte balances
regulation of body fluid osmolality and electrolyte concentrations
regulation of arterial pressure, acid base balance
secretion, metabolism, and excretion of hormones
gluconeogenesis
distribution of body fluids ICF and ECF
Intracellular fluid (ICF)= 2/3 total body water (40% of body weight) Extracellular fluid (ECF)= 1/3 total body water (20% of body weight)
The barrier between ICF and ECF is the cell membrane
Distribution goverened by osmotic forces (osmolarity, osmotic, osmotic pressure, osmosis, tonicity, osmotic equilibrium)
Osmolarity
the concentration of osmotically active particles in total solution and is expressed in tterms of mOsm/liter of water
in body–> 280-300 mOsm/liter. The osmolarity is nearly identical in all major compartments of body fluids
Osmolality is mOsm/kg of water, in dilute solutions (osmolality=osmolarity) like in body
Glomerular filtrate
Ultra filtrate of plasma formed by the net effect of starling forces to move (filter) fluid out of the glomerular capillaries and into bowmans space
The filtered fluid contains the same concentration of most salts and organic substances found in plasma
Most large proteins, substances bound to protein, and cellular element are excluded from the glomerular filtrate
The glomerular filtration rate is a bulk filtration process. The kidneys filter the entire plasma volume every half hour
Mechanism of GFR and RBFlow autoregulation
myogenic mechanism: intrinsic property of blood vessels, stretch of vascular smooth muscle (increased arterial pressure) elicits contraction which elevates vasscular resistance and maintains blood flow and GFR constant
Tubuloglomerular feedback- autoregulatory mechanism unique to the kidney. In response to an elevation of perfusion pressure, increaseed fluid is filtered leading to increased delivery of NaCl to the macula densa–> increase in vascular resistance
hormonal and autacoid control of GFR
NE: decreases GFR EP: decreases GFR Endothelin: decreases GFR Angiotenisn 2 : no change or decreases GFR Endothelial NO: increases GFR Prostaglandins: increase GFR
Filtration barrier consists of 3 layers
Capillary wall withh (700 A fenestrations), freely permeable to small molecules, negative glycoproteins surface
Basement membrane: porous matrix of EC proteins including type4 collagen, laminin, fibronectin and neg proteins
Podocytes: long finger like processes with neg charged proteins
Filtration barrier is size selective and charge selective (more permeable to positively charged molecules)
Proximal tubule
REAB about 65% NA, CL , Bicarb, K, 100% of all glucose and Amino acids
Secrete organic acids, bases, and hydrogen ions
Diuretic : CA inhibitors (acetazolamide), inhibits H secretion, and HCO3 REAB
Thin descending loop of henle
REAB of water secondary to cortical- medullary osmotic gradient
Thin ascending loop of henle
Impermeable to water
Passive REAB of sodium, dilution of tubular fluid
Permeable to urea, urea is secreted
Thick ascending loop of henle
REABs 25% of Filtered Na via Na/K/2Cl transporter
Lumen positive potential drives paracellular REAB of Na K Mg and Ca
Impermeable to water, dilutes tubular fluid
Site of loop diuretics (furosemide)
Early distal tubule
REAB Na Cl Ca and Mg
Impermeable to water
Site of Thiazides
Na Cl symporter
Late distal tubule and cortical collecting duct principle cells
REAB Na, Secretes K
REgulated by Aldosterone
Water permeable via ADH
REAB of Na and secretion of K blocked by K sparing diuretics (eplerenone and spironolactone)
NA REAB inhibited by Na channel blockers via ENac (amiloride and triamtererne)
Medullary collecting duct
REAB Na
ADH stimulated water REAB
Urea REAB in medullary
Aldosterone
Acts in principle cells of late distal tubule and collecting duct, increase Na REAB increases K secretion
