Renal Physiology - Physiology

Regulation of fluid and electrolyte balance Regulation of plasma osmolarity Removal of metabolic wastes, toxins, drugs Endocrine functions (Renin & Erythropoietin) Metabolism Ensuring long-term acid-base balance

Cortical (superficial, located in cortex) - 80% Juxtamedullary (deep) - 20%

Comprised of Glomerulus and Glomerular (Bowman's) capsule

Consist of Capsular outer layer, visceral layer (podocytes), Bowman's space (separates two layers)

Fenestrated endothelium of glomerular capillaries, Basement membrane (negatively charged), and foot processes of podocytes (w/ filtration slits)

*No macromolecules, ONLY H2O, glucose, AAs, nitrogenous wasters, solutes smaller than plasma proteins pass (NO blood cells pass)

specialized for filtration

afferent arteriole --> glomerulus --> efferent arteriole

Low-pressure capillaries adapted for absorption of H2O and solutes; cling to adjacent renal tubules in cortex

Long (thin-walled) vessels parallel to long nephron loops of juxtamedullary nephrons

one per nephron Has three cell populations:

• Macula densa

• Granular cells

• Extraglomerular mesangial cells

Epithelial cells of DCT (near renal corpuscle) Function as chemoreceptors

Granules contain Renin Function as mechanoreceptors (sense blood press. in afferent arteriole)

B/w afferent & efferent arterioles May pass signals b/w macula densa & granular cells

Volume of plasma that is filtered across the glomerular per unit time

• The amt of filtrate kidneys produce each minute (average: 125 mL/min)

• Hydrostatic pressure (forces fluids & solutes thru filtration membrane)

• Oncotic pressure

Hydrostatic pressure in glomerular capillaries (HP (GC)) = glomerular blood pressure (55 mm Hg)

1. Hydrostatic pressure capsular space (HP (BS)) - 15 mmHg

2. Colloid oncotic pressure in capillaries (OP (GC)) - 30 mmHg

Sum of forces, pressure responsible for filtrate formation Main factor controlling glomerular filtration rate

NFP = (HPgc - HPbs) - (onocGC - onocBS) NFP = outward pressures - inward pressures NFP = (55 - 15) - (30 - 0) = 40 - 30 = 10 mm Hg (onocBS is negligible)

1. NFP

2. Total surface area available for filtration

3. Filtration membrane permeability

Three renal processes: Tubular absorption Tubular secretion Glomerular filtration

Cx = Ux * V/ Px

Filtered, but not Reabsorbed or Secreted

Filtered and Reasbored Ex: Na+, Cl-, HCO3-, phosphate, urea, glucose, and amino acids

Filtered and Secreted Ex: para-aminohippuric acid (PAH), creatinine, urea, NH4+, and morphine

Filtered, Reabsorbed and Secreted Ex: H+ and HCO3-

RBF - (1 - HCT)

Normal adult male: RBF = ~1L/min, HCT = ~40% Ex: Renal Handling of PAH (effective RPF)

Decrease RPF Decrease HP (Glomerular Cap) --> Decrease GFR

Decrease RPF Increase HP (Glomerular Cap) --> Increase GFR

1. Autoregulation (local level) intrinsic

2. Hormonal regulation (by kidneys)

3. Autonomic regulation (sympathetic division)

Two types:

1. Myogenic mechanism

2. Tubuloglomerular feedback mechanism

interaction of filtrate flow in descending/ascending limbs of nephron loops of juxtamedullary nephrons --> creates gradient

blood flow in descending/ascending limbs of vasa recta --> maintains gradient

Permeable to water, impermeable to solutes

Impermeable to water

Concentration gradient created in peritubular fluid of medulla

• Na+, K+, 2 Cl- moves out of ascending limb (via Na+-K+/2Cl- transporter) into interstital fluid and then water diffuses out of descending limb --> raising osmolality of intersititial fluid (to max 1200 mL/min)

• Highly permeable to water and solutes

a. Descending limb: water out, NaCl in --> at bottom of loop reaches 1200

b. Ascending limb: water in, NaCl out --> ends @ 325 (slightly higher than 300 start)

Cortical and outer medullary collecting ducts: ADH increases water permeability but NOT urea permeability --> water is absorbed but urea remains --> urea increase

Inner medullary collecting ducts: ADH increases water permeability & facilitated diffusion of urea (UT1) --> helps maintain gradient

Prevents excessive water loss in the urine and increases water absorption

*Targets kidney's collecting ducts

Determines rate of Na+ reabsorption and K+ loss in kidneys

• secreted in response to rising K+ or falling Na+

Released by atrial cells in heart due to stretch (inc BP)

• Effects: Decreases in blood pressure and volume a. Decreased ADH, renin and aldosterone production b. Inc excretion of Na+ and H2O c. Promotes vasodilation directly and dec of angiotensin II

arterial pH > 7.45

arterial pH < 7.35

Hyperventilation (Increase in CO2, slow breathing) Diarrhea (loss of HCO3-) Cell and protein metabolism Ingestion of acid containing food

Hyperventilation (decrease in CO2) Vomiting Urinary acid excretion

pH = Kidney / Lung = [HCO3-] / P(CO2)

Bicarbonate ions are excreted --> H+ ions retained by kidney tubules

Bicarbonate ions are reabsorbed --> H+ ions are secreted

Indicated by: LOW pH HIGH P(CO2) (= cause of acidosis) and bicarbonate levels (compensation)

Kidneys reabsorb more bicarbonate --> create new bicarbonate and secrete more H+

Indicated by: HIGH pH LOW P(CO2) Decreasing HCO3- levels

1. Excretion of buffered H+

2. Excretion of NH4+ (glutamine)