M1 Renal Physiology Flashcards
Very general 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
Regulation of acid-base balance
Secretion, metabolism, and excretion of hormones
Gluconeogenesis
`What is the central physiologic role of the kidneys?
control the volume and composition of the body fluids
What is total body water?
60% of total body weight
How much to total body water is ICF and ECF?
2/3 is ICF
1/3 is ECF
What is the barrier between the ICF and ECF?
cell membrane
What are the major ions of the ECF?
Na+ and Cl- and HCO3-
What are the major ions of the ICF?
K+ and PO4- and protein
What is the concentration of osmotically active particles in total solution and is expressed in terms of mOsm/liter of water?
Osmolarity
What is the average osmolarity of the ECF and ICF?
osmolarity of the ECF and ICF averages 280-300 mOsm/liter - identical in nearly all body fluids
What is expressed in terms of mOsm/kg of solvent?
Osmolality
In relatively dilute solutions, such as those found in the body, how do osmolality and osmolarity relate to each other?
osmolality ≈ osmolarity
What are the 4 kidney processes that determine composition of the urine?
- filtration
- reabsorption
- secretion
- excretion
What is the glomerular filtrate?
ultrafiltrate of plasma containing the same concentration of most salts and organic substances found in plasma
What physical forces cause filtration by glomerular capillaries?
starling forces:
glomerular hydrostatic pressure
glomerular colloid osmotic pressure
bowman’s capsule pressure
What is the equation for GFR?
GFR = Kf x [ (PGC +πBS) - (πGC + PBS)]
Kf = Ultrafiltration Coefficient- the product of the hydraulic permeability (Lp)and the surface area (SA) of the glomerular capillary membranes PGC= Glomerular Capillary Hydrostatic Pressure πGC= Glomerular Capillary Oncotic Pressure PBS= Bowman’s Space Hydrostatic Pressure πBS= Bowman's Space Oncotic Pressure
Over what range of BP can autoregulation help regulate kidney blood flow best?
80-160 mmHg
What are the two mechanisms of autoregulation?
myogenic and tubuloglomerular feedback
What is the myogenic mechanism?
Intrinsic property of blood vessels. Stretch of vascular smooth muscle, as experienced during an increase in arterial pressure, elicits contraction which elevates vascular resistance and maintain blood flow (and GFR) constant
What is tubuloglomerular feedback?
Autoregulatory mechanism unique to the kidney. In response to an elevation of perfusion pressure, increased fluid is filtered leading to increased delivery of NaCl to the macula densa. This increased delivery elicits an increase in vascular resistance.
What hormones can decrease GFR?
Norepinephrine, Epinephrine, Endothelin—decreases GFR
Angiotensin II—no change or decreases GFR
What hormones can increase GFR?
Endothelial derived nitric oxide and Prostaglandins
The filtration barrier consists of what three layers?
capillary wall, basement membrane, and podocytes
What are the characteristics of capillary wall for filtration?
capillary wall is 700 Å fenestrated, freely permeable to small molecules and negatively charged glycoproteins in surface
What are the characteristics of basement membrane for filtration?
porous matrix of extracellular proteins including type IV collagen, laminin, fibronectin and other neg. charged proteins
What are the characteristics of podocytes for filtration?
processes and slit pores-40x140 Å long finger-like processes with neg. charged proteins
Two general traits of the filtration barrier are what?
size-selective: more permeable to small molecules
charge-selective: more permeable to positively charged molecules (proteins generally are negatively charged)
What are the two proteins that make up the slit diaphragm between podocytes?
nephrin (N) and P-cadherin (P-C)
What happens in the THIN Descending loop of Henle?
reabsorption of water secondary to cortical medullary osmotic gradient
What happens in the THIN Ascending loop of Henle?
Impermeable to water.
Passive reabsorption of sodium, dilution of tubular fluid.
Permeable to urea, urea is secreted.
What happens in the THICK ascending loop of Henle?
Reabsorbs 25% of filtered Na+ by the Na/K/Cl transporter
Lumen positive potential drives paracellular reabsorption of sodium, potassium, magnesium and calcium.
Impermeable to water, dilutes tubular fluid
What kind of diuretics act on the Na/K/Cl transporter in the THICK ascending loop of Henle?
loop diuretics
- furosemide
- ethacrynic acid
- bumetanide
What happens in the early distal tubule?
Reabsorbs Na+, Cl-, Ca++ and Mg++
Not permeable to water.
Thiazide-sensitive segment act on Na/Cl symporter.
What happens in the principal cells of the late distal tubule and cortical collecting duct?
Reabsorbs Na+, secretes K+ regulated by Aldosterone.
Water permeability regulated by ADH.
Reabsorption of sodium and secretion of potassium blocked by K-sparing diuretics
What type of sodium channels are on the apical membrane of principal cells?
ENaC (epithelial sodium channel)
What happens in the medullary collecting duct?
Reabsorbs Na+.
ADH-stimulated water reabsorption.
Urea reabsorption
How does aldosterone affect tubular reabsorption?
- Acts in principal cells of late distal tubule and collecting duct
- increases Na+ reabsorption, increases K+ secretion
How does angiotensin II affect tubular reabsorption?
- acts primarily in the proximal tubule
- increases Na+ and water reabsorption, increases H+ secretion
How does antidiuretic hormone (ADH aka vasopressin) affect tubular reabsorption?
- acts in principal cells of late distal tubule and collecting duct, inner medullary collecting duct
- increases water reabsorption
How does atrial natriuretic peptide (ANP or ANF) affect tubular reabsorption?
- acts in distal tubule and collecting duct
- decreases Na+ reabsorption
How does parathyroid hormone (PTH) affect tubular reabsorption?
- in proximal tubule decreases PO4— reabsorption
- in thick ascending loop of Henle and distal tubule increases Ca++ reabsorption
