Chapter 19 The Kidneys Flashcards
(28 cards)
The kidneys regulate
extracellular fluid volume, bp, and osmolarlarity
maintain ion balance, regulate pH, excrete wastes and foreign substances
participate in endocrine pathways
urinary system
composed of 2 kidneys, two ureters, a bladder, and a urethra
kidneys
have about 1 million microscopic nephrons
arranged into an outer cortex and an inner medulla
Renal blood flow
afferent arteriole - glomerulus - efferent arteriole - peritubular capillaries
vasa recta capillaries dip into the medulla
Fluid filters
from the glomerulus into the Bowmans capsule - proximal tubule - the loop of Henle - distal tubule - collecting duct - drains into the renal pelvis
Urine then flows through the ureter to the urinary bladder
filtration
the movement of fluid from plasma into Bowmans capsule
allows most components of plasma to enter the tubule
excludes blood cells and almost all plasma proteins
reabsorption
movement of filtered materials from tubule to blood
secretion
movement of selected molecules from the blood to tubule
average urine volume
1.5 L/day
osmolarity
varies between 50 - 1200 mOsM
solute excreted
= # filtered - # reabsorbed + # secreted
how much renal plasma flow filters into the tubule lumen
1/5
filtration fraction
percentage of total plasma volume that filters
podocytes
specialized cells in the bowman capsule epithelium
they wrap around the glomerular capillaries and create filtration slits
mesangial cells
support the glomerular capillaries
path of filtered solutes
glomerular capillary endothelium - a basement membrane - podocyte filtration slits - then reaches the lumen of Bowmans capsule
hydrostatic pressure in glomerular capillaries
averages 55 mm Hg, favoring filtration
opposing filtration = colloid osmotic pressure = 30 mm Hg
and hydrostatic capsule fluid pressure = 15 mm Hg
the net driving force is 10 mmHg, favoring filtration
can be altered by changing resistance in the afferent and efferent arterioles
glomerular filtration rate
(GFR) amount of fluid that filters in Bowman’s capsule per unit time.
Average GFR is 125 mL/min or 180 L / day
autoregulation of glomerular filtration
is accomplished by a myogenic response of vascular smooth muscle in response to pressure changes
and tubuloglomerular feedback
macula densa cells
when fluid flow through the distal tubule increases it sens a paracrine signal to the afferent arteriole, which constricts
reflex control of GFR
mediated through systemic signals such as hormones, and through the autonomic nervous system
reabsorption
most takes place in the proximal tubule
finely regulated reabsorption takes place in the more distal segments of the nephron
for passive reabsorption of urea and other solutes; active transport of Na+ and other solutes creates concentration gradients
most involves transepithelial transport; some solutes and water are reabsorbed by the paracellular pathway
na+ linked secondary active transport
absorbs glucose, amino acids, ions, and various organic metabolites
renal transport
is mediated by membrane proteins and exhibits saturation, specificity, and competition
