(continuation) Urinary System - Urine Formation I: Glomerular Filtration Flashcards
the fluid in the capsular space
Glomerular filtrate
fluid from the proximal convoluted tubule through the distal convoluted tub
Tubular fluid
fluid that enters the collecting duct
Urine
a special case of the capillary fluid exchange process in which water and some solutes in the blood plasma pass from the capillaries of the glomerulus into the capsular space of the nephron
Glomerular filtration
three barriers through which fluid passes
Filtration membrane
70 to 90 nm filtration pores exclude blood cells
Fenestrated endothelium of glomerular capillaries
Proteoglycan gel, negative charge, excludes molecules greater than 8 nm
Basement membrane
wrap around the capillaries to form a barrier layer with 30 nm filtration slits
Podocyte cell extensions (pedicels)
presence of protein in urine
Proteinuria (albuminuria)
presence of blood in the urine
Hematuria
Blood hydrostatic pressure (BHP)
- Much higher in glomerular capillaries (60 mm Hg
compared to 10 to 15 in most other capillaries) - Because afferent arteriole is larger than efferent arteriole
- Larger inlet and smaller outlet
in capsular space, 18 mm Hg due to high filtration rate and continual accumulation of fluid in the capsule
Hydrostatic pressure
the amount of filtrate formed per minute by the two kidneys combined
Glomerular filtration rate (GFR)
GFR control is achieved by three homeostatic mechanisms:
- Renal autoregulation
- Sympathetic control
- Hormonal control
the ability of the nephrons to adjust their own blood flow and GFR without external (nervous or hormonal) control
Renal autoregulation
Two methods of autoregulation:
- myogenic mechanism
- tubuloglomerular feedback
based on the tendency of smooth muscle to contract when stretched
Myogenic mechanism
the feedback regulation of the GFR in a single nephron based on sensory information about the distal tubule fluid
Tubuloglomerular feedback
complex structure found at the very end of the nephron loop where it has just reentered the renal cortex
Juxtaglomerular apparatus
Three special kinds of cells occur in the juxtaglomerular apparatus
- Macula densa cells
- Juxtaglomerular (JG) cells
- Mesangial cells
Sympathetic nerve fibers richly innervate the renal
blood vessels
Sympathetic Control
Potent vasoconstrictor raising BP throughout the body
Angiotensin II
process of reclaiming water and solutes from the tubular fluid and returning them to the blood
Tubular reabsorption
Two routes of reabsorption:
- Transcellular route
- Paracellular route
water carries with it a variety of dissolved solutes
Solvent drag
Creates an osmotic and electrical gradient that drives the reabsorption of water and other solutes
Sodium reabsorption - the key to everything else
____________ follow the positive sodium ions by electrical attraction
Negative chloride ions
process in which renal tubule extracts chemicals from capillary blood and secretes them into tubular fluid
Tubular secretion
Secretion of hydrogen and bicarbonate ions help regulate pH of body fluids
Acid-base balance
Primary function of ________ is to generate a salinity gradient that enables the collecting duct to concentrate the urine and conserve water
Nephron loop
Two kinds of cells in the Distal Convoluted Tubule (DCT) and collecting duct:
Principal cells
Intercalated cells
the “salt-retaining hormone”
Aldosterone
secreted by atrial myocardium of the heart in response to high blood pressure
Atrial natriuretic peptide (ANP)
secreted by posterior lobe of the pituitary
Antidiuretic hormone (ADH)
secreted from parathyroid glands in response to calcium deficiency (hypocalcemia)
Parathyroid hormone (PTH)
Water diuresis–drinking large volumes of water will produce a large volume of hypotonic urine
hypotonic urine
capillary branching off efferent arteriole in medulla
Vasa recta
formed by blood flowing in opposite directions in adjacent parallel capillaries
Countercurrent system
Exchanges water for salt
Descending capillaries
Exchanges salt for water
Ascending capillaries
