urinary system 2/3 Flashcards
3 basic processes of a nephron?
glomerular filtration
tubular reabsorption
tubular secretion
what is glomerular filtration?
the formation of a protein-free filtrate (ultrafiltrate) of plasma across the glomerular filtration membrane
how many times a day is the body’s entire extracellular fluid volume filtered in an adult?
about 12 times
what is the filtration membrane formed by and what does it do?
glomerular capillaries and podocytes
Permits filtration of water and small solutes.
Prevents filtration of most plasma proteins, blood cells and platelets.
what is net filtration pressure?
the total pressures that drives glomerular filtration
both hydrostatic and osmotic pressures
define the 3 pressures in net filtration pressure
-Blood hydrostatic pressure (55mmHg)
the main force that “pushes” water and solutes through the filtration membrane (promotes filtration).
- Capsular hydrostatic pressure (15 mmHg) exerted against the filtration membrane by fluid in the capsular space (opposes filtration).
- Blood osmotic (oncotic) pressure (30 mmHg) the pressure of plasma proteins “pulling” on water (opposes filtration).
what is the glomerular filtration rate?
the amount of filtrate formed in all the renal corpuscles of both kidneys each minute.
describe the 3 mechanisms that regulate GFR (glomerular filtration rate)
Renal autoregulation occurs when the kidneys themselves regulate GFR.
Neural regulation occurs when the ANS regulates renal blood flow and GFR.
Hormonal regulation involves angiotensin II and atrial natriuretic peptide (ANP).
what is tubular reabsorption?
the process of returning important substances (filtered water, organic solutes such as glucose and ions such as Na+ and Cl-) from the filtrate back into the renal interstitium, then into the renal blood vessels, and ultimately back into the body.
3 steps in the reabsorption process?
- Solutes reabsorbed by active and passive processes
- Water follows by osmosis
- Small proteins by pinocytosis
what is tubular secretion?
the transfer of materials (ions such as H+, NH4+; creatinine and drugs for example, penicillin) from the blood and tubule cells into glomerular filtrate.
name 2 routes of reabsorption
- paracellular (passive, between cells)
2. transcellular (active transport through cells, uses sodium/potassium pump)
review primary and secondary active transport
Primary active transport
-Na+/K+ pump uses energy from ATP to pump ions across membrane
Secondary active transport
- energy stored in an ions electromagnetic gradient drives a substance across membrane
- symporters/antiporters
2 types of osmosis and where they occur?
Obligatory water reabsorption: occurs when water is “obliged” to follow the solutes (Na+, Cl-, and glucose) being reabsorbed (‘water follows sodium’). It occurs in the proximal convoluted tubule and the descending limb of the loop of Henle.
Facultative water reabsorption: adapted to specific needs. It occurs in the collecting duct under the control of antidiuretic hormone.
what is reabsorbed by the proximal convoluted tube (PCT)?
100% of most filtered organic solutes such as glucose and amino acids;
80–90% of the filtered HCO3-
65% of the filtered water, Na+ and K+
50% of the filtered Cl- and filtered urea;
A variable amount of the filtered Ca+, Mg2+ and HPO42-
how does reabsorption of bicarbonates occur?
through facilitated diffusion through the basolateral membrane. For every H+ secreted into the tubular fluid, one filtered bicarbonate eventually returns to the blood.
what is reabsorbed by the Loop of Henle?
15% of the filtered water 20–30% of the filtered Na+, and K+ 35% of the filtered Cl-, 10–20% of the filtered HCO3- a variable amount of the filtered Ca+2, and Mg+2
2 pathways of reabsorption in the Loop of Henle?
- at the apical membrane
- Na+-K+-2Cl- symporters
- leakage channels
- paracellular route - at the basal membrane
- active transport of Na+
- leakage channels
does water reabsorption occur in the ascending or descending limb of the loop of henle?
descending (~15%)
what reabsorption occurs in the distal convoluted tubule (DCT)?
10–15% of the filtered water
5% of the filtered Na+
5% of the filtered Cl-
Reabsorption of Na+ and Cl- is done by Na+ and Cl- (symporters or antiporters)?
symporters
How is Ca2+ reabsorbed in the DCT?
Parathyroid hormone (PTH) stimulates reabsorption depending on the body’s needs
how is water reabsorbed in the DCT?
DCT is not very permeable to water
No/little water reabsorption
Five hormones which affect the tubular reabsorption and secretion in the renal tubules?
Angiotensin II Aldosterone Antidiuretic hormone Atrial natriuretic peptide Parathyroid hormone
