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Physiology Si 11/9/15
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Tubular Structure and Membrane Transport
Which of these situations results in constriction of the vasculature?
High CO2 in systemic arterioles
High CO2 in elastic arteries
High O2 in pulmonary arterioles
High NO in systemic arterioles
What vessels exchange substances with the proximal and distal convoluted tubules?
How Filtrate is Regulated
Renal Tubule (PCT, DCT)
Returning things to the blood stream to remain in the body
Getting rid of things in the blood stream by putting them into the filtrate
Types of Nephrons
Reabsorption and secretion of water and solutes, fine adjustment of filtrate contents
Next to Medulla, loop of Henle dives deep into medulla
Concentration of urine
Blood flow of Cortical Nephron
…Renal Artery → Afferent Arteriole → Glomerular Capillaries → Efferent Arteriole → Peritubular Capillaries → Renal Vein…
Blood flow of Juxtaglomerular Nephron
…Renal Artery → Afferent Arteriole → Glomerular Capillaries → Efferent Arteriole → Vasa Recta → Renal Vein…
Types of cells in Nephron
Proximal Convoluted Tubule
Cuboidal Cells: good for reabsorption and secretion
MOST of reabsorption (70% of volume), some secretion
Descending loop of Henle (thin segment)
Simple Squamous: thin for water reabsorption
Ascending loop of Henle (thick segment)
Cuboidal to columnar: good for reabsorption of solutes
Distal Convoluted Tubule
Cuboidal: good for reabsorption and secretion
Hormone regulated (Aldosterone, ANP, Parathyroid Hormone)
faces blood vessels
Most of reabsorption happens here, methods?
Transport Through APICAL side of PCT cells
Other ions (Ca2+, Mg+, K+)
Na+/Amino Acid symport
Na+/K+ ATPase (primary active)
Ion channel (facilitated)
…Then enter bloodstream through paratubular capillaries to stay in the body
Transport through basolateral membrane (from inside cell)
Na+? _______________________________. Moving from ______ to ______.
K+? ________________________. Moving from ______ to ______.
Glucose, Amino Acids, Vitamins? _________________.
Specific amount of transporters available for solutes (transport max or Tmax)
Glucose in urine means…
Obligatory Water Reabsorption
Certain amount of water ALWAYS reabsorbed because of aquaporins in PCT, called ____________________________.
As solutes cross over into peritubular capillaries, creates osmotic gradient for water to follow
Hormonal control of Reabsorption
Functioning of the kidney to balance water and electrolytes in the body is influenced by humoral hormone concentrations
Hormones of interest:
Cells of collecting ducts
Secreted by the posterior pituitary gland
Anti-diuretic = less urine
Causes the kidneys to reabsorb more water from the filtrate
Cells of the collecting ducts:
Cells of collecting ducts receive ADH from blood
Causes them to insert aquaporins into apical membrane
This allows water to flow from filtrate into cells
Increase in water inside cells
Causing increase of water concentration in cells
Causing water to flow from cells into blood
Reabsorption of water creates more concentrated urine (darker color)
Cells of collecting ducts/DCT
Secreted by the adrenal cortex
Causes sodium Na+ absorption and K+ secretion
Cells of collecting ducts and distal convoluted tubule receive aldosterone
Causes insertion of luminal Na+ and K+ channels
Also insertion of Na+-K+ ATPases into basolateral membrane
Will overall decrease volume and concentration (more clear urine)
Water follows Na+; overall reabsorption
Atrial natriuretic peptide
Secreted by cardiac atrial cells in response to high blood pressure/volume
Opposite effect of aldosterone
Serves to reduce blood Na+ and H2O
Reduces number of Na+ channels on apical membrane
Just know it is secreted by parathyroid glands on back of thyroid in response to low blood Ca2+ levels
Increases Ca2+ reabsorption by increasing Ca2+ channels permeability
(increasing number of Ca2+ channels on membranes)
Opposite of reabsorption
Why doesn’t it just get there during glomerular filtration?
Low concentration in blood
Bound to blood proteins
Produce in the tubular cells
Examples of secreted substances:
Organic acids and bases
Maintenance of Blood Ph!
The kidneys are super important for regulating blood pH!
All of these are to increase blood pH:
Secrete H+ when there is too much CO2 in blood
Reabsorb HCO3- when there is not enough in blood
Create more HCO3- when there is not enough in blood
Occurs in PCT and Collecting Duct
Uses Na+/H+ exchanger on apical membrane
Increased levels of CO2 in peritubular capillaries increased CO2 in tubular cells CO2 + H2O combine using carbonic anhydrase enzyme to produce H+ + HCO3- H+ moves into filtrate via Na+/H+ exchanger and HCO3- moves into blood
Results in and increase in blood pH
Also to increase blood pH, PCT and collecting ducts will reabsorb priorly secreted HCO3-
HCO3- combines with secreted H+ to form H2CO3 H2CO3 uses carbonic anhydrase to form H2O + CO2 CO2 moves into tubular cells CO2 joins with H2O via carbonic anhydrase to form H2CO3 H2CO3 goes to H+ + HCO3- H+ moves back into filtrate via Na+/H+ exchanger and HCO3- moves into blood
Ultimately reabsorbs HCO3- to lower blood pH
Ammonium ion secretion
Used when blood too acidic, body wants to create “new” HCO3- molecules
Metabolize the amino acid glutamine to form 2 NH4+ molecules and 2 HCO3- molecules
2 NH4+ molecules secreted into filtrate
2 HCO3- molecules are absorbed into blood to decrease pH of blood
Without Sodium, what would be affected in reabsorption?
Osmotic reabsorption of water
Retaining water in the body
Vitamin C reabsorption
All of the above
In cases of extreme dehydration, you would expect to see increased ______ and decreased ______ in the blood of the patient.
ADH; Parathyroid hormone
More than one of the above is correct
B and C
e in water inside cells