test 8 part 3

Question 1

Regulation – Tubular Reabsorption

Answer 1

 Glomerulotubular balance
 Peritubular Capillary & interstitial forces
 Arterial blood pressure
 Hormonal control
 Sympathetic nervous effect (minimal changes in reabs)
 Reabsorption of some solutes can be controlled independently

Question 2

Glomerulotubular Balance

Answer 2

 Allows an increase in reabsorption rate when there is an increase in tubular load (increased tubular inflow)
 If GFR went from 125 mls/minute to 150 mls/minute the rate of reabsorption in proximal tubule would go from 81 mls/minute [65% of GFR] to 97.5 mls/minute [65% of GFR]
 Works to maintain sodium and volume homeostasis

Question 3

Relationship of hydrostatic and oncotic pressures

Answer 3

 IN (oncotic capillary 32 + Pif 6 = 38) – OUT (Pc 13 + oncotic if 15 = 28) = 38-
28 = 10 mmHg IN (bulk flow)

Question 4

Relationship of hydrostatic and oncotic pressures AND filtration coefficient

Answer 4

 Normal rate of reabsorption 124 mls/minute
 Reabsorption rate / net force
 124 mls/min / 10 mmHg = 12.4 mls/min/mmHg

Question 5

Factors Affecting Peritubular Capillary Reabsorption (Peritubular hydrostatic pressure (PHP))

Answer 5

[increase PHP -> decreases reabsorption Reabsorption]

Question 6

An increase in arterial P does what to reabsorption

Answer 6

 increase AP -> increase PHP -> decrease reabsorption

Question 7

an increase in Resistance of afferent & efferent arteriole does what to reabsorption

Answer 7

 increase resistance -> decrease PHP -> increase reabsorption

Question 8

Factors Affecting Peritubular Capillary Reabsorption (Peritubular oncotic pressure (POP))

Answer 8

[increase POP -> increase Reabsorption]

Question 9

an increase in Plasma protein concentration does what to reabsorption

Answer 9

 increase plasma protein concentration -> increase plasma oncotic pressure -> increase POP -> increase reabsorption

Question 10

an increase in Filtration fraction (GFR/RPF) does what to reabsorption

Answer 10

 increase filtration fraction ->increase protein concentration (more fluid is actually filtered) -> increase POP -> increase reabsorption

Question 11

A decrease in capillary reabsorption produces

Answer 11

• increase in interstitial solute AND interstitial water
• increase in interstitial hydrostatic pressure AND a decrease in interstitial oncotic pressure
• in net movement (i.e. reabsorption) of solute & water from renal tubules to renal interstitial
  spaces

Question 12

Backflow of water and solute

Answer 12

 Under normal reabsorptive conditions there is always backflow of water & solute from interstitial spaces to tubular lumen (tight junctions not very tight especially in proximal tubule)

Question 13

An increase in Reabsorption Coefficient (RC) does what to reabsorption

Answer 13

• increases reabsorption

- Coefficient remains constant under most physiologic conditions. Will be affected by renal disease.

Question 14

Increasing capillary surface area does what to reabsorption

Answer 14

 incease surface area -> increase RC -> increase reabsorption

Question 15

Increasing capillary permeability does what to reabsorption

Answer 15

 incease permeability -> increase RC -> increase reabsorption

Question 16

Even though autoregulation works to keep GFR and RBF constant as pressure changes (75 mmHg to 160 mmHg), there is a small increase in GFR which results in an increase in urine output. WHY????

Answer 16

 As arterial pressure increases there is a small decrease in the amount of sodium & water reabsorbed
 Small increase in peritubular capillary hydrostatic pressure with subsequent increase in renal interstitial hydrostatic pressure and increase backflow of solute and water
 As arterial pressure increased angiotensin II release is decreased
 Less stimulation of sodium reabsorption by angiotensin II
 Less stimulation of aldosterone production which means less stimulation of sodium reabsorption

Question 17

Hormonal Control

Answer 17

 Kidneys must be able to respond to changes in intake of specific substances without changing output of the other substances
 Hormone secretion provides the control specificity needed to maintain normal body fluid volumes and solute concentrations

Question 18

Aldosterone SITE OF ACTION and EFFECTS

Answer 18

• Collecting tubule and duct
• increase NaCl, H2O reabsorption
• increase K+ secretion

Question 19

Angiotensin II SITE OF ACTION and EFFECTS

Answer 19

• Proximal tubule; Thick ascending loop of Henle / distal tubule; Collecting duct
• increase NaCl, H2O reabsorption
• increase K+ secretion

Question 20

Antidiuretic hormone SITE OF ACTION and EFFECTS

Answer 20

• Distal tubule; Collecting tubule and duct

- increase H2O reabsorption

Question 21

Atrial natriuretic peptide SITE OF ACTION and EFFECTS

Answer 21

• Distal tubule; Collecting tubule and duct

- decrease NaCl reabsorption

Question 22

Parathyroid hormone SITE OF ACTION and EFFECTS

Answer 22

• Proximal tubule; Thick ascending loop of Henle; Distal tubule
• decreases PO4— reabsorption
• increases Ca++ reabsorption

Question 23

Aldosterone

Answer 23

 Secreted by zona glomerulosa cell in adrenal cortex
 Regulate sodium reabsorption and potassium secretion
 Very important regulator of [potassium]
 Principal site of action is principal cells of cortical collecting tubule
 Stimulates increased Na-K ATPase activity (basolateral locations)
 Increases permeability of luminal side membrane to sodium

Question 24

Increased release of aldosterone stimulated by

Answer 24

 Increased extracellular potassium concentration

 Increased angiotensin II levels

Question 25

Excess Aldosterone

Answer 25

- adrenal tumors (Conn’s syndrome)

Question 26

Absence of Aldosterone

Answer 26

- adrenal malfunction or destruction (Addison’s disease)

Question 27

Angiotensin II

Answer 27

 Most powerful sodium-retaining hormone |  Increased production caused by low blood pressure and/or low ECF volume

Question 28

Action of Angiotensin II

Answer 28

 Stimulates aldosterone secretion (increase sodium reabsorption)  Constricts efferent arterioles (increase sodium and water reabsorption)  Helps ensure that normal excretion rates of metabolic wastes are maintained  Direct stimulation of sodium reabsorption in proximal tubules, loop of Henle, distal tubules, and collecting tubules  Stimulate increased Na-K ATPase activity of tubular epithelial cells (basolateral membrane)  Stimulate Na-H exchange in proximal tubule (luminal membrane)  Stimulate Na-Bicarb co-transport (basolateral membrane)

Question 29

Antidiuretic Hormone (Vasopressin)

Answer 29

- Made in the hypothalamus  Two types of magnocellular (large) neurons produce ADH  Once produced ADH moves down the neurons to their tips which are located in the posterior pituitary - Released from neurons in posterior pituitary  Increased osmolarity results in an increase in the number of impulses traveling down the neurons  Increased number of impulses stimulates release of ADH from storage vesicles located in the nerve endings

Question 30

What does Antidiuretic Hormone (Vasopressin) do?

Answer 30

- Controls water permeability of distal tubule, collecting tubule, and collecting duct

Question 31

A decrease in ADH concentration results in

Answer 31

- decrease water permeability so water is not reabsorbed which results in increase urine volume and decrease [solute] = large volumes of dilute urine  Absence of ADH leads diabetes insipidus

Question 32

How does Antidiuretic Hormone (Vasopressin) work?

Answer 32

- Stimulates formation of water channels across luminal membrane  ADH Binds with specific V2 receptors located on basolateral membrane -converts ATP to cyclic AMP -cAMP interacts with protein kinases and causes the aquaporins-2 to move to the luminal side of the cell -aquaporins decrease membrane permeability to water within that protein - Chronic increases in ADH will stimulate an increase in formation of aquaporin-2 molecules -basolateral aquaporins (AQP-3 and AQP-4) are not involved in this interaction

Question 33

Decrease [ADH]

Answer 33

- results in movement of the aquaporin-2 molecules back into the cytoplasm which reduces the number of water channels and decrease water permeability

Question 34

Atrial Natriuretic Peptide

Answer 34

 Secreted by cardiac atrial cells when atria distended by plasma volume expansion  Important response to help prevent sodium and water retention during heart failure

Question 35

Atrial Natriuretic Peptide action

Answer 35

 Direct inhibition of sodium & water reabsorption (especially collecting ducts) -> increases excretion  Inhibits renin secretion (thus inhibits angiotensin II formation) -> increases excretion

Question 36

Parathyroid Hormone

Answer 36

 Most important hormone for regulating calcium  Increases calcium reabsorption (distal tubules)  Inhibits phosphate reabsorption (proximal tubule)  Increases magnesium reabsorption (loop of Henle)

Question 37

Sympathetic Nervous System

Answer 37

 Severe stimulation results in constriction of renal arterioles which -> GFR  Low levels of stimulation activate alpha-receptors on renal tubular epithelial cells (proximal tubule, thick ascending limb of loop of Henle, maybe distal tubule)  Receptor activation stimulates sodium reabsorption which decrease sodium and water excretion  Stimulates release of renin (angiotensin II) which adds to increase in tubular reabsorption of sodium

Question 38

Renal Clearance

Answer 38

- Volume of plasma that is completely cleared (i.e. all of specified solute) by kidneys per unit time - The volume of plasma needed to provide the amount of solute excreted each minute

Question 39

Renal Clearance equation

Answer 39

𝐶𝑧 × 𝑃𝑧 = 𝑈𝑧 × 𝑽 OR Cs = Us x V / Ps  Cs is clearance of solute (mls/minute)  Us is urine concentration of solute (mg/ml)  V is urine flow (mls/minute)  Ps is plasma concentration of solute (mg/ml)

Question 40

What is used to measure the GFR

Answer 40

 Inulin clearance  Freely filtered and neither reabsorbed or secreted SO Filtered = Excreted  Creatinine usually used clinically although small amount is secreted so amount excreted exceeds amount filtered 𝑈s × 𝑉 = 𝐺𝐹𝑅 × 𝑃s

Question 41

Inulin Clearance

Answer 41

 Not digested by enzymes in digestive tract  Not naturally present in the body so usually has to be infused GFR = Uinulin x V / Pinulin

Question 42

Estimation of Renal Plasma Flow

Answer 42

- If a substance is completely cleared then clearance rate should equal the renal plasma flow  PAH clearance provides reasonable estimation of renal plasma flow (90% cleared)  Actual renal plasma flow can be calculated by dividing the PAH clearance rate by the PAH extraction rate Renal Plasma Flow ≈ PAH Clearance / 0.9

Question 43

If equal to inulin clearance

Answer 43

 Substance only filtered, not reabsorbed, not secreted

Question 44

If less than inulin clearance

Answer 44

 Substance must be reabsorbed

Question 45

If greater than inulin clearance

Answer 45

 Substance must be secreted