CASE 7

Question 1

reabsorption involves two types of transport

Answer 1

1. epithelial transport

2. paracellular transport

Question 2

epithelial transport

Answer 2

• substances cross the apical and basolateral membranes of the tubule epithelial cell to reach the interstitial fluid.
• solutes moving down their gradient use open leak channels or facilitated diffusion carriers to cross the cell membrane
• molecules that need to be pushed against their gradient are moved by either primary or indirect, secondary active transport

Question 3

paracellular transport

Answer 3

• substances pass through the cell-cell junction between two adjacent cells.

Question 4

active reabsorption of Na+

Answer 4

• primary driving force for most renal reabsorption
• filtrate entering the proximal tubule is similar in ion composition to plasma, with higher Na+ concentration than is found in cells
• Na+ can enter tubules by moving down the gradient
• NHE, Na+ H+ exchanger plays a major role in Na+ reabsorption

Question 5

sodium linked secondary active transport

Answer 5

• responsible for reabsorption of many substances, like glucose, amino acids, ions

Question 6

urea

Answer 6

• passively reabsorbed

- can move across the epithelium by diffusion if there is a urea concentration gradient

Question 7

concentrations and secretion into the tubule

Answer 7

• Proximal convoluted tubule: secrete uric acids, organic acids
• Loop of Henle: no secretion takes place here
• End of ascending limb: secretion of H+
• distal convoluted tubule: secrete K+ and H+
• end of collecting duct: secretion of H+

Question 8

RAAS, Renin-Angiotensin-Aldosterone System

Answer 8

• control of blood pressure
• juxtaglomerular cell is key cell, they are in the blood vessels of kidney, release renin
• renin helps raising blood pressure
• system shuts down when flow through convoluted distal tubule goes up; it inhibits renin release by granular cells

Question 9

Triggers for release of renin by juxtaglomerular cells

Answer 9

1. low blood pressure is sensed by juxtaglomerular cells and baroreceptors
2. juxtaglomerular cells are triggered by sympathetic nerve cells during a period of stress as it triggers B1 adrenergic receptors, which stimulate renin production
3. Macula densa cells, sense sodium. With low blood pressure not a lot of salt is being reabsorbed. Sense low NaCl concentration –> trigger the juxtaglomerular cells to release renin.

Question 10

Angiotensinogen

Answer 10

• plays a role in RAAS
• produced by liver
• moves around the body in a nonactive state –> when it meets renin –> chops off a big chunk of angiotensinogen –> becomes angiotensin 1.

Question 11

Angiotensin 1

Answer 11

• moves through blood vessels

- endothelial cells in lungs are able to convert angiotensin 1 into angiotensin 2

Question 12

angiotensin 2

Answer 12

• very active hormone
• increases sympathetic activity, vasoconstriction and increased heart rate
• this all converts via ACE, angiotensin converting enzyme

Question 13

Places angiotensin 2 goes to

Answer 13

1. smooth muscle cells. Causes blood vessels to constrict, which causes increased resistance
2. it causes kidney cells to hold on to more water, which increases blood volume
3. pituitary gland –> secretes ADH (vasopressin) (oppose effects are caused by ANP) –> increases resistance of blood vessels and causes kidney to hold on to more water
4. adrenal gland is triggered to produce aldosterone, which tends to promote Na+ and water reabsorption in distal convoluted tubule and lower plasma K+ concentration –> increasing blood pressure

Question 14

dehydration effect on heart rate and respiration

Answer 14

• leads to high blood concentration and low blood pH –> increased respiration rate
• high blood concentration means high viscosity, which increases resistance and increases Mean Arterial Pressure
• dehydration triggers homeostatic responses

Question 15

severe dehydration: compensatory mechanisms are aimed at restoring normal blood pressure, ECF volume and osmolarity by:

Answer 15

1. conserving fluid to prevent additonal loss
2. triggering cardiovascular reflexes to increase blood pressure
3. stimulating thirst so that normal fluid volume and osmolarity can be restored
   - zie pagina 92

Question 16

Decreased volume is sensed by the atrial volume receptors

Answer 16

1. the baroreceptors signal the cardiovascular control center to raise blood pressure
2. decreased peripheral blood pressure directly decreases GFR
3. paracrine feedback causes the granular cells to release renin
4. granular cells respond to decreased blood pressure by releasing renin
5. decreased blood pressure, decreased blood volume, increased osmolarity and increased ang 2 production stimulate ADH

Question 17

The baroreceptors signal the cardiovascular control center to raise blood pressure

Answer 17

a. heart rate goes up as control of AV node shifts
b. the force of ventricular contraction increases under sympathetic stimulation.
c. sympathetic input activates the vasomotor center and causes arteriolar vasoconstriction, increasing peripheral resistance
d. sympathetic vasoconstriction of afferent arterioles in kidneys decreases GFR, helping conserve fluid
e. increased sympathetic activity at the granular cells of kidneys increases renin secretion, which leads to increased reabsorption of water

Question 18

decreased peripheral blood pressure directly decreases GFR

Answer 18

• a lower GFR conserves ECF volume by filtering less fluid into the nephron

Question 19

paracrine feedback causes the granular cells to release renin

Answer 19

• lower GFR decreases fluid flow past the macula densa, which triggers renin release

Question 20

granular cells respond to decreased blood pressure by releasing renin

Answer 20

• the combination of decreased blood pressure, increased sympathetic input onto granular cells, and signals from the macula densa stimulates renin release and ensures increased production of antiotensin 2

Question 21

decreased blood pressure, decreased blood volume, increased osmolarity and increased angiotensin 2 production all stimulate ADH and the thirst centers of hypothalamus

Answer 21

-

Question 22

Control pathways ensure that all four main compensatory mechanisms are activated

Answer 22

1. cardiovascular responses
2. angiotensin 2
3. vasopressin
4. intake of water

Question 23

cardiovascular responses

Answer 23

• combine increased cardiac output and increased peripheral resistance to raise blood pressure

Question 24

angiotensin 2

Answer 24

• stimulation of thirst
• vasopressin release
• direct vasoconstriction
• reinforcement of cardiovascular control center output
• stimulated aldosterone release –> but high osmolarity inhibits aldosterone release

Question 25

vasopressin

Answer 25

- increases water permeability of renal collecting ducts --> water reabsorption to conserve fluid

Question 26

intake of water

Answer 26

- drinking

Question 27

Net result of all four mechanisms

Answer 27

1. resoration of volume by water conservation and intake 2. maintenance of blood pressure through increased blood volume, increased cardiac output and vasoconstriction 3. restoration of normal osmolarity by decreased Na+ reabsorption an increased water reabsorption and intake

Question 28

histamine when dehydrated

Answer 28

- affects respiratory system - histamine causes bronchoconstriction and increased mucus build up --> respiratory rate needs to be increase in order to maintain oxygen levels

Question 29

difference osmolarity and osmolality

Answer 29

osmolality is the number of osmoles of a solute in a kg of solvent. Osmolarity is the number of osmoles of solute in a L of solutin

Question 30

two types of countercurrent mechanisms determine urine concentration and volume

Answer 30

1. countercurrent multiplier: interaction between flow of filtrate through the ascending and descending limbs 2. countercurrent exchanger: the flow of blood through the ascending and descending portions of the vasa recta

Question 31

medullary osmotic gradient

Answer 31

- allows the kidneys to vary urine concentration | - the countercurrent mechanisms maintain an osmotic gradient extending from the cortex through the depths of the medulla

Question 32

countercurrent multiplier

Answer 32

- depends on actively transporting solutes out of the ascending limb. - the more NaCl the ascending limb extrudes, the more water diffuses out of the descending limb and the saltier the filtrate to raise the osmolality of the medullary intersitial fluid even further --> establishes the positive feedback cycle that produces the high osmolality of the fluids in the descending limb and interstitial fluid

Question 33

countercurrent exchanger

Answer 33

- vasa recta acts as countrecurrent exchanger - does not create medullary gradient, but preserves it by preventing rapid removal of salt from the medullary interstial space and by removing reabsorbed water --> blood leaving and reentering the cortex via the vasa recta had almost the same solute concentration

Question 34

Urea recycling and the medullary osmotic gradient: urea is used by the kidney to help form the medullary osmotic gradient

Answer 34

1. urea enters the filtrate by facilitated diffusion in the ascending thin limb of the nephron loop 2. as the filtrate moves on, the cortical collecting duct usually reabsorbs water,leaving urea behind 3. when filtrate reaches the portion of the collecting duct, urea, moves by facilitated diffusion out of the tubule into the interstitial fluid of the medulla.

Question 35

Renal clearance

Answer 35

- the volume of plasma completely cleared of a substance by kidneys per unit time. - higher renal clearance suggests the substance may be cleared alsmost completely - low value describes that a substance may not be eliminated at all - C = (UxV) / P C = clearance (ml/min) U = concentration substance in urine V = urine formation flow rate P = concentration substance plasma