Acid Base Balance And Osmolarity

Question 1

What is the reference range for plasma H+ ions?

Answer 1

35.5 - 44.5 nmol/L

Question 2

How does alkalosis affect calcium?

Answer 2

Lowers free Ca2+
Causes Ca2+ ions to come out of solution
Increased neuronal excitability
Paraesthesia and tetany

Question 3

How does acidosis affect proteins?

Answer 3

Decreased pH due to increased H+ ions
Disturbs/denatures enzymes
Affects muscle contractility, glycolysis and hepatic function

Question 4

About which pH do we consider acidosis severe and then life threatening?

Answer 4

Severe < 7.1

Life threatening < 7.0

Question 5

What number is the constant pK in the Henderson-Hesselbach equation?

Answer 5

6.1

Question 6

What is the normal physiological pH?

Answer 6

7.4

Question 7

How would respiratory acidosis occur?

Answer 7

Hypoventilation
Leads to hypercapnia (increased CO2 in plasma)
This decreases plasma pH
Causing acidosis

Question 8

How does respiratory alkalosis occur?

Answer 8

Hyperventilation causes hypocapnia in the plasma
Fall in CO2 causes increase in pH
Alkalosis

Question 9

How is respiratory acidosis compensated for?

Answer 9

Kidneys increase the level of bicarbonate

Question 10

How is respiratory alkalosis compensated for?

Answer 10

Kidneys decrease the concentration of bicarbonate

Question 11

What is metabolic acidosis?

Answer 11

A fall in pH due to a fall in conc of bicarbonate

Can be compensated for by increased ventilation

Question 12

What is metabolic alkalosis?

Answer 12

A rise in plasma bicarbonate which can only be partially compensated by decreasing ventilation

Question 13

What is a common cause of metabolic alkalosis?

Answer 13

Repeated vomiting

Question 14

How do the kidneys increase bicarbonate levels?

Answer 14

Excrete less bicarbonate in the urine

Make more bicarbonate

Question 15

What do the kidneys use to make bicarbonate?

Answer 15

Kidneys have a high conc of CO2 due to their high metabolic rate - react this with water to form bicarbonate
Also can make bicarbonate from amino acids
(This means ammonium will be present in the urine)

Question 16

Where does the majority of bicarbonate reabsorption take place?

Answer 16

PCT

80%

Question 17

Describe the mechanism for reabsorption of bicarbonate

Answer 17

Na/K/ATPase on basolateral membrane creates the Na+ gradient
Na+ enters cell in exchange for H+ (NHE on apical membrane)
H+ reacts with the bicarbonate to form CO2 and water which can diffuse into the cell
In the cell it is reconverted into HCO3- and H+
HCO3- passes out of the cell via the Na-HCO3 symporter on the basolateral membrane

Question 18

Which amino acid is used to produce bicarbonate?

Answer 18

Glutamine

Question 19

What is the minimum urine pH?

Answer 19

4.5

Question 20

Should there be HCO3- in the urine normally?

Answer 20

No

Question 21

How is acid in the urine excreted?

Answer 21

Buffered by phosphate (titratable)

Reacted with NH3 = NH4+

Question 22

What is the normal H+ excretion per day?

Answer 22

50 - 100 mmol/day

Question 23

Why do we excrete acid in the urine?

Answer 23

To maintain the concentration of bicarbonate in the plasma

Question 24

How does a decreased pH affect the kidneys in order to correct itself??

Answer 24

Enhances activity of Na+/H+ exchanger
Enhances ammonium production in PCT
Enhances activity of H+/ATPase in DCT
Increased capacity to export HCO3- into ECF

Question 25

What is the anion gap?

Answer 25

Difference between the cations (Na+/K+) and the anions (HCO3-/Cl-) (Normal = 10 - 15 mmol/L as there are unaccounted anions)

Question 26

Why does the anion gap increase?

Answer 26

``` Anions from (paired to) metabolic acids replace HCO3- (Other than Cl-) ```

Question 27

Do all forms of metabolic acidosis create an anion gap?

Answer 27

No

Question 28

How do we treat metabolic alkalosis?

Answer 28

Give them an infusion of bicarbonate (Sounds backwards) Causes a rapid excretion of bicarbonate so their levels will reduce

Question 29

Why is there a problem if there is an alkalosis and a volume depletion?

Answer 29

Capacity to lose bicarbonate is reduced because of high rate of Na+ recovery HCO3- will be reabsorbed with the Na+

Question 30

How does hypokalaemia affect the kidneys?

Answer 30

K+ moves out of tubule cells in exchange for H+ This makes the cells more acidic Favours H+ excretion and HCO3- reabsorption Leading to alkalosis

Question 31

How does hyperkalaemia affect the kidneys?

Answer 31

K+ moves into tubule cells in exchange for H+ Makes the cells more alkaline Favours H+ reabsorption and HCO3- excretion Can lead to acidosis

Question 32

What is a normal cell osmolarity?

Answer 32

~ 300 mOsm/kg

Question 33

What is the osmolarity of urine in a normally hydrated person?

Answer 33

500 - 700 mOsm/kg

Question 34

Where are the osmoreceptors located and why is this a good location?

Answer 34

In the OVLT of the hypothalamus (Organum vasculosum of the lamina terminalis) Has fenestrated endothelium therefore in direct correct with the plasma to sense osmolarity

Question 35

What are the 2 responses to an increase in osmolarity?

Answer 35

Thirst - behavioural | ADH - increased renal water reabsorption

Question 36

Why are cells of the supraoptic nucleus close to the OVLT?

Answer 36

Baroreceptors are found here | Therefore changes in BP can cause the release of ADH

Question 37

When facing a massive fluid loss, what is the body's priority?

Answer 37

Saving volume to prevent circulatory collapse | Sacrifice the osmolarity in order to stay alive

Question 38

Describe the delay in correction regarding thirst

Answer 38

Drinking water takes time to correct the osmolarity | However our thirst sensation goes away before it is corrected to prevent us over-drinking

Question 39

What is a regulatory appetite?

Answer 39

Having cravings for something that we have a deficiency in | The body needs it

Question 40

Where is ADH produced and secreted?

Answer 40

``` Produced = hypothalamus Secreted = posterior pituitary gland ```

Question 41

How does ADH work?

Answer 41

Increases the number of AQP2 channels in the apical membrane of cells in the collecting duct of the nephron Increases water uptake

Question 42

Describe central diabetes insipidus

Answer 42

ADH levels are too low for the osmolarity Due to damage in hypothalamus/pituitary gland Large quantity of urine produced Decreased blood volume

Question 43

Describe nephrogenic diabetes insipidus

Answer 43

Insensitivity of the kidney to ADH (Even though ADH levels are appropriate) Produce large volumes of dilute urine

Question 44

How do we treat diabetes insipidus?

Answer 44

ADH injections or a nasal spray

Question 45

What is SIADH?

Answer 45

Syndrome of inappropriate antidiuretic hormone secretion Excessive release of ADH Dilutional hyponatraemia occurs (Increased water reabsorption, conc of Na+ decreases)

Question 46

Briefly describe the counter current mechanism of the LOH

Answer 46

Juxtamedullary nephrons have a long loop of Henle to establish a vertical osmotic gradient Vasa recta help to preserve that gradient due to a blood flow in the opposite direction

Question 47

What is the most crucial part of the LOH for generating the gradient?

Answer 47

Thick ascending limb Pumps Na+ into medulla via NKCC2 Is impermeable to water so water cannot follow

Question 48

Describe what happens to urea in the nephron

Answer 48

Some reabsorbed in PCT Some moves into the interstitium via AQPs with water to increase osmolarity of medulla (increase water reabsorption) Diffuses back into filtrate when conc urea higher in interstitium Some excreted in urine

Question 49

How does the vasa recta help to maintain the medullary concentration gradient?

Answer 49

Taking up all the water that leaves of the loop of henle (Otherwise the water would decrease the conc in the medulla) Flow is in the opposite direction therefore high osmotic blood is near to low osmotic filtrate so that the water moves more easily into the vasa recta