Exam 4 (Lecture 43) - Absorption of Electrolytes and Water

Question 1

What are electrolytes?

Answer 1

Positive or negative ions dissolved in solution.

Question 2

List the electrolytes.

Answer 2

Na+, Cl-, HCO3-, K+

Question 3

What is the term used to describe and increase or decrease for each electrolyte?

Answer 3

1) Sodium = hypo- and hypernatremia

2) Chloride = hypo- and hyperchloremia

3) Bicarbonate = Acidosis or Alkalosis (metabolic)

4) Potassium = hypo - and hyperkalemia

Question 4

What type of blood test would you order to test for electrolytes?

Answer 4

Chemistry panel

Question 5

Majority of GI disorders involve loss of _______ and __________.

Answer 5

Water; electrolytes

Question 6

Where are water and electrolytes absorbed? Where are they reabsorbed?

Answer 6

Absorbed = Small and large intestines

Reabsorbed = kidneys

Question 7

Why is absorption/reabsorption of water important?

Answer 7

To maintain normal blood volume and mean arterial pressure (blood pressure)

Question 8

Why is absorption/reabsorption of electrolytes important?

Answer 8

Vital for numerous physiological functions

Question 9

Describe the absorption pathway for nutrients, water, and electrolytes.

Answer 9

Lumen of small intestine > Brush border ( of simple columnar epithelial cell) > Enterocyte > Basolateral membrane (into the lateral space) > Venous side of blood capillary > Hepatic portal vein > Liver > Cd. VC

Question 10

Why is Na+ important?

Answer 10

1) Depolarization phase of action potential required for cardiac and skeletal muscle contraction

2) ECF (interstitial fluid and blood) and intracellular fluid balance

Question 11

What effect will hyponatremia have on heart rate and skeletal muscles?

Answer 11

• Heart = Bradycardia
• Skeletal muscles = Cramping

Question 12

Describe the three mechanisms of Na+ absorption.

Answer 12

1) Na+ cotransport proteins
- Secondary active transport pathway
- Glucose and AA absorption

2) Na+/H+ antiport exchanger
- Intracellular H+ is exchanged for luminal Na+ across apical membrane
- Once Na+ enters the enterocyte, it is transported across the basolateral membrane to the lateral space by
the action of the Na+/K+ ATPase pump

3) Simple diffusion
- Na+ channels in the apical membrane
- Large electrochemical gradient for Na+ across the enterocyte membrane
- Very little Na+ absorption occurs by this mechanism

Question 13

Why is Cl- important?

Answer 13

1) Required for ECF and ICF balance

2) Maintains the ionic balance between the plasma and erythrocytes

Question 14

Describe the three mechanisms of Cl- absorption.

Answer 14

1) Paracellular Cl- absorption
- Major mechanism of Cl- absorption
- Cl- from the gut lumen passes directly into the lateral spaces through the tight junctions

2) Coupled Na+/Cl- absorption
- Net movement of Cl- and Na+ across the apical membrane

3) HCO3- Dependent Cl- absorption
- Net movement of HCO3- into the gut lumen; increasing luminal pH
- Important in the large intestine of herbivores
- Large concentrations of acids from fermentation are created and require buffering

Question 15

Why is HCO3- important? How is HCO3- measured? How is TCO2 calculated?

Answer 15

1) Acid-base balance and normal blood pH

2) HCO3- mEq/L and TCO2 mmol/L

3) Total CO2 (TCO2) = 0.23 x pCO2 + HCO3-

Question 16

Describe the mechanism of HCO3- absorption.

Answer 16

1) Partially absorbed by the neutralization of HCl from the stomach

2) Remains in the intestine after the neutralization of stomach acid

3) Remaining HCO3- is absorbed primarily in the ileum and colon

Question 17

Why is K+ important?

Answer 17

Required for repolarization phase of action potentials causing cardiac and skeletal muscle relaxation

Question 18

What effect will hyperkalemia have on heart rate and skeletal muscles?

Answer 18

• Heart = Bradycardia
• Skeletal muscles = Weakness

Question 19

Why is a bright orange sticker used when K+ is added to the IV fluid bag?

Answer 19

This is used to write down the date, time, and how many mEq/L were added so that there isn’t more K+ added to the IV fluids before there needs to be.

Question 20

Describe the two mechanisms of K+ absorption.

Answer 20

1) Paracellular passive diffusion
- Primary mechanism of K+ absorption using concentration gradient
- K+ absorption is directly coupled to H2O absorption
- Movement of H2O out of the intestinal lumen results in an increase in the luminal K+ concentration, which
in turn drives K+ absorption

2) H+/K+ ATPas pump

Question 21

Where are the major mechanisms of electrolyte absorption located in the GI tract?

Sodium cotransport?

Bicarbonate absorption?

Answer 21

1) Sodium cotransport = Duodenum and Upper GI tract

2) Bicarbonate absorption = Ileum and Colon

Question 22

Water absorption in small intestine and large intestine occurs via Starling’s law and the Villous Vascular System.

Water moves in direction necessary to keep ingesta _______.

Answer 22

Iso-osmotic

Question 23

Starling’s law: name the two pressures responsible for water movement.

Answer 23

1) Oncotic Pressure

2) Hydrostatic Pressure

Question 24

Define oncotic (osmotic) pressure.

Answer 24

Force exerted by plasma proteins (albumin) that draws water into the capillary lumen

Question 25

Define hydrostatic pressure.

Answer 25

Pressure created by the osmotic effect of absorbed solutes