Membrane transport and osmolarity

Question 1

What are the functions of the proteins in the cell membrane?

Answer 1

1) Channel proteins (passive)
2) Carrier proteins (active)
3) Cell adhesion
4) Receptors

Question 2

What is the function of lipids in a membrane?

Answer 2

Prevents transport of water across the membrane

Cholesterol maintains fluidity and reduces permeability

Question 3

What is the function of carbohydrates in the cell membrane?

Answer 3

Cell surface markers (so that cells recognize each other)

Question 4

What are the types of transport across a cell membrane?

Answer 4

1) Passive transport
- simple diffusion
- facilitated diffusion “in carrier proteins” like glucose and amino acids from BV into the liver cells (limited to the availability of carriers)

2) Active transport (limited by the number of carriers and energy availability, like the Na/glucose pump)
- Primary (produces energy)
- Secondary (uses the energy produced “symporters and antiporters”)

3) Vesicular transport (Limited by the stimulus “hormonal/neural”, and the availability of energy)

Question 5

What is the formula for the rate of diffusion?

Answer 5

Rate of diffusion = K (lipid solubility & MW) * A (surface area of membrane) * (P2-P1 “Concentration gradient across membrane” /D “distance to cover for the substance”)

Question 6

What happens to the rate of diffusion when the lipid solubility increases and the molecular weight is decreased?

Answer 6

It gets higher (like vitamin D, A, K, E & Steroid hormones)

Question 7

How can celiac disease affect the rate of diffusion?

Answer 7

The surface area of the intestine gets lower decreasing the absorption, causing diarrhea and malnutrition

Question 8

What happens to the rate of diffusion in a patient with bronchiectasis?

Answer 8

The distance that must be traveled by the oxygen particles increases which will decrease the rate of diffusion

Question 9

What are the types of vesicular transport?

Answer 9

1) Endocytosis
- Pinocytosis
- Phagocytosis
- Receptor-mediated endocytosis (iron and cholesterol)

2) Exocytosis
- Requires calcium, energy, and docking proteins (secretion of neurotransmitters, and hormones)

Question 10

What is meant by osmolarity?

Answer 10

It is a measure of the total solute concentration in terms of particle numbers, more solute or less solvent will increase the osmolarity

Question 11

What is the difference between osmolarity and tonicity?

Answer 11

osmolarity quantifies the concentration of solutes in a solution, while tonicity is a qualitative measure that refers to the effect of that solution on cell shape and volume

Question 12

What is the major contributor to plasma osmolarity?

Answer 12

Electrolytes, dissolve in water to make ionic bonds

Question 13

What are the forms of tonicity?

Answer 13

1) Hypertonic >0.9% NaCl

2) Isotonic 0.9% NaCl

3) Hypotonic <0.9% NaCl

Question 14

What happens to the body if the osmolarity increases?

Answer 14

in the case of diabetes mellitus and renal diseases, the osmolarity will increase due to the increase in the amount of solutes (urea and glucose) which will lead to water efflux from the brain causing the body to enter into a coma

Question 15

What will happen to the body if the osmolarity decreases?

Answer 15

In case of overhydration, water will flow into the brain causing cerebral edema

Question 16

What are the different types of diarrhea?

Answer 16

1) Osmotic diarrhea (hyperosmotic dehydration)
- when you eat something that the GIT cannot absorb the body will try to lose fluid as the osmolarity is higher inside the GIT. This can be due to molecules like fiber, mannitol, sorbitol, MgSO4, and (lactose in lactose-intolerant individuals), MgSO4 can treat constipation

2) Secretory diarrhea (isoosmotic dehydration)
-when the mucosa is damaged due to infection to the body, the body will lose equal amounts of solutes and water so whatever is left in the body has the same concentration hence the name (isoosmotic)

For both cases, treatment is usually 0.9% saline

Question 17

During diarrhea and vomiting, we lose fluid from which compartment first?

Answer 17

extracellular fluid

Question 18

What happens most of the time in case of diarrhea/vomiting?

Answer 18

we lose water along with Na so the osmolarity does not change thus there is no water movement from the ICF to the ECF, ISOTONIC

Question 19

What happens to the ECF in case of sweating?

Answer 19

We lose more water than Na, thus water will be moving from the ICF to the ECF and the osmolarity will increase (less solvent same solute conc)

Question 20

What causes dehydration?

Answer 20

• insufficient water intake & excessive water loss:
  1) Hemorrhage
  2) Severe burns
  3) Prolonged vomiting or diarrhea
  4) Profuse sweating
• Leads to dry tongue, lips, skin and decreased production of urine

Our body will react by secreting ADH and increasing the thirst sensation

Question 21

What causes overhydration?

Answer 21

1) Renal impairment
2) Excessive water intake
- Leads to syndrome of inappropriate ADH secretion

Our body reacts by making more urine