Cell physiology - Random

Question 1

Name 3 lipid soluble substances (hydrophobic)

Answer 1

CO2
O2
Steroid hormones

Question 2

Name 3 water soluble substances (hydrophilic)

Answer 2

Na+
Cl-
Glucose
K+
H20

Question 3

Cell membranes are composed of… (2)

Answer 3

Phospholipids and proteins

Question 4

How are cell proteins anchored to the cell membrane?

Answer 4

Through hydrophobic interactions

Question 5

Examples of cell membrane proteins

Answer 5

Ion channels
Transport proteins
Receptors
GTP binding proteins

Question 6

Name and describe 2 types of intercellular junctions

Answer 6

Tight junctions
- Attachment between epithelial cells
- Impermeable (ex: renal distal tubule) or permeable (ex: renal proximal tubule, gallbladder)

Gap junctions
- Attachments that permit intercellular communications
- Ex: myocardial cells

Question 7

Name 5 types of transport across cell membranes

Answer 7

1. Simple diffusion
2. Facilitated diffusion
3. Primary active transport
4. Cotransport
5. Countertransport

Question 8

What factors impact permeability of a solute?

Answer 8

• Oil/water partition coefficient
• Radius (size)
• Membrane thickness

Question 9

Which solutes need transporters or pores or channels to cross membranes?

Answer 9

Hydrophilic solutes

Question 10

Name the 3 characteristics of carrier mediated transport.

Answer 10

Stereospecificity
Saturation (transport maximum)
Competition

Question 11

In diabetes mellitus, glucose uptake with insulin is done through which transport mechanism?

Answer 11

Carrier mediated - Facilitated diffusion

Question 12

The Na+-K+-ATPase pump works through which transport mechanism?

Answer 12

Primary active transport
- Na+ is transported from intra- to extra-cellular
- K+ is transported from extra- to intra-cellular

Question 13

How does the proton pump work?

Answer 13

H+, K+-ATPase
- Primary active transport
- Present in gastric parietal cells and renal α-intercalated cells
- Transports H+ into the lumen against its electrochemical gradient

Question 14

Describe secondary active transport

Answer 14

• The transport of two or more solutes is coupled
• Metabolic energy is provided indirectly from the Na+ gradient that is maintained across cell membranes
• Solutes move in the same direction across the cell membrane = cotransport (ex: Na+-glucose cotransport in the small intestine and renal early proximal tubule and Na+–K+–2Cl– cotransport in the renal thick ascending limb)
• Solutes move in opposite directions across the cell membranes = countertransport or exchange (ex: Na+-Ca2+ and Na+–H+)

Question 15

What is osmolarity?

Answer 15

The concentration of osmotically active particles in a solution

Question 16

How do you calculate osmotic pressure (van’t Hoff’s law)?

Answer 16

π = g × C × RT

π = osmotic pressure (mm Hg or atm)
g = number of particles in solution (osm/mol)
C = concentration (mol/L)
R = gas constant (0.082 L—atm/mol—K) T = absolute temperature (K)

Question 17

What do you call osmotic pressure created by proteins?

Answer 17

Oncotic pressure or colloid osmotic pressure

Question 18

What does a reflection coefficient of 1 mean?

Answer 18

Reflection coeficient = ease with which a solute permeates a membrane

Reflection coefficient of 1 = impermeable solute

Reflection coefficient of 0 = completely permeable solute

Question 19

Name a solute with a reflection coefficient of almost 0.

Answer 19

Urea = ineffective osmole

Question 20

What is effective osmotic pressure?

Answer 20

Osmotic pressure X reflection coefficient

If the reflection coefficient is one, the solute will exert maximal effective osmotic pressure. If the reflection coefficient is zero, the solute will exert no osmotic pressure.

Question 21

Voltage-gated channels

Answer 21

Opened or closed by changes in membrane potential.

• The activation gate of the Na+ channel in nerve is opened by depolarization.
• The inactivation gate of the Na+ channel in nerve is closed by depolarization.

When both the activation and inactivation gates on Na+ channels are open, the channels are open and permeable to Na+

Question 22

Ligand-gated channels

Answer 22

Opened or closed by hormones, second messengers, or neurotransmitters.

Question 23

Resting membrane potential

Answer 23

• Expressed as the intracellular potential relative to the extracellular potential
• Established by diffusion potentials that result from concentration differences of permeant ions
• Each permeable ion attempts to drive the membrane potential toward its equilibrium potential.

Question 24

What is the contribution of the Na+-K+ pump to the resting membrane potential?

Answer 24

Contributes only indirectly to the resting membrane potential by maintaining, across the cell membrane, the Na+ and K+ concentration gradients that then produce diffusion potentials.

The direct electrogenic contribution of the pump (3 Na+ pumped out of the cell for every 2 K+ pumped into the cell) is small.

Question 25

Define depolarization

Answer 25

Makes the membrane potential less negative (the cell interior becomes less negative) * Inward current (flow of positive charge into the cell) depolarizes the membrane potential.

Question 26

Define action potential

Answer 26

Property of excitable cells (i.e., nerve, muscle) that consists of a rapid depolarization, or upstroke, followed by repolarization of the membrane potential.

Question 27

Define hyperpolorization

Answer 27

Makes the membrane potential more negative (the cell interior becomes more negative) * Outward current (flow of positive charge out of the cell) hyperpolarizes the membrane potential.

Question 28

Define threshold

Answer 28

Membrane potential at which the action potential is inevitable.

Question 29

What happens during the action potential?

Answer 29

Rapid depolarization caused by inward Na+ current.

Question 30

What is the resting membrane potential?

Answer 30

Approximately -70mV

Question 31

Action potential diagram

Answer 31

Question 32

What is the impact of lidocaine on action potentials?

Answer 32

Blocks voltage-sensitive Na+ channels, abolishing action potentials

Question 33

What happens during repolarization?

Answer 33

Outward K+ current.

Question 34

The velocity of conduction of action potentials along a nerve will be increased by

Answer 34

Increased fibre size Myelination

Question 35

How does hyperkalemia cause muscle weakness?

Answer 35

Elevated serum K+ concentration causes depolarization of the K+ equilibrium potential and therefore depolarization of the resting membrane potential in skeletal muscle. Sustained depolarization closes the inactivation gates on Na+ channels and prevents the occurrence of action potentials in the muscle.

Question 36

Describe the PIP2-IP3 signal pathway

Answer 36

- G-coupled receptors lead to activation of phospholipase C after hydrolysis of GTP (under the action of various ligands, eg. vasopressin on V1 receptor) - Phospholipase C hydrolyzes PIP2 (phosphatidylinositol biphosphate) into IP3 (inositol triphosphate) - IP3 has various functions (eg. opening of Ca2+ channels on endoplasmic reticulum)