Lecture 1-2; Homeostasis And Membrane Transport

Front 1

What is homeostasis?

Back 1

Dynamic steady state of the constituents in the internal fluid environment
-Maintaining relatively stable internal environment even in the face of extreme changes in environment or within body itself

Front 2

What is the primary type of homeostatic control?

Back 2

Negative Feedback
-maintains stability by defending set points
-opposes initial change

Front 3

What are the components of a negative feedback system?

Back 3

Sensor= monitors magnitude of a controlled variable and relays to the integrating center via afferent pathways
Integrator (control center)= compares sensors input with a set point
Effector= receives information from the integrating center via efferent pathways and responds accordingly

Front 4

What is the other type of homeostatic control system?

Back 4

Positive Feedback System
-drives physiological values away from a set point
-amplifies an initial change

Front 5

What are two examples of positive feedback mechanisms in the body?

Back 5

-Uterine contractions -->push on cervix-->increase oxytocin secretion --> increases uterine contractions until baby born

- Na+ channels opening to allow for Na+ entry into the cell during depolarization; opening of some channels causes an influx of Na+ which causes depolarization and the opening of more channels

Front 6

What is the plasma membrane composed of?

Back 6

-Thin layer of lipids and proteins that form outer boundary of every cell

Front 7

What is the function of the plasma membrane?

Back 7

-controls movement of molecules between the cell and its environment -->serves as permeability barrier
-detects chemical messengers on the surface
-links adjacent cells together via membrane junctions
-anchors cells to the extracellular matrix

Front 8

What are the two main fluid compartments in the body?

Back 8

-Intracellular fluid (ICF)= the fluid contained within the bodys cells
-Extracellular fluid (ECF)= fluid in which the cells live; plasma and interstitial fluid components

Front 9

What are the main components of the plasma membrane?

Back 9

-carbohydrates= small amount
-cholesterol= between phospholipid molecules and determines membrane fluidity
- phospholipids= polar (hydrophilic) end and non (hydrophobic) end that makes them amphipathic
- Integral proteins= proteins embedded in the cell membrane
-Peripheral proteins= loosely attached to either intracellular or extracellular side of cell membrane

Front 10

Functions of Membrane Proteins

Back 10

-span membrane to form water-filled pathway or channels across lipid bilayer
- serve as carrier or transporter for molecules
- serve as pumps that use ATP to move ions against gradient
- form receptors that bind an extracellular molecule and initiate an intracellular response
-serve as cell adhesion molecules (CAMs)
- help cell to recognize "self" and in cell-to-cell interactions

Front 11

What two properties of particles influence whether or not they can permeate the cell membrane without assistance?

Back 11

-relative solubility of particle in lipid
-size of the particle

Front 12

What are the types of unassisted membrane transport?

Back 12

- osmosis= movement of water
- diffusion= simple diffusion across a lipid bilayer or through a protein channel

Front 13

What are the types of assisted membrane transport?

Back 13

-carrier-mediated transport= facilitated diffusion and active transport (primary and secondary)
- vesicular transport

Front 14

What is osmosis?

Back 14

-the net diffusion or movement of water down its concentration gradient
-water moves to area of high solute concentration

Front 15

What are aquaporins?

Back 15

-channels formed by membrane proteins for the passage of water
-can allow flow of 1 million water molecules per second

Front 16

If a membrane is permeable to water but impermeable to solutes what occurs?

Back 16

-osmosis

Front 17

If the membrane is semi-permeable with pure water on side 1 and the side 2 has a lower water concentration and a higher solute concentration, what occurs?

Back 17

- Water will move side 1 to side 2 through osmosis down its concentration gradient
- the water and solute concentrations can never be equal because no solutes on side 1
-the tendency for water to diffuse to side 2 is directly balanced by the opposing tendency for hydrostatic pressure difference to push water back to side 1

Front 18

What is osmotic pressure?

Back 18

-results from the difference in water concentration
- depends on the concentration f solute particle in solution
-estimated from van't hoff equation

Front 19

What is hydrostatic pressure?

Back 19

-results from gravitational force on a column of fluid
-usually zero since plasma membranes deform easily and does not provide significant driving force for water

Front 20

What is osmolarity?

Back 20

# osmoles/L solution

-total concentration of particles per liters of solution

1mole NaCl= 2 osmoles (Na+ +Cl-)
1mole glucose= 1 osmole

ICF and ECF osmolarity= 290miliOsmoles/L

Front 21

Define Isoosmolar, Hypoosmolar, and Hyperosmolar

Back 21

-Isoosmolar= having the same osmolarity as normal ECF
-Hypoosmolar= having lower osmolarity than normal ECF
-Hyperosmolarity= having higher osmolarity than normal ECF

Front 22

How do you calculate osmolarity?

Back 22

Osmolarity= g x C
g= number of particles per mole in solution (Osm/mol)
C= concentration (mol/L)

Front 23

What is the effective osmolarity?

Back 23

-refers to the particles that will exert an actual osmotic effect (water movement) on the cell
-only non-permeable particles have an osmotic effect

Front 24

What is tonicity?

Back 24

- refers to the ultimate effect a solution has on cell volume which determines whether the cell size remains same, swells, or shrinks when a particular solutions surrounds a cell

Front 25

If placed in a isotonic/hypotonic/hypertonic solution what will happen to the cell?

Back 25

-Isotonic= the cell size will remain the same
-Hypotonic= the cell size will swell due to water entering
- Hypertonic= the cell size will shrink due to water leaving

Front 26

What is the response to cell swelling?

Back 26

- solute efflux mechanism- Regulatory Volume Decrease is activated
-most commonly Cl- and K+ channels are activated
- net efflux of Cl- and K+ decreases osmolarity and water diffuses out of the cell

Front 27

What is the response to cell shrinkage?

Back 27

- solute uptake mechanism activated= Regulatory Volume Increase
-Most commonly the Na+/H+ exchanger is activated (Na+in/H+out)
-H+ extrusion alkalinizes the cell and activated the Cl-/HCO3- exchanger
-increase in intracellular Na+ and Cl- draws water into the cell and cell volume returns to normal

Front 28

What class of drugs can inhibit the Na+/K+ ATPase?

Back 28

-Cardiac glycosides (ouabain and digitalis)
-cause the intracellular Na+ concentration to increase and the intracellular K+ concentration to decrease
- the cell will swell due

Front 29

What are the two types of secondary active transport?

Back 29

-cotransport= occurs when the uphill solute moves in the same direction as Na+
-countertransport= occurs when the uphill solute moves in the opposite direction of Na+