BIO 2301 Homeostasis & Membrane Transport (chapter 1&2)

Homeostasis

A tendency to maintain a balanced or constant internal state; the regulation of any aspect of body chemistry, such as blood glucose, around a particular level

can be thought of as a state of balance or equilibrium

Components of Homeostatic Mechanism

receptor, control center, effector

Receptor

Detects the change in variable

Variable

What is being kept in balance (homeostasis)

Control Center

determines the set point for the variable. receives input from the receptor about the variable. Also directs the body's response

Effector

Carries out the response to fix the variable

Negative Feedback

Main way homeostasis occurs

Result is to decrease a variable which increased or increase a variable which decreased

Example:

Body temperature, blood glucose, Blood pressure

Positive Feedback

Not used to maintain homeostasis very often

"Explosive system"— results in increase

Examples: blood clotting, oxytocin during childbirth

Cell membrane (plasma membrane)

Consists of :

1. Phospholipids

2.Proteins

3.Carbohydrates

4.Cholesterol

Selectively permeable

Phospholipids molecule arrangement:

Phosphates (head) face the outside

Lipids (tails) face the inside

What does it mean that phospholipids are amphipathic?

Because their phosphate head groups are polar while their fatty acids (tail) are non polar. This will influence transport across the plasma membrane

phosopholipid bilayer

2 layers of phospholipids, with heads facing watery fluids and tails facing each other

Proteins in cell membrane

integral and peripheral proteins

integral proteins

Serve as channels or pores to allow polar (water soluble) molecules to move through the membrane

Peripheral proteins

Just inside the membrane they do not form channels or pores

Transport through the cell membrane

Nonpolar molecules: are "lipid soluble" and will traverse or cross the phospholipid bilayer

Examples: oxygen, carbon dioxide, fats, urea

Polar molecules: are "water soluble" and will enter or exit the cell through a pore channel formed by integral protein

Examples: water, glucose, small ions like sodium or potassium

What are the functions of proteins within the cell membrane?

Actings as antigens, for cell recognition

Acting as enzymes, catalyzing reactions and changing the shape of the cell

Diffusion

Movement of molecules from an area of higher concentration to an area of lower concentration.

solubility diffusion

Lipid soluble diffuse more readily as they pass through the phospholipid bilayer

Molecular size

smaller molecules, faster diffusion

Molecular charge

negatively-charged molecules will migrate faster than positive-charged molecules

concentration gradient

The grater the concentration difference across the membrane, the faster the rate of diffusion

Osmosis

Diffusion of water through a selectively permeable membrane

Osmolarity

measure of total concentration of solute particles

Example : sodium chloride

Isoosmolar

When the weight inside the cell matches or equals that outside of the cell

= 0.3 Osmolar

hypoosmolar

If the solution outside the cell has a lower concentration of solute then the surrounding fluid

< 0.3 Osmolar

Hyperosmolar

If the fluid around the cell has more particles than the interior of the cell

> 0.3 Osmolar

Molarity

the number of moles of solute per liter of solution

M= moles/L

Tonicity

The ability of a solution to change the pressure inside the cell

isotonic solution

when the concentration of two solutions is the same

= 0.3 Osm or 300 mOsm non penetrating

hypotonic solution

Having a lower concentration of solute than another solution

> 0.3 Osm or 300 mOsm of a non penetrating solution

Causes cell to lyse (swell and burst)

hypertonic solution

Solute concentration is greater than that inside the cell; cell loses water

Causes cell to crenate(shrink)

simple diffusion (passive transport)

passes directly through the membrane (high to low concentration)

Does not require energy or atp

facilitated diffusion (mediated/passivetransport)

Movement of specific molecules across cell membranes through carrier protein channels

Example glucose

Filtration

A process that separates materials based on the size of their particles.

Passive Transport (Diffusion)

A process that requires no energy to move molecules down their concentration gradient(from high to low concentration)

active transport

Energy-requiring process that moves material across a cell membrane against a concentration difference

sodium-potassium pump

a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell

Maintains homeostasis

bulk transport

endocytosis and exocytosis

Also known as Vesicle transport

Exocytosis

Is the process whereby the cell uses vesicles to move substances from the cell interior to the extra cellular space

Phospholipids are added to the cell membrane during this process

The substance is "exiting the cell"

Endocytosis

The bulk transport mechanism that is capable of moving large particles or substances into the cells

Pinocytosis

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

"Cell drinking"

All cells do pinocytosis

Phagocytosis

A type of endocytosis in which a cell engulfs large particles or whole cells

"Cell eating"

Only done by certain white blood cells