HKR 2320 - Membrane Transport & Chemical Messengers

Passive transport

Transport not requiring energy, based on a concentration gradient. Ex O2 diffusion

Active transport

Transport requiring energy. Needs carriers to pump in and out. Calcium ATPase pumps are an ex

Chemical driving force

Driving force that refers to a concentration gradient

Electrical driving force

Driving force that arises due to membrane potential. Reflects an unequal anion and cation distribution

Electrochemical driving force

Coupling of chemical and electrical driving forces. Depends on the direction of each driving force

Rate of transport

Refers to the number of molecules that cross the membrane in a given length of time (flux). Affected by concentrate of the solute.

Simple diffusion

Passive transport based on random thermal motion. A population of molecules always moves down its concentration gradient

Facilitated diffusion

Passive transport involving a carrier (protein that undergoes a conformational change to transport the substrate)

Diffusion through ion channel

Passive transport occurring through a channel (transmembrane protein) carrying mostly inorganic ions

- Distance/magnitude of gradient

- Membrane surface area

- Membrane permeability

Factors affecting the diffusion of solutes:

Osmosis

The net movement of a solvent through a selectively permeable membrane

Primary active transport

Energy requiring process, uses ATP as a source of energy. Ex: Na+/K+ pump

Secondary active transport

Energy is stored in a Na+ of H+ concentration gradient. Indirectly uses ATP b/c Na+/K+ pumps are driven by ATP

Symporter

Transport of two solutes through a protein in the same direction

Antiporter

Transport of two solutes through a protein in the opposite direction

Gap junction

Directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells

- Endocrine

- Paracrine

- Autocrine

- Neuroendocrine

Chemical signals communicate with their target cells through four major mechanisms:

Paracrine signaling

Messengers diffuse from the signaling cell to reach the neighboring target cell

Autocrine signaling

Messengers diffuse from the signaling cell to act on itself

Hormone signaling

Messengers diffuse from a an endocrine cell to reach a distant target cell

Neuro-hormone signaling

Messengers diffuse from a neuron cell to diffuse a neurohormone reaching a distance target cell

Neurotransmitter signaling

Messengers diffuse from the presynaptic neuron to reach the receptors of the postsynaptic neuron

Cytokine signaling

Hormone-like factors released from lymphocytes, macrophages and other cells of the immune system that regulate the activity of cells of the immune system

Hydrophobic (lipophilic)

Molecules that are lipid soluble and can easily cross the plasma membrane (phospholipid bilayer)

Hydrophilic (lipophobic)

Molecules that are water soluble and do not readily cross the plasma membrane

Amino acids

Class of chemical messenger that is made up of four main acids that form neurotransmitters in the brain and spinal cord

Amines

Class of chemical messenger derived from amino acids and contain an amine group

Peptides

Class of chemical messengers that are polypeptides or proteins and include many neurotransmitters and hormones and all cytokines

Steroids

Class of chemical messenger that are derived from cholesterol and function as hormones

Eicosanoids

Class of chemical messenger that are derived from arachidonic acid and include paracrines

Hydrophilic messenger

Messengers diffuse from the endocrine cell and dissolved in the blood

Hydrophobic messenger

messengers bound to a carrier protein to be carried through the blood

Receptor specificity

Where receptors bind to only one messenger or class of messengers

Magnitude of response

Where the greater the number of receptors with messenger bound. the greater the cell response

Messenger concentration

Where the greater the concentration of the messenger, the greater the cell response

Receptor concentration

Where the higher the number of receptors on the target cell, the greater the cell response

Receptor affinity

Where the greater the affinity of the receptor for the messenger, the greater the response

Epimysium

Connective tissue dividing the muscle

Fascicle

Bundle of individual muscle fibers

Muscle fibers

Functional unit of skeletal muscle

Endomysium

Connective tissue surrounding muscle fibers