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Chapter 6

VPHY 3100 Chapter Notes - Chapter 6: Endocytosis, Neurotransmission, Voltage


Department
Physiology and Pharmacology
Course Code
VPHY 3100
Professor
Li
Chapter
6

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Vphy Test One Review 9/9/17 2:11 PM
Chapter 6 Interactions Between Cells and the extracellular Environment
Extracellular Environment
- looking at what constitutes our body in the outside environment of cells-
interaction
- where is water?
- 67% of the total body water is contained within the cells in the intracellular
compartment
the remaining 33% of total body water is found in the extracellular compartment
20% of the extracellular fluid is in the cardiovascular system as vascular
fluid (blood plasma)à transports oxygen, carbon dioxide and nutrients
80% is located outside the vascular system in the interstitial fluid
(tissue fluid)
o oxygen, nutrients, and regulatory molecules traveling in the blood
must first pass into the interstitial fluid before reaching the body
cells; waste products and hormone secretions from the cells must
first pass into the interstitial fluid before reaching the blood plasma
membrane
- the cells that compose the organs of our body are embedded within the
extracellular material of connective tissue- material is extracellular matrix
the extracellular environment includes everything that lies outside of cells
- Extracellular matrix
ground substance- gel like
o proteoglycans and glycoprotiens (such as integrins- “glue
betweens cells and the extracellular matrix, joins the intracellular
to the extracellular compartments- they serve to relay signals
between the two compartments, impact polarity of the cells so one
side is distinguished structurally and functionally from another)
protein fibers- provide structural strength to connective tissue
o collagen (underlying epithelial membranes)
o Elastic

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- Selective permeability of cell membranes
not permeable to proteins and nucleic acids
plasma membrane is also selectively permeable to certain ions: this
permits electrochemical currents across the membrane
Carrier- mediated transportà need protein carrier
o Facilitated diffusion
o Active transport
Non-carrier-mediated transport à do not need protein carrier
o Simple diffusion- of lipid soluble molecules through the
phospholipid layers of the plasma membrane
o Simple diffusion of ions through membrane channel proteins into
the plasma membrane
o Simple diffusion of water molecules (osmosis) through aquaporin (
water) channels in the plasma membrane
Based on energy requirements
o Passive transport- movement of molecules/ ions across a
membrane from higher to lower concentration, down a
concentration gradient, does not require energyà non-carrier-
mediated diffusion processes
o Active transport- movement from region of lower to the region of
higher concentration, requires metabolic energy (ATP) that powers
pumps- specific carrier proteins
Simple diffusion: Gases, Small uncharged polar molecules
Carrier mediated transport: large uncharged polar molecules, ions (use
ion channels- many of which are gated), charged polar molecules
Movement through the cell membrane: Diffusion and Osmosis
- Solution
Solvent= water
Solute= molecules dissolved in water
o Concentration= amount of solute relative to the amount of solution
o Net diffusion of solute from a region of higher concentration to a
region of lower concentration
Rate of diffusion: magnitude of the concentration differences,
permeability of the membrane, temperature of the solution, surface area
of the membrane

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Osmosis: net diffusion of water across a membrane from regions of higher
concentrated water to lower concentrations of water
o In order for osmosis to occur:
§ Membrane must be selectively permeable to water
§ Concentration gradient for solute must exist across the
membrane
§ Solute must be “osmotically active”- membrane nearly
impermeable to solute
§ Aquaporins: specific portents present in the plasma
membranes which serve as water channels
- Osmotic pressure= force needed to counteract osmosis
increased solute concentrations increase the osmotic pressure of the
solution
One mole (mol) = 6.02 x 1023
Molarity (M): n/v à moles of solute/ volume of solution in L
Molality (m): mole/ kg à moles of solute/ kg of solvent
Osmolality (Osm) = the total molality of the solution = the sum of the
molalities of all solutes present
**** be aware of ions: 1.0 m NaCl = 2.0 Osm
Tonicity= desribe the effect of a solution on the osmotic movement of
water- look at total concentration of solutes
o Leads to osmotic movment of water
o Water follows solute acress cell membranes as long as a total
solute concentration gradient exists and the membrane is
permeable to water
- Look at external solution:
Isotonic solution Hypotonic solution Hypertonic solution
- water regulation in the body and exracellular fulid must maintianedà blood
plasma cells and ADH in kidneys
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