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18 Cards in this Set

  • Front
  • Back
3 Components of a control mechanism
1. Receptor (sensor)
2. Control center
3. Effector
-Receives output from the control center
-Provides the means to respond
-Effectors are muscles or glands
-Response acts to reduce or enhance the stimulus by feedback
Negative feedback
-The response reduces or shuts off the original stimulus - negates stimulus
-Ex. Regulation of body temperature; Regulation of blood glucose level
Regulation of blood glucose levels, Ex. of Negative feedback
1. Increased blood glucose level
2. Disrupts normal glucose level
3. Receptor on beta cell membrane
4. Beta cell releases insulin
5. Lowers blood glucose levels to normal
Positive feedback
-The response enhances or exaggerates the original stimulus so that output is accelerated
-May exhibit a cascade of amplifying effect
-Usually controls infrequent events, e.g.: Enhancement of labor contractions by oxytocin; Platelet plug formation and blood clotting
Enhancement of labor by oxytocin, Ex. of positive feedback
1. Cervix dilates
2. Stretches receptors
3. Hypothalamus
4. Posterior pituitary
5. Oxytocin
6. Uterine muscle contraction - uterus stretched and more oxytocin released
7. Moves baby
Diabetes Mellitus
-Type I, or juvenile diabetes
-Example of homeostatic imbalance
1. Increased blood glucose level
2. Disrupts normal glucose level
3. Receptor on beta cell membrane
4. Beta cell doesn't release insulin
5. Blood glucose levels remain above normal
6. Hyperglycemia
Plasma membrane lipid composition
-75% Phospholipids - Sphingolipids (Sphingomyelin & glycolipids)
-5%Glycolipids (lipids w/ polar sugar groups on outer membrane surface)
-20% Cholesterol (increases membrane stability and fluidity)
Phospholipid structure
-Phosphorus-containing group (polar end)
-Glycerol backbone
-2 fatty acid chains (nonpolar end)
-Inserted into bilayer b/n phospholipids
-Polar hydroxl group of cholesterol molecule is close to the phospholipid head
-Effect on fluidity of membrane varies w/ temp
-High temps - cholesterol interferes w/ movement of fatty acid chains decreasing membrane fluidity and reducing permeability to small molecules
-Low temps - by interfering w/ interactions b/n fatty acid chains, cholesterol prevents membranes from freezing and maintains membrane fluidity
Lipid rafts in plasma membrane
-Discrete areas of the outer membrane that are enriched in cholesterol and sphingolipids
-Move laterally w/in the pm and may be associated w/ specific membrane proteins
-May function as stable platforms for cell-signaling molecules and the uptake of extracellular molecules by endocytosis
Integral proteins in plasma membrane
-Firmly inserted into the membrane (most are transmembrane)
-Function: transport proteins (channels & carriers), enzymes, or receptors
Peripheral proteins in plasma membrane
-Loosely attached to integral proteins or glycoproteins
-Include filaments on intracellular surface & glycoproteins on extracellular surface
-Function: enzymes, cell-to-cell links, provide support on intracellular surface, and form part of glycocalyx
Fingerlike extensions of the pm that increase the surface area of the cell
Membrane junctions
Glycolipids and glycoproteins, specialized interlocking regions, or specialized membrane junctions linking cells together. Include:
-Tight junctions
-Gap junctions
Tight junctions
-Integral proteins on adjacent cells fuse together to form an impermeable junction in order to prevent fluids and molecules from passing through the extracellular space b/n cells
-Control the movement of materials through cell
-Adhering junctions that attach cells to one another
-Scattered along the sides of adjoining cells that prevent their separation and reduce the chance of tearing when a tissue is stressed
-Found in epi, skin, and heart muscle
Gap junctions
-Transmembrane proteins form pores that allow simple sugars, ions and small molecules to pass from cell to cell
-Present in cardiac and smooth muscle where ion passage from cell to cell synchronizes their electrical activity and contraction