Unit 1 Review
Control of Psychological Functions
Pathophysiology → study of disordered body function.
Homeostasis → maintenance of relatively constant internal environment in face of changing external environment.
Hippocrates and Walter cannon noted body has a dynamic equilibrium
Set point → Ideal normal value of a variable
Nervous system → Uses fast electrical transmission to communication between neurons.
Endocrine system → Uses a whole body transmission through chemical messengers binding to specific receptors, allowing for longer-lasting effects on target organs and systems.
Feedback systems → Regulatory mechanisms that maintain homeostasis by three components:
Sensor mechanism (nerve cell/endocrine gland) → integration center (brain) → effector organ.
Negative feedback → promotes stability; homeostasis
built in brakes to prevent over-compensation
Positive feedback → promotes change in one direction.
Rare; psychological change continues until external brake interferes.
Can result in disease if no external brake occurs.
Feedback Gain = Correct / Error
Movement Through Cell Membranes
Plasma membrane → Oily film of phospholipids with diverse proteins embedded inside it.
Controls interactions, boundaries, and passage.
90-99% of plasma membrane is composed of phospholipids.
75% make up the the phospholipid bilayer.
Hydrophilic heads (phosphate).
Hydrophobic tails in center.
20% of lipids consist of Cholesterol, which affects membrane fluidity.
5% of lipids consist of Glycolipids, which play a crucial role in cell recognition and signaling.
Membrane proteins → consist bout 2% of molecules found in plasma membrane
Although consist of 50% of the weight of the plasma membrane.
Integral (transmembrane) proteins → completely pass through the plasma membrane.
Hydrophobic phosopholipid regions and hydrophilic intra, and extracellular bits.
Most are glycoproteins, conjugated with carbohydrates for signalling.
Peripheral proteins → adhere to intracellular surface to provide anchoring for integral cytoskeletal proteins.
Channel proteins → Integral proteins that form pores (channels) for passage into/out of cell.
Some channels remain open, while some are gated— opening and closing depending on specific circumstances:
Ligand-regulated gates → binding of ligand results in change.
Voltage-regulated gates → potential changes across plasma membrane cause change.
Mechanically regulated gates → physical stress results in activation.
Carrier channels that consume ATP are called Pumps.
Fluid Mosaic Model → Modern concept of plasma membrane structure.
Bilayer of phospholipids with embedded proteins.
Proteins are “icebergs” floating on a sea of “lipids”
Plasma membrane is highly flexible, and constantly changing shape.
Singer and Nicholson.
Processes of Movement through Cell Membranes
Simple Diffusion → directly through lipid bilayer
Passive (without ATP) movement by gradient.
Facilitated Diffusion → through protein channels or carriers
Active Transport → against concentration gradient using energy (ATP)
Endocytosis/exocytosis → Vesicles transport materials into (endocytosis) or out of (exocytosis) the cell, allowing for the bulk movement of substances.
Ion Channels → integral membrane which facilitate ionic movement:
ungated → determined by size, shape, and charge of the ions, allowing for passive diffusion across the membrane.
Always open and responsible for permeability
Specific for one type of ion, although not absolute.
gated → open or close in response to voltage, or to a chemical.
Membrane permeability:
thickness of membrane → increased thickness, decrease rate.
molecular weight → higher mw, lower rate.
number of protein channels → higher pc, higher rate
temperature → higher temperature, increased kinetic energy, higher rate.
concentration gradient → greater difference, increased rate.
viscocity → lower viscosity, easier movement, higher rate of diffusion.
electrical potential → higher electrical potential, greater force on charged particles, increased rate of movement.
Nernst potential → the electric potential difference across a membrane that exactly balances the concentration gradient for an ion, thereby influencing ion movement and cellular excitability.
pressure difference → greater pressure difference, enhanced force driving movement, leading to increased rate of diffusion.
Osmosis → Diffusion of water across selectively permeable membrane
From area of more concentration to area of less concentration.
Aquaporins → specialized water channels that facilitate the rapid transport of water molecules across cell membranes, significantly increasing the rate of osmosis.
Osmotic pressure → pressure required to prevent the flow of water across a selectively permeable membrane, often driven by solute concentration gradients.
Isosmotic → no net movement of water across a semipermeable membrane.
Hyperosmotic → solution with higher solute concentration compared to another solution, leading to water moving out of a cell, which can result in cell shrinkage.
Hypoosmotic → solution with lower solute concentration, causing water to move into a cell, potentially resulting in cell swelling or lysis.
Tonicity → term used to describe solution’s effect on cell placed in it.
Hypotonic → low concentration of nonpermeating solutes; high water.
lyse → when a cell swells excessively due to water influx and ultimately bursts.
Isotonic → solution with equal solute concentration, leading to no net movement of water into or out of the cell, maintaining cell shape.
Hypertonic → solution with higher solute concentration; low water.
crenation → the process by which red blood cells lose water in a hypertonic solution, resulting in the cells shriveling and becoming irregularly shaped.
Osmotic refers to solution conc., while tonic refers to tendency to shrink or swell.
Filtration → movement of particle through selectively permeable membrane by hydrostatic pressure.
Particles move down hydrostatic pressure gradient.
In capillaries, BP forces water, salts, nutrients, and solutes into tissue blood.
Mediated Transport Mechanisms → movement of particles down a concentration gradient with the aid of specific transport proteins in the cell membrane.
Characteristics:
Specificity → specific solute binds to receptor site
Competition → similar molecules compete to bind to same receptor site
affinity
Saturation → rate of transport (Vmax) limited by # of carrier molecules or sites.
Facilitated diffusion → the process by which molecules move across a cell membrane via protein channels down it’s concentration gradient without energy.
solute binds → shape change → solute transported
no mediator or carrier.
Active Transport → the movement of molecules across a cell membrane against their concentration gradient, requiring energy in the form of ATP.
Secondary active transport: the process that utilizes the energy from the primary active transport of one molecule to drive the transport of another molecule against its gradientt.
One solute (typically Na+) is transported “downhill” to provide energy for the “uphill” transport of other solutes.
Cotransport (symport) → solutes move in same direction across membrane.
Countertransport (antiport, exchange) → solutes move in opposite directions across membrane.
Energy needed, and involves a carrier.
Vesicular Transport → bulk transport of large particles or fluids droplets across membrane using a vesicle, also requiring ATP.
Endocytosis → process by which cells engulf substances from their external environment, forming an internal vesicle to transport materials into the cell.
Phagocytosis → a type of endocytosis where cells ingest large particles, such as bacteria or dead cells, by enclosing them in a vesicle.
Pinocytosis → the process of cellular "drinking," where cells take in small droplets of extracellular fluid and dissolved solutes by engulfing them in vesicles.
Receptor mediated → a specialized form of endocytosis where cells internalize specific molecules by binding them to receptors on the cell surface, leading to the formation of vesicles.
Trancytosis → uses receptor mediated endocytosis to move a substance into a cell, and exocytosis to move out the substance to the opposite side of the cell, allowing for efficient transport across cellular barriers.
Sodium-Potassium ATPase (pump)
most common, using 25% of all energy expended by the body.
Na+ binds to carrier, carrier hydrolyzes ATP, changing it’s shape, allowing Na+ in and K+ out.
Regulation of cell volume (anions attract cations which cause osmosis)
Heat production (regulated by thyroid hormone)
Maintenance of resting cell membrane potential.
Secondary active transport → Na+ brings in second solute (e.g., glucose or amino acids) against its concentration gradient, utilizing the energy from the sodium gradient established by the Na+/K+ ATPase pump.
SGLT (sodium-glucose transport) moves both down same gradient.
Calcium (Ca2+) ATPase (Pump)
Present on cell membrane and sarcoplasmic reticulum.
Maintains a low cystolic Ca2+ concentration
Potassium-Hydrogen (K+-H+) ATPase (Pump)
Found in parietal cells of gastric glands (HCI secrection)
Intercalated cells of renal tubules (controls blood pH)
Concentrates H+ ions up to 1-million fold.