Module 1 Study Guide
Everything above, compressed to what you should be able to reproduce without the slides in front of you.
Core ideas¶
Structure dictates function. This is the through-line of the whole course, and it explains why anatomy comes before physiology.
Six levels of organization: chemical, cellular, tissue, organ, system, organism. The course covers muscular, cardiovascular, and respiratory systems using vocabulary from every level.
Four tissue types only: muscular, neural, epithelial, connective.
Homeostasis is dynamic, not static. Negative feedback reverses departures; positive feedback amplifies them and needs an external cutoff.
Gradients make things flow. Concentration moves solutes, osmotic moves water, electrical moves ions, pressure moves blood and air, partial pressure moves gases.
The membrane is a phospholipid bilayer, roughly 50% lipid and 50% protein. The lipid core is the barrier; the proteins do everything else.
Hydrophobic and nonpolar solutes cross unaided. Polar molecules and ions need a transport protein.
Diffusion is passive and runs down a gradient. Active transport runs up a gradient and costs ATP.
Osmosis needs an impermeable solute. If the solute cannot move, water must.
Pumps are what create gradients in the first place, and what restore them after they are spent.
Key terms¶
- Homeostasis
- Dynamic maintenance of a stable internal environment against internal and external perturbation.
- Afferent / efferent
- Toward the region of interest / away from it. Sensors send afferent, effectors receive efferent.
- Semi-permeable
- Selectively permeable. Some solutes cross, others do not.
- Hydrophobic / lipophilic
- Water-fearing, fat-loving. Nonpolar. Crosses the membrane freely.
- Hydrophilic / lipophobic
- Water-loving, fat-fearing. Polar or ionic. Needs a transport protein.
- Ligand
- Any chemical that binds a receptor: hormone, neurotransmitter, or drug.
- Simple diffusion
- Passive movement down a gradient with no protein involved.
- Facilitated diffusion
- Passive movement down a gradient through a channel or carrier.
- Active transport
- Movement up a gradient, powered by ATP. Pumps, formally ATPases.
- Osmosis
- Diffusion of water toward higher solute concentration across a solute-impermeable membrane.
- Osmolality
- Molality corrected for dissociation. Osm/kg. The physiological concentration unit.
- Aquaporin
- Membrane water channel. Roughly a billion water molecules per second per pore.
- Hemolysis / crenation
- Cell bursting in a dilute bath / shriveling in a concentrated bath.
Numbers worth knowing¶
Body water | ~60% of body mass |
TBW, 70 kg person | 42 L |
Intracellular fluid | 2/3 TBW · 28 L |
Extracellular fluid | 1/3 TBW · 14 L |
Membrane composition | ~50% lipid, ~50% protein |
Physiological osmolality | 280–310 mOsm/kg |
Osmolality target | ~290 mOsm/kg |
Body temperature | 37°C = 310 K |
Gas constant R | 62.36 L·mmHg/K·mol |
Na+ out / in | 140 mM / 15 mM |
K+ out / in | 4.5 mM / 140 mM |
Glucose molecular weight | 180.18 g/mol |
NaCl molecular weight | 58.45 g/mol |
Nephrons per kidney | ~1 million |
Distinctions that get mixed up¶
Pair | How to keep them apart |
|---|---|
Polar vs ionic | Polar molecules have uneven internal charge but no net charge. Ions have a net charge. Both are hydrophilic and both need help crossing. |
Channel vs carrier | Channels move ions through a tunnel that can be continuously open. Carriers move polar molecules through a double-gate mechanism that is never open on both sides at once. |
Cotransport vs countertransport | Same direction vs opposite directions. In both, solute A moves down its gradient and supplies the energy. Sodium is usually solute A. |
Facilitated diffusion vs active transport | Both use a protein. Facilitated diffusion runs down the gradient for free. Active transport runs up the gradient and burns ATP. |
Molality vs osmolality | Molality counts moles of solute. Osmolality counts particles after dissociation. 1 molal NaCl is 2 Osm/kg; 1 molal glucose is 1 Osm/kg. |
G protein-coupled vs catalytic | Identical logic, except the catalytic receptor has the enzyme built in and skips the G protein. |
Negative vs positive feedback | Negative reverses a departure and is everywhere. Positive amplifies one, is rare and temporary, and requires an external shutoff. |
Check yourself¶
Try each question before opening the answer.
Solution to Exercise 1
Regulated variable on a seesaw → perturbation → sensor → afferent pathway → integrating center compares with the set point → error signal → efferent pathway → effector. Body temperature: thermoreceptors in skin, brain, muscle, liver → afferent sensory nerves → preoptic anterior hypothalamus (center and set point) → efferent motor nerves → skin vessels dilate and sweat glands sweat. (M1 slides 5–6)
Solution to Exercise 2
Negative feedback removes its own stimulus: as the variable returns to normal the error signal shrinks, so the loop shuts itself off. Positive feedback intensifies its stimulus, so nothing inside the loop stops it. Left running it drives the variable dangerously far from normal, which is why an outside event such as delivery of the baby has to end it. (M1 slide 7)
Solution to Exercise 3
Hydrophilic phosphate heads face the watery fluid on both sides and the hydrophobic fatty acid tails face each other, forming a lipid core. Water and anything that dissolves in water cannot cross that core, so the two watery compartments cannot mix. (M1 slide 14)
Solution to Exercise 4
Mostly C–H bonds with few oxygens and even sharing: nonpolar, crosses unaided by simple diffusion. Covalent with uneven sharing (O–H, many oxygens) and regional partial charges: polar, needs a carrier. Lost or gained electrons and a net charge: ionic, needs a channel. Polar and ionic solutes are both hydrophilic and cannot cross the lipid core. (M1 slides 18–20)
Solution to Exercise 5
Raise the rate: concentration gradient, surface area, temperature, membrane permeability. Lower it: membrane thickness, solute molecular weight, density of the medium. Electrical forces and distance also matter outside the expression. (M1 slide 24)
Solution to Exercise 6
Equilibrium sits halfway, so a 2% gradient only needs a 1% change against 2.5% for a 5% gradient. Less change takes less time (61 s against 79 s). The rate, change divided by time, still fell (0.0164 against 0.0316 %/s) because gradient magnitude drives the rate. (Lecture 1D)
Solution to Exercise 7
Ligand-gated ion channel, G protein-coupled receptor, catalytic receptor, and intracellular receptor. The intracellular receptor is not in the membrane because its ligands are hydrophobic: they cross the membrane on their own and bind inside, then act on gene expression. (M1 slide 16)
Solution to Exercise 8
No ATP is used. Solute A runs down its own gradient and the energy stored in that gradient pushes the “revolving door,” carrying B along even when B moves up its gradient. The transporter only spends an existing gradient, so it counts as passive (the key calls it secondary active, since a pump built the Na+ gradient elsewhere). (M1 slide 28)
Solution to Exercise 9
They are equal, so they pull water equally. NaCl dissociates into two particles; glucose, covalently bonded, stays as one. (M1 slide 33)
Solution to Exercise 10
ECF ends at 4,060 ÷ 276.8 = 14.67 L, ICF at 29.33 L. Right after infusion the ECF held 16 L, so 1.33 L moves into the cells. Assume 1 kg water = 1 L and that no solute crosses. (M1 slide 34)
Solution to Exercise 11
320 mOsm is more concentrated than the cell (about 290), so water leaves the cell. The cell shrivels like a raisin: crenation. Its changed shape impairs its function. (M1 slide 37)
Solution to Exercise 12
Concentrated extracellular fluid pulls water out of the neuron, which shrivels. The shriveling physically pulls open mechanically gated ion channels. Ions flow, the membrane potential changes, and the neuron fires, signaling vasopressin release and thirst. Dilute fluid swells the cell, the channels close, and the signals stop. (M1 slide 37)