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• Solvent

the liquid (often water) in which solutes dissolve

• Solute

any substance dissolved into the solvent

• Solution

a homogeneous mixture of solvent + solute

• Simple diffusion

passive movement of solute molecules down their concentration gradient directly through the lipid bilayer

• Facilitated diffusion

passive movement of solute down its gradient via a membrane protein (carrier or channel)

• Osmosis

passive movement of water across a semipermeable membrane toward the side with higher solute concentration

• Molarity (M)

moles of solute ÷ liters of solution

• Osmolarity (Osm)

molarity × dissociation factor (number of particles formed when solute dissolves)

• Iso osmotic

equal total solute concentration inside vs. outside the cell

• Hypo osmotic

lower total solute concentration outside vs. inside the cell

• Hyper osmotic

higher total solute concentration outside vs. inside the cell

• Tonicity

effect of a solution on cell volume, determined only by non penetrating solute concentrations inside vs. outside

• Isotonic solution

no net water movement → cell volume unchanged

• Hypertonic solution

water exits cell → cell shrinks (crenation)

• Hypotonic solution

water enters cell → cell swells, may lyse

• Factors affecting diffusion rate

Molecular weight (↑ weight → ↓ rate) … Temperature (↑ temp → ↑ rate) … Membrane permeability (small/nonpolar ↑; large/charged ↓ unless carrier mediated) … Surface area (↑ area → ↑ rate) … Concentration gradient (↑ difference → ↑ rate) … Distance (↑ distance → ↓ rate)

• Molecular weight

(↑ weight → ↓ rate)

• Temperature

(↑ temp → ↑ rate)

• Membrane permeability

(small/nonpolar ↑; large/charged ↓ unless carrier mediated)

• Surface area

(↑ area → ↑ rate)

• Concentration gradient

(↑ difference → ↑ rate)

• Distance

(↑ distance → ↓ rate)

• Non penetrating solute example

cell (300 mOsm NP inside) in 400 mOsm NP outside → water exits → cell shrinks (hypertonic)

• Non‑penetrating solute

a solute that cannot cross the cell membrane without active transport, remaining confined to one side and driving osmosis by creating an unequal solute concentration.

• Penetrating solute example

cell (300 mOsm NP inside) in solution of 200 mOsm NP + 200 mOsm P → penetrant equilibrates (100 mOsm moves in), leaving 300 mOsm NP outside → water enters → cell swells (hypotonic)

• Penetrating solute

a solute that can cross the cell membrane (either by simple diffusion if small/lipid‑soluble or via specific channels/carriers), allowing it to equilibrate across both sides.

• Sensation

awareness of a stimulus (raw signal)

• Perception

interpretation of that signal (what/where/how intense)

• Modality

distinct quality of a sensation (e.g., vision, touch, pain, temperature)

• Adequate stimulus

the specific form of energy to which a receptor is most sensitive

• Adaptation

decreased receptor sensitivity during a constant stimulus (firing rate declines)

• Law of Specific Nerve Energies

a receptor’s pathway always conveys the same sensation regardless of stimulus type

• Ipsilateral reflex

stimulus and response occur on the same side of the body

• Contralateral reflex

response occurs on the side opposite the stimulus

• Patellar reflex

tap patellar ligament → quadriceps contraction → knee extension

• Achilles reflex

tap Achilles tendon → plantar flexion

• Biceps reflex

tap biceps tendon → forearm flexion

• Pupillary light reflex

light in one eye → both pupils constrict (consensual)

• Babinski response

stroking sole → toes plantar flex normally; dorsiflexion/fanning in adults = abnormal

• Jendrassik maneuver

clasping/pulling hands ↑ reflex magnitude by lowering spindle threshold

• Physiological zero shift

after adaptation in 20 °C vs. 40 °C water, the same 30 °C feels cold in one hand and warm in the other

• Cold receptors

fire below ~30 °C;

• Warm receptors

fire above ~30 °C; touch adapts fastest, then warm, then cold; extreme (< 10 °C or > 45 °C) triggers pain receptors

• Localization factors

higher receptor density → smaller receptive fields → finer discrimination; more cortical area devoted → better localization

• Mechanoreceptors

Stimulated by physical change such as pressure, touch, vibration. Example

• Thermoreceptors

detect temperature changes. Free nerve endings in the dermis, hypothalamus, and liver. (Free Nerve Ending)

• Nociceptors

detect pain/tissue damage chemicals. Free nerve endings found in the skin, joints, bones, and blood vessels (Free Nerve Ending)

• Photoreceptors

detect light (rods/cones)

• Chemoreceptors

detect chemical stimuli (taste, smell). olfactory, taste, osmolarity, pH, CO2, O2.

• Reflex arc components

receptor → afferent neuron → integration center (CNS) → efferent neuron → effector

• Monosynaptic reflex

single synapse (e.g., patellar reflex)

• Polysynaptic reflex

two or more synapses (e.g., withdrawal reflex)

• General equation for metabolism

Energy in (food) = Energy out (BMR + SDA + physical activity)

• Direct calorimetry

measures heat produced by organism (accurate, expensive)

• Indirect calorimetry

measures O₂ consumption → estimates heat produced (~673 kcal per 6 mol O₂)

• Calorie

heat needed to raise 1 g water by 1 °C

• Calorimetry

measurement of heat production

• Basal Metabolic Rate (BMR)

energy expended at rest, fasting, thermo neutral environment, mentally/physically relaxed, no fever

• Measuring BMR

measure O₂ consumption over time in resting subject → calculate kcal·h⁻¹ using O₂ to heat conversion

• Endotherm

regulates internal temperature; maintains stable metabolic rate

• Ectotherm

relies on external temperature; metabolic rate varies with environment

• Total energy required equation

BMR + SDA + physical activity

• Energy in = Energy out

balance of caloric intake vs. expenditure

• Total energy expended

internal work (heat) + external work (ATP driven) + stored energy

• Unit conversion

1000 cal = 1 kcal (÷ 1000 to go cal → kcal; × 1000 for kcal → cal)

• Mouse respirometer components

Resp. chamber, manometer. Water reservoir.

• Respiration chamber

contains the mouse for gas exchange

• Manometer

measures pressure/volume change as O₂ consumed

• Water reservoir

maintains airtight seal and compensates pressure

• Timer

records time for known volume of O₂ uptake

• O₂ consumption calculation

average time = Σ (trial times) ÷ number of trials

• BMR calculation

use average O₂ consumption rate + environmental variables in provided formula → BMR (kcal·h⁻¹)

• Mouse group results

room temperature → baseline O₂ consumption; cold exposure → ↑ metabolism → ↑ O₂ consumption → higher BMR

• Primary thyroid effect

increased calorigenesis (heat production)

• Secondary thyroid effects

↑ heart rate/stroke volume, ↑ RBC production, ↑ growth, ↑ nervous system development/function

• HPT axis steps

Hypothalamus releases TRH, Anterior pituitary releases TSH, Thyroid gland releases T₃ & T₄, T₃/T₄ ↑ target cell metabolism, Negative feedback T₃/T₄ ↓ TRH & TSH

• T₃ & T₄ synthesis

Iodide uptake & oxidation in colloid, MIT (mono iodotyrosine) & DIT (di iodotyrosine) form on thyroglobulin, MIT + DIT → T₃; DIT + DIT → T₄, Follicular cells endocytose colloid → secrete T₃/T₄ on binding proteins, Peripheral conversion of T₄ → T₃ at target cells

• Hyperthyroidism

excessive T₃/T₄ → heat intolerance, weight loss, anxiety, ↑ BMR (causes

• Hypothyroidism

insufficient T₃/T₄ → cold intolerance, weight gain, lethargy, ↓ BMR (causes