Stage 5 Science – Disease Unit: Body Responses to a Changing Environment (Comprehensive Notes)

Homeostasis: The body's ability to maintain stable internal conditions despite external changes, such as temperature regulation through sweating or shivering.
Immune Response: Activation of the immune system to identify and combat pathogens, involving white blood cells and antibodies.
Stress Response: The release of stress hormones, like cortisol, to handle perceived threats, which can affect various systems within the body.

Accuracy – closeness to true value.
Precision – closeness of repeated measurements.
Reliability – extent identical conditions give similar data.
Validity – extent method measures intended variable.
Homeostasis – ability to maintain stable internal conditions despite external change.
Negative feedback loop – opposes stimulus; returns variable to set point. Example: thermoregulation.
Positive feedback loop – amplifies response. Example: blood clotting.
Receptor / Control Centre / Effector – elements of stimulus-response model.
Endocrine system – glands secreting hormones into blood.
Nervous system – network of neurons transmitting electrical impulses.
Glucagon – hormone elevating blood glucose.
Glycogen – polysaccharide storage form of glucose.
Thermoregulation – maintenance of internal temperature.

Homeostasis is the process by which living organisms regulate their internal environment to maintain a stable, constant condition despite changes in the external surroundings. This regulation is essential for survival, as it enables organisms to adapt to varying conditions such as temperature fluctuations, hydration levels, and nutrient availability. Homeostasis involves several physiological mechanisms, including feedback loops that monitor changes and initiate responses to restore balance, thereby ensuring optimal functioning of biological systems.

Video recap: negative vs positive feedback.
Body-temperature loop: receptors (skin/hypothalamus) → control centre (hypothalamus) → effectors (sweat glands, blood vessels, muscles).
Blood-glucose checkpoint diagram: high glucose → insulin → glycogenesis; low glucose → glucagon → glycogenolysis.
Sample answers emphasise negative loop restoring $\text{[glucose]}_{blood}\approx5\,\text{mmol·L}^{-1}$ .

Hormone definition: chemical messenger secreted by ductless gland, travels via blood, binds specific target receptors.
Major glands: pituitary ‘master’, thyroid (metabolism), adrenals (adrenaline/cortisol), pancreas (insulin/glucagon), gonads (sex steroids).
Key features: slow onset, prolonged, widespread.

CNS = brain (cerebrum, cerebellum, brainstem) + spinal cord.
PNS = sensory + motor pathways; subdivided into Somatic (voluntary) & Autonomic (sympathetic “fight/flight”, parasympathetic “rest/digest”).
Neuron anatomy: dendrites, soma, axon, myelin, synapse.
Stimulus-response sequence: receptor → sensory neuron → CNS (integration) → motor neuron → effector.
Reflex arc bypasses brain for rapid protection (e.g. withdrawal reflex time $\lt50\,\text{ms}$ ).

Three stimuli: visual, auditory (‘drop’), tactile (shoulder tap).
Typical class data: tactile fastest (≈ $10\,\text{cm}$ catch), auditory intermediate, visual slowest (≈ $16\,\text{cm}$ ).
Discussion points: synaptic delays, path length, modality processing times.

Similarities: maintain homeostasis, use receptor–effector pathways, involve feedback.
Differences (see table):
- Signal type: electrical vs chemical
- Transmission path: neurons vs bloodstream
- Speed: $<!\text{ms}$ vs minutes–hours
- Specificity: localised vs systemic
- Duration: brief vs prolonged.
Writing strategy: V-C-F-S (Verb-Content-Focus-Singular).
Connectives for comparison: similarly, likewise, whereas, in contrast.
Example high-level conclusion: “Whereas neuronal impulses give immediate, site-specific adjustments (e.g. pupillary reflex), hormonal secretion such as $\text{T}<em>3/\text{T}</em>4$ modulates metabolic rate over hours, yet both loops converge to keep variables like body temperature within $\pm0.5\ ^\circ\text{C}$ .”

Table construction: title, ruled borders, IV leftmost column, DV with units in headings, mean + trials.
Graphing: choose correct graph (column for discrete IV), axes labelled with units, equal scales, legend, meaningful title.
Statistical reminder: $\text{mean}=\frac{\sum x}{n}$ ; precision judged by small range / SD.
Reliability judgement: multiple trials, consistent pattern.
Validity checklist: controls, appropriate instruments, links to aim.

Risk: slips, insect bites, participant health (heart-rate practical) → controls: dry surface, footwear, EpiPen, teacher first-aid.
Electrical probes near water: secure stands, no frayed cables.
Consent for physical activity; allow modifications for limited mobility.

Diabetes management ↔ blood-glucose feedback.
Climate adaptation: sweating efficiency, vasodilation – occupational health.
Athletic training: HR monitoring, recovery rates as fitness indicators.
Medical diagnostics: abnormal reflexes indicate CNS damage; endocrine disorders (hypothyroidism) reveal hormonal pathway issues.

Mean calculation $\bar x=\frac{\sum x}{n}$ .
Normal core temp range $36.5–37.4\ ^\circ\text{C}$ .
O $_2$ content inhaled $\approx21\%$ ; exhaled $\approx18\%$ (explains CPR efficacy).
Blood glucose set point $\approx5\,\text{mmol·L}^{-1}$ .

Hands-on cup model: strength – tangible feedback; limitation – lacks unconscious neural control.
Ruler-drop: strength – quantifies neural latency; limitation – manual measurement error.
Slow-reveal graph pedagogy: strength – scaffolds data interpretation; limitation – time-consuming.

Use data loggers for reaction time (photogate) to reduce human error.
Compare HR recovery curves pre- and post-training program.
Investigate dual-stimulus reaction (audio+visual) for potential facilitation effect.
Model blood-glucose regulation using digital simulation, introducing insulin-resistance variable.

Homeostasis relies on integrated nervous (rapid) and endocrine (sustained) signalling, both governed by feedback loops.
Reliable, valid data underpins scientific conclusions; graphical literacy and statistical measures convey findings.
Practical modeling and investigations make abstract physiology concepts concrete, revealing both the power and limits of simplified representations.