Year 9 Science – Homeostasis & Endocrine System Study Notes

Learning Intentions & Curriculum Links

• Students should be able to:
  • Name the common Endocrine glands and locate them anatomically.
  • Name and describe the role of different hormones produced by each gland.
  • Apply the Stimulus–Response model (S.R.C.E.R.) to explain regulation of glucose, temperature and water by both the Nervous and Endocrine systems.
• Australian Curriculum link: ACSSU175 – Multicellular organisms rely on coordinated and inter-dependent internal systems to respond to environmental change.

Homeostasis: Definition & Significance

• Definition: Homeostasis = maintenance of a constant internal environment despite external changes.
• Critical because biochemical reactions only work within narrow limits of:
  • Temperature 
  • Glucose concentration 
  • Water balance (osmolarity)
• Everyday illustrations:
  • Prevents “blimping” after drinking water.
  • Prevents overheating on 35\,^{\circ}\text{C} days.
  • Conserves energy for high-demand moments (e.g., sport).
• Key internal chemical processes requiring stability:
  • Cellular respiration (\text{O}2 \rightarrow \text{CO}2+\text{H}_2\text{O})
  • Anabolism (protein synthesis from amino acids)
  • Catabolism (e.g., RBC → bilirubin, haemoglobin recycling)

Body Systems Used in Homeostasis

• Nervous System
  • Rapid electro-chemical control.
• Endocrine System
  • Slower, hormone-mediated, longer-lasting regulation.
• They act together and often share a control centre (hypothalamus).

Structure of a Neuron (Task 1)

• Key parts to label:
  • Dendrites (1)
  • Cell body/soma (2)
  • Nucleus (3)
  • Axon (4)
  • Myelin sheath (5)
  • Axon terminals (6)
• Receptor Table (examples):
  • Photoreceptor – light – eye (rods & cones)
  • Phonoreceptor (hair cells) – sound – ear
  • Chemoreceptor – chemicals – nose/tongue
  • Mechanoreceptor – pressure – skin
  • Thermoreceptor – temperature – skin

Endocrine System: Glands & Locations (Task 2)

• Glands to identify on diagram:
  • Hypothalamus (brain, below thalamus)
  • Pituitary gland (brain, “master gland”)
  • Thyroid (neck)
  • Thymus (above heart, youth-only prominent)
  • Adrenal glands (on kidneys)
  • Pancreas (behind stomach)
  • Ovaries (female pelvis)
  • Testes (male scrotum)

Hormones (Lesson 2)

• Definition: Chemical messengers released by endocrine glands, travel in bloodstream, act on specific target cells/organs to regulate physiology & behaviour.
• Target recognition = “Lock-and-key” fit between hormone shape and receptor proteins on/in target cells.

Major Human Hormones & Functions (Task 3)

• Pituitary: ADH, FSH, LH, GH, TSH
• Thyroid: Thyroxine (metabolic rate)
• Pancreas: Insulin (↓ blood glucose), Glucagon (↑ blood glucose)
• Adrenal medulla: Adrenaline/epinephrine (fight-or-flight)
• Testes: Testosterone (male secondary sex traits)
• Ovaries: Oestrogen & Progesterone (female cycle, pregnancy)

Pheromones (Lesson 2 extension)

• Act between individuals of the same species; released externally.
• Roles:
  • Trail marking (ants)
  • Attracting mates
  • Social fertility control (naked mole-rat queens, termite caste control)
• Act on CNS → behaviour changes; speed can be rapid or slow.
• Sweat & salivary glands are exocrine (ducted) not endocrine.

Stimulus–Response Model (S.R.C.E.R.) (Lesson 3)

• Steps: Stimulus → Receptor → Control Centre → Effector → Response
• Definitions:
  • Stimulus – detectable change in internal/external environment.
  • Receptor – cell/organ detecting stimulus.
  • Control Centre – processes info & coordinates output (e.g., hypothalamus, pancreas).
  • Effector – muscle/gland that carries out response.
  • Response – action restoring homeostasis.
• Response qualities:
  • Voluntary vs Involuntary
  • Positive vs Negative feedback

Feedback Types

• Negative feedback: Response reverses direction of stimulus (e.g., thermoregulation, glucose control).
• Positive feedback: Response reinforces stimulus (e.g., childbirth oxytocin surge; blood clotting).

Comparing Nervous & Endocrine Systems (Task 5)

• Type of message
  • Nervous: electrical impulse + neurotransmitter
  • Endocrine: chemical hormone
• Transmission pathway
  • Nervous: along neurons
  • Endocrine: bloodstream
• Speed
  • Nervous: very fast (milliseconds)
  • Endocrine: slower (seconds → days)
• Duration
  • Nervous: short-lived
  • Endocrine: longer lasting
• Spread
  • Nervous: localised (specific synapse)
  • Endocrine: widespread but only cells with receptors respond

Temperature Regulation Experiments (Lesson 3 activity)

• Measure resting HR, exercise 2 min, measure HR → rises because muscles need more \text{O}2; CO2 removal required (respiration equation \text{C}6\text{H}{12}\text{O}6+6\,\text{O}2 \rightarrow 6\,\text{CO}2+6\,\text{H}2\text{O}+\text{ATP}).
• Exercise generates heat via increased metabolism.

Body Responses

• To increased temperature:
  • Vasodilation, sweating, increased breathing rate, behavioural cooling.
• To decreased temperature:
  • Vasoconstriction, shivering, piloerection, behavioural warming.

Nervous System Thermoregulation (Lesson 4)

• Control centre: Hypothalamus (internal thermostat).
• Receptors: Peripheral thermoreceptors (skin) & internal thermoreceptors (core blood).
• Effectors & involuntary responses:
  • Sweat glands → sweating (evaporative cooling).
  • Blood vessels → vasodilation/vasoconstriction.
  • Skeletal muscles → shivering.
  • Adrenal medulla → adrenaline (↑ metabolic heat).
• Mostly negative feedback; voluntary additions include clothing, seeking shade, drinking water.

Endocrine Thermoregulation

• Involves hormones such as:
  • Thyroxine (thyroid) – ↑ metabolic rate, heat production.
  • Adrenaline & noradrenaline (adrenals) – acute heat production.
• Stimulus–response loop mirrors nervous model but messenger = hormone.

Glucose Regulation (Lesson 5)

• Importance: Energy supply; extremes cause vascular damage or loss of consciousness.
• Storage: Excess glucose → glycogen (liver, muscles).
• Pancreas (Islets of Langerhans) acts as both receptor & control centre.

Endocrine Loop (Task 9)

• High blood glucose:
  • Receptor/Control: \beta-cells of pancreas
  • Hormone: Insulin
  • Effectors: Liver, muscle, adipose cells
  • Response: ↑ glucose uptake, conversion to glycogen/fat → blood glucose falls.
• Low blood glucose:
  • Receptor/Control: \alpha-cells of pancreas
  • Hormone: Glucagon
  • Effectors: Liver & muscles
  • Response: Glycogen → glucose, gluconeogenesis → blood glucose rises.

Diabetes (Task 8 prompts)

• Type 1: Autoimmune \beta-cell destruction → no insulin; ~0.3–0.4 % Australians.
• Type 2: Insulin resistance; lifestyle links; ~5 % Australians and rising.

Water Balance & Osmolarity (Lesson 6)

• Body ≈ 70\% water; solvent for solutes.
• Osmolarity: Concentration of solute particles per litre solution.
  • High water ⟹ low salt concentration (low osmolarity)
  • Low water ⟹ high salt concentration (high osmolarity)
• Endocrine regulation via ADH (antidiuretic hormone):
  • Secreted by posterior pituitary under hypothalamic control.
  • “Anti-diuretic” = prevents urine production.

Effects of ADH

• ADH present:
  • ↓ urine volume, ↑ urine concentration, ↓ blood salt concentration.
• ADH absent:
  • ↑ urine volume, dilute urine, ↑ blood salt concentration.

Scenarios

• Salty popcorn → blood salt ↑ → more ADH released → conserve water.
• Coffee (ADH inhibitor) → less ADH → increased urine output (diuresis).

Stimulus–Response (Task 7)

• Low water (high osmolarity):
  • Receptor: Hypothalamic osmoreceptors
  • Control: Hypothalamus → posterior pituitary
  • Effector: Kidney collecting ducts (add aquaporins)
  • Response: Water reabsorbed, osmolarity normalises.
• High water (low osmolarity): opposite pathway, ADH suppressed.

Glossary & Revision Highlights (Lesson 7)

• Homeostasis, stimulus, receptor, control centre, effector, response, negative feedback, hormone, endocrine gland, target cell, glucose, glycogen, insulin, glucagon.
• Brain centres:
  • Hypothalamus – links nervous ↔ endocrine, homeostasis hub.
  • Pituitary gland – “master” gland controlling others.

Neuron & Brain Terminology (Revision Pages 25–26)

• Neuron structure terms: dendrite, cell body, nucleus, axon, myelin sheath, synapse, neurotransmitter.
• Neuron types: sensory (afferent), interneuron, motor (efferent).
• Reflex arc: receptor → sensory neuron → interneuron (spinal cord) → motor neuron → effector; produces reflex action.
• CNS vs PNS definitions, grey vs white matter, corpus callosum, meninges, cerebrospinal fluid, hippocampus (memory), cerebellum (coordination).

Practical, Ethical & Real-World Connections

• Diabetes management (insulin therapy, lifestyle modification) illustrates endocrine control failures.
• Heatstroke & hypothermia prevention rely on understanding thermoregulation.
• ADH-inhibiting beverages (coffee, alcohol) demonstrate direct endocrine interference.
• Pheromone research influences pest control, animal behaviour studies and even human marketing claims.

Summary Equations, Numbers & Models

• Cellular respiration: \text{C}6\text{H}{12}\text{O}6+6\,\text{O}2 \rightarrow 6\,\text{CO}2+6\,\text{H}2\text{O}+\text{ATP}
• Stimulus–Response shorthand: S.R.C.E.R.
• Normal human core temperature: 36.5–37.5\,^{\circ}\text{C} (regulated via negative feedback).
• Blood glucose set-point: \approx 4–8\,\text{mmol L}^{-1}.

Use these bullet-point notes as a stand-alone study guide for Year 9 Homeostasis & Endocrine System 2025.