UNIT 3 Human Biology ATAR

1. Homeostasis

Key Definitions

• Homeostasis = maintenance of a stable internal environment within tolerance limits.

• Tolerance limits = upper and lower limits the body can function within.

• Negative feedback = reverses a change to return conditions to normal.

• Positive feedback = amplifies a change.

Feedback System

Stimulus → Receptor → Modulator (control centre) → Effector → Response

Fluid Compartments

• Intracellular fluid = inside cells

• Extracellular fluid = outside cells

  • blood plasma

  • tissue fluid

  • lymph

Nervous vs Endocrine Systems

2. Endocrine System

Endocrine vs Exocrine

• Endocrine glands release hormones into bloodstream.

• Exocrine glands release through ducts.

Major Glands + Hormones

Hormone Types

• Steroid hormones → lipid soluble → enter cell

• Protein/peptide hormones → bind membrane receptors

• Amine hormones

Hypothalamus + Pituitary

• Hypothalamus controls pituitary.

• Anterior pituitary controlled by releasing/inhibiting hormones.

• Posterior pituitary stores/release ADH and oxytocin.

3. Blood Glucose Regulation

Important Processes

• Glycogenesis = glucose → glycogen

• Glycogenolysis = glycogen → glucose

• Gluconeogenesis = new glucose made from non-carbs

Insulin

Released when blood glucose HIGH:

• increases glucose uptake

• increases glycogenesis

• lowers blood sugar

Glucagon

Released when blood glucose LOW:

• stimulates glycogenolysis

• increases blood sugar

Conditions

• Hyperglycaemia = high blood glucose

• Hypoglycaemia = low blood glucose

4. Body Fluid Regulation

Key Hormones

ADH

• increases water reabsorption in collecting duct

• less urine produced

Aldosterone

• increases sodium reabsorption

• water follows sodium

Nephron Functions

Key Terms

• Osmotic pressure = movement of water due to solute concentration

• Excretion = removal of metabolic wastes

5. Nervous System

Functions

1. Communication

2. Control

3. Homeostasis

CNS vs PNS

• CNS = brain + spinal cord

• PNS = nerves outside CNS

Neuron Structure

• dendrites

• cell body

• axon

• myelin sheath

• nodes of Ranvier

• axon terminals

Neuron Types

Action Potential

Resting Potential

Inside neuron negative.

Depolarisation

Na⁺ enters cell.

Repolarisation

K⁺ leaves cell.

All-or-none

Impulse either fully happens or not at all.

Saltatory Conduction

Impulse jumps node to node in myelinated neurons.

6. Synapse

Neurotransmitters

Chemical messengers crossing synapse.

Steps

1. Impulse arrives

2. Neurotransmitter released

3. Diffuses across synapse

4. Binds receptors

5. New impulse generated

7. Reflex Arc

Stimulus → receptor → sensory neuron → interneuron → motor neuron → effector

Purpose

Fast protection without conscious thought.

8. Brain Structures

Protection

• Skull

• Meninges

• Cerebrospinal fluid (CSF)

Meninges

1. Dura mater

2. Arachnoid

3. Pia mater

9. Peripheral Nervous System

Divisions

Afferent

Sensory input to CNS

Efferent

Motor output from CNS

Somatic vs Autonomic

Sympathetic vs Parasympathetic

Fight-or-flight Effects

• increased heart rate

• dilated pupils

• bronchiole dilation

• decreased digestion

10. Gas Regulation

Controlled mainly by:

• medulla oblongata

• chemoreceptors

High CO₂

→ lowers pH
→ increases breathing rate

Hyperventilation

Too much CO₂ lost:

• dizziness

• fainting

11. Thermoregulation

Heat Transfer

• conduction

• convection

• radiation

• evaporation

Too Hot

• sweating

• vasodilation

Too Cold

• shivering

• vasoconstriction

Hypothalamus

Main thermoregulation control centre.

12. Response to Infection

Pathogens

Disease-causing organisms:

• bacteria

• viruses

Transmission

• direct contact

• body fluids

• vectors

• contaminated food/water

13. Non-Specific Defences

External Defences

• skin

• mucus

• tears

• stomach acid

• cilia

Inflammation Signs

1. Redness

2. Heat

3. Swelling

4. Pain

Fever

Pyrogens reset hypothalamus temperature set-point.

14. Specific Immunity

Key Terms

• Antigen = foreign molecule

• Antibody = protein made by B cells

Humoral Immunity

• B cells produce antibodies

• targets extracellular pathogens

Cell-Mediated Immunity

• T cells destroy infected cells

• targets intracellular pathogens

T Cell Types

15. Vaccination + Immunity

Active Immunity

Body produces own antibodies.

Natural

Infection

Artificial

Vaccination

Passive Immunity

Ready-made antibodies received.

Natural

Placenta/breast milk

Artificial

Antibody injections

Herd Immunity

High vaccination rates reduce spread.

16. Antibiotics vs Antivirals

Antibiotic Resistance

Caused by overuse/misuse.

17. Biotechnology

DNA Structure

DNA made of nucleotides:

• phosphate

• sugar

• base

Recombinant DNA

DNA from different organisms combined.

Important Enzymes

Plasmids

Used as vectors in bacteria.

18. Recombinant Products

Produced using genetically modified bacteria:

• insulin

• human growth hormone

• Factor VIII

• vaccines

19. Diabetes

Type 1

• autoimmune destruction of beta cells

• insulin dependent

Type 2

• insulin resistance

• lifestyle/genetics linked

20. Thyroid Disorders

Hyperthyroidism

Too much thyroxine:

• weight loss

• rapid heart rate

Hypothyroidism

Too little thyroxine:

• fatigue

• weight gain

• goitre

MOST IMPORTANT EXAM TOPICS

Focus especially on:

• feedback loops

• blood glucose regulation

• ADH + aldosterone

• action potentials

• reflex arcs

• sympathetic vs parasympathetic

• humoral vs cell-mediated immunity

• vaccination/immunity types

• inflammation + fever