Homeostasis and Response

What is Homeostasis?

Definition:
Homeostasis is the regulation of internal conditions of a cell or organism to maintain optimal conditions for function, in response to internal and external changes.

Why is it important?

• Maintains conditions for enzyme action and cell function

Examples of conditions controlled:

• Blood glucose concentration

• Body temperature

• Water levels

Control Systems Include:

• Receptors – detect stimuli (e.g. temperature, glucose)

• Coordination centres – brain, spinal cord, pancreas (process info)

• Effectors – muscles or glands that bring about a response

4.5.2 The Human Nervous System

Structure & Function

Function:

• React to surroundings

• Coordinate behaviour

How it works:
Stimulus → Receptor → Coordinator (CNS) → Effector → Response

• CNS (Central Nervous System): Brain + spinal cord

• Neurones: Carry electrical impulses

• Effectors: Muscles (contract) or glands (secrete hormones)

Reflex Arc

Definition:
A reflex is an automatic and rapid response that bypasses conscious brain.

Pathway:
Stimulus → Sensory neurone → Relay neurone → Motor neurone → Effector → Response

Neurone roles:

• Sensory neurone – carries signal to CNS

• Relay neurone – transfers signal in spinal cord

• Motor neurone – carries signal to effector

Why important?

• Quick protection from harm

Required Practical 6: Reaction Time

Skill:
Plan and carry out an experiment to test how a factor affects human reaction time.

Examples:

• Caffeine

• Distraction

• Sleep

4.5.3 Hormonal Coordination in Humans

4.5.3.1 The Endocrine System

Definition:
The endocrine system is made up of glands that release hormones into the bloodstream to target organs.

Compared to nerves:

• Slower

• Longer-lasting effects

Key Glands (know location):

• Pituitary (master gland)

• Thyroid

• Pancreas

• Adrenal glands

• Ovaries

• Testes

4.5.3.2 Control of Blood Glucose

Monitored by:

• Pancreas

High blood glucose:

• Pancreas releases insulin

• Glucose moves from blood → cells

• Liver/muscle convert excess glucose → glycogen (storage)

Low blood glucose (HT only):

• Pancreas releases glucagon

• Glycogen converted → glucose → into blood

Negative feedback:

• Insulin and glucagon maintain balance

Diabetes

Type 1 Diabetes:

• Pancreas doesn’t produce insulin

• Treated with insulin injections

Type 2 Diabetes:

• Cells no longer respond to insulin

• Treated with controlled diet + exercise

• Linked to obesity

Skill:
Interpret blood glucose graphs (diabetic vs. non-diabetic)

4.5.3.3 Hormones in Human Reproduction

Puberty:

• Oestrogen (female): produced in ovaries, eggs mature

• Testosterone (male): produced in testes, stimulates sperm

Menstrual Cycle

Key Hormones:

• FSH – matures egg

• LH – stimulates ovulation

• Oestrogen + Progesterone – maintain uterus lining

(HT only)

• Be able to describe hormone interactions and interpret hormone level graphs.

4.5.3.4 Contraception

Hormonal Methods:

• Oral pill – prevents FSH so no egg matures

• Injection/implant/patch – slow release of progesterone

Non-Hormonal Methods:

• Barrier – condoms/diaphragms

• IUD – stops embryo implantation

• Spermicides – kill sperm

• Abstinence – avoiding intercourse

• Surgery – sterilisation

Treating Infertility

Fertility Drugs:

• FSH and LH given to stimulate egg release

IVF (In Vitro Fertilisation):

1. FSH + LH to stimulate multiple eggs

2. Collect eggs, fertilise in lab

3. Grow into embryos

4. Implant 1–2 embryos into uterus

Issues with IVF:

• Expensive

• Physically/emotionally stressful

• Risk of multiple births

• Low success rate

Adrenaline & Thyroxine

Adrenaline:

• From adrenal glands

• Increases heart rate, oxygen + glucose to brain/muscles

• "Fight or flight"

Thyroxine:

• From thyroid gland

• Regulates basal metabolic rate

• Controlled by negative feedback