Homeostasis, Nervous System and Hormones

Define homeostasis?

The regulation of internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.

What is negative feedback in homeostasis?

A primary control mechanism where a change in a condition away from the normal set-point triggers a response that restores the condition back to its optimum level.

List three internal conditions controlled by homeostasis in humans?

1. Blood glucose concentration. 2. Body temperature. 3. Water content.

What three components do all control systems include?

1. Receptors (detect stimuli/changes). 2. Coordination centres (brain, spinal cord, pancreas; process incoming info). 3. Effectors (muscles or glands; bring about responses to restore optimum levels).

What is the function of the nervous system?

Enables humans to react to their surroundings and coordinate their behaviour using electrical impulses along specialised neurons.

Trace the pathway of a conscious nervous reaction?

Stimulus -> Receptor -> Sensory neuron -> Central Nervous System (CNS - brain/spinal cord) -> Motor neuron -> Effector -> Response.

Trace the pathway of a reflex arc?

Stimulus -> Receptor -> Sensory neuron -> Relay neuron (in spinal cord/grey matter) -> Motor neuron -> Effector -> Response.

Why are reflex actions important?

They are automatic, rapid, and bypass conscious parts of the brain to protect the body from damage/injury.

What is a synapse and how do signals pass across it?

A gap between two adjacent neurons. When an electrical impulse reaches the synapse, neurotransmitter chemicals are released, diffuse across the gap, and bind to receptors on the next neuron, triggering a new electrical impulse.

What is the endocrine system?

A system composed of glands that secrete chemical messengers called hormones directly into the bloodstream to target organs.

Compare the nervous system and endocrine system?

Nervous: Uses electrical impulses, fast-acting, short-lived effects, precise target areas. Endocrine: Uses bloodborne chemical hormones, slower-acting, longer-lasting effects, broader target areas.

Why is the pituitary gland called the 'master gland'?

It secretes several specific hormones into the blood that act on other endocrine glands, stimulating them to release further hormones.

How does the body lower high blood glucose levels?

1. Pancreas detects high blood glucose. 2. Secretes insulin into bloodstream. 3. Insulin causes liver and muscle cells to take up glucose and convert it into stored glycogen.

How does the body raise low blood glucose levels?

1. Pancreas detects low blood glucose. 2. Secretes glucagon into bloodstream. 3. Glucagon causes liver cells to convert stored glycogen back into glucose and release it into blood.

Describe Type 1 diabetes (cause and treatment)?

Pancreas fails to produce sufficient insulin; characterised by uncontrolled high blood glucose levels. Treated with lifelong daily insulin injections and monitoring diet.

Describe Type 2 diabetes (cause, risk factor, treatment)?

Body cells no longer respond properly to insulin produced by pancreas. Obesity is a major risk factor. Treated with carbohydrate-controlled diet and regular exercise.

What is the role of Follicle Stimulating Hormone (FSH) in the menstrual cycle?

Secreted by pituitary gland; rises at the start of the cycle to cause an egg to mature in an ovary follicle and stimulates ovaries to produce oestrogen.

What is the role of Oestrogen in the menstrual cycle?

Secreted by ovaries; causes uterine lining to thicken/repair; peaks just before LH surge; inhibits FSH release and stimulates LH release from pituitary gland.

What is the role of Luteinising Hormone (LH) in the menstrual cycle?

Secreted by pituitary gland; a surge in LH triggers ovulation (release of a mature egg from the ovary around day 14).

What is the role of Progesterone in the menstrual cycle?

Secreted by empty follicle (corpus luteum) in ovary; peaks in the second half of the cycle to maintain uterine lining; inhibits both FSH and LH release.

How do hormone levels interact across the Menstrual Cycle graph?

1. Days 1-5: FSH rises to stimulate egg maturation and menstruation occurs. 2. Days 5-13: Oestrogen rises, peaking just before ovulation to build the uterine lining. 3. Day 14: LH surge triggers ovulation. 4. Days 15-28: Progesterone peaks in the second half to maintain the lining, then drops if unfertilised.

How do oral contraceptive pills work?

Contain synthetic oestrogen and/or progesterone to inhibit FSH release so no eggs mature.

What are the pros and cons of all major contraceptive methods?

1. Hormonal methods (pill taken daily; patch, injection, and implant last months/years): High efficacy; potential side effects, no STI protection. 2. Condoms (Barrier): Protects against STIs, easy use; risk of tearing. 3. Copper IUD (Non-hormonal): Long-term, no hormones; painful insertion. 4. Spermicide: Easy to obtain; low efficacy on its own. 5. Sterilisation: Permanent; irreversible surgical procedure. 6. Abstinence: 100% effective against pregnancy/STIs; requires behavioural control.

Outline the steps of In-Vitro Fertilization (IVF)?

1. Mother given FSH and LH to stimulate maturation of multiple eggs. 2. Eggs collected and fertilised by father's sperm in laboratory dish. 3. Fertilized eggs grown into embryos in incubator. 4. One or two healthy embryos inserted into mother's uterus.

What are the main drawbacks of IVF?

1. Emotionally and physically demanding/stressful. 2. Low success rates. 3. High risk of multiple births (twins/triplets), posing health risks to mother and babies.

Where is adrenaline produced and what does it do?

Produced by adrenal glands in response to fear/stress; increases heart rate and delivery of oxygen and glucose to brain and muscles, preparing body for 'fight or flight'.

Where is thyroxine produced and what does it do?

Produced by thyroid gland; regulates basal metabolic rate (rate at which chemical reactions occur in body cells) and plays key role in growth/development. Controlled by negative feedback.

How do insulin and glucagon work together to control blood glucose? (Higher tier)

They form a negative feedback cycle. If blood glucose is too high, the pancreas releases insulin, which lowers it. If blood glucose is too low, the pancreas releases glucagon, which raises it. Each reverses the change to bring glucose back to the optimum level.

What is testosterone?

The main male reproductive hormone, produced by the testes; it stimulates sperm production.

What do reproductive hormones do at puberty?

They cause secondary sex characteristics to develop.

What is ovulation and how often does it happen?

At puberty eggs begin to mature and one is released approximately every 28 days. This is called ovulation. Oestrogen is the main female reproductive hormone, produced in the ovary.