B5: Homeostasis and Response

Define Homeostasis.

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

What does homeostasis maintain?

Optimum conditions for enzyme action and cell function.

What does homeostasis control?

-Blood glucose levels
-Water levels
-Temperature

What do receptor cells do?

-Detects stimulus
-Passes on information to co-ordination centre

What does the co-ordination centre do?

-Receives and processes information from receptor cells
-Sends instructions to effector

What does an effector do?

-A muscle or gland which carries out a response
-Restores optimum levels

Which two organs make up the CNS?

-Brain
-Spinal Cord

How is information passes in the nervous system?

Electrical impulses down neurones.

What does the nervous system enable humans to do?

React to their surroundings and co-ordinate their behaviour.

What neurone does electrical impulses from the receptor pass along?

Sensory neurone.

What neurone does electrical impulses from the CNS pass along?

Relay neurone.

What neurone does electrical impulses pass down to the effector?

Motor neurone.

What is a synapse?

A slow chemical signal.

What happens at a synapse?

-A chemical is released.
-Chemical diffuses across the neurone and triggers an electrical impulse.

Briefly describe the stages of the reflex arc.

-Stimulus detected by receptor.
-Impulses pass along sensory neurone to the CNS.
-Reaches a synapse, where a chemical is released.
-Chemical diffuses across to a relay neurone and triggers an electrical impulse.
-Impulse goes down the relay neurone, reaches another synapse.
-Triggers impulse to a motor neurone.
Impulse travels down the motor neurone to effector.
-Effector carries out a response.

Describe a reflex.

-There is no decision making done by the conscious part of the brain, which makes them automatic and rapid.
-As they are rapid they help protect us from danger.

Describe the endocrine system.

-Consists of a number of glands which secrete hormones directly into the bloodstream.
-Blood carries hormones around body.
-Hormones act on specific target organs where it produces an effect.

Compare the endocrine system and the nervous system.

1) - E-system uses hormones carried in bloodstream.
N-system uses electrical impulses that travel down neurones.
2) - E-system tends to produce a slower yet long-lasting effect.
N-system is fast but not as long-lasting

What do the hormones secreted by the pancreas do?

Involved in controlling the concentration of glucose in the blood.

What do the hormones secreted by the ovaries and tests do?

Involved in puberty and reproduction.

What do the hormones secreted by the thyroid gland do?

-Involved in growth.
-Involved in regulating the bodies basal metabolic rate.

What does the adrenal gland do?

Releases adrenaline in times of fear and stress.

What does the pituitary gland do?

-Releases numerous different hormones into the blood depending on conditions.
-Hormones can act on other glands and cause other hormones to
be released.
-By acting on other glands the pituitary hormones can rigger a range of different effects in the body.

Why is glucose needed by every cell?

To release energy by respiration.

What monitors the body's blood glucose concentration?

Pancreas.

What can cause the concentration of glucose in the blood to rise?

A meal rich in carbohydrates.

What happens when the concentration of glucose in the blood rises?

-Sensed by the pancreas.
-Pancreas releases insulin.

What does insulin do?

-Travels in bloodstream all over body.
-Triggers blood cells to take up glucose from the blood.
-Triggers liver and muscle cells to store excess glucose as a storage molecule (glycogen)

How does the concentration of glucose in the blood return to its normal lebe?

Glucose is taken from the blood and stored.

Why do some people have diabetes?

Their blood glucose controls don't work effectively.

What's Type 1 diabetes?

When the pancreas doesn't produce enough insulin.

How do people cope with Type 1 diabetes?

-Monitor their blood glucose concentration.
-Inject themselves with insulin if it rises too much.

What's Type 2 diabetes?

When body cells stop responding to insulin produced by the pancreas.

How do people cope with Type 2 diabetes?

-Exercise.
-Diet with a controlled level of carbohydrates.

What is a major risk factor of Type 2 diabetes?

Obesity.

What happens if the blood glucose concentration falls?

Pancreas releases the hormone glucagon into the bloodstream.

What's the purpose of glucagon?

Triggers liver and muscle cells to convert glycogen stores back into glucose, which is then released into the blood.

Why does our blood glucose concentration rise slightly and fall slightly?

It is controlled by a balance between insulin and glucagon.

How does insulin and glucagon form a negative feedback cycle?

As they have opposite effects on the blood glucose concentration.

During puberty, what do reproductive hormones cause?

Secondary sexual characteristics.

Why do the testes produce testosterone?

Testosterone stimulates the testes to produce sperm.

In preparation for ovulation, what happens to the uterus lining?

It becomes thick and spongey.

What happens if the egg gets fertilised by sperm?

It implants into the uterus and develops a baby.

What happens if an egg is not fertilised?

Egg and uterus lining gets released.

Name the 4 hormones involved in the menstrual cycle.

-FSH
-LH
-Oestrogen
-Progesterone

Where are each of the hormones produced in the menstrual cycle produced?

-Pituitary Gland: FSH,LH
-Ovaries: Oestrogen,Progesterone

What is the function of FSH?

Causes egg to mature in the ovary.

What is the function of LH?

Causes egg to be release.(Ovulation)

What is the function of oestrogen and progesterone?

Maintains uterus lining in case fertilised egg implants.

Describe how these hormones interact.

-FSH released by the pituitary gland and travels in the blood to the ovaries.
-Causes the egg to mature.
-Triggers ovaries to make oestrogen (maintains thick lining).
-Stops pituitary gland from producing FSH.
-Pituitary gland produces LH which triggers ovulation.
-Egg released
-Ovaries produce progesterone
-Stops pituitary gland from releasing FSH and LH to stop more
eggs maturing or released.
-Progesterone keeps uterus thick.

What are oral contraceptives, and how do they work?

-A form of hormonal contraception. (pill)
-Contains hormones which prevent the body from producing FSH.
(prevents any egg from maturing)

What are the advantages of oral contraception?

Highly effective.

What are the disadvantages of oral contraception?

-Must be taken everyday.
-Risk of pregnancy if not.
-Certain pills have risks of side effects.
-Increased risk of breast cancer or blood clots.
-Doesn't protect against STI's

Give 3 other forms of hormonal contraceptives.

-Implant
-Skin patch
-Injection

How do other forms of hormonal contraceptives work?

-Contains progesterone.
-Inhibits egg from maturing and being released.

What are the advantages of other hormonal contraceptives?

-More effective than taking a daily pill.
-Implant: lasts about 3 years.
-Injection: lasts about 13 weeks.
-Patch: lasts about 1 week.

What are the disadvantages of hormonal contraceptives?

-Can have side effects.
-Does not protect against STI's.

What are barrier methods?

-Condom, diaphram.
-Prevents sperm from reaching egg.

What are the advantages of barrier methods?

-Highly effective.
-Don't have side effects. (Doesn't use hormones)
-Protects against STI's

What are the disadvantages of barrier methods?

Can break or slip off.

How can a barrier method be made more effective?

Use a spermicide gel.

What does spermicide do?

-Kills or disables sperm.
-Reduces chance of fertilisation.

What does an IUD do?

Prevents an embryo from impanting.

What do some coils do to reduce chance of fertilisatiton?

Release hormones.

What are the advantages of an IUD?

-Highly effective.
-Can prevent pregnancy for up to 10 years.
-Very few side effects.

What are the disadvantages of an IUD?

Doesn't protect against STI's.

What are surgical forms of contraception?

-Sterilisation.
-Men: Prevents sperm from leaving penis.
-Women: Prevents egg from reaching uterus.

What are the disadvantages of sterilisation?

-Difficult to be reversed.
-Doesn't protect against STI's.

What is a natural form of contraception?

Abstaining from sexual intercourse.

When would someone abstain from sex?

After ovulation.

What are the disadvantages of abstaining from sex?

-Hard to tell when a woman has ovulated.
-Doesn't protect against STI's.

Why do some people struggle with infertility?

-Men: reduced sperm count.
-Women: find it hard to conceive.

What is the fertility drug?

-FSH and LH given to woman.
-Causes woman to ovulate more than usual.
-Increases chance of getting pregnant through sex.

Describe the stages of IVF.

-Mother treated with FSH and LH.
-Causes several eggs to mature.
-Eggs are collected from the mother.
-Uses the father's sperm to fertilise it in a lab.
-Fertilised eggs develop into embryos.
-Inserted back into the mothers uterus.

Why is IVF a good thing?

-Gives the woman a chance of having a baby of her own.

What are the problems with IVF

-Success rate is not high.
-Emotionally stressful for both parents.
-Physically demanding on both parents.
-Can lead to multiple births.
-Risky for mother and babies.

What issues surround IVF?

-Not all embryos are transplanted back into mother.
-Many embryos destroyed. (unethical)
-Expensive.
-Money could be spent on other medical issues. (cancer
treatment)

What is the main effect of adrenaline?

Increased heart rate.

Why does adrenaline increase heart rate?

-Heart is beating faster ---->more oxygen and glucose are delivered in
the blood to the brain and muscles.
-Oxygen and glucose needed for aerobic respiration.
-Prepares body for fight or flight.

What hormone does the thyroid gland produce?

Thyroxine.

What are the two main effects of thyroxine?

-Stimulates body's basal metabolic rate
-Makes chemical reactions take place at a faster rate.
-Growth and development.

What is the level of thyroxine in the blood controlled by?

Negative feedback.

What organ monitors the level of thyroxine in the blood?

Brain.

What happens when thyroxine levels fall?

Pituitary gland releases TSH into blood.

What does TSH do?

Triggers thyroid gland to release more thyroxine into the blood.

What happens when the thyroxine levels increase?

-Detected by the brain.
-Prevents pituitary gland from producing TSH.
-As TSH levels fall, the thyroid gland releases less thyroxine.