[B5] Homeostasis and response

What is homeostasis?

regulation of the internal conditions of a cell or organism to maintain optimum conditions

What conditions are controlled in the human body?

• blood glucose concentration • body temperature • water levels

What two types of responses happen in the body to control conditions?

nervous responses or chemical responses

What three parts are present in all control systems?

1. receptors 2. coordination centres 3. effectors

In the body control system: what do cells called receptors do?

detect stimuli (changes in the environment)

In the body control system: what do coordination centres do?

receive and process information from receptors

Give examples of coordination centres in the human body

the brain, spinal cord and pancreas

In the body control system: what do effectors do?

bring about responses which restore optimum levels (of things like glucose and water)

Give examples of effectors in the human body

muscles and glands

What is the nervous system?

the body system that includes all of the nerve cells, the brain and the spinal cord

What does the nervous system do?

allows humans to react to their surroundings and to coordinate their behaviour

What is the central nervous system?

the brain and spinal cord

What does the central nervous system do?

it coordinates the response of effectors (which may be muscles contracting or glands secreting hormones)

What is the name given to the part of the nervous system which contains only nerves?

The peripheral nervous system.

What happens in the body between a stimulus and a response?

stimulus → receptor → coordinator → effector → response

What is a stimulus?

A change in external environment

What is a reflex action?

An automatic and rapid nervous response which does not require the conscious part of the brain

What does a sensory neurone do?

it transmits electrical impulses from receptors in the sense organs to the CNS

What does a synapse relay neurone do?

it transmits electrical impulses from sensory neurones to motor neurones

What does a motor neurone do?

it carries electrical impulses from the CNS to effectors such as muscles or glands

What is the function of the cerebral cortex?

Controls intelligence, personality, conscious thought and high-level functions, such as language and verbal memory

What is the function of the cerebellum?

Controls balance, co-ordination of movement and muscular activity

What is the function of the medulla?

Controls unconscious activities such as heart rate and breathing rate

What are some of the difficulties of investigating and treating brain function?

The brain is complex and delicate. Treatments such as surgergy can pose huge risks

How can we produce images of the brain?

Using MRI (magnetic resonance imaging) scanning

How does the eye focus on near objects?

• the ciliary muscles contract • the suspensory ligaments loosen • the lens is then thicker and refracts light rays strongly

How does the eye focus on far objects?

• the ciliary muscles relax • the suspensory ligaments are pulled tight • the lens is then pulled thin and only slightly refracts light rays

How does the eye adapt to dim light?

• radial msucles of iris contract • circular muscles of iris relax • pupil dilates

What are the two types of light receptors?

Rods and cones

What is the function of the cornea in the eye?

Refracts light - bends it as it enters the eye

What is the function of the iris in the eye?

Controls how much light enters the pupil

What is the function of the lens in the eye?

Further refracts light to focus it onto the retina

What is the function of the retina in the eye?

Contains the light receptors

What is the function of the optic nerve in the eye?

Carries impulses between the eye and the brain

What is the function of the sclera in the eye?

Tough white outer layer of the eye. It helps protect the eye from injury

What is the scientic name for short sightedness?

Myopia

What is the scientic name for long sightedness?

Hyperopia

Which part of the brain controls body temperature?

The thermoregulatory centre

How is temperature controlled when the body is too cold?

Blood vessels constrict (vasoconstriction), sweating stops and skeletal muscles contract (shiver)

How is temperature controlled when the body is too hot?

Blood vessels dilate (vasodilation) and sweat is produced from the sweat glands

What is the endocrine system?

the body system that includes hormones and glands

What does the endocrine system do?

sends hormones around the body through the blood

What are hormones produced by?

glands

What are hormones?

chemicals which are carried in the bloodstream. They cause effects to happen in organs.

Which is faster: the nervous system or the hormonal (endocrine) system?

the nervous system

Which effects last longer: the nervous system or the hormonal (endocrine) system?

the hormonal (endocrine) system

What does the pituitary gland do?

Produces many hormones which regulate body conditions. Some of these hormones act on other glands, which produce other hormones.

Where is the pituitary gland?

At the base of the brain

Where is the pancreas?

Behind the stomach.

Where is the thyroid?

Along the front of the windpipe.

Where are the adrenal glands?

One above each kidney.

Where are the ovaries?

In the lower abdomen.

Where are the testes?

In the scrotum.

Where is blood glucose concentration monitored?

In the pancreas

What is carbohydrate broken down into?

Glucose

What happens when blood glucose levels are too high?

the pancreas produces the hormone insulin that causes glucose to move from the blood into the cells. In liver and muscle cells excess glucose is converted to glycogen for storage.

What is type 1 diabetes?

the pancreas fails to produce sufficient insulin, so blood glucose can reach dangerously high levels

How is type 1 diabetes controlled and treated?

with insulin injections

What is type 2 diabetes?

the body cells no longer respond to insulin produced by the pancreas

How can type 2 diabetes be controlled?

A carbohydrate controlled diet and an exercise regime

Which type of diabetes is obesity a risk factor for?

Type 2 diabetes

[𝐇𝐢𝐠𝐡𝐞𝐫] What happens when blood glucose levels are too low?

the pancreas produces the hormone glucagon that causes glycogen to be converted into glucose and released into the blood.

[𝐇𝐢𝐠𝐡𝐞𝐫] What is negative feedback?

Receptors detect stimuli, like levels of a hormone being to high. The coordination centre organises a response and the effector produces a response which counteracts the change. The optimum level is restored.

How does water leave the body?

Exhalation, urine amd sweat

How do ions leave the body?

Urine and sweat

Why is water balance important?

If body cells lose or gain too much water by osmosis they do not function efficiently

What happens to the excess amino acids from the digestion of protein?

In the liver these amino acids are deaminated to form ammonia. It is then converted to ammonia for excretion

What does ADH stand for?

anti-diuretic hormone

Where is ADH produced?

The pituitary gland

When does the release of ADH increase?

When the body has too little water

When does the release of ADH decrease?

When the body has too much water

What happens when the producion of ADH increases?

More water reabsorbed by nephrons and urine is more concentrated

What happens when the production of ADH decreases?

Less water reabsorbed by nephrons and urine is more dilute

How can kidney failure be treated?

Kidney transplant or dialysis

What happens at puberty?

reproductive hormones cause secondary sex characteristics to develop

What are the main male and female reproductive hormones?

Male: testosterone Female: oestrogen (Oestrogen and testosterone are produced by both sexes).

What is the main role of testosterone?

it stimulates sperm production

Where is oestrogen produced?

In the ovaries

Where is testosterone produced?

In the testes

What four hormones control the menstrual cycle?

FSH, LH, oestrogen and progesterone.

What do FSH and LH stand for?

Follicule-stimulating hormone. Luteinising hormone.

How many days long is the menstrual cycle (usually)?

28

What is the function of FSH?

causes maturation of an egg in the ovary

What is the function of LH?

stimulates the release of an egg

Which hormones are involved in maintaining the uterus lining?

Oestrogen and progesterone

[𝐇𝐢𝐠𝐡𝐞𝐫] How does oestrogen interact with FSH and LH in the menstrual cycle?

Stimulates release of LH. Inhibits release of FSH.

[𝐇𝐢𝐠𝐡𝐞𝐫] How does progesterone interact with FSH and LH in the menstrual cycle?

Inhibits release of both LH and FSH.

What is contraception?

hormonal and non-hormonal methods of controlling fertility

List hormonal methods of contraception.

Oral contraceptive pills Patch Implant Injection The IUD (intrauterine device, or the coil)

List barrier methods of contraception.

Condoms Diaphragms

How do oral contraceptives control fertility?

they contain hormones to inhibit FSH production so that no eggs mature

How do injections, implants or skin patches control fertility?

they slowly release progesterone to inhibit the maturation and release of eggs for a number of months or years

How do barrier methods control fertility?

they prevent the sperm reaching an egg

How do intrauterine devices control fertility?

they prevent the implantation of an embryo or release a hormone

How do spermicidal agents control fertility?

they kill or disable sperm

How does abstaining from intercourse control fertility?

this tries to make sure there are no sperm in the female reproductive system when an egg may be in the oviduct

How do surgical methods control fertility?

they prevent the sperm reaching an egg by removing tubes in the reproductive systems

What does sterilisation involve?

The falllopian tubes (which connect the ovaries to the uterus) or the sperm duct (the tube between the testes and penis) are cut or tied

[𝐇𝐢𝐠𝐡𝐞𝐫] Give two ways that hormones are used to treat infertility

Fertility drugs, and IVF

[𝐇𝐢𝐠𝐡𝐞𝐫] What are some disadvantages of hormonal fertility treatments?

• it is very emotionally and physically stressful • the success rates are not high • it can lead to multiple births which are a risk to both the babies and the mother.