Homeostasis and response

Homeostasis: regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes

The human nervous system: enables humans to react to their surroundings and to coordinate their behaviour

Human Endocrine System

Control of blood glucose concentration

Hormones in human reproduction

Contraception

The use of hormones to treat infertility

Negative Feedback

in the body this includes the control of:

  • blood glucose concentration
  • body temperature
  • water levels

automatic control systems may involve nervous responses or chemical responses

all control systems include:

  • cells called receptors, which detect stimuli
  • coordination centres that receive and process information from receptors
  • effectors, muscles or glands, which bring about responses which restore optimum levels

stimulus --> receptor --> coordinator --> effector --> response

information from receptors passes along cells (neurones) as electrical impulses to the central nervous system (CNS). The CNA is the brain and spinal cord. The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones

the connection between two neurones is called a synapse. The nerve signal is transferred by chemicals which diffuse across the gap

reflexes help prevent injuries

reflex arc:

1) stimulus is detected by receptors

2) impulses travel along the sensory neurone

3) impulses are passed along a relay neurone, via synapses

4) impulses travel along a motor neurone, via a synapse

5) when impulses reach muscle, it contracts

reflex actions are automatic and rapid; they do not involve the conscious part of the brain

composed of glands which secrete chemicals called hormones directly into the bloodstream. The blood carries the hormone to a target organ where it produces an effect.

Compared to the nervous system the effects are slower but act for longer

hormones are chemical molecules released directly into the blood - control things in organs and cells that need constant adjustment

Pituitary gland: in the brain, is a 'master gland' which secretes several hormones into the blood in response to body conditions.

These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects

pituitary gland - pancreas - thyroid - adrenal gland - ovary - testes

monitored and controlled by the pancreas

if 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

if too low, the pancreas produces glucagon

that causes glycogen to be converted into glucose and released into the blood

Type 1 diabetes

disorder in which the pancreas fails to produce sufficient insulin

it is characterised by uncontrolled high blood glucose levels

normally treated with insulin injections

Type 2 diabetes

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

a carbohydrate controlled diet and exercise regime are common treatments

obesity is a risk factor

during puberty reproductive hormones cause secondary sex characteristics to develop

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

testosterone is the main male reproductive hormone produced by the testes an it stimulates sperm production

Menstrual Cycle

Follicle Stimulating Hormone causes maturation of an egg in the ovary

Luteinising Hormone stimulates the release of an egg

Oestrogen and Progesterone are involved in maintaining the uterus lining

Oral contraceptives that contain hormones to inhibit FSH production so that no eggs mature

Injection, Implant or Skin Patch of slow release progesterone to inhabit the maturation and release of eggs for a number of months or years

barrier methods such as condoms and diaphragms which prevent the sperm reaching the egg

intrauterine devices which prevent the implantation of an embryo or release a hormone

Spermicidal agents which kill or disable sperm

Abstaining from intercourse when an egg may be in the oviduct

Surgical methods of male and female sterilisation

oestrogen can be used to inhibit the production of FSH

progesterone inhibits release of LH & FSH - stimulates the production of thick mucus which prevents any sperm getting through and reaching the egg

Fertility drug: contains FSH and LH - given to a woman who may then become pregnant in the normal way

Intro Vitro Fertilisation treatment

IVF involves giving a mother FSH and LH to stimulate the maturation of several eggs

the eggs are collected from the mother and fertilise by sperm from the father in the laboratory

the fertilised eggs develop into embryos

at the stage when they are tiny balls of cells, one or two embryos are inserted into the mother's uterus

although fertility treatment gives a woman the chance to have a baby of he own:

  • 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

Adrenaline is produced by the adrenal glands in times of fear or stress. It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for 'flight or fight'

Thyroxine from the thyroid gland stimulates the basal metabolic rate. It plays an important role in growth and development - thyroxine levels are controlled by negative feedback