Hormones

Hormones are chemicals secreted by glands in the body. Different hormones affect different target organs. The bloodstream usually transports the hormones from the gland to the organs. Hormones regulate the functions of many organs and cells. 

The Menstrual Cycle

A recurring monthly process in which the living of the uterus is prepared for pregnany. If pregnancy does not hapen the lining is shed at menstruation.

Follicle stimulating hormone (FSH)

• The hormone FSH is secreted by the pituitary gland.
• Causes the egg to mature in the ovary
• It stimulates the ovaries to release the hormone oestrogen

Oestrogen

• Secreted by the Ovaries
• Stops FSH being produced- so that only one egg matures in a cycle
• Stimulates the pituitary gland to realise Luteinizing hormone (LH) which triggers ovulation (release of mature egg from ovary)

Human fertility is controlled by hormones. This means that knowledge of hormones can be used to decide to increase or reduce the chances of fertilisation and pregnancy.

Contraceptives

• The oral contraceptive, (the pill) greatly reduces the chances of mature eggs being produced. 
• Contains oestrogen and progestrone
• These hormones inhibit the production of FSH which stops eggs maturing in the ovaries

Benefits and risks

• Oral contraceptives allow couples to choose the time they start a family, and choose the time they stop having children
• The first birth-control pills contained a lot more oestrogen than the pills today. This caused big side-effects. Such as...Changeds in weight, mood and blood pressure.

Some women have difficulty getting pregnant because they do not produce enough FSH to allow eggs to mature. Fertility drugs contain FSH and LH which stimulate eggs to mature in the ovary.

• IVF involves giving a mother FSH and LH to stimulate the maturation of several eggs
• The eggs are collected form the mother and fertilised by sperm of the rather
• The fertilised eggs develop into embryos. 
• At the stage when they are tiny balls of cells, one of two embryos are inserted into the mothers uterus.

Plants produce hormones and respond to external stimuli (growing towards sources of water and light, which they need to survive.

A Tropism is a growth in repsonse to a stimulus and an auxin is a plant hormone produced in the stem tips and roots, which controls the direction of growth.

Plant hormones are used in weed killers, rooting powder and to control in fruit ripening

Sensitivy in plants

Plants need liht and water for photosynthsis. Tropisms help make sure that any growth is towards sources of light and water.

• Positive tropism - The plan grows towards the stimulus
• Negative tropism- The plant grows away from the stimulus
• Phototropism is a tropism where light is the stimulus 
• Gratitrioism (geotropism) is a tropism where gravity is the stimulus 
• The roots and shoots of a plant repsond differently to the same stumuli

Auxins are a family of hormones found in plants. Mostly made in the tips of the roots and shoots but can diffuse to other parts of the shoots and roots. They chane the rate of elongation in the plant cells. Controlling how long they become.

Shoots and roots respond differently to high concentrations of auxins: 

• Cells in shoots grow more
• Cells in roots grow less

Phototropisms

In a shoot the shaded side (that is not touched by light) contains more auxin. This means the shaded side will row longer, causing the shoot to bend toward the light

Auxins have the oposite effect on root cells, In a root the shaded side contains more auxin but the shaded side grows less than the lit side, this causes the root to bend away from the light

Gravitropisms

 In a root places horizontally, the bottom side contains more auxin than the top side. This makes the boittom side grow less than the top side, causing the root to bend in the direction of the force of gravity.

In a shoot places horizontally the bottom side contains more auxins than the top side. This makes the bottom side grow more than the top side, causing the shoot to bend and grow against the force of gravity

Gravitropisms

 In a root places horizontally, the bottom side contains more auxin than the top side. This makes the boittom side grow less than the top side, causing the root to bend in the direction of the force of gravity.

In a shoot places horizontally the bottom side contains more auxins than the top side. This makes the bottom side grow more than the top side, causing the shoot to bend and grow against the force of gravity

Plant hormones can be used as weed killers and rooting hormones by farmers and plant growers

Weed Killers

• Selective weed killers work on some plants but not others. This can be useful for getting rid of dandelions in a  lawn without killing the grass
• Selective weed killers contain growth hormone that cause the weeds to frow too quickly and then die
• The weed killer is absorbed in larger quantities by the weeds than the beneficial plants, which stay healthy

Rooting Powder

• Rooting powder contains growth hormones to make stem cuttings quickly develop roots.