B11 Hormonal coordination

The endocrine system is a coordination and control system made up of glands secreting hormones directly into the blood, carrying it to the organs, where it takes effect by triggering a response in the cell when the receptors on the cell membrane pick up the hormone. Hormonal effects are slower but longer-lasting than the nervous system.

The pituitary gland releases:

• ADH - which affects the amount of urine made by the kidney
• FSH -  stimulates the ovaries to make oestrogen
• TSH - stimulates the thyroid to make thyroxine controlling metabolic rate
• The pituitary gland makes growth hormone and stimulates the testes to make sperm and testerone.

The pancreas controls blood glucose levels, the adrenal glands prepare the body for stressful situations, the ovaries control the development of the female secondary sexual characteristics and is involved in the menstrual cycle; and the testes control the development of the male secondary sexual characteristics and is involved in the production of sperm.

The body responds to blood glucose level changes so cells have a constant supply of glucose for respiration.
When blood glucose rises, the pancreas make insulin which allows glucose to move to the cells. Insulin controls the storage of glycogen in the liver and muscles. Glycogen can be converted to glucose anytime, and when glycogen stores are full excess glucose is converted to lipids and stored.
When blood glucose falls, the pancreas makes glucagon which breaks down glycogen to glucose to release it back into the blood.

The pancreas keeps blood glucose constant using negative feedback control, switching between the two.

There are two types of diabeties:

• Type 1 diabetes is when the pancreas makes little insulin so blood  glucose may be high, and the kidneys excrete glucose in the urine. More urine is made and you are thirsty more often. You have less energy and lose weight.  Type 1 may be genetic and usually starts in young people.
• Type 2 usually starts in older people and is caused by obesity or lack of exercise, or genetically. The pancreas make less insulin than necessary or the body cells don't respond to insulin.

Type 1 includes:

• Replacement insulin before meals as an injection into the blood. Regular meals are needed, as well as exercise and a certain amount of carbohydrates.
• Doctors can transplant the pancreas but it is risky and difficult, and medicine must be exchanged.
• Pancreatic cells making insulin can also be transplanted.
• There is also genetic engineering, or producing insulin secreting cells from embryonic stem cells, but there are rejection issues and ethical issues. More research is needed.

Type 2:

• Losing weight
• Balanced diet
• Exercise
• Certain drugs
• Insulin injections

Negative feedback systems work to maintain a steady state; whatever the initial change, the response causes the opposite.

The thyroid uses iodine to produce thyroxine which controls metabolic rate and is involved in growth and development. Thyroxine levels in adults are stable as a result of negative feedback control with the pituitary gland and TSH.

The adrenal glands secrete adrenalin which raises mental awareness, dilates the eyes, increases the heart and breathing rate, and boosts the delivery of oxygen to the brain and muscles. It is not a negative feedback loop.

Reproductive hormones control the development of secondary sexual characteristics.

High oestrogen levels trigger the development of secondary sexual characteristics. The menstrual cycle is when an egg starts maturing in the ovaries monthly, and the uterus lining thickens, and the egg is released after 28 days (ovulation), but if it is unfertilised, the uterus lining is shed along with the egg 2 weeks later. 

FSH causes the egg to mature, LH stimulates the release of an egg, and oestrogen and progesterone stimulate the uterus lining build up and maintain the uterus lining.

Eggs are not produced; they mature and are released monthly. Eventually, the supply runs out (the menopause, when you can't have children and are less fertile, and there is a risk of having a baby with genetic problems).

Sperm is produced. The testes make testerone, whose raised levels triggers changes and causes the secondary sexual characteristics to develop.

FSH is secreted by the pituitary gland and stimulates the ovaries to make oestrogen, which is made in response to FSH.

Oestrogen stimulates the uterus lining to grow again after menstruation. High levels of oestrogen inhibit FSH and stimulate LH.

LH levels fall after ovulation. Progesterone maintains pregnancy and inhibits FSH and LH.

Progesterone maintains the uterus lining in the second half of the menstrual cycle.

Contraception prevents the egg meeting the sperm and the egg implanting in the uterus. 

Oral contraceptives - a pill containing oestrogen and progesterone and inhibits FSH, so no eggs mature. The uterus lining stops developing, and the cervical mucus thickens. There are side effects. 

Contraceptive implants lasts 3 years. It slowly releases progesterone. Injections last 12 weeks. A patch contains progesterone and oestrogen, and is stuck to the skin, replaced weekly, and absorbs the hormones.

The rhythm method is not having sex when you are ovulating or the egg is in the oviduct. There are no side effects, but it is unreliable. Ovulation indicators make it more effective.

Spermicide kills or disables sperm, and may not be effective.

A condom collects semen and prevents the egg and sperm meeting. There are no side effects. They offer some protection against STIs but they can still be damaged. It is likely to be more effective with spermicide.

In a vasectomy, the sperm ducts are cut or tied. In female sterilisation, the oviducts are cut or tied. It is effective and permanent, but a general anesthetic is needed.

Artificial FSH stimulates oestrogen production and egg maturation. Artificial LH causes egg release. It is carefully controlled.

IVF is used if the oviducts are damaged, if there are donor eggs, or if there is no cause for long-term infertility. The woman is given FSH to stimulate egg maturation simultaneously, then given LH to ovulate. The eggs are collected and are fertilised with sperm. The embryo is inserted into the uterus.

IVF  is expensive, not always successful, has health risks, has ethical issues, and has the chances of a multiple pregnancy, but it allows infertile couples to have a baby.

Plants produce hormones to coordinate and control growth and responses to light (phototropism) and gravity (gravitropism or geotropism). Unequal distributions of auxin cause unequal growth rates in plant roots and shoots.

Response to light (phototropism) involves the shoots responding to it from only one side. It bends to grow towards the light. Auxin moves from the lit side to the shoot's unlit side, whose cells elongate. Once light falls evenly, auxin levels are the same.

The response to gravity is geotropism or gravitropism. High auxin levels promote shoot growth, but inhibits root growth.

1. Put 10 cress seeds into three differnt Petri dishes, each lined with moist filter paper.

2. Shine a light onto one of the dishes from above and two of the dishes from different directions.

3. Leave your cress seeds alone for one week. The seeds should be growing towards the light. 

Variables:

Number of seeds- Use the smae number of seeds

Type of seed- Use seeds that all come from the same packet

Temperature- Keep the dishes where the tempertaure is stable

Water- Use a measuring cyclinder to add the same volume of water

Light intensity - Keep the distance between the bulb and dish the same. 

Gibberellin initiates seed germination and breaks down the food stores in seeds. Promotes the growth of the stem. It ends seed dormancy and promotes flowering and increases the size of fruit.

Ethene- involved in cell division and used to ripen fruit.

Rooting powder uses auxin to help the cutting grow to a new plant, since auxin stimulates the root to grow. They are effective weed killers also - extra auxin sends weeds into uncontrolled growth, killing them, but crop plants aren't affected because they don't have broad leaves. This removes competition for light and minerals, and increases crop yield. Auxin is also used in tissue cultures to stimulate growth or cell division in the tissue culture.