Hormonal Coordination (H) B1: Humans as Organisms

Hormonal coordination Many process within the body are coordinated by chemicals called hormones. Hormones are secreted by glands into the blood. They are carried in the blood to their target organs. Each hormone has a specific target organ on which it acts to produce a specific effect. The pancreas releases (secretes) the hormones insulin and glucagon which regulate blood glucose concentration. Diabetes is a disease in which blood glucose concentration may rise to a fatally high level because the pancreas does not produce enough insulin. Diabetes may be controlled by careful attention to diet and by injecting insulin into the fat layers under the skin, from where it diffuses into the blood. The quantity of glucose (sugar) in each meal should be regulated. Meals should be taken at regular intervals and related to the insulin intake. What factors in the diet of a diabetic do you think should be controlled?

NormalDiabetic Blood glucose concentration/ millimoles dm Fasting 1 hour after meal 3 hours after meal The bar chart shows the effect of eating 50 grammes of glucose on the blood glucose concentration of a diabetic and a normal person. Label the sets of data as ‘normal’ or ‘diabetic’. Because glucose is an essential substance required for respiration. Why is it necessary for a diabetic to have some glucose? Hormonal coordination

Blood glucose level too lowBlood glucose level too high Hormonal coordination You have already learnt that the pancreas controls the blood glucose concentration by secreting the hormones insulin and glucagon. The pancreas also monitors the blood glucose concentration. It does this by having glucose receptors on the hormone secreting cells. (Beware! Do not confuse the spelling of glucagon and glycogen). Pancreas monitors blood glucose levels and secretes hormones Insulin secreted Glucagon secreted Liver cells convert glucose to insoluble glycogen for storage Liver cells convert glycogen to soluble glucose Blood glucose level returns to normal, detected by pancreas which turns off hormone secretion.

Hormonal coordination The sex organs of both sexes develop before birth but they do not become functional until puberty. Puberty is the stage in development when the sex organs mature. In boys puberty usually occurs between the ages of eleven and fifteen. In girls it usually occurs at the age of twelve or thirteen. The changes that occur in puberty are stimulated by the sex hormones which begin to be secreted in larger amounts at this time. The changes that occur at this time are called secondary sexual characteristics. Testosterone is the male sex hormone and oestrogen is the female sex hormone. These stimulate the development of the secondary sexual characteristics and also stimulate the production of gametes, spermatozoa in the male and eggs in the female.

Hormonal coordination In boys, an increase in secretion of the hormone testosterone (produced by the testes) causes the following secondary sexual characteristics to develop: growth of hair on the face, body and pubis, deepening of the voice, changes in shape and size of the body, which becomes more muscular, changes in behaviour and attitudes, growth of sex organs which start to function. In girls, an increase in the secretion of the hormone oestrogen (produced by the ovaries) causes the following secondary sexual characteristics to develop: growth of pubic hair and hair in the armpits, changes in the shape of the body which becomes more rounded with broader hips, growth of the breasts (mammary glands), changes in behaviour and attitudes, growth of sex organs which start to function, menstrual cycles and periods start to occur.

Hormonal coordination The monthly cycle which controls the release of eggs by a woman’s ovaries is controlled by hormones. These hormones can be deliberately used to increase or reduce fertility. Hormones in the women regulate: the monthly development and release of an egg from the ovaries; the monthly changes in the thickness of the lining of the womb (uterus). A hormone is: A chemical secreted by glands and released into the blood. It is carried to a specific target organ where it causes a particular response.

Hormonal coordination Several hormones are involved in the menstrual cycle of a woman. The hormones that are involved in promoting the development and release of an egg include:- Tissues of ovary Developing egg Structure of the ovary. FSH secreted by the pituitary gland, causes an egg to mature in one of the ovaries, and stimulates the ovaries to secrete hormones, including oestrogen. Oestrogen secreted by the ovaries, inhibits the further production of FSH as well as stimulating the pituitary gland to produce a hormone called LH. LH secreted by the pituitary gland, stimulates the release of the egg from the ovary (ovulation) about the middle of the menstrual cycle and stimulates the secretion of progesterone. Progesterone secreted by the ovaries helps to maintain the thickness of the uterus ready to implant a fertilised egg. In pregnancy it is secreted by the placenta and maintains the uterus in a state suitable to support a pregnancy.

Hormonal coordination Release of FSH Stimulates ovaries to release oestrogen Stimulates egg maturation in ovaries Oestrogen inhibits FSH release Pituitary gland in brain Release of LH Oestrogen stimulates release of LH LH stimulates release of an egg from an ovary (ovulation) Hormones involved in egg maturation and release (ovulation)

Many body hormones can now be synthesized outside the body, by chemical, microbiological or genetic engineering methods. They can be given to people in tablet form, or via injections, if required. Fertility in women can be controlled by giving: hormones that stimulate the release of eggs from the ovaries. These are referred to as fertility drugs because they increase the woman’s fertility. hormones that prevent the release of eggs from the ovaries. These are oral contraceptives (‘the pill’) and they reduce the woman’s fertility. Hormonal coordination

The commonest type of oral contraceptive pill acts by preventing ovulation (the release of mature eggs from the ovaries). It is taken for 21 consecutive days out of every 28 and if taken properly it is the most reliable form of contraception (99% effective). It is also reversible, in the sense that the woman will regain her fertility once she stops taking the pill. However, some women do experience side-effects when taking the pill. Oral contraceptives can only be obtained with a doctor’s prescription. Possible side effects of taking the pill include, weight gain, nausea, development of acne (spottiness of the skin), fatigue, emotional upset and breast tenderness. There is also a slight increase in the risk of cervical cancer and in the tendency of the blood to clot, particularly in the deep leg veins. Apart from protecting against pregnancy oral contraceptives have other advantageous effects. For example, they reduce menstrual blood loss and so reduce the risk of anaemia developing, they reduce the risk of developing cancer of the womb, ovarian cancer and ovarian cysts. They also reduce premenstrual tension and menstrual pain. If given to women after the menopause (when periods have ceased) they reduce the risk of calcium loss from the bones which causes the development of osteoporosis.

Hormonal coordination What are the main reasons for using contraceptive pills? Family planning, birth control, to prevent unwanted pregnancies.The effects are reversible. Contraceptive pills can reduce the risk of developing certain conditions. List some of these. Reduces risk of developing osteoporosis, anaemia, cancer of the womb, ovarian cancer and ovarian cysts. List possible drawbacks of using contraceptive pills. Has possible side-effects such as weight gain, nausea, acne on the face, fatigue, emotional upset and breast tenderness. It may increase the risk of developing cervical cancer or unwanted blood clots.

Hormonal coordination The uses of hormones in controlling fertility include: giving FSH as a ‘fertility drug’ to a woman whose own level of FSH is too low to stimulate eggs to mature – this will induce her to develop eggs and stand a chance of becoming pregnant, but there is a risk of multiple ovulation and too many fetuses being conceived. giving oral contraceptives which contain oestrogen, to inhibit FSH production so that no eggs mature. Thus conception and pregnancy cannot occur.

Hormonal coordination The hormone adrenaline is secreted from the adrenal glands to prepare the body for increased activity. Body responses to adrenaline secretion include:- Increase in the frequency and force of the heart beat. Thus, in a certain time, more oxygen and glucose can be carried to the muscles. The breathing centres in the brain are stimulated so the rate and depth of breathing increases. Thus more oxygen can enter the blood and go to the muscles, also carbon dioxide can be removed more quickly. Arterioles to the skin and to the gut are constricted. Thus less blood goes to these areas and more is available to go to the skeletal muscles. The muscles of the gut relax and peristalsis is reduced. Thus more energy is available for action by the skeletal muscles. The skeletal muscles become tenser. Thus they are more ready for quick, strong action The liver is stimulated to breakdown stored glycogen to glucose. Thus more glucose is available to skeletal muscles as an energy source. Fat deposits are broken down releasing fatty acids. These are available for respiration making more energy available to the skeletal muscles.