Animal Hormones (Edexcel GCSE Biology)

Increased blood flow to the muscles helps the body prepare for fight or flight as greater amounts of glucose and oxygen can be delivered to the cells for aerobic respiration, which releases energy.

False.

The liver is stimulated by adrenaline to change glycogen into glucose.

This raises blood sugar levels for increased respiration and therefore energy release.

Thyroxine controls metabolic rate, e.g. the rate at which carbohydrates are broken down inside cells.

Negative feedback describes a control mechanism that functions to reverse any change in conditions to return to the set point.

Thyroxine is secreted by the thyroid gland in the neck.

If the level of thyroxine falls below normal levels:

1. TRH is released by the hypothalamus

2. this increases the release of TSH from the pituitary gland

3. TSH stimulates the thyroid to release more thyroxine

If the level of thyroxine is too high:

• TRH production is inhibited

• the release of TSH from the pituitary is therefore also inhibited

• less thyroxine is released from the thyroid gland

The menstrual cycle is the sequence of events that includes the thickening of the uterus lining, ovulation and menstruation; it is controlled by a series of hormones.

The stages of the menstrual cycle include:

• days 1-7: the loss of the uterus lining during menstruation

• days 8-14: thickening of the uterus lining

• day 14: release of an egg cell during ovulation

• days 14-28: continued thickening and maintenance of the uterus lining

The days are approximate and will vary between individuals.

Oestrogen is required to stimulate the thickening of the uterus lining.

False.

A decrease in progesterone levels at the end of the cycle results in the loss of the lining during menstruation.

FSH is released by the pituitary gland and causes an egg to start maturing in the ovary.

Oestrogen levels rise from day 1 and peak just before day 14. The peak in oestrogen occurs just before the egg cell is released.

True.

Rising oestrogen levels during the first half of the menstrual cycle inhibit the release of FSH from the pituitary gland..

The pituitary gland releases LH to trigger ovulation (the release of an egg).

The peak in LH occurs as a result of rising oestrogen levels.

Progesterone levels are low from day 1 – 14 and starts to rise once ovulation has occurred. Levels then decrease towards the end of the cycle.

Hormonal contraceptives prevent pregnancy because they prevent the release of a mature egg cell during the menstrual cycle.

False.

Oestrogen is not the hormone responsible for the maturation of the egg. Hormonal contraceptives that inhibit FSH production will ensure that no egg cells mature.

Barrier methods of contraception include:

• condoms

• diaphragms

Barrier methods of contraception might be recommended as:

• they provide protection against sexually transmitted diseases

• the side effects associated with hormonal birth control can be avoided

Infertility refers to the difficulty or inability of a couple to conceive naturally.

ART is technology that increases the chances of pregnancy.

Clomifene is a drug given to women which causes more FSH and LH to be released. This stimulates egg maturation and ovulation.

False.

IVF allows egg cells to be fertilised outside the body.

The main stages of IVF are as follows:

1. mature egg cells are collected from the mother

2. egg cells are fertilised by sperm from the father in the laboratory

3. the fertilised eggs develop into embryos

4. one or two embryos are inserted into the mother's uterus