Birth control

‘Birth control’ means taking control over if and when a couple have a child. It may involve:
- contraception to prevent fertilisation
- use of hormones to prevent pregnancies

1. The birth control pill

The pill contains steroid hormones that suppress ovulation.

These synthetic hormones break down more slowly in the body so they act for longer; they are taken as oral contraceptives

• type 1: progesterone only
• type 2: progesterone and oestrogen combined

The woman takes one pill daily for 21 days and then stops for 7 days during which time menstruation occurs.

• oestrogen and progesterone suppress the secretion of FSH and LH from the anterior pituitary gland (negative feedback effect). This prevents the concentrations of FSH and LH from reaching levels that would stimulate ovulation.
• after 21 days, concentration of oestrogen and progesterone fall (inactive pills taken). The uterine lining is no longer maintained and menstruation occurs

Progesterone may allow ovulation to occur BUT is still a contraceptive because:

• it decreases the ability of sperm to fertilise egg
• it makes the mucus in the cervix more viscous à mucus is less easily penetrated by sperm

2. The morning after pill

The pill is taken up to 72 hours after a woman has had unprotected sex.

It contains a synthetic progesterone-like hormone:

• decreases chances of sperm reaching and fertilising the egg
• prevents pregnancy by stopping the embryo from implanting itself into the uterus lining

15.1  Control and co-ordination in mammals The nervous system provides fast communication between receptors and effectors. Transmission between neurones takes place at synapses. a)   compare the nervous and endocrine systems as communication systems that  co-ordinate responses to changes in the internal and external environment  b)   describe the structure of a sensory neurone and a motor neurone c)   outline  the roles of sensory receptor cells in detecting stimuli and stimulating the transmission of nerve  impulses in sensory neurones (a suitable example is the chemoreceptor cell found in human taste buds) d)   describe the functions of sensory, relay and motor  neurones in a reflex arc e)   describe and explain the transmission of an action potential in a myelinated neurone and its initiation from a resting potential (the importance of sodium and potassium ions in impulse transmission should  be emphasised) f) explain the importance of the myelin sheath (saltatory conduction) in determining the speed of nerve  impulses and the refractory period in determining their frequency g)   describe the structure of a cholinergic  synapse and explain how it functions, including the role of calcium  ions h)   outline  the roles of synapses in the nervous system in allowing transmission in one direction  and in allowing connections between one neurone and many  others (summation, facilitation and inhibitory synapses are not required) i) describe the roles of neuromuscular junctions, transverse system tubules and sarcoplasmic reticulum in stimulating contraction in striated muscle j) describe the ultrastructure of striated muscle with particular reference to sarcomere structure k)   explain the sliding filament  model  of muscular contraction including the roles of troponin,  tropomyosin, calcium  ions and ATP. l) explain the roles of the hormones FSH, LH, oestrogen and progesterone in controlling changes in the ovary and uterus during the human menstrual cycle m)  outline  the biological basis  of contraceptive pills containing oestrogen and/or progesterone