‘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 The uterine lining is no longer maintained and menstruation occurs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 |
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