#122 Hormonal communication

Hormones like adrenaline, insulin, glucagion and ADH

- cell-signalling molecules
- made in endocrine glands; glands are groups of cells that secrete (produce and release) one or more substances
- passed directly into the blood

Steroid hormones are lipid soluble à pass through phospholipid bilayer and binds to receptor molecules inside the cytoplasm/nucleus and activate processes

Menstrual cycle: changes that reoccur in the ovary and uterus every 28 days involving:

• ovulation
• menstruation: the breakdown and loss of the uterus lining

* uterine cycle and ovarian cycle are synchronized

The menstrual cycle is coordinated by glycoprotein hormones secreted by the anterior pituitary gland and ovaries

1. During menstruation, the anterior pituitary gland secretes

• follicle stimulating hormone (FSH)
• luteinising hormone (LH)

Concentrations of FSH and LH increase over the next few days à control activity of ovaries – responsible for ovulation

2. In the ovary, one follicle becomes the ‘dominant’ one

• the presence of FSH and LH stimulates cells surrounding the follicle to secrete oestrogen
• the production of oestrogen induces a negative feedback and decreases the production and concentration of FSH and LH

Oestrogen stimulates the endometrium to:

• grow, thicken
• develop numerous blood capillaries

3. There is a surge of LH secretion and a slight increase in FSH secretion. The high concentration of LH causes the follicle to burst and shed the gamete into the oviduct. The remnants of the follicle collapse and forms the corpus luteum (yellow body)

Corpus luteum secretes:

• progesterone: inhibits the anterior pituitary gland from secreting FSH and LH à no more follicles develop
• some oestrogen

à maintains the uterus lining so that it’s ready to receive an embryo if fertilisation occurs

4. Low stimulation of the corpus luteum causes it to degenerate. As a result, less oestrogen and progesterone is secreted and their concentrations decrease à

• endometrium is not maintained à menstruation begins
• releases inhibition of anterior pituitary gland à FSH gets secreted à another cycle begins!

Syllabus 2016-2018 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