Theory question 107
Hormonal Coordination(a) What are hormones?
(b) In a tabular form, state four differences between nervous coordination and hormonal coordination in humans.
(c) State three effects each of: (i) Over-secretion; (ii) Under-secretion of thyroxin on mammals. (d) Make a diagram 10-12 cm long of the reflex arc and label fully.
Show the model answer
(a) Hormones are chemical messengers produced by ductless (endocrine) glands and carried in the blood to target organs, where they bring about responses.
(b) Nervous vs hormonal: electrical impulses vs chemical substances; carried by neurones vs carried in blood; fast vs slow; short-lived vs long-lasting effect; localised vs widespread effect; can be voluntary vs always involuntary.
(c)(i) Over-secretion (hyperthyroidism): high metabolic rate; weight loss; nervousness and restlessness; fast heartbeat; protruding eyes (exophthalmic goitre); sweating and intolerance of heat.
(ii) Under-secretion: in children – cretinism (stunted growth, mental retardation); in adults – myxoedema (low metabolism, weight gain, sluggishness, puffy skin); goitre; feeling cold.
(d) Diagram 10–12 cm, title, labels: receptor (e.g. skin), sensory neurone, dorsal root and dorsal root ganglion, spinal cord with grey and white matter, relay neurone, motor neurone, ventral root, effector (muscle); arrows showing the direction of the impulse.
Label the direction of the impulse on the reflex arc.