The adrenal glands are located above the kidneys and are composed of an outer cortex and inner medulla. The cortex produces three types of hormones - glucocorticoids, mineralocorticoids, and sex hormones. Glucocorticoids such as cortisol help regulate metabolism and the stress response, while mineralocorticoids like aldosterone control water and electrolyte balance. The medulla secretes adrenaline and noradrenaline in response to sympathetic nervous system stimulation to initiate the fight-or-flight response. Both parts of the adrenal glands help maintain homeostasis during stress.
13. They are essential for life,
regulating metabolism and
responses to stress.
14. Secretion is stimulated by ACTH from the
anterior pituitary and by stress.
In non-stressful conditions secretion
hasmarked circadian variations.
15. The highest level of hormones occurs
between 4 a.m. and 8 a.m. and the lowest,
between midnight and 3 a.m.
16. When the sleeping and waking pattern is
changed it takes several days for
adjustment of the ACTH/cortisol
secretion to take place.
19. Stimulating breakdown of protein,
releasing amino acids,
which can be used for synthesis of other
proteins,
e.g. enzymes, or for energy (ATP)
production.
25. It stimulates the reabsorption of sodium
(Na+) by the renal tubules and excretion of
potassium (K+) in the urine.
26. Sodium reabsorption is also accompanied
by retention of water
and therefore aldosterone is involved in the
regulation of blood volume and blood
pressure too.
27. The blood potassium level regulates the
amount of aldosterone produced by the
adrenal cortex.
28. When the blood potassium level rises,
more aldosterone is secreted.
Low blood potassium has the opposite
effect.
31. Renin converts the plasma protein
angiotensinogen,
produced by the liver, to angiotensin 1.
32. Angiotensin converting enzyme (ACE),
formed in small quantities in the lungs,
proximal kidney tubules and other tissues
converts angiotensin 1 to angiotensin 2,
which stimulates secretion of aldosterone.
33. It also causes vasoconstriction and
increases blood pressure.
34. SEX HORMONES
Sex hormones secreted by the adrenal
cortex are mainly androgens (male sex
hormones) and the amounts produced are
insignificant compared with those secreted
by the testes and ovaries in late puberty
and adulthood.
35. Their role is unclear but it is thought that
they contribute to the onset of puberty.
An elevated level in females causes
masculinisation.
Control of secretion is poorly understood.
36. ADRENAL MEDULLA
The medulla is completely surrounded by
the cortex.
It develops from nervous tissue in the
embryo and is part of the sympathetic
division of the autonomic nervous system.
37. It is stimulated by its extensive sympathetic
nerve supply to produce the hormones
adrenaline and nor adrenaline.
42. Diverting blood to essential organs including
the heart, brain and skeletal muscles by dilating
their blood vessels and constricting those of
less essential organs, such as the skin.
44. Adrenaline has a greater effect on the heart
and metabolic processes whereas
noradrenaline has more influence on blood
vessels.
45. RESPONSE TO STRESS
When the body is under stress homeostasis
is disturbed.
To restore it and, in some cases, to maintain
life there are immediate and, if necessary,
longer-term responses.
46. Stressors include exercise, fasting, fright,
temperature changes, infection, disease and
emotional disturbances/ situations.
48. In the longer term, ACTH from the anterior
pituitary stimulates the release of
glucocorticoids and mineralocorticoids
from the adrenal cortex and a more
prolonged response to stress occurs.