Steroids of the Adrenal Cortex
Topics to Cover
- Anatomy, histology and blood supply of adrenal gland
- Pathways of steroid synthesis
- Actions of glucocorticoids, mineralocorticoids and androgens
- Hypothalamic-pituitary-adrenal axis: ACTH and control of glucocorticoid
secretion
- Clinical consequences of dysfunction
Adrenal gland is divided into two parts the cortex and medulla.
The cortex is the outer layers and secretes steroids, the medulla is the inner layers and
secrete catecholamine’s (mainly adrenaline).
This lecture focuses on the cortex and steroids
There are three classes of these steroids:
Glucocorticoids – Mainly cortisol in mammals
Mineralocorticoids – Aldosterone
Androgens – Have relatively minor effects, are sex steroids (can be metabolised in
other tissues to become more potent)
Excess glucocorticoids = Cushing’s
Adrenal insufficiency: (primarily cortisol): Addisons
Adrenal Blood Flow and Functional Zonation
The adrenals are situated above the kidneys and the blood supply is in such a way that
the arterial blood comes in at the outer cortex, drains through network of capillaries
into and through the medulla, where at the venous end it drains out at the inner
medulla.
The cortical tissue, is divided histologically into three zones: Zona glomerulosa, zona
fasiculata and zona reticularis.
There is layer/tissue specific enzyme expression, meaning the adrenal cortex zones
can each act independently, called functional zonation of the cortex. This allows
different hormones to be made in each layer.
Steroid synthesis in one layer can inhibit different enzymes in subsequent layers.
, Steroid Synthesis in the Adrenal Cortex
Steroid synthesis begins from cholesterol, the diagram below shows the various
pathways. Note you don’t need to learn it completely in detail.
There are cytochrome enzymes on the left and top in bold which allow conversion of
different substances.
Running through this, cholesterol could enter into a cell in the zona glomerulosa,
where it is converted into pregnenolone. Pregnenolone could stay in the cell and be
converted to progesterone or it could enter back into the blood and move down to the
zona fasiculata and under action of a new enzyme become a new molecule. Which
could stay or move on etc.
Topics to Cover
- Anatomy, histology and blood supply of adrenal gland
- Pathways of steroid synthesis
- Actions of glucocorticoids, mineralocorticoids and androgens
- Hypothalamic-pituitary-adrenal axis: ACTH and control of glucocorticoid
secretion
- Clinical consequences of dysfunction
Adrenal gland is divided into two parts the cortex and medulla.
The cortex is the outer layers and secretes steroids, the medulla is the inner layers and
secrete catecholamine’s (mainly adrenaline).
This lecture focuses on the cortex and steroids
There are three classes of these steroids:
Glucocorticoids – Mainly cortisol in mammals
Mineralocorticoids – Aldosterone
Androgens – Have relatively minor effects, are sex steroids (can be metabolised in
other tissues to become more potent)
Excess glucocorticoids = Cushing’s
Adrenal insufficiency: (primarily cortisol): Addisons
Adrenal Blood Flow and Functional Zonation
The adrenals are situated above the kidneys and the blood supply is in such a way that
the arterial blood comes in at the outer cortex, drains through network of capillaries
into and through the medulla, where at the venous end it drains out at the inner
medulla.
The cortical tissue, is divided histologically into three zones: Zona glomerulosa, zona
fasiculata and zona reticularis.
There is layer/tissue specific enzyme expression, meaning the adrenal cortex zones
can each act independently, called functional zonation of the cortex. This allows
different hormones to be made in each layer.
Steroid synthesis in one layer can inhibit different enzymes in subsequent layers.
, Steroid Synthesis in the Adrenal Cortex
Steroid synthesis begins from cholesterol, the diagram below shows the various
pathways. Note you don’t need to learn it completely in detail.
There are cytochrome enzymes on the left and top in bold which allow conversion of
different substances.
Running through this, cholesterol could enter into a cell in the zona glomerulosa,
where it is converted into pregnenolone. Pregnenolone could stay in the cell and be
converted to progesterone or it could enter back into the blood and move down to the
zona fasiculata and under action of a new enzyme become a new molecule. Which
could stay or move on etc.
