This is a low power image of the adrenal gland (Masson's Trichrome
stain). Can you identify the capsule, adrenal cortex and component
regions: zona glomerulosa, zona fasciculata and zona reticularis
and adrenal medulla.
These are a pair of glands, one associated with each kidney.
They have an inner medulla and outer cortex, and there are different
types of endocrine tissue in each.
The embryological origin of the cortex, is similar to that of the
gonads. The embryological origin of the medulla is the same as that
of the sympathetic nervous system.
All the hormones secreted by this region are steroid hormones,
which are all based on cholesterol. Secretory cells, secrete steroid
based hormones, and contain triglyceride droplets. The cortex
can be divided into three regions:
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis
Different hormones are secreted from each of these regions
1. Zona glomerulosa, the outermost zone of the
adrenal cortex secretes mineralcorticoids. These
hormones are important for fluid homeostasis. These include aldosterone,
which regulates absorption/uptake of K+ and Na+ levels in the
The secretory cells are arranged in irregular ovoid clusters
that are surrounded by trabeculae which contain capillaries. Can
you identify them?
The nuclei stain strongly, and the cytoplasm is less pale than
that of the next zone, the zona fasciculata, as there are fewer
lipid droplets in these cells.
2. Zona fasciculata, the middle zone of the
adrenal cortex secretes glucocorticoids which
are important for carbohydrate, protein and lipid metabolism.
An example is cortisol which raises blood glucose and cellular
synthesis of glycogen. Its secretion is controlled by a hormone
from the pituitary - ACTH.
The secretory cells are arranged in cords, often one cell thick,
surrounded by fine strands of supporting tissue. Can you identify
The nuclei of these cells stain strongly, and the cytoplasm is
rich in sER, mitochondria and lipid droplets. The cytoplasm looks
pale and 'foamy' due to the presence of lipid droplets.
3. Zona reticularis, the innermost layer of
the cortex, secretes sex hormones (androgens).
and small amounts of glucocorticoids. These hormones
are secreted by the inner zone of the cortex, which is called
the zona reticularis.
Some brown pigment is seen in some of these cells - this is lipofuscin,
probably an insoluble degradation product of organelle turnover
- an 'age' pigment. The cytoplasm of the cells in this region
stains more darkly, and contains fewer lipid droplets.
identify the secretory cells and pigment?
This region of the adrenal glands contains basophilic staining cells, with a
granular cytoplasm and no stored lipid.
It also contains many venous channels which drain blood from the
sinusoids of the cortex, pass through the medulla, and drain into
the medullary vein.
This is because these cells are actively secreting the peptide
based hormones - nor-adrenaline and adrenalin
(catecholamines), which are stored in the granules.
you identify veins and secretory cells?
Secretion of these hormones is controlled by the sympathetic
nervous system. The targets of these hormones are the adrenergic
receptors in the heart, blood vessels, bronchioles, visceral muscle,
skeletal muscle, and in the liver, where they promote glycolysis
(breakdown of glycogen).