The Endocrine Gland
The endocrine glands refer to the ductless glands. Their secretions are directly released into the blood circulation. As a result, they are highly supplied with blood vessels. The secreted hormones, acts at distance target organs.
It is called the master gland because it controls other glands. It is composed of neural and glandular tissue. It is also called the hypophysis cerebri
- Anatomy- It is spherical in shape and resembles a pea, 1cm in diameter, lies in the sella turcica in the sphenoid bone. The pars intermedia divide the gland into two lobes.
(a) Adenohypophysis which is the anterior lobe has cells that secrete protein hormones. Its embryonic origin is the rathkes pouches on the floor of the mouth.
(b) Neuralhypophysis which is the posterior part is composed of the axons of hypothalamic neurons. They extend downward forming the pituitary stalk. Its embryonic origin is the diencephalon.
- Physiology- the Adenohypophysis is made up of axons from hypothalamic neurosecretory neurons conjugated with glial cells. Secretion of pituitary hormones is controlled by the hypothalamus through a negative feedback system. Inhibitory hormones from the hypothalamus, delivers neuronal impulses to the posterior pituitary gland tissue. They control release of hormones produced in this lobe.
- Organization of structures -Adenohypophysis
(a) Pars distalis – the large section.
(b) Pars tuberalis – tissue that surrounds the infundibular stalk
(c) Pars intermedia – separates posterior lobe from anterior lobe.
(a) Pars nervosa – the bulk of the posterior pituitary
(b) Median eminence – upper section of the Neurohypohysis above the pars tuberalis
(c) (c)Infundibular stalk – the “stem” that connects the pars nervosa to the base of the brain
- Blood supply-
(a)Anterior Pituitary – It gets blood from the superior hypophyseal artery which forms portal vessels and drainage is to the hypothalamic-hypophyseal portal veins.
(c) Posterior arterial blood supply come from the inferior hypophyseal artery.
- Nervous supply-the posterior pituitary is made of axons from the hypothalamus. It receives both the peripheral and autonomic nervous innervations.
- Hormones secreted;
(a) Anterior pituitary Secretes Human Growth Hormone (HGH) or Somatotrophin, Thyrotrophin, Adrenal Cortical Hormone, LH, FSH and Prolactin.
(b) Posterior pituitary- It secretes the Oxytocin which increases uterine contractions and ADH.
- Histology and Cytology- Adenohypophysis is made up of three cell types; acidophils (stain red or orange), basophils (stain blue) and chromophobes (faint staining). Initially, the pars intermedia was thought to be functionless, but some scientists have shown that it produces hormone which control melanocyte formation.