Anterior Pituitary vs. Posterior Pituitary
Hormones secreted by anterior/posterior
Anterior Pituitary vs. Posterior Pituitary
The anterior pituitary is also known as adenohypophysis while posterior pituitary is known as neurohypophysis as it is connected with the hypothalamus neurons. The anterior pituitary secretes its own hormones on the other side a posterior pituitary does not secrete its own hormones but stores and then releases the hormones produced by the hypothalamus. The supply of blood to the anterior pituitary is via the hypothalamic portal system; on the other hand, the supply of posterior pituitary is through inferior hypophyseal arteries. Hormones produced by the anterior pituitary are ACH, LH, FSH, HGH, MSH, TSH and PRL whereas the hormones regulated by the posterior pituitary are antidiuretic hormone and oxytocin. Anterior pituitary targets the adrenal gland, thyroid gland, liver, gonads, mammary gland, and skin while posterior pituitary targets the kidneys, sweat gland, uterus, and mammary gland. Anterior pituitary arises from the infolding of the oral ectoderm while posterior pituitary originates from the myelinated neuronal tissue.
What is Anterior Pituitary?
The anterior pituitary is a lobe of the pituitary gland which regulates several physiological processes like stress, reproduction, growth, and lactation. The anterior pituitary is also called the adenohypophysis. The anterior pituitary arises from the infolding of the oral ectoderm and then forms Rathke’s pouch. This contrasts with the posterior pituitary which arises from neuroectoderm. Endocrine cells of the anterior pituitary are controlled by regulatory hormones that are released from the parvocellular neurosecretory cells present in the hypothalamic capillaries leading to infundibular blood vessels, which in turn lead to a second capillary bed present in the anterior pituitary. This vascular relationship is comprised of the hypothalamo-hypophyseal system. Spreading out of the second capillary bed, the hypothalamic releasing hormone and then binds to anterior pituitary endocrine cells.
The anterior lobe of the pituitary is divided into the pars tuberalis that is also known as pars glandularis and pars distalis that is also known as pars glandularis that constitutes about 80% of the gland. The pars intermedia (the intermediate lobe) is present between the pars distalis and the pars tuberalis, and it is rudimentary in the human, although in all other species it is in a more developed form. It originates from a depression in the dorsal wall of the pharynx that is a stomal part and also known as Rathke’s pouch. The anterior pituitary contains many different types of cells which synthesize and secrete hormones. Generally, there is one type of cell for each major hormone formed in the anterior pituitary.
What is Posterior Pituitary?
The posterior pituitary is a lobe of the pituitary gland which is functionally connected to the hypothalamus with the median eminence through a small tube called the pituitary stalk, and it is also called the infundibulum or infundibular stalk. The posterior pituitary is also known as the neurohypophysis. The posterior pituitary is a neural tissue. It consists of the distal axon of the hypothalamic neurons and makes the neurohypophysis. Posterior pituitary does not secrete its own hormones, but it stores and release the hormones which are created by the hypothalamus. The cell bodies of these axons are present in the paired supraoptic nuclei and paraventricular nuclei. The blood supply for the posterior pituitary is through inferior hypophyseal arteries. Hypophyseal arteries are the branches of the posterior and internal carotid arteries.
The drainage is into the internal jugular veins and cavernous sinus. Two different hormones are secreted by the posterior pituitary. One is oxytocin, and the other one is vasopressin that is also known as the antidiuretic hormone. The targeted areas of the oxytocin are uterus and mammary glands and help in uterine contraction and may help in lactation. Another hormone target the kidneys and arterioles which may stimulate water retention and also raises blood pressure by contracting the arterioles. In case of insufficient secretion of the vasopressin may underlie the diabetes insipidus in which the body loses the capacity to concentrate the urine. But in case of over secretion of the vasopressin causes the syndrome of inappropriate antidiuretic hormone.