Question

In a post of at least 300 words, respond to the following:

1. Compare the pathway for synthesis and delivery of anterior vs posterior pituitary hormones.
2. Discuss the conduits that deliver these hormones to their targets.
3. Trace the pathways by which hormones will take to reach all bodily tissues (i.e., head, fingers, toes, viscera).
4. Predict possible medical conditions that can arise if the endocrine and cardiovascular systems fail to work with each other to maintain homeostasis. Discuss possible anatomical and physiological changes in the body.

Answer 1

The anterior pituitary hormones are-

* Growth hormone - It is a protein and promotes growth of body tissues.

* Prolactin - It is a peptide and promotes milk production from mammary glands.

* Thyroid stimulating hormone - It is a glycoprotein and stimulates the release of thyroid hormone from the thyroid gland

* Adrenocorticotropic hormone - This is a peptide and stimulates the release of hormone from the adrenal cortex.

* Follicle stimulating hormone - It is a glycoprotein and stimulates gamete production in in gonads.

* Luetinizing hormone - This is a glycoprotein and stimulates the production of androgen by gonads.

The posterior pituitary hormones-

* Antidiuretic hormone - It is a peptide and stimulates water reabsorption in the kidneys.

* Oxytocin - This is a peptide and stimulates contraction of uterus during childbirth.

Besides these, there is an intermediate hormone, called Melanocyte stimulating hormone, which stimulates the formation of melanin in the melanocytes.

In fact, the posterior pituitary does not produce hormones but it stores and secretes hormones produced by the hypothalamus. The hypothalamus is a small gland which coordinates the stimulus from the nervous system to the endocrine system. The hormones produced by the hypothalamus travel along the axons into storage sites in the axon terminals of the posterior pituitary. In response to stimulus from the same hypothalmic neurons, the hormones are released from the axon terminals into the bloodstream.

In contrast, the anterior pituitary does produce hormone. The secretion of hormone from the anterior pituitary is controlled by two classes of hormones secreted by the hypothalamus - 'releasing hormones' and 'stimulating hormones'. The hypothalmic hormones are secreted by neurons into the blood stream from where they reach the anterior pituitary. Within the infundibulum there is a bridge of capillaries that connects the hypothalamus to the anterior pituitary. This is called the hypophyseal portal system. The hormones enter the antirior pituitary without entering the systemic circulation. The hormones from anterior pituitary enter a secondary capillary plexus and from here into the circulation, being carried to the target cells or organ.

The release of hormones from the endocrine organs is controlled by a negative feedback loop and is controlled by the pituitary gland. As mentioned above, pituitary hormones are divided into two categories - stimulating hormones, which stimulate the specific gland to secrete hormone, and inhibiting hormones, which tell the specific endocrine organ to stop secreting its hormone. Since the hormones reach the various cells and tissues through the blood, the circulatory system has an important role maintaining hormone homeostasis.

For example-

The thyroid gland secretes the hormone thyroxine on getting stimulated by the Thyroid stimulating hormone [TSH] secreted by the anterior pituitary. When the level of thyroxine in blood reaches the optimum level, signals reach the pituitary to stop secreting TSH, as a result of which, the thyroid gland stops secreting thyroxine. In this way homeostasis is maintained.