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From MyMCAT

Contents 1 Introduction 2 Glands 3 The Hypothalamus 4 The Pituitary Gland 4.1 The Anterior Pituitary 4.2 The Posterior Pituitary

Introduction

A properly functioning endocrine system is vital to the normal development and health of the body. Diabetes, gigantism, and dwarfism are just a few of the limitless list of disorders that can accompany an endocrine disorder. While the MCAT does not expect you to know the exhaustive list of all hormones and their related disorders, you are required to know the major players and be able to reason how changes to their function might effect the body.

Glands

Glands can exist as endocrine or exocrine. In the latter, exocrine glands discharge chemicals into ducts which then allows them to flow to their target. Endocrine glands, on the other hand, release their contents directly into the blood stream. These secreted chemicals, known as hormones, can then flow throughout the entire body until they reach their target. It is these ductless glands that we will discuss below.

The Hypothalamus

The hypothalamus is responsible for many metabolic processes and autonomic nervous system activities. It synthesizes and secretes neurohormones, often called hypothalamic-releasing hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones. The hypothalamus controls body temperature, hunger, thirst,[1] fatigue, and circadian cycles. The hypothalamus has direct control over the pituitary gland in two ways. First, it controls the release of all of the hormones secreted by the posterior pituitary by secreting its own hormones (known as releasing factors) and secondly, it has neurons running into the anterior pituitary which directly secrete hormones into the blood.

The releasing hormones which are used to control the anterior pituitary include TSH-releasing hormone, LH-releasing hormone, Somatostatin (aka GH-inhibiting Hormone), GH-releasing hormone, Corticotropin-releasing hormone, Prolactin-releasing hormone. Note that somatostatin and GH-releasing hormone both control GH but work against each other.

The Pituitary Gland

The pituitary gland, residing at the center of one's brain, is no larger than a pea but capable of producing a powerful array of hormones. The pituitary is made up of two separate halves, the anterior and posterior pituitary respectively, each with its own set of activities.

The Anterior Pituitary

The anterior pituitary is often considered a control center in that four of the six hormones it secretes do not have a direct effect on the body, instead these hormones act on OTHER endocrine glands which in turn to release their own hormones. These hormones that act to stimulate other endocrine glands are called tropic hormones.

Hormone	Effect
Tropic Hormones
Follicle Stimulating Hormone	In females, it stimulates follicles to mature in preparation for ovulation. In males, FSH stimulates maturation of seminiferous tubules and spermatogenesis.
Luteinizing Hormone	In females, LH is used to help mature and maintain the corpus luteum during the menstrual cycle and in the early stages of pregnancy. In males, LH stimulates Leydig cells (in the testis) to produce testosterone.
Adrenocorticotropic Hormone (ACTH)	Stimulates the adrenal gland to synthesize and release gluco- and mineralo-corticosteroids, and androgenic steroids
Thyroid-stimulating hormone	Stimulates the thyroid to synthesize and secrete thyroid hormones (T3 and T4).
Direct Hormones
Prolactin	Prolacin stimulates the mammary glands to produce milk (lactation). Increased serum concentrations of prolactin during pregnancy cause enlargement of the mammary glands of the breasts and increases the production of milk
Endorphin	A secondary product released as a result of ACTH is the synthesis of corticoids such as endorphin.
Growth Hormone (GH)	aka Somatotropin, stimulates growth and cell reproduction and regeneration.

The Posterior Pituitary

Unlike the Anterior Pituitary which is stimulated by hormones from neurons in hypothalamus and trigger it to release its own hormones, the posterior pituitary is actually a a bundle of neurons emanating directly from the hypothalamus which release hormones into the blood stream (in one step rather than two).

Hormone	Effect
Oxytocin	Oxytocin is used both for uterine contraction during labor and to stimulate milk release from the nipple during breast feeding.
Vasopression (or anti-diuretic hormone)	Controls water reabsorption in the collecting ducts of the kidneys thus controlling plasma osmolarity.