The pituitary gland consists of a stalk linking the pituitary to the hypothalamus, which controls release of pituitary hormones. The pituitary gland has two lobes: the anterior and posterior lobes.
The anterior pituitary is a glandular structure under contorl of the hypothalamus. Together, the pituitary gland and hypothalamus control many endocrine functions. They secrete many hormones, some of which are crucial for the female menstrual cycle, preganncy, birth, and lactation. These important hormones include follicle-stimulating hormone (FSH), which stimulates development and maturation of a follicle in one of a woman's ovaries, and leutinizing hormone (LH), which causes the bursting of that follicle (= ovulation) and the formation of a corpus luteum from the remains of the follicle.
The posterior pituitary stores and releases hormones into the blood. Antidiuretic hormone (ADH) and oxytocin are produced in the hypothalamus and transported by axons to the posterior pituitary where they are dumped into the blood. ADH controls water balance in the body and blood pressure. Oxytocin is a small peptide hormone that stimulates uterine contractions during childbirth.
The hypothalamus produces releasing hormone TRH (thyrotropin releasing hormone) that causes the anterior pituitary to release TSH (thyroid stimulating hormone) that cause the thyroid gland to release thyroid hormones. Thyroid hormones (thyroxine and triiodothyroxonine) regulate carbohydrate metabolism by cells, and early in life, are involved in growth. Low circulating levels increase TRH and TSH output; high levels reduce their output. Goiter.
Posterior pituitary gland
Cell bodies in the supraoptic and paraventricular nuclei of the hypothalamus send axons via the pituitary stalk to terminals in the posterior pituitary that release two hormones into the bloodstream. Vasopressin, a.k.a. antidiuretic hormone (ADH), acts on the kidney to inhibit formation of urine, to conserve water and increase blood pressure.
Oxytocin stimulates contraction of the uterus during childbirth, triggers the milk letdown reflex during nursing, and may be the “love” hormone, released by terminals outside the hypothalamus.
Although suckling alone causes oxytocin release at first, the mother may become conditioned to release oxytocin upon hearing the baby’s cry. Thus, higher faculties can control hypothalamic and thus hormonal output.
Anterior pituitary gland (tropic hormones)
Hypothalamic cells produce specific releasing hormones and inhibiting hormones, which they secrete from axon terminals in the median eminence into a portal system of blood vessels to flood the anterior pituitary, causing the latter cells to release their specific tropic hormones. Tropic hormones are pituitary hormones that affect other endocrine glands.
The anterior pituitary releases six tropic hormones:
|Adrenocorticotropic hormone (ACTH)||controls release by the adrenal cortex of steroid hormones.|
|Thyroid-stimulating hormone (TSH)||increases thyroid hormone release.|
|Follicle-stimulating hormone (FSH)||stimulates sperm production or egg-containing follicles.|
|Luteinizing hormone (LH)||stimulates the testes to release testosterone and follicles to form the corpora lutea, which releases progesterone. FSH and LH stimulate the ovaries to release estrogen.|
|Prolactin||stimulates lactation in females and is involved in parenting behavior. Prolactin is secreted by the anterior pituitary. Prolactin is secreted near the end of pregnancy and prepares the breasts for milk production.|
|Growth hormone (GH)||release of which is controlled by somatotropin or somatotropic hormone, influences growth, mostly during sleep. The stomach hormone ghrelin also evokes GH release.|