Overview of Hypothalamic and Pituitary Hormones
You have your hypothalamus and pituitary gland to thank. glands, today we'll focus on just two: the hypothalamus and the pituitary gland. The pituitary consists of an anterior lobe and a posterior lobe, each of which have. Such praise is justified in the sense that the anterior and posterior pituitary secrete a The hypothalamic hormones are referred to as releasing hormones and the anterior pituitary secrete a single hormone (or possibly two in some cases). It has both neural and endocrine functions, producing and secreting many hormones. The hormones secreted by the posterior and anterior pituitary, and the .. the anatomical relationship of the anterior and posterior lobes of the pituitary.
A disease called diabetes insipidus is characterized by chronic underproduction of ADH that causes chronic dehydration. Because little ADH is produced and secreted, not enough water is reabsorbed by the kidneys. Electrolyte imbalances can occur in severe cases of diabetes insipidus.
There are three regions: Recall that the posterior pituitary does not synthesize hormones, but merely stores them. In contrast, the anterior pituitary does manufacture hormones. Like the posterior pituitary the release of hormones from the anterior pituitary is controlled by the hypothalamus.
This control is mediated by secretion of releasing or inhibiting hormones into the blood. Within the infundibulum is a bridge of capillaries that connects the hypothalamus to the anterior pituitary.
This portal system begins with a primary capillary plexus originating from the superior hypophyseal artery, a branches of the internal carotid artery. The anterior pituitary manufactures seven hormones. The hypothalamus produces separate hormones that stimulate or inhibit hormone production in the anterior pituitary.
Hormones from the hypothalamus reach the anterior pituitary via the hypophyseal portal system. The anterior pituitary produces seven hormones. Growth Hormone Growth hormone GHalso called somatotropin regulates the growth of the human body, protein synthesis, and cellular replication. Its primary function is anabolic; it promotes protein synthesis and tissue building through direct and indirect mechanisms Figure Growth hormone GH directly accelerates the rate of protein synthesis in skeletal muscle and bones.
Insulin-like growth factor 1 IGF-1 is activated by growth hormone and indirectly supports the formation of new proteins in muscle cells and bone. A glucose-sparing effect occurs when GH stimulates lipolysis, or the breakdown of adipose tissue, releasing fatty acids into the blood.
As a result, many tissues switch from glucose to fatty acids as their main energy source, which means that less glucose is taken up from the bloodstream. GH also initiates the diabetogenic effect in which GH stimulates the liver to break down glycogen to glucose, which is then released into the blood.
Blood glucose levels rise as the result of a combination of glucose-sparing and diabetogenic effects. GH indirectly mediates growth and protein synthesis by triggering the liver and other tissues to produce a group of proteins called insulin-like growth factors IGFs. These proteins enhance cellular proliferation and inhibit apoptosis, or programmed cell death. IGFs stimulate cells to increase their uptake of amino acids from the blood for protein synthesis.
Skeletal muscle and cartilage cells are particularly sensitive to stimulation from IGFs. For example, gigantism is a disorder caused by the hypersecretion of GH before the growth plates have closed resulting in excessive growth of all bones. Abnormally low levels of GH in children can cause growth impairment—a disorder called pituitary dwarfism also known as growth hormone deficiency which affects all bones.
Achondroplastic dwarfism affects only the bones with growth plates long bones resulting in short arms and legs with normal sized trunk and head. Thyroid-Stimulating Hormone The activity of the thyroid gland is regulated by thyroid-stimulating hormone TSHalso called thyrotropin. TSH is released from the anterior pituitary in response to thyrotropin-releasing hormone TRH from the hypothalamus.
As will be discussed shortly, it triggers the secretion of thyroid hormones by the thyroid gland. In a classic negative feedback loop, elevated levels of thyroid hormones in the bloodstream then trigger a drop in production of TRH and TSH. ACTH come from a precursor molecule known as pro-opiomelanotropin POMC which produces several biologically active molecules when cleaved, including ACTH, melanocyte-stimulating hormone, and the brain opioid peptides known as endorphins.
An Overview of the Pituitary Gland - The Endocrine System’s Master Gland
The release of ACTH is regulated by the corticotropin-releasing hormone CRH from the hypothalamus in response to normal physiologic rhythms.
A variety of stressors can also influence its release, and the role of ACTH in the stress response is discussed later in this chapter. Follicle-Stimulating Hormone and Luteinizing Hormone The endocrine glands secrete a variety of hormones that control the development and regulation of the reproductive system these glands include the anterior pituitary, the adrenal cortex, and the gonads—the testes in males and the ovaries in females.
Much of the development of the reproductive system occurs during puberty and is marked by the development of sex-specific characteristics in both male and female adolescents.
Puberty is initiated by gonadotropin-releasing hormone GnRHa hormone produced and secreted by the hypothalamus. GnRH stimulates the anterior pituitary to secrete gonadotropins—hormones that regulate the function of the gonads. The levels of GnRH are regulated through a negative feedback loop; high levels of reproductive hormones inhibit the release of GnRH. Throughout life, gonadotropins regulate reproductive function. The gonadotropins include two glycoprotein hormones: FSH also promotes ovarian follicular growth in women; these follicles then release estrogens.
Luteinizing hormone LH triggers ovulation in women, as well as the production of estrogens and progesterone by the ovaries. LH stimulates production of testosterone by the male testes. Prolactin As its name implies, prolactin PRL promotes lactation milk production in women.
After birth, it stimulates the mammary glands to produce breast milk. However, the effects of prolactin depend heavily upon the permissive effects of estrogens, progesterone, and other hormones.
The Pituitary Gland and Hypothalamus | Anatomy & Physiology
And as noted earlier, the let-down of milk occurs in response to stimulation from oxytocin. In a non-pregnant woman, prolactin secretion is inhibited by prolactin-inhibiting hormone PIHwhich is actually the neurotransmitter dopamine, released from neurons in the hypothalamus.
The anterior lobe produces and releases hormones. The posterior lobe does not produce hormones per se—this is done by nerve cells in the hypothalamus—but it does release them into the circulation. Hormones of the Pituitary Gland The hormones of the pituitary gland send signals to other endocrine glands to stimulate or inhibit their own hormone production.
The anterior lobe releases hormones upon receiving releasing or inhibiting hormones from the hypothalamus. These hypothalamic hormones tell the anterior lobe whether to release more of a specific hormone or stop production of the hormone. ACTH stimulates the adrenal glands to produce hormones. FSH works with LH to ensure normal functioning of the ovaries and testes. GH is essential in early years to maintaining a healthy body composition and for growth in children. In adults, it aids healthy bone and muscle mass and affects fat distribution.
LH works with FSH to ensure normal functioning of the ovaries and testes. Prolactin stimulates breast milk production. TSH stimulates the thyroid gland to produce hormones.
The posterior lobe contains the ends of nerve cells coming from the hypothalamus. The hypothalamus sends hormones directly to the posterior lobe via these nerves, and then the pituitary gland releases them. This hormone prompts the kidneys to increase water absorption in the blood.