Pituitary Hormones Flashcards
What are the hormones of the anterior pituitary?
Human growth hormone (hGH)
Thyroid-stimulating hormone (TSH) or thyrotropin
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Prolactin (PRL)
Adrenocorticotropic hormone (ACTH) or corticotropin
Melanocyte-stimulating hormone (MSH)
What does human growth hormone (hGH) do?
It stimulates secretion of insulin-like growth factors (IGFs) that promote growth, protein synthesis.
What does thyroid stimulating hormone (TSH) or thyrotropin do?
It stimulates synthesis and secretion of thyroid hormones by the thyroid
What does follicle-stimulating hormone (FSH) do?
The ovaries initiate the development of oocytes and the testes stimulate testosterone production.
What does luteinizing hormone (LH) do?
The ovaries stimulate ovulation and the testes stimulate testosterone production.
What does prolactin (PRL) do?
It promotes milk secretion by mammary glands.
What does adrenocorticotropic hormone (ACTH) or corticotropin do?
It stimulate glucocorticoid secretion by the adrenal cortex.
What does melanocyte-stimulating hormone (MSH) do?
It has an unknown role in humans. But it is known to have a mild inflammatory impact as well as causes pigmentation in amphibians.
What is Proopiomelanocortin (POMC)
It is a large protein that is cleaved into smaller proteins such as beta-endorphin, alpha-melanocyte stimulating hormone (MSH), adrenocorticotropic (ACTH) and others. The pituitary gland synthesizes POMC in response to a signal from the hypothalamus; the signal being corticotroponin-releasing hormone (CRH). The hypothalamus releases CRH in response to physiological stressors such as pain, as in the postoperative period. When the protein products of POMC cleavage accumulates in excess, they turn hypothalamic CRH production off - that is, feedback inhibition occurs.
What is growth hormone?
- It is also known as somatotropin, and is a protein hormone of roughly 190 amino acids that is synthesized and secreted by cells called somatotrophs in the anterior pituitary.
- It is a major participant in control of several complex physiological processes, including growth and metabolism.
- It stimulates overall body growth by spurring target cells to grow in size and divide.
- It is also of interest as a drug used in both humans and animals.
What are the direct effects of growth hormone?
- These are the result of growth hormone binding its receptor on target cells.
- Ex// Fat cells (adipocytes) have growth hormone receptors and growth hormone stimulates them to break down triglyceride (lipolysis) and suppresses their ability to take up and accumulate circulating lipids.
- (anti-insulin effects) such as increased lipolysis and increased glucose mobilization. The direct growth of promoting actions of GH include the induction of insulin resistance in peripheral tissues, it causes hyperglycemia.
What are the indirect effect of growth hormone?
- These are primarily mediate by insulin-like growth factor-1 (IGF-1), a hormone that is secreted from the liver in response to growth hormone.
- A majority of the growth promoting effects of growth hormone is actually due to IGF-1 acting on its target cells.
- The indirect IGF-1 dependent growth-promoting actions of GH include: the induction of protein synthesis, increases muscle mass, cartilage and bone growth, DNA and RNA synthesis, and cell proliferation.
What are the effects of growth hormone on growth?
- Growth is a complex process that requires coordinated action of several hormones. The major roles in growth hormone in stimulating body growth is to stimulate the liver and other tissues to secrete IGF-1.
- IGF-1 stimulates proliferation of chondrocytes (cartilage cells), resulting in bone growth.
IGF-1 also appears to be the key player in muscle growth. If stimulates both the differentiation and proliferation of muscle cells. - It also stimulates amino acid uptake and protein synthesis in muscle and other tissues.
What are the metabolic effects of growth hormone?
- Growth hormone has important effect on protein, lipid, and carbohydrate metabolism. In some cases, a direct effect on growth hormone has been clearly demonstrated, in others IGF-1 is thought to be a critical mediator.
- Protein metabolism: In general GH stimulates protein anabolism (synthesis) in many tissues. This effect reflects increased amino acid uptake and increased protein synthesis. (Builds muscle)
- Fat metabolism: GH enhances the use of fat by stimulating triglyceride breakdown. (Burns fat)
- Carbohydrate metabolism: Increases blood glucose - GH is one of many hormones that serves to maintain blood glucose within a normal range. GH is often said to have anti-insulin activity, because it suppresses the abilities of insulin to stimulate uptake of glucose in peripheral tissues and enhances glucose synthesis in the liver.
How is growth hormone secretion controlled?
There are two primary controllers which are two hypothalamic hormones.
1. Growth hormone-releasing hormone (GHRH) is a hypothalamic peptide that stimulates both the synthesis and secretion of growth hormone.
2. Somatostatin (SS) is a peptide produced by several tissues in the body, including the hypothalamus.
Somatostatin inhibits growth hormone release in response to GHRH and to other stimulatory factors such as low blood glucose.
How does IGF-1 inhibit growth hormone?
When there are high levels of IGF-1 in the blood, this leads to decreased secretion of growth hormone by directly suppressing the somatotroph, but also through stimulating the release of somatostatin from the hypothalamus.
What happens if there is a deficiency of growth hormone or receptor defects?
This results in growth retardation or dwarfism. A growth hormone deficiency depends on the age of onset of the disorder. It can result from either a heritable or acquired disease.
What is growth hormone deficiency (GHD) or hypopituitarism?
This occurs in children, who have a deficient pituitary gland that secretes an inadequate amount of growth hormone.
- GHD is characterized by a decrease in growth, delay in skeletal maturation and absence of other explanations for poor growth.
- Growth failure often is apparent by the end of the first year, and growth rates continue to slow during childhood.
- Children with GHD are normally proportioned for age, tend to be overweight for height and have prominent deposits of abdominal fat.
- Many affected patients do not undergo puberty at the appropriate age because of GHD.
What is the treatment for GHD?
The patient will be treated with human growth hormone, the majority of children treated appropriately will reach genetically expected adult heights. Growth hormone therapy is given by injection, either daily or several times per week.
What are the two disorders cause by an excessive secretion of growth hormone?
Giantism and Acromegaly
What is giantism?
Giantism is result of excessive growth hormone secretion that begins in young children or adolescents. It is a rare disorder, usually resulting from a tumor or somatotropes.
What is acromegaly?
Acromegaly results from excessive secretion of growth hormone in adults. The onset of this disorder is typically insidious. Clinically, an overgrowth of bone and connective leads to changes in appearance that might be described as having “coarse features”. The excessive growth hormone and IGF-1 also lead to metabolic problems, including glucose intolerance.
High exposure to GH produces gigantism in youth prior to epithelial fusion and acromegaly in adults.
What are the treatments for excessive secretion of growth hormone?
- Somatostatin analogs
- Growth hormone receptor antagonist
What is growth hormone receptor?
- GH-R belongs to class 1 cytokine receptor superfamily
- Binding the hormone realigns the subunits by rotation and closer opposition, resulting in juxtaposition of the catalytic domains of the associate tyrosine-protein kinase JAK2 below the cell membrane.
- This changes results in activation of JAK2 by transphosphorylation, the phosphorylation of the receptor tyrosines in the cytoplasmic domain, which enables binding of adaptor proteins as well as direct phosphorylation of target proteins.
What are the physiological effects of prolactin?
- Conventional way to look at prolactin is that its major target organ is the mammary gland, and it functions to stimulate mammary gland development and milk production.
- It is difficult to point to a tissue that does not express prolactin receptors.
- There have been several hundred different actions have been reported for prolactin in various species.
What are the two major roles of prolactin in milk production?
- Prolactin induced alveolar growth of the mammary gland. Alveoli are the clusters of cells in the mammary gland that actually secrete milk.
- Prolactin stimulates lactogenesis or milk production after giving birth. Prolactin, along with cortisol and insulin act together to stimulate transcription of the genes that encode milk proteins.
How does prolactin act in mammals?
- Prolactin appears to have stimulatory effects in some species on reproductive or maternal behaviors such as next building and retrieval of scattered young.
- Prolactin determine pelage characteristics in many mammals.
How does dopamine effect prolactin secretion?
Dopamine is secreted into portal blood by hypothalamic neurons, binds to receptors on lactotrophs, and inhibits both the synthesis and secretion of prolactin.
How does stimulation of the nipples and mammary gland, as occurs during nursing, lead to prolactin release?
This effect appears to be due to a spinal reflex arc that causes release of prolactin-stimulating hormones from the hypothalamus.
How does estrogen impact prolactin secretion?
Estrogen can also stimulate prolactin synthesis and secretion. Estrogen increases during late pregnancy, this increases prolactin secretion which prepares the mammary gland for lactation at the end of gestation.
Which peptides are considered as putative prolactin releasing factors (PRFs)?
Thyrotropin releasing hormone (TRH)
Vasoactive intestinal polypeptide (VIP)
Neurohypophysial hormones (oxytocin and vasopressin)
How does nursing affect women who breastfeed?
Women who breastfeed their children have a longer period of amenorrhea and infertility following delivery than women who do not breastfeed.
What is hyperprolactinemia?
Hyperprolactinemia is the excessive secretion of prolactin, it is a relatively common disorder in humans. The conditions has numerous causes, including prolactin-secreting tumors and therapy with certain drugs.
- When in women, it often leads to amenorrhea (lack of menstrual cycles) and galactorrhea (excessive or spontaneous secretion of milk)
- When in men, they often show hypogonadism with decreases sex drive, decreases sperm production and impotence, they also often show breast enlargement (gynecomastia), but they very rarely produce milk.
This disorder can be the result of antipsychotic drugs that target dopamine.
What is the prolactin receptor (PRL-R)?
PRL-R belonging to class 1 cytokine receptor superfamily.
Prolactin functions by binding cell-surface expressed prolactin receptors, initiating signaling cascades, primarily utilizing Janus kinase-signaling transduced and activator of transcription (JAK-STAT)
What are gonadotropins?
Luteinizing and Follicle Stimulating Hormones
- They are known as gonadotropins because they stimulate the gonads.
- In males they are the testes and in female they are the ovaries. These are not necessary for life, but essential for reproduction. These two hormones are secreted from cells in the anterior pituitary called gonadotrophs.
What are the psychological effects of gonadotropins?
Physiological effects of the gonadotropins are known only in the ovaries and testes.
Together they regulate many aspects of gonadal function in both males and females.
What is the role of luteinizing hormone?
In both sexes, LH stimulates secretion of sex steroids from the gonads, testosterone in males and estrogen in females.
What is the role of follicle-stimulating hormone?
FSH stimulates maturation of ovarian follicles. Administration of FSH to humans and animals induces “superovulation” or development of many mature follicles. FSH is also critical for sperm production in males.
What is hypogonadism?
Hypogonadism is when there is diminished secretion of LH and FSH, this can cause failure in gonadal function. Typically when this condition manifests in males, there is a failure to produce normal numbers of sperm; in females abnormal or absent reproductive cycles are commons observed.
What happens when there is an elevation of LH and FSH?
If there are elevated blood levels of gonadotropins, typically this is reflective of a lack of steroid negative feedback. Removal of the gonads from either males or females (a practice commonly done in domesticated animals) leads to a persistent elevation of LH and FSH.
In humans, excessive secretion of FSH and/or LH are most commonly the result of gonadal failure or pituitary tumors.
