Module 12: The Endocrine System

Lesson 3: The Pituitary Gland and Hypothalamus

Tuyến Yên Và Vùng Dưới Đồi

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Mỗi bài học (lesson) bao gồm 4 phần chính: Thuật ngữ, Luyện Đọc, Luyện Nghe, và Bàn Luận.
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Dưới đây là danh sách những thuật ngữ Y khoa của module The Endocrine System.
Khái quát được số lượng thuật ngữ sẽ xuất hiện trong bài đọc và nghe sẽ giúp bạn thoải mái tiêu thụ nội dung hơn. Sau khi hoàn thành nội dung đọc và nghe, bạn hãy quay lại đây và luyện tập (practice) để quen dần các thuật ngữ này. Đừng ép bản thân phải nhớ các thuật ngữ này vội vì bạn sẽ gặp và ôn lại danh sách này trong những bài học (lesson) khác của cùng một module.

Medical Terminology: The Endocrine System

acromegaly
disorder in adults caused when abnormally high levels of GH trigger growth of bones in the face, hands, and feet
adenylyl cyclase
membrane-bound enzyme that converts ATP to cyclic AMP, creating cAMP, as a result of G-protein activation
adrenal cortex
outer region of the adrenal glands consisting of multiple layers of epithelial cells and capillary networks that produces mineralocorticoids and glucocorticoids
adrenal glands
endocrine glands located at the top of each kidney that are important for the regulation of the stress response, blood pressure and blood volume, water homeostasis, and electrolyte levels
adrenal medulla
inner layer of the adrenal glands that plays an important role in the stress response by producing epinephrine and norepinephrine
adrenocorticotropic hormone (ACTH)
anterior pituitary hormone that stimulates the adrenal cortex to secrete corticosteroid hormones (also called corticotropin)
alarm reaction
the short-term stress, or the fight-or-flight response, of stage one of the general adaptation syndrome mediated by the hormones epinephrine and norepinephrine
aldosterone
hormone produced and secreted by the adrenal cortex that stimulates sodium and fluid retention and increases blood volume and blood pressure
alpha cell
pancreatic islet cell type that produces the hormone glucagon
angiotensin-converting enzyme
the enzyme that converts angiotensin I to angiotensin II
antidiuretic hormone (ADH)
hypothalamic hormone that is stored by the posterior pituitary and that signals the kidneys to reabsorb water
atrial natriuretic peptide (ANP)
peptide hormone produced by the walls of the atria in response to high blood pressure, blood volume, or blood sodium that reduces the reabsorption of sodium and water in the kidneys and promotes vasodilation
autocrine
chemical signal that elicits a response in the same cell that secreted it
beta cell
pancreatic islet cell type that produces the hormone insulin
calcitonin
peptide hormone produced and secreted by the parafollicular cells (C cells) of the thyroid gland that functions to decrease blood calcium levels
chromaffin
neuroendocrine cells of the adrenal medulla
colloid
viscous fluid in the central cavity of thyroid follicles, containing the glycoprotein thyroglobulin
cortisol
glucocorticoid important in gluconeogenesis, the catabolism of glycogen, and downregulation of the immune system
cyclic adenosine monophosphate (cAMP)
second messenger that, in response to adenylyl cyclase activation, triggers a phosphorylation cascade
delta cell
minor cell type in the pancreas that secretes the hormone somatostatin
diabetes mellitus
condition caused by destruction or dysfunction of the beta cells of the pancreas or cellular resistance to insulin that results in abnormally high blood glucose levels
diacylglycerol (DAG)
molecule that, like cAMP, activates protein kinases, thereby initiating a phosphorylation cascade
downregulation
decrease in the number of hormone receptors, typically in response to chronically excessive levels of a hormone
endocrine gland
tissue or organ that secretes hormones into the blood and lymph without ducts such that they may be transported to organs distant from the site of secretion
endocrine system
cells, tissues, and organs that secrete hormones as a primary or secondary function and play an integral role in normal bodily processes
epinephrine
primary and most potent catecholamine hormone secreted by the adrenal medulla in response to short-term stress; also called adrenaline
erythropoietin (EPO)
protein hormone secreted in response to low oxygen levels that triggers the bone marrow to produce red blood cells
estrogens
class of predominantly female sex hormones important for the development and growth of the female reproductive tract, secondary sex characteristics, the female reproductive cycle, and the maintenance of pregnancy
exocrine system
cells, tissues, and organs that secrete substances directly to target tissues via glandular ducts
first messenger
hormone that binds to a cell membrane hormone receptor and triggers activation of a second messenger system
follicle-stimulating hormone (FSH)
anterior pituitary hormone that stimulates the production and maturation of sex cells
G protein
protein associated with a cell membrane hormone receptor that initiates the next step in a second messenger system upon activation by hormone–receptor binding
general adaptation syndrome (GAS)
the human body’s three-stage response pattern to short- and long-term stress
gigantism
disorder in children caused when abnormally high levels of GH prompt excessive growth
glucagon
pancreatic hormone that stimulates the catabolism of glycogen to glucose, thereby increasing blood glucose levels
glucocorticoids
hormones produced by the zona fasciculata of the adrenal cortex that influence glucose metabolism
goiter
enlargement of the thyroid gland either as a result of iodine deficiency or hyperthyroidism
gonadotropins
hormones that regulate the function of the gonads
growth hormone (GH)
anterior pituitary hormone that promotes tissue building and influences nutrient metabolism (also called somatotropin)
hormone
secretion of an endocrine organ that travels via the bloodstream or lymphatics to induce a response in target cells or tissues in another part of the body
hormone receptor
protein within a cell or on the cell membrane that binds a hormone, initiating the target cell response
hyperglycemia
abnormally high blood glucose levels
hyperparathyroidism
disorder caused by overproduction of PTH that results in abnormally elevated blood calcium
hyperthyroidism
clinically abnormal, elevated level of thyroid hormone in the blood; characterized by an increased metabolic rate, excess body heat, sweating, diarrhea, weight loss, and increased heart rate
hypoparathyroidism
disorder caused by underproduction of PTH that results in abnormally low blood calcium
hypophyseal portal system
network of blood vessels that enables hypothalamic hormones to travel into the anterior lobe of the pituitary without entering the systemic circulation
hypothalamus
region of the diencephalon inferior to the thalamus that functions in neural and endocrine signaling
hypothyroidism
clinically abnormal, low level of thyroid hormone in the blood; characterized by low metabolic rate, weight gain, cold extremities, constipation, and reduced mental activity
infundibulum
stalk containing vasculature and neural tissue that connects the pituitary gland to the hypothalamus (also called the pituitary stalk)
inhibin
hormone secreted by the male and female gonads that inhibits FSH production by the anterior pituitary
inositol triphosphate (IP3)
molecule that initiates the release of calcium ions from intracellular stores
insulin
pancreatic hormone that enhances the cellular uptake and utilization of glucose, thereby decreasing blood glucose levels
insulin-like growth factors (IGF)
protein that enhances cellular proliferation, inhibits apoptosis, and stimulates the cellular uptake of amino acids for protein synthesis
leptin
protein hormone secreted by adipose tissues in response to food consumption that promotes satiety
luteinizing hormone (LH)
anterior pituitary hormone that triggers ovulation and the production of ovarian hormones, and the production of testosterone
melatonin
amino acid–derived hormone that is secreted in response to low light and causes drowsiness
mineralocorticoids
hormones produced by the zona glomerulosa cells of the adrenal cortex that influence fluid and electrolyte balance
neonatal hypothyroidism
condition characterized by cognitive deficits, short stature, and other signs and symptoms in people born to people who were iodine-deficient during pregnancy
norepinephrine
secondary catecholamine hormone secreted by the adrenal medulla in response to short-term stress; also called noradrenaline
osmoreceptor
hypothalamic sensory receptor that is stimulated by changes in solute concentration (osmotic pressure) in the blood
oxytocin
hypothalamic hormone stored in the posterior pituitary gland and important in stimulating uterine contractions in labor, milk ejection during breastfeeding, and feelings of attachment (produced by males and females)
pancreas
organ with both exocrine and endocrine functions located posterior to the stomach that is important for digestion and the regulation of blood glucose
pancreatic islets
specialized clusters of pancreatic cells that have endocrine functions; also called islets of Langerhans
paracrine
chemical signal that elicits a response in neighboring cells; also called paracrine factor
parathyroid glands
small, round glands embedded in the posterior thyroid gland that produce parathyroid hormone (PTH)
parathyroid hormone (PTH)
peptide hormone produced and secreted by the parathyroid glands in response to low blood calcium levels
phosphodiesterase (PDE)
cytosolic enzyme that deactivates and degrades cAMP
phosphorylation cascade
signaling event in which multiple protein kinases phosphorylate the next protein substrate by transferring a phosphate group from ATP to the protein
pineal gland
endocrine gland that secretes melatonin, which is important in regulating the sleep-wake cycle
pinealocyte
cell of the pineal gland that produces and secretes the hormone melatonin
pituitary dwarfism
disorder in children caused when abnormally low levels of GH result in growth retardation
pituitary gland
bean-sized organ suspended from the hypothalamus that produces, stores, and secretes hormones in response to hypothalamic stimulation (also called hypophysis)
PP cell
minor cell type in the pancreas that secretes the hormone pancreatic polypeptide
progesterone
predominantly female sex hormone important in regulating the female reproductive cycle and the maintenance of pregnancy
prolactin (PRL)
anterior pituitary hormone that promotes development of the mammary glands and the production of breast milk
protein kinase
enzyme that initiates a phosphorylation cascade upon activation
second messenger
molecule that initiates a signaling cascade in response to hormone binding on a cell membrane receptor and activation of a G protein
stage of exhaustion
stage three of the general adaptation syndrome; the body’s long-term response to stress mediated by the hormones of the adrenal cortex
stage of resistance
stage two of the general adaptation syndrome; the body’s continued response to stress after stage one diminishes
testosterone
steroid hormone secreted by the testes and important in the maturation of sperm cells, growth and development of the reproductive system, and the development of secondary sex characteristics
thymosins
hormones produced and secreted by the thymus that play an important role in the development and differentiation of T cells
thymus
organ that is involved in the development and maturation of T-cells and is particularly active during infancy and childhood
thyroid gland
large endocrine gland responsible for the synthesis of thyroid hormones
thyroid-stimulating hormone (TSH)
anterior pituitary hormone that triggers secretion of thyroid hormones by the thyroid gland (also called thyrotropin)
thyroxine
(also, tetraiodothyronine, T4) amino acid–derived thyroid hormone that is more abundant but less potent than T3 and often converted to T3 by target cells
triiodothyronine
(also, T3) amino acid–derived thyroid hormone that is less abundant but more potent than T4
upregulation
increase in the number of hormone receptors, typically in response to chronically reduced levels of a hormone
zona fasciculata
intermediate region of the adrenal cortex that produce hormones called glucocorticoids
zona glomerulosa
most superficial region of the adrenal cortex, which produces the hormones collectively referred to as mineralocorticoids
zona reticularis
deepest region of the adrenal cortex, which produces the steroid sex hormones called androgens
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The hypothalamus–pituitary complex can be thought of as the “command center” of the endocrine system. This complex secretes several hormones that directly produce responses in target tissues, as well as hormones that regulate the synthesis and secretion of hormones of other glands. In addition, the hypothalamus–pituitary complex coordinates the messages of the endocrine and nervous systems. In many cases, a stimulus received by the nervous system must pass through the hypothalamus–pituitary complex to be translated into hormones that can initiate a response.

The hypothalamus is a structure of the diencephalon of the brain located anterior and inferior to the thalamus (Figure 1). It has both neural and endocrine functions, producing and secreting many hormones. In addition, the hypothalamus is anatomically and functionally related to the pituitary gland (or hypophysis), a bean-sized organ suspended from it by a stem called the infundibulum (or pituitary stalk). The pituitary gland is cradled within the sellaturcica of the sphenoid bone of the skull. It consists of two lobes that arise from distinct parts of embryonic tissue: the posterior pituitary (neurohypophysis) is neural tissue, whereas the anterior pituitary (also known as the adenohypophysis) is glandular tissue that develops from the primitive digestive tract. The hormones secreted by the posterior and anterior pituitary, and the intermediate zone between the lobes are summarized in Table 1.
The posterior pituitary is actually an extension of the neurons of the paraventricular and supraoptic nuclei of the hypothalamus. The cell bodies of these regions rest in the hypothalamus, but their axons descend as the hypothalamic–hypophyseal tract within the infundibulum, and end in axon terminals that comprise the posterior pituitary (Figure 2).

The posterior pituitary gland does not produce hormones, but rather stores and secretes hormones produced by the hypothalamus. The paraventricular nuclei produce the hormone oxytocin, whereas the supraoptic nuclei produce ADH. These hormones travel along the axons into storage sites in the axon terminals of the posterior pituitary. In response to signals from the same hypothalamic neurons, the hormones are released from the axon terminals into the bloodstream.

A. Oxytocin

When fetal development is complete, the peptide-derived hormone oxytocin (tocia- = “childbirth”) stimulates uterine contractions and dilation of the cervix. Throughout most of pregnancy, oxytocin hormone receptors are not expressed at high levels in the uterus. Toward the end of pregnancy, the synthesis of oxytocin receptors in the uterus increases, and the smooth muscle cells of the uterus become more sensitive to its effects. Oxytocin is continually released throughout childbirth through a positive feedback mechanism. As noted earlier, oxytocin prompts uterine contractions that push the fetal head toward the cervix. In response, cervical stretching stimulates additional oxytocin to be synthesized by the hypothalamus and released from the pituitary. This increases the intensity and effectiveness of uterine contractions and prompts additional dilation of the cervix. The feedback loop continues until birth.

Although the high blood levels of oxytocin begin to decrease immediately following birth, oxytocin continues to play a role in female and newborn health. First, oxytocin is necessary for the milk ejection reflex (commonly referred to as “let-down”) in breastfeeding people. As the newborn begins suckling, sensory receptors in the nipples transmit signals to the hypothalamus. In response, oxytocin is secreted and released into the bloodstream. Within seconds, cells in the milk ducts contract, ejecting milk into the infant’s mouth. Secondly, in ball people, oxytocin is thought to contribute to parent–newborn bonding, known as attachment. Oxytocin is also thought to be involved in feelings of love and closeness, as well as in the sexual response.

B. Antidiuretic Hormone (ADH)

The solute concentration of the blood, or blood osmolarity, may change in response to the consumption of certain foods and fluids, as well as in response to disease, injury, medications, or other factors. Blood osmolarity is constantly monitored by osmoreceptors—specialized cells within the hypothalamus that are particularly sensitive to the concentration of sodium ions and other solutes.

In response to high blood osmolarity, which can occur during dehydration or following a very salty meal, the osmoreceptors signal the posterior pituitary to release antidiuretic hormone (ADH). The target cells of ADH are located in the tubular cells of the kidneys. Its effect is to increase epithelial permeability to water, allowing increased water reabsorption. The more water reabsorbed from the filtrate, the greater the amount of water that is returned to the blood and the less that is excreted in the urine. A greater concentration of water results in a reduced concentration of solutes. ADH is also known as vasopressin because, in very high concentrations, it causes constriction of blood vessels, which increases blood pressure by increasing peripheral resistance. The release of ADH is controlled by a negative feedback loop. As blood osmolarity decreases, the hypothalamic osmoreceptors sense the change and prompt a corresponding decrease in the secretion of ADH. As a result, less water is reabsorbed from the urine filtrate.

Interestingly, drugs can affect the secretion of ADH. For example, alcohol consumption inhibits the release of ADH, resulting in increased urine production that can eventually lead to dehydration and a hangover. 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. Although patients feel thirsty, and increase their fluid consumption, this doesn’t effectively decrease the solute concentration in their blood because ADH levels are not high enough to trigger water reabsorption in the kidneys. Electrolyte imbalances can occur in severe cases of diabetes insipidus.
The anterior pituitary originates from the digestive tract in the embryo and migrates toward the brain during fetal development. There are three regions: the pars distalis is the most anterior, the pars intermedia is adjacent to the posterior pituitary, and the pars tuberalis is a slender “tube” that wraps the infundibulum.

Recall that the posterior pituitary does not synthesize hormones, but merely stores them. In contrast, the anterior pituitary does manufacture hormones. However, the secretion of hormones from the anterior pituitary is regulated by two classes of hormones. These hormones—secreted by the hypothalamus—are the releasing hormones that stimulate the secretion of hormones from the anterior pituitary and the inhibiting hormones that inhibit secretion.

Hypothalamic hormones are secreted by neurons, but enter the anterior pituitary through blood vessels (Figure 3). Within the infundibulum is a bridge of capillaries that connects the hypothalamus to the anterior pituitary. This network, called the hypophyseal portal system, allows hypothalamic hormones to be transported to the anterior pituitary without first entering the systemic circulation. The system originates from the superior hypophyseal artery, which branches off the carotid arteries and transports blood to the hypothalamus. The branches of the superior hypophyseal artery form the hypophyseal portal system (see Figure 3). Hypothalamic releasing and inhibiting hormones travel through a primary capillary plexus to the portal veins, which carry them into the anterior pituitary. Hormones produced by the anterior pituitary (in response to releasing hormones) enter a secondary capillary plexus, and from there drain into the circulation.

The anterior pituitary produces seven hormones. These are the growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), beta endorphin, and prolactin. Of the hormones of the anterior pituitary, TSH, ACTH, FSH, and LH are collectively referred to as tropic hormones (trope- = “turning”) because they turn on or off the function of other endocrine glands.

A. Growth Hormone

The endocrine system regulates the growth of the human body, protein synthesis, and cellular replication. A major hormone involved in this process is growth hormone (GH), also called somatotropin—a protein hormone produced and secreted by the anterior pituitary gland. Its primary function is anabolic; it promotes protein synthesis and tissue building through direct and indirect mechanisms (Figure 4). GH levels are controlled by the release of GHRH and GHIH (also known as somatostatin) from the hypothalamus.

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 deposited into the blood. The name “diabetogenic” is derived from the similarity in elevated blood glucose levels observed between individuals with untreated diabetes mellitus and individuals experiencing GH excess. 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.

Dysfunction of the endocrine system’s control of growth can result in several disorders. For example, gigantism is a disorder in children that is caused by the secretion of abnormally large amounts of GH, resulting in excessive growth. A similar condition in adults is acromegaly, a disorder that results in the growth of bones in the face, hands, and feet in response to excessive levels of GH in individuals who have stopped growing. Abnormally low levels of GH in children can cause growth impairment—a disorder called pituitary dwarfism (also known as growth hormone deficiency).

B. Thyroid-Stimulating Hormone

The activity of the thyroid gland is regulated by thyroid-stimulating hormone (TSH), also called thyrotropin. TSH is released from the anterior pituitary in response to thyrotropin-releasing hormone (TRH) from the hypothalamus. As 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 subsequently TSH.

C. Adrenocorticotropic Hormone

The adrenocorticotropic hormone (ACTH), also called corticotropin, stimulates the adrenal cortex (the more superficial “bark” of the adrenal glands) to secrete corticosteroid hormones such as cortisol. ACTH come from a precursor molecule known as pro-opiomelanocortin (POMC) which produces several biologically active molecules when cleaved, including ACTH, melanocyte-stimulating hormone, and the brain opioid peptides known as endorphins.

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.

D. 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 and the ovaries). Much of the development of the reproductive system occurs during puberty and is marked by the development of sex-specific characteristics in adolescents. Puberty is initiated by gonadotropin-releasing hormone (GnRH), a 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 and, in the case of females, the onset and cessation of reproductive capacity.

The gonadotropins include two glycoprotein hormones: follicle-stimulating hormone (FSH) stimulates the production and maturation of sex cells, or gametes, including ova and sperm. FSH also promotes follicular growth; these follicles then release estrogens in ovaries. Luteinizing hormone (LH) triggers ovulation, as well as the production of estrogens and progesterone by the ovaries. LH stimulates production of testosterone by the testes.

E. Prolactin

As its name implies, prolactin (PRL) promotes lactation (milk production). During pregnancy, it contributes to development of the mammary glands, and 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. And as noted earlier, the let-down of milk occurs in response to stimulation from oxytocin.

In non-pregnant females, prolactin secretion is inhibited by prolactin-inhibiting hormone (PIH), which is actually the neurotransmitter dopamine, and is released from neurons in the hypothalamus. Only during pregnancy do prolactin levels rise in response to prolactin-releasing hormone (PRH) from the hypothalamus.
The cells in the zone between the pituitary lobes secrete a hormone known as melanocyte-stimulating hormone (MSH) that is formed by cleavage of the pro-opiomelanocortin (POMC) precursor protein. Local production of MSH in the skin is responsible for melanin production in response to UV light exposure. The role of MSH made by the pituitary is more complicated. For instance, people with lighter skin generally have the same amount of MSH as people with darker skin. Nevertheless, this hormone is capable of darkening of the skin by inducing melanin production in the skin’s melanocytes. People also show increased MSH production during pregnancy; in combination with estrogens, it can lead to darker skin pigmentation, especially the skin of the areolas and labia minora. Figure 5 is a summary of the pituitary hormones and their principal effects.

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at openstax.org.

The hypothalamus region lies inferior and anterior to the thalamus. It connects to the pituitary gland by the stalk-like infundibulum. The pituitary gland consists of an anterior and posterior lobe, with each lobe secreting different hormones in response to signals from the hypothalamus.

Pituitary lobeAssociated hormonesChemical classEffect
AnteriorGrowth hormone (GH)ProteinPromotes growth of body tissues
AnteriorProlactin (PRL)PeptidePromotes milk production from mammary glands
AnteriorThyroid-stimulating hormone (TSH)GlycoproteinStimulates thyroid hormone release from thyroid
AnteriorAdrenocorticotropic hormone (ACTH)PeptideStimulates hormone release by adrenal cortex
AnteriorFollicle-stimulating hormone (FSH)GlycoproteinStimulates gamete production in gonads
AnteriorLuteinizing hormone (LH)GlycoproteinStimulates androgen production by gonads
PosteriorAntidiuretic hormone (ADH)PeptideStimulates water reabsorption by kidneys
PosteriorOxytocinPeptideStimulates uterine contractions during childbirth
Intermediate zoneMelanocyte-stimulating hormonePeptideStimulates melanin formation in melanocytes

Neurosecretory cells in the hypothalamus release oxytocin (OT) or ADH into the posterior lobe of the pituitary gland. These hormones are stored or released into the blood via the capillary plexus.

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.

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.

Major pituitary hormones and their target organs.

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  1. The hypothalamus–pituitary complex is located in the diencephalon of the brain.
  2. The hypothalamus and the pituitary gland are connected by a structure called the infundibulum, which contains vasculature and nerve axons.
  3. The pituitary gland is divided into two distinct structures with different embryonic origins.
  4. The posterior lobe houses the axon terminals of hypothalamic neurons.
  5. It stores and releases into the bloodstream two hypothalamic hormones: oxytocin and antidiuretic hormone.
  6. The anterior lobe is connected to the hypothalamus by vasculature in the infundibulum and produces and secretes six hormones.
  7. Their secretion is regulated, however, by releasing and inhibiting hormones from the hypothalamus.
  8. The six anterior pituitary hormones are: growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, and prolactin.
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