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A major organ of the endocrine system

Endocrine system

In physiology, the endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body. The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts. It derives from the Greek words "endo"...

, the anterior pituitary, also called the adenohypophysis, is the glandular, anterior lobe of the pituitary gland

Pituitary gland

In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...

. The anterior pituitary regulates several physiological processes including stress

Stress (medicine)

Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...

, growth

Human development (biology)

Human development is the process of growing to maturity. In biological terms, this entails growth from a one-celled zygote to an adult human being.- Biological development:...

, and reproduction.

Its regulatory functions are achieved through the secretion of various peptide hormone

Peptide hormone

Peptide hormones are a class of peptides that are secreted into the blood stream and have endocrine functions in living animals.Like other proteins, peptide hormones are synthesized in cells from amino acids according to an mRNA template, which is itself synthesized from a DNA template inside the...

s that act on target organs including the adrenal gland

Adrenal gland

In mammals, the adrenal glands are endocrine glands that sit atop the kidneys; in humans, the right suprarenal gland is triangular shaped, while the left suprarenal gland is semilunar shaped...

, liver

Liver

The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

, bone

Bone

Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

, thyroid gland, and gonad

Gonad

The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...

s. The anterior pituitary itself is regulated by the hypothalamus

Hypothalamus

The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...

and by negative feedback

Negative feedback

Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...

from these target organs.

Disorders of the anterior pituitary are generally classified by the presence of over- or underproduction of pituitary hormones. For example, a prolactinoma

Prolactinoma

A prolactinoma is a benign tumor of the pituitary gland that produces a hormone called prolactin. It is the most common type of pituitary tumor...

is a pituitary adenoma

Pituitary adenoma

Pituitary adenomas are tumors that occur in the pituitary gland, and account for about 15% of intracranial neoplasms. Tumors which exceed 10 mm in size are defined as macroadenomas, and those smaller than 10 mm are referred to as microadenomas...

that overproduces prolactin

Prolactin

Prolactin also known as luteotropic hormone is a protein that in humans is encoded by the PRL gene.Prolactin is a peptide hormone discovered by Henry Friesen...

. In Sheehan's syndrome of postpartum hypopituitarism, the anterior pituitary uniformly malfunctions and underproduces all hormones. Proper function of the anterior pituitary and of the organs it regulates can often be ascertained via blood test

Blood test

A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a needle, or via fingerprick....

s that measure hormone levels.

Anatomy

The pituitary gland

Pituitary gland

is a pea-sized gland that sits in a protective bony enclosure called the sella turcica

Sella turcica

-External links:*...

. It is composed of three lobes: anterior, intermediate, and posterior. In many animals, these three lobes are distinct. However, in humans, the intermediate lobe is but a few cell layers thick and indistinct; as a result, it is often considered part of the anterior pituitary. In all animals, the fleshy, glandular anterior pituitary is distinct from the neural composition of the posterior pituitary

Posterior pituitary

The posterior pituitary comprises the posterior lobe of the pituitary gland and is part of the endocrine system. Despite its name, the posterior pituitary gland is not a gland, per se; rather, it is largely a collection of axonal projections from the hypothalamus that terminate behind the anterior...

.

The anterior pituitary is composed of multiple parts:

Pars distalis: The pars distalis, or "distal part", comprises the majority of the anterior pituitary and is where the bulk of pituitary hormone production occurs. Occasionally, "pars distalis" is incorrectly used as a synonym for the anterior pituitary.

Pars tuberalis: The pars tuberalis

Pars tuberalis

The pars tuberalis is part of the anterior lobe of the pituitary gland, and wraps the pituitary stalk in a highly vascularized sheath.-Histology:...

, or "tubular part", forms a sheath extending up from the pars distalis and wrapping around the pituitary stalk

Pituitary stalk

The pituitary stalk is the connection between the hypothalamus and the posterior pituitary....

. Its function is poorly understood.

Pars intermedia: The pars intermedia

Pars intermedia

Pars intermedia is the boundary between the anterior and posterior lobes of the pituitary. It contains three types of cells - basophils, chromophobes, and colloid-filled cysts. The cysts are the remainder of Rathke’s pouch....

, or "intermediate part", sits between the pars distalis and the posterior pituitary and is often very small in humans.

Hormone secretion

The posterior pituitary as a down growth of the brain, is a neurosecretory organ (Wheater, Burkitt & Daniels, 1987). The secretion of hormones from the posterior pituitary is controlled directly by neurons in the hypothalamus (Marieb, 2004). The connecting stalk between the hypothalamus and the lobes of the pituitary gland, the infundibulum, carries the hormones of the posterior pituitary from nuclei in the hypothalamus. The hypothalmic supraoptic nuclei manufacture anti-diuretic hormone and the hypothalmic paraventricular nuclei manufacture oxytocin. These hormones are then stored in pituitary axons until their release is triggered (Marieb, 2004).

The anterior pituitary is a glandular secretory organ (Wheater, Burkitt & Daniels, 1987). The secretion of hormones from the anterior pituitary is controlled by inhibiting and releasing factors secreted by neurons in the hypothalamus. These inhibiting and releasing factors are released into a primary capillary plexus where they travel, via portal veins, to a secondary capillary plexus where they stimulate the glandular tissue of the anterior pituitary to release its hormones.

Embryology

The anterior pituitary arises from an invagination

Invagination

Invagination means to fold inward or to sheath. In biology, this can refer to a number of processes.* Invagination is the morphogenetic processes by which an embryo takes form, and is the initial step of gastrulation, the massive reorganization of the embryo from a simple spherical ball of cells,...

of the oral ectoderm

Ectoderm

The "ectoderm" is one of the three primary germ cell layers in the very early embryo. The other two layers are the mesoderm and endoderm , with the ectoderm as the most exterior layer...

and forms Rathke's pouch

Rathke's pouch

In embryogenesis, Rathke's pouch is a depression in the roof of the developing mouth in front of the buccopharyngeal membrane. It gives rise to the anterior pituitary , a part of the endocrine system.-Development:...

. This contrasts with the posterior pituitary

Posterior pituitary

, which originates from neuroectoderm

Neuroectoderm

Neuroectoderm is the term for ectoderm which receives Bone Morphogenetic Protein-inhibiting signals from proteins such as noggin, which leads to the development of the nervous system from this tissue....

Major hormones secreted

Hormone	Other names	Symbol(s)	Structure	Secretory cells	Staining	Target	Effect
Adrenocorticotropic hormone Adrenocorticotropic hormone Adrenocorticotropic hormone , also known as 'corticotropin', 'Adrenocorticotrophic hormone', is a polypeptide tropic hormone produced and secreted by the anterior pituitary gland. It is an important component of the hypothalamic-pituitary-adrenal axis and is often produced in response to biological...	Corticotropin	ACTH	Polypeptide	Corticotrophs	Basophil Anterior pituitary basophil An anterior pituitary basophil is a type of cell in the anterior pituitary which manufactures hormones.It is called a basophil because it readily takes up base, and typically stains a relatively deep blue or purple....	Adrenal gland Adrenal gland In mammals, the adrenal glands are endocrine glands that sit atop the kidneys; in humans, the right suprarenal gland is triangular shaped, while the left suprarenal gland is semilunar shaped...	Secretion of glucocorticoid Glucocorticoid Glucocorticoids are a class of steroid hormones that bind to the glucocorticoid receptor , which is present in almost every vertebrate animal cell... s
Beta-endorphin Beta-endorphin β-endorphin is an endogenous opioid peptide neurotransmitter found in the neurons of both the central and peripheral nervous system.The amino acid sequence is:...			Polypeptide	Corticotrophs	Basophil Anterior pituitary basophil An anterior pituitary basophil is a type of cell in the anterior pituitary which manufactures hormones.It is called a basophil because it readily takes up base, and typically stains a relatively deep blue or purple....	Opioid receptor	Inhibit perception of pain
Thyroid-stimulating hormone Thyroid-stimulating hormone Thyrotrophin-stimulating hormone is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid gland.- Physiology :...	Thyrotropin	TSH	Glycoprotein Glycoprotein Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...	Thyrotrophs	Basophil Anterior pituitary basophil An anterior pituitary basophil is a type of cell in the anterior pituitary which manufactures hormones.It is called a basophil because it readily takes up base, and typically stains a relatively deep blue or purple....	Thyroid gland	Secretion of thyroid hormone Thyroid hormone The thyroid hormones, thyroxine and triiodothyronine , are tyrosine-based hormones produced by the thyroid gland primarily responsible for regulation of metabolism. An important component in the synthesis of thyroid hormones is iodine. The major form of thyroid hormone in the blood is thyroxine ,... s
Follicle-stimulating hormone Follicle-stimulating hormone Follicle-stimulating hormone is a hormone found in humans and other animals. It is synthesized and secreted by gonadotrophs of the anterior pituitary gland. FSH regulates the development, growth, pubertal maturation, and reproductive processes of the body. FSH and Luteinizing hormone act...	-	FSH	Glycoprotein	Gonadotrophs	Basophil Anterior pituitary basophil An anterior pituitary basophil is a type of cell in the anterior pituitary which manufactures hormones.It is called a basophil because it readily takes up base, and typically stains a relatively deep blue or purple....	Gonads	Growth of reproductive system Reproductive system The reproductive system or genital system is a system of organs within an organism which work together for the purpose of reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Unlike most organ systems, the sexes...
Luteinizing hormone Luteinizing hormone Luteinizing hormone is a hormone produced by the anterior pituitary gland. In females, an acute rise of LH called the LH surge triggers ovulation and development of the corpus luteum. In males, where LH had also been called interstitial cell-stimulating hormone , it stimulates Leydig cell...	Lutropin	LH, ICSH	Glycoprotein	Gonadotrophs	Basophil Anterior pituitary basophil An anterior pituitary basophil is a type of cell in the anterior pituitary which manufactures hormones.It is called a basophil because it readily takes up base, and typically stains a relatively deep blue or purple....	Gonads	Sex hormone production
Growth hormone Growth hormone Growth hormone is a peptide hormone that stimulates growth, cell reproduction and regeneration in humans and other animals. Growth hormone is a 191-amino acid, single-chain polypeptide that is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior...	Somatotropin	GH, STH	Polypeptide	Somatotrophs	Acidophil	Liver Liver The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion... , adipose tissue Adipose tissue In histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...	Promotes growth; lipid Lipid Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others... and carbohydrate Carbohydrate A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical... metabolism Metabolism Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
Prolactin Prolactin Prolactin also known as luteotropic hormone is a protein that in humans is encoded by the PRL gene.Prolactin is a peptide hormone discovered by Henry Friesen...	Lactogenic hormone	PRL	Polypeptide	Lactotroph Lactotroph Lactotrophs are cells in the anterior pituitary which produce prolactin in response to signals including dopamine, estrogen, progesterone and Thyrotropin-releasing hormone. Dopamine has an inhibitory effect on PRL secretion... s and Mammotrophs	Acidophil	Ovaries Ovary The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries... , mammary gland Mammary gland A mammary gland is an organ in mammals that produces milk to feed young offspring. Mammals get their name from the word "mammary". In ruminants such as cows, goats, and deer, the mammary glands are contained in their udders... s	Secretion of estrogen Estrogen Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal... s/progesterone Progesterone Progesterone also known as P4 is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis of humans and other species... ; milk Milk Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many... production

The acidophilic cells (GH and PRL) have extensive rough endoplasmic reticulum

Endoplasmic reticulum

The endoplasmic reticulum is an organelle of cells in eukaryotic organisms that forms an interconnected network of tubules, vesicles, and cisternae...

and produce single chain polypeptides without any glycosylation

Glycosylation

Glycosylation is the reaction in which a carbohydrate, i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule . In biology glycosylation refers to the enzymatic process that attaches glycans to proteins, lipids, or other organic molecules...

or phosphorylation. Basophilic staining results from lysosome action modifying the hormones (or prohormones in the case of corticotrophs) by glycosylation.

An easy mnemonic to remember the hormones produced and secreted by the anterior pituitary is "FLATPEG".

Regulation

Hormone secretion from the anterior pituitary gland is regulated by hormones secreted by the hypothalamus

Hypothalamus

The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...

. Neuroendocrine neurons in the hypothalamus project axon

Axon

An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....

s to the median eminence

Median eminence

The median eminence is part of the inferior boundary for the hypothalamus part of the human brain. A small swelling on the tuber cinereum posterior to the infundibulum - atop the pituitary stalk - the median eminence lies in the area roughly bounded on its posterolateral region by the cerebral...

, at the base of the brain. At this site, these neurons can release substances into small blood vessels that travel directly to the anterior pituitary gland (the hypothalamo-hypophysial portal vessels).

Etymology

The anterior pituitary is also known as the adenohypophysis, meaning "glandular undergrowth", from the Greek adeno ("gland"), hypo ("under"), and physis ("growth").

External links

Embryology at unc.edu