Anterior pituitary

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Anterior pituitary_table_infobox_0

Anterior pituitary glandAnterior pituitary_header_cell_0_0_0
DetailsAnterior pituitary_header_cell_0_1_0
PrecursorAnterior pituitary_header_cell_0_2_0 oral mucosa (Rathke's pouch)Anterior pituitary_cell_0_2_1
ArteryAnterior pituitary_header_cell_0_3_0 superior hypophysealAnterior pituitary_cell_0_3_1
VeinAnterior pituitary_header_cell_0_4_0 hypophysealAnterior pituitary_cell_0_4_1
IdentifiersAnterior pituitary_header_cell_0_5_0
LatinAnterior pituitary_header_cell_0_6_0 lobus anterior hypophysisAnterior pituitary_cell_0_6_1
MeSHAnterior pituitary_header_cell_0_7_0 Anterior pituitary_cell_0_7_1
NeuroNamesAnterior pituitary_header_cell_0_8_0 Anterior pituitary_cell_0_8_1
NeuroLex IDAnterior pituitary_header_cell_0_9_0 Anterior pituitary_cell_0_9_1
TA98Anterior pituitary_header_cell_0_10_0 Anterior pituitary_cell_0_10_1
TA2Anterior pituitary_header_cell_0_11_0 Anterior pituitary_cell_0_11_1
FMAAnterior pituitary_header_cell_0_12_0 Anterior pituitary_cell_0_12_1

A major organ of the endocrine system, the anterior pituitary (also called the adenohypophysis or pars anterior) is the glandular, anterior lobe that together with the posterior lobe (posterior pituitary, or the neurohypophysis) makes up the pituitary gland (hypophysis). Anterior pituitary_sentence_0

The anterior pituitary regulates several physiological processes, including stress, growth, reproduction, and lactation. Anterior pituitary_sentence_1

Proper functioning of the anterior pituitary and of the organs it regulates can often be ascertained via blood tests that measure hormone levels. Anterior pituitary_sentence_2

Structure Anterior pituitary_section_0

The pituitary gland sits in a protective bony enclosure called the sella turcica (Turkish chair/saddle). Anterior pituitary_sentence_3

It is composed of three lobes: the anterior, intermediate, and posterior lobes. Anterior pituitary_sentence_4

In many animals, these lobes are distinct. Anterior pituitary_sentence_5

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. Anterior pituitary_sentence_6

In all animals, the fleshy, glandular anterior pituitary is distinct from the neural composition of the posterior pituitary. Anterior pituitary_sentence_7

The anterior pituitary is composed of three regions: Anterior pituitary_sentence_8

Anterior pituitary_description_list_0

  • Anterior pituitary_item_0_0

The pars distalis (distal part) comprises the majority of the anterior pituitary and is where the bulk of pituitary hormone production occurs. Anterior pituitary_sentence_9

The pars distalis contains two types of cells, including chromophobe cells and chromophil cells. Anterior pituitary_sentence_10

The chromophils can be further divided into acidophils (alpha cells) and basophils (beta cells). Anterior pituitary_sentence_11

These cells all together produce hormones of the anterior pituitary and release them into the blood stream. Anterior pituitary_sentence_12

Nota bene: The terms "basophil" and "acidophil" are used by some books, whereas others prefer not to use these terms. Anterior pituitary_sentence_13

This is due to the possible confusion with white blood cells, where one may also find basophils and acidophils. Anterior pituitary_sentence_14

Anterior pituitary_description_list_1

  • Anterior pituitary_item_1_1
    • Pars tuberalis: The pars tuberalis (tubular part) forms a part of the sheath extending up from the pars distalis, which joins with the pituitary stalk (also known as the infundibular stalk or infundibulum), arising from the posterior lobe. (The pituitary stalk connects the hypothalamus to the posterior pituitary.) The function of the pars tuberalis is poorly understood. However, it has been seen to be important in receiving the endocrine signal in the form of TSHB (a β subunit of TSH), informing the pars tuberalis of the photoperiod (length of day). The expression of this subunit is regulated by the secretion of melatonin in response to light information transmitted to the pineal gland. Earlier studies have shown localization of melatonin receptors in this region.Anterior pituitary_item_1_2

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  • Anterior pituitary_item_2_3
    • Pars intermedia: The pars intermedia (intermediate part) sits between the pars distalis and the posterior pituitary, forming the boundary between the anterior and posterior pituitaries. It is very small and indistinct in humans.Anterior pituitary_item_2_4

Development Anterior pituitary_section_1

The anterior pituitary is derived from the ectoderm, more specifically from that of Rathke’s pouch, part of the developing hard palate in the embryo. Anterior pituitary_sentence_15

The pouch eventually loses its connection with the pharynx, giving rise to the anterior pituitary. Anterior pituitary_sentence_16

The anterior wall of Rathke's pouch proliferates, filling most of the pouch to form the pars distalis and the pars tuberalis. Anterior pituitary_sentence_17

The posterior wall of the anterior pituitary forms the pars intermedia. Anterior pituitary_sentence_18

Its formation from the soft tissues of the upper palate contrasts with the posterior pituitary, which originates from neuroectoderm. Anterior pituitary_sentence_19

Function Anterior pituitary_section_2

The anterior pituitary contains five types of endocrine cell, and they are defined by the hormones they secrete: somatotropes (GH); Lactotropes (PRL); gonadotropes (LH and FSH); corticotropes (ACTH) and thyrotropes (TSH). Anterior pituitary_sentence_20

It also contains non-endocrine folliculostellate cells which are thought to stimulate and support the endocrine cell populations. Anterior pituitary_sentence_21

Hormones secreted by the anterior pituitary are trophic hormones (Greek: trophe, “nourishment”). Anterior pituitary_sentence_22

Trophic hormones directly affect growth either as hyperplasia or hypertrophy on the tissue it is stimulating. Anterior pituitary_sentence_23

Tropic hormones are named for their ability to act directly on target tissues or other endocrine glands to release hormones, causing numerous cascading physiological responses. Anterior pituitary_sentence_24

Role in the endocrine system Anterior pituitary_section_3

Main article: Hypothalamus Anterior pituitary_sentence_25

Anterior pituitary_description_list_3

  • Anterior pituitary_item_3_5

Hormone secretion from the anterior pituitary gland is regulated by hormones secreted by the hypothalamus. Anterior pituitary_sentence_26

Neuroendocrine cells in the hypothalamus project axons to the median eminence, at the base of the brain. Anterior pituitary_sentence_27

At this site, these cells can release substances into small blood vessels that travel directly to the anterior pituitary gland (the hypothalamo-hypophyseal portal vessels). Anterior pituitary_sentence_28

Anterior pituitary_description_list_4

  • Anterior pituitary_item_4_6

Aside from hypothalamic control of the anterior pituitary, other systems in the body have been shown to regulate the anterior pituitary’s function. Anterior pituitary_sentence_29

GABA can either stimulate or inhibit the secretion of luteinizing hormone (LH) and growth hormone (GH) and can stimulate the secretion of thyroid-stimulating hormone (TSH). Anterior pituitary_sentence_30

Prostaglandins are now known to inhibit adrenocorticotropic hormone (ACTH) and also to stimulate TSH, GH and LH release. Anterior pituitary_sentence_31

GABA, through action with the hypothalamus, has been shown experimentally to influence the level of GH secretion. Anterior pituitary_sentence_32

Clinical evidence supports the experimental findings of the excitatory and inhibitory effects GABA has on GH secretion, dependent on GABA’s site of action within the hypothalamic-pituitary unit. Anterior pituitary_sentence_33

Effects of the anterior pituitary Anterior pituitary_section_4

Anterior pituitary_description_list_5

  • Anterior pituitary_item_5_7

The homeostatic maintenance of the anterior pituitary is crucial to our physiological well being. Anterior pituitary_sentence_34

Increased plasma levels of TSH induce hyperthermia through a mechanism involving increased metabolism and cutaneous vasodilation. Anterior pituitary_sentence_35

Increased levels of LH also result in hypothermia but through a decreased metabolism action. Anterior pituitary_sentence_36

ACTH increase metabolism and induce cutaneous vasoconstriction, increased plasma levels also result in hyperthermia and prolactin decreases with decreasing temperature values. Anterior pituitary_sentence_37

follicle-stimulating hormone (FSH) also may cause hypothermia if increased beyond homeostatic levels through an increased metabolic mechanism only. Anterior pituitary_sentence_38

Anterior pituitary_description_list_6

  • Anterior pituitary_item_6_8

Gonadotropes, primarily luteinising hormone (LH) secreted from the anterior pituitary stimulates the ovulation cycle in female mammals, whilst in the males, LH stimulates the synthesis of androgen which drives the ongoing will to mate together with a constant production of sperm. Anterior pituitary_sentence_39

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  • Anterior pituitary_item_7_9

Main article Hypothalamic-pituitary-adrenal axis Anterior pituitary_sentence_40

The anterior pituitary plays a role in stress response. Anterior pituitary_sentence_41

Corticotropin releasing hormone (CRH) from the hypothalamus stimulates ACTH release in a cascading effect that ends with the production of glucocorticoids from the adrenal cortex. Anterior pituitary_sentence_42

Behavioral effects Anterior pituitary_section_5

Anterior pituitary_description_list_8

  • Anterior pituitary_item_8_10
    • Development: The release of GH, LH, and FSH are required for correct human development, including gonadal development.Anterior pituitary_item_8_11

Anterior pituitary_description_list_9

  • Anterior pituitary_item_9_12
    • Breast-feeding: Release of the hormone prolactin is essential for lactation.Anterior pituitary_item_9_13

Anterior pituitary_description_list_10

Anterior pituitary_description_list_11

Anterior pituitary_description_list_12

  • Anterior pituitary_item_12_18
    • Tactile responding: It has been shown that infant mice who were stroked with a paintbrush (simulating motherly care) had more release and binding of growth hormone (GH) from the anterior pituitary gland.Anterior pituitary_item_12_19

Anterior pituitary_description_list_13

Clinical significance Anterior pituitary_section_6

Increased activity Anterior pituitary_section_7

Main article: Hyperpituitarism Anterior pituitary_sentence_43

Hyperpituitarism is the condition where the pituitary secretes excessive amounts of hormones. Anterior pituitary_sentence_44

This hypersecretion often results in the formation of a pituitary adenoma (tumour), which are benign apart from a tiny fraction. Anterior pituitary_sentence_45

There are mainly three types of anterior pituitary tumors and their associated disorders. Anterior pituitary_sentence_46

For example, acromegaly results from excessive secretion of growth hormone (GH) often being released by a pituitary adenoma. Anterior pituitary_sentence_47

This disorder can cause disfigurement and possibly death and can lead to gigantism, a hormone disorder shown in “giants” such as André the Giant, where it occurs before the epiphyseal plates in bones close in puberty. Anterior pituitary_sentence_48

The most common type of pituitary tumour is a prolactinoma which hypersecretes prolactin. Anterior pituitary_sentence_49

A third type of pituitary adenoma secretes excess ACTH, which in turn, causes an excess of cortisol to be secreted and is the cause of Cushing's disease. Anterior pituitary_sentence_50

Decreased activity Anterior pituitary_section_8

Main article: Hypopituitarism Anterior pituitary_sentence_51

Hypopituitarism is characterized by a decreased secretion of hormones released by the anterior pituitary. Anterior pituitary_sentence_52

For example, hypo-secretion of GH prior to puberty can be a cause of dwarfism. Anterior pituitary_sentence_53

In addition, secondary adrenal insufficiency can be caused by hypo-secretion of ACTH which, in turn, does not signal the adrenal cortex to produce a sufficient amount of cortisol. Anterior pituitary_sentence_54

This is a life-threatening condition. Anterior pituitary_sentence_55

Hypopituitarism could be caused by the destruction or removal of the anterior pituitary tissue through traumatic brain injury, tumor, tuberculosis, or syphilis, among other causes. Anterior pituitary_sentence_56

This disorder used to be referred to as Simmonds' disease but now according to the Diseases Database it is called Sheehan syndrome. Anterior pituitary_sentence_57

If the hypopituitarism is caused by the blood loss associated with childbirth, the disorder is referred to as Sheehan syndrome. Anterior pituitary_sentence_58

History Anterior pituitary_section_9

Etymology Anterior pituitary_section_10

The anterior pituitary is also known as the adenohypophysis, meaning "glandular undergrowth", from the Greek adeno- ("gland"), hypo ("under"), and physis ("growth"). Anterior pituitary_sentence_59

Additional images Anterior pituitary_section_11

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  • Anterior pituitary_item_14_22

See also Anterior pituitary_section_12

This article uses anatomical terminology. Anterior pituitary_sentence_60

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Credits to the contents of this page go to the authors of the corresponding Wikipedia page: pituitary.