Pituitary gland
Encyclopedia
In vertebrate
anatomy
the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g (0.02 oz.), 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 (sella turcica
) covered by a dural
fold (diaphragma sellae
). The pituitary is functionally connected to the hypothalamus
by the median eminence
via a small tube called the infundibular stem (Pituitary stalk
). The pituitary fossa, in which the pituitary gland sits, is situated in the sphenoid
bone in the middle cranial fossa
at the base of the brain. The pituitary gland secretes nine hormone
s that regulate homeostasis
.
(also named the "infundibular stem", or simply the "infundibulum"). It is from the hypothalamus that hypothalamic tropic factors are released to descend down the pituitary stalk to the pituitary gland where they stimulate the release of pituitary hormones. While the pituitary gland is known as the 'master' endocrine gland, both of the lobes are under the control of the hypothalamus
; the anterior pituitary receives its signals from the parvocellular neurons and the posterior pituitary receives its signals from magnocellular neurons.
Somatotropins:
Thyrotropins
:
Corticotropins:
Lactotropins
:
Gonadotropins:
Melanotrophins
These hormones are released from the anterior pituitary under the influence of the hypothalamus
. Hypothalamic hormones are secreted to the anterior lobe by way of a special capillary
system, called the hypothalamic-hypophysial portal system
.
The anterior pituitary is divided into anatomical regions known as the pars tuberalis, pars intermedia, and pars distalis. It develops from a depression in the dorsal wall of the pharynx (stomodial part) known as Rathke's pouch
.
Magnocellular Neurons
:
Oxytocin is one of the few hormones to create a positive feedback loop. For example, uterine contractions stimulate the release of oxytocin from the posterior pituitary, which, in turn, increases uterine contractions. This positive feedback loop continues throughout labor.
), the intermediate lobe
located between the anterior and posterior pituitary is important to many animals. For instance, in fish, it is believed to control physiological color change. In adult humans, it is just a thin layer of cells between the anterior and posterior pituitary. The intermediate lobe produces melanocyte-stimulating hormone
(MSH), although this function is often (imprecisely) attributed to the anterior pituitary.
The division of the pituitary described above is typical of mammal
s, and is also true, to varying degrees, of all tetrapod
s. However, only in mammals does the posterior pituitary have a compact shape. In lungfish
es, it is a relatively flat sheet of tissue lying above the anterior pituitary, and, in amphibian
s, reptile
s, and bird
s, it becomes increasingly well developed. The intermediate lobe is, in general, not well developed in tetrapods, and is entirely absent in birds.
Apart from lungfishes, the structure of the pituitary in fish is generally different from that in tetrapods. In general, the intermediate lobe tends to be well developed, and may equal the remainder of the anterior pituitary in size. The posterior lobe typically forms a sheet of tissue at the base of the pituitary stalk, and in most cases sends irregular finger-like projection into the tissue of the anterior pituitary, which lies directly beneath it. The anterior pituitary is typically divided into two regions, a more anterior rostral portion and a posterior proximal portion, but the boundary between the two is often not clearly marked. In elasmobranchs there is an additional, ventral lobe beneath the anterior pituitary proper.
The arrangement in lamprey
s, which are among the most primitive of all fish, may indicate how the pituitary originally evolved in ancestral vertebrates. Here, the posterior pituitary is a simple flat sheet of tissue at the base of the brain, and there is no pituitary stalk. Rathke's pouch remains open to the outside, close to the nasal openings. Closely associated with the pouch are three distinct clusters of glandular tissue, corresponding to the intermediate lobe, and the rostral and proximal portions of the anterior pituitary. These various parts are separated by meningial
membranes, suggesting that the pituitary of other vertebrates may have formed from the fusion of a number of separate, but closely associated, glands.
Most fish also possess a urophysis, a neural secretory gland very similar in form to the posterior pituitary, but located in the tail and associated with the spinal cord
. This may have a function in osmoregulation
.
There is an analogous structure in the octopus
brain.
Pituitary gland also makes endorphin
to relieve pain and alter mood.
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g (0.02 oz.), in humans. It is a protrusion off the bottom of the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
at the base of the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
, and rests in a small, bony cavity (sella turcica
Sella turcica
-External links:*...
) covered by a dural
Dura mater
The dura mater , or dura, is the outermost of the three layers of the meninges surrounding the brain and spinal cord. It is derived from Mesoderm. The other two meningeal layers are the pia mater and the arachnoid mater. The dura surrounds the brain and the spinal cord and is responsible for...
fold (diaphragma sellae
Diaphragma sellae
The diaphragma sellae or sellar diaphragm is the circular fold of dura mater that almost completely roofs the fossa hypophyseos of the sella turcica of the sphenoid bone within the skull. It retains the pituitary gland in the fossa hypophyseos, with only the infundibulum of the pituitary gland...
). The pituitary is functionally connected to the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
by 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...
via a small tube called the infundibular stem (Pituitary stalk
Pituitary stalk
The pituitary stalk is the connection between the hypothalamus and the posterior pituitary....
). The pituitary fossa, in which the pituitary gland sits, is situated in the sphenoid
Sphenoid bone
The sphenoid bone is an unpaired bone situated at the base of the skull in front of the temporal bone and basilar part of the occipital bone.The sphenoid bone is one of the seven bones that articulate to form the orbit...
bone in the middle cranial fossa
Middle cranial fossa
The middle fossa, deeper than the anterior cranial fossa, is narrow medially and widens laterally to the sides of the skull. It is separated from the posterior fossa by the clivus and the petrous crest....
at the base of the brain. The pituitary gland secretes nine hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s that regulate homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
.
Sections
The pituitary gland consists of two components: the anterior pituitary (or adenohypophysis) and the posterior pituitary (or neurohypophysis), and is functionally linked to the hypothalamus by the pituitary stalkPituitary stalk
The pituitary stalk is the connection between the hypothalamus and the posterior pituitary....
(also named the "infundibular stem", or simply the "infundibulum"). It is from the hypothalamus that hypothalamic tropic factors are released to descend down the pituitary stalk to the pituitary gland where they stimulate the release of pituitary hormones. While the pituitary gland is known as the 'master' endocrine gland, both of the lobes are under the control of the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
; the anterior pituitary receives its signals from the parvocellular neurons and the posterior pituitary receives its signals from magnocellular neurons.
Anterior pituitary (Adenohypophysis)
The anterior pituitary synthesizes and secretes the following important endocrine hormones:Somatotropins:
- Growth hormone (also referred to as 'Human Growth Hormone', 'HGH' or 'GH' or somatotropin), released under influence of hypothalamic Growth Hormone-Releasing Hormone (GHRH); inhibited by hypothalamic Somatostatin
Thyrotropins
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 :...
:
- Thyroid-stimulating hormoneThyroid-stimulating hormoneThyrotrophin-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 :...
(TSH), released under influence of hypothalamic Thyrotropin-Releasing Hormone (TRH)
Corticotropins:
- Adrenocorticotropic hormoneAdrenocorticotropic hormoneAdrenocorticotropic 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...
(ACTH), released under influence of hypothalamic Corticotropin-Releasing Hormone (CRH) - Beta-endorphinBeta-endorphinβ-endorphin is an endogenous opioid peptide neurotransmitter found in the neurons of both the central and peripheral nervous system.The amino acid sequence is:...
, released under influence of hypothalamic Corticotropin-Releasing Hormone (CRH)
Lactotropins
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...
:
- ProlactinProlactinProlactin 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...
(PRL), also known as 'Luteotropic' hormone (LTH), released under influence of multiple hypothalamic Prolactin-Releasing Factors (PRH) including dopamine, estrogen, progesterone and thyrotropin-releasing hormone.
Gonadotropins:
- Luteinizing hormoneLuteinizing hormoneLuteinizing 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...
(also referred to as 'Lutropin' or 'LH' or, in males, 'Interstitial Cell-Stimulating Hormone' (ICSH)) - Follicle-stimulating hormoneFollicle-stimulating hormoneFollicle-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), both released under influence of Gonadotropin-Releasing Hormone (GnRH)
Melanotrophins
- Melanocyte–stimulating hormonesMelanocyte-stimulating hormoneThe melanocyte-stimulating hormones are a class of peptide hormones that are produced by cells in the intermediate lobe of the pituitary gland...
(MSHs) or "intermedins," as these are released by the pars intermedia, which is "the middle part"; adjacent to the posterior pituitary lobe, pars intermedia is a specific part developed from the anterior pituitary lobe.
These hormones are released from the anterior pituitary under the influence of the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
. Hypothalamic hormones are secreted to the anterior lobe by way of a special capillary
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
system, called the hypothalamic-hypophysial portal system
Hypophyseal portal system
The hypophyseal portal system is the system of blood vessels that link the hypothalamus and the anterior pituitary in the brain.It allows endocrine communication between the two structures. It is part of the hypothalamic-pituitary-adrenal axis. The anterior pituitary receives releasing and...
.
The anterior pituitary is divided into anatomical regions known as the pars tuberalis, pars intermedia, and pars distalis. It develops from a depression in the dorsal wall of the pharynx (stomodial part) known as 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:...
.
Posterior pituitary (Neurohypophysis)
The posterior pituitary stores and secretes the following important endocrine hormones:Magnocellular Neurons
Magnocellular neurosecretory cell
Magnocellular neurosecretory cells are large cells within the supraoptic nucleus and paraventricular nucleus of the hypothalamus. They are also found in smaller numbers in accessory cell groups between these two nuclei, the largest one being the nucleus circularis...
:
- OxytocinOxytocinOxytocin is a mammalian hormone that acts primarily as a neuromodulator in the brain.Oxytocin is best known for its roles in sexual reproduction, in particular during and after childbirth...
, most of which is released from the paraventricular nucleusParaventricular nucleusThe paraventricular nucleus is a neuronal nucleus in the hypothalamus. It contains multiple subpopulations of neurons that are activated by a variety of stressful and/or physiological changes. Many PVN neurons project directly to the posterior pituitary where they release oxytocin or vasopressin...
in the hypothalamusHypothalamusThe Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions... - Antidiuretic hormone (ADH, also known as vasopressinVasopressinArginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's...
and AVP, arginine vasopressin), the majority of which is released from the supraoptic nucleusSupraoptic nucleusThe supraoptic nucleus is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. The nucleus is situated at the base of the brain, adjacent to the optic chiasm...
in the hypothalamusHypothalamusThe Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
Oxytocin is one of the few hormones to create a positive feedback loop. For example, uterine contractions stimulate the release of oxytocin from the posterior pituitary, which, in turn, increases uterine contractions. This positive feedback loop continues throughout labor.
Intermediate lobe
Although rudimentary in humans (and often considered part of the anterior pituitaryAnterior pituitary
A major organ of the endocrine system, the anterior pituitary, also called the adenohypophysis, is the glandular, anterior lobe of the pituitary gland...
), the intermediate lobe
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....
located between the anterior and posterior pituitary is important to many animals. For instance, in fish, it is believed to control physiological color change. In adult humans, it is just a thin layer of cells between the anterior and posterior pituitary. The intermediate lobe produces melanocyte-stimulating hormone
Melanocyte-stimulating hormone
The melanocyte-stimulating hormones are a class of peptide hormones that are produced by cells in the intermediate lobe of the pituitary gland...
(MSH), although this function is often (imprecisely) attributed to the anterior pituitary.
Variations among vertebrates
The pituitary gland is found in all vertebrates, but its structure varies between different groups.The division of the pituitary described above is typical of mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, and is also true, to varying degrees, of all tetrapod
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
s. However, only in mammals does the posterior pituitary have a compact shape. In lungfish
Lungfish
Lungfish are freshwater fish belonging to the Subclass Dipnoi. Lungfish are best known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed...
es, it is a relatively flat sheet of tissue lying above the anterior pituitary, and, in amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s, reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s, and bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s, it becomes increasingly well developed. The intermediate lobe is, in general, not well developed in tetrapods, and is entirely absent in birds.
Apart from lungfishes, the structure of the pituitary in fish is generally different from that in tetrapods. In general, the intermediate lobe tends to be well developed, and may equal the remainder of the anterior pituitary in size. The posterior lobe typically forms a sheet of tissue at the base of the pituitary stalk, and in most cases sends irregular finger-like projection into the tissue of the anterior pituitary, which lies directly beneath it. The anterior pituitary is typically divided into two regions, a more anterior rostral portion and a posterior proximal portion, but the boundary between the two is often not clearly marked. In elasmobranchs there is an additional, ventral lobe beneath the anterior pituitary proper.
The arrangement in lamprey
Lamprey
Lampreys are a family of jawless fish, whose adults are characterized by a toothed, funnel-like sucking mouth. Translated from an admixture of Latin and Greek, lamprey means stone lickers...
s, which are among the most primitive of all fish, may indicate how the pituitary originally evolved in ancestral vertebrates. Here, the posterior pituitary is a simple flat sheet of tissue at the base of the brain, and there is no pituitary stalk. Rathke's pouch remains open to the outside, close to the nasal openings. Closely associated with the pouch are three distinct clusters of glandular tissue, corresponding to the intermediate lobe, and the rostral and proximal portions of the anterior pituitary. These various parts are separated by meningial
Meninges
The meninges is the system of membranes which envelopes the central nervous system. The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.-Dura...
membranes, suggesting that the pituitary of other vertebrates may have formed from the fusion of a number of separate, but closely associated, glands.
Most fish also possess a urophysis, a neural secretory gland very similar in form to the posterior pituitary, but located in the tail and associated with the spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
. This may have a function in osmoregulation
Osmoregulation
Osmoregulation is the active regulation of the osmotic pressure of an organism's fluids to maintain the homeostasis of the organism's water content; that is it keeps the organism's fluids from becoming too diluted or too concentrated. Osmotic pressure is a measure of the tendency of water to move...
.
There is an analogous structure in the octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
brain.
Functions
Hormones secreted from the pituitary gland help control the following body processes:- GrowthHuman 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:...
(Excess of HGH can lead to gigantismGigantismGigantism, also known as giantism , is a condition characterized by excessive growth and height significantly above average...
and acromegalyAcromegalyAcromegaly is a syndrome that results when the anterior pituitary gland produces excess growth hormone after epiphyseal plate closure at puberty...
.) - Blood pressureBlood pressureBlood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
- Some aspects of pregnancyPregnancyPregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
and childbirthChildbirthChildbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus...
including stimulation of uterine contractions during childbirth - Breast milkBreast milkBreast milk, more specifically human milk, is the milk produced by the breasts of a human female for her infant offspring...
production - Sex organSex organA sex organ, or primary sexual characteristic, as narrowly defined, is any of the anatomical parts of the body which are involved in sexual reproduction and constitute the reproductive system in a complex organism; flowers are the reproductive organs of flowering plants, cones are the reproductive...
functions in both men and women - Thyroid gland function
- The conversion of food into energyEnergyIn physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
(metabolismMetabolismMetabolism 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...
) - WaterWaterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
and osmolarity regulation in the body - Water balance via the control of reabsorption of waterWaterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
by the kidneys - Temperature regulation
Pituitary gland also makes endorphin
Endorphin
Endorphins are endogenous opioid peptides that function as neurotransmitters. They are produced by the pituitary gland and the hypothalamus in vertebrates during exercise, excitement, pain, consumption of spicy food, love and orgasm, and they resemble the opiates in their abilities to produce...
to relieve pain and alter mood.