What Is the Adenohypophysis?

The pituitary gland is the most important endocrine gland in the body. It is a cherry-shaped organ at the base of the brain near the lower part of the optic mast, and is part of the endocrine system. He secretes a variety of hormones that can stimulate the secretion of hormones in the lower optic mound. There are seven known hormones secreted by the pituitary: growth hormone (HGH), prolactin (PRL), melanin (MSH), thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), and gonadotropin (GTH) (Including FSH and LH)). TSH acts on the thyroid gland, ACTH acts on the adrenal cortex, and GTH acts on the male and female glands (testis and ovaries).

The pituitary gland is the most important endocrine gland in the body. It is a cherry-shaped organ at the base of the brain near the lower part of the optic mast, and is part of the endocrine system. He secretes a variety of hormones that can stimulate the secretion of hormones in the lower optic mound. There are seven known hormones secreted by the pituitary: growth hormone (HGH), prolactin (PRL), melanin (MSH), thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), and gonadotropin (GTH) (Including FSH and LH)). TSH acts on the thyroid gland, ACTH acts on the adrenal cortex, and GTH acts on the male and female glands (testis and ovaries).

Chinese name

Pituitary

Foreign name

The pituitary gland

Attributes

Endocrine glands

Secreted hormone

Growth hormone

Secreted hormone

Prolactin

Secreted hormone

Thyroid stimulating hormone

Secreted hormone

Gonadotropin

Pituitary hormone

The functions of these stimulating hormones will be introduced in their target gland function chapters. This section only introduces the physiological functions and secretory regulation of auxin and prolactin.

Growth hormone (GH)

Human GH is a polypeptide containing 191 amino acids. Its structure is similar to that of PRL, so it overlaps with the role of PRL. The chemical structure and immune characteristics of GH vary greatly among different animals. With the exception of monkeys, GH is not effective in humans.

The main role of GH is to promote growth and development throughout the body. This is because on the one hand, it promotes the growth of bones and makes the body tall, and on the other hand it promotes protein synthesis to make muscles develop. The pituitary gland is removed when the animal is young, and the animal stops growing. If it can be supplemented with GH in time, it can resume its growth. Clinically, children lacking GH due to congenital pituitary damage are short in stature but normal in intelligence, called dwarfism. The proportion of upper body and lower body length of such patients is basically similar to that of normal people. On the contrary, if the amount of GH secretion is too high in childhood, it will make the body grow too tall and form giant disease. If the amount of GH secretion in adulthood is too high, it will stimulate the acromegaly and facial bone hyperplasia and acromegaly. The internal organs of these patients, such as the liver and kidneys, are also excessively enlarged. It can be seen that an appropriate amount of GH plays an important role in maintaining the normal growth of the body. The GH content in normal people's fasting blood is below 5ng / ml.

The mechanism by which GH promotes bone growth has been clarified: under the action of GH, auxin is mainly produced by the liver. It acts on cartilage through blood circulation, accelerates cartilage cell protein synthesis, increases cartilage collagen tissue, promotes chondrocyte division, Cartilage grows and becomes cartilage after cartilage ossification. GH has similar effects on liver cells, skeletal muscle cells and fibroblasts, but has no effect on brain growth and development.

Another important role of GH is to participate in the regulation of intermediate and energy metabolism. Experiments have shown that its role in this regard has nothing to do with auxin mediators. GH promotes protein synthesis by accelerating the synthesis of DNA and RNA. It can also promote fat breakdown and supply energy, thereby reducing tissue fat, especially the fat in the limbs. These effects are beneficial to the body's growth and repair on the one hand, and keep the body's metabolism "young" on the other hand, that is, the body's protein and body fluids are rich, and fat is less. The effect of GH on glucose metabolism is more complex. GH at physiological levels can stimulate insulin secretion from beta cells of islets, which indirectly enhances glucose utilization. In short, GH can promote protein synthesis, accelerate fat decomposition, strengthen the rational use of sugar, and change energy from sugar to energy from lipids. The GH content in the blood of adults and the elderly is still maintained at a certain concentration, which is closely related to the regulation of metabolism and is a factor in the body's important function of adapting to the environment.

GH secretion is dually regulated by the hypothalamus GHRH and GHRIH. In addition, GH secretion is also affected by many factors such as sleep and blood sugar and amino acid content. GH secretion also increases during stress.

Prolactin (PRL)

PRL is a peptide containing 199 amino acids, which is a hormone with a wide range of effects. Its main function is only briefly described.

PRL can promote breast growth and development, cause and maintain breast secretion. In female puberty, the development of the breast is mainly the synergistic effect of sex hormones and other hormones. During pregnancy, PRL and chorionic auxin, estrogen, and progesterone further promote the development of the mammary glands, so that the lactation conditions gradually mature, but do not lactate. After delivery, PRL can play the role of initiation and maintenance of breast secretion. Studies have also shown that PRL also has effects on pigs, monkeys, and human ovaries, which can directly affect luteal function. It acts on the LH receptor to increase the synthesis of progesterone and reduce the decomposition of progesterone, thereby strengthening the function of the corpus luteum.

PRL is also dually controlled by the hypothalamus. Prolactin-releasing factors promote its secretion; prolactin-releasing inhibitors inhibit its secretion, which is believed to often prevail. When the baby sucks the mother's nipple, it stimulates the sensory nerve endings of the nipple, and the impulse is transmitted to the hypothalamus to promote the secretion of prolactin-releasing factors and then cause the PRL secretion. PRL secretion is reduced or stopped after stimulation is stopped. This is a typical neuroendocrine reflex. Studies have found that under stress, PRL often appears simultaneously with increased secretion of ACTH and GH. After stress stimulation stops, all three gradually return to normal levels. The function of PRL under stress is unclear.

Pituitary hormone

Hormone released by the pituitary

The pituitary gland releases two hormones called vasopressin (VP) or antidiuretic (ADH) and oxytocin (OXT). Both are 9 peptides with similar molecular structures. Their physiological effects also overlap.

Vasopressin (VP)

The physiological role of VP and its secretion regulation have been introduced in the relevant sections of the blood circulation system and urinary system in this book, and will not be repeated here.

Oxytocin (OXT)

OXT has the dual effects of stimulating the breast and uterus. When sucking the nipple, the baby also stimulates the sensory nerve endings of the nipple, and the nerve impulses are transmitted to the hypothalamus, which not only causes the release of PRL, but also stimulates the paraventricular nucleus and supraoptic nucleus to cause the secretion of OXT. OXT acts on the myoepithelial cells around the mammary gland, shrinks it, promotes the excretion of milk stored in the mammary gland, and can maintain the milk secreted by the mammary gland.

The effect of OXT on uterine smooth muscle is different for animals of different species, and for non-pregnant and pregnant uterus. If the infertile uterus is not sensitive to it, the pregnant uterus is more sensitive to it. Estrogens increase the sensitivity of the uterus to OXT, while progestins do the opposite. Although much research has been done on the role of OXT in childbirth, the physiological significance of OXT during and postpartum hemostasis is inconclusive. Clinically, the use of OXT in postpartum causes strong contraction of the uterus and reduces postpartum bleeding, but the dose used has exceeded the physiological range and is a pharmacological effect.

Hypohypophysis

Hypopituitary hypofunction (Simon-Sheehan syndrome) is a group of diseases that cause secondary hypofunction of the gonad, thyroid, and adrenal cortex due to damage to the anterior pituitary gland caused by a variety of reasons. Postpartum hemorrhage, pituitary tumors, infections, surgical trauma, etc. can cause adenoid pituitary function decline, usually slow onset, patients often have gonadal atrophy, followed by hypothyroidism and adrenal insufficiency. In severe cases, symptoms of hypoglycemia, coma, and shock may occur. This disease belongs to the category of "deficiency" in traditional Chinese medicine, and treatment is mainly based on warming the spleen and kidney.

[Diagnostic points]

Clinical manifestations: (1) Hypogonadism group: insufficient gonadotropin (FSH, LH) and abnormal prolactin (PRL) secretion cause: no milk after delivery, breast atrophy, long-term amenorrhea, hyposexuality to disappear, reproductive organ atrophy, etc. .

(2) Hypothyroidism group: insufficient thyroid stimulating hormone (TSH) leads to: chills, obesity, dry and rough skin, paler, less shiny, less sweaty, less elastic, severe myxedema, loss of appetite, mental Depression, indifferent expression, etc.

(3) Adrenal insufficiency group: insufficient adrenocorticotropic hormone (ACTH) causes: extreme fatigue, weak physical strength, anorexia, nausea and vomiting, weight loss, low resistance, easy infection, slow heart rate, weak pulse, low blood pressure In severe cases, there is an episode of hypoglycemia.

(4) Pituitary gland or its adjacent tumor compression group: The most common and serious ones are headache, blindness and even blindness caused by optic nerve cross damage. Sometimes hypothalamus syndrome and intracranial hypertension caused by brain tumors can appear.

Adenohypophysis

A general term for a variety of hormones secreted by pituitary cells. There are many kinds of pituitary cells, which secrete their respective hormones. Growth hormone cells (also known as alpha cells) secrete growth hormone; prolactin cells (also known as cells) secrete prolactin; thyroid-stimulating hormone cells (also known as beta 2 cells or theta cells) secrete thyroid-stimulating hormone; Also known as 1 cells) secrete adrenocorticotropic hormone, melanocyte (hormone) hormone, and lipotropin; gonadotrophin cells (also known as delta cells) secrete luteinizing hormone and follicle stimulating hormone. The endocrine function of the pituitary gland is mainly controlled by signals sent by the hypothalamus-related nerve cells. The hormones secreted by certain nerve cells in the hypothalamus (see "Hypothalamic Hormones") are transported to the pituitary gland through the pituitary portal system and control the secretion of pituitary hormones.