The hypothalamus and pituitary gland are the center of the endocrine system of the body. With its help, all processes associated with primitive reactions, such as stress, rage, flight, body temperature, thirst, hunger, sexual activity, that is, those that ensure the survival of a person as a whole, are regulated.
Pituitary gland
The pituitary gland is the structure of the diencephalon the size of a bean and weighing up to 600 milligrams, which is associated with the hypothalamus. It carries both nerve and endocrine functions. It produces and secretes many hormones that help control growth, blood pressure, energy and genital function control, thyroid gland metabolism, as well as some aspects of pregnancy, childbirth, feeding, water balance by controlling the reabsorption of water from the kidneys, temperature regulation and relief pains.
Location
The pituitary gland is located approximately in the center of the human skull below the hypothalamus, in the bone cavity, resembling a saddle. From another part of the brain, it is bounded by a dense membrane. This arrangement really makes sense in light of the role of the hypothalamus, which provides fine-tuning of the pituitary gland. Nerve fibers tightly enclose these two structures, which makes it easy to interact with each other. Similarly, a thin vascular compound that is produced in the pituitary stem facilitates the control of the hypothalamus. In addition, the pituitary gland itself is supplied with branches from the internal carotid artery.
Structure
Structurally speaking, the pituitary gland is noticeably divided into three parts: the anterior, intermediate and posterior, which of course affects its size. And each part can be described in accordance with its unique functions:
- The front part (the adenohypophysis) plays a major role in the development of the human body, which includes the release of hormones that control our growth, reproduction and puberty. They activate the adrenal glands, thyroid gland and gonads. This is a glandular tissue that develops from the epithelium of the posterior wall of the oral cavity. It makes up about 80 percent of the mass of the entire organ.
- An intermediate fraction secretes hormones that stimulate cells to produce melanocytes, a pigment that is responsible for discoloration of the skin.
- The posterior lobe (neurohypophysis) produces antidiuretic hormone (ADH), which allows our kidneys to reabsorb water into the bloodstream to prevent dehydration. Oxytocin is also produced here, which takes an active part in labor.
Dimensions
The size of the pituitary gland is normal and its shape is individual. As a rule, the sagittal size is 5-12 millimeters, the coronal one is 6-8 millimeters and the axial one is 3-5 millimeters. In men, these indicators are slightly less than in women.
Main functions
The main function of the pituitary gland, despite its small size, is the ability to produce hormones that preserve many of our body functions. The anterior and posterior lobes are the primary secretory glands.
The neurohypophysis secretes oxytocin and ADH. Oxytocin not only stimulates uterine contractions to facilitate childbirth, but also forces breast tissue to produce milk in preparation for child care. In men and women, oxytocin is believed to promote bonds between parents and newborns, known as attachment. It is also believed that oxytocin is involved in feelings of love and intimacy, as well as in a sexual reaction. It is believed that the pituitary gland of a woman secrete more oxytocin, so the romantic part of the relationship interests them more often than men. The pituitary gland in the stronger sex produces more vasopressin.
Adenohypophysis produces a whole list of hormones:
- prolactin, which, like oxytocin, triggers the production of milk after childbirth;
- follicle-stimulating hormone (FSH) is released to stimulate sperm production in men and egg maturation in women capable of producing estrogen;
- luteinizing hormone (LH) stimulates the production of testosterone in men and the egg in ovulating women;
- thyroid-stimulating hormone (TSH) stimulates the activity of the thyroid gland, which helps to coordinate metabolic activity, therefore, TSH indirectly helps the thyroid gland to perform all its functions.
- adrenocorticotropic hormone (ACTH) is secreted and stimulates the production of the stress hormone (cortisol), which is necessary for our survival, as it supports normal blood pressure and blood sugar;
- growth hormone (GH), which is responsible for the growth of muscle and bone mass during the development of the body.
Sexual pituitary dimorphism
The sizes of the pituitary gland differ between the sexes when comparing age groups. At the age of 5-9 years, the posterior pituitary gland is larger in boys than in girls. A strong growth spurt of this organ is noted during puberty and is especially noticeable in women. The weaker sex shows a larger pituitary gland than men in the age group from 14 to 17 years. The height of the pituitary gland increases to 29 years, then decreases. The size of the pituitary gland in men is slightly smaller.
This is because they are less than women subject to cyclical fluctuations in hormonal status. In women aged 50 to 59 years, an increase in the height of the pituitary is noted. It is believed that this reflects a change in the rate of secretion of gonadotropin-releasing hormone in women during this period. Both young and older women show a correlation between pituitary volume and age. In men, such changes are less noticeable.
Physiological pituitary hypertrophy in adolescence
Puberty is the activation of the hypothalamic-pituitary-gonadal axis, which leads to the maturation of the gonads. A study of children, adolescents and young people using magnetic resonance imaging revealed that the sequence of normal maturation of the pituitary gland includes a period of physiological hypertrophy in adolescents. Children under 12 years old have a vertical pituitary gland size of not more than 6 millimeters. From the age of 14, the puberty begins and the change in the parameters of this organ.
In girls, this manifests itself in significant changes in both the size and shape of the pituitary gland. At the same time, the boys only have a change in size. The normal size of the pituitary gland for girls in this period is 8-10, and for young men only 7 millimeters. The cause of the significant difference may be the earlier onset of puberty in girls compared with boys.
The size of the pituitary gland is normal in women during pregnancy and after childbirth
Throughout pregnancy, the height of the gland increases linearly by about 0.08 mm per week. The swelling of the gland also changes with increasing gestational age. The largest glands are seen in the postpartum period. The size of the pituitary gland in women in this case can be 10-11.8 mm. After the first week after birth, the glands quickly return to their normal size, which is completely independent of the process of breastfeeding.
Pituitary gland and stress
The pituitary gland is important for determining the response to stress through the hypothalamus-pituitary-adrenal axis (HPA axis). It is critical that pituitary growth in adolescence can be altered by stress at an earlier age, such as childhood abuse or maternal dysphoric behavior. Scientists have identified a correlation between the size of the pituitary gland and the subscale estimates of social anxiety. Children with early adrenal gland development tend to have a larger pituitary gland compared to children with later adrenal gland development.
Deviations from the norm
Lesions of the pituitary gland cause functional disorders and diseases. Deficiency of any of the hormones listed above can cause illnesses that vary in severity. ADH deficiency increases thirst and urination. Lack of prolactin quite predictably leads to inability to lactate. TSH deficiency has symptoms similar to those of a thyroid gland, including fatigue, memory loss, and physical weakness. Lack of LH or FSH leads to decreased libido, irregular periods, erectile dysfunction, and mood changes. ACTH deficiency causes nausea, body aches, poor appetite, low blood sugar, and pressure. Growth hormone deficiency leads to a decrease in muscle mass and bone density.
Overproduction of the hormone has its consequences. Too much growth hormone can lead to gigantism, acromegaly, too much bone and soft tissue growth, which will result in heart problems and cause sleep apnea. Too much TSH leads to trembling limbs, irritability, and high blood pressure. A large amount of prolactin leads to improper production of breast milk, which can occur in women, and to weaken bones. With an excess of adrenocorticotropic hormone, weight increases, bone fragility and mood instability occur. Finally, excess FSH and LH is associated with infertility and irregular menstruation.