Growth disorders – Growth Hormone Deficiency (GHD)
Growth disorders – Growth Hormone Deficiency (GHD)Endocrinology
Growth disorders – Turner's syndrome
Growth disorders – Turner's syndromeEndocrinology
Growth disorders – Growth Hormone Therapy
Growth disorders – Growth Hormone TherapyEndocrinology
Growth disorders – Links
Growth disorders – LinksEndocrinology
Endocrinology is the study of the endocrine system of glands, the regulatory substances (hormones) they produce and disorders of the system.
The endocrine system is a very complex, delicately balanced arrangement of 'hormonal' feedback loops designed to co-ordinate many bodily functions and ensuring they work normally.
The system uses many different hormones as 'messenger' signals. These are produced by a number of different endocrine glands that include the adrenal glands, sex glands (ovaries in women and testes in men), pancreas, parathyroid, pituitary gland and thyroid.
The hormones produced by these glands are secreted directly into the blood stream from within the gland where they are transported throughout the body for action on a wide range of target organs and systems.
The pituitary gland and hypothalamus
The pituitary gland, located on the underside of the brain, was once thought to be the 'master' gland being responsible for producing seven hormones regulating various bodily activities including growth and reproduction.
Although an important endocrine gland, hormone production by the pituitary gland is itself regulated by a small area of the brain called the hypothalamus, an area that provides an important link between the nervous and endocrine systems.
The hypothalamus produces nine different hormones, which (through the response of the pituitary gland) help regulate virtually all aspects of growth, development and metabolism.
Growth hormone is one of the main hormones produced by the pituitary gland, and is a crucial factor in promoting normal growth and development in the body. Its action determines how the body is built, how it functions, and in particular the way bones develop.
Growth hormone is released in a cycle of short bursts throughout the day, roughly once every four hours, though about 70 per cent of the total growth hormone is secreted during the early hours of sleep particularly during dreaming.
Once sufficient growth hormone has been released, the increased concentration in the blood feeds back to the hypothalamus and a second hormone, called somatostatin (also known as GH-inhibiting factor), is released telling the pituitary gland to stop secreting growth hormone for the moment.
Role of growth hormone in growth
During childhood and puberty growth hormone secretion is at its highest causing bone cells to multiply by acting on 'growth plates' at the end of each tubular bone. It is the increase in the length of the long bones in the body that causes the body to grow taller and overall growth causes the skeleton to take on an adult shape.
After growth is complete, the growth plates of the long bones fuse together and close preventing further lengthening, and the secretion of growth hormone gradually falls to the much lower levels typical of adulthood.
Disorders of the endocrine system
The feedback mechanism of the endocrine system is designed to prevent overproduction (hypersecretion) or underproduction (hyposecretion) of any given hormone. However in some disease conditions there is an imbalance in the regulation.
The under- or overproduction of hormones from the pituitary gland cause several problems. Imbalance in the production of growth hormone affects the natural growth of children. Any shortfall in the production of growth hormone during childhood and puberty will affect the height and development of a child, and once the growth plates of the long bones have closed, growth hormone is unable to have any further effect on the height of an individual.
Growth is one of the complex and amazing facts of life that most people take for granted, but it can be a cause for concern for parents who have a child who is shorter than others of the same age and does not appear to be growing any taller.
Causes of delayed growth
There are a large number of medical, genetic and external factors that can delay or inhibit normal growth. These include conditions such as Growth Hormone Deficiency (GHD) in children, Turner's syndrome, Down's syndrome, achondroplasia (defective growth of cartilage cells in the bones of the limbs) and various malfunctions of the endocrine system.
Chronic diseases and illnesses can also have a detrimental effect on growth including Inflammatory Bowel Disease, chronic renal insufficiency and heart disease, as too can factors such as malnutrition, drug and alcohol abuse, neglect, chronic stress and lack of exercise.
However, in many cases the cause of delayed or restricted growth is not known.
Many children are smaller than average during childhood yet end up reaching a normal adult height. But for some, a more normal adult height will not be achieved without treatment with supplemental human growth hormone (hGH). These include children with GHD and Turner's syndrome.
One out of 2,500 to 5,000 children is born with a deficient growth hormone production resulting in impaired physical development, and another one in 2,000 to 2,500 girls are born with the genetic defect Turner's syndrome. Both disorders may result in decreased final height, which may be improved by supplemental somatropin.
Growth Hormone Deficiency (GHD)
A child with an inadequate production of growth hormone (reduced or non-existent) may have a normal height and weight at birth, but the child's physical development following birth is severely impaired.
The under-secretion of human growth hormone during childhood and puberty slows bone growth and teeth development, and also causes the growing plates of the long bones to close before normal height is reached.
In addition, other organs of the body fail to grow and the body proportions remain childlike.
Without treatment the child with GHD risks the development of a range of complications, as well as having a short stature.
Turner's syndrome is a common genetic defect that affects girls and women and occurs in about one out of every 2,000 to 2,500 female births.
In Turner's syndrome all or part of one of the two X-chromosomes is missing, but the reason why this happens is not known. This defect can cause a number of physical and medical problems and in some cases creates educational and behavioural concerns.
Characteristics of Turner's syndrome
As the extent of the defect to the chromosome varies, every case of Turner's syndrome is individual and each affected girl may have only a few of the possible characteristics that can be associated with the syndrome.
Short stature is a common characteristic of Turner's syndrome resulting in a decreased final adult height and is generally accompanied by a failure of the ovaries and infertility.
Growth failure in Turner's syndrome
The reasons for the growth retardation in Turner's syndrome are not entirely understood, but patients are generally not deficient in growth hormone. The pituitary gland produces adequate amounts but the long bones do not respond.
The growth plates appear to be resistant to the action of the body's growth hormone, yet the hormone functions normally in controlling metabolism and organ development. By treating with supplemental hGH the resistance can be overcome, creating growth in the long bones. Female hormones may need to be given as well.
Being a genetic problem the affected individual will be faced with the consequences of the syndrome all her life, but can expect to lead a healthy life with appropriate care and treatment.
Growth Hormone Therapy
Synthetic human growth hormone (hGH) is used to replace the growth hormone short fall in people who do not produce enough of their own, or have an inadequate response to that which is produced.
In all cases supplemental growth hormone has to be given on a daily basis, normally as a nightly injection at bedtime in a dose calculated and adjusted for each individual case.
Use in children
Deficient children require hGH supplements throughout childhood. hGH given to stimulate growth must be administered before the growth plates of the long bones close and prompt treatment can result in the gaining of several extra centimetres of height.
Use in Turner's syndrome
In Turner's syndrome large doses of growth hormone often have to be given and this approach has been found to be effective in increasing final height especially in combination with appropriate very-low-dose oestrogen replacement.
Synthetic growth hormone
Growth hormone from human origins (somatotrophin) has now been replaced by an identical peptide (somatropin) produced using recombinant DNA technology. This 'synthetic' human growth hormone is identical to that produced by, and previously collected from, human sources and can be produced in greater quantities. It is a protein, or peptide chain containing 191 amino acids.
Supplemental hGH cannot be taken orally as being a protein it will be broken down and digested. It therefore has to be injected, but regular injections can be very off-putting, particularly for a child.
The mode of administration can have a strong bearing on the acceptability of treatment and hence ultimate compliance and treatment success. Improvements to injection devices are constantly being developed to make the process easier and more comfortable for patients.
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