Reporter and Curator: Dr. Sudipta Saha, Ph.D.
Hypogonadotropic hypogonadism is a form of hypogonadism that is due to a problem with the pituitary gland or hypothalamus. In this condition, the male testes or the female ovaries produce little or no hormones.
Causes:
Hypogonadotropic hypogonadism is caused by a lack of secretion of the gonadal stimulating pituitary hormones: follicle stimulating hormone (FSH) and luteinizing hormone (LH). Normally, the hypothalamus in the brain releases gonadotropin-releasing hormone (GnRH). This hormone stimulates the pituitary gland to release other hormones, including FSH and LH. These hormones tell the female ovaries and male testes to release hormones that lead to normal sexual development in puberty. Any change in this hormone release chain causes a lack of sex hormones and prevents normal sexual maturity. Failure of the hypothalamus is usually a result of Kallmann syndrome. Kallmann syndrome is an inherited form of hypogonadotropic hypogonadism that can occur with a loss of smell.
Symptoms:
- Erectile dysfunction in men
- Inability to smell (in some cases)
- Lack of development at puberty (development may be incomplete or delayed)
- Lack of secondary sexual characteristics such as pubic, facial, and underarm hair
- Loss of menstrual periods in women
- Short stature (in some cases)
- Underdeveloped testicles
Treatment:
Treatment depends on the source of the problem, but may involve:
- Estrogen and progesterone pills
- GnRH injections
- Injections of testosterone
- Slow-release testosterone skin patch
- Surgery to remove a pituitary tumor
- Testosterone gels
Expectations (prognosis):
With the right hormone treatment, the person can go through puberty and fertility may be restored.
Complications:
- Delayed puberty
- Infertility
- Low self-esteem due to late start of puberty (emotional support may be helpful)
- Sexual dysfunction
Prevention:
Prevention depends on the cause. People who have a family history of inherited conditions that cause hypogonadism may benefit from genetic counseling. Preventing serious head injuries reduces the risk of hypogonadotropic hypogonadism due to pituitary injury.
Source References:
http://www.umm.edu/ency/article/000390.htm
http://health.nytimes.com/health/guides/disease/hypogonadotropic-hypogonadism/overview.html
http://www.ncbi.nlm.nih.gov/books/NBK1278/
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PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.