Biology Study Set 13
Quiz 36 :
Structural Support and Movement
Breast development is the characteristic of sexual maturity in females. The development of breast is under the control of estrogen released by the ovaries. Generally, at the age of 13 to 14 years, development of secondary sexual characters is observed as an indication of sexual maturity. Phthalates are a group of chemical compounds that are used in the plastic and toy preparations. Phthalates are found in the blood samples of people working in the cosmetic, automotive and food canning industries. Phthalates can cross the placenta, and is also found in breast milk. The use of phthalates is banned in toy preparations, but still they are found in cosmetic preparations, shampoos and other personal care products. Phthalates act as weak estrogens and synergise with the actions of physiological estrogens. This property of phthalates is increasing the risk of breast cancer in women exposed to phthalates and also breast development is observed at a very early age. This hypothesis can be tested by taking the blood samples of women exposed to phthalates, and the observation of premature breast development and occurrence of breast cancer in those women should be framed according to their age. By comparing the results with the results of healthy women, we can prove the above hypothesis.
Hormones are the chemical messengers secreted by "endocrine glands" in to the systemic circulation, through which they reach the target site. Hormones regulate various physiological and behavioural activities of the body. Eg: Thyroid hormones (thyroxin, triiodothyronine), pituitary hormones (growth hormone, oxytocin, prolactin), adrenal gland hormones (adrenaline, noradrenaline). Thus, the correct option is (a) hormones Local signalling molecules are secreted by cells into the extracellular fluid, and their inactivation restricts their activity to that local area. For example, release of prostaglandins in response an injury causes blood vessel dilatation in that region. Thus, the option (a) is incorrect. Neurotransmitters are the chemical messengers released by the nerve terminals. The nerve terminals have stores of neurotransmitters in the synaptic vesicles. These neurotransmitters act on receptor structures present on the dendrites of the post synaptic neuron or the effector organ (Eg: muscles and glands). Thus, the option (b) is incorrect. Pheromones are the chemical messengers, which carry the information between the individuals of same species (through olfaction), particularly between the opposite sexes. One of the main functions of "vomeronasal organ" is the detection of pheromones. Thus, the option (c) is incorrect.
The release of growth hormone is influenced by the release of growth hormone releasing hormone (GHRH) from the hypothalamus. GHRH act on anterior pituitary and thus promotes the release of growth hormone. Decreased secretion of growth hormone (somatotropin) from the anterior pituitary results in Dwarfism. Dwarfism is a genetic disorder that is inherited from mother and father equally in an "autosomal (may be from mother or father) dominant (mutation in one copy of the gene can cause the disease) fashion." Receptors are the protienious structures to which various chemical substances bind and produce their effects. These receptors are specific to the chemical substances (Eg: neurotransmitters, hormones), the binding of chemical substance cause conformational change to the receptor structure that is followed by specific physiological changes. The structure of receptors is coded by specific genes; any mutation in these genes causes change in receptor structure. As the receptor structure specifically binds a chemical substance, this new receptor structure coded by the mutated gene would not allow the chemical to bind and bring conformational change in the receptor structure to produce its effects. So, in the present example, because of the mutation in the gene involved in the synthesis of GHRH receptor, the GHRH cannot bind to the abnormal receptor (coded by the mutated gene) and trigger the release of growth hormone from the anterior pituitary gland, though the gene coding for GH is normal.