Tag: control and coordination in living organisms

Vitamin D is a hormone produced by the kidneys that help to control the concentration of calcium in the blood and is vital for the development of strong bones. Thyroxine, also called as 3,5,3,5-tetraiodothyronine, or $T _ 4$, is one of the two major hormones secreted by the thyroid gland. Epinephrine, more commonly known as adrenaline, is a hormone secreted by the medulla of the adrenal glands.

The hormone is a regulatory substance produced in an organism and transported in tissue fluids, such as blood or sap to stimulate specific cells or tissues into action. Usually, it is a class of signaling molecules, produced by glands in multicellular organisms, that are transported by the circulatory system to target distant organs to regulate physiology and behaviour.

Rickets is defective mineralization or calcification of bones before epiphyseal closure in immature mammals due to deficiency or impaired metabolism of vitamin D, phosphorus or calcium, leading to fractures and deformity. 

The local hormones are known as kinins, which are released to overcome changes in body tissues. Kinins help in vasodilation and increase blood supply to the affected part, causing a mild local pain. Thus, they act as the first aid of the body. The sensation of pain at the time of stinging by a poisonous insect, burning or internal injury is due to kinins. So, they are called, first aid hormones.

Pheromones are the chemicals or compounds which have peculiar odour. These are secreted and released by the organisms with the help of glands present on the skin surface at various locations. These pheromones have odour which help in attracting the other member of the same species. The pheromone initiates a neuronal response and there is change in the physiolodical behaviour of the organism. There are various forms of pheromones like alarm pheromeones, food trail phereomeones and sex phereomones.

The chemical substances that are secreted by cells/tissues or glands are categorised as biological substances. It includes digestive juices, hormones and other secretions. Gastrin, thyroxin and oxytocin are the hormones secreted by stomach, thyroid gland and posterior pituitary respectively. These are biochemical substances. Creatinine is a breakdown product of creatine phosphate and does not fall under the biological category of chemical substances. Thus, the correct answer is D.

Juvenile hormone (JH), produced by the corpora allata, regulates two important processes in insects. The first is development; as an insect develops, the degree juvenility of the next stage is determined by the amount of JH in the blood; the lower the JH, the more adult the next stage. The other function of JH is, in many insects, to regulate the production of eggs in the female's ovaries. Because mating behavior is often synchronized with the ovarian cycle, the mating behaviour and pheromone production to be linked with JH.

There are specific receptors for the binding of hormones. Steroid hormones have nuclear receptors. These steroid hormones are composed of cholesterol a dare hydrophobic in nature. They enter the cells through cell membranes. They move towards the nucleus and bind to the respective receptor. They have the activity like repression, initiation or transcription of certain genes and products. 

Larynx lies ventral to the thyroid cartilage. The thyroid cartilage is the largest of the laryngeal cartilages. The thyroid cartilage forms the bulk of the front wall of the larynx. It protects the vocal cords, which are located directly behind it.