Chemical Coordination and Integration Test 0

Second messengers are the low molecular weight molecules that serve to transmit and amplify the signal of hormones, the first messenger, to initiate the downstream enzyme cascade inside the cell. cAMP serves as the second messenger in almost all the cells while ATP and GTP are the energy currencies of the cell. Thus, the correct answer is option B. 

The ovary is a reproductive organ, found in pairs as part of the vertebrate reproductive system in females. Ovaries are gonads and are endocrine glands. They secrete the hormone oestrogen and in less quantity, testosterone and progesterone. Oestrogen is responsible for the appearance of secondary sex characteristics for females at puberty. So, if both the ovaries are removed, then there will be no production of oestrogen.
Thus, the correct answer is the option (B).

• The endocrine system and the nervous system are so closely associated that they are collectively called the neuroendocrine system. 
• The brain sends instructions to the endocrine system. In return, it gets constant feedback from the glands.
• The main neural control center is the hypothalamus. 
• Suspended from the hypothalamus by a thin stalk is the pituitary gland. 
• The hypothalamus sends messages to the pituitary gland which, in turn, releases hormones that regulate body functions.

Endocrine glands release hormones (chemical messengers) into the bloodstream to be transported to various organs and tissues throughout the body.

• Receptor is a molecule usually found on the surface of a cell, that receives chemical signals from outside the cell. 
• When such external substances bind to a receptor, they direct the cell to do something, such as divide, die, or allow specific substances to enter or exit the cell.
• Receptors are proteins embedded in either the cell's plasma membrane (cell surface receptors), in the cytoplasm, or in the cell's nucleus (nuclear receptors), to which specific signaling molecules may attach.

So, the correct answer is option A.

Oxytocin and antidiuretic hormone (ADH) are two hormones synthesized in the hypothalamus, that are stored and secreted from the posterior pituitary gland. Oxytocin promotes the contraction of muscle fibers around the milk secreting glands of the breast that results in the release of milk. It also accelerates contractions of the uterus during labor and the restoration of the uterus to its normal shape after delivery. ADH increases the permeability of the collecting tubules of the nephron allowing water to be absorbed into the circulatory system, thereby concentrating urine. The name vasopressin was originally coined for this hormone to describe the increase in blood pressure of many vertebrates, excluding humans except in high concentrations. In such cases, the hormone constricts the smooth muscle tissue of the renal arteries causing an elevation of blood pressure. 

T cells or T lymphocytes are a type of lymphocytes that plays a central role in cell-mediated immunity. They are called as T-cells because they develop and mature in the thymus.
Thus, the correct answer is option A.

• A gland that makes substances such as sweat, tears, saliva, milk, and digestive juices, and releases them through a duct or opening to a body surface are called the exocrine gland.
  
• Endocrine glands are ductless glands. These pour their secretion in blood.
• Sebaceous glands are exocrine glands in the skin, that secretes oily material called sebum.
• The pineal gland is a small endocrine gland, present in the brain that produces the hormone melatonin (which is responsible for the wake/sleep patterns).
• Salivary glands are exocrine glands in the mouth (with ducts) that produce saliva.
• Mammary glands are present in females; these produce milk to feed the young one.

Thus, the correct answer is option B.

Oestrogen is responsible for the appearance of secondary sexual characteristics (development of breasts, pubic and axillay hair) for females at puberty and for the maturation and maintenance of the reproductive organs in their mature functional state.
Thus, the correct answer is the option (B).

Neurotransmitters are the chemicals, which allow the transmission of signals from one neuron to the next across synapses. They are also found at the axon endings of motor neurons, where they stimulate the muscle fibres. Acetylcholine was the first neurotransmitter to be discovered. It is synthesized by enzyme choline acetyltransferase. After releasing it binds with its receptor present at the postsynaptic terminal. Then it is soon hydrolyzed by an enzyme acetylcholinesterase.