Chapter 39, Problem 1PL

Endocrine glands secrete _______ into the blood.
a. neurotransmitters
b. true hormones
c. paracrine substances
d. autocrine substances

Summary Introduction

Introduction: Chemical synapses are specific junctions of the nervous system, non-neuronal cells like muscles or glands. Across these junctions, the cells pass signals to each other. A chemical synapse that occurs between a motor neuron and a muscle cell. It is known as a neuromuscular junction.

Answer to Problem 1PL

Correct answer: 

The correct answer is the option (b). True hormones.

Explanation of Solution

Explanation/justification for the correct answer: 

Option (b). True hormones. Hormones are chemical messengers secreted into blood or extracellular fluid by one cell that affect the functioning of other cells. Most hormones circulate in blood, coming into contact with essentially all cells. The endocrine system can be defined as a network of glands present in the body which produce the true hormones. These are helpful in important body functions.

True hormones led to the variations in cells by binding to receptors located on target cells. The number of receptors present on a target cell that can rise or drop in response to hormonal activity. Though, a given hormone usually affects only a limited number of cells that are known as target cells. Hence, the option (b) is correct. 

Explanation for the incorrect answer: 

Option (a) Neurotransmitters. A chemical substance that is secreted at the nerve fibre end due to the arrival of a nerve impulse. It diffuses through the junction or synapse, effects the transmit of the impulse to a muscle fiber, nerve fiber, or some other structure. Hence, the option (a) is incorrect. 

Option (c) Paracrine substances. Paracrine signaling is a type of cell-to-cell communication or cell signaling in which a cell releases a signal to provoke the modifications in close by the cells. It can alter the behavior of the cells. Cells produce the paracrine factors and release them into the instant extracellular environment. Hence, the option (c) is incorrect.

Option (d) Autocrine substances. Autocrine signaling is a type of cell signaling. In this signaling a cell secretes a chemical messenger or hormone that is known as the autocrine agent. This substance binds to the autocrine receptors on the same cell and results into the modifications in the cell. Hence, the option (d) is incorrect. 

Conclusion

The endocrine system can be defined as a network of glands present in the body which produce the true hormones. True hormones led to the variations in cells by binding to receptors located on target cells. The number of receptors present on a target cell that can rise or drop in response to hormonal activity. Hence, the option (b) is correct.