Scope of Hormones

Question 1

Endocrinology

Answer 1

The study of the homeostatic chemical adjustments and other activities that hormones accomplish.

Question 2

Hormone

Answer 2

A chemical mediator that is secreted by an endocrine tissue or gland into the ECF (blood), which transports it to its target cells

Question 3

Types of intercellular communication mediated via extracellular chemical messengers

Answer 3

Paracrine secretion
Neurotransmitter secretion
Hormonal secretion
Neurohormone secretion

Question 4

Paracrine secretion

Answer 4

Paracrines are local chemical messengers whose effect is exerted only on neighbouring cells in the immediate environment of the site of secretion. Therefore, as paracrines are distributed by simple diffusion within the interstitial fluid, their action is restricted to short distances.

Question 5

Example of paracrine secretion

Answer 5

One example of a paracrine chemical messenger is histamine, released from a specific type of connective tissue during an inflammatory response within on invaded or injured tissue. One of the actions of histamine is to open blood vessels in the vicinity to increase blood flow, bringing supplies to the affected local area.

Question 6

Neurotransmitter secretion

Answer 6

Neurons communicate directly with the cells they innervate by releasing neurotransmitters. These are short range chemical messengers. These neurotransmitters are released in response to electrical signals/action potentials. Like paracrines, neurotransmitters diffuse from their site of release across a narrow extracellular space to act locally on a target cell. That target cell may be another neuron, a muscle or a gland. Neurons may carry action potentials long distances but the neurotransmitter released at the axon terminal acts only across a very very short range.

Question 7

Hormonal secretion

Answer 7

Hormones are long range chemical messengers specifically secreted into the blood by endocrine cells in response to an appropriate signal. The blood carries the chemical messengers to other sites in the body where they exert their effects on the target cells some distance away from the site of release. It’s ONLY the target cells of a particular hormone that has the receptors for binding that hormone. Non-target cells are not influenced by that hormone.

Question 8

Neurohormone secretion

Answer 8

Neurohormones are released into the blood by neurosecretory neurons. These neurons respond to and conduct electrical signals, releasing a neurohormone into the blood in response to that appropriate stimulation. The neurohormone is then distributed into the blood to distant target cells.