What is a hormone?
Blood‐borne chemical mediator released from endocrine glands that act on distant target cells
What is the difference in the type of chemical messenger used between the nervous system compared to the endocrine system?
Neurotransmitters are released into the synaptic cleft. Hormones are released into the blood.
What is the difference in the distance of action between the nervous system compared to the endocrine system?
NS: Very short distances into synaptic cleft
ES: Long distance (carried by blood)
What is the difference in the means of specificity of action on the target cell between the nervous system compared to the endocrine system?
NS: Dependent on close anatomic relationship between nerve cells and their target cells. ES: Dependent on specificity of target cell binding and responsiveness to a particular hormone.
What is the difference in the speed of response between the nervous system compared to the endocrine system?
NS: Rapid (milliseconds) ES: Slow (minutes to hours)
What is the difference in the duration of action between the nervous system compared to the endocrine system?
NS: Brief (milliseconds) ES: Long (minutes to days or longer)
What is the difference in the major functions between the nervous system compared to the endocrine system?
NS: Coordinates rapid, precise responses
ES: Controls activities that require long duration rather than speed.
Can endocrine glands produce multiple hormones?
Yes - E.g. pituitary gland
Can hormones be produced by multiple endocrine glands?
Yes - E.g. sex steroids.
Can hormones have more than one target and function?
Yes - E.g. sex steroids; GH
In what type of a pattern does the rate of secretion of some hormones vary?
Over time, in a cyclic fashion - E.g. sex steroids.
Can a single cell/organ be influenced by more than one hormone?
Yes - E.g. pancreas; reproductive system.
Can the same chemical messenger be a hormone and a neurotransmitter?
Yes - E.g. noradrenaline.
What are autocrine signals?
Chemical messengers acting on the same cell that secreted them.
What are paracrine signals?
Chemical messengers that are secreted by one cell and diffuse to adjacent cells. Used for local communication.
What cells will respond to hormonal signals?
Those with receptors for the hormone.
What are neurotransmitters?
Chemicals secreted by neurons that diffuse across a small gap to the target cell. Neurons use electrical signals as well.
What are neurohormones?
Chemicals (neurocrines) released by neurons into the blood for action at distant targets.
What are the 3 major groups of neurohormones and where do they originate from?
Hypothalamus → anterior pituitary
Hypothalamus → posterior pituitary
Catecholamines (made by modified adrenal medulla neurons).
What is a tropic hormone?
A hormone that controls the secretion of another hormone
What is a trophic hormone?
A hormone that stimulates growth and development.
What are some examples of tropic hormones?
Thyrotropin (TSH), Corticotropin, ACTH
What does the neurohormone reflex entail?
A stimulus acting at a neuron, which then stimulates a neuroendocrine cell in the CNS to release neurohormones into the circulation which then act at a distant receptor.
What comprises the simple endocrine reflex?
Stimulus acts on endocrine integrating centre, which then releases a hormone into the blood stream to act on a receptor in the target cell (effector)
What are the different schemes of hormone classification?
Structure e.g. Peptides, Amines, Steroids
Solubility e.g. hydrophilic or lipophilic
Binding of Receptor Type e.g. G protein‐coupled receptors, tyrosine kinase‐linked receptors, etc.
When are peptides synthesised and where are they stored?
Made in advance; stored in secretory vesicles.
When are steroid hormones synthesised?
Synthesised on demand
When are catecholamines synthesised and where are they stored?
Made in advance; stored in secretory vesicles
When are thyroid hormones synthesised and where are they stored?
Made in advance; precursor stored in secretory vesicles.
How are hydrophilic/lipophobic hormones released from the parent cell?