Intro to Endocrinology Part 1

What is endocrinology?

Study of endocrine glands and the hormones they secrete; study of communication within a living organism by means of hormones.

What is an endocrine gland?

A ductless gland that secretes hormones into the bloodstream (hemocrine communication).

What is the origin of the term endocrine?

From Greek "endo" (within) and "krinein" (to separate or secrete).

What is a hormone?

A chemical agent synthesized and secreted by specialized glands and transported by blood to stimulate specific target tissues.

What are the major chemical messenger systems?

Neurotransmitters, endocrine hormones, neuroendocrine hormones, paracrines, autocrines, cytokines, and solinocrines.

What is the primary function of chemical messenger systems?

To coordinate body functions and maintain homeostasis.

What are neurotransmitters?

Chemical messengers released by neuron axon terminals into synaptic junctions to act locally.

What are endocrine hormones?

Hormones secreted into the bloodstream that affect cells in distant parts of the body.

What are neuroendocrine hormones?

Hormones released by neurons into the bloodstream that affect distant target cells.

What is paracrine signaling?

Hormones are released into extracellular fluid and act on nearby cells without entering the bloodstream.

What is autocrine signaling?

Hormones act on the same cells that secreted them.

What are cytokines?

Small proteins involved in cell signaling that act through specific receptors on target cell surfaces.

Why do cytokines act through membrane receptors?

Because they cannot cross the lipid bilayer of cells.

What is solinocrine signaling?

Secretion of hormones into a lumen.

Who is considered an important figure in the early history of endocrinology?

Arnold Adolph Berthold.

Who first coined the term "hormone"?

Ernest Starling.

Who worked with Ernest Starling in hormone research?

William Bayliss.

What are the four major classifications of hormones?

Peptide hormones, steroid hormones, amines, and lipids.

What are peptide hormones composed of?

Proteins, glycoproteins, peptides, or their derivatives.

Where are peptide hormones synthesized?

In the endoplasmic reticulum (ER).

How are peptide hormones transported in blood?

Freely dissolved because they are water-soluble.

Do peptide hormones require carrier proteins?

No.

Where are peptide hormone receptors located?

On the cell membrane.

Give examples of peptide hormones.

Hypothalamic hormones, pituitary hormones, parathyroid hormone, insulin, and insulin-like growth factor.

What is the precursor of steroid hormones?

Cholesterol.

What is the chemical nature of steroid hormones?

Organic compounds with four fused rings derived from cholesterol.

Are steroid hormones water-soluble?

No, they are water-insoluble.

Do steroid hormones require carrier proteins?

Yes.

Where are steroid hormone receptors located?

In the cytoplasm or nucleus.

Give examples of steroid hormones.

Adrenocorticosteroids and gonadal/placental hormones.

What are amine hormones derived from?

A single amino acid.

Which hormones are derived from tryptophan?

Melatonin and serotonin.

Which hormones are derived from tyrosine?

Catecholamines, T3, and T4.

Which catecholamines are examples of amine hormones?

Epinephrine and norepinephrine.

Which amine hormones act similarly to steroid hormones?

Thyroid hormones (T3 and T4).

What are lipid hormones derived from?

Fatty acids.

What is the major example of a lipid hormone?

Prostaglandin.

From what fatty acid is prostaglandin derived?

Arachidonic acid.

What is the basic mechanism of hormone action?

A hormone affects target tissues by activating receptors on or within target cells.

What is meant by receptor specificity?

A receptor binds only specific hormones or ligands.

What is receptor affinity?

The strength with which a hormone binds to its receptor.

What does receptor saturation mean?

Receptors can become fully occupied by hormones.

How should hormone-receptor binding occur?

It should be noncovalent and reversible.

What factors affect receptor activation?

Hormone dose and duration of exposure.

What is down-regulation?

A decrease in receptor number or responsiveness.

Give one mechanism of receptor down-regulation.

Receptor destruction by lysosomes after internalization.

What is up-regulation?

An increase in receptor number or intracellular signaling proteins.

What are the three major mechanisms of hormone action?

Change in membrane permeability, activation of intracellular enzymes, and activation of genes.

Which hormones commonly activate intracellular enzymes through membrane receptors?

Peptide hormones.

Which hormones commonly activate genes through intracellular receptors?

Steroid hormones.

What is feedback control in endocrinology?

Regulation of hormone secretion by the effects of circulating hormones produced by the gland itself.

What are the two major feedback mechanisms?

Positive feedback and negative feedback.

What occurs during positive feedback?

Generation of more hormones.

What occurs during negative feedback?

Reduction in hormone secretion.

Which feedback mechanism is most common in endocrine regulation?

Negative feedback.

Why is negative feedback important?

It helps maintain homeostasis and prevents excessive hormone production.