17.2b Stimulation of Hormone Synthesis and Release & 17.3 Categories of Hormones

Reflex

A preprogrammed, involuntary response of a muscle of gland to a stimulus.

Endocrine reflexes

Cause the release of a hormone, intitated by one of the 3 types

• Hormonal stimulation

• Humoral Stimulation

• Nervous System Stimulation

Hormonal Stimulation

• The stimulus for the release of many hormones from an endocrine gland is the binding of another hormone. An example is thyroid-stimulating hormone (which is released from the anterior pituitary) binding to the thyroid gland to cause release of thyroid hormone

Humoral Stimulation

• Some endocrine glands are stimulated to release their hormones in response to a changing level of nutrients (e.g., glucose) or ions (e.g., Calt) within the blood. (The term humoral is a historical term related to blood as one of the four "humors," or fluids, of the body.) When either the nutrient or ion levels decrease or increase within the blood, an endocrine gland is stimulated to release its hormone molecules. An example of humoral stimulation occurs when blood glucose levels increase and the pancreas releases insulin

Nervous System Stimulation

A few endocrine glands are stimulated to release hormone(s) by direct stimulation from the nervous system. The classic example is the release of epinephrine and norepinephrine by the adrenal medulla in response to stimulation by the sympathetic division of the autonomic nervous system

Circulating Hormones

Hormones that are transported within the blood

Local Hormones

Short-lived molecules that influence cells within the local tissue from which they are produced.

Circulating hormones are grouped according to what?

their chemical structure. 3 categories

steroids, biogenic amines, and proteins.

Circulating hormones are synthesized….

within endocrine cells from either cholesterol or amino acids.

Cholesterol

A type of lipid with a four ring structure; motdified in the synthesis of steroid hormones.

Amino acids

The monomers that compose proteins, are the building blocks for both biogenic amines and protein hormones.

Steroids

Lipid-soluble molecules synthesized from cholesterol.

What hormones fall under the steroids category?

-Both hormones produced within the gonads (Estrogen, progesterone, testosterone)

-Hormones synthesized by the adrenal cortex(corticosteroids such as cortisol, mineralocorticoids such as aldosterone)

Calcitriol (Sterioid?)

Hormone produced from vitamin D, sometimes classified as a steroid hormone but it is more accurately cl

Biogenic Amines

Also called monoamines. Are modified amino acids

What falls under the biogenic amine category?

-Catecholamines (Epinephrine, norepinephrine) (released from the adrenal medulla)

Thyroid hormone (released from the thyroid gland)

Melatonin(released from the pineal gland)

Are water-soluble (except for thyroid hormone which is lipid-soluble because it is produced from 2 tyrosine amino acids, which are amino acids that contain a non polar ring)

Proteins

-Most hormones are proteins.

These are molecules composed of small chains of amino acids and include:

-Small peptides

-Large polypeptides

-Glycoproteins

-All hormones in this category are water- soluble.

Local hormones

a large group of short-lived signaling molecules that do not circulate within the blood. Instead, cells synthesize and release these molecules, which then bind with either the same cell that produced them (autocrine stimulation) or neighboring cells (paracrine stimulation). These signaling molecules have properties similar to hormones because the released ligands (signaling molecules) initiate and regulate cellular changes.

They just do so "in the tissue neighborhood."

Eicosanoids

The primary type of local hormones. Includes the following:

-Prostaglandins

-Thromboxanes

-Leukotrienes

Each formed from 20 carbon fatty acid (arachidonic acid) which is cleaved from a phospholipid molecule of a cells’ plasma membrane.

The different eicosanoids are then synthesized through specific enzymes within an enzymatic cascade (see L Clinical View

17.1: "Synthesis of Eicosanoids"). Their production is not limited to one endocrine gland (as circulating hormones typically are), but instead are synthesized by cells composing many tissues located throughout the body. Thus, eicosanoid synthesis and release provides the means for all tissues to locally regulate cellular responses.

Prostaglandins

The most diverse category of eicosanoids.

Their effects are wide-ranging, depending upon both the specific type of prostaglandin molecule and the specific type of cellular receptor to which it binds.

Examples of prostaglandin activity include

1. stimulating the hypothalamus to raise body temperature to induce a fever (see L section 22.3f),

2. inhibiting stomach acid secretion (see ( section 26.2d), (c) acting on mast cells to release molecules that increase inflammation, and

(d) stimulating pain receptors (see

L section 22.3e).