Endocrine system (Part 2)

Hormonal stimulation

hormones from

other endocrine glands

Humoral stimulation

blood levels of

certain ions and nutrients

Neural stimulation

nerve fibers stimulate

the release of action potentials

Types of Endocrine Stimulations?

Hormonal stimulation, Humoral stimulation, Nervous system stimulation.

Three classes of Hormones

Biogenic, Proteins, and Lipids

Steroids

Lipid-soluble, formed from cholesterol, and produced by gonads and adrenal cortex.

Peptides

Water-soluble

• Consists of amino acid chains

• Three subgroups

Polypeptides

Oligopeptides

Glycoproteins

Biogenic Amines

Water-soluble (except thyroid hormone)

Derived from amino acid that is modified (e.g., tyrosine)

Biogenic amines

Dopamine, Epinephrine, and Melatonin.

Local hormones

signaling molecules that don’t circulate in blood

Eicosanoids

a type of local hormone formed from fatty acids within phospholipid bilayer of membrane

Paracrine Messengers

Chemical messengers released into tissue fluid

Paracrine Messengers

Target cells are nearby (“para”)

Paracrine

Examples (anti- inflammatory drugs)

– Histamine

– Nitric oxide

– Prostaglandins (group of messengers, various

functions)

Hormone Transport

Secretion and Distribution of Hormones

Hormone Transport

Free Hormones enter the blood stream for

distribution throughout the body

Hormone Transport

Remain functional for less than 1 hour

Hormone Transport

A hormone is inactivated when it

• binds to receptors

• broken down by liver or kidneys

• broken down by enzymes in blood

Hormones

Hormones and Intracellular Receptors

Hormones

Diffusion across the cell membrane

Hormones

Alter rate of DNA transcription in nucleus

• Change patterns of protein synthesis

• for example, the sex hormone testosterone

stimulates the production of enzymes and proteins

that cause an increase in muscle size and strength

Hormones

Directly affect metabolic activity and structure

of target cell

Hormones

Includes steroids and thyroid hormones

Hydrophilic

Most monoamines and peptides_______

hydrophobic

Steroids and thyroid hormone are____

hydrophobic

Bind to transport proteins (albumins and

globulins synthesized by the liver)

– Bound hormones have longer half-life

• Protected from liver enzymes and kidney filtration

– Only unbound hormone leaves capillaries to

reach target cell

– Transport proteins protect circulating hormones

from being broken down by enzymes in the

plasma and liver, and from being filtered out of

the blood by the kidneys

Hydrophobic

Steroids and

thyroid hormone

Hydrophobic

Receptors in

cytosol or nucleus

Hydrophilic

Peptides and

catecholamines

Hydrophilic

Receptors in

plasma membrane

Hydrophobic Hormones

Example: TH

Hydrophobic

Hormones

Enters cell through plasma membrane

Hydrophobic Hormones

Hormone/receptor

complex binds to and

regulates specific gene

Hydrophobic Hormones

Transcription and

translation of protein

Hydrophobic Hormones

Hours to days for response

Hydrophilic Hormones

Catecholamines (E, NE, and dopamine) and

peptide hormones bind to receptor proteins

at the outer surface of the cell membrane

Hydrophilic Hormones

these hormones do not have direct effects on

the target cell

Hydrophilic Hormones

instead it acts as a first messenger, which

causes the appearance of a second messenger

like cAMP, cGMP, and calcium ions

2nd messenger functions inside the cell as Hydrophilic Hormones

enzyme activator

– enzyme inhibitor

– enzyme cofactor