Principles of Hormonal Control Systems (Part 6)

Chapter 10 John Paul L. Oliveros, MD, DPPS

Summary of Hormones

Hormone structure and synthesis 3 chemical classes of

hormones Amines Peptides and proteins steroids

Amine Hormones Derivatives of

tyrosine Include:

▪ Thyroid hormones▪ Epinephrine▪ Norepinephrine▪ dompamine

Thyroid Hormones Thyroxine (T4) and

Triiodothyronine▪ Secreted by thyroid follicles

Iodine▪ Essential element of thyroid

hormones▪ Food GI tract blood (converted

to iodide) thyroid follicular cells (conversion back to iodine) thyroglobulin (incorportation with tyrosine and thyroglobulin precursor)

Thyroglobulin▪ Found in central spaces between

thyroid follicles▪ Endocytosis into follicular cells

and digested by lysosymes to release thyroid hormones

Thyroid Hormones Thyroxine (T4)

Secreted in large amounts Converted into T3 by most

tissue by deiodination Has no action unless converted

to T3 Persons with defective

deiodination enzyme manifest as thyroid hormone deficiencyeven with normal or increased T4

Triiodothyroxine (T3) More active than T4

Function: Regulation of O2 consumption Growth Brain development and function

Adrenal Medulla Glands and Dopamine Adrenal gland

Adrenal cortex Adrenal medulla▪ Modified sympathetic

ganglion▪ Axons release

secretions into blood (endocrine)

▪ Secrete 2 amine hormones▪ Epinephrine (E)

Secreted 4x more than NE

▪ Norepinephrine (NE)

Dopamine Secreted by cells in

the hypothalamus Function as a

hormone Also secreted by

small amounts in the adrenal glands

Peptide Hormones Composes majority of

hormones preprohormones

(ribosomes) prohormones (endoplasmic reticulum) hormones + peptides (golgi apparatus)

Many also functions as neurotransmitters/ neuromodulators

Steroid Hormones Produced by the adrenal

cortex and gonads, placenta

Cholesterol Steroid produced on a

particular cell depends on the types and concentration of enzymes present

Highly soluble Steroid producing cell

plasma membrane interstital fluid blood binding with plasma proteins

Hormones of the adrenal cortex Aldosterone

Mineralocorticoid Salt (mineral) balance Kidney’s handling of Na+, K+, H+

ions Cortisol and Corticosterone

Glucocorticosteroid Metabolism of glucose and other

organic nutrients Facilitation of response to stress Regulation of immune system

Dehydroepiandrosterone (DHEAS) and Androstenedione Androgens

▪ Include testosterone (testes)▪ Other adrenal androgens function like

testosterone but less potent▪ Play important role in adult female and

both sexes during puberty

Hormones of the adrenal cortex 3 distinct layers of

adrenal cortex Zona glomerulosa▪ High enzyme

concentration to convert corticosterone to aldosterone

Zona fasciculata Zona reticularis▪ Secretes more androgen

and cortisol▪ If less enzyme for

conversion to cortisol, may produce masculinzation in females

Hormones of the Gonads High concentrations

of enzymes to lead to androstenedione

Testes Androstenedione

testosterone Ovaries

High concentrations of aromatase

Androgens estradiol Some ovarian cells

screte progesterone

Hormone transport in blood Concentration of free hormone is more physiologically

important than total concentration

Hormone Metabolism and Excretion Liver and kidneys

Major organs for hormone excretion and metabolism

Target cells May metabolize cetain peptide

hormones Plasma/blood

Rapid elimination of peptide hormones and catecholamines

Less rapid elimination of protein bound hormones (thyroid and steroid hormones)

Metabolism may activate some hormones instead of inactivating them

Mechanisms of Hormone action