"It is not enough to have a good mind. The main thing is to use it well." – Rene Descartes

Fellow warriors, slam down your protein shakes and come hither, for I have a secret to tell you. This secret is of up-most importance. It is vital in understanding who we are and what we are made of. Are you ready?

Inside of each and every one of us there are systems. These systems are made up of organs, which are made up of cells. Billions upon billions of cells, all are working together in flawless synergy. It is mind-boggling. If even a small group of cells is not functioning properly, the entire system may collapse. These cells, these systems make us who we are, they keep us alive, they keep us in balance.

Many weak-willed people live their whole lives not even thinking about these systems. They don't think twice about how it works, just as long as it works.

Those people are not like us, they are not athletes, and they are not bodybuilders.

Warriors of the iron know these systems well. We know their structure, their actions, and their importance. We are in complete control of our internal systems. We have the power to manipulate them to induce growth of massive proportions. We have the power, the will, the knowledge to control these systems, to maximize their efficiency, and to blast our bodies into pure, unhindered hyperplasia. This, fellow warriors, is the systems behind bodybuilding.

By the end of this hardcore series, you will gain complete knowledge of one such system - the endocrine system.

Now that you know the secret, it is time for you to see how it works. I must warn you; however, you may need to down another protein shake.

Let this be the introduction, the gateway, if you will, to a portal beyond your perceived limitations. A portal beyond mere hypertrophy - a portal to hyperplasia inducing euphoria!

You may have realized that I am a big time philosophy buff. I would like to introduce you to one of the greatest philosophers in history – Rene Descartes. Descartes was known as a jack of all trades. He was a military man, a mathematician, and finally a philosopher. In fact, this 17^th century dualist was an intellectual rebel!

Rene decided not to believe anything anyone ever told him and even not trust his own senses! In an attempt to determine whether there was anything utterly inaudible, he proposed to doubt everything. One thing he concluded that he could not deny – the fact that in his very act of doubting, he was thinking. And from this fact, he saw that it followed that he himself must actually exist. Thus he bequeathed to history the most famous piece of philosophical reasoning ever: Cogito ergo sum - I think, therefore I am.

Descartes would not stop here; however, he continued to delve into the depths of the human psyche to come to yet another conclusion.

Descartes believed that there are two basic kinds of substances in existence. There are minds as well as bodies, mental properties as well as physical properties. Descartes characterized such properties: minds may be in time, but they are not in space. They do not have an extension (length, height, breadth, or physical depth) or mass. They have no three-dimensional spread or solidity. They essentially think. That is their nature.

He was most concerned as to where this all came together. Where is the link between the physical and the spiritual? Descartes, also a medical expert, proposed the theory that the answer lies in the endocrine system! In fact, Descartes once stated that the pineal gland was the "seat of the soul."

Throughout history people have made a pseudoscientific connection between the glands of the endocrine system and our intangible self. This is partially due to the fact that we still have a lot to learn about it! Through this series, the entire endocrine system will be completely dissected, torn apart, and laid down on paper for all to see!

When I think of our bodies internal systems, I think of organization. This goes along with the concept of our bodies being an "organism." To be organized, our body’s cells must work synergistically with one another.

You may have heard me use the term synergy before, and I will continue to use it in reference to the body and it’s organization. Webster’s defines synergy as "working together." This is exactly what the billions of cells in our bodies must do.

The endocrine system is made up of 10 glands. Further, there are 7 organs that have partial endocrine function. Below I will give an overview of each of these glands setting the table for more specialized articles to come in the near future.

For this article, we are splitting the pituitary into two parts, anterior and posterior, due to its sheer complexity!

As a whole, the endocrine system controls and regulates body metabolism and produces hormones which, in themselves, carry out a seemingly endless number of functions.

Hormones are a class of molecules, varying in biochemical composition that act as messenger molecules. Just as there are agonist muscle groups that work in opposition to one another to coordinate movements, a number of hormones exist as pairs of hormones that stimulate opposite responses in target tissues.

This system is so in depth it’s insanity! As I already stated, this article sets up the basis for many on this complex subject to follow.

The pineal gland, also known as the epithalamus or epiphysis, plays a big role in metabolic regulation and serves as a boundary of the third ventricle of the cerebrum.

The pineal body does not contain nerve cells but instead is served by the sympathetic ganglia. Two types of cells make up the pineal body, pinealocytes and glial cells. The pineal gland serves as a linkage point for limbic system components. Other structural elements of the epithalamus include the Habenula – broken further to the right and left habenular nuclei (nerve cells), which are important in the regulation of food and water intake – and the stria medullaris (a bundle of fibers terminating on the right and left habenulan nuclei).

The epithalamus plays a regulatory role in the sleep-wake cycle and in controlling mood. Controversy surrounding the physiological function of the pineal gland goes back throughout history. In medieval times, the pineal gland was called the "third eye." As I stated above, Descartes believed the pineal gland was the "seat of the soul." In fact, medieval scientists were convinced the pineal gland had some sort of link from our physical selves to our spiritual selves.

In today’s scientific community, studies show the pineal gland plays a role in the production of melatonin, a derivative of the amino acid tryptophen. The absence of light sparks production of melatonin. It is no wonder why melatonin levels increase at night, when light is scarce. Decreasing levels of melatonin are produced with age and during phases of intense light, such as lying out in the sun. Melatonin’s primary function is to control sleep patterns by inducing drowsiness.

The pineal gland, in conjunction with the hypothalamus, also influences the production of gonadotropins, which we will discuss later.

The pituitary gland is the major and controlling gland of the endocrine system. Also known as the hypophysis or hypophesis ceribri, the anterior pituitary produces a number of hormones that control hormone production in the endocrine glands. The pituitary is situated in the sella turcica, a small indentation located near the base of the brain. About the size of a pea, the pituitary is connected to the hypothalamus by a slender pituitary stalk (hypophyseal stalk). In addition to anatomical connection via the hypophyseal-hypothalamic tract, the hypothalamus regulates pituitary function providing a bridge between the nervous system and the endocrine system through the hypophyseal portal system. The hypophyseal portal system is a localized collection of blood vessels that allow regulating agents secreted by the hypothalamus to travel directly to the pituitary.

Neural imput can be interpreted by the hypothalamus and translated into pituitary control and therefor affect the endocrine response. The connection between the hypothalamus and the pituitary establishes a clear chain of control: nervous signals in the hypothalamus cause changes in pituitary hormone secretion that, in turn, control production of hormones in other endocrine glands.

The anterior lobe, also termed the adenohypophysis, secretes seven different hormones, Growth Hormone (GH), Thyroid-Stimulating Hormone (TSH), Adrenocorticotropic Hormone (ACTH), the Gonadotropins (LH and FSH), Prolactin (PRL), and Melanocyte-Stimulating Hormone (MSH).

Growth Hormone or Somatotropin, acts directly on tissues to stimulate overall body growth. GH acts to stimulate growth by increasing protein synthesis and acts metabolically to shunt glucose from ATP synthesis pathways, while at the same time promoting fat usage. GH stimulates the secretion of somatomedin hormones.

Growth hormone is essential for muscle growth. Hundreds of studies have been conducted on GH and its relation to skeletal muscle growth. In one study, conducted by UCLA indicates weight training increases the release of GH.

Thyroid-Stimulating Hormone (TSH) stimulates thyroid growth and secretion of thyroid hormones, including Thyroxine and Triiodthyronine.

Adrenocorticotropic Hormone (ACTH) stimulates adrenocortical growth (growth of cortex of adrenal glands) and the subsequent secretion of corticosteroids. There is also a negative feedback mechanism involved in ACTH production. Cortisol is the principle corticosteroid produced by the adrenal glands. As levels of cortisol increase in the bloodstream, they act to inhibit further production of ACTH by the anterior pituitary.

The pituitary secretes gonadotropins, LH (lutinzing hormone) and FSH (follicle stimulating hormone). In males, LH is usually referred to as interstitial cell stimulating hormone (ICSH). In females, LH acts to stimulate ovulation and the formation of the corpus luteum on an ovarian follicle. In males, the action of LH acts to stimulate testosterone production. In females, FSH stimulates estrogen secretion and supports the growth and maturation of the ovarian follicle. In males, FSH stimulates spermatogenesis, the formation of sperm cells.

Pituitary stimulation of melanocyte stimulating hormone (MSH) contributes to the regulation of pigmentation of the skin by stimulating melanocytes to produce melanin.

The posterior pituitary is really an extension of the hypothalamus, and its tissue type differs from the anterior pituitary. The posterior lobe, termed the neurohypophysis, produces Oxytocin and Antidiuretic Hormone (ADH). The posterior pituitary is not considered a "true" endocrine gland because it does not contain secretory cells.

SIDE NOTE: Before I continue, I would like to briefly cover a process called neurosecretion. I believe this is vital in understanding the functions of not only the posterior pituitary, but the rest of the endocrine system as well.

The hypothalamic nuclei that connect to the posterior pituitary are called supraoptic and paravantricular and are a true example of neurosecretory cells. In the cell bodies of the neurosecretory neurons, hormone synthesis takes place. Oxytocin and ADH are synthesized as larger prohormone molecules. These prohormone molecules contain the true hormone along with a nonhormonal portion called neurophysin. The true function of neurophysin is somewhat unclear, but it is believed to assist in hormone transport. The prohormones and the neurophysin are packed within special secretory vesicles called herring bodies, which flow down the interior of the axons of the hypothalamo-hypophyseal tract aided by axoplasmic transport.

Before reaching the nerve terminals in the posterior pituitary, the hormone splits. The hormone is then stored in the axon terminals and is then released into the blood capillaries and carried to the target tissues.

Neurosecretory cells (brain cells modified to synthesize and release hormones) then produce action potentials. The stimuli for further hormone release comes from the nerve impulses to the cell body inside the hypothalamus, down the axon membrane and to the nerve terminal. Arrival of this nerve impulse triggers the flow of calcium ions into the terminal. Secretory vesicles then fuse with the terminal membrane, resulting in the release of the hormone.

Oxytocin is secreted by the cells of the paraventricular nuclei. There are no known functions of oxytocin in males. In females, however, oxytocin plays a large role in mammary gland stimulation and contractions during birth.

Antidiuretic Hormone (ADH), also called vasopressin, is synthesized and secreted in the supraoptic nucleus. The primary function of ADH is regulation of body water and is secreted whenever the water levels in the blood are decreased. Decrease of water in the blood can be caused by osmotic diuresis (brought on by an increase in blood glucose levels, ketone bodies, or sodium loss). ADH is also secreted when mechanoreceptors (blood volume receptors) in the heart and pressure receptors in the vasculature are stimulated after blood loss. After a hemorrhage, ADH causes vasoconstriction, which leads to an increase of blood pressure.

SIDE NOTE: Oxytonin and ADH are both polypeptides and contain nine amino acids. They are practically identical except for the substitution, in ADH, of phenylalanine and arginine in place of one of the tyrosines and the leucine found in oxytonin.

The hypothalamus is the controller of the endocrine system. It's the king of the crop. The hypothalamus is the connection from the endocrine system to the brain. Parts of the hypothalamus that are visible in basal and mid-sagittal views of the gross brain include the mammillary body and the infundibulum (tuber cinereum).

The hypothalamus is a region of the brain located just above the pituitary gland. In fact, it’s intimately related to the pituitary and connected via the hypophyseal stalk. The hypothalamus releases six hormones, which regulate function of the pituitary gland.

Thyrotropin-Releasing Hormone (TRH) is a tripeptide hormone released by special hypothalamic secretory cells. TRH moves down the hypophyseal stalk via the hypothalamal-hypophyseal tract and into the anterior pituitary gland. Here, TRH stimulates the release of thyroid-stimulating hormone (TSH) and prolactin.

Gonadotropin-releasing hormone (GnRH) is a peptide hormone consisting of ten amino acids. GnRH stimulates the release of LH and FSH from the anterior pituitary; thus indirectly increasing increased testosterone levels in males and increased estrogen and progesterone levels in females.

Growth hormone-releasing hormone (GHRH) is a very large, powerful and complex hormone. GHRH consists of two peptides, one containing 40 amino acids, and the other containing 44. As the name indicates, GHRH stimulates the anterior pituitary to release GH. GHRH is secreted in pulses preceding the GH release pulse.

Corticotropin-releasing hormone (CRH) is a peptide consisting of 41 amino acids. The hypothalamus secretes CRH into the hypophysial portal blood. CRH then stimulates the release of ACTH (adrenocorticotropin hormone) in the anterior pituitary.

Somatostatin is a mixture of two peptides. One containing 14 amino acids and the other, 28 aminos. Somatostatin can also be called growth hormone-inhibiting hormone (GHIH) due to its effects on the release of GH. Somatostatin inhibits the release of both GH and TSH by the anterior pituitary.

Dopamine derives from the amino acid tyrosine and acts as an inhibiting hormone, much like somatostatin. But rather than inhibiting GH and TSH, dopamine inhibits prolactin production by the anterior pituitary.

Dopamine also effects breathing, as stated here by Doctors T. Nishino and S. Lahiri:

As you can see, the hypothalamus strictly regulates the anterior pituitary. This regulation, or control, is called homeostatic control. The hypothalamus’ neuroendocrine role in conjunction with the pituitary gland and the autonomic nervous system (ANS) control the hormone levels all throughout the body. I discuss how in Part 2 of this series.

The thyroid gland is shaped like a butterfly and is located in the neck, anterior and lateral to the larynx. The thyroid secretes two closely related hormones, thyroxine (T4, tetra-iodothyronine) and tri-iodothyronine (T3).

Thyroid hormones increase the metabolic rate by increasing the rate of oxygen consumption and heat production in body tissues including the heart, muscles, and visceral tissues. This manipulation of metabolism is referred to as a calorgenic action. The thyroid hormones are critical for adaptation to heat and cold. The hormones of the thyroid are slow-acting.

I discuss slow acting hormones and fast acting hormones in part two of this article.

Thyroid hormones also play a role in cardiovascular functions by increasing the heart rate and contractility and vascular responsiveness to catecholamines. This cascade results in an increase in blood pressure. Brain function and even behavior are also affected by T3 and T4 through the catecholamines.

The synthesis and subsequent release of thyroid hormones are controlled by thyrotropin (TSH), the pituitary tropin. TSH increases synthesis and secretion of thyroid hormones.

The brain influences the secretion of thyroid hormones as well. Hypothalamal neurons produce thyrotropin-releasing hormones (TRH), which regulates the release of TSH from the anterior pituitary. The brain senses changes in the external environment through its peripheral thermoreceptors and makes the appropriate adjustments in hypothalamic TRH release.

The thyroid gland consists of many follicles with many blood capillaries between them. Each follicle contains a single row of follicle cells (called thyroid epithelial cells) surrounding a cavity (lumen). The lumen is filled with a colloidal substance, the colloid. The colloid is the storehouse of a protein, thyroglobilin. This protein is synthesized by thyroid cells and secreted into the lumen to help assist in the synthesis of thyroid hormones.

Iodide is actively transported into the thyroid cells by transport proteins and then migrate into the colloid. Here it is oxidized into iodine. Enzymes attach iodine to tyrosine residues in the thyroglobulin. The iodinated-tyrosines are then converted to mono-iodo-thyronine and di-iodothyronin and finally into thyroxine and T3.

The thyroid, on average, produces ten times more T4 than T3. T4 is classified as a prohormone. After entry into target cells, T4 is mostly converted into T3. Further, nuclear receptors for thyroid hormones have a much higher affinity for T3 rather than T4.

Problems: Excess secretion of thyroid hormones (hyperthyroidism) leads to Grave’s Disease and other autoimmune diseases. Individuals with a hyperthyroid have a high Basal Metabolic Rate (BMR). Other serious and deadly problems can occur with an overactive thyroid.

The parathyroid glands consist of four small bodies imbedded in the superior and inferior poles of thyroid tissue. However, there are no physiologic connections between the thyroid gland and the parathyroid glands.

The parathyroid gland houses two types of tissue, chief and oxyphil. The chief cells secrete parathyroid hormone in response to a decrease level of plasma calcium ions. The parathyroid hormone acts on the bones and kidneys to increase the levels of plasma calcium.

Why is the plasma calcium level so important? Plasma calcium regulates the electrical activity of nerve and muscle cells, heart contraction, and blood clotting. The levels of plasma calcium are regulated by many complex hormonal mechanisms. The normal plasma calcium level is 10-mg/100 ml.

The function of oxyphil cells is still not well understood. Some experts suggest they are degenerated chief cells.

The adrenal glands are two endocrine glands in one and are located above the kidneys. The adrenal glands prepare the body to fight stress. The adrenal complex houses both adrenal glands, the outer being the adrenal cortex, the inner being the adrenal medulla.

The adrenal medulla is a part of the sympathetic nervous system and is essentially a modified sympathetic ganglion. The activation of the sympathetic nervous system is directly linked to the hormones produced by the adrenal medulla.

Chromaffin cells (secretory cells of the adrenal medulla) contain vesicles filled with epinephrine (E) and norepinepherine (NE). Collectively, these two hormones are referred to as catecholamines and are synthesized from the amino acid tyrosine. The chemical process looks like this:

Tyrosine > dopa > dopamine > norepinephrine > epinephrine

Endorphin is also secreted by the adrenal medulla. Endorphin has an anti-stress analgesic effect, meaning it can ease the feeling of pain.

The adrenal cortex is the source of corticosteroid hormones. The adrenal cortex can be broken up into three zones, and each zone secretes a different hormone.

ZONE 1 - The outer zone, zona glomerulosa, secretes aldosterone. Aldosterone is a mineralocorticoid and is involved in the regulation of sodium and potassium, blood pressure, and blood volume.

ZONE 2 - The middle zone, zona fasciculata, secretes glucocorticoid hormones, primarily cortisol. Cortisol regulates the metabolism of glucose. We’ll be discussing cortisol in depth in a later issue.

ZONE 3 - The inner zone, zona reticularis, secretes sex steroids such as androgens (chiefly de-hydro-epi-androsterone – DHEA) and small amounts of estrogen and progesterone.

The pancreas is a solid, elongated gland about 10 inches in length. It lies behind the stomach and attaches to the back of the abdominal cavity. Its head is just to the right of the midline of the body and its body and tail point slightly upwards and lie just beneath the extreme edge of the left side of the ribs. The head is attached to the first part of the small intestine, into which the stomach empties partially digested food. This is where the pancreas adds its digestive enzymes.

The pancreas is composed of two types of tissue: exocrine tissue, the acini, which secrete digestive enzymes, and endocrine tissue, the islets of Langerhans, which produce and secrete insulin and glucagon directly into the blood.

SIDE NOTE: The pancreatic islets only make up about 2% of the total pancreatic tissue!

Endocrine tissue contains alpha, beta and delta cells – which are distinguished from one another by their morphology (form and structure). Beta cells produce insulin and alpha cells produce glucagon – two hormones regulating blood glucose levels. Delta cells secrete the hormone somatostatin, which inhibits insulin and glucagon secretion.

The testes (in males) and ovaries (in females) are organs of the reproductive system. The sex steroid hormones are stimulated by the gonadotropin hormones released by the anterior pituitary gland.

Testosterone (T) is the primary testicular hormone and is secreted from the interstitial cells of Leydig at a rate of 10 mg per day. T is a steroid made from cholesterol and is the principal circulating androgen. Other androgenic steroids are di-hydroxy-testosterone (DHT) and de-hydro-epi-androsterone (DHEA). DHEA is a precursor of T synthesis. Androgenic potency of T is less than DHT, but higher than DHEA.

T has widespread effects on the body, and can be divided into three groups. 1) Effects in adult male sexuality and reproduction. 2) Actions on the development of the reproductive system and brain of the fetal male, as well as body growth and behavioral changes. 3) Non-reproductive, anabolic effects in the adult – such as enhancing anabolism in many tissues.

The testes functions are regulated by the anterior pituitary gland, specifically LH and FSH. LH controls T release by Leydig cells and FSH acts on Sertoli cells to control spermatogenesis. LH and FSH follow the following steps:

Bind with plasma membrane receptors > activation of membrane G proteins > activation of membrane adenylate cyclase > formation of cyclic AMP.

In women, the ovaries perform two functions. 1) Formation, development and release of the ovum. 2) Secretion of the female sex hormones, estrogen and progesterone. Estradiol, the most potent estrogen, has two hydroxyl groups, progesterone has two ketone groups. Together, they regulate many key aspects of female reproduction, sexuality and secondary sex characteristics.

The principal actions of estrogen and progesterone in the female reproductive system are on the uterine endometrium. Estrogen promotes endometrial prolification and thickening while progesterone promotes the endometrial glands to secrete proteins and glycogen.

During puberty, estrogen, along with adrenal androgens, enhance bone calcium levels and growth. Some female secondary sex characteristics, such as a high voice, narrow shoulders, smaller bone and body mass, lack of facial and body hair, are due to the absence of make androgens.

The ovaries also depend on LH and FSH. A burst of LH, lasting 2-3 days, stimulates ovulation. This burst and the cyclical changes in LH and FSH during the cycle are directly controlled by the gonadotropic-releasing hormone GnRH from the hypothalamus along with the feedback from estrogen and progesterone.

The kidneys are highly complex organs. For purposes of this article, we will only be covering their endocrine function. The kidneys secrete three hormones, renin, erythropoietin, and calcitriol.

Renin is an enzyme released by specialized cells of the kidney into the blood. It is in response to sodium depletion and/or low blood volume. Renin converts angiotensinogen (a protein released into the blood by the liver) to angiotensin 1. Angiotensin I is converted to angiotensin II by an enzyme in the veins of the lungs. Angiotensin II acts on the adrenal cortex to stimulate the release of aldosterone. Aldosterone acts on the distal tubules of the kidneys to decrease the loss of sodium ions and secondarily fluid. This has the effect of increasing blood pressure. In addition, angiotensin causes constriction of small blood vessels, which also increases blood pressure.

Erythropoietin is a crucial hormone involved in the production of red blood cells. Erythropoietin is secreted by special secretory cells of the kidneys directly into the bloodstream and acts on bone marrow to manufacture red blood cells. People will low amounts of erythropoietin develop anemia.

Calcitriol is a derivative of vitamin D. Vitamin D is converted into vitamin D3 in the liver. In the kidneys, another hydroxyl group is added in the final activation to form 1,25 dihydroxylcholecalciferol, aka calcitriol. Calcitriol has several important actions. It enhances absorption of both calcium and phosphate from the GI tract, promotes release of calcium and phosphate from the bones where they are stored, and causes the kidney not to excrete calcium and phosphate.

The liver produces a single hormone, called somatomedin.

I will let Dr. Broughton, a board certified pathologist explain somatomedin and it’s relation to somatotropin (of the pituitary):

The thymus is a lymphoid gland (also part of the lymphatic system) and is located between the lungs in the anterior superior mediastinum. It’s cortex (external later) is comprised of lymphatic tissue, with the interior portion containing lymphocytes. The thymus has a thick rectangular structure comprised of groups of granular cells enveloped by epithelial cells, known as Hassal’s Corpuscles. Thymine (2, 4-Dihydroxy-5-Methylpyrimidine) is produced here and plays a large role in DNA replication.

The thymus is truly amazing! I would go as far as to say it’s a totally hardcore gland. I feel this way because of its role in the preprocessing of stem cells into different lymphocytes. I’ll explain the process and why it is important in a minute. The end result of the transformation is T lymphocytes ("T" for Thymus). T lymphocytes are a family of specialized white blood cells to help the body fight off infection by binding to foreign antigens. I like to think of white blood cells as fighter jets, whizzing through the blood stream and eliminating every threat in its path!

In the early stages of fetal development, stem cells migrate to the thymus in a series of sequential "waves", where they divide and differentiate. The first wave of stem cells gives origin to T cells with gamma-delta 3 receptors. These T cells are found in the skin where they recognize and attack damaged or infected skin cells. The second wave of stem cells gives origin to T cells with gamma-delta 4 receptors that populate the oral epithelium and the uterus. The following waves give birth to T cells with gamma-delta 2 and gamma-delta 5 receptors, which populate the spleen and gastrointestinal epithelium. T cells, known as helper T cells and killer T cells, carrying alpha-beta receptors are also produced in the thymus. Thus, each T lymphocyte contains a receptor specifically constituted by two chains of different polypeptide sequences (gamma-delta or alpha-beta), which binds to a particular foreign antigen.

The thymus plays a search-and-destroy action against self-antigens through a process called clonal deletion. The thymus tests the young T cells by producing samples of most cell types of body tissues, whose proteins are chopped by an antigen-presenting cell and exposed to the young T cells in a protein molecule known as the major histocompatibility (MHC). Once a strong reaction occurs to a self antigen, the young T cell is induced to apoptosis (program cell deaths or suicide). Therefore, only T cells that show extreme tolerance to self antigens are allowed to survive and migrate to other tissues.

If this process fails, and weak T cells are induced into the rest of the body, autoimmune diseases such as lupus erythematosus, myasthenia gravis and rheumatic fever can occur.

Oddly enough, the heart produces a hormone! The heart produces atrial natriuretic hormone (ANP) from special secretory cells in the atria of the heart. This newly discovered hormone plays an integral role in volume regulation. When extracellular fluid volume is expanded, the plasma concentration of ANP increases and causes an increase in NA+ excretion by the kidney. ANP has also been found to inhibit the release of renin and ADH, and it has been found to desensitize the adrenal cortex to stimuli that increase aldosterone secretion.

All of these effects promote water excretion, helping compensate for the increase in extracellular fluid. Little else is known about this hormone. This goes to show that we have a lot more to learn! But the discoveries are exciting.

The stomach also has hormone-releasing cells. Hormones play a huge role in digestion. The secretory activities of the digestive system are under control of the ANS.

Gastrin is a single-chain peptide hormone secreted by G-cells, isolated endocrine cells in the lateral walls of the stomach glands in the antrum region. Gastrin is secreted into the blood in response to the small peptides in ingested food. The peptides stimulate chemoreceptors of the G-cells. The receptor cells signal the G-cells to release gastrin. Gastrin stimulates the stomach glands and smooth muscles to enhance gastric secretion.

As you can see from the illustration above, the duodenum is attached to the stomach. The duodenum is a part of the small intestine and connects directly to the stomach. The duodenum has been known to have endocrine capabilities. The peptide hormones secretin, choleocystokinin (CCK), glucose-dependent insulinotropic polypeptide (GIP) and motilin are secreted by isolated endocrine cells in the duodenum and the jejunum.

Secretin has been shown to stimulate the release of pancreatic biocarbonates. Secretin actually inhibits functions of gastrin in the stomach to keep the gastrointestinal juices in balance.

Choleocystokinin is a peptide hormone that originates in the duodenal mucosa endocrine cells. CCK is released in the blood after an arrival of chyme (partly digested food) containing fat or acid. CCK targets the gallbladder and the pancreatic acinar cells. Upon the arrival of CCK, the gallbladder contracts, releasing its stored bile into the duodenum. In the pancreas, CCK stimulates pancreatic enzymes which are extremely important for the chemical digestion of various foods in the small intestine.

GIP is a weak duodenal hormone. I say weak because it is believed that only very high levels of GIP can exert significant effects of gastric inhibition. GIP has also been shown to stimulate the release of insulin in response to glucose in the small intestine.

Motilin is the final hormone produced by the duodenum. It is secreted by specialized endocrine cells located in the duodenal mucosa and influences digestion. Motilin acts on the smooth muscles of the small intestine to enhance intestinal contractions and movements, following stomach emptying and arrival of gastric chyme.

Now the foundation has been laid! I suggest you keep this article handy as you read part two of this series. You may need to refer back to it several times.

Joe King, M.S., C.P.T., P.E.S.

Founder, Kingbodybuilding.com

JKing@kingbodybuilding.com