Endocrine System 3/3 - Biology As Poetry

Certain epithelial tissues can secrete chemicals into the blood, known as hormones, that then circulate through the blood to other tissues, where they interact with specific cells and change tissue and therefore bodily functioning in well-defined ways.

Adrenal gland

Kidney associated organs responsible for producing the hormones epinephrine and cortisol among others.

The adrenal glands are associated with and superior to the kidneys, with one gland per kidney. The name itself, in fact, literally means "near kidney" (as "renal" refers to the kidney and "ad" means near).

The adrenal glands are differentiated into what is described as the adrenal medulla versus the adrenal cortex, which represent the inside versus outside or exterior of the gland, respectively. It is from the adrenal cortex that the so-named cortical hormones are produced and released, which are steroid hormones (i.e., corticosteroids). By contrast, it is within the adrenal medulla that the hormones epinephrine and norepinephrine are produced.

The above video is a really quick introduction to the basics of what the adrenal gland is all about.

The above video provides a close look at the anatomy and functioning of the adrenal gland.

Adrenal medulla

Portion of gland responsible for producing the hormones epinephrine as well as norepinephrine.

The adrenal medulla represents the interior of the adrenal gland. Medulla more generally refers to the interior of anatomical units, including that of the kidney.

Stimulation of hormones of the adrenal medulla occurs in response to direct signaling from neurons associated with the sympathetic division of the autonomic nervous system. The result is a systemic, that is, body-wide as well as longer-lasting fight-or-flight response, one which complements the more rapid, but shorter duration, direct action of sympathetic innervation on other body organs.

The above video provides a very quick if not exactly stupendous overview of the adrenal gland histology.

Epinephrine

Substance substantially responsible for hormonally effecting fight-or-flight responses.

The hormone epinephrine is also, though less formally, described as "adrenaline", and also as simply "epi". It is the key hormone associated with the sympathetic division of the autonomic nervous system.

Epinephrine stimulates increased heart rates, increased respiratory rates (that is, breathing), increased glucose release into the blood (from the liver), and also increased anxiety.

The bronchodilation effect of epinephrine, that is, increase in the diameter of the bronchiole of the lungs, can be harnessed to combat the bronchoconstriction that can occur in the course of anaphylactic allergic responses such as to foods or bee stings. Note, though, that this bronchodilation effect is relatively short lived rather than serving as a "cure" for these anaphylactic allergic responses.

The above video discusses generally fight or flight. Consideration of the adrenal medulla, an important component of fight or flight, takes place approximately in the middle of the video, at about 2:40.

Adrenal cortex

Gland associated with the production of glucocorticoid hormones as well as the hormone, aldosterone.

Cortex refers to the outer portion of anatomical structures, such as the cerebral cortex. The adrenal cortex thus is the outer portion of the adrenal gland. The adrenal gland is responsible for producing various steroid hormones, particularly groups of hormones described as glucocorticoids as well as mineralocorticoids.

The glucocorticoids are steroid hormones that have an impact on blood glucose levels. The most notable of the glucocorticoids is the hormone, cortisol.

The mineralocorticoids help to regulate the concentration of minerals, that is, positively charged ions, that are found in the blood. The most prominent of such hormones is aldosterone.

Steroid hormones

Diversity of lipid-soluble, blood circulating compounds that resemble in structure the membrane compound, cholesterol.

The steroid hormones, in addition to possessing a common chemical core structure, also – due to that structure – are able to enter into cells by passing directly through their plasma membrane, that is, without protein facilitation. The receptors for these hormones as a consequence are found within cells rather than on the surface of cells.

In addition, due to their ability to enter into the cytoplasms of cells, steroid hormones in certain cases are acted upon enzymatically within those cells.

Prominent steroid hormones include cortisol and aldosterone, both of which are products of the adrenal cortex, and various sex hormones including androgens and estrogens.

The above video provides a very quick overview of the general mechanism by which steroid hormones effect changes on target cells. It's a little simplistic but nonetheless gets its points across reasonably well.

The above video provides an overview of the various types of steroid hormones that are found in our bodies.

Cortisol

Glucocorticoid involved in the regulation of blood glucose levels as well as levels of body stress.

"Cortisol" is short for hydrocortisone and is produced by the adrenal cortex. The consequence of cortisol production is an increase in blood glucose levels as occurs via stimulation of what is known as gluconeogenesis, i.e., the production of glucose from non-glucose materials, such as amino acids.

Cortisol also plays a role in stimulating the breakdown of the starch found in animal tissues, called glycogen, to also produce glucose (a process called glycogenolysis). Cortisol production is stimulated, in turn, in response to fasting, that is, in response to not eating, but serves also as both an anti-stress and anti-inflammatory hormone.

Basically, cortisol is a response to low-level "emergencies", which we experience as stress, versus epinephrine which is a response instead to high-level emergencies.

Aldosterone

Mineralocorticoid involved in the regulation of blood sodium ion and potassium ion levels.

The result of aldosterone presence in the blood is the retention (reabsorption) of sodium ions as well as water by the kidneys and the release (secretion) of potassium ions. Aldosterone, as a consequence of water reabsorption, further has the effect of increasing blood pressure.

The production of aldosterone is stimulated by decreased blood pressure. In addition, high sodium concentrations in the blood inhibits aldosterone release whereas low sodium concentrations in the blood stimulates aldosterone release.

Erythropoietin

Hormone responsible for stimulating production of new red blood cells.

Erythropoietin is a hormone that is produced by the kidneys as well as the liver and which targets the red bone marrow where red blood cells are produced. The process it stimulates is otherwise called erythropoiesis, and red blood cells otherwise are known as erythrocytes.

What is detected that stimulates the production of erythropoietin, and thus production of additional red blood cells, is reduced oxygen availability within the blood. This occurs when the oxygen carrying capacity of the blood is reduced. Reduced oxygen carrying capacity that is can occur, for example, as a consequence, at least in part, of insufficient red blood cells in the blood (= lower hematocrit level).

Testes (as endocrine gland)	Primary producer of androgens by males.
	The production of especially the androgen testosterone by the testes is in addition, of course, to the production of sperm. The production of testosterone increases substantially upon the onset of puberty and sufficient testosterone levels are required for successful sperm production.

Interesting look at the steps involved in testosterone production by the testes as well as testosterone targeting of tissues along and the importance of further testosterone modification.

Androgens	Various primary male sex hormones.
	The dominant androgen is testosterone. It is secreted primarily by the testicles, in males, but also and primarily by the ovaries in females (though the adrenal glands also secrete some testosterone). During development it is the secretion of testosterone that results in males developing into males.

Ovaries (as endocrine gland)	Primary producer of estrogens by females.
	The production of estrogen by the ovaries is in addition, of course, to the production of eggs. The production of estrogen increases substantially upon the onset of puberty and estrogen levels peak on a monthly cycle in association with egg production.

Estrogens

Various primary female sex hormones.

The major estrogens are estrone (or E1), estradiol (E2), and estriol (E3). These vary in prevalence during the course of a female's life, varying as functions of age as well as pregnancy.

The glands primarily responsible for the production of estrogens include the ovaries and the placenta, though estrogen is also produced by other organs including the adrenal glands.

Note that various non-steroidal substances exist that can mimic the hormonal action of estrogens and thereby serve as drugs or, alternatively, as toxins.

An introduction to consideration of the reproductive system of females, here for the sake of mention of the production of estrogen. It's all very complicated… The figure drawn at the end of the video, however, is pretty awesome!

Glucose (alt link)	Primary means of blood circulation of chemical energy.
	Blood glucose levels are reduced in response to the hormone, insulin, and increased in response to the hormone, glucagon, both as released by the pancreas. Uncontrolled and therefore excessive blood glucose levels are associated with the diabetes mellitus type 1 and diabetes mellitus type 2.

Pancreas (as endocrine gland)	Organ responsible for hormonally regulating blood glucose levels.
	The pancreas is a major exocrine gland, producing digestive enzymes that are released into the small intestine. The pancreas also, however, serves as an endocrine gland, producing the hormone insulin as well as the hormone glucagon, both of which play contrasting roles in regulating blood glucose levels.

Insulin

Hormone responsible for signaling various cell types to take up excess glucose from the blood.

Insulin is secreted by what are known as the beta (β) cells of the islets of Langerhans of the pancreas. Insulin is secreted in response to elevated glucose levels in the blood, and has the effect of stimulating uptake of glucose from the blood by the liver, skeletal muscle, and adipose tissue.

The liver and muscles store this glucose as glycogen whereas the adipocytes of adipose tissue convert the glucose to fat. Type 1 diabetes and type 2 diabetes are insulin- or lack-of-Insulin-associated pathologies.

Though it is tempting to dislike the above video, ultimately it is a good introduction to the physiological role of insulin.

Glucagon

Hormone responsible for signaling various cell types to release glucose into the blood.

Like insulin, glucagon also is released by cells of the pancreas, in fact by the alpha, or α cells of the islets of Langerhans. Glucagon is released in response to too low glucose levels in the blood. Particularly the liver is stimulated by glucagon to break down glycogen (glycogenolysis) into glucose which is then released into the blood.

Glucose also can be produced, by both the liver and kidneys, from various non-carbohydrate ingredients via a process known as gluconeogenesis, which also serves to generate glucose that then can be released into the blood. Basically, blood glucose homeostasis is controlled via the release of glucagon (too low glucose levels) or insulin (too high glucose levels).

The above video is a quick but very superficial overview of mostly insulin but with glucagon covered at the end.

The above video discusses how it is that cells can store and then release glucose following insulin stimulation and following glucagon stimulation.

Diabetes mellitus Type 1

Disease of excessive blood glucose associated with decreased ability to produce insulin.

Type 1 diabetes appears, at least in part, to be an autoimmune disease associated with the destruction of beta (β) cells of the islets of Langerhans of the pancreas. Diabetes mellitus type 1 is also known as juvenile or insulin-dependent diabetes. As such it typically arises earlier in life (in comparison to adult-onset diabetes) and also is treated in part via the administration of insulin via injection in response to elevated blood glucose levels, such as especially can follow a meal.

Uncontrolled type 1 diabetes results in increased urination (due to excessive glucose in the urine which makes it difficult to remove water from urine) and increased thirst (due to increased urination). Increased hunger is also seen with uncontrolled type 1 diabetes.

Though hampered by poor resolution, and the sound also is not well synced with the video, nonetheless the above video is a well done and informative introduction to both insulin and type I diabetes.

Diabetes mellitus type 2

Disease of excessive blood glucose associated with decreased ability of cells to respond to insulin.

Contrasting type 1 diabetes, type 2 diabetes is non- (or less-) insulin-dependent, generally though not exclusively adult onset, and associated with what is known as insulin tolerance.

Here insulin is released in response to excessive blood glucose levels, though not necessarily in sufficient quantities, and the released insulin has a reduced impact (i.e., insulin tolerance) on the tissues otherwise responsible for taking up glucose from the blood (i.e., those target tissues display an insulin resistance).

Type 2 diabetes appears to be especially associated with obesity and is addressable therefore via weight loss as well as diet modification and increased exercise. Symptoms are similar to those associated with diabetes mellitus type 1.