Studying Endocrinology

 As girls and boys enter puberty, they start to develop striking differences in physical appearance and behavior. This is due to the endocrine system.

Source: www.britannica.com
Video1. Introduction to the Endocrine System and how does it works.


Endocrinology

Endocrinology deals with the study of hormones, the glands that produce them and the tissues which are affected by the hormones. The diseases and conditions associated with hormonal imbalance, damage to the glands that make hormones or the use of artificial or natural hormonal drugs and the treatment to these diseases and conditions are also part in studying endocrinology.

Figure1. The Endocrine System

Endocrine system is a facility group of glands. Glands are the organs that makes hormones. Hormones helps to control activities in your body. 

The nervous and endocrine systems act together to coordinate functions of all body systems. Responses of the endocrine system often slower than responses of the nervous system; although some hormones act within seconds, most takes several minutes or more to cause a response. The effects of nervous system activation are generally briefer than those of the endocrine system. The nervous system acts on specific muscles and glands. The influence of the endocrine system is much broader; it helps regulate almost all types of body cells. 

Hormones are chemical messengers that transmit information to cells. It has different types that control reproduction, metabolism - like food burning and waste elimination, and growth and development. They control the way we respond to our surroundings, and they help to provide the proper amount of energy and nutrition our body needs to function. the glands that make up the endocrine system and produces the hormones are pituitary, hypothalamus, thyroid, parathyroid, pancreas, ovaries, testes and  adrenal.   

Figure2. Hormones 

Most hormones are one of two chemical types:

• Peptide-amino acid molecules are water soluble and have relatively short half-lives. These molecules circulate in solution in plasma.
• Steroid-cholesterol molecules have longer half-lives and in some cases transported in the circulation by carrier proteins.

Mechanisms of hormone action:

• Peptide-amino acid hormones or non-steroidal hormones are usually work at the cell surface, binding to receptors that signal changes in cytoplasmic reactions and processes that result in the hormone's effects.
• Steroid-cholesterol hormones and thyroid hormones have their effect in the cell nucleus, where they modify the DNA transcription, this modification results changes in protein synthesis which brings the hormonal effect.

These are glands that make the endocrine system: hypothalamus and pituitary gland, thyroid gland, parathyroid gland, adrenal gland, pancreas, and ovaries and testes.

Hypothalamus and Pituitary Gland

Pituitary gland or hypophysis is called the master endocrine gland/ master gland because it secretes several hormones that control other endocrine glands. This pituitary gland itself has a master and that is the Hypothalamus. This small region of the brain below the thalamus is the major link between the nervous system and endocrine system. Together, these hormones play important roles in the regulation of almost all aspects of growth, development, metabolism and homeostasis.

Table1. Anterior and Posterior Pituitary Hormones

Anterior and Posterior Pituitary Hormones
Anterior Pituitary Hormones
Hormone and Target Tissues	Principal Actions
Human Growth Hormone (hGH)  /  Somatotropin ----- Liver	Stimulates liver and other tissues to synthesize and secrete insulinlike growth factors (IGF); IGF promotes growth of body cells, protein synthesis, tissue repair, lipolysis, and elevation of blood glucose concentration
Thyroid-stimulating Hormone (TSH) / Thyrotropin ----- Thyroid Gland	Stimulates the synthesis and secretion of thyroid hormones by the thyroid gland
Follicle-stimulating Hormone (FSH) ----- Ovaries and Testes	In females, initiates development of oocytes and includes ovarian secretion of estrogens. In males, stimulates testes to produce sperm.
Luteinizing Hormone (LH) ----- Ovaries and Testes	In females, stimulates secretion of estrogens and progesterone, ovulation and formation of corpus luteum. In males, stimulates testes to produce testosterone.
Prolactin (PRL) ----- Mammary Glands	Together with the other hormones, promotes milk secretion by the mammary glands
Adrenocorticotropic Hormone (ACTH) / Corticotropin ----- Adrenal Cortex	Stimulates secretion of glucocorticoids (mainly cortisol) by the adrenal cortex
Melanocyte-stimulating Hormone (MSH) ----- Brain	Exact role in humans is unknown but may influence brain activity; when present in excess, can cause darkening of skin
Posterior Pituitary Hormones
Oxytocin (OT) ----- Uterus and Mammary Glands	Stimulates contraction of smooth muscle cells of the uterus during childbirth. Stimulates contraction of myoepithelial cells in the mammary glands to cause milk ejection.
Antidiuretic Hormone (ADH) / Vasopressin ----- Kidneys, Arterioles and Sudoriferous (Sweat) Glands	Conserves body water by decreasing urine volume. Raises blood pressure by constricting arterioles. Decreases water loss through perspiration.

Figure3. Anatomy of the Pituitary Gland

Thyroid Gland

Regulates your energy and your metabolism.

Table2. Thyroid Gland Hormones

Thyroid Gland Hormones
Hormone and Source	Principal Actions
T3 (Triiodothyronine) and T4 (Thyroxine) ----- Follicular cells	Increase basal metabolic rate, stimulate synthesis of proteins, increase use of glucose and fatty acids for ATP production, increase lipolysis, enhance cholesterol excretion, accelerate body growth, and contribute to development of the nervous system.
Calcitonin (CT) ----- Parafollicular cells	Lowers blood levels of Ca2+ and HPO42- by inhibiting bone resorption by osteoclasts and by accelerating uptake of calcium and phosphates into bone extracellular matrix.

Figure4. Anatomy of the Thyroid Gland

Parathyroid Gland

Secretes the hormone necessary for calcium absorption.

Table3. Parathyroid Gland Hormones

Parathyroid Gland Hormones
Hormone and Source	Principal Actions
Parathyroid Hormone (PTH) ----- Chief cells	Increases blood Ca2+ and Mg2+ levels and decreases blood HPO42- level; increases bone resorption by osteoclasts; increases Ca2+ reabsorption and HPO42- excretion by kidneys; and promotes formation of calcitriol – active form of vit. D, which increases rate of dietary Ca2+ and Mg2+ absorption.

Figure5. Parathyroid Gland

Adrenal Gland

Secretes hundreds of compounds including cortisone & adrenaline which helps you react to emergencies. Regulates your metabolic processes in the cells, water balance, blood pressure, etc.

Table4. Adrenal Gland Hormones 

Adrenal Gland Hormones
Adrenal Cortex Hormones
Hormone and Source	Principal Actions
Mineralocorticoids (mainly Aldosterone) ----- Zona Glomerulosa cells	Increase blood levels of Na+ and water and decrease blood level of K+
Glucocorticoids (mainly Cortisol) ----- Zona Fasciculata cells	Increase protein breakdown (except liver), stimulate gluconeogenesis and lipolysis, provide resistance to stress, reduce inflammation and depress immune responses
Androgens (mainly Dehydroepiandrosterone / DHEA) ----- Zona Reticularis cells	Assist in early growth of axillary and pubic hair in both sexes; in females, contribute to libido and are source of estrogens after menopause
Adrenal Medulla Hormones
Epinephrine and Norepinephrine ----- Chromaffin cells	Produce effects that enhance those of the sympathetic division of the automatic nervous system (ANS) during stress

Figure6. Anatomy of the Adrenal Gland

Pancreas

Aids in the digestion of protein, fats and carbohydrates. Produces insulin which controls blood sugar levels.

Table5. Pancreatic Islet Hormones

Pancreatic Islet Hormones
Hormone and Source	Principle Actions
Glucagon ----- Alpha cells of pancreatic islets	Raises blood glucose level by accelerating breakdown of glycogen into glucose in liver (glycogenolysis), converting other nutrients into glucose in liver (gluconeogenesis) and releasing glucose into the blood
Insulin ----- Beta cells of pancreatic islets	Lowers blood glucose level by accelerating transport of glucose into cells, converting glucose into glycogen (glycogenesis) and decreasing gylcogenolysis and gluconeogenesis
Somatostanin ----- Delta cells of pancreatic islets	Inhibits secretion of insulin and glucagon and slows absorption of nutrients from the gastrointestinal tract
Pancreatic Polypeptide ----- F cells of pancreatic islets	Inhibits somatostanin secretion, gall bladder contraction and secretion of pancreatic digestive enzymes

Figure7. Dissection of the pancreas showing the pancreatic duct leading into the duodenum. The section at the top right shows an islet of Langerhans where hormones are secreted.

Ovaries and Testes

Influences how your blood circulates and determines your mental vigor and your sex drive.

Table6. Ovaries and Testes Hormones

Ovaries Hormones
Hormone and Source	Principle Actions
Estrogens and Progesterone	Together with gonadotropic hormones of the anterior pituitary, regulate the female reproductive cycle, regulate oogenesis, maintain pregnancy, prepare the mammary glands for lactation and promote development and maintenance of female secondary sex characteristics
Relaxin	Increases flexibility of pubic symphysis during pregnancy and helps expand uterine cervix during labor and delivery
Inhibin	Inhibits secretion of FSH from anterior pituitary
Testes Hormones
Testosterone	Stimulates descent of the testes before birth, regulates spermatogenesis and promotes development and maintenance of male secondary sex characteristics
Inhibin	Inhibits secretion of FSH from anterior pituitary

Figure8. Anatomy of the Gonads - Ovaries anr Testes

This is not the end of the work of the endocrine system. There are lots of things to learn about endocrinology. And also the diseases or disorders are not yet mention above. This is just a glimpse of the endocrine system of our body. Follow my blog for more information or for more sharing of knowledge about the effects and abnormalities of the endocrine system and endocrinology-the study of hormones inside our body.

References:

Tortora, Gerald J., Derrickson, Bryan. 2009. Principles of Anatomy and Physiology Twelfth Edition Volume 1. Chapter 18. Page 642 - 673
http://nursingcrib.com/anatomy-and-physiology/anatomy-and-physiology-endocrine-system/
http://www.britannica.com/

http://www.webicina.com/images/images-3269.jpg
http://www.fipapatients.org/pituitary/
http://www.emedicinehealth.com/thyroid_problems/article_em.htm
http://www.pauerhome.com/ryan/endocrine_system/parathyroid_gland.html
http://images.yourdictionary.com/adrenal-gland
http://www.daviddarling.info/encyclopedia/P/pancreas.html
http://www.medicalook.com/human_anatomy/organs/Gonads.html