Endocrinology for writers is the new Monday blog series for March. Endocrinology is the study of the system of hormones and signals the body uses to manage its functions. It’s a complex subject and many people find it confusing. I’m here to help try to make it easier to understand.
Why will this help writers? It allows you to understand important body functions such as responses during stress and fear, illnesses and conditions like diabetes and reproduction. Knowing what each of the important hormones actually do helps you understand and describe the effects and behaviours. So let’s get into it with some definitions.
Endocrinology Definitions
Hormone: signalling molecules secreted by endocrine glands to regulate physiology and behaviours. Hormones take different forms; amino acid complexes, steroids, eicosanoids, leukotrienes and prostaglandins.
Glands: glands that produce and secrete hormones into the bloodstream. Some organs have endocrine functions as well as their other functions in the body.
Neuroendocrine system: thepart of the brain that connects to the endocrine system and controls the release of hormones based on input from the nervous system.
Axis: a sequences of endocrine glands that signal each other in a specific order to control hormone secretions.
Homeostasis: the steady state of optimal physiological function. The endocrine system manages the body in order to maintain this.
Tropic hormones: these hormones target other endocrine glands and organs to stimulate them to produce other hormones. The anterior pituitary gland secretes the majority of these hormones.
Feedback loops: the endocrine system has negative feedback loops that control the production of hormones. For example, high levels of cortisol will cause the hypothalamus to stop producing hormones that stimulate cortisol production. This stops the body producing too much of a hormone.
Endocrine Glands and Organs
The endocrine system involves the entire body and many organs and glands are involved, both secreting hormones and responding to hormones. The neuroendocrine system is the part of the brain responsible for controlling hormone release.
Neuroendocrine System
Pineal gland: the pineal gland within the brain produces melatonin, a homrone derived from serotonin, which regulates the sleep cycle. The pineal gland links to a light sensing organ called the ‘parietal eye’ or ‘third eye’ in reptiles and amphibians. This is most notable in tuataras, a lizard-like reptile that is the last surviving species of its category.
Hypothalamus: this part of the brain organises inputs from all other parts of the brain and responds by releasing hormones and tropic hormones. This triggers the pituitary gland.
Pituitary Gland: there are three lobes of the pituitary gland:
- Anterior: responds to tropic hormones and releases other hormones
- Intermediate: only functional in the foetus
- Posterior: direct nerve connection to hypothalamus and produces oxytocin and vasopressin (anti-diuretic hormone or ADH)
This system controls all aspects of reproduction; bonding, sexual behaviour, spermatogenesis (sperm production), ovarian cycle, parturition (giving birth), lactation (milk production) and maternal behaviour.
It also controls regulation of metabolism, eating and drinking, fat metabolism, mood regulation, fluid and electrolyte homeostasis and blood pressure.
Glands
Glands are organs that specifically produce hormones as their main function. You may know some of them already. So let’s get into the details.
Thyroid gland: The thyroid gland is located just below the larynx and has two lobes. It secretes the thyroid hormones thyroxine (T4) and triiodothyronine (T3) to control metabolism.
Parathyroid glands: Four tiny glands located behind the thyroid gland, hence the name. The parathyroid glands produce parathyroid hormone (big surprise!) an important hormone for calcium homeostasis.
Adrenal Glands: a pair of glands located above the kidneys, split into two regions with different functions. We’ll cover this in detail in a later post.
- Adrenal cortex: produces glucocorticoids, mineralocorticoids and androgens
- Adrenal medulla: adrenaline (epinephrine) and noradrenalin (norepinephrine)
- The adrenal glands also produce dopamine and enkephalin
Gonads: the primary organs producing sex hormones and gametes. I’m including the uterus and placenta too.
- Testes: the male gonads produce androgens such as testosterone, oestradiol (estradiol Am. Eng.) and inhibin.
- Ovaries and Corpus Luteum: progesterones, oestrogens (estrogens Am. Eng.) and inhibin.
- Placenta: progesterone, oestrogens, human chorionic gonadotrophin (hCG) and human placental lactogen.
- Uterus: during pregnancy it produces prolactin, which stimulates milk production, and relaxin which affects blood flow and relaxes the pelvis and birth canal.
Organs With Endocrine Functions
Several organs have endocrine functions in addition to their other functions. Not only do they produce hormones, they also respond to hormones as well as other changes in the body’s physiology.
Pancreas: the pancreas has exocrine functions (digestive enzymes) and endocrine functions related to blood glucose (blood sugar) and metabolism.
- Insulin – produced in the β-islet cells (beta-islet) to reduce blood glucose and stimulate glucose uptake by cells.
- Glucagon – produced in the α-islet cells (alpha-islet) to increase blood glucose and glucose production in the liver.
- Somatostatin – produced in the δ-islet cells (delta-islet) to inhibit release of insulin and glucagon.
Kidneys: the kidneys produce erythropoietin which stimulates production of red blood cells in the bone marrow. They also release renin, which is involved in the RAAS system and calcitrol, the active form of vitamin D3.
Liver: produces insulin-like growth factor (IGF), thrombopoietin (THPO) to stimulate platelet production, hepcidin, angiotensinogen and angiotensin. The later two are also part of the RAAS system, which we’ll cover at a later date.
Heart: ANP (atrial natruiretic peptide) and BNP (brain natruiretic peptide) released from the muscle cells of the heart control blood pressure.
This covers a basic introduction to endocrinology for writers. Over the next few weeks we will cover the important systems that will help you understand how important endocrinology is for our behaviours and emotions. Don’t forget to subscribe for more updates and find me on my social media channels.
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