Academy of Diagnostic & Osteopathic Medicine
THYROID
The thyroid gland is located in the anterior neck, just below the larynx and surrounding the trachea. It has a butterfly shape with two lobes connected by a thin structure called the isthmus. The gland contains follicular cells that produce thyroid hormones (T3 and T4) and parafollicular cells that secrete calcitonin, which regulates calcium levels. The thyroid receives its blood supply from the superior thyroid artery, a branch of the external carotid artery, and the inferior thyroid artery, which comes from the thyrocervical trunk. Venous drainage occurs through the superior, middle, and inferior thyroid veins into the internal jugular and brachiocephalic veins. The thyroid gland’s primary functions are to produce hormones that regulate metabolism (T3 and T4) and calcitonin to maintain calcium balance in the body. Pathologies include papillary thyroid carcinoma, the most common type of thyroid cancer, which is often slow-growing but can spread to lymph nodes; follicular thyroid carcinoma, a more aggressive cancer that can metastasize to the lungs and bones; thyroid adenomas, benign tumors that may sometimes produce excessive hormones; and anaplastic thyroid carcinoma, a rare but aggressive cancer causing rapid neck mass growth and difficulty breathing or swallowing.
PITUITARY
The pituitary gland is located at the base of the brain in the sella turcica, a depression in the sphenoid bone, just below the hypothalamus. It has two distinct lobes: the anterior lobe, or adenohypophysis, which produces hormones like ACTH, TSH, and growth hormone, and the posterior lobe, or neurohypophysis, which stores and releases hormones like oxytocin and antidiuretic hormone (ADH). The pituitary is connected to the hypothalamus via the pituitary stalk. The gland is supplied by the superior and inferior hypophyseal arteries, branches of the internal carotid artery, and its venous drainage occurs through the hypophyseal veins into the cavernous sinus. The pituitary regulates many vital functions through its hormone production, including growth, metabolism, reproduction, and water balance. Common conditions include pituitary adenomas, which are benign tumors that can cause hormonal imbalances like Cushing’s syndrome or acromegaly, and diabetes insipidus, caused by ADH deficiency leading to excessive urination and thirst.
ADRENAL
Adrenal Glands: The Stress and Energy Regulators The adrenal glands are two small, triangular glands sitting on top of each kidney. Each gland has two parts—the adrenal cortex, which produces cortisol, aldosterone, and sex hormones, and the adrenal medulla, which releases adrenaline (epinephrine) and norepinephrine for the fight-or-flight response. Blood supply comes from the superior, middle, and inferior adrenal arteries, and venous drainage occurs through the adrenal veins into the renal and inferior vena cava. The adrenal glands help regulate metabolism, blood pressure, stress response, and electrolyte balance. Common disorders include Cushing’s syndrome, caused by excess cortisol, Addison’s disease, where the body doesn’t produce enough hormones, and pheochromocytomas, rare tumors that overproduce adrenaline.
THYMUS
Thymus Gland: The Immune Trainer The thymus gland is located in the upper chest, behind the sternum, and is most active in childhood, gradually shrinking with age. It produces T-cells, a type of white blood cell essential for immune system development. Blood supply comes from the internal thoracic and inferior thyroid arteries, with venous drainage into the brachiocephalic veins. Its function is to train and mature immune cells, ensuring the body can fight infections. If the thymus is dysfunctional, conditions like myasthenia gravis (an autoimmune disorder affecting muscle strength) and thymomas (tumors of the thymus) can occur.
PARATHYROID
The parathyroid glands are four small, oval-shaped structures located on the posterior surface of the thyroid gland. They are made up of chief cells, which produce parathyroid hormone (PTH), and oxyphil cells, which have an unclear role. Blood supply primarily comes from the inferior thyroid artery, and venous drainage occurs through the parathyroid veins into the thyroid venous plexus. The parathyroid glands secrete PTH, which helps regulate calcium and phosphorus levels in the blood by acting on bones, kidneys, and intestines. Pathologies include hyperparathyroidism, which results from excess PTH production and leads to hypercalcemia, bone pain, and kidney stones, and hypoparathyroidism, where low PTH levels cause hypocalcemia, muscle cramps, and seizures.
HYPOTHALAMUS
Hypothalamus: The Body’s Command Center The hypothalamus is a small but powerful brain structure located just above the pituitary gland. It acts as the link between the nervous and endocrine systems, regulating hormone production, body temperature, hunger, thirst, and circadian rhythms. It receives blood from the anterior cerebral and posterior communicating arteries, while venous drainage occurs through the hypophyseal portal system. Its main function is to control the pituitary gland, releasing hormones that regulate stress, reproduction, and metabolism. It also plays a role in autonomic nervous system responses like heart rate and digestion. Dysfunction in the hypothalamus can lead to hormonal imbalances, temperature regulation issues, and appetite disorders like hypothalamic obesity.
PINEAL
Pineal Gland: The Sleep Regulator The pineal gland is a tiny, pea-shaped structure located deep inside the brain, near the thalamus. It produces melatonin, a hormone that regulates sleep-wake cycles based on light exposure. Blood supply comes from the posterior cerebral artery, and venous drainage occurs through the great cerebral vein. Its main function is to control circadian rhythms, adjusting sleep patterns based on light exposure. Disorders of the pineal gland can lead to sleep disturbances, seasonal affective disorder (SAD), and even calcifications, which may contribute to aging-related sleep issues.
HORMONES
Hormones are chemical messengers produced by glands in the endocrine system that regulate various bodily functions. They are released into the bloodstream and travel to target organs, where they control processes like growth, metabolism, reproduction, and mood. Examples include insulin, which regulates blood sugar levels, and thyroid hormones, which control metabolism. Hormonal imbalances can lead to conditions such as diabetes, caused by insufficient insulin, or hypothyroidism, which results from low thyroid hormone production.
INSULIN
Insulin is the body's master regulator of glucose. Produced by the pancreas, it works like a key, unlocking cells so they can absorb sugar from the bloodstream. When we eat, insulin rises to store energy, and when we fast, it drops to allow fat burning. But when insulin becomes dysregulated, conditions like diabetes emerge, where sugar stays trapped in the blood, leading to nerve damage, kidney failure, and cardiovascular disease.
CORTISOL
Cortisol is the stress hormone, produced by the adrenal glands. It keeps us alert and responsive in emergencies, increasing blood sugar, blood pressure, and inflammation to help us fight or flee. But chronic stress keeps cortisol levels high, leading to anxiety, insomnia, weight gain, and even immune suppression, making us more vulnerable to illness.
GROWTH
Growth hormone, released by the pituitary gland, is essential for cell repair, muscle growth, and metabolism. In children, it drives height and development. In adults, it helps with muscle maintenance and fat metabolism. Too much GH leads to gigantism or acromegaly, while too little can cause stunted growth and muscle loss.
ESTROGEN
Estrogen, the primary female hormone, is produced by the ovaries and affects menstrual cycles, bone density, and mood. It also protects the heart and brain. Too much estrogen, as seen in hormonal imbalances or estrogen dominance, can cause weight gain, mood swings, and increased cancer risk, while too little leads to menopause symptoms like hot flashes and osteoporosis.
GLUCAGON
If insulin is the storage hormone, glucagon is its opposite. Also made by the pancreas, glucagon tells the liver to break down stored glucose and release it into the blood when we’re low on energy—like during fasting or exercise. It keeps blood sugar from dropping too low, preventing hypoglycemia, which can cause dizziness, confusion, and even unconsciousness if severe.
ADRENALINE
Adrenaline (Epinephrine) Adrenaline is the body’s emergency alarm system, released by the adrenal glands when we face danger. It increases heart rate, dilates airways, and sends blood to muscles, giving us that rush of energy when we need to react quickly. But too much adrenaline, whether from stress or medical conditions like pheochromocytoma, can cause high blood pressure, heart palpitations, and anxiety.
TESTOSTERONE
Testosterone, produced mainly by the testes in men and the ovaries in women, is the hormone of strength, libido, and muscle mass. It drives puberty, sperm production, and motivation. Low testosterone can cause fatigue, depression, and low libido, while too much can lead to aggression, acne, and cardiovascular risks.
PROGESTERONE
Progesterone is the balancing hormone to estrogen, preparing the uterus for pregnancy and stabilizing mood. It’s also a natural anti-inflammatory and helps with sleep. Low progesterone is linked to PMS, anxiety, and irregular periods, while excess progesterone can cause fatigue and bloating.
MELATONIN
Melatonin is the sleep hormone, made by the pineal gland in response to darkness. It tells the body when it’s time to rest. Screens, artificial light, and stress lower melatonin, disrupting sleep cycles and leading to insomnia, fatigue, and poor immune function.
OXYTOCIN
Oxytocin, often called the love hormone, is released by the pituitary gland during bonding moments like childbirth, breastfeeding, and intimate touch. It reduces stress, strengthens relationships, and promotes trust. Low oxytocin is linked to social anxiety and difficulty forming emotional connections.
T3
T3 (Triiodothyronine) T3 is the active form of thyroid hormone, controlling metabolism, energy production, and body temperature. It acts quickly, regulating heart rate, digestion, and brain function. When T3 is too high, as in hyperthyroidism, the body speeds up—causing weight loss, anxiety, tremors, and a racing heart. When T3 is too low, as in hypothyroidism, everything slows down—leading to fatigue, depression, cold intolerance, and brain fog.
DOPAMINE
Dopamine is the reward and motivation neurotransmitter. It drives pleasure, focus, and movement, playing a key role in mood, learning, and addiction. When levels are too low, as in Parkinson’s disease, movement slows, and motivation drops. When too high, as in schizophrenia, it can contribute to hallucinations and paranoia. Everyday activities like exercise, music, and achievement trigger dopamine release, reinforcing behavior and habit formation.
T4
T4 (Thyroxine) T4 is the storage form of thyroid hormone, circulating in the blood until the body converts it into active T3 when needed. It helps maintain steady energy levels, heart function, and metabolism. Low T4 levels indicate thyroid dysfunction, while excess T4 can lead to hyperactivity, restlessness, and weight fluctuations. Proper T4 conversion is essential for hormonal balance and overall health.
SEROTONIN
Serotonin is the mood stabilizer, promoting happiness, sleep, and digestion. About 90% of serotonin is in the gut, helping regulate appetite and digestion, while the rest works in the brain to control mood and emotional balance. Low serotonin is linked to depression, anxiety, and sleep disorders, while excess serotonin can cause serotonin syndrome, leading to confusion, high blood pressure, and agitation.
ACETYLCHOLINE
Acetylcholine is the body’s learning and movement neurotransmitter. It controls muscle contractions, memory formation, and even attention span. When you learn something new or focus on a task, acetylcholine is at work, strengthening neural connections. It’s also what allows you to move—every muscle contraction, from blinking to running, depends on it. Low acetylcholine levels are linked to Alzheimer’s and cognitive decline, while optimal levels keep your brain sharp and body responsive. It’s the key to both memory and motion.