lecture 9: endocrine system

Endocrine System

Endocrine System

A system that coordinates the activity of organs through hormones, which are chemical messengers released into the blood from glands.

Homeostasis

involves regulation by the autonomic nervous system (rapid, less precise, short-term changes using neurotransmitters via the central nervous system) and the endocrine system (slower, precise, long-term changes using hormones via the hypothalamus).

Glands

Glands are either exocrine or endocrine. Exocrine glands use ducts to release substances, like saliva or enzymes, while endocrine glands release hormones directly into the blood, such as the pituitary, thyroid, and adrenal glands.

Hormones

Chemical messengers that have specific target cells and can be peptides, steroids, or amino acid derivatives.

Exocrine Glands

Glands that excrete products into ducts leading to body cavities or surfaces, such as salivary and gastric glands.

Endocrine Glands

Ductless glands that secrete hormones directly into the blood, including the pituitary, thyroid, and adrenal glands.

Endocrine tissues

Examples include adipose tissue (leptin, resistin), heart (atrial natriuretic peptide), stomach (ghrelin, gastrin), liver (angiotensinogen, IGF), placenta (hCG, progesterone), kidneys (erythropoietin, calcitriol), and skin (cholecalciferol).

Hormone Receptors

Specific proteins on target cells that hormones bind to, influencing cell activity.

Down-regulation

A process where the number of hormone receptors decreases in response to excess hormone levels.

Up-regulation

A process where the number of hormone receptors increases in response to hormone deficiency.

Pituitary Gland

Often referred to as the master endocrine gland, it controls many other endocrine glands and is regulated by the hypothalamus. It has anterior and posterior regions and links the nervous and endocrine systems.

Hypothalamus

A brain region that produces releasing and inhibiting hormones that regulate the pituitary gland.

Growth Hormone (GH)

A hormone that regulates metabolism, stimulates growth, and promotes the release of insulin-like growth factors.

Thyroid Stimulating Hormone (TSH)

A hormone that stimulates the growth and activity of the thyroid gland, increasing thyroid hormone production.

Adrenocorticotropic Hormone (ACTH)

A hormone that stimulates the output of steroid hormones from the adrenal cortex.

Prolactin (PRL)

A hormone that stimulates lactation and prevents pregnancy during breastfeeding.

Follicle Stimulating Hormone (FSH)

A hormone that stimulates the production of gametes and increases estrogen production in females.

Luteinising Hormone (LH)

A hormone that triggers ovulation and increases progesterone secretion in females.

Melanocyte Stimulating Hormone (MSH)

A hormone involved in skin pigmentation, produced in response to UV light.

Oxytocin

A hormone that contracts the uterus during childbirth and promotes bonding between mother and baby.

Lactation

begins two to three days after birth, with the first breast fluid being colostrum. Colostrum contains water, lacto-sugar, and antibodies, and acts as a laxative to help newborns pass waste and bilirubin from their intestines.

Antidiuretic Hormone (ADH)

A hormone that reduces urine output by stimulating water reabsorption in the kidneys.

Pituitary gland pathologies

often caused by tumors or autoimmune diseases, leading to either excessive or insufficient secretion of pituitary hormones. The symptoms depend on which hormones are affected.

Gigantism

Excess growth hormone in childhood, causing abnormal height, large hands and feet. Symptoms include joint pain and muscle weakness. Complications: hypertension, type 2 diabetes, cardiomegaly. Treatment: Surgery and lifelong medications.

Acromegaly

Excess growth hormone after puberty, causing enlarged hands, feet, and facial features. Symptoms include joint pain and soft-tissue swelling. Complications: hypertension, osteoarthritis, type 2 diabetes. Treatment: Surgery and lifelong medications.

Hyperprolactinaemia

Excess prolactin production, often due to a pituitary tumour, acromegaly, or medications. Symptoms include galactorrhoea, amenorrhoea, reduced libido, and subfertility. Treatment targets the cause.

Diabetes Insipidus

A condition characterized by a deficiency of ADH, leading to excessive urination and thirst.

Cushing Syndrome

a rare disorder caused by prolonged high cortisol levels. It can result from corticosteroid use, adrenal adenomas, or pituitary tumors. Symptoms include central weight gain, moon face, buffalo hump, insulin resistance, depression, thin skin, muscle weakness, osteoporosis, and hypertension.

Addison’s Disease

adrenal insufficiency caused by low cortisol and aldosterone, often from autoimmune atrophy. Symptoms include fatigue, hypotension, hyperpigmentation, and weight loss. Addisonian crisis causes severe lethargy, low blood pressure, and hypoglycemia.

Type I Diabetes

an autoimmune condition where the body destroys pancreatic beta cells, leading to insulin deficiency and hyperglycemia. Causes include genetics, viruses, and dietary factors. Symptoms include excessive thirst, urination, hunger, weight loss, fatigue, blurred vision, and ketoacidosis (fruity breath). Treatment involves insulin.

Type II Diabetes

caused by genetic factors, poor lifestyle, and insulin resistance. Symptoms include thirst, frequent urination, hunger, and acanthosis nigricans. It’s diagnosed through blood tests and treated with diet, exercise, and medications like metformin.

Thyroid Hormones

Hormones produced by the thyroid gland that regulate metabolism, growth, and development.

Pineal gland: melatonin

a pea-sized brain gland, produces it to regulate circadian rhythms. production is stimulated by darkness and reduced by daylight or irregular sleep patterns. It is highest in children, declines with age, and acts as a potent antioxidant.

Thymus gland and thymosin

The thymus, located behind the sternum, supports immune development by producing it, which matures T-lymphocytes. It atrophies after puberty, and mature T-cells migrate to the lymphatic system.

Thyroid gland

a butterfly-shaped gland near the trachea, regulates metabolism and supports growth in early life. Follicular cells produce T3 and T4 hormones using iodine and tyrosine, while parafollicular cells secrete calcitonin to lower blood calcium. The gland stores iodine and thyroglobulin in its colloid-filled follicles.

Thyroid hormones

T4 converts to active T3, regulating metabolism, growth, and CNS function. Stimulated by TSH, stress, or exercise, they boost metabolism and heat. High TSH signals thyroid issues. Tests include TSH, free T3/T4, and thyroid antibodies.

Hypothyroidism

Underactive thyroid caused by Hashimoto’s thyroiditis, iodine deficiency, thyroid destruction (surgery, medications, or fluoride). Treated with levothyroxine for hormone replacement.

Hyperthyroidism

causes elevated/overactive thyroid hormone levels, often due to autoimmune overstimulation (Graves’ disease). Symptoms include nervousness, weight loss, sweating, and palpitations, with signs like goitre and tremors. Treatment includes carbimazole, radioactive iodine, β-blockers, or surgery.

Calcitonin

a thyroid gland, produced by thyroid parafollicular cells and is vital for childhood bone growth. It lowers blood calcium by inhibiting calcium reabsorption and osteoclast activity. Production is stimulated by high blood calcium and inhibited by low levels.

Parathyroid glands

are four small glands located on the posterior surface of the thyroid's lateral lobes. They produce parathyroid hormones, which regulate calcium and phosphate levels in the blood.

Parathyroid hormone (PTH)

raises blood calcium by stimulating osteoclasts, increasing kidney reabsorption, and promoting calcitriol production. It’s released when calcium is low and inhibited when it’s high. Calcium is crucial for muscle, nerve, and clotting functions.

Hyperthyroidism

caused by an overproduction of parathyroid hormone, usually from a tumour. Symptoms may include hypercalcaemia, kidney stones, osteoporosis, low energy, and depression. Severe cases may involve nausea, vomiting, constipation, and muscle paralysis.

Hypoparathyroid

caused by low levels of parathyroid hormone, often due to surgery or radiation. Symptoms include hypocalcaemia, muscle cramps, spasms, tingling, dry hair, brittle nails, and cataracts. Children may also have weakened tooth enamel.

Adrenal glands

located above the kidneys, have two parts: the medulla, which produces adrenaline, noradrenaline, and dopamine, and the cortex, which produces cortisol, aldosterone, and androgens.

Adrenaline and Noradrenaline

they are produced by the adrenal medulla. They enhance the sympathetic response, with adrenaline affecting the heart and noradrenaline affecting blood vessels. They are released during stress, exercise, or emotional triggers. Adrenaline increases heart rate, blood pressure, metabolism, and glucose levels, while noradrenaline causes vasoconstriction in the digestive tract and dilates pupils.

Glucocorticoids

primarily cortisol, are steroid hormones from the adrenal cortex that regulate metabolism and stress response. They stimulate gluconeogenesis, proteolysis, lipolysis, and glucose production. They reduce immune response and inflammation, which is why steroids are used therapeutically. They also promote weak sodium and water reabsorption in the kidneys.

Mineralocorticoids

mainly aldosterone, regulate water and electrolyte balance. They promote sodium reabsorption in the kidneys, water retention to increase blood volume and pressure, and potassium excretion. Stimulated by low blood pressure or volume and high blood potassium, they are inhibited by low blood potassium.

Sex Hormones

mainly androgens like DHEA, promote pubic and axillary hair growth, increase muscle mass, and are converted to testosterone and oestrogen (boosting libido in females). Produced by CRH and ACTH, their levels are lower than those from the ovaries and testes during puberty and adulthood.

Pancreas

has both endocrine and exocrine functions. Its endocrine function is performed by the islets of Langerhans, which include alpha cells (produce glucagon) and beta cells (produce insulin). The main role is to regulate blood glucose levels (4-7 mmol/L).

Pancreas: Insulin

lowers blood glucose, amino acids, and fatty acids by stimulating cells to uptake glucose and promoting protein, glycogen, and fat synthesis. It is stimulated by high blood glucose, elevated amino acids, eating, and sweet taste, and reduced by low blood glucose, starvation, and glucagon.

Pancreas: Glucagon

raises blood glucose by converting glycogen to glucose (glycogenolysis), stimulating gluconeogenesis, and promoting lipolysis. It is stimulated by low blood sugar, exercise, and stress, and reduced by insulin and hyperglycemia.

Diabetes Mellitus

a metabolic disorder with hyperglycemia caused by insufficient insulin production or resistance. Types include: Type I (autoimmune), Type II (insulin resistance), secondary (due to medications or pancreatitis), and gestational (during pregnancy, increasing Type II risk later).

Diabetic Complications

chronic hyperglycaemia include heart disease, retinopathy, nephropathy, and peripheral neuropathy. It also increases the risk of hypertension and hypercholesterolaemia.

Ketoacidosis

occurs when cells can't use glucose, leading to the breakdown of fatty acids and the production of ketones. High ketone levels can be toxic, causing coma or death. Key signs include fruity-smelling breath and increased thirst. Ketones can be tested with a urine dipstick.

Hypoglycaemia

in diabetics can occur from insulin or glucose-lowering drugs. Symptoms include shaking, sweating, tingling in lips and tongue, hunger, irritability, headache, slurred speech, confusion, tiredness, and in severe cases, ketoacidosis or coma.

Local Hormones

include histamine (inflammation), prostaglandins, leukotrienes, thromboxanes (various processes), serotonin (clotting, appetite, sleep), dopamine (muscle tone), erythropoietin (red blood cells), and CCK (bile and pancreatic juice secretion).

metabolism

the chemical reactions in the body's cells that change food into energy.