Endocrinology PDF

## Endocrinology ### Homeostasis - The body regulates itself through homeostasis, which involves maintaining a stable internal environment despite external changes. - This regulation occurs through various mechanisms, including hormonal and nervous systems. ### Endocrinology - Endocrinol...

## Endocrinology ### Homeostasis - The body regulates itself through homeostasis, which involves maintaining a stable internal environment despite external changes. - This regulation occurs through various mechanisms, including hormonal and nervous systems. ### Endocrinology - Endocrinology is the branch of biology and medicine that studies hormonal production, function, and related disorders. - Hormones are molecules produced by endocrine glands, secreted into the bloodstream, and transported to target cells where they bind to specific receptors, triggering biological actions. - Hormonal actions maintain homeostasis by regulating metabolism, growth, development, tissue function, reproduction, sleep, mood, and many other bodily functions. ### The Endocrine System - The endocrine system is a collection of glands that produce hormones, such as: - Pituitary Gland - Thyroid Gland - Parathyroid Glands - Adrenal Glands - Pancreas - Ovaries (females) - Testes (males) ### Hormonal Cycle - Hormone production is regulated through a complex cycle involving synthesis, storage, release, transport, utilization, and inactivation. - **Synthesis:** Hormones are synthesized from precursor molecules like cholesterol or amino acids. - **Storage:** Synthesized hormones are stored within vesicles or granules within the gland until needed. - **Release:** Hormones are released from the gland through exocytosis, where they are transported into the bloodstream. - **Transport:** Hormones travel through the bloodstream often bound to carrier proteins. - **Utilization:** Hormones bind to specific receptors on target cells, triggering intracellular events. - **Inactivation:** Hormones are degraded into inactive forms by enzymes or the liver and kidneys. ### Chemical Messengers - Hormones act as chemical messengers, influencing various physiological functions by regulating cellular processes and activities. - Two main mechanisms of hormone action: - **Protein (peptide) hormones:** Bind to cell surface receptors, generating a chemical signal inside the cell. Subsequent intracellular events trigger a response. - **Steroid hormones:** Pass through the cell membrane and bind to intracellular receptors, influencing gene expression and protein synthesis. ### The Endocrine System - A diagram depicts the endocrine glands and their location in the body, highlighting the key components of the endocrine system. ### The Pituitary Gland - The pituitary gland, located at the base of the brain, is the "master gland." - It is divided into anterior and posterior lobes, each responsible for secreting different hormones. ### The Anterior Pituitary - The anterior pituitary secretes a variety of hormones that regulate other endocrine glands and play a role in growth, metabolism, and reproduction. - **Tropic hormones:** These hormones stimulate other endocrine glands to produce their own hormones. - **ACTH:** Stimulates the adrenal cortex to produce cortisol. - **TSH:** Stimulates the thyroid gland to produce thyroid hormones. - **FSH & LH:** Stimulate the ovaries (females) and testes (males) to produce sex hormones. - **Direct-acting hormones:** - **Growth Hormone (GH):** Promotes growth of bones and tissues. - **Prolactin:** Stimulates milk production in females. ### The Posterior Pituitary - The posterior pituitary stores and releases hormones produced by the hypothalamus: - **ADH (Antidiuretic Hormone):** Regulates water balance in the body. - **Oxytocin:** Stimulates milk ejection from the mammary glands and uterine contractions during childbirth. ### Diabetes Insipidus - Diabetes insipidus is a disease characterized by excessive urination due to a deficiency in ADH production or lack of kidney response to ADH. - Two main types: - **Central diabetes insipidus:** Deficiency in ADH secretion from the hypothalamus. - **Nephrogenic diabetes insipidus:** The kidneys are unable to respond to ADH. ### The Thyroid Gland - The thyroid gland, located below the larynx, produces thyroid hormones T3 and T4, which regulate metabolism and numerous bodily functions. - **Hormone synthesis:** The thyroid gland traps iodine from the bloodstream and incorporates it into thyroglobulin molecules. - **Hormone release:** T3 and T4 are released from the thyroid gland when stimulated by TSH. - **Iodide pump:** The thyroid gland actively concentrates iodide ions, concentrating them from the bloodstream and trapping them within the thyroid follicles. ### Hypothyroidism - Hypothyroidism occurs when the thyroid gland does not produce sufficient thyroid hormones. - Symptoms include fatigue, weight gain, dry skin, and cold intolerance. - Types: - **Endemic goiter:** Resulting from iodine deficiency. - **Nontoxic goiter:** Enlarged thyroid gland due to a goitrogen (substance that interferes with thyroid hormone synthesis). - **Hypothyroidism:** The thyroid gland becomes inactive. ### Hyperthyroidism - Hyperthyroidism occurs when the thyroid gland is overactive. - Symptoms include high basal metabolic rate, weight loss, excessive sweating, and nervousness. - Types: - **Grave's disease (toxic goiter):** An autoimmune disease where antibodies stimulate the thyroid, causing hyperthyroidism. - **Thyroiditis (inflammation of the thyroid gland):** May cause temporary hyperthyroidism. ### The Parathyroid Gland - The parathyroid glands are small glands located near the thyroid gland. - They produce parathyroid hormone (PTH), which regulates blood calcium levels. - **PTH function:** - **Bone resorption:** PTH stimulates the release of calcium from bones. - **Calcium reabsorption:** PTH promotes reabsorption of calcium in the kidneys. - **Increased calcium absorption:** PTH stimulates the absorption of calcium from the intestines. ### Hypoparathyroidism - This condition occurs due to a lack of PTH production or a deficiency in parathyroid gland function. - Hypoparathyroidism causes hypocalcemia (low blood calcium), leading to muscle cramps, tetany, and seizures. ### Hyperparathyroidism - This condition occurs due to excessive production of PTH, often caused by a tumor in the parathyroid gland. - Increased PTH levels lead to hypercalcemia, characterized by weakness, bone pain, kidney stones, and kidney damage. ### The Adrenal Gland - The adrenal glands are located on top of each kidney, composed of the adrenal cortex (outer layer) and the adrenal medulla (inner layer). ### The Adrenal Cortex - The adrenal cortex secretes hormones that regulate various bodily functions: - **Mineralocorticoids (aldosterone):** Regulate electrolyte balance, particularly affecting sodium and potassium levels. - **Glucocorticoids (cortisol):** - Regulate carbohydrate metabolism, increasing glucose levels. - Promote protein catabolism, releasing amino acids into the bloodstream. - Promote lipolysis, releasing fatty acids into the bloodstream. - **Sex hormones:** Adrenal cortex also secretes small amounts of sex hormones like estrogen and androgen. ### Addison's Disease - Addison's disease develops when the adrenal cortex is damaged, leading to insufficient production of mineralocorticoids and glucocorticoids. - Symptoms include fatigue, weakness, weight loss, low blood pressure, and low blood sugar. ### Cushing's Syndrome - Cushing's syndrome occurs due to excessive production of glucocorticoids, often caused by a tumor in the adrenal cortex or the anterior pituitary gland. - Symptoms include: - Weight gain, primarily in the abdomen, face, and neck. - Hypertension. - Muscle weakness. ### The Adrenal Medulla - The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine, which are involved in the "fight or flight" response. ### The Thymus Gland - The thymus gland is an important part of the immune system responsible for the maturation and development of T-lymphocytes (a type of white blood cell). - The thymus gland secretes several hormones that regulate immune function, supporting the development and maturation of T-cells. ### Pineal Gland - The pineal gland is located in the brain and secretes melatonin, a hormone that regulates circadian rhythms (sleep-wake cycles) and influences mood and seasonal changes. ### The Pancreas - The pancreas is both an exocrine and endocrine gland. - **Exocrine function:** Secretes digestive enzymes into the duodenum. - **Endocrine function:** Secretes hormones that regulate blood glucose levels: - **Insulin:** Produced by beta cells, reduces blood glucose levels. - **Glucagon:** Produced by alpha cells, increases blood glucose levels. ### Diabetes Mellitus - Diabetes mellitus is a disease characterized by high blood glucose levels due to either a deficiency in insulin production or a lack of response to insulin. - Two main types: - **Type 1 diabetes:** Autoimmune destruction of beta cells in the pancreas, preventing insulin production. - **Type 2 diabetes:** Insulin resistance, where the body fails to respond properly to insulin. ### Eicosanoids - Eicosanoids are a group of hormones derived from arachidonic acid, a polyunsaturated fatty acid. - Include prostaglandins, thromboxanes, and leukotrienes. - Eicosanoids play various roles in inflammation, pain, fever, blood pressure regulation, and other physiological processes. ### Reproductive System - **Male reproductive system:** - **Testes:** Primary sex organs responsible for sperm production and testosterone secretion. - **Scrotum:** A sac that holds the testes, regulating temperature for sperm production. - **Epididymis:** A coiled tubule where sperm mature and are stored. - **Vas deferens:** A tube that carries sperm during ejaculation. - **Seminal Vesicles:** Secretes fluids that make up the ejaculate. - **Prostate Gland:** Secretes fluids that provide nutrients and protect sperm. - **Bulbourethral gland:** Secretes fluids that lubricate the urethra before ejaculation. - **Female reproductive system:** - **Ovaries:** Primary sex organs responsible for egg (ova) production and hormone secretion. - **Fallopian Tubes:** Tubes that carry ova from the ovaries to the uterus. - **Uterus:** A muscular organ that houses a developing fetus. - **Cervix:** The lower portion of the uterus that connects to the vagina. - **Vagina:** A muscular canal that receives sperm during sexual intercourse. ### Hormones involved in Reproduction - Several hormones influence the reproductive systems: - **FSH (Follicle-stimulating hormone):** Stimulates follicle development in the ovaries and sperm production in the testes. - **LH (Luteinizing hormone):** Triggers ovulation in females and testosterone production in males. - **Estrogen:** A female sex hormone that promotes the development of secondary sexual characteristics and prepares the uterus for pregnancy. - **Progesterone:** A female sex hormone that helps maintain pregnancy and prepares the mammary glands for lactation. - **Testosterone:** A male sex hormone that promotes sperm production and the development of secondary sexual characteristics. ### Menstrual Cycle - The menstrual cycle is a recurring series of events in a female's reproductive system, lasting approximately 28 days. - It involves hormonal changes that regulate the development and release of eggs from the ovaries, the preparation of the uterus for pregnancy, and the shedding of the uterine lining if pregnancy does not occur. ### Pregnancy - Pregnancy begins with fertilization, where a sperm cell fuses with an egg cell. - The fertilized egg develops into an embryo that implants into the uterine wall. - The placenta, a structure that develops during pregnancy, provides nutrients and oxygen to the developing fetus. - Hormonal changes, particularly progesterone, regulate the course of pregnancy and prepare the body for childbirth. - Parturition (childbirth) occurs through a series of uterine contractions and the expulsion of the fetus. ### Lactation - Lactation is the process of milk production in the mammary gland. - It is triggered by hormones like prolactin, which is stimulated by suckling and the release of oxytocin. - Colostrum, a rich, antibody-laden fluid, is produced initially, providing essential nutrients and immune protection to the newborn. - Milk production continues until the infant is weaned. ### Endocrine Disruptions - Hormonal imbalances can disrupt normal physiology and contribute to various health problems. - Endocrine disruptors are chemicals that interfere with the normal function of hormones. - Endocrine disruptors can mimic the effects of natural hormones, block the action of hormones, or alter hormone metabolism, leading to disease.