Hormones and Endocrine Glands

• A hormone is a chemical messenger secreted by glands in the endocrine system, traveling through the bloodstream to regulate processes like growth, metabolism, and reproduction.
• Endocrine glands secrete hormones directly into the bloodstream without ducts, while exocrine glands release substances through ducts to external or internal surfaces.

Hormone Release

• Humoral stimuli involve changes in blood levels of ions or nutrients triggering hormone secretion.
• Example: Low calcium levels stimulate the parathyroid gland to release parathyroid hormone (PTH).

Hormone Types

• Amino acid-based hormones bind to cell surface receptors and activate second-messenger signaling pathways to alter cell activity.
• Examples include insulin and epinephrine.
• Steroid-based hormones, derived from cholesterol, pass through the cell membrane and bind to intracellular receptors to affect gene expression.
• Examples include cortisol, estrogen, and testosterone.
• Tropic hormones regulate other endocrine glands, stimulating them to release their hormones.
• Example: Thyroid-stimulating hormone (TSH) stimulates the thyroid gland.
• Transcription factors are proteins that bind to DNA sequences to regulate gene transcription, with steroid hormones acting as transcription factors.

Pituitary Gland

• The anterior pituitary produces hormones that regulate growth, metabolism, and reproduction.
• The posterior pituitary stores and releases hormones produced by the hypothalamus, such as oxytocin and antidiuretic hormone (ADH).
• Growth hormone (somatotropin) stimulates growth, cell reproduction, and regeneration.
• Prolactin stimulates milk production in females and regulates immune function and metabolism.
• Follicle-stimulating hormone is crucial for reproductive processes, stimulating ovarian follicle growth in women and sperm production in men.
• Luteinizing hormone triggers ovulation in women and stimulates testosterone production in men.
• Thyroid-stimulating hormone stimulates the thyroid gland to produce thyroid hormones, regulating metabolism.
• Adrenocorticotropic hormone stimulates the adrenal cortex to release cortisol, involved in stress response and metabolism.

Hypothalamus

• The hypothalamus regulates autonomic functions and produces hormones that control the pituitary gland.
• Oxytocin stimulates uterine contractions during childbirth and milk ejection during lactation and involves social bonding and emotional responses.
• Antidiuretic hormone (ADH) regulates water balance by promoting water reabsorption in the kidneys.

Other Key Hormones

• Thyroid hormone regulates metabolism, energy production, and growth.
• Calcitonin lowers blood calcium levels.
• Parathyroid hormone increases blood calcium levels.
• Osteoclasts break down bone tissue, releasing calcium.
• Glucocorticoids help regulate metabolism, reduce inflammation, and control the stress response.
• Cortisol, a stress hormone, manages stress, regulates blood sugar, reduces inflammation, and controls metabolism.
• Androgens are male sex hormones important for male traits and are present in both males and females.
• Estrogen regulates female reproductive functions, influences the menstrual cycle, and promotes female physical traits.
• Catecholamines, including norepinephrine and epinephrine, are involved in the fight-or-flight response, increasing heart rate, blood pressure, and energy levels.
• Insulin lowers blood sugar levels, while glucagon raises blood sugar levels.
• Glycogen is stored glucose in the liver and muscles.
• An antagonist blocks or reduces a hormone's effect.

Additional Glands and Hormones

• The pineal gland produces melatonin, which regulates sleep-wake cycles.
• The thymus gland produces thymosin, which stimulates T-cell production for the immune system.
• Gonads (testes and ovaries) produce gametes and sex hormones.
• Progesterone plays a key role in the menstrual cycle, pregnancy, and embryonic development.
• Menopause marks the end of a woman's reproductive years.
• Leptin regulates energy balance by inhibiting hunger.
• Ghrelin stimulates appetite.
• Hyposecretion is insufficient hormone production, and hypersecretion is excessive hormone production.
• Diabetes mellitus is high blood sugar due to insufficient insulin or insulin resistance.
• Adrenal insufficiency (Addison’s Disease) results from inadequate adrenal hormone production.
• Cushing’s Disease is caused by excessive cortisol production.
• Acromegaly results from excessive growth hormone production in adulthood.
• Gigantism results from excessive growth hormone production in childhood.
• Pituitary Dwarfism results from insufficient growth hormone production in childhood.
• Hyperthyroidism involves the overproduction of thyroid hormones.
• Hypothyroidism involves insufficient thyroid hormone production.
• Polycystic Ovary Syndrome (PCOS) is a hormonal disorder affecting women, characterized by irregular periods, excess androgen levels, and ovarian cysts.

The Endocrine System Overview

• The endocrine system is composed of glands that produce hormones that work slower than the nervous system
• These hormones impact maintaining homeostasis of the body
• Endocrine glands secrete hormones directly into the bloodstream, while exocrine glands secrete products into ducts.
• Endocrine glands are stimulated to produce and release hormones by other glands, the nervous system and chemical receptors in the blood
• Hormones affect only target cells with specific receptors for that hormone
• Amino acid-based hormones bind to receptors on the cell surface, while steroids pass through the plasma membrane.
• Amino acid based hormones bind to receptors on the surface of the cell and alert a second messenger molecule that activates an enzyme or cellular protein, or influences gene expression.

Pituitary Gland Details

• The pituitary gland, often called the "master gland," controls the function of other glands.
• The anterior pituitary produces growth hormone, prolactin, follicle-stimulating hormone, luteinizing hormone, and thyrotropic hormone.
• The posterior pituitary stores and releases hormones made by the hypothalamus, including oxytocin and antidiuretic hormone.
• The hypothalamus regulates the pituitary gland through releasing and inhibiting hormones.
• Oxytocin stimulates uterine contractions and milk ejection and plays a role in bonding.
• Antidiuretic hormone (ADH) causes the kidneys to reabsorb more water.

Other Hormones Detailed

• The thyroid gland secretes thyroid hormone and calcitonin.
• Parathyroid glands secrete parathyroid hormone (PTH), which increases blood calcium levels antagonistically with calcitonin.
• The adrenal glands consist of the central medulla and outer cortex.
• Mineralocorticoids, such as aldosterone, maintain salt and water balance.
• Glucocorticoids, primarily cortisol, regulate metabolism and act as anti-inflammatories.
• The adrenal medulla releases catecholamines in the fight-or-flight response.
• Pancreatic islets produce insulin and glucagon regulating levels of glycemia
• The pineal gland secretes melatonin, regulating sleep-wake cycles.
• The thymus gland produces thymosin, which aids in the development of T-cells.
• Ovaries produce estrogen and progesterone, which establish the menstrual cycle and maintain pregnancy.

Hormonal Control of Appetite

• Leptin suppresses appetite.
• Ghrelin increases appetite.

Hormonal Disturbances

• Hyposecretion is too little hormone, while hypersecretion is too much hormone.
• The body regulates hormones through negative feedback loops
• Note the gland that isn't responding “as it should”
• Determine whether the gland is hyposecreting or hypersecreting
• Follow the arrows in the loop step by step to determine how other hormone levels would be impacted.