Endocrine System Flashcards

Endocrine vs. Exocrine

• Endocrine Glands

  • Ductless glands that secrete hormones directly into the bloodstream.

  • Hormones are secreted into the blood and act as chemical messengers produced by the gland.

  • Richly supplied with capillaries for hormone entry into the bloodstream.

  • Examples include the pituitary gland, thyroid gland, adrenal glands, and parts of the pancreas and ovaries/testes

  • Hormones travel throughout the body to reach target cells that possess specific receptors, ensuring that only the cells meant to respond do so.

• Exocrine Glands

  •     Secrete their products into ducts that lead to the external     environment, rather than directly into the bloodstream.     Examples include sweat glands, salivary glands, and glands     in the gastrointestinal tract.

    • Possess ducts through which chemical secretions are transported to specific locations, such as the skin surface or digestive tract.

    • Examples include sweat glands, salivary glands, mammary glands, and digestive glands in the stomach and intestines.

Terminology

• Hormones: Organic chemical substances secreted by an endocrine gland, transported in the bloodstream to a target organ to regulate metabolic reactions.

  • Divided into two main classes: amino acid-based hormones (proteins and peptides) and steroid hormones (derived from cholesterol).

  • Amino acid-based hormones usually bind to receptors on the cell membrane, activating a signaling cascade inside the cell.

  • Steroid hormones can pass through the cell membrane and bind to receptors inside the cell, often affecting gene expression directly.

• Target Organ: Cells that respond to a hormone with receptor sites.

  • Target cells have specific receptors that match the hormone's structure, ensuring a specific response.

  • The number of receptors on a target cell can change, affecting sensitivity to a hormone.

• Endocrine Gland: Vascular, ductless gland that secretes hormones directly into the bloodstream.

  • Highly vascularized to ensure hormones can quickly enter the circulation.

  • Hormone secretion is often regulated by feedback loops to maintain homeostasis.

Endocrine System - Male & Female

• Key Glands and Organs:

  • Pineal gland: Secretes melatonin, which regulates sleep-wake cycles.

  • Hypothalamus: Controls the pituitary gland and regulates body temperature, hunger, and thirst.

  • Pituitary Gland: Often referred to as the \"Master Gland,\" it controls other endocrine glands.

  • Thyroid: Produces hormones that regulate metabolism.

  • Parathyroid: Regulates calcium levels in the blood.

  • Thymus: Important for immune function, especially during childhood.

  • Adrenal Cortex: Produces hormones like cortisol and aldosterone.

  • Kidney: Produces erythropoietin, which stimulates red blood cell production.

  • Pancreas: Secretes insulin and glucagon to regulate blood sugar levels.

  • Testes (Male): Produce testosterone, which is crucial for male sexual development and function.

  • Ovary (Female): Produces estrogen and progesterone, essential for female sexual development, menstruation, and pregnancy.

  • Uterus (Female): Supports fetal development during pregnancy.

• Each gland and organ plays a vital role in maintaining hormonal balance, affecting various bodily functions.

Pituitary Gland

• Often referred to as the "Master Gland."

• Size of a pea and located at the base of the brain within the sella turcica.

• Connected to the hypothalamus by the pituitary stalk.

• Posterior Lobe:

  • Stores and secretes hormones produced by the hypothalamus: ADH (Anti-Diuretic Hormone) and oxytocin.

  • Secretes ADH (Anti-Diuretic Hormone).

    • Also known as vasopressin, regulates water balance by increasing water reabsorption in the kidneys.

    • Deficiency can cause diabetes insipidus, characterized by excessive thirst and urination.

  • Secretes Oxytocin.

    • Stimulates uterine contractions during childbirth and milk ejection during breastfeeding.

    • Also involved in social bonding and trust.

• Anterior Lobe:

  • Produces and secretes several key hormones, each affecting different target organs.

  • Secretes GH (Growth Hormone).

    • Promotes growth and development of bones and muscles.

    • Stimulates protein synthesis and fat breakdown.

    • Regulated by growth hormone-releasing hormone (GHRH) and somatostatin.

  • Secretes TSH (Thyroid Stimulating Hormone).

    • Stimulates the thyroid gland to produce thyroxine (T4) and triiodothyronine (T3).

    • These hormones regulate metabolism, body temperature, and energy levels.

    • Controlled by thyrotropin-releasing hormone (TRH) from the hypothalamus.

  • Secretes FSH (Follicle-Stimulating Hormone).

    • In females, promotes follicle development in the ovaries; in males, stimulates sperm production.

    • Essential for reproductive function in both sexes.

  • Secretes LH (Luteinizing Hormone).

    • In females, triggers ovulation and formation of the corpus luteum; in males, stimulates testosterone production.

    • Works in conjunction with FSH to regulate the menstrual cycle and spermatogenesis.

  • Secretes Prolactin.

    • Stimulates milk production in mammary glands after childbirth.

    • Can be affected by certain medications and medical conditions.

• The pituitary gland's function is critical for overall endocrine regulation.

Disorders

• Hyper-: Indicates over-secretion of a hormone.

  • Can be caused by tumors or autoimmune disorders, leading to excessive hormone levels and related symptoms.

• Hypo-: Indicates under-secretion of a hormone.

  • Can be caused by gland damage, genetic factors, or other medical conditions, leading to hormone deficiencies and related symptoms.

• Growth Hormone (GH) Disorders:

  • Gigantism: Excessive growth due to over-secretion of GH.

    • Typically begins in childhood or adolescence, leading to significantly increased height and bone growth.

  • Dwarfism: Stunted growth due to under-secretion of GH.

    • Can be treated with GH injections if diagnosed early, improving growth and development.

  • Acromegaly: Abnormal growth of hands, feet, and face, caused by over-secretion of GH in adults.

    • Often associated with a pituitary tumor, leading to gradual changes in physical appearance and potential health complications.

• Thyroid Gland & Thyroxin Disorders

  • Hyperthyroidism: Overactive thyroid, excessive thyroxin secretion.

    • Symptoms include weight loss, increased heart rate, anxiety, and heat intolerance.

  • Hypothyroidism: Underactive thyroid, insufficient thyroxin secretion.

    • Symptoms include weight gain, fatigue, depression, and cold intolerance.

  • Myxoedema: Type of hypothyroidism in adults

    • Characterized by swelling of the skin and tissues, along with other symptoms like lethargy and cognitive impairment.

  • Cretinism: Congenital hypothyroidism.

    • Can lead to developmental delays if not treated early; early diagnosis and treatment are critical for normal development.

• Pancreas

  • Functions as both an endocrine and exocrine gland.

  • Alpha cells secrete Glucagon.

    • Raises blood glucose levels by stimulating the liver to break down glycogen into glucose.

  • Beta cells secrete Insulin.

    • Lowers blood glucose levels by facilitating glucose uptake into cells and converting glucose into glycogen in the liver.

  • Diabetes: A disorder related to the pancreas, specifically with insulin production or utilization.

    • Type 1: Insulin-dependent, typically diagnosed in childhood; the body does not produce insulin.

    • Type 2: Insulin resistance, often associated with obesity and lifestyle factors; the body does not respond effectively to insulin.

• Understanding these disorders is crucial for proper diagnosis and management.

Adrenal Gland

• Located on top of the kidneys

• Consists of two main parts: the adrenal cortex and the adrenal medulla.

• Secretes:

  • Adrenalin (Epinephrine).

    • Involved in the "fight or flight" response, increasing heart rate, blood pressure, and energy levels during stress.

  • Aldosterone.

    • Regulates sodium and potassium levels, helping to maintain fluid balance and blood pressure.

• Cortisol: Regulates metabolism, immune response, and stress response.

Ovaries

• Responsible for producing Estrogen and Progesterone.

• Estrogen

  • Steroid hormone important in the reproductive development of females.

  • Produced by the growing Grafian follicle in the ovaries.

  • Secreted by ovaries prior to ovulation; also produced by the placenta during pregnancy.

  • Secretion is regulated by FSH, which stimulates follicle growth and estrogen production.

  • Involved in the formation and maintenance of secondary sex characteristics; also important in bone resorption and cardiovascular health.

  • Involved in the enlargement of the uterus and breasts during pregnancy, preparing the body for childbirth and lactation.

• Progesterone

  • Steroid hormone that prepares the uterus for pregnancy and supports the early stages of pregnancy.

  • Produced by the corpus luteum after ovulation.

  • Secreted by the ovaries after ovulation; also produced by the placenta during pregnancy.

  • Secretion is regulated by LH, which stimulates the formation and maintenance of the corpus luteum.

  • Involved in the formation and maintenance of endometrium and uterus, creating a suitable environment for implantation and fetal development.

  • Involved in the reduction of contractility of the uterus and stimulates the growth of mammary glands, ensuring the uterus remains relaxed and the breasts develop for milk production.

• Menstruation Cycle:

  • Phases include follicular phase, ovulation, and luteal phase, each associated with varying levels of estrogen and progesterone.

  • Hormonal fluctuations throughout the cycle regulate endometrial changes, preparing the uterus for potential pregnancy.

• The interplay between estrogen and progesterone is essential for female reproductive health.

Testes

• Produces Testosterone, the primary male sex hormone.

• Negative Feedback Loop: Regulates Testosterone Production

  • Stimulus: Testosterone levels get too low.

  • Hypothalamus: Releases gonadotropin releasing hormone (GnRH), which stimulates the pituitary gland.

  • Pituitary gland: Releases Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH), which act on the testes.

  • Testes: Stimulated by LH and FSH to produce testosterone and Inhibin B.

  • Increased levels of testosterone and inhibin B in the blood: Negative feedback to hypothalamus and pituitary to stop GnRH, LH, and FSH release, maintaining hormonal balance.

• Testosterone is crucial for the development and maintenance of male secondary sex characteristics and muscle mass.

Homeostasis

• All body cells are surrounded by fluids, such as interstitial fluid and plasma.

• The composition of these fluids changes constantly, influencing cell function; maintaining a stable internal environment is critical for cell survival.

• Maintaining a constant internal environment in the body irrespective of the external environment; this dynamic equilibrium ensures optimal conditions for cellular function.

• Conditions that must be kept constant for optimal functioning:

  • Glucose levels: Essential for energy production.

  • Water content: Necessary for cellular processes and hydration.

  • Salt concentration: Crucial for nerve function and fluid balance.

  • O2 and CO2 concentrations: Necessary for respiration and pH balance.

  • Body temperature: Important for enzyme function and metabolic rate.

  • Metabolic waste: Removal prevents toxicity and maintains cell health.

  • pH: Essential for enzyme activity and cellular function.

• Negative Feedback Mechanism (NFM)

  • Mechanisms are in place to bring any deviations back to normal, ensuring conditions stay within optimal ranges.

  • NFM are responsible for maintaining homeostasis; they are essential for survival.

  • When a deviation is detected, it results in a reaction that counters the change to return to normal; this corrective response helps to stabilize the internal environment.

  • Once it is back to normal, the corrective measure is switched off, preventing overcorrection.

  • Components: Receptor (sensor), Control Center, Effector.

  • Stimulus $\rightarrow$ Change Detected $\rightarrow$ Information Sent to Control Center $\rightarrow$ Information Sent to Effector $\rightarrow$ Response to Return to Homeostasis

• The NFM is a fundamental process in maintaining physiological stability.

Blood Glucose Levels

• When blood sugar is too high:

  • Beta cells detect the raised glucose levels, releasing insulin.

  • Insulin goes to liver and muscles, promoting glucose uptake.

  • Glucose is converted to glycogen and stored in the liver and muscles.

  • Cell membranes become more permeable to glucose, facilitating glucose entry into cells.

  • Glucose levels are reduced, restoring normal blood sugar levels.

• When blood glucose level is too low:

  • Alpha cells detect the decreased glucose levels, releasing glucagon.

  • Glucagon goes to liver, stimulating glycogen breakdown.

  • Glycogen is broken down into glucose, releasing glucose into the bloodstream.

  • Glucose levels are increased, restoring normal blood sugar levels.

• Maintaining proper blood glucose levels is vital for energy balance and preventing complications such as diabetes.

Male Reproductive Hormones

• When testosterone is too low:

  • The pituitary gland will be stimulated to release more FSH and LH.

  • More testosterone will be released by the testes.

  • This causes spermatogenesis to occur, increasing sperm production.

  • More sperm is being produced, ensuring