Endocrine System Quiz

Endocrine System Overview

• Homeostasis is regulated by two systems: nervous and endocrine.
• Endocrine and nervous systems share features: release chemicals that bind to specific receptors, share some chemical messengers (e.g., norepinephrine, epinephrine), regulate activity by negative feedback, and have a common goal of homeostasis.
• Hormones control several major body processes including reproduction, growth and development, maintaining electrolyte, water, and nutrient balance of the blood, regulating cellular metabolism and energy balance, mobilizing body defenses, and maintaining homeostasis.

Hormone Overview

• Hormones are produced by specialized cells.
• Cells secrete hormones into extracellular fluids.
• Blood transfers hormones to target sites.
• Hormones regulate the activity of other cells.
• Target cells must have specific protein receptors for hormones to act on them; ensuring that only specific hormones affect a particular target cell/organ.
• Hormone-binding alters cellular activity.
• Effects caused by hormones include changes in plasma membrane permeability or electrical state, synthesis of proteins (e.g., enzymes), activation or inactivation of enzymes, stimulation of mitosis, and promotion of secretory activity.

Organs of the Endocrine System

• Organs or glands of the endocrine system are small and not often talked about.
• Located throughout the body, producing and secreting hormones.
• Ductless; hormones are secreted directly into the blood.
• Hormones circulate to all organs of the body but affect only certain cells (target cells or target organs).
• Each target cell has a specific protein receptor on the cell membrane or inside the nucleus.

Chemistry of Hormones

• Hormones are classified chemically as either amino acid-based (non-lipid soluble) or lipid-based (lipid soluble).
• Amino acid-based hormones include proteins, peptides, and amines.
• Lipid-based hormones are made from cholesterol and include sex hormones, corticosteroids, and prostaglandins.
• Two mechanisms in which hormones act: second-messenger system (for amino acid-based hormones) and direct gene activation (for lipid-based hormones).

Hormone Mechanisms

• Hormone binds to a receptor in the target cell membrane, activates an enzyme.
• The activated enzyme produces a 2nd messenger.
• The 2nd messenger causes intercellular changes.
• Hormone enters directly into the cell into the nucleus, binds to a receptor protein.
• The complex binds to the cell's DNA, resulting in formation of mRNA.

Hypothalamus

• The hypothalamus is not considered a gland; it is the major controller of the pituitary gland.
• It integrates activities of nervous and endocrine systems through three mechanisms: synthesis and transport of two hormones to posterior pituitary, secretion of regulatory hormones to anterior pituitary, and autonomic centers.

Hypothalamic Regulatory Hormones

• Hypothalamic regulatory hormones either stimulate or inhibit the secretion of pituitary hormones. (Diagram shows these stimulating and inhibiting hormones).

Autonomic Centers

• Exert direct neural control over endocrine cells (in adrenal medulla).
• Active when the sympathetic division is stimulated.
• Adrenal medulla responds by releasing epinephrine and norepinephrine.

Pituitary Gland

• Roughly the size of a grape, hangs from the infundibulum of the hypothalamus.
• Controlled by hypothalamus.
• Called the master gland because it controls activity of so many endocrine glands.
• Has two functional lobes: anterior and posterior.
• Anterior pituitary is glandular tissue.
• Posterior pituitary is nervous tissue.

Hormones of the Posterior Pituitary

• 1. Antidiuretic Hormone (ADH)
  • Released in reaction to low blood volume or decreased blood pressure, rise in solute concentration.
  • Purpose is to conserve water and prevent urine production to prevent dehydration (targeting the kidneys).
  • In large amounts, causes vasoconstriction and increased blood pressure.
• 2. Oxytocin (OXT)
  • Stimulates contractions of the uterus during labor.
  • Causes milk ejection (let-down reflex).
  • Synthetic oxytocin can be used to stimulate labour, control post-partum bleeding, or stimulate milk ejection

Thyroid Gland

• Largest endocrine gland.
• Located on anterior surface of trachea.
• Two lobes connected by a narrow isthmus.
• Produces two hormones: thyroid hormone (T3 and T4) and calcitonin.

Thyroid Hormone

• Inside cell, binds to receptors and increases rate of ATP production or activates specific genes or changes rate of transcription.
• Affects concentration of enzymes and metabolic activities
• Raises metabolic rate; increases heart rate and force of contraction; increases sensitivity to SNS stimulation; maintains sensitivity of respiratory centers; and stimulates RBC formation.
• Necessary for regulating reproductive system.

TH Regulation

• Hypothalmus secretes thyroid releasing hormone (TRH) which stimulates the anterior pituitary, which secretes thyroid stimulating hormone (TSH) and stimulates the thyroid gland to secrete thyroid hormone (TH).
• Negative feedback controls TRH release.

Calcitonin and C Cells

• C cells (also called parafollicular cells) produce calcitonin (CT) which decreases blood calcium levels by targeting bones or kidneys.
• The secretion of calcitonin is controlled by humoral negative feedback (with blood calcium levels).

Parathyroid Glands

• Four parathyroid glands are embedded in the posterior surface of thyroid gland.
• They are shaped like small peas.
• Produce parathyroid hormone (PTH).
• Secreted in response to low blood calcium levels.

PTH Target Organs

• PTH has three target organs: bone, kidney, and intestines.

Calcitonin and PTH Interactions

• Calcitonin and PTH act antagonistically, both controlled by blood calcium levels.
• Calcitonin decreases blood calcium levels.
• PTH increases blood calcium levels.

Adrenal Glands

• Sit on top of the kidneys.
• Two regions:
  • 1. Adrenal cortex (outer): produces mineralocorticoids (i.e. aldosterone), glucocorticoids (i.e. cortisol), and sex hormones.
  • 2. Adrenal medulla (inner): produces epinephrine and norepinephrine.

Hormones of the Adrenal Cortex

• Mineralocorticoids (mainly aldosterone): target organ is the kidney
• Aldosterone reabsorbs Na+ and H₂O and eliminates K+ in urine
• Regulates electrolytes (specifically Na+ and K+)
• Regulates blood volume and blood pressure
• Production stimulated by renin
• Atrial natriuretic peptide (ANP) prevents aldosterone release and performs other functions related to the regulation of blood pressure and volume

Hormones of the Adrenal Cortex

• Glucocorticoids (include cortisone, cortisol) and sex hormones.
• Glucocorticoids convert fats and amino acids to glucose (gluconeogenesis); ensuring a steady supply of glucose for the brain and other cells.
• These hormones assist the body to resist long-term stress by increasing blood glucose levels.
• Cortisol (also known as the stress hormone):
  • Secreted in times of stress
  • Physiological and emotional stress increase the release of cortisol.
  • Has anti-inflammatory effects.
  • Drug form (prednisone): reduces inflammation.

Hormones of the Adrenal Cortex

• 3. Sex hormones: made in inner layer of the adrenal cortex
• Mostly androgens, but some estrogens.
• They are essential for life.

Hormones of the Adrenal Medulla

• Produces two similar hormones (catecholamines): epinephrine and norepinephrine.
• Catecholamines prepare the body for brief or short-term stressful situations.
• Glucocorticoids (cortisol) assist the body with long-term stress.

Pancreas

• Located close to the stomach in upper abdominal cavity.
• Functions as both an endocrine and exocrine gland (digestion of food).
• Consists of pancreatic islets (Islets of Langerhans), located throughout the pancreas and secrete hormones including insulin and glucagon.
• Secretes enzymes needed for digestive processes.

Pancreatic Islets

• Insulin
  • Moves glucose from blood into skeletal muscle, liver and fat cells (adipose tissue)
• Glucagon
  • Allows glucose to enter from the liver and fat cells (adipose tissue)
• Both act as antagonists to regulate blood sugar homeostasis.

Insulin

• Elevated blood glucose levels stimulate beta cells in the islets of Langerhans to secrete insulin.
• Insulin helps transport glucose into various cells, converted for energy or stored as fat.

Diabetes Mellitus

• Due to inability of pancreas to produce insulin (Type I), reduced insulin production (Type II), or resistance of cells to insulin.
• Cells need glucose but obtain energy from fats.
• Without insulin, some cells (i.e. RBCs and neurons) become energy-deficient and die.
• High blood glucose causes glucose to build up in blood, spilling out of blood into urine, followed by the loss of water to keep the body balanced, resulting in frequent urination. This leads to dehydration and thirst.
• Without sufficient glucose, cells lose ability to fight infections, and blood becomes acidic due to fat being used for energy. Uncorrected ketosis can cause coma and death. Symptoms: polyphagia (excessive hunger), polyuria (excessive urination), and polydipsia (excessive thirst).

Glucagon

• Released by alpha cells of the islets
• Aids in regulating blood sugar levels by increasing blood glucose levels, having the opposite effect to insulin.
• Stimulated by low levels of blood glucose (hypoglycemia).
• Target organ is the liver; promotes the conversion of glycogen to glucose in the liver (glycolysis) and stimulates the release of glucose from the liver into the blood, ensuring that cells have enough glucose.

Pineal Gland

• Small, pea-sized gland close to the thalamus.
• Cells produce melatonin, a derivative of serotonin; rate of production controlled by visual pathway - higher at night and lower during the day.
• Main function is to set circadian rhythms (daily changes in physiological processes).

Thymus Gland

• Located posterior to the sternum in the thoracic cavity.
• Largest in infants and children.
• Decreases in size with age.
• Produces thymosin to mature some types of white blood cells and aid in development of the immune system.

Testes and Ovaries

• Testes (Interstitial cells): produce androgens, predominantly testosterone, responsible for adult male secondary sex characteristics, sex drive, growth, and maturation of the reproductive system, and sperm cell production.
• Ovaries: produce two hormones:
  • Estrogen: produced by follicles or placenta; stimulates secondary female characteristics, matures female reproductive organs, and prepares the uterus to receive a fertilized egg, and promotes breast development.
  • Progesterone: produced by the corpus luteum and eventually placenta; helps maintain pregnancy (quiets myometrium), prepares breast tissue for lactation, and acts with estrogen to bring about the menstrual cycle.

Placenta

• Produces hormones that maintain pregnancy, playing a part in the delivery of the baby, including human chorionic gonadotropin (hCG), human placental lactogen (hPL) and relaxin.
• hCG, estrogen, and progesterone maintain pregnancy, hPL prepares the breasts for lactation, and relaxin relaxes pelvic ligaments and pubic symphysis.

Stress Response

• Includes a pattern of hormonal and physiological adjustments (General Adaptation Syndrome, GAS).
• Three phases:
  • 1. Alarm phase: “fight or flight” response, SNS activation, mobilizing energy reserves (primarily glucose), preparing body through “fight or flight” responses with epinephrine and norepinephrine.
  • 2. Resistance phase: if stress is longer than a few hours, glucocorticoids are dominant with help from epinephrine, GH, and thyroid hormone; energy demands are still higher than normal (especially neural tissue) and glycogen reserves are nearly exhausted. The body mobilizes metabolic reserves and shifts away from glucose metabolism.
  • 3. Exhaustion phase: if reserves are depleted, the body enters this phase; mineral imbalances (sodium and potassium) cause neuron and muscle fiber malfunction. Without immediate correction of these imbalances, organ systems fail, causing death.

Endocrine System (Summary)

• The endocrine system functions as a complex network communicating throughout the body to regulate numerous physiological and metabolic processes.
• Hormones play a vital role in these processes and include amino acid based (e.g., proteins, peptides, and amines) and lipid based (e.g., sex hormones, corticosteroids, prostaglandins).
• Hormones are synthesized and released from specific endocrine glands involved directly or indirectly in homeostasis.

Test your knowledge on the functions and hormones of the pituitary gland, thyroid, and adrenal medulla. This quiz covers hormone classification, secretion mechanisms, and effects related to the endocrine system. Perfect for students studying human biology or related fields.