Endocrine System Quiz

Endocrine System Overview

• The endocrine system is a complex network of glands and organs that secrete hormones into the bloodstream to regulate various bodily functions.
• These functions include metabolism, growth, development, mood, sexual function, and homeostasis.
• Unlike the nervous system, which uses electrical signals to communicate quickly, the endocrine system uses chemical signals (hormones) to communicate more slowly over longer durations.

Components of the Endocrine System

• Endocrine Glands: Specialized organs that secrete hormones directly into the bloodstream.
• Hormones: Chemical messengers produced by glands that regulate specific functions.
• Target Organs/Cells: Organs or cells that are affected by specific hormones.
• Feedback Mechanisms: Processes that regulate hormone production and secretion.

Hypothalamus

• Location: Small region of the brain just below the thalamus.

• Function: The hypothalamus is responsible for maintaining the body's internal balance (homeostasis) and regulating the endocrine system by controlling the release of hormones.

• Regulates: • Endocrine regulation by producing releasing and inhibiting hormones that control the pituitary gland. • Thirst and water intake • Hunger and food intake • Autonomic nervous system regulation • Biological circadian rhythm • Body temperature • Blood pressure • Breastfeeding • Learning and memory • Emotional expression • Sexual drive

Hormones Regulating the Anterior Pituitary

• Releasing Hormones (e.g., TRH, GnRH): Stimulate hormone release. • Thyrotropin-releasing hormone (TRH): Stimulates TSH release. • Corticotropin-releasing hormone (CRH): Stimulates ACTH release. • Gonadotropin-releasing hormone (GnRH): Stimulates LH and FSH release. • Growth hormone-releasing hormone (GHRH): Stimulates GH release.

• Inhibiting Hormones (e.g., Somatostatin): Inhibit hormone release. • Somatostatin: Inhibits growth hormone (GH) and thyroid-stimulating hormone (TSH). • Dopamine: Inhibits the release of Prolactin.

Hormones Released to the Posterior Pituitary

• Oxytocin: Stimulates uterine contractions during childbirth, triggers milk ejection during breastfeeding, plays a role in bonding and trust.
• Antidiuretic Hormone (ADH, Vasopressin): Promotes water reabsorption in the kidneys to regulate water balance, and constricts blood vessels, helping maintain blood pressure.

Hypothalamus Disorders

• Kallmann Syndrome: Rare genetic disorder affecting hypothalamus development, often associated with anosmia (absence of smell) and delayed or absent puberty.
• Prader-Willi Syndrome: Genetic condition characterized by hypotonia in infancy, developmental delay, and an insatiable appetite leading to obesity in adulthood.
• SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion): Excess ADH release, leading to water retention, low blood sodium, and swelling.
• DI (Diabetes Insipidus): Insufficient ADH production leading to excessive urination and extreme thirst.
• Other Disorders: Hypopituitarism (insufficient pituitary hormone secretion), obesity, eating disorders, and sleep disturbances.

Pineal Gland

• A small, pea-shaped endocrine gland located in the brain, playing a vital role in regulating biological rhythms, particularly the sleep-wake cycle, by secreting the hormone melatonin.

Thyroid Gland

• A butterfly-shaped endocrine gland located in the neck below the larynx (voice box) and in front of the trachea.
• Function: Regulates metabolism, growth, development, temperature regulation, and calcium homeostasis. • Has two lobes and an isthmus (connecting band) • Two main cell types: Follicular cells (produce T3 and T4) and parafollicular cells (produce calcitonin).

Thyroid Hormones (T3 and T4)

• Regulate metabolism, energy production, and protein synthesis.
• T3 is more potent than T4 and has similar effects on metabolism, heart rate, and body temperature, influencing development, particularly in the nervous system during fetal and early childhood stages.
• Calcitonin lowers blood calcium levels by inhibiting osteoclast activity (cells that break down bone) and promotes calcium storage in bones.

Regulation of Thyroid Hormone Secretion

The hypothalamic-pituitary-thyroid axis is the primary regulator. This involves the release of TRH from the hypothalamus, which stimulates the pituitary to release TSH, which stimulates the thyroid to produce T3 and T4. Elevated levels of T3 and T4 provide negative feedback, inhibiting further TRH and TSH release.

Thyroid Disorders

• Hypothyroidism: Underactive thyroid, characterized by fatigue, weight gain, cold intolerance, slow heart rate, and depression. Can lead to myxedema in adults or cretinism in children.
• Hyperthyroidism: Overactive thyroid, characterized by weight loss, rapid heartbeat, heat intolerance, nervousness, and bulging eyes (exophthalmos).
• Goiter: Enlarged thyroid gland, often due to iodine deficiency or autoimmune disease.
• Thyroid Nodules/Cancer: Benign or malignant growth within the thyroid gland.

Parathyroid Glands

• Small, pea-shaped endocrine glands located on the posterior surface of the thyroid gland.
• Function: Regulate calcium and phosphorus balance in the blood, with Parathyroid Hormone (PTH) playing a key role.

Parathyroid Hormone (PTH)

• Increases blood calcium levels by acting on bones, kidneys, and the gastrointestinal tract, maintaining normal calcium levels crucial for muscle contraction, nerve conduction, and blood clotting. It also promotes calcium reabsorption and phosphate excretion in the kidneys and indirectly increases calcium absorption through vitamin D.

Parathyroid Disorders

• Hyperparathyroidism: Overproduction of PTH, leading to elevated blood calcium levels (hypercalcemia), weak bones (osteoporosis), kidney stones, fatigue, muscle weakness, and cognitive issues.
• Hypoparathyroidism: Insufficient PTH production, leading to low blood calcium levels (hypocalcemia), muscle cramps, spasms (tetany), tingling sensations, seizures, and heart rhythm abnormalities.
• Pseudohypoparathyroidism: Target tissues are resistant to PTH, resulting in symptoms similar to hypoparathyroidism.

Thymus

• Located in the upper chest, behind the sternum, it is the largest in childhood and begins to shrink after puberty.
• Two lobes.
• Function: T-cell maturation and education; immune system development; and secretion of immune-modulating hormones. • The outer cortex is where pre-T cells migrate, proliferate, and mature. • The inner medulla is where mature T-cells undergo further selection and differentiation.

Thymus Disorders

• Thymic Atrophy: Reduced thymus function, often due to diseases like HIV/AIDS, leading to a weakened immune system.
• DiGeorge Syndrome: Genetic disorder affecting thymus development, leading to an underdeveloped or absent thymus, resulting in severe immunodeficiency due to lack of functional T-cells.
• Thymomas: Tumors of the thymus, which can interfere with T-cell development and lead to autoimmune diseases, such as myasthenia gravis and other autoimmune diseases.

Adrenal Glands

• Two small, triangular endocrine glands located atop each kidney.
• Function: Respond to stress, manage homeostasis, and produce various hormones involved in metabolism, immune response, blood pressure regulation, and other functions. • Made of two zones: a superficial cortex and a core medulla. • The cortex is organized into three zones—glomerulosa, fasciculata, and reticularis—producing different hormones. • The medulla produces adrenaline and noradrenaline for the stress response.

Adrenal Hormones

• Glucocorticoids (cortisol): Regulate metabolism, stress response, and immunity. Produced by Zona Fasciculata
• Mineralsocorticoids (aldosterone): Regulate sodium, potassium, and water balance. Produced by Zona Glomerulosa.
• Androgens (e.g., dehydroepiandrosterone–DHEA): Minor role in sexual development and reproduction. Produced by Zona Reticularis.
• Catecholamines (e.g., adrenaline/epinephrine and noradrenaline/norepinephrine): Acute stress response. Produced by the medulla.

Adrenal Disorders

• Cushing's Syndrome: Excess cortisol production. Symptoms include weight gain, round face, high blood pressure, and weak bones.
• Hyperaldosteronism: Excess aldosterone production. Symptoms include high blood pressure and low potassium levels.
• Pheochromocytoma: Tumor of the adrenal medulla causing excess adrenaline and noradrenaline. Symptoms include severe hypertension, palpitations, and anxiety.
• Addison's Disease: Insufficient cortisol and aldosterone production, causing fatigue, weight loss, low blood pressure, and darkening of the skin.
• Adrenal Crisis: Acute, life-threatening insufficiency of adrenal hormones.

Pancreas

• A vital glandular organ located behind the stomach, with both endocrine and exocrine functions. It is important for maintaining digestion and glucose regulation. • Composed of exocrine acinar cells (produce digestive enzymes) and endocrine islets of Langerhans cell (produce hormones).

Pancreas Hormones

• Insulin: Lowers blood glucose levels, promoting energy storage.
• Glucagon: Raises blood glucose levels, promoting energy release.
• Somatostatin: Inhibits insulin, glucagon, and digestive functions.
• Pancreatic Polypeptide: Regulates digestive enzyme and bile secretion.
• Ghrelin: Stimulates appetite and energy intake.

Pancreas Disorders

• Diabetes Mellitus: Insufficient or ineffective insulin action, leading to high blood glucose (hyperglycemia). Can be type 1 autoimmune and type 2.
• Hypoglycemia: Excess insulin production, leading to low blood glucose (hypoglycemia).
• Pancreatitis: Inflammation of the pancreas, often due to digestive enzyme activation within the pancreas, which can be acute or chronic.
• Pancreatic Cancer: Affects endocrine or exocrine cells, often aggressive and difficult to diagnose early.
• Hyperinsulinism: Excess insulin secretion, leading to recurrent hypoglycemia.

Gonads

• General: Ovaries (in females) and testes (in males) are essential components of the endocrine system. They serve dual roles as endocrine glands and reproductive organs, producing sex hormones that regulate sexual development, reproductive functions, and secondary sexual characteristics.
• Males (Testes): • Location: In the scrotum. • Function: Produce sperm cells (spermatogenesis) and secrete testosterone and smaller amounts of other androgens under hypothalamic-pituitary-gonadal (HPG) axis regulation.
• Females (Ovaries): • Location: In the pelvic cavity. • Function: Produce eggs (ova) through oogenesis and secrete estrogen and progesterone under the HPG regulation.

Gonads Hormonal Regulation

• The hypothalamic-pituitary-gonadal (HPG) axis regulates gonadal hormones. This involves the hypothalamus releasing GnRH, which stimulates the pituitary to release FSH and LH. • In males: LH stimulates Leydig cells to produce testosterone, and FSH supports spermatogenesis. • In females: LH triggers ovulation and progesterone production; FSH promotes follicular growth and estrogen synthesis. Negative feedback mechanisms regulate the HPG axis.

Gonadal Disorders

• Hypogonadism: Insufficient sex hormone production due to primary (testis/ovary failure) or secondary (HPG axis dysfunction) causes. • Males: Klinefelter syndrome, testicular injury, varicocele, undescended testes. • Females: Premature ovarian insufficiency.

• Polycystic ovary syndrome (PCOS): Common endocrine disorder characterized by irregular menstrual cycles, elevated androgen levels, and ovarian cysts.

• Congenital adrenal hyperplasia (CAH): Genetic condition affecting adrenal glands, leading to imbalances in sex hormones.

• Other issues: Anovulation, Endometriosis, Gonadal Dysgenesis, Klinefelter syndrome, and Turner syndrome.

Hormonal Feedback Mechanisms

• Negative Feedback: A hormone’s action reduces its own production. An example is thyroid hormone regulating its own production through feedback to the hypothalamus and pituitary. Negative feedback mechanisms are more common and maintain homeostasis by preventing overproduction of hormones. 

• Positive Feedback: Increases its own stimulus for production. An example is oxytocin release during childbirth, where uterine contractions stimulate further oxytocin release until delivery. Positive feedback is less common but crucial in situations needing rapid and amplified responses.