Endocrine Glands: Study Notes

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Endocrine Glands:

The human endocrine system is a complex network of glands and hormones that regulate various physiological processes. The glands secrete hormones directly into the bloodstream, which travel to target organs and tissues to regulate bodily functions such as metabolism, growth, and reproduction. Here is an overview of the major endocrine glands, their hormones, and their functions:

1. Hypothalamus

• Hormones: The hypothalamus is responsible for releasing hormones that regulate the pituitary gland.
• Actions: It releases hormones that influence the posterior pituitary, as well as hormones that control the anterior pituitary gland.
• Regulated by: The hypothalamus itself does not have a direct regulating factor but is influenced by various internal body conditions.

2. Pituitary Gland

• The pituitary gland, often referred to as the "master gland," controls other endocrine glands and regulates vital body functions.
• Posterior Lobe (releases hormones made by the hypothalamus):
  • Oxytocin: A peptide hormone that stimulates uterine contractions during childbirth and milk ejection in breastfeeding.
  • Antidiuretic hormone (ADH): Also known as vasopressin, this peptide hormone promotes water retention by the kidneys, helping to regulate water balance in the body.
• Anterior Lobe:
  • Growth hormone (GH): A protein hormone that stimulates growth, particularly of bones, and regulates various metabolic processes.
  • Prolactin (PRL): Stimulates milk production in mammary glands after childbirth.
  • Follicle-stimulating hormone (FSH): A protein hormone that stimulates the production of ova in females and sperm in males.
  • Luteinizing hormone (LH): Works alongside FSH to regulate the reproductive system, triggering ovulation in females and testosterone production in males.
  • Thyroid-stimulating hormone (TSH): Stimulates the thyroid gland to produce thyroid hormones (T3 and T4).
  • Adrenocorticotropic hormone (ACTH): Stimulates the adrenal cortex to secrete glucocorticoids, which help regulate metabolism and stress responses.

3. Pineal Gland

• Hormone: Melatonin
• Action: Melatonin plays a crucial role in regulating circadian rhythms, such as the sleep-wake cycle. It is produced in response to light/dark cycles.

4. Thyroid Gland

• Hormones: Thyroxine (T₄) and Triiodothyronine (T₃), Calcitonin
• Actions: Thyroid hormones regulate metabolism, growth, and development. Calcitonin helps lower blood calcium levels by inhibiting the release of calcium from bones.
• Regulated by: TSH from the anterior pituitary gland.

5. Parathyroid Glands

• Hormone: Parathyroid hormone (PTH)
• Action: PTH raises blood calcium levels by promoting the release of calcium from bones and increasing calcium reabsorption in the kidneys.
• Regulated by: Calcium levels in the blood.

6. Thymus

• Hormone: Thymosin
• Action: Thymosin is essential for the development and differentiation of T-cells, which are crucial for immune responses.

7. Adrenal Glands

• The adrenal glands consist of two parts: the adrenal medulla and the adrenal cortex.
• Adrenal Medulla:
  • Hormones: Epinephrine (adrenaline) and Norepinephrine (noradrenaline)
  • Actions: These hormones increase blood glucose levels, enhance metabolic activity, and constrict certain blood vessels in response to stress (fight-or-flight response).
• Adrenal Cortex:
  • Hormones: Glucocorticoids (e.g., cortisol), Mineralocorticoids (e.g., aldosterone), Androgens
  • Actions: Glucocorticoids increase blood glucose, especially during stress. Mineralocorticoids regulate sodium and potassium balance. Androgens contribute to the development of secondary male sexual characteristics in both males and females.

8. Pancreas

• Hormones: Insulin and Glucagon
• Actions: Insulin lowers blood glucose levels by facilitating its uptake into cells, while glucagon raises blood glucose levels by stimulating the release of glucose from the liver.

9. Testes

• Hormones: Androgens (primarily testosterone)
• Actions: Androgens support sperm production and the development and maintenance of male secondary sexual characteristics such as facial hair and deep voice.
• Regulated by: FSH and LH from the anterior pituitary.

10. Ovaries

• Hormones: Estrogens and Progesterone
• Actions: Estrogens stimulate the growth of the uterine lining and the development of female secondary sexual characteristics. Progesterone supports pregnancy by promoting the growth of the uterine lining.
• Regulated by: FSH and LH from the anterior pituitary.

11. Other Hormone-Producing Cells

• Stomach and Intestine: Secrete hormones such as secretin, gastrin, and cholecystokinin, which are involved in digestion and appetite regulation.
• Kidneys: Produce erythropoietin, which stimulates the production of red blood cells in response to low oxygen levels in the blood.
• Heart (Atria): Release atrial natriuretic peptide (ANP) in response to increased blood volume, promoting salt and water excretion to reduce blood pressure.

Disorders of the Endocrine System

The endocrine system, which regulates various vital functions in the body through hormones, can be affected by various disorders. These conditions often arise from either overproduction or underproduction of specific hormones. Below is a list of common endocrine disorders, their descriptions, and signs and symptoms:

Pituitary Gland Disorders

• Gigantism: This condition occurs due to the overproduction of growth hormone (GH) during childhood or adolescence, leading to excessive growth and extraordinary height.
  • Signs and Symptoms: Continued abnormal growth, particularly in height, beyond the normal growth limit.
• Acromegaly: Hypersecretion of growth hormone in adults causes abnormal growth of bones and tissues. It is often characterized by the enlargement of hands and feet, thickened skin, and changes to facial features.
  • Signs and Symptoms: Enlarged hands and feet, abnormal broadening of the jaw, enlarged bony ridges above the eyes.
• Dwarfism: This condition occurs when there is underproduction of growth hormone during childhood, resulting in stunted growth and short stature.
  • Signs and Symptoms: Short stature, delayed growth, possible developmental delays.

Thyroid Gland Disorders

• Hypothyroidism: Insufficient secretion of thyroid hormones (T3 and T4) leads to a slowing down of metabolic processes.
  • Signs and Symptoms: Symptoms include fatigue, weight gain, cold intolerance, dry skin, and hair loss.
• Cretinism: A condition caused by the insufficient secretion of thyroid hormones in childhood, leading to stunted growth and developmental delays.
  • Signs and Symptoms: Stunted growth, mental retardation, coarse facial features, delayed physical development.
• Myxedema: Caused by hypothyroidism in adults, this condition results in a sluggish metabolic rate and other related symptoms.
  • Signs and Symptoms: Weight gain, sluggish appearance, cold intolerance, dry skin, hair loss, confusion, and depression.
• Hyperthyroidism: An overproduction of thyroid hormones, often due to conditions like Graves' disease, leads to an overactive metabolic state.
  • Signs and Symptoms: Restlessness, insomnia, high heart rate, irritability, bulging eyes (exophthalmos), weight loss, and heat intolerance.
• Goiter: Enlargement of the thyroid gland due to iodine deficiency, which disrupts the production of thyroid hormones.
  • Signs and Symptoms: Swelling in the neck (goiter), difficulty swallowing or breathing, visible enlargement of the thyroid.

Abnormal Insulin Output

• Diabetes Mellitus: This disorder occurs when there is insufficient insulin production or improper insulin action, leading to persistently high blood glucose levels.
  • Signs and Symptoms: Increased blood glucose, glycosuria (glucose in urine), polyuria (frequent urination), polydipsia (excessive thirst), weight loss, and accumulation of ketone bodies.
• Type-I Diabetes Mellitus / Insulin-Dependent Diabetes Mellitus (IDDM): An autoimmune disorder where the body's immune system attacks and destroys insulin-producing beta cells in the pancreas, resulting in a lack of insulin. It is typically diagnosed in children and young adults.
  • Signs and Symptoms: Similar to those of diabetes mellitus, including frequent urination, excessive thirst, and weight loss.
• Type-II Diabetes Mellitus / Non-Insulin-Dependent Diabetes Mellitus (NIDDM): This form of diabetes is characterized by decreased insulin production or insulin resistance, usually occurring after the age of 40 and becoming more prevalent with age.
  • Signs and Symptoms: Increased blood glucose, fatigue, slow healing of wounds, and increased risk of infections.

Adrenal Cortex Disorders

• Cushing’s Syndrome: This condition occurs when there is an overproduction of cortisol by the adrenal cortex, often due to tumors or prolonged use of corticosteroid medications.
  • Signs and Symptoms: Obesity (especially around the face and abdomen), "moon face" appearance, high blood glucose, muscle wasting, and hypertension.
• Addison’s Disease: A disorder caused by the insufficient production of cortisol and other adrenal cortex hormones, often due to autoimmune destruction of the adrenal glands.
  • Signs and Symptoms: Low blood glucose, low blood pressure, weight loss, weakness, and fatigue.

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