Endocrine System Essentials: Glands, Hormones, and Body Regulation

Understanding the Endocrine System: Glands, Hormones, and Functions

Exocrine vs. Endocrine Glands

Exocrine glands have ducts that secrete substances such as mucus, saliva, cerumen, sebaceous oils, and sweat.

Endocrine glands produce hormones (chemical messengers) and secrete them directly into the bloodstream.

The Pituitary Gland: Master Regulator of Hormones

The pituitary gland (hypophysis), often called the "master gland," primarily functions to secrete vital hormones into the bloodstream.

Key Pituitary Hormones and Their Functions

• ACTH (Adrenocorticotropic hormone or corticotropin): Stimulates the release of steroid hormones by the adrenal cortex.
• TSH (Thyroid-stimulating hormone or thyrotropin): Targets the thyroid gland and triggers the release of thyroid hormones.
• GH (Growth hormone or somatotropin): Stimulates cell growth and division by accelerating the rate of protein synthesis.
• PRL (Prolactin): Helps to stimulate mammary gland development in females.
• FSH (Follicle-stimulating hormone): Promotes follicle development in females and, in combination with luteinizing hormone, stimulates the secretion of estrogens by ovarian cells.
• LH (Luteinizing hormone): Induces ovulation, the release of a reproductive cell in females.
• MSH (Melanocyte-stimulating hormone): Stimulates melanocytes in the skin, increasing their production of melanin (a brown, black, or yellow-brown pigment). Dopamine inhibits MSH release.
• Antidiuretic hormone (ADH), also known as vasopressin (VP): Released in response to stimuli such as an increase in blood solute concentration or a decrease in blood volume or blood pressure.
• Oxytocin (OXT): Stimulates smooth muscle contraction in the uterine wall, promoting labor and delivery.

Blood Glucose Regulation: Insulin and Glucagon

Rise in blood glucose levels: Beta cells secrete insulin, which stimulates the transport of glucose across the plasma membrane into target cells.

Drop in blood glucose levels: Alpha cells secrete glucagon, which stimulates glycogen breakdown and glucose release by the liver.

Managing Blood Sugar Imbalances

• Symptoms of excessive insulin (hypoglycemia): Sweating, disorientation, and excessive shaking.
• Treatment: Administer glucagon to raise blood sugar levels.

Classification of Hormones by Chemical Structure

Amino Acid Derivatives

• Derivatives of Tyrosine: Thyroid hormones (T3, T4), Catecholamines (epinephrine and norepinephrine).
• Derivatives of Tryptophan: Dopamine, Serotonin, Melatonin (a hormone that aids sleep).

Peptide Hormones

Peptide hormones are chains of amino acids.

• Glycoproteins: Proteins composed of more than 200 amino acids.
  • Examples: Thyroid-stimulating hormone (TSH), Luteinizing hormone (LH), Follicle-stimulating hormone (FSH).
• Target Organs: Thyroid and reproductive organs.

Lipid Derivatives

Lipid derivatives are fat-derived hormones.

• Eicosanoids: Paracrine factors that coordinate cellular activities and affect enzymatic processes (e.g., blood clotting).
• Steroid Hormones: Derived from cholesterol.
  • Released by:
    • Reproductive organs (e.g., androgens from testes in males; estrogen and progestin from ovaries).
    • Adrenal Gland Cortex (corticosteroids).
    • Kidneys (calcitriol).