Comprehensive Notes on Endocrine System and Hormones

Glands and Hormones

Location of Glands

• Brain:
  • Hypothalamus
  • Pituitary
  • Pineal gland
• Neck:
  • Thyroid
  • Parathyroids
• Kidneys:
  • Adrenal glands (one on top of each kidney)
• Abdomen:
  • Pancreas (left upper quadrant)
• Reproductive:
  • Ovaries (females)
  • Testes (males)

Endocrine System

• Works closely with the nervous system to control body systems.
• Maintains balance in the body, known as homeostasis. Imbalance leads to sickness.
• Uses chemical messengers called hormones to create changes in the body.
• These hormones are found everywhere from the brain to the lower abdomen.

Endocrine vs. Exocrine

• Endocrine glands: Do not have ducts; secrete hormones into the bloodstream.
• Exocrine glands: Have ducts (e.g., sebaceous glands, sweat glands).
• Hormones travel in the bloodstream to target tissues, where they act on cells.
• Uses negative feedback loops to control hormone production.

Partnership Between Endocrine and Central Nervous System

• The hypothalamus controls hormone release in the anterior pituitary gland.
• Anterior pituitary gland produces six hormones.
• Posterior pituitary gland stores two hormones (oxytocin and ADH) that are synthesized in the hypothalamus, analogous to how bile is synthesized in the liver but stored in the gallbladder.
• The hypothalamus controls when these hormones are released.

Pineal Gland

• Located near the thalamus.
• Functions as the body's biological clock, regulating sleep-wake cycles.
• Produces melatonin: regulates the internal clock and sleep cycles; often taken as an over-the-counter sleep aid.

Anterior Pituitary Gland Hormones

• Six hormones are produced; acronym to remember: "Pro Athletes Got To Grow."
  • Prolactin (PRO): Stimulates the breasts to create milk; think of lactose, the natural sugar in milk.
  • Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal glands to produce their hormones.
  • Gonadotropic Hormones (GOT):
    • Follicle Stimulating Hormone (FSH): Develops the ova and sperm cells.
    • Luteinizing Hormone (LH): In women, initiates ovulation; in men, stimulates testosterone release.
  • Thyroid Stimulating Hormone (TSH): Stimulates the thyroid gland to produce T3 (triiodothyronine) and T4 (tetraiodothyronine).
  • Growth Hormone (GRO): Deals with everyday cellular growth and mitosis, not just height. Essential for bone, head, body, and organ growth.

Precocious Puberty

• Early onset of puberty leading to an early final growth spurt.
• Endocrinologists may intervene to delay puberty and/or provide growth hormone replacement.
• Affected children could experience menstruation as young as six or seven years old.

Posterior Pituitary Gland Hormones

• Two hormones stored, but not synthesized, in the posterior pituitary gland.
  • Antidiuretic Hormone (ADH):
    • Causes the kidneys to reabsorb water in the collecting duct.
    • Aldosterone acts in the distal convoluted tubule, while ADH acts in the collecting duct
    • Increases fluid volume, thereby increasing blood pressure.
  • Oxytocin:
    • Responsible for contractions of the uterus during labor and milk release during breastfeeding.
    • Pitocin is a synthetic version of oxytocin used to stimulate or induce labor.

Thyroid Gland

• Sits below the voice box (larynx), wrapping around the trachea but not completely circular.
• Produces T3 (triiodothyronine) and T4 (tetraiodothyronine).
• Hypothyroidism: Low T3 and T4 levels, often treated with thyroxine replacement.
• T3 and T4: Control metabolic rate and regulate growth and development.

Parathyroid Glands

• Four small glands embedded in the posterior aspect of the thyroid gland.
• Regulate calcium levels between the blood and bones.
• Tell the bones to release calcium into the bloodstream if needed.

Adrenal Glands

• Sit on top of the kidneys (one on each side of the body).
• Hormones are produced in both the adrenal medulla (inside) and the adrenal cortex (outer layer).

Adrenal Medulla

• Fast response team; kicks in during fight or flight situations.

Adrenal Cortex

• Helps control blood pressure, energy use, response to stress, and body growth.
  • Mineralocorticoids (e.g., aldosterone):
    • Salt-saving hormone that causes reabsorption of water in the distal convoluted tubules.
    • Regulates fluid and electrolyte homeostasis by sparing sodium ions.
    • Increases fluid volume, helping to keep blood pressure stable.
  • Glucocorticoids (e.g., cortisol):
    • Helps the body respond to stress and controls how the body uses fats and sugars for energy.
    • Reduces swelling and inflammation.
    • Found in over-the-counter steroid creams like cortisone to relieve itching and redness.
  • Androgens:
    • Found in both males and females.
    • Affect growth and development.
    • Testosterone is an example.

Hormones released by the adrenal medulla:

• Adrenaline (epinephrine): Released in fear, excitement, or danger.
• Increases heart rate and breathing rate.
• Causes the release of sugar for energy during fight or flight response.
• Norepinephrine: Raises blood pressure and increases blood flow to the heart and muscles.
• Anxiety and stress can also trigger the release of adrenaline or norepinephrine.

Pancreas

• Contains special cells called the islets of Langerhans, which include alpha and beta cells.
• These cells produce hormones that regulate blood sugar.

Role of Insulin

• After a meal, blood sugar is elevated.
• Insulin escorts sugar molecules out of the bloodstream into tissues and cells.
• In aerobic cellular respiration: glucose + oxygen \rightarrow ATP + carbon \ dioxide + water + heat
• Approximately 30 ATP are produced per one molecule of glucose.

Role of Glucagon

• Produced in the alpha cells of the islets of Langerhans.
• Regulates blood glucose when it decreases.
• Triggers the liver to convert glycogen to glucose, preventing hypoglycemia (low sugar).
• Insulin helps to prevent hyperglycemia (high sugar).

Clinical Scenario: Hypoglycemia

• A nursing student encounters an unresponsive, diaphoretic, and hypotensive patient in a nursing home.
• The patient's skin is cold and clammy, and their gown is saturated.
• The patient has a PICC line and a blood sugar of 37.
• The nurse administers glucagon and provides orange juice to raise the blood sugar.

Gonads

Testes

• Produce testosterone, the male sex hormone.
• Helps boys grow taller, builds muscle, broadens shoulders, deepens voice, grows facial hair, and is instrumental in sperm production.

Ovaries

• Produce estrogen and progesterone, the female sex hormones.
• Controls menstrual cycle, prepares the body for pregnancy, breast growth, and the widening of hips to accommodate fetal growth.

Other Organ-Specific Hormones

Kidneys

• Produce erythropoietin, which stimulates red blood cell production in the distal ends of the long bones and the bone marrow.
• Red blood cells live for approximately 80-90 days.

Heart

• Produces atrial natriuretic peptide (ANP), which regulates blood pressure and fluid balance.

Placenta

• Produces human chorionic gonadotropin (hCG), which is tested for in pregnancy tests.
• HCG supports the pregnancy.