Seeleys - Anatomy & Physiology (Eleventh Edition) - McGrawHill,

18 Learn to Predict

  • Dylan, a 10-year-old boy, exhibits symptoms indicating a hormonal imbalance, specifically related to insulin regulation, likely pointing to diabetes mellitus.

    • Symptoms include:

      • Constant hunger despite large food intake

      • Rapid weight loss

      • Constant thirst and frequent urination

      • Weakness and lethargy

      • Sweet or acetone-like breath odor

  • Impact of Sugary Foods:

    • Eating candy and drinking sugary sodas can exacerbate Dylan's condition, leading to further dehydration and potential irritability. Excess sugars can also lead to an increase in adipose tissue if Dylan's insulin levels are adequately managed, thus resulting in sudden weight gain.

    • Maintaining a healthy diet is crucial to manage diabetes and avoid spikes in blood glucose.

Overview of the Endocrine System

Key Regulatory Functions:

  1. Regulation of metabolism

  2. Control of food intake and digestion

  3. Tissue maturation and development

  4. Regulation of ion levels

  5. Control of water balance

  6. Regulation of heart rate and blood pressure

  7. Control of blood glucose and nutrient levels

  8. Regulation of reproductive functions and uterine contractions

  9. Modulation of immune functions

18.2 Pituitary Gland and Hypothalamus

Location and Structure

  • The pituitary gland, often termed the master gland, has anterior and posterior lobes, each secreting different hormones.

Functions:

  • Anterior Pituitary:

    • Secretes key hormones regulating growth, metabolism, and reproductive functions including GH, TSH, ACTH, LH, FSH, and PRL.

    • Regulates through releasing (e.g., GHRH, TRH) and inhibiting hormones (e.g., GHIH).

  • Posterior Pituitary:

    • Stores and releases ADH (regulates water balance) and oxytocin (involved in labor and lactation).

18.3 Thyroid Gland

Structure

  • Consists of follicles that store thyroglobulin, which is converted to T3 and T4 hormones regulating metabolism.

  • Calcitonin: Secreted by parafollicular cells in response to increased blood calcium levels, promoting calcium storage in bones.

18.4 Parathyroid Glands

  • Secretes PTH, which increases blood calcium levels by promoting osteoclast activity, kidney reabsorption of calcium, and activation of vitamin D for intestinal absorption.

18.5 Adrenal Glands

Structure

  • Composed of the adrenal cortex (zona glomerulosa, fasciculata, reticularis) and adrenal medulla.

  • **Cortex Hormones:

    • Aldosterone:** Increases sodium reabsorption and potassium excretion in the kidneys.

    • Cortisol: Regulates metabolism, stress response, and immune function.

    • Androgens: Influence secondary sexual characteristics.

Medulla Hormones

  • Epinephrine and Norepinephrine: Key in fight-or-flight response, increasing heart rate, glucose release, and blood flow to muscles.

18.6 Pancreas

  • Contains both exocrine (digestive juices) and endocrine (insulin and glucagon) functions.

Insulin and Glucagon Function

  • Insulin: Lowers blood glucose, promotes uptake in liver, muscle, and adipose tissues.

  • Glucagon: Raises blood glucose levels by promoting glycogen breakdown in the liver.

18.7 Hormonal Regulation of Nutrient Utilization

  • Post-Meal: Insulin secretion is elevated, facilitating nutrient uptake by cells, transitioning to utilization of lipids and proteins over time.

  • During Exercise: Increased glucagon and decreased insulin allow for the mobilization of energy stores.

18.8 Hormones of the Reproductive System

  • Testes: Secrete testosterone, important for sperm production and secondary sexual characteristics.

  • Ovaries: Secrete estrogen and progesterone, regulating the menstrual cycle and maintaining pregnancy.

Aging and Endocrine Function

  • Age-related decline in many hormonal secretions including GH, melatonin, and thyroid hormones. However, parathyroid hormone levels remain stable. This leads to increased osteoporosis risk and reduced metabolic flexibility.