26.1 Introduction to the Adrenal Cortex, Pituitary, and Hypothalamus

The hypothalamus, pituitary gland, and adrenal cortex work together to regulate the body's endocrine system. These structures produce and release hormones that control vital functions like metabolism, growth, and stress response.

Understanding how these glands interact is crucial for nurses. Their hormones affect nearly every bodily system, from blood pressure to reproduction. Knowing how they maintain balance helps explain many health conditions and treatments.

Hypothalamus, Pituitary Gland, and Adrenal Cortex

Key functions in regulating endocrine system

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• Hypothalamus
  • Primary link between nervous and endocrine systems integrates signals from the brain and body to coordinate endocrine function
  • Regulates pituitary gland secretes releasing and inhibiting hormones that control pituitary hormone production
  • Controls body temperature, hunger (appetite), thirst, sleep, and circadian rhythms (sleep-wake cycle) maintains homeostasis
• Pituitary gland
  • "Master gland" of endocrine system central regulator of many endocrine functions
  • Anterior and posterior lobes
    • Anterior lobe produces and secretes several hormones (growth hormone, TSH, ACTH, FSH, LH, prolactin) in response to hypothalamic releasing hormones
    • Posterior lobe stores and releases hormones produced by hypothalamus (ADH, oxytocin) acts as a storage and release site
• Adrenal cortex
  • Outer portion of adrenal gland located above the kidneys
  • Produces and secretes steroid hormones glucocorticoids (cortisol), mineralocorticoids (aldosterone), and androgens (DHEA)
  • Regulates metabolism (glucose, protein, fat), immune response (inflammation), blood pressure, and electrolyte balance (sodium, potassium) maintains homeostasis

Major hormones and primary effects

• Hypothalamus hormones
  • TRH stimulates anterior pituitary to release TSH regulates thyroid function
  • CRH stimulates anterior pituitary to release ACTH regulates adrenal cortex function
  • GnRH stimulates anterior pituitary to release FSH and LH regulates reproductive function
  • ADH (vasopressin) regulates water balance (urine concentration) and blood pressure
  • Oxytocin stimulates uterine contractions during labor and milk ejection during breastfeeding
• Anterior pituitary hormones
  • GH promotes growth and development (bone, muscle), regulates metabolism (glucose, protein, fat)
  • TSH stimulates thyroid gland to produce and secrete thyroid hormones (T3, T4) regulates metabolism
  • ACTH stimulates adrenal cortex to produce and secrete glucocorticoids (cortisol) regulates stress response
  • FSH and LH regulate reproductive function in males (spermatogenesis, testosterone) and females (follicle development, ovulation, estrogen, progesterone)
  • PRL stimulates milk production in mammary glands after childbirth
• Adrenal cortex hormones
  • Glucocorticoids (cortisol) regulate metabolism (glucose, protein, fat), immune response (anti-inflammatory), and stress response (fight-or-flight)
  • Mineralocorticoids (aldosterone) regulate blood pressure and electrolyte balance (sodium retention, potassium excretion)
  • Androgens (DHEA) serve as precursors for sex hormones (testosterone, estrogen) and have mild androgenic effects (male characteristics)

Maintaining homeostasis and responding to stress

• HPA axis
  • Complex feedback system regulates body's response to stress and maintains homeostasis
  • Stress triggers hypothalamus to secrete CRH $\rightarrow$ stimulates anterior pituitary to release ACTH $\rightarrow$ stimulates adrenal cortex to produce and secrete glucocorticoids (cortisol)
  • Cortisol helps body respond to stress increases blood glucose (energy), suppresses immune system (reduces inflammation), modulates metabolism (mobilizes energy stores)
  • As cortisol levels rise, they provide negative feedback to hypothalamus and pituitary $\rightarrow$ reduces CRH and ACTH secretion $\rightarrow$ maintains homeostasis prevents excessive cortisol production
• Homeostatic regulation
  • Hypothalamus monitors physiological parameters (body temperature, blood glucose, blood pressure) and releases appropriate hormones to maintain balance
  • Pituitary gland responds to hypothalamic hormones by secreting its own hormones targets various endocrine glands (thyroid, adrenals, gonads) and tissues (liver, muscle, bone)
  • Adrenal cortex produces hormones that help regulate metabolism (glucose, protein, fat), blood pressure, electrolyte balance (sodium, potassium), and stress response
  • Negative feedback loops ensure hormone levels remain within optimal range for maintaining homeostasis prevents excessive or insufficient hormone production