Endocrine System Flashcards//STUDIED

Overview

• The endocrine system regulates long-term processes like growth and reproduction, offering a slower but longer-lasting response compared to the nervous system.

• The endocrine and nervous systems are the body’s major control systems.

Intercellular Communication

• Direct communication: rare, requires physical contact between cells (e.g., gap junctions).

• Paracrine communication: uses chemical signals within a single tissue.

• Endocrine communication: hormones released into the bloodstream for long-distance communication.

  • Hormones affect target cells with specific receptors, altering metabolic activities.

Comparison of Nervous and Endocrine Systems

• Both systems:

  • Release chemicals binding to specific receptors.

  • Share chemical messengers.

  • Use negative feedback.

  • Maintain homeostasis.

Hormones

• Classes:

  • Amino acid derivatives: tyrosine (thyroid hormones, epinephrine), tryptophan (melatonin).

  • Peptide hormones: insulin, TSH, LH, FSH, ADH, oxytocin, GH, prolactin.

  • Lipid derivatives:

    • Eicosanoids: paracrine communication (leukotrienes, prostaglandins).

    • Steroid hormones: cholesterol-derived (sex hormones, corticosteroids, calcitriol).

• Secretion/Distribution:

  • Free circulation: short-lived.

  • Bound to transport proteins: longer-lasting reserve.

Mechanisms of Hormone Action

• Hormones affect cells with matching receptors, located on the cell membrane or within the cell.

• External cell membrane receptors:

  • For amino acid derivatives and peptide hormones.

  • First messenger: hormone binds to receptor.

  • Second messenger: triggers changes (e.g., cyclic-AMP).

• Inner surface of the cell membrane

  • For eicosanoids hormones.

• Intracellular receptors:

  • Steroid hormones pass through the cell membrane to act on genes.

Endocrine Reflexes and Hypothalamus

• Simple: involves one hormone.

• Complex: involves multiple steps/hormones.

• Hypothalamus:

  • Highest endocrine control level.

  • Integrates nervous and endocrine systems.

  • Releases regulatory hormones (releasing/inhibiting factors), ADH, and oxytocin.

Pituitary Gland

• Located in sella turcica, connected to hypothalamus via infundibulum.

• Releases nine peptide hormones using cyclic-AMP as a second messenger.

• Anterior Lobe:

  • Controlled by hypothalamic releasing/inhibiting hormones.

  • Hormones: TSH, ACTH, FSH, LH, prolactin, GH, MSH.

• Posterior Lobe:

  • Stores/releases ADH and oxytocin.

Thyroid Gland

• Anatomy: anterior to larynx, two lobes connected by an isthmus, contains thyroid follicles.

• Thyroid Hormones: requires iodine for T3 (triiodothyronine) and T4 (thyroxine) synthesis.

• Hormone Release:

  • Controlled by TSH from the anterior pituitary.

  • Hormones bind to thyroid-binding globulins for transport.

• Functions: affects almost every cell, increases ATP production, controls metabolism.

• Abnormalities:

  • Hypothyroidism: cretinism (infants), myxedema (adults).

  • Hyperthyroidism: Grave’s Disease.

• C Cells: produce calcitonin to decrease blood calcium levels.

Parathyroid Glands

• Anatomy: four glands on the posterior thyroid, contain chief cells.

• Function: regulate blood calcium levels via parathyroid hormone (PTH), which increases calcium.

• Effects of PTH:

  • Stimulates osteoclasts.

  • Inhibits osteoblasts.

  • Increases calcium reabsorption in kidneys.

  • Stimulates calcitriol secretion.

Adrenal Glands

• Anatomy: atop each kidney, with cortex and medulla regions.

• Adrenal Cortex:

  • Produces steroid hormones: aldosterone, cortisol, androgens.

• Adrenal Medulla:

  • Produces epinephrine and norepinephrine (fight or flight).

  • Effects: increased muscle strength, fat release, glycogen breakdown, increased heart rate.

Pineal Gland

• Location: posterior roof of the third ventricle.

• Function: Synthesizes melatonin, regulating sleep/wake cycles (circadian rhythm).

Pancreas

• Functions: both exocrine (digestion) and endocrine (glucose regulation).

• Insulin (beta cells):

  • Decreases blood glucose by promoting glucose uptake into cells.

• Glucagon (alpha cells):

  • Increases blood glucose by stimulating glycogen breakdown.

  • Note: Pancreatic cells monitor glucose independently of the brain and nervous system.

Endocrine Tissues of Other Systems

• Intestines: coordinate digestive activities.

• Kidneys: calcitriol, erythropoietin (EPO), renin.

• Heart: natriuretic peptides decrease blood volume/pressure.

• Thymus: thymosins for immune function.

• Gonads: ovaries (estrogen, progesterone), testes (testosterone).

• Adipose Tissue: leptin (appetite), resistin (insulin sensitivity).

Hormonal Interactions and Stress Response

• Interactions:

  • Antagonistic: opposing effects (insulin/glucagon).

  • Synergistic: additive effects (PTH/calcitriol).

• Growth: Requires GH, thyroid hormones, insulin, PTH, calcitriol, reproductive hormones.

• Stress Response (GAS):

  • Alarm Phase: epinephrine (fight or flight).

  • Resistance Phase: cortisol/aldosterone (glucose conservation).

  • Exhaustion Phase: homeostatic breakdown.

Effects of Hormones on Behavior

• Many hormones affect the CNS, influencing intellectual capabilities, memory, learning, and emotional states.

Aging and Hormone Production

• Some endocrine tissues become less responsive; GH and reproductive hormone levels decline.

Clinical Patterns

• Primary disorders: problems with the endocrine organ itself.

• Secondary disorders: problems in other organs/target tissues.