Endocrine System Study Notes

Endocrine System Overview

• Collaboration: Endocrine and nervous systems work together for communication.
• Endocrine System:
  • Releases hormones into the bloodstream.
  • Effects take hours, but last longer.
• Nervous System:
  • Releases neurotransmitters.
  • Results occur in milliseconds, with brief effects.

Overview of Cell Communications

• Importance: Necessary for integration of cell activities.
• Mechanisms of Communication:
  • Gap Junctions: Pores in cell membranes for chemical signaling.
  • Neurotransmitters: Released by neurons to signal other cells.
  • Paracrine Hormones: Local hormones affecting nearby cells.
  • Hormones: Chemical messengers traveling in the bloodstream.

Differences Between Nervous and Endocrine Systems

• Communication Means:
  • Nervous: Electrical and chemical.
  • Endocrine: Only chemical.
• Speed and Persistence:
  • Nervous: Quick (1-10 ms) and short response.
  • Endocrine: Slower (seconds to days) and prolonged effects.
• Response Adaptation:
  • Nervous: Adapts quickly, response declines.
  • Endocrine: Persistent responses.
• Area of Effect:
  • Nervous: Targeted and specific.
  • Endocrine: General and widespread effects.

Similarities Between Nervous and Endocrine Systems

• Some chemicals act as both hormones and neurotransmitters (e.g., norepinephrine, dopamine).
• Hormones can be secreted by neuroendocrine cells (e.g., oxytocin).
• Both systems can regulate each other.

General Functions of Hormones

• Regulate:
  • Extracellular fluid, metabolism, biological clock, muscle contraction, glandular secretion, immune functions.
• Support growth, development, and reproduction.

Endocrine Glands Defined

• Exocrine Glands:
  • Secrete products into ducts (e.g., sweat, oil).
  • Extracellular effects.
• Endocrine Glands:
  • Secrete hormones into bloodstream (e.g., pituitary, thyroid).
  • Intracellular effects.

Components of the Endocrine System

• Major Organs:
  • Hypothalamus, pituitary gland, pineal gland, thyroid, parathyroid, adrenal glands, pancreas, gonads, thymus, kidneys, liver, heart.
• Hormones:
  • Chemical messengers influencing other tissues.

Control of Hormone Secretion

• Regulated by signals from the nervous system or blood chemistry.
• Negative Feedback Control:
  • Most common; regulates hormone levels inversely.
• Positive Feedback Control:
  • Increases in hormone lead to more release (e.g., oxytocin during childbirth).

Hypothalamus and Pituitary Gland

• Master Glands: Control other endocrine glands.
• Hypothalamus:
  • Integrates neural signals and releases hormones that regulate the pituitary.
• Pituitary Anatomy:
  • Infundibulum connects hypothalamus to pituitary.
  • Anterior lobe (75%) and posterior lobe (25%).

Pituitary Hormones

• Anterior Lobe:
  • Hormones include FSH, LH, TSH, ACTH, PRL, GH.
  • Tropic Hormones: Target other endocrine glands.
• Posterior Lobe:
  • Stores and releases hormones like oxytocin and ADH.

Growth Hormone (GH)

• Effects: Promotes tissue growth, protein synthesis, lipid metabolism.
• Regulation:
  • Stimulated by low blood sugar and inhibited by high blood sugar.
• Diabetogenic Effect: Excess GH can raise blood glucose levels.

Thyroid Gland

• Role: Produces T3 and T4; regulates metabolism.
• Calcitonin: Lowers blood calcium levels.
• Control of Secretion: Negative feedback from TSH.

Adrenal Glands

• Structure: Outer cortex and inner medulla.
• Cortex Hormones: Mineralocorticoids (aldosterone), glucocorticoids (cortisol), androgens.
• Medulla Secretion: Epinephrine and norepinephrine for stress response.

Pancreatic Hormones

• Insulin: Lowers blood glucose by promoting its uptake.
• Glucagon: Raises blood glucose through glycogenolysis.
• Somatostatin: Regulates insulin and glucagon.

Gonadal Hormones

• Ovaries: Produce estrogen and progesterone; regulate menstrual cycle and pregnancy.
• Testes: Produce testosterone; regulate male reproductive functions.

Disorders of the Endocrine System

• Diabetes Mellitus: Type I (insulin deficiency) and Type II (insulin resistance).
• Thyroid Disorders: Hyperthyroidism (excess TH) and hypothyroidism (low TH).
• Adrenal Disorders: Cushing's syndrome (excess cortisol) and Addison's disease (glucocorticoid deficiency).

Aging and the Endocrine System

• Changes in hormone production and receptor sensitivity.
• Impacts metabolism, muscle mass, and reproductive functions.