Endocrine Systems

Endocrine System Overview

• The endocrine system is a complex system of specialized glands that produce and secrete hormones.
• These glands are not anatomically connected but function as a unified system.
• The system uses hormones to control and integrate organ systems, regulating metabolism, digestion, blood pressure, and growth.

Endocrine System Components

• Hypothalamus: Regulates aspects like hunger, thirst, sleep, body temperature, and involuntary functions.
• Pituitary Gland: Controls other endocrine glands and influences growth, metabolism, and regeneration.
• Thyroid Gland: Responsible for regulating body energy and metabolism.
• Parathyroid Glands: Secrete hormones necessary for calcium absorption.
• Thymus: Supports immune function by helping build disease resistance.
• Adrenal Glands: Secrete a variety of compounds, including hormones that help the body react to emergencies, regulate metabolic processes, water balance, and blood pressure.
• Pancreas: Aids in digestion and controls blood sugar levels through insulin and glucagon production.
• Ovaries (and Testes): Influence processes like blood circulation, mental vigor, sex drive, and reproductive functions.

Hormone Types and Transport

• Hormones are chemical messengers in the body coordinating different functions.

• Over 50 hormones exist.

• Hormones regulate various functions like growth, reproduction, sleep cycles, and mood regulation.

• Hormones are of three main types:

  • Lipid-derived (Steroids): Derived from cholesterol; water-insoluble, transported by carrier proteins; cross cell membranes and bind to intracellular receptors.
  • Amino acid-based (Peptides and Proteins): Chains of amino acids; water-soluble; bind to cell surface receptors.
  • Amino acid derivatives: Derivatives of tyrosine or tryptophan; act as messengers, bind to intracellular receptors; examples include thyroid hormones, epinephrine, norepinephrine, melatonin.

• Hormones bind to specific receptors in target cells activating biochemical pathways to produce a response.

Hormone Transport

• Hormones circulate freely or bound to proteins in the bloodstream.

• Free hormones circulate freely, while others bind to transport proteins.

• Transport proteins protect the hormones from breakdown and ensure they reach target tissues.

• The liver and kidneys clear hormones from the body via metabolism and excretion, sometimes by cells.

• Peptide hormone removal is relatively fast, while steroid hormone removal is slower.

Hypothalamic-Pituitary Axis

• The hypothalamus and pituitary gland work together as a central link between the endocrine and nervous systems.
• The hypothalamus regulates temperature, hunger, thirst, sleep cycles, and mood, and controls pituitary release.
• The pituitary gland, in turn, produces/ releases hormones that affect various target tissues. The anterior pituitary (75%) produces trophic hormones influencing other endocrine glands. The posterior pituitary (25%) stores and releases hormones produced elsewhere.

The Thyroid Gland

• The thyroid gland regulates metabolism, growth, and development.
• Produces two primary hormones: T3 (triiodothyronine) and T4 (thyroxine).
• Thyroid hormone action affects a wide array of bodily functions in virtually every organ system.
• Iodine is critical for thyroid hormone production.
• Thyroid disorder results from problems with the production, storage, or secretion of thyroid hormones.

Peripheral Endocrine Glands

• Several key glands, like thyroid, adrenal, pancreas, thymus, and gonads, comprise the peripheral endocrine system.

Learning Outcomes

• Compare and contrast the nervous and endocrine systems.
• Describe the types of hormones and their transportation.
• Understand the role of hormones in feedback loops and homeostasis.
• Describe the relationship between the hypothalamus and the pituitary gland.
• Give examples of peripheral endocrine gland function.