3. Endocrine (1)

Endocrine System Overview

• The endocrine system consists of glands and tissues that facilitate communication via hormones.

• Endocrine Glands: Ductless organs that secrete hormones directly into the bloodstream; distinct from exocrine glands, which secrete chemicals into ducts (e.g., digestive enzymes).

Hormones

• Hormones are chemical messengers that:

  • Influence cell metabolism.

  • Affect growth and development of body parts.

  • Maintain homeostasis.

• Hormones can be categorized as:

  • Protein hormones: Composed of amino acids.

  • Steroid hormones: Lipid-based molecules.

Interaction with the Nervous System

• The endocrine system works closely with the nervous system, maintaining balance via:

  • Negative feedback mechanisms: Hormone levels are regulated based on the body’s needs; excess hormone inhibits further release.

  • Antagonistic hormones: Hormones that work against each other to regulate bodily functions.

Major Endocrine Glands

• Hypothalamus: Links the nervous system with the endocrine system; regulates the pituitary gland.

• Pituitary Gland: Divided into anterior and posterior sections, it controls various hormones.

  • Anterior: Produces various hormones affecting other glands.

  • Posterior: Stores and releases hormones like ADH and oxytocin.

• Thyroid Gland: Produces hormones that regulate metabolism; requires iodine for function.

• Adrenal Glands: Regulate stress response and maintain mineral balance; consist of medulla (produces epinephrine/norepinephrine) and cortex (produces glucocorticoids/mineralocorticoids).

• Pancreas: Produces insulin (lowers blood glucose) and glucagon (raises blood glucose).

• Gonads (Ovaries/Testes): Produce sex hormones (estrogen, progesterone, testosterone).

Hormonal Action Mechanisms

• Steroid Hormones: Pass through the plasma membrane, bind to receptors in the nucleus, and affect gene expression, leading to protein synthesis.

• Peptide Hormones: Bind to receptors on the plasma membrane; activate a second messenger (e.g., cAMP) to trigger an enzyme cascade for biological responses.

Feedback Mechanisms in Hormone Regulation

• Hormones are primarily regulated through negative feedback:

  • Tropic hormones act on other endocrine glands.

  • Non-tropic hormones act directly on tissues.

Hypothalamus and Pituitary Interactions

• The hypothalamus releases hormones influencing both the anterior and posterior pituitary functions:

  • Anterior pituitary secretes TSH, ACTH, GH, PRL, and gonadotropic hormones.

  • Hormones are involved in metabolic control and growth.

Disorders Related to Hormones

• Hyposecretion of hormones: Leads to conditions like Addison's disease, causing fatigue and bronzing of the skin.

• Hypersecretion of hormones: Leading to conditions like Cushing's syndrome, characterized by obesity and high levels of cortisol.

Thyroid Gland Functions

• Produces T3 (triiodothyronine) and T4 (thyroxine) for metabolism regulation; requires iodine.

• Calcitonin lowers blood calcium levels; the parathyroid hormone raises it.

• Deficiencies or excesses lead to goiters or metabolic disorders slightly characterized by changes in weight and metabolism.

Pancreatic Hormones

• Insulin (from beta cells): Lowers blood glucose; makes cells more glucose-permeable.

• Glucagon (from alpha cells): Raises blood glucose; stimulates glycogen breakdown.

Diabetes Mellitus Types

• Type I: Autoimmune condition with no insulin production; requires insulin injections.

• Type II: Insulin resistance due to lifestyle factors; often managed by diet.

Summary of Key Functions

• Hormonal imbalances can severely affect metabolic processes across various systems, leading to conditions such as diabetes or thyroid dysfunctions.

• Understanding these paths helps in diagnosing and treating endocrine disorders effectively.