Endocrine System Basics

The Endocrine System

• The endocrine system consists of cells, tissues, and organs that secrete hormones as a primary or secondary function.
• The primary function of endocrine glands is to secrete hormones directly into the surrounding fluid, which is then transported by the blood vessels to reach the target cells.

Endocrine Glands

• The major endocrine glands include:
  • Pituitary gland
  • Thyroid gland
  • Parathyroid glands
  • Adrenal glands
  • Pineal gland
  • Thymus gland
  • Ovaries and testes
• Some organs have both endocrine and non-endocrine functions, such as the pancreas, which produces digestive enzymes and hormones.

Hormones

• Hormones are chemical messengers that travel through the bloodstream to reach their target cells.
• Hormones can be classified into two major groups based on their chemical structure:
  • Amino acid-derived hormones (amine hormones)
  • Lipid-derived hormones (steroid hormones)
• Examples of amine hormones include epinephrine, norepinephrine, and melatonin.
• Examples of peptide and protein hormones include antidiuretic hormone (ADH) and atrial-natriuretic peptide.
• Examples of steroid hormones include testosterone and estrogens.

Pathways of Hormone Action

• Hormone receptors recognize molecules with specific shapes and side groups and respond only to those hormones that are recognized.
• The response triggered by a hormone depends on the hormone and the target cell.
• Hormone receptors can initiate signaling events or cellular mechanisms that result in the target cell's response.

Regulation of Hormone Secretion

• Hormone levels must be tightly controlled to prevent abnormal hormone levels and potential disease states.
• Feedback loops govern the initiation and maintenance of most hormone secretion in response to various stimuli.
• Positive feedback loops involve the release of additional hormones in response to an original hormone release.
• Negative feedback loops involve the inhibition of further secretion of a hormone in response to adequate levels of that hormone.

Organs of the Endocrine System

• Thyroid gland: produces triiodothyronine (T3) and thyroxine (T4) hormones, involved in regulating metabolism.
• Parathyroid glands: produce parathyroid hormone (PTH), involved in regulating blood calcium levels.
• Adrenal glands: produce steroid hormones involved in regulating stress response, blood pressure, and electrolyte balance.
• Pancreas: produces hormones such as glucagon and insulin, involved in regulating blood sugar levels.
• Hypothalamus: produces releasing hormones that regulate the synthesis and secretion of hormones from the pituitary gland.
• Pituitary gland: the "master gland" that produces hormones that regulate growth, development, and reproductive functions.

The Pineal Gland and Thymus Gland

• Pineal gland: produces melatonin, involved in regulating sleep patterns.
• Thymus gland: involved in the development and maturation of immune cells (T-lymphocytes).

Disorders of the Endocrine System

• Addison's disease
• Hyper and hypothyroidism
• Diabetes
• Dwarfism
• Gigantism
• Goiter
• Hyperinsulinism
• Hypoglycemia

Lab Tests

• Blood and urine hormone tests
• Fasting blood sugar
• Glucose tolerance test
• Thyroid function tests (T4, T3, TSH)