The Endocrine System Overview

The Endocrine System

• A system of glands involving the release of hormones
• Works alongside the nervous system to control body systems
• Nervous system is fast and direct, affecting specific glands and muscles throughout the body
• Endocrine system is slower acting, widespread, affecting various organs and tissues for a longer time
• Hormones are distributed through the bloodstream, released by glands

Endocrinology

• The study of hormones
• Hormones work at a distance, not by direct mechanical attachment
• Composed of amino acids

Types of Signaling

• Endocrine: hormones travel through the bloodstream to target cells
• Paracrine: hormones act locally on neighboring cells
• Autocrine: hormones act on the same cell that secreted them

Functions of the Endocrine System

• Regulates metabolism
• Promotes growth and development
• Controls puberty
• Maintains tissue function
• Regulates internal environment(temperature and water balance)
• Affects mood

Function: Information Signals

• Endocrine system uses blood vessels as information channels, similar to the nervous system which uses nerves
• Glands are located throughout the body, including the brain
• Glands release hormones (chemical messengers) into the bloodstream

Hormones

• Distributed through the bloodstream
• Pass through cells or along plasma membranes until reaching a receptor
• Only affect cells with appropriate receptors
• Some hormones are tropic, triggering the release of other hormones in different glands

Major Hormones and Systems

• The hypothalamus controls the endocrine system's activity
• The hypothalamus releases factors stimulating the anterior pituitary to release hormones affecting peripheral endocrine glands

Hypothalamus

• The control center of the nervous and endocrine systems
• Stimulates the pituitary gland and releases ADH (fluid regulation) and oxytocin (uterus contractions)

Pituitary Gland

• Located in the front of the brain
• Controls:
  • Growth
  • Other gland functions
  • Water level in the blood
  • Lactation
  • Reproduction
  • Ovulation and menstrual cycle
  • Reduces sensitivity to pain
• Master Gland: other endocrine glands depend on the pituitary for function
• Example of functions:
  • Thyroid gland: Metabolism
  • Parathyroid: Calcium regulation
  • Adrenal: Fluid balance/stress response
  • Gonads: Sex hormones

Anterior Lobe Hormones

• Adrenocorticotropic hormone (ACTH): responds to stress, stimulates adrenal glands to produce cortisol. Cortisol regulates metabolism, blood pressure, blood sugar, and reduces inflammation
• Follicle-stimulating hormone (FSH): stimulates sperm production in males and egg development in females (gonadotropic hormone)
• Thyroid-stimulating hormone (TSH): stimulates thyroid gland to produce hormones that manage metabolism, energy, and nervous system
• Growth hormone (GH): stimulates growth in children and maintains healthy muscles and bones in adults, affecting metabolism
• Luteinizing hormone (LH): stimulates ovulation in females and testosterone production in males (gonadotropic hormone)
• Prolactin: stimulates breast milk production (lactation) after childbirth, but can affect fertility

Posterior Lobe Hormones

• Antidiuretic hormone (ADH), or vasopressin: regulates water and sodium balance
• Oxytocin: stimulates uterine contractions during childbirth

Endocrine Glands

• Hypothalamus
• Pituitary
• Thyroid
• Parathyroid
• Pancreas
• Adrenal
• Gonads (ovaries and testes)

Thyroid/Parathyroid Glands

• Located in front of the trachea (windpipe)
• Thyroid controls:
  • Metabolic rate
  • Bone growth
  • Brain development
  • Nervous system development
• Parathyroid has 4 glands located on sides of the thyroid
  • Helps maintain normal calcium, magnesium, and phosphate levels

Adrenal Glands

• Located on top of the kidneys

• Regulates salt and water balance

• Stimulates "fight or flight" response (adrenaline)

• Increases blood pressure and heart rate

• Cortex produces steroids

  • Cortisol: Stress
  • Aldosterone: Blood volume

• Medulla produces catecholamines

  • Adrenaline: Fight or Flight

Pancreas

• Located between stomach and small intestine
• Controls insulin secretion based on blood glucose levels circulating through the pancreas
• Regulates blood glucose through insulin and glucagon production

Gonads

• Males: Testes secrete testosterone, regulating body changes, facial hair growth and deepening of voice, muscle growth and strength
• Females: Ovaries secrete estrogen and progesterone, controlling sexual development & involved in pregnancy and menstrual cycles

Common Endocrine Diseases

• Type 1 diabetes: insulin production is low or absent
• Thyroid disease: overactive or underactive thyroid
• Hyperthyroidism: overactive thyroid
• Hypothyroidism: underactive thyroid
• Growth disorders (related to pituitary issues)
• Obesity