PCBI101: ENDOCRINE SYSTEM

• Endocrine System


  Consists of the ductless glands, coordinates with the nervous system, involved in the synthesis and secretion of hormones, includes energy production, utilization, and the control of the composition of the extracellular water and electrolytes, involved in maintaining normal growth and development

  
• Hormones


  Organic substances needed by the body in enough quantities to express a neurological response
• Hypothalamus


  • A small gland located at the base of the brain, intimately associated with the pituitary gland, secretes hormones that travel by the fertile system and stimulate the anterior pituitary glands, production of ADH, oxytocin, and regulatory hormones

  
• Pituitary Gland


  • A small gland located at the base of the brain, connected to the brain with a short stalk called the "infundibulum", divided into anterior lobe (ACTH, TSH, GH, PPL, FSH, LH, and MSH) and posterior lobe (release of oxytocin and ADH)

  
• Thyroid Gland


  • Secretes thyroxine (T4), triiodothyronine (T3), and calcitonin (CT)
• Parathyroid Glands

  • Located on the posterior surface of the thyroid gland, secretes parathyroid hormone (PTH)

  
• Thymus

  • Located between the upper part of the sternum and pericardium, undergoes atrophy during adulthood, secretes thymosins which control metabolic weight and are involved in the formation of white blood cells

  
• Adrenal Glands

  • Small glands located above the kidneys, adrenal medulla secretes epinephrine and norepinephrine, adrenal cortex secretes cortisol, aldosterone, androgens, and corticosterone

  
• Pancreas/Pancreatic Islets

  • Consists of both an exocrine (with ducts) and an endocrine (ductless) gland, pancreatic islets secrete the hormone insulin which lowers blood sugar, also secretes glucagon
• Gonads


  • Located in the testes or ovary, testes secrete androgens (testosterone) and inhibins, ovary secretes estrogen, progestins, and inhibins

  
• Kidney


  • Secretes renin, erythropoietin (EPO), and calcitriol
• Heart


  • Secretes natriuretic peptides: ANP and BNP
• Adipose Tissue

  • Secretes leptin and resistin

  
• Digestive Tract

  • Secretes numerous hormones
• Pineal Gland

  • Secretes melatonin
• Nervous System

  The complicated network of nerves that carry messages or signals from and to the spinal cord and brain to other parts of the body
• Endocrine System

  The collection of glands that produce hormones that function in regulating the body's growth and development, metabolism, tissue function, reproduction, sleep, anger, emotions and other internal functions

  
• Functions of the Endocrine System


  • Controls homeostasis, maintains water balance, controls uterine contractions, controls milk production, regulates ions, regulates metabolism and growth, regulates heart rate and blood pressure, monitors blood glucose levels, aids the immune system, regulates reproductive functions
• Components of the Endocrine System

  Endocrine glands that secrete their product directly into the bloodstream, chemical signals that are molecules released from one location and move to another location to produce a response

  
• Types of Chemical Signals

  • Intracellular (produced in one part of a cell and move to another part), Intercellular (released from one cell and bind to receptors on another cell)
• Types of Intercellular Signals

  • Autocrine (released by cells and have a local effect on the same cell type), Paracrine (released by cells that affect other cell types in close proximity), Neurotransmitter and neuromodulators (secreted by nerve cells), Pheromones (secreted into environment and modify behavior and physiology of other individuals in same species), Hormones and neurohormones (secreted into blood and bind to receptor sites)

  
• Components of Hormones

  Receptor site (location on a cell where hormone binds), Target tissues (group of cells that respond to specific hormones), Specificity (specific hormones bind to specific receptor sites)
• How Hormones Work

  Hormones are secreted by endocrine glands directly into the bloodstream, hormones travel to all parts of the body, hormones bind to receptor sites on target tissues, response occurs

  
• How Hormones Cause Change

  Alter cell activity of target tissues by increasing or decreasing cell's normal processes, change the permeability of the cell membrane by opening or closing ion channels, synthesis of proteins (replication, translations, transcription by DNA)

  
• Types of Proteins


  • Structural Protein (e.g. keratin in hair and skin), Regulatory Protein (e.g. enzymes and hormones)
• Types of Hormones


  • Water soluble (e.g. growth hormone, antidiuretic, prolactin), Lipid hormones (e.g. LH, FSH, androgens)
• Steroid Hormones


  Manufactured from cholesterol, composed of a central structure of four carbon rings attached to distinctive side chains, synthesized in the smooth endoplasmic reticulum, fat-soluble and can pass through the membrane of a target cell, attach to a protein receptor molecule in the cytoplasm and then enter the nucleus to activate a specific gene

  
• Nonsteroid Hormones


  Composed of proteins, peptides, or amino acids, not fat-soluble so they usually do not enter cells to exert their effect, bind to receptors on the surface of target cells and trigger a specific chain of chemical reactions within the cell

  
• The endocrine system produces two main types of hormones: steroid hormones and nonsteroid hormones

  
• Blood levels of chemicals regulate the secretion of hormones
• Steroid hormone mechanism of action


  1. Steroid hormone enters target cell

  2. Binds to protein receptor in cytoplasm

  3. Hormone-receptor complex enters nucleus

  4. Binds to and activates specific gene on DNA

  5. Activated gene produces enzyme that initiates desired chemical reaction

  
• Nonsteroid hormones


  Composed of proteins, peptides, or amino acids, not fat-soluble so usually do not enter cells, instead bind to receptors on cell surface and trigger chemical reactions

  
• Regulation of hormones

  • Blood levels of chemicals (e.g. insulin regulating blood glucose)
  • Other hormones (e.g. TSH signaling thyroid gland)
  • Nervous system (e.g. epinephrine and fight or flight)
  • Negative feedback (tells body when homeostasis is reached)

  
• Hormone receptor and mechanism of action types

  • Lipid soluble hormones bind to nuclear receptors
  • Water soluble hormones bind to membrane-bound receptors
  • Intracellular receptor hormones

  
• Pituitary gland


  • Small gland in brain, controlled by hypothalamus, divided into anterior and posterior regions, secretes at least 6 hormones

  
• Growth hormone (GH)


  Stimulates growth of bones, too much causes giantism, too little causes pituitary dwarfism
• Thyroid-stimulating hormone (TSH)


  Regulates thyroid gland secretions, too much causes thyroid gland enlargement, too little causes thyroid gland shrinkage
• Luteinizing hormone (LH)


  For females: promotes ovulation and progesterone production, for males: promotes sperm production and testosterone

  
• Follicle-stimulating hormone (FSH)


  For females: promotes follicle maturation and estrogen secretion, for males: promotes sperm production

  
• Antidiuretic hormone (ADH)


  Conserves water, low ADH causes diabetes insipidus leading to dehydration and thirst