Endocrine System

• Endocrine system


  Secondary messenger system of the body that uses chemical messengers called hormones released into the blood

  
• Endocrine glands


  • Ductless glands that secrete hormones into the interstitial blood
  • Organs with the richest blood supply are the endocrine glands (such as the adrenal gland & the thyroid gland)
• Pancreas


  • Can be an endocrine & exocrine gland
  • Endocrine: secretes hormones
  • Exocrine: secretes digestive enzymes
• Ovaries & Testes


  Some portion secretes hormone, but other parts produce oocytes (female sex cells) or sperm cells (male sex cells)

  
• Processes controlled by hormones

  • Reproduction
  • Growth and development
  • Mobilization of body defenses
  • Maintenance of homeostasis
  • Regulation of metabolism (Thyroid gland)

  
• Hormones


  Chemical messengers produced by specialized cells to stimulate target sites

  
• Chemical classification of hormones

  • Amino acid-based hormones (proteins, peptides, amines)
  • Steroids
  • Prostaglandins
• Types of hormonal action

  • Endocrine
  • Paracrine
  • Autocrine
  • Juxtacrine
  • Exocrine
  • Neuroendocrine

  
• Mechanism of hormone action

  • Protein receptors are present at the surface of the target cells
  • Hormones affect only certain tissues/organs (target cells or organs)
  • Target cells must have specific protein receptors
  • Hormone binding influences the working of the cells

  
• Effects caused by hormones

  • Changes in plasma membrane permeability/electrical state
  • Synthesis of proteins, such as enzymes
  • Activation/inactivation of enzymes
  • Stimulation of mitosis
  • Promotion of secretory activity
• Direct gene activation: steroid hormone mechanism

  1. Diffuse through the plasma membrane of target cells

  2. Enter Cytoplasm

  3. Enter the nucleus

  4. Bind to a specific protein within the nucleus

  5. Bind to specific sites on the cell's DNA Activate genes that result in synthesis of new proteins

  
• Second-messenger system: nonsteroid hormone mechanism

  1. Hormone binds to a membrane receptor & it does not enter the cell

  2. Sets off a series of reactions that activates an enzyme catalyzing a reaction that produces a second messenger molecule (cyclic AMP)

  3. Oversees additional intracellular changes to promote a specific response

  
• Control of hormonal release

  • Hormonal
  • Humoral
  • Neural
• Hormonal stimulus


  • Hypothalamus stimulates anterior pituitary gland to secrete hormones causing it to message other glands to produce hormones
  • Endocrine glands are activated by other hormones

  
• Humoral stimulus


  Changing blood levels of certain ions stimulate hormone release

  
• Neural stimulus


  Nerve impulses stimulate hormone release
• Pituitary gland


  • Approximately the size of a pea
  • Hangs by a stalk from the hypothalamus
  • Protected by the sphenoid bone
  • Has 2 functional lobes: anterior pituitary (true endocrine gland) and posterior pituitary (nervous tissue)

  
• Hormones produced by the anterior pituitary gland

  • Growth Hormone (GH)
  • Prolactin
  • Follicle-stimulating Hormone (FSH)
  • Luteinizing Hormone
  • Thyrotropic Hormone
  • Adrenocorticotropic Hormone

  
• Posterior pituitary gland


  • Not an endocrine gland, acts only as a storage area for hormones made by hypothalamic neurons
  • Hormone stored: Oxytocin and Antidiuretic hormone (ADH) or vasopressin

  
• Hypothalamus


  Neuroendocrine gland that controls the pituitary gland by producing releasing and inhibiting hormones

  
• Thyroid gland


  • Found at the base of the throat
  • Consists of 2 lobes & a connecting isthmus
  • Thyroid hormone secretion is regulated by hormones from the hypothalamus & pituitary gland

  
• Thyroid hormones


  • Thyroid hormone (T3 & T4)
  • Calcitonin

  
• Parathyroid gland


  • Tiny masses on the posterior of the thyroid
  • Chief cells secrete parathyroid hormone that stimulate osteoclasts to remove calcium from bone, stimulate the kidneys & intestine to absorb more calcium, and raise calcium levels in the blood

  
• Adrenal gland


  • Sit on top of Kidneys
  • Has 2 glands: cortex (produces corticosteroids) and medulla (produces catecholamines)
• Adrenal cortex zones


  • Zona glomerulosa (mineralocorticoids)
  • Zona fasciculata (glucocorticoids)
  • Zona reticularis (androgens)

  
• Pancreatic islet


  • Produces insulin
  • Little masses of hormone-producing tissue scattered among the enzyme-producing acinar tissue of the pancreas
• Cells of the pancreatic islet

  • Alpha (A) cells (secrete glucagon)
  • Beta (B) cells (secrete insulin)
• Adult males


  Hormones secreted by the testes
• Adult females


  Hormones influence the female sex drive
• Abnormally high hormone secretion


  • Exaggerated male characteristics develop in both males & females
• Pancreas


  Flattened organ that measures about 12.5-15 cm (5-6 in.) in length, located in the curve of the duodenum
• Pancreatic islets (islet of Langerhans)

  Produces insulin
• Pancreatic islet cells


  • Alpha (A) cells (17%) secrete glucagon
  • Beta (B) cells (70%) secrete insulin
  • Delta (D) cells (7%) secrete somatostatin
  • F cells (6%) secrete pancreatic polypeptide
• Glucagon


  Acts on several tissues to make energy stored in glycogen and fat available through glycogenolysis and lipolysis; increases blood glucose content
• Insulin


  Acts on several tissues to cause entry of glucose into cells and promotes decrease of blood glucose content
• Somatostatin


  Inhibits release of other islet cell hormones through local paracrine action; inhibits release of GH and TSH in anterior pituitary and HCl secretion by gastric parietal cells

  
• Pancreatic polypeptide


  Stimulates activity gastric chief cells; inhibits bile secretion, pancreatic enzyme and bicarbonate secretion, and intestinal motility
• Normal blood glucose level: about 90mg/100mL
• Pineal gland


  A small, cone-shaped gland found hanging from the roof of the 3rd ventricle of the brain, secretes melatonin
• Melatonin


  Contributes to the setting of the body's biological clock, peak levels are at night & lowest levels is during daylight (noon)