Endocrine system

• Endocrine glands


  Pituitary, thyroid, parathyroid, adrenal, pineal, and thymus
• Hormone


  A chemical substance released by a group of cells to control the function of other type of cells
• Hypersecretion


  Excessive secretion of a hormone
• Hyposecretion


  Insufficient secretion of a hormone
• Primary endocrine glands


  • Pituitary
  • Thyroid
  • Parathyroid
  • Adrenal
  • Pancreas
  • Ovaries
  • Testes
• Steroid hormone action


  Steroid hormones pass through the cytoplasm and enter nucleus where they bind with a receptor (lock-and-key model)
• Nonsteroid hormone action


  Hormone-receptor interaction (first messenger), enzyme activation, release of the second messenger, effects on cellular function
• Prostaglandins (PGs)


  Chemical substances that have important physiological functions
• Conditions from hyposecretion or hypersecretion

  • Gigantism
  • Diabetes insipidus
  • Goiter
  • Cretinism
  • Diabetes mellitus
  • Glycosuria
• The endocrine system is the body's second great controlling system which influences metabolic activities of cells by means of hormones
• The hypothalamus has both neural functions and releases hormones
• Other tissues and organs that produce hormones include adipose cells, pockets of cells in the walls of the small intestine, stomach, kidneys, and heart
• Hormones can exert their effects at distance from their site of production
• Neurohormone


  Specialized neurons that secrete chemicals into the blood rather than synaptic cleft
• Roles of the endocrine system

  • Homeostasis: maintenance of the internal environment
  • Metabolic regulation: storage and use of energy substrates
  • Responses to external stimuli
  • Control of growth, reproduction and development
• Classes of hormones


  • Proteins and polypeptides
  • Steroids
  • Derivatives of the amino acid tyrosine
• There are no known polysaccharide or nucleic acid hormones
• Peptide (protein) hormones


  Can dissolve in water (plasma)
• Steroid hormones


  Secreted by gonads, adrenals cortex, placenta, derived from cholesterol, cross membranes (no storage), usually bound to carrier proteins
• Amine hormones


  Derived from amino acid tyrosine, include thyroid hormones, epinephrine, norepinephrine, dopamine
• Hormone receptors


  Large proteins, 2000-100,000 receptors/cell, highly specific for a single hormone, located on cell membrane, in cytoplasm, or in nucleus
• Clearance of hormones


  Controlled by rate of secretion and rate of removal (metabolic clearance), cleared by metabolic destruction, excretion in bile and urine, clearance of protein-bound hormones is slower
• Negative feedback


  Original stimulus reversed, most feedback systems in the body are negative, used for conditions that need frequent adjustment
• Positive feedback


  Original stimulus intensified, seen during normal childbirth
• Prostaglandins (PGs)


  Powerful substances found in a wide variety of body tissues, often produced in a tissue and diffuse only a short distance to act on cells in that tissue
• Classes of PGs


  • Prostaglandin A (PGA)
  • Prostaglandin E (PGE)
  • Prostaglandin F (PGF)
• Prostaglandins


  • Influence many body functions, including respiration, blood pressure, gastrointestinal secretions, and reproduction
• Pituitary gland


  Two-lobed organ that secretes important hormones
• Adenohypophysis


  Anterior lobe, made up of glandular tissue that synthesizes and secretes a number of hormones
• Neurohypophysis


  Posterior lobe (neural tissue) that receives, stores, and releases hormones from the hypothalamus
• Hormones of the anterior pituitary

  • Growth hormone (GH)
  • Prolactin (PRL)
  • Thyroid-stimulating hormone (TSH)
  • Adrenocorticotropic hormone (ACTH)
  • Follicle-stimulating hormone (FSH)
  • Luteinizing hormone (LH)
• Trophic effects of anterior pituitary hormones

  • High blood [hormone] causes target organ to hypertrophy, low blood [hormone] causes target organ to atrophy
• TSH


  Stimulates growth of the thyroid gland and its secretion of thyroid hormone
• ACTH


  Stimulates growth of the adrenal cortex and its secretion of glucocorticoids (mainly cortisol)
• FSH


  Initiates growth of ovarian follicles each month in the ovary and stimulates one or more follicles to develop to the stage of maturity and ovulation, stimulates estrogen secretion by developing follicles, stimulates sperm production in the male
• LH


  Acts with FSH to stimulate estrogen secretion and follicle growth to maturity, causes ovulation, causes luteinization of the ruptured follicle and stimulates progesterone secretion by corpus luteum, causes interstitial cells in the testes to secrete testosterone in the male
• GH


  Stimulates growth by accelerating protein anabolism, accelerates fat catabolism and slows glucose catabolism, tends to increase blood glucose to higher than normal level (hyperglycemia)
• PRL


  Stimulates breast development during pregnancy and secretion of milk after the delivery of the baby
• Hypothalamic Control of the Anterior Pituitary

  Hormonal control rather than neural, hypothalamus neurons synthesize releasing and inhibiting hormones, hormones are transported to axon endings of median eminence, hormones secreted into the hypothalamo-hypophyseal portal system regulate the secretions of the anterior pituitary, no direct neural contact with the hypothalamus, vascular connection through the hypothalmic-hypophyseal portal system
• Hypothalamic Control of Posterior Pituitary

  Hypothalamus neuron cell bodies produce ADH and oxytocin, transported along the hypothalamo-hypophyseal tract, stored in posterior pituitary, release controlled by neuroendocrine reflexes