ENDOCRINE SYSTEM

• Endocrine System - Second messenger system of the body.
• Hormone


  are produced by specialized cells  Cells secrete hormones into extracellular fluids  Blood transfers hormones to target sites  These hormones regulate the activity of other cells
• Steroids


  made from cholesterol
• Prostaglandins


  made from highly active lipids
• Pituitary Gland


  Size of a grape  Hangs by a stalk from the hypothalamus  Protected by the sphenoid bone

   Has two functional lobes

   Anterior pituitary – glandular tissue

   Posterior pituitary – nervous tissue
• Growth Hormone


  General metabolic hormone  Major effects are directed to growth of skeletal muscles and long bones  Causes amino acids to be built into proteins  Causes fats to be broken down for a source of energy
• Prolactin


  Stimulates and maintains milk production following childbirth Function in males is unknown
• Adrenocorticotropic hormone

  Regulates endocrine activity of the adrenal cortex
• Thyroid-stimulating hormone


  Influences growth and activity of the thyroid
• Gonadotropic hormones - Regulate hormonal activity of the gonads
• Follicle-stimulating hormone


  Stimulates follicle development in ovaries Stimulates sperm development in testes
• Luteinizing hormone


  Triggers ovulation  Causes ruptured follicle to become the corpus luteum Stimulates testosterone production in males
• Oxytocin


  Stimulates contractions of the uterus during labor Causes milk ejection
• Antidiuretic hormone


  Can inhibit urine production  In large amounts, causes vasoconstriction leading to increased blood pressure
• Thyroid Gland


  Found at the base of the throat  Consists of two lobes and a connecting isthmus

   Produces two hormones

   Thyroid hormone

   Calcitonin
• Thyroid Hormone


  Major metabolic hormone  Composed of two active iodinecontaining hormones
• Thyroxine


  T4 – secreted by thyroid follicles
• Triiodothyronine


  T3 – conversion of T4 at target tissues
• Calcitonin


  Decreases blood calcium levels by causing its deposition on bone  Antagonistic to parathyroid hormone  Produced by C (parafollicular) cells F
• Parathyroid Glands


  Tiny masses on the posterior of the thyroid  Secrete parathyroid hormone Stimulate osterclasts to remove calcium from bone Stimulate the kidneys and intestine to absorb more calcium Raise calcium levels in the blood
• Adrenal Glands


  Two glands  Cortex – outer glandular region in three layers

   Medulla – inner neural tissue region

   Sits on top of the kidneys
• Mineralocorticoids


  (mainly aldosterone) Produced in outer adrenal cortex Regulate mineral content in blood, water, and electrolyte balance Target organ is the kidney Production stimulated by renin and aldosterone Production inhibited by atrial natriuretic peptide
• Glucocorticoids


  (including cortisone and cortisol) Produced in the middle layer of the adrenal cortex Promote normal cell metabolism Help resist long-term stressors Released in response to increased blood levels of ACTH
• Sex hormones


  Produced in the inner layer of the adrenal cortex  Androgens (male) and some estrogen

  (female)
• Produces two similar hormones (catecholamines)  Epinephrine  Norepinephrine  These hormones prepare the body to deal with short-term stres
• Pancreatic Islets


  The pancreas is a mixed gland  The islets of the pancreas produce hormones  Insulin – allows glucose to cross plasma membranes into cells from beta cells  Glucagon – allows glucose to enter the blood from alpha cells These hormones are antagonists that maintain blood sugar homeostasis
• Pineal Gland


  Found on the third ventricle of the brain  Secretes melatonin Helps establish the body’s wake and sleep

  cycles

   May have other as-yet-unsubstantiated

  functions
• Thymus


  Located posterior to the sternum  Largest in infants and children  Produces thymosin  Matures some types of white blood cells  Important in developing the immune system
• Estrogens


  Matures female reproductive organs
• Estrogen 


   Helps prepare the uterus to receive a fertilized egg  Helps maintain pregnancy Prepares the breasts to produce milk
• Progesterone


  Produced by the corpus luteum Acts with estrogen to bring about the menstrual cycle Helps in the implantation of an embryo in the uterus
• Testosterone


  Responsible for adult male secondary sex characteristics Promotes growth and maturation of male reproductive system Required for sperm cell production