Endocrine system

I Endocrine System

 A) Function
  1) control systems, maintain homeostasis
   a) control chemical and water balance in body
   b) control growth and metabolism
   c) control embryonic development and preparation for nurturing
    a newborn
   d) influence sexual behavior, stimulate growth and 
    maturation of the gonads 
   e) feedback to the nervous system
   f) early studies on insect molt
 B) How does it work?  - Basic Overview of the Feedback System
  1) Nervous systems monitors environment
  2) If aberrations are detected - nervous system sends message to endocrine glands
  3) Endocrine glands produce and secrete hormones into blood
  4) Hormones hit target organ
  5) Target organ produces substance
  6) Substance is picked up by receptors and brain stops sending message to
   endocrine glands
 
II Endocrine System - Components

 A) Components
  1) Endocrine glands
  2) Chemical messages = hormones
  3) works intimately in conjunction with the nervous and circulatory systems
   Example: Hypothalamus - Anterior Pituitary
   Example: Hypothalamus - Posterior Pituitary
  4) Disorders - homeostatic imbalances
    Hyposecretion of hormones by glands - low levels of 
     hormones being produced
    Hypersecretion of hormones by glands - high levels of 
     hormones being produced
 B) Humans as an example of typical vertebrate endocrine system
  1) Anterior pituitary gland and its hormones (base of the brain)
   a) GH - growth hormone, stimulates muscle and skeletal growth,
    1) Target organ - liver, stimulates liver to produce growth factors
     that stimulate bone and cartilage growth
    2) disorders
      Hypo (pituitary dwarfism)
      Hyper (early development leads to gigantism; abnormal growth 
        of hands and feet - acromegaly in adulthood)
   b) TSH - Thyroid stimulating hormone, stimulates Thyroid Gland to 
    produce hormones
    Disorder: Hyper - Goiter (overstimulation of thyroid)
   c) FSH - follicle stimulating hormone, stimulates 
    development of follicles
   d) LH - luteinizing hormone, stimulates development of testes and 
    ovaries
   e) ACTH - stimulates adrenal glands to produce hormones
   f) PRL (prolactin) - stimulates mammary gland growth and milk production
  2) Posterior Pituitary
   a) Oxytocin - stimulates uterine contractions, milk ejection reflex
    in the mammary glands
   b) ADH - antidiuretic hormone, stimulates retention of water
    action blocked by alcohol and caffeine
  3) Thyroid Gland (neck)
   a) Thyroxine
     Target organs - primarily skeletal, muscle tissue
     stimulates metabolic rate for growth
     increases oxygen consumption and cell metabolism
    Disorders
     Hyper - hyperthyroidism (increases temperature and BP, weight loss, irritability)
     Hypo - lethargy, weight gain, cretinism in children (abnormal skeletal growth and retardation)
   b) Calcitonin - regulates Ca++ levels in the blood (decreases concentration)
    Target organs - kidney, bone, digestive system 
  4) Adrenal Glands (on top of kidneys) - hormones in the 
    fight/fright response
   a) Glucocorticoids - raises glucose levels in the 
    blood, stimulates glucose production by cells
   b) Epinephrine - complement supply from the sympathetic system
    function is to give the body an energetic boost, increase metabolic rate,
    dilates bronchioles in the lungs, increases heart rate, etc.
    Target - most systems of the body
   c) Mineralocorticoids - retention of ions
  5) Pancreas (at junction of stomach and small intestine)
   a) Insulin - lowers blood sugar levels (secreted by beta cells)
    Target organs - liver, skeletal, adipose (fat) tissues
    Diabetes - Hypo
     Type I - autoimmune disorder (destroys ability to produce insulin)
     Type II - due to aging, lifestyle, heredity and other lifestyle (diet) factors
      decreased responsiveness by cells of target organs to insulin
   b) Glucagon - increases blood sugar levels (secreted by alpha cells)
    Target organs - liver, skeletal, adipose (fat) tissues
  6) Male gonads - testes (pelvic region on men)
   a) testosterone, maintain secondary sexual characteristics,  
    stimulate sperm production
  7) Female gonads - ovaries (pelvic region of women)
   a) estrogen and progesterone, maintain secondary 
    sexual characteristics,  
    regulate reproductive cycle
 C) How do hormones work?
  1) 2nd messenger system - most hormones attach to 
   receptors on the cell 
   membrane, they never enter the cell, the receptor 
   delivers the message, 
   usually in the form of cAMP
  2) Direct system - only steroids (sex hormones) can pass through
   the cell membrane and directly affect DNA or chemical