Lecture 33

• Hormones of the Hypothalamus:
  
  • secretes two hormones via the posterior pituitary
    

     
     

    • 
      Oxytocin
      
      • Always being produced by the body at least at low levels
        
        • released in a positive feedback mechanism (more oxytocin released more that is released)
          
      • Actions:
        
        • Causes milk let down of the breasts
          
          • When the baby starts nursing the mother's breast, oxytocin will increase contracting the breast and milk will come out quicker, nursing continues to increase the oxytocin until the milk is gone
            
        • Birthing: Oxytocin causes uterine contractions which stretch the cervix, stretch receptors in the cervix send positive stimuli to release more oxytocin until the baby comes out
          
        • Increases in both men and women during sexual intercourses, surges during orgasm
          

           
           

    • ADH = Anti-Diuretic Hormone = Vasopressin
      
      • Vasopressin is a brand name!
        
      • Increased by the same things that cause thirst
        
        • Increased osmotic pressure of the blood (main regulator)
          
          • osmotic receptors in hypothalamus
            
        • Decreased firing of blood pressure baroreceptors
          
        • Increased angiotensin II
          
        • Stress
          
      • Actions:
        
        • Causes an increase in water uptake by the kidney
          
        • Increase glucogenolysis of liver (minor action)
          
          • More glycogen in blood stream
            
        • Increase ACTH (minor action)
          

           
           

  • Hormones that are regulators of the anterior pituitary
    
    • Releasing inhibiting hormone system
      
      • two hormones produced to regulate the secretion of a hormone in the anterior pituitary (two hormone system)
        
        • have a releasing hormone and an inhibiting hormone
          
      • In this system of the hypothalamus the inhibiting hormone is being fired and created tonally and it is the one regulating
        
      • Inhibiting produced by tonally firing neurons - more firing, more hormone
        
        • May need episodic spikes when more hormone is needed
          
          • Generated by releasing hormone, which is released periodically
            

             
             

    -Hormones regulated by this system include:
    

     
     

    • Growth Hormone (GH)
      
      • Regulated by GIH (Somatostatin) and GRH
        
      • GIH created on a tonal base
        
      • GRH not created all the time and is left until you need a spike
        
        • Released by:
          
          • Low blood levels of growth hormone
            
          • Hypoglycemia (low blood sugar)
            
          • Increase in blood a.a.
            
          • Decrease in blood free fatty acids
            
          • Exercise and stress
            
      • Actions of GH:
        
        • GH causes the liver to secrete insulin like growth factor #1
          
        • actions of insulin like growth factor #1
          
          • increase growth in young
            
          • increase protein anabolism (building)
            
          • inhibits insulin
            
          • increase free fatty acids in the plasma
            
            • turns off the release of GRH and GH and increase the release of GIH
              
    • Prolactin
      
      • Prolactin inhibiting hormone = PIH (dopamine)
        
        • Released tonally
          
      • PRH (releasing)
        
        • Is released episodically in response to:
          
          • Estrogen and breast feeding
            
      • Actions of prolactin
        
        • Stimulate the secretion of milk
          
        • Increases maternal behavior in the female
          
        • No known role for prolactin in the male????
          
        • Increase PIH release
          

           
           

    B. (single hormone system) Stimulating Hormone Releasing
    

     
     

    • Thyroid stimulating hormone (TSH)
      
      • Thyrotropin releasing hormone (TRH) is being made by the hypothalamus which will stimulate the release of thyroid stimulating hormone by the anterior pituitary
        
        • Stimulates TSH
          
      • TSH stimulates the release of T3 and T4 by the thyroid gland
        
        • TRH increased when the environment is cold and also during pregnancy
          
        • TRH decreases when envt warm, stress, and anxiety
          
        • Have balls of epithelial cells in thyroid (colloid)
          
        • Colloid produces hormones from glycoprotein thyroglobulin
          
          • In here, Tyrodine??? Changed and iodine atoms are added - 3 or 4
            
        • T3 and T4 (number referring to the number of iodine atoms)
          
        • T4 is secreted by the thyroid, T3 is the most active form it changes to in the target tissue
          
        • 93% of what is released is T4
          
        • T3 is 4x as active as T4
          
        • almost all of T4 is changed to TS at the target tissue
          
        • T3 - Triodylsomthin
          
        • T4 - Thyroxin
          
          • Physiologists piss off chemists with inability to call right thing, just call it T3/T4
            
      • Actions of T3 and T4
        
        • Increase ALL aspects of glucose metabolism
          
        • Increase ALL aspects of fat metabolism
          
        • Decrease plasma levels of cholesterol, phospholipids, and triglycerides
          
        • Increase the basal metabolic rate
          
        • Increase HR
          
        • Increase protein catabolism
          
        • Affect Sleep
          
          • high levels of T3/T4 will have insomnia
            
          • low levels of T3/T4 you sleep too much
            
        • Promotes normal growth/activity in children
          
          • Lack and become stunted
            
        • Feedback on TRH (minor effect)
          
        • Feedback on TSH (major effect)
          

           
           

  • Sex Hormones
    

     
     

    • LHRH = Luteinizing Hormone Releasing Hormone
      
      • It was originally called LHRH but then they found that it also released FSH so they changed the name to GnRH
        
        • Pulsatile release of LH didn't match release of FSH (might be other way around??)
          
      • They found GnRH had three different isoforms, but only one of these isoforms released FSH and no LH so they called it FSHRF
        
      • LHRH is released in a pulsatile fashion by the hypothalamus
        
      • En Utero it was released in a pulsatile fashion as part of fetal development, but when you were born it stopped being released in pulsatile fashion but was still being released, when LHRH released pulsatile it causes
        
        • LHRH stops being produced in a pulsatile fashion, no LH released
          
        • Puberty: LHRH pulsating again and you get LH production
          
      • LH release by the anterior pituitary
        
        • LH is produced by the pulsatile release of LHRH
          
        • LH release also pulsatile
          
      • LHRH is inhibited by estrogen and testosterone
        
      • Action of LH in the male is to cause interstitial cells of the seminiferous tubules to secrete testosterone
        
        • Actions of testosterone
          
          • Cause spermatogenesis in seminiferous tubules
            
          • Secondary sex characteristics in the male
            
            • low voice, increased aggression, increased muscle mass, increased body hair, decreased sensitivity to pain
              

            3. decreases LH and LHRH secretion
            

      • ONLY 2 ANDROGENS
        
        • Testosterone
          
        • Dihydroteststerone
          
        • These are the only ones that can interact with androgen receptors
          
      • Action of LH in the female:
        
        • cause the theca interna cells on follicle to secrete estrogen and or androstenedione (is a precursor to estrogen)
          
        • androstenedione shares the responsibility for final follicular maturation of FSH (FSH solely responsible for taking you up to the tertiary stage of follicle maturation)
          
        • Stimulates ovulation, ovulation comes from the LH spike
          
        • Causes the formation of the corpus luteum (produces mainly progesterone, relaxin, and estrogens)