Lecture 36

Pancreatic Hormones, cont.

 
 

1. 
   Glucagon
   
   1. produced by the alpha cells of the pancreas
      
   2. secretion due to low glucose levels of blood entering pancreas
      
   3. cortisol stimulating glucagon
      
   4. exercise will stimulate glucagon
      
   5. direct sympathetic innervation
      
   6. Actions of glucagon:
      
      1. increase glycogen breakdown by the liver
         
      2. decrease glucose uptake by the cells
         
      3. increase gluconeogenesis
         
      4. increase protein catabolism
         
      5. increase amino acid uptake and destruction by the liver
         
      6. increase lipolysis (breakdown of adipose tissue)
         
   7. ***blood metabolite levels are increased***
      

       
       

2. Somatostatin
   
   1. produced by the delta cells of the pancreas
      
   2. is growth hormone inhibiting hormone but not actually working on growth hormone
      
   3. secretion stimulated by CCK and by same factors that cause insulin release
      
   4. action to inhibit the secretion of the other three hormones
      
   5. sympathetic nervous system is helping to close the _____ duct
      

       
       

3. Pancreatic
   Polypeptide
   
   1. prodcued by the pancreatic polypeptide (pp) cells of the pancreas
      
   2. released in response to the
      
      1. protein meal
         
      2. Fasting
         
      3. Exercising
         
      4. low blood sugar
         
   3. Hypoglycemia will cause release
      
   4. Actions:
      
      1. slow food absorption, make it more constant
         

    
    

   Pineal Gland
   

    
    

4. Melatonin
   
   1. See chart in notes
      
   2. Produced by parenchymal cells
      
   3. Secreted in response to sympathetic stimulation will originate in the paraventricular nucleus of the hypothalamus
      
   4. The suprachiasmatic nucleus (SCN) where have circadian clock suppresses the paraventricular nucleus during the daytime and does nto suppress it at night, this pineal gland is not receiving light input it is receiving sympathetic stimulation, so less melatonin
      
   5. Constant during light, increases in dark (circadian night) and then spikes at 4am, then levels off to baseline in the light
      
   6. Actions:
      
      1. Thought to play a role in the sleep/wake cycle, but not well understood
         
      2. Affects LHRH release in some animals, not due to direct stimulation but due to in way of passing day length information to other parts of the brain
         
      3. In human children melatonin stimulates growth hormone release and that's the reason that we seem to have growth spurts, night growth spurts
         
      4. Blind kids don't grow as fast unless they get melatonin injections
         

    
    

5. Erythropoeitin
   
   1. Produced by
      
      1. kidneys (85%) and the liver (15%)
         
   2. Secretion is due to
      
      1. hypoxia (low partial pressure of oxygen)
         
      2. There is a heme type protein in liver and kidney and when the protein is not oxygenated it stimulates the secretion of EPO, when it is oxygenated it inhibits EPO
         
      3. Testosterone
         
   3. Actions of EPO are
      
      1. to stimulate RBC production, shorten maturation time
         

          
          

6. Leptin
   
   1. Produced by adipose cytes
      
   2. More fat you have more leptin you have
      
   3. Leptin levels are monitored by the weight regulatory system of the hypothalamus and they respond, low levels increase food intake and reduce metabolism, high levels or leptin decrease food intake and increase metabolism
      

    
    

   (end of endocrineology)
   

    
    

   Reproduction
   

    
    

7. Male
   
   1. Spermatogenesis is the entire production of sperms
      
      1. Takes place in the seminiferous tublules of the testes
         
      2. Scrotum makes environment ideal for sperm production
         
         1. Has temp. of about 32 Deg. C - ideal
            
      3. Panpiniform plexus wraps around cord
         
         1. Venus blood is cooling constantly
            
            1. Testosterone is going from veins to arteries to maintain high level of testosterone (casusing spermatogenesis)
               
      4. Spermatogonia -
         
         1. 3 types:
            
            1. Type A Dark - True Stem cells
               
               1. Undergo mitosis to form 2 more spermatogonia
                  
               2. Become
                  
            2. type A Pale cells
               
               1. The cells of these don't break apart they stay together and form strings of cells with thin bridges of cytoplasm between them
                  
               2. the bridges are going to mean that the whole strand of cells will be synchronized in cell divisions
                  
                  1. the number of mitotic cell divisions done in human is not known
                     
               3. Eventually all the Type A pale produce a
                  
            3. Type B spermatogonia
               
               1. Type B spermatognia are still linked together
                  
               2. each of the type B are two primary spermatocytes
                  
               3. the string of primary spermatocytes enter meiosis I
                  
                  1. crossover of the parents chromatids occur in Meiosis I prophase
                     
                  2. this creates new gene combinations
                     

                      
                      

         2. Type A dark on the basilar lamina between the sarcoma cells, each successive generations from the initial multiplication has been rising up between the sertoli cells
            
         3. the sertoli cells have a tight junction, which will open up and allow the string of cells to rise up and then will close behind it
            
         4. during meiosis I the homologous c'somes will separate (govern the same trait)
            
         5. at the end of meiosis I this string has become a string of secondary spermatocytes
            
         6. the secondary spermatocytes enter into meosis II, spreading into a string of spermogens which are still strung together but can be easily broken apart
            
         7. spermogens have a haploid number
            
         8. Spermatogenesis – conversion of spermatids to spermatozoa
            
            1. no further cell division, it is a metamorphosis
               
         9. the spermatids are near the lumen of the seminiferous tubule and will form a special bond with the sertoli cell and the spermatid becomes completed surrounded by the plasma membrane of the sertoli cell
            
         10. tail starts to form outside PM and will grow into the lumen of the tubule of the sertoli cells
             
         11. head stays embedded, but has cytoplasm around it, as metamorphosis proceeds orientation is maintained and tail starts to grow and the head grows and the whole thing moves towards the edge of the sertoli cells
             
         12. towards the end of metamorphosis the head is stripped of cytoplasm and moves away from the sertoli cells
             
         13. sertoli cell releases head and holds onto the extra cytoplasm = spermeation
             
             1. 64 days have passed since first pale cell
                
         14. excess cytoplasm is called residual body and is destroyed by the sertoli cell
             
         15. newly formed spermatozoa can't swim yet, but to move it the sertoli cell secretes huge amount of fluid, the fluid flows out of the seminiferous tubules to the efferent ductules and the head of the epidydymis is absorbing the fluid, ciliated cells push the sperm
             
         16. efferent ductules and epidydimis have smooth muscle elements that help move the sperm along by peristaltic contractions
             
         17. in the epidydmis itself the sperm become mobile, this is maturation of the sperm, a matter of aging, epidydimis not doing anything to cause this to occur
             
         18. although they're mobile they will still be pushed along by peristaltic contractions through the vas deferens
             
         19. during ejaculation the sperm become hypermobile
             
         20. the sperm are fixed in various fluids during ejaculation, 60% of the fluid comes from seminal vesicle, 30% comes from the prostrate gland, 10% epidydimis and vas deferens = SEMEN
             
         21. Cowper's gland secretes a clear thick mucus that neutralizes acid from urine and lubricates the urethra and is done pre-ejaculatory, can contain sperm, this is why do not use withdrawal method for protection
             
         22. pH of semen = 7.5
             
         23. semen contains fructose and citric acid as well as prostoglandins (make cervical mucus more receptive to sperm, theory that it possibly generates reverse peristalsis in uterus and fallopian tubes to move sperm along)
             
         24. semen contains TGF-beta, same in bone remodeling
             
             1. sperm will use this to suppress the female immune system, so she doesn't have an immune response to the sperm