Answer:  
If phospholipid bilayer diffusion is normally negligible, there will be tissues (largely lacking in transporters that may be expressed elsewhere) which, despite the relative functional similarity of their phospholipids, are very poor at taking up drugs: the blood–brain [33], blood–testis [34], and blood–retina
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The respiratory system brings air into the lungs supplying the blood with oxygen. Oxygen is carried throughout the body to the organs and keeps the heart pumping and when the blood circulates back to the lungs the process starts over again.
        
             
        
        
        
The answer to this question would be: frequency
The higher intensity of the stimulus, the higher frequency of the action potential will be sent. The nerve can't send a higher action potential, so it firing at higher at higher intensity instead. So when you felt an intense pain, that means the pain receptor is firing more stimulus per second compared to low or mild pain.
        
             
        
        
        
Organisms need nutrients in order to living organism
        
                    
             
        
        
        
The layer of connective tissue, called the _perimysium_ , extends inward from the epimysium and separates the muscle tissue into small sections. these sections contain bundles of skeletal muscle fibers called _fascicles_ . 
Additionally, bundles of contractile proteins called fibrils fill a muscle cell, called a fiber. Outside of each fiber, is the connective tissue endomysium. Bundles of fibers form fascicles, surrounded by perimysium. Bundles of fascicles and perimysium comprise the entire muscle organ, which is enclosed by epimysium.