Answer to Question 1
The brain has several transport mechanisms. Small, uncharged molecules, including oxygen and carbon dioxide, cross freely. Water crosses through special protein channels in the wall of the endothelial cells. Also, molecules that dissolve in the fats of the membrane cross easily. Examples include vitamins A and D and all the drugs that affect the brainfrom antidepressants and other psychiatric drugs to illegal drugs such as heroin. How fast a drug takes effect depends partly on how readily it dissolves in fats and therefore crosses the blood brain barrier.
For a few other chemicals, the brain uses active transport, a protein-mediated process that expends energy to pump chemicals from the blood into the brain. Chemicals that are actively transported into the brain include glucose (the brain's main fuel), amino acids (the building blocks of proteins), purines, choline, a few vitamins, iron, and certain hormones.
Answer to Question 2
b
Cerebral angiography. The four angiograms each reveal the distribution of blood vessels supplying th
Lateral View of the human brain in cross section
A) Sagittal section of the brain; (B) lateral view of the brain.
Vegetable oils are good sources of essential fatty acids
The Central Nervous System Includes the Brain and Spinal Cord
Parts of a Brain