Question

the blood - brain barrier
no other body organ is so absolutely dependent on a constant internal environment as is the brain. other body tissues can withstand the rather small fluctuations in the concentrations of hormones, ions, and ( 1 ) that continually occur, particularly after eating or exercising. if the brain were exposed to such chemical changes, uncontrolled neural activity might result—remember that certain ions (sodium and potassium) are involved in initiating nerve impulses and that some amino acids serve as neurotransmitters.
consequently, neurons are kept separated from ( 2 ) substances by the blood - brain barrier, composed of the least permeable capillaries in the whole body. these capillaries are almost seamlessly bound together by tight junctions all around. of water - soluble substances, only water, glucose, and essential amino acids pass easily through the walls of these ( 3 ). metabolic wastes, such as urea, toxins, proteins, and most drugs, are prevented from entering brain tissue. nonessential amino acids and potassium ions not only are prevented from entering the brain, but also are actively pumped from the brain into the blood across capillary walls. although the bulbous “feet” of the ( 4 ) that cling to the capillaries may contribute to the barrier, the relative impermeability of the brain capillaries is most responsible for providing this protection.
the blood - brain barrier is virtually useless against fats, respiratory gases, and other fat - soluble molecules that diffuse easily through all plasma membranes. this explains why bloodborne alcohol, nicotine, and ( 5 ) can affect the brain.

1. nutrients 2. bloodborne 3. capillaries 4. astrocytes 5. anesthetics
2. bloodborne 2. capillaries 3. astrocytes 4. anesthetics 5. nutrients
3. astrocytes 2. anesthetics 3. nutrients 4. bloodborne 5. capillaries
4. anesthetics 2. nutrients 3. bloodborne 4. capillaries 5. astrocytes
5. capillaries 2. astrocytes 3. anesthetics 4. nutrients 5. bloodborne

Explanation:

1. After eating or exercising, there are fluctuations in hormones, ions, and nutrients in the body.
2. Neurons are separated from blood - borne substances by the blood - brain barrier.
3. Water, glucose, and essential amino acids pass easily through the walls of capillaries.
4. Astrocytes' "feet" cling to capillaries and may contribute to the barrier.
5. Fat - soluble substances like anesthetics can affect the brain as the blood - brain barrier is less effective against them.

Answer:

1. nutrients 2. bloodborne 3. capillaries 4. astrocytes 5. anesthetics