Chapter 20 Answers
Circulation and Respiration
Visual Understanding
Figure 20.7
Does being a dedicated “couch potato” or “computer geek” ever cause circulatory problems?
Blood in the veins does not receive the strong push that blood in the arteries gets from the action
of the heart. Blood moves through the veins, say all the way down in your toes, back towards the
heart with much less force, pushed along by the contraction of your leg muscles and kept from
flowing backwards by valves. If you are not exercising the muscles of your arms and legs they
are not helping your blood to circulate efficiently.
Over long periods, months and years, the lack of muscle tone and the lack of movement can
cause serious problems, especially for the cells in your hands and feet that depend on the steady
flow of nutrients and oxygen to stay healthy. This is one reason why people who are confined to
a bed for long periods of illness need someone such as a physical therapist to help them move
their bodies, arms and legs daily.
This is just one of several reasons why doctors advise people to get some exercise several times a
week, and to take short breaks at least every 30 minutes or so when studying, watching
television, playing video games or using a computer.
Figure 20.30
What conclusions can you draw about cigarette smoking and women’s health? Explain.
The incidence of lung cancer in men followed a sharp increase about 20 years after men began
smoking in large numbers. As the numbers of cigarettes smoked leveled off and held steady, the
number of lung cancer sufferers also leveled off at about 90 men per 100,000 per year. The
number of cigarettes smoked for women has not yet leveled off and held steady, and it has
surpassed the number for men.
The incidence of lung cancer for women looks very much as if it will follow the same sort of
curve that the incidence of lung cancer for men followed. However, since it looks as if the
number of cigarettes smoked per capita may still be increasing, it follows that the incidence of
lung cancer for women may end up much higher than it did for men. We will need at least
another 20 years of data to have a better idea of what will happen.
Challenge Questions
Circulation
Your friend, Masaji, has a painful paper cut on his finger and it’s bleeding. Disgusted, because it
already stained his new shirt, he asks you why the blood is so important, anyway. What do you
tell him?
You explain that the bloodstream has three major functions, transportation, regulation, and
protection.
Your blood carries oxygen and nutrients to all your cells, and picks up all sorts of wastes to be
removed from the body. Where your blood is directed, and which capillaries are closed off or
opened, helps you regulate body temperature and perform other functions. Because the blood
also carries hormones, your body’s messenger system, it also helps you control a wide variety of
other functions. Your blood also helps you defend against many kinds of invaders. Offer Masaji
some sympathy and a bandage.
Evolution of Vertebrate Circulatory Systems
Explain how the mnemonic “VAVA Lungs, VAVA Body” describes the path of the blood in
humans.
V = Vena cava, the large veins leading from the body into the
A = right Atrium which leads to the
V = right Ventricle. When the ventricle contracts, it sends the blood into the
A = pulmonary Artery and into the
Lungs where the blood becomes oxygenated.
The blood then returns to the heart through the
V = pulmonary Veins which empty into the
A = left Atrium which leads to the
V = left Ventricle. When the ventricle contracts, it sends the blood into the
A = Aorta which carries the blood out and into the
Body
Respiration
Sometimes when people are eating, they take a bite that is too big, or is not completely chewed,
and when they swallow it becomes stuck partway down the esophagus. Because the esophagus
is a soft, muscular tube that lies just behind the trachea, a somewhat stiffer tube, this bulge of
food in the esophagus can sometimes push hard enough on the trachea to close it off. In this
case, people have been trained to do the Heimlich maneuver, which is a method of pushing up
rapidly on the diaphragm, compressing the lungs. Why might this help?
If you push up rapidly on the diaphragm and compress the lungs, the air that was in the lungs
must go someplace. Its only choice is to push up through the trachea and try to escape through
the mouth and nose.
Since the trachea is being pinched closed by the food in the esophagus, the strong blast of air
coming up the trachea from the lungs can sometimes bump into the stuck place with enough
force to shove the food back into the throat and out the mouth. It often takes several tries, but
the food will fly out of the mouth with considerable force, just like a bb from an air gun or a wad
of paper from a straw.
Lung Cancer and Smoking
Why can cigarette smoking be linked to an increased incidence of many kinds of cancer?
The p53 protein constantly patrols the DNA in your cells looking for damage. If it finds a
problem it sets in motion events to either repair the DNA or kill the cell to prevent mutations,
such as those that cause cancer, from reproducing. There are chemicals in cigarette smoke that
attach to the gene that controls the manufacture of the p53 protein, keeping it from being made.
So the cigarette smoke keeps p53 protein from being made, the p53 protein is not available in the
cell to check on the DNA, and if any of the mutations that cause any of the different types of
cancer occur, there is no way to stop it.