Ch. 8 final
During exercise, arterial blood pressure changes very little. However, cardiac output may double and blood flow to exercising muscle may go up to 10-fold, while at the same time the blood flow to kidneys may decline by nearly 50%. Explain possible mechanisms that might account for these very different changes.
During exercise the metabolic demands on skeletal muscle increase dramatically. This causes the blood vessels supplying the muscle to dilate, increasing blood flow to skeletal muscle. Meanwhile, an increase in sympathetic nervous system activity (and decrease in parasympathetic activity) causes heart rate and contractility to increase so that cardiac output is increased to supply the extra blood to muscle. The sympathetic nervous system also causes constriction of blood vessels in organs not essential during exercise, such as the kidneys. The overall effect is that more blood is going to those tissues and organs that need it most during exercise.
Inflammation of the pericardium can lead to a condition called pericardial effusion, in which fluids collected in the space surrounding the heart. What effect would this have on the functioning of the heart? How might the condition be treated?
If fluid builds up in the layers surrounding the heart it may exert an external pressure that prevents the heart from filling properly with blood. Therefore the heart may not pump as much blood with each contraction, leading to a decline in cardiac output. The inflammation should be treated with anti-inflammatory drugs, and antibiotics may be used to treat an underlying infection. In severe cases the excess fluid in the pericardial space is removed using a long needle.
When a coronary artery bypass graft (CABG) is performed, the vessels used for the bypass grafts are usually veins taken from the patient's legs. Over time the grafted veins take on many of the characteristics of arteries; that is, they become thicker and stiffer. What might this suggest about the possible cause(s) of the structural differences between arteries and veins? Hypothesize what might happen if you took a section of artery and implanted into a vein.
It implies that at least part of the thickness of arteries is an adaptation to exposure to higher blood pressures. If this is true, then you might expect that if an artery were implanted into the venous circulation it would lose some of its thickness over time and take on more of the characteristics of a vein. It's a lot like what happens to skeletal muscle; when it is exercised it gets bigger and stronger, and when it is not exercised it loses some of its mass and strength.
VSD or ventricular septal defect is a condition that accounts for half of all congenital cardiovascular anomalies. In this condition a hole exists in the septum, the muscular wall between the ventricles, which allows blood from the right and left side of the heart to mix. What sort of problems might this condition cause?
Since blood pressure in the left side of the heart during contraction is greater than in the right, oxygenated blood will tend to flow from the left side of the heart to the right side with each heart beat. The right ventricle will then pump some oxygenated blood back to the lungs rather than sending only deoxygenated blood to the lungs. In effect, some blood ends up passing through the lungs twice which is very inefficient. Also, the heart will have to work harder to get enough oxygenated blood moving throughout the whole cardiovascular system, since some of what it pumps goes back through the hole to the right side.
Workers who spend hours per day standing can develop circulation problems in their legs. A recommended solution is to wear graduated compression stockings. These stockings are tighter around the ankles and less tight higher up on the legs. Why does standing for long periods sometimes lead to circulatory problems, and how can wearing something tight on the legs help prevent this?
Standing for long periods leads to pooling of blood in the veins of the leg, causing the veins to swell. This can lead to valve failure and permanently swollen and distended veins, called varicose veins. Moving around would help prevent this condition, but this may not be possible. Wearing a tight fitting stocking that's tightest at the bottom applies an external pressure on the veins and forces the blood upwards toward the heart. This helps prevent pooling of blood in the veins, fatigue and varicose veins.
Ventricular fibrillation is a potentially fatal condition where the cells of the heart are no longer coordinated in their contractions. Why is it important that contraction of the heart muscle occurs nearly all at once?
Think of the heart as a bag filled with blood. Only when all of the cells contract (and shorten) at once is it able to exert force on the blood inside, pumping it out through the aortic and pulmonary valves. A good analogy would be a balloon nearly filled with water. If you randomly poke it in many places, the water just moves around in the balloon. But if it's a small balloon that you can get your hands around, and you squeeze all at once, water squirts out of the balloon.
Soldiers have to stand in formation at full attention for long periods of time. Sometimes this can cause otherwise very fit and healthy young people to pass out during long inspections. What would cause this?
When you are moving around, skeletal muscles in the legs contract and squeeze the blood through the one-way valves in the veins, returning the blood to the heart. If a person has to stand very still without moving a muscle for long periods of time, blood pools in the leg veins and venous return to the heart can be reduced. This can cause a drop in blood pressure and the person can actually pass out.
Last night you and your roommate were sound asleep when the phone rang. Your roommate, startles awake, jumped from her bed and rushed for the phone across the room. Before she reached the phone she suddenly felt dizzy and had to sit down to avoid fainting. What happened?
Your roommate experienced an episode of orthostatic hypotension, also called postural hypotension. When you sleep, venous blood vessels in the lower extremities relax because they are not exposed to the extra pressure of gravity. When your roommate was startled awake and jumped upright suddenly, the blood vessels did not have time to adjust. The result was gravity-induced pooling of blood in the lower extremities, leading to a decreased venous return to the heart, decreased cardiac output and a low blood pressure in the brain. The dizziness was caused by the reduced blood supply to the brain.
