Download The heart has four main chambers: the left ______, the left

Heart and circulation worksheet
Please fill in the blanks. In some cases I have given you options e.g.
“sympathetic/parasympathetic” - one of these is the correct answer - and these options
will be found in brackets after the blank space.
The heart has four main chambers: the left and right atria, and the left and right
ventricles. Blood leaving the left side of the heart is oxygenated and is pumped to the
systemic circulation; blood leaving the right side of the heart is de-oxygenated and is
pumped to the lungs (through the pulmonary artery) in order to pick up oxygen.
The electrical impulse that causes the heart to contract begins in the sinoatrial (SA)
node, the natural “pacemaker” of the heart. Excitation spreads across both right and
left atria until it reaches the atrioventricular (AV) node, which introduces a delay. The
impulse then enters the ventricles and causes them to contract.
Blood pressure can be measured by putting a cuff around the upper arm and inflating
it to around 200 mmHg, and listening for blood flowing past the cuff. Pressure is
gradually lowered until the first sounds are heard: this corresponds to systolic blood
pressure and typical values are around 120 mmHg. Pressure is lowered further, and
the sounds become louder and clearer until suddenly they disappear: the pressure at
which the sounds disappear is the diastolic blood pressure and typical values are
around 80 mmHg.
The receptors that measure blood pressure are called baroreceptors, and are situated in
the aorta and the carotid sinus. These receptors monitor pressure of blood leaving the
heart and entering the brain respectively. Signals from these receptors pass into the
brainstem centre that controls blood pressure. The output of this centre passes into the
sympathetic and parasympathetic branches of the autonomic nervous system.
A drop in blood pressure increases sympathetic nerve activity and this causes the
heart rate to speed up and resistance of the blood vessels to increase. The combination
of these effects increases blood pressure and thus maintains it at the correct level.
Since blood pressure is maintained at a stable level, blood supply to different parts of
the circulation can be easily controlled by changing the resistance. The main
resistance vessels are called arterioles, and are placed between the large arteries and
the capillaries. During exercise, the most striking changes are an enormous increase in
blood supply to the skeletal muscle; conversely, the amount of blood flowing to the
digestive system is greatly reduced in exercise.