Chap 42

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Measurement of blood pressure.

The units are mm of mercury (Hg). A stethoscope is used to listen for sounds of blood flow below the cuff through an artery. The cuff is inflated until the pressure closes the artery, and there is no sound of blood flowing. The cuff is gradually deflated until blood begins to flow under pressure, which is heard as a rushing sound with the stethoscope; this is the systolic pressure. The cuff is loosened further until the blood flows freely and the sounds disappear; this is the diastolic pressure remaining in the artery when the heart is relaxed.

Measurement of blood pressure.
The units are mm of mercury (Hg). A stethoscope is used to listen for sounds of blood flow below the cuff through an artery.		The cuff is inflated until the pressure closes the artery, and there is no sound of blood flowing.		The cuff is gradually deflated until blood begins to flow under pressure, which is heard as a rushing sound with the stethoscope; this is the systolic pressure.		The cuff is loosened further until the blood flows freely and the sounds disappear; this is the diastolic pressure remaining in the artery when the heart is relaxed.

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The cardiac cycle.

During a relaxation phase (atria and ventricles in diastole), blood returning from the large veins flows into the atria and ventricles.
A brief period of atrial systole then forces all remaining blood out of the atria into the ventricles.
During the remainder of the cycle, ventricular systole pumps blood into the large arteries.

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Amphibians have a three-chambered heart and two circuits of blood flow: pulmonary and systemic. Some mixing of blood occurs in a single ventricle.

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Fishes have a two-chambered heart and a single circuit of blood flow. There is no segregation of oxygen-rich and oxygen-poor blood.

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Mammals and birds have a four-chambered heart that completely segregates oxygen-rich and oxygen-poor blood.

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Reptiles other than birds have a three-chambered heart and two circuits of blood flow. A septum divides the single ventricle, reducing mixing of oxygen-rich and oxygen-poor blood.

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The mammalian respiratory system.

Blood pressure decreases as blood flows from the arterial end of a capillary to the venule end, resulting in a net loss of fluid into the interstitial fluid.

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The mammalian cardiovascular system.

Arteries carry blood away from the heart, while veins carry blood to the heart. Oxygen-rich blood is colored red, while oxygen-poor blood is colored blue.

Pulmonary (lung) circuit:

The right ventricle pumps blood to the lungs via
the pulmonary arteries.
Blood in capillaries loads O₂ and unloads CO₂.
Oxygen–rich blood returns via the pulmonary veins to the left atrium, then to
the left ventricle.

Systemic circuit:

Oxygen–rich blood leaves the left ventricle via the aorta to
capillaries in the head and arms, and also to
capillaries in the abdominal organs and legs.
Oxygen–poor blood from the anterior return via the anterior (or superior) vena cava.
The posterior (or inferior) vena cava drains blood from the trunk and hind limbs.
The two venae cavae empty their blood into the right atrium, then into the right ventricle.

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The mammalian heart. Notice the valves, which prevent backflow of blood within the heart, and the relative thickness of the walls of the heart chambers.

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The control of heart rhythm.

The sinoatrial (SA) node (pacemaker) generates electrical impulses, which spread rapidly through intercalated disks between cells , causing both atria to contract in unison. The impulses pass to the atrioventricular (AV) node, where they are delayed for 0.1 second to ensure that the atria empty completely before the ventricles contract. Specialized muscle fibers called bundle branches and Purkinje fibers conduct the signals to the apex. Signals spread throughout the ventricles.

The control of heart rhythm.
The sinoatrial (SA) node (pacemaker) generates electrical impulses, which spread rapidly through intercalated disks between cells , causing both atria to contract in unison.		The impulses pass to the atrioventricular (AV) node, where they are delayed for 0.1 second to ensure that the atria empty completely before the ventricles contract.		Specialized muscle fibers called bundle branches and Purkinje fibers conduct the signals to the apex.		Signals spread throughout the ventricles.

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The mammalian respiratory system. From the nasal cavity and pharynx, air passes through the larynx, trachea, and bronchi to the bronchioles, which end in microscopic alveoli. The pulmonary artery conveys oxygen-poor blood to the alveoli; the pulmonary vein transports oxygen-rich blood back to the heart.