The heart contains four chambers: two atria, which receive venous blood,and two ventricles,which eject blood into arteries. The right ventricle pumps blood to the lungs, where the blood becomes oxygenated; the left ventricle pumps oxygenated blood to the entire body. The proper flow of blood within the heart is aided by two pairs of one-way valves.
About the size of a fist, the hollow, cone-shaped heart is divided into four chambers. The right and left atria (singular, atrium) receive blood from the venous system; the right and left ventricles pump blood into the arterial system. The right atrium and ventricle (sometimes called the right pump) are separated from the left atrium and ventricle (the left pump) by a muscular wall, or septum. This septum normally prevents mixture of the blood from the two sides of the heart.
Remember that Jason has a ventricular septal defect (a hole in the septum that separates the ventricles). Gven that the blood is under higher pressure in the left ventricle than the right during ventricular contraction, what effect could Jason's septal defect have on the blood in his heart?
1. State the normal pH range of arterial blood plasma and explain how it is affected by the concentration of carbon dioxide in the blood. Explain how the plasma carbon dioxide concentration is regulated.
2. Explain how bicarbonate helps to maintain acid-base balance and describe the conditions that may result in metabolic acidosis or alkalosis.
Between the atria and ventricles, there is a layer of dense connective tissue known as the fibrous skeleton of the heart. Bundles of myocardial cells (described in chapter 12) in the atria attach to the upper margin of this fibrous skeleton and form a single functioning unit, or myocardium. The myocardial cell bundles of the ventricles attach to the lower margin and form a different myocardium. As a result, the myocardia of the atria and ventricles are structurally and functionally separated from each other, and special conducting tissue is needed to carry action potentials from the atria to the ventricles. The connective tissue of the fibrous skeleton also forms rings, called annuli fi-brosi, around the four heart valves, providing a foundation for the support of the valve flaps.
Superior vena cava
Left atrium Pulmonary artery Pulmonary vein
Inferior vena cava
■ Figure 13.9 A diagram of the circulatory system. The systemic circulation includes the aorta and venae cavae; the pulmonary circulation includes the pulmonary arteries and pulmonary veins.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.