Ure 1542

Figure

Blood is carried to the lungs through branches of the pulmonary arteries, and it returns to the heart through pulmonary veins.

Alveolar capillary

Blood flow

1. Slight net outflow of fluid from capillary

2. Solutes fail to enter alveoli but contribute to the osmotic pressure of the interstitial fluid

Blood flow

4. Fluid from the interstitial space enters lymphatic capillary or alveolar (blood) capillary

Interstitial space

Interstitial space

Lymphatic capillary

Lymph flow

Blood flow

4. Fluid from the interstitial space enters lymphatic capillary or alveolar (blood) capillary

3. Any excess water in alveolus is drawn out by the higher osmotic pressure of the interstitial fluid

Figure 15.43

Cells of the alveolar wall are tightly joined. The relatively high osmotic pressure of the interstitial fluid draws water out of them.

The ductus arteriosus is a fetal blood vessel that joins the aorta and the pulmonary artery. It normally closes shortly after birth, forcing blood to circulate through the lungs, which it did not do during fetal existence. Failure of this vessel to close, a condition called patent ductus arteriosus, can result in heart failure.

To treat a condition called hypoplastic left heart syndrome, physicians keep the ductus arteriosus open. This severe underdevelopment of the left side of the heart causes 8% of fatal heart problems before the age of a year. If surgery cannot correct the condition, a heart transplant is the only option. In order to transplant a heart, surgeons must keep the ductus arteriosus open. They do this by giving the small patient a prostaglandin drug, or by inserting a mold, called a stent, that keeps the vessel open.

Pulmonary edema, in which lungs fill with fluid, can accompany a failing left ventricle or a damaged bicuspid valve. A weak left ventricle may be unable to move the normal volume of blood into the systemic circuit. Blood backing up into the pulmonary circuit increases pressure in the alveolar capillaries, flooding the interstitial spaces with fluid. Increasing pressure in the interstitial fluid may rupture the alveolar membranes, and fluid may enter the alveoli more rapidly than it can be removed. This reduces the alveolar surface available for gas exchange, and the person may suffocate.

Essentials of Human Physiology

Essentials of Human Physiology

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.

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