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Chapter 7. Cardiovascular System

A researcher opens the chest of an anesthetized mouse and microinjects a small amount of a fluorescent dye into a single cardiac muscle cell at the base of the left ventricle. Over time, the dye spreads toward the left atrium. Which structure listed below is most likely responsible for facilitating this spread?

A. Endomysium

B. Intercalated discs

C. Parasympathetic fibers

D. Sarcoplasmic reticulum

E. T tubules

The answer is B: Cardiac myocytes form a functional syncytium because of the presence of intercalated discs that link cells mechanically and electrochemically. Gap junctions in the intercalated discs will allow the diffusion of the dye from cell to cell. The other structures listed, endomysium, parasympathetic fibers, sarcoplasmic reticulum, and T tubules, while present in the heart, would not be involved in facilitating this process.

While hiking in Canyonlands National Park, a 24-year-old medical student experienced a puncture wound on her leg from a cactus needle. Several days later, she noticed that the wound was swollen and tender, indicating an infection. Because of a class she had taken, she knew that immune system cells are attracted from the blood to the connective tissue involved. What barrier did these cells most likely have to move past to exit the blood and enter the infected tissue?

A. Collagen fibers of the tunica adventitia

B. Elastic fibers of the tunica intima

C. Smooth muscle of the tunica media

D. Tight junctions between endothelial cells

The answer is D: Cells will gain entry to connective tissue by the process of diapedesis (also called extravasation), crawling between endothelial cells of capillaries and postcapillary venules. This indicates that tight junctions between endothelial cells are the barriers that they must pass to gain access to the connective tissue.

Endothelial cells of a capillary bed can regulate the amount of blood flowing into the bed by releasing signaling molecules that affect which nearby structure?

A. End arteries

B. Lymphatics

C. Metarterioles

D. Pericytic venules

E. Vasa vasorum

The answer is C: Smooth muscle sphincters of metarterioles regulate the flow of blood into the capillary beds they supply. The smooth muscle cells are sensitive to chemical signals, including those released ...

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