Research Paper: Cardiac Cycle: Diastole and Systole

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[. . .] " (Chute, 2012, p.1) Capillaries are walls that are comprised by "thin tunica interna, one cell thick" and are reported to allow "only a single RBC to pass at a time." (Chute, 2012, p.1) Capillaries have percytes located on the outer surface, which serve to provide stability to their walls. There are reported to be three structural types of capillaries including those stated as follows:

(1) Continuous -abundant in the skin and muscles, and have: (a) Endothelial cells that provide an uninterrupted lining; (b) Continuous capillaries of the brain; (c) Have tight junctions completely around the endothelium; and (d) Constitute the blood-brain barrier; (e) Adjacent cells that are held together with tight junctions; and (f) Intercellular clefts of unjoined membranes that allow the passage of fluids. (Chute, 2012, p.1)

(2) Fenestrated: These are reported as found "wherever active capillary absorption or filtrate formation occurs." These are located in the small intestines, endocrine glands and kidneys. These are reported to be characterized by:

(1) An endothelium riddled with pores (fenestrations); and (2) Greater permeability to solutes and fluids than other capillaries. (Chute, 2012, p.1)

(3) Sinusoids in which:

(1) Blood flows sluggishly, allowing for modification in various ways;

(2) Are found in the liver, bone marrow, lymphoid tissue, and in some endocrine organs;

(3) Are highly modified, leaky, fenestrated capillaries with large lumens;

(4) Allowed are large molecules (proteins and blood cells) to pass between the blood and surrounding tissues. (Chute, 2012, p.1)

The heart's capillary beds are reported to be a "microcirculation of interwoven networks of capillaries, consisting of the following:

(1) Vascular shunts - metarteriole-thoroughfare channel connecting an arteriole directly with a postcapillary venule;

(2) True capillaries - 10 to 100 per capillary bed, capillaries branch off the metarteriole and return to the thoroughfare channel at the distal end of the bed;

(3) Precapillary sphincter;

(4) Cuff of smooth muscle that surrounds each true capillary;

(5) Regulates blood flow into the capillary; and (6) Blood flow is regulated by vasomotor nerves and local chemical conditions, so it can either bypass or flood the capillary bed. (Chute, 2012, p.1)

The heart's venous system is comprised by 'venules' which are reported to be formed when capillary beds in the heart become joined. Venules allow both fluids and WBCs to pass into the tissues from the bloodstream. Postcapiallary venules are the smallest venules and are comprised of endothelium and a few pericytes. Large venules are reported to have one or two layers of smooth muscle or tunica media. The 'veins' of the heart are formed when venules converge and are comprised by three tunics stated to have a "…thin tunica media and a thick tunica externa consisting of collagen fibers and elastic networks as well as the Capacitance vessels (blood reservoirs) which contain 65% of the blood supply." (Chute, 2012, p.1) It is reported that veins contain much lower blood pressure and have walls that are thinner than arteries. As well veins are reported to have "special adaptations" allowing them to return blood to the heart including "large diameter lumens, which do not resist flow and values that serve to prevent blood backflow which results in varicose veins. Venous sinuses are reported to be "specialized, flattened veins with extremely thin walls." (Chute, 2012, p.1) Vascular Anatomoses contain merging blood vessels, which are more common in veins than in arteries. The arterial anastomoses make provision of "alternate pathways for blood to reach a given body region." (Chute, 2012, p.1) In the event that a branch becomes blocked it is reported that the "…collateral channel can supply the area with adequate blood supply." (Chute, 2012, p.1)

Summary and Conclusion

The practitioner must have a thorough understanding of the mechanics of the cardiac phase in order to diagnose and treat heart patients with cardiac phase disruption related disorders.


Chute, RM (2012) Chapter 19: The Cardiovascular System: Blood Vessels. Retrieved from:

Fukuta, H. And Little, W.C. (2008) The Cardiac Cycle and the Physiological Basis of Left Ventricular Contraction, Ejection, Relaxation, and Filling. Heart Fail Clin. 2008. Jan 4(1):1-11. Retrieved from:

Klabunde, R.E. (2012)… [END OF PREVIEW]

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APA Format

Cardiac Cycle: Diastole and Systole.  (2012, December 2).  Retrieved April 23, 2019, from

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"Cardiac Cycle: Diastole and Systole."  2 December 2012.  Web.  23 April 2019. <>.

Chicago Format

"Cardiac Cycle: Diastole and Systole."  December 2, 2012.  Accessed April 23, 2019.