Cardiovascular System CVS Summary, Summaries of Medicine

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Portal circulation is a unique blood system where a capillary bed drains into another capillary bed via a portal vein, bypassing the heart to transport substances directly between organs. The most well-known is the hepatic portal circulation, which takes nutrient-rich blood from the intestines, stomach, and spleen to the liver to be processed before entering the general systemic circulation.

In an ideal system, a substance in motion would remain in motion. However, no system is ideal because all movement creates friction. Just as a ball rolled across the ground loses energy to friction, blood flowing through blood vessels encounters friction from the walls of the vessels and from cells within the blood rub bing against one another as they flow. The tendency of the cardiovascular system to oppose blood flow is called the system’s resistance to flow. Resistance (R) is a term that most of us understand from everyday life. We speak of people being resistant to change or taking the path of least resistance. This concept translates well to the cardiovascular system because blood flow also takes the path of least resistance. An increase in the resistance of a blood vessel results in a decrease in the flow through that vessel. We can express that relationship as Flow α 1/R (2) This expression says that flow is inversely proportional to resistance: if resistance increases, flow decreases; and if resistance decreases, flow increases.

Valves prevent backflow: atrioventricular and semilunar valves ensure one-way movement of blood.

THIS IS IMPORTANT BECAUSE BLOOD SHOULD ALWAYS BE MOVING

FORWARDS = Pathologies in cardiology can involve backflow or regurgitation. When heart valves do not close properly, they are often described as incompetent or insufficient and this leads to the backflow or regurgitation of blood. The resulting valvular heart disease can range from benign to lethal. Some of these conditions are congenital, that is, the individual was born with the defect, whereas others may be attributed to disease processes or trauma.

The heart is a remarkable pump composed largely of cardiac muscle cells that are incredibly active throughout life. Like all other cells, a cardiomyocyte requires a reliable supply of oxygen and nutrients, and a way to remove wastes, so it needs a dedicated, complex, and extensive coronary circulation to supply the thick myocardium. And because of the critical and nearly ceaseless activity of the heart throughout life, this need for a blood supply is even greater than for a typical cell. However, coronary circulation is not continuous; rather, it cycles, reaching a peak when the heart muscle is relaxed and nearly ceasing while it is contracting.

The position of the heart in the torso between the vertebrae and sternum allows for individuals to apply an emergency technique known as cardiopulmonary resuscitation (CPR) if the heart of a patient should stop. By applying pressure with the flat portion of one hand on the sternum in the area between the line at T4 and T9, it is possible to manually compress the blood within the heart enough to push some of the blood within it into the pulmonary and systemic circuits. This is particularly critical for the brain, as irreversible damage and death of neurons occur within minutes of loss of blood flow. Current standards call for compression of the chest at least 5 cm deep and at a rate of 100 compressions per minute, a rate equal to the beat in “Staying Alive,” recorded in 1977 by the Bee Gees. If you are unfamiliar with this song, a version is available on www.youtube.com. At this stage, the emphasis is on performing high-quality chest compressions, rather than providing artificial respiration. CPR is generally performed until the patient regains spontaneous contraction or is declared dead by an experienced healthcare professional.