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Basics of
the cardiovascular system
The heart
A septum separates the human heart into the left and right
halves of the heart, each of which consists of a chamber (ventricle) and an
atrium (atrium). Heart valves are used as check valves between the atria and
the rooms and between the rooms and the adjacent large vessels so that the
blood can only flow in one direction. healthandbeautytimes
The bloodstream
The heart works like pressure and suction pump. With each
contraction of the muscular left ventricle - which happens about 60 to 80 times
per minute under physiological conditions - the oxygen-enriched blood is pumped
via the large artery (aorta) and further via elastic arteries, arterioles, and
capillaries to the organs and tissues. In the body tissues, gas exchange occurs
at the capillary walls, with oxygen being taken up by the cells and carbon
dioxide being released into the capillary blood. The oxygen-poorer and more
carbon dioxide-enriched blood then flow back into the heart's right atrium via
the vena cavae. themarketingguardian
In the pulmonary circulation, the blood leaves the right
ventricle via the pulmonary artery (Truncus pulmonalis) and flows to the two
lungs, where oxygen is enriched. Via the pulmonary vein (pulmonary vein), the
oxygen-enriched blood is pumped through the left atrium into the left ventricle
and then returned to the circulatory system through the aorta.
The blood pressure
The arterial blood pressure is given as a pair of systolic
and diastolic pressures in mm Hg. The systolic arterial pressure is the maximum
pressure created by the heart muscle contraction during the ejection phase.
Diastolic bp is the lowest pressure during the heart's relaxation phase when
the heart chambers fill with blood from the atria. imtechies
The specification in millimeters of mercury (mm Hg)
describes that 1 mm Hg corresponds to the pressure generated by a 1 mm high
column of mercury. While the blood pressure in the heart when the blood is
ejected (systole) is around 160 mm Hg, 100-130 mm Hg is still measured in humans'
arm artery. The pressure in the capillaries is only about 20 mm Hg. techiesguardian
Blood pressure is a variable and depends on the performance
that the cardiovascular system has to provide. Among the factors that determine
blood pressure, the blood volume that the heart ejects per minute and the total
peripheral vascular resistance is central. healthsunlimited
Cardiac output (HMV) or cardiac output (CO)
The cardiac output agrees to the blood volume that the heart
pumps into the bloodstream via the aorta per minute. Under physiological
conditions, this corresponds to about 4.5-5 liters. The HMV increases with
physical exertion and anemia or an overactive thyroid. In contrast, it is
reduced in hypothyroidism or diseases that reduce the heart's pumping capacity.
Peripheral vascular resistance
All blood vessels put up physical resistance to the blood
flow through wall tension. The various sections of the circuit's resistances
differ significantly from one another. The most significant opposition comes
from the small arteries and arterioles. The sum of the individual vessel
resistances is called the total peripheral resistance.
The vascular resistance is determined by:
·
active contraction of the vascular wall muscles
(regulated by vasoconstrictive and vasodilatory signals such as hormones or
nerve messengers)
·
Vessel diameter
·
The viscosity of the blood
Structure
of the blood vessels
The circulatory system is divided into:
·
Arteries that carry oxygen-rich blood to organs,
tissues, and the heart,
·
Veins that carry oxygen-depleted,
carbon-dioxide-enriched blood away from tissues and
·
Capillaries enable the exchange of substances in
the blood in the body tissues.
Regardless of their size, all blood vessels have roughly the
same three-layer wall structure:
The intima layer (tunica interna) lines the blood vessels'
inside. This consists of a layer of flattened endothelial cells, which enables
smooth blood flow in the intact blood vessel and prevents the undesired
attachment of blood particles.
Various messenger substances involved in blood pressure
regulation are formed in the endothelial cells. Of particular importance is
nitric oxide (NO) obtained from arginine and causes vasodilation
(vasodilation).
The media layer (tunica media) consists of smooth muscle
fibers running in a ring around the vessel, traversed by a network of
collagenous and elastic fibers. In the arteries close to the heart, this layer
provides the necessary elasticity to regulate blood pressure.
The media is traversed by sympathetic nerve fibers that regulate
the vessels via adrenaline and noradrenaline. Noradrenaline and high doses of
adrenaline have a vasoconstrictive effect (vasoconstrictive).
The adventitia layer (tunica adventitia) consists of
connective tissue that anchors the blood vessel to the environment. While
smaller vessels are supplied by the blood flowing through, the large vessels'
adventitia is permeated with tiny blood vessels. In arteriosclerotic vascular
changes, these blood vessels can grow into the intima.
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