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Module 1 - Medical Transcription Tutorials
Section V - Cardiovascular System (Heart)
Blood Pressure - Arteriole - Blood Vessels
Blood pressure
Systemic arterial pressures, are generated by the forceful contractions of the heart's left ventricle.
Healthy resting arterial pressures, are relatively low, mean systemic pressures typically being under 100 mmHg, about 1.8 lbf/inČ, above surrounding atmospheric pressure (about 760 mmHg or 14.7 lbf/inČ at sea level).
To withstand and adapt to the pressures
within, arteries are surrounded by varying thicknesses of
smooth muscle, which have extensive elastic and inelastic
connective tissues.
The pulse pressure, i.e. Systolic vs. Diastolic difference,
is determined primarily by the amount of blood ejected by
each heart beat, stroke volume, versus the volume and
elasticity of the major arteries.
Over time, elevated arterial blood sugar
(see Diabetes Mellitus), lipoprotein cholesterol, and
pressure, smoking, and other factors are all involved in
damaging both the endothelium and walls of the arteries,
resulting in atherosclerosis. Diabetes Mellitus also leads
to capillary damage.
Arteriole
An arteriole is a blood vessel that extends and
branches out from an artery and leads to capillaries.
Arterioles have thick muscular walls and are the primary
site of vascular resistance. The mean blood pressure in the
arteries supplying the body is a result of the interaction
between the cardiac output (the volume of blood the heart is
pumping per minute) and the vascular resistance, usually
termed total peripheral resistance by physicians and
researchers.
The up and down fluctuation of the arterial blood pressure
is due to the pulsatile nature of the cardiac output and
determined by the interaction of the stroke volume versus
the volume and elasticity of the major arteries.
The muscular contraction of arterioles is targeted by drugs
that lower blood pressure (antihypertensives), for example
the dihydropyridines (nifedipine and nicardipine), which
block the calcium conductance in the muscular layer of the
arterioles, causing relaxation. This decreases the
resistance to flow into peripheral vascular beds, lowering
overall systemic pressure.
Capillary
The word capillary is used to describe any very narrow tube
or channel through which a fluid can pass. See capillary
action for details.
Capillaries are the smallest of a body's blood vessels,
measuring 5-10 μm. They connect arteries and veins, and most
closely interact with tissues. Capillaries have walls
composed of a single layer of cells, the endothelium. This
layer is so thin that molecules such as oxygen, water and
lipids can pass through them by diffusion and enter the
tissues. Waste products such as carbon dioxide and urea can
diffuse back into the blood to be carried away for removal
from the body. Capillary permeability can be increased by
the release of certain cytokines.
The endothelium also actively transports nutrients,
messengers and other substances. Large molecules may be too
big to diffuse across endothelial cells. In some cases,
vesicles contained in the capillary membrane use endocytosis
and exocytosis to transport material between blood and the
tissues.
In an immune response, the endothelial cells of the
capillary will upregulate receptor molecules, thus
"catching" immune cells as they pass by the site of
infection and aiding extravasation of these cells into the
tissue.
The "capillary bed" is the network of capillaries supplying
an organ. The more metabolically active the cells, the more
capillaries it will require to supply nutrients. The
capillary bed usually carries no more than 25% of the amount
of blood it could contain, although this amount can be
increased through autoregulation (e.g. active muscle cells)
by constricting smooth muscle.
Venule
A venule is a small blood vessel that allows blood to return
from the capillary beds to the larger blood vessels called
veins. Venules have three layers: An inner endothelium
composed of squamous epithelial cells that act as a
membrane, a middle layer of muscle and elastic tissue and an
outer layer of fibrous connective tissue. The middle layer
is poorly developed so that venules have thinner walls than
arterioles.
Vein
In biology, a vein is a blood vessel, which returns
blood from the microvasculature to the heart. Veins form
part of the circulatory system. The vessels carrying blood
away from the heart are known as arteries.
Veins have one-way valves to prevent backflow caused by
gravity.
In systemic circulation, de-oxygenated blood from the
capillary blood vessels is taken by veins to the right part
of the heart. Differently, in the pulmonary circulation
oxygenated blood from the lungs is taken to the left part of
the heart by pulmonary veins. Another special case is portal
circulation where the portal vein transports blood rich in
products of digestion from the intestines to the liver.
NAMES OF IMPORTANT VEINS:
Pulmonary veins
Portal vein
Superior vena cava
Inferior vena cava
Femoral vein
Great saphenous vein
Veins are used medically as points of
access to the blood stream, permitting the withdrawal of
blood specimens (venipuncture) for testing purposes, and
enabling the infusion of fluid, electrolytes, nutrition, and
medications. The latter is called intravenous delivery. It
can be done by an injection with a syringe, or by inserting
a catheter (a flexible tube).
If an intravenous catheter has to be inserted, for most
purposes this is done into a peripheral vein (a vein near
the surface of the skin in the hand or arm, or less
desirably, the leg.) Some highly concentrated fluids or
irritating medications must flow into the large central
veins, which are sometimes used when peripheral access
cannot be obtained. Catheters can be threaded into the
superior vena cava for these uses: if long term use is
thought to be needed, a more permanent access point can be
inserted surgically.
The precise location of veins is much more variable from
person to person than that of arteries.
VENAE CAVAE
The superior and inferior venae cavae are the veins
that return the blood from the body into the heart. They
both empty into the right atrium.
The inferior vena cava travels up
alongside the abdominal aorta with blood from the lower part
of the body.
The superior vena cava is above the heart, and forms from a
convergence of the left and right brachiocephalic veins that
contain blood from the head and the arms. The vena cava
carries blood from the body to the right atrium of the
heart.
PULMONARY ARTERIES
The pulmonary arteries carry blood from the heart to the
lungs. They are the only arteries (other than umbilical
arteries in the fetus) that carry deoxygenated blood.
In the human heart, the pulmonary trunk begins at the base
of the right ventricle. It is short and wide - approximately
5 cm (2 inches) in length and 3 cm (1.2 inches) in diameter.
It then branches into two pulmonary arteries, which connect
to the base of each lung.
Role in disease
Pulmonary hypertension occurs alone and as a consequence of
a number of lung diseases. It can be a consequence of heart
disease (Eisenmenger's syndrome) but equally a cause
(right-ventricular heart failure); it also occurs as a
consequence of pulmonary embolism and scleroderma. It is
characterized by reduced exercise tolerance. Severe forms,
generally, have a dismal prognosis.
PULMONARY VEINS
The pulmonary veins carry oxygen rich blood from the lungs
to the left atrium of the heart. They are the only veins in
the adult human body that carry oxygenated blood.
There are four of them:
Right inferior
Right superior
Left inferior
Left superior
MAJOR BLOOD VESSELS
HEAD: ARTERIES: carotid - common carotid - internal carotid
(ophthalmic, retinal, anterior cerebral, middle cerebral,
posterior communicating) - external carotid (facial,
maxillary, superficial temporal artery) - posterior cerebral
- anterior communicating - basilar - circle of Willis -
middle meningeal VEINS: jugular - vein of Galen
ARMS: ARTERIES: axillary (superior thoracic, thoracoacromial, lateral thoracic, subscapular, anterior circumflex humeral, posterior circumflex humeral) - brachial - radial - ulnar - dorsal scapular VEINS: axillary - brachial - radial - ulnar - median cubital - basilic - cephalic
THORAX: ARTERIES: aorta - brachiocephalic - bronchial - thoracic (lateral thoracic, internal thoracic) - subclavian - vertebral - axillary - pulmonary VEINS: venae cavae (superior - inferior) - brachiocephalic - subclavian - portal - ductus venosus - azygos - pulmonary
ABDOMEN: ARTERIES: celiac artery - marginal - artery of Adamkiewicz - gastroduodenal - gastroepiploic - left gastric - umbilical - mesenteric (superior - inferior) iliac (common - external - internal) - Internal pudendal - renal - hepatic - common hepatic - splenic VEINS: mesenteric (inferior, superior) iliac (common - external) - renal - hepatic - splenic
LEGS: ARTERIES: dorsalis pedis - femoral - peroneal - popliteal - profunda femoris - tibial (anterior, posterior) VEINS: femoral - saphenous (great, small) - peroneal - popliteal - profunda femoris - tibial (anterior tibial, posterior tibial)
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