Download Circulatory and Cardiovascular System

Circulatory and Cardiovascular System
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The functions of the cardiovascular system depend primarily on the activity of the
heart, which distributes blood to the lungs and the rest of the body.
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The heart acts like a pump that generates pressure to keep blood flowing.
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Each day the heart beats approximately 100,000 times, at a rate of about 70
beat/minute.
PATH OF BLOOD:
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The heart pumps blood into two closed circulatory systems of the body:
 Closed circulatory system—means that blood flow is confined within the heart
and blood vessels that have continuously connected walls.
1. The pulmonary circulation--which carries oxygen-poor blood to the lungs and
then picks up oxygenated blood and gives up carbon dioxide
2. The systemic circulation--which supplies the body cells, tissues, and organs with
oxygenated blood. There oxygen is used and carbon dioxide is produced.
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Stages of Blood flow:
1. heart pumps blood into large-diameter arteries (left half)
2. blood flows into small, muscular arterioles
3. which branch into small-diameter capillaries
4. into small venules
5. then into large diameter veins (right half) that return blood to the heart
After completing the systemic circuit, blood returns to the heart through two veins:
1. The superior vena cava--receives blood from veins from the upper body
2. The inferior vena cava—receives blood from all veins below the diaphragm or
lower body
 The vena cavae meet at the right atrium.
HEART
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During our lifespan, the heart beats some 2.5 billion times.
The heart is mostly cardiac muscle tissue protected by a tough outer membrane.
Its inner chambers are lined with connective tissue and epithelial cells called
endothelium—found only in the heart and blood vessels.
From the right atrium, the blood flows down through the tricuspid valve, which is
also called the right atrioventricular (AV) valve.
 This valve has 3 flaps, or cusps.
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Strands of connective tissues called chordae tendinae support the valve and prevent
the cusps from flapping back into the right atrium, and the papillary muscles hold the
chordae tendinae in position.
Now the blood enters the right ventricle, which is the smaller of the two ventricles;
Blood flows into this ventricle and, when it contracts, the blood is forced upward
Note the substantial size of the interventricular septum that separates the right and left
ventricles.
The blood is forced out through the pulmonary semilunar valve, and then into the
pulmonary trunk. The semilunar valve prevents the blood from flowing back into the
ventricle.
The pulmonary trunk now divides to become the left pulmonary artery and the right
pulmonary artery, which lead to the two lungs.
This begins the pulmonary circuit--blood is circulated to the lungs for oxygenation,
then returns to the heart for distribution to the rest of the body.
PATH OF BLOOD THROUGH THE LEFT SIDE OF THE HEART:
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Oxygenated blood returns to the heart by means of the left pulmonary veins.
Since the blood is oxygenated, the blood now enters the left atrium, which is the
second receiving chamber.
The left atrium is separated from the right atrium by the intra-atrial septum.
Blood now flows through the left atrioventricular valve, which is also called the
mitral valve, and enters the left ventricle, which is the larger of the two ventricles.
When the ventricle undergoes contraction, the blood is forced up to the aorta, passing
through the aortic semilunar valve, which cannot be seen because it lies behind the
pulmonary trunk.
On passing the through the valve, oxygenated blood enters the arch of the aorta. The
aorta turns to the posterior region and flows behind the heart.
It can be seen emerging as the descending aorta. Arteries that arise from the aorta
travel to the thorax, abdomen, pelvic cavity, and lower extremities.
This is the systemic circuit.
ELECTRICAL CONTROL OF THE HEART AND THE HEART CYCLE:
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The cells of the heart are self-excitable, which means that they can contract without
first receiving a signal from the nervous system.
Their contraction is caused by a region of the heart called the sinoatrial (SA) node,
which is also sometimes called the pacemaker.
 Sometimes these contractions occur 70 to 80 times a minute.
The SA node is located at the wall of the right atrium.
When the SA node contracts, a wave of excitation travels through the heart wall,
causing the 2 atria to contract in unison.
At the boundary of the atria is the atrioventricular node or AV node.
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The impulse travels to the AV node, where it is delayed for a fraction of a second in
order to allow the atria to empty completely, and then spreads through the ventricles
via Purkinje fibers, which causes them to contract.
The heart cycle refers to the sequence of events that occur during the course of a
heartbeat.
There are two phases of this cycle:
1. Systole--in which the heart contracts and blood is pumped
2. Diastole--in which the heart is relaxed
These two phases are approximately equal in duration.
BLOOD CELLS
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Blood is the medium for the transportation of oxygen from the lungs to the body’s
cells, as well as carbon dioxide from the cells to the lungs.
It also transports nutrients and chemical waste products and participates in the
immunological defense of the body.
The blood is composed of a pale, somewhat yellow fluid known as plasma in which
three basic types of blood cells are suspended.
1. Red blood cells (RBC), also known as the erythrocyte.
 Technically, RBCs are not true cells because they have little internal
organization, no nucleus, and no organelles.
 They are membranous sacs filled with hemoglobin and used for the
transportation of oxygen.
 There are approximately 5. 4 million RBCs per cubic millimeter in an adult
male and about 4.8 RBCs per cubic millimeter in a female.
 RBCs are biconcave discs (meaning that they are thinner at the center than at
the edge), and are approximately 7.8 um in diameter.
 They are produced in the red marrow of bones, and they contain hemoglobin,
which complexes with oxygen outside the cell to form oxyhemoglobin.
 This complex diffuses into the cell.
 RBCs circulate for approximately 120 days and then are destroyed in the
spleen and other organs.
2. White blood cells (WBCs), also known as leukocytes.
A. Neutrophils
 Neutrophils comprise about 60% of the total WBC count.
 They have granular cytoplasm.
 Their nuclei have between two and five lobes.
 Neutrophils are responsible for phagocytosis at infection sites.
B. Eosinophil.
 These cells also have granular cytoplasm, and each cell is approximately 10 to
14 um in diameter.
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Eosinophils make up approximately 1% of the total WBCs and are believed to
play a role in allergic reactions.
C. Basophil
 Basophils also have granular cytoplasm and a multilobed nuclei.
 Basophils constitute about 1% of the total WBC and are believed to function
in allergic reactions, clotting, and inflammation.
D. Monocyte.
 This cell, about 15 to 20 um in diameter, is the largest type of WBC.
 Monocytes make up 6 to 8% of the WBCs and have large nuclei that are
indented along one wall.
 Their nuclei are surrounded by nongranular cytoplasm.
 Monocytes squeeze through the walls of capillaries to enter the tissues, where
they phagocytosize microorganisms.
 They also transform into large phagocytic cells called macrophages
E. Lymphocyte
 Which measures about 8 to 10 um in diameter
 Have circular nucleus that takes up almost the entire nongranular cytoplasm
 Lymphocytes account for about 30% of all WBCs.
 They include B-lymphocytes and T-lymphocytes, both of which are important
in the immune process.
3. Platelet
 Platelets are cell fragments that are approximately 1 to 2 um in diameter.
 They are also known as thrombocytes and consist of small amounts of
cytoplasm enclosed by membranes.
 They form from large cells called megakaryocytes.
 Approximately three hundred thousand platelets exist per cubic millimeter of
blood.
 They function in platelets plugs (which form at severed parts of a blood
vessel), where they react with collagen fibers, and are also present in blood
clots.
PRINCIPAL ARTERIES OF THE BODY:
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The arteries of the circulatory system transport blood away from the heart.
Their main purpose is to carry oxygen and nutrients to body tissues, but they also
transport hormones, elements of the body’s immune system, and metabolic waste.
All of the arteries of the body branch from the aorta.
Veins return the blood to the heart through the vena cava.
Arising from the left ventricle of the heart is the largest artery of the body, the aorta.
An artery is seen curving to the right to become the thoracic (ascending) aorta.
A. The thoracic aorta passes down along the spine and through the diaphragm to
become the abdominal aorta, which in turn splits to become the common iliac
arteries.
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A branch of the aorta at its first major arch is the brachiocephalic trunk, which is also
called the innominate artery.
A. It branches into the common carotid artery (2), which in turn branches into the left
common carotid and the right common carotid artery.
 The carotid arteries supply the neck and head with blood.
B. The third branch from the brachiocephalic trunk is the right subclavian artery.
 The left subclavian artery arises from the arch of the aorta.
A. The subclavian artery supply the upper limbs with blood.
 Arising from the right subclavian artery is the vertebral artery, which supplies
the vertebrae, deep muscles of the neck, and spinal cord with blood.
 Also arising from the subclavian arteries are the left and right axillary arteries.
A. Axillary arteries supply the muscles of the shoulder and the thoracic
muscles, and give rise to the brachial arteries, which service the arm.
 The radial arteries and ulnar arteries arise from the brachial arteries and carry
blood to muscles of the forearm.
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Arising from the aorta just as it leaves the left ventricles, the coronary arteries pass
into the heart muscle, where they supply this organ with oxygen and nutrients.
Another trunk emerges from the aorta after it has passes through the diaphragm. This
is an unpaired artery called the celiac trunk.
A. Arteries from the celiac trunk branch to the liver, stomach, and spleen, as well as
other regions of the upper abdomen.
The hepatic artery branches from the celiac trunk and extends to the liver.
From the abdominal aorta, the gastric artery supplies the stomach, and the splenic
artery moves in the direction of the spleen.
Also extending from the celiac trunk are the paired, renal arteries.
A. The left renal artery supplies the left kidney, and the right renal artery extends to
the right kidney.
Next we see the unpaired superior mesenteric artery. This artery carries blood to the
small intestine, pancreas, and portions of the large intestine.
The gonadal artery leads to arteries that supply the ovaries in females and the testes in
males.
Beyond the gonadal artery is the inferior mesenteric artery—transport oxygen and
nutrients to the colon and rectum
Further down the celiac trunk, two major arteries arise; the common iliac arteries.
The iliac arteries lead to the left and right femoral arteries.
A. Blood from these arteries services the leg muscles.