Chapter 16: Circulatory System
Chapter 16: Circulatory System
Functions and Major Components of the Circulatory
System (pp. 521522)
- The circulatory system transports oxygen and
nutritive molecules to the tissue cells and carbon dioxide and other wastes
away from tissue cells; it also carries hormones and other regulatory molecules
to their target organs.
- Leukocytes and their products help to protect
the body from infection, and platelets function in blood clotting.
- The components of the circulatory system are
the heart, blood vessels, and blood, which constitute the cardiovascular system,
and the lymphatic vessels and lymphoid tissue and organs of the lymphatic
Blood (pp. 523529)
- Blood, a highly specialized connective tissue,
consists of formed elements (erythrocytes, leukocytes, and platelets) suspended
in a watery fluid called plasma.
- Erythrocytes are disc-shaped cells that lack
nuclei but contain hemoglobin. There are approximately 4 million to 6 million
erythrocytes per cubic millimeter of blood, and they are functional for about
- Leukocytes have nuclei and are classified as
granular (eosinophils, basophils, and neutrophils) or agranular (monocytes
and lymphocytes). Leukocytes defend the body against infections by microorganisms.
- Platelets, or thrombocytes, are cytoplasmic
fragments that assist in the formation of clots to prevent blood loss.
- Erythrocytes are formed through a process called
erythropoiesis; leukocytes are formed through leukopoiesis.
- Prenatal hemopoietic centers are the yolk sac,
liver, and spleen. In the adult, bone marrow and lymphoid tissues perform
Heart (pp. 529538)
- The heart is enclosed within a pericardial sac.
The wall of the heart consists of the epicardium, myocardium, and endocardium.
- The right atrium receives blood from the
superior and inferior venae cavae, and the right ventricle pumps blood
through the pulmonary trunk into the pulmonary arteries.
- The left atrium receives blood from the
pulmonary veins, and the left ventricle pumps blood into the ascending
- The heart contains right and left atrioventricular
valves (the tricuspid and bicuspid valves, respectively); a pulmonary
semilunar valve; and an aortic (semilunar) valve.
- The two principal circulatory divisions are
the pulmonary and the systemic; in addition, the coronary system serves the
- The pulmonary circulation includes the vessels
that carry blood from the right ventricle through the lungs, and from
there to the left atrium.
- The systemic circulation includes all other
arteries, capillaries, and veins in the body. These vessels carry blood
from the left ventricle through the body and return blood to the right
- The myocardium of the heart is served by
right and left coronary arteries that branch from the ascending portion
of the aorta. The coronary sinus collects and empties the blood into the
- Contraction of the atria and ventricles is produced
by action potentials that originate in the sinoatrial (SA) node.
- These electrical waves spread over the atria
and then enter the atrioventricular (AV) node.
- From here, the impulses are conducted by
the atrioventricular bundle and conduction myofibers into the ventricular
- During contraction of the ventricles, the intraventricular
pressure rises and causes the AV valves to close; during relaxation, the pulmonary
and aortic valves close because the pressure is greater in the arteries than
in the ventricles.
- Closing of the AV valves causes the first sound
(lub); closing of the pulmonary and aortic valves causes the second sound
(dub). Heart murmurs are commonly caused by abnormal valves or by septal defects.
- A recording of the pattern of electrical conduction
is called an electrocardiogram (ECG or EKG).
Blood Vessels (pp. 538542)
- Arteries and veins have a tunica externa, tunica
media, and tunica interna.
- Arteries have thicker muscle layers in proportion
to their diameters than do veins because arteries must withstand a higher
- Veins have venous valves that direct blood
to the heart when the veins are compressed by the skeletal muscle pumps.
- Capillaries are composed of endothelial cells
only. They are the basic functional units of the circulatory system.
Principal Arteries of the Body (pp. 542554)
- Three arteries arise from the aortic arch: the
brachiocephalic trunk, the left common carotid artery, and the left subclavian
artery. The brachiocephalic trunk divides into the right common carotid artery
and the right subclavian artery.
- The head and neck receive an arterial supply
from branches of the internal and external carotid arteries and the vertebral
- The brain receives blood from the paired
internal carotid arteries and the paired vertebral arteries, which form
the cerebral arterial circle surrounding the pituitary gland.
- The external carotid artery gives off numerous
branches that supply the head and neck.
- The upper extremity is served by the subclavian
artery and its derivatives.
- The subclavian artery becomes first the
axillary artery and then the brachial artery as it enters the arm.
- The brachial artery bifurcates to form the
radial and ulnar arteries, which supply blood to the forearm and hand.
- The abdominal portion of the aorta has the following
branches: the inferior phrenic, celiac trunk, superior mesenteric, renal,
suprarenal, testicular (or ovarian), and inferior mesenteric arteries.
- The common iliac arteries divide into the internal
and external iliac arteries, which supply branches to the pelvis and lower
Principal Veins of the Body (pp. 554560)
- Blood from the head and neck is drained by the
external and internal jugular veins; blood from the brain is drained by the
internal jugular veins.
- The upper extremity is drained by both superficial
and deep veins.
- In the thorax, the superior vena cava is formed
by the union of the two brachiocephalic veins and also collects blood from
the azygos system of veins.
- The lower extremity is drained by both superficial
and deep veins. At the level of the fifth lumbar vertebra, the right and left
common iliac veins unite to form the inferior vena cava.
- Blood from capillaries in the GI tract is drained
via the hepatic portal vein to the liver.
- This venous blood then passes through hepatic
sinusoids and is drained from the liver in the hepatic veins.
- The pattern of circulation characterized
by two capillary beds in a series is called a portal system.
Fetal Circulation (pp. 560562)
- Structural adaptations in the fetal cardiovascular
system reflect the fact that oxygen and nutrients are obtained from the placenta
rather than from the fetal lungs and GI tract.
- Fully oxygenated blood is carried only in the
umbilical vein, which drains the placenta. This blood is carried via the ductus
venosus to the inferior vena cava of the fetus.
- Partially oxygenated blood is shunted from the
right to the left atrium via the foramen ovale and from the pulmonary trunk
to the aorta via the ductus arteriosus.
Lymphatic System (pp. 562566)
- The lymphatic system returns excess interstitial
fluid to the venous system and helps to protect the body from disease; it
also transports fats from the small intestine to the blood.
- Lymphatic capillaries drain interstitial fluid,
which is formed from blood plasma; when this fluid enters lymphatic capillaries,
it is called lymph.
- Lymph is returned to the venous system via two
large lymph ductsthe thoracic duct and the right lymphatic duct.
- Lymph filters through lymph nodes, which contain
phagocytic cells and lymphatic nodules that produce lymphocytes.
- Lymphoid organs include the lymph nodes, tonsils,
spleen, and thymus.
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