Blood Vessel Summary

Introduction (page 581)

The cardiovascular system provides oxygen and nutrients to tissues and removes wastes.

Structure of the Heart (page 581)

1. Size and location of the heart a. The heart is about 14 centimeters long and 9 centimeters wide.

b. It is located within the mediastinum and rests on the diaphragm.

2. Coverings of the heart a. A layered pericardium encloses the heart.

b. The pericardial cavity is a space between the visceral and parietal layers of the pericardium.

3. Wall of the heart a. The wall of the heart has three layers.

b. These layers include an epicardium, a myocardium, and an endocardium.

4. Heart chambers and valves a. The heart is divided into four chambers—two atria and two ventricles—that communicate through atrioventricular orifices on each side.

b. Right chambers and valves

(1) The right atrium receives blood from the venae cavae and coronary sinus.

(2) The tricuspid valve guards the right atrioventricular orifice.

(3) The right ventricle pumps blood into the pulmonary trunk.

(4) A pulmonary valve guards the base of the pulmonary trunk.

c. Left chambers and valves

(1) The left atrium receives blood from the pulmonary veins.

(2) The bicuspid valve guards the left atrioventricular orifice.

(3) The left ventricle pumps blood into the aorta.

(4) An aortic valve guards the base of the aorta.

5. Skeleton of the heart a. The skeleton of the heart consists of fibrous rings that enclose the bases of the pulmonary artery, aorta, and atrioventricular orifices.

b. The fibrous rings provide attachments for valves and muscle fibers and prevent the orifices from excessively dilating during ventricular contractions.

6. Path of blood through the heart a. Blood that is relatively low in oxygen concentration and high in carbon dioxide concentration enters the right side of the heart from the venae cavae and coronary sinus and then is pumped into the pulmonary circulation.

b. After the blood is oxygenated in the lungs and some of its carbon dioxide is removed, it returns to the left side of the heart through the pulmonary veins.

c. From the left ventricle, it moves into the aorta.

7. Blood supply to the heart a. The coronary arteries supply blood to the myocardium.

b. It is returned to the right atrium through the cardiac veins and coronary sinus.

Heart Actions (page 591)

1. Cardiac cycle a. The atria contract while the ventricles relax; the ventricles contract while the atria relax.

b. Pressure within the chambers rises and falls in cycles.

2. Heart sounds a. Heart sounds can be described as ¡ubb-dupp.

b. Heart sounds are due to the vibrations that the valve movements produce.

c. The first part of the sound occurs as A-V valves close, and the second part is associated with the closing of pulmonary and aortic valves.

3. Cardiac muscle fibers a. Cardiac muscle fibers connect to form a functional syncytium.

b. If any part of the syncytium is stimulated, the whole structure contracts as a unit.

c. Except for a small region in the floor of the right atrium, the fibrous skeleton separates the atrial syncytium from the ventricular syncytium.

4. Cardiac conduction system a. This system, composed of specialized cardiac muscle tissue, initiates and conducts depolarization waves through the myocardium.

b. Impulses from the S-A node pass slowly to the A-V node; impulses travel rapidly along the A-V bundle and Purkinje fibers.

c. Muscle fibers in the ventricular walls form whorls that squeeze blood out of the contracting ventricles.

5. Electrocardiogram (ECG)

a. An ECG records electrical changes in the myocardium during a cardiac cycle.

b. The pattern contains several waves.

(1) The P wave represents atrial depolarization.

(2) The QRS complex represents ventricular depolarization.

(3) The T wave represents ventricular repolarization.

6. Regulation of the cardiac cycle a. Physical exercise, body temperature, and concentration of various ions affect heartbeat.

b. Branches of sympathetic and parasympathetic nerve fibers innervate the S-A and A-V nodes.

(1) Parasympathetic impulses decrease heart action; sympathetic impulses increase heart action.

(2) The cardiac center in the medulla oblongata regulates autonomic impulses to the heart.

Blood Vessels (page 602)

The blood vessels form a closed circuit of tubes that transport blood between the heart and body cells. The tubes include arteries, arterioles, capillaries, venules, and veins. 1. Arteries and arterioles a. The arteries are adapted to carry relatively high pressure blood away from the heart.

b. The arterioles are branches of arteries.

c. The walls of arteries and arterioles consist of layers of endothelium, smooth muscle, and connective tissue.

d. Autonomic fibers that can stimulate vasoconstriction or vasodilation innervate smooth muscles in vessel walls.

2. Capillaries b.

Capillaries connect arterioles and venules. The capillary wall is a single layer of cells that forms a semipermeable membrane.

a. Capillary permeability

(1) Openings in the capillary walls are thin slits between endothelial cells.

(2) The sizes of the openings vary from tissue to tissue.

(3) Endothelial cells of brain capillaries are tightly fused, forming a blood-brain barrier through which substances move by facilitated diffusion.

b. Capillary arrangement

Capillary density varies directly with tissue metabolic rates.

c. Regulation of capillary blood flow

(1) Precapillary sphincters regulate capillary blood flow.

(2) Precapillary sphincters open when cells are low in oxygen and nutrients and close when cellular needs are met.

3. Exchanges in the capillaries a. Gases, nutrients, and metabolic by-products are exchanged between the capillary blood and the tissue fluid.

b. Diffusion provides the most important means of transport.

c. Diffusion pathways depend on lipid solubilities.

d. Plasma proteins generally remain in the blood.

e. Filtration, which is due to the hydrostatic pressure of blood, causes a net outward movement of fluid at the arteriolar end of a capillary.

f. Osmosis due to colloid osmotic pressure causes a net inward movement of fluid at the venular end of a capillary.

g. Some factors cause fluids to accumulate in the tissues.

4. Venules and veins a. Venules continue from capillaries and merge to form veins.

b. Veins carry blood to the heart.

c. Venous walls are similar to arterial walls but are thinner and contain less muscle and elastic tissue.

Blood Pressure (page 608)

Blood pressure is the force blood exerts against the insides of blood vessels.

1. Arterial blood pressure a. The arterial blood pressure is produced primarily by heart action; it rises and falls with phases of the cardiac cycle.

b. Systolic pressure occurs when the ventricle contracts; diastolic pressure occurs when the ventricle relaxes.

2. Factors that influence arterial blood pressure a. Heart action, blood volume, resistance to flow, and blood viscosity influence arterial blood pressure.

b. Arterial pressure increases as cardiac output, blood volume, peripheral resistance, or blood viscosity increases.

3. Control of blood pressure a. Blood pressure is controlled in part by the mechanisms that regulate cardiac output and peripheral resistance.

Cardiac output depends on the volume of blood discharged from the ventricle with each beat and on the heart rate.

(1) The more blood that enters the heart, the stronger the ventricular contraction, the greater the stroke volume, and the greater the cardiac output.

(2) The cardiac center of the medulla oblongata regulates heart rate.

c. Changes in the diameter of arterioles, controlled by the vasomotor center of the medulla oblongata, regulate peripheral resistance.

4. Venous blood flow a. Venous blood flow is not a direct result of heart action; it depends on skeletal muscle contraction, breathing movements, and venoconstriction.

b. Many veins contain flaplike valves that prevent blood from backing up.

c. Venous constriction can increase venous pressure and blood flow.

5. Central venous pressure a. Central venous pressure is the pressure in the right atrium.

b. Factors that influence it alter the flow of blood into the right atrium.

c. It affects pressure within the peripheral veins.

Paths of Circulation (page 619)

1. Pulmonary circuit a. The pulmonary circuit consists of vessels that carry blood from the right ventricle to the lungs, alveolar capillaries, and vessels that lead back to the left atrium.

b. Alveolar capillaries exert less pressure than those of the systemic circuit.

c. Tightly joined epithelial cells of alveoli walls prevent most substances from entering the alveoli.

d. Osmotic pressure rapidly draws water out of alveoli into the interstitial fluid, so alveoli do not fill with fluid.

2. Systemic circuit a. The systemic circuit is composed of vessels that lead from the heart to all body parts (including vessels supplying the heart itself), except the lungs, and back to the heart.

b. It includes the aorta and its branches as well as the system of veins that return blood to the right atrium.

Arterial System (page 622)

1. Principal branches of the aorta a. The branches of the ascending aorta include the right and left coronary arteries.

b. The branches of the aortic arch include the brachiocephalic, left common carotid, and left subclavian arteries.

c. The branches of the descending aorta include the thoracic and abdominal groups.

d. The abdominal aorta terminates by dividing into right and left common iliac arteries.

2. Arteries to the neck, head, and brain include branches of the subclavian and common carotid arteries.

3. Arteries to the shoulder and upper limb a. The subclavian artery passes into the arm, and in various regions, it is called the axillary and brachial artery.

b. Branches of the brachial artery include the ulnar and radial arteries.

4. Arteries to the thoracic and abdominal walls a. Branches of the subclavian artery and thoracic aorta supply the thoracic wall.

b. Branches of the abdominal aorta and other arteries supply the abdominal wall.

5. Arteries to the pelvis and lower limb

The common iliac artery supplies the pelvic organs, gluteal region, and lower limb.

Venous System (page 632)

1. Characteristics of venous pathways a. The veins return blood to the heart.

b. Larger veins usually parallel the paths of major arteries.

2. Veins from the head, neck, and brain a. The jugular veins drain these regions.

b. Jugular veins unite with subclavian veins to form the brachiocephalic veins.

3. Veins from the upper limb and shoulder a. Sets of superficial and deep veins drain the upper limb.

b. The major superficial veins are the basilic and cephalic veins.

c. The median cubital vein in the bend of the elbow is often used as a site for venipuncture.

4. Veins from the abdominal and thoracic walls include tributaries of the brachiocephalic, and azygos veins drain these walls.

5. Veins from the abdominal viscera a. The blood from the abdominal viscera generally enters the hepatic portal system and is carried to the liver.

b. The blood in the hepatic portal system is rich in nutrients.

c. The liver helps regulate the blood concentrations of glucose, amino acids, and lipids.

d. Phagocytic cells in the liver remove bacteria from the portal blood.

e. From the liver, hepatic veins carry blood to the inferior vena cava.

6. Veins from the lower limb and pelvis a. Sets of deep and superficial veins drain these regions.

b. The deep veins include the tibial veins, and the superficial veins include the saphenous veins.

Life-Span Changes (page 63 7)

1. Some degree of cholesterol deposition in blood vessels may be a normal part of aging, but accumulation is great enough to lead to overt disease.

2. Fibrous connective tissue and adipose tissue enlarge the heart by filling in when the number and size of cardiac muscle cells fall.

3. Blood pressure increases with age, while resting heart rate decreases with age.

4. Moderate exercise correlates to lowered risk of heart disease in older people.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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