ch16 (1)

Chapter 16: The Cardiovascular System: Blood Vessels and Circulation

© 2013 John Wiley & Sons, Inc. All rights reserved.


The Cardiovascular System: Blood Vessels and Circulation Blood vessel structure and functionBlood flow through blood vesselsCirculatory routesChecking circulationAging and the cardiovascular system

Blood Vessel Structure and Function Arteries carry blood away from the heart. Their walls consist of three layers.

The structure of the middle layer gives arteries their two major properties, elasticity and contractility.

Arterioles are small arteries that deliver blood to capillaries. Through constriction and dilation, arterioles play a key role in regulating blood flow from arteries into capillaries.

Capillaries are microscopic blood vessels through which materials are exchanged between blood and interstitial fluid. Precapillary sphincters regulate blood flow through capillaries.

Capillary blood pressure “pushes” fluid out of capillaries into interstitial fluid (filtration). Blood colloid osmotic pressure “pulls” fluid into capillaries from interstitial fluid (reabsorption).


Blood Vessel Structure and Function Autoregulation refers to local adjustments of blood flow in response to

physical and chemical changes in a tissue.

Venules are small vessels that emerge from capillaries and merge to form veins. They drain blood from capillaries into veins.

Veins consist of the same three layers as arteries but have less elastic tissue and smooth muscle. They contain valves that prevent backflow of blood. Weak venous valves can lead to varicose veins.

Venous return, the volume of blood flowing back to the heart through systemic veins, occurs due to the pumping action of the heart, aided by skeletal muscle contractions (the skeletal muscle pump), and breathing (the respiratory pump).


Blood Vessel Structure and FunctionFunctions of Blood Vessels1. Blood vessels form a closed system of tubes that carries

blood away from the heart (in arteries), transports it through the tissues of the body (in arterioles, capillaries, and venules), and then returns it to the heart (in veins).

2. Exchange of substances between the blood and body tissue cells occurs as blood flows through the capillaries.

3. Nutrients and oxygen diffuse from the blood through interstitial fluid into tissue cells. Waste products, including carbon dioxide, diffuse from tissue cells through interstitial fluid into the blood.



Blood Vessel Structure and Function


Blood Vessel Structure and Function


Capillary Exchange


Animation:

You must be connected to the internet to run this animation.

• Capillary Exchange


Skeletal Muscle Pump1) While you are standing at rest, both the venous valve closer to the heart and the one farther from the heart in this part of the leg are open, and blood flows upward toward the heart.

2) Contraction of leg muscles, such as when you stand on tiptoes or take a step, compresses the vein. The compression pushes blood through the valve closer to the heart, an action called milking. At the same time, the valve farther from the heart in the uncompressed segment of the vein closes as some blood is pushed against it. People who are immobilized through injury or disease lack these contractions of leg muscles. As a result, their venous return is slower and they may develop circulation problems.

3) Just after muscle relaxation, pressure falls in the previously compressed section of vein, which causes the valve closer to the heart to close. The valve farther from the heart now opens because blood pressure in the foot is higher than in the leg, and the vein fills with blood from the foot.


Animation:


• Vascular Regulation

Blood Flow Through Blood Vessels Blood flow is determined by blood pressure and vascular resistance.

Blood flows from regions of higher pressure to regions of lower pressure. Blood pressure is highest in the aorta and large systemic arteries; it drops progressively as distance from the left ventricle increases. Blood pressure in the right atrium is close to 0 mm Hg.

An increase in blood volume increases blood pressure, and a decrease in blood volume decreases it.

Vascular resistance is the opposition to blood flow mainly as a result of friction between blood and the walls of blood vessels. It depends on the size of the blood vessel lumen, blood viscosity, and total blood vessel length.

Blood pressure and blood flow are regulated by neural and hormonal negative feedback systems and by autoregulation.


Blood Flow Through Blood Vessels The cardiovascular (CV) center in the medulla oblongata helps regulate

heart rate, stroke volume, and size of blood vessel lumen.

Vasomotor nerves (sympathetic) control vasoconstriction and vasodilation.

Baroreceptors (pressure-sensitive receptors) send impulses to the cardiovascular center to regulate blood pressure.

Chemoreceptors (receptors sensitive to concentrations of oxygen, carbon dioxide, and hydrogen ions) also send impulses to the cardiovascular center to regulate blood pressure.

Hormones such as angiotensin II, aldosterone, epinephrine, norepinephrine, and antidiuretic hormone raise blood pressure; atrial natriuretic peptide lowers it.



Blood Pressure Changes


The Cardiovascular Center


Negative Feedback Regulation of Blood Pressure


Animation:


• Negative Feedback Control of Blood Pressure

Circulatory Routes The two major circulatory routes are the systemic circulation and the

pulmonary circulation.

The systemic circulation takes oxygenated blood from the left ventricle through the aorta to all parts of the body and returns deoxygenated blood to the right atrium.

The parts of the aorta include the ascending aorta, the arch of the aorta, the thoracic aorta, and the abdominal aorta (see Exhibit 16.A). Each part gives off arteries that branch to supply the whole body (see Exhibits 16.B–16.C).

Deoxygenated blood is returned to the heart through the systemic veins (see Exhibit 16.D). All veins of the systemic circulation flow into either the superior or inferior vena cava or the coronary sinus, which empty into the right atrium (see Exhibits 16.E–16.G).


Circulatory Routes The pulmonary circulation takes deoxygenated blood from the right

ventricle to the air sacs of the lungs and returns oxygenated blood from the air sacs to the left atrium. It allows blood to be oxygenated for systemic circulation.

The hepatic portal circulation collects deoxygenated blood from the veins of the gastrointestinal tract and spleen and directs it into the hepatic portal vein of the liver. This routing allows the liver to extract and modify nutrients and detoxify harmful substances in the blood. The liver also receives oxygenated blood from the hepatic artery.

Fetal circulation exists only in the fetus. It involves the exchange of materials between fetus and mother via the placenta. The fetus derives O2 and nutrients from and eliminates CO2 and wastes into maternal blood. At birth, when pulmonary (lung), digestive, and liver functions begin, the special structures of fetal circulation are no longer needed.



Circulatory Routes


Anatomy Overview:


• Comparison of Circulatory Routes


Aorta and itsBranches


Aorta and itsBranches


Arch of Aorta


Arch of Aorta


Arteries of the Pelvis and Lower Limb


Arteries of the Pelvis and Lower Limb


Veins


Veins


Veins of the Head and Neck


Veins of the Head and Neck


Veins of the Hand

Principal Veins of the Upper Right Limb


Principal Veins of the Upper Right Limb



Veins of the Pelvis and Lower Limbs


Veins of the Pelvis and Lower Limbs


Hepatic Portal Circulation


Hepatic Circulation


Fetal Circulation

Checking Circulation Pulse is the alternate expansion and elastic recoil of an artery with

each heartbeat. It may be felt in any artery that lies near the surface or over a hard tissue.

A normal pulse rate is about 75 beats per minute.

Blood pressure is the pressure exerted by blood on the wall of an artery when the left ventricle undergoes systole and then diastole. It is measured by a sphygmomanometer.

Systolic blood pressure (SBP) is the force of blood recorded during ventricular contraction. Diastolic blood pressure (DBP) is the force of blood recorded during ventricular relaxation. The normal blood pressure of a young adult male is less than 120/80.


Aging and the Cardiovascular SystemHypertension

About 50 million Americans have hypertension, or persistently high blood pressure. It is the most common disorder affecting the heart and blood vessels and is the major cause of heart failure, kidney disease, and stroke. In May 2003, the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure published new guidelines for hypertension because clinical studies have linked what were once considered fairly low pressure readings to an increased risk of cardiovascular disease. The new guidelines are as follows:

Category Systolic (mm Hg) Diastolic (mm Hg)

Normal Less than 120 and Less than 80

Prehypertension 120–139 or 80–89

Stage 1 hypertension 140–159 or 90–99

Stage 2 hypertension Greater than 160 or Greater than 100


Hypertension


Aging and the Cardiovascular SystemAneurysm

An aneurysm (AN-ū-rizm) is a thin, weakened section of the wall of an artery or a vein that bulges outward, forming a balloonlike sac. Common causes are atherosclerosis, syphilis, congenital blood vessel defects, and trauma. If untreated, the aneurysm enlarges and the blood vessel wall becomes so thin that it bursts. The result is massive hemorrhage along with shock, severe pain, stroke, or death.


Aging and the Cardiovascular System General changes associated with aging include

reduced elasticity of blood vessels, reduction in cardiac muscle size, reduced cardiac output, and increased systolic blood pressure.

The incidence of coronary artery disease (CAD), congestive heart failure (CHF), and atherosclerosis increases with age.



End of Chapter 16

Copyright 2012 John Wiley & Sons, Inc.All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information herein.

ch16 (1)

Documents

john wiley sons

blood flows

volume of blood

backflow of blood

microscopic blood vessels

capillary blood pressure

rights reserve

blood colloid osmotic