The Cardiovascular System 12 Chapter

The Cardiovascular System

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Anatomy of the Heart

o In the thoracic cavity within the mediastinum

o Heart functions:• Keeps O2-poor blood separate from

O2-rich blood

• Keeps the blood flowing in one direction

• Creates blood pressure• Regulates the blood supply


o The Wall and Coverings of the Heart• Pericardium

Two-layered serous membrane that encloses the heart Visceral pericardium (epicardium) forms the outer

surface of the heart• Myocardium

Thickest part of heart wall Made of cardiac muscle

• Endocardium Inner layer of heart Composed of simple squamous epithelium

• Pericardial fluid Secreted by epicardium and parietal pericardium Reduces friction as the heart beats

• The coverings of the heart: Protect the heart Confine it to its location Prevent it from overfilling

Fig 12.2


o Chambers of the Heart• Right atrium

Receives O2-poor blood Vessels that empty into right atrium:

Superior vena cava Inferior vena cava Coronary sinus

Venous blood leaves right atrium through the an atrioventricular (AV) valve (tricuspid)

Directs the flow of blood Prevents backflow Has three cusps

• Right ventricle Chordae tendineae

Fibrous cords connected to the tricuspid valve Connected to the papillary muscle in ventricle

Blood passes through the pulmonary semilunar valve into the pulmonary trunk


• Left atrium Receives O2-rich blood Blood enters atrium through 4 pulmonary

veins Blood leaves left atrium through an AV

valve (bicuspid or mitral)

• Left ventricle Forms the apex of the heart Blood leaves the left ventricle through the

aortic semilunar valve and enters the aorta

Fig 12.3


o Operation of the Heart Valves • AV valves

Normally open When ventricle contracts

AV valves shut Papillary muscles contract, preventing valve

from reverting into an atrium

• Semilunar valves Normally closed Contraction of ventricles forces valves

open


o Heart Sounds• First sound, “lub”

Heard when ventricles begin to contract AV valves close Lasts longer and has a lower pitch

• Second sound, “dup” When ventricles relax Semilunar valves close

• Heart murmurs Due to ineffective, leaky valves Valves do not close properly Allows blood to backflow into atria or

ventricles after valves have closed


o Coronary Circulation• Heart cells are not nourished by the blood in

the chambers• The left and right coronary arteries branch

from the aorta Coronary arteries branch numerous times Heart is encircled by small blood vessels

• After blood passes through cardiac capillaries it enters the cardiac veins

• Cardiac veins enter the coronary sinus• Coronary sinus enters the right atrium

Fig 12.4

Physiology of the Heart

o Conduction System of the Heart• Initiates and stimulates contraction of

the atria and ventricles• Is intrinsic – does not require nervous

stimulation• Coordinates contraction of atria and

ventricles


• Nodal Tissue Has muscular and nervous characteristics SA (sinoatrial) node – upper posterior wall

of the right atrium Initiates the heartbeat Sends out an excitation impulse every 0.85

seconds Pacemaker of the heart

AV (atrioventricular) node – base of the right atrium

Impulse is delayed Signals the ventricles to contract

Atrioventricular bundle (AV bundle) Purkinje fibers

Fig 12.5


Artificial pacemaker may be implanted if the SA node fails to work properly

Heart block – slow beating of the heart due to a damaged AV node

Ectopic pacemaker An area other than the SA node that can

become the pacemaker May cause an extra beat Caffeine and nicotine can stimulate an ectopic

pacemaker Electrocardiogram

Electrolyte changes within the myocardium can be detected by electrical recording devices

Helps a physician detect and diagnose the cause of an irregular heartbeat (arrhythmias)


• Cardiac Cycle All events that occur during one heartbeat Systole – contraction of heart muscle Diastole – relaxation of heart muscle Three phases of the cardiac cycle:

Phase 1: Atrial Systole Both atria are in systole Ventricles are in diastole Both AV valves are open The semilunar valves are closed

Phase 2: Ventricular Systole Both ventricles are in systole The atria are in diastole Semilunar valves are forced open Both AV valves are closed

Phase 3: Atrial and Ventricular Diastole Both atria and both ventricles are in diastole Both AV valves are open The semilunar valves are closed

Fig 12.6


• Cardiac Output (CO) Volume of blood pumped out of a ventricle in one

minute Average CO is 5,250 ml/minute Dependent on two factors:

Heart rate Beats per minute Can be altered by the autonomic nervous system Temperature affects the heart rate Proper electrolytes are needed to keep the heart

rate regular Stroke volume

Amount of blood pumped by a ventricle each time it contracts

Depends on the strength of contraction Influenced by blood electrolyte concentration

and the activity of the autonomic nervous system

Venous return and difference in blood pressure also affect the strength of contraction

Fig 12.7

Anatomy of Blood Vessels

o Vessels function to:• Transport blood and its contents• Carry out gas exchange• Regulate blood pressure• Direct blood flow

o Arteries and Arterioles


o Arteries and Arterioles• Transport blood away from the heart• Thick, strong walls composed of:

Tunica interna - endothelium Tunica media – smooth muscle and elastic fibers Tunica externa – outer connective tissue layer

• Elasticity allows an artery to expand and recoil

• Arterioles are small arteries Constriction and dilation affect blood distribution

and blood pressure Autonomic nervous system regulates the number

of arterioles that are contracted


o Capillaries• Microscopic blood vessels• One layer of endothelial cells• Site of nutrient and gas exchange• Not all capillary beds are in use at the

same time Most have a shunt Precapillary sphincters control the

entrance of blood into capillaries

Fig 12.9


o Veins and Venules• Return blood to the heart• Venules

Drain blood from the capillaries Join together to form veins

• Vein walls are thinner than arterial walls• Valves in veins prevent backward flow of

blood• Varicose veins and phlebitis

Varicose veins Abnormal and irregular dilations in superficial veins Hemorrhoids are varicose veins in the rectum Develop when the valves of the veins become weak

Phlebitis Inflammation of a vein Thromboembolism can occur

Fig 12.8

Physiology of Circulation

o Velocity of Blood Flow• Slowest in capillaries

Cross-sectional area is at its maximum Allows time for gas and nutrient exchange

• Blood flow increases as venules combine to form veins

• Velocity of blood returning to the heart is low compared to that of blood leaving the heart

Fig 12.10


o Blood Pressure• The force of blood against blood vessel walls• Highest in the aorta• Decreases with distance from left ventricle

and is lowest in the venae cavae• Fluctuates between systolic blood pressure

and diastolic blood pressure• Mean arterial blood pressure

Pressure in the arterial system averaged over time Equals cardiac output x peripheral resistance

Increasing CO increases MABP Peripheral resistance is the resistance to flow

between blood and the walls of a blood vessel The smaller the blood vessel or the longer the

blood vessel the greater the resistance The greater the resistance the higher the blood

pressure

Fig 12.11


• Blood pressure and cardiac output The faster the heart rate the greater the

cardiac output As cardiac output increases, blood

pressure increases The larger the stroke volume, the greater

the blood pressure Stroke volume and heart rate increase

blood pressure only if the venous return is adequate


Venous return depends on: A blood pressure difference The skeletal muscle pump and the respiratory

pump Contraction of skeletal muscles compress

the walls of veins causing blood to move past a valve

During inhalation, thoracic pressure falls and abdominal pressure rises and blood will flow from an area of higher pressure to an area of lower pressure

Total blood volume If blood volume decreases, blood pressure

falls If blood volume increases, blood pressure

rises

Fig 12.12


• Evaluating circulation Pulse

Alternating expansion and recoil of arterial walls

Can be felt in superficial arteries (pulse points) Radial artery Common carotid

Pulse rate normally indicates the rate of the heartbeat

Fig 12.14


Blood pressure Usually measured in

brachial artery Sphygmomanometer is an

instrument that records pressure changes

The blood pressure cuff is inflated until no blood flows through the artery

Korotkoff sounds produced when the

pressure in the cuff is released and blood begins to hit the arterial walls

Systolic pressure When sounds end

diastolic pressure is recorded

Fig 12.15


Normal blood pressure is 120/80 Higher number is systolic pressure –

pressure recorded when the left ventricle contracts

Lower number is diastolic pressure – pressure recorded when the left ventricle relaxes

Hypertension is high blood pressure When the systolic pressure is 140 or greater When the diastolic pressure is 90 or greater

Circulatory Routes

o Pulmonary circuit• Blood from the body collects in the

right atrium• Blood moves into the right ventricle• Right ventricle pumps blood into the

pulmonary trunk• Blood flows into the pulmonary

capillaries in the lungs• Blood flows from the lungs through

the pulmonary veins and into the left atrium

Circulatory Routes

o Congestive Heart Failure• Damaged left side of the heart fails to pump

adequate blood• Blood backs up in the pulmonary circuit

Pulmonary blood vessels have become congested Causes pulmonary edema

• Indicated by shortness of breath, fatigue, and a constant cough

• Treatment Diuretics – increase urinary output Digoxin – increases the heart’s contractile force Dilators – relax blood vessels

Circulatory Routes

o Systemic circuit• Includes all other arteries and veins of the

body• Aorta and venae cavae are the major

pathways for blood in the systemic circuit Aorta is the largest artery Superior and inferior venae cavae are the largest

veins

• Begins in the left ventricle• The left ventricle pumps blood into the aorta• Branches from the aorta go to the major

body regions and organs

Circulatory Routes

Table 12.1

Fig 12.16

Circulatory Routes

Table 12.2

Fig 12.17

Circulatory Routes

o Special Systemic Circulations• Hepatic Portal System

Carries venous blood from the stomach, intestines, and other organs to the liver

Capillaries of the digestive tract empty into the superior mesenteric and the splenic veins

Superior mesenteric and splenic vein join to form the hepatic portal vein

Gastric veins empty into the hepatic portal vein Nutrients and wastes diffuse into liver cells The hepatic veins drain the liver and enter the

inferior vena cava

Fig 12.18

Circulatory Routes

• Hypothalamus-Hypophyseal Portal System

• Blood Supply to the Brain Anterior and posterior cerebral arteries

and the carotid arteries supply the brain with arterial blood

Cerebral arterial circle (circle of Willis) The blood vessels form a circle Provides alternate routes for supplying arterial

blood to the brain Equalizes blood pressure in the brain’s blood

supply

Fig 12.19

Circulatory Routes

• Fetal Circulation Four circulatory features not present in adult circulation

Foramen ovale Ductus arteriosus Umbilical arteries Ductus venosus

Related to the fact that the fetus does not use its lungs Path of blood in the fetus

From the right atrium Most blood enters the left atrium via the foramen ovale Blood that has entered the right ventricle and then the

pulmonary trunk is shunted to the aorta through the ductus arteriosus

Exchange between maternal and fetal blood occurs at the placenta

Blood in the umbilical arteries is oxygen poor Blood in the umbilical veins is oxygen rich

Enters the ductus venosus The ductus venosus then joins with the inferior vena

cava

Fig 12.20

Effects of Aging

o Heart• Grows larger with age• In many middle-aged people, heart is

covered by a layer of fat• Number of collagenous fibers in the

endocardium increases• Valves become thicker and more rigid• The myocardium loses contractile

power and ability to relax• Resting heart rate decrease

Effects of Aging

o Arteries• Atherosclerosis and arteriosclerosis

are common• Chances of coronary thrombosis and

heart attack increase• Occurrence of varicose veins

increases Thromboembolism Pulmonary embolism

Homeostasis

o Maintaining blood composition, pH, and temperature

• Growth factors regulate the manufacture of formed elements in the red bone marrow

• The digestive system absorbs nutrients into the blood

• The lungs and kidneys remove metabolic wastes from the blood

• The kidneys help maintain the pH of blood• The blood distributes heat• Blood vessels in the skin dilate or constrict

in response to changing temperatures

Homeostasis

o Maintaining blood pressure• Sensory receptors within the aortic

arch detect a decrease in blood pressure

• The lymphatic system collects excess tissue fluid, which helps regulate blood volume and pressure

• The endocrine and nervous systems work together to regulate blood pressure

• Venous return is aided by the muscular and respiratory systems

The Cardiovascular System 12 Chapter

Documents

Transcript of The Cardiovascular System 12 Chapter