the cardiovascular system 12 chapter
TRANSCRIPT
The Cardiovascular System
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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
Anatomy of the Heart
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
Anatomy of the Heart
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
Anatomy of the Heart
• 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
Anatomy of the Heart
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
Anatomy of the Heart
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
Anatomy of the Heart
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
Physiology of the Heart
• 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
Physiology of the Heart
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)
Physiology of the Heart
• 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
Physiology of the Heart
• 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
Anatomy of Blood Vessels
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
Anatomy of Blood Vessels
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
Anatomy of Blood Vessels
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
Physiology of Circulation
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
Physiology of Circulation
• 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
Physiology of Circulation
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
Physiology of Circulation
• 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
Physiology of Circulation
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
Physiology of Circulation
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