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The Cardiovascular System

The Cardiovascular System
A closed system of the heart and blood vessels
The heart pumps blood
Blood vessels allow blood to circulate to all parts of the body

The functions of the cardiovascular system
To deliver oxygen and nutrients to cells and tissues
To remove carbon dioxide and other waste products from cells and tissues

The Heart
Location
Thorax between the lungs in the inferior mediastinum
Orientation
Pointed apex directed toward left hip
Base points toward right shoulder
About the size of your fist

The Heart: Coverings
Pericardium—a double-walled sac
Fibrous pericardium is loose and superficial
Serous membrane is deep to the fibrous pericardium and composed of two layers
Visceral pericardium
Next to heart; also known as the epicardium
Parietal pericardium 
Outside layer that lines the inner surface of the fibrous pericardium
Serous fluid fills the space between the layers of pericardium

The Heart: Heart Wall
Three layers
Epicardium
Outside layer
This layer is the visceral pericardium
Connective tissue layer
Myocardium
Middle layer
Mostly cardiac muscle
Endocardium
Inner layer
Endothelium

The Heart: Chambers
Right and left side act as separate pumps

Four chambers
Atria
Receiving chambers
Right atrium
Left atrium
Ventricles
Discharging chambers
Right ventricle
Left ventricle

The Heart: Septa 
Interventricular septum 
Separates the two ventricles
Interatrial septum 
Separates the two atria

The Heart’s Role in Blood Circulation
Systemic circulation
Blood flows from the left side of the heart through the body tissues and back to the right side of the heart
Pulmonary circulation
Blood flows from the right side of the heart to the lungs and back to the left side of the heart

The Heart: Valves
Allow blood to flow in only one direction to prevent backflow
Four valves
Atrioventricular (AV) valves—between atria and ventricles
Bicuspid (mitral) valve (left side of heart)
Tricuspid valve (right side of heart) 
Semilunar valves—between ventricle and artery
Pulmonary semilunar valve
Aortic semilunar valve

AV valves 
Anchored in place by chordae tendineae (“heart strings”)
Open during heart relaxation and closed during ventricular contraction
Semilunar valves
Closed during heart relaxation but open during ventricular contraction
Notice these valves operate opposite of one another to force a one-way path of blood through the heart

Cardiac Circulation
Blood in the heart chambers does not nourish the myocardium
The heart has its own nourishing circulatory system consisting of
Coronary arteries—branch from the aorta to supply the heart muscle with oxygenated blood
Cardiac veins—drain the myocardium of blood
Coronary sinus—a large vein on the posterior of the heart, receives blood from cardiac veins
Blood empties into the right atrium via the coronary sinus

The Heart: Associated Great Vessels
Arteries
Aorta
Leaves left ventricle
Pulmonary arteries
Leave right ventricle
Veins
Superior and inferior venae cavae
Enter right atrium
Pulmonary veins (four)
Enter left atrium

Blood Flow Through the Heart
Superior and inferior venae cavae dump blood into the right atrium
From right atrium, through the tricuspid valve, blood travels to the right ventricle
From the right ventricle, blood leaves the heart as it passes through the pulmonary semilunar valve into the pulmonary trunk
Pulmonary trunk splits into right and left pulmonary arteries that carry blood to the lungs
Oxygen is picked up and carbon dioxide is dropped off by blood in the lungs
Oxygen-rich blood returns to the heart through the four pulmonary veins
Blood enters the left atrium and travels through the bicuspid valve into the left ventricle
From the left ventricle, blood leaves the heart via the aortic semilunar valve and aorta

The Heart: Conduction System
Intrinsic conduction system (nodal system)
Heart muscle cells contract, without nerve impulses, in a regular, continuous way
Special tissue sets the pace
Sinoatrial node = SA node (“pacemaker”), is in the right atrium
Atrioventricular node = AV node, is at the junction of the atria and ventricles
Atrioventricular bundle = AV bundle (bundle of His), is in the interventricular septum
Bundle branches are in the interventricular septum
Purkinje fibers spread within the ventricle wall muscles

Heart Contractions
Contraction is initiated by the sinoatrial node (SA node)
Sequential stimulation occurs at other autorhythmic cells
Force cardiac muscle depolarization in one direction—from atria to ventricles
Once SA node starts the heartbeat
Impulse spreads to the AV node 
Then the atria contract
At the AV node, the impulse passes through the AV bundle, bundle branches, and Purkinje fibers
Blood is ejected from the ventricles to the aorta and pulmonary trunk as the ventricles contract

Homeostatic imbalance
Heart block—damaged AV node releases them from control of the SA node; result is in a slower heart rate as ventricles contract at their own rate
Ischemia—lack of adequate oxygen supply to heart muscle
Fibrillation—a rapid, uncoordinated shuddering of the heart muscle
Tachycardia—rapid heart rate over 100 beats per minute
Bradycardia—slow heart rate less than 60 beats per minutes

The Heart: Cardiac Cycle & Heart Sounds
Atria contract simultaneously
Atria relax, then ventricles contract
Systole = contraction
Diastole = relaxation

Cardiac cycle—events of one complete heart beat
Mid-to-late diastole
Pressure in heart is low
Blood flows from passively into the atria  and into ventricles
Semilunar valves are closed
Atrioventricular valves are open
Atria contract and force blood into ventricles

Ventricular systole
Blood pressure builds before ventricle contracts
Atrioventricular valves close causes first heart sound, “lub”
Semilunar valves open as blood pushes against them
Blood travels out of the ventricles through pulmonary trunk and aorta
Atria are relaxed

Early diastole
At the end of systole, all four valves are briefly closed at the same time
Second heart sound is heard as semilunar valves close, causing “dup” sound
Atria finish refilling as pressure in the heart drops
Ventricular pressure is low
Atrioventricular valves open

The Heart: Cardiac Output
Cardiac output (CO)
Amount of blood pumped by each side (ventricle) of the heart in one minute
Stroke volume (SV)
Volume of blood pumped by each ventricle in one contraction (each heartbeat)
Usually remains relatively constant 
About 70 mL of blood is pumped out of the left ventricle with each heartbeat
Heart rate (HR) 
Typically 75 beats per minute

The Heart: Cardiac Output
CO = HR  SV 
CO = HR (75 beats/min)  SV (70 mL/beat)
CO = 5250 mL/min

Starling’s law of the heart—the more the cardiac muscle is stretched, the stronger the contraction
Changing heart rate is the most common way to change cardiac output

The Heart: Regulation of Heart Rate
Increased heart rate
Sympathetic nervous system
Crisis
Low blood pressure
Hormones
Epinephrine
Thyroxine
Exercise
Decreased blood volume
Decreased heart rate
Parasympathetic nervous system
High blood pressure or blood volume
Decreased venous return

Blood Vessels: The Vascular System
Transport blood to the tissues and back
Carry blood away from the heart
Arteries
Arterioles
Exchanges between tissues and blood
Capillary beds
Return blood toward the heart
Venules
Veins

Blood Vessels: Microscopic Anatomy
Three layers (tunics)
Tunic intima
Endothelium
Tunic media
Smooth muscle
Controlled by sympathetic nervous system
Tunic externa
Mostly fibrous connective tissue

Structural Differences Among Blood Vessels
Arteries have a thicker tunica media than veins
Capillaries are only one cell layer (tunica intima) to allow for exchanges between blood and tissue
Veins have a thinner tunica media than arteries
Veins also have valves to prevent backflow of blood
Lumen of veins are larger than arteries

Venous Aids for the Return of Blood to the Heart
Veins:
Have a thinner tunica media
Operate under low pressure
Have a larger lumen than arteries
To assist in the movement of blood back to the heart:
Larger veins have valves to prevent backflow
Skeletal muscle “milks” blood in veins toward the heart

Movement of Blood Through Vessels
Most arterial blood is pumped by the heart
Veins use the milking action of muscles to help move blood
Capillary Beds
Capillary beds consist of two types of vessels
Vascular shunt—vessel directly connecting an arteriole to a venule
True capillaries—exchange vessels
Oxygen and nutrients cross to cells
Carbon dioxide and metabolic waste products cross into blood

Major Arteries of Systemic Circulation
Aorta
Largest artery in the body
Leaves from the left ventricle of the heart
Regions
Ascending aorta—leaves the left ventricle
Aortic arch—arches to the left
Thoracic aorta—travels downward through the thorax
Abdominal aorta—passes through the diaphragm into the abdominopelvic cavity

Arterial branches
of the ascending aorta
Right and left coronary arteries serve the heart

Arterial branches of the aortia arch (BCS)
Brachiocephalic trunk splits into the
Right common carotid artery
Right subclavian artery
Left common carotid artery splits into the
Left internal and external carotid arteries 
Left subclavian artery branches into the
Vertebral artery
In the axilla, the subclavian artery becomes the axillary artery  brachial artery  radial and ulnar arteries

Arterial branches of the thoracic aorta
Intercostal arteries supply the muscles of the thorax wall
Other branches of the thoracic aorta supply the
Lungs (bronchial arteries)
Esophagus (esophageal arteries)
Diaphragm (phrenic arteries)

Arterial branches of the abdominal aorta
Celiac trunk is the first branch of the abdominal aorta.  Three branches are
Left gastric artery (stomach)
Splenic artery (spleen)
Common hepatic artery (liver)
Superior mesenteric artery supplies most of the small intestine and first half of the large intestine
Left and right renal arteries (kidney)
Left and right gonadal arteries 
Ovarian arteries in females serve the ovaries
Testicular arteries in males serve the testes
Lumbar arteries serve muscles of the abdomen and trunk
Inferior mesenteric artery serves the second half of the large intestine
Left and right common iliac arteries are the final branches of the aorta
Internal iliac arteries serve the pelvic organs
External iliac arteries enter the thigh  femoral artery  popliteal artery  anterior and posterior tibial arteries

Superior and inferior vena cava enter the right atrium of the heart
Superior vena cava drains the head and arms
Inferior vena cava drains the lower body

Major Veins of Systemic Circulation

Veins draining into the superior vena cava
Radial and ulnar veins  brachial vein  axillary vein 
These veins drain the arms
Cephalic vein drains the lateral aspect of the arm and empties into the axillary vein
Basilic vein drains the medial aspect of the arm and empties into the brachial vein
Basilic and cephalic veins are jointed at the median cubital vein (elbow area)
Subclavian vein receives
Venous blood from the arm via the axillary vein
Venous blood from skin and muscles via external jugular vein
Vertebral vein drains the posterior part of the head
Internal jugular vein drains the dural sinuses of the brain
Left and right brachiocephalic veins receive venous blood from the
Subclavian veins
Vertebral veins
Internal jugular veins
Brachiocephalic veins join to form the superior vena cava  right atrium of heart
Azygous vein drains the thorax


Veins draining into the inferior vena cava
Anterior and posterior tibial veins and fibial veins drain the legs
Posterior tibial vein  popliteal vein  femoral vein  external iliac vein
Great saphenous veins (longest veins of the body) receive superficial drainage of the legs
Each common iliac vein (left and right) is formed by the union of the internal and external iliac vein on its own side
Right gonadal vein drains the right ovary in females and right testicle in males
Left gonadal vein empties into the left renal vein
Left and right renal veins drain the kidneys
Hepatic portal vein drains the digestive organs and travels through the liver before it enters systemic circulation
Left and right hepatic veins drain the liver

 Arterial Supply of the Brain
Internal carotid arteries divide into
Anterior and middle cerebral arteries
These arteries supply most of the cerebrum
Vertebral arteries join once within the skull to form the basilar artery
Basilar artery serves the brain stem and cerebellum
Posterior cerebral arteries form from the division of the basilar artery
These arteries supply the posterior cerebrum

 Circle of Willis
Anterior and posterior blood supplies are united by small communicating arterial branches
Result—complete circle of connecting blood vessels called cerebral arterial circle or circle of Willis

 Fetal Circulation
Fetus receives exchanges of gases, nutrients, and wastes through the placenta
Umbilical cord contains three vessels
Umbilical vein—carries blood rich in nutrients and oxygen to the fetus
Umbilical arteries (2)—carry carbon dioxide and debris-laden blood from fetus to placenta
Blood flow bypasses the liver through the ductus venosus and enters the inferior vena cava  right atrium of heart
Blood flow bypasses the lungs 
Blood entering right atrium is shunted directly into the left atrium through the foramen ovale
Ductus arteriosus connects the aorta and pulmonary trunk (becomes ligamentum arteriosum at birth)

 Hepatic Portal Circulation
Veins of hepatic portal circulation drain
Digestive organs
Spleen
Pancreas 
Hepatic portal vein carries this blood to the liver 
Liver helps maintain proper glucose, fat, and protein concentrations in blood
Major vessels of hepatic portal circulation
Inferior and superior mesenteric veins
Splenic vein
Left gastric vein
 
Pulse
Pressure wave of blood
Monitored at “pressure points” in arteries where pulse is easily palpated
Pulse averages 70 to 76 beats per minute at rest

Blood Pressure
Measurements by health professionals are made on the pressure in large arteries
Systolic—pressure at the peak of ventricular contraction 
Diastolic—pressure when ventricles relax
Write systolic pressure first and diastolic last (120/80 mm Hg)
Pressure in blood vessels decreases as distance from the heart increases

Blood Pressure: Effects of Factors
BP is blood pressure
BP is affected by age, weight, time of day, exercise, body position, emotional state
CO is the amount of blood pumped out of the left ventricle per minute
PR is peripheral resistance, or the amount of friction blood encounters as it flows through vessels
Narrowing of blood vessels and increased blood volume increases PR
BP = CO  PR

Neural factors
Autonomic nervous system adjustments (sympathetic division)
Renal factors
Regulation by altering blood volume
Renin—hormonal control

Blood Pressure: Effects of Factors
Temperature
Heat has a vasodilating effect
Cold has a vasoconstricting effect
Chemicals
Various substances can cause increases or decreases
Diet

 Variations in Blood Pressure
Normal human range is variable
Normal
140 to 110 mm Hg systolic
80 to 75 mm Hg diastolic
Hypotension
Low systolic (below 110 mm Hg)
Often associated with illness
Hypertension
High systolic (above 140 mm Hg)
Can be dangerous if it is chronic

Capillary Exchange
Substances exchanged due to concentration gradients
Oxygen and nutrients leave the blood
Carbon dioxide and other wastes leave the cells

Capillary Exchange: Mechanisms
Direct diffusion across plasma membranes
Endocytosis or exocytosis
Some capillaries have gaps (intercellular clefts)
Plasma membrane not joined by tight junctions
Fenestrations (pores) of some capillaries

 Fluid Movements at Capillary Beds
Blood pressure forces fluid and solutes out of capillaries
Osmotic pressure draws fluid into capillaries
Blood pressure is higher than osmotic pressure at the arterial end of the capillary bed
Blood pressure is lower than osmotic pressure at the venous end of the capillary bed

 Developmental Aspects of the Cardiovascular System

A simple “tube heart” develops in the embryo and pumps by the fourth week
The heart becomes a four-chambered organ by the end of seven weeks
Few structural changes occur after the seventh week

Aging problems associated with the cardiovascular system include
Venous valves weaken
Varicose veins
Progressive atherosclerosis
Loss of elasticity of vessels leads to hypertension
Coronary artery disease results from vessels filled with fatty, calcified deposits