Chapter 15

Anatomy ∙ Physiology II Chapter 15, Section 1

The Cardiovascular System

FUNCTIONS OF THE HEART

It pumps 7000L (1800 gallons) of blood through our body every day.

The heart contracts 2.5 billion times in a lifetime.

The heart is composed of two pumps The systemic circuit carries blood to the body

The pulmonary circuit carries blood to the lungs

The heart is located within the mediastinum It is about the size of a fist (14cm x 9cm) 2/3 of the heart is left of the midline

1/3

2/3

The heart is posterior to the sternum

Base attachment of major vessels 2nd intercostal space

Apex Pointed inferior margin 5th intercostal space

The heart is surrounded by a pericardial membrane.

The fibrous pericardium forms a thick outer layer of connective tissue.

The parietal pericardium is a serous membrane attached directly to the fibrous layer.

A visceral pericardium is a serous membrane that forms the outer layer of the heart wall.

The pericardial cavity contains serous fluid.

The wall of the heart contains 3 layers

The epicardium is also called the visceral pericardium

The myocardium contains a thick layer of cardiac muscle, with blood vessels and nerves

The endocardium is a smooth layer of squamous epithelium that lines the heart chambers and valves

The heart contains 4 chambers

The right atrium receives blood from the body

The left atrium receives blood from the lungs

The right ventricle pumps blood towards the lungs

The left ventricle pumps blood towards the body

Interventricular septum

A pocket, called the auricle increases the capacity of the atria.

blood enters the heart through the great veins The superior vena cava returns blood from the upper body to the heart

Four pulmonary veins return blood from the lungs to the heart The coronary sinus returns blood from the myocardium to the heart The inferior vena cava returns blood from the lower body to the heart

Great arteries carry blood away from the heart The aorta delivers oxygenated blood to the systemic circulation

The pulmonary trunk* delivers deoxygenated blood to the lungs

* The pulmonary trunk immediately divides into a left and right pulmonary artery.

AV valves prevent backflow into the atria. *AV = atrioventricular

The tricuspid valve guards the right AV orifice

The bicuspid (mitral) valve guards the left AV orifice

AV valves are anchored to the ventricles by chordae tendineae

Chordae tendineae anchored to the cusps papillary muscles

Papillary muscles contract to pull the valves tightly shut

Mitral Valve Prolapse – cusp of the mitral valve protrudes into atrium.

Symptoms include: chest pain, heart palpitations, and fatigue.

Semilunar valves prevent backflow of blood into the ventricles

A pulmonary valve is located at the base of the pulmonary trunk

An aortic valve (not shown) is located at the base of the aorta

Each cusp of a semilunar valve is shaped like a crescent moon

path of blood through the right heart 1. Blood enters right atrium through the SVC, IVC, and coronary sinus

1 2. It passes through the tricuspid valve into the right ventricle

4 4

3. Blood is pumped from the right ventricle, through the pulmonary valve, and into the pulmonary trunk.

2 4. Blood passes into the pulmonary arteries towards the lungs

3

1

path of blood through the left heart 5. Oxygenated blood is returned to the heart through 4 pulmonary veins.

6. Blood enters the left atrium.

9

7. Blood passes through the bicuspid valve into the left ventricle.

8. The left ventricle pumps blood through the aortic valve into the aorta.

9. Blood enters systemic circulation to the tissues throughout the body.

9 9

8 5

5 6

7

Section 2, Chapter 15 Cardiac Cycle & Cardiac Conduction

The cardiac cycle The left and right sides of the heart contract together in a coordinated fashion

Systole – contraction Diastole – relaxation

Ventricular Systole • Ventricles contract to expel blood • Atria are in diastole during ventricular systole, filling with blood • Semilunar valves are opened, while AV valves are closed

Ventricular Diastole • Ventricles are relaxed, filling with blood • Ventricles are 70% full before atria contract • Atrial systole pushes the remaining 30% of blood into ventricles • AV valves are opened while semilunar valves are closed

Heart Sounds The heart valves produce a distinct sound as they close, which can be heard through a stethoscope.

Lubb-Dupp Lubb (S1) = sound of AV valves closing occurs during ventricular systole

Dupp (S2) = sound of semilunar valve closing occurs during ventricular diastole

murmur = abnormal sound from the cusps not closing completely

Heart Sounds - Ausculation aortic valve (A) heard at 2nd intercostal space, right of the sternum 1

pulmonary valve (P) heard at 2nd intercostal space, left of the sternum

2 3 4 5

tricuspid valve (T) heard at 5th intercostal space, either right or left of the sternum

6 7 8 9

mitral valve (M) heard at 5th intercostal space, below left nipple

10

Image from Grant’s Atlas of Anatomy. Each heart valve is indicated by a colored oval and the area of auscultation of the valve is indicated as a circle of the same color containing the first letter of the valve name.

Cardiac Conduction of the Heart The heart is autorhythmic: Specialized cardiac tissue initiate and distribute electrical impulses that generate heart contractions.

Syncytium – intercalated discs contain gap junctions that transmit action potentials from cell-to-cell. Cardiac muscles contract as a functional unit (syncytium) Atrial Syncytium – left and right atria contract together Ventricular Syncytium – left and right ventricles contract together

Cardiac Conduction of the Heart sinoatrial (SA) node Pacemaker of heart Initiates atrial syncytium Fires 80 impulses per minute Parasympathetic inhibition keeps heart rate at about 72 beats per minute

junctional fibers conduct impulses towards towards AV node Figure 15.18 Illustrates the cardiac conduction system.

Cardiac Conduction of the Heart atrioventricular (AV) node Located within inferior wall of interatrial septum Provides a junction between atrial and ventricular syncytia

AV Bundle (Bundle of His)

Only known conduction pathway between atria and ventricles divides into left and right bundle branches Figure 15.18 Illustrates the cardiac conduction system.

Cardiac Conduction of the Heart bundle branches (left and right) Conduction pathways along the interventricular septum Gives rise to Purkinje Fibers

purkinje fibers Transmits action potentials to ventricular myocardium and papillary muscles Initiates ventricular syncytium at apex of heart

Figure 15.19 Summarizes the cardiac conduction system

Figure 15.20 Muscle fibers of the ventricles are whorled shape, which increases the blood output during ventricular systole.

End of Section 2, Chapter 15

section 3, chapter 15 Electrocardiogram

An electrocardiogram, or ECG (or EKG) is a recording of the electrical changes in the myocardium during the cardiac cycle.

Electrocardiogram P Wave atrial depolarization that initiates atrial contraction conduction of electrical impulse across atria from right to left and downward

QRS Complex Ventricular depolarization that initiates contraction of the ventricles This massive wave hides the atria repolarization

Electrocardiogram T Wave represents repolarization of ventricles

Normal ECG pattern

Heart Arrhythmias: normal

ECG of a regular heart rhythm at 75 beats per minute

Atrial Flutter. Atria fire 250-350 times per minute. For every QRS complex there may be 4 or more P waves.

Examples of Heart Arrhythmias. Arrows indicate p Wave.

Bradycardia – cardiac rhythm less than 60 beats per minute.

Tachycardia– cardiac rhythm greater than 100 beats per minute.

Examples of Heart Arrhythmias, fibrillation

Atrial fibrillation. Instead of contracting, the atria become quivering chambers. The ventricles respond only to impulses that make it to the AV node.

Ventricular fibrillation = Life threatening arrhythmia. Ventricles quiver, and are unable to pump blood properly. Requires immediate defibrillation.

regulation of cardiac cycle The heart rate is controlled intrinsically by the SA node, but sympathetic and parasympathetic fibers alter the rate at which the pacemaker fires.

Cardiac Control Center Located within Medulla Oblongata Receives sensory impulses from throughout the cardiovascular system and relays motor impulses to heart in response.

The cardiac control centers include a Cardioinhibitor & cardioaccelerator reflex center

Cardioinhibitor reflex center Parasympathetic fibers from vagus nerves innervate SA & AV nodes.

Vagus nerves release Acetylcholine (ACh) that decreases the firing rates of SA & AV nodes.

Heart rate decreases

Cardioaccelerator reflex center Sympathetic fibers from accelerator nerves innervate SA & AV nodes.

Norepinephrine released from fibers increases the firing rates of SA & AV nodes.

Heart rate and force of contraction increases

Cardioinhibitor & cardioaccelerator reflex centers alter the heart rate in response to sensory impulses from receptors Baroreceptors – monitor blood pressure Located within aortic arch and carotid sinuses • Rising blood pressure stimulates cardioinhibitor center •

`

Figure 15.24b Illustration of the baroreflex arc

End of Section 3, Chapter 15

Section 4, Chapter 15 Blood Vessels

Veins

Arteries

• Returns blood towards the heart

• Convey blood away from the heart

Venules

Arterioles

• Receives blood from capillaries

• Thinner vessels that convey blood towards capillaries

Capillaries • Site of exchange between blood and body tissues

Walls of the blood vessels consists of 3 Layers Tunica Interna (inner) Endothelium A layer of smooth simple squamous • epithelium Secretes biochemicals with a wide • variety of functions.

Basement membrane Bed of connective tissue with elastic & • collagenous fibers

3 Layers of the blood vessel wall Tunica Media (middle) Smooth Muscles Vasoconstriction – muscles contract, • decreasing diameter of vessel Vasodilation – muscles relax, allowing vessel • diameter to increase

Elastic Connective tissue Recoil of elastic fibers helps propel • blood through vessels

3 Layers of the blood vessel wall Tunica Externa (outer) Fibrous Connective Tissue Elastic and collagenous fibers Attaches blood vessel to organs

Vasa Vasorum “vessels of the vessels�

Provide blood supply to walls of thicker arteries

Arterioles Arterioles are smaller divisions of arteries. metarterioles – small arterioles that join capillaries Arteriovenous shunt – connects an arteriole directly to a venule Shunt allows blood to bypass a capillary bed.

Figure 15.27 An arteriovenous shunt provided by a metarteriole.

Capillaries Capillaries smallest diameter blood vessels that consists of a single layer of endothelial cells Site of gas, nutrient, and waste exchange Slits Spaces between endothelia that facilitate diffusion across vessel wall

Figure 15.28 Substances are exchanged through openings (slits) separating endothelial cells.

Capillaries Precapillary sphincters Smooth muscles that regulate the flow of blood through a capillary

Closes a capillary bed when oxygen demand to an organ is low

Figure 15.26 A precapillary sphincter at the base of a capillary.

Capillaries Sinusoids large cavities within discontinuous capillaries Sinusoids allow a rapid exchange of nutrients, debris, proteins, and even cells. located throughout the liver and spleen.

Artificially colored electron micrograph depicts sinusoids throughout the liver.

Venules Continue from capillaries and merge to form veins

Veins Convey blood from body back to the atria of heart Veins follow a pathway roughly parallel to arteries Vessel wall of veins has 3 layers (tunics) similar to arteries

Differences between veins and arteries Veins have poorly developed tunica media Thinner walls, and a larger lumen than arteries

Tunica Interna of veins contain valves Valves prevent blood from flowing backwards towards capillaries.

Veins act as blood reservoirs Most blood (60-70%) is in the veins and venules.

Figure 15.31. Venous valves (a) open as blood moves towards the heart, but (b) close to prevent blood from moving backward away from the heart.

Differences between veins and arteries

Figure 15.25 Blood vessels (a) the wall of an artery. (b) The wall of a vein. (c) cross section of an arteriole (bottom) and a venule (top).

End of Section 4, Chapter 15

Blood Pressure Section 5, Chapter 15

Blood Pressure Blood pressure is the force the blood exerts against the inner walls of the blood vessels Usually refers to pressure in systemic arteries

Arterial blood pressure: Rises with ventricular contractions and falls as ventricles relax Systolic pressure is the maximum pressure during ventricular contraction Diastolic pressure is the minimum pressure when the ventricles relax

Factors that influence blood pressure Cardiac Output- volume of blood ejected from one ventricle per minute .1

cardiac output = stroke volume (mL) X heart rate (beats/minute) Stroke Volume Volume of blood expelled from ventricle with each contraction Average = 70 milliliters per beat (mL/beat) for adult male

Heart Rate Average = 72 beats per minute

Stroke Volume example:

70 mL/beat

Heart Rate X

70 beats/minute

Cardiac Output

=

5040mL/minute

Factors that influence blood pressure Cardiac output (and blood pressure) increases with an increase in stroke volume or heart rate.

heart rate increases

or

blood pressure increases

stroke volume increases

Factors that influence blood pressure Blood Volume Average blood volume in adults = 5 Liters (1.3 gallons) As blood volume increases, blood pressure initially increases Peripheral Resistance Peripheral resistance = friction between blood and blood vessels Vasoconstriction increases resistance and increases blood pressure Vasodilation decreases blood pressure Viscosity of blood Viscosity = resistance of a fluid to flow (thickness of a fluid).

Blood cells and some plasma proteins increase the viscosity of blood.

Anemia (deficiency of red blood cells) reduces viscosity & lowers blood pressure

Factors that influence blood pressure

blood volume increases

heart rate increases

stroke volume increases

peripheral resistance increases

blood viscosity increases

blood pressure increases

Some of the factors that influence arterial blood pressure

Increased blood pressure

heart rate decreases

stroke volume decreases

cardiac output decreases

peripheral resistance decreases

blood pressure is maintained

cardiac output increases

heart rate increases

peripheral resistance increases

stroke volume increases

decreased blood pressure

Control of Blood Pressure

Factors that affect stroke volume End-diastolic volume (EDV) Volume of blood in ventricles at the end of ventricular diastole Ventricles are filled with blood

End-systolic volume (ESV) Volume of blood in ventricles at the end of ventricular systole Only 60% of blood is expelled from heart during a normal contraction Increasing the force of ventricular contractions decreases ESV

Stroke volume = EDV– ESV Increase stroke volume by increasing EDV or decreasing ESV

stroke volume Stroke Volume is directly related to the force of ventricular contraction.

Two events that occur in the ventricles coincide with stroke volume:

1. End-diastolic volume (EDV) Volume of blood in ventricles at the end of ventricular diastole As ventricles fill with blood, muscle fibers are mechanically stretched - preload

2. End-systolic volume (ESV) Volume of blood in ventricles at the end of ventricular systole A normal health heart expels 60% of blood present in ventricle.

stroke volume Stroke Volume is the difference between end diastolic volume (EDV) and end systolic volume (ESV): Stroke Volume = EDV - ESV Frank-Starling Principle: The ability of a heart muscle to generate force depends on the original stretch of a muscle prior to contraction (similar to stretching a rubber band)

The degree of stretch (preload) of the myocardial fibers before contraction determines the stroke volume

A greater end diastolic volume results in a greater force of contraction, leading to a greater stroke volume.

Venous Return Blood pressure rapidly decreases as the blood moves through the arterial system and into the capillary network.

Little pressure remains in the veins, therefore heart actions contribute very little to venous return.

Figure 15H Blood pressure decreases as blood moves away from the heart.

Venous Return Venous return depends on: Skeletal muscle contractions – massaging actions push blood towards heart Respiratory movements – generates pressure in abdominal and thoracic cavities Changes in pressure pushes blood along veins Vasoconstriction – contraction of smooth muscles in tunica media Sympathetic reflexes vasoconstrict the smooth muscles in veins, which can propel additional blood from venous reservoir towards the heart.

Arterial System

Aorta Main trunk of the systemic circulation

Divisions of the aorta Aortic root = attachment to heart Ascending Aorta Aortic arch Thoracic aorta Abdominal aorta

Components of the aortic root

Aortic Valve Aortic Sinus Swelling at aortic root Right and left coronary arteries Supply blood to myocardium of the heart Myocardial infarction = blocked coronary artery

Aortic Bodies Chemoreceptors - monitor CO2 & O2 levels in blood

Branches of the aortic arch Brachiocephalic Artery Brachiocephalic artery divides into: Right common carotid artery Supplies blood to right side of face and head Right subclavian artery - Supplies blood to right arm

Left common carotid artery supplies blood to left side of face and head

Left subclavian artery supplies blood to left arm

Figure 15.42 The major branches of the aortic arch are highlighted in yellow.

End of Section 5, Chapter 15

Section 6, Chapter 15

Arterial Divisions Aorta - Main trunk of the systemic circulation.• Divisions of the aorta• Aortic root = attachment to heart•

Ascending Aorta• Aortic arch• Thoracic aorta • Abdominal aorta•

Section 6, Chapter 15 Systemic arteries and veins

Arterial Divisions Aorta - Main trunk of the systemic circulation.

Divisions of the aorta Aortic root = attachment to heart

Ascending Aorta Aortic arch Thoracic aorta Abdominal aorta

Structures at the aortic root Aortic Valve Aortic Sinus - Swelling at aortic root Aortic Bodies Chemoreceptors - monitor CO2 & O2 levels in blood

4. Right and left coronary arteries

Coronary Arteries Right Coronary Artery branches Posterior interventricular artery: supplies walls of both ventricles Marginal artery: supplies right atrium and right ventricle

Left Coronary Artery branches Anterior interventricular artery: supplies walls of both ventricles

Circumflex Artery: supplies left atrium and left ventricle

Blocked coronary artery = myocardial infarction

Branches of Aortic Arch Brachiocephalic artery supplies Right common carotid artery: right neck and head Right subclavian artery: supplies right arm

2. Left common carotid artery supplies left neck and head

3. Left subclavian artery Supplies left arm

Branches of Thoracic Aorta

Grant’s Anatomy. Branches of the thoracic aorta

Bronchial Arteries – supplies bronchi Pericardial artery – supplies pericardium Esophageal arteries – supplies esophagus

Branches of Abdominal Aorta Phrenic arteries supply diaphragm Celiac Trunk Gastric a. - supply stomach Splenic a. – supply spleen & pancreas Hepatic a. – supplies liver with O2 blood Suprarenal a.

Supplies adrenal glands Superior Mesenteric a.

Supplies small intestine

Branches of Abdominal Aorta Renal arteries Supplies kidneys

Gonadal arteries.

Male = testicular arteries Female = Ovarian arteries

Lumbar arteries Supplies skin and muscles of lower back Inferior mesenteric artery Supplies most of large intestine

Arteries to the Brain, Head, and Neck Divisions of Common Carotid Arteries External Carotid Arteries Supplies blood to face, neck, and scalp

Internal Carotid Arteries Supplies blood to brain Provides 75% of blood to brain

Carotid Sinus - point of bifurcation Carotid bodies – chemoreceptors Carotid baroreceptors Common site of stenosis (narrowing)

Arteries to the Brain, Head, and Neck Branches of Internal Carotid Artery 1. Ophthalmic artery supplies eyes 2. Anterior cerebral artery supplies medial surface of brain 3. Middle cerebral artery Supplies lateral surface of brain

Internal carotid arteries

Arteries to the Brain, Head, and Neck Vertebral Arteries Provides 25% of blood supply to brain Branch from subclavian arteries Pass through transverse foramen of cervical vertebrae Enter skull through foramen magnum

Arteries to the Brain, Head, and Neck Basilar Artery Both vertebral arteries merge to form a basilar artery at the base of the brain.

Supplies blood to brainstem Branch: Posterior cerebral artery Supplies occipital and temporal lobes

Arteries to the Brain, Head, and Neck Cerebral Arterial Circle (Circle of Willis) Joins the internal carotid arteries with basilar artery at base of brain Provides anastomoses (alternate routes) for blood flow

Arteries to the Shoulder and Upper Limb Axillary Artery Arises from subclavian artery Brachial Artery Continuation of axillary artery Used for measuring blood pressure

Ulnar Artery Continues along medial arm to wrist

Radial Artery Continues along lateral arm to wrist Convenient vessel for taking your pulse

Veins that drain the head and neck External Jugular Veins Drains blood from face, scalp, and neck

Internal Jugular Veins Drains blood from brain and deep face Arise from dural sinuses Dural Venous Sinuses Located between 2 layers of dura mater Major CSF draining pathway from brain

Veins that drain the arm Ulnar & Radial Veins drain forearm and hands Merge for form brachial veins Basilic Vein Located on medial aspect of arm Joins the brachial vein near the axilla Axillary Vein Formed from the merging of basilic and brachial veins Cephalic Vein Courses upward on the lateral arm Joins axillary vein to form subclavian vein Median Cubital Vein Joins basilic and cephalic veins at elbow Often the site of venipuncture

Hepatic Portal System Portal System – drains blood from one capillary bed into a second capillary bed.

Hepatic Portal Vein (HPV) Carries nutrient rich blood from abdominal viscera to the liver for processing

•

Hepatic Portal System Tributaries of Hepatic Portal Vein Gastric vein – blood from stomach Splenic vein – blood from spleen & pancreas Superior mesenteric vein – blood from small intestine Inferior mesenteric vein – blood from large intestine

Pathway of Hepatic Portal System

heart

aorta

abdominal viscera

HPV

liver

hepatic vein

IVC

heart

End of Chapter 15