Cardiovascular System Overview

Introduction

• The blood is kept in motion by the heart
• Nutrient and oxygen supplies run out and waste products build up if blood ceases moving
• Approximately 100,000 heartbeats occur daily, which is about 70 beats per minute
• The heart pumps approximately 1.5 million gallons of blood annually
• That equates to about 2.9 gallons each minute with fluctuations ranging from 5-30 liters per minute

Overview of the Cardiovascular System

• Roughly the size of a clenched fist, the heart
• Two atria and two ventricles form the heart's four chambers
• Blood is pumped by the heart across two circuits: pulmonary and systemic

Overview of Pulmonary and Systemic Circuits

• Arteries carry blood away from the heart
• Veins carry blood towards the heart
• Capillaries link arteries and veins together

The Pericardium

• The heart is surrounded by the pericardium which consists of two parts
• The heart is surrounded by an outer fibrous pericardium
• An inner serous pericardium of two layers:
  • An inner visceral layer, is also called epicardium and is attached to the heart's surface
  • An outer parietal layer that is adjacent to the fibrous pericardium
• The pericardial cavity is a space between the two serous layers that contains pericardial fluid
• Pericardial fluid lubricates to reduce friction

Heart Wall Structure

• The heart's wall consists of three layers: -The epicardium, an external surface, consists of visceral pericardium -The myocardium consists of cardiac tissue including cardiac muscle cells, connective tissue, blood vessels and nerves
• The endocardium is an internal endothelial surface

Cardiac Muscle Tissue

• Cardiac Muscle Tissue has a striated appearance
• Relies on aerobic respiration for fuel
• Contains numerous mitochondria and myoglobin
• Cardiac muscle tissue relies on an extensive circulatory supply
• Cardiac muscle cells contracts involuntarily
• Cells are linked by intercalated discs

Cardiac Muscle Tissue: Intercalated Discs

• Cardiac cells have specialized junctions from cell to cell
• Plasma membranes of adjacent cells are bound by desmosomes
• The myofibrils of neighboring cells are connected through intercalated discs
• Cardiac muscle cells linked via gap junctions
• Ions pass directly from cell to cell giving a direct electrical connection
• As one unit, the muscle cells are able to form a functional syncytium and contract

Cardiac Skeleton

• Each cardiac cell is wrapped is an elastic sheath
• Each muscle layer is wrapped in a sheet of fibrous material
  • These fibrous sheets isolate the superficial layer from the deep layer muscles
• The base of the pulmonary trunk, ascending aorta and valves are encircled by these fibrous sheets

Function of the Cardiac Skeleton

• Stabilizes the position of cardiac cells, including the heart valves
• Provides support for blood vessels and nerves in the myocardium
• Helps distribute the forces of contraction to prevent overexpansion of the heart
• Provides elasticity so the recoils after contraction
• Isolates the atrial cells from the ventricular cells

Heart Orientation and Anatomy

• The heart is slightly to the left of the midsagittal plane
• Located in the mediastinum
• The base sits at the superior border
• The apex lays at the inferior portion
• Only the right atrium forms the right border, while the right ventricle forms the inferior border
• The heart is slightly rotated towards the left
• The right atrium, right ventricle and left ventricle form the anterior surface
• The left atrium and part of the right atrium make up the posterior surface
• The right and left ventricles form the diaphragmatic surface

Heart Chambers

• Sulci (grooves) on the external surface distinguish the four chambers
• The left and right atria are separated by an interatrial groove
• The atria and ventricles are separated by the coronary sulcus
• The left and right ventricles are separated by an anterior interventricular sulcus and a posterior interventricular sulcus

Left and Right Atria

• Positioned superior to the coronary sulcus, the left and right atria both have thin walls
• Each has an expandable auricle anteriorly

Left and Right Ventricles

• Positioned inferior to the coronary sulcus, the left and right ventricles both have walls that are thicker than that of the atria
• The left ventricular wall is thicker than the right ventricular wall

Heart: Internal Anatomy

• The frontal section displays the left and right atria separated by an interatrial septum, and left/right ventricles separated by an interventricular septum
• Folds of endocardium forming both atrioventricular valves exist between the atria and ventricles

The Right Atrium

• Receives deoxygenated venous blood by way of the superior vena cava, the inferior vena cava and the coronary sinus
• The coronary sinus enters at the posterior side
• Contains pectinate muscles on the anterior wall and auricle
• Contains the fossa ovalis a remanent of the foramen ovale, located on the interatrial septum and allowed fetal blood to bypass the lungs

The Right Ventricle

• Receives deoxygenated blood from the right atrium
• Blood flows into the right ventricle by way of the right atrioventricular valve, a tricuspid valve
• Blood leaves to the pulmonary trunk, flowing through the pulmonary valve to the right and left set of pulmonary arteries

Right Ventricle Valves

• The right AV valve connects to the papillary muscles by chordae tendineae
• There are three fibrous flaps (cusps) and papillary muscles
• Each cusp connects by chordae tendineae to distinct papillary muscles
• Papillary muscles and chordae tendineae prevent valve inversion during ventricular contraction

Right Ventricle Internal Surface

• The internal surface of the right ventricle consists of
• Muscular ridges called trabeculae carneae
• A moderator band exists only in the right ventricle
• The moderator band is a muscular band extending from the interventricular septum to the ventricular wall
• Prevents overexpansion of the thin-walled right ventricle

The Left Atrium

• Receives oxygenated blood from the lungs by way of the left and right pulmonary veins
• Pectinate muscles restricted to the auricle
• Blood passes by way of the left atrioventricular valve
• This is a bicuspid valve or left AV valve, also known as the mitral valve

The Left Ventricle

• Has a thicker wall for strong contractions that propels blood through the entire systemic circuit
• The right ventricle has a thinner wall as it only has to pump to the pulmonary circuit
• No moderator band
• Does have prominent trabeculae carneae
• Chordae tendineae connect the left AV valve to two cusps, and two papillary muscles

Blood Flow from the Left Ventricle

• Blood exits the left ventricle by flowing through the aortic valve, called the aortic semilunar valve
• Blood enters into the ascending aorta then travels to the aortic arch
• After the aortic arch, it travels down the descending aorta and into body parts (systemic)

Ventricle Structural Differences

• Right Ventricle
• Thinner wall that carries out weaker contractions. it contains a moderator band
• Left Ventricle
• Thicker wall that is the source for 6-7x more powerful contractions compared to the right ventricle

Valves of The Heart

• There are four valves
• Includes two atrioventricular (AV) valves: tricuspid and bicuspid
• Features two semilunar valves that contains aortic and pulmonary valves

Heart Valves

• Each atrioventricular (AV) valve has four parts:
• Ring of connective tissue which connects it to heart tissue while being a part of the heart's fibrous skeleton
• Contains cusps that connect to the papillary muscles by the chordae tendineae
• Papillary muscles contract in a manner as to prevent the inversion of AV valves during contraction.

Atrioventricular Valves During Cardiac Cycle

• Papillary muscles relax, opening the AV valves due to pressure in the atria
  • Blood flows from atria to ventricle in this state. During this time is prevents backflow when the ventricles contract and increases pressure as the semilunar valves open
• Closure of valves prevents regurgitation of blood back into the atria which forces blood through open semilunar valves

Coronary Blood Vessels

• Originate at the base of the ascending aorta
• Supplies tissue by way of coronary circulation
• Contains these major arteries:
  • Right Coronary Artery (RCA)
    • Atrail Branches including a right marginal and posterior interventricular branch
  • Left Coronary Artery(LCA)
  • A curcumflex branch with left marginal and anterior interventricular branches

Right Coronary Artery

• The right auricle and the pulmonary trunk pass between each other
• Major branches are artial, right marginal, posterior interventricular and the conducting system branches

Major Branches of the Left Coronary Artery

• Major branches include the anterior interventricular which Branches to the posterior interventricular, which then leads to anatomoses
• Circumflex branch
• branches to the left marginal branch
• also has branches to the posterior left ventricle

Coronary Veins

• Coronary veins ultimately drain the venous blood to the right atrium
• This includes the main coronary veins
• Great cardiac vein that delivers blood to the coronary sinus
• Middle cardiac vein which also delivers blood to the coronary artery(vein)
• The coronary sinus drains directly into the posterior of the right atrium.

The Main Coronary Veins Include

• Posterior vein of the left ventricle parallels the posterior left ventricular branch,
• A small cardiac vein that parallels the right coronary artery
• An anterior cardiac vein with branches from the right ventricle cardiac cells

Coordination of Cardiac Contraction

• The cardiac cycle has alternating periods of contraction and relaxation
• The contraction is called systole that also is referring to the blood flowing into the ventricles (Atrial Systole & Ventricular Systole)
• Ventricular Systole also ejects blood into the arteries and the ascending aorta
• Relaxation is diastole as the chambers fill with blood

Cardiac Cycle Coordination

• Conducting cells coordinate cardiac contractions of cardiac cycle
• Nodal Cells includes sinoatrial and atrioventricular nodes which establish the rate with automatic membrane depolarization
• Conducting cells then Distributes stimuli to the myocardium

The Sinoatrial(SA) Node

• The SA node is located in the posterior wall of the right atrium close to where the superior vena cava is
• It is called cardiac pacemaker
• the pacemaker cells generates about 80-100 action potential per minute and can cause either of the following
• Bradycardia- slower than normal or Tachycardia that refers to a faster than normal heart rate
• The Atrioventricular (AV) node sits within the floor of the right atrium

Summary of Cardiac Conduction

• Impulse travels along internodal pathways from the SA node to the AV node, resulting in the atrial contraction
• The AV node slows the impulse
• The impulse goes from AV Node to the AV bundle

Cardiac Cycle: AV Bundle

• The AV bundle conducts the impulse moving along the interventricular septum before dividing to form the right and left bundle branches
• serves the right and left ventricle
• The Purkinje fibers receive the signals by the bundle branches
• those fibers connect to cardiac muscle cells where Ventricular Contraction follows

Autonomic Control of Heart Rate

• The heart rate can be altered by the SA Node settings
• Heart Rate is modified by impulses from the autonomic nervous system
• Nerves in the ANS innervate to these locations
• SA node, AV node, Cardiac cells, Smooth muscles in blood vessels
• The nodal tissue is affected by presence of various chemicals from the ANS
• Norepinephrine from the sympathetic division increases heart rate + force of the contraction.
• Acetylcholine decreases the heart rate and the forces of contraction from the parasympathetic

Cardiac Centers

• Heart rate gets modified by cardiac centers in the medulla oblongata by:
• Cardioacceleratory center
• Stimulates the sympathetic neurons that then increases heart rate increases
• Cardioinhibitory center
  • which activates parasympathetic neurons
    • the Vagus nerve plays a role and the Heart rated decreases