Heart
Overview
Arteries: transport blood away from the heart
Veins: transport blood back to the heart
The heart is the center of the cardiovascular system - nonstop pumping, average 75 beats per minute (that comes to over 8 million beats before you turn 21)
The arteries and veins entering and leaving the heart are called great vessels
Overview
Heart valves ensure blood flow is unidirectional
The heart is two side-by-side pumps that work at the same rate and pump the same volume of blood
- One pump directs blood to the lungs where it picks up oxygen
- One pump directs blood to body tissues where the blood delivers the oxygen
The heart generates blood pressure through alternate cycles of contraction and relaxation
- Blood pressure is the force of the blood pushing against the inside walls of blood vessels
- It is essential to circulate blood throughout the body
Pulmonary and Systemic Circulations
Pulmonary circulation:
- Starts with the right side of heart pumping deoxygenated blood through pulmonary
arteries to lungs
-After oxygen pickup and carbon dioxide release, pulmonary veins carry blood to left side of heart
Systemic circulation:
-Left side of the heart pumps oxygenated blood through systemic arteries to body’s cells
-Nutrients, repiratory gases and wastes are exchanged, and systemic veins carry the blood back to the right side of the heart
Position of the heart
Heart is located slightly left of midline, deep to the sternum, in space called the mediastinum
Heart is slightly rotated
-Right border is located more anteriorly
-Left border is located more posteriorly
Base of the heart (posterosuperior surface) is mainly made up of the left atrium
Superior border is formed by the great arterial vessels and the superior vena cava
Apex is the inferior conical end
Inferior border is formed by the right ventricle
Characteristics of the Pericardium
Heart is enclosed within a tough sac called the pericardium
Restricts heart movements so that it moves only slightly within the thorax
Composed of two parts:
-Fibrous pericardium: tough outer sac
-Serous pericardium: composed of parietal and visceral layers
-Pericardial cavity: thin space between layers of serous pericardium containing serous fluid
Heart Wall Structure: three layers (from superficial to deep)
Epicardium: visceral layer of serous pericardium and areolar connective tissue
Myocardium: cardiac muscle; thickest of the three layers
Endocardium: internal surface of heart chambers' simple squamous epithelium and areolar connective tissue
Note: pericarditis is an inflammation of the pericardium, typically caused by viruses, bacteria, or fungi
External Heart Anatomy
Heart composed of four hollow chambers:
- Two superior, smaller atria and two inferior, larger ventricles
- Anterior part of each atrium forms an auricle
-Blood passes from right atrium to right ventricle, pulmonary trunk, pulmonary circulation
-Blood passes from left atrium to left ventricle, aorta, systemic circulation
Coronary sulcus: groove separating atria and ventricles
Anterior interventricular sulcus and posterior interventricular sulcus are located between the right and left ventricles
Internal heart anatomy: chambers and valves
Heart has four hollow chambers: right atrium, right ventricle, left atrium, left ventricle
Heart has four valves:
-Two atrioventricular (AV) valves "lubb"
-Two semilunar valves at base of great arteries "dubb"
Fibrous skeleton
Dense regular connective tissue between the atria and ventricles
Provides structural support and acts as an electrical insulator between atria and ventricles
Right atrioventricular valve
Cardiac muscle cells are arranged in spiral bundles around the heart chambers attached to the fibrous skeleton - when the ventricles contract, the action is similar to the
wringing of a mop that begins at the Pulmonary semilunar valve apex and compresses superiorly
Right atrium
Receives venous blood from heart and systemic circulation through three large veins:
-Superior vena cava
-inferior vena cava
-Coronary sinus
Interatrial septum: divides right atrium from left Pectinate muscles: ridges on internal surface of atrial wall
Right atrioventricular valve (tricuspid valve):
ensures one-way blood flow from right atrium to right ventricle through atrioventricular opening
Right ventricle
Receives deoxygenated blood from right atrium
Interventricular septum: thick wall between right and left ventricles
Papillary muscles: cone-shaped muscle projections anchoring chordae tendinee
- Chordae tendineae attach muscle to atrioventricular valve and prevent cusps from flipping into atrium when ventricle contracts
Conus arteriosus: smooth funnel shaped region at superior end of right ventricle leading to pulmonary semilunar valve - ensures one-way flow from ventricle to pulmonary trunk
Left atrium
Oxygenated blood from the lungs travels through the pulmonary veins to the left atrium
Left atrioventricular valve controls flow through opening between left atrium and ventricle
-Aka bicuspid (two-flap) or mitral valve
-Valve is forced shut when the left ventricle contracts
Left ventricle
Pumps blood through entire systemic circulation- generates very high pressure
Aortic semilunar valve: controls flow from left ventricle to aorta - located at superior end of left ventricle
Left ventricular wall is typically three times thicker than the right
Coronary circulation
The right and left coronary arteries travel within coronary sulcus and supply heart wall with oxygen and nutrients - branch off ascending aorta just superior to aortic semilunar valve Selfish!
Venous return of blood from the heart wall occurs through three major veins: great, middle, and small cardiac veins
How the heart beats: electrical properties of cardiac muscle tissue
For the heart to be an effective pump, contraction of chambers needs to be coordinated This is possible due to the heart's conduction system
Cardiac muscle is striated with extensive capillary networks (similar to skeletal muscle)
Also many differences compared to skeletal muscle:
- Less SR quantity and organization
- No terminal cisternae
-Less contact between ST and T-tubules
Innervation of the heart
Heart is innervated by sympathetic and parasympathetic divisions of the autonomic nervous system
-Their fibers make up the cardiac plexus
-Autonomic innervation does not initiate a heartbeat, but it can increase or decrease the rate of the heartbeat
Sympathetic innervation starts with neurons T1-5
segments of the spinal cord
- Preganglionic axons enter sympathetic trunk and synapse on ganglionic neurons
- Postganglionic axons project from cervical and thoracic ganglia and travel to the heart via cardiac nerves
-Sympathetic input increases rate and force of heart contractions
Parasympathetic innervation starts with neurons in the medulla oblongata via the left and right vagus nerves (CNX) - parasympathetic activity decreases heart rate but generally has no effect on force of contraction
Aging of the heart
Decreased tissue elasticity with age often impairs heart valve function
Decreased efficiency of heart's conducting system can impair heart's ability to pump extra blood needed during stress
High blood pressure increases work required of heart and can head to problematic hypertrophy of myocardium
The four problems caused by tetralogy of Fallot include:
1. Ventricular septal defect (VSD). An opening in the ventricular septum, or dividing wall between the two lower pumping chambers of the heart known as the right and left ventricles.
2. Pulmonary (or right ventricular outflow tract) obstruction. A muscular obstruction in the right ventricle, just below the pulmonary valve, that decreases the normal flow of blood to the lungs. The pulmonary valve may also be small.
3. Overriding aorta. The aorta (main artery leaving the heart) is shifted towards the right side of the heart so that it sits over the ventricular septal defect.
4. Right ventricular hypertrophy. The right ventricle becomes thickened as it tries to pump blood past the obstruction into the pulmonary artery.