Heart Valves and Blood Circulation

Heart Valves and Circulation of Blood

• Heart valves open and close in response to pressure changes as the heart contracts and relaxes.
• Dense connective tissue rings surround the valves of the heart, providing:
• Support for heart valves
• Insertion point for cardiac muscle bundles
• Electrical insulator between atria and ventricles

Electrical Conductance

• Electrical conduction pathway:
• SA-Node (in right atrium)
• AV-Node
• AV-Bundle (Bundle of His)
• Right & Left Bundle Branches
• Purkinje Fibres

Regulation of Heart Rate

• Nervous control from cardiovascular centre in the medulla:
• Sympathetic impulses increase heart rate and force of contraction
• Parasympathetic impulses decrease heart rate
• Baroreceptors (pressure receptors) detect changes in BP and send info to the cardiovascular center:
• Located in the arch of the aorta and carotid sinuses
• Heart rate is also affected by:
• Hormones (adrenaline, noradrenaline, thyroid hormones)
• Ions (Na+, K+, Ca2+)
• Age, gender, physical fitness, and temperature

Physiological Functions of the Cardiovascular System

Heart

• Pumps over 1 million gallons per year
• Over 60,000 miles of blood vessels

Vessels

• Retain and circulate blood
• Help regulate pulse pressure

Blood

• Erythrocytes:
• Distribute Oxygen from & CO₂ to lungs
• Leukocytes:
• Circulating immune cells to combat infection

Electrocardiogram (ECG or EKG)

• Measures action potentials of all active cells
• Components:
• P wave: atrial depolarization
• P to Q interval: conduction time from atrial to ventricular excitation
• QRS complex: ventricular depolarization
• T wave: ventricular repolarization
• Q-T Interval: time for ventricular depolarization and repolarization to occur
• S-T segment: ventricular fibres are depolarized (plateau phase of AP)

Circulatory Routes

• Systemic circulation: left side heart to body & back to heart
• Hepatic Portal circulation: capillaries of GI tract to capillaries in liver
• Pulmonary circulation: right-side heart to lungs & back to heart
• Foetal circulation: from fetal heart through umbilical cord to placenta & back

Cardiovascular System

Organs/Structures

• Organs:
• Heart
• Blood vessels
• Blood
• Structures:
• Layers of the heart
• Pericardium
• Epicardium
• Myocardium
• Endocardium
• Valves
• Chambers
• Major vessels
• Major cell types of blood

Gross Anatomy

Right Side of the Heart (Anterior View)

• Brachiocephalic trunk
• Superior vena cava
• Ascending aorta
• Right pulmonary artery
• Parietal pericardium (cut)
• Right Auricle of Right Atrium
• Right coronary artery
• Right Atrium
• Coronary Sulcus
• Right ventricle
• Inferior vena cava

Left Side of the Heart (Anterior View)

• Left common carotid artery
• Left subclavian artery
• Arch of aorta
• Ligamentum arteriosum
• Left pulmonary artery
• Pulmonary trunk
• Left pulmonary veins
• Left Auricle of Left Atrium
• Branch of left coronary artery
• Left ventricle
• Anterior interventricular sulcus
• Descending aorta

Cell Types

Heart

• Pericardium
• Epicardium
• Myocardium (Cardiac myocytes)
• Valves
• Conducting Nerve Bundles (SA/AV Nodes)
• Pericardium

Blood Vessels

• Endothelium

Blood

• Leukocytes: white blood cells
• Erythrocytes: red blood cells

Layers of Heart Wall

• Pericardium:
• Dense irregular connective tissue
• Epicardium:
• Visceral layer of serous pericardium
• Myocardium:
• Cardiac muscle layer
• Endocardium:
• Chamber lining & valves, smooth lubricating layer

Thickness of Cardiac Walls

• Myocardium of left ventricle is thicker than right ventricle

Cardiac Muscle Histology

• Branching, intercalated discs with gap junctions, involuntary, striated, single central nucleus per cell
• Desmosomes between myocytes allow depolarization of adjacent fibers

Arteries and Veins

Arterial Branches of Systemic Circulation

• 4 major divisions of aorta:
• Ascending aorta
• Arch of aorta
• Thoracic aorta
• Abdominal aorta

Veins of the Systemic Circulation

• Drain blood from entire body and return it to the right side of the heart
• Deep veins parallel the arteries in the region
• Superficial veins are found just beneath the skin
• All venous blood drains to either superior or inferior vena cava or coronary sinus

Arteries & Veins

Tunica Interna

• Endothelium
• Basement Membrane
• Internal Elastic Lamina

Tunica Media

• Smooth Muscle
• External Elastic Lamina

Tunica Externa

Elastic Arteries

• Large arteries with more elastic fibers and less smooth muscle
• Conducting arteries because they conduct blood from the heart to medium-sized muscular arteries

Muscular Arteries

• Medium-sized arteries with more muscle than elastic fibers in tunica media
• Capable of greater vasoconstriction and vasodilation to adjust rate of flow
• Walls are relatively thick
• Called distributing arteries because they direct blood flow

Arterioles

• Small arteries delivering blood to capillaries
• Tunica media containing few layers of muscle
• Metarterioles from branches into capillary bed
• To bypass capillary bed, precapillary sphincters close, and blood flows out of bed in the thoroughfare channel
• Vasomotion is intermittent: contraction and relaxation of sphincters that allow filling of capillary beds 5-10 times/minute

Capillaries

• Found near every cell but more extensive in highly active tissue (muscles, liver, kidneys & brain)
• Entire capillary bed fills with blood when tissue is active
• Capillary walls are composed of only a single layer of cells (endothelium) and a basement membrane
• Red blood cells passing through a capillary

Venules

• Small veins collecting blood from capillaries
• Tunica media contains only a few smooth muscle cells and scattered fibroblasts
• Very porous endothelium allows for escape of many phagocytic white blood cells
• Venules that approach size of veins more closely resemble structure of veins

Learn about the function and structure of heart valves and their role in blood circulation, including their response to pressure changes and support systems.