Cardiovascular System Quiz

Systems Physiology

• This is a course on systems physiology
• The course outline includes:
  • Cardiovascular physiology
  • Respiratory physiology
  • Kidney function and water/inorganic regulation
  • Digestion and absorption of food
  • Regulation of organic metabolism and energy balance
  • Endocrine system
  • Reproduction
  • Medical physiology: Integration

Cardiovascular System Overview

• The circulatory system is a closed loop
• Blood is composed of formed elements (cells and cell fragments) suspended in plasma
• Hematocrit is the percentage of blood volume that is erythrocytes
• It's measured by centrifuging a blood sample
• The plasma remains on top and the leukocytes and platelets form a thin layer called the buffy coat
• Blood flow throughout the body is generated by the pumping action of the heart
• Most cells are within a few cell diameters of a capillary
• Nutrients and waste products move between capillary blood and the interstitial fluid via diffusion
• Only about 5% of the total circulating blood is in the capillaries at any given moment
• Capillaries are responsible for supplying nutrients and removing waste products
• The circulatory system is composed of two circuits: pulmonary and systemic
• The heart is divided into two halves (right and left) with two chambers each (atrium and ventricle)
• There is usually no direct blood flow between the atria or the ventricles
• The heart receives blood via the vena cava and pumps it through the aorta

Heart Anatomy

• The heart is a muscular organ enclosed in a pericardium
• The myocardium is primarily composed of cardiac muscle cells
• Endothelial cells line the inner chambers and blood vessels
• The heart is divided into right and left halves
• Each half consists of an atrium and a ventricle
• Atrioventricular (AV) valves allow blood to flow from atrium to ventricle (and not backward)
• The right AV valve is the tricuspid valve
• The left AV valve is the bicuspid (or mitral) valve
• The openings of each ventricle into the pulmonary trunk and aorta contain valves (pulmonary and aortic valves)
• There are no valves at the entrances of the superior and inferior venae cavae into the right atrium, and at the entrances of the pulmonary veins into the left atrium
• The heart receives autonomic innervation (sympathetic and parasympathetic)
• The heart has a rich blood supply via coronary arteries

Cardiac Muscle

• Cardiac muscle is electrically excitable and similar to smooth and skeletal muscles
• Action potentials propagate along cell membranes, Ca2+ enters the cytosol, and force-generating cross-bridges are activated
• Approximately 1% of cardiac cells do not contract (conducting system)
• The conducting system is composed of specialized cells that initiate and spread action potentials

Heart Beat Coordination

• The sinoatrial (SA) node is the normal pacemaker of the heart
• Electrical excitation of the heart is coupled with contraction
• The SA node's discharge rate determines the heart rate
• Depolarization through gap junctions spreads through the atria, and then the ventricles via the conducting system
• The conducting system (modified cardiac cells) conducts action potentials with a low resistance

The Electrocardiogram (ECG)

• Records the electrical activity of the heart
• Action potentials in many myocardial cells simultaneously generate currents detectable at the surface of the skin
• An idealized normal ECG is represented by waves on a graph
• Abnormal heart functions alter the shapes and timing of the waves

Excitation-Contraction Coupling

• Cardiac muscle action potentials to contraction are detailed in muscle physiology
• A single action potential releases sufficient Ca²⁺ to saturate the troponin sites, activating contraction
• The main mechanism for preventing summation is inactivation of Na⁺ channels

Mechanical Events of Cardiac Cycle

• Atrial and ventricular contractions and relaxations occur in a recurring cardiac cycle
• There is a period with all valves closed during isovolumetric ventricular contraction and relaxation
• The AV valves open during ventricular filling as blood flows into the ventricles
• Atrial contraction occurs near the end of diastole, filling ventricles
• Ventricular ejection empties most of the ventricles before contraction
• The pressure changes in the heart and the related movements are shown in graph form

Pulmonary Circulation

• The pressure changes in the right ventricle and pulmonary arteries are similar to those in the left ventricle and aorta
• The pressures are lower in the pulmonary circuit
• The pressures (pulmonary and systemic) are very different in magnitude

Heart Sounds

• Two heart sounds result from cardiac contraction
• Murmurs are caused by turbulent blood flow

The Cardiac Output

• Cardiac output (CO) is the volume of blood each ventricle pumps per minute
• It is calculated as heart rate (HR) x stroke volume (SV)
• Factors that influence heart rate and stroke volume are included

Control of Stroke Volume

• The strength of ventricular contraction influence stroke volume
• Stroke volume increases with end-diastolic volume ("Frank-Starling" mechanism)
• Factors that alter stroke volume (end-diastolic volume, sympathetic nervous system input, and afterload) are identified

Control of Heart Rate

• The heart's inherent autonomous discharge rate is approximately 100 beats per minute (controlled by the SA node)
• Sympathetic and parasympathetic activity to the SA node influence beating rate
• When sympathetic activity dominates, the heart rate increases; Conversely, parasympathetic activity decreases heart rate

Measurement of Cardiac Function

• Human cardiac output and function are measured by various techniques, including echocardiography and cardiac angiography

The Vascular System: Arteries

• Arteries are the vessels that carry blood away from the heart
• Arterial blood pressure has a specific pattern
• Factors affecting pulse pressure (stroke volume, ejection speed, artery compliance) are enumerated

The Vascular System: Arterioles

• Arterioles are the major factor affecting mean arterial pressure, and they control the distribution of blood within organs.
• Several autoregulating mechanisms for local control of arteriole resistance are considered: Active hyperemia, flow autoregulation, and reactive hyperemia
• Extrinsic controls (sympathetic neurons) on arteriolar smooth muscles and hormones (epinephrine, angiotensin II) are elaborated
• This is a mechanism used in specific organs, such as the heart, skeletal muscle, lungs, and in the splanchnic organs

The Vascular System: Capillaries

• Capillaries are critical in tissue function for substance exchange
• The structure of capillaries enable rapid exchange across capillary walls: diffusion, vesicle transport, bulk flow, and mediated transport
• Blood flow characteristics of capillaries are given and compared to other blood vessels

The Vascular System: Veins

• Blood is returned to the heart through veins
• Venous pressure and venous return to the heart are determined by factors such as the activity of sympathetic nerves to veins, blood volume, and the skeletal muscle pump
• The venous pressure mechanism is explained via a diagram

The Vascular System: Lymphatic System

• The lymphatic system is a network of lymph nodes and lymphatic vessels that remove interstitial fluid and carry immune cells
• Lymph flow is propelled/regulated by lymphatic vessel smooth muscle contractions and sympathetic neuron innervation

Integration of Cardiovascular Function

• Mean systemic arterial pressure is determined by the product of cardiac output and total peripheral resistance
• Short-term mechanisms (reflexes) and long-term mechanisms (affecting blood volume) for regulating arterial pressure are discussed
• Also, other reflexes and responses involved in regulation of blood pressure are analyzed
• The medullary cardiovascular center in the medulla oblongata is the primary integration center

Test your knowledge on the cardiovascular system with this comprehensive quiz. Explore topics such as hematocrit, blood flow, and the cardiac cycle. Answer questions about the role of baroreceptors and cardiac action potentials to deepen your understanding of how the circulatory system operates.