Cardiovascular Physiology

Cardiovascular System

• A circulatory system evolved to support the complexity of large multicellular organisms.

• Diffusion alone is insufficient to transport nutrients and remove waste over long distances.

• Circulation maintains steep concentration gradients near cells, enabling rapid material exchange.

Hemodynamics

• Basic signs of cardiovascular health include cardiac output or arterial pressure, and blood circulation.

• Explains the physical laws which govern blood flow.

• Looks at the relationship between blood flow, BP, and resistance.

Ohm’s Law

• F = ∆P/R

• Where F is flow (mL/min)

• ∆P is the pressure difference between two fixed points (mmHg).

• R = resistance to flow (mmHg/mL/min)

Flow

• Blood flow is directly related to the pressure difference between two fixed points and inversely proportional to resistance.

• High to low pressure.

• It is the pressure difference between two points that creates flow, not the absolute pressure at each point.

• To have flow, ∆P > R.

Hydrostatic Pressure

• Pressure exerted by a fluid.

• The major mechanism for changing flow in the cardiovascular system is to alter the resistance of the BVs (specifically arterioles).

• This will change flow and perfusion of the tissues + organs in our body.

Blood Friction

• Blood is not a homogenous fluid.

• Although plasma is composed of water, it also contains molecules such as electrolytes and proteins such as albumin and fibrinogen.

• Formed elements of blood: RBCs, WBCs, and platelets.

• Interactions between these components in blood produces friction.

  • Resistance.

Viscosity

• Friction between molecules of a flowing fluid.

• Hematocrit affects viscosity.

  • # of RBCs in the blood.

• The more viscous the blood is, the more friction is produced, the greater the resistance to flow.

• Has a limited range and does not contribute significantly to resistance.

Concentric

• Blood flows through in vessels in concentric layers.

• The movement of adjacent layers of blood flow through a vessel helps to reduce energy losses in the flowing blood by minimizing viscous interactions between the adjacent layers of blood and the wall of the blood vessel.

Length

• Determines amount of contact between moving blood and stationary wall of vessel.

• A vessel with longer length will produce more friction.

• Blood flows through vessel in concentric layers.

Diameter

• Determines amount of contact between moving blood and stationary wall of vessel.

• Can change based on constriction or dilation.

• A large diameter blood vessel = less friction.

• Small diameter blood vessel = more friction.

Poiseuille’s Equation

• R = 8ηl / πr⁴

  • R = resistance to blood flow

  • η = viscosity of blood

  • l = length of vessel

  • r = radius of vessel (raised to fourth power)

Poiseuille’s Equation Relationship

• The relationship between viscosity, vessel radius, and vessel length, defined by this equation, which states that resistance is equal to 8ηl / πr⁴.

• Applies to laminar flow.

Cardiovascular System Functions

• To deliver oxygen and nutrients and remove waste products of metabolism

• Fast chemical signaling to cells by circulating hormones or neurotransmitters

• Thermoregulation

• Mediation of inflammatory and host defense responses against invading microorganisms

Main Organs

• Heart (the pump)

• Blood vessels (the pipes)

• Blood (the fluid to be moved)

Thermoregulation

• A homeostatic process that maintains a steady internal body temperature despite changes in external conditions.

Heart

• The pump; pumps the blood through the circulatory system by rhythmic contraction and dilation.

Blood Vessels

• Channels that carry blood throughout your body.

Blood

• The fluid being moved.

Arterioles

• Small branching vessels with high resistance.

Capillaries

• Transport blood between small arteries and venules; exchange of materials.

• Smallest BV in the body.

• Play an important role in the exchange of materials.

• Permeable to plasma and most solutes, except plasma proteins.

Arteries

• Part of the circulation system by which blood (oxygenated) is conveyed from the heart to all parts of the body, away from the heart.

Veins

• Part of the blood circulation system of the body, carrying in most cases oxygen-depleted blood toward the heart.

Venule

• A very small vein, especially one collecting blood from the capillaries.

Closed Circulatory System

• Blood confined to vessels.

• Generates greater pressures.

• Moving blood to be pumped faster in our bodies.

Atria

• Thin-walled

• Low pressure chambers

• Receive blood returning to the heart

• The left and right atria are conduits that receive blood turning back to the heart.

Ventricles

• Forward propulsion of blood.

• Thicker walls than the atria and responsible for the forward propulsion of blood.

Septa

• A wall, dividing a cavity or structure into smaller ones.

Interatrial Septum

• Separates left and right atria.

Interventricular Septum

• Separates left and right ventricles.

Dual pump

• Left Side: pumps highly oxygenated blood to the systemic circuit.

• Right Side: pumps poorly oxygenated blood to the pulmonary circuit.

• Most arteries carry highly oxygenated blood away from the heart.

Carrying Blood

Vessel Type	Normal Function	Exception
Arteries	Oxygenated blood away from heart	Pulmonary arteries: deoxygenated to lungs
Veins	Deoxygenated blood to the heart	Pulmonary veins: oxygenated from lungs

Pulmonary Circulation

• Blood to and from the gas exchange surfaces of the lungs

• Blood entering lungs = poorly oxygenated blood

• Oxygen diffuses from lung tissue to blood

• Blood leaving lungs = oxygenated blood

Systemic Circulation

• Blood to and from the rest of the body

• Blood entering tissues = oxygenated blood

• Oxygen diffuses from blood to body tissues

• Blood leaving tissues = poorly oxygenated blood

Left Heart

• Receives blood from pulmonary circulation and pumps to systemic circulation.

Right Heart

• Receives blood from systemic circulation and pumps to pulmonary circulation.

Series Flow

• Within the cardiovascular system.

• Blood must pass through the pulmonary and systemic circuits in sequence

Parallel flow

• In the systemic circuit, each organ is supplied by a separate artery.

• Blood does not flow between organs.

• Each organ receives fully oxygenated blood and regulates its own flow.

• Exception: Liver

  • Also receives blood from digestive organs via the portal vein.

  • This blood is partially deoxygenated.

Pericardium

• A fibrous sac that encloses the heart and great vessels.

  1. Stabilization of the heart in thoracic cavity

  2. Protection of the heart from mechanical trauma, infection

  3. Secretes a pericardial fluid to reduce friction

  4. Limits overfilling of the chambers, prevents sudden distension

Pericardium - Stabilization

• The outer layer of the pericardium is attached to components within the thoracic cavity, including the coastal cartilage, diaphragm, and sternum.

• The ligamentous attachments limit the hearts motion within the chest cavity.

Pericardium - Infection

• A fluid-filled sac that protects mechanical truama to the cehest.

• Also protects from infection.

Pericardium - Friction

• The fluid lubricates layers of the heart as it contracts and twists in the pericardial space.

Pericardium - Distension

• As it is a fibrous sac, its distensibilituy is limited.

• Does not stretch properly; will resists a rapid increase in cardiac size, preventing over-distension.

Fibrous Pericardium

• Outermost layer of the pericardial sac.

• Provides, protects. and stabilizes heart in the thoracic cavity (attaches to structures in the chest such as the coastal cartilage, diaphragm, and sternum).

• Composed of connective tissue.

Serous Pericardium

• Composed of the parietal and visceral pericardium.

• Layer composed of cells that secrete a fluid.

Parietal Pericaridum

• Composed of cells that secrete a fluid.

• Lies underneath the fibrous pericardium and is attached to it.

Pericardial cavity

• Pericardial fluid decreases friction.

• Separates the parietal pericardium from the visceral pericardium.

Visceral Pericardium

• The innermost layer of the paracardial sac.

• Lies next to the heart and a part of the heart wall.

Layers of the Pericardium

• At the base of the great vessels, the parietal layer folds over and continues as the visceral layer on the heart surface.

• The fibrous and parietal pericardium are fused.

• The parietal and visceral layers are separated by the pericardial cavity.

• These layers secrete fluid into the cavity to reduce friction.

Pericarditis

• Pericarditis is inflammation of the pericardium.

• Causes include bacteria, trauma, fungi, viruses, or malignancy.

• Increases capillary permeability, leading to fluid buildup in the pericardial cavity.

• Severe cases compress the heart, limit movement, and prevent proper chamber filling.

Cardiac tamponade

• Compression of heart chambers due to excessive accumulation of pericardial fluid.

• Can be treated aspiring the fluid with a needle and treating the cause of fluid buildup.

• Heart is unable to pump blood.

• Decreases ventricular filling.

Left Ventricle

• thicker (wall) than the right ventricle.

• Develops higher pressure.

• The increased thickness allows the left ventricle to generate higher pressures as it contracts.

• the increased pressure allows the left ventricle to pump blood around the entire systemic circulatory system.

Right Ventricle

• Pouch-like in shape.

• Only needs to pump blood to the lungs, so it does not need to develop increased pressures.

Myocardium

• Muscular wall.

• Cardiac muscle (myocytes), BVs, nerves.

Endothelium on BVs

• The heart valves and the BVs are lined by endothelium, which forms a interface between the blood and the heart chamber of the BV wall, providing a smooth surface for blood to flow over.

• The three layers are bound on both ventricles and atria, with variation between the two.

  • The ventricles have more muscle.

Endocardium

• Endothelium covering inner surfaces of heart and heart valves

Myocyte

• Cardiac muscle cell.

• Branched (“Y”) and joined longitudinally

• Allows for greater connectivity; one Y-shaped myocyte may be attached to two different myocytes.

• Striated, one nucleus per cell, many mitochondria (energy; ATP).

Intercalated disk

• Interdigitated region of attachment.

• Desmosones and gap junctions.

• The opposing membrane of two different myocytes are closely opposed and very intertwined at their region of attachement.

Desmosomes

• Anchor cells together in tissues subject to considerable stretching

• Mechanically couple cells.

• Contains cadherins → anchors cells together.

• Connections are strong.

Gap Junctions

• Communicating junctions

• Transmembrane channels linking adjacent cells

• Electrically couple heart cells

  • Small molecules and ions

  • Spreading action potentials across the atria or ventricles

Myocardium

• Consists of interlacing bundles of cardiac muscle fibers.

• Arranged spirally around circumference of heart

Wringing Effect

• When the cardiac muslce contracts and shortens, a wringin effect is profuced, efficiently pushed blood upwards towards the exit of major arteries.

Figure 8 - Step 1

• Chamber walls contract like a squeezing fist, applying pressure to the blood.

• Cardiac muscle fibers are arranged in a figure 8 around the atria and base of the great vessels.

• Deeper ventricular fibers also form a figure 8, extending toward the apex.

• Superficial ventricular layers wrap around both ventricles.

Figure 8 - Step 2

• Atrial contraction pushes blood into the ventricles.

• Ventricular contraction reduces chamber diameter and pulls the apex upward in a twisting motion.

• This spiral motion directs blood upward toward the major arteries.

• Spiral arrangement ensures efficient ventricular emptying.

Valves

• Thin flaps of flexible, endothelium-covered fibrous tissue attached at the base to the valve rings.

  • Leaflets or cusps.

  • Collagen.

• The semilunar valves or atrial vales are found between the ventricles and the arteries where the ventricles pump their blood.

Valve Rings

• Cartilage.

• Site of attachment for the heart valves.

  • Stabilizes position.

Valve Blood Flow

• One-way valves open due to forward pressure gradients.

• No energy or muscles are required—movement is passive.

• Valve opens when pressure is greater behind it.

• Valve closes when pressure is greater in front, preventing backflow.

• Valves cannot open in the reverse direction.

Valve - Unidirectional Flow

• There is unidirectional flow of blood through heart.

• The orientation of the four valves ensures unidirectional flow.

• Important so blood flowing into doesn’t mix with the blood flowing out.

Atrioventricular (AV) Valves

• AV valves are located between atria and ventricles.

• Prevent backflow into atria during ventricular contraction.

• Open when atrial pressure exceeds ventricular pressure, allowing ventricular filling.

• Close when ventricular pressure exceeds atrial pressure.

Tricuspid Valve

• Right AV valve

• Three leaflets (cusps)

Bicuspid valve (Mitral Valve)

• Left AV valve

• Two leaflets (cusps)

AV Valve Apparatus

• Cusps, chordae tendineae and papillary muscles.

• Prevents eversion of the AV valves into the atria during contraction of the ventricles.

• Valves open and close due to pressure gradients, not from contraction and relaxation of papillary muscles.

AV Valve Apparatus - Relaxed

• the aortic semilunar valve is close, the bicuspid valve is open, the chordinae tendinae are slack and they have low tension.

• The papillary muscle and the cardiac muscle are relaxed.

• The left ventricles will fill with blood as the bicuspid valve is open and when the aortic valve is closed.

• Left artia → open AV valve → left ventricke.

AV Valve Apparatus - Contract

• As the left ventricle fills, it contracts and increases internal pressure.

• When ventricular pressure exceeds atrial pressure, the bicuspid valve closes.

• Papillary muscles contract, pulling chordae tendineae taut to prevent valve prolapse.

• Once ventricular pressure exceeds aortic pressure, the aortic valve opens, allowing blood to exit.

Chordae tendineae

• Tendinous-type tissue

• Extend from edges of each leaflet to papillary muscle

Papillary Muscles

• Cone shaped muscles

• Contraction of papillary muscle causes the chordae tendineae to become taut

  • Holds the valve in closed position.

Arterial (Semilunar) Valves

• Between the ventricle and artery

Pulmonary Valve

• Pulmonary trunk, right ventricle

Aortic Valve

• Aorta, left ventricle

• No chordae tendineae, papillary muscles

• Prevent the backflow of blood from the arteries into ventricles when ventricles relax

Semilunar Valves

• No valve apparays associated with the semilunar valves.

• The arties into which the ventricles eject their blood do not contract.

• As a result, when the semi-lunar valves close and the ventricles begin to relaz, they do not need musclar craces the hold them in a closed postion.

  • Pressure is not high enough to force eversion/

Cardiac Skeleton

• Fibrous skeleton is dense connective tissue.

• Separates atria from ventricles.

• Electrically inactive—blocks direct impulse spread.

• AV node and Bundle of His are the only electrical link between atria and ventricles.

• Provides structural support.

• Anchors valve leaflets and myocardium.

• Helps coordinate depolarization by isolating conduction paths.

Coronary Circulation

• Movement of blood through tissues of the heart.

• Blood in heart chambers does not exchange nutrients with myocardial cells.

• Diffusion from chamber blood is too slow to meet metabolic demands.

• The heart requires a constant O₂ and nutrient supply for ATP production.

• Relies heavily on aerobic metabolism with little anaerobic capacity.

Coronary Arteries

• Originate at aortic sinuses at base of ascending aorta.

• the aortic sinus is at dilation or an out-pocketing of the ascending aorta.

• The left and right coronary arteries lead a branching network of smaller vessels that run along the surface of the heart and dive deeper into the heart wall.

Coronary Veins

• Drain into the coronary sinus, which empties into the right atrium.

Coronary Sinus

• The cardiac veins collect deoxygenated blood from the myocardium (heart muscle).

• These veins drain into a large vessel which acts is a collection site for this blood.

• Then empties directly into the right atrium, allowing the deoxygenated blood from the heart tissue to re-enter the circulation.

Systole (Contraction)

• Myocardial blood flow almost ceases.

• Compression reduces vascular diameter, increases resistance, and decreases blood flow.

Diastole (Relaxation)

• Myocardial blood flow peaks

Coronary Artery Diseases

• Coronary artery disease due to atherosclerosis of coronary arteries

Atherosclerosis

• Arteries supplying blood to heart become hardened and narrow due to plauqe in arterial walls.

• Begins with an injury to an artery wall such as smoking, high BP, or increase of blood lipids and cholestrol.

Plaque

• Fat, cholesterol, calcium, other substances in the blood

  • Reduces lumen of vessel and blood flow

• A fatty stretch develops at the site and smooth muscle grows over the lesion.

• Fibrous tissue covers the smooth muscle and calcium invades the tissue to harden it, forming a plaque.

Angina

• chest pain or discomfort

• blood flow to heart muscle is reduced

Myocardial infarction

• Heart attack.

• Blood supply to the heart is completely blocked, muscle dies.

• Occurs if the plaque is so large it covers the artery.

The Cardiac Syncytium

• Cardiac muscle cells (myocytes) communicate with each other, called a syncytium

  • Set of cells that act together

Functional Syncytium

• The cardiac muscle cells are so tightly bound that when one of these cells become excited, the AP spreads to all of them.

• if one cell is excited, the excitation spreads over both ventricles (or both atria)

• 2 syncytia: atrial syncytium and ventricular syncytium

All-or-None Property

• The synchronous excitation and contraction of myocardial cells is required to produce the force necessary to pump blood throughout the body.

Cardiac Muscle

• Contractile Cells: mechanical work of pumping, propel blood; do not initiate action potentials.

• Conductive Cells: initiates APs.

• Action potentials lead to contraction of heart muscle cells.

Automaticity (autorhythmicity)

• Cardiac muscle contracts in the absence of neural or hormonal stimulation, as a result of APs it generates itself.

Contractile Cells

• Mechanical work of pumping, propel blood; do not initiate action potentials.

• Contract when stimulated by an AP passed to them through gap junctions.

• Adjacent cells that have been stimulated by an AP or stimulated by a conductive cell.

Conducting Cells

• Specialized myocytes (1%) initiate and conduct action potentials.

• Do not rely on nervous or hormonal stimuli.

• Contain few myofibrils and do not contribute to contraction or blood movement.

  • Conducting system.

Membrane Potential

• Difference in electrical potential between the interior and exterior of a cell

  • More negative inside than outside at rest

• Provides an electrical force that influences the movement of ions across a membrane.