Cardiovascular System and Circulation

• Systemic circulation carries blood from the heart to the body and back.
• Pulmonary circulation takes blood to the lungs for oxygenation and returns it to the heart.
• Coronary vessels supply the heart muscle with nutrients; blockage can lead to a heart attack.
• Cardio refers to the heart.
• Vascular refers to the blood vessel transport system.
• Circulatory/circulation is the movement of blood around the body.
• Arterial vessels (arteries and arterioles) transport blood away from the heart.
• Venous vessels (veins and venules) transport blood towards the heart.
• Portal veins carry blood from one capillary bed to another without passing through the heart.
• The hepatic portal vein transports nutrient-laden blood from the gut to the liver for processing.
• Capillaries are small vessels that allow only one red blood cell to pass at a time.
• Capillaries facilitate the exchange of materials between blood and body tissues due to their thin walls.

Systemic Blood Flow

• The aorta, a great artery, is an elastic artery that smoothes pulsatile blood flow.
• Muscular arteries maintain continuous blood flow with smooth muscles in the wall.
• Arterioles are smaller arteries carrying blood.
• Capillaries are the smallest vessels and the site of gas exchange.
• Venules are smaller veins.
• Veins are larger veins.
• The vena cava delivers blood to the heart for pulmonary circulation.

Blood Vessel Layers

• Tunica Intima:
  • Arteries have a distinct internal elastic lamina (IEL).
  • Veins have an IEL that is hard to see.
  • Capillaries consist of a single cell layer.
• Tunica Media:
  • Arteries consist of muscle.
  • Veins have muscle and collagen fibers.
  • Capillaries do not have tunica media.
• Tunica Externa:
  • Arteries have a thicker tunica externa compared to the media.
  • Veins have a thicker tunica externa.
  • Capillaries do not have tunica externa.
• Arterial pressure is higher (80-120 mmHg), while venous pressure is lower (2-5 mmHg).
• Capillary pressure is intermediate, allowing continuous blood flow without vessel damage (15-35 mmHg).
• Blood flow direction is away from the heart in arteries and towards the heart in veins.
• Heart pumping drives arterial flow; veins use valves and muscle action to prevent backflow.
• Flow within big arteries are big arteries and pulsatile.
• Flow within veins is supported by muscles pushing blood and valves preventing backflow.
• Capillary flow is slow to allow gas and fluid exchange.

Nursing Related Items

• Arteries need to facilitate a smooth blood flow.
• Blood pressure must be considered.
• IV administration is a task relevant to nurses
• Capillary refill indicates tissue perfusion.
• Vessels need to be small enough for blood to reach every cell.
• Vasodilation widens blood vessels by relaxing smooth muscle.
• Vasoconstriction narrows blood vessels by contracting smooth muscle.
• Atherosclerosis involves fat deposits narrowing the lumen.
• An aneurysm is a stretched vessel with a thin wall that may rupture.

Fluid Dynamics

• Hydrostatic pressure is the force of water on vessel walls, driven by the heart's pumping action.
• Hydrostatic pressure is influenced by heart pumping strength and blood volume.
• Osmotic pressure is the force exerted by solutions of differing concentrations to balance concentrations.
• Oncotic/colloid osmotic pressure is a name for osmotic pressure.
• Osmotic pressure moves water due to solute concentration differences.
• Filtration occurs at the arterial end of capillaries due to hydrostatic pressure and moves fluids, nutrients, and oxygen out to tissues.
• Absorption occus at the venous end of capillaries due to osmotic pressure, moving fluids, wastes, and CO2 into the blood.

Overall Process

• At the arterial end, high hydrostatic pressure pushes fluids into tissues.
• Oxygen and nutrients feed the cells in the tissues.
• Fluid volume decreases, increasing osmotic pressure due to plasma proteins.
• The higher vessel osmotic pressure helps retrieve fluids at the venous end.

Heart Features

• The heart is enclosed in a double-layered, fluid-filled bag with three layers:
  • Visceral pericardium (touching the heart muscle).
  • Pericardial fluid.
  • Parietal pericardium (outer layer, thicker than the inner layer).
• The membranes helps prevent friction as the heart pumps .
• Parietal pericardium does not stretch in order to prevent overfilling of the heart.
• Superior and inferior vena cava, right atrium, tricuspid valve, right ventricle, and pulmonary valve are elements, alongside the pulmonary veins, left atrium, mitral valve, left ventricle, aortic valve, and semilunar valves.
• Right ventricle pressure is 0-25, while left ventricle pressure is 0-120.
• Pulmonary artery pressure is 5-25, while aorta artery pressure is 80-120.
• Atria are small chambers that help fill the ventricles with blood and make heart more efficient.
• Ventricles are large chambers that generates force to pump blood to the arteries.
• The left side of the heart generates more force, as it must pump blood against gravity.
• Valves maintain a one-way direction of blood flow.
• Atrioventricular valves prevent blood from going into the atrium.
• AV valves have valve flaps and chordae tendinae, which anchors it to the ventricle.

Cardiac Physiology

• Heart Rate (HR): Number of heartbeats per minute.
• Stroke Volume (SV): Volume of blood exiting the ventricle per heartbeat.
• Cardiac Output (CO): Volume of blood pumped per minute (HR x SV).
• Cardiac output determines the amount of blood/delivery to the body.
• The heart skeleton prevents electricity from spreading from the atria to the ventricles, except through (AV) Atrioventricular node
• ECG trace records the heart's electrical activity.
• P wave represents atrial depolarization and causes atrial contraction.
• QRS complex represents ventricular depolarization and causes ventricular contraction; atria are also relaxing.
• T wave represents ventricular repolarization, which what causes the ventricles to relax.
• Adrenaline is a neurotransmitter/hormone that speeds up the heart.
• Thyroxine increases heart rate and metabolism.
• Acetyl Choline slows down the heart (parasympathetic) The cardioacceleratory center speeds up the heart.
• The cardioinhibitory center slows down the heart.
• Na, K, and Ca are involved in depolarization/repolarization and contraction.
• Venous return is the amount of blood entering the heart and can increase during exercise.
• End Diastolic Volume is the volume of blood in the ventricles at the end of relaxation.
• End Systolic Volume is the volume of blood in the ventricles at the end of contraction, roughly 30% of the EDV.
• Preload is the volume of blood inside the heart.
• Afterload is the blood pressure in the artery, opposing the hearts, determining stroke volume.
• Myocontractility is the force of contraction of the heart muscle.
• Ejection Fraction is the percentage of blood inside the ventricle that is pumped out.

Muscular actions & Potentials

• Depolarization is the action when a cell becomes more positive and is associated with muscle contraction.
• Repolarization is the process when a cell becomes more negative.
• Cardiac muscle cells are branching and connected by intercalated discs, allowing electricity to spread.
• Conductivity is the ability of electrical charge to spread.
• Electrogenic means "to create electricity".
• The SA node spontaneously depolarizes, which is how electricity is made.

Electricity

• SA Node
  • In the right atrium
  • Spontaneously depolarises
  • Pacemaker of the heart
• Myocardium of the atria of the heart
  • Electricity spreads through the atria
  • Atria causes the atrium to contract
• AV Node
  • Between the atria and the ventricles
  • Delays electricity spread
  • Gives the atria enough time before electricity spreads
• Bundle of His
  • Conducts electricity down the interventricular septum
  • Speeds electricity down
• Bundle branches
  • It splits and goes to each ventricle
• Purkinje fibres
  • Spread electricity through ventricular muscle quickly
  • Ventricular muscle contract

Heart Rate Factors

• Autonomic innervation
• Hormones
• Fitness levels
• Age

Stroke Volume Factors

• Heart size
• Fitness levels
• Gender
• Contractility
• Duration of contraction
• Preload (EDV)
• Afterload (resistance)

Additional Information

• Blood pressure depends on the following
• Volume pumped
• Resistance
• Stroke volume/heart rate

Baroreceptors

• Stretch receptors
• Aortic Arch-body
• Carotid Body-brain
• Cardioinhibitory Centre
  • Stimulate
  • Medulla oblongata
• Cardioacceleratory Centre
• Vaso motor Centre

Resistance

• This refers to the peripheral/systemic vascular resistance.
• Resistance is lower in vessels which are dilated and have a larger lumen diameter as well.
• Low resistance results in lower pressure.
• Resistance is higher in vessels which are constricted.
• High resistance increases pressure
• A larger amount of watery/serous and mobile blood result in lower resistance.
• Blood is more viscous when there is high surface tension.

Additional Points

• Baroreceptor is stimulated by high blood pressure.
• Low blood pressure.
• This decreases urine output, increases reabsorption.
• Renal:
  • Baroreceptor or JGA (juxtaglomerular apparatus).
  • Glomerular filtration rate decreases.
  • Water reabsorption increase.
  • Renin causes vasoconstriction.

Circulatory shock

• This leads to a hypotensive state.
• Can be caused by anaphylaxis, septic, hypovolemic, neurogenic, cardiogenic.
• Circulatory shock leads to hypoperfusion, which leads to ischaemia.