Cardiovascular System: Anatomy and Function

• Cardiovascular system includes the heart and blood vessels
• Circulatory system consists of the heart, blood vessels, and blood

Heart Function

• The left side receives fully oxygenated blood from the lungs and delivers it to the body via the aorta
• The right side receives deoxygenated blood from the vena cavas and sends it to the lungs

Blood Vessels

• Arteries are more muscular and ticker compared to veins
• Arteries are usually smaller than veins
• Veins collapse easier than arteries and are bigger

Valves

• Atrioventricular valves control blood flow from the atria to the great arteries
• Semilunar valves control blood flow from the ventricles into great arteries
• The pulmonary valve controls the opening between the right ventricle and the pulmonary trunk
• The aortic valve controls the opening between the left ventricle and the aorta

Heart Sounds

• S1 sound is a "lub" sound, caused by the closing of the atrioventricular valves
• S2 sound is a "dub" sound, caused by the closing of the semilunar valves
• S3 sounds are normal in children

Blood Flow

• Blood flow through the chambers is determined by pressure
• During ventricular relaxation (diastole), pressure in the ventricles decreases
• AV valves open during diastole, allowing blood to flow from the atria to the ventricles
• During ventricular contraction (systole), pressure in the ventricles increases
• AV valves close during systole
• Semilunar valves open in systole because the ventricular volume is decreasing

Heart's Circulatory System

• The heart has its own circulatory system
• 5% of the blood that the heart pumps is pumped through the heart itself

Heart Conditions

• Angina pectoris is chest pain resulting from reduced blood flow to the heart muscle
• Myocardial infarction occurs when heart muscle cells die due to a lack of blood supply

Cardiac Conduction

• Cardiac conduction is automatic and regulated by the heart itself
• All pacemaker cells are capable of spontaneous depolarization
• Rhythmicity becomes spontaneous due to the rhythm of muscle cells
• Regular generation of action potentials occurs through the heart's conduction system
• Pacemaker cells generate action potentials
• Contractile cells (cardiomyocytes) contract when activated
• The conduction system coordinates the heartbeat
• Heart muscle contraction is initiated by electrical signals (action potentials), which travel through gap junctions
• Pacemaker cells have an unstable resting potential and gradually leak Na
• Na inflow depolarizes the membrane, triggering more Na channels
• Na channels close when the cell depolarizes and peaks at +30
• Ca enters through a slow Ca channel
• Ca stimulates the release of more Ca from the sarcoplasmic reticulum which prolongs depolarization
• Ca binds to troponin, causing heart contraction
• Ca channels then close and K channels open
• Ca is transported out of the cell
• K outflow brings the cell back to the resting potential

ECG

• ECGs are electrocardiograms that measure heart function using cardiac output
• Cardiac output is Heart rate x Stroke volume
• Stroke volume refers to the amount of blood pumped with each heartbeat
• Heart rate is modulated by the nervous and endocrine systems

Heart Rate

• Tachycardia is defined as a heart rate over 100 beats per minute
• Bradycardia is defined as a heart rate under 60 beats per minute

Brain Medulla Information

• Cardiac centers in the medulla of the brain receive peripheral information
• Proprioceptors detect activity from muscles and joints, signaling the medulla to increase heart rate
• Baroreceptors detect changes in blood pressure in the aorta and internal carotid arteries
• Chemoreceptors detect blood pH, carbon dioxide, and oxygen levels in the aortic arch, carotid arteries, and medulla

Nervous System

• The autonomic nervous system Influences the rate of impulse generation (chronotropic) and strength of contraction (ionotropic)

Heart Failure

• Left-sided heart failure results in pressure backing up into the pulmonary tissue (lungs)
• Right-sided heart failure results in fluid backing up into systemic tissue (the body and limbs)

Blood Flow

• Resistance opposes blood flow
• Greater resistance results in lower blood flow, mainly determined by vessel diameter and length
• Pressure is the force exerted on a liquid per unit area
• Blood pressure is the force blood exerts against a vessel wall, measured at the brachial artery to approximate pressure at the exit of the left ventricle

Blood Pressure

• Systolic pressure is the peak arterial BP during ventricular contraction
• Diastolic pressure is the minimum arterial BP during ventricular relaxation
• Blood pressure is pulsatile and determined by cardiac output, blood volume, and resistance to flow
• Blood pressure declines as it moves away from the heart due to arterial elasticity and friction of the vessel wall

Blood Pressure Levels

• Pulse pressure measures the driving force on circulation (systolic - diastolic pressure)
• Mean arterial pressure influences the risk of anemia, fainting, kidney failure, atherosclerosis, and aneurysms
• Mean arterial pressure is Diastolic pressure + 1/3 (pulse pressure)
• Atherosclerosis involves fat building up in the arteries
• Atherosclerosis increases blood pressure, resistance, damages blood vessels, and cause clots that can move through the body

Factors That Affects Resistance

• Blood viscosity is the thickness and increases from RBC and decreases from anemia
• Vessel length affects resistance
• The farther from the heart increases friction, the decrease in pressure
• Vessel radius has the most powerful influence because radius changes can have large changes in blood flow
• Laminar flow flows in layers, therefore faster in the center of the vessel
• Vasoconstriction occurs when smooth muscle vessels contract
• Vasodilation occurs when smooth muscle vessels relax
• As blood travels from the aorta to the capillaries, the velocity decreases

Changes in Resistance

• Velocity decreases when radius of vessels decrease as there's a distance increase
• Cross sectional area increases (more capillaries)
• As blood travels from capillaries to the vena cava, the velocity increases
• The veins get larger, there is convergence of vessels

Hypotension Causes

• Hypotension can be caused by blood loss, dehydration, and anemia, which can weaken arteries, cause aneurysms, and heart failure

Venous Return

• Venous return is the flow of blood back into the heart and is affected by
  • The pressure gradient
  • Gravity
  • Skeletal muscle pump in the limbs
  • Thoracic pump (when inhalation happens the abdominal pressure increases forcing blood up)

Vasoreflexes

• Vasoreflexes- quick and powerful regulators of blood pressure and flow in the form of dilation and constriction
• Local control of vasoreflexes in the form of autoregulation/vasoactive chemicals
• Neural control of vasoreflexes in the form of sympathetic, baroreflexes, chemo reflex and medullary ischemic reflex

Hormones

• Hormonal control of blood pressure
  • Angiotensin II- increases BP
  • Atrial natriuretic peptide- lowers BP
  • ADH- raises BP
  • Epinephrine and norepinephrine- vasoconstriction and dilation

Capillary Exchange

• Capillary exchange- happens between blood and tissues, its a two way movement through capillary walls
• Water, oxygen, glucose, amino acids, lipids, minerals, antibodies, hormones, wastes, carbon dioxide, and ammonia pass through by means of diffusion, transcytosis, filter action and reabsorption
• Filters out of arterial end of capillary and osmotically reabsorbed in at venous end
• Driven by opposing forces (blood hydrostatic pressure= fluid out of, colloid osmotic pressure= draws fluid into capillaries)

Edema

• Edema- accumulation of excess fluid in tissue
• When filtration is greater then reabsorption
• Causes- increased capillary filtration, reduced capillary reabsorbtion, obstructed lymphatic drainage (kidney failure, liver disease)

Explore the anatomy and function of the cardiovascular system, including the heart, blood vessels, and blood. Learn about the roles of arteries, veins, and valves. Understand heart sounds and blood flow through the heart.