cardiovascular system

• Arteries (and arterioles)


  • Carry blood away from the heart to the capillaries
• Capillaries


  • Exchange of substances between tissues and blood
• Veins (and venules)


  • Carry blood to the heart
• Blood vessels require oxygen and nutrients like all tissues
• Larger blood vessels have blood supplies of their own
• Arteries


  Walls have 3 layers: innermost endothelium, middle smooth muscle and elastic tissue, outer fibrous connective tissue
• Arteries


  • Largest artery is the aorta
  • Arteries branch into smaller arterioles
• Arterioles


  • Middle layer is mostly smooth muscle, important in control of blood pressure

  
• Capillaries


  • Walls consist of single layer of endothelium
  • Total surface area of capillary beds in body is 6000 square meters
  • Not all capillary beds are open at any one time
• Veins


  • Have less developed muscle and connective tissue layers than arteries
  • Tend to be distensible and can expand to "store" blood
  • Up to 70% of blood is in venous side of the circulation at any one time
  • Have valves to prevent backflow of blood

  
• Heart


  • 4 chambers: 2 upper atria, 2 lower ventricles
  • Heart wall has major portion as myocardium (cardiac muscle), inner surfaces lined with endocardium, outer surfaces lined with epicardium

  
• Heart valves

  • Atrioventricular valves (mitral, tricuspid)
  • Semilunar valves (aortic, pulmonary)
  • Control the flow of blood through the heart

  
• Passage of blood through the heart

  1. Superior and inferior vena cavae bring O2-poor blood to the right atrium

  2. Blood flows through tricuspid valve to right ventricle

  3. From right ventricle blood passes through the pulmonary valve to the pulmonary artery

  4. Blood picks up oxygen in the lungs and returns to the heart through the pulmonary veins

  5. Pulmonary veins empty oxygenated blood into the left atrium

  6. Blood flows through the mitral valve to the left ventricle

  7. From the left ventricle blood flows through the aortic valve to the aorta

  8. Aorta carries blood out to the body

  
• Heart

  • Right side is the pulmonary pump, pumps deoxygenated blood to pulmonary circuit and lungs
  • Left side is the systemic pump, pumps oxygenated blood out to systemic circulation
  • Left ventricle pumps blood under higher pressure, left ventricular wall is more muscular

  
• Cardiac cycle

  1. Systole (contraction of heart muscle)

  2. Diastole (relaxation of heart muscle)

  3. Normal heart rate at rest is about 60-80 beats per minute

  4. "Lub dup" heart sounds are produced by turbulence and tissue vibration as valves close

  
• Intrinsic control of heartbeat


  • Heart has its own intrinsic conduction system
  • Autorhymicity - cardiac muscle can contract without neural stimulation
  • Autonomic nervous system regulates heart rate
  • SA node and AV node are nodal tissue that can generate action potentials to cause contraction
  • Normal conduction pathway: SA node -> atrial muscles -> AV node -> AV bundle -> Purkinje fibers -> ventricles

  
• Extrinsic control of the heartbeat


  • Cardiac control center in the medulla has inputs to heart through the ANS
  • Parasympathetic stimulation decreases heart rate
  • Sympathetic stimulation increases heart rate and contractility
  • Hormones like epinephrine and norepinephrine can also control heartbeat

  
• Electrocardiogram (ECG)

  • Records electrical activity of the heart
  • Can indicate if conduction pathway is working normally
  • P wave - atrial depolarization
  • QRS complex - ventricular depolarization
  • T wave - ventricular repolarization

  
• Cardiac arrhythmias


  • Tachycardia: pulse over 100 bpm
  • Bradycardia: pulse under 60 bpm
  • Sinoatrial block: no P wave
  • Atrioventricular block: P-R interval too long
  • Ventricular fibrillation: erratic quivering of ventricles
  • Cardiac arrest: flatline

  
• Pulmonary circuit

  1. Right ventricle pumps deoxygenated blood to pulmonary artery

  2. Blood distributed to alveolar capillaries in lungs

  3. Oxygen diffuses into the blood and carbon dioxide diffuses out

  4. Oxygenated blood travels through pulmonary veins to the left atrium
• Systemic circuit

  1. Oxygenated blood pumped from left ventricle to aorta

  2. Blood travels through systemic arteries and capillaries, dropping off oxygen and picking up carbon dioxide

  3. Deoxygenated blood returned by venules and veins to the vena cavae

  4. Inferior vena cava drains body below chest, superior vena cava collects blood from head, chest, and arms

  
• Coronary circulation


  • Supplies the heart muscle
  • Coronary arteries are first branches off the aorta
  • Coronary veins enter right atrium

  
• Hepatic portal system


  • Collects nutrient-rich blood from digestive tract
  • Blood carried in hepatic portal vein to liver
  • Nutrients absorbed, toxins detoxified, clean blood carried out by hepatic veins to inferior vena cava
• Blood flow

  • Blood pressure - pressure of blood against vessel walls
  • Highest pressure is systolic, lowest is diastolic
  • Normally 120/80mmHg
  • Blood pressure accounts for flow through arteries and arterioles, decreases as blood distributes throughout system

  
• Coronary circulation


  • Supplies the heart muscle
  • Coronary arteries are the first branches off the aorta
  • Lie on surface of heart and distribute blood to the heart muscle
  • Blood is collected in venules and emptied into coronary veins
  • Coronary veins enter into right atrium

  
• Capillaries


  • Exchange of substances between tissues and blood
• Veins (and venules)


  • Carry blood to the heart
• Blood vessels require oxygen and nutrients like all tissues
• Larger blood vessels have blood supplies of their own
• Arteries


  Walls have 3 layers: innermost endothelium, middle smooth muscle and elastic tissue, outer fibrous connective tissue

  
• Aorta


  Largest artery
• Arterioles


  Branches of arteries, middle layer is mostly smooth muscle, important in control of blood pressure
• Capillaries


  • Walls consist of single layer of endothelium, allow exchange of oxygen, carbon dioxide, nutrients, wastes, total surface area is 6000 square meters
• Not all capillary beds are open at any one time, each has an arteriovenous shunt which allows capillaries to be bypassed
• Heart


  • 4 chambers: 2 upper atria, 2 lower ventricles, separated by septa, wall is mostly myocardium (cardiac muscle), lined with endocardium and epicardium

  
• Heart valves


  • Atrioventricular valves (mitral, tricuspid) between atria and ventricles, semilunar valves (aortic, pulmonary) between ventricles and great vessels, control flow of blood through the heart

  
• Passage of blood through the heart

  Deoxygenated blood from vena cavae to right atrium, through tricuspid valve to right ventricle, through pulmonary valve to pulmonary artery, oxygenated blood from pulmonary veins to left atrium, through mitral valve to left ventricle, through aortic valve to aorta

  
• Pulmonary pump


  Right side of heart pumps deoxygenated blood to pulmonary circuit and lungs

  
• Systemic pump


  Left side of heart pumps oxygenated blood out to systemic circulation
• Cardiac cycle


  Events of each heartbeat, highly coordinated contraction of atria and ventricles, systole (contraction) and diastole (relaxation)