compendium 6

• Describe the position of the heart within the mediastinum.

  · Size of a closed fist (larger in males)

  · Shape

  o Apex: Blunt rounded point of cone. Most inferior part. (Left)

  o Base: Flat part at opposite of end of cone. Superior part.

  · Oblique angle with most of the heart on the left side of the body, hence left lung is smaller.

  · Located in thoracic cavity in mediastinum
• Functions of the Heart

  · Main function is to contract, Generating blood pressure - moves blood through vessels.

  · 2 pumps in one and circulates blood flow through 2 circulations

  o Routing blood: separates pulmonary and systemic circulations.

  · Ensuring one-way blood flow.

  · Regulating blood supply pumped around the heart, body and tissues

  · Changes to match need (increase and decrease blood pumping)

  o Eg. Exercise or sleep
• Describe the major anatomical structures of the heart - Coverings

  Double layered closed sac surrounding the heart. Consists of:

  Fibrous pericardium: Tough fibrous outer layer, prevents over distention; Anchors heart in the mediastinum.

  
  

  Serous pericardium: Thin, transparent, inner layer, simple squamous epithelium.

  · Parietal pericardium: lines the fibrous outer layer - attaches to diaphram

  · Visceral pericardium: covers heart surface

  · The two are continuous and have a pericardial cavity between them filled with pericardial fluid
• What makes up the wall of the heart? (3 tissue layers of cardiac muscle and the pectinate muscles and trabecular carneae)


  Three layers of tissue

  1. Epicardium: Serous membrane; smooth outer surface of heart. Underlying connective tissue.

  2. Myocardium: Middle layer composed of cardiac muscle cells - contractility.

  3. Endocardium: Smooth inner surface of heart chambers.

  
  

  Pectinate muscles: muscular ridges in auricles and right atrial wall. Increase power of contraction.

  
  

  Trabeculae Carneae: muscular ridges and columns on inside walls of ventricles that increase turbulence/movement of blood in the ventricles.
• Describe the major anatomical structures of the heart - Chambers

  Atria - superior (slightly posterior)

  RECIEVES DEOXYGENATED BLOOD FROM BODY

  · Right atrium: three major openings to receive deoxygenated blood returning from the body via superior vena cava, inferior vena cava (veins), coronary sinus

  · Left atrium: four openings that receive blood from pulmonary veins from the lungs, these are the L & R pulmonary veins

  
  

  Ventricles - inferior (slightly anterior)

  RECIEVES DEOXYGENATED BLOOD FROM LUNGS

  · Atrioventricular canals: openings between atria and ventricles. R&L atrioventricular valves.

  · Right ventricle: Blood from R atrium through AV valve into R Ventricle, opens to pulmonary trunk and then goes off to the lungs.

  · Left ventricle: Deoxygenated blood from lungs come in and moves through L AV valve to the L ventricle and opens to aorta - very muscular wall. Interventricular septum: between the two ventricles.
• The great vessels of the heart

  Blood into the heart:

  · Bring deoxygenated blood into Right Atrium - superior and inferior vena cava

  · Bring oxygenated blood into Left Atrium - left and right pulmonary veins

  
  

  Blood out of the heart:

  · Deoxygenated blood out of right ventricle - pulmonary trunk

  · Oxygenated blood out of left ventricle - aorta
• Describe the major anatomical structures of the heart - Valves

  Atrioventricular valves (AV valves)

  · Each valve has leaf-like cusps that are attached to cone- shaped papillary muscles by tendons (chordae tendineae).

  · Right has three cusps (tricuspid).

  · Left has two cusps (bicuspid, mitral).

  · When valve is open, blood flows from A to V.

  · When it is closed, blood exits ventricle.

  
  

  Semilunar valves

  · Right (pulmonary); left (aortic).

  · Each cusp is shaped like a cup.

  · When cusps are filled, valve is closed - stop backflow.

  · When cusps are empty, valve is open - blood exits heart.
• Characteristics of Arteries VS Veins

  1. Carries blood to or away from heart?

  2. Branches?

  3. Is the wall thick or thin?

  4. Lumen is round or flat

  5. Carry oxygenated or deoxygenated blood?

  6. Valves?

  1. A - Away, V - To

  2. A - Elastic, Muscular, Arterioles, V - Large, medium, small, venules

  3. A - Thick, V - Thinner walls than arteries, contain less elastic tissue less smooth muscle

  4. A - Round, V - Flat

  5. A - Oxygenated except for the pulmonary arteries which carry deoxygenated blood to lungs, V - Deoxygenated besides pulmonary veins which carry oxygenated blood

  6. A - None, V - Valves to prevent backflow and push blood back to heart against forces of gravity
• Histology of Arteries and Veins

  Tunica intima: Endothelium

  
  

  Tunica media: smooth muscle cells arranged circularly around the blood vessel.

  · Vasoconstriction: smooth muscles contract, decrease in blood flow

  · Vasodilation: smooth muscles relax, increase in blood flow

  
  

  Tunica externa (adventitia): connective tissue
• Capillaries

  Site of exchange with tissues (interstitial fluid)

  · Capillary beds - extensive networks for exchange.

  · Wall consists of endothelial cells (simple squamous epithelium), basement membrane and a delicate layer of C.T.

  · Substances move through capillaries by diffusion
• Components of Blood

  · Plasma = 55%

  Water, ions, nutrients, gases, proteins

  · Formed elements = 45%

  Red blood cells

  · Buffy Coat

  Platelets and white blood cells

  - Platelets assist with clotting

  - WBC - Immunity and inflammation and protect from invading pathogens
• How do Red Blood Cells Carry Oxygen and CO2?

  No nucleus & bi-concave shape to increase SA and thus oxygen carrying capacity.

  · Oxygen carried in blood from lungs to body cells:

  o 98.5% attached to haemoglobin protein

  o 1.5% dissolved in plasma

  · How carbon dioxide is carried in the blood

  o 1. Plasma (7%)

  o 2. Haemoglobin (23%)

  o 3. Bi-carbonate ions (70%)
• Functions of Blood

  · Transport: gases, nutrients, waste products, processed molecules, hormones, enzymes

  · Regulation of pH and osmosis (normal pH 7.4)

  · Maintenance of body temperature

  · Protection against foreign substances

  · Clot formation - platelets
• Describe the flow of blood through the heart (11 steps)

  1. Blood enters RA from S&I vena cavae.

  2. Blood in RA flows through tricuspid valve into RV.

  3. Contraction of RV forces pulmonary SL valve open.

  4. Blood flows through pulmonary SL valve into pulmonary trunk.

  5. Blood is distributed by right and left pulmonary artery to the lungs = unload CO2 and loads O2.

  6. Blood returns from lungs via pulmonary veins to LA.

  7. Blood in LA flows through bicuspid valve into LV.

  8. Contraction of LV (W/ step 3) forces aortic SL valve open.

  9. Blood flows through aortic SL valve into a sending aorta.

  10. Blood in aorta is distributed to every organ in body where it unload O2 and loads CO2.

  11. Blood returns to RA via S&I Vena Carvae
• Pulmonary Circulation Pathway


  · Gas exchange in the lungs.

  · Deoxygenated blood enters right atrium and flows into right ventricle.

  · Exits heart through Pulmonary trunk.

  · Pulmonary trunk divides into left and right pulmonary arteries.

  · Blood travels to right and left lung - gas exchange.

  · Oxygenated blood travels in left or right pulmonary veins and enters the left atrium.
• Systemic Circulation Pathway

  · Capillary exchange in the body/cells.

  · Oxygenated blood enters left atrium. Blood flows into left ventricle.

  · Left ventricle contracts and pushes blood out of heart through aorta.

  · Aorta branches into Ascending aorta, Aortic arch, Descending aorta.

  · Blood is delivered to all cells and tissues in the body for gas/nutrient/fluid exchange.

  · Deoxygenated blood travels back to heart and re-enters right atrium through vena cava
• Cardiac cycle

  Repetitive contraction (systole) and relaxation (diastole) of heart chambers - moves blood through the heart and body.
• Cardiac Output

  Heart rate x Stroke Volume.
• How does the Nervous system and hormones control cardiac output?

  Nervous System:

  · Maintains blood pressure and thus blood flow. Re-routing blood flow where needed.

  o E.G. Increase BP with exercise. Re-route blood flow away from skin and viscera towards brain and cardiac muscle in response to blood loss / injury.

  
  

  Hormonal Control:

  · Epinephrine (adrenaline) from adrenal gland - increase heart rate and stroke volume (cardiac output), vasoconstriction in response to stress.
• Heart's Conduction System

  Action potential - a rapid change in membrane potential. Acts as an electrical signal / impulse.

  
  

  The heart can generate it's own action potentials.

  
  

  Auto-rhythmicity - repetitive contractions.

  
  

  Sinoatrial node (SA) - pace maker.

  · Located in right atrium near base of superior vena cava

  · Patch of modified cardiocytes which initiates each heartbeat, determines heart rate

  · Signals spread throughout atria

  
  

  Atrioventricular node (AV)

  · Located near right AV valve

  · Electrical gateway to ventricles

  
  

  Action potentials spread through the conducting system of the heart to all cardiac muscle cells - as a result the cardiac muscle cells contract. Blood is 'pumped'.
• How does the heart contract?

  1. Action potentials originate in the SA node and travel across the wall of the atrium from the SA node to that AV node.

  2. Action potentials passed through the AV node and along the AV bundle, which extends from the AV node, through the fibrous skeleton, into the interventricular septum.

  3. The AV bundle divide into right and left bundle branch is, and action potentials descend to the apex of each ventricle along the bundle branches.

  4. Action potentials are carried by the Purkinje fibres from the bundle branches to the ventricular walls and papillary muscles.
• Differentiate between systemic and pulmonary circulation.

  Pulmonary Circulation

  · Carries O2 poor blood to lungs for gas exchange then returns O2 rich blood to the heart

  · Supplied by right half of heart

  
  

  Systemic Circulation

  · Supplies O2 rich blood to every organ of the body then returns O2 poor blood to the heart

  · Supplied by left half of heart
• Describe the effects of exercise on cardiac output.

  Cardiac Output increases with exercise to supply the cells (skeletal and cardiac muscle), which are working a lot harder than they were at rest, with the extra oxygen and nutrients they need, and to remove wastes.
• Capillary Exchange

  The movement of substances into and out of capillaries. How cells receive what they need to survive and eliminate waste products.
• Describe the transport of carbon dioxide and oxygen in the blood.

  1. Oxygen defuses into the arterial end of pulmonary capillaries and CO2 defuses into the alveoli because of differences in partial pressures.

  2. As a result of diffusion at the Venous end of pulmonary capillaries the PO2 in the blood is equal to the PO2 in the alveoli and the PCO2 in the blood is equal to the PCO2 in the alveoli.

  3. The PO2 of blood in the pulmonary veins is less than the pulmonary capillaries because of mixing with D oxygenated blood from veins draining the bronchi and bronchioles.

  4. O2 defuses out of the arterial end of tissue capillaries and CO2 defuses out of the tissue because of differences in partial pressures.

  5. As a result of diffusion at the Venus ends of tissue capillaries, the PO2 in the blood is equal to the PO2 in the Tissue and the PCO2 in the blood is equal to the PCO2 in the tissue.

  REPEAT
• The lymphatic system and capillaries

  Fluid moves out of capillaries into interstitial (intercellular) space and most returns to capillaries.

  The fluid which remains in tissues is picked up by the lymphatic system then eventually returned to venous circulation.
• Artery

  A blood vessel that carries blood away from the heart
• Atrioventricular (AV) valve

  A valve located in between the atrium and ventricle. Prevents backflow of blood from ventricle to atrium.
• Atrium

  Superior heart chambers - right or left.
• Capillary

  The smallest and most common blood vessel type. Gas and nutrient exchange occurs across the walls of the capillaries.
• Chordae tendinae

  Small chord like tendons that act to open and close the AV valves
• Lumen

  The inner space of a blood vessel (or other tubular structure).
• Mediastinum

  Central cavity located in the thorax, contains the heart, thymus and large blood vessels.
• Papillary muscle

  Small cone shaped muscles that act to open and close the AV valves
• Pericardium

  The heart is located within the pericardium, which consists of the outer fibrous pericardium and the inner serous pericardium.
• Pulmonary circulation

  The system of blood vessels carrying blood from the right ventricle of the heart to the lungs and back to the left atrium.
• Semilunar valve

  Small cup like valves located in the pulmonary trunk (right) and aorta (left).
• Systemic circulation

  The system of blood vessels that carries blood from the left ventricle of the heart to the tissues of the body and back to the right atrium.
• Vein

  A blood vessel that carries blood towards the heart
• Ventricle

  Inferior heart chambers - right or left