The Heart

• Location: Located between the 2nd and 5th rib, between vertebrae levels T4 and T9. Found within the pericardium in the middle mediastinum.

• Overview:

  • Pulmonary Circuit: Right side takes in deoxygenated blood from the body and sends it to the lungs to be oxygenated.

  • Systemic Circuit: Left side takes in newly oxygenated blood from the lungs and sends it to the rest of the body.

  • Pericardium: Can be divided into Fibrous and Serous pericardium which can be further divided into Parietal, Pericardial, and Visceral layers. The pericardial cavity lying between the parietal and visceral layer has about 15-50ml of pericardial fluid in it and acts as a lubricant so the heart can move without friction.

Circulation from the heart

• Structure: Three layers (tunica): Intima, Media, and Adventitia. Different thicknesses of layers in vessels, most distinct in arteries. Veins have different sizes, arteries have muscular specializations and capillaries can only fit 1 blood cell at a time.

• Great Vessels:

  • Superior Vena Cava: Drains deoxygenated blood from the thorax, upper limbs, head, neck, and brain.

  • Inferior Vena Cava: Drains deoxygenated blood from the abdomen and lower limbs.

  • Aortic Arch: Supplies the entire body with oxygenated blood.

  • Pulmonary Track: Takes deoxygenated blood from the heart to the lungs to be oxygenated.

  • Pulmonary Veins: Leave the lungs carrying oxygenated blood and deliver it to the heart ready to be circulated around the body.

• Coronary Circulation: Refers to the oxygenated blood sent to the heart for functional purposes. The left and right coronary arteries form the coronary sulcus that branches around the interventricular sulci converging to the apex of the heart. These drain through the cardiac veins emptying into the right atrium.

• Conduction: The SA Node sends impulses to;

  • Internodal Tracts: Stimulate contraction of the right atrium

  • Bachmann’s Bundle: Stimulate contraction of the left atrium

  • AV Node: Passing signals to the ventricles

  • Bundle of His: Splits into right and left branches that continue to Purkinje fibers.

• Cardiac Cycle:

  • Systole: The period of contraction that the heart undergoes while it pumps blood.

  • Diastole: The period of relaxation that occurs as the heart chambers fill with blood.

Lymphatic System:

• Lymphatic System: A series of organs, vessels, and nodes that collect and filter excess tissue fluid (lymph) before returning it to the venous circulation

• Function:

  • Drains excess interstitial fluid from tissues into the venous system

  • To produce and transport immune cells (lymphocytes) that will mount an immune response against pathogens.

  • To transport dietary lipids from the GI tract into the blood.

• Drainage: Lymph drains back into venous circulation near the heart. However, the duct via which it drains depends on where in the body the lymph is.

  • Thoracic Duct: Collects lymph from the left head, neck, thorax, upper limb, and lower half of the body (40 cm long)

  • Right Lymphatic Duct: Collects lymph from the right head, neck, thorax, and upper limb (1cm long)