Systemic & Pulmonary Circulation

• Circulation pathways involve the cardiovascular system.
• Animations for Cardiovascular System Overview, Pulmonary & Systemic Circulation, Heart Fly Through, Blood Flow Through the Heart, and Conduction System of the Heart are available.

Left Heart and Systemic Circulation

• Consists of the left heart and systemic vessels.
• Oxygenated blood is returned from the lungs to the left atrium via pulmonary circulations.
• Blood within systemic arteries is oxygenated.
• Oxygen diffuses to tissues in the systemic capillaries.
• Systemic veins carry deoxygenated blood which is returned to the right atrium.

Right Heart and Pulmonary Circulation

• Consists of the right heart and pulmonary vessels.
• Blood is largely deoxygenated and oxygenation ocuurs in pulmonary capillaries

Structural differences between ventricular walls

• The right ventricular wall is thin.
• The right ventricle pumps blood a short distance to the lungs.
• Blood pressure is low in the pulmonary trunk and arteries.
• The left ventricular wall is thick.
• The left ventricle pumps blood to the entire body.

Circulation Pathway

• Systemic veins drain into the superior and inferior vena cavae and coronary sinus.
• The blood from the systemic veins moves into the right atrium, then through the tricuspid valve to the right ventricle.
• Blood moves through the pulmonary semilunar valve to the pulmonary trunk and arteries to perform gas exchange in the lungs.
• From the lungs, the blood moves through the pulmonary veins into the left atrium where it passes through the bicuspid valve to the left ventricle.
• Blood moves through the aortic semilunar valve into the Aorta and then to the systemic arteries.
• Gas and nutrient exchange occurs in peripheral tissues.

Thoracic components of the Aorta

• Ascending aorta: the segment of aorta immediately superior to the aortic semilunar valve.
• Arch of the aorta: includes 3 branches:
  • Brachiocephalic, which further branches into the right subclavian and right common carotid arteries.
  • Left common carotid.
  • Left subclavian.
• Descending aorta: posterior to the heart, and also called the thoracic aorta.

Abdominal Portion of Aorta

• The aorta passes through an opening posterior to the diaphragm called the aortic hiatus.
• Inferior to the diaphragm, the descending aorta becomes the abdominal aorta.
• The abdominal aorta ends where it divides into the two common iliac arteries.

Arteries of Thorax

• Subclavian Artery: gives off the Internal Thoracic Artery.
  • The Internal Thoracic Artery contributes medial mammary branches to the breast.
• Axillary Artery: continuation of the subclavian.
  • Gives off the Lateral Thoracic Artery just lateral to the rib cage.
  • The Lateral Thoracic Artery contributes lateral mammary branches to the breast.
• Descending Thoracic Aorta: gives off 12 pairs of posterior Intercostal Arteries, which supply the posterior wall.

Arteries of the Abdomen

• The gastrointestinal (GI) Tract organs receive branches from the unpaired arteries of the Abdominal Aorta.
• Foregut: Distal Esophagus, Stomach, most of Duodenum and associated organs (Liver, Gallbladder, Pancreas, and Spleen).
  • Unpaired Branch of Aorta: Celiac Trunk Artery (celiac artery or celiac trunk).
• Midgut: Jejunum, Ileum, Cecum, Appendix, Ascending Colon, and proximal 2/3 of Transverse Colon.
  • Unpaired Branch of Aorta: Superior Mesenteric Artery (SMA).
• Hindgut: Distal 1/3 of Transverse Colon, Descending Colon, Sigmoid Colon, and Superior Rectum.
  • Unpaired Branch of Aorta: Inferior Mesenteric Artery (IMA).

Arteries to the Gut: Celiac Trunk Artery

• The Celiac trunk artery is very short and branches from the abdominal aorta just below the respiratory diaphragm.
• It immediately divides into 3 branches:
• Left Gastric Artery: the superiormost branch to the left side of lesser curvature at junction with esophagus.
• Splenic Artery: tortuous path to the spleen
• Common Hepatic Artery: travels toward the liver.

Arteries to the Gut: Superior Mesenteric Artery (SMA)

• The Superior Mesenteric Artery arises from the abdominal aorta just inferior to the Celiac artery.
• Runs posterior to neck of the pancreas (with SMV).
• Gives 12-15 branches to the jejunum and ileum of the small intestine and supplies the large intestine until the proximal 2/3.

Arteries to the Gut: Inferior Mesenteric Artery (IMA)

• The Inferior Mesenteric Artery arises from the abdominal aorta inches above the abdominal aortic bifurcation.
• It is smaller in diameter in comparison to the Celiac or SMA.
• Supplies distal 1/3 of transverse colon, sigmoid, and sends its last branch, the superior rectal a..

Abdominal Aorta and Paired (Bilateral) Branches

• Inferior Phrenic Arteries: to the inferior diaphragm.
• Renal Arteries: to the kidneys.
• Gonadal (Ovarian/Testicular): to female/ male gonads.
• Lumbar arteries: to the body wall of the lumbar region.
• The abdominal Aorta bifurcates into the left and right common iliac arteries which branch into:
  • External Iliac a.
  • Internal Iliac a.

Arteries of the Pelvis

• Pelvic structures receive branches from:
  • Abdominal Aorta:
    • Gonadal (Ovarian/ Testicular) artery: Branches bilaterally from the Abdominal Aorta.
  • Internal Iliac artery: further branches into the Umbilical A, Lateral Sacral A, and Superior Vesical A.
  • Inferior Mesenteric Artery:
    • Superior Rectal artery: Branches from Inferior Mesenteric Artery.

Veins of Thorax: Draining Head and Upper Limbs

• Right and left subclavian veins: drain upper limbs.
• Right and left brachiocephalic veins: formed by junction of subclavian and internal jugular veins.
• Superior vena cava: formed by union of the 2 brachiocephalic veins.
• Right and left external and internal jugular veins: drain the head, neck and face.

Veins of Thorax: Draining Body Wall

• On the right side, intercostal veins empty directly into the Azygos Vein which ascends the lateral vertebral column.
• The Azygos Vein ascends behind the pericardium and right lung until it arches forward to enter the posterior Superior Vena Cava.
• Blood from the posterior wall of the thorax is drained by Intercostal Veins.
• On the left side, intercostal veins 4-8 empty directly into the Accessory Hemiazygos V.
• Left intercostal veins 9-11 and the lumbar veins drain into the Hemiazygos V.

Veins of Abdomen

• Hepatic veins drain the liver to IVC.
  • Hepatic veins are the final drainage of the hepatic portal system.
• Renal Veins (from kidneys) are tributaries that drain into the IVC.
• IVC drains to the right atrium.
• Two common iliac veins form the Inferior Vena Cava (IVC).

Veins of the Pelvis

• Gonadal (Ovarian/ Testicular) vein drainage:
  • Left gonadal vein drains into the left renal vein.
  • Right gonadal vein drains directly into the IVC.
• Superior Rectal Vein drains into the inferior mesenteric vein (IMV).
• IMV drains to splenic vein.
• Splenic vein drains to hepatic portal vein; Hepatic portal circulation is discussed in the Special Circulations section.