BIO475 Lecture Study Guide #14

BIO475 Lecture Study Guide #14 – February 16, 2026

Chapter 3 – The Thorax (Part 5 – Pages 117-144) Mediastinum, Heart, and Great Vessels

General Notes

• Note: The section “Cardiac skeleton” can be skipped.

Coronary Arteries

1. Point of Origin and Pathway of the Two Coronary Arteries

   • The coronary arteries originate from the aortic sinus just above the aortic valve.

     • Right Coronary Artery (RCA): Originates from the right aortic sinus and travels to the right side of the heart.

     • Left Coronary Artery (LCA): Arises from the left aortic sinus and branches into the left anterior descending (LAD) and circumflex arteries.

   • Pathway includes distinguishing branches supplying various cardiac structures.

2. Pathway and Destination of the Main Coronary Vein

   • The great cardiac vein accompanies the left anterior descending artery, eventually draining into the coronary sinus, located in the right atrium.

3. Four Main Branches of the Right Coronary Artery:

   • a) Sinoatrial (SA) Node Branch

   • b) Right Marginal Artery

   • c) Posterior Interventricular Artery

   • d) Atrioventricular (AV) Node Branch

4. Two Main Branches of the Left Coronary Artery:

   • a) Left Anterior Descending (LAD) Artery

   • b) Circumflex Artery

5. Supply Areas of the Two Coronary Arteries:

   • a) Right Coronary Artery: Supplies the right atrium, most of the right ventricle, and parts of the left ventricle including the inferior wall.

   • b) Left Coronary Artery: Supplies the left atrium, anterior two-thirds of the left ventricle, and the interventricular septum.

6. Variations in Coronary Artery Branching Patterns:

   • a) Right Coronary Artery-Dominant (Most Common): RCA provides blood supply to the inferior wall of the heart.

   • b) Left Coronary Artery-Dominant (Least Common): LCA supplies blood to both the anterior and inferior regions of the heart.

Cardiac Pacemakers and Veins

7. Variation in Artery Branching for Pacemakers:

   • Potential variations exist where the arterial supply to the sinoatrial (SA) node and atrioventricular (AV) node may also come from branches of the left coronary artery. This context may affect the cardiac conduction system.

8. Four Major Veins Returning Blood to the Coronary Sinus:

   • a) Great Cardiac Vein

   • b) Middle Cardiac Vein

   • c) Small Cardiac Vein

   • d) Posterior Vein of the Left Ventricle

9. Function of the Cardiac Conduction System:

   • The cardiac conduction system generates and propagates electrical impulses, coordinating heartbeats and ensuring efficient blood pumping.

10. Four Major Components of the Cardiac Conduction System:

    • a) Sinoatrial (SA) Node

    • b) Atrioventricular (AV) Node

    • c) Atrioventricular Bundle (Bundle of His)

    • d) Purkinje Fibers

11. Location and Function of the Sinoatrial Node:

    • The SA node is located in the wall of the right atrium near the entrance of the superior vena cava and acts as the primary pacemaker of the heart.

12. Location and Function of the Atrioventricular Node:

    • The AV node is located at the junction of the atria and ventricles, facilitating the conduction delay between atrial and ventricular contraction.

13. Atrioventricular Bundle:

    • The atrioventricular bundle originates from the AV node and carries impulses to the ventricles. The terminal part of this structure is known as Purkinje fibers, which trigger ventricular contraction.

14. Primary Role of the Autonomic Nervous System (ANS) Innervation of the Heart:

    • a) Adjusts heart rate.

    • b) Modulates force of contraction.

    • c) Regulates coronary blood flow.

15. Tissues Affected by ANS Innervation:

    • Cardiac muscle tissue, pacemaker cells, and vascular smooth muscle in the coronary arteries.

Cardiac Plexus and ANS Divisions

16. Cardiac Plexus:

    • This structure is a network of nerve fibers that supplies the heart and has two parts:

      • Anterior Cardiac Plexus: Located anterior to the ascending aorta.

      • Posterior Cardiac Plexus: Located posterior to the ascending aorta.

17. Parasympathetic Division Function in the Heart:

    • The parasympathetic division decreases heart rate and constricts coronary arteries. Preganglionic neuron axons are carried via the vagus nerve, with postganglionic neurons located in the walls of the heart.

18. Sympathetic Division Function in the Heart:

    • Sympathetic stimulation increases heart rate and myocardial contractility. Preganglionic neuron axons travel through the sympathetic trunk, with postganglionic neurons located in the sympathetic ganglia. Postganglionic axons then innervate the heart via cardiac nerves.

19. Visceral Afferents in Cardiac Innervation:

    • a) Via the Vagus Nerve: Transmits sensory information such as baroreceptors and chemoreceptors.

    • b) Via the Sympathetic Trunk: Primarily involved in the perception of pain associated with ischemia or myocardial infarction.

Heart Attack and Medical Procedures

20. Heart Attack:

    • A heart attack, or myocardial infarction, occurs when blood flow to a part of the heart is blocked, often due to a clot or atherosclerosis. The most common cause is coronary artery disease.

21. Percutaneous Coronary Intervention (PCI):

    • PCI involves using a catheter to open up blocked coronary arteries, often supplemented by the placement of a stent to keep the artery open following a heart attack.

22. Coronary Artery Bypass Grafts (CABG):

    • CABG involves grafting blood vessels taken from other parts of the body to bypass blocked coronary arteries, restoring normal blood flow to the heart muscle in cases of severe blockages.

23. Pain Associated with Heart Attacks:

    • The nature of pain is typically described as crushing or squeezing, and is often felt in the chest, abdomen, and can radiate to the left arm and neck due to referred pain from the heart.

24. Symptoms of Heart Attacks in Men and Women:

    • Symptoms may vary; women often report atypical symptoms such as fatigue or gastrointestinal distress, whereas men typically experience the classic signs like chest pain and left arm pain.

Blood Vessels and Mediastinum

25. Pulmonary Trunk:

    • The pulmonary trunk starts at the right ventricle and bifurcates into the right and left pulmonary arteries, carrying deoxygenated blood to the lungs for oxygenation.

26. Aorta:

    • The aorta is the largest artery in the body, beginning at the left ventricle and initially termed the ascending aorta. The aorta changes name to the aortic arch shortly after its origin. The very first arterial branches from the ascending aorta are the right coronary artery and left coronary artery.

27. Remaining Large Blood Vessels in the Middle Mediastinum:

    • The superior vena cava and inferior vena cava enter the right atrium, converging in a straight line at this chamber.

28. Boundaries of the Superior Mediastinum:

    • The superior mediastinum is bounded superiorly by the thoracic inlet, inferiorly by the sternal angle, anteriorly by the sternum, and laterally by the mediastinal pleura.

29. Major Contents of the Superior Mediastinum:

    • Contents include the thymus gland, great vessels (aortic arch and its branches), trachea, esophagus, and nerves including the vagus and phrenic nerves.

30. Thymus Gland:

    • The thymus gland is located in the anterior superior mediastinum and its appearance varies with age and individual development because it is larger in children and diminishes in size in adults.

31. Two Large Tributaries of the Superior Vena Cava:

    • a) Left Brachiocephalic Vein

    • b) Right Brachiocephalic Vein

    • Each brachiocephalic vein is formed by the internal jugular and subclavian veins from their respective sides.

32. Three Large Branches of the Arch of the Aorta:

    • a) Brachiocephalic Trunk: (further divides into the right subclavian artery and right common carotid artery)

    • b) Left Common Carotid Artery

    • c) Left Subclavian Artery

33. Ligamentum Arteriosum:

    • This structure is a remnant of the fetal ductus arteriosus, which diverts blood from the pulmonary artery to the aorta in the embryo, closing after birth.

34. Conduits Through the Superior Mediastinum:

    • Respiratory: Trachea (can be palpated just above the sternum).

    • Digestive: Esophagus.

35. Functions of the Vagus Nerve as it Passes Through the Mediastinum:

    • The vagus nerve plays key roles in parasympathetic innervation, affecting heart rate, bronchoconstriction in the lungs, and peristalsis in the digestive system.

36. Branch of the Left Vagus Nerve:

    • The recurrent laryngeal nerve makes a U-turn around the arch of the aorta, innervating the larynx; its impairment can lead to hoarseness of voice.

37. Other Critical Nerve through the Superior Mediastinum:

    • The phrenic nerve also travels through this region, innervating the diaphragm and affecting respiratory function.

38. Boundaries of the Posterior Mediastinum:

    • The posterior mediastinum is bounded by the thoracic vertebrae posteriorly, the pericardium anteriorly, and the thoracic inlet superiorly.

39. Major Contents of the Posterior Mediastinum:

    • Includes the esophagus, thoracic aorta, azygos and hemiazygos veins, and sympathetic trunks.

40. Esophagus:

    • The esophagus is a muscular tube responsible for transporting food from the pharynx to the stomach, starting at the larynx and ending at the stomach. It passes behind the trachea and heart; it is located anterior to the bodies of thoracic vertebrae.

41. Implications of Esophageal Compression:

    • The esophagus can be constricted at four specific points which can complicate swallowing and lead to potential obstructions or reflux conditions.

42. Swallowing Process:

    • a) Muscle Fiber Type – Superior: Skeletal muscle, allowing for voluntary control of swallowing.

    • b) Muscle Fiber Type – Inferior: Smooth muscle, transitioning to involuntary control.

    • c) Motor Efferents – Superior: Supplied by somatic nerves.

    • d) Motor Efferents – Inferior: Supplied by autonomic nerves.

    • e) Sensory Afferents: Conduct sensations from the esophagus and initiate reflexes associated with swallowing.

43. Plexus Around the Esophagus:

    • The esophageal plexus is formed by the left and right vagal trunks, with branches emerging to innervate abdominal viscera, such as the gastric nerves.

44. Azygos Vein System:

    • a) The azygos vein system is a network of veins running along the thoracic vertebrae that receives blood from the thoracic wall and abdomen.

    • b) Azygos Vein (Right Side Only): Drains the right side of the thorax.

    • c) Hemiazygos Vein (Left Side Only): Drains blood from the lower left side of the thorax.

    • d) Accessory Hemiazygos Vein (Left Side Only): Drains the upper left side.

    • e) The azygos veins empty into the superior vena cava.

45. Thoracic Duct:

    • The thoracic duct is the largest lymphatic vessel, running from the abdomen to the neck, collecting lymph from the body and ending at the junction of the left subclavian and internal jugular veins. The swelling along its length before entering the posterior mediastinum is known as the cisterna chyli.

46. Sympathetic Trunks:

    • Sympathetic trunks consist of paired bundles of nerve fibers located on either side of the thoracic spine, serving to distribute sympathetic innervation throughout the thoracic cavity.

47. Distinction of Nerves from the Sympathetic Trunk:

    • a) Nerves from Upper Ganglia: These nerves carry sympathetic fibers that innervate upper body structures (e.g., heart).

    • b) Nerves from Lower Ganglia: Include greater splanchnic nerve, lesser splanchnic nerve, and least splanchnic nerve which supply the abdominal viscera,