Unit 1 - Heart Functional Anatomy

Dr. Swartz A&P 2 Lecture

Basic Functional Features

• Mostly cardiac muscle

• Highly metabolic (lots of mitochondria)

• Contains connective tissue, epithelia, and nerve

  • Connective → Fibroblast and fat

  • Epithelia → endothelium lines surfaces and blood vessels

  • Nerves → Autonomic nerves

    • Sympathetic postganglionic

    • Parasympathetic ganglia

• Heart rate and contractile strength are modulated by the autonomic system

• Cyclical contraction - relaxation cycle that is self-paced

• Highly vascularized by coronary vessels.

• Heart = a continuous active pump that develops pressure.

• Systole → shortening of myocytes decreases volume, forcing the blood to be pumped OUT of the chamber

  • Blood is incompressible, so a decrease in volume = increase pressure

• Diastole → relaxation of myocytes and back-pressure refills the pump

• Valves prevent backflow and maintain pressure in vessels.

Describe the anatomy of the heart within the thorax

• 4 chambers with different muscle wall thickness

  • atria thin walls, ventricle thicker walls

• Located in the mediastinum of the thoracic cavity

• Posterior to the sternum between 2nd rib and 5th intercostal space

• ~300g of mass

• Anterior to the vertebrae, esophagus, and large vessels

• Atria superior right, ventricles inferior left

• Ventricle apex points towards the left hip

Name the coverings of the heart

• Pericardium: double-walled sac enclosing the heart

  • Tough fibrous pericardium outer: fibrous connective tissue

  • Serous pericardium inner: simple squamous epithelia

    • Parietal layer: thin outer layer that lines the fibrous pericardium

    • Pericardial cavity: contains thin serous fluid to reduce friction

    • Visceral layer (epicardium): thin inner layer lines the heart surface

    • Allows free movement of the heart within the pericardium

  • Inflammation causes pericarditis

    • Minor → pain in the sternum and sticking layers together, limiting heart movement

    • Major → excess fluid accumulation in the pericardial cavity, limiting heart pumping

      • Treat by Tamponade (via draining fluids)

Describe the functional anatomy of the three layers of the heart

• Epicardium (outer): simple squamous epithelium, part of visceral pericardium

  • Can contain fat

• Myocardium (middle): cardiac muscle arranged spirally/circularly to “squeeze” blood out of chambers; thickest layer

• Endocardium (inner): endothelium + connective tissue lining chambers; interfaces with blood

Describe the functional anatomy of the chambers of the heart including major (great) vessels leading to and from the heart

4 Chambers:

• Atria: thin-walled, contain auricles (flaps) and pectinate muscles

  • Right: receives blood from superior/inferior vena cava + coronary sinus

  • Left atrium: receives blood from 4 pulmonary veins

• Ventricle: thick-walled, contains trabeculae carneae (ridges of muscle) and papillary muscles connecting to valves via tendons (chordae tendineae)

  • Right: pumps blood to pulmonary arteries

  • Left: pumps blood to aorta

Septa

• Interatrial and interventricular septa separate left/right chambers

Sulci

• Coronary sulcus between atria and ventricles

• Completely around the heart like a crown

Name the heart valves and describe their location, function, and mechanism of operation

• Atrioventricular (AV) Valves:

  • Tricuspid: right AV valve (3 flaps)

  • Mitral (bicuspid): left AV valve (2 flaps)

  • Prevent backflow from ventricles to atria

  • Anchored by chordae tendineae to papillary muscles

  • Flaps are forced closed when ventricles contract due to higher pressure being in the ventricle compared to atria

• Semilunar Valves:

  • Pulmonary valve: right ventricle → pulmonary artery

  • Aortic valve: left ventricle → aorta

  • Pocket-like, prevent backflow into ventricles

  • Not attached by tendons

  • Contraction of ventricles increases pressure to force the valves to open

• Valve defects:

  • leaky valves → incompetent or insufficient valves → needs to pump more in order to maintain flow and pressure
    

  • AV valve prolapse → stretchy chordae tendineae → blood regurgitation (into atria)
    

  • Stiff valves → valvular stenosis → needs to pump harder to open valve

• Valves can be replaced using mechanical devices or transplants from human, cow, or pig valves.

Trace the path of blood through the heart

• Systemic venous return:

  • Superior/inferior vena cava + coronary sinus →

• Right atrium →

• Right AV valve →

• Right ventricle →

• Pulmonary valve →

• Pulmonary arteries →

• Lungs/Pulmonary Circuit (gas exchange) →

• Pulmonary veins →

• Left atrium →

• Left AV valve →

• Left ventricle →

• Aortic valve →

• Aorta → systemic and coronary circulation

Name the major branches and describe the distribution of coronary arteries

• Left Coronary Artery (from aorta):

  • Anterior interventricular artery (LAD): feeds septum & anterior walls

  • Circumflex artery: feeds left atrium and posterior wall

• Right Coronary Artery:

  • Right marginal artery: lateral right heart

  • Posterior interventricular artery: feeds apex & posterior walls

• Coronary arteries branch to capillaries → cardiac veins → coronary sinus → right atrium

• Disorders: atherosclerosis, thrombosis, ischemia, detectable via troponin I/T

• Can anastomose slowly (angiogenesis)

Describe the functional anatomy of cardiac muscle and how it differs from skeletal muscle

• Similarities:

  • Striated with sarcomeres

• Differences:

  • Branched, mono/binucleated, rectangular

  • Nucleus is central

  • Intercalated discs with gap junctions for electrical syncytium

  • More mitochondria (~30%)

  • T-tubules at Z-lines, one per sarcomere

  • Dyads, not triads

  • Calcium-induced calcium release (not mechanically triggered like in skeletal)

  • Cannot tetanize due to long absolute refractory period

  • Relies on aerobic metabolism

  • Force is graded by calcium levels, not motor unit recruitment