MPharm Programme - Circulatory System

MPharm Programme - Normal Systems - The Circulatory System

• This lecture series is about the circulatory system
• The circulatory system is broken into three basic components (Blood, The Heart, & Blood Vessels)
• Blood is a transport medium carrying dissolved or suspended material (oxygen, carbon dioxide, nutrients, electrolytes, hormones, and metabolic wastes) over long distances in the body
• The heart serves as a pump generating pressure and cardiac output, delivering blood to organs and tissues
• Blood vessels form a conduit network distributing blood from the heart to all body parts and back to the heart
• The circulatory system performs multiple functions, including:
  • Transportation: of respiratory gases (oxygen and carbon dioxide), nutrients, and metabolic waste
  • Regulation: of hormones, homeostasis (pH and electrolyte balance), and temperature
  • Protection: through haemostasis (blood clotting) and immunity (leukocytes, cytokines, and complement)

Blood

• Blood is a specialized liquid connective tissue, essential for short-range and long-range material transport between cells and the external environment
• Total blood volume varies dependent on body size, fluid & electrolyte concentration and adipose tissue
• Blood makes up 8% of body weight, with 5-6 liters in males and 4-5 liters in females
• Blood composition consists of:
  • Plasma (55%): A straw-colored liquid primarily composed of water (92%) and dissolved solutes (proteins, electrolytes, nutrients, hormones, and metabolic wastes)
  • Formed or Cellular Elements (45%): Red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes)
• Erythrocytes (red blood cells) are the most abundant and carry hemoglobin responsible for oxygen transport
• Blood composition can be analyzed further using centrifugation; revealing the percentage of plasma, buffy coat, and erythrocytes after being withdrawn into a tube. This will indicate the relative concentration of formed elements present in the sample.

The Heart

• A four-chambered muscular pump driving circulatory functions
• Located in the mediastinum, between the sternum and the vertebrae
• Surrounded by the pericardium, a double-layered membrane (visceral and parietal pericardium) with a lubricating fluid-filled cavity.
• The heart pumps blood throughout the body, driving both pulmonary and systemic circulation pathways
• Right side pumps deoxygenated blood to the lungs
• Left side pumps oxygenated blood to the body

Vessels of the Heart

• Great Cardiac Vessels: include the superior and inferior vena cavae, pulmonary artery, pulmonary veins, and aorta
• Coronary Vessels: specialized vessels forming the coronary circulation, supplying blood to the cardiac muscle tissue. These vessels include the coronary arteries, coronary sinus, and various cardiac veins.

Cardiac Cells

• Two main types

  • Contractile cells - comprise 99% of heart cells, primarily responsible for the mechanical pumping action

  • Electrical or Autorhythmic cells specialized for initiating and conducting action potentials (electrical impulses). The impulses activate contraction in the muscle cells. The electrical cells include the sinoatrial (SA) node, atrioventricular (AV) node, Bundle of His, and Purkinje fibers.

• General Properties of Cardiac Cells:

  • Resting Membrane Potential (RMP): Cell membrane at rest is polarized, inside being negative compared to the outside. Unequal distribution of ions across the cell membrane determines it.
  • Excitability: Ability of heart cells to react to electrical stimuli by generating and propagating action potentials. The action potentials lead to contraction of the adjacent cardiac cells..
  • Types of Action Potentials: Fast and slow. The differences are due to differences in voltage and time-dependent ion-channel opening/closing. The two types lead to differences in conduction characteristics.

Heart Valves

• Four heart valves ensure unidirectional blood flow through the heart.
• Atrioventricular (AV) valves include the tricuspid and bicuspid (mitral) valve, situated between the atria and ventricles; preventing backflow into the atria during ventricular contraction
• Semilunar valves (Pulmonary and Aortic) are situated between the ventricles and their respective arteries; preventing backflow into the ventricles during ventricular relaxation.

The Heart Valves' Function

• The heart valves ensure unidirectional blood flow through the heart.

Heart Wall Layers

• The three distinct layers comprise; 
  • The innermost: Endocardium,  lines the heart chambers; permitting efficient blood flow while preventing clotting.
  • Myocardium, thick, middle layer of cardiac muscle tissue. It is mainly responsible for the heart's pumping function.
  • Epicardium, the outermost layer, is a protective membrane covering the heart and embedding coronary blood vessels.

Components Summary

• These components work in concert to allow constant blood flow and support all body functions.
• Coordination of the system is crucial for maintaining homeostasis.
• Irregularities or failures in any one of these components can lead to significant health issues.

This quiz covers the fundamentals of the circulatory system, including blood, the heart, and blood vessels. It outlines the system's essential functions such as transportation, regulation, and protection within the body. Test your understanding of how these components work together to maintain overall health.