Introduction to Circulatory System

Learning Objectives

• Recognize components of the circulatory system.
• Understand circulation dynamics through the heart.
• Describe pulmonary and systemic circulations and their characteristics.
• Identify types of blood vessels.
• Gain insight into the lymphatic system and its functions.
• Discuss clinical issues associated with the circulatory system.

Overview of the Circulatory System

• Comprises two primary systems: the cardiovascular system (CVS) and lymphatic system.
• Responsible for transporting fluids throughout the body.

Cardiovascular System

• Includes the heart and blood vessels.
• Main function: transport blood, delivering oxygen, nutrients, hormones, and waste products to and from tissues.

Structure of the Heart

• Hollow, fibromuscular organ, functioning as both pump and suction device.
• Shape: conical/pyramidal.
• Weights approximately 300 g (male) and 250 g (female).
• Located centrally in thoracic cavity, mostly left of midline.
• Comprised of four chambers: two atria and two ventricles.

Blood Circulation

• Heart operates as two muscular pumps, dividing circulation into:
  • Pulmonary Circuit: transports deoxygenated blood from the right ventricle (RV) to lungs and back to left atrium (LA).
  • Systemic Circuit: carries oxygenated blood from left ventricle (LV) to right atrium (RA).

Types of Blood Vessels

• Three primary types: arteries, capillaries, veins.

Arteries

• Transport blood under higher pressure away from the heart.
• Typically convey oxygen-rich blood.
• Manifest pulsatile nature, allowing palpation.
• Smallest arteries: arterioles.
• Major artery: aorta, branching into ascending, arch, and descending aorta.

Arterial Communication

• Anastomosis forms connections between artery branches, enabling collateral circulation.
• Courses include:
  • End-to-end anastomosis: direct artery communication.
  • Convergent arteries: merging vessels such as vertebral arteries forming basilar artery.
  • Transverse anastomosis: connecting large arteries transversely.

Capillaries

• Simple endothelial tubes facilitating material exchange between blood and extracellular space.
• Arranged in capillary beds between arterioles and venules.
• Starling forces regulate fluid movement in and out of capillaries.

Venous System

• Returns mostly deoxygenated blood to the heart.
• Thinner-walled vessels, lacking pulsation or spurting.
• Nutrient and hormone transport, often for drug administration.

Types of Veins

• Venules: smallest veins draining capillary beds.
• Medium veins: drain venous plexuses, often possessing valves.
• Large veins: encompass substantial muscle bundles and thick walls (e.g., superior vena cava).

Characteristics of Veins

• Outnumber arteries and exhibit variable patterns.
• Larger diameters but thinner walls in comparison to arteries.
• Serve as capacitance vessels, containing roughly 80% of total blood volume.

Vascular Relationships

• Venae commitantes: help in heat exchange.
• Vascular sheath and arteriovenous (A-V) pumps aid blood flow.

Vascular Patterns

• Shunts and anastomoses allow direct connections between arteries and veins, bypassing capillary beds as required.
• Blood flow to capillary beds adjusts based on local demands.

Factors Affecting Blood Flow

• Left ventricular contraction and right ventricular relaxation.
• Intrathoracic pressure changes and muscular contractions (e.g., calf muscles).
• Arterial pulsations and unidirectional valves.

Clinical Applications

• Common conditions include:
  • Arteriosclerosis: arterial thickening and loss of elasticity.
  • Atherosclerosis: fat accumulation in arterial walls.
  • Ischemia: reduced blood flow leading to tissue damage.
  • Infarction: local tissue death, e.g., myocardial infarction or stroke.
  • Varicose veins: swollen and twisted veins.

Lymphatic System

• Complementary to the circulatory system, critical for immunity and fluid balance.
• About 3 liters of extracellular fluid remain unabsorbed by the venous system daily.

Key Components of the Lymphatic System

• Lymphatic vessels: disseminated throughout the body, except in bone marrow, teeth, and CNS.
• Lymph: fluid similar to blood, containing lymphocytes.

Major Lymphatic Vessels

• Right lymphatic duct: drains the right side of the head, neck, and upper limb into the right brachiocephalic vein.
• Thoracic duct: drains the rest of the body into the left brachiocephalic vein, originating as cisterna chyli in the abdomen.

Lymph Nodes

• Small, bean-shaped structures situated along lymphatic vessels.
• Contain immune cells to filter and remove harmful materials from lymph.

Naming of Lymph Nodes

• Classified based on location relative to deep fascia, identified as either superficial or deep.

This quiz focuses on the components of the circulatory system, detailing the blood circulation process through the heart, as well as the differences between pulmonary and systemic circulation. Designed for students of B.Hottor's course, it aims to reinforce key concepts about organ systems. Test your understanding of how the circulatory system functions.