Blood and Vascular System Overview

Blood and Vascular System Overview

• Blood serves as the main transport medium, facilitating the movement of molecules between organs.
• The vascular system is a closed circulatory system, unlike an open irrigation system.

Circulatory Systems

• Cardiovascular System: Transports oxygen, carbon dioxide, nutrients, metabolic waste, immune cells, hormones, and clotting factors.
• Lymphatic System: Drains extracellular fluid, returns it to the blood after lymph node filtration, and aids in lipid absorption from the gut.

Types of Blood Vessels

• Arteries: Elastic, muscular, and arterioles; carry blood away from the heart.
• Veins: Venules, large veins; return blood to the heart.
• Capillaries: Site of exchange between blood and tissues.

Structure of Blood Vessels

• Walls consist of three layers:
  • Tunica Intima: Inner layer with simple squamous endothelium in contact with blood; contains basal lamina and myo-intimal cells.
  • Tunica Media: Middle layer of smooth muscle and connective tissue; controls vessel diameter and resistance.
  • Tunica Adventitia: Outer layer of connective tissue; includes vasa vasorum (small vessels supplying larger vessels) and vasa nervosa (nerves).

Segments of the Vascular System

• Comprises elastic arteries (e.g., aorta), muscular arteries, arterioles, capillaries, venules, small/medium-sized veins, and large veins (e.g., vena cava).

Elastic Arteries

• Examples include the aorta and pulmonary arteries; thick media with elastic fibers allows expansion with cardiac contractions, minimizing pressure spikes.

Muscular Arteries

• Make up most named arteries; contain highly contractile smooth muscle layers and distinct elastic laminae.

Arterioles

• Smallest arteries (diameter < 100 microns); regulate systemic blood pressure and local blood flow; can dilate or constrict in response to various stimuli.

Capillaries

• Smallest blood vessels (4-10 μm); form networks for nutrient and waste exchange; consist of a layer of endothelial cells, a basal lamina, and occasional pericytes.

Types of Capillaries

• Continuous (somatic): Most common; tight junctions limit fluid leakage; exchanges via diffusion or transcytosis.
• Fenestrated (visceral): Contain perforations for enhanced exchange; found in endocrine tissues, intestines, and kidneys.
• Sinusoidal: Wider lumen with large gaps, allowing passage of macromolecules and cells; located in bone marrow, liver, lymph nodes, and spleen.

Venules

• Increasingly larger venules connect capillaries to veins, facilitating blood drainage back to the circulatory system.

Atherosclerosis

• Thickening of arterial walls due to white blood cell invasion, leading to reduced elasticity and increased pressure; caused by chronic inflammation, high LDL, and low HDL levels.

Vascular System Overview

• Vasa vasorum and vasa nervosa supply small blood vessels and nerves to the vascular media.
• Thicker walls are characteristic of veins compared to arteries.

Segments of the Vascular System

• Elastic Arteries: Includes the aorta and pulmonary artery; features a thick media with abundant elastic fibers.
• Muscular Arteries: Comprises most named arteries; has highly contractile media with smooth muscle and elastic laminae.
• Arterioles: Diameter less than 100 microns; they adjust lumen size to regulate blood pressure and flow.
• Capillaries: Smallest vessels facilitating molecule exchange between blood and tissues.
• Venules: Small vessels transitioning blood from capillaries to veins.
• Veins: Include small, medium-sized, and large veins like the vena cava.

Elastic Arteries

• Major components include the aorta, pulmonary artery, and their branches.
• The thick media allows lumen expansion during heart contractions, leading to minimal pressure rise during systole.
• The intima is generally folded when empty, while the adventitia is thinner than the media.

Muscular Arteries

• Most named arteries, such as the ophthalmic artery, fall into this category.
• They possess a highly muscular media featuring distinctive internal and external elastic laminae.

Arterioles

• Act as resistance vessels; regulate systemic blood pressure and direct blood flow to specific tissues.
• Respond dynamically to various stimuli by either dilation or constriction.
• Connect capillary beds, which can be bypassed in cold conditions via direct shunts.

Blood and Circulatory Systems

• Blood serves as the primary medium for transporting nutrients, gases, immune cells, and hormones.
• The circulatory system is closed, distinguishing it from open irrigation systems.
• Comprises two main systems:
  • Cardiovascular System: Transports gases, nutrients, and hormones.
  • Lymphatic System: Drains extracellular fluid, involved in lipid absorption.

Types of Blood Vessels

• Arteries: Elastic, muscular, and arterioles.
• Veins: Capillaries, venules, small/medium veins, and large veins.

Wall Structure of Blood Vessels

• Composed of three layers:
  • Tunica Intima: Inner layer with endothelial cells.
  • Tunica Media: Middle layer with smooth muscle and connective tissue; regulates vessel diameter.
  • Tunica Adventitia: Outer layer of fibroelastic connective tissue.

Tunica Intima

• Contains simple squamous endothelium in direct contact with blood.
• Features a basal lamina with contractile myo-intimal cells assisting in phagocytosis and tissue synthesis.

Tunica Media

• Contains concentric layers of smooth muscle and fibroelastic connective tissue.
• Controls vessel diameter affecting blood resistance.
• Often has internal and external elastic laminae.

Tunica Adventitia

• Composed of fibroelastic connective tissue, providing structural support to blood vessels.

Atherosclerosis

• Characterized by arterial wall thickening due to white blood cell invasion.
• Leads to decreased elasticity, increased pressure, and impaired blood flow.
• Chronic inflammation underlies this condition, worsened by high LDL and low HDL levels.

Capillaries

• Smallest vessels (4-10 μm) where blood and tissue exchanges occur.
• Walls consist of a single layer of endothelial cells, a basal lamina, and occasionally pericytes.

Types of Capillaries

• Continuous (Somatic) Capillaries: Most prevalent; tight junctions limit fluid leakage.
• Fenestrated (Visceral) Capillaries: Allow greater molecule exchange with perforations present.
• Sinusoids (Discontinuous) Capillaries: Wider lumen with significant gaps allowing exchange of macromolecules and cells.

Venules

• Progressively larger and more organized vessels connecting capillaries to veins.