Circulatory System Overview

Study Notes

Function: Transports blood, oxygen, carbon dioxide, nutrients, and metabolic waste. Regulates temperature.
Components:
- Blood vascular system:
  - Blood vessels (arteries, veins, capillaries)
  - Heart
  - Blood
- Lymph vascular system: Collects tissue fluids
  - Lymphatic capillaries
  - Lymphatic vessels
  - Lymph nodes
  - Lymphoid organs (spleen, thymus)

Chambers:
- Right atrium: Receives blood from the body
- Left atrium: Receives blood from the lungs
- Right ventricle: Propels blood to the lungs (pulmonary circulation)
- Left ventricle: Propels blood to the body (systemic circulation)
Heart wall:
- Endocardium (inner layer): Epithelial tissue (simple squamous epithelium) and connective tissue (loose connective tissue)
  - Myoelastic layer (middle layer): Smooth muscle fibers and connective tissue
  - Subendocardial layer: Modified cardiac muscle tissue (Purkinje fibers) responsible for impulse conduction, contributing to heart contraction.
- Myocardium (middle layer): Thickest layer due to the strong force of blood pumping. Composed mainly of cardiac muscle arranged in a spiral pattern which allows for twisting motion during contraction
  - Cardiac muscle function: Contraction to pump blood out of the heart, followed by relaxation for refilling.
  - Fibrous skeleton: Composed of collagen fibers (for insulation and structural support) and elastic fibers (allows heart to return to shape after contracting).
  - Contains numerous blood vessels
- Epicardium (outer layer): More delicate layer than the pericardial sac. Directly in contact with the heart’s surface. Composed of epithelial tissue (simple squamous epithelium) and connective tissue (loose connective tissue).

Double-walled:
- Parietal pericardium (pericardial sac): Anchors the heart to the aorta and vena cava
  - Tough outer fibrous layer: Provides structural support
  - Thin serous lining: Composed of epithelial tissue
- Visceral pericardium (epicardium): In direct contact with the heart's surface.
Pericardial fluid:
- Found between the pericardial sac and the epicardium.
- Function: Reduces friction caused by the pumping heart.
- Can accumulate due to heart disease/inflammation, compressing the heart and restricting pumping.

Three layers:
- Tunica intima (inner layer): Endothelium (simple squamous epithelium) and connective tissue (loose connective tissue)
- Tunica media (middle layer): Smooth muscle fibers and connective tissue
- Tunica adventitia (outer layer): Connective tissue

The left ventricle is thicker than the right ventricle due to the greater force required to pump blood throughout the body.
The fibrous skeleton of the heart provides structural support for the heart and acts as an insulator for electrical impulses.
Purkinje fibers are specialized cardiac muscle tissue that help conduct the electrical impulses needed for heart contraction.
Pericardial fluid serves as a lubricant to reduce friction between the heart and the surrounding structures.