Overview
This lecture introduces the circulatory (cardiovascular) system, focusing on its transport functions, the heart’s structure, and the layers protecting and forming the heart.
Functions of the Circulatory System
- The circulatory system transports oxygen, nutrients, and waste between body cells and the environment.
- Blood delivers oxygen and glucose for cellular respiration, supplying energy (ATP) to cells.
- Removes metabolic waste products like carbon dioxide, hydrogen, urea, and ammonia from cells.
- Maintains homeostasis by regulating glucose, calcium, pH, and body temperature via blood flow.
Blood Vessels and Exchange
- The system allows exchange in the lungs (oxygen in, carbon dioxide out) and GI tract (nutrients absorbed).
- "Lumen" refers to the inside space of a tubular structure, like the intestine where nutrient absorption occurs.
Heart Structure and Location
- The heart is about the size of a fist, located in the mediastinum (between lungs, behind sternum), with the apex resting on the diaphragm.
- It has four chambers: two smaller atria (top) and two larger ventricles (bottom).
Heart Wall and Coverings
- The heart is surrounded by the pericardium, with an outer fibrous layer (protection, anchoring, prevents overfilling).
- The serous pericardium has parietal (lines cavity) and visceral (touches heart, aka epicardium) layers.
- The pericardial cavity between layers contains serous fluid, reducing friction.
- Inflammation of this area is called pericarditis (too little fluid) or can result in excess fluid compressing the heart (needles remove excess).
Layers of the Heart Wall
- Epicardium (visceral pericardium): outer, protective connective tissue with blood vessels and nerves.
- Myocardium: thick, middle muscular layer (especially thick on left side for systemic circulation).
- Endocardium: thin, inner lining of heart chambers and valves, composed of simple squamous epithelium and connective tissue.
- The endocardium is continuous with the endothelium of blood vessels, creating a smooth internal surface.
Fibrous Skeleton of the Heart
- Dense connective tissue rings provide structural support for heart valves and muscle attachment.
- Prevents valve over-dilation and helps synchronize atrial and ventricular contractions.
Key Terms & Definitions
- Lumen — the inner space of a tubular organ.
- Pericardium — sac surrounding the heart.
- Fibrous pericardium — tough, protective outer layer of the pericardium.
- Serous pericardium — double-layered inner portion (parietal and visceral/epicardium).
- Pericardial cavity — space with serous fluid between pericardial layers.
- Epicardium — outer layer of heart wall, same as visceral pericardium.
- Myocardium — thick middle muscle layer of the heart.
- Endocardium — inner lining of the heart chambers and valves.
- Pericarditis — inflammation of the pericardium.
- Fibrous skeleton — connective tissue framework supporting the heart.
Action Items / Next Steps
- Review serous membrane structure in the lab manual (page 10).
- Prepare to identify heart chambers and layers in lab.