Understanding the Cardiac Cycle and Connective Tissue Types
The Cardiac Cycle
The cardiac cycle is the period between one cardiac contraction and the next. It is divided into three stages:
- Atrial systole: Lasts 0.1 seconds. It produces contraction of the atria. Blood passes through the mitral and tricuspid valves into the ventricles. Meanwhile, the semilunar valves are closed, preventing blood from leaving the ventricles.
- Ventricular systole: Lasts 0.3 seconds. Once blood reaches the ventricles, they contract; the mitral and tricuspid valves close to prevent backflow into the atria. Semilunar valves open, allowing blood to leave the ventricles. This opening is passive due to increased intraventricular pressure, and the outflow of blood is intermittent, perceived as the arterial pulse.
- General diastole: Lasts 0.4 seconds. Both the atria and the ventricles are relaxed and expanded, creating negative pressure that draws blood into the atria. The ventricles continue to expand, lowering their pressure below that of the atria, which causes the valves to open and blood to move from the atria to the ventricles. At the end of this phase, the ventricles contain nine-tenths of their capacity. A new atrial systole then propels the remaining blood into the ventricles, completing the cycle.
Connective Tissue Components
- Fibroblasts: Produce fibers and amorphous matrix substance. At maturity, they lose activity and are called fibrocytes.
- Histiocytes (Macrophages): Possess the capacity to phagocytose particles and foreign substances.
- Mast cells: Contain numerous cytoplasmic granules filled with substances released at specific times.
- Adipocytes: Specialized cells that store fat.
- Blood cells: Lymphocytes from the blood and plasma cells produce antibodies.
Types of Connective Tissue
- Loose (Lax) tissue: Cells, fibers, and ground substance are in equal proportion, making it flexible and resistant to traction. It supports linings and fills gaps between organs.
- Dense tissue: Contains abundant collagen fibers, making it inflexible and resistant to traction. Fibers can be arranged in parallel, as in tendons, or irregularly, as in the dermis.
- Elastic (Stretch) tissue: Contains an abundance of elastic fibers that provide great elasticity. It is located in organs that require expansion or dilation, such as the bronchi.