Understanding the Human Circulatory System: Blood, Heart, and Lymph
The Human Circulatory System
The circulatory system is vital for transporting nutrients, oxygen, and waste throughout the body. It comprises the internal environment, the blood circulatory system, and the lymphatic circulatory system.
1. The Internal Environment
The internal environment consists of fluids surrounding the body’s cells. Cells extract nutrients and oxygen from this environment and release waste and carbon dioxide into it. In humans, the internal environment mainly includes interstitial fluid and plasma, circulating as blood and lymph.
- Plasma: The liquid component of blood.
- Interstitial Fluid: A nutrient-rich fluid between cells.
- Blood: Transports substances through blood vessels.
- Lymph: Fluid derived from plasma, circulating through lymphatic vessels.
Maintaining stable conditions within this environment is called homeostasis.
2. The Blood Circulatory System
The blood circulatory system distributes nutrients and oxygen while collecting metabolic waste products for elimination.
Vasculature
Vasculature refers to the network of vessels through which blood circulates:
- Arteries: Carry blood from the heart to organs.
- Veins: Carry blood from organs back to the heart.
- Capillaries: Connect arteries and veins, facilitating substance exchange.
3. Blood
Blood is a viscous, red fluid circulating within blood vessels. It plays crucial roles in:
- Nutrition
- Respiration
- Excretion
- Defense
- Thermal Regulation
Blood Composition
- Plasma: A yellowish liquid, primarily water (90%), with proteins responsible for many of blood’s properties. Serum is plasma without certain proteins.
- Blood Cells:
- Red Blood Cells (Erythrocytes): Small, biconcave cells without nuclei.
- White Blood Cells (Leukocytes): Larger cells with nuclei, involved in immune defense.
- Platelets (Thrombocytes): Cell fragments without nuclei, essential for blood clotting.
4. The Heart
The heart’s walls consist of myocardial tissue, responsible for its contraction. The heart is divided into two halves, each with two chambers: an upper atrium and a lower ventricle.
Atria and ventricles communicate through atrioventricular valves:
- Mitral Valve: Connects the left atrium and ventricle, composed of two leaflets.
- Tricuspid Valve: Connects the right atrium and ventricle, composed of three leaflets.
Routes of Entry and Exit
Veins enter the atria, and arteries exit the ventricles. Semilunar valves regulate blood flow.
The heart requires its own blood supply through the coronary arteries and veins, separate from the blood circulating within its chambers.
5. Heart Function
The heart functions through coordinated movements of the atria and ventricles, involving contraction (systole) and relaxation (diastole).
6. Dual Circulation
- Pulmonary Circuit: Between the heart and lungs, facilitating gas exchange.
- Systemic Circuit: Between the heart and body organs, delivering oxygen and nutrients.
7. The Lymphatic Circulatory System
The lymphatic system collects excess fluid from between cells, returning it to the blood, and transports fats absorbed in the intestine.
8. Diseases of the Circulatory System
- Arteriosclerosis: Hardening of the arteries, primarily due to fat and cholesterol deposition.
- Myocardial Infarction: Blockage of a coronary artery, leading to the death of heart muscle cells.