Essential Concepts of Human Circulation and Lymphatic Health
Key Functions of the Lymphatic System
The lymphatic system performs several vital roles:
- Fluid Collection: Collects excess interstitial fluid and returns it to the blood circulation.
- Fat Absorption: Absorbs and transports dietary fats in the intestine.
- Immune Defense: Defends the body from bacteria and other foreign particles.
This filtering process is primarily carried out by lymphocytes, which are especially abundant in the lymph nodes. When there is an infection, lymph nodes typically swell (become inflamed).
Blood Vessels: Arteries, Veins, and Capillaries
Arteries
Arteries transport blood away from the heart to the tissues. They generally carry blood rich in oxygen (O₂), with the exception of the pulmonary arteries, which carry CO₂-rich (deoxygenated) blood to the lungs.
- Walls: Thick and elastic.
- Valves: Absence of valves.
- Flow: Blood flows faster and under high pressure (pulsatile flow).
- Location: Typically circulating internally (deeply located).
Veins
Veins transport blood toward the heart from the tissues. They generally carry blood rich in carbon dioxide (CO₂), with the exception of the pulmonary veins, which are rich in O₂ (oxygenated blood).
- Walls: Thin and less elastic than arteries.
- Valves: Contain valves throughout their length to prevent backflow.
- Flow: Blood circulates slowly and under low pressure.
- Location: Superficial veins are common.
Capillaries
Capillaries are microscopic vessels that form a network, joining the endings of the arteries with the start of the veins. Through their fine epithelial walls, the essential exchange of nutrients, oxygen, carbon dioxide, and waste substances occurs between the blood and the body’s cells.
Blood Components
Blood is composed of plasma and cellular elements:
Erythrocytes (Red Blood Cells)
These are anucleated and flattened cells containing hemoglobin, responsible for carrying oxygen (O₂).
Leukocytes (White Blood Cells)
Leukocytes are crucial for immune defense. Types include:
- Neutrophils
- Eosinophils (Acidophils)
- Basophils
- Lymphocytes
- Monocytes
Platelets
These are cellular fragments essential for blood coagulation (clotting).
Cardiac Anatomy and Cycle
Heart Structure (Key Components)
- Right Atrium
- Tricuspid Valve
- Right Ventricle
- Left Atrium
- Mitral Valve (Bicuspid Valve)
- Left Ventricle
- Aortic Semilunar Valve
- Aorta
- Vena Cava
- Pulmonary Artery
- Pulmonary Veins
- Pericardium
- Myocardium
- Endocardium
Cardiac Cycle Terminology
- Systole: The contraction movement of the heart chambers.
- Diastole: The relaxation movement of the heart chambers.
The Two Blood Circuits
The body utilizes two main blood circuits:
- Pulmonary Circuit (Lesser Circulation): Blood flows from the right atrium to the right ventricle, which pumps it via the pulmonary artery to the lungs for oxygenation.
- Systemic Circuit (Greater Circulation): Driven from the left ventricle through the thick aorta, this circuit distributes oxygenated blood to all organs of the body.
Homeostasis and Internal Fluids
Homeostasis Defined
Homeostasis is the set of processes that maintain a constant and stable internal environment within the organism.
The Internal Environment
The internal environment is the collection of fluid surrounding the cells of an organism. In this environment, cells extract the nutrients and oxygen they need, and subsequently dump waste substances and carbon dioxide produced during metabolism. It is comprised mainly of circulating fluids: blood, lymph, and interstitial fluid.
Key Body Fluids
- Interstitial Fluid: A fluid located between cells, serving functions of defense and nutrition. It originates from blood plasma filtered through the thin walls of capillaries.
- Blood: A means of transport for substances that circulates inside the blood vessels.
- Lymph: A fluid formed from interstitial fluid and plasma that circulates through lymphatic vessels. These vessels eventually drain into the blood circulatory system.
Lymphatic System Structures
Lymphatic Capillaries
These are blind-ended, very small vessels distributed throughout all tissues, responsible for collecting the interstitial fluid.
Lymphatic Vessels
These vessels drain into the blood circulatory system, discharging their contents. They contain a series of valves that ensure flow in only one direction.
Lymph Nodes
Lymph nodes are small expansions or swellings that occur along lymphatic vessels. They are very abundant in areas such as the armpits, the groin, the neck, and around the ears.
Vascular Pathology
Arteriosclerosis
Arteriosclerosis is the hardening of the arteries. It occurs mainly due to the deposit of fat and cholesterol on the inner wall of the arteries, which decreases the internal diameter and obstructs the passage of blood. This obstruction can lead to the formation of blood clots (thrombi), causing blockages called thrombosis. If these clots reach vital organs (such as the heart, brain, or lungs), they can obstruct blood flow and cause serious events like a stroke or myocardial infarction.