Similarities Between Lymphatic Vessels and Blood Vessels

Lymphatic vessels and blood vessels are tubular structures with thin walls. They branch off to form small vessels. In addition, they penetrate different tissues in the body.  The main function of both types of vessels is to assist the transport of different types of fluids throughout the body.  These are the main similarities between lymphatic vessels and blood vessels.

However, lymphatic vessels carry lymph while blood vessels carry blood. Moreover, lymphatic vessels are a component of the lymphatic system while blood vessels are a component of the cardiovascular system. Meanwhile, the lymphatic system is not a closed system while the cardiovascular system is a closed system. Lymphatic capillaries also have a wide diameter than blood capillaries. 

Key Areas Covered 

1. What are Lymphatic Vessels
     – Definition, Structure, Types, Function
2. What are Blood Vessels
     – Definition, Structure, Types, Function
3. What are the Similarities Between Lymphatic Vessels and Blood Vessels
     – Outline of Common Features

Key Terms 

Blood Vessels, Cardiovascular System, Lymphatic Vessels, Lymphatic System, Tubular Structures 

What are Lymphatic Vessels 

Lymphatic vessels are thin tubes which carry lymph or the lymphatic fluid along with white blood cells through the lymphatic system.  They are valved structures. Significantly, lymphatic vessels are one of the two types of vessels found in the body.

Lymphatic Vessels Structure

The general structure of lymphatic vessels is more similar to that of blood vessels. Basically, the endothelium is the inner layer of the lymphatic vessels. Moreover, it is made up of a single layer of flattened epithelial cells called simple squamous epithelium. In addition, the second layer is the circular smooth muscles. The activity of smooth muscles helps to pump the lymph through the vessel slowly. The outer layer of a lymphatic vessel is the adventitia, consisting of fibrous tissue.

Figure 1: Lymph Capillaries

Furthermore, valves are one of the major structural components of lymphatic vessels. Their function is to prevent the backflow of lymph. However, the main factor responsible for the movement o lymph through lymphatic vessels is compression, which occurs during contraction of adjacent skeletal muscle and arterial pulsation. Generally, the main function of the lymphatic vessels is to carry lymph towards the heart in a unidirectional manner. Moreover, it is an open system, which starts from lymphatic capillaries. These lymphatic capillaries collect lymph from the interstitial fluid. In addition, lymphatic vessels show a dense distribution near lymph nodes, which are the bundles of lymphoid tissue that filter the lymph fluid of pathogens and abnormal molecules.

Figure 2: Lymphatic System  

Lymphatic Vessels – Types and Function

The two main types of large lymphatic vessels are the afferent efferent lymphatic vessels. The afferent lymphatic vessels carry unfiltered lymph towards the lymph nodes while the efferent lymphatic vessels carry filtered lymph out of the lymph nodes. Moreover, the efferent lymphatic vessels in the left and lower side of the body drain into the left subclavian vein through the thoracic duct while the efferent lymphatic vessels of the right side of the body drain into the right subclavian vein through the right lymphatic duct. Lymphatic capillaries and lymphatic vessels play a key role in the fluid pressure regulation, preventing the accumulation of edema or the abnormal swellings in tissues. 

What are Blood Vessels 

Blood vessels are the tubular structures, carrying blood through the tissues and organs. However, they are the second type of vessels found in the body.

Blood Vessels Types

Generally, the five types of blood vessels are arteries, arterioles, capillaries, venules, and veins. Arteries carry blood away from the heart under the pumping pressure generated by the heart. They branch off to form smaller arteries called arterioles. Then, these arterioles branch off further to form tiny blood capillaries. Next, capillaries form venules and then veins, which carry blood towards the heart. Moreover, the exchange of nutrients, oxygen, carbon dioxide, and nitrogenous wastes occur through blood capillaries. Therefore, arteries and arterioles carry oxygenated blood away from the heart while venules and veins carry deoxygenated blood towards the heart.

Figure 3: Blood Vessels

Blood Vessels – Structure and Function

The wall of the blood vessels consists of three layers: tunica intima, the tunica media, and the tunica externa. Tunica intima is the inner layer made up of endothelial cells of simple squamous epithelium. Tunica media is the middle layer rich in vascular smooth muscles. On the other hand, tunica externa or adventitia is a connective tissue layer. Moreover, blood vessels form two circuits of circulation. They are the systemic circulation and the pulmonary circulation. Basically, the systemic circulation carries blood through the body while pulmonary circulation carries blood through the lungs. Therefore, systemic circulation supply oxygen and nutrients to the metabolizing tissues of the body while removing metabolic wastes. In contrast, pulmonary circulation removes carbon dioxide from the blood while helping the intake of oxygen into the blood in the lungs.  

Similarities Between Lymphatic Vessels and Blood Vessels  

• Lymphatic vessels and blood vessels are two types of vessels found in the body. 
• Both are tubular structures, consisting of a thin wall and a lumen. Moreover, they branch off to form small vessels. The smallest type of vessels of both lymphatic and blood vessels are the capillaries. 
• The basic structure of both types of vessels is the same. This means they consist of an inner endothelial layer made up of simple squamous epithelium, the middle smooth muscle layer, and an outer connective tissue layer. 
• Moreover, both lymphatic vessels and veins contain valves to prevent the backflow of fluids. 
• In addition, the movement of fluids inside the lymphatic vessels and veins occur due to the compression during contraction of adjacent skeletal muscle and arterial pulsation.   
• Therefore, both lymphatic vessels and veins do not operate by the pumping pressure of the heart. 
• Both lymphatic vessels and veins drain fluids towards the heart. 
• The main function of lymphatic and blood vessels is to carry fluids, which are different versions of the blood plasma. The main component of these fluids is water. In addition, both types of fluids contain white blood cells. 
• Both types of vessels occur in different types of tissues in the body. However, lymphatic vessels do not occur in bone and nerve tissues. 
• They play a key role in the management of fluid pressure in the body. 
• Furthermore, they play an important role in the immunity of the body. 

Conclusion 

Lymphatic vessels and blood vessels are the two types of vessels found in the body. Their main function is to carry lymph and blood, respectively. In addition, large vessels branch off to form smaller vessels and the smallest types of vessels are the capillaries. Structure-wise, both types of vessels contain an inner layer of endothelial cells, a middle layer of circular smooth muscles, and an outer layer of connective tissues. Significantly, both lymphatic vessels and veins contain valves. Moreover, they operate by the action of skeletal muscle contractions. This is the summary of the similarities between lymphatic vessels and blood vessels in terms of structure and function. 

References:

1. “Lymphatic Vessels.” Lumen|Boundless Anatomy and Physiology, Available Here.
2. “131 20.1 Structure and Function of Blood Vessels.” Chapter 20. The Cardiovascular System: Blood Vessels and Circulation, Pressbooks. Available Here.

image Courtesy:

1. “Illu lymph capillary” (Public Domain) via Commons Wikimedia   
2. “Illu lymphatic system” (Public Domain) via Commons Wikimedia   
3. “Blood vessels (retouched) -en” By Kelvinsongderivative work: Begoon – This file was derived from Blood vessels-en.svg: (CC BY-SA 3.0) via Commons Wikimedia