Question

Explain the relationships among plasma, tissue fluid, and lymph, in terms of movement of water throughout the body. (p. 324)

Short answer

Question: Explain the relationships among plasma, tissue fluid, and lymph in terms of the movement of water throughout the body. Answer: Plasma, tissue fluid, and lymph are interconnected components of the circulatory system that facilitate the movement of water, nutrients, gases, and waste products throughout the body. Plasma filters out of capillaries to form tissue fluid in the interstitial space, which then exchanges substances with surrounding cells. Some tissue fluid is reabsorbed back into the capillaries due to osmotic pressure difference, while excess tissue fluid is collected by the lymphatic system and becomes lymph. Lymph is ultimately returned to the circulatory system, helping to maintain fluid balance and overall body homeostasis.

Step-by-step solution

Introduction

Plasma, tissue fluid, and lymph are all important components of the circulatory system. They facilitate the movement of water, nutrients, gases, and waste products throughout the body.

Plasma

Plasma is the liquid component of blood, making up about 55% of its total volume. It is composed mainly of water (around 90%) and contains various dissolved substances such as proteins, ions, glucose, and hormones. Plasma serves as the medium for transporting these dissolved substances, enhances gas exchange, and contributes to maintaining blood pressure and pH balance.

Tissue Fluid (Interstitial Fluid)

Tissue fluid, also known as interstitial fluid, surrounds the cells of our body, providing them with nutrients and a means to eliminate waste products. It is similar in composition to plasma but has a lower protein concentration. Tissue fluid is formed as a result of filtration from blood capillaries into the interstitial space and is constantly being exchanged between the blood capillaries and the cells.

Lymph

Lymph is a clear fluid that is derived from the interstitial fluid and is collected by the lymphatic system. It contains a much lower concentration of proteins compared to plasma and interstitial fluid. Lymph serves to maintain fluid balance in the body, aids in the removal of waste products and excess fluid from tissues, and plays a critical role in the immune system.

Formation of Tissue Fluid from Plasma

As blood flows through the capillary bed, the pressure difference across the capillary wall causes water and small solutes (like nutrients, ions, and oxygen) from the plasma to filter out into the interstitial space, forming tissue fluid. This process is known as filtration.

Exchange of Substances between Tissue Fluid and Cells

Once the tissue fluid is formed in the interstitial space, it bathes the cells and allows exchange of nutrients, gases, and waste products between the blood and the cells. Oxygen and nutrients diffuse from the tissue fluid into the cells, while waste products and carbon dioxide diffuse from the cells into the tissue fluid.

Reabsorption of Tissue Fluid into Plasma

After the exchange process, some of the tissue fluid is reabsorbed back into the capillaries due to the osmotic pressure difference created by the higher protein content in the plasma compared to the tissue fluid. This process is called reabsorption.

Formation of Lymph from Tissue Fluid

Not all tissue fluid is reabsorbed into the capillaries. The excess tissue fluid, along with waste products and particulate matter, is collected by the lymphatic system and is now referred to as lymph.

Return of Lymph to the Circulatory System

The lymphatic system drains the lymph through a network of vessels, eventually returning it to the circulatory system via the thoracic duct and the right lymphatic duct, which empty into the subclavian veins. This process helps maintain fluid balance within the body. In conclusion, plasma, tissue fluid, and lymph are interconnected components that facilitate the movement of water throughout the body, allowing for the transport and exchange of nutrients, gases, and waste products between blood and the cells. Their dynamic relationship is key to maintain fluid balance and overall body homeostasis.