The two vessel types depicted are capillaries and arteries/veins, respectively. The capillary slide shows a single layer of flattened epithelial cells, which are endothelial cells, surrounding a narrow lumen. This structure is characteristic of a capillary. The artery/vein slide shows a thick tunica media composed of smooth muscle and elastic fibres, and a distinct tunica externa. This is characteristic of an artery or vein.

Structural Differences and Functional Relationships:

• Capillaries: Single layer of endothelial cells. This thin wall allows for efficient diffusion of gases, nutrients, and waste products between the blood and the surrounding tissues. The narrow diameter facilitates rapid exchange.
• Arteries: Thick tunica media with abundant smooth muscle and elastic fibres. This allows arteries to withstand high blood pressure generated by the heart and to expand and recoil with each heartbeat, maintaining a relatively constant blood flow. The elastic fibres allow for compliance.
• Veins: Thinner tunica media compared to arteries, with less smooth muscle and elastic fibres. The walls are thinner and less elastic. Veins have valves to prevent backflow of blood, especially in the limbs, as blood pressure in veins is much lower.

Water constitutes approximately 90% of blood plasma and tissue fluid, making it the dominant component. This composition is crucial for efficient transport in mammals due to water's unique properties.

Solvent Action: Water is an excellent solvent, capable of dissolving a wide range of substances, including nutrients, oxygen, carbon dioxide, hormones, and waste products. This allows these substances to be transported effectively throughout the body. For example, oxygen dissolved in the blood plasma is essential for cellular respiration. Similarly, nutrients absorbed from the digestive system are dissolved in water to be transported to cells. The ability to dissolve waste products like urea also facilitates their removal from the body via the kidneys.

High Specific Heat Capacity: Water has a high specific heat capacity, meaning it requires a significant amount of energy to change its temperature. This property acts as a temperature buffer within the body. Blood and tissue fluid absorb heat from metabolically active tissues (e.g., muscles) and prevent drastic temperature fluctuations. This is vital for maintaining a stable internal body temperature, which is essential for enzyme function and overall physiological processes. Without water's high specific heat capacity, tissues would overheat rapidly, potentially damaging cells.

In summary, water's solvent properties enable the transport of essential substances and waste, while its high specific heat capacity helps maintain a stable internal temperature, both of which are vital for efficient mammalian transport systems.

Pulmonary circulation is the circuit that carries blood between the heart and the lungs. Deoxygenated blood from the right ventricle is pumped to the lungs via the pulmonary artery. In the lungs, carbon dioxide is released, and oxygen is absorbed. The oxygenated blood then returns to the left atrium of the heart via the pulmonary vein.

Systemic circulation is the circuit that carries blood between the heart and the rest of the body. Oxygenated blood from the left ventricle is pumped to the aorta, which branches into arteries that supply blood to all the organs and tissues of the body. As blood travels through the tissues, oxygen and nutrients are delivered, and carbon dioxide and waste products are picked up. Deoxygenated blood then returns to the right atrium of the heart via the vena cavae.

Here's a summary: