ℹ️ Mammal Vein Section
A typical mammalian vein section would showcase a trilayered structure. The innermost layer, the tunica intima, consists of a single layer of endothelial cells lining the lumen. The middle layer, the tunica media, is composed of smooth muscle cells and connective tissue, but the smooth muscle layer would be generally thinner compared to arteries reflecting the lower pressure requirements in veins. The outermost layer, the tunica adventitia, is composed primarily of dense connective tissue anchoring the vein to surrounding structures. In some veins, particularly larger ones, valves might be present to prevent backflow.
Source: https://my.clevelandclinic.org/health/body/22619-vena-cava

ℹ️ Artery c.s.
An artery cross-section would display a thicker wall compared to a vein due to the higher blood pressure it needs to withstand. The tunica intima, the innermost layer, would still be lined by endothelial cells. The tunica media, the middle layer, would be the most prominent, consisting of multiple layers of smooth muscle cells responsible for vasoconstriction and vasodilation for blood pressure regulation. The outermost layer, the tunica adventitia, would be composed of dense connective tissue providing structural support. In contrast to veins, valves wouldn’t be present in arteries.
Source: https://www.ncbi.nlm.nih.gov/books/NBK470401/

ℹ️ Spleen, Human Section
A human spleen section would reveal a capsular structure with red and white pulp regions. The red pulp is densely packed with red blood cells undergoing phagocytosis by macrophages within specialized structures called splenic cords. Scattered throughout the red pulp are white pulp areas containing lymphoid tissue, including B and T lymphocytes, responsible for immune function. Sinusoids, specialized wide blood vessels, wind through the red pulp allowing for the filtration and removal of old or damaged blood cells.
Source: https://pubmed.ncbi.nlm.nih.gov/17067939/