
Organs
An organ is a grouping of two or more tissues into an organized structure to serve a particular function(s). Groups of organs may be assembled, in turn, into organ systems, that also serve a specific function(s), such as the digestive system or urinary system. Left 10x; Right 10x, 40x

Small intestine >
Organs have different shapes and appearances depending on their functions. Some organs, like the small intestine, are hollow, tubular structures, composed of epithelium to absorb nutrients, connective tissues for padding, and muscle to propel food through the digestive tract. A blood and nerve supply would also be present.

Kidney >
Other organs appear solid, like the kidney, without a central lumen.

Seminal vesicle >
The structural diversity of organs reflects their function, as depicted by the seminal vesicle, with its secretory epithelium, connective tissue padding, muscular tunic to expel secretory product, and blood and nerve supplies.

Lumens >
The shape of the lumen (blue arrows) can vary depending on the organ, from highly folded to smooth. Also visible are lumens of blood vessels that supply these organs (black arrows).

Epithelium >
The type of epithelium varies widely among different organs and is highly indicative of the function of that organ.

Connective tissue >
All organs contain connective tissues and many also contain muscle tissue.

Muscle
All organs contain connective tissues and many also contain muscle tissue.