Nutrition absorption in the small intestine is very much important to sustain the life. To enhance the efficiency of this process, the anatomy of the small intestine is modified to increase the surface area of absorption. Other than this, structures like microvilli can be found in some other areas of the body, as well. Major modifications of the luminal surface area include valvulae conniventes, villi, and microvilli. Out of these three, villi are most prominently seen while microvilli can be observed by a microscope.
Villi
Finger-like projections found in the inner surface of the small intestine are referred to as villi. They are formed by folding the mucosa of the small intestine in order to increase the surface area of nutrition absorption. Other than nutrition absorption, they also help to absorb minerals and electrolytes, as well. Each villus contains brush border cell layer. Small blood vessels and a lymph vessel are connected to each villus helping the movement of substances to and from the bloodstream. The outer layer of the villi has gland cells that release digestive enzymes to the lumen. Villi have low permeability to passive diffusion.
Microvilli
Microvilli are small projections of cell membranes that increase the surface area of cells. The main functions of microvilli are absorption, secretion, cellular adhesion, and mechanotransduction. These microvilli are organized to form a structure called brush border. Microvilli are found in some epithelial cells of the small intestine, on the plasma surface of eggs, and on white blood cell surface. The function of them depends on the place where they are found in the body. For example, microvilli found in the small intestine increase the absorption surface, whereas microvilli found on the surface of egg help to anchor the sperm cells. Plasma membrane makes the boundary of microvilli and the inside is filled with cytoplasm. Since microvilli are microscopic structures, they do not contain any cellular organelle in them. Each microvillus contains a bundle of cross-linked actin filaments, which form the structural core of it.
What is the difference between Villi and Microvilli?
• Villi are bigger than microvilli.
• Villi are found on the layer of tissue, whereas microvilli are found on cells.
• Microvilli, unlike villi, are cellular structures.
• Unlike in the villi, core of microvilli contains cross-linked actin filaments.
• Villi and microvilli are both found in the small intestine, whereas only microvilli are found in surface of eggs and white blood cells.
• Microvilli make brush border, while villi do not.
• The cells with microvilli are found in the outermost cell layer of villi.