Finger-like projections

The oviducts are also known as the Fallopian tubes or uterine tubes. The wall of the oviduct consists of three layers a mucosa, a muscular layer and an outer layer of connective tissue. When the ovum is released by the ovary, it is taken up by the oviduct. The ends of the oviducts are not directly attached to the ovaries but open into the abdominal cavity close to them. The opening of each is funnel-shaped and surrounded by long finger-like projections, fimbriae, with ciliated epithelium which catch the ovum as it is released. The other ends open directly into the uteras. The lower end of the latter is known as the cervix and opens into the vagina. 

The inner surface of the small intestine is not smooth and flat but wrinkled into a large number of finger-like projections called villi, which project into the lumen. If we look at each villus under the microscope (Fig. 1) we find it, in turn, has small fingerlike processes projecting out into the lumen - the microvilli. The result of this is that the surface of the small intestine (which is only 300 cm in length - in the relaxed state after death it may measure 6-7 metres), is estimated to have an area of 250 m. It is obviously designed to absorb, particularly, nutrients and this is also where most of any drug taken by mouth is absorbed. 

Q1 The mucosa is a mucous membrane which forms the innermost layer of the intestine. In the small intestine the mucosal surface area is increased greatly by folds and by villi, finger-like projections containing a core with a lymph capillary (lacteal) and blood vessels. Villi are covered by absorptive columnar epithelial cells whose luminal surface is further increased by microvilli (brush border) on which digestive enzymes and transport mechanisms for inorganic ions are located. 

Microvilli "Microvilli" is the pural form "Microvillus" is the singular form. Microvilli are finger-like projections on the outer-surface of the cell. Not all cells have microvilli. Their function is to increase the surface area of the cell, which is the area through which diffusion of materials both into, and out of, the cell is possible. 

Helix-loop-helix motif A structural motif found in some DNA-binding proteins. It consists of an a helix followed by a turn and then another a helix. This provides a finger-like projection that can fit in a groove of DNA. 

Microvilli minute finger-like projections from the cell surface about 0.1 pm in diameter. 

The mucosa or lining of the small intestine is enormous. A characteristic feature of the small intestine is the mucosal lining, which is principally composed of enterocytes that contain numerous villi that serve as absorptive areas. The villi extend into the lumen and appear as finger-like projections covered with epithelial cells. The villi also contain microvilli, which are also composed of microfilaments that form a brush border. Absorption of nutrients is also enhanced by motility of the small intestine, which places food in proximity to capillaries and lymphatic lacteals that serve as absorptive channels, and by the direct movement of villi. 

The proximal tubule cells contain numerous finger-like projections on the luminal surface, which markedly increase the luminal surface area of the cells and help promote reabsorption of substances filtered at the glomerulus. Under normal conditions. 

LDL is bound to receptors that cluster in clathrin-coated pits. (3) The pits are endocytosed to form coated vesicles. (4) Clathrin is recycled to the surface, leaving uncoated endosomes. (5) ATP-dependent proton pumps in the endosomal membrane lower the intravesicular pH, resulting in the separation of ligand and receptor. (6) Multivesicular bodies form, as receptors are segregated into finger-like projections. (7) Most receptors are recycled to the cell surface. (8) Multivesicular bodies fuse with primary lysosomes to form secondary lysosomes, which digest LDL to free cholesterol and amino acids. = LDL Y = LDL receptor ... 

The small intestine, which comprises the duodenum, the jejunum and the ileum, is the main absorption site and contains a series of finger-like projections, the vilh, which greatly increase the surface area available for absorption of nutrients. Each villus contains an arteriole and venule, together with a drainage tube of the lymphatic system, a lacteal. The venules ultimately drain into the hepatic portal system, and the lacteals into the thoracic lymphatic duct. The luminal side of each villus is covered with projections, the microvilli, which are often referred to as the brush border. 

In Yucca and Nolina at least, the stomata are sunken within crypts which can open and close with finger-like projections (Fig. 5.28). During water stress, the leaves curl and seal the stomata within the crypts. 

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