Medical Physiology - Cellular Locomotion and Ciliary Motility

Medical Physiology - Cellular Locomotion and Ciliary Motility
The primary kind of movement in the body is generated by specialized muscle cells in skeletal, cardiac, and smooth muscle, which comprise nearly 50% of total body mass. Two more forms of movement are observed in other cells: ameboid locomotion and ciliary movement. Amoeboid locomotion refers to the movement of a whole cell in relation to its environment. An illustration of ameboid locomotion is the migration of leukocytes.

Ameboid movement generally commences with the extension of a pseudopodium from one extremity of the cell. This arises from persistent exocytosis, which generates a new cell membrane at the forefront of the pseudopodium, and ongoing endocytosis of the membrane in the central and posterior regions of the cell. Two additional effects are also crucial to the cell's onward progression. The initial impact is the adhesion of the pseudopodium to the adjacent tissues, securing it in a leading position while the rest of the cell body is drawn forward towards the attachment site. This connection is mediated by receptor proteins that line the interiors of the exocytotic vesicles. The second prerequisite for motility is the availability of energy necessary to propel the cell body towards the pseudopodium. All cells contain molecules of the protein actin in their cytoplasm. Upon polymerization, these molecules create a filamentous network that contracts upon contact with another protein, specifically an actin-binding protein like myosin. The complete process, powered by ATP, occurs within the pseudopodium of a motile cell, where a network of actin filaments develops inside the expanding pseudopodium. The primary cause that typically triggers ameboid movement is chemotaxis, which occurs due to the presence of specific chemical agents in the tissue known as chemotactic

Ciliary movement refers to the whip-like motion of cilia on cell surfaces. Ciliary movement is present exclusively in two locations inside the body: the inner surfaces of the pulmonary airways and the inner surfaces of the uterine tubes (fallopian tubes) in the reproductive system. The cilia in the nasal cavity and lower respiratory airways exhibit a whip-like action that propels a mucus layer into the pharynx at approximately 1 cm/min, so ensuring the continuous clearance of passages obstructed by mucus or entrapped particles. The cilia in the uterine tubes facilitate the gradual passage of fluid from the ostium toward the uterine cavity, primarily transporting the ovum from the ovary to the uterus. The mechanism underlying ciliary movement remains incompletely elucidated; nonetheless, two essential elements are identified: (1) the availability of ATP and (2) suitable ionic conditions, encompassing enough amounts of magnesium and calcium.