Ameboid Movement and Chemotaxis

 

📌 previous Notes: 

https://mednotesbyrazaullah.blogspot.com/2026/08/functions-of-endoplasmic-reticulum-and.html

Cell Locomotion

Cell locomotion represents one of the most remarkable physical capabilities of specialized animal cells, allowing them to crawl through tissues to execute essential physiological tasks. Unlike the passive movement seen in blood flow, true cellular crawling termed ameboid movement relies on a dynamic internal framework that constantly reshapes the cell. Initiated when the leading edge of the cell extends a thin, fan-like projection called a pseudopodium, this process is driven by the rapid polymerization of actin filaments beneath the cell membrane. As the pseudopodium reaches forward, it anchors itself to surrounding tissue structures through specialized receptor proteins, establishing a firm mechanical footing from which the rest of the cell can pull itself ahead.

Once the leading edge is anchored, the trailing body of the cell must contract to pull the cytoplasm forward and complete the step. This contractile force is generated inside the cell through the interaction of actin filaments with myosin motor proteins, operating via an energy-dependent mechanism similar to muscle contraction. Cellular energy in the form of ATP fuels this continuous cycle of membrane extension, focal attachment, and trailing end contraction. Ameboid locomotion is vital for human physiology, enabling white blood cells like neutrophils and tissue macrophages to migrate toward infection sites through chemotaxis, while allowing fibroblasts to move into damaged tissues to rebuild structural extracellular matrix during wound healing.

• Muscle cells provide primary body movement.
• Muscle mass constitutes 50 percent body mass.
• Ameboid locomotion occurs in specialized non-muscle cells.
• Ciliary movement occurs in specialized cell types.

Mechanism of Ameboid Movement:

• Ameboid movement moves entire cells relative to surroundings.
• White blood cells exhibit typical ameboid locomotion.
• Locomotion begins with pseudopodium protrusion.
• Pseudopodium projects outward from the cell body.
• Pseudopodium secures itself in new tissue areas.
• The remaining cell body pulls toward fixed pseudopodium.
• New cell membranes continually form at pseudopodium edges.
• The membrane continually absorbs in the middle and rear.
• Exocytotic vesicle receptors evert at leading pseudopodium.
• Receptors protrude outside attaching to surrounding tissue.
• Rear receptors detach forming new endocytotic vesicles.
• Endocytotic vesicles stream forward toward leading pseudopodium.
• Recycled vesicles form new pseudopodial membranes.
• Actin molecules polymerize forming internal filamentous networks.
• Actin networks contract binding myosin protein molecules.
• ATP supplies energy pulling the cell body forward.
• Actin networks contract within ectoplasm beneath membranes.

Types of Cells Exhibiting Ameboid Locomotion:

• White blood cells exhibit ameboid locomotion.
• White blood cells move into tissue forming macrophages.
• Fibroblasts exhibit ameboid movement repairing damaged tissues.
• Skin germinal cells move toward cut areas.
• Ameboid locomotion drives embryonic and fetal development.
• Embryonic cells migrate long distances during development.

Control of Ameboid Locomotion by Chemotaxis:

• Chemotaxis initiates and controls ameboid locomotion.
• Chemotaxis results from chemical substances in tissues.
• Chemotactic substances cause directional cell movement.
• Positive chemotaxis moves cells toward higher concentrations.
• Negative chemotaxis moves cells away from chemical sources.
• Chemotactic substances trigger pseudopodial protrusion on exposed sides.

Location in Human Body:

• Exists in respiratory airways and fallopian tubes.
• Respiratory cilia move mucus 1 cm/min toward pharynx.
• Fallopian cilia move fluid to transport the ovum.

Structure of a Cilium:

• Projects 2 to 4 micrometers from the cell surface.
• Up to 200 cilia exist per respiratory cell.
• Covered completely by the cell membrane.
• Supported by 11 microtubules (9 outer pairs, 2 central).
• Grows directly from an underlying basal body.

Flagellum Comparison:

• Sperm flagella have a similar internal structure.
• Flagella are longer than cilia.
• Flagella moves in waves rather than whiplike strokes.

Ciliary Movement Mechanics:

• Beats 10 to 20 times per second.
• Fast forward stroke bends sharply to push fluid.
• Slow backward stroke returns cilium with minimal force.
• Synchronized movement propels fluid in one direction.

Mechanism & Energy Needs:

• The tubule array and linkages form the axoneme.
• Axonemes can beat even without the cell membrane.
• Requires ATP energy to maintain beating.
• Requires calcium and magnesium ions to function.
• Dynein arms use ATP to crawl along tubules.
• Differential tubule sliding causes the bending motion.
• Central single tubules likely transmit activation signals.

Note: 

Chapter 02 is completed. Next up is Chapter 03.

Regarding:

Razaullah Khattak 

DPT Medical Professional