Page 29 - Headlines Histology2024_Neat

• The microtubules of a doublet (subunit A and B) share a common wall of
two to three protofilaments.

• Adjacent doublets are linked to each other via protein bridges called nexins
and are also linked to the central sheath by radial spokes.

• On each doublet, there are short dynein arms projecting from subunit A.
• At its base, the axoneme inserted into a structure called a basal body that is

similar in its structure to that of a centriole,
Functions
• In the respiratory airways, cilia beat in wave-like rhythm propelling mucus

secreted by goblet cells towards the throat where it is swallowed thus
keeping the airways clean.
• In the oviducts, ciliary action plays a part in transporting the ovum from the
ovary towards the uterus.
Microvilli
• They are minute finger-like projections of the luminal plasma membrane
found in many epithelial cells particularly those specialized for absorptive
function (i.e. intestinal epithelium).
• Individual microvilli are too small (0.5-1 ?m in length) to be resolved by
LM. In certain cells such as in the small intestine and proximal renal
tubules, the microvilli are so numerous and regularly arranged that under
the LM the cell surface appears striated and is called striated or brushes
border.
• With EM, the core of each microvillus contains actin filaments that insert
into the terminal web that is specialization of the cytoskeleton lying
immediately beneath the cell surface. At the tip of each microvillus, the
filaments attach to an electron-dense part of the plasma membrane.
• Function: increase the surface area for absorption.
Steriocilia
• They are extremely long, branched microvilli.

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