36 Questions
Which of the following is NOT a type of apical surface modification?
Lysosomes
What is the main function of microvilli?
To increase the surface area for absorption
What is the approximate length of microvilli?
1 μ
What is the composition of microvilli?
A bundle of parallel actin filaments
Where are microvilli typically found?
In epithelial cells specialized for absorption
What is the appearance of microvilli under a light microscope?
A border of vertical striations
What happens to the linkages holding neighboring doublet microtubules together when axonemes are exposed to trypsin?
They are broken
What is the function of dynein arms in axonemes?
To create cross-bridges between microtubules
What is required for ciliary movement?
ATP and Ca ions
What is the structure at the base of each cilium?
Basal body
What is the composition of the wall of the basal body?
Nine sets of triplet microtubules
What happens to the sliding of doublet microtubules in an intact axoneme?
It is converted to bending
What is the function of the basal body?
To form the lower portion of a ciliary axoneme
What is the shape of the basal body?
Cylindrical
What forms the core of a microvillus?
Actin filaments cross-linked by the actin-bundling proteins
What are the lateral arms attached to the plasma membrane composed of?
Myosin I and calmodulin
What is the characteristic of glycocalyx around the microvilli?
Thicker around the microvilli
What is the length of cilia?
5-10μ long
What is the function of cilia in the respiratory tract?
To clear the mucus toward the mouth
What is the structure seen at the base of each cilium?
Basal body
What is the function of cilia in uterine tubes?
To transport the ovum toward the uterus
What is the function of cilia in ductus efferentes?
To propel the spermatozoa toward the epididymis
What is the role of basal bodies in cilia?
To organize the axoneme microtubules
What is the composition of a triplet microtubule in the basal body?
One complete microtubule and two incomplete microtubules
What is the function of the rootlet in the basal body?
To anchor the basal body to the apical cytoplasm
What is the significance of ciliary movement during development?
It determines the left-right asymmetry of organs
What is the characteristic of cilia in patients with Kartagener's Syndrome?
They lack dynein arms
What is the relationship between basal bodies and centrioles?
Basal bodies are more complex than centrioles
What is the primary reason for male infertility in Kartagener's syndrome?
Immotile sperm due to the absence of dynein
What is the function of radial linkers in cilia and flagella?
Converting the sliding of microtubules into bending of cilia
What is the significance of Afzelius's experiment in 1978?
It demonstrated the role of dynein in cilia and flagella motility
What is the consequence of the absence of dynein in the axoneme of cilia and flagella?
Immotility of cilia and flagella
What is the characteristic feature of situs inversus totalis?
A complete transposition of the thoracic and abdominal organs
What is the effect of the absence of dynein on the respiratory tract in Kartagener's syndrome?
Impaired mucus transport in the tracheobranchial system
What is the mechanism of dynein movement along the axoneme?
Dynein walks along the adjacent doublet
What is the consequence of the absence of dynein in the sperm flagellum?
Immotile sperm
Study Notes
Epithelial Cells and Polar Differentiation
- Epithelial cells exhibit polar differentiation, with apical, lateral, and basal surfaces.
- They have modifications on their surfaces, including microvilli, cilia, and flagella.
Apical Surface Modifications
- Apical surface modifications are specialized structures on the free surface of epithelial cells.
- These modifications are used for cell movement, absorption, and other functions.
Microvilli
- Microvilli are finger-like projections from the cell surface.
- Function: increase the surface area for absorption.
- Localizations: intestinal epithelium, proximal tubule of the kidney, and epithelium of the gall bladder.
- Structure: finger-like protrusions, 1 μm in length, 0.1 μm in diameter, enclosed in an extension of the plasma membrane.
- Contains a bundle of straight parallel filaments (20-30 actin filaments).
- Actin filaments extend 0.5 μm down into the apical cytoplasm and enter into the terminal web.
Cilia and Flagella
- Cilia are eyelash or hair-like processes from the cell surface.
- Motile processes, longer than microvilli (5-10 μm long, 0.2 μm in diameter).
- Under the electron microscope, they have a complex internal structure (composed of microtubules).
- Function: to move the fluid over the surface of the cell.
- Localizations: respiratory tract, uterine tubes, and efferent ducts.
- Each cilium has a dense granule (basal body) at its base.
Ciliary Movement
- Cilia beat in a rhythmical wave-like manner, moving the fluid over the surface of the cell.
- Functions: to move mucus over epithelial surfaces in the respiratory tract, to transport the ovum toward the uterus, and to propel the spermatozoa toward the epididymis.
Dynein
- Dynein is essential for motility of cilia and flagella.
- A congenital form of human infertility, Kartagener's syndrome, is characterized by the absence of dynein arms.
- Dynein arms form temporary cross-bridges between microtubule A of one doublet and microtubule B of the adjacent doublet.
- During sliding, they undergo a cyclic break and reattachment.
Basal Body
- At the base of each cilium, there is a dense granule (basal body).
- Basal bodies are cylindrical structures of 0.2 μm wide and 0.4 μm long.
- They are composed of nine sets of triplet microtubules, forming the wall of the basal body.
- Basal bodies resemble centrioles but contain some accessory structures such as basal foot and rootlet.
Cilia and Development
- Ciliary movement is important during development.
- Nodal cilia can not move during development, and internal organs cannot be located at their normal positions.
- Helical beating of cilia at the node, and the origins of left-right asymmetry.
Test your knowledge of microvilli, a type of apical surface modification found in cells. Learn about their function, composition, and more.
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