Question

2) Answer the following :

A) Compare and contrast microvilli, cilia and stereocilia—make a chart of structures (know the details), functions, clinical correlations. Where on a cell and within the body would you find these structures?

B) What are the three major types of cell junctions? Where on the cell would you find them? What happens if they are defective?

C) What receptors and cytoskeletal elements are associated with each cell junction?

D) What is the difference between epithelium and glands? How do exocrine and endocrine glands differ?

Answer 1

A)

Microvilli are folds of the cell membrane that are extended outwards from cell surface and results in increased surface area, thus allowing for more materials to be absorbed at a quicker rate. They are observed in specialized organs for absorption, such as the digestive tract or kidneys.Microvilli are stable and they won't move. Microvilli contains actin filaments.

Cilia are tiny hair like structures on the surface of certain cells and moves in a rhythmic, sweeping motion to move particles or cells. Cilia lining respiratory tract removes germs, mucus, dust particles away from the respiratory tract. Cilia contains microtubules.

Stereocilia are cytoplasmic extensions found on the cochlea in the inner ear, ductus deferens, and epididymis. They are non motile and functions as mechanosensing apparatus and helps in equilibrium, balance, and mechanical sensing.

B) there are three types of cell junctions which are found on each cell membrane and in cell-cell and cell-extra cellular matrix junctions. These cell junctions causes selective permeability of membrane and holds the cells together. Defects in cell junctions results in loss of integrity, shape, morphology and also results in loss of functions of particular tissues as in fibrosis, intestinal bowel disease, cardiovascular abnormalities and in cancers.

1. Occluding junctions - prevents leaking of small molecules from one side to the other

2. Anchoring junctions - mechanically attach cells to their neighboring cells or to the extracellular matrix

3. Communicating junctions- mediates chemical or electrical signals between cells

C)

1. Occluding junctions - tight junctions attaches to the actins of adjacent cells through occlidins, claudins and junctional adhesion molecules

2. Anchoring junctions - microfilaments anchor the cell and extracellular matrix through Cadherins and integrins

3. Communicating junctions-six connexin proteins are arranged as a cylinder with a pore in the centre known as connexon and these connexon complexes stretches across the cell membrane and interact with adjacent connexons

D) Epithelium lines the surface of organs and helps in absorption, secretion, protection while glands are considered as selective epithelium which are secretary in function.

Exocrine glands contains ducts and their secretions are delivered through these ducts. E.g. sweat glands, lacrymal glands

Endocrine glands are ductless glands and secrets directly into blood stream. E.g. pituitary gland, thyroid, pancreas.