Histology 01/20

Histology lecture 3:


Apical = on the surface
Basel = on the bottom

Microvilli, stereocilia, cilia
Microvilli are very short, brush border, they increase the surface area like in the small intestines. Each villus is made of actin filaments (microfilaments)  and actin binding proteins.
Stereocilia are longer than microvilli, are in the epididymis and are immotile
Cilia: are highly motile, made of microtubules (larger). Are found in the respiratory tract.
E.M. of axoneme (shaft) of cilia: 2 central microtubules surrounded by 9 pairs of microtubules.
Function of cilia is movement of fluid.
Flagella: found in the tail of the sperm.


Junctions:
1: tight junctions (zonula occludens): apical in position, zonula indicates that junctions form bands completely encircling each cell. No intercellular space.
2: adherent junction (zonula adherens): is immediately below the zonula occludens.
3: desmosomes (macula adherens): this junction resembles a single spot and does not form a belt around the cell. It is the most powerful junction.
4: hemidesmosome: it is the junction binding the cells to the underlying basement membrane. It is half of the desmosomes.
5: gap junction: this type mediates cellular communication rather than adhesion, unlike previous types. Proteins called connexions are found in gap junctions.
Quiz only includes the junctions.



Lecture 4: connective tissues:

They are made of cells, fibers, and a matrix.
Components of connective tissues:
Fibers:
Three types:
Collagen is the most common. It is sensitive and is affected and dissolved by by boiling, string acids and alkalines. Digested by collagenase enzyme. Appears acidophilic (red) with H&E and
Elastin: it is resistant, digested by elastase enzyme, yellow by van geison's chain
Reticular fiber: not stained with H&E, stained black by silver stain.

Cells:
Two groups:
Fixed cells: undifferentiated mesenchymal cells UMC, can give origin to all other types of connective tissue cells.
Fibroblasts: most common connective tissue cells. They are responsible for wound healing.
Macrophages: contain kidney shaped eccentric nuclei. Have a cytoplasm that is rich in lysosomes. They are responsible for phagocytosis
Fat cells (adipocytes): can contain one fat vacuole (uni locular with a flat nucleus). Can contain multiple fat globules (multi locular) with a rounded nucleus.
Free cells:
Plasma cells: cartwheel shaped.
Mast cells: central rounded nucleus. They secrete histamine and heparin.
Other blood leukocytes (WBCs) at times of need.

Connective tissue matrix: intercellular substance between cells and fibers. Contain solid and liquid parts.

Connective tissue types:
Connective tissue proper (soft), cartilage (rubbery), and bone (hard).
C.T. proper:
Areolar loose c.t. (most common type). Contains all types of cells and fibers.
White fibrous c.t. (mainly fibrous) collagen fibers. Separated by fibrocytes. Forms tendons if muscles and ligaments of joints.
Yellow elastic c.t. found in bronchial tree
Reticular c.t. (mainly fibrous).  Found in the stroma of all organs
Mucoid c.t. (mainly matrix). Found in the rye, umbilical cord.
Adipose c.t. is divided into white adipose (containing uni locular) (found subcutanoeus in adults) and brown (containing multi locular) (found in adults and newborn.
Only study components for quiz.