1. Descriptive Histology CLS 222
Ch 3: Connective tissue
Descriptive Histology
CLS 222
Saida Almashharawi

2. Objectives Definition of connective tissue
Function of connective tissue
Structure of connective tissue
Characteristics of connective tissue
Cells of connective tissue
Extra cellular matrix

3. Introduction DEFINITION
It is one of the four general classes of animal tissues- as well as epithelial, muscle and nervous tissues.
Is a kind of animal tissue that connects, supports, binds, or separates other tissues or organs of the body.
It is the most diverse tissue and is found throughout the body
Unlike epithelial tissue, connective tissue has relatively little intimate contact between the cells that make up part of its structure

4. Function Storage of energy Protection of organs
Provision of structural framework for the body
Connection of body tissues
Connection of epithelial tissues to muscle fiber.
Transportation of fluids and dissolved substances
Defend the body against microorganisms
Repair of body tissue

5. Structure of connective tissue
Structurally, connective tissue  is made up of cells and extracellular matrix.
The extracellular matrix is made up of protein fibers in and polysaccharide matrix, secreted and organized by cells in the extracellular matrix.
Variations in the composition of the extracellular matrix, determines the properties of the connective tissue.
For example, if the matrix is calcified, it can form bone or teeth.

6. Characteristics of connective tissue
Cells are spread through an extracellular fluid.
Ground substance - A clear, colorless, and viscous fluid containing glycosaminoglycans and proteoglycans to:
fix the body water and the collagen fibers in the intercellular spaces,
fills the space between the cells and contains the fibers.
Ground substance slows the spread of pathogens.
Fibers. Not all types of CT are fibrous. Examples of non-fibrous CT include adipose tissue and blood.

7. Cells of connective tissue
A variety of cells with different origins and functions are present in connective tissue
Fibroblasts
Mast cells
Macrophages
plasma cells
Adiposities cells

8. Cell types Extracellular matrix Ground substance Macrophage Fibers
• Collagen fiber
• Elastic fiber
• Reticular fiber
Fibroblast
Lymphocyte
Capillary
Fat cell
Mast cell
Neutrophil

9. Cells of connective tissue
Origin of cells :
Fibroblasts :
Originate from undifferentiated mesenchymal cells
spend all their life in connective tissue
mast cells, macrophages, and plasma cells :
Originate from hematopoietic stem cells in bone marrow
These are all types of Immune cell.
circulate in the blood, and then move into connective tissue where they remain and execute their functions.

10. Cells of connective tissue
Fibroblasts
They are mainly responsible for secreting the non-rigid extracellular matrix including the fibers collagen, elastin or fibronectin.
Two stages of activity:
active fibroblasts
inactive fibroblasts.
Cells with synthetic activity are morphologically distinct from inactive fibroblasts that are scattered within the matrix they have already synthesized.

11. Cells of connective tissue
Active fibroblast
Large, euchromatic, oval nucleus
Cytoplasm not usually visible but contains abundant rough endoplasmic reticulum and Golgi apparatus
Elongated, spindle-shaped cells
High synthetic activity

12. Active fibroblast

13. Cells of connective tissue
Inactive fibroblast
Small, heterochromatic, flattened nucleus.
Reduced cytoplasm and organelles.
Low synthetic activity.

14. Cells of connective tissue
2.Macrophages
Derived from blood monocytes
Enter connective tissue from the bloodstream and rapidly transform into macrophages
Are large cells with more cytoplasm than lymphocytes or plasma cells.
They have no granules and function to ingest other cells and bacteria by phagocytosis, antigen processing, and cytokine secretion.

15. Cells of connective tissue
3.Mast cells
Releasing immune modulators from cytoplasmic granules, in response to antigen binding with cell surface antibodies.
Mast cells secrete histamine, heparin and other factors.
They are important in the uptake of fatty acids from the blood into fat cells.

16. Cells of connective tissue
4.Plasma cells
Secrete antibodies to provide humeral immunity
Derived from B-lymphocytes take up residence in lymph nodes, bone marrow, and loose connective tissue where they synthesize and secrete specific antibodies.

17. Cells of connective tissue
5. Adipose cells
Adipocytes are connective tissue cells that have become specialized for storage of neutral fats or for the production of heat.

18. Extracellular matrix Fibers: Collagen fibers Reticular fibers
Elastic fibers

19. Collagen fiber
Collagen is the most common protein found in the human body.
It is found in almost all organs and body parts.
In general, collagen winds itself into a fiber mesh that adds structural stability to that specific body part.
It is commonly associated with skin integrity, but is critical for proper function of many other body parts too.
At least 12 types of collagen exist, four of which are commonly found in different body parts.
Type I collagen is the most abundant type

20. Reticular fiber
 Composed of type III collagen secreted by reticular cells.
Reticular fibers crosslink to form a fine meshwork (reticulin).
This network acts as a supporting mesh in soft tissues such as liver, bone marrow, and the tissues and organs of the lymphatic system.

21. Elastic fiber
 Are bundles of proteins (elastin) found in extracellular matrix of connective tissue 
produced by fibroblasts and smooth muscle cells in arteries.
These fibers can stretch up to 1.5 times their length, and snap back to their original length when relaxed.
Elastic fibers include elastin, elaunin and oxytalan.

22. Extracellular matrix Ground substances
It is a jelly like substance having proteins and sugars,
-in bone the ground substance include minerals, and
- in blood the ground substance is the plasma

23. Homework #2 1- Define the connective tissue?
2-What are the functions of the connective tissue?
3- What are the types of cells present in connective tissue ?
4- What are the types of fibers present in the C.T.?