ANA 203 Histology Connective Tissue and Cartilage Flashcards
What is connective tissue made up of?
Extracellular matrix (ground substance and protein fibers)
Connective tissue cells
Origin of connective tissue
The CT originates from the mesenchyme, an embryonic tissue
formed by elongated undifferentiated cells, the mesenchymal cells
Functions of connective tissues
Connective tissue supports organs and cells
Acts as a medium for exchange of nutrients and wastes
between the blood and tissues
Protects against microorganisms
Repairs damaged tissues
Stores fat
Describe the ECM
It is the major constituent of Connective tissue
It consists of different combinations of protein fibers (collagen, reticular, and elastic) and ground substance.
What is ground substance of the ECM?
Ground substance is a colorless, highly hydrophilic, transparent, gel-like material in which the cells and fibers of connective tissue are embedded.
What is ground substance made up of?
It is a complex mixture of glycosaminoglycans,
proteoglycans, and glycoproteins
Function of ground substance
i. lubricant
ii. Prevent invasion of tissues by foreign agents, and resists
forces of compression
Describe fibers in the ECM
Fibers are long, slender protein polymers present in different proportions in different types of connective tissue.
- predominantly composed of collagen,
constitute tendons, aponeuroses, capsules of organs and membranes that envelop the
central nervous system (meninges)
Which fibers are formed by collagen
Collagen and reticular fibers
Fibers are distributed equally in the ECM TRUE/FALSE
FALSE they are distributed unequally
4 major components of connective tissue
Fibroblast: originate form undifferentiated mesenchymal cells
Macrophage
Mast cell
Plasma cell
What is cartilage?
It is an avascular specialized fibrous connective tissue characterized by an extracellular matrix (consisting of ground substance enriched with glycosaminoglycans and proteoglycans) macromolecules that interact with protein fibers (collagen and elastic fibers).
Functions of cartilage
1. bear mechanical stresses without permanent distortion.
2. support soft tissues.
3. Because it is smooth surfaced and resilient, cartilage is a shock-absorbing and sliding area for joints and facilitates bone movements.
4. Essential for the development and growth of long bones both before and after birth
Function of chrondrocytes
synthesize and secrete the
extracellular matrix and the cells themselves are located in matrix cavities called lacunae
Where are chondrocytes located
Lacunae
Mechanisms of chondrogenesis
Interstitial Growth
Appostional Growth
Describe interstitial growth
Resulting from the mitotic
division of pre-existing chondrocytes.
It occurs only during the EARLY phases of cartilage formation
Where does interstitial growth occur?
in the epiphyseal plates of long bones
within articular cartilage.
In the epiphyseal plates for increasing the length of long
bones and in providing a cartilage model for endochondral bone formation
Describe appositional growth
resulting from the differentiation of perichondrial cells (aka chondroblast) located in the perichondrium
Cartilage then grows in girth (width) only by apposition.
What occurs during chondrogenesis?
During chondrogenesis,
chondroblast produce and deposit type II collagen fibers and ECM (hyaluronic acid and GAGs, mainly chondrotin and keratin sulfate) until chondroblasts are separated and trapped within spaces in the matrix called lacunae.
The cells are then called
chondrocytes
Each cluster of chondrocytes ( known as an isogeneous group) enveloped the territorial matrix is separated by a wide but pale interterritorial matrix
Which is the least important of the two processes of growth
Interstitial
Factor affecting chondogenesis (look for more in the textbook)
Cartilage growth depends mainly on the hypophyseal growth hormone somatotropin.
This hormone does not act directly on cartilage cells but
promotes the synthesis of somatomedin C in the liver.
Somatomedin C acts directly on cartilage cells, promoting their growth
What is the principal macromolecules present in all types of cartilage matrix?
Collagen
hyaluronic acid
proteoglycans
Glycoproteins (small qty)
What is the perichondrium?
The perichondrium is a sheath of dense connective tissue that surrounds cartilage in most places, forming an interface between the cartilage and the tissue supported by the cartilage.
The perichondrium harbors the vascular supply for the avascular cartilage and also contains nerves and lymphatic vessels
Types of cartilage
Hyaline cartilage
Elastic cartilage
Fibrocartilage
Describe hyaline cartilage in a fetus and adults
In fetus :
it serves as a temporary skeleton in the fetus before it is reabsorbed and replaced by bone through a process known as endochondral ossification.
In adults:
hyaline cartilage is located in the articular surfaces of the movable joints,
in the walls of larger respiratory passages (nose, larynx, trachea, bronchi)
in the ventral ends of ribs, where they articulate with the sternum
in the epiphyseal plate, where it is responsible for the longitudinal growth of bone
Features of hyaline cartilage
It is avascular
It is surrounded by perichondrium (except in articular cartilage). The perichondrium has an outer fibrous layer, an inner chondrogenic layer, and blood vessels
It consists of chondrocytes surrounded by territorial and interterritorial matrices containing type II collagen interacting with proteoglycans
It occurs in the temporary skeleton of the embryo, articular cartilage and the cartilage of the respiratory tract (nose, larynx,trachea, and bronchi) and costal cartilages.
What does hyaline cartilage contain?
. Cells
2. Fibers (type II collagen synthesized by
chondrocytes)
3. ECM ( also synthesized by chondrocytes)
However, small amounts of collagen types IX, X, XI and others are frequently present
ECM contains hyaluronic acid, proteoglycans and high water content.
Aggrecan is a large proteoglycan characteristic of cartilage
Location of elastic cartilage
The auricle of the ear,
Walls of the external auditory canals,
Auditory (eustachian) tubes
the epiglottis
the cuneiform cartilage in the larynx
Difference between elastic and hyaline cartilage
Elastic cartilage is essentially identical to hyaline cartilage except that it contains an abundant network of fine elastic fibers in addition to collagen type II fibrils.
Why is fresh elastic cartilage yellowish?
Fresh elastic cartilage has a yellowish color owing to the presence of elastin in the elastic fibers
Features of elastic cartilage
Elastic cartilage has the following features:
It is avascular
It is surrounded by perichondrium
It consists of chondrocytes surrounded by
territorial and interterritorial matrices
containing type II interacting with
proteoglycans and elastic fibers which can be
stained by orcein for light microscopy.
It occurs in the external ear, epiglottis and
auditory tube
Describe fibrocartilage
Fibrocartilage is a tissue intermediate between dense connective tissue
and hyaline cartilage.
Locations of fibrocartilage
Intervertebral disks,
in attachments of certain ligaments to the cartilaginous surface of bones
in the symphysis pubis.
Fibrocartilage is always associated with dense connective tissue and the border areas between these two tissues are not clear-cut, showing a gradual transition.
Fibrocartilage contains chondrocytes, either singly or in isogenous groups, usually arranged in long rows separated by coarse collagen type I fibers.
Because it is rich in collagen type I, the fibrocartilage matrix is acidophilic.
Locations of fibrocartilage
Intervertebral disks,
in attachments of certain ligaments to the cartilaginous surface of bones
in the symphysis pubis.
Fibrocartilage is always associated with dense connective tissue and the border areas between these two tissues are not clear-cut, showing a gradual transition.
Fibrocartilage contains chondrocytes, either singly or in isogenous groups, usually arranged in long rows separated by coarse collagen type I fibers.
Because it is rich in collagen type I, the fibrocartilage matrix is acidophilic.
Components of the intervertebral discs
the fibrous annulus fibrosus and the nucleus
pulposus
Types of connective tissue cells and their examples
Fixed connective tissue cells
fibroblasts
pericytes
adipose cells
mast cells
fixed macrophages
What are transient cells
These are cells which originate in the hematopoietic stem cells in bone marrow and remain only temporarily in connective tissue
Examples of transient cells
Certain macrophages
lymphocytes
plasma cells
neutrophils
Eosinophils
basophils
Discuss fibroblasts
arise from undifferentiated mesenchymal cells and are the predominant cells in connective tissue proper.
Often possess an oval nucleus with two or more nucleoli.
May differentiate into other cells
Fibroblasts synthesize collagen, elastin, glycosaminoglycans, proteoglycans and multiadhesive glycoproteins.
Responsible for the synthesis of extracellular matrix components.
Two stages of activity—active and quiescent
Clinical consideration of fibroblasts
Fibroblasts undergo mitosis only during wound healing
Difference between active and quiescent fibroblasts
Active fibroblast are spindle-shaped (fusiform) and contain well-developed rough endoplasmic reticulum and many golgi complexes with large ovoid nucleus and fine chromatin
Quiescent fibroblasts are elongated cells with thin cytoplasmic extensions and condensed chromatin.
Describe adipose cells
Arise from mesenchymal cells and perhaps from fibroblasts
They do not normally undergo cell division because they are fully differentiated cells.
However, they do increase in number in early neonatal life.
They are surrounded by a basal lamina and are responsible for the synthesis, storage and release of fat
Difference between Unilocular and multilocular adipose cells
a. Unilocular adipose cells (white adipose tissue)
contain a single large fat droplet.
(1) These cells have plasmalemma receptors for insulin, growth hormone, norepinephrine and glucocorticoids to control the uptake and release of free fatty acids and triglycerides.
(2) They are surrounded by a basal lamina and are responsible for the synthesis, storage and release of fat.
b. Multilocular adipose cells (brown adipose tissue) are smaller than unilocular adipose cells and the fat is stored as many small fat droplets, and thus the spherical nucleus is centrally located.
Describe mast cells
arise from myeloid stem cells in bone marrow and
usually reside near small blood vessels.
They possess a central spherical nucleus; their cytoplasm is filled with coarse, deeply stained metachromatic granules
Their surfaces are folded, and in electron micrographs they have a well-developed Golgi complex, scant RER, and many dense lamellated granules. Two populations of mast cells exist.
Mast cells function in the localized release of many bioactive substances with roles in the inflammatory response, innate immunity, and tissue repair
Types of mast cells and their function
Connective tissue mast cells possess secretory granules containing heparin.
The other population, the smaller mucosal mast cells whose secretory granules contain chondroitin sulfate, is located in the mucosa of the alimentary canal and of the respiratory tract.
Discuss macrophages
Macrophages are the principal phagocytosing cells of
connective tissue.
They are responsible for removing large particulate matter and assisting in the immune response.
They also secrete substances that function in wound healing.
MACROPHAGES originate in the bone marrow as monocytes, circulate in the bloodstream, then migrate into the connective tissue, where they mature into functional macrophages.
Different name is possessed by macrophages
Kupffer cells in the liver
osteoclast in the bone
microglia cell in the CNS
Features of macrophages in the connected tissue
They contain abundant lysosomes required for the breakdown of phagocytic materials.
Active macrophages have numerous phagocytic vesicles (or phagosomes) for the transient storage of ingested materials.
The nucleus has an irregular outline.
Describe lymphoid cells
Arise from lymphoid stem cells during hemopoiesis
They are located throughout the body in the subepithelial connective tissue and accumulate in the respiratory system, gastrointestinal tract and elsewhere in areas of chronic inflammation.
a. T lymphocytes (T cells) initiate the cell-mediated immune response.
b. B lymphocytes (B cells), following activation by an antigen, differentiate into plasma cells, which function in the humoral immune response.
c. Natural killer cells (NK cells) lack the surface determinants characteristic of T and B lymphocytes but may display cytotoxic activity against tumor cells
Describe plasma cells
are antibody-manufacturing cells that arise from activated B
lymphocytes and are responsible for humoral immunity.
a. These ovoid cells contain an eccentric nucleus possessing clumps of heterochromatin, which appear to be arranged in a wheel-spoke fashion.
b. Their cytoplasm is deeply basophilic because of an abundance of RER.
c. A prominent area adjacent to the nucleus appears pale and contains the Golgi complex (negative Golgi image).
d. They are most abundant at wound entry sites or in areas of chronic inflammation..
Describe granulocytes
are white blood cells that possess cytoplasmic granules and arise from myeloid stem cells during hemopoiesis.
At sites of inflammation, they leave the bloodstream and enter the loose connective tissue, where they perform their specific functions .
Types of granulocytes and their functions
Neutrophils phagocytose, kill, and digest bacteria at sites of acute inflammation.
b. Eosinophils bind to antigen–antibody complexes on the surface of parasites (e.g.,helminths) and then release cytotoxins that damage the parasites.
They are most prevalent at sites of chronic or allergic inflammation.
c. Basophils are similar to mast cells
Describe loose connective tissue
contains more cells than collagen fibers
generally found in the mucosa and submucosa of various organs and surrounding blood vessels, nerves and muscles, papillary layer of the dermis, hypodermis, linings of the peritoneal, pleural cavities, glands, mucous membranes supporting the epithelial cells.
Well vascularized, flexible, and not very resistant to stress.
• It usually supports epithelial tissue
• It is more abundant than dense connective
tissue
• The most numerous cells are fibroblasts and macrophages, but other types of connective tissue cells are also present.
• Collagen, elastic, and reticular fibers also appear in this tissue.
Which cartilage is devoid of perichondrium
Articular cartilage
Discuss the structural glycoprotein chondronectin
A macromolecule that binds to glycosaminoglycan‘s and collagen type II mediating the Terrance of chondrocytes to the extra cellular matrix
What is a major characteristic of the cartilage matrix surrounding each chondrocytes
The cartilage matrix surrounding each chondrocytes is rich in glycosaminoglycan and poor in collagen
This capsular matrix stains differently
Role if intervertebral discs
Act as a lubricated cushion that prevents adjacent vertebrae from being eroded by abrasive forces during movements of the spinal column
Classification of CT
Embryonic connective tissue
■ Connective tissue proper
■ Specialized connective tissue
