Connective tissue Flashcards
What are the 2 sublayers of connective tissue in the dermis?
Papillary layer → Loose CT
- More apical
Reticular layer → dense irregular CT
What defines Loose vs Dense CT?
Loose → more cells than fibers
Dense → more fibers than cells
What defines Regular vs Irregular CT?
*Both are subclasses of dense CT bc loose CT doesn’t have enough fibers to qualify them
Regular → regular/organized patterning of the fibers (ex: tendons)
Irregular → fibers are not running in a specific order/direction
Why is CT important for the epitheliums around it?
In the case of the dermis, is supports the epidermis
Carries nerves and blood vessels that provide innervation and blood supply to the epidermis and other epithelia
CT proides support and connecting framework to other tissues of the body
Give 2 examples of supporting CT. What makes them supportive?
Cartilage
Bone
→ produce extracellular matric with firm consistency
- Allows tissue to support mechanical stress without distortion + provide support to adjacent soft tissues
Give an example of CT with special properties.
Hematopoietic-bone marrow
*It is CT because of where it derived from
Where does ALL connective tissue originate from?
From mesenchymal cells in the mesoderm of the embryonic cells
Mesenchymal cells are pluripotent stem cells
- They are in Euchromatin state → expansion, DNA transcription, cell dividing, making protein, very active
What different CT tissue cells can mesenchymal cells differentiate into?
Lipoblasts, Chondroblasts, Osteoblasts → active/euchromatin state → secrete collagen and other elements of ECM
Mast cells, Macrophages, lymphocytes, Plasma cells → immun function
Adipocytes → store fat
What is the role of fibroblasts, what can they differentiate in?
Fibroblasts → some euchromatin, some heterochromatin → still very active cells → make ECM components, collagen, glycoproteins, proteoglycans
can divide into 2 fibroblasts or differentiate into fibrocyte
What are the characteristics of fibrocytes/lipocytes/chondrocytes?
Heterochromatin → dormant state, no transcription
- Can still divide → isogenic groups
- Found/embedded in ECM
What is special about wound healing?
It is the only situation in which fibrocytes can de-differentiate into fibroblasts to become active again
How is connective tissue different from epithelial tissue?
The epithelial tissue has little to no extracellular space
CT has lots of extracellular space → cells scattered within ECM
→ Cells are not directly attached to one another (unlike epithelial cells), they are separated by ECM
Also, CT is derived from mesenchyme unlike epithelial tissue which is derived from ectoderm and endoderm
What is the connective tissue matrix composed of?
Ground substance and fibers
What is ground substance? (In general, bone and blood)
In ordinary CT → ground substance = water, stabilized by GAGs, proteoglycans, glycoproteins
*GAGs hold water as they are negatively charged
In bone → ground substance includes minerals
In blood → plasma (plasma is considered to be part of ECM)
How the ECM produced?
Produced by fibroblasts (or other related cells type → chondroblasts in cartilage, osteoblasts in bones)
What are the 2 main types of fibers in the ECM?
Principal fiber type = Collagen → most abundant protein in the body →confers tensile strength with flexibility
Elastic fibers confer resilience (only non collagen fiber)
What tissue is Collagen Type I found in?
Dermis
Tendon
Bone
Lamina Propria
What tissue is Collagen Type II found in?
Hyaline Cartilage
What tissue is Collagen Type III found in?
Reticular fiber
What tissue is Collagen Type IV found in?
Basement membrane
What tissue is Collagen Type V found in?
Fetal tissues (in embryos)
What phenotype is seen in Fibulin-5-KO mice? Why?
The skin is too stretchy because Fibulin is glycoprotein involved in CT in the skin (dermis)
What are the different GAGs? Why are there different types?
Chondroitin SO4 + core protein → in cartilage
Dermatan SO4 + core protein → mostly in the skin, but also in the heart, etc.
Heparan SO4 + core protein
Keratan SO4 + core protein
What is fibronectin?
It is a glycoprotein (in ground substance)
10% sugars + 90% protein
- Binds plasma membrane to heparan-sulfate
What genes are involved in collagen synthesis?
a1 gene → 2x peptide/preprocollagen
a2 gene → 1x peptide/preprocollagen
What are the steps leading to the export of procollagen out of the cell?
- a1 and a2 genes are transcribed in the nucleus
In the ER: - They are translated → polypeptide chains
- Hydroxylation of the Lysine and Proline residues
- Attachement of glucosyl and galactose to the hydroxylated lysine residues
- preprocollgen assembles from interaction between sugars → procollagen triple helix is shipped to Golgi
In the Golgi: - Packaged outside of the cell to the extracellular space as procollagen triple helix
In the extracellular space, how do procollagen assemble to eventually from a collagen fiber bundle?
- Procollagen peptidase cleaves both ends → Tropocollagen
- Self-aggregation → microfibrils
- Self-aggregation → collagen fibrils
- Collagen fibers
- Bundle of collagen fibers
How long is tropocollagen?
280nm
What explains the periodicity of collagen?
Stepwise overlapping (light)of tropocollagen when it self-aggregates due to interaction between the sugars ~ 10% of tropocollagen length
Leaves a lacunar region (dark space) and an overlapping region (between start and end of tropocollagens)
→ 64nm periodicity (lacunar + overlapping
What are the roles of the different immune cells found in CT?
Lymphocytes → Produce immunoglobulins → humoral response
Mast cells → Produce heparin and histamine (anti-clogging, inflammation)
Plasma cells → Produce Ab
Macrophages → Cellular defense/Phagocytosis
What are chondroplasts?
The space the cells are in (lacuna specific to cartilage)
Chondroplast = lacunae + isogenic group
What are the 3 types of cartilage?
Hyaline cartilage (hyalos-glassy) (trachea)
Elastic cartilage (ears, nose, larynx)
Fibrocartilage (intervertebral discs)
Which fiber are found in the different types of cartilage?
Hyaline Cartilage → collagen type II (produced by chondrocytes)
Elastic cartilage → elastic fibers (+ collagen type II)
Fibrocartilage → collagen type I + II (no perichondrium)
What ground substances are found in cartilage?
Glycoprotein → Chondronectin
Proteoglycans → keratan SO4, Chondroitin SO4
Other ground substance → hyaluronic acid
What are the different layer of perichondrium?
Fibrous layer:
- Fibrocytes (would have been fibroblasts during embryonic dev.)
- Collagen type I
- No growth
Chondrogenic layer:
- Chondroblasts
- Collagen type I
- Appositional growth
What type of tissue is the perichondrium?
Dense irregular connective tissue
What cells are fround in Hyalin cartilage? What type of growth do they do?
Chondrocytes
(differentiated from the chondroblasts of the chondrogenic layer)
- They can’t differentiate, but can divide by mitosis → Interstitial growth
What ECM form the hypodermis?
Collagen type I + few fibrocytes
(Mostly just adipose cells which are not part of the ECM)
Is articular cartilage and fibrocartilage the same?
NO
Both don’t have a perichondrium, but fibrocartilage is stronger (strongest)
Articular cartilage is found at the end of long bones
What thype of growth gives more thickness to cartilage?
Appositional growth
Which hormones are responsible for stimulation of protein synthesis in cartilage growth?
- Growth Hormone
- Thyroid Hormone (T3, T4)
- Testosterone
Which hormones are responsible for retarding protein synthesis in cartilage?
- Corticosteroid
- Estradiol
- Retionoids (Vitamin A)
Which 2 types of tumours can occur in cartilage?
Chondroma
Chondrosarcoma (usually more painful, grow faster, more malignant)
