Specialized Connective Tissue: Cartilage

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Questions and Answers

What is the primary role of the extracellular matrix (ECM) in connective tissues?

To bear stress and support tissue structure (correct)

To facilitate muscle contraction

To store energy for cellular metabolism

To provide direct cell-cell contact

Which of the following types of cartilage is characterized by being the least flexible and containing the highest amount of collagen?

Elastic cartilage

Hyaline cartilage

Fibrocartilage (correct)

Articular cartilage

How does the extracellular matrix (ECM) contribute to intercellular communication?

By facilitating the transport of signaling molecules (correct)

By storing chemical signals within its structure

By acting as a conduit for electrical signals between cells

By directly linking cells through tight junctions

What is essential for maintaining a healthy extracellular matrix (ECM)?

A balance between synthesis and breakdown of matrix components Signup and view all the answers

Which type of cartilage serves as a precursor for bone development?

Hyaline cartilage Signup and view all the answers

What are the key components found in articular cartilage that contribute to its strength and support?

Collagen type II and aggrecan Signup and view all the answers

Which syndrome is associated with defective deposition of collagen leading to hyperextensible joints?

Ehlers-Danlos syndrome Signup and view all the answers

What type of cell is primarily found in adult cartilage?

Chondrocyte Signup and view all the answers

Which transcription factor is crucial for the differentiation of mesenchymal stem cells into chondrocytes?

Sox-9 Signup and view all the answers

What process replaces the cartilage model with bone during fetal development?

Endochondrial ossification Signup and view all the answers

What initiates the formation of long bones?

Differentiation of mesenchymal stem cells into osteoblasts Signup and view all the answers

Which signaling molecules are crucial for the spatial patterning of chondrocytes in bone formation?

Morphogens Signup and view all the answers

Which family of proteins is involved in inductive signaling during cartilage and bone formation?

Hedgehog family Signup and view all the answers

What role does PTHrP play in chondrocyte proliferation?

It enhances chondrocyte proliferation through a feedback loop Signup and view all the answers

What happens to Cubitus interruptus (Ci) in the absence of hedgehog signaling?

Ci is cleaved and not able to activate gene expression Signup and view all the answers

Which of the following interactions is critical for maintaining chondrocyte proliferation in the presence of IHH?

PTHrP and IHH Signup and view all the answers

What cellular process is precedented by the death of chondrocytes during bone formation?

Bone ossification Signup and view all the answers

Which receptor does PTHrP bind to in its signaling pathway?

G-protein coupled receptor Signup and view all the answers

What effect does Hedgehog signaling have on Smoothened?

It activates Smoothened, preventing Ci cleavage Signup and view all the answers

Study Notes

Specialized Connective Tissue and ECM: Cartilage

Connective tissues have reduced cellular content and increased extracellular matrix (ECM) content, compared to epithelial, muscle, and nervous tissue.
ECM is the main stress-bearing component of connective tissues, and facilitates cell-cell contact indirectly.

Composition of the ECM

ECM is a network of fibrous proteins and hydrated proteoglycans that surround cells in tissues.
It strengthens and supports tissues, guides cell migration and polarity, transports nutrients and waste, and permits intercellular communication.
ECM maintenance requires a balance between synthesis and breakdown of its components; it is not a static framework.

Cartilage Types

Hyaline cartilage: Found in ribs, nose, larynx, trachea, and articular joints.
Fibrocartilage: Found in joint capsules, ligaments. (Least flexible, fewest cells, highest collagen content).
Elastic cartilage: Found in ear, epiglottis, and larynx.

Cartilage Structure and Function

Articular cartilage is a type of hyaline cartilage, specifically found in joints.
It's vital for load-bearing and joint movement. It's critical that the articular cartilage structure maintains its integrity for normal function.
Composed primarily of collagen (type II) and aggrecan, these are vital for strength and support.
Loss of collagen integrity leads to loss of matrix strength.

Collagen Biosynthesis

Collagen synthesis occurs in a series of steps, beginning in the rough endoplasmic reticulum, continuing through various Golgi modifications, and concluding with extracellular fiber formation.
Essential for the formation of the cartilage matrix.

Ehlers-Danlos Syndrome

A genetic condition caused by defective collagen deposition.
Results in hyperextensible joints.

Diseases Associated with Collagen Mutations

Various diseases arise from mutations in collagen genes or collagen-processing enzymes, which significantly impact collagen's structure and function.

Aggrecan (Complex PG)

A crucial part of the cartilage ECM.
Composed of a core protein, link proteins, and various glycosaminoglycans (GAGs), specifically chondroitin sulfate and keratan sulfate, which are bound to the core protein.
Hyaluronic acid forms a large molecule outside of the complex, which contributes substantially to a gel-like consistency of the cartilage.
GAGs' negative charges attract and bind a large amount of water, which leads to the hydrated gel found in cartilage and enables load-bearing.

Chondrocytes

Adult cartilage is largely composed of only this single cell type.
They represent 5-10% of the ECM volume.
They are large and mature, found in groups of 2-8 cells.
They are rich in RER and Golgi, and secrete high amounts of type II collagen and aggrecan.
They are avascular, lymphatic, and non-neuronal.
They differentiate from mesenchymal stem cells (MSCs) during embryonic development, and are vital in creating the extracellular matrix.
Highly specialized cells that have a particular importance in chondrocyte proliferation, ECM synthesis, and cartilage formation.

MSC Differentiation to Chondrocytes

Differentiate into chondrocytes during embryonic development from MSCs.
ECM components for cartilage are secreted by them.
Key transcription factors like Sox-9 are crucial.
Various growth factors, including TGF-β, fibroblast growth factor (FGF), insulin-like growth factor (IGF-1), and parathyroid hormone-related protein (PTHrP), are required for proliferation and ECM synthesis.

Bone Formation (Ossification)

Chondrocytes are crucial for the formation of bone from the cartilage model, specifically with endochondral ossification during fetal development, especially with bones such as the long bones.
The cartilage model is substituted by bone.
Primary ossification centers are established first in long bones.
Secondary ossification centers appear in epiphyses later.
Hyaline cartilage is deteriorated, and a cartilage matrix is created with spongy bone formation at the primary ossification centers.
Later, blood vessels and cells invade the cartilage matrix to drive ossification further.
The cartilage model is replaced by new bone matrix.

Inductive Signaling (Spatial patterning of chondrocytes during bone formation)

Morphogens, such as IHH and PTHrP, influence chondrocyte location and fate.
Signaling molecules pass between cells through the developing ECM, resulting in different chondrocyte proliferation and death rates in various locales.
For example, hedgehog family proteins like IHH and Sonic hedgehog (Shh) play a crucial role, maintaining chondrocyte proliferation in specific locations.

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Description

Explore the specialized connective tissue known as cartilage in this quiz. Learn about the composition and functions of the extracellular matrix, as well as the different types of cartilage including hyaline, fibrocartilage, and elastic cartilage. Test your knowledge on their locations and characteristics.