Connective Tissue II + III

Question 1

List the phases of wound healing

Answer 1

1. Inflammation phase
2. proliferation phase
3. Remodeling phase

Question 2

Describe the inflammation phase of wound healing

Answer 2

1. Blood clotting occurs due to the recruitment of thrombocytes
2. Mast cells release histamine, leading to vasodilation. This causes capillaries to become leaky, allowing for water and cells from the blood to infiltrate the wounded area.
3. damaged tissue as well as macrophages and other cells in the wound area release cytokines, which recruit more white blood cells to the area and induce fibroblast upregulation.

Question 3

Describe the proliferation phase of wound healing

Answer 3

1. fibroblasts are upregulated by cytokines, leading to proliferation and increased formation of ground substance.
2. macrophages in the area start digesting debris from damaged cells
3. Macrophages release factors to start angiogenesis.
4. Epithelial stem cells begin proliferating to regenerate the damaged epithelium.

Question 4

Describe the remodeling phase of wound healing

Answer 4

1. decrease in cellularity as unneeded cells die.
2. Contraction of wounded areas via myofibroblasts
3. Morphogenesis: formation of normal tissue morphology (superficial wound), or formation of scar (deeper or larger wound).

Question 5

List the functions of cartilage

Answer 5

1. to provide a resilient but pliable support structure

2. to direct the formation and growth of bone.

Question 6

Describe the function of a chondrocyte

Answer 6

-Chondrocytes make cartilage matrix and tissue.

• They develop from mesenchymal stem cells.
  Some cells on the periphery of a cartilaginous structure become the perichondrium.

-As chondrocytes differentiate and form matrix, they encapsulate themselves in lacunae.

Question 7

List and describe the different types of cartilage

Answer 7

1. Hyaline cartilage: thin collagen fibrils, and ground substance rich in proteoglycans and hyaluronic acid.
2. Elastic cartilage: thin collagen fibrils, abundant elastic fibers in sheets.
3. Fibrocartilage: large bundles of collagen, very strong to resist compression and sheer forces.

Question 8

Describe osteoprogenitor cells

Answer 8

• stem cells that are capable of generating osteoblasts and osteocytes.
• They are present in both the periosteal and endosteal surfaces.

Question 9

Describe osteoblasts

Answer 9

• contained in the inner layer of the periosteum and endosteum
• secrete an un-mineralized bone ECM called osteoid.
• Also pinch off matrix vesicles full of calcium phosphate destined to become hydroxyapatite
• connected via gap junctions

Question 10

Describe osteocytes

Answer 10

• Do not divide
• Extend tiny processes called canaliculi through the calcified matrix, to form gap junctions w/ other osteocyte canaliculi.

Question 11

Describe osteoclasts

Answer 11

• derived from monocytes

Fxns:
1. degrade cartilage or bone matrix to allow for inward growth of blood vessels during bone formation.

2. resorb synthesized bone to promote remodeling of bone matrix
3. resorb bone to mobilize Ca2+

Question 12

Describe the process of intramembranous ossification

Answer 12

1. mesenchymal cells come together (condensation)
2. They transform into osteoprogenitors
3. Osteogenitors become osteoblasts
4. Osteoblasts secrete osteoid
5. Osteoclasts and blood move in between the forming trabecular bone and mold it, leading to the flat, laminar bone of flat bones of the skull.

Question 13

Describe the process of endochondral ossification

Answer 13

1. Mesenchymal cells become chondrocytes
2. Chondrocytes secrete their matrix and become encased in lacunae.
3. Chondrocytes at the surface of the bone (perichondrium) undergo appositional growth, where as chondrocytes embedded in matrix undergo interstitial growth.
4. Perichondrium is changed into periosteum
5. Invading osteoclasts grow into the degraded regions of the bone, pulling with them blood vessels and osteoblasts, eventually setting up primary (diaphyseal) sites of ossification.
6. Osteoblasts form bone where cartilage once was
7. Two secondary (epiphyseal) ossifcation centers later form, leaving the epiphyseal plate as the sole region of cartilage in bone growth at birth.

Long bones are lengthened via interstitial growth, while their diameter is increased only through appositional growth

Question 14

List the factors important for bone formation, remodeling, and calcium homeostasis

Answer 14

1. short-range signals:
   
   • Bone morphogenic proteins
2. Long-range signals:
   
   • steroid hormones, parathyroid hormone, and calcitonin.
3. mechanical stress
4. neuronal stimulation: parasympathetic nervous system