histology: cartilage, bone, and tendon

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What are the four main types of basic tissues?

 Epithelium, Connective Tissue, Muscular Tissue, Nervous Tissue.

Which of the following is a specialized connective tissue: Collagenous connective tissue, Adipose tissue, Cartilage, or Reticular connective tissue?

Cartilage. Specialized connective tissues: Cartilage, Bone, and Blood.

What is the term used to describe CCT supporting an epithelium?

Lamina Propria 

What are the three categories of connective tissue proper?

Collagenous connective tissue (CCT)

1. Reticular connective tissue
2. Elastic connective tissue
3. Mucous connective tissue

What are the two types of adipose connective tissue?

1. Unilocular adipose tissue (white fat)
   2. Multilocular adipose tissue (brown fat)

What are the three types of specialized connective tissue?

1. Cartilage 2.Bone 3.Blood

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Match the tissue type to its cells and matrix:

• Loose connective tissue

• Dense connective tissue

• Adipose tissue

• Blood

• Cartilage

• Bone

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• Loose CT: Fibroblasts, adipose, WBCs; loose elastin/collagen

• Dense CT: Fibroblasts; dense elastin/collagen

• Adipose: Adipocytes; lipid

• Blood: RBCs, WBCs, platelets; plasma

• Cartilage: Chondrocytes; collagen

• Bone: Osteoclasts, osteoblasts, osteocytes, osteoprogenitor cells; collagen, mineral

What are the key characteristics of cartilage? 

1. Supportive role in the body

2. Tensile strength and weightbearing abilitie

3. Avascular, aliphatic (no fat), and aneural (no nerves)

4. Receives nutrients through diffusion by nearby capillaries

What are the two functional cells of cartilage and their roles?

• Chondrocytes: Mature cells that synthesize fibers, ground substance, and chondronectin; embedded in their matrix residing in lacunae

• Chondroblasts: Immature cells arising from mesenchymal cells; found in the inner layer of the perichondrium that surrounds cartilage

 What are the three types of cartilage?

1. hyaline
   2. elastic
   3. fibrous (fibrocartilage)

 Describe hyaline cartilage: location, matrix composition, and key features.

• Most common type

• Found in: respiratory system, fetal skeleton, growth plate, articular cartilage

• Extracellular matrix: firm gel containing ground substance, collagen fibrils, and proteoglycans

• Matrix zones: Capsular, Territorial, Interterritorial

• Covered by perichondrium

 Describe elastic cartilage: location, structural components, and functional property.

• Most flexible
• Found in: external ear, eustachian tubes, larynx
• Same structural components as hyaline cartilage plus elastic fibers
• Covered by perichondrium

Describe fibrous cartilage (fibrocartilage): location, structural components, and functional property.

• Strongest and least flexible

• Found in: intervertebral disks, around tendons and ligaments

• Prominent collagen fibers in extracellular matrix

• More flattened and organized cell rows

Label the matrix zones of hyaline cartilage from outside to inside.

1. Capsular Matrix (around lacunae)

2. Territorial Matrix

3. Interterritorial Matrix

• Perichondrium surrounds the entire cartilage

What are the five functions of bone?

1. Solid support

2. System of levers for movement

3. Protection

4. Encloses medullary spaces containing bone marrow — site of developing blood cells

5. Calcium and phosphate reservoir (tight regulation for homeostasis)

What are the anatomical regions of a long bone?

• Epiphysis: Ends of bone (articular cartilage, epiphyseal cartilage)

• Metaphysis: Region between epiphysis and diaphysis (contains physis/growth plate)

• Diaphysis: Shaft of bone (cortical bone, endosteum, medullary cavity/bone marrow, periosteum)

 Compare compact bone and cancellous bone.

• Compact (cortical) bone: Found along the collar of long bones; organized into osteons

• Cancellous (spongy/trabecular) bone: Makes up interior portion; has trabeculae (spicules); bone marrow fills medullary spaces

What are the three functional cells of bone and their origins?

• Osteoblasts: Mesenchymal cell origin

• Osteocytes: Osteoblasts entrapped in their own matrix

• Osteoclasts: Derived from fusion of macrophages (multinucleated)

Describe osteoblasts: location, function, and morphology (active vs inactive).

• Location: On the surface of bone

• Function: Synthesize organic portion of bone (lay down new bone)

• Active: Cuboidal with nucleus at one end (flag cell); perinuclear Golgi zone may be seen

• Inactive: Spindle shaped

Describe osteocytes: location and function.

• Osteoblasts that get entrapped in their own matrix

• Maintain the bone territorial matrix

• Found embedded within the mineralized matrix

Describe osteoclasts: location, origin, morphology, and function.

• Location: On the surface of bone

• Origin: Fusion of macrophages

• Morphology: Multinucleated, large with many nuclei uniform in size

• Function: Bone resorption, remodeling, raises blood calcium levels

What is an osteon (Haversian system)? Describe its structure.

• Structural unit of compact bone
• Concentric lamellae around a vascular canal (osteonal/Haversian canal)
• Makes bone very strong
• Vascularized by blood vessels arising from periosteum
• Contains lacunae containing osteocytes
• Interstitial lamellae between osteons
• Circumferential lamellae

What is the periosteum? What does it contain?

• Dense connective tissue covering bone

• Contains osteogenic progenitor cells

• Has inner and outer layers

• Vascularized by blood vessels

 What are Volkmann's canals?

 Horizontal canals in bone that connect Haversian canals (vertical) to each other and to the periosteum

Describe the process of bone remodeling.

• Continuous remodeling throughout life for mechanical needs, repair, and maintaining plasma calcium homeostasis

• Bone resorption: Osteoclasts digest old bone

• Bone formation: Osteoblasts lay down new bone

• Cycle: Quiescence → Resorption → Renewal → Formation → Mineralization → Quiescence

What is the sequence of bone remodeling?

Quiescence → Resorption → Renewal → Formation → Mineralization → Quiescence

compare intramembranous and endochondral ossification in terms of bones formed and mechanism.

• Intramembranous: Flat bones; mesenchymal cells differentiate into osteoblasts and produce bone directly (absence of pre-existing cartilage model)

• Endochondral: Long bones, short bones, irregular bones; mineralized cartilage acts as struts on which bone is deposited

What are the four steps of intramembranous ossification?

1. Ossification center appears in fibrous connective tissue membrane

2.Bone matrix (osteoid) is secreted within the fibrous membrane

3.Woven bone and periosteum form

4.Bone collar of compact bone forms and red marrow appears

 Where does endochondral ossification occur?

• Metaphyseal growth plates (physes)

• Articular-epiphyseal-cartilage complex (AECC)

 What are the four zones of the metaphysis in endochondral ossification (from resting to calcifying)?

1. Resting zone (R)

2. Proliferation zone (P)

3. Hypertrophic zone (H)

4. Calcifying zone (C)

 What is the function of the metaphysis in endochondral ossification?

 Responsible for lengthening bone

In endochondral ossification, what happens to chondrocytes in the hypertrophic zone?

Chondrocytes become hypertrophic (enlarged) and the cartilage matrix begins to calcify

What is the AECC?

Articular-Epiphyseal-Cartilage Complex — the region where endochondral ossification occurs in the epiphysis

 What is a tendon? What is its function?

• Band of dense fibrous connective tissue

• Connects muscle to bone

• Transmits forces

 What are the specialized fibroblasts in tendons called?

Tendon cells (tenocytes)

What do tenocytes produce?

Collagen

What is the organizational hierarchy of a tendon from smallest to largest?

1. Collagen

2. Fibril

3. Fiber

4. Fascicle

5. Tendon

What is the endotenon and what does it surround?

 Endotenon surrounds fascicles

What is the epitenon and what does it surround?

 Epitenon surrounds tendons

 Label the tendon organization from smallest to largest: Collagen → ? → ? → ? → ?

Collagen → Fibril → Fiber → Fascicle → Tendon

 What is the role of tenocytes in tendon structure?

Tenocytes produce collagen, which forms the fibrils, fibers, fascicles, and ultimately the tendon

What are the connective tissue coverings of tendons and what do they surround?

• Endotenon: Surrounds fascicles

• Epitenon: Surrounds tendons