Supportive Connective Tissues
Learning Objectives:
o Describe the microscopic structure and molecular compositions of the three types of cartilage, and correlate them with their locations and functions
o Explain the process of chondrogenesis and distinguish interstitial and appositional cartilage growth
o Describe the general histological organization and function of bone tissue
o Compare the histological composition, locations, and functions of periosteum vs. endosteum
o Compare spongy and trabecular bone
o Explain the role of biomechanical forces and hormones in the processes of bone remodeling and blood calcium homeostasis
o Compare and contrast the processes of intramembranous and endochondral ossification
o Describe the histology of the five zones of an epiphyseal plate
SLU Slide 35: Trachea; Slide 79: Bronchus; Slide 80: Trachea
Iowa Virtual Slidebox: Hyaline cartilage (112)
Sketch a section of hyaline cartilage as seen in one of the above slides, or take a screenshot and annotate it. Your sketch should include or make note of the matrix, lacuna, chondrocytes in isogenous groups, and perichondrium.
Compare and contrast the two mechanisms by which cartilaginous tissue can grow.
Interstitial growth occurs as the mitotic growth of pre-existing chondrocytes, during the early stages of cartilage formation, and within an existing mass of cartilage.
Appositional growth occurs as the differentiation of perichondral cells. Chondroblasts from the perichondrium proliferate, then surround themselves with matrix. Occurs at the surface.
SLU Slide 65: Epiglottis, (elastic stain)
Iowa Virtual Slidebox: Elastic cartilage (113, 116, and/or 215)
Compare this section of cartilage with one of the sections of hyaline cartilage that you examined before. The epiglottis is a cartilaginous “flap” that closes the trachea during swallowing to prevent food from entering it. Reflect on how the matrix of this tissue section promotes and fulfills the dual roles of mobility and stability.
Elastic fibers are able to expand and shrink back to their original length without permanent distension. The other components of the matrix, such as hyaluronic acid, proteoglycans, and collagen fibers, provide a firm gel that maintains the shape of the epiglottis.
Iowa Virtual Slidebox: Fibrocartilage (114)
Compare this section of fibrocartilage with the two types that you’ve examined above (note that this slide has been prepared with a stain other than H&E, so you cannot directly compare basophilia/eosinophilia). What is different about the matrix of fibrocartilage compared to the other types of cartilage?
Fibrocartilage has a high density of densely-packed, mostly parallel-oriented collagen fibers in its matrix. In this way, it combines the properties of both dense regular onnective tissue and hyaline cartilage.
Electron micrograph of a chondrocyte
Observe the abundance, or lack thereof, of mitochondria in this EM. What does that tell you about cartilage? What implications can that have for injury to this tissue?
It tells us that chondrocytes are not very energetically active (have a slow metabolism). The effect of this is that cartilage is slow to heal. Cartilage is also avascular, which also contributes to its delayed healing.
SLU Slide 95: Compact bone
Iowa Virtual Slidebox: Decalcified rib: bone marrow (102 and/or 273)
Sketch a section of compact bone, as demonstrated in one of these histological preparations. Pay attention to the locations of different bone cells, including osteoblasts, osteocytes, osteoclasts, and bone lining cells.
Where are osteoblasts typically found?
Single layer of cells on the surface of growing bone
Where are osteocytes typically found?
Osteocytes are found in the cortex of the bone, enclosed by bone matrix.
Where are osteoclasts typically found? What features distinguish them from other bone cells?
Osteoclasts are typically found on the surface of bone in a small depression called a resorption bay. You can distinguish them based on their size and that they are multinucleate.
SLU Slide 2: Bone ground section
Iowa virtual slidebox: Ground bone (101).
What are the differences between a ground bone preparation and a section of decalcified bone? What are you able to visualize in a ground section that you cannot in a decalcified section, and vice versa?
A ground bone section will show the inorganic/mineral components of bone, while a decalcified section will show the organic components of bone, including cells and matrix. Ground sections are therefore better at allowing you to visualize osteons and lamellae, whereas decalcified bone will allow you to visualize individual cells, such as osteocytes, osteoblast, and osteoclasts.
SLU Slide 75: Finger Joint
Explore this slide to see if you can find regions of cortical bone, vs. regions of trabecular bone. Where, in general, do you find each?
Cortical bone is found on the outside of a bone, while trabecular is found on the inside, especially at metaphyses and epiphyses.
What occupies the spaces in between trabeculae?
Bone marrow.
SLU Slide 85: Developing membranous bone
Draw and label a developing membranous bone. What kind of cells are involved in membranous bone development?
Mesenchymal cells, which transition directly into an osteoprogenitor cell, and then an osteoblast.
What is osteoid?
Non-mineralized bone matrix. (I.e, it has not been mineralized yet)
SLU Slide 4: Fetal digit
Iowa Virtual Slidebox: Endochondral ossification (398).
Draw and label a growing long bone (a particular bone, or just a generic long bone, as you wish). Your sketch should include the epiphyseal plate, compact and spongy bone, periosteum, osteoid, and at least one blood vessel.
Examine and list the zones of within a growth plate, paying close attention to what the cells in each layer are doing.
Zone of reserve cartilage/Resting zone - No proliferation of cells or matrix production
Zone of proliferation - Cells divide and organize into distinct columns
Zone of hypertrophy - Cells enlarge, accumulate glycogen (clear), Secrete Vascular endothelial growth factor (VEGF), which initiates vascular invasion
Zone of calcified cartilage - Hypertrophied cells begin to degenerate; Cartilage matrix becomes calcified, serving as a scaffold –
Zone of resorption (ossification) - Small blood vessels invade cavities left by chondrocytes, bringing osteoblasts & clasts; Remodeling of calcified cartilage scaffold