Cartilage

1. CARTILAGE & BONE CT
MUTALIFE F. MWEEMBA

2. Objectives
 By the end of this lecture, learners to be
able to;

3. CARTILAGE
 is a tough, flexible form of CT
 characterized by an extracellular matrix
(ECM)
 with high concentrations of GAGs and
proteoglycans,
 interact with collagen and elastic fibers.
 firm consistency allows it bear mechanical
stress without permanent distortion

4. Function of cartilage
 It supports soft tissues
 Provides smooth articular surface at bone
ends
 Structural support in special areas (trachea,
pinna,
 Acts as shock absorber because of its
resilience
 guides development and growth of long
bones, both before and after birth

5. Cartilage cont..
 Cells
◦ Chondroblast &
◦ Chondrocytes
embedded in extensive
ECM
◦ Located in matrix
cavities called lacuna
◦ Synthesise and maintain
ECM
 ECM
◦ Collagen
◦ Hyaluronic acid
◦ proteoglycans

6. 3 types of cartilage
 Hyaline -most common
 Elastic – more pliable and distensible
 Fibrocartilage - a substantial amount of
collagen fibers
 cartilage is avascular, lack lymphatic vessels
and nerves
 receives nutrients by diffusion from capillaries in
adjacent CT (perichondrium)
 Perichondrium
◦ Sheath of dense CT surrounds cartilage except for
articular cartilage
◦ Contains blood vessels, nerves , lymphatic vessels

7. Hyaline cartilage
 Characterised by the presence of highly basophilic
homogeneous matrix.
 Chondrocytes are isogenous in clusters
 Fresh is bluish-white and translucent
 has type II collagen chondrotin sulfates, keratan sulfate
 Found in embryo, costal cartilage, respiratory tract, articular
surfaces, epiphyseal plate.

8. Elastic cartilage
 Characterised by presence of abundant network
of elastic fibres (elastin)
 elastic fibres are thinner at the periphery and
thicker & branching in the interior of the cartilage
 collagen type II

9. Elastic Cartilage cont..
Sites;
 Auricle of ear
 cuneiform cartilage in the
larynx
 Auditory (Eustachian) canal
 Epiglottis
 Similar to hyaline but
abundant elastic fibers
 Yellowish in colour
 Has perichondrium
 No degeneration

10. Fibrocartilage
 Characterised by dense bundles of type 1 collagen
fibers
 oriented in the direction of functional stress
 with rows of chondrocytes between the bundles.
 No perichondrium
 found in intervertebral discs, and in the pubic
symphysis

11. Cartilage formation
 All cartilage forms from embryonic mesenchyme
in the process of chondrogenesis.
 The first indication of cell differentiation is the
rounding up of the mesenchymal cells, which retract
their extensions, multiply rapidly, and become more
densely packed together.
 The dividing cells are typically called chondroblasts
 chondrocytes when proliferation has ceased
 both have basophilic cytoplasm rich in RER for
collagen synthesis

12. Cartilage repair
 damaged cartilage undergoes slow and often
incomplete repair,
 primarily by activity of cells in the perichondrium,
which invade the injured area and produce new
cartilage.
 In extensively damaged areas the perichondrium
produces a scar of dense CT instead of forming
new cartilage.
 The poor capacity of cartilage for repair or
regeneration is due in part to the avascularity
and low metabolic rate
 hyaline cartilage is susceptible to calcification
during aging

13. Cartilage growth
 Uses 2 processes
1. Interstitial growth the cartilage tissue
enlarges both by, resulting from the mitotic
division of deeply placed chondrocytes
 Interstitial growth in the articular cartilage and
epiphyseal plates of long bones is important in
increasing the length of long bones

15. Cont…
2. Appositional growth which involves
differentiation of new chondroblasts from
the perichondrium
 Appositional growth of cartilage is more
important during postnatal development

16. BONETISSUE
 is a specialized CT composed of
mineralised (calcified) extracellular
material, the bone matrix , and
 Has 3 major cell types
 It is highly vascular
 Metabolically very active
 It is not static but highly dynamic

17. Components
 the great majority of its cells are
embedded in an extracellular matrix
composed of
 organic materials (about 40% dry
weight in mature bone) and
 inorganic salts rich in calcium and
phosphate.
◦ confer the hardness and much of the rigidity
of bone, and are the main reason that bone is
easily seen on radiographs

18. Functions
 Mechanical support
 Protects vital organs
 Locomotion
 Metabolic reservoir –calcium, phosphates
 Bone marrow for haematopoiesis

19. Composition
 Supporting cells
 Organic component - collagen and GAGs
 Inorganic component - salt deposits
◦ Calcium hydroxyapatite, magnesium, sodium
 Remodeling cells

20. Supporting cells
 Osteoblasts
 Osteocytes
 Osteoclasts

22. Osteoblasts
 deposit collagen type I, proteoglycans and
glycoproteins
 deposition of the inorganic component depends
on the presence of viable osteoblasts
 Located on the surface of bone side by side like
an simple epithelium
 Active cells are cuboidal or columnar with
basophilic cytoplasm
 Reduced activity cells are flattened and less
basophilic

23. Cont…
 Osteoblast that get surrounded by matrix
become osteocytes
 Found in cavities called lacuna
 Have cytoplasmic extensions extending into
small channels called canaliculi
 Newly formed bone not yet calcified is known
as osteoid
 Bone turnover more in children

24. Osteoid and bone matrix
 90% collagen
 Defects in collagen may cause bone fragility
 Bone proteins osteocalcin, osteonectin
have affinity for calcium
 Deposition may be regular pattern or
haphazard
 Excess osteoid is seen in pathological
conditions

25. osteocytes
 Derived from
osteoblasts
 Found in lacuna
 One cell per lacuna
 Cytoplasmic
extensions in canaliculi
 Contacts other cells by
gap junctions
 Function: maintenance
of bone matrix

26. osteoclasts
 Large multinucleated cells
 5 – 50 nuclei
 Found in areas of bone undergoing
resorption,
 osteoclasts lie within enzymatically etched
depressions or cavities in the matrix known
as resorption cavities (Howship lacuna).
 Osteoclast stimulating factor are hormones
from thyroid gland and parathyroid

28. Periosteum & Endosteum
 External and internal surfaces of bone are
covered by tissue layers with bone forming
cells, called periosteum & endosteum
respectively.
 The outer layer is dense CT, with small blood
vessels, collagen bundles, and fibroblasts.
 Bundles of periosteal collagen fibers, called
perforating (Sharpey) fibers, penetrate the
bone matrix, binding the periosteum to bone.

29.  The inner region of periosteum is a more
cellular layer containing bone lining cells,
osteoblasts, and mesenchymal stem cells
called osteoprogenitor cells.
 With the potential to proliferate and
differentiate into osteoblasts

30. Diseases of CT
 Osteogenesis imperfect: Mutation in gene
responsible for collagen synthesis
 Ehlers Danlos syndrome genetic CT disorders
characterised by hypermobility of joints
 Marfan’s syndrome: associated with mutation
of gene responsible for fibrilin synthesis.
 Oedema is the excessive accumulation of water
in the extracellular spaces of connective tissue

31. Marfan Syndrome
 An inherited disorder caused by a defective
gene for the glycoprotein fibrilin resulting in
abnormal development of elastic fibers.
 This causes tissues that contain many elastic
fibers to be malformed or weak
 including the covering of bone, ligament that
suspends the lens of the eye, and the walls of
large arteries
 People with Marfan syndrome are often tall,
have long arms, legs, fingers and toes, blurred
vision, and weakened aortic walls that may
burst.

33. Activity
 Outline the types of CT.
 Differentiate between the types of CT
 Analyse the appearances of the CT
 Describe the functions of CT
 State the components of CT

34. Thank you