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Flashcards in Cartilage and Bone Deck (35)
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1

What are the 3 types of cartilage?

1. Hyaline (most wide spread, weakest)
2. Fibrocartilage (Strongest)
3. Elastic (springiest)

2

Cartilage Facts

Avascular
No Nerves
Shock absorbing
Prevents friction in joints
More Flexible
Composed of 80% water

3

3 Components of Cartilage

1. Cells
2. Ground Substance
3. Fibers

4

Cells of Cartilage

1. Chondroblasts: immature cells
2. Chondrocytes: Mature cells located in cavities called lacunae.

5

Ground Substance of Cartilage

Gel-like ECM rich in PROTEOGLYCANS

6

Fibers of Cartilage

Collagen I (most abundant)
Collagen II
Collagen III
All forms of collagen give strength to tissues so they can withstand pressure

7

Proteoglycans

Where: GROUND SUBSTANCE of Cartilage
Backbone: Protein
Coming off the Backbone: GAGs
Hyaluronic Acid with Chondroitin Sulfates (negatively charged一>electrostatic repulsion一> compressive resistance)

8

Hyaline Cartilage Locations

Costal cartilage
Articular surfaces (joints)
Respiratory cartilage (larynx and trachea)

9

Hyaline Cartilage Overview

Weakest of the 3 cartilages
ONLY type II collagen
Support, flexibility, resilience
Has a perichondrium
*Only cartilage that has the ability to calcify into bone* (endochondral ossification)

10

Endochondral Ossification

Occurs as chondroblasts are gradually replaces with osteoblasts

11

Perichondrium

DICT (Dense Irregular CT) perimeter of cartilage- 2 Layers
1. Outer Fibrous Layer: girdle to resist expansion when compressed
2. Inner Chondrogenic Layer (less fibrous): Collagen I, vascular, chondrogenic cells
*NOT FOUND ON FIBROCARTILAGE*

12

Fibrocartilage Locations

Menisci of knees
Intervertebral discs
Pubic symphysis

13

Fibrocartilage Overview

Strongest - more fibers, fewer cells
Collagen I & II
LACKS PERICHONDRIUM (slower to repair)
Highly Compressible

14

Elastic Cartilage Locations

Ear
Auditory Tube
Epiglottis
Nose?

15

Elastic Cartilage Overview

Springiest
Has a perichondrium
Collagen II & Elastin
Strong but flexible

16

Bone Function

Structural (support, shape, protect)
Assist Movement
Mineral Homeostasis (Ca storage, 99%!)
Blood Cell Production

17

Bone vs. Cartilage

BOTH: Living cells (osteocytes vs chondrocytes)
Fibrous CT covering (periosteum vs perichondrium)
BONE: Vascular - CARTILAGE: Nonvascular
BONE: More collagen than cartilage, mineralized

18

Compact Bone

Outer layer of bones
Composed of Osteons (tree rings) with Haversian canal (VAN) in the middle
80% of bone in the body

19

Cancellous (Spongy) Bone

Inner layer of bones
Composed of thread-like trabeculae
20% of bone in the body

20

Bone Matrix

Type I Collagen
Weight for weight it is strong as steel!

21

Bone Remodeling

Bones are constantly being turned over/remodeled
1. old bone is ABSORBED via osteoClasts
2. new bone FORMATION via osteoBlasts

22

Osteoblasts

Blasts Build!
Modified fibroblasts that lay down new type I collagen to form new bone matrix at/near where osteoClasts absorb

23

Osteoclasts

Clasts Clobber!
Attach to bone via interns at areas called sealing zones
H+ ATPases acidify sealing zone
pH dissolves hydroxyapatite & collagen
Endocytose the digested bone (Ca2+) and release it into interstitial fluid
*If Ca is low in the body, clasts break bone to access the Ca storage for plasma*

24

Regulation Hormones for Remodeling

PTH: parathyroid hormone INCREASES reabsorption
1, 25 (OH)2 Vitamin D (activated Vitamin D): INCREASES reabsorption
Calcitonin (PTH counterpart): INHIBITS reabsorption

25

PTH

Secreted by Chief cells of parathyroid glands
Mobilizes Ca from bone
Increases urinary phosphate excretion
DIRECTLY triggers reabsorption by stimulating generation of new osteoclasts (osteoclastogenesis)
INDIRECTLY triggers osteoclasts via osteoblast RANKL signaling

26

Bone Calcium Reservoirs

Mostly from BONE
1. Rapid exchangeable (small amount)
2. Stable exchange (vast majority of bone Ca)
Some from GI TRACT (diet)

27

Activated Vitamin D

90 %Formed from vitamin D precursors in skin via sun
一> hydroxylations in liver and kidney一>
Small amts in food (fish, meats, via D fortified foods)
Increases Ca reabsorption from intestine
Increases Ca in bone

28

Activating Vitamin D

sunlight activates Vitamin D3 in the skin一>
Hydroxylation occur in liver 一>
Hydroxylation in kidney一>
Activated Vitamin D AKA 1,25 -dihydroxy blah blah AKA CALCITRIOL

29

PTH and Calcitonin

PTH increases blood levels of Ca when plasma calcium levels get too low
Calcitonin inhibits reabsorption of Ca from bone (turns off bone breaking) when plasma calcium levels get too high
*They do opposite things to maintain homeostasis*

30

PTH Effects

1. Increases bone Ca reabsorption to INCREASE plasma levels of Ca
2. Increases reabsorption of Ca in the kidney and phosphate excretion in urine
3. Increases plasma 1,25 dihydroxycholecalciferol (inactivated vitamin D) levels in the kidney 一> increases gut Ca absorption

31

Calcitonin

Decreases Ca levels in the blood 4 ways (opposes PTH)
1. inhibits Ca absorption by intestines
2. inhibits osteoclast activity
3. stimulates osteoblast activity
4. inhibits renal tubular cell reabsorption of Ca so it is excreted in urine
Secreted by parafollicular cells of thyroid

32

Other hormones of Ca metabolism

1. Glucocorticoids: Lower plasma Ca by inhibiting osteoclast formation and activity
2. Growth hormone: increases Ca excretion in urine and intestinal absorption for a net result of increase in calcium levels
3. Estrogens: prevent osteoporosis (inhibit stimulatory effects of cytokines on osteoclasts)
4. Insulin: increases bone formation

33

Rickets/Osteomalacia

Defective bone matrix calcification due to vitamin D and/or Ca deficiency.
Rickets= children
Osteomalacia= adults

34

Osteopetrosis

Impaired/dormant osteoclasts so osteoblasts operate unopposed and create fragile distorted bone.
Treatment: Large doses of vitamin D

35

Osteoperosis

Excess osteoclast causes "pores" in the bone matrix. Happens as we age but can slow the process with Ca supplements
Can be caused by Biphosphonate treatment (for ONJ)一> Inhibit osteoclasts