Il TESSUTO CARTILAGINEO - un tessuto connettivo di sostegno — Transcript

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1. 0:01We have talked about connective tissue
2. 0:03and how it is always made up of cells
3. 0:05and extracellular matrix. We then
4. 0:11listed and analyzed the connective
5. 0:12tissues proper and explored the levels
6. 0:14slightly below the first major
7. 0:16distinction, that between dense and
8. 0:17loose connective tissues proper. As I
9. 0:24have repeated and will repeat, however,
10. 0:26the term connective tissue is
11. 0:27characterized above all by
12. 0:29heterogeneity, and we are exploring it.
13. 0:33In this lesson, we will begin to
14. 0:35address supporting connective tissues,
15. 0:37starting with cartilaginous tissue. If
16. 0:53you remember the lesson on connective
17. 0:55tissue in general, number 88, there we
18. 0:57classified connective tissues based on
19. 0:59the different functions they perform:
20. 1:01connective tissues proper, which we
21. 1:03have discussed; connective tissues with
22. 1:05trophic function, which we will talk
23. 1:07about soon; and supporting connective
24. 1:09tissues, let's talk about them now.
25. 1:15Supporting connective tissues are
26. 1:17tissues that support. Would you have
27. 1:20ever guessed? Yes. But what does it
28. 1:22mean to support? It means that
29. 1:27cartilaginous tissue and bone tissue,
30. 1:29the two supporting connective tissues,
31. 1:30are the specialized connective tissues
32. 1:32that form the body's scaffolding. Now,
33. 1:38surely, if you think of the body's
34. 1:40scaffolding, you think of the skeletal
35. 1:42system, the bones, and therefore bone
36. 1:44tissue. However, do not think only of
37. 1:48adult human beings. Cartilaginous
38. 1:51tissue constitutes the scaffolding of
39. 1:53the embryo and the developing fetus.
40. 1:59The cartilaginous skeleton in human
41. 2:00beings is obviously temporary and is
42. 2:02replaced during the second half of
43. 2:04pregnancy by the much more resistant
44. 2:05bone tissue. But let's go in order.
45. 2:14Cartilaginous tissue consists of a
46. 2:16small percentage of cellular component
47. 2:18in an abundant extracellular matrix,
48. 2:20endowed with a certain elasticity and
49. 2:22notable resistance to mechanical stress
50. 2:24. The cells that are part of
51. 2:35cartilaginous tissue are the usual
52. 2:37mesenchymal cells that become
53. 2:39chondroprogenitor cells, chondroblasts
54. 2:41that derive from chondroprogenitor
55. 2:42cells, chondrocytes that derive from
56. 2:44chondroblasts, and finally
57. 2:46chondroclasts, which instead derive
58. 2:47from the progenitors of the
59. 2:49monocyte-macrophage line. Chondroblasts
60. 2:56, from the Greek chondros, meaning
61. 2:58cartilage, and blastos, meaning germ,
62. 3:00are the cells responsible for producing
63. 3:02collagen fibers and other constituents
64. 3:04of the cartilaginous extracellular
65. 3:06matrix. By producing, the chondroblasts
66. 3:13remain isolated within the matrix they
67. 3:15themselves produced in spaces called
68. 3:16lacunae, a bit like when you wash the
69. 3:18floor and get stuck in a corner waiting
70. 3:20for it to dry. The chondroblasts
71. 3:27trapped within the matrix undergo some
72. 3:29mitotic divisions, and therefore, in
73. 3:31mature cartilage, isolated
74. 3:33chondroblasts are rare. The groups of
75. 3:39chondroblasts generated in this way are
76. 3:41called isogenous groups because they
77. 3:42derive from the division of a single
78. 3:44cell and therefore have the same genes.
79. 3:50Chondrocytes are cells that belong to
80. 3:52the same cell type as chondroblasts,
81. 3:54but at a different functional moment,
82. 3:56the functional moment when the
83. 3:57biosynthetic activity of the
84. 3:59chondroblasts decreases. Chondroclasts,
85. 4:05whose suffix "clast" comes from the
86. 4:07Greek "klastes," meaning to break.
87. 4:10Finally, they are cells with phagocytic
88. 4:12functions. They are phagocytic cells,
89. 4:18particularly numerous during the
90. 4:20ossification of cartilaginous tissue,
91. 4:22especially when the transition from
92. 4:24cartilage to bone occurs. The
93. 4:33extracellular matrix of cartilage
94. 4:35consists of a small percentage of
95. 4:37fibrillar components, represented by
96. 4:38collagen and elastic fibers, in an
97. 4:40abundant amount of amorphous substance,
98. 4:42represented by glycoproteins like
99. 4:44chondronectin and proteoglycans like
100. 4:46aggrecan. The water content in the
101. 4:52extracellular matrix of cartilaginous
102. 4:54tissues is very high. Cartilaginous
103. 5:02tissue has the characteristic of
104. 5:04resisting traction forces and, unlike
105. 5:06other connective tissues, it lacks
106. 5:08nerves, blood vessels, and lymphatic
107. 5:10vessels. The cells of the cartilaginous
108. 5:17tissue therefore receive nutrients via
109. 5:19diffusion through the extracellular
110. 5:21matrix from blood vessels in the
111. 5:22surrounding connective tissues. In most
112. 5:31cases, cartilage is covered by the
113. 5:33perichondrium, a sheath of dense
114. 5:34fibrillar connective tissue. The
115. 5:42perichondrium consists of an outer
116. 5:44fibrous layer and an inner chondrogenic
117. 5:46layer, rich in undifferentiated
118. 5:48chondroprogenitor cells which, as seen,
119. 5:50mature into chondroblasts.
120. 5:57Chondroblasts produce extracellular
121. 5:59matrix, and thus the growth of
122. 6:00cartilaginous tissue occurs by the
123. 6:02apposition of matrix from the outside,
124. 6:04made possible by the perichondrium.
125. 6:10Furthermore, the perichondrium is also
126. 6:12necessary for any repair processes of
127. 6:14cartilage in adults. Besides the
128. 6:18process of growth by external
129. 6:20apposition, cartilage can also grow by
130. 6:22interstitial growth, i.e., from the
131. 6:24inside. The chondroblasts of an
132. 6:29isogenous group, by continuing to
133. 6:31produce extracellular matrix, tend to
134. 6:33move away from each other to form
135. 6:34separate lacunae, which contributes to
136. 6:36the increase in volume and growth of
137. 6:38the cartilage from within. Let's now
138. 6:43understand where cartilage is found in
139. 6:45the human body. adult. But first, we
140. 6:49distinguish three types of cartilage:
141. 6:51hyaline cartilage, elastic cartilage,
142. 6:53and fibrocartilage. Hyaline cartilage
143. 7:01has a solid consistency and is
144. 7:03relatively elastic. It features
145. 7:06numerous isogenous groups housed in
146. 7:08lacunae within an extracellular matrix
147. 7:10composed primarily of compact amorphous
148. 7:12substance. The distribution of collagen
149. 7:16fibers in hyaline cartilage is not
150. 7:18homogeneous. Collagen fibers are
151. 7:22relatively scarce in territorial areas,
152. 7:24i.e., near the cells, and increase
153. 7:26progressively further away from the
154. 7:28cells in the interterritorial matrix.
155. 7:33Hyaline cartilage is the most common
156. 7:35form of cartilage in the human body and
157. 7:37makes up almost the entire
158. 7:39cartilaginous skeleton of the embryo
159. 7:41and fetus. In the adult body, it is
160. 7:46found in the respiratory system, nasal
161. 7:48septum, larynx, trachea, and bronchi;
162. 7:51in the area where the ribs attach to
163. 7:53the sternum, where it is called costal
164. 7:55cartilage; and on the joint surfaces of
165. 7:57bones, such as in the elbow, where it
166. 7:59is called articular cartilage. A
167. 8:05characteristic feature of articular
168. 8:07cartilage is that it lacks a
169. 8:08perichondrium. The absence of
170. 8:12perichondrium in articular cartilages
171. 8:14explains why they are the first to
172. 8:16undergo the degenerative process known
173. 8:18as osteoarthritis. Lacking a
174. 8:22perichondrium, this cartilage cannot
175. 8:24repair itself. Finally, in long bones,
176. 8:31we find the hyaline epiphyseal
177. 8:33cartilage, a form of transient growth
178. 8:35cartilage that contributes to bone
179. 8:37elongation during an individual's
180. 8:39growth. Elastic cartilage is
181. 8:48characterized by numerous elastic
182. 8:50fibers and few collagen fibers.
183. 8:54Compared to the previously seen hyaline
184. 8:56cartilage, in elastic cartilage,
185. 8:58isogenous groups are less numerous and
186. 9:00contain fewer cells, and the ground
187. 9:02substance is less abundant. In the
188. 9:08adult body, elastic cartilage is found
189. 9:10in the external ear, the pinna, the
190. 9:12external auditory canal, and the deeper
191. 9:14auditory tube or Eustachian tube. In
192. 9:19the larynx. The vibrations of the
193. 9:24elastic cartilages of the larynx are
194. 9:26what enable phonation, the very things
195. 9:28allowing me to speak, and in the
196. 9:30epiglottis, an elastic membrane located
197. 9:32behind the tongue that covers the
198. 9:34superior opening of the larynx. You may
199. 9:40have heard of it because it is the
200. 9:42membrane that closes off the larynx
201. 9:43during the swallowing of a food bolus.
202. 9:48Which translated means that the
203. 9:49epiglottis is the gate that keeps food
204. 9:51from taking the wrong path, entering
205. 9:53the larynx instead of the esophagus,
206. 9:55where it should go. The gate that
207. 9:59prevents food from going down the wrong
208. 10:00pipe. All that remains is fibrous
209. 10:07cartilage, a type of cartilage where
210. 10:09the perichondrium is absent. It is very
211. 10:12similar to dense connective tissue, and
212. 10:14we could therefore define it as a
213. 10:16transition form between dense
214. 10:17connective tissue and cartilage. It is
215. 10:21rich in collagen fibers grouped in
216. 10:23parallel bundles and is poor in cells,
217. 10:25represented mostly by isolated
218. 10:27chondrocytes. In the adult body, it is
219. 10:32found in the articular menisci, the
220. 10:34cushions that contribute to joint
221. 10:35stability. The knee meniscus is
222. 10:39infamously known among soccer players
223. 10:40for injuries. In the intervertebral
224. 10:45discs, the shock absorbers present
225. 10:47between one vertebra and another in the
226. 10:49spinal column, in the area where
227. 10:51tendons insert into bones, and in the
228. 10:52pubic symphysis. The cartilaginous
229. 10:58joint that connects the body of the
230. 10:59right pubic bone with the body of the
231. 11:01left pubic bone. Well guys, I would say
232. 11:05that is everything for cartilaginous
233. 11:07tissue as well. In the next lesson, we
234. 11:10will deal with the other supporting
235. 11:12connective tissue: bone tissue. Help me
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240. 11:23soon and happy studying, everyone.