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I TESSUTI CONNETTIVI PROPRIAMENTE DETTI — Transcript

by Biologia con Giulia · 1,591 words · 282 segments · language en · Watch on YouTube

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0:02All connective tissue consists of two
0:05common structural components: the
0:07extracellular matrix and the connective
0:10cells that synthesize and secrete the
0:12extracellular matrix itself. The key
0:17word when discussing connective tissue,
0:20however, is heterogeneity. We talked
0:23about this in the last lesson when I
0:26tried to show you the characteristic
0:28variety of connective tissue,
0:30emphasizing that both bone and blood
0:33are, in fact, connective tissue. From
0:38here, we begin to explore the variety
0:40of connective tissue types, starting
0:43with connective tissues proper. We
0:56already addressed the extracellular
0:58matrix in the previous lesson. Now we
1:01begin to analyze connective cells,
1:03starting with those characteristic of
1:06connective tissues proper. When
1:13speaking of the cells present in
1:15connective tissues proper, we
1:17distinguish between fixed or resident
1:19cells—which are long-lived,
1:21stationary, stable, and less mobile—
1:24and wandering cells, which are
1:26short-lived cells that migrate. These
1:30are cells that originate in the bone
1:32marrow, migrate into the bloodstream,
1:35and then, following various stimuli,
1:37enter the connective tissue where they
1:39perform their specific functions.
1:44Within the fixed or resident cells, we
1:47distinguish various types: fibroblasts
1:50and fibrocytes, macrophages, adipocytes
1:54, mast cells, and mesenchymal cells.
1:57Let's look at them one by one.
2:01Fibroblasts and fibrocytes: fibroblasts
2:04are the cells that synthesize the
2:06extracellular matrix and provide for
2:09tissue repair and scarring processes in
2:12connective tissues proper, while
2:14fibrocytes are inactive fibroblasts. If
2:19we analyze the word fibroblast, knowing
2:22that the suffix "-blast" comes from the
2:26Greek "blastos," meaning germ, we
2:28translate fibroblast as "fiber germ."
2:33Fibroblasts produce fibers and
2:35therefore have their characteristic
2:38location near bundles of collagen
2:40fibers. Collagen fibers, in fact,
2:43organize themselves in the
2:45extracellular matrix starting from
2:47tropocollagen molecules. Tropocollagen,
2:51as we have already seen, is the
2:53precursor molecule of collagen and is
2:56found in vesicles within fibroblasts.
3:00Macrophages are cells dedicated to
3:03phagocytosis—that is, the ingestion
3:06and digestion of inert foreign bodies,
3:08bacteria, cellular debris, and aged red
3:11blood cells—but they are also
3:13dedicated to non-specific immunity.
3:17Phagocytosis comes from the Greek "
3:20phagein," to eat, and "kytos," cell.
3:24Macrophages engulf foreign bodies,
3:26partially degrade them, and display the
3:29resulting antigenic parts on their own
3:32membrane. T-helper lymphocytes, a type
3:36of white blood cell, recognize these
3:38antigens and trigger the specific
3:40immune response. We will eventually
3:44study these topics in more detail. For
3:46now, remember that macrophages
3:48phagocytize, eat foreign material, and
3:51participate in the non-specific immune
3:54response. Adipocytes, fat cells that
3:59are voluminous cells responsible for
4:01lipogenesis, meaning the synthesis and
4:04storage of triglycerides, and lipolysis
4:07, meaning the enzymatic breakdown of
4:09triglycerides to produce fatty acids
4:12and therefore energy. In both terms,
4:16lipogenesis and lipolysis, the prefix
4:19lipo-derives from the Greek lipos,
4:22which means fat or grease. The
4:25difference between the two terms lies
4:27in the two suffixes. Genesis, from the
4:30Greek genesis which comes from the verb
4:32to be born, but in Italian genesis
4:35means the same thing, and lysis from
4:37the Greek lusis which means dissolution
4:40, separation. Excuse the simplification
4:43, but lipogenesis is the generation of
4:46fat or triglycerides, lipolysis is the
4:50destruction of fat or triglycerides.
4:54Triglycerides, as we said in lesson 18,
4:56are the lipids with the main function
4:59of energy reserve because they are
5:02accumulated in adipose tissue and when
5:04needed provide much more energy per
5:07gram than carbohydrates. Mast cells,
5:12immune system cells involved in
5:14allergic responses, are the cells that
5:17stimulate the inflammatory process in
5:19the presence of foreign substances
5:21called. Allergens, mast cells act by
5:25releasing the contents of their
5:27granules, content consisting of heparin
5:30which we said is a glycosaminoglycan,
5:32but it is also an anticoagulant and
5:34histamine which is a vasodilator.
5:39Finally, mesenchymal cells, that is,
5:41stem cells of the mesenchyme from which
5:43other connective cells derive. Inside
5:48the wandering cells, instead, we find
5:50white blood cells and free macrophages
5:52which are cells that migrate and enter
5:54the connective tissue to perform their
5:57function, namely to deal with the entry
5:59of microbes or foreign bodies. But we
6:03will talk better about these two types
6:04of cells in a future lesson. Now,
6:08having seen the different types of
6:11cells that can reside or visit the
6:13connective tissue proper, let us list
6:15the different types of connective
6:17tissue proper. Within the scope of
6:25connective tissues proper, the first
6:28distinction to make is between loose
6:30connective tissue, permeable and
6:32dedicated to metabolic exchanges and
6:35defense, and dense connective tissue,
6:37robust and dedicated to resisting
6:40mechanical traction stresses. Loose
6:44connective tissue connects primarily
6:47from a functional point of view. The
6:50most represented component in the
6:51extracellular matrix, therefore, is the
6:53hydrated fundamental substance. They
6:56are loose tissues, containing few
6:58barriers to exchanges and few fibers.
7:02Dense connective tissue connects
7:04primarily from a mechanical point of
7:06view. The most represented component in
7:09the extracellular matrix is given by
7:11the fibers. They are dense tissues that
7:14must provide resistance, that must have
7:16many fibers. Let's go down one step in
7:20our classification scale of connective
7:22tissues proper. Within the category of
7:27loose connective tissue, we distinguish
7:29mesenchyme, mucous tissue, loose
7:32fibrillar tissue, and reticular tissue.
7:35Let's look at them. Mesenchyme, as we
7:38have repeated several times, is the
7:40embryonic connective tissue. Mesenchyme
7:44consists of mesenchymal cells, which
7:46are irregularly shaped stem cells in an
7:48abundant matrix rich in amorphous
7:50substance and poor in fibers. Mucous
7:55tissue is the tissue found in the
7:57umbilical cord and dental pulp,
7:59consisting of fibroblasts, macrophages,
8:02and numerous mesenchymal stem cells in
8:05abundant hydrated amorphous substance
8:07and thin bundles of collagen fibers.
8:11Loose fibrous tissue is the most
8:13widespread filling tissue and is
8:16therefore ubiquitous, meaning it is
8:18widely distributed throughout the body.
8:22Loose fibrous tissue consists of
8:23various types of cells in an abundant
8:26gelatinous matrix containing all three
8:28types of fibers, but primarily
8:29amorphous substance. Loose fibrous
8:33tissue is found, for example, in the
8:36hypodermis, which is the subcutaneous
8:38area. Subcutaneous, under the skin,
8:43where the skin is made up of the
8:46epidermis seen in lesson 86 and the
8:48dermis, which we will mention shortly.
8:53The hypodermis is therefore located
8:55under the dermis, that is, under the
8:57skin, where it serves to attach the
9:00skin to the underlying organs.
9:04Reticular tissue contributes, for
9:05example, to the formation of the
9:07basement membrane and constitutes the
9:09reticular component of the blood
9:11capillary walls. Reticular tissue
9:15consists of reticular cells—that is,
9:17certain types of white blood cells,
9:20free macrophages, and fibroblasts—
9:22closely attached to thin, widely
9:25branched reticular fibers found in the
9:27loose ground substance. Let us now stay
9:32on the same step of the ladder, but
9:34move slightly to the side. Within the
9:37category of dense connective tissue,
9:40based on the orientation of the fibers
9:42that are numerous and prevalent
9:45compared to the other components of the
9:47connective tissue, we distinguish
9:50regular dense fibrous tissue, in which
9:52bundles of collagen fibers run
9:54regularly in parallel or crossed
9:56bundles, and irregular dense fibrous
9:59tissue, in which the organization of
10:01collagen fibers is not regular. Let us
10:06go down another step, and within the
10:09scope of regular dense fibrous tissue,
10:12we distinguish regular dense fibrous
10:15tissue with parallel bundles, which
10:17consists of bundles of collagen fibers
10:20that, unsurprisingly given the name,
10:23run parallel, packed, and aligned along
10:26lines of tension. In this type of
10:31tissue, cells and amorphous substance
10:34are sparsely represented. It is found,
10:37for example, in tendons, which are the
10:39connections between muscles and bones;
10:41in ligaments, which are the connections
10:44between bones; and in aponeuroses,
10:46which are the connections between
10:48muscles. Regular dense fibrous tissue
10:53with crossed bundles, on the other hand
10:55, also unsurprisingly, consists of
10:58bundles of collagen fibers that are
11:00arranged crossed at a right angle. In
11:04this type of tissue, the main cells are
11:07fibroblasts and fibrocytes, and the
11:09amorphous substance is very scarce. It
11:12is found, for example, in the cornea.
11:15Within the scope of irregular dense
11:17fibrous tissue. Finally, we distinguish
11:20irregular dense collagenous fibrous
11:23tissue, where the most abundant fibers
11:27are collagen fibers, exactly. Which are
11:31arranged in interlaced bundles,
11:33offering resistance to tension in
11:35various planes of space. In this type
11:38of tissue, cells and amorphous ground
11:40substance are scarce. Irregular dense
11:44collagenous fibrous tissue is found,
11:46for example, in the dermis, which is
11:48the connective tissue that together
11:50with the epidermis forms the skin, but
11:53also in the sheaths of tendons, muscles
11:55, and nerves and in the outer capsules
11:57of numerous organs. And irregular dense
12:03elastic fibrous tissue, in which we
12:05mainly find large bundles of elastic
12:08fibers interspersed with collagen
12:10fibers oriented in multiple directions.
12:14From a cellular point of view, this
12:17tissue contains few fibrocytes. In this
12:21type of tissue, elasticity is important
12:23, and that means exactly what you
12:25imagine. The moment a pulling force is
12:30applied, the moment the elastic is
12:33pulled, the elastic fibers stretch,
12:36only to return to their original
12:38dimensions the moment the force ends,
12:41the moment you stop pulling the elastic
12:44. Irregular dense elastic fibrous
12:48tissue is found, for example, in the
12:51walls of blood vessels, especially in
12:53the walls of large-caliber arteries.
12:57Known as elastic arteries. Well guys,
13:02we’ve had an overview of connective
13:04tissues proper, but above all, I hope
13:07I’ve given you the confidence to
13:09often look for the answer in the very
13:12names of things. That is why I like
13:15etymologies. Stay connected with me and
13:18with biology, and if you've stumbled
13:20upon this for the first time, subscribe
13:23to the channel so you don't miss the
13:25next lessons. Like and comment as usual
13:28if I’ve been helpful to you. Bye, and
13:31happy studying everyone.

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