Ch 5: Connective Tissue

Question 1

Connective Tissue serves what purpose?

Answer 1

: provides supportive and connective framework for all tissues in body

Question 2

CLASSIFICATION OF CONNECTION TISSUE:

what are the 4 types?

Answer 2

1. Connective Tissue Proper
– Loose connective tissue
*Areolar
* Adipose
* Reticular
– Dense connective tissue
* Regular
* Irregular
* Elastic

• *2. Cartilage**
• • Hyaline cartilage
• • Elastic cartilage
• • Fibrocartilage
• *3. Bone Tissue**
• • Compact bone
• • Spongy bone

4. Blood

Question 3

Which are considered specialized connective tissue?

Answer 3

Adipose

Blood

Bone

cartilage

hemoportic

lymphatic

Question 4

Define Mucous tissue / the umbilical cord

Answer 4

most of the connective tissue between the vessels consists of collagen fibers.

• Between the collagen fibers are small cells staining red, they are fibrocytes and fibroblasts.
• white space is ground substance.

Question 5

Loose Connective Tissue

characterized by a loose irregular arrangement of connective tissue fibers and
abundant ground substance. Collagen fibers, fibroblasts(most numerous), mast cells and macrophages
predominate in loose connective tissue.
- thickest lighter staining strands are
collagen fibers.
- thinner darker staining fibers is elastic
fibers.
- fibroblasts lie along the length of collagen
fibers.
Stain: H&

Answer 5

Question 6

Dense Connective tissue / Tendon

• Dense regular connective tissue is present in ligaments and tendons.
• consists of long collagen fibers (typically type I)
• between the densely packed collagen fibers are flatten nuclei of
• *fibroblasts.**

Answer 6

Question 7

Adipose Tissue:

Adipose cells are closely packed and separated by thin strips of connective tissue septa in which are found compressed fibroblasts, arterioles, venules, nerves and capillaries

(non is visible in slide).

• the adipose cell nuclei are located peripherally. (not visible in slide).
• adipocytes are derived from lipoblasts that are derived from mesenchymal cells.
• lipid droplets are present inside the adipose cell.

Answer 7

Question 8

Unlike the other tissue types (epithelium, muscle, and nerve), which consist mainly of cells, what makes up most of Connective tissue?

Answer 8

composed of fibroblasts and other cells that make up the
extracellular matrix (ECM) of various protein fibers,
all of which are surrounded by watery ground substance

Question 9

Where does Connective Tissue come from?

Answer 9

Mesenchyme, which are undifferentiated cells with large nuclei, with prominent nucleoli and fine chromatin and are spindle shaped.

Question 10

What do Fibroblast do in Connective Tissue? other cells found in here, such as macrophages , plasma cells , and mast cells.

Answer 10

originate locally from mesenchymal cells and are permanent residents of connective tissue; and are the most common cells in connective tissue, produce and maintain most of the tissue’s extracellular components. Fibroblasts synthesize and secrete collagen (the most abundant protein of the body) and elastin, which form large fibers, as well as the GAGs, proteoglycans, and multi adhesive glycoproteins that comprise the ground substance.

Question 11

What else does Fibroblast do for connective tissues?

Answer 11

They are targets of many families of proteins called growth factors that influence cell growth and differentiation.

-involved in wound healing, sometimes called myofibroblasts, have a well-developed contractile function and are enriched with a form of actin also found in smooth muscle cells.

Question 12

Adipocytes

Answer 12

These large,
mesenchymally derived cells are specialized for cytoplasmic
storage of lipid as neutral fats, or less commonly for the production
of heat. The large deposits of fat in the cells of adipose
connective tissue also serve to cushion and insulate
the skin and other organs.

Question 13

Macrophages & the Mononuclear
Phagocyte System

Answer 13

phagocytic ability and specialize in turnover of protein fibers
and removal of dead cells, tissue debris, or other particulate
material.

A typical macrophage measures between
10 and 30 μm in diameter and has an eccentrically located,
oval or kidney-shaped nucleus.

Macrophages are also secretory cells producing an
array of substances, including various enzymes for
ECM breakdown and various growth factors or cytokines
that help regulate immune cells and reparative
functions.

Question 14

What else does Macrophages able to do in the system?

Answer 14

Macrophages derive from bone marrow precursor cells
that divide, producing monocytes that circulate in the blood.
These cells cross the epithelial wall of venules to penetrate connective
tissue, where they differentiate further, mature, and
acquire the morphologic features of phagocytic cells. Therefore,
monocytes and macrophages are the same cell at different
stages of maturation.

Question 15

Mast cells are

Answer 15

oval or irregularly shaped connective tissue cells,
between 7 and 20 μm in diameter, whose cytoplasm is filled with
basophilic secretory granules.

Because of their high content of
acidic radicals in their sulfated GAGs, mast cell granules display
metachromasia, which means that they can change the color of
some basic dyes

Question 16

Mast cells release numerous bioactive substances with the roles in the inflammatory response. Below are 6 of them.

Answer 16

Heparin, a sulfated GAG that acts locally as an anticoagulant
■■ Histamine, which promotes increased vascular permeability
and smooth muscle contraction
■■ Serine proteases, which activate various mediators of
inflammation
■■ Eosinophil and neutrophil chemotactic factors,
which attract those leukocytes
■■ Cytokines, polypeptides directing activities of leukocytes
and other cells of the immune system
■■ Phospholipid precursors for conversion to prostaglandins,
leukotrienes, and other important lipid mediators
of the inflammatory response.

Question 17

mast cells are especially numerous near small blood vessels in the skin and
mesenteries (perivascular mast cells) and in the tissue that lines
digestive and respiratory tracts.

Answer 17

mast cells place themselves strategically
to function as sentinels detecting invasion by microorganisms.
Mast cells originate from progenitor cells in the bone
marrow. The progenitor cells circulate in the blood, cross
the wall of venules and capillaries, and penetrate connective
tissues, where they differentiate.

Question 18

Release of certain chemical mediators stored in mast cells
also promotes the allergic reactions, also known as

Answer 18

immediate
hypersensitivity reactionsbecause they occur within a
few minutes after the appearance of an antigen in an individual
previously sensitized to the same or a very similar antigen.

Question 19

Plasma cells are:

Answer 19

are B-lymphocyte–derived, antibody-producing
cells.

These large, ovoid cells have basophilic cytoplasm due
to their richness in RER

They have a clock like face.

They are also specific antibodies.

Question 20

White blood cells: Leukocytes

Answer 20

Leukocytes, or white blood cells, make up
a population of wandering cells in connective tissue. They
leave blood by migrating between the endothelial cells lining
venules to enter connective tissue by a process called diapedesis.

Question 21

The fibrous components of connective tissue are elongated
structures formed from proteins that polymerize after secretion
from fibroblasts: Name them:

Answer 21

collagen, reticular, and elastic fibers.

Question 22

Describe the realtion of the 3 main types of fibers.

Answer 22

Collagen and
reticular fibers are both formed by proteins of the collagen family,
and elastic fibers are composed mainly of the protein elastin.

These fibers are distributed unequally among the different types
of connective tissue, with the predominant fiber type usually
responsible for conferring specific tissue properties.

Question 23

Collagen is a key element in all connective tissue as well as epithelial basement membranes and the external laminae of muscle and nerve cells.

It is also the most abundant protein.

Answer 23

They constitute a family of proteins selected during
evolution for their ability to form a variety of extracellular
structures. The various fibers, sheets, and networks made
of collagens are all extremely strong and resistant to normal
shearing and tearing forces.

Question 24

Fibrillar collagens:

Answer 24

Collagen type I, the most abundant and
widely distributed collagen, forms large, eosinophilic
bundles usually called collagen fibers. These often
densely fill the connective tissue, forming structures such
as tendons, organ capsules, and dermis.

Question 25

Sheet-forming collagens such as type IV collagen

Answer 25

have subunits produced by epithelial cells and are the major structural proteins of external laminae and the basal lamina in all epithelia.

Question 26

Linking/anchoring collagens

Answer 26

are short collagens that link fibrillar collagens to one another (forming larger fibers) and to other components of the ECM. Type VII collagen binds type IV collagen and anchors the basal lamina to the underlying reticular lamina in basement membranes.

Question 27

Collagen synthesis occurs in many cell types but is a specialty of cells that produce the various kinds of connective tissue. Where is the intial part of them made?

Answer 27

The initial procollagen α chains are made in the cells’ abundant RER.

Question 28

Keloids:

Answer 28

is a local swelling caused by abnormally large amounts of collagen that form in scars of the skin. Keloids occur most often in individuals of African descent and can be a troublesome clinical problem to manage. Not only can they be disfiguring, but excision is almost always followed by recurrence.

Question 29

Key steps in Collagen formation: 1. Hydroxylase 2. Procollagen peptidase 3. Lysyl Oxidase 4. Collagenases

Answer 29

**Hydroxylase** enzymes in the ER cisternae add hydroxyl groups to some prolines and lysines in important reactions that require O2, Fe2+, and ascorbic acid (vitamin C) as cofactors. Outside the cell, specific proteases called **procollagen peptidases** remove the terminal globular peptides, converting the procollagen molecules to collagen molecules. Fibrillar structure is reinforced and disassembly is prevented by the formation of covalent cross-links between the collagen molecules, a process catalyzed by the enzyme **lysyl oxidase.** Degradation is initiated by specific enzymes called **collagenases,** which are members of an enzyme class called matrix metalloproteinases (MMPs). Collagenases clip collagen fibrils or sheets in such a way that they are then susceptible to further degradation by nonspecific proteases.

Question 30

Reticular Fibers

Answer 30

Found in delicate connective tissue of many organs, they consist mainly of _collagen type III_. This collagen forms an extensive network (reticulum) of extremely thin heavily _glycosylated fibers_. Reticular fibers are seldom visible in hematoxylin and eosin. They are termed **argyrophilic**.

Question 31

Elastic Fibers

Answer 31

thinner than the type I collagen fibers and form sparse networks interspersed with collagen bundles in many organs, particularly those subject to much bending or stretching.

Question 32

In the wall of large blood vessels, especially arteries, elastin also occurs as fenestrated sheets called

Answer 32

elastic lamellae

Question 33

Elastic fibers (and lamellae) are a composite of

Answer 33

**fibrillin** microfibrils embedded in a larger mass of cross-linked elastin. Both components are secreted from **fibroblasts** (and smooth muscle cells in vascular walls) and produce elastic fibers in a stepwise manner.

Question 34

Elastin molecules are rich in....

Answer 34

glycine, proline, and lysine, giving much of the protein a random-coil conformation.

Question 35

What makes up the so called "**Ground Substance"** of the ECM.

Answer 35

highly hydrated (with much bound water), transparent, complex mixture of macromolecules, principally of three classes: glycosaminoglycans (GAGs), proteoglycans, and multiadhesive glycoproteins. It fills the space between cells and fibers in connective tissue and, because it is viscous, acts as both a lubricant and a barrier to the penetration of invaders.

Question 36

What are **GAGS**?

Answer 36

(also called mucopolysaccharides) are long polysaccharides consisting of repeating disaccharide units, usually a uronic acid and a hexosamine. The hexosamine can be glucosamine or galactosamine, and the uronic acid can be glucuronic or iduronic acid. The largest, almost unique, and most ubiquitous GAG is hyaluronic acid (made by **hyaluronate synthase**)

Question 37

What are some of the other smaller **GAGS**?

Answer 37

The four major GAGs found in proteoglycans are dermatan sulfate, chondroitin sulfates, keratan sulfate, and heparan sulfate, all of which have different disaccharide units and tissue distributions. They are also hydrophilic.

Question 38

**Proteoglycans** are composed of a core protein to which are covalently attached various numbers and combinations of the sulfated GAGs. distinguished by their diversity, like **Decorin,** **Syndecan, and Aggrecan**

Answer 38

**Decorin** has few GAG side chains and binds fibrils of type I collagen. Cell surface proteoglycans such as **syndecan** have transmembrane core proteins and serve as additional attachments of the cell to the ECM. One of the best known proteoglycans, **aggrecan**, is very large (250 kDa), with a core protein bearing many chondroitin sulfate and keratan sulfate chains.

Question 39

Both matrix- linked and cell surface proteoglycans also bind and sequester certain signaling proteins, for example fibroblast growth factor (FGF).

Answer 39

Degradation of proteoglycans during the early phase of tissue repair releases these stored growth factors that then stimulate new cell growth and ECM synthesis.

Question 40

``` The third class of ground substance components, the **multiadhesive glycoproteins.** ```

Answer 40

Which all have multiple binding sites for cell surface receptors (**integrins**) and for other matrix macromolecules. The adhesive glycoproteins are very large molecules with branched oligosaccharide chains and have important roles in the adhesion of cells to their substrate.

Question 41

``` The large (200-400 kDa), trimeric, cross-shaped glycoprotein **laminin** ```

Answer 41

provides adhesion for epithelial and other cells, with binding sites for integrins, type IV collagen, and specific proteoglycans.

Question 42

Glycoprotein **Fibronectin**

Answer 42

synthesized largely by fibroblasts, is a 235-270 kDa dimeric molecule, has binding sites for collagens and certain GAGs, and forms insoluble fibrillar networks throughout connective tissue.

Question 43

The **integrin** family of integral membrane proteins act as matrix receptors for specific sequences on **laminin, fibronectin**, some collagens, and certain other ECM proteins....

Answer 43

**Integrins** bind their ligands in the ECM with relatively low affinity, allowing cells to explore their environment without losing attachment to it or becoming glued to it.

Question 44

structures called **focal adhesions**

Answer 44

Integrins and other proteins associated with intermediate filaments form the hemidesmosomes of epithelia clustered integrin-microfilament complexes in fibroblasts form structures. This type of adhesive junction is typically present at the ends of actin filaments bundled by α-actinin as cytoplasmic stress fibers

Question 45

Outside of Ground substance, what is theother liquid space called?

Answer 45

In addition to the hydrated **ground substance** of connective tissue, a small quantity of free **interstitial fluid**, with ion composition similar to that of blood plasma, is also present. Interstitial fluid contains plasma proteins of low molecular

Question 46

Two forces act on the water in capillaries

Answer 46

The **hydrostatic pressure** of the blood caused by the pumping action of the heart, which forces water out across the capillary wall ■■ The **colloid osmotic pressure** produced by plasma proteins such as albumin, which draws water back into the capillaries

Question 47

In adults we have 2 connective tissue types, **Loose** and **Dense**:

Answer 47

It comprises a thick layer (the lamina propria) beneath the epithelial lining of the digestive system and fills the spaces between muscle and nerve fibers. thin layers of **loose connective tissue** surround most small blood vessels of the body. Also called **areolar tissue** **Dense connective tissue** is adapted to offer stress resistance and protection. Has more collagen fibers over ground subtance.

Question 48

In **Dense irregular connective tissue**

Answer 48

bundles of collagen fibers appear randomly _interwoven, with no definite orientation_. The collagen fibers form a tough three-dimensional network, providing resistance to stress from all directions. Often these are found closely associated with loose connective tissue, with the two types frequently grading into each other and making distinctions between them somewhat arbitrary

Question 49

type I collagen bundles of **dense regular connective tissue**

Answer 49

are arranged according to a _definite pattern_, with fibers and fibroblasts aligned in parallel for resistance to prolonged or repeated stresses exerted in the same direction. Examples: tendons, ligaments.

Question 50

In some tendons, the dense irregular connective tissue sheath is covered by flattened **synovial cells** of mesenchymal origin, which produce lubricant fluid

Answer 50

However, tendons are poorly vascularized, as to why it takes so long to heal.

Question 51

In **reticular tissue fibers** of type III collagen

Answer 51

form a delicate 3D network that supports various types of cells. The fibrous network of this specialized connective tissue is produced by **modified fibroblasts** called **reticular cells** that remain associated with and partially covering the fibers.

Question 52

**Mucoid** (or mucous) connective tissue: which is another embryonic type of connective tissue, found mostley in fetal organs.

Answer 52

**Mucoid tissue** is the principal component of the umbilical cord, where it is referred to as **Wharton’s jelly .** With abundant ground substance composed chiefly of **hyaluronan**, mucoid tissue is gelatinous, with sparse collagen fibers and scattered fibroblasts. Included among the fibroblastic cells are many **mesenchymal stem cells**, which are being studied for their potential in regenerative medicine.