[10] ANATOMY - Connective Tissues

Mesoderm

What is the embryonic origin of connective tissues?

Parenchyma

These are the functional elements of tissue/organ

True

TRUE OR FALSE: The following are the functions of connective tissues

• Binds body parts but allows some degree of mobility 

• Forms the stroma/supporting framework 

• Envelopes muscles to protect against friction

• Avenue for blood vessels and nerves

• Venue for gas and substance exchange between blood & tissue 

• Provides arena & cells to protect the body

Extracellular Substance and Cells

What are the composition of connective tissue?

Ground substance

Amorphous (no shape), homogeneous, transparent, hydrated gel

Water

What is the main component of the connective tissue?

Proteoglycans, Hyaluronic acid (Hyaluronan), Mineral salts, Glycoproteins

What are the other components that stabilize water in the ground substance?

Water

Main component of ground substance. Abundant in the ground substance. Oxygen, nutrients and other materials diffuse easily from blood to connective tissue. Waste products of metabolism diffuse easily from connective tissue to the blood

Proteoglycans

Main structural constituent of extracellular substance. Responsible for the gelatinous character of the ground substance. Macromolecules that consist of a core protein with covalently attached disaccharides (glycosaminoglycans or GAGs)

GAGs (glycosaminoglycans)

Make the ground substance acidic due to the sulfate and carboxyl groups in sugar

Keratan sulfate, Chondroitin sulfate, Dermatan sulfate, Heparin sulfate

What are the common GAGs?

Hyaluronic Acid or Hyaluronan

A glycosaminoglycan. Most abundant GAG in the connective tissue. Backbone of proteoglycans to form bigger molecules called proteoglycan aggregates or complexes. Does not have any sulfate groups attached (unlike proteoglycans). Does not covalently attach to a core-protein

Glycoproteins

At least two of the glycoproteins are fibrillar in the form of microfibrils

Fibrillin

Larger of the 2 fibrillar glycoproteins. Non-sulfated; 10 to 12 nm in diameter. In an electron micrograph, it has an electron-lucent core surrounded by electron-dense area. An essential part of elastic fibers

Smaller microfibril

Not named. Not much is known. 3 to 5 nm in diameter

Fibronectin, Laminin, Thrombospondin

What are the other glycoproteins involved in cell adhesion and migration?

Cells (scarce)

These cells are not bound to each other and are scattered in the matrix

Extracellular matrix (abundant)

Further contains blood vessels and nerve fibers

Collagen fibers

Present in all connective tissues in varying amounts. Found especially in collagenous connective tissue (most commonly occurring type of connective tissue). Colorless (individually) but appears white if abundant (such as in tendons). 2 to 10 µm in diameter

Collagen

Accounts for approximately 25% of body’s dry weight. Family of structural proteins numbered I to XXVIII

Type I, II and III

Type of collagen fibers present in connective tissue

Type I

Type of collagen fiber that particularly only makes up collagen fiber

B, D, F, E, A, C

ARRANGE THE FOLLOWING BASED ON THE FORMATION OF COLLAGEN FIBERS:

A. Collagen microfibrils will group together to form collagen fibrils of collagen macrofibrils (0.3-0.5 µm)

B. Fibroblasts and mesenchymal cells produce the precursor protein of collagen fiber called procollagen (α-chain)

C. Collagen fibers are formed when collagen macrofibrils group together in a parallel fashion

D. Produced procollagen are secreted into the extracellular matrix where extra amino acids are enzymatically removed

E. Tropocollagen will aggregate to form collagen microfibrils (45-100 nm)

F. 3 right-sized procollagen will twist around each other are bound by hydrogen bonds to form tropocollagen

Elastic Fibers

Not as widely distributed as collagen fibers. Branch and anastomose with each other (which collagen fibers do not). Grossly impart a yellow color. Average 1 µm diameter

H&E stain

In elastic fiber staining, using this stain, it appear as refractile pinkish-yellow lines which are indistinguishable from collagen fibers

Orcein stain

In elastic fiber staining, using this stain, it appear blue to black

Resorcin-fuchsin and aldehyde-fuchsin

What other stains are used for elastic fibers?

elastin

Elastic fibers are made of ________ at its core, surrounded by longitudinal microfibrils, mostly fibrillin

Elastin

A highly insoluble protein but very elastic. Resistant to boiling and hydrolysis of acids, alkali and most enzymes

elastase (pancreatic enzyme)

Elastin can by hydrolyzed by a protease called?

elastic lamellae

Elastin appear in the form of elastic fibers or elastic sheets called?

• Ligamentum flavum

• Elastic cartilages of auricle and external acoustic meatus

• External nose

• Auditory tube

  • Epiglottis and larynx

Elastic Fibers are abundant in structures with frequent stretching like?

A, C, F, E, D, B

ARRANGE THE FOLLOWING BASED ON ELASTOGENESIS:

A. Fibroblasts and mesenchymal cells secrete microfibrils to the extracellular matrix → further aggregate to form bundles

B. In its development, more elastin and microfibrils are added once there is enough elastin

C. The same fibroblasts and mesenchymal cells produce tropoelastin, the precursor of elastin

D. Elastin is incorporated into the outer aspect of the microfibril bundles

E. Tropoelastin polymerizes to form elastin

F. Microfibrils and tropoelastin are secreted into the ECM

smooth muscle cells

Elastic fibers are formed by _______________ that lay elastin in fenestrated sheets or lamellae in concentric layers

Reticular fibers

Made of collagen type III. Surrounding structure of the parenchyma. Branch and anastomose like elastic fibers. 0.5 nm to 2.0 µm diameter. Stains black with silver salts

Kidneys, Lymph node, Spleen, Pancreas, Bone marrow

They are the main extracellular fibers of reticular tissue in?

lamina fibroreticularis

Fibrillar component of ____________________ of the basement membrane of epithelial tissues

False

TRUE OR FALSE: The formation of reticular fibers is similar to the of collagen fiber except they are produced by fibrilin.

Reticular cells

Special type of fibroblast that synthesize procollagen

Mesenchymal cells

Multipotent stem cells. Give rise to numerous cell types but are limited. They are scarce in adults but are present in most organs where they replace dead or damaged cells

zygote

The union of male and female gametes

totipotent stem cell

This can give rise to any human cell, placental cell, or cell of the fetal membranes (amnion and chorion)

Pluripotent stem cells

These arise from totipotent stem cells which can form any cell type of the body, but cannot produce a human being (i.e., they can no longer give rise to placental cells and cells of the fetal membrane)

stellate

Mesenchymal cells are ____________ (star-shaped) cells with delicate cytoplasmic processes and oval nuclei with fine chromatic and distinct nucleoli ​​

Fibroblasts, Reticular cells, Adipocytes, Osteoprogenitor cells, Myoblast

Mesenchymal cells are stem cells of most connective tissue cells such as?

Fibroblasts

The most abundant cells in most connective tissues. Active. Responsible for synthesizing and marinating extra cellular components of connective tissue (e.g. proteins, glycoproteins, GAGs of the ground substance and precursors of collagen and elastic fibers)

Fibroblasts

They have a well-developed rER which are used for protein synthesis making their cytoplasm basophilic. Capable of mitosis, however, infrequently as they are sturdy and long-lived.

Fibrocytes

Fibroblasts that are not actively producing extracellular connective tissue components. Inactive.

wound healing

In appropriate conditions, they can become fibroblasts like in ________________ wherein extracellular connective tissue components are needed for wound closure.

a. pointed by arrow

What cell is inactive?

a. pointed by arrow b. circular

Reticular cells

Specialized fibroblasts that produce the precursor of type III collagen that make up reticular fibers

Adipose cells or Adipocytes

It can also be called a fat cells or lipocytes. It is a specialized cell that stores lipids or fats (mainly triglycerides) in its cytoplasm

lipoblast

Several fat globules in cytoplasm. usually seen in the young, and could be a malignancy if present in adults.

Adipocyte

Only one fast globule inside

signet ring

Due to the large droplet of fat in the cells the nucleus is pushed to one side, making the cell look like a?

glutaraldehyde or osmic acid

If adipocytes are fixed with these, they will be seen as grey or black globules.

brown adipose

A small population of fat cells stores fat in their cytoplasm as multiple small droplets. These fat cells are seen in _______________ (mostly in infants, disappear in adults).

False

TRUE OR FALSE: Adipocytes are capable of mitosis.

preadipocytes (pre-fat cells)

Adipocytes are sourced from mesenchymal cells called?

Mast cells

Also called mastocytes; histaminocytes. Large (15 to 20 µm), ovoid cells with centrally located nuclei and numerous cytoplasmic granules

toluidine blue

This stain is used so that mast cells can be recognized by their dark purple granules

Heparin

Anticoagulant. Thins out the blood by preventing coagulation

Histamine

Dilates blood vessels and makes it permeable. Stimulates smooth muscles especially bronchioles. Also an anticoagulant

True

TRUE OR FALSE: The following are the functions of mast cells

• Involved in inflammation and immediate-type hypersensitivity reaction (allergic reaction)

  • Severe type is anaphylactic shock

• Synthesize and release leukotrienes, prostaglandins and certain cytokines

• Role in wound healing 

• Defense against pathogens

Colony Forming Unit Mast cell (CFU-Mast)

Mast cells come from this from the bone marrow

lamina propria of GI tract

Mast cells are abundant where?

Lamina propria

This is just under the mucosa so foreign substances will be caught

Macrophages

Are phagocytes derived from monocytes. Present in all tissues, not only the connective tissue. Have different names in different parts of the body.

Monocytes

are WBCs that migrate to connective tissue by crossing the wall of venules and differentiate to macrophages.

histiocytes

Macrophages that migrate to connective tissue

pulmonary alveolar macrophages

Macrophages that migrate in the lungs or alveoli

Kupffer cells

Macrophage that can be found in liver sinusoids.

True

TRUE OR FALSE: Macrophages are easier to recognize under the light microscope when they have phagocytosed materials in their cytoplasm

antigen presenting cells

The macrophage function as immune defense system and serves as what to lymphocytes?

Fixed macrophage

Attached to collagen fibers. Can become free macrophages once they have detached from collagen fibers

Free macrophage

Wandering freely in the extracellular matrix. Can become fixed macrophages if they attach themselves to collagen fibers

Resident macrophages

Permanently inhabit a given tissue. Less immunologically active. Increase in number by limited local proliferation or from monocytes in connective tissue

Inflammatory macrophages

Migrate to a site in response to stimulus (e.g., if there is infection in connective tissue). More immunologically active. Increase in number only from monocytes (they cannot do local proliferation)

Plasma Cells

Also known as plasmocytes. They are bigger than red blood cells (RBCs)

B lymphocytes (B cells)

Plasma cells differentiate into what type of WBC?

immunoglobulins or antibodies

Plasma cells produce these

True

TRUE OR FALSE: Plasma cells have a limited number in all connective tissues but numerous in connective tissues that are readily accessible to foreign proteins and bacteria (e.g. lamina propria of the digestive tract)

Leukocytes

They are also known as white blood cells (WBCs). These are the nucleated cells in the blood

False

TRUE OR FALSE: In post-natal life, all leukocytes are produced in the bone marrow except for the monocytes

thymus, lymph nodes, spleen, tonsils

Lymphocytes are also produced in the lymphoid tissues and organs such as the?

neutrophils, basophils, eosinophils, monocytes, lymphocytes

What are the types of white blood cells?

diapedesis

For the leukocytes to go to the connective tissue from blood vessels, they need to squeeze through the endothelial gaps in the blood vessels, this process is called?

amoeboid movement

Once in the connective tissue, the leukocytes exhibit

Collagenous Connective Tissue

Most abundant type of connective tissue in the body. Referred to as ordinary connective tissue or just connective tissue.

collagen fiber type I

What is the most abundant extracellular fiber?

type III collagen

What type of collagen can be seen in reticular fiber?

fibroblast

What is the most abundant cell in collagenous connective tissue?

Dense Collagenous Connective Tissue

Characterized by scanty ground substance. Abundant and closely packed collagen fibers. Relatively few cells embedded

Dense regular connective tissue

Collagen fibers arranged in a definite pattern (one direction). Comprises tendons, ligaments, and fibrous membranes

Dense irregular connective tissue

Collagen fibers run in various directions (haphazard). Comprises the dermis of skin, capsule of lymph nodes, liver, spleen & testes, nerve sheaths, periosteum and dura mater

Loose Connective Tissue

Abundant extracellular substance. Haphazardly arranged few collagen fibers. More cellular than Dense CT. Highly vascular. Seen in hypodermis (subcutaneous tissue), tunica adventitia of blood vessels, lamina propria & submucosa of digestive, respiratory & urogenital tracts

Adipose tissue

Represents the largest energy storage site. Functions as thermal insulator (poor heat conductor; can save heat in the body). Serves as shock absorber (kidneys & soles of feet)

Adipocyte

Specialized cell that stores fat which represents excess dietary calorie intake then released if needed in form of fatty acids

reticular fibers

In the lobules, the adipocytes are supported mainly by

yellow and brown fat

What are the two kinds of adipose tissue?