HIPA: Connective Tissue

Question 1

Connective Tissue Structure

Answer 1

Few Cells, lots of ECM

Question 2

Connective Tissue Functions

Answer 2

a. The most important function of the connective tissue is to provide structural support
for the body.
b. Connective tissues are used for storage of metabolites.
c. Connective tissues play an important role in defense and protection of the body by
mediating immune, inflammatory, and allergic responses.
d. Connective tissues are used to “repair” other tissues and organs through the formation of
the fibrous scar.

Question 3

Fiber Types

Answer 3

Three main types of fibers are present in connective tissue, collagen fibers,
reticular fibers, and elastic fibers. These fibers are formed by several types of fibrillar
proteins. Collagen and reticular fibers are composed of different types of collagen, while
the elastic fibers are composed of elastin and fibrillin.

Question 4

Collagen

Answer 4

Collagen is an extracellular fibrillar protein and is the most abundant protein in the
human body. Collagen fibers are the principal structural components of most
connective tissues. They are flexible and have a high tensile strength. Collagen is
produced principally by fibroblasts. There are more than 28 different types of
collagens present in our body.

Question 5

collagen structure

Answer 5

a. Collagen molecule measures ~300 nm and consists of three polypeptide
chains that form a triple helix. The synthesis and formation of collagen will
be covered in Biochemistry course.

b. Collagen molecules are polymerized laterally and head-to-tail to form
collagen fibrils. Fibrils cannot be visualized in the light microscope, but
have a distinctive banding when viewed with an electron microscope. The
banding is due to the presence of small gaps between collagen molecules,
which absorb stain.

c. Collagen fibrils in several types of collagens are assembled into collagen or
reticular fibers, which can be visualized in a light microscope.
d. Collagen fibers can be assembled into larger structures called the collagen
bundles, formed only by type I collagen.

Question 6

Collagen Hierarchy

Answer 6

Bundle, Fibers, Fibrils, Molecules

Question 7

T1 Collagen

Answer 7

Type I collagen is the principal type of collagen. It is found in the dermis of
the skin, tendons, ligaments, fascia, bone, and most connective tissues
proper. Type I collagen forms fibrils that are assembled into fibers, which
can be assembled into larger bundles.

Question 8

Type II

Answer 8

Type II collagen is found in cartilage. This type of collagen forms fibrils,
but not fibers. Fibrils cannot be visualized in a light microscope and this
gives the cartilage its glassy appearance.

Question 9

T3 Collagen

Answer 9

forms banded fibrils that assemble into reticular fibers,
which form a supporting framework for the cells of various tissues and
organs, such as the loose connective tissue, walls of blood vessels, lymphoid
tissues, bone marrow, smooth muscle, nerves, lung, etc. Reticular fibers are
named so because of their arrangement into a meshwork, or a network
(=reticulum).

Question 10

T4 Collagen

Answer 10

Type IV collagen does not form banded fibrils, but forms sheet-like
meshwork of beaded filaments found in the basal lamina.

Question 11

Ehlers-Danlos syndrome (EDS)

Answer 11

It is a congenital disorder, which is caused
by the impaired extracellular modification of collagen, which results in the
formation of defective collagen fibers. There many different types of EDS,
which have different symptoms. Typically, patients present with skin hyper
elasticity, loose, unstable joints that are prompt to dislocation, low muscletone/muscle weakness, and various bone abnormalities including deformities of the spine, osteopenia (low bone density), and others.

Question 12

Elastic Fibers function

Answer 12

respond to stretch and distention

Question 13

elastic fiber arrangement

Answer 13

thinner fibers in a branching pattern to form a network

Question 14

elastic fiber stain

Answer 14

eosin may/may not work, orcein for selective staining,

Question 15

Elastin

Answer 15

hydrophobic domain, cross-linked covalent bonds, fibers or lamellar layers (bl. vessels)

Question 16

Elastin Function

Answer 16

elasticity (coming back) of conn. tissue, elastin molecules coil back into original shape

Question 17

Fibrillin

Answer 17

glycoprotein, thin microfibrils that surround elastic fibers and provide substrate for assembly.

Question 18

Marfan’s Syndrome

Answer 18

CV, skeletal, and ocular defects- mitral valve prolapse, rupture of arteries, arachnodactyly

Mutation in Fibrillin Gene

Question 19

Ground Substances Function

Answer 19

Fill in ECM

Question 20

Ground Substances Components

Answer 20

glycosaminoglycans (GAGs), proteoglycans,
and multiadhesive glycoproteins

Question 21

GAGs structure

Answer 21

most abundant, long-chain, unbranched, highly neg charged polysaccharides

Question 22

GAGs and water

Answer 22

hydrophilic so form a gel

Question 23

GAGs function

Answer 23

resist compression/deformation, diffusion of water sol. particles

Question 24

Hyaluronic Acid

Answer 24

GAG, always present in ECM, long molecule w/ no sulfate, does not form proteoglycans

Question 25

Common Types of GAGs (CNCT)

Answer 25

Chondroitin sulfate, dermatan sulfate, keratan sulfate, and heparan sulfate are some of the more common types of GAGs found in the connective tissue. These GAGs attach to proteins to form proteoglycans.

Question 26

Proteoglycan Structure and Hyaluronic Acid Aggregates

Answer 26

GAGs covalently attached to core protein, form brush structure, attach non-covalently to hyaluronic acid to form giant aggregates (hyaluronic acid aggregates)

Question 27

Hyaluronic Acid Aggregates

Answer 27

Account for Connective Tissue ability to resist compression without losing flexibility (Q)

Question 28

Multi-adhesive Glycoproteins Function

Answer 28

cross links between collagen, ECM, and Cells (think hemidesmosomes, focal adhesions)

Question 29

Fibronectin pt. 1

Answer 29

most abundant glycoprotein in cnet tissue

Question 30

Fibronectin pt. 2

Answer 30

can assemble into thin fibers, dimer that has binding domains for ECM (1,2,3 collagen), GAGs, integrin, fibrin, etc. Integrin is a big one

Question 31

Laminin

Answer 31

Basal Lamina, binding to 4 collagen, integrin, etc. Three disulfide linked polypeptides Cell adhesion sites

Question 32

Resident Cells Characteristics

Answer 32

(fixed cells), mitose in the cnet tissue and spend most of life there

Question 33

Fibroblast

Answer 33

principal resident cell

Question 34

Fibroblast Function

Answer 34

produce components of ECM (see notes)

Question 35

Fibroblast location

Answer 35

typically near collagen

Question 36

Active Fibroblasts Where?

Answer 36

actively growing cnct tissue, wound repair; loose connective tissue

Question 37

Active Fibroblasts Characteristics

Answer 37

abundant cytoplasm with many thin processes, abundant RER and Golgi, see notes for cellular ch.

Question 38

Inactive Fibroblasts (Fibrocytes)

Answer 38

Dense ct (not growing), see notes for ch. (self-ex.)

Question 39

Myofibroblasts

Answer 39

both fibroblast and smooth muscle ch. Fib.- RER and Golgi Sm.- actin filament bundles and dense bodies Can contract but not smooth muscle (have differing ch.) Seen at wound sites, imp. for wound closure. Pull ends together.

Question 40

Mesenchymal Cells

Answer 40

Present in embryonic tissue, multipotent ct cells. See notes for ch.

Question 41

Adipocytes

Answer 41

store fat and produce hormones

Question 42

unilocular adipocytes Where?

Answer 42

either w/in loose ct, or forming aggregates (white adipose tissue)

Question 43

Unilocular Adips.

Answer 43

large spherical cells, single droplet, flattened nuclei

Question 44

Multilocular adipocytes

Answer 44

BAT (around root of aorta in newborns), These cells are characterized by multiple fat droplets and presence of large number of mitochondria, which give the tissue its brown color. The nucleus is usually centrally placed and not flattened. Metabolism of lipid in multilocular adipocytes generates heat

Question 45

Macrophages

Answer 45

derived from monocytes (in bone marrow), can divide, hard to ID, Features that can help you identify them include the presence of ingested material in the cytoplasm and indented (kidney- shaped) nucleus. Both of these features can be difficult to see due to the variable orientation of the cell on the slide.

Question 46

Macrophage Function

Answer 46

Phagocytosis of bacteria and senescent cells, tissue cleanup

Question 47

Macrophage Immune

Answer 47

MHC II on surface , antigen presenting cells, produce cytokines to activate other immune cells

Question 48

mononuclear phagocytic lineage

Answer 48

shared lineage of all macrophages in body (from bone marrow

Question 49

Cells of M.P.L.

Answer 49

Histiocytes- CT Osteoclasts- Bone Dendritic Cells- Lymph and Spleen (Langerhans in the skin) Microglial- CNS Kupffer- Liver

Question 50

DCs

Answer 50

Dendritic cells are important for processing and presentation of antigens to T lymphocytes; the distinctive function of DCs is to initiate responses in quiescent lymphocytes generating primary T-lymphocyte–dependent immune response

Question 51

Mast Cells

Answer 51

Mast cells originate in the bone marrow, and then migrate into the connective tissue, where they proliferate and differentiate. They are most common in the connective tissue of the skin and mucous membranes and are absent from CNS

Question 52

Mast Cells Shape

Answer 52

Oval shaped with central nucleus

Question 53

Defining Ft. Mast Cells

Answer 53

Basophilic Granules in cyto.

Question 54

Basophilic Granules components

Answer 54

heparin sulfate (acidic), chondroitin sulfate, chemotactic mediators, histamine

Question 55

Mast Cells Ig

Answer 55

Receptors for IgE

Question 56

Mast Cells are similar to...

Answer 56

basophils (diff. nuclear morph.)

Question 57

Mast Cells Fnct.

Answer 57

Mast cells function in mediating the inflammatory and hypersensitivity reactions, allergy, and anaphylaxis.

Question 58

Mast Cells Antigen Exposure

Answer 58

Activation of a mast cell occurs during the first exposure to the antigen, when plasma cells produce large amounts of IgE, which becomes bound to the surface of mast cells. ii. During the subsequent exposure, the antigen binds to surface-bound IgE on mast cells causing its cross-linking on the extracellular side. iii. The cross-linking of IgE results in clustering of receptors on the cytoplasmic side of the plasma membrane of a mast cell causing its degranulation.

Question 59

Mast Cells (Post-Granulation Effects)

Answer 59

Histamine causes vasodilation and increases vascular permeability. This promotes emigration of white blood cells into connective tissue. 2. Histamine and several other agents cause bronchoconstriction and increased mucus production in the bronchial mucosa. 3. Chemotactic mediators attract white blood cells, eosinophils and neutrophils.

Question 60

Mast Cell Ch.

Answer 60

These reactions, usually mild and local (e.g. in the area of an insect bite), sometimes in hyperallergic persons can turn into a severe hypersensitivity reaction and an anaphylactic shock.

Question 61

Transient Cells

Answer 61

don't divide in ct, immune cells

Question 62

Types of Transient Cells

Answer 62

WBCs and Plasma Cells

Question 63

Plasma Cells

Answer 63

AB producing cells from B Lymphs. Prominent RER and Golgi., clock-face pattern (dark and light alternating)

Question 64

Leukocytes (WBC)

Answer 64

area of inflammation

Question 65

3 types of C.T.

Answer 65

1. embryonic 2. Proper 3. Specialized

Question 66

Embryonic CT

Answer 66

embryo and umbilical cord, then differentiates

Question 67

Mesenchyme

Answer 67

found in embryo, abundant ground substance, few call/reticular fibers

Question 68

Mucous Connect. Tissue

Answer 68

Found only in U. cord, lots of Hyaluronic Acid. Few C/R Fibers Wharton's Jelly

Question 69

Types of Connective Tissue Proper

Answer 69

Loose (areolar) and Dense

Question 70

Loose (Areolar)

Answer 70

thin and relatively sparse collagen type I fibers, usually no bundles The ground substance is abundant and has a viscous, gel-like consistency. Mostly Fibroblasts Transient Cells- large pop Beneath internal surfaces as "filter-tissue" surrounds blood and lymphatic vessels and nerves

Question 71

Dense CT

Answer 71

lots of C1 and bundles, fewer cells, little ground substance Irregular and Regular

Question 72

Dense Irregular Connective Tissue

Answer 72

dense irregular connective tissue are oriented in various directions and are interwoven into a meshwork that resists stress from all directions. The main type of cell present is the fibroblast, the transient cells are scarce or absent. Most of the fibroblasts in this tissue are inactive. STRENGTH

Question 73

Dense Irregular Where?

Answer 73

Dermis and Internal Organs (Spleen/ Testis)

Question 74

Dense Regular CT

Answer 74

Dense regular connective tissue is composed of densely packed collagen bundles that are oriented in the same direction to resist tensile forces. There is very little space left for ground substance and cells. Thin, sheet-like inactive fibroblasts are located in-between the collagen bundles. They have compressed, heterochromatic nuclei. Tendons, ligaments, and aponeuroses are formed of dense regular connective tissue.

Question 75

Adipose Tissue

Answer 75

receives rich blood supply, Innervated by autonomic NS, Receptors for Hormones

Question 76

White Adipose Tissue

Answer 76

White adipose tissue is the predominant type of adipose tissue. It is composed of unilocular adipocytes, which contain a single lipid droplet. This tissue accumulates energy. It contains receptors for growth hormone, insulin, and noradrenalin. White adipose tissue is a poor heat conductor and this tissue contributes to the thermal insulation of the body. Visceral adipose tissue fills in spaces between internal organs and helps to keep some organs in place. It also plays an important shock-absorption function.

Question 77

BAT

Answer 77

Brown adipose tissue is not present in adult humans, but is found in newborns. This type of adipose tissue is composed of multilocular adipocytes. These cells contain large number of mitochondria and oxidize fatty acids at up to 20 times the rate in white adipose tissue increasing body heat production threefold.

Question 78

Radicular CT

Answer 78

Reticular connective tissue is a loose connective tissue found in the stroma of the organs of the lymphoid system, such as lymph nodes, spleen, and bone marrow. This type of connective tissue is supported by a network of reticular fibers that form thin, branching, interconnected threads.

Question 79

Blood

Answer 79

elements- RBC, WBC, platelets; plasma

Question 80

plasma

Answer 80

Plasma represents a solution of nutrients and gases. It consists of more than 90 % of water and various solutes, such as albumin, globulins, and clotting factors.

Question 81

Erythrocytes

Answer 81

Erythrocytes, or red blood cells (RBC) are anucleate biconcave disks that are 8 by 2.5 m in size. The biconcave shape of RBCs allows more surface area for gas exchange and decreases the distance that oxygen must diffuse through the cell. Mature RBCs do not contain organelles and are simply sacks with hemoglobin, which can bind oxygen. Most carbon dioxide is converted to bicarbonate by the enzyme anhydrase inside RBCs and transported this way

Question 82

Leukocytes

Answer 82

much rarer in the blood, than erythrocytes, so there are 600 RBCs per one WBC. Leukocytes are nucleated cells of the blood. The normal leukocyte count is between 5,000 and 9,000 per mm3. The condition with more than 12,000 per mm3 is called leukocytosis, and the condition when the leukocyte count is less than 5,000 is called leukopenia. The increase or decrease of WBCs levels in the blood can be due to inflammations, infections, or intoxications. White blood cells use blood as a transport system to get to the target area. They perform ameboid movement (using pseudopodia) to move through the tissue towards the chemotactic agents that attract them.

Question 83

Types of WBC

Answer 83

neutrophils, eosinophils. basophils, lymphocytes, Monocytes

Question 84

Neutrophils

Answer 84

Neutrophil is the most common white blood cell in the peripheral blood (55 – 70 % of all leukocytes). Neutrophils are fairly large cells (10-12 m) with multilobed nuclei and so are often called polymorphonuclear leukocytes (PMNs). The cytoplasm of neutrophils contains granules with bactericidal proteins. Neutrophils perform selective phagocytosis of bacteria. Neutrophils produce IL1, which induces increase in body temperature and causes fever. The dead neutrophils and cell debris form the pus.

Question 85

Eosinophils

Answer 85

Eosinophils are overall rare in the normal peripheral blood (2-4 % of all WBCs). They are slightly larger than neutrophils (11-14 m) and have a bilobed nucleus and numerous eosinophilic granules in the cytoplasm. The granules contain cytotoxins that are designed to destroy protozoan and helminthic parasites. Eosinophils are most common in the peripheral blood during parasitic infestations and allergic reactions as they destroy parasites and modulate allergic response by breaking down histamine and inhibiting mast cell degranulation

Question 86

Basophils

Answer 86

Basophils are the rarest WBCs and constitute only 0.5-1.5 % of all leukocytes. They are the smallest of granulocytes (8-10 m) and have a lobed nucleus. Their cytoplasm is filled with numerous basophilic granules that contain histamine and heparin. The major function of basophils is to produce histamine. Basophils are very similar to mast cells. When exposed to the antigen, they degranulate.

Question 87

Lymphocytes

Answer 87

Lymphocytes are second most common white blood cells (20-30 %). Lymphocytes have a large spherical or slightly indented heterochromatic nucleus surrounded by a tiny rim of cytoplasm, which does not contain specific granules. Lymphocytes circulate through blood and internal organs, mature, and divide. There are three main populations of lymphocytes: T-cells that are the most common type in the peripheral blood (80 % of all blood lymphocytes), B-cells that constitute ~ 15 % of all peripheral blood lymphocytes, and very scarce (<5 %) natural killer cells

Question 88

B Lymphocytes

Answer 88

B-lymphocytes arise and mature in the bone marrow. B- lymphocytes are characterized by the presence of surface immunoglobulin bound to their plasma membrane. B- lymphocytes reside in lymphoid and connective tissues, such as spleen and lymph nodes, where they are programmed for viruses, bacteria, or other foreign proteins. Upon reaching the target destination they proliferate into plasma cells, which start actively producing antibodies.

Question 89

NK Cells

Answer 89

Natural killer cells (NK cells) are large lymphocytes that are programmed during their development to kill certain virus- infected cells and some types of tumor cells. It has been shown that circulating NK cells display high cytolytic activity against tumor cells. They can also play an important role in the rejection of body transplants.

Question 90

Monocytes

Answer 90

Monocytes circulate through the peripheral blood, adhere to the walls of blood vessels and use ameboid movement (using pseudopodia) to get to the target object. When they get to the tissue, they become macrophages. Monocytes constitute 4-6 % of all peripheral blood leukocytes. These are large cells (12-20 m) with a bean-shaped (or kidney-shaped) nucleus. Their cytoplasm contains many lysosomes and small mitochondria.

Question 91

Platelets

Answer 91

Platelets are the anucleate particles that are abundant in human blood (200,000 – 300,000 per mm3). They have a lifespan of 8-10 days. Platelets are biconvex discoid particles. They contain few mitochondria and many granules with adhesion proteins and clotting factors.

Question 92

T-Lymphocytes

Answer 92

T-lymphocytes (T cells) arise from bone marrow and embryonic hemopoietic organs. They use blood to transmit from bone marrow into thymus, where they mature and multiply to reenter the blood stream again. T-cells are characterized by the presence of T-cell receptor (TCR) on the cell surface. Binding of the TCR to antigen-MHC II complexes presented by macrophages activates CD4+ T cells, which produce cytokines that are designed to direct and recruit other cells of the immune system. CD8+ T cells recognize defective MHC I complex of other cells and destroy them.