histology exam 2 review.1

8/12/2019 Histology Exam 2 Review.1

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TISSUE AND ORGAN BIOLOGY

CRITERIA FOR SUCCESS: At the conclusion of this course, students should be able to

1) Identify correctly all of the tissues and organs of the human body at the microscopic level;

2) Describe the diagnostic architectural and functional features of the tissues and organs and their specific cells; andhow these features are interrelated;

3) Associate and correlate the important clinical conditions that were presented as examples with their tissues andorgans; and also continue to make these associations as new clinical conditions are encountered.

Tissues can be defined as societies of cells, which together with their associated extracellular matrix (ECM), arespecialized to carry out specific functions.

In mature tissues, there are 4 primary phenotypes:

1) Epithelium;2) Connective Tissue;3) Muscle;4) Nervous Tissue.

In embryonic tissues, there are 2 primary phenotypes:1) Epithelium;2) Mesenchyme.

Lecture #1 Cells, Tissues & Organs: Methods of Study

1. Understand the basic principles behind tissue preparation for microscopic

examination.

a. Fixative is typically a chemical agent, which may consist of a simple

solution; e.g., 10% formalin: formaldehyde dissolved in an aqueous or buffered medium

b. The end result is cross-linking and denaturation of tissue components,

particularly proteins.c. Dehydration and rehydration steps to move tissue between phases

i. If the fixative is aqueous and the material in which the tissue is to be embedded is paraffin wax then a dehydration sequence is employed to introduce an organic phase thatwill be compatible with the wax embedding medium.

2. Learn and recognize certain specific stains along with their particular characteristics

and shortcomings.

a. Proteins are amphoteric (possess both acidic and basic groups); at the

isoelectric point (pI ), the net charge is zero and minimal dye binding

occurs.

i. However, if staining is performed at a pH below their isoelectric

point1. Basic groups (primarily amino) are positively charged and

bind dyes that are anionic/acidic, and the substances

stained (proteins) are termed acidophilic (acid-loving).a. Anionic dye is Eosin (binds Eosinophic proteins)

2. If staining takes place above the isoelectric point, its acidic

groups (phosphate, carboxyl, or sulfate) will be negatively



charged and can combine with a positively charged

cationic dye (such as tolidune blue or methylene blue).

a. Since this type of dye is binding to an acidic (-)

group, it is termed a basic dye (+) and the

substance stained is termed basophilic (base-

loving) b. Other cellular components that are basophilic: (dueto the phosphate groups in their nucleic acids)

include DNA, RNA, nuclei, nucleoli, and

ribosomes b. A commonly used combination of dyes is

hematoxylin and eosin (H&E).

i. The hematoxylin (+ dye) can be

considered as a stain for nucleic acids ii. The eosin (- dye) for proteins

c. Trypan blue and India ink are taken up and

stored by macrophages;form colloidal suspensions in

water. Since these large particulates will not diffuse into cells,they will be cleared by the phagocytic activity of macrophages, andare thus excellent markers for members of the mononuclear

phagocyte system (MPS) i. Euchromatin = transcriptionally active; open &

unfurled; diluted dye

ii. Heterochromatin = not active; compact; darker

dyed. Lipid colorants such as Sudan black and Oil Red O

are soluble in lipid and are used to demonstrate fat in

tissues if the lipid has not been extracted

e. Periodic acid-Schiff (PAS) i. This technique is widely used for the

demonstration of certain carbohydrates by first converting side groups to

aldehydes (with periodic acid) and then identifying these aldehyde groups using theSchiff stain.

f. Silver impregnation methods are employed todemonstrate the Golgi apparatus, reticular

fibers, neurofibrils g. Connective tissue stains: the Masson procedure

i. Collagen fibers of connective tissue are stained either1. Blue (aniline blue), or

2. Green (fast green)ii. Cytoplasm, in contrast, will be red-orange to red-lilac.

h. Immunohistochemistry (IHC) uses the principles ofimmunology to locate and identify specific antigens with labeled antibody

i. Bromodeoxyuridine detection: for analyzing cell proliferation; the

thymidine analog 5-bromodeoxyuridine (BrdU) – which is incorporated into nuclear

DNA during S-phase before mitosis - is localized in tissue sections with an antibody andreveals cells that have recently undergone cell division

Hematoxylin = basophilic nuclei

Eosin = acidophilic myofibrils

Periodic acid Schiff (PASmucins within goblet cells

basement membrane along basal surface of epithe

SILVER STAINGolgi Apparatus



Lecture #2 Connective Tissue

1. Know and be able to identify the types of connective tissues (CTs), and their

functional properties.a. Classification of a connective tissue is based on its predominant extracellular component

b. Each collagen fibril is composed of numerous (rod-like) collagen molecules that are linearly arrangedwith respect to one another in a precisely staggered manner

c. Dense Connective Tissue

i. Dense regular connective tissue:

1. Tightly packed collagen fibers arranged in a parallel fashion.2. E.g. tendons (which connect muscle to bone), and ligaments

(which connect bone to bone).

3. These structures derive their strength from the regular,

longitudinal arrangement of the bundles of collagen fibril

4.

Elongated nuclei

18

Protein Packaged and Modified By

Addition of Sugar Moieties Pigment of aging

Skin cells (melanin

Melanin is polarize

protects from UV w

‘cap’ on apical side

nucleus (where UV

always pointed)

DENSE REGULAR CONNECTIVE TISSUE (TENDON)

Collagen (fibers/

fibrils)

Fibroblast (nuclei)



ii. Dense irregular connective tissue:

1. Densely packed collagen fibers2. However these fibers course irregularly through the tissue but

still impart strength to the tissues in which they are found

3.

e.g., the dermis of skin

d. Loose/ Areolar Connective Tissuei. Loose CT is the most common type

of CT

ii. All loose CT is irregular

1. Loose organization of fibers ina large amount of ground

substance (where hyaluronic

acid & proteoglycans are

localized)

DENSE IRREGULAR CONNECTIVE TISSUE (skin)

Nerve

Nerve

Collagen

Fibroblast (nuclei)

FIBROBLASTS: major cell of both these types of CTs (and also in other CTs).

Synthesize extracellular matrix components (e.g., collagens, elastin, proteoglycan

Surfboard nuclei (thin & long from side; wide and flat from top)

Collagen

Fibroblast(nuclei)

TEM of Collagen fibrils/fibers in longitudinal

(banded) and X-section (round) profiles.TEM OF FIBROBLASTS AND COLLAGEN FIBRILS/FIBERS

Fibroblast nucleus (1) and cytoplasm (2)

Bundles of collagen fibrils (3)

Ground Substance (4)

LOOSE / AREOLAR CONNECTIVE TISSUE

Collagefibrils

Fibroblast (nuclei)

Blood vessel



iii. Holds organs in place & attaches epithelial tissues to itself and other

underlying tissues

iv. Surrounds blood vessels & nervesv. Relatively poor in extracellular fibers, but rich in immigrant cells

(such as macrophages, plasma cells, mast cells, leukocytes)

e. Elastic connective tissuei. Contain a large proportion of extracellular matrix as rubber-like

elastin which is a macromolecule complex able to undergo stretching

and subsequently return to its original length; occurs in two forms:

ii. Lamellar1. Elastin is predominantly in form of lamellae (sheets/layers) in

large blood vessels (e.g. elastic arteries, rectifying the pulsatile

flow of blood coming from the heart)

iii. Fibrillar1. Elastin is present in form of branched fibers/fibrils in

nonvascular tissue (e.g. skin)a. In fibrils, elastin is complexed with a micofibrillar

component (fibrillin) which forms a scaffolding for

deposition of elastin & polymerizes it

f. Basement membranes/ Basal Laminae

i. Generally (but not always) associated with the basal surface of

epithelial tissues and are complex structures with a number ofcomponents

2. Know and be able to identify the cellular constituents and functions of the different

types of CTs.a. Cellular Componentsi. Indigenous cells: arise within the CT itself: (e.g., Mesenchymal cells,

Fibroblasts, Adipocytes (fat cells)

1. Adipose Tissue

a. White

i. Fat (lipid) storage

ELASTIC CONNECTIVE TISSUE (Lamellar) (giveselasticity to blood vessel)

ELASTIC CONNECTIVE TISSUE (FIBRILS)(gives elasticity to tissues such as skin)

Branched

Elastic Fibrils



ii. Major cell type is adipocytes (large, fat

storage cells)

b. Brown

i. Heat productionii. Numerous mitochondria (colored

cytochromes) and large number of blood

vesselsiii. Generally smaller cells than white fat in order

for mitochondria (which is between) to access

fatty droplet

iv. Cells have a large number of lipid droplets ofvarious sizes

v. Small droplets surrounded by aqueousenvironment and mitochondria; nucleus isusually centrally placed; also much more

vascular than white fat and transfers heat to

the blood in surrounding capillaries1. Versus white droplet which is large and

surrounded by aqueous environment

White Adipose Tissue

Adipocyte (nucleus)

ADIPOSE TISSUE

Dense irreg. C.T.

Ducts and

Glands Loose C.T.

Fat droplets

Brown adipose tissue

This photomicrograph shows

brown adipose tissue whose

cells (arrow) have numerous

lipid vacuoles. Also shown are

a small blood vessel(BV), and

white adipose tissue (along the

top).



ii. Immigrant cells: originate from hematopoietic stem cells in bonemarrow, circulate in the blood, and then move into connective tissue where they undergo

differentiation and perform their functions; E.g. Macrophages (derived from monocytes),Lymphocytes, Plasma Cells (derived from B- Lymphocytes) and Mast cells

1. Macrophagesa. Large cells that phagocytose material such as:

i. Cellular debris (from apoptosis)ii. Foreign bodies

iii. Air-born particles b. Also present antigens to lymphocytes & produce cytokines

c. Can fuse with one another, forming large,

multinuclear, giant cells; or become osteoclasts and

function in bone resorptiond. Large eukromatic nuclei

e. Can have multi-nucleated cells lots of transcription more phagocytic enzymes produced

2. Plasma Cellsa. B lymphocytes that have left circulation

b. Initiate the synthesis of immunoglobulins

c. Characterized by:

i. Oval shape, with one side forming an

“apron” of basophilic cytoplasm, and the

other side having a nucleus which is eccentric and

whose heterochromatin has a distinctive cartwheel or clock-face arrangement.

ii. Basophilic staining of the cytoplasm reflectslayers of ER (where the IG proteins are being

synthesized)

Nuclei Phagosomes

Distinguishing characteristics are large size, large irregularly shaped nuclei,and cytoplasmic vacuoles (phagosomes) that contain phagocytosed material.



iii. Between basophilic cytoplasm and the nucleus

is a clear area, indicative of the Golgi (where

glycosylation & further processing of IGs occurs)

3. Mast cells

a. Participate in allergic reactions b. Characteristics:

i. Presence of numerous small cytoplasmic

granules (generally blue)

ii. Dense central nucleusc. Medical implications: mast cell granules contain

heparin (an anticoagulant) & histamine (a vasodilator

that renders venules & capillaries leaky- releasing blood components and cells into surrounding CT)

4. Polymorphonuclear leukocytes: blood cells that (upon

stimulation) migrate from blood stream to CT

a. Includes neutrophils & eosinophils; both have bilobed/

multilobed nuclei & each has its own type of specific

granule

i. Granule of neutrophils are light pink; ofeosinophils are bright red

b. Neutraphils (micophages)

i. Most abundant type of WBCii. First cell into connective tissue for

inflammatory response; recruited by cytokines

iii. Phagocytose bacteria, resulting in the

formation of intracellular vacuoles(phagosomes)

iv. Connective tissue is like the field where the

battle takes place

v. Exocytose genome after an attack whichallows them to use their „sticky‟ DNA as a net

for parasites

vi. Results in lobbed nucleus

Plasma Cells



vii. The granules stain the basic dye and the

acid dye, so you have both and they cancel

either out resulting in a lighter dyeviii. Very toxic when they degranulate

c. Eosinophils are recruited if parasites are too big for

neutraphilsi. Prevalent in asthma

1. Have been co-opted because humans don‟t have parasitic infections as much anymore; end upattacking themselves

d. Medical implications:

i. Neutrophils

1. The subsequent killing involvesreleasing (from their granules) into the

phagosome antibacterial substances2. e.g., superoxide anions and hydrogen peroxide,

lysozyme (which cleaves a cell wall component ofcertain bacteria), and lactoferrin (that binds iron whichis a crucial component of bacterial nutrition)

ii. Eosinophils

1. Have cytotoxic effects on the parasite(through the release of peroxidase and

other toxic substances).

2. Involved in mechanisms associated withallergies

3. e.g., modulating inflamation (by neutralizing histmineand by phagocytosing antigen-antibody complexes

b. Extracellular Matric Components

i. Fibrous constituents: Collagen fibers, Elastic fibers, Reticular

fibers

1. Reticular Connective Tissues a. Forms a supportive, flexible network within/around

organs & structures that are subject to changes in form

or volume (e.g. spleen, sinusoids, lymph nodes) b. Characterized by extremely thin fibers (reticular

fibers) which consist of collagen type III (a fibrillar

collagen) complexed with a large amount ofcarbohydrate

Eosinophil

Eosinophil



c. Not visible in H&E preparations but stained black in silver salts

ii. Ground substance (amorphous): non-fibrillar material betweencells

1. Binds tissue components together, mediates metabolite

exchange, lubricates joints, and provides reversiblecompressibility

2. Consists of: Proteoglycans, Glycosaminoglycans and

Glycoproteinsa. Proteoglycans are linear polymers of disaccharides [glycosaminoglycans

(GAGs)], covalently linked to a protein corei. Highly negatively charged (sulfate groups on the sugar

residues)

ii. Can be hydrophilic (attract and bind H2O, accounting for the porous nature of CT that allows diffusion of metabolites and

waste products to traverse to and from blood vessels)iii. Proteoglycans can range in size from quite small (e.g., the

heparan sulfate proteoglycans) to extremely large complexes(in cartilage)

b. Glycoproteins are multifuctional proteins that have attachedoligosaccharides

i. Are capable of binding cells to matrix molecules, both foradhesion and cell-matrix signaling (e.g. fibronectin andlaminin)

3. Know the extracellular (matrix) components of the different types of CTs, and their

properties and functions.a. The fibrillar collagens (long rod-like)

i. Major structural component of many connective tissues

ii. Comprise ~30% of body‟s protein

iii. Different types:

1. Type I: most ubiquitous typea. Polymerized in different ways to make different

outcomes

b. E.g. bone vs cornea (polymerized so light can passthrough)

2. Type II: the major collagen of cartilage matrix

3. Type III: rich in blood vessels and reticular CT

Sinusoids

Retic ular

fibers



iv. Structure: Each collagen is comprised of three chains found into a

triple-helical structure1. Every 3rd residue is glycine (necessary for triple-helix formation)2. Enzymatic hydroxylation of proline to hydroxyproline stabilizes TH

3. Hydroxylation of lysine is involved in crosslinking

v. Synthesis: Collagen molecules are synthesized as soluble precursors (procollagens) that

have short, non-collagenous peptides (termed propeptides) at both the NH2 and COOHterminal ends

1. Proteolytic removal of these propeptides – by enzymestermed procollagen peptidases – is necessary for the collagen

molecules to associate with one another in a fibrillararrangement

a. These caps prevent polymerization until procollagen peptidase cleavesthem; act as a failsafe so collagen synthesis does not occur in fibroblasts

b. Mutation in a procollagen peptidase leads to skin

loss 2. Once the molecules are assembled in the staggered arrangement, the amino groups

on some of the lysines and hydroxylysines are enzymatically converted to reactive

aldehydes – by the enzyme lysyl oxidase – that then go on tospontaneously form the intra- and inter- molecular crosslinks

4. Know the pathological conditions discussed.a. Progressive systemic sclerosis:

i. Results from an over-accumulation of collagen (fibrosis)

ii. Results in hardening and functional impairment that can affect a

number of different organs (e.g., skin, the digestive tract and muscle)

b. Keloidsi. Results from abnormal accumulations of collagen.

ii. Are localized conditions that result in swellings that can be

disfiguringiii. Occur most often in individuals of black African descent, and be clinically difficult to

correct as their removal is frequently followed by recurrence.

iv. A similar, less severe condition of excessive scar formation is the

hypertrophic scar.

c. Scurvyi. Deficiency in Vitamin C (ascorbic acid) results in defective collagen

synthesis

ii. Vitamin C is required for activity of prolyl hydroxylase & lysyl

hydroxylase (enzymes responsible for hydroxylation of proline & lysine) 1. These posttranslational modifications stabilize the helical

structure & form the crosslinks that stabilize fibrils

iii. Defective fibrilogenesis causes a general loss of connective tissuefunction, including fragile capillaries, resulting in abnormal bleeding and loss of teeth due to degeneration of the periodontal

ligamentiv. Can result in perifolicular hemorrhage on legs

d. Ehlers-Danlos syndromei. Inherited CT disorders caused by variety of defects in CT synthesis

ii. Severity can range from mild to life-threatening



iii. Examples:

1. Aortic and or intestinal rupture (caused by faulty

transcription or translation of collagen type III)2. Hyperelastic skin

3. Eye fragility

4.

Progressive curvature of the spine (scoliosis; caused by faultylysine hydroxylation)5. Hyperextensible joints & dislocations (luxation); caused by

decreased procollagen peptidase activity iv. Type VII: decreased procollagen peptidase activity

1. Possible defect in triple helix formation

e. Cutis Laxa

i. Involves a number of gene involved with elastin

ii. Clinical features:1. Skin that is loose, hanging, wrinkled, and lacking in elasticity;

premature aging appearance

2.

Joints may be Hyperextensible3. Can also affect certain internal organs

f. Marfan Syndrome

i. Mutations of the fibrillin gene

ii. Can affects a number of organ systemsiii. Clinical features:

1. Skeletal abnormalities: greater than normal height; long slender

limbs; scoliosis; Hyperextensible joints2. Cardiovascular system: dilated aorta or an aortic aneurysm (

fatal aortic dissection)

Lectures #3 & #4 Skeletal Tissues: Cartilage and Bone (I and II) 1. The morphological characteristics of the different types/forms of cartilage and bone

a. In the mature, adult skeleton most of the bones are in the form of “long bones”i. Consist of a shaft comprised of bone tissue whose ECM has organic and mineral components

ii. Cartilage covering both ends (forming the articular surface)

iii. Bone has blood vessels, but adult cartilage is avascular

iv. Both collagen & the calcium phosphate salts (hydroxy apetite) to make the

bone strong

b. Hyaline Cartilage

i. Two components: 1. Type II cartilage (collagen fibrils)

a. Fibril associated collagen (the darker molecules with a kink)

b. Have a collagen domain and also a bending domain; caninteract with each other and other type II collagens

c. Stabilize matrix through cross-links

d. Only on the surface of the molecule

e. Arthritis may be due to degradation of cross-linked regions



2. Cartilage proteoglycan (give it the resiliency)

a. A protein core with glycosaminoglycan (GAG) side chains that

are predominantly chondroitin sulfate b. Is also termed aggrecan for the ability of numerous of these proteoglycans to bind to a

hyaluronic acid molecule

c. Highly hydrated, and the side chains, due to their negative

charge, repel one another d. Are attached through their core protein to linear hyaluronic acid

molecule and form extremely large suppramolecular complexes ii. The cells (termed chondrocytes) are enclosed within this matrix in regions

termed lacunae (which means lake)

iii. Covers the articular surfaces; found in respiratory tree, nose and transientlyduring endochondral bone formation

iv. Resilient (shock absorber) and has a smooth, slippery surface, especially at

joints in conjunction with synovial fluid

c. Cartilage growth

i. INTERSITIAL 1. Isogenic clusters of chondrocytes reflect coordinate cell division 2. After the chondrocytes divide, they deposit matrix between them and

gradually move apart

Hyaline Cartilage (light micrograph)

Cartilagematrix

Chondrocytes inlacunae

In mature hyaline cartilage, chondrocytes are largely present as

individuals with a lot of matrix inbetween

RAPIDLY GROWING CARTILAGE undergoing interstitial growth (isogenic clusters ofchondrocytes) and appositional growth (perichondrial cells becoming chondrocytes).

Interstitial growth;Isogenic clusters of

chondrocytes

Appositionalgrowth

LIGHT MICROGRAPH (low power) OF HYALINE CARTILAGE WITH THE SURROUNDING(FIBROBLASTIC) PERICHONDRIUM

Perichondr

Chondrocytes in lucanae



ii. APPOSITIONAL 1. Occurs at the surface of the cartilage 2. Involves the perichondrium

a. Fibrous CT over the surface of most cartilages (except articulat) which attaches the

cartilage to adjacent tissue3. Perichondrial cells (which are fibro-blast like) undergo a

progressive transformation to chondrocytes

d. Specialized types of cartilage

i. Intervertebral disc

1. Outer ring of fibrocartilage (the annulus fibrosis), and an inner

gelatinous component (the nucleus pulposus) 2. Fibrocartilage

a. Has features of both a dense connective tissue (type I collagen

fibers), and cartilage matrix (type II collagen fibrils and

cartilage proteoglycan)

3. Elastic cartilage

a. Has cartilage matrix components and also networks of elasticfibers

b. Provides flexibility; can withstand repeated bending

e. Bone Tissue

i. Extracellular matrix of organic & inorganic components 1. Organic (30%) is type I collagen (large diameter fibrils)

2. Inorganic (65%) is calcium- phosphate in a crystalline form

CHONDROCYTESIN LUCANAE

ELASTIC FIBERS (withincartilage matrix)



(hydroxyapatite)

ii. Osteoid: newly synthesized & uncalcified bone; undergoes mineralization

1. Unlike type II, these collagen fibers are long and banded due to the

precise arrangement iii. Restoration/reconstruction of bone: can be achieved by implanting decalcified

bone matrix 1. bone morphogenic proteins (BMPs) 2. This matrix "induces" cells within the responding tissue to undergo a

complete sequence of endochondral bone formation

2. The molecular composition and the characteristics of bone and cartilage matrixa.

3. The cell types found in cartilage and bone and their characteristics.a. Bone cells

i. Osteoblasts (OB)

1. Mesenchymal origin 2. Single layer of cells over the surfaces where the new bone is being

deposited3. Adopt a cuboidal shape and have an “epithelioid” (epithelial-like)

arrangement 4. Responsible for the synthesis and secretion of the unmineralized matrix

of bone (called osteoid)

T.E.M. of a region of newly forming bone



ii. Osteocytes (O) are the mature cells of bone tissue

1. Derived from osteoblasts that have become buried within the bone

matrix

2. Reside within lacunae of the bone matrix 3. Canaliculi: small channels that extend from one osteocyte to another;

they all get the same information

a. Osteocyte cell processes grow into the canaliculi and form gap junctions

iii. Osteoclasts are responsible for bone removal/resorption

1. Monocyte derivatives; monocytes fuse making the osteoclasts multi-

nucleated cells 2. During bone development they are found along the surface of spicules

(pieces) of bone at sites where bone resorption is occurring.

3. Make acid & MMPs to break down the collagen 4. Make a tight connection with the piece of bone where everything will

be done

5. Typically osteoclasts will be making bone in one area while osteoblasts break down bone in the other area

4. The types of bone development and their salient featuresa.

5. The steps involved in the remodeling of mature bone during growth and during fracture

healing.a.

6. The pathological conditions of cartilage and bone that are discusseda. Arthritis: irreversible destruction of cartilage matrix (& sometimes adjacent bone)

through production of matrix metalloproteinases and enzymes that degrade cartilage

LIGHT MICROGRAPH OF NEWLY FORMING BONE

Bone with osteocytes

Osteoblasts and osteoid

Mesenchymal cells and blood vessels



proteoglycans (e.g. MMP1 cleaves certain fibrillar collagens, including Type I)

i. Osteoarthritis

1. Acquired from “wear & tear”and/or injury

2. Joint pain, swelling, stiffness

3.

Diagnosed radiographically by bony changes (joint spacenarrowing)

4. Osteoclasts are breaking down

the bone; all the cartilage isgone and now even the bone is

being broken down

ii. Rheumatoid arthritis

1. System autoimmune, inflammatory disease 2. Chronic condition characterized by both joint inflammation and

destruction of bone and articular cartilage 3. The synovium is thought to play a major role in the destructive processes whereas in OA its role

is minor

a. Synovial hypertrophy (enlargement) is due to the influx of

monocytes and lymphocytes from the circulation, and from thelocal proliferation of fibroblasts

b. In RA, the initial, and main cellular sources of the degradative enzymes are thought

to be the synovial lining cells and macrophages c. In O.A. cartilage breakdown initially occurs at the articular surface itself

b. Herniated disc

i. Rupture of the annulus fibrosus (the fibrocartilage), which results in expulsion

of the gelatinous nucleus pulposus and a concomitant flattening of the diskwhich can compress the nerve

ii. Fusing the vertebrae can help alleviate the pain

c. Osteogenesis Imperfecta i. Vast majority of individuals with OI have mutations in one of the chains of

type I collagen.

ii. The mild forms are usually caused by mutations that result in a reducedamount of normal type I collagen.

iii. The more severe forms result from mutations that produce structural defects in

the collagen molecule – the most common being disruption of the helical

structure by substitution of a glycine residue – every third residue of which

is required for formation of the collagen triple helix

d. Osteoporosis

i. Loss of calcium from the bone due to excessive production of parathyroid

hormone (hyperparathyroidism) ii. Increased osteoclastic activity which causes an imbalance in skeletal

turnover, so that bone resorption exceeds bone formation iii. Can be prevalent in post-menopausal women

e. Osteopetrosis i. A genetic disorder that results from defective osteoclasts and is characterized

by dense, heavy bones.

ii. As bone resorption is defective this results in their overgrowth, thickening,

Histological Section showing cartilage destruction of a knee

due to osteoarthritis



and hardening.

iii. Also, the bone marrow cavities can be obliterated, depressing blood cell formation

Lectures #5 & #6 Epithelial Cells II – Tissues 1. To learn to classify types of epithelia and to be able to cite examples of where they are

found in the body.a.

2. To recognize structural specializations present within epithelia:a. morphologically

b. functionallyc. biochemically

3. To understand how defects in epithelial specializations can affect epithelial integrity and

cause diseasea.

histology exam 2 review.1

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