Mammalian histology

ZY- 332 (Paper II)
Mammalian Histology
Total lectures: 48

1 Introduction                                        1
1.1 Definition and scope
2 Tissues:                                                6
2.1 Definitions and review of tissues (location, structure and functions): epithelial,
connective, nervous and muscular
3 Histological study of following organs
3.1 Skin (V.S.)                                              3
3.2 Tooth (V.S.)                                              2
3.3 Tongue(C.S.) with reference to mucosa papillae and taste buds                          2
3.4 Alimentary canal: Basic histological organization with reference to: Oesophagus
(T.S.), stomach (T.S.), duodenum (T.S.) Ileum (T.S.) and rectum (T.S.)                       8
3.5 Glands associated with digestive system:                                                              6
Salivary glands – parotid (C.S.), submandibular (C.S.) sublingual (C.S.), liver
(C.S.) and pancreas (C.S.) including both exocrine and endocrine components
3.6 Respiratory organs: Trachea (T.S.) and lung (C.S.)                                               2
3.7 Blood vessels: Artery (T.S.), vein (T.S.) and capillaries (T.S.)                             2
3.8 Kidney (L.S.), Structure of nephron and juxtaglomerular complex                     4
3.9 Reproductive organs:                                                                                            6
a) Testis (T.S.) with reference to Seminiferous Tubules and cells of Leydig
b) Ovary (C.S.) - primary, secondary and matured (Graffian) follicle, corpus
luteum and corpus albicans
4 Histology of endocrine glands :                                                                                 6
4.1 Pituitary gland
4.2 Thyroid gland
4.3 Adrenal gland





 
Epithelial tissue: good one see this...

epithelial tissue:
TISSUE TYPES / EPITHELIAL TISSUES
Tissue = collection of cells + associated intercellular materials specialized for a
particular function.
There are 4 basic tissues in the body:

1. Epithelium = characterized by a virtual lack of intercellular substances between
adjacent cells; forms skin and lines interior surfaces of body (gut, peritoneum, etc.);
epithelial cells can also be arranged in masses with a secretory function.
2. Connective Tissue = cells usually are widely separated by an abundant intercellular
matrix; includes blood, cartilage, bone, tendons, adipose (fat); 2 Major Divisions =
CT Proper andCT Supportive.
3. Muscle Tissue = elongate cells separated by fine, vascular (many blood vessels and
capillaries) connective tissue. Three types occur: skeletal, cardiac, and smooth -
each is specialized for particular functions.
4. Nervous Tissue = cells are grouped into masses or bundles, many with long
processes; specialized for sensory reception and transmission of impulse functions.

EPITHELIAL TISSUES - General Features

1) Closely packed cellular arrangement
2) Cover or line surfaces (interior or exterior)
3) Form ducts and secretory portions of glands (= parenchyma), connective tissue
forms glandular support (= stroma)

a) Exocrine Glands (have ducts) - secrete to some surface
b) Endocrine Glands (lack ducts) - secrete to bloodstream by diffusion
- Both types develop in the same manner, as outgrowths of epithelial membranes

4) All cells of epithelia are joined by cementing substances + mechanical processes

a) Neutral Mucopolysaccharides (glycosaminoglycans) = make up cementing
substance
- PAS stain specific for carbohydrate groups on GAGs, results in reddish-purple color.
b) Interdigitations exist between cells (mechanical cementing)

5) All epithelia are anchored to underlying tissues by a basement membrane
composed of an upper basal lamina and a lower layer of reticular fibers (a CT fiber
type).
6) Avascular - no blood vessels in epithelial tissues, cells derive nutrients by diffusion
from blood vessels in surrounding CT

EPITHELIAL FUNCTIONS

1. Protective = prevents desiccation (skin), abrasion
2. Absorption = digestive and excretory tracts
3) Secretory = oils, water, enzymes, hormones, salts (in some animals)
4) Excretion = removal of harmful wastes (e.g., Loop of Henle, Chloride cells in fish
gills)

EPITHELIAL TISSUE CLASSIFICATION

1) Cell Shape

a) flat = squamous
b) square = cuboidal
c) elongate = columnar
2) Layering or Stratification

a) Simple - 1 cell-layer thick
b) Stratified = > 2 cell-layers thick

I. Simple Epithelia Types (All 1 layer thick)

1) Simple Squamous = flat or spindle-shaped in cross-section. In surface view gives
appearance of "tiled floor" so it is also named "pavement epithelium." Found in thin
Loop of Henle (kidney medulla), endothelial vessel walls, lining of body cavity
(mesothelium), pulmonary alveoli, etc.
2) Simple Cuboidal = square cells found in covering of ovaries, convoluted and
collecting tubules in kidney, ducts of most glands.
3) Simple Columnar = column-shaped cells found in absorptive/secretory lining of
digestive tract, larger ducts, lining of uterine cervix, etc. Many have microvilli (= brush
border in intestinal lining) on apical surface, some have cilia (e.g., fallopian
tubes).
Goblet Cells = mucus-secreting cells within simple secretory epithelium, mucus aids
passage of contents down digestive tract, out of respiratory tract.
II. Pseudostratified Columnar Epithelium (PSC) = all cells are in contact with
basement membrane (EM necessary to distinguish this), but not all cells reach
epithelial surface, and nuclei reside at more than 1 level. This gives the appearance of
>1 layer, when in fact only one layer is present. PSC occurs lining larger excretory
ducts, larger ducts of male reproductive system, and respiratory tract. PSC lining
respiratory tract has numerous goblet cells and is ciliated.
III. Stratified Epithelium (classify by the outer layer of cells)

1) Stratified Squamous = thick membrane, only the outer layer(s) is squamous. Basal
layers often demonstrate considerable irregularity. In Amniotes (reptiles, birds,
mammals) this epithelium usually becomes keratinized to decrease water loss and
protect from abrasion (skin).
- Keratinized = surface cells die and transform into soft scales of keratin, but remain
strongly adherent to live cells below.
- Nonkeratinized = fairly rare, lines mouth, esophagus, and vagina.
2) Stratified Cuboidal/Columnar = usually only two layers thick, rare. Cuboidal
present only in the ducts of sweat glands in humans, skin of aquatic vertebrates.
Columnar found in parts of male urethra, larger excretory ducts, and conjunctiva of
eye.
3) Transitional Epithelium = composed of several layers of cells, thickness influenced
(as is cell shape) by the state of the organs which it lines. Present only in
distensible surfaces of excretory tract (bladder, ureters, pelvis of kidney).
- In contracted state, it is many layers thick. The basal layer is cuboidal to columnar,
intermediates layers are polyhedral, surface layer with large rounded cells.
- In distended state, upper cells become flat and the entire epithelium appears as a thin
(2-5 layers thick) stratified squamous epithelium.
- Rounded surface cells may be binucleate.

CELL ADHESION IN EPITHELIAL MEMBRANES
- Cell Junctions are of three general types:
1) Occluding Junctions (Tight Junctions) = cell membranes of adjacent cells are fused
by interlocking ridges, probably composed of integral membrane proteins,
providing an impermeable seal between cells. This type of junction is exclusive to
epithelial tissues.
2) Adhering Junctions = cell junctions acting to mechanically hold cells together.
3) Gap Junctions = cytoplasmic interconnections between cells allowing cell-to-cell
communication.

 EPITHELIAL TISSUES (cont.)
Cell Borders:

1. Cuticular = non-living proteinaceous secretion covering cellular surface (not
present in vertebrates, present in exoskeletons of invertebrates)
2. Striated (Brush) Border = composed of microvilli (small, fingerlike projections of
apical cell surface), acts to increase surface area for absorption. Present in tissues with
absorption as primary function (e.g., intestinal and kidney tubule epithelium).
3. Ciliated = fine hair-like processes of free apical surface, motile. Function to transport
material in one direction along the epithelial membrane surface; also may serve
receptor function (inner ear and retina). Found in respiratory and reproductive
tracts.
4. Stereociliated = long slender, sometimes branching processes from apical cell surface.
Not true cilia - structurally different and non-motile. Found only in ductus
epididymis and vas deferens of male reproductive tract and hair cells of inner ear. May be both
absorptive and secretory in epididymis, sensory in hair cells.

SPECIALIZED EPITHELIUM = Neuroepithelium

1. Olfactory Epithelium - SEE HANDOUT
2. Taste Bud = similar to olfactory epithelium - same 3 cell types, arranged in barrel-
shaped clump. Taste Receptor Cells (instead of olfactory cells) have short microvilli
on apical end, basal end synapses with sensory fibers of facial and glossopharyngeal
nerves. Acts as a chemoreceptor - stimulated by dissolved substances.

EPITHELIAL GLANDS

Two types:
1) Exocrine = secretes through ducts to epithelial surface.
2) Endocrine = no ducts, secretes into bloodstream
- Both originate as outgrowths of epithelial membranes, except for goblet cells =
single-celled exocrine gland.

EXOCRINE GLANDS - have secretory units and duct(s).

- Secretory Unit = group of secretory epithelial cells enclosing a lumen
- Duct = epithelial-lined tube from secretory unit to surface
- Usually surrounded by CT capsule with septa extending into interior giving lobular appearance, lobes subdivided into lobules.

CRITERIA USED FOR CLASSIFICATION OF EXOCRINE GLANDS - SEE HANDOUT
ENDOCRINE GLANDS = no duct system, secretion diffuses from secretory cells into
blood vessels in surrounding CT. Secretory cells are intimately grouped around
wide capillary-like vessels. Secretions = Hormones (usually).

- Capsule = thin covering of CT enclosing the gland as a whole (characteristic of most
endocrine glands)
- Trabeculae (Septa) = projections or extensions of exterior capsule into interior of
gland, often divides the gland into lobes
- Supporting tissue within gland is sparse and associated with capillaries into which
secretory cells release hormones.
Two Histological Types of Endocrine Glands:

1) Cord-and-Clump Type = by far the most common; cells are arranged in
interconnecting cords and clumps between dilated blood capillaries; store hormone
intracellularly.
2) Follicle Type = thyroid glands; a group of cells forms a vesicle enclosing a central
cavity in which hormone is stored. Hormone is released as needed by passing back
through secretory cells and into blood capillaries lying between follicles.
- Some glands in the body are composite = having both endocrine and exocrine
functions.
EXAMPLES:

1) Liver - produces and secretes bile into duct system; releases glucose from glycogen
stores directly into blood.
2) Pancreas - secretes serous solution with digestive enzymes; releases insulin and
glucagon (involved in carbohydrate metabolism) into bloodstream

MYOEPITHELIAL CELLS (BASKET CELLS)
-

Present in some exocrine glands
- Located between secretory epithelial cells and basal lamina
- Appear as small dark nuclei at periphery of tubule or acinus, with little cytoplasm (cytoplasm extends as long, thin arms to encircle secretory endpiece)
- Contain microfilaments and are contractile
- Help eject secretion from gland

Connective tissue: good one see this

Connective tissue : good two see this

CONNECTIVE TISSUE
- 2 general types: CT Proper and CT Supportive.
- CT Proper classified on the basis of intercellular material (types, arrangement and
density of fibers). Intercellular material contains a variety of fibers embedded in a
semi-fluid ground substance (amorphous intercellular substance). Fibers + ground substance = Matrix.

1) Fibers (protein composition)

a) Collagen Fibers = actually a family of > 20 related proteins
-          Most abundant protein in the body (30% of dry weight)
-          4 Categories according to structure/function:
                                                                          i.      Form long fibrils
                                                                        ii.      Fibril-associated collagens (bind collagen fibers to extracellular matrix)
                                                                      iii.      Form anchoring fibrils (e.g., attach basal lamina to underlying reticular fiber layer)
                                                                      iv.      Form networks (e.g., basal lamina)
-          1-20 micrometers in diameter, indeterminate length, unbranched
-          fibers are wavy in tissues, provides some capacity for stretch even though the
actual fibers are relatively inelastic
-          Divisions of Collagen Fiber: Fiber ® Fibril ® Microfibril = Tropocollagen
Molecule
-          Tropocollagen molecule composed of 3 polypeptide chains forming a right-
handed superhelix
-          Tropocollagen molecules staggered giving periodic striations to fibril (only
visible under EM). Periodicity of striations = 64 nm (approx. 25% of length of
tropocollagen molecule). 
b) Elastic Fibers = thinner than collagen fibers (1-4 micrometers), threadlike and
highly branched, great elasticity

- can form sheets (25 micrometers in diameter) in elastic ligaments
- stain poorly in H&E, can stain with orcein or resorcin-fuchsin
- homogenous rather than fibrillar ultrastructure (glycoprotein microfibrils form
tube enclosing amorphous elastin) elastin glycoprotein microfibrils
c) Reticular Fibers = delicate collagen fibers (composed of tropocollagen) 0.5-1
micrometers in diameter

- lack staining properties of collagen so don't stain with H&E, special stain = silver
impregnation (argyrophilic fibers)
- branch to form delicate network
- non-elastic, found in tissues with little tension (e.g., glands, lymph nodes); also
found in other tissues providing support for capillaries, nerves and muscle cells

2. Ground Substance (Intercellular Material)

- transparent, colorless, homogenous, semi-fluid
- functions as a medium through which nutrients and waste products can diffuse
between capillaries and cells
- composed of glycosaminoglycans (GAGs) and glycoproteins. GAGs =
polysaccharides usually containing two types of alternating monosaccharide units, at
least one of which has N- containing prosthetic group Repeating unit of
Hyaluronic Acid (a common type of GAG)

CONNECTIVE TISSUE CELLS OF CT PROPER
1) Undifferentiated Mesenchymal Cells = embryonic, some persist in adult as
precursors to other CT cells; stellate with elongated nuclei and coarse chromatin
2) Fibroblasts = responsible for production of fibers and ground substance

- stellate with wide cytoplasmic processes (difficult to see) when active, in side view
appear spindle-shaped
- basophilic cytoplasm; prominent elongate or oval nucleus with prominent nucleoli
and fine granular chromatin
- old inactive fibroblasts = fibrocytes, have less basophilic cytoplasm and condensed
nucleus

3) Fat Cells = found in areolar (loose) and adipose CT - not capable of mitotic
division as adult cell 2 Types:
a) White Fat = most common, serves as storage tissue for lipid (energy reserve)

- during development accumulates lipid droplets which coalesce to form a large
central droplet (unilocular); cell therefore takes on "signet-ring" appearance -
cytoplasm = ring, flattened nucleus on periphery = signet

b) Brown Fat = occurs only in mammals; relatively scarce, found in anterior regions of
body (e.g., between scapulas) in neonates, hibernators and cold-adapted mammals.

- functions in thermogenesis = heat production
- histologically: contains multiple lipid droplets (multilocular), central nucleus, high
numbers of mitochondria; brown color from high concentration of cytochrome in
mitochondria

4) Macrophages = phagocytic cells forming from monocyte (=histiocyte)

- almost as numerous as fibroblasts in areolar CT
- may be attached to collagen fibers (fixed) or loose within matrix (free)
- when stimulated, fixed macrophages detach and migrate to sites of bacterial invasion
or tissue injury - nucleus stains darkly and is indented; cytoplasm often round, but can be variable in
shape

5) Mast Cells = large, rather round cells with basophilic granules in cytoplasm
and central pale nucleus; similar to basophil, but may arise from several sources
not just bone marrow

- usually found associated with blood vessels
- granules contain heparin and histamine; stimulation by antigen or tissue damage results in degranulation and an allergic response; heparin = clearing of plasma lipids, blood anticoagulant; histamine = vasodilation, increased permeability of venules, mediates inflammation

6) Chromophores = (e.g., Melanoblast/cyte --- brown/black)

- Melanoblasts/cytes derived from neural crest cells embryonically; have long
cytoplasmic processes
- when stimulated (UV light) produce pigment (melanin), leads to suntan
- found under skin epidermis

7) Plasma Cells = rare in most CT, more common in lymph nodules and
reticular CT of blood-forming organs

- resemble lymphocytes but are larger with more cytoplasm; cytoplasm basophilic,
nucleus with chromatin like "cartwheel"
- derived from hemopoietic stem cells and B-lymphocytes; major function = Ab
production

8) WBCs - most common types in CT are lymphocytes and eosinophils

CONNECTIVE TISSUE TYPES - CT PROPER
1) Mesenchyme = embryonic, mesenchymal stellate cells in semi-fluid matrix;
enables cells to move about easily
2) Mucous = transient tissue appearing in normal development of CT and as
Wharton's Jelly of umbilical cord

- contains large stellate fibroblasts; matrix contains delicate collagen fibers in
mucoprotein gelatinous ground substance

3) Areolar (Loose Irregular) = very common, serves connective and supportive
functions

- most common cells are fibroblasts and macrophages (histiocytes)
- collagen fibers common, elastic fibers less so, reticular present but abundant only near
borders of other structures

4) Adipose - 2 Types:
a) White Fat = aggregations of unilocular fat cells, each cell surrounded by a web of
reticular fibers

- also occurring are fibroblasts, lymphocytes, eosinophils, magrophages and mast cells
- penetrated by blood vessels, dealing with mobilization and deposition of fat; serves as
a storage tissue for lipid

b) Brown Fat (BAT) = aggregations of smaller multilocular fat cells

- very rich vascularization
- supporting tissue similar to WAT

5) Reticular = composed of reticular fibers and reticular stellate cells
(appearance like mesenchyme with reticular fibers)

- forms framework of lymph organs, bone marrow and liver
- crowded with lymphocytes and other cell types (principally blood cells)

6) Dense Irregular = like a densely packed areolar CT with little ground substance

- majority of fibers are collagen, elasic and reticular fibers also present in lesser
numbers
- principal cell = fibroblast
- locations: fascia, dermis of skin, fibrous sheath of bone (periosteum) and cartilage
(perichondrium), fibrous capsules of lymph node, liver, some glands

7) Dense Regular = fibers are densely packed and lie parallel to each other,
provides great tensile strength; found in tendons, ligaments, aponeuroses (flat sheets
connecting muscle to bone), some organ capsules

TENDON STRUCTURE
1. Collagen fibers = primary tendon bundles (covered by areolar CT = endotendineum)
2. Primary bundle grouped into fascicles (covered by dense CT = peritendineum)
3. Fascicle grouped into tendon (covered by dense CT = epitendineum)
4. Fibrocytes (inactive) occur in longitudinal rows between collagen fibers, in c.s.
fibrocytes appear stellate ("winged fibroblasts")

- ligaments and aponeuroses similar but arrangement is less regular

8) Elastic = coarse parallel elastic fibers bound together by a small amount of delicate
CT with fibroblasts, collagen fibers

- frequent branching and fusion of elastic fibers - found in elastic ligaments (e.g., true
vocal cords, surrounding aorta as fenestrated membranes)

9) Lamellated = condensation of dense irregular CT around blood vessels, nerves and
gland ducts




CONNECTIVE TISSUE TYPES - CT PROPER
1) Mesenchyme = embryonic, mesenchymal stellate cells in semi-fluid matrix;
enables cells to move about easily
2) Mucous = transient tissue appearing in normal development of CT and as
Wharton's Jelly of umbilical cord

- contains large stellate fibroblasts; matrix contains delicate collagen fibers in
mucoprotein gelatinous ground substance

3) Areolar (Loose Irregular) = very common, serves connective and supportive
functions

- most common cells are fibroblasts and macrophages (histiocytes)
- collagen fibers common, elastic fibers less so, reticular present but abundant only near
borders of other structures

4) Adipose - 2 Types:
a) White Fat = aggregations of unilocular fat cells, each cell surrounded by a web of
reticular fibers

- also occurring are fibroblasts, lymphocytes, eosinophils, magrophages and mast cells
- penetrated by blood vessels, dealing with mobilization and deposition of fat; serves as
a storage tissue for lipid

b) Brown Fat (BAT) = aggregations of smaller multilocular fat cells

- very rich vascularization
- supporting tissue similar to WAT

5) Reticular = composed of reticular fibers and reticular stellate cells
(appearance like mesenchyme with reticular fibers)

- forms framework of lymph organs, bone marrow and liver
- crowded with lymphocytes and other cell types (principally blood cells)

6) Dense Irregular = like a densely packed areolar CT with little ground substance

- majority of fibers are collagen, elasic and reticular fibers also present in lesser
numbers
- principal cell = fibroblast
- locations: fascia, dermis of skin, fibrous sheath of bone (periosteum) and cartilage
(perichondrium), fibrous capsules of lymph node, liver, some glands

7) Dense Regular = fibers are densely packed and lie parallel to each other,
provides great tensile strength; found in tendons, ligaments, aponeuroses (flat sheets
connecting muscle to bone), some organ capsules

TENDON STRUCTURE
1. Collagen fibers = primary tendon bundles (covered by areolar CT = endotendineum)
2. Primary bundle grouped into fascicles (covered by dense CT = peritendineum)
3. Fascicle grouped into tendon (covered by dense CT = epitendineum)
4. Fibrocytes (inactive) occur in longitudinal rows between collagen fibers, in c.s.
fibrocytes appear stellate ("winged fibroblasts")

- ligaments and aponeuroses similar but arrangement is less regular

8) Elastic = coarse parallel elastic fibers bound together by a small amount of delicate
CT with fibroblasts, collagen fibers

- frequent branching and fusion of elastic fibers - found in elastic ligaments (e.g., true
vocal cords, surrounding aorta as fenestrated membranes)

9) Lamellated = condensation of dense irregular CT around blood vessels, nerves and
gland ducts


CT SUPPORTIVE -- Cartilage and Bone

I. CARTILAGE - contains fibers, ground substance and cells - no vascularization, cells receive nutrients via long-range diffusion - cells = chondrocytes(blasts) – produce ground substance and fibers

TYPES OF CARTILAGE
1. Hyaline - most common; found covering articular surfaces of most joints, costal cartilages, larger respiratory tubes, nasal cartilages; embryonically and in young it provides temporary model for endochondral bone development

a) Chondrocytes = present in lacunae (holes) in matrix (up to 40 micrometers in diameter)

- Sequence of Development: Mesenchymal cell ® Fibroblast ® Chondroblast ® Chondrocyte
- Chondroblasts at periphery of cartilage, mature to chondrocytes as they are enveloped in matrix; cells attain a more rounded state
- Young chondroblasts capable of cell division, daughter cells secrete a layer of matrix around themselves = isogenous nests -                       composed of 2-4 cells

b) Matrix = appears homogenous, glasslike, stains basophilic

- Matrix composed of fine collagen fibers (invisible w/o special staining) and amorphous gel of proteoglycans (GAGs + proteins)

c) Perichondrium = dense irregular CT that surrounds cartilage; composed of 2 layers:

1) Fibrous Zone = normal dense irregular CT outer layer
2) Chondrogenic Zone = inner layer, gives rise to chondroblasts

d) Cartilage Growth of 2 types:

1) Appositional = adding new layers to outside
2) Interstitial = formation of isogenous nests + secretion of matrix around nests (territorial cartilage)

2. Elastic = adapted to resist bending; found in external ear, epiglottis, some laryngeal cartilages

- similar to hyaline cartilage in appearance and composition except that matrix contains extensive network of elastic fibers
- not prone to undergo degeneration or calcification as sometimes occurs in hyaline cartilage
- surrounded by perichondrium

3. Fibrocartilage = structurally intermediate between dense regular CT and cartilage; contains collagen bundles + chondrocytes with    minimum amount of matrix.

- occurs where tough support or high tensile strength is needed (e.g., intervertebral discs, certain joints)
- functions to attach dense regular CT to cartilage or bone
- lacks perichondrium
- chondrocytes tend to be grouped in short rows (capsules) between collagen bundles

II. BONE - rigid supportive tissue making up most of the skeleton in evol. advanced vertebrates - composed of cells and matrix with a dense CT periosteum covering

a) Cells - 4 general types:

1) Osteogenic Cells = precursor cells derived from mesenchyme; capable of mitotic division; found near bone surfaces and    in inner portion of periosteum
2) Osteoblasts = deposit bone matrix, found at margins of growing bone
3) Osteocytes = occupy lacunae (holes) in bone matrix
4) Osteoclasts = multinucleated cells acting in dissolution of bone; derived from monocytes which collect at sites of bone resorption and fuse together

b) Matrix = contains collagen fibers in bundles which act as strengthening framework, ground substance of matrix becomes impregnated with calcium salts (mainly hydroxyapatite = crystalline calcium phosphate - 3Ca₃[PO₄]₂Ca[OH]₂)

- Bone is highly vascularized, unlike cartilage
- Canaliculi = tiny canals interconnecting osteocyte lacunae; eventually connect lacunae (directly or indirectly) to a fluid surface; contain cytoplasmic processes of osteocytes - so allow nourishment and gas exchange for osteocytes



- Bone growth occurs by appositional growth only, since osteocytes become embedded in hard matrix, no interstitial growth possible

BONE STRUCTURE - 2 Types of Bony Tissue, differ in architecture only.
1) Spongy (Cancellous) Bone = consists of a latticework of slender trabeculae enclosing large numbers of marrow cavities; found in flat bones of the skull, sternum and epiphysis of long bones


- Blood cells and red bone marrow found in marrow cavities
2) Compact Bone = lamellar bone made of osteons (Haversian Systems) = concentric layers of bone surrounding central Haversian canal; small amount of soft tissue present


- Haversian Canals = carry nerves, blood and lymph vessels along longitudinal plane of bone
- Volkman's Canals = carry nerves, blood and lymph vessels between marrow cavity, Haversian systems, and periosteum
- Sharpey's Fibers = direct extensions of dense irregular CT from periosteum into compact bone. Functions to anchor tendon (with fibers penetrating periosteum to bone) to bone. Formation by appositional bone growth around original attachment site.
- Transition between compact bone and periosteum:

1) outer bone layers = outer circumferential lamellae, enclose entire bone
2) Periosteum outside of circumferential lamellae - 2 zones:

a) Osteogenic Zone = gives rise to osteogenic cells
b) Fibrous Zone = dense irregular CT

DEVELOPMENT OF BONE - 2 CATEGORIES:
1. Intramembranous (Direct) - forms spongy bone and eventually may form compact bone

a) forms directly from mesenchyme
b) ossification centers (centers of osteogenesis) form from dense vascular regions of mesenchyme
c) Mesenchymal cells ® Osteoblast ® Secrete matrix which eventually becomes calcified (ossified) as thin needlelike spicules
d) when osteoblasts become embedded in calcified matrix --- osteocytes
e) new osteoblasts on surface of spicules continue to lay down bone by appositional growth, form trabeculae = radiating network of spongy bone. 

2. Endochondral - bone forms replacing cartilage "model"

I. Formation of Primary Center of Ossification

a) hyaline cartilage model is formed
b) cells in the middle of model enlarge, absorb matrix, leaving irregular cartilage spicules which subsequently calcify
c) capillaries + osteogenic cells + mesenchyme cells invade disintegrating cartilage as osteogenic bud from periosteum (perichondrium)
d) simultaneous with "c" osteoblasts form from inner perichondrium and begin laying down a tube of periosteal bone encircling the middle third of the cartilage model. Periosteal bone forms as intramembranous (spongy) bone but fills
in to form compact bone.
e) ossification of calcified cartilage spicules internally to form trabeculae and primary marrow from osteogenic bud
f) with continued formation of periosteal bone, get trabecular resorption inside leaving primary marrow cavity (osteoclasts involved in resorption)

II. Expansion of Primary Center of Ossification

a) as bone increases in size by appositional growth, primary center of ossification expands toward ends of bone as adjacent cartilage regions become osteogenic
b) epiphyses at each end continue interstitial production of cartilage, but epiphyseal regions don't expand because cartilage is replaced on diaphyseal side by bone at same rate as it is produced
c) epiphyseal plate extends horizontally across bone and is the region where cartilage replacement during expansion occurs. This plate consists of 4 regions:

1)      Zone of Resting Cartilage = chondrocytes are not actively contributing to bone growth, acts to anchor epiphyseal plate to epiphysis

2)      Zone of Proliferation = chondrocytes proliferate to replace dying chondrocytes from calcification; chondrocytes are stacked into parallel columns

3)      Zone of Maturation = chondrocytes hypertrophy and accumulate glycogen and lipid, secrete alkaline phosphatase - involved in formation of calcified cartilage spicules

4)      Zone of Calcification = hypertrophied cells become surrounded by calcified cartilage and die; trabeculae form as osteoblasts secrete bone onto calcified cartilage spicules SEE HANDOUT FOR REVIEW OF ENDOCHONDRAL BONE FORMATION 

III. Formation of Secondary Center of Ossification = develop in epiphyses of long bones sometime after birth

- chondrocytes in middle of epiphyseal zone hypertrophy and mature, matrix      between them calcifies and disintegrates, osteogenic bud then invades giving rise to osteoblasts which deposit bone on cartilage spicules

BONE REMODELING OCCURS IN ADULTS
- bone growth stops at about 20 yrs. of age in humans - adult bone continuously adapts to prevailing stresses by appropriate deposition and resorption - deposition and resorption are under hormonal control - integrated with regulation of blood calcium levels

1) Parathyroid Hormone = promotes resorption, increases blood calcium
2) Calcitonin = reduces resorption, decreases blood calcium

- intense activity increases blood lactic acid levels (decreases pH), causes dissolution of bone and can increase blood calcium levels

Muscle tissue: short and quick introduction of three types of Muscels. wathc this.

Muscle tissue histology

Nerve tissue:

Nerve tissue:

 

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Histology: (535 items)

Anatomy and Histology of Normal Skin - Contents

Medical Histology Index

THE HISTOLOGY PAGE Gallery of Slides To the Gallery updated 3.12

Histology, Full Year Course 2004-2005 - OpenCourseWare - Tufts ...

Histology Laboratory Index

UW Histology homepage

Guide to Histology Sites and Pages

HISTOLOGY- Bio 332/333

Histology CD

Histology.to

Deltabase Histology Atlas

Digital Atlas of Histology

Blue Histology - Searchable Large Images

Digital Atlas of Fathead Minnow Histology: HOMEPAGE

Laboratory Exercises

General Histology

Lab Histology and Embryology - ICBAS

BLOOD CELLS

Eye & Ear

Histology Methods Page. University of Bristol, School of Clinical

WebAnatomy Histology

Histology and Histopathology

Endocrine Histology

What is histology? - barrettsinfo.com

Histology Course PTH225

Archives of Histology and Cytology

Hate Histology

Neuroanatomy & Neuropathology on the Internet: Histology

Histology Home Page

Histology - tissues

Oral Histology

Medical Histology - Main Index

Histosearch: The Histology Search Engine

Online Exercise for Histology

CATS Histology Lab Index

Histology Lab Manual

Histology definition

Histology Imagebase: Set 1 of 2

BUBL LINK Catalogue of Internet Resources

Other Histology Web Sites

Hyperlinked Histology Human - Davidson College Immunology Course

Histology Imagebase - low bandwidth

HISTOLOGY STUDY GUIDE

Histology and Immunohistochemistry Protocol Database

Human Histology Web Site

Histology and Tissue Processing -- Home

Web Histology

CATS Histology

Nervous System Histology

Histology I

Histology

Working Procedures in Microwave Histology

Histology

Histology home page

Dinosaur Bone Histology: Home

Self-Teaching Programme Histology - Introduction

Clickable Visual Index for Histology Lab-Work

Listing by Alphabetical Subject Heading: Histology

Histology

AMBI - Anatomy Histology

Peripheral Nerve Histology

HISTOLOGY LINKS

Histology-World!

PLoS Genetics: Virtual Histology of Transgenic Mouse Embryos for

Histology Explorer - Welcome

Trout Histology Image Collection: US Fish & Wildlife Service

Histology Protocols - The Jackson Laboratory

Histol Histopathol, issues

View by Tissue Type

Histology of the Pancreas

Histology and Cell Biology

Histology and Immunohistochemistry Shared Resource

MICROSCOPIC HISTOLOGY IMAGES

Web Tutorials on Histology Materials

Histology - First year - UMMS Educational Links - UMass Medical School

Dr. Galil's Anatomy and Oral Histology Quizzes + CDROM

Histology - The Web Laborator

HistoLab2.htm

MicroCT-based virtual histology

HISTOLOGY, Lab Directory

Microanatomy and Histology of Skin

HMDS Techniques: Histology and Immunocytochemistry

U of M: General College: web anatomy

The Histology Guide

Histology

Histology and Electron Microscopy core facility

Anatomy & Histology of the Eye

Histology & Immunohistochemistry Shared Resource

Resources of Scholarly Societies - Cell Biology, Cytology & Histology

Histology Series

ZOOLOGY 441/661 HISTOLOGY

histology

Histology and Microscopic Anatomy of the Ear

Histology

Histology Module

HistoWeb Univ. South Dakota

University of British Columbia

University of Western Australia - includes lecture/lab notes and many images.

Blue Histology University of Western Australia

University of Florida College of Medicine

Kansas University Medical Center

Histology World

3-D Structural Histology Sechenov Institute for Evolutional Physiology RAS

Bone Thin Sections Department of Archaeology and Prehistory at Sheffield, UK

Electron microscopic atlas of mammalian tissues in the Internet Univ. Mainz, Germany.

nterent Atlas of Histology College of Medicine, University of Illinois - Urbana/Champagne

Histology Wet Lab - Temple University

Visual Slide Box of Histology - University of Iowa

Visual Histology Atlas

Net Vet