SPECIAL HISTOLOGY ORGANOLOGY

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SPECIAL HISTOLOGY (ORGANOLOGY) The Study of
Organs Organ Architecture Tissues structural
units Arrangement of tissues in organs Tissue
Adaptations Organogenesis developmental course
to form organ(s)
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Organ independent part of body (partially) Perfor
ms specific function An aggregate of tissues
with characteristic arrangement One tissue is
primary Others are secondary (auxiliary) Fibrou
s framework Enveloping fibrous
capsule Individual supply of blood, lymph, and
nerves
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Parenchyma Essential, characteristic,
functional cells Stroma Internal, auxiliary,
supporting tissue Typically the epithelium is
the parenchyma and the connective tissue bed is
the stroma.
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Organ System Set of organs Organs carry out
related functions! Similarities of structure
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• Germ Layer of Origin
• Designates only the primary tissue
• A few are composites
• Ectoderm
• Epidermis and derivatives (nails, hairs,
  cutaneous glands)
• Nervous system
• Sense organs
• External orificial linings (mouth, nose, anus)
• Salivary glands
• Hypophysis
• Suprarenal glands

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• Mesoderm
• Circulatory system
• Lymphoid organs
• Kidney and ureter
• Gonads and ducts
• Suprarenal cortex
• Muscles
• Supporting organs (tendons, ligaments, fascias,
  skeleton)
• Lining of body cavities

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Endoderm

• Epithelia of
• Digestive tube
• Liver
• Pancreas
• Respiratory tract
• Thyroid
• Parathyroids
• Bladder
• Urethra and associated glands

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THE CIRCULATORY SYSTEM VASCULAR
LYMPHATIC Heart, Blood Vessels, Lymphatic
Vessels Blood Vessels all organs Lymphatic
Vessels most organs Heart is a blood
vessel Arteries blood away from
heart Capillaries meshwork Veins blood to
heart Lymphatic Vessels lymph from tissue spaces
to blood stream
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BLOOD VESSELS Capillary fundamental simplest
vessel Add accessory coats to form other
types Simple, endothelial tube Connect
arteriole to venule 60,000 miles 1.5 acres
(surface area) Cross sectional area 800 times
that of Aorta Rate of blood flow 0.4
mm/sec. Aorta rate 320 mm/sec.
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Capillary size 8µ RBC pass single
file Resting capillaries are narrower than
functioning capillaries Capillary
arrangement Meshwork flattened or
spongy Commonly isodiametric (lung
mesentery) Elongate structures diamond
shaped Metabolic intensity determines closeness
of mesh
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• Capillary structure
• Cells elongate (long axis of vessel)
• Cell margins overlap
• Margins blackened with silver nitrate
• Cell curving, thin plate, nucleus ovoid to
  elongate
• 2 to 3 cells at any level
• Cells staggered narrow part to wide part
• Thin basement membrane
• Supporting bed of connective tissue
• Macrophages Fibroblasts nearby

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False Capillaries Resemble capillaries Features
not found in capillaries Sinusoids Special
vessels between larger vessels Arteriole to
Venule Venule to Venule Interconnect
lymphatic vessels Unique Broad (up to 30µ),
dia. not uniform, lining incomplete, fixed
macrophages, flat cells, lining closely applied
to parenchyma
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• Rete Mirabile
• Capillary-like plexus
• In course of arteriole or venule
• Uncommon in mammals
• Renal glomerulus
• Sinusoids of anterior hypophysis (similar)
• Lymph nodes (lymphatic-sinusoid- lymphatic)

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PRECAPILLARY POSTCAPILLARY Intermediate between
capillary and arteriole / venule Incomplete
accessory coats Arterial Precapillaries Less
than 40µ dia. Endothelial tube smooth muscle
fibers Muscle encircles vessel Muscle not a
complete coat Largest precapillaries add C.T.
fibers Discontinuous layers
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Venous Postcapillaries Less than 200µ
dia. Smallest endothelium scattered
C.T. Largest add smooth muscle fibers Muscle
fibers discontinuous layer
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BLOOD VESSELS STRUCTURAL PLANS Common plan
above level of precapillaries Specific vessel
types show characteristic adaptations Feature of
common plan Emphasized Reduced Omitted
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Three concentric coats (tunics) Tunica interna
(intima) Tunica media Tunica externa
(adventitia)
Tunica interna
Tunica media
Tunica externa
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Tunica interna (intima) Endothelium (simple
squamous epithelium) Lines lumen Subendothelium
delicate fibro-elastic tissue Fibers
longitudinal Internal Elastic Membrane Outer
layer Fenestrated membrane May split into 2 or
more layers May reduce to simple network of
fibers Empty vessel membrane folds
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Subendothelium
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Tunica media Circularly arranged smooth muscle
dominates Elastic fibers common
addition Circularly arranged fibrous
networks Greatest development concentric
tubes Networks/Elastic Tubes alternate with
smooth muscle
Pink smooth muscle fibers Black lines fibers
of elastic net
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Tunica externa (adventitia) Elastic tissue
commonly concentrates near T. media Elastic
layer (if definite external elastic
membrane) Further out elastic fibers
predominantly longitudinal Remainder of T.
externa moderately compact fibro-elastic
tissue T. externa grades into Areolar C.T.
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Vasa vasorum Blood vessels gt1mm. have nutrient
vessels In arteries supply T. externa In veins
may penetrate deeper extend through T.
media Lymphatic vessels in wall of larger blood
vessels Nerves Unmyelinated nerve fibers
(networks in T. externa) terminate on T. media
smooth muscle fibers vasomotor Nerves
Myelinated sensory fibers arborize in T.
externa may reach T. interna
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ARTERIES Classified in three groups Arterioles
smallest, predominantly muscular Small to
Medium Arteries predominately muscular Large
Arteries predominately elastic Divisions are
arbitrary no sharp limits Transition from
elastic to muscular is gradual Intermediate
arteries mingle features (mixed) Size and
composition not always correlated
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ARTERIOLE Not visible to unaided eye 0.04 mm. to
0.30 mm. dia. Wall thicker relative to lumen
T. interna thin no subendothelial tissue
internal elastic membrane network of fibers. T.
media purely muscular thickest coat 1 5
layers
T. externa fibro-elastic, thinner than media no
definite external elastic layer/membrane
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SMALL MEDIUM SIZED ARTERIES Muscular
arteries Most named arteries and small unnamed
arteries Smallest just visible to unaided eye
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Tunica interna Subendothelial layer (may be
thin) Prominent internal elastic membrane May
split with age (2 or more layers)
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Tunica media Muscle layers dominate up to 40
layers
Larger vessels elastic tissue largest with
true elastic membranes White fibrous tissue
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Tunica externa May be thick Thinner than T. media
(usually) Elastic layer near T. media Varies
from weak representation to actual external
elastic membrane Peripherally T. externa is
primarily collagenous
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LARGE ARTERIES Elastic type arteries Colors wall
yellowish Aorta Brachiocephalic (innominate)
Common Carotid Subclavian (Vertebral Internal
Mammary) Common Iliac Wall thin compared to
lumen
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Tunica Interna Endothelial cells
polygonal Subendothelium fairly thick with many
elastic fibers Internal elastic membrane not
significant
Endothelium
Subendothelium
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Tunica media Thickest coat Elastic Collagenous
tissue 40 to 60 elastic membranes, each 2.5µ
thick
Interspaces Fibroblasts Amorphous ground
substance Fibro-elastic tissue Sparse muscle cells
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Tunica externa Thin Unorganized Lacks external
elastic layer/membrane Collegenous fibers
longitudinally spiral courses Restrains expansile
T. interna and T. media
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SPECIALIZED ARTERIES Deviate from generalized
plan Reflect adaptations to location and
functional demands
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CAROTID BODY Location bifurcation of common
carotid artery Contains epitheliod cells,
dilated capillaries, many nerves A sensory
chemoreceptor Similar to Aortic Body in arch of
Aorta Carotid and Aortic bodies respond to
oxygen tension of blood role in intitiation of
respiratory reflex
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• VEINS
• Three Classes
• Venules
• Small to Medium sized Veins
• Large Veins
• Cannot be used rigidly
• Size structure not well correlated with veins

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VENULES Diameter 0.2 to 1 mm.
Tunica interna limited to endothelium Tunica
meda very thin, only smooth muscle Tunica
externa relatively thick collagenous fibers
elastic fibers few or lacking
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SMALL MEDIUM SIZED VEINS Diameter 1 mm. to 9
mm. Includes Cutaneous branches Deeper veins
forearm leg Veins of head, trunk, viscera
(except main vessels and their tributaries
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Tunica interna Subendothelium delicate, often
absent Bundles longitudinal smooth muscle fibers
(a few vessels) Elastic fibers vary absent to
dense, net-like membrane Not clearly demarcated
from T. media
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Tunica media Smooth muscle, reduced or absent
Thin, feeble coar Tunica externa Thickest
coat Prominent smooth muscle bundles
(longitudinal) No external elastic layer/membrane
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VALVES Well represented in limbs Usually in
pairs Located just distal to entry of
tributary Prevent backflow of blood aid moving
blood toward heart Formation Folding of T.
interna Internally network of elastic fibers
(current side) External surface endothelium
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LARGE VEINS Superior Vena Cava Inferior Vena
Cava Portal Vein main tributaries (include
veins from upper arm thigh) Tunica
interna Subendothelial layer thicker may have
smooth muscle bundles Internal elastic membrane
sometimes (delicate)
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Tunica media Smooth muscle reduced to
lacking Thin feeble coat Tunica
externa Thickest coat Prominent smooth muscle
bundles (longitudinal) Most of extremely broad
tunic No external elastic membrane
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SPECIALIZED VEINS As with arteries, veins
structure may reflect special needs for location
/or function
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ARTERIO-VENOUS ANASTOMOSES Arterioles and Venules
connect directly (no capillary bed) Endothelium
on specialized T. media Modified smooth muscle
forms sphincter Location Skin of exposed parts
of body (palm, sole, terminal phalanx, lips,
nose, eyelids) Metabolic activity is
intermittent (mucous membrane of
gastro-intestinal tract, thyroid) Regulate
circulation and blood pressure
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COCCYGEAL BODY Small mass 2.5 mm. Location tip
of coccyx Group of arterio-venous anastomoses
with epitheliod muscle. Embedded in C.T. (T.
externa) Function ?