Glossary of Histology I

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Are thymic epithelioreticular cells associated with reticualr fibers?
What is structure of lymph node medulla?
Made of medullary cords tat are separated by dilated, capillary like structures called medullary lymphoid sinuses.
What color is white pulp when stained? Why?
Blue, ddue to presence of more nucleii than in bloody red pulp.
What is a lymph node medullary cord?
Branched extension of inner cortex tthat contains B cells and soe plasma cells
What are medullary lymphoid sinuses?
capillary like structures separating medullary cords
contain lymph
partially lined by reticular cells and macrophages
communicate with subcapsular sinuses via intermediate sinuses
Flow of lymph in lymph nodes
Afferent vessels pour lymph into subcapsular sinus
lymph drains into intermediate sinuses parallel to CT trabeculae
Then drains into medullary sinues in medulla
Lymph collected by efferent lymphatic veessels at hilum.
Blood flow in lymph nodes
Small arteries enter hilum
Form capillaries in nodules
Flow into venules
small veins exit at hilum
How do lymphocytes return to lymph nodes once in blood?
Leave blood through high endothelial venules
Describe HEV
have tall cuboidal endothelial lining
lymphocytes can travel between them
Where can you find high endothelial venules?
lymphoid organs (but not spleen)
Does spleen have capsule?
Does spleen have trabeculae?
Does splenic pulp have lymphatic vessels?
What is red pulp of spleen made of?
Elongated structures called splenic cords, lying between the sinusoids
T/F Thymus has a capsule
T/F Thymus does not have trabeculae.
What is main component of thymus cortex?
T lymphocytes
Where are epithelial reticular cells found?
what happens in thymus cortex?
Development of immature T lmphocytes
What happens to T cells in thymus cortex?
Either die via apoptosis (mainly) or migrate to medulla and enter bloodstream via venule walls
Then thy migrate to secondary lymphoid structures...
Where are Hassall;s corpuscles found?
thymus medulla
What are Hassall's corpuscles?
concentrically arranged, flattened epithelial reticular cells that degenerate and somemetimes calcify.
Are there more epithelial reticular cells in thymic cortex or medulla?
Describe vascularization of thymus
Arteries pierce capsule
floow septa of connective tissue.
Arteriols leave septa and penetrate parenchyma between cortex and medulla zones.
Ateriaoles give capillaries taht penetrate cortex
They drain into venules in the medulla.
veins drain and penetrate septa and leave thru capsule
Does thymus have afferent lymphatic vessels?
Do lymph nodes have a capsule?
Are lymph nodes trabeculated?
Is CT capsule around thymus thick or thin?
Does lymph node have a thin or think CT capsule
thicker than thymus
What are the subcapsular layers of a lymph node?
Outer cortex
inner cortex
Where is lymph node subcapsular sinus?
Between capsule and outer cortex
What is main component of outer cortex of lymph node?
B cells
(also reticular cells and fibers)
What is a lymphoid nodule?
Nodule rich in B cells that react with antigen, increas in size, and proliferate, resulting in large basophilic cells called immunocytes.
What are germinal centers?
Lighter staining areas in lymphoid nodules. Produce plasma cells.
What is main component of inner cortex of lymph node?
T cells. Few, if any nodules..
Normal white count breakdown:
45-70% neutrophills
20-25% lymphocytes
3-8% monocytes
0-5% band cells
2-4% eosinophils
0-1% basophils
noteworthy characteristic of basophilic eryrthroblasts:
checkerboard condensations of chromatin within nucleus
Megakaryocyte characteristics
giant cell (35-150)
in bone marrow
irreularly lobulated nucleus
with maturity: numerous invaginations of PM ramify throughout cytoplasm
monocyte characteristics
12-15 um
indented nucleus
fine granules
Promyelocyte characteristics
18-20 um
large nucleus w/nucleolus
azurophilic granules
no specific granules
myelocyte characteristics
specific granules present
nucleus eccentric; flattened or slightly indented
metamyelocyte characteristics
slightly smaller than myelocyte
nucleus in shallow U or V shape
no conspicuous azurophilic granules
Band cell characteristics
Only seen in neutrophilic series
horseshoe shaped condensed nucleus
nucleus beginning to lobulate
may be seen in peripheral blood (may have left marrow)
2 types of platelet granules
what do alpha granules of platelets contain?
platelet factors
acid hydrolases
what do dense granules of platelets contain?
Two types of cell lines from pluroipotential hematopoietic stem cells
Myeloid cells (develop in bone marrow: granulocytes, monocytes, erthrocytes, and megakaryocytes)
What do myeloccyte multipotential cells develop into?
Basically everything but lymphocytes
Features of red bone marrow
hematopoietic cords
sinusoidal capillaries
Where does RBC development occur?
bone marrow
Stages of RBC maturation
basophilic erythroblast
polychromatophilic erythroplast
orthochromatophilic erythorblast
mature erythrocyte
Basophilic erythroblast characteristics
strongly basophilic cytoplasm (due to many polyribosomes-->hemoglobin production)
condensed nucleus
Polychromatophilic erythroblast characteristics:
multi colored cytoplasm
orthochromatophilic erythroblast
nucleus condensed more than polychromatophilic
no cytoplasmic basophilia evident
this exam is?
Which has more developed tunica media--ateries or veins?
Exceptions to the flow order artery-->capillary-->vein
1) arteriovenous annastomoses: blood flow directly from artery to vein (e.g. in skin)
2) venous portal systerm: cap to vein to cap
3) arterial portal system: cap to arteriole to cap
What are the layers in a spun hematocrit tube?
buffy coat of leuocytes
What are reticulocytes?
Young erythrocytes that still contain residual ribosomal RNA
2 groups of leukocytes
What are reticular fibers mainly made of?
Collagen type III
What is a haversian system
Whole complex of concentric lamellae of bone surrounding a canal containing blood vessels, nerves, and loose connective tissue
Organization of lamellae in compact bone
haversian systems
outer circumferential lamellae
inner circumferential lamellae
interstitial lamellae
structure of haversian system
long, often bifurcated cylinder
central canal w/ 4-20 concentric lamellae
lined by endosteum
contains blood vessels, nerves, and loose CT
communicate with marrow cavity, periosteum, and one another through Volkmann's cannals
do vollkmann's canals have concentric lamellae
No, they perforate the lamellae
Is diameter of osteon constant?
No, great variability due to constant bone tissue remodeling.
2 methods of bone formation?
1) intramembranous ossification
2) endochondral ossification
What is the source of most flat bones?
Intramembranous ossification
Where does intramembbranous ossification occur
Within condensations of mesenchymal tissue (specifically starts in a primary ossification area.)
Where does endochondral ossification take place?
Within a piece of hyalione cartilage whose shape resembles a small version of the bone to be formed
What type of bone is endochondral ossification primarily responsible for?
short and long bones
Process of endochondral ossification
1) first bone tissue appears as hoolow bone cylinder surrounding mid portion of cartilage model (bone collar)
2) local cartilage undergoes PCD with hypertrophy and matrix calcification
3) this begins in diaphysis of model
4) osteoblasts adhere to calcified cartilage matrix and make continuous laers of primary bone that surrounds cartilaginous matrix remnants
5) this makes a primary ossification center
6) secondary ossification centers appear at epihyses (SOC)
76) in SOC, growth in length occurs at epiphyseal plate (growth in length)
What is a bone collar
ollow bone center that surrounds mid portion of cartilage model at beginning of endochondral ossification
5 zones of epiphyseal cartilage
1) resting zone
2) proliferative zone
3) hypertrophic cartilage zone
4) calcified cartilage zone
5) ossification zone
resting zone
hyaline cartilage w/o morpholigic changes in cells
proliferative zone
chondrocytes divide rapidlty and form colums of stacked cells parallel to long axis of bone
hypertrophic cartilage zone
large chondrocytes whose cytoplasm has accumulated glycogen
calcified cartilage zone
chondrocytes have died and the thin septa of cartilage matrix between them becomes calcified
what does parathyroid hormone do in bone?
Promotes osteoclastic reorption of the bone matrix and liberation of Calcium
What does calcitonin do in blood?
inhibits matrix resorption.
does intramembranous ossification use a cartilage template?
what does the marrow cavity contain?
stem and precursor populations of mature blood cells/platelets
what compound accounts for bone mineralization?
hydroxyapatite crystals
what is the ECM in bone primarily made of ?
collagen I
Is collagen matrix of bone basophilic, acidophilic, or other?
2 types of agranulocytes
Neutrophil characteristics
12-15 um
2-5 lobed nucleus
some azurophilic granules
many specific granules that are hard to see in LM
Incidence of neutrophils among leukocytes
2-4 % of leukocytes
12-15 um diameter
characteristic bilobed nucleus
Many refractive specific granules stained by eosin.
Basophil characteristics
less than 1% of leukocytes
12-15 um
Irregular-lobed nucleus, but basophilic specific granules usually obscure any divisions.
Specific granules stain metachromatically.
What to basophil specific granules contain?
heparin and histamine
Lymphocyte characteristics
Small: 6-8 um
(some are larger).
Spherical nucleus, sometimes w/1 indentation
Intensely stained nucleus
Scanty cytoplasm that is slightly b-philic
What stains are good for staining elastic lamellae?
Van Giesen or Verhoff's
Why do haversian systems have light and dark layers when viewed under polarized light?
due to changing orientation of collagen fibers in the lamellae.
Process of intramembranous ossification
1) group of mesenchymal cells differentiate into osteoblasts
2) O-blasts make bone matrix
3) calcification follows
3) calcification encapsulates some osteoblasts, whcih become osteocytes
4) bone islands delineate cavities containing capillaries, bone marrow, etc
5) osssification centers grow radially and fuse
ossification zone
where endochondral bone tissue appears
Do all osteons have the same number of lamellae
Which lamellae in a bone osteon are the oldest?
The outermost.
Are all osteons same size? Why or why not?
No, due to constant bone remodeling
What is present in the canaliculi of bone tissue?
Thin cytoplasmic processes of osteocytes.
What are pseudounipolar neurons?
They have a single process that is close to the perikaryon and divides into two branches. The process then forms a T shape, with one branch extending to a peripheral ending and the other toward the CNS. During maturation process, axon and peripheral fibers fuse, becoming one fiber.
Where are bipolar neurons found?
Cochlear ganglia
Vestibular ganglia
olfactory mucosa
Where are pseudounipolar neurons found?
Spinal ganglia (dorsal root ganglia)
Cranial ganglia
Where are multipolar neurons found?
Most everywhere in the body, except where the other kinds are (that is, dorsal root ganglia, cranial ganglia, cochlear and vestiubular ganglia, retina, olfactory mucosa
What are Nissl bodies
RER and free riosomes that stain as basophilic granular areas; in cell b ody
Where are Purkinje cells found?
What is an axon hillox?
Pyramidal shaped region of perikaryon ffrom which axon originates.
What do you call the plasm amembrane of an axon?
T/F: there are polyribosomes and RER in the axon.
What do oligodendrocytes do?
Produce the myelin shealth around neurons in CNS.
What binds neurons to capillaries and to the pia matter?
how do astrocytes communicate with each other?
Directly, via gap junction connections.
Where are ependymal cells and what do they do?
lining ventricles of rain and central canal of spinal cord. cometimes have cilia to move CSF.
Characteristic feature of most neurons:
large spherical nucleus
prominent nucleolus
dispersed chromatin
Which motor is for retrograde movement in axon?
Which direction is anterograde?
Toward axon terminal
What are phagocytic cells that represent the mononuclear phagocytic system in nerve tissue?
What causes the different appearance of white and gray matter?
differential distribution of myelin in CNS (main component of white matter is myelinated axons)
Where in the brain is gray matter prevalent?
Cerebral and cerebellar cortex (surface)
What does gray matter contain?
neuronal cell bodies, dendrites, initial unmyelinated portions of axons and glial cells.
Why is there a blood brain barier?
Reduced permeability that is a properrty of blood capillaries of nerve tissue (mainly due to occluding junctions.)
What type of staining preserves lipids, staining them black?
Osmium tetroxide
What is a pacinian corpuscle?
A mechanoreceptor located in the dermis. Looks like an onion bulb. Surrounds an afferent nerve fiber. See 3661, 3166 on the slide.
What is a Meissners corpuscle?
Oval, encapsulated mechanoreceptors lying in dermal ridges just deep to the stratum germinativum. Has a connective tissue capsulee. Seem to be smaller than pacinian corpuscle.
What are nerve sattelite cells?
small glial cells that suround spinal ganglia nerve cell hbodies.
Which motor is for anterograde movement in axon?
How do oligodendrocytes differ from schwann cells (other than location)?
OD's can envelop segments of several axons, where schwann cells only envelop one.
Layers around nerves
1) epineurium
2) perineurium
3) endoneurium
What is endoneurium made of?
Thin layer of reticular fibers (made by schwann cells)
Do sympathetci ganglia have few or many myelinated axons?

Most of the axons are unmyelinated postganglionic fibers.
What surrounds pseudounipolar sensory neuron bodies in the dorsal root ganglion?
Sattelite cells and a thin layer of CT
What are ganglia?
Ovoid structures containing neuronal cell bodies and glial cells supported by connective tissue
What are sattelite cells?
small glial cells that abundantly surround spinal root ganglia
What kind of neurons are found in sensory ganglia?
Which ganglia have onnective tissue capsules: sensory or autonomic?
what kind of neurons do autonomic ganglia usually have?
what chemical mediator is found at all pregangliionic autonomic endings?
What does PNS mainly develop from?
Ectoderm (neural crest)
where are pyramidal cells found?
What cells line the spinal cord central canal?
Ependymal cells
what are neurofilaments?
10 nm intermediate filaments formed by 3 different proteins
What do you call the small projections of some dendrites that are covered with synapses?
Which type of special sensory receptors use pseudounipolar neurons?
1) free endings that conduct touch, pain, and temp impulses
2) stretch receptors
3) tactile and pressure receptors
Do schwasnn cells cover peripheral nerves continuously?
Yes. But the myelin is produced discontinuously.
Are there synapses in sensory ganglia?
What are the components of a ganglion?
1) neuronal cell bodies
2) ...covered by sattelite cells
3) CT
4) axons
5) dendrites
6) synapses (except in sensory (dorsal root) ganglia, where there is just the cell body of the pseudounipolar neuron)
Which parasympathetic plexus of ganglia is found in the gut between muscle layers?
Myenteric plexus
Which parasympathetic plexus of ganglia is located just underneath the gut epithelium?
Submucosal plexus
Do sensory ganglia have multipolar neurons?
Do autonomic ganglia contain synaptic connections?
Yes. Sensory ganglia do not.
Is the crease in the spinal cord dorsal or ventral?
Which are bigger: sympathetic ganglia neurons or sensory ganglia neurons?
Sensory ganglia neurons (generally)
distinguishing feature of longitudinal section of peripheral nerve?
they follow a wavy zig-zag course
What replaces the tunica media in capillaries and post-capillary venules?
Layers surrounding muscle tissue?
Dark bands of skeletal muscle are called:
A bands
Light bands of skeletal muscle
I bands
The dark transverse line bisecting each I band
Z line
Lighter zone in middle of A band
H band
Line bisecting H band
M line
What does a cross section thru the A band look like?
Mysoin thick filament surrounded by 6 thin filaments in form of hexagon?
What anchors actin to the Z line?
Likely alpha actinin
What are T tubules?
Invaginations of sarcolemma that incircle boundaries of the A-I bands oif each sarcomere in every myofibril.
What are terminal cisternae?/
They are sxpanded parts of the sarcoplasmic reticulum that are adcjacent to opposite sides of each T tubule. Forms a TIAD.
What happens at the triad?
This is where depolarization of the T tubules is transmitted to the SR membrane
How does contraction occur?
When calcium is available, it binds to troponin. This causes a conformationl change that drives the associated tropomyosin molecule deep into the actin helix groove. This exposes the myosin binding sit on the actin, so it is free to bind to myosin.

When G-actin binds myson head, ATP in myosin is hyydrolzed and head of mysoin bends.

Myosin head detaches only after myosin binds a new ATP. If no ATP, myson head never detaches.
what happens to H band width on contraction?
it narrows.
What are junctional folds?
Folds in the sarcolemma at the NMJ
What are muscle spindles?
T capsile surrounding a fluid filled space that has a few thick and a few thin muscle fibers in it.

Nerves in the capsule detect distension of the muscles and relay the info to the spinal cord. (Proprioceptors.)
What do golgi tendon organss do?
Contribute to proprioception by detecting tensional differences in tendons
What are Type I muscle fibers?

Dark red, rich in sarcoplasm/myogloibin.

Related to continuous contraction, get energ from FA ox-phos.
What are Type II muscle fibers?
Related to rapid discontinous contraction.

Less myoglobin, more light red.
What are the fastest acting type of muscle fibers?
Type IIB.
do muscle cells have a lot of RER/ribosomes?
No. They do little protein synthesis (when mature.)
What are intercalated disks?
Junctional complexes found at the interfase between adjacent cardiac muscle cells.
Do cardiac muscle cells have triads?
No, they usually have diads (one T tubule and one SR cisternae).
How are atrial and ventricular cardiac myocytes different?
For one, Atrial myocytes are sommewhat smaller and have markedly fewer T tubules.
What type of muscle nucleus looks like a corkscrew upon coontraction?
smooth muscle
Do smooth muscle cells have T tubules?
Does smooth muscle have a tropomyosin complex?
How is smooth muscle contraction mechanism different?
Ca complexes with calmodulin, which activates MLCK, which phosphorylates myosin. Myosin phosphorylation allows myosin to interat with actin.
How are cAMP and smooth muscle contraction related?
when cAMP ioncreases, MLCK is activated, myosin is phosphorlyated, and SM contracts.
What are dense bodies?
Membrane associated or cytoplasmic bodies where thin and intermediate filaments insert, transmitting contractile force to adjacent smooth muscle cells
How doees skeletal muscle regenerate?
Via satellite cells--a sparse population of spindle shaped cells in basal lamina surrounding each muscle fiber. They can proliferate to form new skeletal muscle fibers.
what is the endomysium rich in?
Reticular fibers
What is something responsible for the knee-jerk reflex?
muscle spindle.
Match red and white muscle fibers with slow or fast contraction and hi or low myoglobin/mito content.
Red: slow, high myo/mito
White: fast, low myo/mito.
Where is cardiac muscle diad located?
Z line
What is the major source of Ca ions for contraction initiation in cardiac muscle?
Extracellular ca, not SR calcium
What three structures make up an intercalated disk?
fascia adherens
gap junctions
is cardiac muscle more like red or white skeletal muscle?
Red. slow contraction.
What shape are smooth muscle cells?
Fusiform (bigger in the middle, tapered toward end)
what are multiunit smooth muscles?
They have a rich innervation and can produce pricise and graded contractions (like in the Iris)
What type of smooth muscle has worse innervation than multiunit smooth muscle?
Visceral smooth muscle. This relies more on abundant gap jxns to propogate nerve impulses.
Does nucleus of BV endothelium bulge into lumen or away from lumen?
Into lumen, ususally.
What are perictytes?
Cells along capillaries and venules;
Enclosed in their own basal lamina, which may fuse with that of the endothelial cells.
Has myosin, actin, etc--suggest s it has a contractile function
Can proliferate to form new BV after tissue injuries.
4 Types of capillaries
1) continuous
2) fenestrated
3) renal glomuleral
4) discontinuous sinusoidal
What is a continous capillary characterized by?
Absence of fenestrae in its walls
Where are continuous capillaries found?
All kinds of muscle
expcrome g;amds
mervpis tossie
Where are fenestrated capiltaries found?
Tissues where rapid interchange of substances occurs btwn tissues and lood:

kidney , intestine, endocrine glands
What is distinctive about a renal glomular capillary
Like a fenestrated cap but w/o the diaphragm in the fenestrae.
What are the characteristics of a discontinuous sinusoidal capillary?
1) tortuous path
2) greatly enlarged diameter
3) endothelial cells form a discontinous layer and are separated by wide spaces (!!)
4) multiple fenestrations w/o diaphragms
5) macrophages located among or outside of endothelial cells
6) discontinous basal lamina
Where are discontinuous sinusoidal cpaillaries found?
1) liver
2) hematopoietic organs (bone marrow, spleen)
Name the layers, inside to out, of an artery"
1) endothelium (tunica intima)
2) internal elastil lamina
3) tunica media
4) external elastic lamina (part of 3)
5) tunica adventitia
What is tunica intima made of?
Layer of endothelial cells + subendothelial layer of loose CT.

(separated from media by interal elastil camina)
What is the tunica media made of?
Concentric layers of helically arranged SM cells, with elastic fibers, reticular fibers, PH, GP, etc einterspersed.
What is the tunica adventitia made out of?
Mainly collagen (type I) and elastic fibers.
Where is vasa vasorum found?
Tunica adventitia and outer part of teh media.
Match muscular/elastic with medium/large arteries?
Blood circulation in spleen
Splenic artery divides as it penetrates hilum
branches into trabecular arteries that follow trabeculae
Leave trabeculae to enter parenchyma
Then are immediately enveloped by a sheath of PALS (the are then called central arteries)
Central artery course thru white pulp nodes eccentrically
sends off radial branches
Central artery leaves white pulp and sibdivides into penicillar arterioles
Then divides to capillariries that carry blood to sinusoids in red pulp
Blood colected by red pulp veins, which join to form trabecular veins
spenic vcein emerges from spleen hilum
What is splenic white pulp?
Lymphoid tissue that sheathes the central arteries and nodules appended to the sheaths
Are lymphoid nodules mainly B or T lymphocytes?
Mainly B
Are PALS formed by mainly T or mainly B cells?
mainly T
What does spenic white pulp do?
Produces lymphocytes that migrate to red pulp and reach the lumens of sinusoids
What are centrocytes?
Cells from the center (clear area) of a germinal center
Are tonsils completely encapsulated by CT?
no, only partially
Where did thymus develop from?
Endodermal derivative of the foregut
What do lymphoid tissue nodules contain?
follicular dendritic cells
interdigitating dendritic cells
What happens in light and dark zones of germinal center?
Light zone (center): maturation
Dark zone (outside): proliferation
What is the splenic marginal zone?
Between the white pulp and red pulp
Consists of many sinuses and loos lympoid tissue
Few lymphocytes
Many active macrophages
Abundance of antigens
What is distinctive about viewing the splenic sinuses?
Nuclei of sinusoids are widely spaced
Does thymus have trabeculae?
NOT SEEN IN THYMUS (note possible wrong card out there)
Structure of basal lamina?
Lamina densa (type 4 collagen and other stuff)
Surrounded on 1 or both sides by lamina lucida, lighter staining in EM
Collagen VII anchors basal lamina to anchoring fibrils in underlying CT

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