Histology Test 3

MSK and Skin

Hyaline Cartilage

Most common type

Avascular

ECM contents: TYPE 2 COLLAGEN, chondroitin sulfate, keratan solfate, hyaluronic acid, chondronectin

Found the most throughout our body

Elasic Cartilage

Type 2 collagen + elastic fibers

Avascular

requires special stains for elastic fibers (ex. Verhoeff, Silver Stain)

ECM Content: Elastic Fibers + Same as Hyaline cartilage (TYPE 2 COLLAGEN, chondroitin sulfate, keratan solfate, hyaluronic acid, chondronectin)

Found in ear and nose

Fibrocartilage

dense network of type 1 collagen fiber bundles

Avascular

intermediate between dense CT and hyaline

Found in intervertebral discs and some ligaments

Chondroblast

Immature precusor cell of cartilage

Chondrocyte

Main cell of cartilage

Lacunae

Space/cavity of matrix where condrocyte is located

Perichondrium

Sheath of dense CT surrounding cartilage (contain blood, nerves, lymphatics)

Chondrogenesis

making cartilage—mesenchymal cells turn into chondrocytes that build a gel-like matrix

1. Condense: Mesenchymal cells gather into a tight nodule

2. Differentiate: They become chondroblasts/chondrocytes (driven by SOX9)

3. Build matrix: Cells secrete type II collagen + proteoglycans forming cartilage

4. Mature & expand: Chondrocytes sit in lacunae and proliferate

Interstitial Cartilage Growth

Mitotic division of pre-existing chndrocytes

Appositional Growth

Differentiation of perichondrial cells

Bone Matrix

Inorganic Portion

• mostly hydroxyapatite crystals (65% of dry weight)

Organic Portion - 95% Type 1 Collagen (some type 5)

• Chroitin sulfate, keratan sulfate, hyaluronic acid

Periosteum

Layer of non-calcified connective tissue

Surrounds the outer bone except at the sunovial articulations and muscle attachments

Contain osteoprogenitor cells and osteoblasts

Sharpey fibers

attach periosteum to bone surface

Endosteum

Thin layer of connective tissue lining the marrow cavities of bone

houses osteoprogenitors, osteoblasts, and osteoclasts for bone remodeling and repair

Osteoblasts

Derived from osteoprogenitor cells

Stellate shaped but can be cuiboidal near bony surface

Found at surface of bone matrix

Will appear basophilip during active phase

Main Role = Osteoid Deposition

Have parathyroid hormone receptors

Communicate via gap junctions

Become entrapped in a lacunae surrounded by matrix > osteocyte

Osteocytes

Mature cells of bones (entrapped in their own lacunae)

Main Role = maintenance of the bone matrix

Abundant cell processes extend in canaliculi

communicate via gap junctions

Abundant Heterochromatin

Osteoclasts

Derived from the mononuclear phagocyte system

Large, motile, multinucleated

Have calcitonin receptors on their cell surface

Signals from osteoblasts stimulate osteoclasts

• MCSF - stimulates Osteoclats to undergo mitosis

• RANKL - causes OC to become multinucleated and begin bone resorption (breakdown of bone)

Canaliculi

Related to Osteocytes, nutrient/waste exchange and cell-to-cell signaling

Osteoprotegerin

Signal from Osteoblats to Osteoclasts

• inhibits osteoclasts by blocking RANKL receptors

Macroscopic Bone Classification

Spongy (trabecular or Cacellous)

• bony spicules

• surrounded by marrow

• Traveculae lined by osteoblasts on both sides

• Surrounded by compact bone

Compact (Dense)

• no traveculae or marrow cavity

• Haversian system (osteon)

Microscopic Bone Classificaiton

Primary

• Immature bone

• Many osteocytes and type 1 collagen

• Low mineral content

• First bone laid down during fetal growth or repair

Secondary

• Mature Bone (lamellar)

• Calcified matrix arranged in layers

• Osteocytes in lacunae

Haversian System (Osteon)

the basic unit of compact bone

concentric rings (lamellae) of hard bone wrapped around a central canal with blood vessels and nerves

Osteocytes sit in spaces between the rings and connect through tiny canals (canaliculi)

Interstitial Lamellae

thin, irregular layers of old lamellar bone that fill the spaces between osteons in compact bone

Intramembranous Ossification

Type of Osteogenesis

Mesenchyme > Osteoblasts > Osteoid > Flat Bone Formation

1. Mesenchyme condensates near vascular centers

2. Osteoblants begin making osteoids

3. Calcification leads to trabeculae formation

4. Traveculae create spongy bone and Periosteum + endosteum develop

5. Lamellae are formed

Endochondral Ossification

Type of Osteogenesis

Hyaline cartilage mold replaced by Bone Matrix

Long Bone Formation

length growth at the epiphyseal (growth) plates

Zone of Reserve Cartilage

1st zone of Epiphyseal Growth Plate

Inactive cartilage wating to enter mitosis

Zone of Proliferation

2nd zone of Epiphyseal Growth Plate

Cartilage undergoing mitosis

Zone of Hypertrophy

3rd zone of Epiphyseal Growth Plate

Chondrocytes undergo hypertrophy

they grow getting closer to the zone of calcified cartilage then die

Zone of Calcified Cartilage

4th zone of Epiphyseal Growth Plate

Chondrocytes die, osteoblasts begin depositing osteoid on their remains

Zone of Resorption

5th zone of Epiphyseal Growth Plate

Bone deposition and remodeling begin

Matrix Calcification

Osteocalcin secreted by osteoblasts bind Calcium

Osteoblasts secrete alkaline phosphatase

• The vesicles housing alkaline phosphatase serve as the foci for the formation of hydroxyapatite crystals (exclusive to bone)

Process continues until collagen is embedded in calcified material

Calcium Mobilization

Mainly resorbed from spongy bone

PTH: inhibits osteoblasts causing them to secrete osteoclasts stimulating factor

Matrix is broken down and calcium is delivered to interstitial fluid (when Ca is low)

Fracture Repair

• When bone breaks, blood vessels break too causing hemmorhages

• Osteocytes die locally

• blood clots

• granulation tissue formed from fiibroblasts

• Callus formed with cartilage bars

• bony sleeve surrounds callus

• blood vessels enter callus

• Spongy bone replaces callus which is then replaced with compact bone

• excess bone resorbed

• bone returns to normal shape

Glial Cells

Support and protection of the neurons

short processes

Neruons

Structural and functional unit of the nervous system

From Neuroectoderm (CNS) or neural crest (PNS)

• Cell Body - trophic center of the neuron

• several dendrites - shorter processes that transmit impulses toward cell body, receive stimulus at synapses

• Axon - transmits impulses away

Multipolar Neuron

Most abundant

1 axon, 2 dendrites

Dendritic Arbor - very branched dendritic processes

Bipolar Nueron

Rare

1 Dendrite 1 Axon

Special sensory system (retina, olfactory, inner ear)

Unipolar Neuron

Spinal ganglia

Longer branch of dendrites that go to the periphery and to the CNS

Anaxonic Neuron

Lacks true axon

present in the CNS

does not produce action potential

regulates local electrical charges of adjacent neurons

Axosomatic Synapse

Axon connected to cell body to send signals

Axodendritic Synapse

Axon sending signals to a dendritic spine

Axoaxonic Synapse

Axons sending signals to other axons

Excitatory Neurotransmitters

Causes membrane depolarization (Na+ mediated)

ACh, Glutamate, Serotonin

Inhibitory Neurotransmitters

Causes membrane hyperpolarization (Cl- mediated)

GABA, glycine

Anterograde Transport

From the cell body > Synapse

Kinesin motor ( - > + )

Retrograde Transport

From synapse > cell body

dynein motor ( + > - )

Oligodendrocytes

insulates CNS axons

allows faster action potential propagation

derived from neuroectoderm

Each oligodendrocyte myelinates up to 30 CNS axons

mostly in glial cells in white matter

Oligodendrocytes Nissil Stain

small nuclei with dark chromatin and a little cytoplasm

Oligodendrocytes H & E stain

fried egg appearance

Astrocytes

multiple processes going all around

Provide physical and metabolic support

maintenance of blood-brain barrier

largest glial cell

nuclei: salt and pepper pattern

Intermediate filament = GFAP

Astrocytes GFAP Stain

star shaped cell

Astrocytes H&E stain

irregular, potato shaped nuclei

Ependymal Cells

Columnar cells that line the ventricles of the brin and central canal of spinal cord

Single layer of cuboidal to columnar cells

clear cytoplasm, rounded nuclei

Has both microvilli and cilia

Microglial cells

phagocytes of CNS

scavengers of the CNS responding to tissue damage

part of the mononuclear phagocyte system

Schwann Cells

Surrounds and insulates PNS axons

allows for faster action potentials

saltatory conduction - one node of Ranvier to the next

one per axonal segment

Satellite Cells

Structural and metabolic support for neuron cell bodies

Electrically insulates PNS cell bodies

around the cell body of the PNS neuron

Indistinct cell boundaries

Gray matter

in the periphery of the brain / Central part of spine

most neuronal perikarya - cellular portion

White Matter

Central part of the brain / Periphery of spine

wher eaxons are concentrate

Cerebellar Cortex Molecular Layer

Thick outer layer with a lot of neuropils and scattered neuronal cell bodies

Cerebellar Cortex Purkinjie Cells

Thin and large

dendrites extend throughout the molecular layer as a branching basket of nerve fibers

Axons through granular layer

Cerebellar Cortex Granular Layer

thick inner containing small dense neurons

Spinal Cord Anterior Horns

gray matter

contain cell bodies of large motor neurons

make up the ventral roots

Spinal Cord Posterior Horns

Contain interneurons which receive sensory fibers from neurons in the spinal ganglia

Dura Mater

dense irregular connective tissue

organized as an outer periosteal layer and an inner meningeal layer

Arachnoid Meninges

Shet of connective tissue in contact with dura mater

loosely arrange trabeculae composed of collagen and fibroblasts

Arachnoid Villi - penetrate the dura mater and enter blood filled venous sinuses - function in releasing excess CSF to blood

Pia Mater

flattened, mesenchymal derived cells closely applied to entire surface of CNS tissue

Blood Brain Barrier

Prevents circulating blood substances from reaching CSF/CNS

More functional barrier than most tissue

tight junctions, basement membrane, astrocyte foot processes

Cerebrospinal fluid

made by ependymal cells of choroid plexus

consists of ependyma and vascularized pia mater, projecting many thin folds

CSF is reabsorbed by arachnoid granulations and drained into dural venous sinuses

Myelination Steps

1. Contact & Recognition – The oligodendrocyte (CNS) or Schwann cell (PNS) recognizes and attaches to the axon.

2. Membrane Wrapping – The glial cell membrane begins to spiral around the axon multiple times.

3. Compaction – The layers of membrane squeeze together tightly, expelling cytoplasm and forming a dense myelin sheath.

4. Maturation – Nodes of Ranvier are established, and the myelin sheath stabilizes to enable fast saltatory conduction.

Small Cells

Not typically fully myelinated

in close relation with schwann cells, but no full myelinated layers wrapped around

Skeletal Muscles

Long, cylindrical

multi nucleated - located in periphery of the cell

striations caused by alternating thin and thick filament

Fascicle

Bundle of muscle fibers

Epimysium

Connective tissue arround muscle

Perimysium

Connective tissue around fascicles

Endomysium

connective tissues around individual myofibers

Sarcomere

A sarcomere is the repeating structural and functional unit of a myofibril, extending from one Z-disc to the next. It is responsible for muscle contraction.

SR/T-Tubule System

SR - Calcium Reservoir

T-Tubules - Invaginations of sarcolemma

Two SR cisternae flanking a section of t-tubule = Triad

• exclusive to skeletal muscle

• found at A-I band junction

Muscle Contraction Steps

• ACh released at NMJ

• ACh binds to receptors on sarcolemma

• depolarizing wave spreads via T-tubules

• Depolarization opens Ca2+ channels in SR

• Ca2+ enters the sarcoplasm

Myasthenia Gravis

autoimmune disorder in

antibodies block or destroy ACh receptors at the neuromuscular junction, leading to impaired transmission of nerve signals to muscles

symptoms: droopy eyelid

Slow Type 1 Muscle Fibers

Slow contractions, prolonged time, little fatigue

rich in mitochondria and myoglobin (dark red appearance)

Fast Type 2b Muscle Fibers

rapid short term contractions

anareobic metabolism, few mitochondria

rapid fatigue

Z-discs (lines)

define the boundaries of a sarcomere

anchor actin

M-line

center of the sarcomere

stabilizes and anchors myosin

Fast Type 2A

oxidative-glycolytic

Intermediate of Type 1 and 2A

Good balance between fast and slow

A Band

Dark region

contains entire length of thick filaments

I-Band

light region

only contain thin filaments and span between two sarcomeres

H-Zone

central part of the A-Band with only thick filaments

Duchenne’s Muscle Dystophy

Defective Dystrophin

skeletal Muscle fibers start to lose structure

Mostly boys

Cardiac Muscle Features

Striations

Intercalated Discs

Sparse SR

Underdeveloped T-tubules

• T-tubules and some SR form a complex - dyad

• can be found at the Z - disc

abundant large mitochondria

Gap junctions!

Smooth Muscle Features

no sasrcomere

rudimentary SR

myosin shape differs

dense boies

Contraction requires binding of Calcium to Calmodulin - activation of MLCK

Caveoli and Gap junctions!

Skeletal Muscle Regeneration

limited capacity for regeneration

satellite cells may differentiate into skeletal muscle cells

Cardiac Muscle Regeneration

no satellite cells, no capability for regeneration

hear attacks - fibroblasts - scar formation

Smooth Muscle Regeneration

High capability for regeneration

repairs itself