Histology

Question 1

4 basic tissues in human body

Answer 1

Epithelia- aggregated polyhedral cells, small amount ECM
Connective tissue- several types of few fixed cells and some wandering cells, form basal lamina, abundant amount ECM
Neural tissue- elongated contractile cells, moderate amount ECM
Muscle tissue- elongated cells with extremely fine processes, very small amount

Question 2

Tissues have two components

Answer 2

Cells and extracellular matrix

Question 3

ECM

Answer 3

Consists of many kinds of large molecules, fibres and fluids with its minor component cells interspersed within
Mostly looks like an aparticulate space on histology may or may not stain depends on ground substance
ECM= fibres (reticular, collagen or elastic) and ground substance

Question 4

Ground substance

Answer 4

Proteoglycans
Glycosaminoglycans covalently bound to proteoglycans, responsible for physical properties of ground substance
Multi adhesive glycoproteins
The ECM provides mechanical and structural support as well as tensile strength, ECM components form a dynamic and interactive system that informs cells about the biochemical and mechanical changes in their extracellular environment

Question 5

Glycosaminoglycans

Answer 5

• Hyaluronan- synovial fluid, lubricant and shock absorber maintain large structures in matrix
  -Chondoitin 4-sulfate - cartilage bones heart valves, fundamental component of aggrecan
  -Chondroitin 6-sulfate- cartilage bone, heart valves
  -keratan sulfate- bone cartilage cornea, cellular recognition of protein ligands, axonal guidance, cell motility, corneal transparency and embryo implantation

Highly negative charged (sulfate and carboxyl groups on many of the sugars) thus generally stain with basic dyes hematoxylin
High negative charge density attracts water forms hydrated gel permitting rapid diffusion of water soluble molecules and the rigidity provides structural scaffolding for cells

Question 6

Hyaluronan

Answer 6

Made in the cell membrane so not metabolised
Very long, synthesised by enzymes on cell surface (not post translationally modified like other GAGs)
Doesn’t contain sulfate
Simple structure repeating disaccharide chains of N-acetyl-glucosamine and glucuronic acid
Hydroviscous substance extremely hydrophilic
Binds to lots water
Voluminous expanded random coil structure in aqueous physiological solutions
Via link proteins proteoglycans bind to HA to form giant macromolecules called proteoglycans aggregates which allow cartilage the ability to resist compression without inhibiting flexibility making them excellent shock absorbers
Size of HA and it’s bonds can influence mobilations of cancer cells, microorganisms and other migrating macromolecules

Question 7

Proteoglycans

Answer 7

Aggrecan- binds via a link protein to H, cartilage and chondrocytes, responsible for hydration of extracellular matrix of cartilage
Decorin
Versican
Syndecan

Question 8

Embryonic connective tissue

Answer 8

Mesenchyme- mucous connective tissue

Question 9

Connective tissue proper

Answer 9

Loose or dense connective tissue
Dense: regular or irregular

Question 10

Specialised connective tissue

Answer 10

Cartilage
Bone
Adipose tissue
Blood
Hemopoietic tissue
Lymphatic tissue

Question 11

What determines the type of connective tissue

Answer 11

Fixed or resident cells
They determine the function of the tissue

Question 12

Hyaline cartilage

Answer 12

ECM stains contains lots of negatively charged ions, avascular
Chondrocytes- prominent nucleus present in lacunae
15% collagen
60-80% intracellular water
Rest is non collagenous proteins
Glossy appearance
Surrounded perichondrium except in articular cartilage
Perichondrium has a outer fibrous layer and inner chrondogenic layer and blood vessels
Consists of chondrocytes surrounded by territorial and interterritorial matrices containing type II collagen interaction with proteoglycans
Occurs in temporary skeleton of embryo, articular cartilage, cartilage of respiratory tract and costal cartilage

Question 13

Elastic cartilage

Answer 13

Avascular
Surrounded by perichondrium
Consists of chondrocytes surrounded by type II collagen interacting with proteoglycans and elastic fibres which can be stained by orcein for light microscopy
Occurs in external ear, epiglottis, auditory tube
Lots dark staining elastic fibres

Question 14

Fibrocartilage

Answer 14

Generally Avascular
Lacks a perichondrium
Consists of chondrocytes and fibroblasts
Surrounded by type I collagen and a less rigid extracellular matrix, Fibrocartilage is considered an intermediate tissue between hyaline cartilage and dense connective tissue
Predominates in intervertebral discs, articular discs of knee- menisci , mandible, sternoclavicular joints and pubic symphysis, TMJ
Chondrocytes are aligned along lines of stress

Question 15

Osteogenic cells

Answer 15

Form and maintain bone
Varying morphology:
-osteoprogenitors:
-osteoblasts- make bone, inner osteogenic layer/cambium layer
-osteocytes- maintenance
Osteoclasts- bone resorbing cells, able to make acid, increases amount calcium and phosphate in blood

Question 16

Osteoblasts

Answer 16

Secrete:
-type I collagen, several glycoproteins and proteoglycans (osteonectin), membrane enclosed matrix vesicles containing:
- enzyme- alkaline phosphatase
-other enzymes (to increase local PO43- ions concentrations)
- protein called osteocalcin binding Ca2+ and local concentration becomes increased
Calcified nanocrystals form
Eventual formation of calcium hydroxyapatite which surrounds collagen and merges into confluent solid mass
Osteoid forms first- unmineralised
Binding of calcium and phosphate ions forms clusters in random arrangements- eventually intra and extrafibrillar collagen spaces are entirely mineralised

Question 17

Osteogenesis

Answer 17

Bone development
-Intramembranous ossification: pre-existing medium of mesenchyme, osteoblasts differentiate directly from mesenchymal cells and begin to secrete osteoid, non hyaline cartilage predecessor, head and face bones
- endochondral ossification: pre-existing hyaline cartilage, populated by osteoblasts that begins to secrete osteoid, bone on cartilage surface (periosteal bony collar) later penetrate diaphysis to form primary ossification centre, secondary ossification centres develop later in epiphysis, primary and secondary ossification centres separated by epiphyseal growth plate

In both processes woven bone (immature) is produced first (irregular collagen network) which will mature lamellar bone (collagen arranged in concentric layers), during the growth of bone areas of osteoid deposition, woven bone and lamellar bone and resorption all exist contiguous to one another

Question 18

Resorption lacunae/ howships lacunae

Answer 18

Enzymatically edged depression or cavity in matrix where the osteoclasts are
Ruffled border seen in EM

Question 19

Osteoclasts

Answer 19

Have multiple nuclei
Similar lineage to macrophages

Question 20

Osteoid vs mineralised

Answer 20

Osteoid stains lighter
More mineralised stains darker

Question 21

Reticular fibres

Answer 21

In bone marrow only seen if stained with silver
Markedly increased reitculin fibrosis (dark fibres), in myelofibrosis , reticular fibres normally present in bone marrow but not as much as this, this patient is at risk of developing leukaemia

Question 22

Epiphyseal growth plate

Answer 22

Hyaline cartilage
Zones:
- reserve cartilage- matrix production
-proliferation- matrix production and mitosis
-hypertrophy - accumulation of lipid, glycogen, alkaline phosphatase and matrix calcification
-calcified cartilage - cell death
-resorption- in metaphysis

Question 23

How does bone grow in length and maintain general shape

Answer 23

Bone resorption on some surfaces
Bone deposition on other surfaces

Question 24

Lacunae

Answer 24

Between concentric lamellae contain osteocytes
Osteocytes interconnected with other osteocytes and osteonal canal via canaliculi

Question 25

Vasculature and innervation of bones

Answer 25

Bones are richly supplied with blood vessels
Ends of bones are supplied by metaphyseal and epiphysial arteries that arise from arteries that supply joints
Nutrient artery pass obliquely through compact bone of the long bone shaft via nutrient foramina, divides in medullary cavity into longitudinal branches to proceed towards each end, supplying bone marrow, spongy bone and deeper portions of compact bone
Most of the compact bone is nourished by branches from periosteal arteries of periosteum
Blood reaches osteocytes in compact bone by Haversian canals osteons
Veins accompany arteries through nutrients foramina, lymphatic vessels are also abundant in the periosteum
Nerves accompany blood vessels supplying bones, the periosteum is richly supplied with sensory periosteal nerves that carry pain fibres, the periosteum is especially sensitive to tearing or tension, which explains the acute pain from bone fractures. Bone itself is relatively sparsely supplied with sensory endings

Question 26

Fracture healing

Answer 26

For the fracture to heal property the broken ends must be brought together- reduction of fracture
During bone healing surrounding fibroblast proliferate and secrete collagen which forms a callus to hold bones together
Callus calcification via mineralisation occurs forming woven bone and callus hardens
Along with remodelling in the fracture area woven bone matures into lamellar bone with clinical resorption of the callus
After several months little evidence of the fracture remains, especially in young people

Initial response is fracture hematoma, devitalised fragments undergo necrosis

Question 27

Synovial joints

Answer 27

Capable wide range of movements between articulating bones
Articulates surfaces of bones maintained in apposition by fibrous joint capsule and ligaments
Surfaces lubricated by synovial fluid
Known as diarthroses
Some have plates of Fibrocartilage between articular surfaces

Question 28

Non synovial

Answer 28

Limited range of movement
Articulating bones have no free articular surfaces but are joined
Dense fibrous tissue:
- sutures, syndesmoses, synostoses when replaced by bone, gomphosis
Hyaline cartilage: synchondrosis/ primary cartilaginous joint unites first rib with sternum
Fibrocartilage: opposing surfaces covered with hyaline instead of synovial plate, direct connection with fibrocartilaginous plate, symphyses/secondary cartlaginous joints occur in pubic symphysis and intervertebral disc, Fibrocartilage disc of pubic symphysis develops a central cavity and Fibrocartilage disc in IVD have a fluid filled central cavity

Question 29

Synovium

Answer 29

Inner surface of synovial joint capsule and tendon sheaths is lined by a specialised collagenous tissue, synovium, which forms lubricating synovial fluid

Question 30

Synovial cells

Answer 30

Not connected by junctional complexes and do not rest of basement membrane
Mesenchymal origin
Majority are plump with feature suggestive of macrophages others resemble fibroblasts (type b synoviocytes)
Synovial fluid is little more than a thin film covering articular surfaces
Because articular space not demarcated by an epithelium synovial fluid represents a highly specialised fluid form of extracellular matrix in contrast to secretion
Major constituents are hyaluronic acid associated glycoproteins expressed by type B synoviocytes, fluid component is a transudate from synovial capillaries, this allows for oxygen, carbon dioxide and metabolite transference between blood
Synovial fluid provides major source of metabolic support

Question 31

The intervertebral disc

Answer 31

Vertebral bodies united by symphysial joints with intervertebral discs permitting movement between the bodies while maintaining powerful union. IVD comprise Fibrocartilage arranged in concentric rings forming annulus fibrosus with a central cavity that contains viscous fluid the nucleus pulposus
Circumferential ligaments reinforce the annulus fibrosus peripherally a thick ligament extending down the anterior aspect of the spinal column merges with and reinforces the annulus fibrosus whilst a similar but thinner ligament reinforces the posterior aspect
The vertebral arches articulate with eachother by synovial joints known as a facet or zygapophyseal joints. Strong elastic ligaments connecting to bony processes of the vertebral arches contribute to the stability of the spinal column

Question 32

IVD

Answer 32

Annulus fibrosus darker staining
Nucleus pulposus gelatinous matrix lighter staining

Question 33

Tendon insertions

Answer 33

Tendons attach to bone by collagen fibres of tendon and periosteum intermingling
Fibres of the tendon also penetrate directly into the bone in form of sharpey fibres
Some of the collagen fibres from the tendon penetrate the muscle to form a complex interdigitation (myotendinous junction) this would be location of some proprioceptors