Histology Flashcards
What do epithelia form barriers for?
Protection (skin)
Absorption (gut)
Secretion (pancreas)
What is simple epithelia?
A single layer of cells on a basement membrane
What is stratified epithelia?
-Two or more layers of cells on a basement membrane
-Continually worn down and replaced
-Protective function
-At sites of abrasion
Describe simple squamous epithelia
-Single layer of flattened cells on a basement membrane
-Parallel oval nuclei (1 per cell)
-Line inside of blood vessels, mesothelium and peritoneum
Describe simple cuboidal epithelia
-Single layer of cells with similar height/width on a basement membrane
-Central spherical nuclei
-Line kidney tubules and small ducts (sweat glands, salivary, pancreas)
Describe simple columnar epithelia
-Single layer of taller cells on a basement membrane
-Line stomach, intestine and uterus
-May or may not have cilia/microvilli
What are microvilli?
-Tiny projections on luminal surface of absorptive cells
-Increase surface area
-Intestinal brush border
-Need an electron microscope to see
What are cilia?
-Microscopic motile projections on luminal surface
-In respiratory and reproductive tract
Where are stratified squamous epithelia?
Non-keratinising: mouth, oesphagus, vagina, oropharynx
Keratinising: waterproof layer in skin
What’s psuedostratified epithelia?
-Single layer of cells of varying heights, mimicking multiple layers
-All cells in contact with basement membrane
-Line conducting airways
Describe urothelium
-Surface layer of umbrella cells
-Pseudostratified between umbrella cells
-Lines collecting part of urinary tract
What are epithelial junctions?
-Occluding junctions prevent diffusion between cells
-Desmosomes joins cytoskeletons of adjacent cells
-Gap junctions allow transfer of small molecules and ions between adjacent ep cells
What can undifferentiated mesenchymal cells give rise to?
- mast cell
- fibroblast
- chondroblast
- osteoblast
- adipocyte
Three divisions of connective tissue
Fibrous: loose/dense
Hard: cartilage/bone
Fatty: white/brown
What are the 5 different types of collagen?
1: skin
2: cartilage
3: (reticulin), in liver, bone marrow and spleen
4: basement membranes of epithelia
5: placenta
Characteristics of collagen
- Extracellular fibres stain pink with H+E
- variable thickness and lengths
- often run in bundles
Characteristics of loose connective tissue
- widely spaced thin collagen fibres
- fibroblasts/cytes
- unstained ground substance
Characteristics of dense connective tissue
- closely spaced thick collagen fibres
- fibroblasts/cytes
- unstained ground substance
- irregular or regular
Characteristics of reticulin
- type 3 collagen
- scaffold to bone marrow, liver, kidney, lymph node and spleen
- not visible on H+E, need a silver stain
Characteristics of elastin
- produced by fibroblasts
- fine fibres or sheets of elastin
- stains pink on H+E
- may be branched
Characteristics of white adipose tissue
large cells with single fat globule
usually appear empty as fat extracted
Use of H+E + colours
H stains nuclei and RNA blue
E stains colloidal proteins, most components of cell cytoplasm, and keratin pink/red
Use of Van Gieson stain and colours
Collagen pink/red
elastic van gieson stain elastic fibres brown/black
Muscle stained yellow
Use of Alcian Blue and colours
GAG, mucous goblet cells, mast cell granules and cartilage matrix all blue
Use of PAS and colours
Hexose sugars especially in complex carbohydrates, e.g. goblet cell mucins, cartilage matrix, glycogen, basement membranes, all stain magenta
Use of Perl’s stain
Ferric iron. prussian blue
Use of Romanovsky stains and colours
Chromatin, azurophils, neutrophils - purple
Erythrocytes - red/pink
Lymphocyte and monocyte cytoplasm - dark blue/purple
Use of Toluidine blue and colours
Nuclei, ribosomes, cytoplasm - dark blue
Cartilage matrix, mast cell - pale blue
GAG-rich components - bright purple
Structure of arteries
Lumen
Endothelium
Basement membrane
Intima
Internal elastic lamina
Media (sheets of elastin)
External elastic lamina
Adventitia
Where would you find elastic arteries?
Near the heart, e.g. pulmonary, aorta
What are the muscular arteries?
Most abundant
Media comprised of smooth muscle, little elastin
E.g. radial and splenic artery
What are arterioles?
3 or fewer muscle layers in media
Resistance vessels
Elastic laminae poorly defined
General structure of capillaries
Lumen
Endothelium
Basement membrane (fenestrated capillaries have gaps)
Pericytes on outside
General structure of veins
Lumen (wider than arteries)
Endothelium
Basement membrane
Intima
Internal elastic media
Media (thinner than arteries)
Adventitia
What are venules?
Associated with arterioles
Thin walls
Pericytes wrap around outside and form layer
Perictyes swap to smooth muscle when become veins
About veins
Walls thinner than arteries but thicker than venules
Smooth muscle may be circular or longitudinal
About lymphatics
Walls similar thickness to veins
Have valves
Have eosinophilic lymph not blood
Structure of peripheral nerves
Composed of axons
Axons supported by schwann cells (produce myelin)
Most myelinated (m faster and larger than unmyelinated)
Parts of a myelinated peripheral nerve
Endoneurium: connective tissue, binds together axons
Perineurium: connective tissue, binds groups of axons
Epineurium: binds perineurium groups
About myelin
Silver stain
Insulating layer formed by spiral of Schwann cell membranes
Gaps between schwann cells are nodes of ranvier
Where are motor neuron cell bodies found?
Spinal cord grey matter
Where are sensory neuron cell bodies found?
dorsal root ganglion
Where are sympathetic neuron cell bodies found?
grey matter of spinal cord and in adjacent sympathetic ganglia
Where are parasympathetic neuron cell bodies found?
brain and local ganglia
What are the constituents of blood?
56% Plasma- salts, minerals, plasma proteins, clotting factors, hormones, water
43%- Erythrocytes
1%- Leucocytes
Serum (fluid component) is plasma minus clotting factors
About erythrocytes
- 4-6 million per mL of blood
- Lifespan of 4 months
- Enucleate, biconcave discs, larger than the smallest capillaries
- Produced in foetus liver or haematopoetic bone marrow
- 6.5-8.5µm in diameter
- Destroyed in liver and spleen
- Main protein is haemoglobin
- Cell membrane has endoskeleton attached (spectrin)
What are the categories of white blood cells?
- Granulocytes (visible granules): neutrophils, eosinophils, basophils
- Agranulocytes (no visible granules): lymphocytes, monocytes
- Platelets (cell fragments)
About neutrophils
- Commonest white blood cell & granulocyte
- Phagocytic, contains myeloperoxidase
- Multi-lobed nucleus
- Larger than RBC,12-14 µm
- Circulate in blood and invade tissue spaces
What are 3 types of granules neutrophils contain?
- Primary granules: lysosomes (contain enzymes: myeloperoxidase and acid hydrolase)
- Secondary granules: specific, secrete substances that mobilize inflammatory mediators
- Tertiary granules: contain gelatinases and adhesion molecules
About eosinophils
- 1% total of white blood cells
- 12-17µm
- Increase in parasitic infections
- Bi lobed nucleus
- Antagonistic action to basophils and mast cells
- Phagocytic, affinity for antigen-antibody complexes
- Restrict inflammatory response: neutralise histamine & inhibit mast cell secretion
- Receptors for IgE
About basophils
- 0.5% of WBC
- Bi lobe nucleus
- 14-16µm
- Granules contain histamine
- Involve inflammatory reactions
- Prevent coagulation
- Receptors for IgE
- Release histamine and other vaso-active agents in allergen response
What are the types of lymphocytes and their roles?
- T helper cells: helps B and activate macrophages
- T cytotoxic cells: kill marked target cells
- T suppressor cells: suppress helper and the immune response
- B cells: become plasma cells and secrete antibodies
- Natural killer cells: mainly kill virus infected cells
- In histology, all lymphocytes look the same
About monocytes
- Immature, circulate briefly, differentiate
- Reniform nucleus
- 15-20µm
- Phagocytic role
- Small cytoplasmic granules, despite being agranulo
What can monocytes differentiate into?
- Tissue macrophages
- Kupffer cells
- Osteoclasts
- Antigen presenting cells
- Alveolar macrophages
About platelets
- 1-3µm
- Fragments of megakaryocytes from bone marrow
- Responsible for clotting of blood, particularly when endothelial lining is breached
What are the 3 series on haematopoesis histology?
- Myelon: next to bone, gives rise to WBC
- Erthryon: in between bony trabeculae, gives rise to erythrocytes
- Megakaryocytes: in between bony trabeculae, gives rise to platelets
Describe eythropoesis
- reduction in cell size
- Haemoglobin produced
- loss of organelles
- basophilia in early precursors change to eosinophilia as haemoglobin increases
- loss of nucleus
- mediated by EPO
Describe granulopoeisis
- Increasing numbers of granules
- Increasing complex shape of nucleus
- stored pool of neutrophils in marrow
Describe the pericardium
- Outermost layer of the heart
- Single layer of squamous mesothelial cells, rest on thin layer of fibrous connective tissue
- visceral pericardium is outer surface layer
- parietal pericardium is layer on inner surface of fibrous sac
Describe the epicardium
- lies immediately underneath pericardium
- underlying adipose connective tissue, vessels and nerves
Describe the myocardium and myocytes
- thickest layer of the heart
- below epicardium
- specialised cardiac muscle that is striated, centrally located nuclei, branching, intercalated discs
- between myocytes, there is loose fibrous connective tissue (endomysium)
- largest myocytes in wall of left ventricle
- artial myocytes smaller as lower pressure
Describe the intercalated discs in the myocardium
- connect adjacent cardiac myocytes
- contain: gap junctions, adhering junctions and desmosomes
What does the heart secret as an endocrine organ?
- atrial natriuretic peptide
- perinuclear neuroendocrine granules secrete
Describe the endocardium
- innermost layer of the heart
- thin layer of fibrous connective tissue lined by a single layer of endothelial cells (simple squamous)
- covers the cardiac valves
Describe the valves of the heart
- 3 separate layers, hard to see on H&E
- dense layer of fibrous connective tissue: fibrosa
- layer of loose fibrous connective tissue immediately beneath fibrosa: spongiosa
- looser layer of collagen and elastin on ventricular surface: ventricularis
- both sides of cardiac valve are covered by vascular endothelial cells
Describe skeletal muscle
Fibres are individual cells formed by fusion of multiple myoblasts during embryonic life
Long fibre like structures
Multiple nuclei, hundreds per fibre, on edge
Eosinophilic striated cytoplasm
Myofibrils in register
Unbranched
Describe cardiac muscle
Striated muscle
Myocytes remain as individual cells throughout life
Single nucleus in centre
Individual myocytes joined by intercalated discs
Branched
Describe smooth muscle
Spindle cells in longitudinal sections
Single nucleus in centre of cell
Cytoplasm eosinophilic but not striated
Unbranched
Is the muscle striated? yes/no which
No: smooth muscle
Yes: cardiac or skeletal
Function of the respiratory tract
Filtration
Humidifying
Warming
Olfaction
Gas transport and exchange
Protection against infection
Speech
Describe respiratory epithelium
- lines tubular part
- pseudostratified columnar (rests on basement membrane)
- ciliated
- interspersed goblet cells
Describe the nose (epithelium)
- keratinising, stratified squamous epithelium at front of nostril, further back non-keratinising
- nasal cavity lined by resp epithelium
- connective tissue under resp epithelium contain seromucinous glands
What is olfactory epithelium?
- pseudostratified columnar
- in roof of nasal cavity and extending down septum and lateral wall
- stereocilia (non-motile)
- serous glands of bowman below secrete a watery fluid
- large number of nerves also in underlying tissue
- bipolar neurones extend to surface (seen in silver stains not H+E)
What lines the nasopharynx and nasal sinuses?
Respiratory epithelia
Describe histology of the larynx
- Respiratory epithelium (not for vocal chords)
- beneath respiratory epithelium, loose fibrocollagenous stroma with seromucinous glands, blood vessels and lymphatics
What lines the vocal cords?
Thin stratified squamous epithelium
Overlies loose irregular fibrous tissue
Describe histology of the trachea
- lined by resp epithelium
- seromucinous glands in submucosa
- c shaped ring of hyaline cartilage
- trachealis muscle posterior
Describe histology of the bronchi
- smooth muscle
- partial cartilagenous rings
- respiratory epithelium
- serimucinous glands and goblet cells
- some basal neuroendocrine cells
Describe histology of the bronchioles
- smooth muscle cells
- some basal neuroendocrine cells
- columnar ciliated resp epithelium
- clara cells
What are clara cells?
- found in terminal bronchioles
- pale staining cytoplasm
- abundant mitochondria and smooth muscle
- secretory granules
- no cilia
Describe the histology of resp bronchioles
- cuboidal ciliated epithelia
- spirally arranged smooth muscle
- no cartilage
Function of the respiratory bronchioles
Gas transport
Gas exchange
Link terminal bronchioles and alveolar ducts
Describe the histology of alveoli
- 150-400 million per lung
- 250 microns in diameter
- type 1 and 2 pneumocytes found in alveoli
- also have alveolar macrophages
What are type 1 pneumocytes in alveoli?
- 90% of surface lined by squamous type 1 pneumocyte
- flattened cells, flattened nucleus
- 40% of cell pop in alveoli
What are type 2 pneumocytes?
- 5-10% of cell surface
- rounded to columnar
- central rounded nucleus
- mitochondria and ER
- produce surfactant
- 60% of cells in alveoli
Describe the alveolar macrophages
- found in interstitial connective tissue and lumen of alveoli
- derived from blood monocytes
- phagocytose bacteria and particulates
- pigmented, can contain carbon pigment
- removed via lymphatics or mucociliary escalator
Describe the alevoli-blood-air barrier
- type 1 pneumocyte that rests on basement membrane shared by endothelial cell of adjacent capilliary
- 200-800nm thin
- surfacant layer
What is interstitium connective tissue?
- loose fibrous connective tissue
- collagen and elastic fibres (very little in alveoli), produce by fibroblasts
What are the pores of Kohn?
- holes in alveolar walls,
- equalize pressure, allows lungs to inflate equally and evenly
- infection rapidly spreads through (pneumonia)
Describe the histology of the visceral pleura?
- flat mesothelial cells
- loose fibrocollagenous connective tissue
- irregular external elastic layer
- interstitial fibrocollagneous layer
- irregular internal elastic layer
What does the alveolar interstitium contain?
blood vessels
lymphatics
macrophages
collagen and elastin
What epithelia is in the oral cavity?
Lined with stratified squamous epithelium (robust to avoid ulcers)
What epithelia is in the salivary glands?
Secretory glandular epithelium
What type of epithelia is in the oesophagus?
Squamous (robust)
Also contains secretory submucosal glands
What surrounds the lumen of the intestines?
lumen (where food is)
epithelium
basement membrane
lamina propria
muscularis mucosae (smooth muscle)
submucosa (connective tissue, loose collagen and blood vessels)
muscularis propia (innermost circular and outermost longitudinal)
serosal surface (mesothelial cells resting on a basement membrane)
What surrounds the lumen of the stomach?
lumen
epithelia
basement membrane
lamina propria
muscularis mucosae
submucosa
musclaris propria (inner oblique layer, middle circular, outermost longitudinal)
