Histology ๐ฉโ๐ฌ Flashcards
Outline simple columnar epithelia
Taller than wide
Oval nucleus with longer parts adjacent to the longer sides of the cell
Often either have cilia (resp tract) or microvilli (gut erythrocytes)
Outline intestinal epithelium
Enterocytes interspersed with goblet cells
More goblet cells in large intestine than small intestine
Brush border of microvilli
Microvilli- what, why, make up, where
Projections from columnar cells
Canโt see them individually but seen as a brush border
Increased SA for absorption
Glycocalyx on outer surface
Found on most epithelial cells esp. on absorptive ones e.g in gut + kidney
Contain actin and myosin filaments
Ciliated epithelium- where, how many per cell and what does it do
- Lines nose, larynx +bronchial tree w goblet cells
- 300ish cilia per cell, help move mucus to the throat after it has trapped inhaled particles
- Also found in the fallopian tube to transport the ovum
Outline cuboidal epithelium
- Square in profile with a round nucleus
- Rarely over 2 layers of cells
- Occur in the ducts of glands e.g sweat and salivary and the pancreas
- Form much of nephron in the kidney
Outline squamous epithelia
- Single layer
- Surrounds most thor +abd organs (aka serosa)
- Also lines pleural and peritoneal cavities
- Flattened cells
- Kept moist by watery (serous) extrudate -> lubes it so organs can slide over each other
- If destroyed organs can stick together forming adhesions
Outline compound (stratified) epithelia
- Multi layered
- Found in wear and tear situations
- Most common is stratified squamous
- Keratinised form forms epidermal layer of skin
- Cells replaced from stem cells in basal layer of tissue
- Cells discarded when they reach the top layer
Outline the layers of keratinising stratified squamous epithelium
- Lower layers similar to moist stratified
- Upper layers synthesise proteins which interacts with cytoskeleton to produce keratin
- Once filled with keratin the upper layers die off
Outline Pseudo-stratified epithelium
- Appears stratified but is more like simple epithelium
- Appears multi-layered but is actually single layered when stretched
- Lines trachea + bronchi allowing for expansion in inspiration (also in urothelium)
Outline cell junctions
- Cells have to be tightly joined together to act as barriers so macromolecules +/or fluids canโt go past
- 3 typed of cell-cell contact: Desmosomes, tight (adherent) junctions and gap junctions
Outline epithelia
- One or more sheet of cells resting on basement membrane
- For protection, absorption and secretion
- Simple - single layer
- Stratified - 2 or more layers
How does cilia move?
Using tubulin and dynein
What is basement membrane mostly made up of?
Type 4 collagen
What do desmosomes do?
Bind cells to eachother
What do hemidesmosomes do?
Bind cells to the basement membrane
What are the 3 types of cell junctions?
Occluding junctions
Anchoring junctions
Communicating junctions
Outline occluding junctions
- Links cells to form impermeable barrier
- In secretory or absorpatory tissue
Outline the scaffolding of tissues
- Most tissues have scaffolding of extracellular fibres set in a jelly like matrix
- Governs functional organisation of the tissue and dictates the shape of organs
Outline the main fibres of the extracellular scaffolding of tissues
- Main fibres collagen and elastin
Used because of: - High molecular weight
- Strongly hydrophilic and negatively charged polysaccharide polymers
-> Retain water to help with turgor pressure
What are glycosaminoglycans?
Jelly like complexes
What synthesises glycosaminoglycans?
Can be synthesised by many different cells incl. epithelial, muscle, cartilage and bone
But mainly by fibroblasts which can synthesise many different extracellular constituents depending on the environment and mode of stimulation
What can undifferentiated mesenchymal cells become?
Osteoblasts (bone)
Chondroblast (cartilage)
Fibroblast (connective tissue)
Outline soft connective tissue
Flexible and gel-like
Present in most tissues between major tissue elements
Divisible into fibrous or fatty connective tissue
Outline hard connective tissue
Various forms of cartilage and bone
Outline fibrous connective tissue
Contains a large number of fibres e.g collagen, elastin or reticulin
Described as loose irregular if few visible fibres that are random or dense irregular if lots of fibres but random
Dense regular contains lots of fibres arranged in long parallel bundles
Outline fatty connective tissue
Contains mainly fat cells with intervening blood vessels particularly capillaries
Outline differentiation between types of collagen
With conventional stained histology you can tell if there are differences in length and thickness but precise composition canโt be determined
At least 12 types of collagen- biochemical compositions are different
But all collagen fibres are not elastic or contractile
What does type I collagen do?
Type I- Skin, Bones, teeth, capsules of organs
What does type II collagen do?
Cartilage
What does type III collagen do?
Liver, kidney, spleen arteries, uterus
What does type IV collagen do?
Type IV- Basement membranes
What does type V collagen do?
Placenta
Outline the structure of collagen
Individual collagen fibrils are made up of overlapping linear strands of tropocollagen (gives rise to characteristic bonding of collagen)
Fibrils are aligned side to side to create larger collagen fibres of variable thickness
Outline the tropocollagen subunits
Made up of 3 linear polypeptide chains (2 similar and 1 not)
Wound together in an alpha helix
Outline the connective tissues of the penis
Loose to dense irregular
3 erectile compartments surrounded by a capsule of dense irregular connective tissue surrounding and a tissue with fewer fibres between nerves, blood vessels + lymphatic vessels are also components of connective tissues
Outline the structure of elastic tissue
Consists of microfibres of fibrillin and an amorphous matrix of elastin
Forms fine fibres or flat sheets
Where is elastic tissue found?
Present in most connective tissues and in walls of blood vessels
Outline the staining of elastic tissue
Elastin fibres stain pink with H+E stain
Sometimes hard to distinguish from collagen but may stain more strongly than collagen and sometimes produce a glassy and refracting light appearance
Outline adipose tissue
Some connective tissues contain it
2 types- white and brown
Outline white adipose tissue
Most abundant
Large cells each with a single fat droplet
Protect vital organs and serve as energy stores
Fat is deposited alongside capillaries and so usually displays a rich network of fine blood vessels
Outline brown fat
Brown fat is abundant in newborns but less so in later life
Described as multi-locular as cells contains numerous droplets of fat rather than a single one
How is cartilage related to bone?
Along with bone is rigid
Closely related to it
Bone is ossified cartilage
Outline the formation of cartilage
Initially formed by chondroblasts- get trapped in a dense glycosamino rich matrix
Matures into chondrocytes
Surrounded by fibrous capsule of collagen and perichondrium
Contains undifferentiated progenitor- capable of differentiating into chondroblasts if needed
Variable amounts of collagen and elastic tissue
What are the 3 types of cartilage?
Hyaline
Elastic
Fibrous
Outline the makeup of hyaline cartilage
Has fine fibrils of collagen and elastic
(Canโt see elastic on light microscope but have glossy appearance on matrix)
Hyaline cartilage with staining
Stains poorly with H+E stain
Where do you find hyaline cartilage?
Articular surfaces e.g cartilage in trachea
All bones are formed from hyaline cartilage which is replaced by bone in a process called endochondral ossification
Outline the structure of the elastic cartilage
Fibres a re irregularly arranged and can be seen in the matrix, contains chondrocytes and lots of elastic fibres
Where can you find elastic cartilage?
Epiglottis and pinna of ear
Outline fibrous cartilage make up
Matrix of cartilage fibrils filled with collagen in bands
What is made up of fibrous cartilage?
Intervertebral discs
What are the 3 types of muscles and where do you find it?
Smooth muscle- many internal organs and blood vessels
Cardiac muscle- heart
Skeletal- mainly attached to bony skeleton + is responsible for its stability and movement
Outline other cells with contractile properties
Pericytes- along small blood vessels
Myofibroblasts- involved in scar formation
Myoepithelial cells- assist in expression of milk during lactation
Outline the structure of smooth muscle
Discrete cells coupled together by cell junctions
They appear fusiform with cylindrical nuclei when cut longitudinally (and round when transversely)
Contractile proteins in it are not arranged regularly in repeating sarcomeres (anchored focally in clumps to cell membrane
Key features of smooth muscle cells that help it to function
Secrete reticulin external lamina (basement membrane)
Joined by gap junctions which permit the stimulus to pass rapidly through the muscle
Also have surface receptors to respond to hormonal stimuli
Outline gap junctions
Joins 2 smooth muscle cells together
Vital for coordinated contraction of smooth muscle
The guarded central pole allows small signal molecules to pass from one cell to the next in the chain
It electrically couples them and means the signal doesnโt need to be transported across the membranes
What is the gap junction?
Each one consists of 6 connection proteins that span the cell membranes
Forming a central pole
Layers of blood vessels from inner to outer
Endothelium
Basement membrane
Intima
Internal elastic lamina
Media
External elastic lamina
Adventitia
Outline elastic arteries
Near the heart- aorta and pulmonary
Media contains abundant concentric sheets of elastin (seen as red lines)
Outline muscular arteries
Most abundant
Media made up of layers of smooth muscle with little elastin
E.g radial artery, splenic artery
Outline arterioles
Resistance vessels
Have 3 or fewer layers or fewer muscle layers in their media
Up to 100 um diameter
Elastic laminae poorly defined
Outline structure of capillaries
Only have lumen, endothelium and basement membrane
Pericytes on outside to regulate size-> discontinuous layer on outside of small ones which become continuous as they get larger
No surrounding muscles or connective tissue
Outline fenestrated capillaries
Most tissues have closed capillaries but some have leaky/ fenestrated ones e.g kidney + liver
Have holes in endothelium for movement into and out of surrounding tissues
Outline veins
No external elastic lamina
Thinner walls and larger lumen- media is thinner (than arteries) although large veins thicker compared to venules
Smooth muscle in wall might be circular or longitudinal
Outline venules
Associated with arterioles
Thin walled
Contractile pericytes wrap around the outside of endothelial cells and form a complete layer as venules get larger
Pericytes replaced by smooth muscle as venules become veins
Outline lymphatics
Thin walled similar to capillaries and veins
Have valves
No blood
Contains eosinophilic lymph and maybe lymphocytes (those are mostly in blood tho)
nerves
Outline plasma
It is blood without the cells
Made of water, salt + minerals, plasma proteins (albumin globulins and fibrinogen), hormones, signal molecules, other clotting factors ect.
What is serum?
Plasma without clotting factors
Outline erythrocytes
Enucleate biconcave discs
6.5-8.5 um in diameter (slightly larger than the smallest capillaries)
Live for 4 months
Main protein is haemoglobin
Cell membrane has an important endoskeleton attached (in which the main protein is spectin)
Where are erythrocytes produced and destroyed?
Produced in the liver (foetus) and bone marrow
Destroyed in the liver and the spleen producing bilirubin
What are the different types of leukocytes?
Granulocytes: Neutrophils (40-75%), Eosinophils (5%), Basophils (0.5%)
Agranulocytes: Lymphocytes (20-50%), Monocytes (1-5%)
Outline neutrophils
Commonest wbc and granulocyte
Multi lobed nucleus, granular cytoplasm, 12-14 um in diameter
Circulate in the blood and invade tissue spaces
Contain myeloperoxidase- for respiratory burst
outline the phagocytic nature of neutrophils
engulf and destroy bacteria and other foreign macromolecules via respiratory burst
What are the 3 types of cytoplasmic granule?
Primary granules
Secondary granules
Tertiary granules
Outline primary granules
Lysosomes (myeloperoxidases + acid hydrolases)
Outline secondary granules
Specific granules (secrete substances that mobilise inflammatory mediators
Outline tertiary granules
Gelatinases and adhesion molecules
Outline Eosinophils
1% of total number of wbcs
12-17 um in diameter
Bi-lobed nucleus
Distinctive large red cytoplasmic granules with crystalline inclusions
Have receptors for IgE
Outline granules in eosinophils
Large and red with crystalline cores
lozenge shaped granules
What do eosinophils do?
Numbers increase in parasitic infections or allergic conditions
Antagonistic action to basophils- play a role in phagocytosis and to mast cells as they inhibit their secretion
Phagocytic with a particular affinity for antigen/antibody complexes
Neutralise histamine- restricting inflammatory response
Outline basophils
0.5% of white cell series
14-16 um in diameter
Bi-lobed nucleus + prominent dark blue-stained cytoplasmic granules
Granules contain histamine
Have receptors for IgE
Circulating form of the tissue mast cell
What do basophils do?
Involved in inflammatory regulations and act to prevent coagulation and agglutination
Release histamine and vaso-active agents in response to allergens -> results in immediate hypersensitivity reaction - Aka anaphylaxis
Outline lymphocytes
Most common agranulocytes
2 main sub types-
B Cells
T Cells
Very few cytoplasmic inclusions so clear blue/grey cytoplasm
All subtypes look the same in histological sections on H+E - have to use histochemistry
Only blood cell capable of cell division
Outline B cells
Become plasma cells and secrete antibodies
Called B cells bc they mature in bone marrow
Outline T Cells
Are involved in cell mediated immunity
Called that because they mature in the thymus
Outline T Helper (TH) cells
Help B cells and activate macrophages
Outline T cytotoxic (TC) cells
Kill previously marked target cells
Outline T Suppressor (TS) cells
Suppress the TH cells so suppress the immune response
Natural killer (NK) cells
Mainly kill virus infected cells
Outline monocytes
Characteristic reniform nucleus (bean shaped)
Although an agranulocyte- it has small cytoplasmic granules (mostly lysosomes)
What do monocytes do?
Immature cells circulate briefly in the blood
Differentiate into several different cell types within tissue
Major phagocytic and defensive role
Some cells become APCs, passing antigen fragments to lymphocytes
What do monocytes differentiate into?
Tissue macrophages (anywhere)
Kupffer cells (liver)
Osteoclasts (bone)
APCs (everywhere)
Alveolar macrophages (lung)
Outline platelets
Fragments of cells derived from large multi-nucleated megakaryocytes in bone marrow
1-3 um in diameter
Surrounded by cell membrane
Contains vesicles with coagulation factors
Responsible for clotting of blood notably when endothelium lining blood vessels is breached
Outline haematopoiesis
All blood cells form in the haematopoietic bone marrow in adults
And liver in foetus
Outline myelon series
Lies next to bone and gives rise to white blood cells
Outline erythron series
Lies in between trabeculae and gives rise to erythrocytes
Outline megakaryocytes
Lie in between bony trabeculae and gives rise to platelets
Outline erythropoiesis
Reducing cell size -> haemoglobin production increases -> reduction + loss of organelles -> basophillian early precursors changes to eosinophillian late precursors -> loss of nucleus -> mediated by erythropoeitin
Outline Granulopoiesis
Morphologically similar for neutrophils, eosinophils + basophils
Increasing number of granules
Increasing complex shape of the nucleus
Outline the storage of wbcs
Large pool of stored mature neutrophils in marrow
No storage of monocytes and lymphocytes complete their precursor maturation either in the thymus or the lymph nodes
Outline pericardium
Outermost layer of the heart
Has a layer of squamous mesothelial cells resting on thin layer of connective tissue
Visceral (outer surface of the heart)
Parietal (inner surface of fibrous sack containing the heart)
Outline the epicardium
Sometimes used interchangeably with pericardium
Strictly it is adipose connective tissue, vessels and nerves
Between pericardium and myocardium
Outline the myocardium
Thickest layer of the heart
Specialised cardiac muscle
Endomysium
Largest myocytes in wall of left ventricle- smallest in atria
Contain perinuclear endocrine granules (atrial naturetic peptide)
The heart is an endocrine organ
What is a key difference between the action of atrial myocytes and ventricular myocytes?
Atrial myocytes secrete hormones but ventricular myocytes donโt
Outline the cardiac muscle
Striated, central nuclei (only 1), branching, intercalated discs (only found in myocardium)
What is endomysium?
Loose fibrous connective tissue between muscle fibres
What are intercalated discs?
Connect adjacent myocytes
Contain: gap junctions, adhering junctions, desmosomes
Outline the parts of the conducting system of the heart
Sinoatrial node, atrioventricular node, bundle of His, purkinje fibres- specialised myocytes
Stains with periodic acid shift- highlights glycogen rich cells
Subendocardial, large vacuolated muscle cells
Outline the endocardium
Innermost layer of the heart
Thin layer of fibrous connective tissue
Endothelial cells on innermost layer
Outline valves
Covered by endothelium
Attached to central fibrous body
Fibrosa (dense fibrous CT)
Spongiosa (loose fibrous CT)
Ventricularis (collagen + elastin)
Outline skeletal muscle
Striations - yes
Nuclei - multinucleated and on the edge
Branching - no
Outline cardiac muscle
Striations - yes
Nuclei - uni-nucleated and centred
Branching - yes (via intercalated discs)
Outline smooth muscle
Striations - No
Nuclei - Uni-nucleated
Branching - No
Outline respiratory epithelium
Lines tubular portion of the respiratory system
Pseudostratified- all cells connected to the basement membrane
Ciliated epithelial cells interspersed with goblet cells
What is the purpose of the nose?
Filtration
Humidification
Warming
Olfaction
What is the nose lined with?
Made of keratinising and non-keratinising squamous epithelium and respiratory epithelium
Key tissue that makes up the nose
Richly vascular lamina propria containing seromucinous glands
Borders of the olfactory area
Roof of nasal cavity extending down the septum and lateral wall
What is the olfactory area lined with and what glands does it have?
Pseudostratified columnar epithelium of olfactory receptor cells with supporting sustentacular cells and basal cells
Glands- serous glands of bowman
Outline the nasopharynx functions and epithelial lining
Functions- gas transport, humidification, warming, olfaction
Lined by respiratory epithelium
Outline the nasal sinuses function and epithelial lining
Functions- lower the weight of the skull, add resonance to the voice, humidify and warm inspired air
Lined by respiratory epithelium
Outline the larynx function and what it is made up of
Cartilaginous box (hyaline cartilage)
Function- voice production
Made of - respiratory epithelium, loose fibrocollagenous stroma with seromucinous glands
lymphatics and blood vessels common
Outline the function of and what vocal cords are made from
Function- voice production
Made of - stratified squamous epithelium overlying loose irregular fibrous tissue
Also no lymphatics but has blood vessels
Outline reinkeโs space
A potential space between the vocal ligament and the overlying mucosa.
Outline the trachea function and what it is made of
Function- conducts air to and from the lungs
Made of- respiratory epithelium, seromucinous glands in the submucosa
Trachealis muscle posteriorly, c-shaped cartilagenous rings
Gap filled by vertically orientated smooth muscle called treachealus
Layers of the bronchi
Smooth muscle
Partial cartilagenous rings
Respiratory epithelium
Some basal neuroendocrine cells
Seromucinous glands and goblet cells
What are the layers of bronchioles?
Smooth muscle
Ciliated columnar epithelium
Some basal neuroendocrine cells
Few goblet cells and clara cells
Outline Clara cells make up and location
Most numerous in terminal bronchioles
Contain mitochondria, smooth ER, secretory granules
Donโt contain cilia and have vesicular cytoplasm
What do we think that clara cells do?
Secrete a lipoprotein that helps to prevent luminal collapse during exhalation and keeps from sticking together
Might play a role in oxidising inhaled toxins, antiprotease function, surfactant production/elimination, stem cells
Outline the function and make up of respiratory bronchioles
First part of the distal respiratory tract
Function- gas exchange as well as transport, they link terminal bronchioles and alveolar ducts
Made up of- cuboidal ciliated epithelium and spirally arranged smooth muscle but no cartilage
Size and number of alveoli
150-400 million/lung
250 um in diameter
Function of alveoli
Gas exchange
Cell types in alveoli
Type 1 pneumocytes
Type 2 pneumocytes
Alveolar macrophages
Outline type 1 pneumocytes
40% of cell population but 90% of surface area
Made up of flattened cells, flattened nucleus + few organelles
Type 2 pneumocytes
60% of cell population + 5-10% of surface area
Made up of rounded cells, round nucleus, rich in mitochondria, smooth and rough ER, spherical bodies
Produce surfactant
Outline alveolar macrophages
Luminal cells also present in the interstitium, phagocytose particulates including dusts and bacteria-> then either lymphatics or leave via mucocilary escalator
Outline the blood air barrier
Made of type 1 pneumocytes- fused basement membrane of pneumocyte and capillary vascular endothelial cells
200-800 nm thick
Outline the interstitium
Where endothelial cells are not in direct contact with pneumocytes
Made of collagen and elastin fibres, fibroblasts, macrophages
Contains pores of Khon- holes in the wall of alveoli helping to equalise pressure
Outline visceral pleura
Made of- flat mesothelial cells, loose fibrocollagenous connective tissue
Layers- irregular external elastic layer, interstitial fibrocollagenous layer, irregular internal elastic layer
Outline oral cavity
What does it do -> receive food, chews food, starts digestion
Epithelium -> stratified squamous epithelium on top of connective tissue with keratin layer on top
Pathology -> oral cancer-> from SE-> squamous cell carcinoma
Outline oesophagus
What does it do-> swallows food
Epithelium -> squamous epithelium
Submucosal glands
Outline stomach
What does it do-> digests food
Made up of gastric fundic mucosa => mucus, gastric body mucosa, parietal cells => hydrochloric acid, chief cells => pepsinogen and lipase, gastric antral mucosa
Pathology- sometimes contains helicobacter pylori - causes inflammation
Intestines function and features to maximise this
What does it do-> digests food, absorbs food, absorbs water, resist bugs
Arranged in crypts and villi for larger surface area