Histology 👩🔬 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
Can’t 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 can’t 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 can’t 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
(Can’t 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 doesn’t 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 don’t
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 reinke’s 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
Don’t 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
Layers of the intestines
Epithelium -> Mucosa glandular epithelium all the way down, contains endocrine cells affects timing movement
submucosa (all connective tissue)
Muscularis propria
Crypts- what are they and what do they do
Are moat-like invaginations of the epithelium around the villi. Are lined largely with younger epithelial cells involved primarily in secretion.
Contain stem cells at their base, which continually divide and provide the source of all the epithelial cells in the crypts and on the villi.
Extend down to the muscularis mucosae.
Outline the muscularis propria
2 layers, all smooth muscle, contains ganglion cells
Interstitial cells of kahal (pacemaker cells)- can cause tumours called GIST
Outline the serosal surface
Outside of the transverse colon
Contains- blood vessels, mesentry, mesothelium
Parts of the small intestine and what are they covered in
Duodenum, jejunum, ileum
Have villi on the folds and microvilli on them
contains mucosa associated lymphoid tissue
Outline the function of the duodenum
Digests food, absorbs food and resists bugs, bile and digestive enzymes come into it
Outline the functions of the jejunum and ileum
Digests food, absorbs food and resists bugs
Some diseases of the small intestine
Giardia lambila- parasites on the mucosa
Coeliac disease- villi lost and crypt hypoplasia
lots of lymphocytes, response to gluten
Outline the appendix
What does it do -> Safehouse for the bugs in the gut in case they are all cleared out in response to infection
Epithelium -> flat mucosa bc less absorption
Outline the colon
Parts of it -> Ascending, transverse, descending, sigmoid
What does it do -> absorbs (some) food and water + kills bugs
Features-> Villi + folds in the colon
Pathology -> ulcerative colitis (inflammation of the mucosa)
What are the layers of the muscularis of the stomach?
Innermost oblique layer
Middle circular layer
Outermost longitudinal layer
What is in the portal tract?
Portal veins
Arteries
Bile ducts
Describe make up of the liver
Made up of hepatocytes arranged in cords with intervening sinusoids
Liver is divided into lobules
Outline the ‘classic lobule’
Area drained by one central hepatic venule
artificial construct so we can understand hepatic architecture
Roughly hexagonal
Some hepatocytes will be more richly oxygenated than others
Outline the acini of the liver
An architectural concept based around the blood supply rather than the drainage
An artificial construct for understanding hepatic architecture
Outline hepatocytes
Principle functional cells of the liver
Polyhedral epithelial cells
What are the 3 important surfaces of hepatocytes?
Sinusoidal (70%)- permits exchange of material with blood (space of Disse)
Canalicular (15%)- permits the excretion of bile
Intercellular (15%)
What do hepatocytes contain?
-Abundant mitochondria (looks like granules)
-Large central spherical nuclei
-Prominent nucleoli
-Might be binucleate
-Active golgi apparatus
-Prominent endoplasmic reticulum
-Numerous peroxisomes
Outline sinusoids
Highly specialised blood vessels
Thin, discontinuous fenestrated endothelium
No basement membrane
Contains scattered Kupffer cells
Outline the inter-hepatic biliary tree
Epithelium- Simple to cuboidal to columnar epithelium
Small: canaliculi -> Bile ductules -> trabecular ducts -> bile ducts :Large
Outline canaliculi
Lie between hepatocytes
Can’t be seen on light microscopy
Outline the gallbladder
Functions- concentrates and stores bile, expels bile via common bile duct into duodenum
No muscularis mucosa but does contain specialised mucosa and smooth muscle layer
Outline specialised mucosa in the gallbladder
Simple columnar epithelium with microvilli
Thrown into folds, adapted for water and salt absorption
Contains connective tissue - lamina propria
Outline the exocrine pancreas
Functions -> To synthesise + secrete enzymes + bicarbonate-rich fluid into the duodenum
Has a poorly defined fibrous capsule with septa dividing gland into lobules
Epithelial cells arranges in acini
Outline acinar cells
Epithelial cells, pyramidal shape
Basally - rich in RER
Apically - zymogen granules (enzyme precursors)
Outline ducts of the liver
Centro acinar cells (fuse to form each other), intercalated ducts, interlobular ducts, main pancreatic duct
What are the 3 areas of the kidney?
Cortex
Medulla
Pelvis
What is in the renal cortex?
Glomeruli
PCTs
DCTs
What is a medullary ray?
A collection of loops of Henle and collecting ducts that are in the cortex
It occurs when then nephrons have their glomeruli close to the renal capsule
Outline the contents of the renal medulla
Comprised of loops of Henle and collecting ducts as well as blood vessels orientated radially from the cortex to the medulla
Outline the glomerulus
Tuft of convoluted fenestrated capillaries
Glomerular basement membrane
Lined by podocytes
Supported by mesangial cells
Encased in Bowman’s capsule
Most cells are either glomerular endothelial cells or mesangial cells
Outline the glomerular endothelial cells
Nuclei on the inside of capillaries
Endothelial cells line the capillaries
Outline mesangial cells
Nuclei lie between capillaries
Comprise smooth muscle and structural support for the kidney
Contraction of it tightens capillaries + reduces glomerular filtration rate
Important part of tubular glomerular feedback caused by chemical changes in the glomerulus
What are the 3 layers of cells of the glomerulus?
Glomerular capillary wall
Basement membrane
Foot processes of podocytes
Outline the endothelial cells of the glomerular basement membrane
Inner layer
Fenestrated
Not so much that it lets big molecules like albumin
Outline the basement membrane of the bowman’s capsule
Double thickness
Fusion of bms, podocytes and epithelial basement membrane
Has a lamina lucida, double thickness lamina densa and a lamina externa
Contains collagen and -ively charged heparin sulphate molecules
So -ive ions in plasma experience repulsive force
Outline podocytes in the glomerular basement membrane
Have foot process that interdigitate
Made up of several proteins
Leaves a small space bridged by a -ively charged membrane
Outline juxtaglomerular apparatus
2 components- afferent arteriole, distal convoluted tubule
Afferent arteriole contributes granular cells
Secrete renin in response to low BP
DCT has macula densa cells
Outline macula densa cells
Patch of closely packed endothelial cells along the tubule
Senses NaCl conc. and regulates tuboglomerular feedback
Outline lacis cells
In juxtoglomerular apparatus
Don’t know what they do
Outline the lining of the proximal convoluted tubule
Lined by cuboidal epithelium
Round central/ basal nuclei
Brush border of microvilli on apical end
Many mitochondria so appears eosinophillic
What is the function of the PCT and where is it?
Reabsorption of NaCl, proteins, polypeptides, amino acids, glucose
In renal cortex
Outline the loop of Henle
Descending and ascending limbs
Both with thick and thin segments
supplied by rich vasa recta in between the loop
Epithelial lining of the loop of Henle
Simple squamous epithelium
Outline the epithelial lining of the DCT
Simple cuboidal epithelium
Numerous mitochondria
Shorter than PCT
What does the DCT do?
Regulates acid base by secreting H+ and absorbing HCO3- (via cellular carbonic anhydrase)
Regulates Na+ level by exchanging Na+ for K+
Outline the collecting duct
Principal cells respond to aldosterone and ADH
Intercalated cells exchange H+ for HCO3-
3 types: cortical, medullary and papillary ducts
What are the 3 types of collecting ducts lined with?
Cortical collecting ducts - simple cuboidal epithelium
Medullary collecting ducts - simple columnar epithelium
Papillary ducts - simple columnar epithelium
Progression of the kidney blood supply (from source to nephron)
Abd aorta -> Renal artery at L1 -> Anterior + posterior division -> Interlobar artery -> Arcuate artery (corticomedullary) -> Interlobular artery -> Afferent arteriole
Progression of the blood supply to the loop of Henle
Efferent arteriole (from renal corpuscle) -> Peritubular arteries -> Vasa recta -> Renal veins -> Inferior vena cava
Outline the renal pelvis
Collecting ducts drain into it
Lined by urothelium - multi-layered stratified
Transmits filtrate from nephron to ureter
Outline urothelium
Specialised epithelium found in the collection/ drainage parts of the urinary tract
Complex stratified epithelium
What are the layers of the urothelium
Layer of large dome shaped umbrella cells overlies a pseudostratified layer of polygonal cells
Intermediate layer
Basal layer- cuboidal cells can stretch
Outline ureters
Lined by urothelium (transition epithelium)
Spiral muscular tube
Inner ‘longitudinal’
Outer ‘circular’
(different to GI arrangement)
No serosa
Loose adventitis
Outline the layers of the urinary bladder
Layers- urothelium, lamina propria, muscularis mucosa (poorly developed), submucosa, muscularis propria(well developed), subserosa, serosa
Functional valve prevents reflux into ureter
bc of passage of ureters thru muscularis propria
Outline the female urethra
4-5cm long
Lined by -> Proximally: transitional epithelium; Distally: squamous epithelium
Paraurethral and periurethral glands open into urethra
Outline the male urethra
20cm long
Parts-
1. Prostatic urethra
2. Membranous urethra- lined by urothelium
3. Penile urethra- lined by pseudostratified epithelium proximally, stratified squamous epithelium distally
Outline the testis
Paired organ in the scrotum
Average weight 15-19g
What are the 3 layers of the capsule of the testis (outer to inner)?
Tunica vaginalis-
Tunica albuginea
Tunica vasculosa
Outline the tunica vaginalis
Projection of the peritoneum
Flattened layer of mesothelial cells on a basement membrane)
Outline the tunica albuginea
Collagen fibres with some fibroblasts, myocytes and nerve fibres
Outline the tunica vasculosa
Loose connective tissue containing blood vessels and lymphatics
Pathway of spermatozoa out of the testes
Seminiferous tubules -> Straight tubules -> Rete testis -> Efferent ductules in the head of the epididymis -> Epididymis -> vas deferens -> Ejaculatory duct -> Membranous urethra -> Penile urethra
Describe testicular parenchyma lobules
Divided into lobules by septa originating from the capsule
Around 250 lobules
Each lobule contains 1-4 seminiferous tubules
What cells are in seminiferous tubules?
Germ cells in various stages of maturation
Sertoli cells
Progression of sperm maturation from spermatozoon to type A spermatogonia
Spermatozoon -> Spermatid -> secondary spermatocyte -> Primary spermatocyte -> Type B spermatogonia -> Type A spermatogonia
What are type B spermatogonia?
Differentiating progenitor cell
Has spherical nuclei with densely stained masses of chromatin
What are the two versions of type A spermatogonia?
Darkly stained (Ad)
Pale stained (Ap)
Outline sertoli cells
Columnar cells on the basement membrane of the tubule
Send cytoplasmic projections around the sperm cells
Nuclei are irregularly shaped, folded and have prominent nucleolus
Cytoplasm is eosinophilic and may contain lipid granules
What do sertoli cells do?
Supportive, phagocytic and secretory functions
What are the different parts of spermatozoa?
Head
Neck
Midpiece
Principle piece
End piece
What is included in the head of the spermatozoa?
Acrosomal cap and nucleus
What is included in the midpiece of the nucleus?
Spiral mitochondria around the axomere
What is in the neck and tail of spermatozoa?
Axomere and plasma membrane
What does the axomere do?
Responsible for cell motility
Basically long cillia
Outline leydig cells
Present singly and in clusters in the interstitium between tubules
Abundant cytoplasm containing lipid
Contain peinke’s crystalloids- eosinophilic crystalloids (not seen before puberty)
Produces testosterone
Outline the rete testis
Anastomosing network of tubules at the hilum of the testis
Receive luminal contents from seminiferous tubules
Lined by simple squamous or low columnar epithelium on a relatively thick basement membrane
Have cilia at luminal surface
Function of the rete testis
Mixing chamber for contents of the seminiferous tubules
Possible secretions
Reabsorption of protein from luminal contents
Outline the efferent duct
12-15 convoluted tubules which empty into the epididymis
Lined by ciliated and non ciliated simple columnar epithelium with interspersed cuboidal cells (basal cells) giving pseudostratified appearance
Outline the epididymis
A tubular structure 4-5cm long containing highly convoluted epididymal duct
Lined by tall columnar cells with long atypical cilia
Epithelium is supported by a thick basement membrane surrounding which is a well defined muscular coat
What does the epididymis do?
Site of absorption of testicular fluid
Phagocytosis pf degenerous spermatozoa
Produces secretion rich in glycoproteins, amino acid and glycerophosphyl choline
Play a role in maturation of the spermatozoa
Outline the vas deferens
30-40cm tubular structure arising from the caudal portion of the epididymis
Distal part enlarged to form the ampulla which joins the excretory duct of the secretory vesicle to form the ejaculatory duct
Lined by pseudostratified columnar epithelium comprising columnar and basal cells
Has a thick muscular wall of 3 layers
Shape, weight and position of the prostate
Pear shaped glandular organ
Weighs up to 20g in young adults (enlarges with age)
Surrounds the bladder neck and prostatic urethra
What are the lobes of the prostate gland?
Anterior
Middle
Posterior
2 lateral lobes
What are the gland regions of the prostate?
Peripheral- (most common site of cancer)
Central
Transitional
Periurethral
Key parts of the prostate gland
Covered by ill defined fibroconnective tissue capsule
Glandular and non-glandular components
Ducts- large primary and small secondary
Acini- 30-50 tubuloalveolar glands with convoluted edges
What are acini of the prostate lined by?
Lined by secretory cells, basal cells and neuroendocrine cells
Cells rest on a basement membrane
What do secretory cells do and where are they in the acini?
Located in the luminal side of the glands Secrete PSA and PAP into the seminal fluid
Helps to liquify the semen
What do the basal cells of acini form?
A continuous layer
What is stroma made up of?
Smooth muscle
Fibroelastic fibres
Blood vessels
Nerves
What happens to stroma and glands of prostate with increasing age?
Undergo hypoplasia
Outline seminal vesicles
Paired, highly coiled tubular structures posterolateral to the bladder
The duct empties into the ejaculatory duct
Lined by tall, non-ciliated columnar epithelium
Vacuoles and lipofuscin
Secretions act as nutrients for spermatozoa
What are the layers of the seminal vesicles?
Mucosa (folded)
Smooth muscle (2 layers)
Adventitia
Outline the 3 components of the erectile tissue
Left and right corpora cavernosa on the dorsal side (lined by vascular endothelial cells)
Corpus spongiosum on the inferior side
Outline the make up of erectile tissue of the penis
Comprises irregular vascular spaces separated by fibroeslastic tissue and smooth muscle
Has a rich nerve supply
Outline the ovary
Paired organ either side of the uterus close to the pelvis wall
What are the attachments of the ovaries?
To broad ligament by mesovarium
To uterus by utero ovarian ligament
To pelvic wall by suspensory ligament
What is the ovary made up of?
Covered by a single layer of modified mesothelium
A poorly defined connective layer called tunica albuginea
Stroma
Outline the stroma of the ovary
Divided into the cortex and medulla with indistinct boundaries
What is the hilum of the ovary?
Point blood vessels and lymphatics enter
What is the ovarian cortex?
Spindle stromal cells arranged in whorls/storiform pattern
What do ovarian follicles contain?
Some leutinised cells
What is in the ovarian medulla?
Loose fibrous elastic tissue with blood vessels, lymphatic and nerves
Outline the rete ovary
Similar to the rete testis, present at hilum of ovary
Outline primordial follicles
Located in periphery of the cortex
Contains primary oocyte in a resting state
Surrounded by a single layer of epithelial cells (granulosa cells)
30-40 develop at once
Primary follicles- how are they formed
- Cyclic FSH secretion from ant. pit.
- Stimulates follicular development
- Follicular epithelial cells proliferate
- Oocyte enlarges
- Stromal cells organise to form a connective tissue sheath
- Zona pellucida forms around oocyte
What does the epithelium of the stroma change from and to?
Squamous to cuboidal/columnar
Glycoproteins between granulosa cells and oocyte
What is the antrum?
Space filled with follicular fluid
Describe the formation of secondary follicles
Formation of the antrum
Theca differentiates into inner theca interna and outer theca externa
Oocyte is supported in antrum by a stalk of granulosa cells (clumbus oophorus)
Outline the mature (graafian) follicles
Ovum surrounded by thick zona pellucida, corona radiata, basal lamina, theca interna and externa
Has a cumulus oophorus which suspends the ovum in the grafian follicle
Corpus luteum
Forms from follicle
Via luteinisation of granulosa cells and theca cells (stimulated by LH)
These cells become polygonal and have lots of cytoplasm containing lipid
Secretes progesterone and oestrogen
What is the corona radiata?
Layer of granulosa cells that surrounds the oocyte
Numbers of eggs made and released in ovaries
Approx 1 mill at birth but only 400-500 mature
At ovulation 1 follicle ruptures out of the ovary (leads to bleeding in antral space)
Common features of the endocrine system
- Glandular epithelium apart from post. pituitary gland
- Richly vascularised
- Secrete a variety of hormones
- Controlled by +ve and -ve feedback loops
Pituitary overview
- Coordinates the endocrine organs through the feedback loops
- Two functional components:
- Post. pituitary
- Ant. pituitary
Posterior pituitary
- Downward extension of the hypothalamus
- Neural tissue:
- Axons
- Glial cells
- Stores/secretes:
- Oxytocin
- ADH
Anterior pituitary
- Nested epithelial pituicytes
- Richly vascular fibrous stroma
- Several different types of pituicyte not distinguishable on H+E
Can be stained with reticulin
Anterior pituitary cell make up
Cell % Hormone
Somatotrophs 50% Growth hormone
Lactotrophs 25% Prolactin
Corticotrophs 15-20% ACTH, a-MSH,
b-lipotrophin, b-endorphin
Gonadotrophs 10% FSH, LH
Thyrotrophs 1% TSH
Somatotrophs- Ant. pituitary
- Diffuse cytoplasmic GH +ve (stains with it)
- Lateral wings of ant. pituitary
- Present throughout gland
Lactotrophs - Ant. pituitary
- Polygonal cells
- Cytoplasmic processes wrap around other cells
- Variable Prolactin staining- stains cytoplasm brown
Thyrotrophs- Anterior pituitary
- Angular chromophobes - Don’t stain with H+E
-Elongated cytoplasmic processes - Variable TSH staining
Gonadotrophs- Anterior pituitary
- Scattered round/oval cells
- Stain with either:
- Alpha subunit
- Beta LH
- Beta FSH
Corticotrophs- Anterior pituitary
- Round basophilic cells
- Stain dark purple on H + E
- Median of gland
- Large cytoplasmic vacuoles (“enigmatic bodies”)
Supporting cells- Anterior pituitary
- Sustentacular cells
- Surround the normal follicles
- S100 +ve (stains brown with it)
Pineal gland
- Located just below the posterior end of the corpus callosum - covered by meninges
- Irregular lobules
- Pinealocytes in rosettes (neuron-like)
- Secretes melatonin- in response to autonomic stimulation
- Eosinophillic cytoplasm + round central nuclei
- Brain sand- accumulation of calcium
Thyroid
- In neck anterior and lateral to the trachea
- Combination of follicular cells and colloid
- Richly vascular
- Produces thyroxine and calcitonin
Parathyroid glands
- 4 glands, variably located in the neck
- Produce parathyroid hormone (PTH)- important in calcium homeostasis
- 3 cell types:
- Chief cells
- Oxyphils
- Adipocytes
Chief cells- parathyroids
- Functional cells of the gland
- Polygonal cells
- Scant cytoplasm - so tissue appears blue bc of lots of nuclei
- Secrete PTH
- Raises serum Ca2+
- Bone
- Kidney
- Gut
Staining of chief cells (parathyroid)
- Strong immunoreactivity for PTH
- No calcium oxalate crystals (unlike thyroid so can be used to determine what the tissue is)
Oxyphil cells- parathyroid
- Large polygonal cells
- Increase with age
- Abundant eosinophilic cytoplasm
- Finely granular- rich in mitochondria?
- Unknown function
Endocrine pancreas
Islets of langerhans
Islets of Langerhans
- Approx 1 million
- Balls of cells
- Thin fibrous capsule
- Mostly in pancreatic tail
Hormones secreted by the islets of Langerhans
Cell % Hormone
B (beta) cells 70% Insulin
A (alpha) cells 20% Glucagon
D (delta) cells 5-10% Somatostatin
PP cells 1-2% Pancreatic polypeptide
Adrenal cortex
- Back of abdomen (retroperitoneal) on top of kidneys
- 2 layers- Cortex and medulla
Adrenal cortex
- Zona Glomerulosa
- Mineralocorticoids
- Zona Fasciculata
- Glucocorticoids
- Zona Reticularis
- Androgneic steroids
Zona glomerulosa (outermost layer of the adrenal cortex)
- Secretes aldosterone
- Thin, incomplete layer
- Small cells
- Vacuolated cytoplasm
Zona fasciculata (middle layer of the adrenal cortex)
- Secretes cortisol
- Most prominent layer
- Large polygonal cells
- Almost clear cytoplasm (bc of abundance of lipid)
Zona reticularis (inner layer of the adrenal cortex)
- Produces androgenic steroids
- Anastomosing columns of small polygonal cells
Adrenal medulla
- Centre of adrenal gland
- Chromaffin cells
- Large, polyhedral
- S100 +ve (stains with it)
- Produces adrenaline and noradrenaline
Outline the corpus albicans
Well circumscribed structure with convoluted borders almost entirely composed of densely packed collagen with occasional follicles
Eventually they may be resorbed/replaced by ovarian stroma
What happens to the corpus luteum if there is no pregnancy?
It regresses as 8-9 days after ovulation granulosa cells change size and develop pyknotic nuclei + accumulate abnormal lipid
cells then undergo dissolution and are phagocytosed
There is progressive fibrosis by ingrowth of connective tissue
What are the 4 segments of the fallopian tube?
Intramural- inside uterine wall
Isthmus- 2-3 cm thick walls
Ampulla- expanded area
Infundibulum- trumpet shaped opening to the peritoneum
Outline the fallopian tube
Run thru the length of the broad ligament
Transport the ovum to the uterus
Fertilisation occurs here
Endometrium in menstrual phase
Progesterone stimulation withdrawn
Stromal haemorrhage and granulocytes
Stromal and granular fragmentation
Might see mitotic figures
Outline the mucosa of the female reproductive tract
Thrown into branching folds (plicae)
2 Cell types:
- Secretory- Most prevalent at uterine end
- Ciliated- most prevalent at infundibular end
(peg cells and basal cells)
Outline the muscularis (myosal pinx)
Inner circular layer- tightly wound spiral
Outer longitudinal layer- looser spiral
Fallopian serosa
Connective tissue covered by mesothelium
Endometrium in menstrual phase
Progesterone stimulation withdrawn
stromal haemorrhage and granulocytes
Stromal and granular fragmentation
Might see mitotic figures
3 layers of the uterus
Endometrium
Myometrium
Serosa
Endometrium in secretory phase
Progesterone stimulation
Early -> below nuclear glycogen vacuoles
Mid -> vacuoles above and below nucleus and intraluminal secretions, glands more rounded, stromal oedema (no H+E staining)
Late -> Elongated and saw toothed glands with more intraluminal secretions -> stroma-spiral arterioles and decidual change
Outline the endometrium in proliferation phase
Oestrogen stimulation
Straight proliferating glands with mitotic activity
No luminal secretions
Stromal cells are spindled and show mitotic activity
What are the 2 layers of the endometrium?
Deep basal layer- stratum basalis- reserve of endometrial cells- replenished
Superficial layer- stratum compactum (towards the surface and stratum spongiosum- lost during each menstrual cycle
What does it mean for the endometrium to be hormonally responsive?
Its appearance changes depending on the phase of the menstrual phase
Outline the myometrium
Thick muscular wall with 3 ill defined layers of smooth muscle:
Inner longitudinal
Middle circular
Outer longitudinal
What are the 2 layers of the cervix?
Endocervix
Ectocervix
Outline the endocervix
Loose fibromuscular stroma lined by simple columnar ciliated epithelium
Thrown into crypts- crypts not glands as epithelium is all the same
Outline the ectocervix
Dense smooth muscle stroma lined by non-keratinised stratified squamous epithelium
Site of squamocolumnar junction varies (most common site for cervical cancer) - might lie at os or ectocervix
Atrophic in post menopausal women
Mucosa of the vagina
Lined by non-keratinising stratified squamous epithelium
Stroma contains elastic fibres and a rich vascular network
Key facts about the epithelial lining of the mucosa of the vagina
Accumulates glycogen -> maximal around ovulation
It becomes more spongy
Outline the muscular wall of the vagina
Smooth muscle cells
Inner circular
Outer longitudinal
Adventitia of the vagina
Loose connective tissue
Structures of the vulva
Mons pubis, clitoris, labia minora, labia majora, vulvar vestibula, hymen, urethral meatus, skein’s gland, bartholin’s gland, introitus
Outline the labia majora epithelium
Looks like normal skin
Lined by keratinising stratified squamous epithelium and has skin adnexae
Outline the labia minora epithelium
Mostly non- keratinising stratified squamous epithelium
Outline Bartholin’s gland
Tubuloalveolar glands-> acini
lined by mucus secreting epithelium
Minor vestibular glands
Simple tubular glands lined by mucus- secreting epithelium
Skein’s glands (periurethral glands)
Analogous to prostate
lined by pseudostratified columnar epithelium
Outline the lining of the hymen
Lined by non-keratinising squamous epithelium
Outline the clitoris
Erectile tissue rich in blood vessels and nerves
Contractile cells that are not muscle
Pericytes, myo-fibroblasts, myoepithelial cells
Outline skeletal muscle components
Myoblasts fused to form multi-celled syncitium
Sarcomeres joined end to end to form myofibrils
Cytoplasm filled with myofibrils to form muscle fibre
Muscle fibres clump together to form fascicles
Held together by connective tissue endomycium, perimycium and epimycium
Key facts about skeletal muscle fibres
Multi-nucleated- bc formed from multiple cells
Dark stained nuclei (at edges)
Pink stained cytoplasm with striations
10cm long and 50-60um wide- elongated fibres
Voluntary
Non branching
What is in a skeletal muscle cell?
Cell membrane- aka sarcolemma
Nuclei
Contractile proteins
Mitochondria
Endoplasmic reticulum- sarcoplasmic reticulum
Glycogen-rich cytoplasm- sarcoplasm
Why is skeletal muscle striated?
Myofibrils are in register
So light bands and dark bands of each sarcomere line up
Difference between a myocyte, myofibril and sarcomere
Myocyte- whole cell
Myofibril- arrangement of contractile proteins in a muscle fibre
Sarcomere- functional units of the myofibrils
What makes up the sarcomere?
Actin- thin filaments
Myosin- thick filaments
Accessory proteins
How are the proteins arranged in sarcomeres
Actin filaments anchored by accessory proteins that form Z lines (sarcomere is what is between 2 z-lines)
Areas where there is only actin (i-bands) and only myosin (a-bands)
Different types of skeletal muscle fibre
2 broad types
Not distinguishable on H+E
Type 1- rich in fibrillar ATPase, slow twitch
Type 2- rich in fibrillar ATPase, fast twitch (also split up into fatigue sensitive and fatigue resistant)
How do muscle spindles detect stretch and tension?
Fibrocollagenous capsule
Intrafusal muscle fibres (wrapped around by gamma efferent nerve fibres)
Detect stretch and tension
Outline Endomysium
Collagenous connective tissue between muscle fibres
Perimysium
Fibrocollagenous connective tissue
Binds muscle fibres to form fascicles
Epimysium
Connective tissue that binds all of the fascicles together around the outside
Sharpey’s fibres
Connect muscle to bone (and penetrate bone)
Bundles of collagen linking epimysium to periosteum
Attach muscle to bone over a wide area
e. g rotator cuff muscles attached to scapula
Tendons
Connect muscle to bone over a small area
Made of parallel bundles of collagen with intervening fibroblasts
e.g rotator cuff muscles attached to humerus
What are the cells that make up bone?
Osteoprogenitor cells
Osteoblasts
Osteocytes
Osteoclasts
What is in the extracellular matrix?
Collagen and calcium hydoxyapatite
Outline osteoblasts and osteocytes
- Derived from embryonic mesenchyme (osteoprogenitor cells)
- Secrete osteoid (unmineralised bone)
- Become trapped in their own matrix
- Connect to surrounding cells via canaliculi (where oxygen and nutrients diffuse)
Difference between osteoblasts and osteocytes
Osteocytes are osteoblasts that have moved from the outer layer of the bone into the matrix and have been trapped there
Outline osteoclasts
- Derived from monocytes
- Large, multinucleate cells
- Absorb bone- sit in Howship’s lacunae- depressions in the bone
- Activity is linked to osteoblasts (via rank ligand)
What are the ways we can differentiate types of bone?
By origin
By gross appearance (2 ways)
By mode of formation
What are the two categories of bone differentiation by origin?
Primary (woven)
Secondary (lamellar)
What are the 2 categories of bone by gross appearance (1)?
Spongy/cancellous
Compact
What are the 2 categories of bone by bone formation?
Membranous
Endochondrial
What are the 2 categories of bone by gross appearance (2)?
Osteons
Appositional
What is osteoid?
An extracellular matrix rich in type 1 collagen, glycosaminoglycans and proteoglycans
How is bone formed?
Osteoblasts lay down osteoid, in which the glycosaminoglycans include osteocalcin which has a strong affinity for calcium ions
Osteoid then mineralised when there is a high conc. of calcium and phosphate ions via osteocalcin and alkaline phosphatase
Calcium deposited in bone as calcium hydroxyapatite
Lamellar bone
Osteoid is deposited in parallel sheets
Remodelled from woven bone
Woven bone (aka primary bone)
Osteoid is deposited haphazardly and is laid down rapidly in foetal bone and at fracture sites
Has a disorganised collagen fibre architecture
and is mechanically weak
Cement line
Faint blue line (on H+E)
Between osteoid and bone
Osteocalcin- what does it do?
Binds calcium ions to osteoid
Outline secondary/lamellar bone
Stronger
- Forms as osteons
- Has central Haversian canal containing blood vessel
- Surrounding concentric rings of lamellar bone with osteocytes
How is secondary bone usually stained and examined?
Typically examined as a decalcified section stained with H+E
What bones are formed by intramembranous formation?
Flat bones of the skull
Some cortical bone shafts
What bones are formed by endochondrial formation?
All other bones- formed from cartilagenous formation
Key facts about Intramembranous ossification
Formation of bone from a membranous precursor
Occurs in the formation of flat bones of the skull
Bone deposited directly in an embryonic mesoderm- without a cartilaginous proforma
Begins in second trimester
Outline the process of intramembranous ossification
Initially, small clusters of progenitor cells within a primitive mesenchyme transform into osteoblasts and deposit islands of bone
These islands coalesce as the enlarge creating an open meshwork of bone and continue to do so until they form a primary plate of bone
Woven bone then remodelled to lamellar bone
Endochondrial ossification
Converts a hyaline cartilaginous template into bone
Cartilaginous proformas form in the second trimester
Outline the process of endochondral ossification
Shaft/dyaphisis becomes calcified and blood vessels grow into developing bone
Osteoprogenitor cells then differentiate into osteoblasts which lay down bone to form a primary centre of ossification
Proforma cartilage is eroded away as new bone forms
Later secondary centres of ossification form head/ epiphysis of bones
As ossification centres expand, cartilage is restricted to epiphyseal growth plates and articular surface
Do bones have centres of ossification at birth
By birth most bones have primary centres of ossification and some have secondary ones
What are epiphyseal growth plates
Separate the epiphysis from the diaphysis
How is the zone of hyperplasia formed from the resting cartilage?
Chondrocytes in the resting cartilage divide creating columns of new cells - a zone of hyperplasia
How is the zone of hypertrophy formed from the zone of hyperplasia?
Cells of zone of hyperplasia enlarge
How is the zone of ossification formed from the zone of hypertrophy?
As chondrocytes enlarge they erode the extracellular matrix
The remaining strands of matrix become calcified and serve as a substrate for the attachment of osteoblasts
Outline synovium
- Lines the inside of the joint capsule
- 1-4 layers of synovial cells
- Type A- phagocytes
- Type B- rich in RER
- Variable shapes- squamous to cuboidal
- Richly vascular and highly innervated
