Histology Flashcards
What is a cell?
The basic structural unit of all living organisms. The human body contains many different cell types that have different functions.
What percentage of a cell is made up of water?
80%
What type of cells have the most water?
Embryonic, old cells have the least
Name five features common to all eukaryotic cells
An outer membrane
An inner cytosol
A cytoskeleton
Organelles
Inclusions
What is the inner cytosol?
A solution of proteins, electrolytes and carbohydrates. It has both fluid and gel-like properties and makes up the majority of the inside of the cell.
What does the cytoskeleton do?
Determines the shape and fluidity of the cell, it provides structural integrity.
What is the purpose of the Plasmalemma?
It separates the cytoplasm from the outside environment as a selective, structural barrier.
Describe the composition of the plasmalemma
It is a bimolecular layer of amphipathic phospholipid molecules with their hydrophobic heads at the outer and inner surfaces and their hydrophobic fatty acid chains facing towards the middle of the two layers.
A phospholipid bilayer with integral and peripheral proteins and cholesterol embedded into it.
What does it mean if a molecule is amphipathic?
Has a hydrophilic head and a hydrophobic tail.
The plasmalemma contains integral proteins which the cell inserts into the membrane. Name five examples….
Receptors
Channels
Transporters
Enzymes
Cell attachment proteins
What two things can a cell do to move material through the plasmalemma?
Exocytose and endocytose material
What are the two key features of a cell membrane?
- It is fluid.
- It is selectively permeable
What do we mean when we say the cell membrane is ‘fluid’?
It is deformable and can change its shape
Why are many proteins not distributed equally within the cell membrane?
Membrane proteins can diffuse laterally in the cell membrane BUT many are anchored.
What do we mean by ‘selectively permeable’?
Highly permeable to: water, oxygen, small hydrophobic molecules.
Virtually impermeable to charged ions (e.g. Na+)
Why does the plasmalemma need to be a phospholipid bilayer?
The outside environment surrounding the cell is a watery environment and so is the cytoplasm inside the cell. So there needs to be hydrophilic (polar) heads facing inside and outside.
What are the two classifications of structures in the cytoplasm depending on their functions?
Organelles and Inclusions
What are organelles?
Small, intracellular ‘organs’ with a specific function and structural organization. They are essential to life and membrane bound.
Give 6 examples of organelles in the cytoplasm and their functions
- Mitochondria- energy production
- Rough endoplasmic reticulum- protein synthesis
- Smooth endoplasmic reticulum- cholesterol & lipid synthesis/detoxification
- Golgi apparatus- modification and packaging of secretions
- lysosomes- hydrolytic enzymes for intracellular digestion
- nucleus-contains genetic code
What are inclusions?
Structures in the cytoplasm which may or may not be membrane bound. They are dispensible and may be present only as transients.
They represent components that have been synthesised by the cell itself (pigment, glycogen stores, lipid droplets, presecretion product) or taken up from the extracellular environment (endocytotic vesicle).
What is the maiin difference between organelles and inclusions?
Inclusions are not essential for life.
(Some cells have inclusions which they produce as a waste product they simply cannot get rid of)
Describe the cytoplasm- what is it?
A set of filamentous cytosolic proteins which become attached to the cell membrane and to eachother by anchoring and joining proteins to form a dynamic 3D internal scaffolding in the cell.
What are the three main classes of filaments in the cytoskeleton?
- Microfilaments
- Intermediate filaments
- Microtubules
Describe key features of microfilaments and there composition
- Hollow tubule composed of two types of tubulin subunits, a & ß in an alternating array
- 7 nanometers in diameter
- Are composed of the protein actin
- can be assembled and disassembled
- include stabilizing proteins: microtubule-associated proteins (MAPs)
- participate in the production of spindle, necessary for cell division.
Which protein filament which makes up the cytoskeleton is >10 nanometers in diameter and composed of 6 main proteins varying in cell type?
Intermediate filaments
what are the key features of intermediate filaments?
- bind intracellular elements together and to the plasmalemma providing substantial structural integrity
- 10-15nm (>10nm) in diameter
- more than 50 types, divided into classes
- classes are used in pathology to identify tumour origins
- composed of 6 main proteins which vary in cell types
Where do microtubules originate?
From a special organising centre called the centrosome.
Which cytoskeletal filament serves as the ‘motorway’ network of the cell and how does it go about this?
Microtubules
Two proteins, dynein and kinesin attach to the microtubules and move along them. They associate with the membranes of organelles and vesicles and ‘drag’ them along the microtubule.
Which cytoskeletal filament is important in cilia, flagella and mitotic spindle?
Microtubules
Kinesin is an ATPase that moves toward the cell ______
periphery
Dynein is an ATPase that moves toward the cell ______
Centre
Why are kinesin and dynein important?
Important in the movement of components in cells with long processes, for example the very long axonal process of many neurons.
What is the nucleus enclosed by?
A nuclear envelope, composed of an inner and outer nuclear membrane with nuclear pores.
What is the purpose of the nucelar pores in the nuclear membrane?
Provide continuity with the cytoplasm
What lies between the two sheets/nuclear membranes?
perinuclear cistern
Which cistern is the perinuclear cistern continuous with?
The cistern of the endoplasmic reticulum
What is a cistern?
A fluid filled space
The outer nuclear membrane is studded with _________ and is continuous with the cytoplasmic ________ ___________ _____________.
- Ribosomes
- Rough endoplasmic reticulum
What does the nucleus contain?
chromosomes
What is synthesised in the nucleus?
RNA
Which types of RNA are transcribed in the nucleus and which in the nucleolus?
mRNA and tRNA are transcribed in the nucleus
rRNA is transcribed in the nucleolus
What is the nucleolus?
A1-3 µm diameter dense area within the nucleus
What two types of DNA does the nucleus contain?
Eurochromatin
Heterochromatin
What is the difference between euchromatin and heterochromatin?
Eurochromatin is DNA that is more dispersed and is actively undergoing transcription.
Heterochromatin is DNA that is highly condensed and not undergoing trasncription.
Where are ribosomes formed?
In the nucleolus
What is the function of ribosomes?
They are instrumental in protein synthesis.
What are the two subunits which make up the ribosome and what do they do?
small subunit- binds RNA
large subunit- catalyses the formation of peptide bonds
What does the export of ribosomes depend on?
The nuclear pore complex
What does reticulum mean?
‘net-like structure’
What does the endoplasmic reticulum do?
Forms a network of interconnecting membrane-bound compartments in the cell.
How does the endoplasmic reticulum appear in micrographs?
As flattened membrane sheets or elongated tubular profiles.
What are the 2 types of endoplasmic reticulum?
Rough endoplasmic reticulum (RER)
Smooth endoplasmic reticulum (SER)
Why is the RER called ‘rough’?
It is studded with ribosomes
What does the rough endoplasmic reticulum do?
It plays a vital role in the synthesis of proteins destined for insertion into membranes or for secretion.
It is associated with the initiation of glycoprotein formation.
What determines the relative amount of endoplasmic reticulum in the cell?
Amount of ER present varies with how active the cell is. Cells that are relatively metabolically inactive have relatively little ER and vice versa.
Where are proteins destined to remain unpackaged in the cytosol synthesised?
On polysomes floating free within the cytosol
Why do plasma cells contain a lot of rough endoplasmic reticulum?
Plasma cells are important in immunity and produce antibodies. Antibodies are proteins so the plasma cell needs a lot of RER to produce a lot of protein antibodies.
What is the function of the smooth endoplasmic reticulum?
Continues the processing of proteins produced in the RER.
Plays a vital role aas the site of the synthesis of lipids
How much smooth endoplasmic reticulum do most cells contain?
Most contain relatively little SER, but in some (e.g. cells synthesizing steroid hormones) it is extensive.
Which organelle is composed of a group of flattened, membrane bound cisternae arranged in sub-compartments?
The golgi apparatus (complex)
Where do transport vesicles go after the SER/RER?
Arrive at the golgi
What is the role of golgi cisterns?
Give 3 examples
Function in the modification and packaging of macromolecules that were synthesised in the ER.
- Adds sugars
- Cleaves some proteins
- Sorts macromolecules into vesicles
Describe the physcial structure of mitochondria
- oblong, cylindrical, typically 0.5-2µm in length
- composed of an outer and inner membrane
- contain their own DNA (Eukaryotic) and system for protein production.
The inner membrane of the mitochondria is extensively folded (invaginated) to form cristae, what do these do?
Act to increase the available surface area.
What is the function of mitochondria?
- Power generators of the cell.
- They function in the generation of ATP via oxidative phosphorylation
- and in the synthesis of certain lipids and proteins
Every cell contains mitochondria but what does it mean if there is a high number of mitochondria?
Active cell, highly metabolic
What are intracellular junctions?
Specialised membrane structures which link individual cells together into a functional unit.
(To build a tissue with individual cells you need something to put them together which is accomplished through intracellular junctions)
Name the three types of intracellular junctions
- Occluding junctions
- Anchoring junctions
- Communicating junctions
What is another name given to occluding junctions?
Tight junctions or Zonula Occludens
What do occluding junctions do?
- Link cells to form a diffusion barrier
- Prevent diffusion
- focal region of close apposition between adjacent cell membranes
What do anchoring/adhering junctions do?
Provide mechanical strength
What other names are given to Anchoring junctions?
Adherent junctions or zonula adherens
How do anchoring junctions work?
- transmembrane cadhern molecules bind to eachother in the extracellular space, and, through link molecules, to actin of the cytoskeleton.
Name two types of anchoring junctions
Adherent junctions
desmosomes
How do anchoring junctions known as adherent junctions work?
Link submembrane actin bundles of adjacent cells
How do anchoring junctions known as desmosomes work?
Link submembrane intermediate filaments of adjacent cells.
What is another name given to desmosomes?
Macula adherens
Where are desmosomes commonly found?
In the skin where they provide mechanical support.
What is the purpose of communicating/gap junctions?
Allow selective diffusion of molecules between adjacent cells.
How do gap junctions look?
Each junction is a circular patch studded with several hundred pores
Which type of proteins produce pores in gap junctions?
Connexon proteins
Name 3 places gap junctions are found?
Epithelia
Some smooth muscle
caridiac muscle
Why are there gap junctions in cardiac muscle?
Critical for the spread of excitation
What is a junctional complex?
What are 3 ways material can move across the cell membrane?
- Diffusion
- Via transport proteins (pumps or channels)
- By incorporation into vesicles (vesicular transport)
What are the 2 main types of vesicular transport?
Endocytosis
phagocytosis
Describe endocytosis
The cell membrane invaginates, fuses and newly made endocytotic vesicle (endososme) buds into the cell. This process is often receptor mediated.
__________ works in the reverse fashion to endocytosis to discharge material.
Exocytosis
Which substances in the extracellular space can be incorporated into the cell by phagocytosis?
Bacteria
Larger particulate material
How does phagocytosis occur?
The bacterium binds to cell surface receptors triggering extensions of the cell to engulf it forming a phagosome. The phagosome binds with a lysosome carrying digestive enzymes producing a phagolysome.
What is the purpose of a fixodent?
Stops the processes which would otherwise degrade a tissue.
Describe, step by step, the histological techniques involved in viewing a specimen under a microscope
- Tissue is often ‘fixed’ to preserve it in as life like a state as possible. Usually a chemical that cross-links proteins like formalin, is used.
- Tissue has to be thinly sliced (1-15µm) to allow light to penetrate the tissue.
- Must impregnate tissue with a support material, usually wax (not necessarily for cell smears). To do this tissue is: dehydrated, put into organic solvent and placed in hot wax until it has fully penetrated the tissue.
- Thin sections are cut on a microtome and put onto microscope slides, the wax is washed out and the tissue rehydrated.
The process carried out to view a section of tissue under a microscope can produce distortions/changes from the original tissue. What are these called?
Artifacts e.g. shrinkage
Why can you not see tissue under a microscope without a stain?
Thin tissue has no contrast which is why you cannot see anything.
Once prepared how can a section of tissue be viewed under the micrscope? How do we produce contrast so it can be seen?
Expose the section to various coloured dyes, termed stains, that differentially bind to particular types of molecules.
Which is the most common stain used when viewing tissues?
A combination of Haemotoxylin (purple) and Eosin (pink). Abbreviated ‘H&E’.
What type of dye is Haemotoxylin and what is it therefore attracted to? What colour does it stain these molecules?
A basic dye
Has an affinity for acidic molecules and stains them purplish blue e.g. the nucleus or ribosomes.
What type of dye is Eosin and what is it therefore attracted to? What colour does it stain these molecules?
An acidic dye that has an affintiy for basic molecules and stains them pinkish red.
Most proteins in the cytoplasm are basic and so the cytoplasm of the cell is usually stained pink or red.
Name the 4 basic tissue types
- Epithelium
- Connective tissue
- Muscle
- Nervous tissue
Give a brief overview of epithelia
Epithelia (singular=epithelium) cover surfaces of the body or line hollow organs, and also form many glands. They occur as sheets of cells and vary widely in size, shape, orientation and function.
Give a brief overview of connective tissue
Connective tissue forms the framework of the body, but beyond that it has a dynamic role in the development, growth and homeostasis of tissues, and, via fat, in energy storage.
Give a brief overview of muscle tissue
Muscle cells are specialised to generate force by contracting. There are three major kinds within the body.
Allows us to move
Pumps blood
Moves food along the gut for example
Give a breif overview of nervus tisse
Consists of neurons and their supporting cells. Nervous tissues serves a control function and allows for rapid communication between different parts of the body.
Give 4 common features of epithelia
- Adhesion between epithelial cells is strong, thus forming sheets of cells, with a minimum of intracellular space. They are therefore perfect to cover surfaces and line body cavities.
- All have, at their basal surface, a layer of extracellular matrix components, called a basal lamina (basement membrane), to which the cells are atatched.
- All are non-vascular. Nutrients from capillaries in underlying tissue must diffuse across the basal lamina.
- The cells are usually polarized, that is the apical and basal ends of the cell differ.
What do surface epithelia do?
Cover or line surfaces, cavities and tubes.
The liver, the largest organ in the body, is composed of which tissue?
Epithelia which can also form solid organs and glands.
Provide 6 functions of epithelia
- Mechanical barrier (e.g. skin)
- chemical barrier (e.g. lining of stomach)
- absorption (e.g. lining of intestine)
- secretion (e.g. salivary gland)
- containment (e.g. lining of urinary bladder)
- locomotion (by cilia) (e.g. oviduct)
Minor functions include: sensation (neuroepithelium, e.g. taste buds) and contractility (myoepithelial cells)
Which 4 features are used in classifying covering epithelia?
- Cell shape
- The number of layers
- Cell surface, or tissue surface, specialisations
- The presence of Specialized cell types
What are the 3 possible cell shapes of epithelia?
- squamous (flattened, like a fish scale/plate)
- cuboidal (cube shaped, height similar to width)
- columnar (like a column, relatively tall and thin, height 2-5 times width)
What is ‘simple’ epithelia?
One layer of epithelia
What is ‘stratified’ epithelia?
Two or more layers
What is ‘Pseudostratified’ epithelia?
Tissue appears to have multiple layers, but in fact all cells are in contact with the basal lamina.
Give 3 examples of cell surface, or tissue surface, specializations of epithelial tissue
- prominent microvilli (termed a ‘brush border’)
- cilia
- presence of layers of keratin proteins on the tissue surface (termed keratinized)
What does glandular epithelia do?
Produce secretory products
Give 6 examples of the secretory products produced by glandular epithelia….
- sweat
- milk
- oil
- hormones
- mucous
- enzymes
and others
Where is the product secreted in endocrine glands and where is it then headed?
Toward the basal end of the cell (end sitting on basal lamina)
Distributed through the vascular system throughout the body.
Why are endocrine glands termed ‘ductless’?
There is no tube to take the product away it will likely be delivered into the vascular system to travel around the body.
Where is the product secreted in exocrine glands and from which end of the cell?
Product secreted toward the apical end of the cell either into the lumen of an internal space, into a duct, or onto the body surface. Termed ‘ducted’ glands.
What are the 3 types of connective tissue?
- Soft connective tissue: tendons, ligaments, mesentery, stroma of organs, dermis of the skin, etc
- Hard connective tissue: bone and cartillage
- Blood and lymph: many authors consider blood and lymph a specialised
The type of connective tissue is determined by the types and relative amounts of which 2 components?
- cells
- extracellular matrix
Which three elements make up the extracellular matrix?
- fibres: collagen, reticular and elastic fibres
- ground substance: an amorphous, space occupying material made of huge unbranched polysaccharide molecules called glycosaminoglycans (GAGs), most of which are bound to protein cores to form glycoproteins
- tissue fluid
Which 4 cell types are found in connective tissue?
- fibroblasts: widely distributed cells that produce and maintain the extracellular matrix.
- adipose cells: fat cells, found scattered in many connective tissues
- osteocytes: cells of bone
- chondrocytes: cells of cartillage
What are the 2 types of soft connective tissue?
Loose
Dense
Describe loose connective tissue
Loosely packed fibres separated by abundant ground substance. Cells are relatively plentiful.
How is dense connective tissue composed?
Densely packed bundles of collagen fibres. Can be dense regular CT if the fibres are aligned (e.g. tendon) or dense irregular CT if the fibre bundles run in many directions (e.g. dermis of the skin).
What type of tissue is cartilage?
Strong, flexible, compressible, semi-rigid tissue
Where does the semi-rigid nature of the matrix in cartilage come from?
The highly hydrated nature of the ground substance (GACs and proteoglycans)
What does avascular mean?
Not penetrated by blood vessels
What is the word used to describe the fact cartilage recieves nutrients from adjacent tissues by diffusion through its matrix?
Avascular
What are the 3 types of cartilage?
- Hyaline- most common, nose, trachea
- elastic- pinna of ear
- fibrocartilage- tough, intervertebral discs
Name 4 sites where the most common type of cartillage, Hayaline cartilage, is found?
Articular surfaces
Tracheal rings
Costal cartilage
Epiphyseal growth plates
What are the 2 types of bone that can be recognised in a longitudinal section through a long bone (limb bone)?
cortical bone
cancellous or tribecular bone
What is the name of the bone shaft?
Diaphysis
What is the name of the end of the bone?
The epiphyses
An outer shell of dense ________ bone makes up the shaft (dyaphysis).
Cortical
________ or _________ bone occupies the ends of the bone (the epiphyses)
Cancellous
Trabecular bone
Describe cancellous bone
A fine meshwork of bone that looks a bit like the inside of the aero bar.
Is bone a living tissue or a dead one?
Living
What type of living cells does bone contain?
osteocytes
Bone is penetrated by small canals called _______________ for blood vessels and nerves.
Haversion canals
What is different about muscle cells that makes them highly specialized for the production of contractile force?
All cells contain some contractile fibres in their cytoskeleton, but in muscle cells the cytoplasm is packed with these fibres.
How is force produced in muscle cells?
By the movement of actin fibres over myosin fibres, with the aid of a number of accessory proteins.
What are the 3 major types of muscle tissue?
- smooth
- skeletal
- cardiac
Describe smooth muscle
- Also called involuntary or visceral, is strutcurally the simplest of muscle types.
- It is calld smooth because it has no visible striations
- Involuntary because it is not under conscious control, and
- Visceral because it is predominnatly found in organs.
- Individual fibres are elongated, spindle-shaped cells with great range in length (20-200µm)
- Cigar shaped nucleus lies near the centre of each fibre
What other names are given to skeletal muscle?
Voluntary
Striated
Why are none of the terms skeletal, voluntary nor striated entirely accurate?
Some skeletal muscles are not always under the control of will, and all striated muscles are not skeletal, eg cardiac.
Which type of muscle constitutes the muscles of the body thaat respond to conscious control?
Skeletal muscle
Describe the structure of skeletal muscle fibres?
Typical skeletal muscle fibre is a giant multinucleated, cylindrical cell. Fibres may attain considerable lengths (1 to 40nm), with a diameter ranging from 10 to 100 µm.
Each fibre has many nuclei that are elongated and located at the periphery of the cell, just internal to the cell membrane.
What is the periphery of muscle cells called?
sarcolemma
What does cardiac muscle do?
Forms the major part of the heart chambers and origins of the great vessels.
What similarity does cariac muscle have with skeletal muscle?
It also has striations, however they are less prominent.
Describe 2 features of cardiac muscle
- Single nucleus located near the centre of the cell.
- Intercalated discs, can be seen passing across the fibres at irregular intervals.
What are intercalated discs?
Sites of end-to-end attachments between adjacent cells. Not surprisingly these contain multiple intracellular junctions to maintain mechanical integrity.
What two components is nervous tissue comprised of?
- neurons
- support cells (glia)
_______ outnumber neurons by about 10:1 in the CNS
Glia
Nervous tissue is surrounded by a connective tissue ‘coat’ what is the name of this ‘coat’ in the CNS and the peripheral nervous system (PNS)?
CNS= meninges
PNS= Epineurium
What are the 3 types of neuron? Describe them.
- Multipolar- most common, many dendrites (D), one axon (A)
- Bipolar- one dendrite one axon
- Pseudounipolar- short process gives rise to axon in both directions
Name the 3 principle glia of the CNS and state their functions
- Astrocytes- support, ion transport, induce blood brain barrier
- Oligodenrocytes- produce myelin in the brain and spinal cord which increases the action potential (communication) speed.
- Microglia- provide immune surveilance
Name the principle glia of the PNS and state their role
Schwann cells: produce myelin and support axons
Name the 4 basic tissue types
- Epithelium
- Connective tissue
- Muscle
- Nervous tissue
What are organs made up of?
Although the cells of organs perform specific, specialized tasks, organs are essentially composites of the 4 basic tissues.
What is the digestive tract made up of?
- Comprises the mouth, the esophagus, the stomach, the small intestine, the large intestine, the rectum and the anus.
- Most fluid is absorbed in the small intestine, some reaches colon
- some secreted with colon
- large intestine dries out the faeces
Name the 3 major salivary glands aswell as the many smaller salivery glands scattered in the oral mucosa
- parotid
- submandibular
- sublingual
What does serous mean?
Serous means watery, serous cells stain intensely
Describe how the form of the 3 main salivery glands follows their function
- Parotid gland has a very long duct, you wouldn’t want to secrete mucus into a very long duct so it has many serous secreting cells.
- The sublingual duct has a very short duct system so it is convenient for mucus and has less serous secreting cells
- Submandibular gland is inbetween
What is one unusual feature of salivary glands?
The striated ducts
In most glands with ducts the duct only conveys the secretory product, but the striated ducts actually modify the saliva that is passing through them.
How do the striated ducts modify saliva?
By pumping salt out of the fluid so that our saliva is hypotonic to blood (which is why saliva doesn’t taste very salty) to preseserve the salt in the body.
What are the 4 major layers that make up the digestive tract proper?
From the oesophagus to the anal canal the architecture of the digestive tract is composed of 4 major layers (starting from the lumen and going out):
- Mucosa: 3 parts
- Submucosa
- Muscalaris externa
- Serosa or adventitia
What are the 3 parts of the mucosa in the digestive tract?
- Epithelium: sits on a basal lamina
- lamina propria: loose connective tissue
- Muscularis Mucosae: thin layer
What is the submucosa in the digestive tract?
A layer of loose connective tissue
What is the muscularis externa of the digestive tract?
Two thick layers of smooth muscle, an inner circular layer and an outer longitudinal layer
Describe the serosa or adventita of the digestive tract
Outer layer of connective tissue that either suspends the digestive tract or attaches to other organs.
Describe protective mucosa in the digestive tract and where it can be found
- Non-keratinized, stratified squamous epithelium.
- oral cavity, pharynx, oesophagus, anal canal
Describe secretory mucosa in the digestive tract and state where it can be found
- simple, columnar epithelium with extensive tubular glands
- stomach
Describe absorptive mucosa in the digestive tract and state where it can be found
- Simple, columnar epithelium with villi and tubular glands
- small intestine
- villi provide a large surface area for absorption- nutrients etc
Describe protective & absorptive mucosa of the digestive tract and state where it can be found
- simple, columnar epithelium with tubular glands
- large intestine
What is another name given to the small intestine?
The ileum
The digestive tract has its own nervous system, what is its name?
The enteric nervous system
Where does the enteric nervous system receive input from?
The autonomic nervous system, but it is also capable of co-ordinating gut motality locally
In the digestive tract most of the neurons live in groups between the 2 muscle layers that make up the muscularis externa, what are these groups called?
Ganglia
After the airway, what are the three layers of the trachea?
- Respiratory epithelium
- lamina propria- connective tissue made up of extracellular fibres, there for connectivity and strength
- hyaline cartilage of tracheal ring
Compare bronchi and bronchioles
- Bronchi are lage diameter airways and have hyaline cartilage in their wall.
- Bronchioles are smaller airways, have no cartilage and smooth muscle predominates their wall.
Columnar cells of the epithelium tend to get ________ the further down the respiratory tree you go.It is important to realise that gas exhange ___________ occur across these epithelia.
- Shorter
- Does not
What are alveoli lined by?
Simple, squamous epithelium
What is the liver made up of?
A large no. of lobules each with a similar hexagonal arrangement.
What is found at each corner of the hexagonal lobule arrangement?
A branch of the hepatic portal vein and hepatic artery, each delivering blood to the lobule.
Also a bile duct
What is found in the centre of the hexagons in the liver?
The central vein whcih drains to the hepatic vein
Blood passing from the corner to the centre via hepatic ____________ passes sheets of liver cells called ___________.
- sinusoids
- hepatocytes
Why is the pancreas unusual?
It is both an exocrine and an endocrine gland
What does the exocrine pancreas do?
Produces about a litre each day of digestive juices containing proteases to break down proteins, lipases to break down lipids, nucleases to break down DNA/RNA, etc. These enter the duodenum via the pancreatic duct.
Is the majority of the pancreas exocrine or endocrine?
Exocrine
What does the endocrine pancreas consist of and what do they do?
Small, scattered islands of tissues calles islets of langerhans, which produce a number of hormones including insulin.
What are the 3 layers of blood vessels?
- Inner layer- tunica intima
- Middle layer- tunica media
- Outer layer-tunica adventitia
Describe the inner layer of blood vessels- Tunica intima
A single layer of squamous epithelial cells termed endothelial cells supported by a basal lamina and a thin layer of connective tissue.
Describe the middle layer of blood vessels- tunica media
Made up predominnatly of smooth muscle. Thickness of this layer varies tremendously.
Describe the outer layer of blood vessels- tunica adventitia
Made up of supporting connective tissue, fairly dense
The tunica intima is separated from the tunica media by a layer of elastic tissue called the _________ _________ membrane.
Internal elastic
The tunica media is separated from the tunica adventita by a layer of elastic tissue called the ________ _______ membrane.
External elastic
Are elastic fibres stained using common stains (including H&E)?
No, but they can be visualized with special stains.
Give an example of how the general architecture varies in blood vessels using the largest arteries
In the largest arteries e.g. the aorta, a significant amount of the smooth muscle in the tunica media is replaced by sheets of elastic fibres. These are called ‘elastic arteries’.
Why are the very largest arteries e.g. the aorta called elastic arteries
Because they have many sheets of elastic fibres in their tunica media to provide elastic recoil.
Why is the smooth muscle replaced with elastic fibres in the largest vessels?
The large vessels very close to the heart are receiving a large bolus of ejected blood spurting out of the heart during systole.
Then during diastole ventricles stop pumping and are filling .
If vessels near the heart weren’t elastic, your blood pressure would sky rocket during systole and plummet during diastole.
The stretched vessels recoil they do not contract.
In the larger arteries, only the inner part of the wall can obtain nutrients from the lumen, therefore these will have their own vascular supply: The _____ ________.
Vaso Vasorum
(essentially the vessel of the vessel, occurs in any vessel of a decent size)
What happens as arteries become smaller?
They lose smooth muscle from the t.media, until arterioles have only one or two layers of smooth muscle in their tunica media and almost no adventitia.
Typical diameter:30-200µm. These are particularly important in controlling blood flow in a tissue.
What are capillaries composed of?
Endothelial cells and a basal lamina.
This makes sense them having no tunica media as they need to be very thin walled to allow gas exchange.
What is the typical diameter of capillaries?
4-8µm
What are the 3 types of capillaries?
- continuous
- fenestrated: have small pores (50nm)
- discontinuous or sinusoidal: have large gaps
Where can continuous capillaries be found?
- Muscle
- nerve
- lung
- skin
Fenestrated capillaries are places where fluid exchange is easily accomplished by the blood vessels, capillaries and surrounding tissues. Name 3 places they can be found.
- Gut mucosa
- endocrine glands
- kidney
Discontinuous capillaries have vascular spaces with substantial openings, generally not big enough for cells to go through, liquid component is very free to move between tissue and blood vessel. Name 3 places they can be found.
- liver
- spleen
- bone marrow
Capillaries typically form an ____________ network. Peresites often surround capillaries (may act as stem cells). These may have _________ properties which can change the flow through the capillary.
- anastomitic
- contractile
Where do capillary networks drain?
Post capillary venules
Describe post-capillary venules
- 10-30µm diameter
- endothelial cell lined
- thin layer of connective tissue
- important sites for exchange
- generally no associated smooth muscle
Once post capillary venules begin to acquire intermittent smooth muscle cells in a tunica media layer, they are referred to as ____________ (generally >50µm).
Venules
Describe veins
- Contain tunica intima
- Thin but continuous tunica media
- Typically consist of a few layers of smooth muscle cells.
- Obvious tunica adventitia
- carry low pressure so thick muscle unnecessary
Describe large veins
The largest veins (e.g.vena cava) have a thick tunic adventitia which incorporates bundles of longitudinally orientated smooth muscle.
Many small veins have valves (inwards extensions of the tunica intima). Why?
To prevent backflow of blood
Describe the lymph vascular system
- system of relatively thin walled vessels that drain excess tissue fluid (lymph) into the blood stream
- transports lymp to lymph nodes for immunological surveillance
- no central pump
- smooth muscle in walls, hydrostatic pressure in the tissue and compression of the vessels by voluntary muscles, combined with valves in the vessels, produces flow.
- no smooth muscle unil a decent sized lymph vessel.
Where is the majority of blood in the body at any given time?
Peripheral veins
Capillaries have a huge _________ _____ but very small vessels so hence their cumulative _________ is rather small.
- surface area
- vollume
What is the average adult volume of blood?
4.5-6 litres
What percentage of the blood is plasma and what percentage is formed elements?
Formed elements- 45%
Plasma-55%
What is plasma made up of?
Plasma is 90% water
Proteins (mostly albumin, immunoglobulins, clotting factors)
Nutrients, salts
What are the three groups of formed elements which make up 45% of the blood?
- Red blood cells (erythrocytes)
- White blood cells (Leukocytes)
- platelets
What are the two divisions of white blood cells?
Granulocytes and Agranulocytes
What are the 3 types of granulocytes?
- Neutrophils
- Eosinophils
- Basophils
Granulocytes are “philled” with granules
What are the 2 types of agranulocytes?
Lymphocytes and monocytes
How can blood be separated?
By spinning it in a centrifuge
How do erythrocytes, leukocytes and plasma separate in the centrifuge?
Red cells are densest and after spinning are found at the bottom of the tube.
white cells are next
Plasma which is the liquid portion is found on top
What is the liquid called after being in the centrifuge if clotting factors had already been removed?
Serum
How is serum usually obtained?
By allowing the blood to clot, then removing the clot before spinning the blood.
What essentially is serum?
Plasma without clotting factors
Describe erythrocytes (red blood cells, RBCs)
- biconcave disks about 7µm in diameter
- Mature RBCs are not true cells as they have no nucleus or organelles
- deformable bags with about 1/3 of their volume taken up by iron-containing protein haemoglobin
- contain a network of flexible cytoskeletal elements that allow them to deform and slip through spaces smaller than themselves
How long do erythrocytes last in circulation approximately?
4 months
Which structures remove aged red blood cells from the circulation?
The spleen and liver
Name the most abundant type of white blood cells
Neutrophils
State the 5 types of WBCs in order of decreasing prevalence
- neutrophils (40-75%)
- Lymphocytes (20-50%)
- Eosinophils (5%)
- Monocytes (1-5%)
- Basophils (0.5%)
Describe neutrophil structure and how they appear on stains
- granulocytes
- cytoplasm contains many granules but these stain poorly with acidic or basic dyes
- prominent, multi-lobed nucleus
- one lobulated nucleus- often called polymorphonuclear leukocytes.
- extra bit sticking out of some nuclei is the bar body or drumstick chromosome- extra X chromosome which has been packaged up typically in females.
Neutrophils circulate in an ________ state, but if stimulated, for example by the presence of bacteria or inflammation, they enter the tissue where they are highly motile _____________.
- inactive
- phagocytes
Neutrophils are both abundant and short-lived which means that a significant portion of the ____ ______ is devoted to their production.
bone marrow
Describe the structure of eosinophils and how they stain
- Prominent granules have an affinity for the red acidic dye eosin.
- slightly larger than neutrophils
- typically bilobed nucleus
*
How long do eosinophils circulate before moving into the tissue (particularly spleen, lymph nodes and GI tract) where most eosinophils live.
8-12 hours
Why are eosinophils important?
- Their granules contain a variety of hydrolytic enzymes and they are important in inducing and maintaining inflammation, particularly in allergic reactions and asthma.
- Also important in fighting parasitic infection
Describe basophils and how they stain
- Prominent granules in their cytoplasm have an affinity for basic dyes such as methylene blue and stain intensely purple-blue with this dye.
- bilobed nucleus often obscured by the granules.
What do the granules in basophils contain?
- histamine
- heparin
- other inflammatory mediators
What do basophils do?
Act as effector cells in allergic reactions
High affinity IgE receptors in their cell membrane are directed against a particular allergen and when they bind to their antigen the cell is stimulated to release its granules (degranulation)
This leads to hayfever, allergic asthma, allergic dermatitis etc
Monocytes serve as the precursors of tissue macrophages and together they form what is termed the ________ __________ __________.
Mononuclear phagocyte system
Macrophages are widely distributed in the body, but are particularly found where?
In loose connective tissue
Describe the appearance of monocytes
- Numerous small lysosomal granules in their cytoplasm
- Largest cells circulating in the blood
- non-lobulated nucleus which often appears kidney bean shaped.
Many members of the mononuclear phagocytic system are ‘wanderers’ but some remain resident within particular tissues, give 3 examples…
- Kupffer cells in the liver
- microglia in the brain
- Langerhan’s cells in the skin
Describe the appearance of lymphocytes
- round nucleus surrounded by a thin to moderate rim of cytoplasm
- cytoplasm has no visible granules
Name the 2 classes of lymphoctes
B cells and T cells
Can B cells and T cells be distinguished in routine stained sections?
No
Both types of lymphocyte arise in the _____ _________, but T cells differentiate in the ________. Both cell types participate in the _______ immune response.B cells give rise to antibody secreting _______ cells while T cells form a complex set of cells that perform many defence functions (aiding other immune cells, killing defective cells,etc).
- bone marrow
- thymus
- specific
- plasma
What are platelets and what do they do?
- formed elements
- small cell fragments about 2µm in diameter found in large numbers in the blood
- Play a key role of haemostasis (the prevention of blood loss)
- clots are largely contributed by platelets
Describe the structure of platelets
- well developed cytoskeleton which paticipates in extrusion of granules and in clot reactivation
- some organelles but no nucleus
- conspicuous granules that include, among other things, some coagulation factors.
Where and when is the earliest site of erythrocyte production?
Outside the embryo in the yolk sac, beginning at about 3 weeks gestation.
Later, during the second trimester, where is the principal site of blood formation?
The liver
It and to some extent the spleen is colonized by hemopoietic stem cells.
By birth where is the main site of blood formation?
The bone marrow, essentially all bones participate.
What happens regarding hemopoeisis as the bones enlarge?
There is excess capacity and so hemopoeisis is shut down in many bones.
By the time the skeleton reaches maturity, which bones retain hemopoiesis?
- Vertebrae
- ribs
- skull
- pelvis
- proximal femurs
What happens to marrow in other bones which do not retain hemopoeisis?
Marrow in other bones is largely adipose tissue, although in an emergency, they can revert back to blood formation.
What are Megakaryocytes and what do they do?
Large (30-100µm) cells of bone marrow that produce platelets.
Platelets are formed as extensions at the outer margin of the cell which fragment from the cell.
Why do megakaryocytes have very large nuclei?
Their nuclei undergo multiple duplications of its nuclear material but doesn’t undergo cytokenesis (cell division).
