histology Flashcards
Histology
the study of biological tissues
What is a tissue ?
A tissue is a collection of one or more cell types working together for a common purpose
Tissues are the building blocks of organs
four major types of tissue in the human body
Epithelial
Connective
Muscle
Nervous
Epithelial
Secretion, protection and absorption
Connective
Support, binding, transport and protection
Muscle
Movement
Nervous
Co-ordination
The Nature of Epithelial Tissues
Epithelial tissues are found resting on a structure called the basement membrane. The basement membrane is composed of peptidoglycan (proteins and sugars)
two major categories of epithelial tissue
Simple epithelia
Stratified epithelia
Simple epithelia
Consist of a single layer of cells resting on a basement membrane
Stratified epithelia
Consist of multiple layers of cell stacked on to of each other like layers of bricks in a brick wall
squamous meaning
resembling a “fish scale” and hence these cell types are thin and flat
where is Simple squamous epithelium found?
places where thin membranes are necessary and it is perfectly adapted for the diffusion of gases such as oxygen and carbon dioxide
squamous epithelial cells
squamous epithelial cells are relatively elastic, this property is exploited in the alveolar air sacs of the lungs
what is alveolar air sac or alveolus surrounded by?
a dense network of blood capillaries
What is the inner layer of each artery and vein called?
endothelium - mainly made from a layer of simple squamous epithelial cells
endothelial layer is in direct contact with the blood
the smooth squamous epithelial cells ensure that resistance to blood flow is minimal
elastic nature of the squamous cells ensures that the blood vessel can dilate to increase blood flow and constrict to reduce blood flow
vasodilation
dilate to increase blood flow
vasoconstriction
constrict to reduce blood flow
what chemicals do squamous cells produce
Nitric Oxide (NO) which help regulate blood flow
Capillaries
smallest blood vessels and found infiltrating virtually all parts of the human body where they function as distribution vessels to ensure blood is delivered to the proximity of all cells and tissues
shape of capillary
formed from a rolled up tube of simple squamous epithelial cells
Between each adjacent squamous epithelial cell are slits which render the capillary permeable
When blood is forced into a capillary, fluid is driven out through these slits and collects in the tiny spaces (interstitial spaces) which are found surrounding the cells of the body
This fluid is called tissue fluid or interstitial fluid and is important in facilitating the movement of oxygen and nutrients into cells
fluid-producing membranes
lined by a layer of simple squamous epithelial cells
exists throughout the body
this squamous layer when examined surface on has an appearance resembling “crazy paving”
squamous epithelium aka “pavement epithelium”
squamous layer secretes a thin watery fluid called “serous fluid” this is found forming a natural slippery lubricant in many regions of the body.
Peritoneum or Peritoneal Membrane
peritoneum is found lining the abdominopelvic cavity - produces serous fluid to lubricate the surface of the internal viscera - prevent potential damage from abrasion during physical bodily movements
peritoneum is moist - susceptible to infection e.g. following a perforated gastric or duodenal ulcer.
Infection of the peritoneum results in significant inflammation and is known as peritonitis
Layers Of The Gut - The Serosa
The outer layer of the gut is a serous membrane called the serosa
the serosa produces a lubricating serous fluid which coats the outer layer of the gut
this fluid with that produced by the peritoneum, help prevent abrasion and damage
The layers of the pericardium
The pericardium is a compound membrane surrounding the heart
protects the heart and anchor it in position within the thorax
the pericardial sac is lined by a thin membrane called the parietal pericardium which is a serous membrane formed from a simple squamous epithelium
The serous fluid produced by the parietal pericardium is termed pericardial fluid - fills up the pericardial sac forming a layer of lubricating fluid which protects the beating heart
what are the lungs surrounded by?
The lungs are surrounded by two serous membranes which are known as the pleural membranes
what is the parietal pleural membrane attached to?
the inner surface of the thoracic cavity (ribcage)
what is the visceral pleural membrane attached to?
the outer surface of the lungs
what is between the two serious membranes
a cavity aka pleural cavity which is filled with a serous fluid produced by the pleura
what is the fluid produced by the pleura called and what does it do?
pleural fluid - helps to adhere the outer surface of
the lungs to the inner chest wall
Pleural fluid often can become infected leading to inflammation to the pleural membranes which is known as pleurisy
what is the simple cuboidal epithelium composed of?
a single layer of cube-shaped cells
A good example of its location is the kidneys where it forms the walls of the kidney tubules
Some simple cuboidal epithelial cells are ciliated
what does Simple cuboidal epithelium have a great volume of?
a much greater volume of cytoplasm compared to simple squamous epithelial cells
the cytoplasm of the cell - primarily involved in biochemical processing
what are Simple cuboidal epithelium excellent at in the kidney tubules
regulating the composition of renal filtrate (the precursor to urine) where they ensure that waste products remain within the tubules whilst simultaneously ensuring that useful chemicals such as glucose, amino acids and hormones are reabsorbed back into the blood
what are ependymal cells
specialised cuboidal epithelial cells which line the ventricles hollow chambers within the brain
where are Ependymal cells found?
in greatest densities in areas known as the choroid plexus within the ventricles
which fills the ventricles and surrounds the brain and spinal cord
what produces the cerebrospinal fluid (CSF)
the choroid plexus
fills the ventricles and surrounds the brain and spinal cord
CSF functions as a cushion with the brain and spinal cord effectively suspended in this fluid which acts as a shock absorber
The outer layer of cilia help ensure that the CSF remains mobile
what is the Simple Columnar epithelium
a single layer of column-shaped cells found lining the gastrointestinal (GI) tract
Large cytoplasmic volume ensures slow absorption of nutrients into the blood
microvilli
Many columnar epithelial cells have their surface area increased by small finger-like projections termed microvilli
enhances the absorption of nutrients and in the ileum have enzymes embedded into their surfaces which help complete the process of chemical digestion
layer of columnar epithelial cells lining the gut have mucus producing goblet cells - helps lubricate the passage of food through the GI tract and also coats the intestinal mucosa preventing chemical autodigestion
Goblet cells
Goblet cells produce mucin granules
On release mucin granules expand on contact with water
appearance of freshly produced mucus
transparent and very sticky ensuring it coats the mucosal surfaces
When mucus traps particulate material it becomes darker in colour
what does mucus contain
a variety of antimicrobial compounds such as lysozyme which can kill some forms of bacteria by attacking their cell walls initiating lysis (bursting)
Ciliated columnar epithelium
Some forms of columnar epithelium have mobile hair-like projections called cilia extending from their apical surface
where is Ciliated columnar epithelium found?
found lining the fallopian tubes
Ciliated columnar epithelium function
the cilia beat in co-ordinated waves where they function to transport the ova released during ovulation along the fallopian tubes into the uterus
Chlamydia trachomatis
Chlamydia is the most common sexually transmitted disease (STD) in the UK
In some women it can migrate into the fallopian tubes damaging the ciliated columnar epithelium thereby preventing it from acting as an effective transport mechanism for ova
leading cause of infertility in females
Loss of the ability to transport ova into uterus
ectopic pregnancy
Ectopic pregnancy is a medical emergency since there is a risk that the tube can rupture
If an ovum is fertilised there is a risk that it can become stuck within the fallopian tube potentially leading to an ectopic pregnancy
Stratified squamous epithelium
Composed predominantly of multiple layers of thin flat (squamous) cells
The first layer of cells resting on the basement membrane are cube- shaped and continually dividing by mitosis
example of a stratified squamous epithelium
the epidermis of the skin
what happens in the epidermis
newly produced layers of cells gradually get pushed to the surface and become flattened as they are compressed by the overlaying layers
what do the epidermal cells gradually accumulate?
the protein keratin as they move to the surface; this protein renders the cells impermeable to oxygen and so they gradually die
The outer layers of epidermal cells are entirely dead and gradually slough off at the surface to make way for the newer cells beneath
Stratified cuboidal epithelium
A relatively rare tissue composed of multiple layers of cube-shaped cells
Found surrounding developing follicles within the ovaries
A strong epithelium which allows a build-up of pressure within the follicle as it enlarges
Eventually the pressure causes the stratified cuboidal layer to rupture expelling the ovum into the fallopian tube during ovulation
Stratified columnar epithelium
Composed of multiple layers of column-shaped cells
A rare tissue found lining the male urethra and the conjunctiva of the eyes
Also found in portions of the pharynx (throat) and vas deferens (sperm ducts)
relatively thick and robust tissue with its major role being protection
Pseudostratified epithelium
pseudostratified means “falsely stratified” because on superficial inspection this tissue appears to be composed of multiple layers of cells but in reality this is a single layer of cells with each cell in contact with the basement membrane
where is Pseudostratified epithelium found
lining the respiratory tract where it forms the mucociliary escalator
what do Goblet cells in the pseudostratified layer produce
mucus which traps particles inhaled into the airway.
The beating cilia then moves this contaminated mucus upwards toward the pharynx (throat) where it is swallowed before being sterilised in the acidic gastric juice of the stomach
why does Pseudostratified epithelium have a falsely stratified appearance
some cells in the layer extend all the way to the surface while other smaller cells remain compressed below.
The larger cells extending to the surface are ciliated with their hair-like cilia beating in sweeping, co-ordinated waves
what causes Whooping Cough
The bacterium Bordetella pertussis causes whooping cough
This bacterium infects the respiratory tract damaging the mucociliary escalator.
Since the contaminated mucus cannot be cleared effectively it sinks down into the respiratory tract triggering a vigorous coughing reflex
Because of a drop-off in the uptake of the whooping cough vaccine, this disease has become more prevalent in the UK
Whooping cough is a potentially deadly infection, particularly in young children
Transitional epithelium
An elastic stratified epithelium lining certain hollow organs such as the bladder;
Called transitional because the cells change shape according to the current volume of fluid in the organ.
When the bladder is full the cells are compressed and flat (squamous), as the
bladder progressively empties the cells transition from flat to cube-shaped and eventually column-shaped when fully empty
The outer cells of the tissue slough off and collect in the urine where they may contribute to sediment found in urine samples
