Session 5.2d - Lecture 1 - Epithelial Tissues and Glands Flashcards
Slides 50 - 64
What is stratified squamous keratinized epithelium mainly made up of?
Keratinocytes
In what structure are keratinocytes the predominant cell?
Stratified squamous keratinised epithelium (epidermis)
What is a keratinocyte?
An epidermal cell which produces keratin.
What are the four layers of the epidermis?
Horny layer (stratum corneum) Granular layer (stratum granulosum) Prickle cell layer (stratum spinosum) Basal layer (stratum basale)
What are the four layers of the epidermis by their English translation?
Horny layer
Granular layer
Prickle cell layer
Basal layer
What are the four layers of the epidermis by their Latin name?
Stratum corneum
Stratum granulosum
Stratum spinosum
Stratum basale
What are the terms of the epidermis commonly used by dermatologists and pathologists?
Stratum corneum
Granular layer
Basal layer
Which term is more commonly used - horny layer or stratum corneum?
Stratum corneum
Which term is more commonly used - granular layer or stratum granulosum?
Granular layer
Which term is more commonly used - prickle cell layer or stratum spinosum?
Neither is really spoken about much
Which term is more commonly used - basal layer or stratum basale?
Basal layer
What is mitosis?
Cell division
What is the term for cell division?
Mitosis
Where does keratinocyte mitosis occur?
Mainly in the BASAL LAYER
Why is the basal layer significant?
(Almost all) of the keratinocyte mitosis occurs here.
What happens to the daughter keratinocytes that are produced from mitosis?
They move upwards from the basal layer, differentiate, and lose their ability to divide.
In which direction do keratinocytes move?
Upwards from the basal layer, after dividing there, they differentiate and lose this ability to divide.
What do keratinocytes synthesise?
Keratins
What are keratins?
Large masses of fibrous proteins
Where are keratins produced from?
Keratinocytes (found in the epidermis of the skin).
Other than collagen, what contributes to the strength of the epidermis?
Keratins
What is the function of keratins?
Contributes to the strength of the epidermis.
What are keratins the main constituents of?
Hair and nails (and animal horns)
What are your hair and nails predominantly made out of?
Keratin, they are just pure keratin really.
What is the normal transit time of a keratinocyte from basal layer to stratum corneum?
28-40 days (around 5 weeks)
21-28 days: 3-4 weeks NHS
The normal transit time of a keratinocyte is 28-40 days (around 5 weeks). What is this referring to?
Its differentiation from basal layer to stratum corneum.
Of which cell in the epidermis, is the normal transit time 28-40 days (around 5 weeks)?
Keratinocytes
What is psoriasis?
Psoriasis is a skin condition that causes red, flaky, crusty patches of skin covered with silvery scales.
What is the transit time of a keratinocyte in psoriasis?
5-6 days
3-7 days NHS
Explain what a normal transit time of a keratinocyte is and how associated problems with this can lead to disease.
The normal transit time of a keratinocyte is 28-40 days (~5 weeks). This describes how long it takes for the keratinocyte to differentiate in the basal layer of the epidermis, and move upwards to the outermost layer of skin (stratum corneum) where it drops off.
In some diseases, such as psoriasis, this transit time is greatly reduced (to about 3-7 days [about 5-6]), so that masses of stratum corneum is formed, which presents as silvery scales.
How does psoriasis present on the skin?
As silvery scales
What part of the skin produces the silvery scales seen on the skin in psoriasis?
Stratum corneum (build up of dead cells)
What is the pathophysiology of psoriasis?
The transit time is reduced, such that stratum corneum is produced in abundance as silvery scales.
How does psoriasis affect the patient?
It has huge psychosocial impact - masses of skin dropping off everywhere they go/every time they sit/stand etc. can be very distressing to the patient. Similarly, we have so much of our skin on show, so any ‘deformities’ have very obvious negative physical connotations socially, thus can impact heavily psychosocially.
NHS: The effect that psoriasis can have on physical appearance means low self-esteem and anxiety are common among people with the condition. This can lead to depression, especially if the psoriasis gets worse.
Your GP or dermatologist will understand the psychological and emotional impact of psoriasis, so talk to them about your concerns or anxieties.
Describe the psychosocial impact psoriasis has on a patient.
It has huge psychosocial impact - masses of skin dropping off everywhere they go/every time they sit/stand etc. can be very distressing to the patient due to the social impact. Similarly, we have so much of our skin on show, so any ‘deformities’ have very obvious negative physical connotations socially, thus can impact heavily psychosocially.
NHS: The effect that psoriasis can have on physical appearance means low self-esteem and anxiety are common among people with the condition. This can lead to depression, especially if the psoriasis gets worse.
Your GP or dermatologist will understand the psychological and emotional impact of psoriasis, so talk to them about your concerns or anxieties.
What can VERY rarely arise from skin due to keratin?
‘Horns’ of keratin (cutaneous horn)
How often can keratin horns arise from the skin?
Very rarely
What are ‘horns’ of keratin known as?
Cutaneous horns
What is a cutaneous horn?
A horn of keratin that has arisen.
How do you treat a keratin horn?
Surgical removal quite easily
Fig. 52 (left)
What are these images showing?
Keratin horns
Draw an image of a keratin horn (straight).
See Fig. 52 (left)
- they more often occur in older patients
- can have a risk of malignancy associated with it
- often occur on the head bc it’s sun exposed
Other signs and symptoms, see below:
https://www.dermnetnz.org/topics/cutaneous-horn/
Draw an image of a keratin horn from the side.
See Fig. 52 (top right)
- they more often occur in older patients
- can have a risk of malignancy associated with it
- often occur on the head bc it’s sun exposed
Other signs and symptoms, see below:
https://www.dermnetnz.org/topics/cutaneous-horn/
Draw an image of a keratin horn (spiral).
See Fig. 52 (bottom right)
- they more often occur in older patients
- can have a risk of malignancy associated with it
- often occur on the head bc it’s sun exposed
Other signs and symptoms, see below:
https://www.dermnetnz.org/topics/cutaneous-horn/
As well as keratinocytes, what other cell types are found in the epidermis?
- Langerhans cells
- Melanocytes
Where, specifically, are Langerhans cells found?
In all cell layers of the epidermis, but predominantly, the prickle cell layer (stratum spinosum) - roundabout in the middle.
What are Langerhans cells?
Dendritic cells (antigen-presenting immune cells) which have a huge immunological function.
What are the dendritic cells found in the epidermis called?
Langerhans cells.
Which layer of the epidermis are melanocytes found?
In the basal layer
What do melanocytes produce?
Melanin
What does melanin do to our skin?
Gives our skin its colour, especially, and more so if we’re exposed to sunlight.
Fig. 53
Caption the image
High power photomicrograph of human epidermis, with S100 monoclonal antibody staining to demonstrate Langerhans cells and melanocytes (by coincidence these two unrelated cell types stain with the same reagent)
Fig. 53
Label the image
- Langerhans cells (prickle cell layer)
- Melanocytes (basal cell layer)
(Stratum corneum visible at the top
Granular layer underneath
Dermis visible with interdigitation of epidermis/dermis boundary clearly demarcated)
Draw a photomicrograph of a human epidermis,
See Fig. 53
- Langerhans cells (prickle cell layer)
- Melanocytes (basal cell layer)
(can be same colour as they react to the same reagent in dye - but must be in different layers)
(Stratum corneum visible at the top
Granular layer underneath
Dermis visible with interdigitation of epidermis/dermis boundary clearly demarcated)
Name 4 facts about melanocytes (other cells of the epidermis).
- occur at intervals(1:8 of basal layer of epidermis)
- difficult to see histologically without special stains
- produce melanin, the main pigment that gives the skin its colour
- produce more melanin but are not increased in number in black or tanned skin
Name 4 facts about Langerhans cells (other cells of the epidermis).
- difficult to see histologically without special stains
- highly specialised capacity to present antigens to T lymphocytes
- mediate immune reactions e.g. allergic contact dermatitis
How prominent are melanocytes in our skin?
They occur at intervals, they’re about 1 in 8 of all the basal cells of the epidermis, the rest are keratinocytes,
What is the ratio of melanocytes to the rest of the basal cells?
1:8 (in all ethnic origins)
Melanocytes appear at an interval of 1:8 in the basal layer. What are the other cells?
Keratinocytes
What cells of the skin are difficult to see histologically without special stains?
- Melanocytes
- Langerhans cells
What cells makes up the basal layer of the skin?
Melanocytes and keratinocytes in a 1:8 ratio
How do we get our skin colour?
Melanocytes in the basal layer produce melanin, the main pigment that gives the skin its colour
What makes black/tanned skin people darker than white?
Although the melanocyte numnber is the same (1:8 ratio in basal layer; same ratio of melanocytes as we have to normal keratinocytes), it’s just that if we have more colour, we produce more melanin and also breaks down more slowly
What is the ratio of melanocytes to keratinocytes in people with tanned/dark skin?
It is the same (more melanin is produced/slower breakdown to give the darker colour)
What happens to the melanin produced by melanocytes in people with darker/tanned skin?
A More is produced and there is less breakdown
B. The melanin is conjugated with an enzyme and used for other purposes
C. The amount produced by the melanocyte is the same, but there are more melanocytes
D. More is produced but breakdown is the same
E. The same amount is produced but the breakdown is less.
A. More is produced and there is less breakdown
The amount of melanocytes stay the same, no matter what colour skin, but the amount of melanin produced differs with race.
What are melanosomes?
Organelles produced by melanocytes for synthesising, storing and transporting melanin.
Define these terms:
Melanin
Melanosome
Melanocyte
Melanocyte: cell found in the basal layer of the epidermis (at a 1:8 ratio, regardless of race) which produces melanin
Melanosome: organelle found in the melanocyte which synthesises, stores and transports melanin
Melanin: pigment produced by melanocytes in the melanosome, which gives skin its colour
How do melanosomes differ for different races?
In a lighter person, the body tends to break down the melanosomes quite quickly, whereas in people of colour, it would do so much more slowly and would have a limit
What is the function of Langerhans cells?
They have a highly specialised capacity to present antigens to T lymphocytes
How do Langerhans cells act to help immunologically?
- highly specialised cells
- can present T cells to an antigen
- found in our outermost layer of our epidermis
- look for anything foreign, if they find it, they
- engulf it
- break it down
- puts on MHC Class II molecules
- travels through lymphatic system
- shows to T lymphocytes
- tells them to clone and expand
- T lymphocytes migrate back preferentially to the skin and they react
How do Langerhans cells recruit T lymphocytes?
Once a foreign antigen has been located, they engulf it and break it down, putting it onto an MHC Class II molecule. This is then able to travel through the lymphatic system which can be recognised by T lymphocytes, which, in turn, clone and expand, before they migrate back (preferentially to the skin) where they react.
What do Langerhans cells particularly have a role in?
They particularly mediate immune reactions.
What disease can Langerhans cells be involved in?
Allergic contact dermatitis.
What do melanocytes look like?
They sit in the basal layer with their long processes.
What is the function of the long processes of the melanocytes?
They wriggle around amongst the keratinocytes
How do keratinocytes and melanocytes interact?
It’s thought that the keratinocytes actually phagocytose off bits of these long processes [from the melanocytes] together with the little melanosomes inside them, and they come to line therefore, the melanosome come to line the keratinocytes, giving the skin its colour.
What is the mechanism which gives skin it’s colour?
It’s thought that the keratinocytes actually phagocytose off bits of these long processes [from the melanocytes] together with the little melanosomes inside them, and they come to line therefore, the melanosome come to line the keratinocytes, giving the skin its colour.
Where in the basal layer do the melanocytes lie, specifically?
It’s thought that they come to lie on the ‘sunny side’ as it were, the outer surface of the nuclei bc they’re main job is to protect the DNA from UV radiation so we don’t develop cancers
Why is it thought that melanocytes lie on the outer surface of the nuclei?
Bc they’re main job is to protect the DNA from UV radiation so we don’t develop cancers