The integumentary system lectures 17&18 Flashcards
1
Q
The integumentary system
A
Composed of the skin, hypodermis, glands, hair and nails
• Key function: ‘Protects the body from the external environment
2
Q
functions of the integumentary system
A
protection
regulation
sensation (detects stimuli)
metabolic
3
Q
How does the integumentary system support other systems?
A
• Synthesises vitamin D3, which governs for Ca and P absorption
(digestive system) and which is required for bone maintenance and growth (skeletal system) and muscle contraction (muscular
system)
• Vitamin D 3 is also a precursor of the hormone calcitrol (endocrine system)
• Receptors in dermis and deep epidermis provide sensory input to nervous system
• Keratinised epidermis limits fluid loss through skin, maintaining
body’s water balance (urinary system)
• Provides physical barrier that prevents entry of pathogens;
Langerhans cells and macrophages resist infection (immune system)
4
Q
Components of the integumentary system
A
skin
hypodermis
5
Q
skin
A
made up of 2 layers • Epidermis – Greek epi, ‘upon’ and derma, ‘skin’ – Thick, epithelial superficial layer • Dermis – Fibrous connective tissue
6
Q
hypodermis
A
- Greek hypo, ‘under’
- Subcutaneous fibrous connective tissue
Lies between dermis and underlying organs
Consists of
– areolar tissue (general connective tissue)
–adipose tissue (similar to areolar tissue, but with many more fat cells) – more predominant
Anchors skin to underlying muscles
7
Q
what cells is the epidermis made up of?
A
- Keratinocytes (~90% of epidermis)
- Melanocytes (~8%)
- Merkel cells (~1%)
- Langerhans cells (~1%)
8
Q
keratinocytes
A
- Most abundant cell of the epidermis
- Develop from stem cells at the base of epidermis
- Pushed up as new cells form beneath them; eventually die
- Produce keratin, a fibrous protein – tough, scaly, water-resistant
- Keratinocytes also produce antibiotics and enzymes to detoxify chemicals to which the skin is exposed
- Millions of these cells rub off every day; the epidermis is totally replaced about every 30 days
9
Q
Melanocytes
A
- Originate from embryonic cells called neural crest cells
- Produce the skin pigment, melanin, in granules called melanosomes
- Melanin transferred to nearby keratinocytes, so keratinocytes can contain more melanin than melanocytes
- Melanin shields cell nuclei from U V radiation, which can damage DNA and cause cancer
- In Caucasians, melanin digested by lysosomes just above the stratum basale
- Skin colour differences due to levels of melanin, not numbers of melanocytes
- In all but the darkest people, melanin increases with exposure to UV; this is suntanning
10
Q
Merkel cells
A
- Associated with sensory nerve endings – lots on finger tips and oral cavity
- Play a role in sensing touch
11
Q
Langerhans cells (epidermal dendritic cells)
A
- Star-shaped
- Part of immune system – unique population of tissue-resident macrophages
- Arise in bone marrow and migrate to epidermis
- Take up foreign proteins (antigens) that have entered the epidermis, and transport them to killer T lymphocytes (Antigen-presentation cells).
12
Q
layers of the epidermis
A
Thick skin (palms and soles) • Stratum corneum • Stratum lucidum • Stratum granulosum • Stratum spinosum • Stratum basale (basal layer) Thin skin (everywhere else) • Stratum corneum • Stratum granulosum • Stratum spinosum • Stratum basale (basal layer)
13
Q
Stratum corneum
A
- Thick; thicker in thick skin than in thin skin
- 20-30 cells thick, accounting for about 75% of epidermis
- High in dead keratinocytes, filled with keratin after nuclei/organelles disintegrate after cell death
- Keratin and thickened plasma membrane of cells protect the skin against abrasion/penetration
- Glycolipid between cells keeps layer waterproof
14
Q
Stratum lucidum (clear layer), or transition layer
A
- Thick skin only; absent in thin skin
- Thin translucent band under light microscope
- Consists of a few rows of dead keratinocytes
15
Q
Stratum granulosum (granular layer)
A
- Consists of 3-5 layers of flattened keratinocytes
- Contain waterproofing glycolipid
- Above the stratum granulosum, cells are too far from dermal capillaries and die
16
Q
Stratum spinosum (spiny layer)
A
- Keratinocytes in this layer typically have spiny extensions; however these do not occur in living cells – they are an artefact created as cells shrink during preparation
- Contain thick bundles of intermediate filaments called tonofilaments
- Also contain Langerhans cells
17
Q
Stratum basale (basal layer)
A
- Deepest layer of epidermis
- Continually renewing cell population
- Single layer of cells with the youngest keratinocytes
- Also contains occasional Merkel cells
- 10-25% of cells in basal layer are melanocytes
18
Q
the dermis
A
• Strong, flexible connective tissue
• Consists of
o fibroblasts ( secrete proteins that make collagen/reticular/elastic fibres – provides support)
o macrophages (non-specific phagocytes)
o mast cells (secretory cells)
o scattered white blood cells
• Contains sebaceous glands, sweat glands, hair follicles - APPENDAGES
• Consists of two layers:
– Superficial papillary layer (20% of dermis)
– Deep reticular layer (80% of dermis)
19
Q
appendages of the skin
A
The integumentary system includes the following derivatives of the epidermis: • Hair and hair follicles • Sebaceous glands • Sweat glands • Nails
20
Q
hair
A
- Hair is a flexible strand made of dead, keratinised cells
- This keratin is harder than the keratin found in the epidermis
- The life span of scalp hairs is approximately 4 years; in the eyebrows, only about 4 months
- Scalp hair is not in synchrony - otherwise, approximately every 4 years all of the hair on your head would fall out at once!
- Since chemotherapy drugs target rapidly dividing cancerous cells, they also destroy hair stem cells, leading to baldness
21
Q
Hair colour and shape
A
- Hair pigment (either black-brown, or rust) is made by melanocytes at the base of the follicle and transferred to the cells of the hair root
- The proportions of these two pigments determine hair colour
- White or grey hair is due to an absence of melanin, and its replacement in the shaft with air bubbles
22
Q
sebaceous glands
A
• Occur over the whole body, except the palms of the
hands and the soles of the feet
• Produce oily sebum; this accumulates within secretory epithelial cells and is released when these cells burst
• Mostly associated with hair follicles
• Softens and lubricates hair and skin, slows water loss and kills bacteria
23
Q
acne
A
- In acne, too much sebum is produced and blocks the sebaceous gland
- Sebum forms ‘whitehead’; this can dry and oxidise to form a blackhead
- Blocked sebaceous glands are more susceptible to infection leading to inflammation: spots
24
Q
sweat glands
A
• Humans have > 2.5 million sweat glands
• All over skin, except nipples and external genitalia
• We produce about 500ml of sweat per day
• Sweat glands are unique to mammals, and prevent overheating
• Sweat is 99% water, with some salts plus urea, ammonia and uric acid
• Acidic, so also retard growth of bacteria
• Two main types of sweat glands (eg mammary glands are modified sweat glands):
– Eccrine glands
– Apocrine glands
25
Eccrine glands
* More numerous
* Produce true sweat
* Most abundant on palms, soles of feet and forehead
26
Apocrine glands
* Axillary, anal and genital areas
* Larger
* Produce sweat which also contains fatty substances and proteins
* Initially odourless but can be decomposed by skin bacteria and starts to smell: B O!
* Begin to operate at puberty
27
nails
• Modified part of epidermis, comprising hard
keratin (as in hair)
• Nails comprise:
– distal free edge
– body
– proximal root embedded in the skin
• Rests on epidermal nail bed, corresponding to deeper parts of epidermis; the nail itself corresponds to the outer, keratinised layers
• Nails appear pink because of rich blood supply, except at the nail matrix, the actively growing part, which is thicker and appears as a white crescent: the lunula
28
Developmental disorders of the integumentary system
* Chromosomal abnormalities such as trisomy 21 (Down syndrome) can lead to distinctive ridge patterns on hands and feet
* These include so-called simian lines, which are otherwise rare
29
Ichthyosis
refers to a group of disorders resulting from excessive keratinisation
o Skin is hard and dry, with some resemblance to scales
30
Angiomas
of the skin (which may not be true tumours) arise
transitory or surplus blood/lymphatic vessels persist
o Those composed of blood vessels may be arterial, venous, cavernous or mixed
o True angiomas are benign endothelial tumours: birthmarks
31
Albinism
skin, hair and retina lack pigment (the iris may be pigmented) because melanocytes fail to produce melanin because of an enzyme deficiency
32
Macule
Flat lesion with skin discolouration, <1cm
33
Nodule
Round, elevated lesion,
| >1cm
34
Plaque
Superficial, elevated flat lesion > 1cm
35
Vesicle
Fluid filled lesion (blister) <1cm
36
Bullae
Fluid filled lesion > 1cm
37
Pustule
Vesicle containing pus (inflammatory cells)
38
Papule
Superficial solid elevated lesions <1cm
39
vitiligo
Pale white patches on skin – lack of melanin
40
Freckles (ephelides)
Small, light brown/tan mark on the skin
Particularly common in fair-skinned individuals
Inherited characteristic – produce more pigment (melanin)
Typically sun-exposed sites such as the nose and cheeks, can fade during winter months
41
Melasma, also called “mask of pregnancy”
Skin pigmentation – dark, blotchy skin in exposed areas – typically in young women during pregnancy
42
lentigo
Type of freckle:
o tan/brown/black spot
o darker than freckles
o DOES NOT FADE IN THE WINTER
43
NAEVI (Pigmented Mole)
* Melanocytes cluster together to form naevi
* Some moles are present at birth (congenital), others develop during childhood/early adulthood (acquired)
* The MAIN thing is to differentiate from melanomas (cancers)
* 3 main types of acquired melanocytic naevi:
* Junctional (more pigmented, more closely associated with melanoma)
* Intradermal
* Compound (both)
44
Junctional nevus
flat
| brown to black
45
compound nevus
slightly elevated
| brown or light brown
46
intradermal nevus
dome shaped, warty or sessile
| light brown or flesh coloured
47
MALIGNANT MELANOMA
* Type of skin cancer that starts in the melanocytes
* Related to the sun/UV
* Used to be uniformly deadly as quickly metastises
* Has both vertical and horizontal growth phase
* Prognosis related to VERTICAL and linked to staging
* Staging (how far has it spread) TNM (Tumour, Node, Metastasis) and thickness BRESLOW
* Difficult to differentiate from nevus clinically and often microscopically
48
How to check your moles – ABCDE(EFG) principle
* Asymmetrical – two halves maybe different
* Borders (irregular)
* Colour (variegated, uneven)
* Diameter (greater than 6 mm)
* Evolving over time (enlarging, changing)
Nodular melanoma
• Elevated above the skin surface
• Firm to the touch
• Growing
49
Acanthosis nigricans,
often associated with diabetes mellitus
• Thickened (acanthosis), hyperpigmented zones of skin
• Commonly flexural regions – armpits, folds of neck
50
URTICARIA (Hives)
• Common disorder characterised by:
o localised mast cell degranulation (histamine)
o Dermal oedema and dilatation of vascular spaces
o Itchy raised oedematous plaques called WHEALS
• Caused by allergic reaction (e.g food), drugs, cold/heat exposure
51
ECZEMA (aka, acute eczematous dermatitis)
* A myriad of ACUTE inflammatory disorders, with allergic, drug related, sun related aetiologies
* The common histologic feature is spongiosis
52
PSORIASIS
* Common chronic inflammatory dermatoses – affects about 1-2% of people in the UK
* Frequently affects skin of elbows, knees , scalp
* Typical lesion is well-demarcated pink to salmon-coloured plaque covered by loosely adherent scales (silver-white in colour)
* Affects all ages – can be associated with arthritis, heart disease
53
First-degree burns
affect only the epidermis; limited to redness and pain, very COMMON include sunburn, touching a hot iron/stove
54
Second-degree burns
involve the superficial (papillary) dermis and sometimes the deep (reticular) dermis. Characterised by redness, pain, swelling and blistering
55
Third-degree burns
occur when the epidermis is lost with damage to the subcutaneous tissue. Result in scars and may require grafts
56
Fourth-degree burns
are life-threatening, and associated with major damage or loss of the hypodermis,
damage to muscle, tendon, and ligament tissue. Grafting is required if the patient survives
57
Severe burns: dehydration and treatment
* Damaged tissue releases ‘middle molecules’ (leukotrienes, prostaglandins, oxygen free radicals and histamine) into the circulation, leading to a systemic increase of capillary permeability
* Burns victims lose catastrophically high amounts of liquid
* The body attempts to compensate for this loss by shifting fluid around the body’s organs to keep each functioning
* Kidneys, liver and brain are compromised by displacement of the loss of fluids and proteins – ORGAN HYPOPERFUSION and tissue injury – ‘BURN SHOCK’ – can be FATAL
58
Parkland formula
* Fluid needed in first 24 hrs = Total Body Surface Area (TBSA) burned (%) x W t (kg) x 4mL
* Give half of fluid in first 8 hours and remainder in next 16hrs
* So an average man (approx. 80kg) with 18% full thickness burns requires 5.76L of fluid, with 2.88L in the first 8 hours
* The aim is to maintain fluid level to a point where urine output is 1 ml/kg/hour
59
skin grafts
* Autologous –from the same individual
* Isogeneic –from a different, genetically identical, individual
* Allogeneic – from a different individual
* Xenogeneic – from a different species
* Prosthetic – using artificial tissue
60
Split thickness skin grafts (STSG)
* Take just the epidermis and a portion of the dermis
| * The parts of the dermis containing follicles and sebaceous glands remains in place
61
Full thickness skin grafts (FTSG)
• More complicated, and may involve muscles and blood vessels
