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HUBS192 > Skin > Flashcards

Skin Flashcards

1
Q

What percentage of body weight is the skin?

A

16%

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2
Q

How much surface area does the skin cover?

A

1.5 to 2 metres squared

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3
Q

What about human skin makes us unique?

A

It’s bare (little skin) and has a large number of sweat glands per unit area.

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4
Q

How does our large number of sweat glands help us?

A

We can cool ourselves down very well.

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5
Q

Name the eight functions of the skin and accessory structures.

A
  1. Protect underlying tissues and organs
  2. Excrete salt, water and organic waste
  3. Maintain normal body temperature (insulating/ cooling)
  4. Produce melanin which protects from UV radiation
  5. Produce keratin which serves as a water repellent and protects against abrasion
  6. Synthesise vitamin D3 which is converted into calcitriol
  7. Store lipids in adipocytes (dermis) and adipose tissue (subcutaneous layer)
  8. Detect stimuli and relay information to nervous system
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6
Q

Which tissue type makes up skin?

A

All four (epithelial, connective, muscle and nervous).

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7
Q

Name the three layers of the skin.

A

Epidermis
Dermis
Hypodermis

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8
Q

Which two layers of the skin are cutaneous? What is the other?

A

Epidermis and dermis. The hypodermis is subcutaneous.

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9
Q

Which is the dominant cell type in the dermis layer of the skin?

A

Keratinocytes

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10
Q

Why doesn’t a shallow cut bleed?

A

The epidermis is avascular- there are no blood vessels.

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11
Q

What gives the dermis layer of the skin its strength?

A

Protein fibres: collagen and elastin

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12
Q

Is the dermis layer of the skin vascular? What does it do?

A

Yes, it nourishes the epidermal layer by transporting nutrients through the blood.

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13
Q

Which tissue makes up the hypodermis?

A

Adipose

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14
Q

Name the two layers of the dermis.

A

Papillary layer

Reticular layer

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15
Q

Why is the papillary layer of the dermis wavy where it meets the epidermis?

A

To provide a large surface area for more nourishment from capillaries.
To prevent the two layers delaminating from abrasion.

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16
Q

Describe the composition of the reticular layer of the dermis.

A

Collagen and elastin fibres form a mesh-like structure.

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17
Q

Name the five layers of the epidermis in order from outermost to innermost layer.

A 
Stratum corneum
Stratum lucidum (only in thick skin)
Stratum granulosum
Stratum spinosum
Stratum basale
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18
Q

Describe stratum corneum.

A

Outermost layer of the epidermis. Dead, dried-out, hard cells without nuclei.

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19
Q

Describe stratum granulosum.

A

2nd outermost layer of the epidermis. Contains granules that promote dehydration and cross-link the keratin fibres.

Waxy material is secreted into the spaces between cells, forming a barrier.

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20
Q

Describe stratum spinosum.

A

2nd innermost layer of the epidermis. Desmosomes link the cells together to form a barrier. Cells flatten as they move out/ up.

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21
Q

Describe stratum basale.

A

Innermost layer of the epidermis. Columnar, regenerative cells which divide and supply cells that move out/ up into the stratum spinosum.

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22
Q

Which layer of the skin can be completely removed?

A

Stratum corneum

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23
Q

Name the dominant tissue type in the epidermis.

A

Epithelial tissue

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24
Q

What type of epithelial cells predominantly make up the epidermis?

A

Squamous cells

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25
Q

What is the function of adipose tissue in the hypodermis?

A

It insulates and stores energy.

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26
Q

Where is thick skin found on the human body?

A

Palms of the hands and soles of the feet. Areas of high abrasion.

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27
Q

What separates thick skin from thin skin?

A

Thick skin has no hair and an extra epidermal layer (stratum lucidum).

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28
Q

What are eight features of aging skin?

A
  • drier epidermis
  • thinner epidermis and dermis
  • fewer melanocytes
  • altered distribution of hair and fat
  • fewer active hair follicles
  • slower skin repair due to reduced blood supply
  • decreased perspiration (which impairs cooling ability)
  • diminished immune response
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29
Q

Name four accessory structures of the skin.

A

Hair
Sweat glands
Nails
Receptors

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30
Q

Name the components of a hair (4).

A

Hair shaft
Hair follicle
Arrector pili muscle
Sebaceous gland

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31
Q

What is the function of the arrector pili muscle?

A

Contracts to make hair stand up on skin which increases its insulating effect.

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32
Q

What is the function of a sebaceous gland?

A

It produces sebum which acts as a natural moisturiser/ water repellent.

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33
Q

Where are sebaceous glands most abundant? Why?

A

On the face, scalp and shoulders.

These are the areas most hit by raindrops, so more sebum is produced to repel the water.

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34
Q

What can too much sebum on the skin cause? Describe this condition.

A

Acne, the blockage and infection of hair follicles.

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35
Q

What are the two types of sweat glands? Describe their locations and functions.

A

Eccrine- everywhere, thermoregulate

Apocrine- deeper in the skin, release an oily substance into the base of hair follicle

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36
Q

How do fingernails enhance sensation?

A

The sensory receptors are deep in the skin, and require tissue deformation to be activated. The nails provide rigidity behind the finger which allows the tissue to deform.

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37
Q

What is the function of melanin pigment?

A

Protects cells form UV light damaging their DNA.

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38
Q

Where is melanin produced and carried?

A

Melanin is produced in melanocytes, and transferred to epidermal cells by melanosomes (vesicles).

39
Q

How are moles and freckles formed?

A

Sun exposure can cause:

  1. Over-proliferation of melanocytes, forming a cluster (mole).
  2. Overproduction of melanosomes by melanocytes, forming a freckle.
40
Q

Where are melanocytes found?

A

In the stratum basale (so they’re not shed).

41
Q

Where are melanosomes found?

A

Throughout the epidermis (they are shed with keratinocytes).

42
Q

Does the density of melanocytes vary between races?

A

No, but it does throughout places in the body.

43
Q

Rickets

A

A disease caused by vitamin D deficiency/ lack of UV exposure, and characterised by bowed legs.

44
Q

Under what circumstances are cases of Rickets common?

A

When an individual’s skin pigmentation does not match the amount of UV exposure they’re getting. (dark skin, not enough UV)

45
Q

Describe a basal cell carcinoma.

A

A common, but relatively benign skin tumour.
Originates in the stratum basale.
Metastasis is rare.

46
Q

Describe a malignant melanoma.

A

A rare and deadly skin tumour (if not treated).
Originates in melanocytes, so it is pigmented.
Highly metastatic.

47
Q

Which characteristic of a melanoma indicates its likely mortality rate? Why?

A

Its thickness- the thicker the melanoma, the higher the mortality rate.

A thicker melanoma is more likely to reach the lymphatic or circulatory system, and metastasise.

48
Q

Why are tattoos permanent?

A

The ink is captured inside immune cells/ scar tissue of the dermis (not shed).

49
Q

When might a melanoma actually be a tattoo?

A

When the ink pigments the lymph nodes.

50
Q

Is there one sensory receptor for each stimuli?

A

No, receptors can often respond to several different stimuli. But, each is particularly sensitive to one type.

51
Q

Name five touch receptors of the skin.

A 
Free nerve endings
Tactile/ Merkel discs
Tactile corpuscles
Lamellar corpuscles
Bulbous corpuscles
52
Q

Which is the most common receptor found in the skin?

A

Free nerve endings

53
Q

Describe the structure of free nerve endings.

A

Small diameter fibres, mostly myelinated that extend into the epidermis. They have small swellings at their distal ends called sensory terminals.

54
Q

What is the function of sensory terminals in free nerve endings?

A

They are receptors that act as cation channels, allowing depolarisation of the nerve terminal and generation of AP.

55
Q

What do free nerve endings respond to?

A

Temperature
Pain
Movement and pressure (some)
Itch (some)- histamine activates histamine receptors
Bending of hairs (some)- wrap around hair follicles and act as light touch receptors

56
Q

What are tactile/ Merkel discs? What are they associated with?

A

Epithelial cells which detect the stimulus and cause a depolarisation in the nerve terminal. (possibly using serotonin)

Free nerve endings located in the deepest layer of the epidermis.

57
Q

In which body part are tactile/ Merkel discs abundant?

A

In fingertips, they have very small receptive fields and good discrimination.

58
Q

What do tactile/ Merkel discs respond to?

A

The physical features of an object: texture, shape and edges.

Fine touch and light pressure

59
Q

Where are tactile corpuscles located?

A

In the papillary layer of the dermis, especially in hairless skin (eyelids, lips, soles of feet).

60
Q

Describe the structure of tactile corpuscles.

A

Spiralling/ branching unmyelinated nerve terminal that is surrounded by Schwann cells (supporting, not myelinating).

A thin oval fibrous connective tissue capsule surrounds it.

61
Q

What occurs when the capsule of a tactile corpuscle is deformed?

A

Na+ ions enter the nerve terminal= depolarisation= AP

62
Q

What do tactile corpuscles respond to?

A

Delicate fine, discriminative touch
Light pressure
Low frequency vibration

63
Q

Where are lamellar corpuscles located?

A

Deep in the dermis and hypodermis

64
Q

Describe the structure of lamellar corpuscles.

A

A single dendrite lying within concentric layers of collagen fibres and specialised fibroblasts. Gelatinous fluid separates the collagen layers.

65
Q

What is the function of the gelatinous fluid in lamellar corpuscles?

A

It transmits stimuli/ vibrations by distorting the collagen layers until it reaches the dendrite in the middle.

66
Q

What do lamellar corpuscles respond to?

A

Deep pressure

Vibration (high frequency)

67
Q

Where are bulbous corpuscles located?

A

Dermis and subcutaneous tissue

68
Q

Describe the structure of bulbous corpuscles.

A

Network of nerve endings intertwined with collagen fibres, continuous with the collagen fibres of the surrounding dermis. Capsule surrounds structure.

69
Q

What do bulbous corpuscles respond to, and how?

A

Sustained deep pressure/ stretching and distortion of the skin. Collagen fibres are continuous, so they are stretched and transmitted to the bulbous corpuscle.

Joint rotation (proprioception)

70
Q

What are precapillary sphincters?

A

Bands of smooth muscle at the start of capillary beds.

71
Q

Describe, in detail, how skin blood flow is reduced.

A

Constriction of precapillary sphincters or arteries, which are under sympathetic nervous control.

Noradrenaline from sympathetic nerves acts on alpha-1 adrenergic receptors. These receptors are coupled with G-proteins (activate second messenger pathway). Intracellular Ca2+ is increased, and more cross bridging can occur in the smooth muscle tissue.

72
Q

What is normal core body temperature?

A

37 (36.5-37.5)

73
Q

What happens if our core body temperature is too high?

A

Our proteins start to denature.

74
Q

What happens if our core body temperature is too low?

A

Our nervous system starts to shut down.

75
Q

What are the primary mechanisms of heat transfer?

A

Radiation
Evaporation
Conduction
Convection

76
Q

How can eccrine sweat glands be stimulated? (2)

A

ACh from sympathetic cholinergic neurons is released onto muscarinic ACh receptors (mAChRs).

Also adrenaline in the bloodstream acting on beta receptors (nervous sweating).

77
Q

What does the preoptic area of the hypothalamus do?

A

Regulates blood temperature through heat and cold sensitive neurons, by activating the heat loss centre, or the heat gain centre.

78
Q

Describe the actions of the heat loss centre.

A

Decrease of SNS activation of alpha-1 on skin blood vessels (vasodilation)- more heat loss through skin.

Increase of SNS cholinergic neuron activation of mAChRs- increase sweating.

Increase respiratory rate- more heat loss across the mucosa of the respiratory system, and across the tongue.

Behavioural changes

79
Q

Describe how the actions of the heat gain centre generate heat.

A
  • shivering: oscillatory contractions of agonistic and antagonistic muscles, by stretching muscle spindles in the each other
  • non-shivering thermogenesis: increase in SNS, adrenaline/ noradrenaline from adrenal medulla, glycogenolysis (metabolism), in infants- use oxidative phosphorylation to produce heat instead of ATP
  • increase in thyroxine, BMR (takes several weeks for this to happen)
80
Q

Describe how the actions of the heat gain centre conserve heat.

A
  • vasoconstriction (constriction of blood vessels, less heat loss through skin)
  • countercurrent exchange: heat from arteries moving away from trunk is transferred to veins moving towards trunk (heat doesn’t travel to surface)
81
Q

What happens when noradrenaline binds to the alpha-1 receptor of an arrector pili muscle?

A

It contracts and pulls the hair shaft up vertical. It also creates a dimple in the epidermis (goosebump)- more useful for hairy animals.

82
Q

How does our body use feedforward when it’s cold?

A

Goosebumps, shivering and vasoconstriction before core body temperature even drops.

83
Q

Describe a first-degree burn.

A

Involves outer layers of epidermis
Red/ pink, dry and painful
Skin remains a water and bacterial barrier

84
Q

Describe a second-degree burn.

A

Epidermis and varying amounts of the dermis
Painful, moist, red/ whiteish, blistered
Some tactile receptors may be lost (not painful)
Some sweat glands and hair follicles may be affected
May result in some loss of sensation and scarring

85
Q

Describe a third-degree burn.

A

Extends into subcutaneous tissue and may involve muscle and bone.
Waxy white to deep red or black, dry and leathery
Not painful- sensory nerve endings are destroyed
May require skin grafting

86
Q

Why do burns lead to fluid loss?

A

The epidermis is damaged, so its waterproof effect is no longer working. Blood vessels are inflamed and damaged, and leak fluids.

87
Q

Name the percentages of skin on the head, upper limbs, trunk, genitalia and lower limbs.

A 
Head- 9%
Upper limbs- 9% each
Trunk- 36%
Genitalia- 1%
Lower limbs- 18% each
88
Q

Name three complications of severe burns relating to skin function.

A

Dehydration and hypovolemic shock (heart cannot pump enough blood due to fluid loss)
Infection/ sepsis
Hypothermia

89
Q

Name the three cavities the thoracic cavity is divided into.

A

Pleural cavity
Pericardial cavity
Mediastinum

90
Q

Define peritoneum.

A

Serous membrane associated with some organs of the GI tract.

91
Q

Name three serous membranes.

A

Peritoneum
Pericardium
Pleura

92
Q

What structure separates the thoracic cavity from the abdominal cavity?

A

Diaphragm

93
Q

What type of junction connects the epidermis to the dermis?

A

Hemidesmosomes- attach the deepest epithelial cells to the basement membrane

HUBS192 (6 decks)

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