W2 - Skin Flashcards
LO1: Describe the basic structure of a body membrane and the specific structures of serous and mucous membranes (describe body membrane)
The internal cavities and passageways of the body are lined by membranes and these membranes are composed of epithelium with underlying connective tissue. These include serous membranes, mucous membranes and skin, which can be considered the cutaneous membrane of the body (‘cutaneous’ = skin).
LO1: Describe the basic structure of a body membrane and the specific structures of serous and mucous membranes (mucous membrane)
A mucous membrane, also called a mucosa, lines all internal body passageways that open to the external environment.
These include the respiratory, digestive, urinary and reproductive tracts. A mucous membrane is composed of an epithelial layer and an underlying layer of areolar connective tissue called the lamina propria.
They often contain mucous-producing cells or glands that produce mucous to lubricate and protect the mucous membrane.
LO1: Describe the basic structure of a body membrane and the specific structures of serous and mucous membranes (serous membrane)
Also called serosa, lines internal body cavities including the thoracic and abdominopelvic cavities and reflects onto the surface of some of the organs in those cavities.
Composed of simple squamous epithelium, called mesothelium due to its origin from the mesoderm and an underlying layer of areolar connective tissue.
A serous membrane can be divided into two parts – an outer parietal layer which lines the internal surface of the body cavity, and an inner visceral layer which lines the external surface of some of the organs in the cavity.
In between these two layers is a potential space containing a thin film of fluid called serous fluid that is produced by the serous membrane to reduce friction.
LO2: Name the primary germ layers that the skin is derived from
The primary germ layers that the skin is derived from are the ectoderm and mesoderm, with the epidermis being derived from the ectoderm and the dermis being derived from the mesoderm.
LO3: Describe the functions of skin
Referred to as the integument and forms the integumentary system of the body.
Protection
The skin acts as a physical barrier to protect the body from physical injury, chemicals, microbes, excessive temperatures and ultraviolet radiation.
Water Regulation
The skin is water-resistant and helps prevent unnecessary water loss or gain
Temperature Regulation
The skin contains many blood vessels and sweat glands, which help to regulate heat loss from the body. When the body is hot, the blood vessels dilate to help dissipate the heat and the sweat glands release sweat onto the skin’s surface, helping to cool it as the sweat evaporates. When the body is cold, the blood vessels constrict to reduce blood flow to the skin and therefore conserve heat.
Metabolic Regulation
The skin produces vitamin D when it is exposed to ultraviolet radiation, which is essential for the absorption of calcium and phosphate and the regulation of their levels in the blood.
Immune Defence
The skin contains immune cells that are important in initiating an immune response against pathogens that have invaded the body via the skin.
Sensory Reception
The skin is rich in sensory receptors which detect different stimuli such as pressure, vibration and temperature.
Secretion
The skin excretes waste products such as water, salts and urea through sweat. It also contains sebaceous glands which secrete oil onto the skin’s surface to lubricate it.
LO4: Describe the structure of the epidermis and dermis (overall structure of the skin)
Two main layer - dermis and epidermis
Epidermis = superficial, composed of stratified squamous keratinised epithelium
- external location explains origin from ectoderm (most external primary germ layer of embryo)
- skin is classified as thick or thin depending on the relative thickness of the epidermis.
Dermis = deep, composed of connective tissue
- origin from mesoderm as all connective tissue is from mesoderm (why skin can be considered a body membrane)
Deep to the dermis is layer called the subcutaneous layer (‘sub’ = underneath, ‘cutaneous’= skin) or hypodermis (‘hypo’ = below), composed of areolar and adipose connective tissue (not part of the skin, but helps to anchor the skin to the underlying tissue and contains blood vessels to help supply the skin)
LO4: Describe the structure of the epidermis and dermis (epidermis)
keratinised stratified squamous
come lets grab some beer: stratum (coroneum, lucidum, granulosum, spinosum, basale)
The stratum lucidum is only present in thick skin, which is found in locations such as the palms of the hands and the soles of the feet.
The most abundant cell type in the epidermis are keratinocytes, which are found in every layer. They produce the protein keratin, which gives skin its strength and water resistance.
There are also other cell types in the epidermis, including melanocytes, tactile or Merkel cells and epidermal dendritic or Langerhans cells.
LO4: Describe the structure of the epidermis and dermis (epidermis, coroneum)
This is the most superficial layer of the epidermis and is composed of 20 to 30 layers of flattened, dead keratinocytes that are entirely filled with keratin. It is from this layer that the dead keratinocytes are shed. The average lifespan of a keratinocyte, from the time of its formation in the stratum basale to the time it is shed from the stratum corneum, is around one month.
LO4: Describe the structure of the epidermis and dermis (epidermis, lucidum)
This layer is only present in thick skin. It is a thin, translucent layer with only 2 to 3 layers of flattened, dead keratinocytes.
LO4: Describe the structure of the epidermis and dermis (epidermis, granulosum)
This is the darkest layer of the epidermis and is composed of 3 to 5 layers of keratinocytes with granules in their cytoplasm, which is where this layer gets its name from. Some of these granules contain lipids which contribute to the water resistance of the skin.
Other granules are involved in the process of keratinisation, which begins in this layer and is where the keratinocytes start to fill with keratin. As they do, they become flatter, lose their organelles and start to die. This is the last layer of the epidermis containing living cells.
LO4: Describe the structure of the epidermis and dermis (epidermis, spinosum)
This is the thickest layer of living cells in the epidermis and is composed of several layers of polygonal keratinocytes. The keratinocytes are attached to each other via extensions that give them a spiny appearance, which is where this layer gets its name from.
As well as keratinocytes, the stratum spinosum contains epidermal dendritic or Langerhans cells, which are immune cells that initiate an immune response against pathogens that have invaded the epidermis.
LO4: Describe the structure of the epidermis and dermis (epidermis, basale)
This is the deepest layer of the epidermis. It is composed of a single layer of cuboidal to low columnar keratinocytes that are attached to a basement membrane separating the epidermis from the underlying dermis.
The keratinocytes in this layer are stem cells which divide to produce new keratinocytes that migrate towards the skin’s surface to replace the dead keratinocytes that have been shed. Scattered amongst the keratinocytes are melanocytes, which produce the pigment melanin in response to ultraviolet radiation.
The melanocytes transfer the melanin they produce to the surrounding keratinocytes via cytoplasmic processes. Melanin acts to protect the keratinocytes from ultraviolet radiation and is what gives skin its colour (more melanin = darker skin). Tactile or Merkel cells are also found scattered amongst the other cells in the stratum basale and are sensitive to touch.
LO4: Describe the structure of the epidermis and dermis (dermis)
Composed of two types of connective tissue = areolar and dense irregular connective tissue.
This connective tissue primarily contains fibroblasts and collagen fibres, but there are also elastic and reticular fibres present.
The dermis contains blood vessels to supply the epidermis, as the epidermis is avascular and relies on diffusion of nutrients from the dermis. It also contains structures such as sweat glands, sebaceous or oil glands and hair follicles, which are collectively referred to as epidermal appendages as they are derived from the epidermis.
Two main layer = superficial papillary layer and deep reticular layer.
LO4: Describe the structure of the epidermis and dermis (dermis, papillary layer)
This is the thinner, superficial layer of the dermis. It is composed of areolar connective tissue. Its name is derived from the finger-like projections of the dermis towards the epidermis, called dermal papillae. The dermal papillae interdigitate with projections of the epidermis called epidermal ridges.
This interdigitation increases the surface area for contact between the dermis and epidermis, which facilitates the diffusion of nutrients from the capillaries in the dermal papillae to the epidermis. It also makes the dermal-epidermal junction appear wavy on histological slides. As well as blood vessels, the papillary layer of the dermis contains sensory receptors which detect touch.
LO4: Describe the structure of the epidermis and dermis (dermis, reticular layer)
This is the thicker, deeper layer of the dermis, forming the major portion of the dermis. It is composed of dense irregular connective tissue. Its name is derived from the network of collagen fibres within this layer (reticular = network). It contains blood vessels and sensory receptors which detect pressure, vibration and stretch. It is also the layer in which the epidermal appendages are found.
