30 Questions
Which cell type in the epidermis is derived from monocytes and functions as antigen presenting cells?
Langerhans cells
What is the predominant cell type of the epidermis?
Keratinocytes
Where are Merkel cells mainly located in the skin?
Stratum basale
Which type of cells are described as neural crest derivatives that produce and distribute melanin into keratinocytes?
Melanocytes
In which layer of the dermis is the microvascular subpapillary plexus located?
Subpapillary plexus
What is the main function of Langerhans cells in the epidermis?
Present antigens
What is the main function of the epidermis?
Serving as a protective barrier
Which cells in the epidermis are responsible for synthesizing pigment?
Melanocytes
What is the role of hypodermis in the skin?
Storing adipose tissue
Which of the following is NOT a derivative of the skin?
Langerhan cells
What is the main function of dermal papillae?
Connecting the dermis to the epidermis
Which of the following is a key function of the skin's epidermal ridges?
Enhancing grip sensation
What type of secretion do apocrine sweat glands exhibit?
Merocrine secretion
When do the apocrine sweat glands become fully functional?
After puberty
Which region of the body is largely associated with apocrine sweat glands?
Axillary and perineal
What is the main function of sebum in relation to the skin?
Maintaining the stratum corneum
What do the secretory components of apocrine glands look like?
Cells with large lumens and numerous secretory granules
Where do the ducts of apocrine glands usually open?
Into hair follicles
What is the outermost layer of the hair root called?
Cuticle
Which part of the hair root completely surrounds the initial part but degenerates above the level of the attached sebaceous glands?
Internal root sheath
In which layer of the hair bulb can two layers be recognized?
Epithelial root sheath
What is the name of the hard plates of keratin on the dorsal surface of each distal phalanx?
Nail plate
At what level does the external root sheath extend all the way to in the epidermis?
Basal layer
How do hairs grow in terms of growth periods and rest periods?
At different rates in different regions
What is the main difference between the papillary layer and the reticular layer of the skin?
The reticular layer consists of loose connective tissue while the papillary layer consists of dense irregular connective tissue.
Which type of receptors are the unencapsulated Merkel cells in the skin?
Tonic receptors for light touch
Where are free nerve endings primarily located in the epidermis?
Stratum basale
What is the main function of Pacinian corpuscles in the skin?
Specialized for coarse touch, pressure, and vibrations
What is the function of root hair plexuses in the skin?
Detecting movements of the hairs
Why are encapsulated mechanoreceptors considered phasic receptors?
They rapidly respond to stimuli on the skin
Study Notes
Skin Structure
- The skin consists of two main layers: epidermis and dermis
- Epidermis is the epithelial layer of ectodermal origin
- Dermis is the layer of mesodermal connective tissue
- Beneath the dermis lies the subcutaneous tissue or hypodermis, a loose connective tissue layer
Epidermis
- Composed of stratified squamous keratinized epithelium
- Cells called keratinocytes make up the majority of the epidermis
- Other cell types in the epidermis include:
- Langerhans cells: antigen-presenting cells
- Melanocytes: pigment-producing cells
- Merkel cells: tactile epithelial cells
Dermis
- Consists of two layers: papillary layer and reticular layer
- Papillary layer:
- Thin
- Includes dermal papillae
- Composed of loose connective tissue
- Contains types I and III collagen fibers, fibroblasts, and scattered mast cells, macrophages, and other leukocytes
- Reticular layer:
- Much thicker
- Composed of dense irregular connective tissue
- Contains a network of elastic fibers
- Fewer cells than the papillary layer
Subcutaneous Tissue (Hypodermis)
- Consists of loose connective tissue
- Binds the skin loosely to subjacent organs
- Allows the skin to slide over underlying structures
Epidermal Ridges and Dermal Papillae
- Epidermal ridges: extensions of the epidermis into the dermis
- Dermal papillae: connect the dermis to the epidermis
Hair Follicles
- Hair growth is asynchronous, cyclic, and occurs at different rates in different regions of the body
- Hair growth cycle has three major phases
- Hair follicles are surrounded by a web of sensory fibers called root hair plexuses that detect movements of the hairs
- Each hair follicle has a hair root, a hair shaft, and a hair bulb
- The hair root has a cortex, medulla, and cuticle
Nails
- Composed of heavily keratinized, densely packed cells
- The nail plate is the hard plate of keratin on the dorsal surface of each distal phalanx
- The proximal part of the nail is the nail root, which is covered by a fold of skin and the epidermal stratum corneum extends as the cuticle
Sweat Glands
- Apocrine sweat glands:
- Confined to skin of the axillary and perineal regions
- Development depends on sex hormones and is not complete and functional until after puberty
- Produce pheromones
- Eccrine glands:
- Found all over the body
- Produce sweat in response to heat, emotional stimuli, and other factors
Skin Function
- Thermoregulation: sweat production helps to cool the body
- Metabolic: skin cells synthesize vitamin D3 through the local action of UV light on the vitamin's precursor
- Protective: skin acts as a barrier against external factors
- Sensory: skin contains various receptors that respond to different stimuli, such as touch, pressure, temperature, and pain
Learn about the layers and derivatives of the skin, specifically focusing on the epidermis and dermis. Explore structures like hair follicles, sweat glands, sebaceous glands, and nails, which are considered as separate organs or tissues. Dive into the thermoregulatory mechanisms for heat loss acceleration.
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