Skin Flashcards
Why is the epidermis impermeable to water
To protect against dehydration
In thick skin what is different to thin skin
The number of epithelial cell layers and the thickness of the keratin layer are greater
In areas where the cells are exposed to abrasion the surface epithelial layers are covered by a layer of what
Keratin
What is keratin
A fibrous proteins synthesised in the cells as they move upwards towards the surface
Which layer of the epidermis does cell division occur in
Stratum germinativum/ stratum basale
One daughter cell remains as a stem cell and the other moves and differentiates to become part of the protective barrier
Describe the layer of the epidermis which is only present in thick skin
The stratum lucidum
A layer of flattened dead cells, rich in keratin
It is inert and impervious
Which layer are spot / punctate desmosomes most obvious in the epidermis
Stratum spinosum
What are the granules within the cells of the stratum granulosum known as
What do they contain
Keratohyalin granules
Contain proteins that promote aggregation of keratin fibres eg filaggrin
What are the two types of sweat gland and how do both types release their products
Eccrine / merocrine
Apocrine
Via merocrine secretion, which involves exocytosis of secretory vacuoles
Discuss eccrine sweat glands
Secrete a watery secretion and Are distributed all over the body
They are simple tubular glands with a coiled secretory part and a straight excretory duct
They extend from the dermis to the skin surface
Where Does the coiled secretory part of eccrine sweat glands lie and what epithelium lines it
Lies deep in the dermis
It is lined by one layer of columnar or high cuboidal cells surrounding a central lumen into which the secretion is extruded
Describe the straight excretory ducts of eccrine cells
Lined by stratified cuboidal epithelium (usually two layers)
The cells are smaller in diameter and show darker staining than those in a secretory portion
What do apocrine do
Secrete a fatty sweat and are usually associated with hair follicles
Where are apocrine sweat glands usually found
In humans they are mainly found in the armpits, genital region, areola of the breast, eyelids and in the ear
What is the structure of apocrine sweat glands
They are simple coiled tubular glands with a secretory part deep in the dermis and hypodermis
The excretory duct opens into the hair follicle
What does sweat contain
Water, electrolytes and waste products
What control are eccrine sweat glands under
Sympathetic cholinergic control
What do sebaceous glands do
Discharge a fatty sebum into the hair follicles to lubricate growing hairs
Describe the arrector pili muscles
They are small bundles of smooth-muscle that attach to the hair follicle at one end and to the dermal connective tissue at the other
Where are sebaceous glands found
Throughout the hard skin of all mammals
What is sebum
And oily secretion composed of triglycerides, phospholipids, and cholesterol,
Describe the structure of a sebaceous gland
Consists of a solid mass of large epithelial secretory cells surrounded by a sheath of connective-tissue
The secretory cells are full of lipid droplets
What kind of gland are sebaceous glands
Holocrine glands
What does holocrine secretion involve
The discharge of the whole cells, released as a cell fragments, forming sebum
Describe the structure of the hair shaft
It consists of an inner core (the medulla), and outer ring (the cortex) and a surface layer (the cuticle)
The cortex and cuticle contain hard keratin, which does not form scales and is more permanent and soft keratin
How is hair produced
From a group of cells at the bottom of the follicle
All the layers of the epidermis invaginate to form the top of the cylindrical follicle, but the structure becomes simpler further down until there is only the stratum germinativum that forms the hair
What is the Panician corpuscle
A sensory Mccanna receptors are located in the hypodermis
It responds to deep pressure and vibration
Describe the structure of the Pacinian corpuscle
Often of large diameter, it consists of a fine capsule enclosing concentric layers of flatten cells that give the appearance of an onion
At the centre of the corpuscle there is a non-myelinated afferent nerves fibre that becomes myelinated as it leaves the corpuscle
How big is the diameter of a Panician corpuscle
1-2mm long by 0.5 -1 mm in diameter
