Skin Histology lecture and layers with their cells

This is a skin histology slides it involves all the layers that are there in the skin and all the cells that form the skin together with the nerves that supply the skin with environmental signals or stimulis

1. School of Laboratory Medicine and Medical Sciences MBChB 1 Skin Histology Dr Zama Msibi ( [email protected] )

2. Objectives Identify the different layers of skin and their components Functions of skin Difference in structure between thick and thin skin Skin pigmentation and its function Skin appendages Sensory nerve endings

3. Skin External body surface Largest organ in the body both in weight and surface area Two types Thick skin – soles of feet Thin skin – upper and lower eyelids

4. Functions of skin Protective – protects against UV light, mechanical, thermal and chemical stresses, moisture control, invasion by microorganisms Langerhans cells – antigen presenting cell acts when skin is breached – immune response initiated Sensory – receptors that sense touch, pressure, pain and temperature changes Thermoregulatory – regulating temperature of the body, e.g. sweat glands, hair and adipose tissue Metabolic – subcutaneous adipose tissue involved in production of vitamin D and triglycerides Disease indicator – overall appearance of skin clinically important as indicator of health

5. Integumentary system components Skin  Glands Hair   Nails

6. Skin structure The skin has three main layers:

7. Epidermis keratinized stratified squamous epithelium with four distinct cell types and four distinct layers Cell types: Keratinocytes Melanocytes Merkel cells Langerhans’ cells Layers: Stratum corneum Stratum granulosum Stratum spinosum Stratum basale

8. Epidermis cells 1- Keratinocytes : most abundant produce keratin (fibrous protein) protective; waterproofing the skin continuous mitosis form in the deepest layer called the stratum basale 2- Melanocytes : cells produce brownish/black pigment called melanin. (8% of epidermal cells) stratum basale branching processes (dendrites) melanin accumulates in melanosomes and transported along dendrites of the melanocytes to keratinocytes. melanin accumulates on the superficial aspect of the keratinocyte shielding its nucleus from harmful UV light. lack of melanin: albino

9. Epidermis cells 3- Merkel cells: stratum basale epidermis of hairless skin attach to keratinocytes by desmosomes make contact with a sensory neuron ending called a Merkel disc (touch). 4- Langerhans’ cells: star-shaped cells arising from bone marrow that migrate to epidermis. epidermal dendritic cells interact with a WBC called a T- helper cell easily damaged by UV light

10. Epidermis layers 1 . Stratum corneum (horny layer) layer has many rows of dead cells filled with keratin Continuously shed and replaced effective barrier against light, heat and bacteria 2. Stratum granulosum nuclei of cells flatten out keratohyaline granules (darkly stained) accumulate lamellated granules secrete glycolipids into extracellular spaces to slow water loss in the epidermis

11. Epidermis layers 3- Stratum spinosum : “prickle cell layer” 8-10 rows of polyhedral (many sided) cells appearance of prickly spines shrink when prepared for slide melanin granules and Langerhans’ cell predominate 4. Stratum basale : deepest epidermal layer single row of cells, attached to dermis mostly columnar keratinocytes with rapid mitotic division contain merkel cells and melanocytes

12. Dermis and hypodermis Dermis - thicker inner portion of connective tissue sensation, protection and thermoregulation a) papillary layer - small blood vessels, lymph and nerves, fine collagen and elastic fibers b) reticular layer - vascular plexus, lymph , nerves and appendages, compact collagen fibers and thick elastic fibers Subcutaneous layer ( Hypodermis) - underneath the dermis - contains adipose tissue and sweat glands - responsible for metabolic functions

13. Thick vs thin skin structure Thick skin Thin skin Five layers in the epidermis Four layers in the epidermis - stratum lucidum is absent Thinner dermis Thicker dermis - easier to suture when damaged Does not contain hairs, sebaceous glands or apocrine sweat glands Contains hairs, sebaceous glands and apocrine sweat glands Found in areas of abrasion - fingertips, palms and soles of feet Found all over the body Well developed eccrine / merocrine sweat glands Fewer eccrine / merocrine sweat glands More cells per unit time enter the stratum corneum Fewer cells per unit time enter the stratum corneum Dermal papillae - longer and closely spaced, extensive interface between the dermis and epidermis Dermal papillae - restricted interface between the dermis and epidermis

14. Thick vs thin skin structure

15. Pigmentation Melanocytes make the pigment melanin found in the stratum basal layer Overall skin colour depends on: a. Carotene pigments in subcutaneous fat (adipose tissue) (orange-yellow colour ). b. Amount of blood and how much oxygen its carrying - haemoglobin (red colour ). c. Amount of a pigment called melanin that there is in the epidermis (brown colour ).

16. Damaged and healthy skin

17. Epithelial glands Sebaceous glands – branched acinar (spherical) glands which secrete oily substance called sebum. Coats hair and thin skin – soft, supple and waterproof Open to the skin surface or into hair follicles. a. Sebocytes (S) fill with lipid droplets. Disintegrate at the ducts (D) near the hair (H) shaft. b. Glands capsule and sebocyte at higher magnification. Peripheral cells inside the capsule push sebum into the ducts.

18. Sudoriferous glands Eccrine/ merocrine and apocrine sweat glands – thermoregulatory Eccrine found throughout the body and function throughout your life Apocrine occur at puberty and throughout adulthood. Found in armpits, areolar, genital and anal areas Both contain myoepithelial cells – contracts, squeeze and discharge secretions

19. Merocrine secretion

20. Epithelial glands a. Eccrine glands open directly onto the skin's epidermis and lumen is smaller. b. Apocrine glands release their sweat at the root of hair follicles and lumen is larger. Secretory portion (S), duct (D), hair follicle (H)

21. Skin appendage - Hair Elongated keratinized structure Develop from epidermis & invade the dermis & hypodermis Primary function is protection guards the scalp from injury and sunlight eyebrows - eyelashes protect the eye ears and nostrils keep out foreign objects Helps regulate body temperature Touch receptors associated with hair follicles

22. Arrector Pili Muscle Bundle of smooth muscles associated with each hair that makes the hair stand up when contracted cold frightened aggressive posturing emotions

23. Skin appendage - Nails Highly keratinized epithelial cells arranged in plates of hard keratin Develop from nail matrix nail root

24. Sensory nerve endings Free nerve endings - receptors that sense touch and pressure. They are common in the epithelial tissues. Meissner's corpuscles  - receptors that sense light touch. They are common in hairless portions of the skin, such as the lips, fingertips and palms. Pacinian corpuscles  - receptors that sense heavy pressure. Found deep in the reticular dermis near subcutaneous tissue, muscle tendons and joint ligaments.

25. Somatosensory Receptors

26. Sensory nerve endings a. Tactile ( Meissner ) corpuscules are elliptical. b. Lamellated ( Pacinian ) corpuscules are large oval structures.

27. THANK YOU!

28. References Young, B. et al .,2014. Wheater’s Functional Histology. A Text and Colour Atlas (Sixth edition). Churchill Livingstone Elsevier. p159-179. Mescher , A.L ., 2010. Junqueira’s Basic Histology. Text and Atlas. McGrawHill Lange International Edition (Twelfth Edition). p316-331.