Anatomy-lec1-Sereen.pdf

 Histology of the Skin Dr. Mustafa Saad (2023) To be more specific , tha largest internal organ is the liver co The Skin ❑ The skin is the largest organ in the body, accoun...

 Histology of the Skin Dr. Mustafa Saad (2023) To be more specific , tha largest internal organ is the liver co The Skin ❑ The skin is the largest organ in the body, accounting for about 20% of total body weight with a surface area of about 2m2. covering ❑ Also called the cutaneous layer and integument, it’s the boundary between the internal and external environment of the body. twolayer under theskin we have ❑ It’s formed of the epidermis and dermis. A fatty layer called the hypodermis (subcutaneous layer) connects the skin to the underlying tissues. Other structures found in the skin include: ▪ Sensory organs ▪ Arrector pili muscle ▪ Hair The skin Derived from the epidermis ▪ Nail Epidermal derivatives ▪ Sebaceous and sweat gland ▪ Mammary glands 2 Fig.1: The skin. Fatty layer under the skin 3 Functions of the skin protease 1) Protective function: ▪ Physical barrier against thermal and mechanical stresses and against harmful substances. ▪ Protection against microorganisms. ▪ Protection against ultraviolet light. UVL I ▪ Prevent the excessive loss of water through the skin. Because of selective permeability of the skin Because of this function , it permits life to be terrestial so we could live on lands in despite of the presence of many dehydration factors like winds and sun by presevation of water that our body needs Skin has a lipid-rich layer that makes it a selectively permeable 1,7T membrane. It allows the passage of lipophilic substance (like drugs) through ‫سة‬the skin, but prevents water loss. This has ‫القدرة على العيش على الياب‬ permitted life to be terrestrial. Without this function of the skin, the organism must spend a lot of time submerged me in water. What is the first step in the treatment of extensive burns? (the entire skin is lost ) ‫الحرق مغطي مساحة كبيرة من الجسم أو الحرق من الدرجة الثالثة‬ is replenish of fluids ‫ج‬C‫ولى بالع‬D‫اء عشان هيك الخطوة ا‬L‫بالتالي رح يفقد الجسم الكثير من ا‬ 4 2) Sensory function: ▪ Mechanical, thermal, pain. 3) Thermoregulatory function: Skin preserves body heat within normal ranges ▪ Insulation. ▪ Sweating. ▪ Superficial vasculature. Effing T.it t I The active form of vitamin D , requires UV light to be formed 4) Metabolic function: ▪ Synthesis of vitamin D3 through the action of UV light. ▪ Excretion of excess electrolytes with the sweat. ‫ساسية للتعرق هو تبريد‬1‫الوظيفة ا‬ ً ‫أيضا عنده وظيفة‬ ‫الجسم لكن‬ excretion of ‫ وهي‬B‫ثانوية أ‬ ▪ Storage of energy as fat in the subcutaneous layer. excess electrolytes 5  The Epidermis Keriatine ❖ Stratified squamous keratinized epithelium formed mainly of to epithelial cell called keratinocytes arranged in strata (layers) and connected with each other by desmosomes. Obtained it’s name because it contains a specific type of intermediate filament which is keratin ❖ Other cells found in the epidermis are melanocytes, Merkel cells, and Langerhans cells. T cK Not epithelial cells Very important ‫ وومصدرها‬epithelial cells ‫ ولكنها موجودة ب* ال‬epidermis ‫; تدخل في تكوين ال‬ PYES ( keratinocytes ‫ ) عكس ال‬epithelium ‫الجنيني مختلف عن خ>يا ال‬ ❖ Histologically, the skin can be classified into thin and thick skin nn according to the thickness of the epidermis. In the palms and soles we have thick skin with a much thicker epidermis formed of 5 strata; elsewhere, we have thin skin with a thinner epidermis formed of only 4 strata. On the back we have the thickest skin , but do we have a thick or thin skin ? Thin Whih means that we have a very thick dermis and thin epidermis ❖ Total skin thickness, however, is the thickness of both the epidermis and dermis. It’s thickest on the back and thinnest on the eyelids. Thin skin , so both dermis and epidermis are thin 6  startginulosum Fig.2: The epidermis. 7  ‫نقسام وتصعد‬+‫ تستمر با‬stratum basale ‫وجودة بال‬5‫يا ا‬8‫الخ‬ ‫ل‬8‫ وخ‬epidermis ‫على الى أن تصل الى سطح ال‬E‫تتدريج ّيا ل‬ The layers of the epidermis ‫ختلفة بصير فيها تغيرات من حيث الشكل‬5‫صعودها الى الطبقات ا‬ vtT ‫وجود فيها‬5‫ ا‬keratin ‫والوظيفة وال‬ i. Stratum basale YI.hr o The deepest layer lying directly on the basal lamina. o Formed of a single layer of basophilic cuboidal cells. o Cells are connected to basal lamina by hemidesmosomes and to adjacent keratinocytes in the stratum basale and spinosum by desmosomes. o The cells are highly mitotic and are the progenitor Iff cells of all epidermal layers. As these keratinocytes mature they migrate upwards (superficially) until they reach the surface where they are shed. baste startum Turn over o Renewal of the epidermis takes about 15-30 days. Depends on the thickness of the epidermis o A characteristic intermediate filament called keratin is found in all keratinocytes. The time from cell birth until death is turn over The formation of keratin starts in stratum basale ‫ويستمر في باقي الطبقات‬ 8  ii. Stratum spinosum A thickepidermalloyen g o A thick epidermal layer. It’s thicker in thick skin. v o Formed of polyhedral cells active in keratin synthesis. o The cells close to the stratum basale are also mitotically active and together they’re called the stratum germinativum. These cells in addition to statum basale are called stratum germinativum o Keratin filaments become thick tonofibrils attached to desmosomes. When the tissue is prepared, the cells shrink and these desmosomes and tonofibrils appear as spines on the surface of the cell, hence the name. In the living tissues , cells have no spines on ‫ل عملية تحضير النسيج لدراسته تحت ا?جهر نستخدم مواد كيميائية تؤدي الى فقدان بعض‬K‫خ‬ shrinkage of the cells ‫يا بالتالي رح يصير‬K‫السوائل من الخ‬ thier surface But tonofibrils are strong protien structures so they don’t shrink , so apear as spines like structures at the surface of cell and this is why this layer is called stratum spinosum Fig.3: The spines of the Keratin tonofibrils stratum spinosum. Left, light microscope. Right, electron microscope. Note the tonofibrils attached to the desmosomes. When a I can see a feature under the light microscope ,but it’s not an actual feature of the cell 9 It’s called Artifacts , like these spines iii. Stratum granulosum o Formed of 3-5 layers of cells. Keriatin tonefibr ers witheprotein associated o Cells contain two types of granules: nonm Keratohyaline Granules Lamellar Granules Contain keratin tonofilaments associated Contain various lipids with proteins Non-membranous Membranous Contents are released to the Contents remain in cell outside of the cell Appear as basophilic Seen as oval structures with structures under the light several lamellae under the microscope electron microscope non membranous 10 o The lipids of the lamellar granules are released to the outside by exocytosis filling the intercellular space with lipid. This creates a hydrophobic barrier that prevents water loss. Fig.4: The lamellar granules of the stratum granulosum and the lipid-rich intercellular barrier. ‫شفافة‬ ‫ فيه عنا أربع طبقات وبال‬thin skin ‫حكينا بال‬ iv. Stratum lucidum for.‫ الفرق بينهم هو هاي الطبقة‬، ‫ خمس طبقات‬thick o A translucent layer found only in thick skin. o Formed of eosinophilic squamous cells with no nuclei and organelles. ‫يا ميتة‬G‫خ‬ o Cytoplasm filled with keratin. 11 v. Stratum corneum o Most superficial layer. Thicker in thick skin. e_ o Formed of 15-20 layers of thin squamous cells which are called squames. These are nothing more than cell membranes filled with keratin. o The cells of the deeper layers of the stratum corneum are surrounded by the lipid-rich barrier and the most superficial cells are continuously shed. so Calluses are areas of thickened stratum corneum due to repeated friction. (you may already have one in your middle finger from excessive use of pens/pencils/stylus). 12 Other cells of the epidermis Melanocytes ix to o Neural crest derived cells found in the stratum basale and the hair follicles and produce the black (or red) pigment melanin. o The pale-staining cell body is found between the keratinocytes of the stratum basale but is not attached to them. The cell body, however, is attached to the basal lamina by hemidesmosomes. o The cytoplasm contains mitochondria, rough endoplasmic safe reticulum, and Golgi apparatus. Several processes extend between the cells of the stratum basale and spinosum. n Melang o Melanin inside melanocytes is stored in granules called melanosomes. These are transported to the processes. The tips of these processes are engulfed by keratinocytes and the melanosomes form a supranuclear cap to protect DNA from the harmful effects of UV light. o Either 13 o Although produced by melanocytes, there’s more melanin in keratinocytes than melanocytes ‫ن) يتكون بال‬+‫ي‬-‫يعني صح ا‬ in melanocytes. keratinocytes ‫لكنه سرعان ما يتوزع لل‬ o A melanocyte and its associated keratinocytes form an epidermal-melanin unit. The density of these units is the same in all individuals. It’s the rate and amount of production that differs. Fig.5: Melanocytes. Note how the cell ‫شخاص سواء بشرتهم فاتحة أو غامقة ولكن‬M‫ هو نفسه عند جميع ا‬melanocytes ‫اذن عدد ال‬ amount and rate of production which is higher in dark skin ‫ف بال‬+‫خت‬M‫ا‬ body is found within the stratum basale (SB) and the processes extend into the Color of the skin is the result of stratum spinosum. several factors, the most important are (1)melanin pigment, (2)carotene pigment, and (3)blood in the vessels. 14  VD Melanin and Vitamin D UVL m Ñnoᵈyt I ftp.iiiiei Exposure to sunlight (UV light) stimulates melanocytes to produce more melanin to protect against the damaging effect of UV light. This UV light, however, is required for the synthesis of vitamin D in skin. Therefore, production of melanin affects the synthesis of vitamin D. Because the UV light will not pass the skin because of melanin and this will make the synthesis of Vit D more difficult Is there a difference in vitamin D level between fair-skinned people and people with dark-complexion? Yes, dark skin people have less vit D level and sometimes they need supplements Skin Tan To enjoy his Summer holiday, Ahmed, who has a fair skin, went to the swimming pool several times a week. One day, while looking at himself in the mirror, he noticed that he has developed quite a tan! Has Ahmed’s skin color changed permanently or will it return to its usual complexion? Why? It will return to normal ً ‫وأيضا ال‬ )‫ن‬+‫ي‬-‫ رح يقل انتاج ا‬UV light ‫عند توقف التعرض لل‬ epidermis was renewed 15 Langerhans cells o Antigen-presenting cells found mainly in the stratum spinosum with processes extending between keratinocytes. o They bind and present antigens to lymphocytes, thus playing an important immune role. to t.es Merkel cells oeaiiiii fif o Mechanoreceptors for light touch. Most abundant in fingertips. ummmm o Found between the cells of the stratum basale. Cell body and processes attached to adjacent cells by desmosomes. o Cytoplasm contains neurosecretory granules. I o Basal surface is in contact with the expanded terminal of an unmyelinated nerve fiber. 16  Dermal-epidermal junction ✓ A basement membrane is found between the epidermis and dermis. Hemidesmosomes attach the stratum basale of the epidermis to this membrane and collagen anchoring fibrils attach the dermis to it. ✓ The surface of the dermis in contact with the epidermis is irregular with several dermal projections (dermal papillae) interdigitating with projections of the epidermis (epidermal ridges). ✓ This interdigitation is very prominent in thick skin that it shows on the surface of the skin as a pattern of grooves and ridges which are the basis of fingerprints. Fig.6: The dermal-epidermal junction. 17 ✓ Importance of the jigsaw-like epidermal ridges-dermal papillae arrangement: 1. Increase surface area of contact between epidermis and dermis reinforcing the junction between them. 2. Increase the density of Merkel cells and Meissner corpuscles increasing tactile sensitivity. Responsible for light touch 3. Reflection of this pattern on the surface increases the surface area of the grip of the hand or foot by increasing friction. 4. The ducts of sweat glands open on the tops of the surface epidermal ridges as sweat pores. The sweat and ridges form fingerprints (or footprints) when a smooth object is touched. Since the pattern of the ridges is genetically determined, this can be used to identify an individual. Fig.7: Epidermal ridges on surface of thick skin. 18