Human Anatomy: The Integumentary System, BIOL 2002SEF Lecture 2

BIOL 2002SEF Human Anatomy The Integumentary System Lecture 2 Dr CHEUNG Ka Tik BIOL 2022SEF 2024 1 Integumentary System Includes: Skin (cutaneous membrane) Subcutaneous tissue below the skin Accessory Structures Sweat glands Sebaceous or oil gland...

BIOL 2002SEF Human Anatomy The Integumentary System Lecture 2 Dr CHEUNG Ka Tik BIOL 2022SEF 2024 1 Integumentary System Includes: Skin (cutaneous membrane) Subcutaneous tissue below the skin Accessory Structures Sweat glands Sebaceous or oil glands Hair Nails BIOL 2022SEF 2024 2 Anatomy of skin 1. Human skin is divided into two layers a. epidermis (outermost) b. dermis ( innermost) 2. Separated by basement membrane (BM) 3. A layer of loose connective tissue beneath the dermis called hypodermis, or subcutis BIOL 2022SEF 2024 3 BIOL 2022SEF 2024 4 Skin Facts Largest organ of the body (15% of body weight). Weighs about 6 pounds Average about 3000 square inches Fastest to regenerate Covers 1.5 – 2 square meters Most skin is 1 – 2 mm thick but can range from 0.5 – 6 mm Receives 1/3 of the body’s blood volume BIOL 2022SEF 2024 5 Major functions of skin Regulate body temp Protect underlying tissue Excrete H20 and salt (Sweat) Receives stimuli for touch, pain, temp change, etc. Immunity Metabolism BIOL 2022SEF 2024 6 Body Temperature When your body temperature rises, the many small blood vessels in the dermis dilate, blood flow increases, and body heat is lost by radiation. Also glands in the dermis produce sweat in response to an increase in body temperature As sweat evaporates, water changes state from liquid to vapor, and heat is lost. When you are cold, the blood vessels in the skin constrict and heat is conserved. BIOL 2022SEF 2024 7 Vitamin D When exposed to UV light, dermis cells produce Vitamin D that aids in absorption of calcium into blood BIOL 2022SEF 2024 8 Pimples & Wrinkles Pimples (acne) are a build up of dirt and oils. Wrinkles occur because of getting less elastic with age and producing less oil becoming dryer. BIOL 2022SEF 2024 9 Cause of Pimples Layers Of The Skin Epidermis – outer composed of stratified squamous epithelium Dermis – inner anchored to a subcutaneous layer Hypodermis Integumentary glands (sweat, oil, etc.) Hair and Nails BIOL 2022SEF 2024 12 Identify the different layers of the skin and their components BIOL 2022SEF 2024 13 Epidermis Outer layer of skin Composed of stratified squamous epithelium Avascular as it has no blood supply of its own Oxygen and nutrients diffuse from the underlying dermis BIOL 2022SEF 2024 14 Epidermis: The outer layer of skin BIOL 2022SEF 2024 15 BIOL 2022SEF 2024 16 Epidermis (cont:) The epidermis is a keratinized stratified squamous epithelium. Five structurally different layers can be identified: Stratum Corneum Stratum Lucidum Stratum Granulosum Stratum Spinosum Stratum Basale- (Germinativum) BIOL 2022SEF 2024 17  Stratum Corneum Stratum Lucidum Stratum Granulosum Stratum Spinosum Stratum Basale- (Germinativum) BIOL 2022SEF 2024 18  Keratinocytes (90%)- waterproofs & protects skin, nails, hair, stratum corneum Melanocytes (8%)- produce melanin Merkel Cells- slow mechanoreceptors Langerhans’ Cells- immunological defense BIOL 2022SEF 2024 19 BIOL 2022SEF 2024 20 The Stratum Basale (first layer) It is the deepest layer of the epidermis (closest to the dermis). It consists of a single layer of columnar or cuboidal cells that rest on the basement membrane. Basal cells are the stem cells of the epidermis and their mitotic activity replenishes the cells in more superficial layers as these are eventually shed from the epidermis. BIOL 2022SEF 2024 21 The Stratum Basale (first layer cont:) The renewal of the epidermis takes about 3 to 4 weeks in humans as millions of cells are produced daily. Cells die as they are pushed away from the source of nourishment. Cells undergo keratinization as a tough protein, keratin, is deposited within the cell. Keratin hardens and flattens the cells as they move outward and it waterproofs the skin. BIOL 2022SEF 2024 23 The Stratum Spinosum (second layer) The cells become irregularly arranged. The cells are often separated by narrow, translucent clefts. These clefts are spanned by spine- like cytoplasmatic extensions of the cells (hence the name of the layer and of its cells: spinous cells), which interconnect the cells of this layer. BIOL 2022SEF 2024 24 The Stratum Granulosum (third layer) It consists, in thick skin, of a few layers of flattened cells. Only one layer may be visible in thin skin. BIOL 2022SEF 2024 25 The Stratum lucidum (fourth layer) It consists of several layers of flattened dead cells. Nuclei already begin to degenerate in the outer part of the stratum granulosum. In the stratum lucidum, faint nuclear outlines are visible in only a few of the cells. The stratum lucidum can usually not be identified in thin skin. BIOL 2022SEF 2024 26 The Stratum Corneum (fifth layer) It is the final layer of epidermis and there cells are keratinized and form a layer that is about 30 cells thick. Individual cells are difficult to observe because: (1) nuclei can no longer be identified, (2) the cells are very flat. (3) the space between the cells has been filled with lipids, which cement the cells together into a continuous membrane. BIOL 2022SEF 2024 27 The Stratum Corneum ((fifth layer cont:) Closest to the surface of the epidermis, the stratum corneum has a somewhat looser appearance. Cells are constantly shed from this part of the stratum corneum. This layer makes up three fourths of the epidermal thickness. The protection of the body by the epidermis is due to the functional features of the stratum corneum. BIOL 2022SEF 2024 28 Dermis BIOL 2022SEF 2024 29 Dermis or Corium Inner layer of skin The dermis, or corium, consists of dense fibrous connective tissue with numerous collagenous and elastic fibers. The dermis is much thicker than the epidermis. In thick skin, dermal papillae create a very irregular border between epidermis and dermis. BIOL 2022SEF 2024 30 Dermis: The inner layer of skin BIOL 2022SEF 2024 31  papillary dermis reticular dermis BIOL 2022SEF 2024 32 a. Cellular Fibroblasts (synthesize collagen, elastin, and reticulin), histiocytes, endothelial cells, perivascular macrophages and dendritic cells, mast cells, smooth muscle, and cells of peripheral nerves and their end-organ receptors. b. Fibrous Collagen & reticulin - provide tensile strength Elastic fibers- provide for restoration of shape after a deformation c. Ground substance glycosaminoglycans: hyaluronic acid, chondroitin sulfate, and dermatan sulfate. BIOL 2022SEF 2024 33 The Hypodermis Known as subcutaneous tissue or superficial fascia Has more adipose than dermis Functions energy reservoir thermal insulation Hypodermic injections into subcutaneous tissue since highly vascular Hypodermis BIOL 2022SEF 2024 34  Hypodermis This layer contains adipose tissue and serves to attach the dermis to its underlying tissues. BIOL 2022SEF 2024 35 Accessory Organs of the Skin 1. Hair 2. Skin glands 3. Nails BIOL 2022SEF 2024 36 Accessory Structures of the Skin Hair A characteristic feature of the human skin is the apparent lack of hair on most of the body surface. This is actually not quite true. Most of the skin is haired although the hair in most areas is short, fine and only lightly pigmented. Truly hairless are only the palms of hands and soles of feet, the distal phalanges and sides of fingers and toes and parts of the external genitalia. BIOL 2022SEF 2024 37 Hair (cont:) In those parts of the skin which we perceive as "hairy" we find terminal hairs. The free part of each hair is called the shaft. The root of each hair is anchored in a tubular invagination of the epidermis, the hair follicle, which extends down into the dermis and, usually, a short distance into the hypodermis. The hair that you groom daily is actually dead keratinized cells. Each hair follicle has an associated bundle of smooth muscle, the arrector pili muscle. This muscle inserts with one end to the papillary layer of the dermis and with the other end to the dermal sheath of the hair follicle. This makes your hair stand up on its end. BIOL 2022SEF 2024 39 Hair Color and Texture Hair color is determined by the amount and type of melanin present. Melanocytes become less active with age. Gray hair is a mixture of pigmented and non-pigmented hairs. Red hair results from a a modified type of melanin that contains iron. The shape of the hair shaft determines texture. Round shaft – straight hair Oval shaft – wavy hair Flat shafts – curly or kinky hair Perms use chemicals to flatten shafts and makes hair curly. Alopecia is the term for hair loss. 40 BIOL 2022SEF 2024 Accessory Structures of the Skin Nails Plates of stratified squamous epithelial cells with hard keratin Protect distal ends of phalanges Cells are keratinized in the nail root Nail growth occurs in the lunula Cuticle is a fold of stratum corneum on the proximal end of the nail BIOL 2022SEF 2024 42 Exocrine Glands Sebaceous glands or oil glands are simple branched areolar glands. They secrete the sebum (seb = oil) an oily product. Sebum is usually secreted into a hair follicle. Sebum is a natural skin cream: it helps hair from becoming brittle, prevents excessive evaporation of water from the skin, keeps the skin soft and contains a bactericidal agent that inhibits the growth of certain bacteria. Sebaceous glands are scattered all over the surface of the skin except in the palms, soles and the side of the feet. Vernix caseosa - white covering on fetus. Blackhead Pimple BIOL 2022SEF 2024 43  Exocrine Glands Sweat glands or sudoriferous glands are simple coiled tubular glands. They are divided into two principal types: eccrine and apocrine. Eccrine glands are the most common. Their secretory portion can be located in the dermis or in the hypodermis. They produce sweat, a watery mixture of salts, antibodies and metabolic wastes. Sweat prevents overheating of the body and thus helps regulate body temperature. Apocrine glands are found mainly in the skin of the armpits, of the anogenital areas and of the areola of the breasts. Their secretory portion can be located in the dermis or in the hypodermis. Their excretory ducts open into hair follicles. Their secretion is more viscous than that of the eccrine glands. They start secreting at puberty and may be analogous to the sexual scent glands of other animals. BIOL 2022SEF 2024 44 Exocrine Glands Ceruminous glands (or ear wax glands) and mammary glands are modified apocrine sweat glands. BIOL 2022SEF 2024 45  Function of the Skin Protection - the epidermis provides a barrier to fluid loss from the body (this protective function is impaired in patients with burns). Barrier function - intact skin prevents the entry of micro-organisms into the body. Antimicrobial proteins are produced by the epidermis - they act by piercing holes in the outer membranes of micro-organisms. Resistance to wear and tear - continuous replacement of the outer epidermal cells that wear off - new cells are produced in the deepest layer of the epidermis and gradually migrate towards the surface BIOL 2022SEF 2024 46  Skin can excrete water, salt, and small amounts of waste products such as urea. Vitamin D can be synthesized in skin exposed to sunlight (vitamin D can also be obtained from the diet) The skin provides a barrier to ultraviolet light. The melanocytes contain melanin, which absorbs UV radiation, and also distribute the pigment to neighboring cells. Skin exposed to sunlight becomes wrinkled and creased. Changes seem to be due to disruption of collagen and elastin in dermis, and loss of fibroblasts which make new proteins. BIOL 2022SEF 2024 47  The integumentary system is well-supplied with receptors for touch, pain, temperature, vibration and pressure Sensory information is relayed to the central nervous system via sensory nerves Social interactions are influenced by facial expressions, blushing, touching, etc. BIOL 2022SEF 2024 48 Interactions with other organ systems The skin and other parts of the integumentary system work with other organ systems to maintain homeostasis. The skin works with the immune system to defend the body from pathogens by serving as a physical barrier to microorganisms. Vitamin D is needed by the digestive system to absorb calcium from food. By synthesizing vitamin D, the skin works with the digestive system to ensure that calcium can be absorbed. To control body temperature, the skin works with the cardiovascular system to either lose body heat, or to conserve it through vasodilation or vasoconstriction. To detect certain sensations from the outside world, the nervous system depends on nerve receptors in the skin.  Skin Burn Local Changes Burn causes coagulative necrosis of the epidermis and underlying tissues depth of injury: temperature & duration of exposure area of cutaneous injury First degree Red, erythematous (Superficial) Very sensitive to touch Very painful Usually moist No blisters Second degree Erythematous or whitish with a fibrinous (partial- exudate thickness) Wound base is sensitive to touch and Painful Commonly have blisters Surface may blanch to pressure Third degree Surface may be: White, Black, leathery, Pale (Full thickness) or Bright red Generally anesthetic or hypoesthetic Subdermal vessels do not blanch No blisters Hair easily pulled from its follicle Fourth degree Involves deep tissues including fascia, Assessment of The Burn Wound (cont’d) Total percentage of body surface area (TBSA) 1. Lund-Browder chart  Rule of Nines  Fun Facts House dust is mainly skin flakes! If you laid out all your skin on a flat surface, it would have an area of about 2 square meters. Skin weighs about 2.5 kilograms - the largest organ in the body. What hurts if you pull it, but doesn't hurt if you cut it? Your hair, of course! Skin is elastic - it springs back into shape when stretched. Some medicines (estrogen, nicotine) can pass through the skin, but others cannot (insulin). Why is that? Because only fat-soluble substances can enter the skin, not water-soluble ones. Your hair stands on end and you develop 'goose bumps' because there are tiny muscles attached to the hair follicles and they contract when you are frightened or cold. BIOL 2022SEF 2024 56 THANK YOU BIOL 2022SEF 2024 57