Biology 1103/1109 Human Anatomy & Physiology I Course Notes Week 7 Fall 2024 PDF

Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 7 Fall 2024 WEEK 7 Integumentary System Readings: OpenStax Textbook Unit 11 Identify and describe the components of the integumentary system. A system is an association of organs that...

Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 7 Fall 2024 WEEK 7 Integumentary System Readings: OpenStax Textbook Unit 11 Identify and describe the components of the integumentary system. A system is an association of organs that have a common function. The integumentary system consists of the skin and its derivatives, including hair, glands, nails and several specialized sensory receptors. The sensory receptors detect stimuli such as touch, pressure, temperature, and pain. See Figure 5.1 of Marieb & Hoehn (11th ed.); Figure 11.1 in OpenStax. I. Identify and describe the five layers of the epidermis of the skin, including the location and function of keratinocytes and melanocytes. The skin is composed of two regions or major layers called the epidermis and dermis. The epidermis is the outer layers and consists of closely packed epithelial cells. The dermis lies below the epidermis and consists of dense irregular connective tissue. Consider the five layers of the epidermis. First look at Figure 5.2 of Marieb & Hoehn (11th ed.; Figure 11.4 in OpenStax ). This diagram shows the relationship between the epidermis and dermis. Note that the outer region, the epidermis, can be further broken down into a number of layers. These layers, starting from the outside (most superficial) and working inwards to the inner or deeper layers are as follows: The outer layer is called the stratum corneum and it consists of many flat, closely packed dead cells. A fibrous protein called keratin has replaced the cytoplasm of the cells. These keratinized cells are often referred to as being cornified or horny. The stratum corneum is the outer protective layer that gradually gets sloughed off (or shed) as a result of abrasion. At the same time as cells are lost, cells from lower layers become keratinized as they move upward from where they are produced. Between these cells are lipids from lamellar granules which form a water-repellant barrier. The second layer is called the stratum lucidum. This layer is usually found only in areas where the skin is thick such as the skin of the palms of the hand and soles of the feet. The stratum lucidum consists of several rows of clear flat, dead cells. The cells contain a clear substance called eleidin that is eventually transformed into keratin. The third layer is called the stratum granulosum. The stratum granulosum consists of three to five rows of flattened cells. These cells contain granules of a substance called keratohyalin. Keratohyalin is the substance that is connected to the substance eleidin mentioned earlier. As the granules increase in size, the nuclei of the cells disintegrate, which results in the outermost cells of this layer being dead cells. The next layer below the stratum granulosum is the stratum spinosum. This layer contains 8 to 10 rows of many-sided cells that are packed tightly together. The surfaces of each cell have a prickly or spiny appearance when viewed microscopically, hence the name stratum spinosum. 1 Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 7 Fall 2024 The deepest layer of the epidermis of the skin is called the stratum basale. This layer is comprised of rapidly dividing cells which replenish the cells in the layers above it. The overview of the relationships between the six layers is that, as cells are rubbed off the surface of the skin, they are replaced by cells from the next layer below as those cells undergo various changes. This happens from layer to layer on a continual gradual basis with the stratum basale or deepest layer of the epidermis being the one which produces new cells as cells are gradually lost on the outside. The two types of cells found in epidermis are keratinocytes and melanocytes. See Figure 5.2 Marieb & Hoehn (11th ed.; Figure 11.4 in OpenStax). Keratinocytes are cells that undergo keratinization. That is, they produce keratin, a tough protein that helps waterproof and protect the skin and deeper tissues. Melanocytes are cells that produce melanin, one of the major pigments responsible for skin colour. The melanocytes are located in the deeper layers of the epidermis. The number of melanocytes does not vary much in races of different colour, thus differences in skin colour are the result of different amounts of melanin produced. Other cells of the epidermis take up the melanin produced by melanocytes. The melanin (pigment) granules provide protection against UV radiation. II. Specify the function(s) of epidermal derivatives, including hair, sebaceous glands, sudoriferous glands, ceruminous glands, nails. Hair is present in varying amounts over most of the body. The only hairless regions are the lips, soles of the feet and palms of the hands. Figure 5.6 Marieb & Hoehn (11th ed. ; Figure 11.9 & 11.10 in OpenStax) illustrates the structure of individual hairs. Although the hair follicle or base projects down into the dermis, you will see from the diagram that the epidermis also folds down to surround the root follicle. Hairs grow as a result of cells dividing at the base of the follicle. Hair serves primarily for protection. For example, hair protects the scalp from the harmful rays in sunlight. Hairs around the eye (eyelashes and eyebrows) and hairs 1  Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 7 Fall 2024 in the external ear canal and nostrils protect these structures from insects and dust. Hairs also provide an increased sensitivity to touch as a result of having nerve endings around each hair follicle that are stimulated when the hair is moved. Another structure derived from the epidermis is the sebaceous gland (oil gland). These are shown in Figure 5.8a in Marieb & Hoehn (11th ed. ; Figure 11.9 in OpenStax). Most sebaceous glands are located near hair follicles and secrete an oily fluid called sebum into hair follicles. The oil keeps the hair from drying out and becoming brittle. The oil also helps keep the skin waterproof, soft and pliable. The oil is also toxic to some bacteria. Sudoriferous glands (sweat glands) are shown Figure 5.8b in Marieb & Hoehn (11th ed. ; Figure 11.1 in OpenStax). The secretory portion of the gland lies deep in the dermis, but the glands developed from the same tissues as did the epidermis. Ducts carry the sweat to the surface of the skin where it is released through pores. The release of sweat functions primarily to control body temperature. It also helps to eliminate some chemical wastes and also has a protective function. Ceruminous glands, are modified sudoriferous (sweat) glands that lie deep in the skin of the auditory or ear canal. Ceruminous glands produce a substance called cerumen, which, when combined with the secretions of the sebaceous glands, is known as earwax. Earwax and hairs help protect the ear against entry by insects and other foreign bodies. Nails are hard, keratinized masses of cells that cover the posterior surfaces of the ends of fingers and toes. See Figure 5.7 in Marieb & Hoehn (11th ed. ; Figure 11.10 in OpenStax). The nails primarily function to assist in grasping and manipulating objects and to provide protection against trauma to the ends of the digits. They allow us to scratch ourselves and can also be used for defense. III. Describe five major functions of the integumentary system. The skin and associated structures perform a number of activities that may be grouped into major functions. We will identify and briefly describe these major functions. The order in which we deal with these is not intended to reflect their importance. Many of these functions may also involve the associated structures such as the glands of the skin. a) Protection - The skin covers the body and provides a physical barrier that helps prevent abrasion (physical damage) and is also a barrier to bacteria and other organisms that may try to enter the body. Secretions of glands in the skin also reduce the chance of bacteria entering the body. The skin also protects against excessive water loss (dehydration) and protects against ultraviolet light which are harmful rays of sunlight. b) A second function of the skin is to assist in body temperature regulation. One important way by which the skin does this is by the production of perspiration by sweat glands when the body gets too warm. Perspiration evaporates from the skin surface and cools the body. 4 Biology 1103/1109 Human Anatomy & Physiology I Course Notes Wk 7 Fall 2024 c) A third function of the skin is sensation. The skin contains various receptors, which can detect stimuli related to pressure, pain, touch and temperature. d) A fourth function of skin is excretion. Excretion is the process of removal of waste products from the body. Sweat contains a variety of chemical wastes, although relatively small amounts are excreted as compared to the amounts removed by other systems of the body. e) A fifth function of the skin is to assist in the conversion of Vitamin D to its most active form. Sunlight (which contains ultraviolet light) stimulates the skin to convert a form of Vitamin D (7-dehydrocholesterol derived from cholesterol) to a more active form. Ultraviolet light is harmful in high amounts as it can cause sunburn and a form of skin cancer. While UV light (a component) of sunlight is harmful in excessive amounts, it is useful in small amounts to help convert Vitamin D. f) The sixth function of the skin is its role in helping to provide immunity to disease. Immunity is the ability to resist injury from agents foreign to the body such as bacteria or harmful chemicals. Certain specialized cells of the skin, discussed later in this unit, help stimulate the production of antibodies which play a key role in one form of immunity. 4