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Home , Arrector pili muscle, Dermis, Epidermis, Goose bumps, Integumentary system, Sebaceous gland

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BIOL 2210L Unit 3: Authors: Terri Koontz and Megan Hancock, CNM Department

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Terms to Know for Unit 3 Layers of the Integument Accessory Structures of the Additional Instructor Terms follicle Hair root Hypodermis Hair shaft Cells of the Epidermis Sebaceous sebum Sweat glands Meissner’s corpuscle Pacinian corpuscle

Layers of the Epidermis Layers of the Dermis Papillary layer dermal papillae Reticular Layer

Membranes Serous Membranes Specific Serous Membranes Mucous membranes (Mucosae) Serosa Parietal Serous membranes (Serosae) Serous fluid Visceral pericardium Cutaneous membrane Parietal serosa Parietal pleura Visceral serosa Visceral pleura Parietal Visceral peritoneum Learning Objectives (modified from HAPS learning outcomes) 1. Membranes (mucous, serous, cutaneous) a. Describe the structure and function of mucous, serous, and cutaneous membranes. b. Describe locations in the body where each type of membrane can be found. 2. General functions of the skin & the subcutaneous layer a. Describe the general functions of the skin. b. Describe the general functions of the subcutaneous layer (also known as the hypodermis). 3. Gross & microscopic of skin a. With respect to the epidermis: i. Identify and describe the type making up the epidermis. 2

ii. Identify and describe the layers of the epidermis, indicating which are found in thin skin and which are found in thick skin. iii. Correlate the structure of thick and thin skin with the locations in the body where each are found. b. Identify and describe the dermis and its layers, including the tissue types making up each dermal layer. 4. Roles of specific tissue layers of skin & the subcutaneous layer a. With respect to the epidermis: i. Describe the functions of the epidermis. ii. Explain how each of the five layers, as well as each of the following types and substances, contributes to the functions of the epidermis: stem cells of stratum basale, keratinocytes, melanocytes, keratin, and extracellular . b. With respect to the dermis: i. Describe the overall functions of the dermis. c. With respect to the subcutaneous layer: i. Describe the functions of the subcutaneous layer. 5. Anatomy & functional roles of accessory structures a. With respect to the following - sweat glands (eccrine and ), sebaceous glands, hair (follicle and arrector pili muscle), and sensory receptors (Meissner’s & Pacinian corpuscles and receptor): i. Identify each structure. ii. Describe the location of each structure in the body. iii. Describe the anatomy of each structure. iv. Describe the function of each structure. Explanation of Anatomy In this lab, we will begin our study of membranes. A membrane is a simple that contains two tissue types: an and an underlying . There are three covering membranes of the body: mucous, serous, and cutaneous. After learning about mucous and serous membranes, we will explore the cutaneous membrane in depth. The cutaneous membrane, our “skin”, is part of the integumentary system and serves as the boundary between our internal environment and the external world. Each layer of the skin has a functional role that aids in maintaining this boundary. The epidermis and dermis are discrete layers of skin that are themselves comprised of layers. There is a deep third layer of the integumentary system called the hypodermis, and this is not a true layer of the skin. We will finish the unit by exploring accessory structures of the integumentary system such as hair and glands.

Think about how many internal diseases have manifestations on the skin that can be observed externally. Take a moment to consider how much time, effort, and money are devoted over the course of our lifetimes to grooming this organ. Our self-esteem is tied to how nice this organ looks. When a disease affects the skin’s appearance, it can be uncomfortable both physically and emotionally. What is ? Why do we have a ? Is there a cure for flaky skin? The skin can reflect our physical and understanding the anatomy of this incredible organ can assist with providing patient care. Membranes Membranes of the body are simple organs. The definition of an organ is a structure that contains two or more tissues that perform a specific function. Membranes are comprised of two tissue types, making it a 3

“simple organ”. The two tissue types that make up membranes are epithelial and connective tissues. Membranes cover body areas and their primary function is protection.

There are three types of covering membranes: mucous (mucosa), serous (serosa), and cutaneous.

Mucous membranes are wet membranes, as they are bathed in fluid. Mucous membranes are associated with body tracts (i.e. digestive, respiratory, urinary, and reproductive tracts) that come into contact with the external environment. All mucous membranes contain stratified squamous epithelium in the areas that switch between the “internal” and external environment. This type of epithelium protects organ walls from abrasion as objects coming from the outside world come into contact with this membrane. Other types of epithelium found in mucous membranes reflect the function of a particular part of that ’s body tract.

Mini Activity: Review epithelial tissues

1. What type of epithelial tissue is associated with the digestive system because it has the function of making large enzymatic that chemically digest ingested ?

2. What type of epithelial tissue is associated with the because it has the function of sweeping , containing trapped inhaled debris, to the back of the throat?

3. What type of epithelial tissue is found only in the ?

The type of epithelial tissue in a varies according to the function of the body tract at a particular location along that tract. For example, the mucous membrane epithelia in the respiratory system are pseudostratified ciliated columnar epithelium (PCCE) in the and the large tubes of the lower respiratory system, stratified squamous in the throat region, simple columnar and simple cuboidal in the smaller tubes of the lower respiratory system, and simple squamous in the tiny air sacs where occurs. Each epithelial tissue type is directly related to its function at that location.

The connective tissue layer that all mucous membranes share is loose areolar connective tissue, which provides nutrients to the epithelium it underlies. The loose structure of areolar tissue allows for the quick diffusion of needed nutrients from the digestive and respiratory systems into the bloodstream. Serous membranes Serous membranes allow for internal organs to rub against one another in a relatively frictionless environment. The double layer membrane of serous membranes contains tissue types that are structured to perform diffusion: simple squamous epithelium and areolar connective tissue. The inner membrane of this double membrane attaches directly to the organ while the outer membrane attaches to the wall. The double layer serous membrane is also referred to as serosa. 4

Mini Activity: “Seeing” the double layering of serosa

Take a piece of paper and fold it in half. Put the folded piece of paper on the table in front of you. Write parietal on the side that is not in contact with the table and write visceral on the side that is touching the table. The table represents an organ in the body.

1. What does visceral mean?

2. Now take your four , which in this activity represent four , and put them on top of the paper next to the word parietal. Ribs make up the wall of the thoracic body cavity. The word parietal is derived from a Latin word that means wall.

Looking at the table, the folded paper, and your four fingers, can you correctly identify in the image below which letter represents the visceral serosa and which letter represents the parietal serosa?

Write what you think are the correct identifications for those two serosal layers on the blank lines next to letters A and B.

Image 1: Pleura

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The visceral serosa attaches to an organ. The word visceral means inner organ. The parietal serosa attaches to the body cavity wall. The space between these two serosal layers contains serous fluid. Serous fluid allows body organs to slip and slide against one another with very little friction, preventing abrasive forces that could cause organ damage. Specific serous membranes Three areas in the body have serous membranes: , , and digestive organs. 5

The mini activity that you just did relates to the serosa surrounding the lungs (see Image 1). Lungs are encased in serous membranes specifically called pleura. The visceral pleura (labeled B.) directly attaches to the , whereas the parietal pleura (labeled A.) directly attaches to the thoracic body cavity wall.

The serosa that surrounds the heart also has its own specific name called the pericardium. Peri- translates to “surrounds” (just like the perimeter of a building). Cardium means heart. The visceral pericardium directly attaches to the heart and the parietal pericardium is the outer serosal layer.

Digestive organs are surrounded by their own serosa that is specifically called peritoneum. Visceral peritoneum attaches to digestive organs like the small intestines and . The parietal peritoneum attaches to the abdominal body cavity wall. Layers of the Integument The integumentary system contains one of the largest organs of the body, the skin. The skin has a surface area of about one and half square meters and weighs approximately nine pounds, which is three times the weight of the average brain! The word integument means covering, and this external organ is our first line of defense against the world. Yet the skin has many more functions beyond protection. Our skin allows us to sweat to cool our bodies and to get rid of waste. Receptors located within the skin detect the external environment. Our skin metabolizes the precursor to . Also, with its many dermal vessels, the skin serves as a blood reservoir.

Image 2: Layers of the integumentary system

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The skin is the third type of membrane, called cutaneous, and it is a dry membrane. The skin is made up the epidermis and dermis. Below these two layers of skin is the third, and deepest, layer of the integument, the hypodermis. The hypodermis is predominantly composed of and like the dermis, it contains many blood vessels. Functions of the hypodermis include storage, shock , and insulation. Image 2 shows the three main (major) layers of the integumentary system. Cells of the Epidermis The epidermis is composed of stratified squamous epithelium that contains keratinocytes, the main cell type of this layer. New keratinocytes replace old keratinocytes continuously as these cells move up through the epidermis towards the external surface of our skin. In about a month’s time, our epidermis undergoes a complete turnover and is comprised of an entirely new batch of cells. Keratinocytes found deep within the epidermis perform important metabolic functions such as building proteins and synthesizing glycolipids. As keratinocytes migrate towards the more superficial layers of the skin, they move farther from the supportive connective tissue layer below and lose access to nutrients and oxygen. As a result, these cells die. The flattened, dead, scale-like keratinocytes no longer contain organelles and are packed with a tough called keratin. Keratin makes the epidermis a great physical barrier, as it protects our insides from the outside environment.

Image 3: Epidermis showing structure of keratinocytes and melanocytes

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Another abundant cell found in the epidermis is the . Melanocytes make up about 15% of the epidermis and are found dispersed throughout the deepest row of epidermal cells. Melanocytes have long, arm-like projections that travel into adjacent epidermal layers above. Melanocytes produce a pigmented protein called melanin. Melanin blocks the sun’s radiation, protecting the dividing cells of the epidermis. Consider what happens when you are exposed to sunlight for any length of time. You get a tan as melanocytes increase melanin production to protect DNA of dividing basal cells, precursors to keratinocytes. The color of skin is not correlated with the number of melanocytes a person has but rather by the amount of melanin a person produces (see Image 3). Layers of the Epidermis The epidermis is composed of four or five distinct layers, or strata, depending upon whether it is categorized as thin (four layers) or thick (five layers). Thin skin covers most of the body and typically there are present, whereas thick skin is limited to a few locations on the body that are subject to much abrasion. The word stratum means layer, and the deepest layer of epidermal tissue is called the stratum basale, the base layer. This stratum is a single row of actively mitotic stem cells.

Beginning deep in the tissue and moving superficially through the layers of the epidermis are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum (see Image 4). One way to remember the order of these five distinct layers of the epidermis is to devise a mnemonic such as “Boys See Girls Like Crazy”. Boys for stratum basale, See for stratum spinosum, Girls for stratum granulosum, Like for stratum lucidum, and Crazy for stratum corneum.

Superficial to the stratum basale is the stratum spinosum. The stratum spinosum is named the “spiny layer” because when tissue samples are prepared, this layer appears to have cells with tiny spines. This spiny appearance of the stratum spinosum is due to its many , which are anchoring junctions. These anchoring junctions allow the stratum spinosum to resist pulling forces as the skin stretches. The main function of the stratum spinosum is to produce pre-keratin.

Superficial to the stratum spinosum is the stratum granulosum, so named for its many visible granules that are stained during tissue preparation. The granules in the stratum granulosum contain glycolipids that are released to form a waterproof barrier in the upper layers of the epidermis. This waterproofing allows our bodies to retain fluids and not lose them to the environment, a primary function of the integumentary system. The stratum granulosum is thin, about four rows of cells, and this is the last layer of living cells.

Superficial to the stratum granulosum in thick skin is the stratum lucidum. This stratum contains all dead cells and is only found in thick skin. Thick skin is located on the palms of the and soles of the feet, where much abrasion occurs. This stratum is a thin, translucent layer of cells that contain keratohyaline, an additional tough protein that provides extra protection where skin is constantly rubbing against solid objects. The stratum lucidum of thick skin is situated between the stratum granulosum and the most superficial layer of the epidermis, the stratum corneum.

The stratum corneum is the most superficial layer for both thin and thick skin. Corneum means horn, like a cornucopia. This distinct layer of the epidermis contains twenty to thirty layers of flattened, scale- like cells that act as the body’s most superficial shield. This layer of dead keratin-packed cells is sloughed off continuously, shedding roughly 50,000 dead cells a minute! 8

Mini Activity: Listing the layers of the epidermis

List in order from deep to superficial the layers of the epidermis found at the plantar body region.

Image 4: Distinct layers of the epidermis

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Layers of the Dermis The dermis is made up of two layers of connective tissue: a papillary layer and a reticular layer (see Image 5). The papillary layer contains dermal papillae, peg-like structures that resemble a turned over egg carton. This is composed of loose areolar connective tissue with much and numerous blood vessels. Recall that loose areolar connective tissue underlies and supports most epithelium. The papillary layer provides nutrients to the epidermis, as many of its dermal papillae contain beds. Other papillae may contain sensory receptors involved in detecting light touch. The dermal papillae of the papillary layer may take the shape of ridges and swirls and is responsible for the impressions that we see as .

Making up to 80% of the dermis, the thicker of the two layers is called the reticular layer. This layer of the dermis takes its name from the Latin word reticulum, which means small net. This refers to the delicate network of blood vessels that reside within. Dense irregular connective tissue makes up the reticular layer of the dermis. The reticular layer is a strong layer whose function relates to resisting forces from multiple directions as it contains bundles of fibers that are irregularly arranged. Leather is the reticular layer of that has been processed by stabilizing the many collagen fibers that are found in this layer of the dermis.

Image 5: Layers of the dermis from a slide

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Mini Activity: Thin or thick skin?

In Image 5, are you looking at thin or thick skin? What made you pick one over the other?

Accessory Structures of the Skin Along with the many layers of the skin, there are other structures that may be present that help the skin perform its many functions. Hair protects and insulates, glands aid in and , and sensory receptors detect changes in our environment (see Image 6).

Hair is present on most skin except in high abrasion areas like the palms of the hands and highly sensitive areas like the . The part of the hair that is visible is called the shaft. The hair that is not seen and is surrounded by the epidermis and dermis is called the root. A follicle surrounds the hair strand and is attached to a smooth called the arrector pili muscle. The arrector pili muscle contracts in response to or low . It is this contraction of the arrector pili muscle that gives us . Putting this in an evolutionary context, the raising of hair when had more of it made humans appear bigger, and also warmed humans by trapping and heating air among raised hair strands.

Image 6: Hair shaft, hair root, hair follicle and arrector pili muscle

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Eccrine and apocrine glands are types of sweat glands while sebaceous glands are oil glands. Eccrine glands produce and secrete sweat for thermoregulation of body temperature through evaporative cooling, but also excrete nitrogenous wastes such as ammonia and urea. You might notice that your palms sweat when you are nervous, while your forehead sweats when you are hot. Those two areas of the body have high numbers of eccrine glands. Overall, there are three to four million eccrine sweat glands found in adult skin. Apocrine glands are not as abundant as eccrine glands. Apocrine glands are found in abundance in the groin and axillary regions of the body. One example of apocrine glands are mammary glands that produce and secrete . Sebaceous glands are always associated with hair. These glands produce and secrete sebum, an oil that acts as a lubricant for both hair and the skin. As thick skin does not have hairs present, these areas of the body also do not contain sebaceous glands. Image 7 shows a comparison of sweat and sebaceous glands.

Lumen of sweat

Sebaceous gland

Image 7: Comparison of a sweat gland and

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Receptors allow us to detect our environment. Three notable receptors of the skin are Meissner’s corpuscles, located within the dermal papillae of the papillary layer of the dermis, Pacinian corpuscles, found in the reticular layer of the dermis and hypodermis, and hair follicle receptors surrounding hair follicles. The more superficial of the receptors, the Meissner’s corpuscle, detects soft touch whereas the Pacinian corpuscle, located deeper in the integument, detects deep pressure and vibration. The hair follicle receptor detects stimuli that bend a hair, such as when an lands on your arm.

In Image 8, you may observe how the Meissner’s corpuscle has a cotton candy-like appearance and the Pacinian corpuscle has layers like an onion.

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Meissner’s Pacinian corpuscle corpuscle within a within the dermal hypodermis papilla

Image 8: Meissner’s and Pacinian corpuscle

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Activity 1: Locating Structures on Models Use the models set up in the lab. Identify the following layers and structures: a. epidermis, b. dermis, c. eccrine gland, d. sebaceous gland, e. hair follicle, f. arrector pili muscle

Use painter’s tape provided in the lab and label the above layers and structures on the model.

Draw the integumentary system or take a picture for future reference.

Activity 2: Comparing Thin and Thick Skin using Microscope Slides Using microscope slides provided by your instructor, draw thin and thick skin.

Thin Skin Thick Skin

What layer is found in thick skin and not thin skin?

What areas of the body have thick skin and why?

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Activity 3: Finding Skin Accessory Structures using Microscope Slides Using microscope slides provided by your instructor, find and draw a sweat gland, sebaceous gland, Meissner’s corpuscle, and a Pacinian corpuscle.

Sweat gland Sebaceous gland

What are some key features that distinguish the two glands from one another histologically? Label those features in your drawing.

Meissner’s corpuscle Pacinian corpuscle

What are the key features (what do you notice about the location of the two receptors drawn above) that will help you distinguish between the two? Mark those observations on your drawings.

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Activity 4: Apply what you know about the Integumentary System You will either self-select or your instructor will divide the class into groups.

Within your group, use electronic devices to find a skin disease/abnormality or research a skin disease that your instructor has assigned your group. Some ideas for skin diseases and abnormalities: , steatocystoma, pilar , pilaris, , milia, eczema, plaque , or .

Take ten to fifteen minutes to research and prepare a short and informal presentation. Be mindful that many people suffer from these diseases, so treat this exercise as though you are a caregiver.

What skin disease did your group pick or was assigned?

Notes on skin disease:

How will your group present the skin disease? Some ideas include a powerpoint presentation, a drawing, a flyer, a play. Use the ideas included here or come up with your own.

If time permits, your instructor may show the class some short video clips of skin diseases/abnormalities.

(Alternative) Activity 4: Difference between 1st, 2nd, and 3rd degree Explore the skin model(s) that show the difference between the three levels of burns. Take notes on the depth of the tissue damage observed for each type of , including what layers have been damaged, the appearance of the skin (cherry red, blackened, ), and whether you would suspect that the burn victim will experience pain.

1st degree burn

Depth of damage, what layers have been injured:

Appearance of skin:

Will a person with this degree of burn experience pain? Explain your answer.

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2nd degree burn

Depth of damage, what layers have been injured:

Appearance of skin:

Will a person with this degree of burn experience pain? Explain your answer.

3rd degree burn

Depth of damage, what layers have been injured:

Appearance of skin:

Will a person with this degree of burn experience pain? Explain your answer.