Anatomy: Skin and Subcutaneous Tissues

Fred's looking at a histological section taken from near the surface of the body. Fred observes numerous, large cells that have a single droplet of fat in their cytoplasm. What layer is Fred observing under the microscope?

Superficial fascia

dermal papillae?

The epidermal/dermal junction, that is where the epidermis and the dermis meets, is not regular. There are projections of the dermis called dermal papillae into the epidermis. This creates a peg-in-socket arrangement and increases surface area for contact between these two layers.

thick vs thin skin in gross anatomy vs histology?

gross anatomy: skin thickness = epidermis + dermis histology: skin thickeness = epidermis only - The image on the left is of thin skin, while the image on the right is of thick skin. Again, thin skin versus thick skin, histologically speaking, is looking at the thickness of the epidermis only. The epidermal regions in both images are labelled with "Epi".

tissue that makes up papillary layer?

loose (areolar) CT The more superficial and thinner layer of the dermis is the papillary layer. This papillary layer includes the dermal papillae discussed in the earlier slide. The papillary layer is composed of loose (areolar) connective tissue, which has equal amount of cells, protein fibers, and ground substance. In other words, with loose (areolar) connective tissue, no one component of the connective tissue stands out.

dermis is derived from...

mesoderm

thinnest skin in histology?

most locations, including superior back

fascia?

sheet of CT that separates, supports, and/or interconnects different structures route by which blood vessels, nerves, and lymphatics can travel!

largest organ of body?

skin -- major component of integumentary system

organ?

structure composed of at least 2 of the primary tissues, which allows for complex functions

thickest dermis?

superior back region

thickest skin in histology?

thick skin ONLY found on palms of hands/soles of feet where abrasion is the greatest

what are the 2 layers of the skin?

1. epidermis -- superficial; keratinized stratified squamous epithelium 2. dermis -- deep; CT epidermis: these densely packed cells of the epithelium are pushed towards the surface as cells in the deepest layer of the epithelium are undergoing mitosis. As the cells are pushed towards surface, they produce a protective protein called keratin and go through a process called keratinization. The cells at the surface are dead epithelial cells full of this protective protein called keratin. These cells are then sloughed off and are a major component of dust. You slough off approximately 40 pounds of these cells throughout an average lifetime. Additionally, you replace your epidermis approximately every 15 to 30 days. The dermis is the deep layer of the skin. It is composed of connective tissue. This connective tissue contains lots of blood vessels, nerves, hair follicles, and parts of glands. The connective tissue provides mechanical support, strength, and thickness to skin.

layers of the dermis?

1. papillary layer -- superficial 2. reticular layer -- deep

name the 5 major functions of the integumentary system

1. protection (skin acts as a chemical, physical, and biological barrier which protects against frictional forces, pathogens, ultraviolet radiation, and water loss or uptake) 2. sensation (the integumentary system contains sensory receptors that detect stimuli in the external environment) 3. temperature regulation (through the activities of sweat glands and dense vasculature in the connective tissue, the integumentary system is vital in temperature regulation) 4. metabolic (skin cells can synthesize vitamin D using ultraviolet light) 5. waste elimination (the integumentary system can excrete substances in its different secretions, wastes such as ammonia, urea, uric acid, water, and salt, although the kidneys are the main location for these actions)

what is the integumentary system composed of?

1. skin 2. accessory structures/epidermal derivatives (=skin appendages) - sebaceous (oil) glands - sudoriferous (sweat) glands - hair - nails

superficial fascia vs deep fascia?

1. superficial fascia aka subcutaneous layer aka hypodermis - immediately deep to dermis of skin and superficial to deep fascia; primarily composed of *white (unilocular) adipose tissue* and *loose areolar CT* 2. deep fascia - deep to superficial fascia; superficial to deeper regions of the body (ex: muscles); primarily composed of dense CT (fibrous, very tough)

So, from superficial to deep, what layers do we find?

First, the skin is composed of the superficial epidermis and the deep dermis. Then, we find the superficial fascia, also called the subcutaneous layer or hypodermis. Then, we find the deep fascia. Finally, beneath the deep fascia, we find the deeper regions of the body such as skeletal muscles.

skin and subcutaneous structures in leg cross section?

In these cross-sections of the thigh and leg, you can see the different body components previously discussed. First, you can see the skin. However, most of what you are visualizing with the naked eye, is actually the dermis of the skin, as it is thicker than the epidermis. Deep to the skin, is the superficial fascia (=subcutaneous layer, =hypodermis), which can vary in thickness from one region of the body to another region of the body. Deep to the superficial fascia, is the deep fascia. In certain regions, this deep fascia gets special names. In the thigh, this deep fascia is call the *fascia lata*, while in the leg it is called the *crural fascia*. Remember, that deep fascia will invest the deeper regions of the body, such as areas containing skeletal muscles. Additionally, in certain areas, such as the thigh and leg, the deep fascia has inward extensions called *intermuscular septa* that form muscular compartments and permit the travel of neurovascular structures to/from the muscles. The inward extensions of the fascia lata create 3 compartments in thigh (i.e., anterior, medial, and posterior), while in the leg the inward extension of the crural fascia also creates 3 compartments (i.e., anterior, lateral, and posterior). fascia lata = lotta fascia in thigh because bigger crural fascia = rural because its far away further down the leg

functions of superficial fascia?

It contains an extensive vascular network. It varies in thickness from one region of the body to another region of the body. The superficial fascia thickens as one gains weight, but not uniformly throughout body. First, it binds the skin to the underlying tissues, yet still permits the movement of the skin over these deeper areas. It is also a location for neurovascular structures to travel, many heading to/from the skin. It is also serves as an energy (fat) reserve, as well as serves as thermal insulation for the body by reducing the rate of heat loss. In this image, we see a section of skin, with its keratinized stratified squamous epithelium of the epidermis, as well as its loose (areolar) connective tissue and dense irregular connective tissue of the dermis. Deep to the skin, and specifically deep to the dermis, you find the hypodermis, also known as the superficial fascia or subcutaneous layer. This layer contains loose (areolar) connective tissue and white (unilocular) adipose tissue. The image on the right is a higher magnification of the white (unilocular) adipose tissue of the hypodermis. In this image, you can see individual adipocytes (i.e., fat cells), especially where their single lipid droplet would reside, if it had not been lost during tissue processing for light microscopy.

functions of deep fascia?

It covers deeper regions of the body, such as areas containing skeletal muscles. It has inward extensions called *intermuscular septa* that form muscular compartments and permits the travel of neurovascular structures to/from the muscles. It also thickens in certain regions to form *retinacula* that hold tendons in place, as well as a structure in the lateral thigh called the iliotibial tract. As this fascia is investing around the muscles of the upper and lower limbs, it acts like an elastic stocking around these muscles and prevents the outward movement of the contracting muscles, making muscular contraction more efficient at compressing deep veins to push blood back towards the heart.

what else is skin considered?

cutaneous membrane, a dry epithelial membrane that covers the surface of the body

tissue that makes up reticular layer?

dense irregular CT The deeper and thicker layer of the dermis is the reticular layer. This reticular layer is composed of dense irregular connective tissue, where collagen fibers outnumber cells and ground substance and these collagen fibers are arranged in an irregular pattern. There are also a number of elastic fibers here which add to the elasticity characteristic of skin.

what are skin appendages derived from?

down-growths of the superficial epidermal epithelium during development

epidermis is derived from...

ectoderm

what kinds of tissues is skin composed of?

epithelial tissue and CT

dissection: "the big picture"

hypodermis/superficial fascia aka subcutaneous layer using finger for blunt dissection note that the epidermis AND dermis are above the finger

thinnest skin in gross anatomy terms?

scalp

thickest skin in gross anatomy terms?

upper portion of the back