Integumentary System
The _______ system is one of three systems that support and move the body. The integumentary system includes the _______ , _______ , and _______ . It covers and protects the entire body and may be the most familiar body system. You see the integumentary system as you look at another person and when you look in the mirror. It is the only body system completely exposed to the world outside the body.
Skin
The _______ is the largest organ in the human body (Figure 2.2). If spread flat, the skin would cover _______ square feet, about the size of a bedsheet. Skin protects the body and does a surprising number of important jobs. Taking care of the skin ensures it can do these jobs. Some of the tasks the skin performs include the following:
keep out _______ that could infect the body
remove some waste and make _______ D to build strong bones
house nerve endings that allow people to _______ , touch, and pressure
The skin houses various nerves, pores, _______ , veins, and hair follicles. These items are housed within the three main layers of the skin: the epidermis, the dermis, and the hypodermis, as you saw in Figure 2.2.
The outermost layer of the skin is the epidermis. The epidermis, which consists of _______ of its own, is the thinnest layer of the skin. The main function of the _______ is to protect the body from infection by stopping foreign substances from entering into the body.
The middle layer of the skin is the _______ . This layer contains two proteins, collagen and elastin. These proteins provide support to the skin and give skin the ability to stretch and return to its normal shape. With age, the body creates less of these proteins, which leads to the appearance of wrinkles and sagging skin.
The innermost layer of the skin is the _______ . This layer consists of fat, _______ , and nerve endings. It also connects the skin to the bone and muscle underneath. Additional functions of each layer of skin are listed in Figure 2.3.
Hair and Nails
Hair and nails are made by cells in the skin. Both _______ are made of the protein keratin. Hair grows on all skin surfaces except the palms, soles, lips, nipples, and some areas of the genitals. Each hair grows from a specialized cell called a hair follicle. Hair, like the skin, helps _______ the body. For example, eyelashes and eyebrows shield the eyes. Nose hair prevents dust and particles from entering the airways. Head hair helps regulate temperature and protects the head from _______ .
_______ protect the ends of fingers and toes. They grow on the upper sides of fingers and toes near the ends. As they grow, the older _______ are pushed out, making the nails longer.