Protection,+Support+and+Locomotion

=  Protection, Support, and Locomotion   = = Skin: the Body’s Protection  =

Structure and Functions of the Integumentary System
Skin is the main organ of the integumentary system. It has four types of tissues: epithelial tissue, which is the outer layer of skin; connective tissue, which holds the body together; muscle tissue, which allows you to respond to stimuli; and nervous tissue, which detects external stimuli.

Epidermis: The Outer Layer of Skin
The epidermis is the outermost layer of skin. It is made up of layers of dead, flattened, cells. These cells contain the protein keratin, which protects the living cell layer underneath from chemicals, bacteria, and heat. The interior layer of the epidermis contains living cells that continuously divide to replace the dead cells. Some of these contain melanin, which colors the skin and protects it from solar radiation.

Dermis: The Inner Layer of Skin
The second layer of skin is the dermis. It is the inner, thicker portion, and contains blood vessels, nerves, hair follicles, sweat glands, and oil glands. The skin is attached to underlying tissues by the subcutaneous layer, which consists of fat and connective tissue. The fat helps the body absorb impact, retain heat, and store food.

Functions of the Integumentary System
Skin helps maintain homeostasis by regulating internal body temperature. Blood vessels in the dermis dilate and constrict depending on body temperature. The body cools itself by sweating. Skin also produces vitamin D when exposed to ultraviolet light.

Skin Injury and Healing
If the body is injured, it first closes the break, which is accomplished through blood clotting in the wound and forming a scab. Afterwards, skin cells beneath the scab multiply and fill in the gap. There are three kinds of burns: first-degree burns, which cause redness and mild pain; second-degree burns, which damage the dermis and the epidermis; and third-degree burns, which destroy both the dermis and the epidermis. = Bones: the Body’s Support  =

Skeletal System Structure
The adult human skeleton contains 206 bones. The axial skeleton includes the skull and the bones that support it, and the appendicular skeleton contains bones pertaining to the limbs and related structures.

Joints: Where Bones Meet
Invertebrate joints are found where two or more bones meet. Joints facilitate the movement of bones in relation to one another. Joints are often held together by ligaments. A ligament is a tough band of connective tissue that attaches bones to each other. Joints with large ranges of motion typically have more ligaments. In movable joints, the ends of bones are covered by cartilage. Cartilage allows for smooth movement between bones. Joints such as in the shoulder and knee have fluid-filled sacs called bursae, which decrease friction and are located on the outside of the joints.

Compact and Spongy Bone
Bones are composed of two different types of bone tissue, compact bone and spongy bone. Compact bone is a hard layer of living bone cells that receive oxygen and nutrients from small blood vessels. Compact bone surrounds spongy bone, which contains many holes and spaces.

Formation of Bone
Vertebrate skeletons are made up of cartilage. In the ninth week of human development, bone begins to replace cartilage. Blood vessels stimulate cells in cartilage to become osteoblasts, which are potential bone cells. The adult skeleton is almost all bone, with cartilage found only in places where flexibility is needed.

Bone Growth
Bones grow in both length and diameter. It occurs on the outer surface of the bone. Increased production of sex hormones during teen years causes osteoblasts to divide more rapidly, causing a growth spurt. However, this also causes the growth centers at the ends of the bone to degenerate, eventually slowing growth.

Skeletal System Functions
The primary functions of skeletons are to provide framework for the body and protection for internal organs. They also allow for efficient body movement. The skeleton provides attachment points for muscles, which need firm points to pull against to work effectively. There are two kinds of marrow. Red marrow produces blood cells, and yellow marrow consists of stored fat.

Bones Store Minerals
Stored minerals include calcium and phosphate.

Bone Injury and Disease
Bones become more brittle with age. A disease called osteoporosis causes loss of bone volume and mineral content, which makes bones more porous and brittle. When bones are broken, a doctor moves them back into position and immobilizes them with a cast or splint until bone tissue regrows. = Muscles for Locomotion  =

Three Types of Muscles
Nearly half of the body is made up of muscle, which is made up of bound together fibers. Most muscle fibers have been there since birth. The main types of muscles are: Smooth muscle, which is found in the walls of internal organs; cardiac muscle, which is an interconnected muscle found in the heart; and skeletal muscle, which is attached to and moves the bones.

Skeletal Muscle Contraction
Any kind of movement contracts some muscles and moves others. Muscles are made up of fibers, which are long, fused muscle cells.

Muscle Strength and Exercise
Muscle strength is based on the strength of fibers and amount that contract together, not the amount. Regular exercise stresses muscles, resulting in an increase in diameter. Muscle cells use aerobic respiration, unless there isn’t enough oxygen, in which case they use lactic acid fermentation. Lactic acid is built up during exercise, and when a person catches their breath, it’s broken down.