Chapter 32 Notes: The Integumentary, Skeletal, and Muscular Systems

The Integumentary System The integumentary system is a system of organs in the body that covers and protects the body. The main organ of this system is the skin. Skin is composed of four different types of tissues. Those four different types of tissues found in the body and in our skin are epithelial tissue, connective tissue, muscle tissue and the nerve tissue.

Structure of the Skin

The Structure of the Skin The top layer of the skin is called the epidermis. The epidermis is a layer of cells about 10 to 30 cells thick that is made up of epithelial cells. The epidermis is about as thin as paper. The cells of the epidermis contain a protein substance called keratin, which waterproofs and protects the cells and tissues below it.

The Epidermis

The Epidermis The very top layer of cells of the epidermis are constantly being shed. In fact, a large portion of the dust in your house consists of dead skin cells from the epidermis. An entire layer of skin cells can be lost and replaced each month. The inner layer of epidermis contains cells that are continually dividing by mitosis.

The Epidermis Cells that are found in the inner layer of the epidermis called melanocytes contain a protective pigment called melanin. Melanin is a pigment that absorbs (UV) ultraviolet radiation. The amount of melanin in a person’s skin determines the color of the skin. Skin color is primarily determined by genes, but it can also be produced in response to bright sunlight when a person gets a suntan.

Melanin

Structure of the Skin Below the epidermis is the dermis. Dermis is about 15–40 times thicker than the epidermis. The dermis consists mostly of connective tissue. The function of this connective tissue is to prevent the skin from tearing, and it makes the skin more elastic. Within the dermis there is also nerves, muscles, glands, and hair follicles.

Structure of the Skin Below the dermis is the subcutaneous layer. The subcutaneous layer is also a layer of connective tissue that stores fat and insulates the body. Hair, fingernails and toenails are also part of the integumentary system that are made of keratin.

Structure of the Skin Hair cells grow out of narrow cavities in the dermis called hair follicles. Most hair follicles have sebaceous glands or oil glands associated with them. Sebaceous glands lubricate the skin and hair. Acne occurs when the sebaceous glands and hair follicles get blocked.

Hair Follicles and Sebaceous Glands

Functions of the Integumentary System Temperature regulation – insulating fat, arrector pili muscles, and sweat glands are just some of the ways that skin can regulate body temp. Blood vessels can also constrict and dilate to regulate body temp. Vitamin production – skin responds to sunlight by producing vitamin D. Vitamin D increases absorption of calcium into the bloodstream for bone growth. Protection – first line of defense against disease and foreign substances. Prevents water loss.

Damage to the Skin Cuts and scrapes – minor cuts and scrapes only affect the epidermis. When deep cuts occur, blood clots must form a scab (with platelets) and white blood cells remove bacteria from the wound. Burns – minor (first degree) burns generally affect the epidermis and redness and swelling may occur, But severe (second and third degree) burns go deep into the dermis and subcutaneous layers, and blisters or loss of skin function may occur.

Damage to the Skin Skin Cancer – too much exposure to the sun or tanning beds is believed to cause skin cancer. Skin cancer is the most common form of cancer in the United States. There are two types of skin cancer: melanoma and non-melanoma. Melanoma begins in the melanocytes in the epidermis. Melanoma is the deadliest form of skin cancer. 1 person dies every hour from melanoma in the U.S.

The Muscular System The human body has three different muscle tissues; smooth, cardiac, and skeletal muscles. Smooth muscle – involuntary (can not be consciously controlled) muscles that control internal organs like the stomach and intestines. No striations. Cardiac muscle – involuntary muscle that controls the heart. Few nuclei connected by gap junctions. The main structural difference between smooth and cardiac muscle is that cardiac muscle has striations and smooth muscle does not.

The Muscular System Most muscles of the body are skeletal muscles. Skeletal muscles – voluntary (can be consciously controlled) muscles that are attached to bones by tendons. Muscles striated and contain many nuclei. Skeletal muscles are responsible for movement. Tendons – tough bands of connective tissue that connect skeletal muscles to bones. Skeletal muscles are striated like cardiac muscles. Cardiac muscles have bands called intercalated discs that separate different muscle cells.

Muscle Types

Muscle Types

Skeletal Muscle Structure and Function Most skeletal muscles are arranged in opposing, or antagonistic pairs. A good example of this is your biceps and triceps. They work against each other. Skeletal muscles are arranged into fibers. Each fiber is arranged into smaller strands of muscle tissue called myofibrils. Myofibrils are made up of small protein filaments called myosin and actin.

Skeletal Muscle Structure and Function The myofibrils are arranged into different sections called sarcomeres. A sarcomere is the part of the muscle that contracts. The striations of skeletal muscles are the result of sarcomeres. When a nerve impulse is sent to a muscle, the actin filaments slide in toward the myosin filaments in the center of the sarcomere.

Skeletal Muscle Contraction

Are you a long distance runner or a sprinter? Believe it or not, this probably has more to do with genetics than you may think. Slow-twitch muscles – more endurance, less fatigue, more mitochondria, more myoglobin which means more oxygen, darker colored. Fast-twitch muscles – rapid burst of speed, more strength, muscles fatigue easily, less mitochondria available, less myoglobin which means less oxygen, more lactic acid, lighter colored, increased number of myofibrils, increased muscle size (diameter).

The Structure of the Skeletal System The human body has 206 bones. The human skeleton is divided into two different divisions: the axial skeleton and the appendicular skeleton. The axial skeleton includes the skull, the vertebral column, the ribs, and the sternum. The appendicular skeleton includes the bones of the shoulders, arms, hands, legs, and feet.

The Axial and Appendicular Skeleton

The Structure of Bone There are two types of bone tissue; compact bone and spongy bone. Compact bone is dense and strong, and it provides strength and protection. The outer layer of all bones are composed of compact bone. Spongy bone is less dense, it is porous and has many cavities that contain bone marrow, and is usually found in the center or end of bones.

Compact and Spongy Bone

The Structure of Bone Running the length of compact bones are tube-like structures called osteons. Osteons contain blood vessels and nerves. The blood vessels provide oxygen and nutrients to living bone cells called osteocytes. There are two types of bone marrow; red bone marrow and yellow bone marrow. Red blood cells, white blood cells and platelets are produced in the red bone marrow. Yellow bone marrow consists of stored fat.

Compact Bone Structure

Bone Formation and Maintenance During early fetal development, cartilage develops into bone forming cells. The process of bone formation from osteoblasts is called ossification. Osteoblasts are bone forming cells. Osteoblasts are responsible for bone growth and repair. Cells that are responsible for breaking down old, worn out bones are called osteoclasts.

Joints and Ligaments Joints occur wherever two or more bones meet. Ball and socket – hips and shoulders Pivot – one example is the radius and ulna Hinge – elbows and knees Gliding – wrists, ankles, and some vertebrae Sutures – immovable joints like the sutures that attach all of the bones of the skull. The bones connected at joints are held together by tough bands of connective tissue called ligaments.

Functions of the Skeletal System Support – legs, pelvis and vertebral column support the entire body. Protection – Skull protects the brain, vertebrae protects the spinal cord, rib cage protects the vital organs (heart, lungs, liver). Formation of blood cells – red bone marrow produces blood cells and platelets. Reservoir – stores calcium and phosphorus. Movement – attachment point for muscles.