Protection, Support and Locomotion Chapter 34

Skin The body’s first line of defense against pathogens. Part of the Integumentary System Made up of skin and its appendages (hair and nails) Several functions: Maintain homeostasis by regulating body temperature Sensory response Protects internal structures Produces Vitamin D when exposed to UV radiation Vitamin D is used in absorption of Calcium into the blood

Structure of Skin 3 layers Epidermis (visible layer) Dermis Hypodermis (lowest layer)

Epidermis Outermost layer of skin Made up of 2 layers External layer Consists of dead cells These cells contain keratin, a protein that provides a hardened layer to protect internal structures Internal layer Contains living cells that will soon die Some of these cells contain a color-pigment called melanin Causes skin color and absorbs UV radiation The melanin darkens as it absorbs UV radiation (sun tan) The living cells will eventually die and replace the external layer You lose and replace thousands of skin cells each day Skin appendages push through the epidermis from the dermis

Dermis Inner layer of skin Beneath the internal epidermis Much thicker than the other layers of skin Contains many structures, each with their own purpose Blood vessels-carry blood Nerves-sensation Hair follicles- hair is used for protection and insulation Sweat glands-aid in cooling body Oil glands-prevents hair and skin from drying and inhibits bacterial growth Muscles- Arrector pili causes goosebumps

Hypodermis (Subcutaneous layer) Innermost layer of skin Made up of fat tissue Insulates body

Structure of Skin

Damage and Repair When skin is injured, such as a scrape, epidermal cells in the inner layer divide to replace the injured cells (mitosis) When the injury is deeper, into the dermis, blood flows and clots (scabs) form White blood cells (phagocytes) are released into the injured area to fight any pathogens Skin cells undergo mitosis to fill the injured area, pushing the scab off Burns 1 st degree burns damage the epidermis 2 nd degree burns damage both the epidermis and the upper portion of the dermis 3 rd degree burns destroy the dermis 4 th degree burns destroy the hypodermis and expose bone Graphic images ahead. Turn away if sensitive!!!! You have been warned!

Skeletal System The adult body has 206 bones Newborn babies have about 270 Several fuse during development 2 main parts Axial skeleton Center of body Includes spinal column, ribs, and skull Appendicular skeleton Bones of arms and legs, along with the bones associated with them

Bones that you will need to know You will learn the bones of the appendicular skeleton. I’ll expect you to be able to identify the following: Clavicle Scapula Humerus Radius Ulna Carpals Metacarpals Phalanges (both hand and foot) Pelvis Femur Patella Tibia Fibula Tarsals Metatarsals

Functions of Skeletal System Your bones (organs) compose your skeletal system (organ system) It serves several important functions 1.Gives shape and support to your body 2.Protects internal organs 3.Provide attachment points for muscles 4.Forms blood cells 1.Red marrow forms red and white blood cells 5.Stores minerals 1.Yellow marrow stores fat

Structure of Bone External Bone Bone is covered in a membrane called periosteum Veins, arteries and nerves run through the periosteum into the internal bone Internal Bone Made up of 2 tissues (Compact Bone and Spongy Bone) Compact Bone Hard, strong layer directly under the periosteum Composed of calcium phosphate deposits Protects bone from damage or fracture Spongy bone Many small, open spaces Keep bone lightweight Contain cavities filled with bone marrow

Bone Formation During embryonic development, your skeleton was composed of cartilage The cartilage was broken down and replaced by bone Bone-forming cells are called osteoblasts They deposit Calcium and Phosphorus in bones, which causes the bone to become hardened This creates bone cells, called osteocytes Another type of cell, called Osteoclasts, break down bone tissue

Joints Any place where 2 or more bones come together Many are areas where movement occurs Knee Some do not move Skull consists of 22 total bones, only a few of which move Joints are often held together by ligaments Tough bands of connective tissue Ones you may know: Lateral Collateral Ligament (LCL) Medial Collateral Ligament (MCL) Anterior Cruciate Ligament (ACL)

Types of Movable Joints Gliding Joints Allow bones to glide past one another Found in wrist and ankles Hinge joint Allow for flexion and extension of bones Knee and elbow Pivot Joint Allow bones to rotate Radius and ulna/humerus, head/vertebrae Ball and Socket Joint Allows for circular motion Humerus/scapula

The Muscular System 3 main types of muscle Smooth muscle Line digestive and reproductive system Usually involuntary Do not require conscious control Cardiac muscle Found in the heart Involuntary Skeletal muscle Attached to bones by tendons (thick connective tissue) Mostly voluntary Require conscious control Most of the muscles in your body

Muscle Structure Muscles are composed of muscle fibers Each fiber is composed of smaller units called myofibrils Myofibrils are composed of smaller filaments Thick filaments are called myosin Smaller, inner filaments are called actin Myofibrils are broken into segments called sarcomeres

Sliding Filament Theory Nerve impulses cause the release of ions Actin filaments slide towards one another, shortening the sarcomere Myosin does not move The shortening of the sarcomere causes the contraction of the muscle

Building Muscle You cannot increase the number of muscle fibers that you have Strength does not depend on number Strength depends on the thickness of the fibers Strength training strains the muscle fibers To compensate, the muscles add myofibrils