Introduction to Body Structure Ch. 38 Biology Ms. Haut
Levels of Structural Organization • Cell—smallest functional unit • Tissue—group of similar cells performing a common function • Organ—combination of 2 or more tissues that work together • Organ system—combination of 2 or more organs working together to perform a common function
Epithelial Tissue • Lines most body surfaces— inside and out • Protects other tissues from dehydration and physical damage
Nervous Tissue • Consists of nerve cells (neurons) • Carries messages throughout the body
Connective Tissue • • • Support, protect, and insulate the body Fat Cartilage Bone Tendons blood
Muscle Tissue • Skeletal – Voluntary—can control contractions – Moves bones in trunk and limbs • Smooth – Involuntary—can’t control contractions – Slow, long-lasting contractions – Line blood vessels and digestive tract • Cardiac – Involuntary – Found only in the heart
Skeletal Muscle
Smooth Muscle
Cardiac Muscle
Body Cavities • House and protect major internal organs • Organs suspended in fluid that supports their weight
Endothermy • Mammals are endothermic – Have ability to maintain a constant internal body temperature • Humans maintain a body temp. of 38 C (99 F ) – The body uses a lot of energy to maintain a stable internal condition (homeostasis)
Skeletal System • Functions to support the body • Two Main Parts – Axial skeleton • Bones of the skull, spine, ribs, and sternum – Appendicular skeleton • Forms the appendages (limbs) • Bones of the arms, legs, pelvis, and shoulder
Bone Structure
Bone Growth • In early development the skeleton is made mostly of cartilage – Serves as template for bone formation • Cartilage is gradually replaced by bone as calcium and minerals are deposited • New bone cells (osteocytes) are added in layers around hollow channels (Haversian canals) which contain blood vessels
Compact Bone Concentric rings of bone surround the Haversian canals
Longitudinal Growth occurs along the Growth Plate in Bones
Importance of Calcium: Got Milk? • Almost all of the body's calcium (99%) is present in the bones and teeth. The remaining 1% is found in the blood and some nerve cells • The amount of calcium in the blood must remain at a steady level • If your calcium intake is inadequate, the body uses the 'stored' bone calcium to maintain the blood calcium. – This mobilization of bone calcium can lead to osteoporosis, i. e. , a reduction in the amount of calcium in the bone leading to weak and thin bones.
Joints Fasten Bones Together • Pads of cartilage cushion the ends of the bones of a joint • Bones of a joint are held together by ligaments (connective tissue)
Muscular System • Skeletal muscles move the body • Muscles are attached to bones by tendons • Muscles typically work in opposing pairs
Opposing Muscle Pairs
Muscles Move Skeletal Parts • Skeletal Muscle – Each muscle fiber is a single cell with many nuclei – Each fiber is composed of a bundle of myofibrils which contain myofilaments • Thin filaments—actin • Thick filaments—myosin – Striated appearance due to sarcomeres (basic functional unit)
Muscle Contractions: “Sliding-Filament Model” • Thin and thick filaments of the sarcomere slide past one another to shorten the length of the muscle
Cyclic Interaction Between Actin and Myosin in Muscle Contraction
Sliding-Filament Model
Integumentary System • • Skin, hair, and nails Skin is the largest organ of the body Protects the body from injury Provides 1 st line of defense against disease
Skin has 2 Distinct Layers • Epidermis – Outermost layer – Made up of several layers of epithelial cells – Flattened, dead cells that contain keratin (protein that waterproofs skin) – Damaged cells replaced by cells below – Inner layer contains melanin—absorbs UV radiation
Skin has 2 Distinct Layers • Dermis – Functional layer of skin – Presence of connective tissue makes it tough and elastic – Contains nerve cells, blood vessels, and hair follicles – Nerve cells sense temperature and pain – Blood vessels responsible for regulating temperature – Sweat glands—evaporation of sweat from skin cools body
Acne • Chronic inflammatory condition that involves the skin’s oil-producing glands • Oil glands release sebum (oily secretion that lubricates the skin) – Released through ducts (exocrine glands) • Acne results from the duct pores being clogged with oil, dirt, and bacteria • Surrounding tissue gets infected and inflamed, and pores accumulate pus, producing pimples
Skin Cancer • Results from genetic mutations from overexposure to UV radiation • Carcinoma—originates in cells without melanin – Can be treated early on • Malignant melanoma— mutation occurs in melanin producing cells – Grow quickly and spread easily
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