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 38C (99F )

– 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 1st 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