Download Chapter 19: The Animal Body and How It Moves

Chapter 19: The Animal Body and How It Moves
19.1 Innovations in Body Design
•Four key innovations have led to the diversity seen in the phylum Animalia
Radial Versus Bilateral Symmetry
•In radial symmetry, the parts of the body are arranged around a central axis
•In bilateral symmetry, the body has a right and left half that are mirror images of each other
–Allows different organs to be located in different parts of the body
•Ultimately led to cephalization
–Evolution of a definite head and brain area
No Body Cavity Versus Body Cavity
•The body cavity supports organs, distributes materials and fosters complex development
•Three body arrangements
–Acoelomates: No body cavity
•Example: Sponges and flatworms
–Pseudocoelomates: Body cavity (pseudocoel) forms between the endoderm and
mesoderm
•Example: Nematodes
–Coelomates: Body cavity (coelom) forms entirely within the mesoderm
•Example: Mollusks, arthropods and vertebrates
Nonsegmented Versus Segmented Bodies
•Segmentation is the subdivision of the body into segments
•Two advantages result from embryonic segmentation
–1. Each segment may develop a more or less complete set of adult organ systems
–2. Locomotion is far more effective because of increased flexibility of movement
Protostomes Versus Deuterostomes
•Deuterostomes evolved from protostomes > 630 mya
•While both are coelomates, they differ in three aspects of embryonic growth
Protostomes
Deuterostomes
How cleavage forms a
hollow ball of cells
Spiral cleavage
Radial cleavage
How the blastopore
determines body axis
Blastopore forms the
mouth
Blastopore forms the
anus
How developmental fate of Determinate cleavage
embryo is fixed
Indeterminate cleavage
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19.2 Organization of the Vertebrate Body
•All vertebrates have the same general architecture:
•Food flows through a long tube from mouth to anus
•Tube is suspended in coelom, which is divided into
•Thoracic cavity – Heart and lungs
•Abdominal cavity – Stomach and intestines
•Body is supported by a skeleton made up of jointed bones
•The skull protects the brain
•The vertebral column protects the spinal cord
•Tissues
–Cells of the same type are organized into tissues
–Tissues form as the vertebrate body develops
–Three fundamental layers of cells
•Endoderm ; Mesoderm ; Ectoderm
•They differentiate into > 100 different cell types
–Adult tissues are grouped into 4 general classes
•Epithelial
•Connective
•Muscle
•Nerve
•Organs
–Structures composed of several different tissues grouped into large structural and
functional units
•Organ systems
–Groups of organs that work together to carry out an important function
Vertebrates contain 11 principal organs systems
•Skeletal system
•Bones, skull, cartilage, ligaments
•Circulatory system
•Heart, blood vessels, blood
•Endocrine system
•Pituitary, adrenal, ductless glands
•Nervous system
•Nerve, sense organs, brain, spinal cord
•Respiratory system
•Lungs, trachea, other air passages
•Immune system
•Lymphocytes, macrophages, thymus, lymph nodes
•Digestive system
•Mouth, esophagus, stomach, intestines
•Urinary system
•Kidneys, bladder, associated ducts
•Muscular system
•Skeletal, cardiac and smooth muscles
•Integumentary system
•Skin, hair, nails and sweat glands
•Reproductive system
•Testes or ovaries
•Associated structures
•
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19.3 Epithelium is Protective Tissue
•The vertebrate body consists of one tube (digestive tract) suspended into another (body cavity:
coelom)
•The outside of the body is covered with cells (skin) derived from embryonic ectoderm
tissue
•The body cavity is lined with cells derived from embryonic mesoderm tissue
•The hollow inner core of the digestive tract is lined with cells derived from embryonic
endoderm tissue
Epithelial cells are produced from all 3 germ layers
–Collectively called the epithelium
–Three important functions
1. Protect tissues from dehydration and mechanical damage
2. Provide sensory surfaces
3. Secrete materials
Epithelium possesses amazing regenerative abilities
•
Epithelial cells are classified into three types according to their shape
•Squamous
•Cuboidal
•Columnar
•
There are three general kinds of epithelial tissue
–Simple epithelium
•Only a single layer thick
•Found in the lining of the lungs and major body cavities
–Stratified epithelium
•Several layers thick
•Found in the skin
–Glands
•Involved in secretion
•Endocrine glands secretes hormones into the blood
•Exocrine glands use ducts to secrete sweat, milk, saliva and digestive enzymes out of the
body
•
•
19.4 Connective Tissue Supports the Body
•Connective tissue is derived from the mesoderm
–Three functional categories
•1. Immune system - Body defense
•2. Skeletal system - Body suppor
•3. Blood and fat cells - Storage and distribution of substances
Immune Connective Tissue
•Two principal immune cells are
•1. Macrophages
•Engulf and digest invading microbes
•2. Lymphocytes
•Make antibodies - Or •Attack virus-infected or cancerous cells
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Skeletal Connective Tissue
•1. Fibroblasts
–The most common kind
–Secrete structurally strong proteins such as collagen into spaces between cells
–2. Cartilage
–Collagen matrix forms in long parallel arrays along lines of mechanical stress
–Found in joint surfaces
–3. Bone
–Collagen fibers are coated with calcium phosphate
•
Storage and Transport Connective Tissue
•Includes
•Adipose tissue
•Accumulates fat
•Erythrocytes (RBC)
•Transport O2 and CO2 in the blood
•The fluid portion of blood is called plasma
•Contains nutrients, wastes and antibodies
A Closer Look at Bone
•Bone is a dynamic tissue that is constantly being reconstructed
–Outer layer is very dense and compact
•Called compact bone
–Interior is a more open lattice structure
• Called spongy bone
New bone is formed in two stages
–1. A matrix of collagen fibrils is secreted by cells called osteoblasts
–2. The fibrils are impregnated by crystals of a calcium phosphate mineral called hydroxyapatite
•Bone is laid down in thin layers around a narrow central channel
–This central canal (or Haversian canal) runs parallel to the length of the bone
•
Two cell types are responsible for bone “remodeling” during growth
•Osteoblasts
•Deposit bone
•Osteoclasts
•Secrete enzymes that digest the bone matrix
Osteoporosis
Excessive bone loss
Usually associated with aging
•
19.5 Muscle Tissue Lets the Body Move
•The distinguishing characteristic of muscle cells is the abundance of contractible protein fibers
–These microfilaments (myofilaments) are made up of actin and myosin
•Muscle contraction occurs when actin and myosin slide past each other
The vertebrate body possesses three different kinds of muscle cells :
Smooth
Skeletal
Cardiac
•
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Smooth Muscle
•Cells are long and spindle-shaped
–Each contains a single nucleus
•Cellular microfilaments are loosely organized
•Found in the walls of blood vessels, stomach and intestines
•Power rhythmic involuntary contractions
Skeletal Muscle
•Produced by fusion of several cells at their ends
–This creates a very long muscle fiber that contains all the original nuclei
–Microfilaments are bunched together into myofibrils
–Found in voluntary muscles
–Power voluntary contractions
Cardiac Muscle
•Composed of chains of single cells, each with its own nucleus
–Chains are interconnected, forming a latticework
–Each heart cell is coupled to its neighbors by gap junctions
–Allow electrical signals between cells
–Cause orderly pulsation of heart
19.6 Nerve Tissue Conducts Signals Rapidly
•Nerve tissue is composed of two kinds of cells
–1. Neurons - Specialized for the transmission of nerve impulses
–2. Glial cells - Support neurons with nutrients, support and insulation
Neuron plasma membranes are rich in ion-selective channels
–These maintain a voltage difference between the cell’s interior and exterior
•Depolarization is the temporary loss of this voltage difference
–It results in a wave of electrical activity, or nerve impulse
•
Each neuron consists of three parts
•1. Cell body – Contains the nucleus
•2. Dendrites – Bring nerve impulses to the cell
•3. Axon – Carry nerve impulses away from the cell
•
Neurons are separated by tiny gaps termed synapses
–Neurons communicate by passing neurotransmitters across these synapses
•Note: A nerve is made up of the axons of many neurons
•
19.7 Types of Skeletons
•There are three types of skeletons in animals
–1. Hydraulic skeleton
•Fluid-filled cavity encircled by muscle fibers
–2. Exoskeleton
•Rigid hard case surrounding the body
•Found in arthropods
•3. Endoskeleton
•Rigid internal skeleton to which muscles attach
•Found in vertebrates and echinoderms
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The Human Skeleton - Made up of 206 individual bones
•Axial skeleton
–Supports the main body axis
–Skull, backbone (spine) and rib cage
–80 bones in all
•Appendicular skeleton
–Supports the arm and legs
–Pectoral and pelvic girdles
–126 bones in all
19.8 Muscles and How They Work
•The major human muscles include the following:
•Pectoralis major, Biceps, Rectus abdominis, Sartorius, Quadriceps, Gastrocnemius
•Skeletal muscles are attached to bones by straps of connective tissue called tendons
•Bones pivot about flexible joints pulled back and forth by attached muscles
–The origin of the muscle is the end attached by a tendon to a stationary bone
–The insertion is the end attached to a bone that moves during muscle contraction
Muscles in movable joints are attached in opposing pairs
–Flexors retract limbs
–Extensors extend limbs
•
Limb movement is always the result of muscle contraction
–Never muscle extension
•There are two types of muscle contraction
–Isotonic
•Muscle shortens, thus moving the bones
–Isometric
•Muscle does not shorten, but it exerts a force
Muscle Contraction
•Myofilaments are made up of actin and myosin
–Actin filaments consist of two chains of actin molecules wrapped around one another
–Mysosin filaments also consist of two chains wound around each other
•One end consists of a very long rod
•The other consists of a double-headed globular region or “head”
•An ATP-powered myosin head-flex mechanism allows the actin filament to slide past myosin
•
In vertebrate skeletal muscle, contraction is initiated by a nerve impulse
•Nerve fibers are embedded in the surface of the muscle fiber forming a neuromuscular junction
–When a signal reaches the end of a neuron
•The neuron releases acetylcholine into the gap between neuron and muscle
–This causes depolarization of the muscle cell
•
Role of Calcium Ions in Contraction
•When a muscle is relaxed, attachment sites for myosin heads are blocked by tropomyosin
For the muscle to contract, tropomyosin must be moved by another protein called troponin
The troponin-tropomyosin complex is regulated by calcium ion concentrations in the
muscle cell
++
•Muscle fibers store Ca
in the sarcoplasmic reticulum - Nerve activity causes the release of
Ca++ and ultimately muscle contraction
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