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Biology 1215 Outline

Biology 1215 Lecture Notes

Chapter 40: An Introduction to Animal Structure and Function
Outline

  • Levels of structural organization
  • Function correlates with structure in the tissues of animals
  • Epithelial tissue
  • Connective tissue
    • Loose connective tissue
    • Adipose tissue
    • Fibrous connective tissue
    • Cartilage
    • Bone
    • Blood
  • Muscle tissue
  • Nervous tissue
  • Organ systems of an animal are interdependent
  • Body plans and the external environment
  • Regulating the internal environment
  • Introduction to the bioenergetics of animals
  • Metabolic rate provides clues to an animal’s bioenergetic "strategy"
  • Metabolic rates vary
  • Body size and metabolic rate

Levels of structural organization

  • All life is characterized by hierarchical levels of organization:
    • Atoms; molecules; organelles; cell; tissues; organs; organ systems; organism; super-organism?
    • Cell is lowest level of organization capable of living autonomously.

Function correlates with structure in the tissues of animals

  • Tissue = organized collection of cells, together with the material between them, that performs one or a few specific functions. Reflects the fact that cells cooperate.
  • Histology = the study of tissues.
  • Cells in tissues may be held together by a sticky coating or woven together in a fabric of extracellular fibers.
  • There are four types of tissues:
    1. Epithelial tissue
    2. Connective tissue
    3. Muscle tissue
    4. Nervous tissue.

Epithelial tissue (Fig 40.1)

  • Composed of epithelial cells forming sheets of tightly packed cells. Epithelial tissue plays vital role in creating an internal environment that is drastically different from the external environment and maintaing physical and chemical conditions inside an animal that are relatively constant.
  • Covers external and internal body surfaces, lines body cavities and ducts, and forms secretory portions of most glands.
  • Nearly always sit on a basement membrane serving to attach epithelium to underlying connective tissue
  • Two broad categories of epithelial tissue:
    • 1. Covering epithelial tissue
      • solid sheet of cells that acts as a covering or lining. e.g. skin, line the respiratory, digestive, urinary, and genital tracts, line body cavities, cover many organ surfaces, line blood vessels, and form ducts
      • always exhibit a free surface
      • functions in protection of underlyling tissues (skin) from mechanical injury, invasion by microbes, and fluid loss.
      • transport of substances into or out of the body or from one site in the body to another (i.e across epithelial cells)
    • 2. Glandular epithelial tissue
      • collection of epithelial cells forming a secreting structure known as a gland (not all glands are epithelial)
      • involved in secretion, movement from the inside of a cell to the outside (e.g. mucous, digestive enzymes, sweat, milk, wax, most hormones).
  • Categorized by number of layers and shape of the free surface cells:
    • Simple epithelium = one layer of cells
    • Stratified epithelium = multiple layers
    • Pseudostratied epithelium = one layer, but appear to be multiple because cells vary in length.
    • Cell shapes: cuboidal, columnar, squamous (Flat door tiles).
  • Structure correlated with function:
    • simple squamous epithelium is leaky and is specialized for exchange of materials by diffusion (such as in blood vessel linings and air sacs in lungs).
    • ciliated cells (lining of respiratory tracts and fallopian tubes) move materials over surface of epithelium.
    • simple columnar cells of intestine have microvilli to maximize surface area for absorption of digested food
    • stratified squamous epithelium ideal for protection of underlying tissues. Also continually divide, pushing cells "above" them upward, where they are shed from surface. Found in body surfaces subject to friction (e.g. outer layer of skin (keratinized) and linings of the mouth, esophagus and vagina)

Connective tissue (Fig 40.2)

  • Characterized by sparse cell density. Cells scattered through an extensive extracellular matrix.
    • matrix functions to bind and support other tissues.
    • matrix is web of fibers embedded in a homogenous ground substance (may be liquid, semisolid, or solid).
  • Occur everywhere in the body. It's the "glue" of the body.
  • Generally functions in support, protection and binding together of other body tissues
  • Major types of connective tissue include
    • 1) loose connective tissue
    • 2) adipose tissue
    • 3) fibrous connective tissue
    • 4) cartilage
    • 5) bone and
    • 6) blood
  • Loose connective tissue
    • Holds organs in place and attaches epithelia to underlying tissues. Serves as filler between body parts.
    • Most common connective tissue.
    • Consists of a loose wieve of 3 types of proteinaceous fibers:
      • Collagen fibers: bundles of fibers containing 3 collagen molecules each. Provides tensile strength; resists stretching.
      • Elastic fibers: long threads of protein called elastin. Elastic properties gives tissues a resilience to quickly return to the original shape.
      • Reticular fibers: branched and form a tightly woven fabric joining connective tissue to adjacent tissues.
    • Consists of two cell types:
      • Fibroblasts: secrete the proteins of the extracellular fibers.
      • Macrophage: phagocytic amoeboid cells functioning in immune defense of body.
  • Adipose tissue
    • Loose connective tissue specialized to store fat in adipose cells.
    • Little intercellular material between cells.
    • Functions in insulation and storage.
  • Fibrous connective tissue
    • Dense due to arrangement of a large number of collagenous fibers in parallel bundles, which imparts great tensile strength.
    • Found in tendons, and ligaments.
  • Cartilage
    • Composed of collagen fibers embedded in chondroitin sulfate, a glycoprotein ground substance.
    • Cartilage cells (chondrocytes).
      • secrete both collagen and chondroitin sulfate, making cartilage both strong and flexible.
      • confined to lacunae, scattered spaces within ground substance.
    • Comprises the skeleton of all vertebrate embryos.
      • In most vertebrates, eventually replaced with bone. Retained in nose, ears, trachea, intervertebral disks, and ends of some bones.
      • Sharks retain cartilagenous skeleton as adults.
    • Not vascularized. Lack of blood supply means that chondrocytes must exchange nutrients and and wastes by diffusion. Explains its limited capacity for growth and repair.
  • Bone
    • Mineralized connective tissue.
    • Osteoblasts, bone-forming cells, deposit matrix of collagen and calcium phosphate which hardens into the mineral hydroxyapetite. Combination of collagen and hydroxyapetite make bone hard but not brittle.
    • Consists of repeating Haversian systems (concentric layers or lamellae deposited around a central canal containing blood vessels and nerves.
    • Osteocytes are located in spaces called lacunae surrounded by a hard matrix and are connected to each other by cell extensions called canaliculi.
    • In long bones, only the outer area is hard and compact; the inner area is filled with spongy bone tissue called marrow.
  • Blood
    • Blood is the river of life that surges within us. All cells in the body are sustained by this river to obtain nutrients and carry away metabolic wastes. It is the liquid that flowswithind the cardiovascular system.
    • Functions in the transport of substances from one site in the body to another, functionally connecting different body parts. The main functions of blood are:
      • Substance distribution
        • delivery of oxygen from lungs and nutrients from digestive tract to all body cells
        • transporting metabolic wastes
      • Regulating blood levels of particular substances.
      • Body protection.
    • Liquid extracellular matrix of plasma, which contains water, salts and proteins. Fluid matrix of blood not secreted by the cells of this tissue.
      • plasma accounts for ~55% of blood volume.
      • only tissue that's a liquid
      • collagen and elastin fibers typical of other connective tissues are absent from the blood, but dissolved fibrous proteins become visible as fibrin strands when blood clotting occurs.
    • Cellular component contains:
      • leukocytes
        • white blood cells that work on various ways to protect the body.
      • erythrocytes (oxygen transport)
        • make up most of cell mass (45% total vol).
        • Hematocrit = % erythrocytes per volume of blood.
      • platelets (cell fragments functioning in clotting)
      • Blood cells are made in red marrow of long bones).
    • Physical characteristics:
      • sticky, opaque fluid with a metallic taste.
      • blood more dense than water (~5X more viscous).
      • slightly alkaline: pH = 7.35 - 7.45.
      • accounts for ~8% of body weight; average adult contains 5 -6 L.
    • Blood is enormously important in the practice of medicine. Clinitians examine it more than any other tissue when trying to determine the cause of disease..

Muscle tissue (Fig 40.4)

  • Muscle tissue consists of long, excitable cells capable of contraction.
  • In muscle cell cytoplasm are parallel bundles of microfilaments made of contractile proteins, actin and myosin.
  • Most abundant tissue in most animals.
  • Three types of muscle tissues:
    • Skeletal muscle; responsible for voluntary movements
      • attached to bones by tendons
      • microfilaments aligned to form banded striated appearance.
    • Cardiac muscle; forms contractile wall of heart
      • cells are striated and branched
      • Ends of cells joined by intercallated disks, which relay contractile impulse from cell to cell.
      • involuntary control
    • Visceral muscle (smooth muscle); walls of internal organs and blood vessels.
      • Spindle-shaped cells contract slowly, but can retain contracted condition longer than skeletal muscle.
      • responsible for involuntary movements (eg. churning of stomach).

Nervous tissue

  • Nervous tissue senses stimuli and transmits signals from one part of the animal to another .
    Neuron = nerve cell specialized to conduct an impulse (Fig 40.3). Consists of:
    • cell body
    • dendrites
    • axon

Organ systems of an animal are interdependent

  • Tissues are organized into organs in all but the simplest of animals.
  • May be layered, such as dermis of human.
  • Many organs suspended by sheets of connective tissue called mesenteries.
  • Organs may be organized into organ systems.
    Organ system = several organs with separate functions that act in a concerted manner (e.g. digestive, respiratory, circulatory, nervous systems) (Table 40.1)
  • Systems are interdependent; an organism is a living whole greater than the sum of its parts.

Body plans and the external environment

  • Physical laws constrain animal form (e.g. fusiform shape of marine animals enables fast movement in water)
  • Body plans and exchange with the environment
    • Animal cells must have enough surface area in contact with an aqueous medium to allow adequate environmental exchange of dissolved oxygen, nutrients and wastes. This requirement imposes constraints on animals size and shape.
    • Unicellular organisms must have sufficient surface area of plasma membrane to service entire volume of cytoplasm and thus are limited in size.
    • Some multicellular animals have a body plan that places all cells in direct contact with their aqueous environment. Such body plans include (Fig 40.7):
      • Two layered sac (hydra)
      • Flat-shaped body (planaria).
    • Most complex animals have a smaller surface volume ratio thus lack adequate area for exchange on the outer surface (Fig 40.8).
      • Instead, highly folded, moist internal surface exchange these specialized materials with environment.
      • The circulatory system shuttles materials between these specialized exchange surfaces.
    • Although logistic problems occur with environmental exchange, there are some distinct advantages to compact body form:
    • Environmental exchange surfaces are internal and protected from desiccation, so the animal can live on land.
    • Cells are bathed with internal fluid, so the animal can control the quality of the cells immediate environment.

Regulating the internal environment

  • Homeostatic mechanisms regulate an animal’s internal environment
  • Interstitial fluid = the internal environment of vertebrates, composed of fluid between the cells. Exchanges nutrients and wastes with blood carried in capillaries.
  • Homeostasis = Dynamic state of equilibrium in which conditions remain relatively stable; steady state. Internal conditions kept constant even when external environment changes.Depends on negative feedback circuits.
  • Negative feedback = Homeostatic mechanism that stops or reduces the intensity of the original stimulus and consequently causes change in a variable that is opposite in direction to the initial change.
    • Most common homeostatic mechanism in animals.
    • Lag time between sensation and response, so variable changes slightly above and below set point.
    • Nonbiological example is thermostat. (Fig 40.9)
    • Biological examples include regulation of blood calcium levels (Fig 45.9), temperature regulation (Fig 44.10 ) and blood glucose levels (Fig 41.1).

Introduction to the bioenergetics of animals

Metabolic rate provides clues to an animal’s bioenergetic "strategy"

    • Animals, as living organisms, exchange energy with the environment. Animals are heterotrophic, i.e. acquire energy from organic molecules synthesized by other organisms (Fig 40.7)
    • Bioenergetics, the study of the dynamic balance between energy intake and loss in an organism, gives clues to how an animal adapts to its environment. By measuring the rate of energy use, physiologists can determine:
      • How much food energy an animal needs just to stay alive.
      • The energy costs for specific activities such as walking or running.
        Metabolic rate = total amount of energy an animal uses per unit time; usually measured in kilocalories.
      • Can be determined by:
        • Measuring amount of oxygen consumption for respiration.
        • Measuring amount of heat loss per unit time.

Metabolic rates vary:

    • Minimal rates support basic life functions (breathing)
    • Maximal rates occur during peak activity (can be 4-5 fold higher than minimal rates).
    • Between these extremes, metabolic rates are influenced by many factors:
      • age, sex, size
      • body temp
      • environmental temp
      • food quality and quantity
      • activity level
      • amount of available oxygen
      • hormonal balance
      • time of day
    • Endotherms = animals that generate their own body heat metabolically (mammals and birds)
      • Require more calories to sustain life than ectotherms
        - e.g at 20°C, a human at rest has a metabolic rate of 1300 to 1800 kcal per day, whereas a similar sized ectotherm (croc) has metabolic rate of only 60 kcal per day at 20°C.
      • Many are also homeothermic, as their body temperature must be maintained within narrow limits.
        Basal Metabolic Rate (BMR) = An endothermic animal’s metabolic rate measured under resting, fasting and stress-free conditions.
      • Average human BMR is 1600-1800 kcal/day for adult males; 1300-1500 kcal/day for adult females.
    • Ectotherms = Animals that acquire most of their body heat from their environment.
      • Include fish, amphibians, reptiles and invertebrates.
      • Are energetically different from endotherms; body temp and metabolic rate changes with environmental temp.
      • Because influenced by temp, an ectotherm’s minimal metabolic rate (SMR) must be determined at a specific temp.
      • Standard Metabolic Rate (SMR) = An ectotherm’s metabolic rate measured under controlled temps and under resting, fasting and stress-free conditions.

Body size and metabolic rate

    • Inverse relationship between metabolic rate and size.
      • Smaller animals consume more calories per gram than larger animals.
      • Correlated with a higher metabolic rate and need for faster O2 delivery to tissues. Smaller animals also have higher breathing rates, blood volume (relative to its size), and heart rate.
      • This inverse relationship holds true for endotherms and ectotherms, and is not simply a function of surface area to volume ratio.
    • Body size and shape affect its interactions with its external environment.
    • An animal’s body plan results from a developmental pattern programmed by its genes, a product of natural selection.
    • Body size, Proportions and Posture
      • Body proportions and size-weight relationships change in animal bodies as they become larger.
      • Body design must accommodate the greater demand for support that comes with increasing size. (Strain on body supports depends on an animal’s weight, which increases as the cube of its height or other linear dimension).
      • In mammals and birds, the most important design feature in supporting body weight is posture- leg position relative to main body - rather than bone size. For example:
        • The legs of an elephant are in a more upright position than those of small mammals.
        • Large mammals run with legs extended (reduces strain); whereas small mammals run with legs bent and crouch when standing.
      • Bioenergetics also plays an important role in load-bearing, since crouched posture is partly a function of muscle contraction, powered by chemical energy.

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