1. An Introduction to Animal Structure and Function
Chapter 36
AP BIOLOGY

2. Outline Levels of Structural Organization
Function correlates with structure in the tissues of animals.
The organ systems of an animal are interdependent
Introduction to the Bioenergetics of Animals.
Animals are heterotrophs that harvest chemical energy from the food they ingest.
Metabolic rate provides clues to an animal’s bioenergetic strategy
Metabolic rate per gram is inversely related to body size among similar animals.

3. Outline cont. Body Plans and the External Environment
Physical support on land depends on adaptations of body proportions and posture.
Body size and shape affect interactions with the environment.
Regulating the internal environment.
Mechanisms of Homeostasis moderate changes in the internal environment
Homeostasis depends on feedback circuits.

4. Levels of Structural Organization
All life is characterized by hierarchical levels of organization with the cell being the lowest level that can live independently as an organism.
In most animals, combinations of tissues make up functional units called organs. Organs work together to form organ systems.
An example is the human digestive system which consists of stomach, small intestine, large intestine, gall-bladder, and several other organs.

5. Function correlates with structure in the tissues of animals.
Tissues are groups of cells with a common structure and function. A tissue may be held together by a sticky extracellular matrix that coats the cells or weaves them together in a fabric of fibers .
Tissue – from Latin “weave”
Epithelial tissue covers the outside of the body and lines organs and cavities within the body. This tissue occurs in sheets of tightly packed cells. They are closely joined with little material between them.

6. Epithelial tissue cont.
In many epithelia, the cells are riveted together by tight junctions. This tight packing enables the epithelium to function as a barrier protecting against mechanical injury, invasive microorganisms, and fluid loss.
The free surface of the epithelium is exposed to air or fluid whereas the cells at the base of the barrier are attached to a basement membrane, a dense mat of extracellular matrix.

7. Epithelial tissue cont
Basement membranes perform many different functions such as helping organize events in cellular metabolism, filtering wastes from the blood in the kidney, and providing routes of migration for cells during development.
A simple epithelium has a single layer of cell, whereas a stratified epithelium has multiple layers of cells. A pseudostratified epithelium is single layered but it appears stratified because the cells vary in length. The shape of the cells that are at the free surface of an epithelium cuboidal, columnar, or squamous.

8. Epithelial tissue cont
As well as protecting the organs they line, some epithelium absorb or secrete chemical solutions. The epithelial cells that line the lumen of the digestive and respiratory tracts form a mucous membrane. This membrane secretes a mucus that keeps the surface moist. The free epithelial surfaces of some mucous membranes have beating cilia that move the film of mucus along the surface. An example would be the ciliated epithelium of our respiratory tubes.

10. Connective Tissue
Connective tissue serves mainly to bind and support other tissue. These tissue have a sparse population of cells scattered throughout an extracellular matrix. In most cases the substances of the matrix are secreted by the cells of the connective tissue. Connective tissue fibers are of three kinds. Collagenous fibers are made of collagen, the most abundant protein in the animal kingdom. These don’t tear easily when pulled lengthwise.
Elastic fibers are long threads made of a protein called elastin. This fiber is responsible of restoring the shape of your skin after you pinch it.

11. Reticular Fibers
Reticular fibers are very thin and branched Composed of collagen and continuous with Collagenous fibers, they form a tightly woven fabric that joins connective tissue to adjacent tissues.
In vertebrates, the major types of connective tissues are loose connective tissue, adipose tissue, fibrous connective tissue, cartilage bone, and blood.

12. Connective Tissues
Loose connective tissue is the most widespread in vertebrates. It holds organs in place by binding epithelia to underlying tissues.
Loose connected tissue has two types of cells. Fibroblasts secrete the protein ingredients of the extracellular matrix while the macrophages amoeboid cells that engulf bacteria and the debris of dead cells by phagocytosis.
Adipose tissue is a form of loose connective tissue that stores fat. Heredity, exercise, and the amount of fat we eat can affect the amount of fats adipose cells store.

13. Fibrous Connective Tissue.
This type of tissue is dense due to its large numbers of Collagenous fibers. This type of connective tissue is found in tendons and in ligaments.
Cartilage has an abundance of Collagenous fibers embedded in a rubbery matrix. Chondroitin sulfate and collagen are secreted by Chondrocytes, cells confined to scattered places. The skeletons of sharks are made of cartilage. Most of the cartilage in human embryos is replaced by bone as the embryo matures.

14. Bone
Bone is a mineralized connective tissue supporting the body of most vertebrates. Osteoblasts are bone forming cells which deposit a matrix of collagen but they also release calcium, magnesium, and phosphate ions. These harden within the matrix into the mineral hydroxyapatite. The combination of hard mineral and collagen makes bone harder than cartilage without being brittle. Hard mammalian bone consists of repeating units called Haversian systems. In long bones such as the femur in your thigh, only the outer region is hard compact bone.

15. Blood
Blood functions differently from other connective tissues it meats the requirements of having an extensive extracellular matrix. In blood the matrix is a liquid called plasma. Plasma consists of water, salts, and many dissolved proteins. Two types of blood cells are red blood cells, which carry oxygen and white blood cells which function in defense against viruses, bacteria, and other invaders. Platelets aid in blood clotting.

17. Nervous Tissue
Nervous tissue senses stimuli and transmits signals from one part of the animal to another. The functional unit of nervous tissue is the neuron, or nerve cell. Neurons consist of a cell body and two or more extensions called dendrites and axons which may be as long as a meter in humans. Dendrites transmit impulses from their tips toward the rest of the neuron. Axons transmit impulses toward another neuron or toward an effector, a structure that carries out a body response.

18. Muscle Tissue
Muscle tissue is composed of long cells called muscle fibers that are capable of contracting when stimulated by nerve impulses. Muscle is the most abundant tissue in most animals and muscle contraction accounts for much of the energy consuming cellular work in an active animal.
Attached to bones by tendons, skeletal muscle is responsible for voluntary movements of the body. Skeletal muscle is also known as striated muscle because the arrangement of overlapping filament gives the cells a striped appearance.

20. Muscle
Cardiac Muscle forms the contractile wall of the heart. It is striated like skeletal muscle, but cardiac cells are branched and the ends of the cells are joined by intercalated discs.
Smooth muscle lacks striations and is found in the walls of the digestive tract, bladder, arteries, and other internal organs. Smooth muscles are responsible for involuntary movements of the body, such as the churning of the stomach.

22. The organ systems of an animal are interdependent.
In some organs, such as the skin of a a vertebrate, the tissues are arranged in layers. The vertebrate stomach has four major tissue layers. A thick epithelium lines the lumen and secretes mucus into it. Yet another layer of connective tissue encapsulates the entire stomach.
Many of the organs of vertebrates are suspended by sheets of connective tissue called mesenteries in body cavities filled or moistened with fluid. Mammals have a thoracic cavity housing the lungs and heart that is separated from the lower abdominal cavity by a sheet of muscle called the diaphragm.

23. Organ Systems
Organ systems carry out the major body functions of most animals. Each organ system consists of many organs that have specific functions, but the efforts of all organs must be coordinated for the animal to survive.
Any organism weather a protist or an assembly of organ systems is a coordinated living whole rather than just the sum of its parts.

24. Introduction to the Bioenergetics of Animals
One of the defining features of life is the exchange of energy with the environment. Food consumed by heterotrophs is digested by enzymatic hydrolysis and energy containing molecules are observed by body cells. Cells harvest chemical energy from some of the molecules by cellular respiration and fermentation. Chemical energy remaining after the needs of staying alive are met can be used in biosynthesis, reproductive products and new tissues develop as cells construct their own macromolecules using chemical energy.

25. Metabolic Rate provides clues to animal’s bioenergetic strategy.
The total amount of energy an animal uses is called its metabolic rate. Energy is measured in calories or kilocalories. Metabolic Rate can be measured by monitoring an animal’s heat loss per unit of time. This is done by placing the animal in a calorimeter. Another way to determine metabolic rate is to measure the amount of oxygen consumed by the animal’s cellular respiration. Maximal metabolic rates occur during peak activity. Minimal rates support the basic functions that maintain life.

27. Metabolic Rate provides clues to animal’s bioenergetic strategy.
Birds, humans, and insects are usually active and have the highest metabolic rates. Birds and mammals are endothermic, meaning their bodies are warmed by heat generated by metabolism. Their body temperature must be maintained at a certain level to sustain life.
The metabolic rate of an endotherm at rest with an empty stomach, and experiencing no stress is called the basal metabolic rate (BMR) The average human BMR is 1500 – 1600 kcal.

28. Standard Metabolic Rate
Ectotherms are energetically different from endotherms. Their body temperature changes with the temperature of their surroundings, and so does their metabolic rate. The metabolic rate of a resting, fasting, nonstressed ectotherm is called its standard metabolic rate (SMR). Metabolic rates are highest during intense physical exercise, with maximal rates about five to ten times greater than BMR or SMR.

29. Metabolic Rate per Gram is inversely related to body size among similar animals.
Physiologists have determined that the amount of energy it takes to maintain each gram of body weight is inversely related to body size. Each gram of a mouse consumes more energy than the gram of an elephant, even though the whole elephant uses far more calories than the mouse. The smaller mammal also has a higher breathing rate, greater blood volume, and a higher heart rate. One hypothesis for this is stems from the surface are to volume relationship. This hypothesis is not supported by tests and so answers to this inverse relationship are still to be found.

30. Body Plans and the External Environment.
An animals body design must account for the greater demand for support that comes with increasing size. Imagine an elephant with the legs of a mouse, the feeble legs would collapse under the body’s huge weight. Body posture, the placement of legs relative to the main body is a more important design for support. Muscles and tendons which hold the legs of most animals straight and under the body bear most of the load .

31. Body size and shape affect interactions with the environment.
An animals body must be arranged so that all of its living cells are bathed in an aqueous medium, as a requirement of maintaining the fluid integrity of the cells plasma membranes. Exchange with the environment occurs as dissolved substances diffuse and are transported across plasma membranes. A large cell has less surface area relative to its volume than a smaller cell of the same shape. This is one reason nearly all cells are microscopic.

33. Body size and shape cont.
Multicellular animals are composed of microscopic cells each with its own plasma membrane that functions as a loading and unloading platform for a modest volume of cytoplasm. A flat body shape is another way to maximize exposure to the surrounding medium. Two layered sacs and flat shapes are designs that put a large surface are in contact with the environment, but these simpler forms don’t allow complexity in internal organization.

34. Animal Structure
Whales and most other animals have extensively folded or branched internal surfaces specialized with exchange with the environment. Although exchange with the environment is a problem for animals whose cells are mostly internal, complex body forms have distinct benefits. Because the internal body fluid is the immediate environment for the cells, the animals organ systems can control the composition of the solution bathing its cells.

36. Regulating the Internal Environment.
The internal environment of vertebrates is called the interstitial fluid. This fluid exchanges nutrients and wastes with blood contained in microscopic vessels called capillaries. A pond dwelling hydra is powerless to affect the temperature of the fluid that surrounds it but a human can easily maintain its internal pond. Our bodies can also control our pH. There are times of course in the human development where changes in the internal environment are programmed to occur and therefore cannot be stopped.

37. Homeostasis
French physiologist Claude Bernard constant internal environment idea is incorporated into the concept of homeostasis, which means steady state. Actually, the internal environment of an animal always fluctuates slightly.
Homeostasis is a dynamic state, an interplay between outside forces that tend to change the internal environment and internal control mechanisms that oppose such changes.

38. Homeostasis depends on feedback circuits
Any homeostatic control system has three functional components. A receptor, a control center, and an effector. The receptor detects a change in some variable of the animals internal environment, such as a change in body temperature. The control center processes information it receives from the receptor and directs an appropriate response by the effector.

40. Homeostasis cont.
A type of control circuit called negative feedback occurs when a change in the variable being monitored triggers the control mechanisms to counteract further change in the same direction.
In contrast to negative feedback, positive feedback involves a change in some variable that triggers mechanisms that amplify rather than reverse the change. Regulated change is essential to normal body functions.