Table of Contents
Organization of the Animal Body | Epithelial Tissue | Connective Tissue | Muscle Tissue
Nervous Tissue | Learning Objectives | Terms | Review Questions | Links
Organization of the Animal Body |
Animals are multicellular heterotrophs whose cells lack cell walls. At some point during their lives, all animals are capable of movement, although not all animals have muscles they use for this. In the most commonly encountered animals, the mobile stage is the adult, although some animals (such as corals and sponges) have sessile (or nonmobile) adult phases and mobile juvenile forms. Both animal and plant evolutionary history show the development of multicellularity and the move from water to land (as well as a secondary adaptation back to water, for example dolphins, whales, duckweed, and elodea).
Animals developed external or internal skeletons to provide support, skin to prevent or lessen water loss, muscles that allowed them to move in search of food, brains and nervous systems for integration of stimuli, and internal digestive systems.
Organs in animals are composed of a number of different tissue types. For example, the stomach shown in Figure 1, has epithelial tissue making linings and secreting gastric juices, connective tissues
Figure 1. Cells and tissues that comprise the stomach. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
Plants are simpler organisms than animals, having three organ systems and fewer organs than do vertebrate animals. Organs are composed of tissues, which are in turn composed of cells. Plants have three tissue types: ground, dermal, and vascular. Animals have four: epithelial, connective, muscle, and bone.
Epithelial Tissue |
Epithelial tissue covers body surfaces and lines body cavities. Functions include lining, protecting, and forming glands. Three types of epithelium occur:
• Squamous epithelium is flattened cells.
• Cuboidal epithelium is cube-shaped cells.
• Columnar epithelium consists of elongated cells.
Any epithelium can be simple or stratified. Simple epithelium has only a single cell layer. Stratified epithelium has more than one layer of cells. Pseudostratified epithelium is a single layer of cells so shaped that they appear at first glance to form two layers.
Figure 2. Cuboidal epithelium. The image is cropped from Loyola University's LUMEN site at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl1-04.jpg. Note the single layer of simple cuboidal epithelium lining either side of a tubule.
Figure 3. Epithelium lining the intestine of a rat, as seen with SEM. This image is from http://130.102.208.100/FMRes/FMPro?-db=images.fp3&key=32816&-img, used by permission of Nanoworld.
Figure 4. Columnar epithelial cells. The above image is cropped and modified from Loyola University's LUMEN site at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl1-12.jpg. Note: I have outlined one of the columnar epithelium cells.
Functions of epithelial cells include:
• movement materials in, out, or around the body.
• protection of the internal environment against the external environment.
• Secretion of a product.
Glands can be single epithelial cells, such as the goblet cells that line the intestine. Multicellular glands include the endocrine glands. Many animals have their skin composed of epithelium. Vertebrates have keratin in their skin cells to reduce water loss. Many other animals secrete mucus or other materials from their skin, such as earthworms do.
Figure 5. Glandular epithelium. The image is from Loyola University's LUMEN site at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl1-24.jpg).
Connective Tissue |
Connective tissue serves many purposes in the body:
• binding
• supporting
• protecting
• forming blood
• storing fats
• filling space
Connective cells are separated from one another by a non-cellular matrix. The matrix may be solid (as in bone), soft (as in loose connective tissue), or liquid (as in blood). Two types of connective tissue are Loose Connective Tissue (LCT) and Fibrous Connective Tissue (FCT). Fibroblasts (LCT) are separated by a collagen fiber-containing matrix. Collagen fibers provide elasticity and flexibility. LCT occurs beneath epithelium in skin and many internal organs, such as lungs, arteries and the urinary bladder. This tissue type also forms a protective layer over muscle, nerves, and blood vessels.
Figure 6. Adipose tissue, a type of connective tissue. The image is cropped from Loyola University's LUMEN page at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl2-11.jpg. 
Adipose tissue, shown in Figure 6, has enlarged fibroblasts storing fats and reduced intracellular matrix. Adipose tissue facilitates energy storage and insulation.
Fibrous Connective Tissue has many fibers of collagen closely packed together. FCT occurs in tendons, which connect muscle to bone. Ligaments are also composed of FCT and connect bone to bone at a joint.
Cartilage and bone are "rigid" connective tissues. Cartilage, shown in Figure 7, has structural proteins deposited in the matrix between cells. Cartilage is the softer of the two "rigid" connective tissues. Cartilage forms the embryonic skeleton of vertebrates and the adult skeleton of sharks and rays. It also occurs in the human body in the ears, tip of the nose, and at joints such as the knee and between bones of the spinal column.
Figure 7. Cartilage, a type of "soft" connective tissue. The image is cropped from Loyola University's LUMEN page at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl4A-36.jpg. 
Bone, shown in Figure 8, has calcium salts in the matrix, giving it greater rigidity and strength. Bone also serves as a reservoir (or sink) for calcium. Protein fibers provide elasticity while minerals provide elasticity. Two types of bone occur. Dense bone has osteocytes (bone cells) located in lacunae connected by canaliculi. Lacunae are commonly referred to as Haversian canals. Spongy bone occurs at the ends of bones and has bony bars and plates separated by irregular spaces. The solid portions of spongy bone pick up stress.
Figure 8. Bone. The first image of bone is cropped from Loyola University's LUMEN page at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl4A-40.jpg. Note the haversian canal and surrounded by osteocytes and a mineralized matrix. The second image shows the structure and vascularization of bone. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
Blood is a connective tissue of cells separated by a liquid (plasma) matrix. Illustrations of blood cells are shown in Figure 9. Two types of cells occur. Red blood cells (erythrocytes) carry oxygen. White blood cells (leukocytes) function in the immune system. Plasma transports dissolved glucose, wastes, carbon dioxide and hormones, as well as regulating the water balance for the blood cells. Platelets are cell fragments that function in blood clotting.
Figure 9. Elements of the blood. The left image below is cropped from Loyola University's LUMEN site at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl2B-51.jpg. Note the red blood cells and the single neutrophil. The right image below is cropped from Loyola University's LUMEN site at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl2B-64.jpg. Erythrocytes as seem with the SEM. The bottom image is human red blood cells, platelets and T-lymphocyte (erythrocytes = red; platelets = yellow; T-lymphocyte = light green) (SEM x 9,900). This image is copyright Dennis Kunkel at http://www.denniskunkel.com/, used with permission.
Muscle Tissue |
Muscle tissue facilitates movement of the animal by contraction of individual muscle cells (referred to as muscle fibers). Three types of muscle fibers occur in animals (the only taxonomic kingdom to have muscle cells):
• skeletal (striated)
• smooth
• cardiac
Muscle tissue and organization is shown in Figure 10.
Figure 10. Organization of muscle tissue. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. 
Muscle fibers are multinucleated, with the nuclei located just under the plasma membrane. Most of the cell is occupied by striated, thread-like myofibrils. Within each myofibril there are dense Z lines. A sarcomere (or muscle functional unit) extends from Z line to Z line. Each sarcomere has thick and thin filaments. The thick filaments are made of myosin and occupy the center of each sarcomere. Thin filaments are made of actin and anchor to the Z line.
Skeletal (striated) muscle fibers, shown in Figure 11, have alternating bands perpendicular to the long axis of the cell. These cells function in conjunction with the skeletal system for voluntary muscle movements. The bands are areas of actin and myosin deposition in the cells.
Figure 11. Striated muscle cells. The left image of striated muscle fibers is cropped from Loyola University's LUMEN site at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl3A-45.jpg. The right image is from http://130.102.208.100/FMRes/FMPro?-db=images.fp3&key=32948&-img.
Smooth muscle fibers, shown in Figure 12, lack the banding, although actin and myosin still occur. These cells function in involuntary movements and/or autonomic responses (such as breathing, secretion, ejaculation, birth, and certain reflexes). Smooth muscle fibers are spindle shaped cells that form masses. These fibers are components of structures in the digestive system, reproductive tract, and blood vessels.
Figure 12. Smooth muscle cells. The image of smooth muscle cells is cropped from Loyola University's LUMEN site at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl3A-42.jpg.
Cardiac muscle fibers are a type of striated muscle found only in the heart. The cell has a bifurcated (or forked) shape, usually with the nucleus near the center of the cell. The cells are usually connected to each other by intercalated disks, as shown in Figure 13.
Figure 13. Cardiac muscle cells. The top image of cardiac muscle cells is cropped from Loyola University's LUMEN site at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl3A-48.jpg. Note the dark band of the intercalated disk that separates two muscle cells. The bottom image is of a heart muscle cell (nucleus, mitochondria, actin-myosin) (TEM x15,400). This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission.
Nervous Tissue |
Nervous tissue, shown in Figure 14, functions in the integration of stimulus and control of response to that stimulus. Nerve cells are called neurons. Each neuron has a cell body, an axon, and many dendrites. Nervous tissue is composed of two main cell types: neurons and glial cells. Neurons transmit nerve messages. Glial cells are in direct contact with neurons and often surround them.
Figure 14. Organization of a neutron. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
The neuron is the functional unit of the nervous system. Humans have about 100 billion neurons in their brain alone! While variable in size and shape, all neurons have three parts. Dendrites receive information from another cell and transmit the message to the cell body. The cell body contains the nucleus, mitochondria and other organelles typical of eukaryotic cells. The axon conducts messages away from the cell body. Neurons are shown in Figure 15.
Figure 15. Neurons. The left image of large multipolar neuron (center of image) is cropped from Loyola University's LUMEN site at http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl3-03.jpg. The right image shows Pyramidal Neurons from the Central Nervous System (SEM x3,960). This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission.
Learning Objectives | Be able to list the major functions of each of the four major animal tissue types.
• Distinguish between simple and stratified epithelial tissue.
• Compare and contrast the different types of connective tissues: loose, dense, fibrous, cartilage, bone, blood, adipose. Be able to list the function of each type.
• Know the three types of muscle and be able to differentiate them visually and according to their functions.
• Be able to diagram a typical neuron and its three areas: dendrite, axon, and cell body.
• Know the characteristics of the various types of animal tissues. Learn the types of cells that compose each tissue type and be able to give some examples of organs that contain significant amounts of each tissue type.
• Detail the functions carried out by epithelial tissue and state the general location of each type.
• Be able to discuss the meaning of the term gland, cite three examples of glands, and state the extracellular products secreted by each.
• Describe the basic features of connective tissue, and explain how the cells of this tissue type enable connective tissue to carry out its various tasks.
• List three of the functions of blood.
• List two functions of bone and/or cartilage.
• Distinguish among skeletal, cardiac, and smooth muscle tissues in terms of location, structure, and function.
• Muscle tissues contain specialized cells that can contract.
• Neurons are organized as lines of communicaiton.
Review Questions | Which of these is not an animal tissue? a) connective; b) xylem; c) epithelial; d) nervous ans is b
1. Tissues are made of _______. a) groups of cells that perform a different set of functions; b) collections of cells that perform similar or related functions; c) subellular structures that aid in the performance of the cell's role; d) none of these ans is b
2. Which of these is NOT a function of epithelial tissue? a) covering surfaces; b) secretion; c) support of the body; d) lining internal exchange areas ans is c
3. Layered epithelial tissue is referred to as which of these? a) squamous; b) stratified; c) voluntary; d) pseudostratified ans is d
4. Which of these cell types covers the inside of the mouth? a) squamous epithelium; b) cartilage; c) blood; d) cuboidal epithelium ANS is a
5. Protection of the body from infectious organisms is accomplished by which of these tissues? a) bone; b) muscle; c) nerve; d) blood ANS is d
6. Linking of bone to bone in a skeletal system is accomplished by which of these tissues? a) epithelial; b) connective; c) muscle; d) nervous ANS is b
7. Cells that line the tubules in the kidney make up which of these tissues? a) adipose; b) squamous epithelium; c) cuboidal epithelium; d) stratified epithelium ANS is c
8. The storage of fat is accomplished by which of these cell types? a) adipose; b) squamous epithelium; c) cuboidal epithelium; d) stratified epithelium ANS is a
9. Glands are composed of which of these tissue types? a) epithelium; b) connective; c) muscle; d) nervous ANS is a
10. Hard parts of the body would be made of which of these cell/tissue types? a) blood; b) bone; c) muscle; d) nerves ANS is b
11. Bone acts as a reservoir for which of these elements? a) carbon; b) nitrogen; c) calcium; d) hydrogen ANS is c
12. The major function of bone is ___. a) covering body surfaces; b) support; c) movement; d) integration of stimulus ANS is b
13. New blood cells are formed in the ___. a) matrix; b) bone marrow; c) liver; d) adipose cells AMS is b
14. The blood cells that transport oxygen within the body are the ___. a) macrophages; b) erythrocytes; c) platelets; d) leukocytes ANS is b
15. The liquid part of the blood is ___. a) plasma; b) adipose; c) cartilage; d) platelets ANS is a
16. When you move your arm to use your computer mouse, which of these muscle cell types is involved? a) cardiac; b) skeletal; c) smooth ANS is b
17. Contraction of your heart is accomplished by which of these cell types? a) cardiac; b) skeletal; c) smooth ANS is a
18. Contractions of the uterus during birth are accomplished by which of these cell types? a) cardiac; b) skeletal; c) smooth ANS is c
19. The junctions between nerve cells are known as ___. a) gap junctions; b) synapses; c) tight junctions; d) villi ANS is b
20. Transmission of the nerve message within the neuron is ___ in nature. a) chemical b) electrical ANS is b
Links |
• Muscle Cell Types from Human Anatomy On-line
• Histology Lab Orientation Online lectures and quizzes for the introductory histology as well as more advanced histology students.
• Histology entry at Wikipedia offers a discussion of aspects of histology.
• Internet Atlas of Histology, COM-UIUC More histology than you might want, but a superb resource open to students and interested parties, featuring a frame-based atlas with zoomable images that simulate the microscope experience!
Table of Contents
Homeostasis | The Internal Environment | Control Systems | Feedback Systems in Homeostasis
Body Systems and Homeostasis |
We are all familiar with many of the organ systems that comprise the body of advanced animals: such as the circulatory system, nervous system, etc. More of us are aware of the essential nature of the immune system in these days of HIV, AIDS, and emergent viral diseases such as Ebola and Hanta. Later chapters will focus on animals, such as sponges that have no organs at all, and other organisms that lack many of the organ systems we take for granted. Recall that in the Introduction chapter we discussed the levels of organization we see in biology, from atoms to organ systems that makeup a multicellular organism. We have also seen somewhat of the myriad cells and tissues that occur in humans (and by extension in other animals). This chapter will introduce you to the eleven organ systems that function within our own bodies, and how they coordinate to keep us functioning within a dynamic range of internal conditions we refer to as homeostasis.
Animal organs are usually composed of more than one cell type. Recall that the stomach contains all four animal tissue types: epithelium to line the stomach and secrete gastric juices; connective tissues to give the stomach flexibility to expand after a large meal; smooth muscle tissues to churn and digest that meal without the need for conscious thought (indeed, we are aware of that action only when we burp or suffer some sort of gastric distress!); and nervous tissues to monitor the progress of food as it is worked on by the stomach, and to direct secretion and muscle activity. Each organ typically performs a given function set. The stomach is an organ composed of tissues that aid in the mechanical and chemical breakdown of food. Most organs have functions in only one organ system. The stomach is involved only in the digestion of food as part of the digestive system. Organ systems, such as the digestive system, are collections of organs that perform a major function for the organism.
Homeostasis |
Homeostasis is the maintenance of a stable internal environment. Homeostasis is a term coined in 1959 to describe the physical and chemical parameters that an organism must maintain to allow proper functioning of its component cells, tissues, organs, and organ systems.
Recall that enzymes function best when within a certain range of temperature and pH, and that cells must strive to maintain a balance between having too much or too little water in relation to their external environment. Both situations demonstrate homeostasis. Just as we have a certain temperature range (or comfort zone), so our body has a range of environmental (internal as well as external) parameters within which it works best. Multicellular organisms accomplish this by having organs and organ systems that coordinate their homeostasis. In addition to the other functions that life must perform (recall the discussion in our Introduction chapter), unicellular creatures must accomplish their homeostasis within but a single cell!
Single-celled organisms are surrounded by their external environment. They move materials into and out of the cell by regulation of the cell membrane and its functioning. Most multicellular organisms have most of their cells protected from the external environment, having them surrounded by an aqueous internal environment. This internal environment must be maintained in such a state as to allow maximum efficiency. The ultimate control of homeostasis is done by the nervous system. Often this control is in the form of negative feedback loops. Heat control is a major function of homeostatic conditions that involves the integration of skin, muscular, nervous, and circulatory systems.
The difference between homeostasis as a single cell performs it and what a multicelled creature does derives from their basic organizational plan: a single cell can dump wastes outside the cell and just be done with it. Cells in a multicelled creature, such as a human or cat, also dump wastes outside those cells, but like the trash can or dumpster outside my house/apartment, those wastes must be carted away. The carting away of these wastes is accomplished in my body by the circulatory system in conjunction with the excretory system. For my house, I have the City of Phoenix sanitation department do that (and get to pay each month for their service!).
The ultimate control of homeostasis is accomplished by the nervous system (for rapid responses such as reflexes to avoid picking up a hot pot off the stove) and the endocrine system (for longer-term responses, such as maintaining the body levels of calcium, etc.). Often this homeostatic control takes the form of negative feedback loops. There are two types of biological feedback: positive and negative. Negative feedback turns off the stimulus that caused it in the first place. Your house’s heater (or cooler for those of us in the Sun Belt) acts on the principle of negative feedback. When your house cools off below the temperature set by your thermostat, the heater is turned on to warm air until the temperature is at or above what the thermostat is set at. The thermostat detects this rise in temperature and sends a signal to shut off the heater, allowing the house to cool of until the heater is turned on yet again and the cycle (or loop) continues. Positive feedback causes an amplification of the stimulus by the reaction. Examples of each will be presented below.
The Internal Environment |
There are two types of extracellular fluids in animals:
• the extracellular fluid that surrounds and bathes cells
• plasma, the liquid component of the blood.
Internal components of homeostasis:
1. Concentration of oxygen and carbon dioxide
2. pH of the internal environment
3. Concentration of nutrients and waste products
4. Concentration of salt and other electrolytes
5. Volume and pressure of extracellular fluid
Control Systems |
Open systems are linear and have no feedback, such as a light switch. Closed Systems has two components: a sensor and an effector, such as a thermostat (sensor) and furnace (effector). Most physiological systems in the body use feedback to maintain the body's internal environment.
Extrinsic
Most homeostatic systems are extrinsic: they are controlled from outside the body. Endocrine and nervous systems are the major control systems in higher animals.
The nervous system depends on sensors in the skin or sensory organs to receive stimuli and transmit a message to the spinal cord or brain. Sensory input is processed and a signal is sent to an effector system, such as muscles or glands, that effects the response to the stimulus.
The endocrine system is the second type of extrinsic control, and involves a chemical component to the reflex. Sensors detect a change within the body and send a message to an endocrine effector (parathyroid), which makes PTH. PTH is released into the blood when blood calcium levels are low. PTH causes bone to release calcium into the bloodstream, raising the blood calcium levels and shutting down the production of PTH.
Some reflexes have a combination of nervous and endocrine response. The thyroid gland secretes thyroxin (which controls the metabolic rate) into the bloodstream. Falling levels of thyroxin stimulate receptors in the brain to signal the hypothalamus to release a hormone that acts on the pituitary gland to release thyroid-stimulating hormone (TSH) into the blood. TSH acts on the thyroid, causing it to increase production of thyroxin.
Intrinsic
Local, or intrinsic, controls usually involve only one organ or tissue. When muscles use more oxygen, and also produce more carbon dioxide, intrinsic controls cause dilation of the blood vessels allowing more blood into those active areas of the muscles. Eventually the vessels will return to "normal".
Feedback Systems in Homeostasis |
Negative feedback control mechanisms (used by most of the body's systems) are called negative because the information caused by the feedback causes a reverse of the response. TSH is an example: blood levels of TSH serve as feedback for production of TSH.
Positive feedback control is used in some cases. Input increases or accelerates the response. During uterine contractions, oxytocin is produced. Oxytocin causes an increase in frequency and strength of uterine contractions. This in turn causes further production of oxytocin, etc.
Homeostasis depends on the action and interaction of a number of body systems to maintain a range of conditions within which the body can best operate.
Body Systems and Homeostasis |
Eleven major organ systems are present within animals, although some animals lack one or more of them. The vertebrate body has two cavities: the thoracic, which contains the heart and lungs; and the abdominal, which contains digestive organs. The head, or cephalic region, contains four of the five senses as well as a brain encased in the bony skull. These organ systems can be grouped according to their functions.
Figure 1. The integumentary, skeletal, and muscular systems. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
• Muscular System (shown in Figure 1) facilitates movement and locomotion. The muscular system produces body movements, body heat, maintains posture, and supports the body. Muscle fibers are the main cell type. Action of this system is closely tied to that of the skeletal system.
• Skeletal System (shown in Figure 1) provides support and protection, and attachment points for muscles. The skeletal system provides rigid framework for movement. It supports and protects the body and body parts, produces blood cells, and stores minerals.
• Skin or Integument (shown in Figure 1) is the outermost protective layer. It prevents water loss from and invasion of foreign microorganisms and viruses into the body. There are three layers of the skin. The epidermis is the outer, thinner layer of skin. Basal cells continually undergo mitosis. Skin is waterproof because keratin, a protein is produced. The next layer is the dermis a layer of fibrous connective tissue. Within the dermis many structures are located, such as sweat glands, hair follicles and oil glands. The subcutaneous layer is composed of loose connective tissue. Adipose tissue occurs here, serving primarily for insulation. Nerve cells run through this region, as do arteries and veins.
• Respiratory System moves oxygen from the external environment into the internal environment; also removes carbon dioxide. The respiratory system exchanges gas between lungs (gills in fish) and the outside environment. It also maintains pH of the blood and facilitates exchange of carbon dioxide and oxygen.
• Digestive System digests and absorbs food into nutrient molecules by chemical and mechanical breakdown; eliminates solid wastes into the environment. Digestion is accomplished by mechanical and chemical means,breaking food into particles small enough to pass into bloodstream. Absorbtion of food molecules occurs in the small intestine and sends them into circulatory system. The digestive system also recycles water and reclaims vitamins from food in the large intestine.
The system is summarized in Figure 2.
• Circulatory System () transports oxygen, carbon dioxide, nutrients, waste products, immune components, and hormones. Major organs include the heart, capillaries, arteries, and veins. The lymphatic system also transports excess fluids to and from circulatory system and transports fat to the heart.
• Immune System (Lymphatic system, Figure 3) defends the internal environment from invading microorganisms and viruses, as well as cancerous cell growth. The immune system provides cells that aid in protection of the body from disease via the antigen/antibody response. A variety of general responses are also part of this system.
Figure 4. The excretory system. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
• Excretory System regulates volume of internal body fluids as well as eliminates metabolic wastes from the internal environment. The excretory system removes organic wastes from the blood, accumulating wastes as urea in the kidneys. These wastes are then removed as urine. this system is also responsible for maintaining fluid levels.
Figure 5. The nervous and endocrine systems. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
• Nervous System, illustrated in Figure 5, coordinates and controls actions of internal organs and body systems. Memory, learning, and conscious thought are a few aspects of the functions of the nervous system. Maintaining autonomic functions such as heartbeat, breathing, control of involuntary muscle actions are performed by some of the parts of this system.
• Endocrine System, illustrated in Figure 5, works with the nervous system to control the activity internal organs as well as coordinating long-range response to external stimuli. The endocrine system secretes hormones that regulate body metabolism, growth, and reproduction. These organs are not in contact with each other, although they communicate by chemical messages dumped into the circulatory system.
Figure 6. The urogenital and reproductive systems of males (top) and females). Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
• Reproductive System, shown in Figure 6, is mostly controlled by the endocrine system, and is responsible for survival and perpetuation of the species. Elements of the reproductive system produce hormones (from endocrine control) that control and aid in sexual development. Organs of this system produce gametes that combine in the female system to produce the next generation (embryo).
Learning Objectives | List the principal organ systems in humans and match each to its main task.
• Explain how, if each cell can perform all its basic activities, organ systems contribute to cell survival.
• Draw a diagram that illustrates the mechanism of homeostatic control.
• Be able to diagram an example of positive feedback as well as an example of negative feedback, either from everyday life or dealing with specific body systems.
• List one body system and the types of interactions it has with other body organ systems.
• Explain what a reflex is by drawing and labeling a diagram and telling how it functions.
Review Questions |
Which of these is not a characteristic of living things? a) reproduction and heredity; b) metabolism; c) response to stimulus d) all of the are characteristics of life ANS is d
1. Control of homeostasis in the body is accomplished by ____. a) Nervous system; b) Circulatory system; c) Endocrine system; d) both a and c control homeostasis ANS is d
2. Which of these would be the effector for a negative feedback system to heat your house? a) thermostat; b) wiring; c) heater; d) air conditioner ANS is d
3. When we are cold we shiver. This releases heat from which organ system? a) Skeletal system; b) Muscular system; c) Digestive system; d) Circulatory system ANS is b
4. Heat released when we shiver is transported from its source to the rest of the body by which of these organ systems? a) Skeletal system; b) Muscular system; c) Digestive system; d) Circulatory system ANS is d
5. The digestive process consists of three subprocesses. Which of these is not part of the digestive process? a) mechanical breakdown of food; b) circulation of food in the blood and lymph; c) absorption of food into the blood or lymph; d) assimilation of the food into cells of the body ANS is c
6. Which of these is not a function carried out by the Integumentary system? a) protection from invaders; b) storage of fats; c) prevention of water loss; d) removal of excess heat by sweating ANS is b
7. Hormones are produced directly by organs and tissues of which of these body systems? a) Endocrine; b) Circulatory; c) Reproductive; d) Nervous ANS is a
8. The removal of organic wastes from the body is accomplished by the ___ system? a) Digestive; b) Excretory; c) Circulatory; d) Lymphatic ANS is b
9. Which of these is part of the central nervous system? a) brain; b) nerve ganglia; c) spinal cord; d) a and b; e) a and c ANS is e
10. The spinal cord is located on which side of the body? a) dorsal; b) ventral; c) abdominal; d) cranial ANS is a
11. Which of these is not part of the male reproductive system? a) testis; b) penis; c) ovary; d) vas deferens ANS is C
12. Gametes are produced by which of these cell division processes? a) mitosis; b) binary fission; c) photosynthesis; d) meiosis ANS is d
13. Blood leaves the heart through which of these types of blood vessels? a) capillaries; b) arteries; c) veins; d) lymphatic vessels ANS is b
14. Storage of important ions such as phosphorous and calcium is done by which of these organ systems? a) Skeletal; b) Muscular; c) Digestive; d) Excretory ANS is a
15. Movement of the body is accomplished directly by the actions of which of these organ systems? a) Muscular; b) Skeletal; c) Digestive; d) a and b e) b and c ANS is d
Links |
• How the Body Works A Canadian site with way cool "fig" leaves!
• Homeostasis A collection of links dealing with organ systems and homeostasis.
• The Atlas of the Human Body An online atlas from the American Medical Association. Check out the system of your choice.
• The Virtual Body This site presents information about the Brain, Digestive System, Heart, and Skeleton through use of a series of Shockwave® animations. You will need the plugin to view those animations, but can access it from the Virtual Body site.
• Human Anatomy Online This site offers some Java-assisted fun activities about the human body.
• Human Anatomy and Physiology Case Study Project Learn about human anatomy and physiology by studying actual cases.
• Vesalius, an online graphical resource for the medical and surgical communities This site provides anatomical illustrations, many of which are posted for your viewing. An interesting feature is the mark up section, allowing registered users (registrations is currently free) to annotate posted drawings.
• Virtual Pig Dissection No fuss, no muss, no smell, no wastes to dispose of. This site, intended for high school level, offers systemic information about a commonly dissected specimen, Babe the Pig!
• Atlas Plus Virtual demonstrations covering aspects of anatomy and body systems, but not the histology section (University of Michigan). This site uses Java, so your browser will need to be Java-compliant.
• Click the Bones and They Will Speak Not just for Haloween fun, this site offers some very well done information about the bones and how to properly pronounce them. Maybe with this site I might not have left animals for plant science!
• Online Biology Book chapters covering the human body and its organ systems.
o THE INTEGUMENTARY SYSTEM
o THE CIRCULATORY SYSTEM
o LYMPHATIC SYSTEM AND IMMUNITY
o THE DIGESTIVE SYSTEM
o THE NERVOUS SYSTEM
o THE ENDOCRINE SYSTEM
o THE REPRODUCTIVE SYSTEM
o THE MUSCULAR AND SKELETAL SYSTEMS
o THE RESPIRATORY SYSTEM
o THE EXCRETORY SYSTEM
The Nature of ATP | How to Make ATP | Learning Objectives | Terms | 
The Nature of ATP |
Adenosine triphosphate (ATP), the energy currency or coin of the cell pictured in Figfures 1 and 2, transfers energy from chemical bonds to endergonic (energy absorbing) reactions within the cell. Structurally, ATP consists of the adenine nucleotide (ribose sugar, adenine base, and phosphate group, PO4-2) plus two other phosphate groups.
Figure 2. A cartoon and space-filling view of ATP. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
Energy is stored in the covalent bonds between phosphates, with the greatest amount of energy (approximately 7 kcal/mole) in the bond between the second and third phosphate groups. This covalent bond is known as a pyrophosphate bond.
We can write the chemical reaction for the formation of ATP as:
a) in chemicalese: ADP + Pi + energy ----> ATP
b) in English: Adenosine diphosphate + inorganic Phosphate + energy produces Adenosine Triphosphate
The chemical formula for the expenditure/release of ATP energy can be written as:
a) in chemicalese: ATP ----> ADP + energy + Pi
b) in English Adenosine Triphosphate produces Adenosine diphosphate + energy + inorganic Phosphate
An analogy between ATP and rechargeable batteries is appropriate. The batteries are used, giving up their potential energy until it has all been converted into kinetic energy and heat/unusable energy. Recharged batteries (into which energy has been put) can be used only after the input of additional energy. Thus, ATP is the higher energy form (the recharged battery) while ADP is the lower energy form (the used battery). When the terminal (third) phosphate is cut loose, ATP becomes ADP (Adenosine diphosphate; di= two), and the stored energy is released for some biological process to utilize. The input of additional energy (plus a phosphate group) "recharges" ADP into ATP (as in my analogy the spent batteries are recharged by the input of additional energy).
How to Make ATP |
Two processes convert ADP into ATP: 1) substrate-level phosphorylation; and 2) chemiosmosis. Substrate-level phosphorylation occurs in the cytoplasm when an enzyme attaches a third phosphate to the ADP (both ADP and the phosphates are the substrates on which the enzyme acts). This is illustrated in Figure 3.
Figure 3. Enzymes and the formation of NADH and ATP. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
Chemiosmosis, shown in Figure 4, involves more than the single enzyme of substrate-level phosphorylation. Enzymes in chemiosmotic synthesis are arranged in an electron transport chain that is embedded in a membrane. In eukaryotes this membrane is in either the chloroplast or mitochondrion. According to the chemiosmosis hypothesis proposed by Peter Mitchell in 1961, a special ATP-synthesizing enzyme is also located in the membranes. Mitchell would later win the Nobel Prize for his work.
Figure 4. A typical representation of an electron transport chain. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
During chemiosmosis in eukaryotes, H+ ions are pumped across an organelle membrane by membrane "pump proteins" into a confined space (bounded by membranes) that contains numerous hydrogen ions. This is shown in Figure 4 and 5. The energy for the pumping comes from the coupled oxidation-reduction reactions in the electron transport chain. Electrons are passed from one membrane-bound enzyme to another, losing some energy with each tansfer (as per the second law of thermodynamics). This "lost" energy allows for the pumping of hydrogen ions against the concentration gradient (there are fewer hydrogen ions outside the confined space than there are inside the confined space). The confined hydrogens cannot pass back through the membrane. Their only exit is through the ATP synthesizing enzyme that is located in the confining membrane. As the hydrogen passes through the ATP synthesizing enzyme, energy from the enzyme is used to attach a third phosphate to ADP, converting it to ATP.
Usually the terminal phosphate is not simply removed, but instead is attached to another molecule. This process is known as phosphorylation.
W + ATP -----> W~P + ADP where W is any compound, for example:
glucose + ATP -----> glucose~P + ADP
Glucose can be converted into Glucose-6-phosphate by the addition of the phosphate group from ATP.
ATP serves as the biological energy company, releasing energy for both anabolic and catabolic processes and being recharged by energy generated from other catabolic reactions.
Learning Objectives |
Describe the components, organization, and functions of an electron transport system.
ATP is composed of ribose, a five-carbon sugar, three phosphate groups, and adenine , a nitrogen-containing compound (also known as a nitrogenous base). What class of organic macromolecules is composed of monomers similar to ATP?
ATP directly or indirectly delivers energy to almost all metabolic pathways. Explain the functioning of the ATP/ADP cycle.
Adding a phosphate to a molecule is called phosphorylation. What two methods do cells use to phosphorylate ADP into ATP?
Terms | Back to Top
adenine nucleotide
Adenosine diphosphate
Adenosine triphosphate (ATP)
anabolic
catabolic
chemiosmosis
chloroplast
covalent bonds
cytoplasm
electron transport chain
endergonic
enzyme
mitochondrion
oxidation-reduction
phosphorylation
ribose
second law of thermodynamics
Links |
- Energy View an online slideshow (102 slides) by Susan Blanchard that covers thermodynamics, ATP and all that stuff.
- The Nobel Prize in Chemistry 1997 Three scientists were awarded the Nobel Prize in 1997 for their work studying enzymes involved with the formation and use of ATP. The press release is of particular note.
- The Nobel Prize in Chemistry 1978 Press Release Peter D. Mitchell proposed a wild idea about how ATP was made...and he was subsequently validated by other researchers. Read the Nobel Foundation Press release announcing the prize.
- Small Molecules for Modern Biology This site requires the Chime Plugin (available from that site) for your browser. You can view images of a variety of small molecules, including ATP.
- Mitochondrial Mysteries Demystified This site uses the Shockwave Plugin to provide a multimedia tour of the mitochondrion and its role in cellular metabolism.
