1. Chapter 20: Introduction to Animal Physiology
Principles of animal organization and function
Lecture by Jennifer Lange, Chabot College

2. Learning Objectives Understand and be able to explain the following:
Why the body needs to maintain its internal environment in a dynamically constant state.
How internal temperature is maintained while exchanging heat with the environment.
How osmotic balance and solute concentrations are maintained. 2

3. Learning Objectives Understand and be able to explain the following:
The relationship between the levels of organization of the body.
How the unique characteristics of each tissue type relate to their function.
The major tasks of each organ system. 3

4. Section 20-1 Opener
Heat radiates from warm bodies in cold weather.

5. 20.1 Our bodies function best within a narrow range of internal conditions.
Figure A cooling soak after a tough workout can prevent hyperthermia.

6. Take-home message 20.1
Failure to maintain a consistent internal environment can lead to many problems and can result in death.

7. 20.2 Animals regulate their internal environment through homeostasis.
Homeostasis: maintenance of relatively constant internal chemical and physical environment in the face of constantly changing environmental factors.
The cells of our body operate optimally within a narrow range of temperature, pH, carbon dioxide and oxygen concentrations, water-solute balance, and blood sugar levels. If large deviation were to occur, cell functions would falter, which could result in organ malfunction and even death. So when you are in a sweltering desert or in a freezing water hole, your body is actively attempting to keep the core body temperature at 98.6 degrees.
In the first part of this class we will explore the basic mechanisms used to both maintain and disturb (temporarily) homeostasis, then we will discuss in more detail temperature regulation and water balance and solute concentration regulation.
Figure 20-2 Homeostasis: maintaining a stable internal environment.

8. Take-home message 20.2
The internal environment of multicellular animals is continuously influenced by their external environment.
Animals still keep many internal variables—temperature, pH, blood sugar—within a constant range.

9. Section 20-2 Opener
Relief from heat: A young orangutan seeks shelter under a leaf.

10. 20.3 Negative and positive feedback systems influence homeostasis.
Perturbation away from set point results in corrective action, known as negative feedback.
Homeostasis operates on the same principle as your home heating and air conditioning system.
You set the desired air temperature for your room; for example, 70 degrees.
If the temperature drops to 69 degrees, the sensor in the thermostat detects the change and takes corrective action by signaling the heater to turn on.
The operation of the heater warms the room, bringing it back to your desired temperature of 70 degrees. At this point, the sensor recognizes the set temperature and signals that heater to turn off because it is no longer needed.
In this example, the action of the heater negatively affected the perturbation in air temperature—it undid the temperature decrease. This process is called negative feedback. The systems of our body act in much the same manner—they react to undo a perturbation in temperature, blood sugar level, etc.
Figure 20-3 A negative feedback loop restores the internal environment to a set point.

11. Regulators vs. Conformers
Organisms that maintain homeostasis for a particular variable are called regulators. But this is not the only strategy: variables can be allowed to fluctuate with the environment, which is called conforming.
A single organism can utilize one strategy or the other for all of its potential variables, or it can simultaneously utilize both for different variables. In the fish seen here, it is regulating the concentration of salt in its body, while at the same time allowing its body temperature to change with water temperature. It is both a regulator and a conformer!
Figure 20-4 Regulate or conform? Two strategies to cope with a changing environment.

12. Non-Homeostatic Mechanism
In specific instances, perturbation can result in further movement away from setpoint, known as positive feedback.
A third strategy is also non-homeostatic: in positive feedback a change away from the normal condition drives an increase in the change.
For instance, during child-birth, hormones released by the fetus stimulate uterine contractions in the mother. In order to push the baby through the birth canal, the uterine contractions need to continue and become stronger, not weaker, so using a positive feedback strategy is called for. The uterine contractions cause hormones to be released that increase contraction strength and frequency, which then releases more hormones and further increases the contractions.
Another example is the blood-clotting—an injured blood vessel simulates platelets to form a clot. This process becomes amplified as these blood clotting molecules stimulate the release of more molecules into the bloodstream. The response becomes amplified in order to speed up the clotting and prevent excessive blood loss.
However, in neither of these examples does the amplification continue indefinitely—the child is born and uterine contractions are no longer necessary; the tear in the blood vessel is filled, and blood loss has been stopped. The shutting down of these processes is part of a larger loop that operates on negative feedback: once the original stimulus has been removed (fetus isn’t releasing hormones into the mother’s blood, the tear in the blood vessel wall has been filled), the response shuts down.
Figure 20-5 Patching a tear. The blood clot that forms after an injury is a result of a positive feedback system.

13. Take-home message 20.3
Physiological variables have a set point to which the organism can return.
Through negative feedback, sensors detect changes in the internal environment and trigger effectors to oppose or reduce the change.

14. Take-home message 20.3
Positive feedback systems are less common than negative feedback systems.
Positive feedback systems push the body away from normal conditions and increase change in the same direction.

15. 20.4 Temperature control is a component of homeostasis.
Thermoregulation
How is body heat generated?
Now that you are familiar with the general strategies for regulating and conforming, we will look at two specific instances in which homeostasis is maintained, starting with body temperature.
The maintenance of body temperature is called thermoregulation. Heat can be obtained from two sources—internally and externally.

16. Endotherms
Those organisms who generate body heat internally are called endotherms (endo being a prefix meaning “inside”). This group includes those organisms we commonly refer to as “warm-blooded”—most mammals and birds. Internal heat is a by-product of ATP production and use. Recall that energy cannot be created or destroyed, only transferred from one form to another. If the energy conversion inside the body from one form to another is not 100% efficient, the non-captured energy is released as heat. Organisms with higher metabolic rates that are more physically active do more energy conversion, and therefore generate more heat.
Figure 20-6 Strategies to heat the body.

17. Ectotherms
Those organisms who obtain heat primarily from their environment are ectotherms (ecto being a prefix meaning “outside”). This group includes those organisms we commonly refer to as “cold-blooded”—the invertebrates, fish, amphibians, and reptiles. Organisms with slower metabolic rates that are less physically active do not generate as much heat internally, so they must warm themselves using outside sources such as the sun or a warm rock. Lizards typically bask in the sun in the morning, soaking up heat to warm their bodies to their optimal temperature to go about their daily business. Prior to reaching this optimal temperature, their systems react sluggishly, making lizards much easier to catch in the morning than later in the day!
Figure 20-6 Strategies to heat the body.

18. Thermoregulation Is temperature constant or fluctuating?
The descriptive terms “warm” and “cold” do not entirely reflect the temperature of the blood of endotherms and ectotherms. Many mammals hibernate in the winter, during which time their core body temperature decreases and their blood could be described as “cold.” Similarly, a basking lizard can raise its body temperature to match air temperature, which can be quite “warm”!
To accommodate these organisms, we need a second type of classification—homeotherms vs. heterotherms. The prefix “homeo” means same, so this group includes organisms that usually have the same body temperature. The prefix “hetero” means different, so this group includes organisms that have multiple temperature set-points or whose temperature mirrors environmental temperature.
When classifying an organism’s temperature strategy, both types of class classification need to be expressed—heterotherm or homeotherm and ectotherm or endotherm.
Figure 20-7 Stable body temperature versus variable body temperature.
Both conditions are regulated.

19. Heat Exchange Mechanisms
Body heat is a combination of internal heat generation and exchange with the external environment through four mechanisms:
conduction
convection
radiation
evaporation
No matter which of these strategies an organism employs, all organisms exchange heat with their environment. As you walk from class to class on a sunny day, your muscles generate heat, which may cause you to sweat and then seek a cold drink and an air-conditioned room. This simple sequence of events illustrates four mechanisms by which heat is transferred between the body and the environment:
conduction
convection
radiation
and
4. evaporation

20. Conduction is the transfer of heat between two objects that are in direct contact—such as between you and your cold beverage. The heat from your body is moving into the cold liquid, causing that liquid to warm up and you to cool down.
Convection is the transfer of heat to a passing fluid or to passing air. As your blood rushed past your working muscles, it picked up heat and carried it to other regions of the body, particularly to your skin. Some of this heat is lost to the surrounding air by the breeze created by your movement, particularly to the air of the air- conditioned room (with its fans circulating cool air throughout the room).
Radiation is the transfer of heat between two objects that are not in direct contact. The heat from the sun (object 1) transferred to you (object 2) as you walked.
Evaporation is the loss of heat by using energy to convert a liquid to a gas, in this case to dry your sweat. The liquid on your skin is heated by the warm blood, causing it to change to a gas and move into the air.
Figure 20-8 How organisms acquire or dissipate heat.
In addition to illustrating the mechanisms by which heat can be exchanged, this series of events also illustrates several of the methods used to actively alter the process of heat exchange.

21. Heat Exchange Mechanisms
How do organisms adapt to heat transfer?
Physiological methods of managing heat transfer are processes that our body systems undertake to increase or decrease the rate of heat exchange. Sweating is an action by the integumentary system that involves the creation and secretion of fluid onto the skin surface. To then lose heat through evaporation, our nervous and cardiovascular systems act together to direct more blood flow to the skin, transferring heat from the body core to the surface, then to the evaporation of sweat.
Dingos and other types of dogs do not have the ability to produce sweat. Instead they adopt a similar physiological method by breathing hot air through their mouth in order to transfer heat through evaporating liquid in the respiratory system.
Seeking an air-conditioned room and a cold beverage are behavioral methods of regulating heat transfer. We alter our current behavior to seek out locations and objects that will absorb our body heat, or, in a different scenario, provide us with their heat. Other behaviors include seeking shade (or creating it with an umbrella or a tail), seeking sun, huddling close to others, or donning a coat.
Figure 20-9 Adaptations that aid in temperature regulation.

22. Heat Exchange Mechanisms
How do organisms adapt to heat transfer?
Not seen in the scenario we are considering are physical and cellular methods of regulating heat transfer, as these two are less dependent on rapidly deployable strategies.
Physical methods are related to body size, shape, and composition. A common heat retention strategy is adding insulation to the body, in the form of fat or blubber, so that heat cannot be as easily extracted from the skin. Perhaps this is why we gravitate toward fatty, high-calorie foods in the winter.
Cellular methods require alterations in the process of ATP manufacture. Baby fat, called “brown fat,” has more mitochondria than typical adult, or “white,” fat. These mitochondria should be able to generate more ATP, but, due to a change in protein transcription, the mitochondrial membrane of this type of fat is leaky to hydrogen ions, allowing them to travel down their gradient through the membranes instead of through the enzyme that creates ATP. Thus, instead of storing the potential energy in the bonds of ATP, it is dissipated as heat.
Figure 20-9 Adaptations that aid in temperature regulation.

23. Figure Heat exchange. Sweating can help cool us off through evaporation. By leaning up against a cool rock wall, we can also lose some heat through conduction.

24. Take-home message 20.4
The control of body temperature, called thermoregulation, is an important component of homeostasis.
Body temperature is a function of internal heat production and heat transfer between an organism and its environment.

25. Take-home message 20.4
Heat transfer to and from the environment is regulated physically, behaviorally, physiologically, and at the cellular level.

26. 20.5 Animals must balance their water content within a narrow range.

27. Osmoregulation: the regulation of water content and dissolved solute concentrations by balancing water gain and loss.
GAIN
Drinking
Eating
Osmosis
Cellular respiration
LOSS
Urination
Defecation
Evaporation
Osmosis
Organisms that live in fresh water are hypertonic to their environment, and therefore must regulate the amount of water entering their bodies or they will swell up and burst. Organisms that live on land are hypotonic to their environment, thus they run the constant risk of dehydration. Osmoregulation involves controlling the balance between the intake and output of water by regulating the ways in which water is gained and lost.

28. Osmoregulation
Living in air, salt water, and freshwater pose different challenges, but all organisms use one of two strategies:
Different strategies have evolved for handling the variety of challenges posed by the environment.
Most invertebrates that live in salt water, such as this jellyfish, are osmoconformers: they allow their internal fluid concentration to vary along with the surrounding water.
Most vertebrates, no matter their environment, and terrestrial invertebrates are osmoregulators: they maintain their internal fluids and solute concentrations within narrow ranges that may differ drastically from those of the environment. Examples of structures that have evolved to handle this challenge are Malphighian tubules in insects and kidneys in vertebrates. Both are designed to excrete excess solutes while retaining water.
Figure Two strategies for regulating the amount of salt and water in the body.

29. Take-home message 20.5
Many organisms maintain their water content within a narrow range.
Organisms must be able to take up water and get rid of water and they must be able to regulate concentrations of ions in their body fluids.
Various mechanisms and strategies have evolved for coping with these challenges.

30. 20.6 In humans, the kidney is the chief excretory organ.
The primary organ in vertebrates regulating water balance and solute concentrations is the kidney.
Humans have two kidneys, one on each side of the spine, just inside the lower ribs. (They have the same general color and shape as kidney beans!)
Each kidney:
has over 1 million nephrons
filters 2000 L of blood per day
reabsorbs all but 1.5 L
This means that all of your blood is filtered by your kidneys approximately 275 times per day, and % is returned to the circulation.
Figure Structure of the kidney. Human kidneys filter blood, reabsorb water and solutes, and excrete waste.

31. As blood passes through specialized, leaky blood vessels in the kidneys called glomerular capillaries, blood pressure forces water, ions, and small molecules out of the capillaries and into the entrance to the nephron, called Bowman’s capsule. As this filtrate moves through the tubular nephron, water is reabsorbed due to osmotic differences between the filtrate and the surrounding fluid. Salts and other valuable molecules are actively transported from the filtrate, which increases the difference in osmotic pressure and causes even more water to be reabsorbed. All water and other molecules that are not reabsorbed are excreted from the body.
Some animals have kidneys that are so efficient at reabsorbing water, that they almost never need to drink!
In addition to water, the kidneys excrete solutes that are potentially toxic to the body such as nitrogenous wastes from protein and nucleic acid breakdown, as well as excess ions such as sodium, potassium, chloride, and hydrogen. Medications, both prescription and nonprescription, and their breakdown products leave the body through the kidneys as well. If kidney function is compromised, these drugs have the potential to rise to damaging, even lethal, levels, which is why most of these products have warnings stating they should not be taken by individuals with reduced kidney function.
Figure The nephron is the fundamental unit of the human kidney. One million nephrons enable the human kidney to regulate water balance and solute concentration in body fluids while producing urine.

32. Take-home message 20.6
The kidney is the organ in vertebrates that helps maintain homeostasis by:
regulating water balance and solute concentrations in body fluids
filtering blood
removing potentially harmful ions and waste products, excreting them in urine.

33. Section 20-3 Opener
An elephant uses its trunk to forage for tree-top leaves.

34. Form Follows Function
This general rule applies to all levels of body organization: from the organism itself down to the cells that comprise it.
Figure Adapted for swimming: the streamlined body of the penguin.

35. Figure 20-16 From cells to organ systems.

36. Tissues, by definition, are cells, and their extracellular materials, acting together to perform a specific function. [this is an incomplete sentence]
In animals there are four basic tissue types: connective, epithelial, muscle, and nervous tissues. Each tissue has a unique structure, and, therefore, a unique function.

37. Take-home message 20.7
Animal bodies are highly organized, and at all levels of organization, the physical features are related to function.
In most animals, cells with similar structure and function are organized into tissue.

38. Take-home message 20.7
There are four types of tissue: connective tissue, epithelial tissue, muscle tissue, and nervous tissue.
Tissues are often organized into organs, which serve specialized functions and can contain several types of tissue.
Organs can be organized into organ systems that accomplish highly complex tasks.

39. 20.8 Connective tissue provides support.
Connective tissues give shape, structure, and support to other tissues, to organs, and to the entire body. As such, they are widely distributed and are the most abundant tissue type.
All connective tissues share two major components: scattered cells and extensive extracellular material. The general cell type is the fibroblast, which functions in the production of the extracellular proteins and regulation of the surrounding ground substance.
The differences between types arise from the arrangement, composition, and relative abundance of these components.
Figure Connective tissues consist of cells embedded in an extracellular matrix.

40. The subtypes of connective tissues can be divided into two categories based on the viscosity of their extracellular material: connective tissue proper has a flexible matrix, whereas special connective tissues have either a rigid or a liquid matrix.
Within the connective tissue proper category, we have two major types: loose connective tissues and dense connective tissues. These are descriptive terms referring to the density of the protein fibers within the surrounding material. Loose connective tissues have fibers that are randomly arranged and have relatively more surrounding material. Thus, they visually appear to have more space within them, and hence are “looser.” Dense connective tissues have fibers that are bundled together within relatively less surrounding material. They visually appear to have less space, and are therefore described as “dense.”
Figure Connective tissues: the most abundant tissues in most animals.
Loose connective tissues are not as strong at resisting deformative forces, so they are found in areas where light support and cushioning are needed, such as between tissue layers and around organs. Dense connective tissues are stronger, and are found in locations that are under higher stresses, such as holding joints together and attaching muscles to bones.
The special connective tissues of bone and cartilage have surrounding material that ranges from semi-solid to solid and abundant protein fibers, which makes them more rigid than dense connective tissue and allows them to serve as an excellent supportive and protective framework for the body. Bone, which is structurally stonger than steel, comprises our skeleton and serves as a storage reservoir for calcium and phosphate ions. Cartilage has a semi-solid matrix that is strong, but flexible, making it better for cushioning in joints and supporting more flexible structures such as our external ear and our windpipe (trachea).
Blood is unique among the connective tissues, with no fibroblasts and no protein fibers. This leaves only a liquid extracellular matrix (water) with dissolved ions and molecules. The resultant fluidity makes it easy to move throughout the body, so it serves as a transport mechanism for immune cells, nutrients, and wastes.

41. Take-home message 20.8
The most abundant type of tissue in most animals is connective tissue.
Connective tissue is a collection of cells arranged within an extracellular matrix, usually containing collagen, that holds the cells together and gives them shape, structure, and support to other body tissues.

42. 20.9 Epithelial tissue protects.
Epithelial tissues have a single layer or multiple layers of cells that are tightly adhered to each other. This makes it an excellent selectively permeable membrane because anything that wants to cross has to pass through the cells instead of between them. Thus, epithelial tissues are found mainly at the junctions between the external and internal environments: your skin and your digestive, respiratory, urinary, and reproductive tracts. They are also found lining blood vessels and body cavities.
Glands are specialized epithelial tissues that are pushed in, away from the surface, and produce secretions that are used elsewhere in the body. These glands come in a variety of shapes and sizes, and produce secretions ranging from sweat and tears to hormones to stomach acid and digestive enzymes.
Figure Epithelial tissue forms with two distinct sides.

43. In its function as a selectively permeable membrane, epithelial tissues can serve three major functions: protection, transport, and secretion.
A selectively permeable membrane is protective because it can prevent harmful substances from entering the body, such as stomach acid, bacteria, and splinters. It also prevents useful substances, such as water, from exiting the body and, thereby, prevents dehydration.
It can conduct both passive transport as small, uncharged molecules such as oxygen and carbon dioxide and easily pass through the lipid bilayer of the plasma membrane; it can conduct active transport by utilizing different protein transporters to bring molecules, such as glucose, in one side of the cell and extrude it out the other side. Only substances that can cross using one of these two processes can move from the outside of the body to the inside, or vice versa.
Secretion is a special case of transport, as it moves products created inside the epithelial cells to the outside of those cells either into a body fluid or onto a body surface. Secretion is highly regulated, and products are only released as they are needed to, for example, digest the components of the sandwich you just ingested.
Figure The multiple roles of epithelial tissue.

44. Take-home message 20.9
Epithelium is a very thin, sheet-like tissue that covers most of the exterior and interior surfaces of an animal’s body.
Epithelium acts as a barrier between the inside and outside of an organism and also aids in secretion and transport of molecules.

45. 20.10 Muscle tissue enables movement.
Muscle tissues are specialized to prevent and regulate the movement of the body and the movement of substances through tubes within the body (think blood vessels and digestive tract). They do this with intracellular proteins that are arranged to allow for contraction and extensibility, which physically shortens and elongates cells.
The body is moved through space by skeletal muscle, which is also known as striated muscle because of the striped appearance of the regular, repeating pattern the protein arrangement gives to the rod-shaped cells. This type of muscle is found in all of our skeletal muscles (biceps, gluteus maximus) as well as in our tongue and our throats to aid in swallowing and vocalization. All can be controlled consciously (at will), but some are typically under unconscious control (so we do not have to constantly think about breathing, swallowing, and blinking our eyes).
Cardiac muscle has a protein arrangement similar to that of skeletal muscle, but because its cells are more variable in shape, the striped pattern is not as distinct as in skeletal muscle. Its cells are branched (they look like they have split ends, on both ends) and have connecting channel proteins that allow ions to carry electricity from cell to cell. This makes the cells contract simultaneously, which is crucial because they make up the walls of the heart and their function is to pump blood to the lungs and to the other tissues of the body. Cardiac muscle is always under unconscious control, so even though we can think peaceful thoughts that will slow the heart’s rate of contraction, we cannot think “heart, slow down” and cause the cells to contract at a slower pace. Cardiac muscle cells will continue to contract, even if you disconnect all nerves running to it , because they can generate their own electrical signal to contract. This is why a heart can continue to beat even after it has been removed from the body!
Smooth muscle tissue has no striations (hence the smooth appearance). It is found in the walls of tubular organs such as the digestive, respiratory, and urinary tracts as well as blood vessels. Contractions in this tissue cause a decrease in tube diameter or a shortening of the tube, both of which cause or prevent movement of substances through the tube. This tissue is under unconscious control.
Figure Muscle tissues are made up of elongated cells capable of generating force when they contract.

46. Take-home message 20.10
Muscle tissue consists of elongated cells capable of generating force when they contract.
Skeletal muscle is responsible for generating movement.

47. Take-home message 20.10 Cardiac muscles cause the heart to pump blood.
Smooth muscle generates slower contractions that can gradually move blood, food, and other substances.

48. 20.11 Nervous tissue transmits information.
The fourth basic tissue type is nervous tissue, which is found only within the nervous system (brain, spinal cord, peripheral nerves, sensory organs). The system, and therefore its tissue, detects environmental stimuli, processes them, and then signals effector organs to enact a response. It is responsible for rapid communication throughout the body, as it stores and transmits information.
There are two cell types in nervous tissue: neurons and glia. The neurons are the “excitable” cells that respond to and transmit electrical and chemical signals, and their shape is specialized for these tasks. Glial cells support the functioning of neurons by providing insulation and maintaining the extracellular fluid environment.
Figure Neuron and glial cells.

49. Figure 20-24 The vertebrate nervous system: brain, spinal cord, and neurons.

50. Take-home message 20.11
Nervous tissue is specialized to store and transmit information.
There are two types of nervous tissue cells: (1) neurons, which can receive and transmit a signal, and (2) glial cells, which assist and provide nutrients for neurons.

51. 20.12 Each organ system performs special tasks.
Tissues are organized into organs, which operate together in organ systems to achieve a common function.
These systems interact to support the growth and reproduction of the entire organism.
Eleven major systems will be introduced in this chapter and will be explored in detail in later chapters.

52. Figure 20-25 The major organ systems of animals.

53. Figure 20-25 The major organ systems of animals.

54. Figure 20-25 The major organ systems of animals.

55. Figure 20-25 The major organ systems of animals.

56. Figure 20-25 The major organ systems of animals.

57. Figure 20-25 The major organ systems of animals.

58. Take-home message 20.12
In nearly all animals, some tissues are organized into organs (such as the heart, brain, lungs, and liver).
Organs serve specialized functions and consist of multiple tissue types.

59. Take-home message 20.12
Some tissues are organized into organ systems (such as the circulatory system).
Organ systems carry out the various physiological processes necessary for the growth, development, maintenance, and reproduction of the organism.