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CHAPTER 1.6
| Question | Answer |
|---|---|
| Organization | Living things exhibit a far higher level of organization than the nonliving world around them. They expend a great deal of energy to maintain order, and a breakdown in this order is accompanied by disease and often death. |
| Cellular composition | Living matter is always compartmentalized into one or more cells. |
| Metabolism | Living things take in molecules from the environment and chemically change them into molecules that form their own structures, control their physiology, or provide them with energy. |
| Metabolism | is the sum of all this internal chemical change. |
| Metabolism | There is a constant turnover of molecules in the body |
| Metabolism | Although you sense a continuity of personality and experience from your childhood to the present, nearly every molecule of your body has been replaced within the past year. |
| Responsiveness and movement | The ability to sense and react to stimuli (changes in the environment) is called responsiveness or excitability. |
| Responsiveness and movement | It occurs at all levels from the single cell to the entire body, and it characterizes all living things from bacteria to you |
| Responsiveness | is especially obvious in animals because of nerve and muscle cells that exhibit high sensitivity to environmental stimuli, rapid transmission of information, and quick reactions. |
| Responsiveness & Movement | Most living organisms are capable of self-propelled movement from place to place |
| Responsiveness & Movement | and all organisms and cells are at least capable of moving substances internally, such as moving food along the digestive tract or moving molecules and organelles from place to place within a cell. |
| Homeostasis | though the environment around an organism changes, the individual maintains relatively stable internal conditions—for example, a stable temperature, blood pressure, and body weight. |
| Growth and development | Development is any change in form or function over the lifetime of the organism. |
| Growth and development | (1) differentiation, the transformation of cells with no specialized function into cells that are committed to a particular task; and (2) growth, an increase in size. Some nonliving things grow, but not in the way your body does. |
| Some ---- things grow, but not in the way your body does. | nonliving |
| If you let a saturated sugar solution evaporate, crystals grow from it, but not through a change in the composition of the sugar. | They merely add more sugar molecules from the solution to the crystal surface. |
| The growth of the body, by contrast, occurs through ----; for the most part, your body is not composed of the molecules you ate but of molecules made by chemically altering your nutrients. | chemical change (metabolism) |
| Reproduction | Living organisms produce copies of themselves, thus passing their genes on to new, younger containers—their offspring. |
| Evolution | All living species exhibit genetic change from generation to generation and therefore evolve. |
| Evolution | This occurs because mutations (changes in DNA structure) are inevitable and environmental selection pressures favor the transmission of some genes more than others. |
| Evolution | Unlike the other characteristics of life, evolution is a characteristic seen only in the population or gene pool as a whole. |
| Evolution | No single individual evolves over the course of its life |
| Clinical and legal criteria of life differ from these | biological criteria |
| A person who has shown no brain waves for 24 hours, and has no reflexes, respiration, or blood flow other than what is provided by artificial life support, can be declared legally ----- | dead |
| At such time, however, most of the body is still biologically alive and its organs may be useful for ----. | transplant |
| Earlier we considered the clinical importance of variations in human anatomy, but ---- is even more variable. | Physiology |
| ------ variables differ with sex, age, weight, diet, degree of physical activity, genetics, and environment, among other factors. | Physiological |
| Failure to consider such variation leads to medical mistakes such as overmedication of the elderly or medicating women on the basis of research done on young men | Physiological |
| If a textbook states a typical human heart rate, blood pressure, red blood cell count, or body temperature it is generally assumed, unless otherwise stated | that such values refer to a healthy 22-year-old weighing 58 kg (128 lb) for a female and 70 kg (154 lb) for a male, and a lifestyle of light physical activity and moderate caloric intake (2,000 and 2,800 kcal/day, respectively). |
| The human body has a remarkable capacity for | self-restoration |
| Hippocrates | commented that it usually returns to a state of equilibrium by itself, and people recover from most illnesses even without the help of a physician. |
| Homeostasis | This tendency results from----, the body's ability to detect change, activate mechanisms that oppose it, and thereby maintain relatively stable internal conditions, even in spite of greater changes in the surrounding environment. |
| French physiologist ---- observed that the internal conditions of the body remain quite constant even when external conditions vary greatly. | Claude Bernard (1813-78) |
| Claude Bernard (1813-78) | For example, whether it is freezing cold or swelteringly hot outdoors, the internal temperature of the body stays within a range of about 36° to 37°C (97°-99°F) |
| Walter Cannon (1871-1945) | coined the term homeostasis for this internal stability. |
| Walter Cannon (1871-1945) | homeostasis has been one of the most enlightening theories in physiology. |
| We now see ---- as largely a group of mechanisms for maintaining homeostasis, and the loss of homeostatic control as the cause of illness and death | physiology |
| Pathophysiology | is essentially the study of unstable conditions that result when our homeostatic controls go awry. |
| Do not, however, overestimate the degree of | internal stability |
| Internal conditions | aren't absolutely constant but fluctuate within a limited range, such as the range of body temperatures noted earlier. |
| The internal state of the body is best described as a ----, in which there is a certain set point or average value for a given variable (such as 37°C for body temperature) and conditions fluctuate slightly around this point. | dynamic equilibrium (balanced change) |
| Negative Feedback | Fundamental mechanism that keeps a variable close to its set point is; a process in which the body senses a change and activates mechanisms that negate or reverse it. By maintaining stability, negative feedback is the key mechanism for maintaining health. |
| Negative Feedback | By maintaining stability, negative feedback is a key mechanism for maintaining health |
| These principles can be understood by comparison to a home | heating system |
| Suppose it is a cold winter day and you have set your thermostat for 20°C (68°F) | the set point |
| If the room becomes too cold, a temperature-sensitive switch in the thermostat turns on the furnace | The temperature rises to slightly above the set point, then the switch breaks the circuit and turns off the furnace. |
| This is a ---- process that reverses the falling temperature and keeps it within a narrow range of the set point | negative feedback |
| When the ---- turns off, the temperature slowly drops again until the switch is reactivated-thus, the ---- cycles on and off all day. | furnace |
| The room ---- doesn't stay at exactly 20 ̊C but fluctuates slightly—the system maintains a state of dynamic equilibrium in which the ---- averages 20°C and deviates only slightly from the set point. | temperature |
| Because feedback mechanisms alter the original changes that triggered them (temperature, for example), they are often called | feedback loops |
| Room Temperature falls to 19 C (67 F) -> Thermostat activates furnace -> Heat output -> Room Rises to 20 C (68 F) -> Thermostat shuts off furnace -> Room cools down | feedback loops |
| 36.5 *C (97.7 *F) | Vasoconstriction (Shivering) |
| Negative Feedback in Thermoregulation | (a) The negative feedback loop that maintains room temperature. |
| Negative Feedback | Negative feedback usually keeps the human body temperature within about 0.5°C of a 37°C set point. |
| Cutaneous vasoconstriction | and shivering set in when the body temperature falls too low, and soon raise it. |
| Cutaneous vasodilation | and sweating set in when body temperature rises too high, and soon lower it. |
| How does vasodilation reduces | Vasodilation allows more blood to flow close to the body surface and to lose heat through the skin; thus, it cools the body |
| Body temperature | is similarly regulated by a "thermostat❞—a group of nerve cells in the base of the brain that monitor the temperature of the blood. |
| If you become overheated, the --- triggers heat-losing mechanisms | thermostat |
| One of these is ---- (VAY-zo-dy-LAY-shun), the widening of blood vessels. | vasodilation |
| When vessels of the ----, warm blood flows closer to the body surface and loses heat to the surrounding air. | skin dilate |
| If this isn't enough to return your temperature to normal, sweating occurs; the ---- of water from the skin has a powerful cooling effect. | evaporation |
| Conversely, if it is cold outside and your body temperature drops much below 37°C, these nerve cells activate | heat-conserving mechanisms |
| The first to be activated is -----, a narrowing of the blood vessels in the skin, which serves to retain warm blood deeper in your body and reduce heat loss. | vasoconstriction |
| If this isn't enough, the brain activates ----- that generate heat. | shivering-muscle tremors |
| English physician Charles Blagden (1748–1820) | staged a rather theatrical demonstration of homeostasis long before Cannon coined the word. |
| In 1775, ---- spent 45 minutes in a chamber heated to 127°C (260°F)—along with a dog, beefsteaks and eggs, and some research associates. | Blagden |
| Being dead and unable to maintain ---- , the steaks were cooked well done in as little as 13 minutes and almost dry in 47 minutes, and the eggs were cooked hard. | homeostasis |
| But being alive and capable of evaporative cooling, the dog panted and the men sweated profusely. | homeostasis |
| Even at such extreme room temperatures, the men's oral temperatures were only | 37° to 38°C (98°-100°F). c |
| Blagden said their nostrils felt scorched each time they inhaled the hot room air, and cooled each time they exhaled. Everyone including the dog survived, but history does not record whether the men ate the steak in celebration or shared it with the . | dog |
| Let's consider one more example-homeostatic control of blood pressure. | When you first rise from bed in the morning, gravity causes some of your blood to drain away from your head and upper torso, resulting in falling blood pressure in this region—a local imbalance in homeostasis |
| This is detected by sensory nerve endings called baroreceptors in large arteries above the heart. | Local imbalence of Homeostasis |
| They transmit nerve signals to the brainstem, where we have a cardiac center that regulates the heart rate. | Baroreceptors |
| Cardiac Center | responds by transmitting nerve signals to the heart, which speed it up. |
| The faster heart rate quickly raises the blood pressure and restores normal | homeostasis |
| In elderly people, this ---- is sometimes slow to respond, and they may feel dizzy as they rise from a reclining position and their cerebral blood pressure falls. This sometimes causes fainting. | feedback loop |
| Step 1: ---- Step 2: The blood from his upper body drains which in turn creates a homeostatic imbalance. Step 3: The baroreceptors above the heart respond to the drop in blood pressure. The arteries from the aorta of the heart are the receptors. | Step 1: The person rises from his bed. |
| Step 1: The person rises from his bed Step 2: ---- Step 3: The baroreceptors above the heart respond to the drop in blood pressure. The arteries from the aorta of the heart are the receptors. | Step 2: The blood from his upper body drains which in turn creates a homeostatic imbalance. |
| Step 1: The person rises from his bed. Step 2: The blood from his upper body drains which in turn creates a homeostatic imbalance. Step 3: --- | Step 3: The baroreceptors above the heart respond to the drop in blood pressure. The arteries from the aorta of the heart are the receptors. |
| Step 4: --- Step 5: The heart is the effector. The heartbeat accelerates in response to the cardiac center. Step 6: The blood pressure rises to normal, therefore the homeostasis is restored and back to normal. | Step 4: The brain is the integrating center. The baroreceptors send signals to the cardiac center of the brainstem. |
| Step 4: The brain is the integrating center. The baroreceptors send signals to the cardiac center of the brainstem. Step 5: --- The heartbeat accelerates in response to the cardiac center. Step 6: The blood pressure rises to normal, therefore the homeosta | Step 5: The heart is the effector. |
| Step 4: The brain is the integrating center. The baroreceptors send signals to the cardiac center of the brainstem. Step 5: The heart is the effector. The heartbeat accelerates in response to the cardiac center. Step 6: --- | Step 6: The blood pressure rises to normal, therefore the homeostasis is restored and back to normal. |
| This reflexive correction of --- illustrates three common, although not universal, components of a feedback loop: a receptor, an integrating center, and an effector. | blood pressure (baroreflex) |
| The ---- is a structure that senses a change in the body, such as the stretch receptors that monitor blood pressure. | receptor |
| such as the cardiac center of the brain, is a mechanism that processes this information, relates it to other available information | Integrating (Control) Center |
| (for example, comparing what the blood pressure is with what it should be), and makes a decision about what the appropriate response should be. | Integrating (Control) Center |
| The effector is the cell or organ that carries out the final corrective action. | In the example, it's the heart |
| receptor | The response, such as the restoration of normal blood pressure, is then sensed by the ----, and the feedback loop is complete. |
| is a self-amplifying cycle in which a physiological change leads to even greater change in the same direction, rather than producing the corrective effects of negative feedback. | Positive feedback |
| Positive feedback | is often a normal way of producing rapid change. |
| When a woman is giving birth, for example, the head of the fetus pushes against her cervix (the neck of the uterus) and stimulates its nerve endings | Positive feedback |
| Nerve signals travel to the brain, which, in turn, stimulates the pituitary gland to secrete the | hormone oxytocin |
| travels in the blood and stimulates the uterus to contract. | Oxytocin |
| This pushes the fetus downward, stimulating the cervix still more and causing the ---- to be repeated. | positive feedback loop |
| Labor contractions therefore become more and more intense until the ---- is expelled. | fetus |
| Other cases of beneficial positive feedback are seen later in this book in, for example | blood clotting, protein digestion, and the generation of nerve signals. |
| ------ -> Nerve impulses from cervix transmitted to brain -> Brain stimulates pituitary gland -> Oxytocin stimulates uterine contractions and pushes fetus towards cervix | Head of fetus pushes against cervix |
| Head of fetus pushes against cervix -> ---- -> Brain stimulates pituitary gland -> Oxytocin stimulates uterine contractions and pushes fetus towards cervix | Nerve impulses from cervix transmitted to brain |
| Head of fetus pushes against cervix -> Nerve impulses from cervix transmitted to brain -> ---- -> Oxytocin stimulates uterine contractions and pushes fetus towards cervix | Brain stimulates pituitary gland |
| Head of fetus pushes against cervix -> Nerve impulses from cervix transmitted to brain -> Brain stimulates pituitary gland -> ---- | Oxytocin stimulates uterine contractions and pushes fetus towards cervix |
| Could childbirth as a whole be considered a negative feedback event? Discuss | Yes; one could say that pregnancy activates a series of events leading to childbirth, the termination of the pregnancy. Thus, it has the qualifies of a negative feedback loop. |
| Frequently, however, positive feedback is a harmful or even life-threatening process. | This is because its self-amplifying nature can quickly change the internal state of the body to something far from its homeostatic set point. |
| Consider a high fever, for example. | A fever triggered by infection is beneficial up to a point, but if the body temperature rises much above 40°C (104°F), it can create a dangerous positive feedback loop. |
| This high temperature raises the metabolic rate, which makes the body produce heat faster than it can get rid of it. | Thus, temperature rises still further, increasing the metabolic rate and heat production still more. |
| This "vicious circle" becomes fatal at approximately 45°C (113°F). | Thus, positive feedback loops often create dangerously out-of-control situations that require emergency medical treatment. |
| Another fundamental concept that will arise repeatedly in this book is that matter and energy tend to | flow down gradients |
| This simple principle underlies processes as diverse as blood circulation, respiratory airflow, urine formation, nutrient absorption, body water distribution, temperature regulation, and the action of nerves and muscles. | flow down gradients |
| A physiological gradient | is a difference in chemical concentration, electrical charge, physical pressure, temperature, or other variable between one point and another. |
| If matter or energy moves from the point where this variable ---, we say it flows down the gradient-for example, from a warmer to a cooler point, or a place of high chemical concentration to one of lower concentration. | has a higher value to the point with a lower value/ Movement in the opposite direction is up the gradient. |
| Outside of biology, ---- can mean a hill or slope, and this affords us a useful analogy to biological processes fig. 1.10a). | gradient |
| A wagon released at the top of a hill will roll down it (“flow”) spontaneously, without need for anyone to exert energy to move it. | Similarly, matter and energy in the body spontaneously flow down gradients, without the expenditure of metabolic energy. |
| Movement up a gradient does require an energy expenditure | just as we would have to push or pull a wagon to move it uphill. |
| The first illustration shows a small boy sliding down a small slope in a cartwheel. | The slope is marked with a down arrow and labeled 'Down gradient.' |
| The second illustration shows the small boy pulling up the cartwheel and walking up the slope. | The slope is marked with an up arrow and labeled 'Up gradient.' |
| If you open a water tap with a garden hose on it, you create a pressure gradient; water flows down the hose from the high-pressure point at the tap to the low-pressure point at the open end. | Each heartbeat is like that, creating a gradient from high blood pressure near the heart to low pressure farther away; blood flows down this gradient away from the heart (fig. 1.10b). |
| When we inhale, air flows down a ----- from the surrounding atmosphere to pulmonary air passages where the pressure is lower. | pressure gradient |
| A ---- also drives the process in which the kidneys filter water and waste products from the blood. | pressure gradient |
| Chemicals flow down | concentration gradients. |
| When we digest starch, a high concentration of sugars accumulates in the small intestine | The cells lining the intestine contain only a low concentration of sugars, so sugars flow from the intestinal space into these cells, thus becoming absorbed into the body's tissues. |
| through cell membranes and epithelia by osmosis, from the side where it is more concentrated to the side where it is less so. | Water flows |
| Charged particles flow down electrical gradients | Suppose there is a high concentration of sodium ions (Na†) just outside a cell and much lower concentration inside, so the outer surface of the cell membrane has a relatively positive charge and the inner surface is relatively negative |
| If we open channels in the membrane that will let sodium pass, sodium ions rush into the cell, flowing down their electrical gradient. | Because each Na* carries a positive charge, this flow constitutes an electrical current through the membrane. |
| We tap this current to make our nerves fire, our heart beat, and our muscles contract. | Electrical Gradient |
| In many cases, the flow of ions is governed by a combination of concentration and electrical charge differences between two points, and we say that ions flow down | Electrochemical Gradients. |
| Heat flows down a thermal gradient. | Suppose there is warm blood flowing through small arteries close to the skin surface, and the air temperature around the body is cooler |
| Heat | will flow from the blood through the tissues and to the surrounding air, down its thermal gradient, and be lost from the body. |
| heat flow | is also important in preventing the testes from overheating, which would otherwise prevent sperm production. |
| Biological criteria of life include organization | List four biological criteria of life and one clinical criterion: ----, metabolism, responsiveness, and reproduction. |
| metabolism | List four biological criteria of life and one clinical criterion: Biological criteria of life include organization, -----, responsiveness, and reproduction. |
| responsiveness | List four biological criteria of life and one clinical criterion: Biological criteria of life include organization, metabolism, ----, and reproduction. |
| reproduction | List four biological criteria of life and one clinical criterion: Biological criteria of life include organization, metabolism, responsiveness, and ----. |
| Explain how a person could be clinically dead but biologically alive | Clinically, a heartbeat or brain activity is often used. A person can be clinically dead, lacking heartbeat or brain activity, yet biologically alive if cellular processes continue. |
| Dynamic equilibrium | refers to the state where internal conditions fluctuate within a narrow range, maintaining balance despite external changes. |
| Homeostasis doesn't prevent change but regulates it to keep conditions stable. | Why would it wrong to say homeostasis prevents internal change? |
| Explain why stabilizing mechanisms are called negative feedback | Negative feedback mechanisms stabilize the body by sensing changes and initiating responses to counteract or reverse them. Imagine a thermostat maintaining room temperature. |
| Explain why stabilizing mechanisms are called positive feedback | Positive feedback amplifies changes. In biological systems, this can lead to rapid, destabilizing changes, disrupting homeostasis. For instance, during childbirth, contractions intensify as hormones increase, pushing the process forward. |
| Activates tissues generate carbon dioxide, which diffuses out the tissue into the bloodstream, to be carried. Is this diffusion into the blood a case of flow up a gradient or down? | When active tissues produce carbon dioxide, it diffuses into the bloodstream down a concentration gradient. This movement from high to low concentration is akin to water flowing downhill, driven by gravity, ensuring equilibrium. |
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