 Welcome to Physiology. In this first video, I will define physiology and apply this definition to examples. What is physiology? Physiology is the scientific study of the biochemistry and physics of the body's functions. Physiology is the study of biological function and it's intimately related to anatomy, the study of biological structures. In the images below, we have illustrations of two organs, two major biological structures, the brain on the left and the heart on the right. Now just describing the anatomy of these organs was not enough for us to understand the physiology. Early philosophers and anatomists that looked at the brain and saw how wrinkled it was and how much blood supply there was to the brain, thought perhaps this structure is important for helping to cool the blood down, functioning like a radiator that helps reduce the temperature of the body as blood flows through it radiating heat away. Of course now we know that that's not the major function of the brain, instead the brain is important for sensation, processing sensory information from the environment as well as the control of movement, sending commands to other organs, for example our muscles to enable us to move around, and also the cognitive functions of thought, our ability to process and think about information. These are all major functions of the brain. Now early philosophers like Aristotle thought that it was the heart that was responsible for sensation, the control of movement and consciousness. And of course today we know its functions are really to pump blood, the heart pumps blood and those functions of sensation and the control of movement are functions of the brain. But how did we learn that? Mostly through a loss of function approach where we study people who have damage to one of these organs. If you have damage to part of the brain you might lose sensory function. For example if part of the brain in the back known as the occipital lobe is damaged you might lose visual functions, whereas if a different part of the brain towards the front is damaged you might become paralyzed and lose the ability to control movement. Whereas if the heart is damaged such as in a heart attack you could lose the ability to pump blood throughout the body. Now we've also learned from gain of function approaches, so we can really demonstrate that the function of the heart is pumping blood because if someone has a heart attack and their heart stops beating the blood flow through the body will slow down and stop, but then we could put them on a bypass machine, a machine that will replace the pumping action of the heart and keep blood flowing throughout the body and the person will stay alive. Similarly a heart transplant can be used to keep somebody alive and this proves that the function of the heart is primarily pumping blood and not the functions that are essential to sensation and the control of movement that are functions of the brain. So another example of physiology thinking about what this field is is to think about the function of a type of formed element in the blood known as a platelet. So what is the function of platelets? One way to answer that question is to say that platelets help stop bleeding. They're involved in a mechanism known as hemostasis or this is commonly referred to as the blood clotting process. So in general, how do platelets function or what is the function of platelets is blood clotting or hemostasis, but in physiology we will be more specific, we'll describe the mechanism of hemostasis. So how do platelets stop bleeding? What is the mechanism of hemostasis? It starts with an injury to a blood vessel that will initiate the mechanism of hemostasis. So there are receptors on the surface of platelets that can recognize when a blood vessel wall is damaged. Protein in the wall of the blood vessel called collagen is not normally exposed to the platelets, if the blood vessel wall becomes damaged the platelets can bind to exposed collagen. And this will then activate the platelets to start the hemostasis mechanism where platelets will start to change their shape and clump together. They'll start to stick to the damaged blood vessel and they will also start releasing chemical signals. One of these chemical signals is called adenosine diphosphate abbreviated ADP. And ADP will act as a signal to stimulate more platelets to become activated. This will then stimulate those platelets to in turn release ADP as they become activated and start sticking to the damaged blood vessel. They will release ADP to activate even more platelets. This is what we call a positive feedback mechanism where the signal that stimulates activation of platelets is becoming stronger as the mechanism progresses until eventually bleeding stops. And the hemostasis mechanism has achieved its purpose to control bleeding and maintain the blood volume. So a major theme in the fields of anatomy and physiology which applies throughout biology is the idea that structure determines function. And that is anatomy determines physiology. Physiological mechanisms are dependent upon the biological structures. A great example of the relationship between structure and function is sickle cell anemia. Anemia refers to a low oxygen carrying capacity in the blood. Anemia you might feel tired because cells in your body cannot get enough oxygen to support their metabolism, their chemical reactions that fuel the work that the cells need to do. So normally red blood cells also known as erythrocytes transport oxygen throughout the body in the blood. And that oxygen is bound to a protein inside of the red blood cells known as hemoglobin. In sickle cell anemia there is a mutation in the gene for hemoglobin. This mutation means that the hemoglobin protein will have a different shape. Normally hemoglobin has a globular shape where the proteins are fairly round. But in sickle cell anemia this mutation causes an abnormal hemoglobin shape that forms strands or fibers inside of the red blood cells. This change in the structure of hemoglobin leads to a change in the shape of the red blood cells. The red blood cells become sickle shaped or elongated and not as round but more curved and pointy. Now these sickle shaped cells cannot flow as easily through the blood vessels because they're not as round. They tend to stick to each other and get trapped inside of blood vessels. This can cause disruption of blood flow to a tissue. But another aspect of this is that the blood cells that are sickle shaped will break more easily. They won't live as long in the blood. This leads to a lower number of red blood cells that are able to transport oxygen. That leads to the condition of anemia where you will feel very tired if you don't have enough oxygen to support the metabolism of cells throughout your body. Sickle cell anemia is showing us that the function of the organism of the entire body can be disrupted. You can feel very tired and you can end up having pain from these blood vessels that are getting sickle shaped cells trapped in them. They can lead to organ damage because the blood isn't flowing readily through organs. This can starve the organ and eventually lead to death of an organ. So that structure of the hemoglobin protein and the structure of the red blood cell leads to a change in the function of the red blood cell and eventually this affects the function of the entire body. Physiology involves the integration of information from multiple levels of biological organization. There are six distinct levels of increasing complexity from the smallest and simplest level, the chemical level, to the largest and most complex level, the organismal level. The entire body is an organism. Examples at the chemical level we see here include atoms like hydrogen and oxygen and these atoms can be held together through chemical bonds to form molecules like water. While molecules like water, proteins, nucleic acids, and lipids are essential for life, these molecules are not themselves alive. The smallest living units are cells. We'll see there's a wide variety of cell types in the human body, over 200 different cell types, and each cell will contain some smaller functional structures known as organelles. While the organelles themselves are not alive, the entire cell is living. Some organisms are just a single cell such as a yeast, an amoeba, or a bacterial cell. However, animals like humans are multicellular organisms. A tissue is a community of similar cells. For example, here we see a smooth muscle tissue that is a collection of smooth muscle cells that work together to contract. Smooth muscle tissue is found lining many hollow organs in the body. One example would be the urinary bladder. So an organ like the urinary bladder consists of two or more different tissues. The urinary bladder contains some smooth muscle tissue, but there's also an inner layer of epithelial tissue that forms a lining to help contain the urine within the bladder. There's also some connective tissue that helps support the structure and some nervous tissue that's responsible for sensing the stretching of the bladder as it fills with urine and stimulating contraction of the smooth muscle to empty the bladder. An organ system is two or more organs that work closely together for a set of functions. For example, the urinary system includes the kidneys that produce the urine, ureters that transport the urine from the kidneys to the bladder, and the urethra that transports urine out of the urinary bladder. The human body, the organismal level, consists of 11 organ systems. In addition to the urinary system, there is the reproductive system that's essential for the perpetuation of the species producing the next generation. There's the digestive system that's responsible for obtaining nutrients. There's the respiratory system that's essential for gas exchange, obtaining oxygen from the atmosphere and removing carbon dioxide from the blood. There's the cardiovascular system that transports nutrients and waste around the body in the blood, the nervous system, and endocrine systems that are responsible for regulating other organ systems. The intigumentary system is the skin, hair, and nails that help to provide a protective barrier between the body and the external environment. The lymphatic and immune system helps to protect against infection and maintain a balance of water in the body. The muscular system is working together with a skeletal system to enable movement. Together, all 11 organ systems of the human body create an organism, one individual body. Physiology is the scientific study of the biochemistry and physics of the body's functions, so it's important for us to think about what physics is. Physics is the branch of science that's concerned with the properties of matter and energy. A major subdiscipline of physics is mechanics. Mechanics deals with the study of motion and forces. On the left here we see an illustration of a person throwing a ball, and the equation known as Newton's Second Law, F equals MA, helps us to describe the motion of the ball based on the amount of force that the ball is pushed and how much mass the ball has. There will be a proportionate increase in the velocity, that is, there will be a proportional increase of acceleration. The acceleration of the ball is proportional to its mass, and the force applied to that mass. Another major subdiscipline of physics is thermodynamics. We see here the first law of thermodynamics. The change in the energy of a system is equal to the amount of heat transferred minus the amount of work done. When an object, when a mass is moved through space, that's work that's being done. For example, if you are throwing a ball, the force that causes that ball to move a distance, that mass of the ball moving a distance is work that's been done. The force that you apply to that mass is the energy being transferred from the system of your body, from a potential energy stored in your body, to the system of the ball to form the kinetic energy of the ball's motion. This first law of thermodynamics describes the conservation of energy, the idea that energy can never be created or destroyed. Energy can only be transferred or transformed. Electromagnetism is the subdiscipline of physics concerned with electricity and the movement of electrical charge. The equation we see here is known as Ohm's law. I represents the current, the movement of charge. V is the voltage or separation of charge and R is the resistance or how difficult it is for the charge to flow from one location to another. We will study the example of electromagnetism applied to understanding the communication in nervous tissue, how information is rapidly relayed through the body, through electrical signals, that is the flow of charged chemicals across the cell. If there are more positively charged chemicals outside the cell and negatively charged chemicals inside the cell, that separation of charge is a voltage. And that voltage will be a source of potential energy to drive a current, a flow of positive charge into the cell. When channels open to allow positively charged ions to move across the plasma membrane of the cell, then a current will be produced as ions are flowing through. And that current will be proportional to the voltage and inversely proportional to the resistance. And the resistance can be changed by opening more channels for the current to flow through. So we can see that electromagnetism will be important for us to understand the nervous system. Electromagnetism will also be applied to help us understand the muscular system and the functions of the muscle in the cardiovascular system. We will also see applications of Ohm's law as we study the flow of blood in the cardiovascular system, as well as to describe the flow of air through the airways as we study the respiratory system. Another field of science that's fundamental to physiology is biochemistry. Biochemistry is the study of chemicals in biological systems and organisms. And so the chemistry that we will study will be biochemistry because this is a physiology class where we'll be studying biological functions, the functions of the biological structures of our body. And some of those structures are chemicals. Metabolism refers to chemical reactions. All of the chemical reactions in your body collectively are your metabolism. We can subdivide metabolism into two branches. Catabolism are all of the chemical reactions that take large molecules and break them down, producing smaller molecules, smaller products. And as large molecules are broken down to produce smaller molecules, energy is released. The other division of metabolism is known as anabolism. Anabolism will take smaller building block molecules and join them together to form larger molecules. And these chemical reactions will require the input of energy. Because catabolism releases energy and anabolism requires energy, catabolism can be used to fuel anabolism. A major subdiscipline of physiology, electrophysiology is the application of electromagnetism to the study of biology. The example we see here is the electrocardiogram where electrodes are placed on the surface of the skin and measure the electrical activity of the heart. Electrical signals normally spread through the heart to stimulate the contractions that enable the pumping function of the heart. The electrocardiogram enables us to monitor the normal electrical activity of the heart, but can also be useful for diagnosis of abnormal electrical activity. Electrophysiology is also very important for studying the functions of the nervous system. Developmental biology is a subdiscipline of physiology that studies how biological structures change, especially during the embryonic and fetal stages of life before birth. For example, the process of gastrulation occurs at the beginning of the third week of embryonic development. During gastrulation, three layers of tissue known as the germ layers form in the embryo. The outer layer known as ectoderm will later develop into the nervous system as well as the skin. The middle layer, the mesoderm, will go on to develop into the circulatory system and muscles. Then the innermost layer, the endoderm, will go on to develop into most of the digestive organs as well as the inner layers of the lungs. Another subdiscipline of physiology is ecophysiology, the study of adaptations of organisms to their environmental conditions. For example, on the left here of the image we can see camels, which are especially adapted to living in a hot, arid environment with very little water supply. They're able to survive in the desert. And then the image on the right here, we can see a couple of humans. Now, you'll notice that they are not furry, they don't have hair all over their body. We only have a little bit of hair on our body and that helps us to cool our body down when we're hot. We also have sweat glands distributed in the skin that helps to cool our body down. Another adaptation to help protect against the damaging effects of sun is the production of melanin in the skin, which gives a brownish color to the skin. People with darker skin color have an adaptation that helps protect them from the damaging effects of ultraviolet light in the sun, which could cause cancer or other damaging effects in the body. But having a darker skin color from the pigment melanin is protective against those damaging effects of ultraviolet light. And this is why we see a distribution of skin color, where darker skin color is more common closer to the equator, where the intensity of the sun is greater. Another interesting example of human adaptations to their environmental conditions is the Baju or C nomads of Southeast Asia, Southern Philippines. They have traditionally obtained food by spearfishing, where they hold their breath, swim deep to spearfish. These people have been getting their food for many generations by spearfishing, and they have developed adaptations that help them hold their breath for a very long time. These adaptations include larger spleens. This spleen can serve as a reservoir of red blood cells that are released during a dive reflex. And the dive reflex is enhanced in the Baju, where one aspect of the dive reflex is to release more red blood cells from the spleen. Another part of the dive reflex is to decrease the heart rate as they're holding their breath during the dive. And together, these adaptations help them maintain sufficient oxygen levels in their blood to dive for a long period of time and catch fish. Exercise physiology is another subdiscipline of physiology. This is the study of functional changes that occur with exercise. For example, we can discuss how exercise influences the heart. You're probably familiar with the idea that your heart rate increases when you're exercising. If you're out running, your muscles are working hard, and they need to have lots of blood flow through them in order to carry lots of nutrients in and lots of waste out. And that's why the heart will start beating faster to help speed up the blood flow through those working muscles. And this will involve the nervous system sending commands to the heart. And here we can see there are nerves going to the heart known as the vegas nerve, which is a nerve that contains parasympathetic motor neurons. And then there's also sympathetic cardiac nerves that also control the heart, but these have opposite functions. So the parasympathetic motor neurons would decrease the heart rate and the sympathetic motor neurons would increase the heart rate as well as increasing the force of contraction. And so when you're exercising, if you're out for a run, your sympathetic motor neurons will send commands to your heart that leads to an increased heart rate. Another major subdiscipline of pathophysiology is the study of functional changes in disease. For example, we could study high blood pressure known as hypertension, and the pathophysiology of hypertension could involve studying how does high blood pressure develop. High blood pressure is more common in individuals that are overweight. So we could study the cause of hypertension in obesity. How does obesity cause hypertension? And so studies have looked at the hormones that are released from fat as we become overweight. We have more hormones being released from fat that can stimulate the sympathetic nervous system and stimulate the renin angiotensin aldosterone hormone system. And so by having more of these hormones that come from fat, our heart can be stimulated to start working harder and our kidneys could be stimulated to start pulling more sodium and water back from the forming urine. And that leads to a larger volume of blood. And as the heart is working harder to pump that blood, the blood pressure rises. And so that's an example of how pathophysiology can explain the cause of a disease state.