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Human Physiology: Feedback Systems, Proteins, and Cell Communication, Assignments of Human Physiology

Athabasca UniversityHuman Physiology

An in-depth exploration of various aspects of human physiology, including feedback systems, protein function and regulation, and cell communication. It covers topics such as baroreceptors, protein-protein interactions, cell identification, and membrane proteins. The document also delves into cell death mechanisms, metabolism, and endocytosis, offering a comprehensive overview of human physiology for students.

Typology: Assignments

2023/2024

Uploaded on 03/30/2024

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jennifer-gallop 🇨🇦

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Acknowledgement of Academic Responsibility
Answers to assignment questions must be original; that is, you must write them all yourself. You can
base your answers on information in the course textbook or other sources, but if you use sources other
than the textbook, you must cite them appropriately.
Plagiarism is a form of academic misconduct that has serious consequences. It is your responsibility to
read and understand the statement on Academic Integrity in the Student Manual and the Student
Academic Misconduct Policy in the AU undergraduate Calendar. If plagiarism is detected, and if an
investigation concludes that you must rewrite the assignment, then your assignment grade will be
reduced by 20 marks.
“By filling in my name and ID number below, I acknowledge my responsibility to academic
integrity and confirm that none of the wording in my answers has been copied or plagiarized in
any way from any source.”
Student’s name:
Student's AU ID number: Click or tap here to enter text.
NOTE: This assignment will not be marked if it is submitted without the above two lines filled in.
Biology 230: Human Physiology Assignment 1 (Revision 11)
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Acknowledgement of Academic Responsibility

Answers to assignment questions must be original; that is, you must write them all yourself. You can base your answers on information in the course textbook or other sources, but if you use sources other than the textbook, you must cite them appropriately. Plagiarism is a form of academic misconduct that has serious consequences. It is your responsibility to read and understand the statement on Academic Integrity in the Student Manual and the Student Academic Misconduct Policy in the AU undergraduate Calendar. If plagiarism is detected, and if an investigation concludes that you must rewrite the assignment, then your assignment grade will be reduced by 20 marks. “By filling in my name and ID number below, I acknowledge my responsibility to academic integrity and confirm that none of the wording in my answers has been copied or plagiarized in any way from any source.” Student’s name: Student's AU ID number: Click or tap here to enter text. NOTE: This assignment will not be marked if it is submitted without the above two lines filled in.

Assignment 1

Chapters 1–

Total marks: 100 Each question is worth 5 marks. Answer each question with as much detail as possible. Submit your completed assignment via the Assignment 1 Drop Box on the course home page.

Chapter 1: An Introduction to Physiology

  1. When have you used the scientific method, or perhaps certain aspects of the scientific method, in your life? Are there other fields besides physiology in which the scientific method is useful? How could you apply the method to your daily life? Please see the chapter review for section 1.5 on page 17 of the customized textbook for a description of the scientific method. The scientific method consists of four steps, observation, forming hypotheses, designing an experiment, and interpreting data. During my academic career I have had to use the scientific method several times. One time that comes to mind is an experiment I designed in my undergrad with bean beetles where I had to formulate a hypothesis, design the experiment, observe, and interpret the data into a report. I chose to compare egg emergence in various temperatures and hypothesized that the emergence would increase with an increase in temperature. However, observation and interpretation were different than my hypothesis and in fact decreased with an increase in temperature. There are many fields besides physiology that require the scientific method. Virtually, and science field uses the scientific method, because they have theories that need to be tested and proven or disproven. Psychology is another field that has used the scientific method. For example, the Bandura Experiment or the Stanford Prison Experiment are social experiments that have been conducted, where a hypothesis was generated, experiment was designed, observations occurred, and interpretation of the data was produced in a published study. Any field that needs to prove something will use the scientific method. The scientific method can be applied to my daily life if I want to change any aspect of my life. For example, if I wanted to lose weight, I would hypothesize that if I change my eating habits or work out more, I will achieve weight loss. I would design an experiment by selecting heathy food to consume or create a workout regimen that I would follow for X number of days. I would control variables by eliminating junk food from my house or setting timers for the length of the work out. Over a period of time, I would record data such as my weight and observe physical changes in appearance (inches in circumference lost). Finally, I would interpret the data as successful or not. This is simply one example that can be implemented in my life. I could also see my reaction with various foods, hair products, or anything that can produce an outcome.
  2. Define a feedback system. What is a controlled variable? A feedback system is a regulatory process that relies on its own internal parameters to monitor, evaluate, and adjust in order to maintain homeostasis. A controlled variable is a constant that is held during an experiment or event. In the case of a feedback system, a controlled variable is a monitored parameter that sends information out if adjustments need to be made to the system. For example, the human body
  1. Your best friend decides to begin frying his eggs in margarine instead of butter because he heard that eating butter is bad for his heart. Is this a wise choice? Are there other alternatives? My friend would be correct, frying an egg with margarine is a better option than butter. Butter is a saturated fat, meaning it only contains single covalent bonds between the carbon atoms and hydrocarbon chain. At room temperature butter is a solid and is derived from animal fat (milk) which diets with large amounts of saturated fats are associated with heart disease. An alternative to butter and margarine is oil. At room temperature oil is a liquid due to the double bonds in their hydrocarbon chains, also known as monounsaturated and polyunsaturated fats. The double bonds cause kinks in the chain not allowing the fatty acids to pack densely together and solidifying. Oils are also believed to be a better a healthier alternative and can decrease the risk of heart disease.
  2. What are the functions of water in the human body? Water is the most abundant and essential inorganic compound that is important for all living organisms. In the body, the majority of the reactions that occur are done in a watery medium. Water is a polar compound because it has uneven valence electrons which cause it to have a partial negative charge for oxygen and a partial positive charge for hydrogen. Due to water’s polarity, it allows it to be resistant to temperature, gives water molecules cohesion and acts as a solvent for ionic and polar substances. As water can dissolve substances, within the body it can dissolve waste products allowing them to be flushed from the body in forms such as urine. When inorganic acids, bases and salts are mixed with water, they dissolve and dissociate. Salts in particular, when they dissolve in the body, they dissociate into charge ions such as electrolytes that carry electrical currents for example, in nerves and muscle tissues. Water is also essential for lubrication in the chest, abdomen, joints and organs where they have to touch and move around each other. Within the GI tract, mucus and secretions moisten food and allow it to move through the digestive system.

Chapter 3: Cells

  1. What is your favorite organelle? Why is it your favorite? Imagine what the cell would be like without that particular organelle and describe how that cell would be able to function (or not) without your chosen organelle. The mitochondria are my favorite organelle because it is traditionally known as the powerhouse of the cell. The mitochondria are called the powerhouse because it produces ATP which is the energy required for the body to function. Mitochondria generates most of the ATP through aerobic respiration and if eukaryotic cells didn’t have mitochondria the organism would not function. Mitochondria produces ATP as its main energy source and has hundreds to thousands of them within various cells. Therefore, producing large amounts of ATP and without the mitochondria a cell would not be able to produce this energy required for survival. The absence of mitochondria would inhibit the reactions of the Krebs cycle and ETC which occur within the mitochondria.
  2. How do membrane proteins perform the following functions? Provide one example each for a. and b.
    1. Communication Membrane proteins perform communication by using receptors or cellular recognition sites. Receptors are integral proteins that can either extend into or completely through a lipid bilayer.

These proteins can recognize and bind to specific types of molecules or ligands which alter the cell’s function. An example of communication is when an antidiuretic hormone binds to receptors in kidneys. When this occurs, signals are sent out to initiate a change in water permeability of various plasma membranes.

  1. Enzymatic functions Enzymes can be either an integral or peripheral membrane protein. This type of protein catalyzes reactions on both the interior or exterior side of a cell. The catalytic reaction, however, is dependent on the direction the active site faces. An example of an enzyme protein is lactase, as it extends past the epithelial cells of the small intestine. Lactase splits disaccharide lactose that are found in dairy products which help in the digestion process.
  2. Cell identification Cell identification is done by proteins such as glycoproteins and glycolipids. These proteins distinguish and recognize their own cells when new tissue forms and recognize and respond to invading foreign cells.
  3. Tight junctions Tight junctions are membrane proteins that consist of weblike strands fusing them together with the outer surface of adjacent plasma membranes. The fusion seals off passageways and gaps between the adjacent cells. This is an important mechanism as it prevents substances from passing from one cell to another when it is not supposed to. It also prevents contents from various organs leaking into blood or other tissues.
  4. Gap junctions Gap junctions have membrane proteins known as connexins that connect to adjacent membranes via connexons which are tiny fluid-filled tunnels. These junctions are not fused but are separated by narrow intercellular gaps. The connexons allow passage of ions from one cell cytosol to another. The purpose of gap junctions is to allow cells in tissues to communicate with one another.
  5. Compare and contrast apoptosis with necrosis. Apoptosis and necrosis are both ways that cause cells to die within the body. Apoptosis is initiated by internal causes such as genes and enzymes. Necrosis is initiated by external cause such as injuries which elicits an inflammatory response. Apoptosis is a genetically programmed cell death cycle. A cascading set of events occur which initiate the production of enzymes that will damage the cell such as disruption of its cytoskeleton and nucleus. As disruption and decay occurs, the cell will begin to shrink and pull away from its neighboring cells. The cells plasma membrane will remain intact but the DNA in the nucleus will fragment and cytoplasm starts to shrink. As the cell decays, phagocytes ingest the cell by binding the plasma membrane to a lipid of the plasma membrane of the suicidal cell. The purpose of apoptosis is to remove unneeded cells such as those in fetal development. For example, removing the webbing between digits and regulating the number of tissue cells by eliminating potentially dangerous cells.

Chapter 4: Metabolism

  1. Briefly describe:
    1. Anaerobic glycolysis. Anaerobic glycolysis is the process of breaking down glucose to produce lactic acid when oxygen is not present. In glycolysis a 6-carbon glucose molecule is converted to two 3-carbon pyruvic acid molecules, which is then converted into two lactic acid molecules that yield 2 ATP molecules.
    2. Ketogenesis. Ketogenesis is the process of fatty acid catabolism in which the liver converts acetyl CoA into ketone bodies. As lipids go through lipolysis, which is the process where triglycerides are broken down into glycerol and fatty acids. Fatty acid catabolism begins with beta oxidation in the mitochondrial matrix. During which enzymes remove two carbon atoms from the fatty acid carbon chain and attach it to coenzyme A to create acetyl CoA. Most of acetyl CoA then enters the Krebs cycle, however the acetyl CoA that does not continue in this pathway will generate APT through ketogenesis and is converted to ketone bodies. Ketone bodies consist of acetoacetic acid, beta-hydroxybutyric acid, and acetone, which when the three of them are produced, it is known as ketogenesis.
    3. Where lipogenesis occurs. Lipogenesis occurs in the liver and adipose tissue cells, when individuals consume more calories than they need. It is the process of synthesizing lipids.
    4. How fatty acids are anabolized (built). Fatty acids are anabolized through lipogenesis. There are two pathways in lipogenesis, one forms glycerol and the other fatty acids. The pathway for fatty acids is as follows: glucose → glyceraldehyde 3-phosphate → pyruvic acid → acetyl CoA → fatty acids.
    5. How glycerol is anabolized. Glycerol is anabolized through the first pathway in lipogenesis by using glucose and converting it to glycerol. The pathway to form glycerol is as follows: glucose → glyceraldehyde 3- phosphate → glycerol.
    6. How triglycerides and phospholipids are anabolized. Phospholipids are anabolized by having a glycerol backbone joined by two fatty acid chains that are attached to the first two carbons and a phosphate group linked to the third carbon. Triglycerides are anabolized similarly to a phospholipid. Triglycerides also have a glycerol backbone joined by three fatty acid chains which form an ester linkage.
  1. High-protein, low-carbohydrate diets like the Atkins diet are often called ketogenic diets. After reading this chapter, can you explain why? What might be a good reason to go on a diet like this? What might be a good reason not to go on a diet like this? The ketogenic diet, also known as the keto diet, is primarily made up of consuming protein, fats and very little carbohydrates. When someone begins the keto diet, it forces our bodies into ketosis which is when the concentration of ketone bodies increases in the blood. This process occurs as a result of excessive beta-oxidation from lipids metabolizing. Keton bodies are created in the liver through the process of ketogenesis which converts acetyl CoA into acetoacetic acid, beta-hydroxybutyric acid, and acetone. As ketones leave the liver, they can be used as fuel for the body when they enter the blood and enter the Krebs cycle to produce ATP. This diet can be beneficial if an individual is looking to lose weight and body fat. As glucose is the main source of energy for the body and the body would have a limited supply of carbohydrates, glucose will be derived from stored triglycerides to produce ATP. This diet may not be ideal for some people because carbohydrates can be found in a mass variety of food including heathy ones, some vegetables and fruits. This diet is quite restrictive and if someone was to cut out all the food that contains carbs, the person will begin to lack other nutrients necessary for their body to remain healthy. Also, being on this diet an individual may feel more fatigued because their body has to work twice as hard to make the necessary ATP as glucose will not be readily available.

Chapter 5: Transport Across the Plasma Membrane

  1. What real-life situations could lead to crenation of your blood cells? What about hemolysis? Describe a situation in your life or a situation you have heard about in which someone has experienced or has come close to experiencing one of these processes. Crenation occurs when water molecules leave a cell faster than the enter, thus causing the cell to shrink. This event typically occurs when cells are placed into hypertonic environments. Crenation can occur in blood cells when the concentration of nonpenetrating solutes is higher in the solution outside the blood cell. Water has a tendency to move from low to high solute concentration therefore, water would leave the blood cell faster than it enters, causing the cell to shrink. When an individual does not drink enough water, hypertoxicity can occur and lead to crenation in blood cells. Hemolysis occurs when water molecules enter a cell faster than they can leave, causing the cell to swell. This situation occurs when cells are placed in hypotonic environments. Hemolysis occurs in blood cells when the concentration of nonpenetrating solutes is lower in the solution outside the blood cell. The water will then move into the cell faster than it leaves moving from a higher concentration. The water enters in excess and causes the cell to burst or lyse.
  2. Briefly describe each of the following plasma membrane functions:
    1. Importing Plasma membrane can import substances through vesiculas transport such as endocytosis. Endocytosis is the process in which vesicles detach from the plasma membrane and import material into the cell. Endocytosis a active process that requires the use of ATP to form the vesicles and import the material. There are three types of endocytosis, receptor-mediated which

receptor site on the extracellular side of the plasma membrane. This binding site is located at the clathrin-coated pits where clathrin proteins attach to the membrane on the cytoplasmic side forming a the clathrin-coated vesicle around the LDL. Once it has entered the vesicle quickly becomes uncoated and fuses with an endosome and separates from the receptors. The LDL then fuses with a lysosome and uses digestive enzymes to break down the LDL into amino acids, fatty acids, and cholesterol. The receptors are then taken back to the membrane to be recycled.

Chapter 6: Cell Signaling

  1. Have you ever heard of someone becoming less sensitive to something as the result of increased exposure to it? Provide an example of this. Do you think it could be the result of down-regulation? Explain. Yes, I have heard of people becoming less sensitive to things due to repeated exposure. This has happened to me with my animals. When I was younger, I was allergic to dogs and cats and had minor symptoms of itchy eyes and sneezing when I would get their hair on me. Growing up, I always had wither a cat or dog, if not both at the same time and over time I discovered my allergies became less and less to them as if I was developing a tolerance to my animals. This could be an example of down-regulation because down-regulation is the process of removing/decreasing the number of target receptors due to an excess of extracellular messengers. Some of the receptors may be removed from the plasma membrane and degraded. Another method of down regulation could be that the receptors were chemically modified via the antihistamines I would take to be around my animals, disrupting the pathway that caused me to have allergic reactions.

Chapter 7: The Nervous System and Neuronal Excitability

  1. If a stimulus is very small, it may only trigger a small graded potential in the sensory neuron. Can you think of a time when a stimulus was so small you didn’t even detect it? Why does a small graded potential result in no signal being sent? What would need to happen for you to detect the stimulus? When a hair falls from my head (without being pulled) is such a small graded stimulus that I do not feel it when it happens. Graded potentials can be larger or smaller depending on the amount of ligand-gated or mechanically gated channels open and how long they remain open. The ion channels alter the number of ions moving across the plasma membrane causing the graded potential. If the stimulus is small enough it may not deviate far enough from the resting membrane potential of - 70mV. An action potential does not occur when there is a subthreshold stimulus, which is a weak depolarization that does not bring the potential to threshold. Therefore, no detection in the CNS occurs. In order for a stimulus to be detected, there must be enough force to open the ligand-gated or mechanically gated channels. The membrane potential would need to depolarize to become less negative, reaching the membrane potential threshold, then repolarizing, releasing an action potential. The action potential works in an all-or-none principle which means that the stimulus must be strong enough to have an effect or there will be none.
  2. Where is each of the following types of gated channels located, and what function does each of these channels serve?
  3. ligand gated

Ligand-gated channels can be found on the plasma membrane of dendrites of some sensory neurons such as pain receptors and cell bodies of interneurons and motor neurons. These channels open and close in response to the ligand stimulus. Neurotransmitters, hormones, food or odor can cause the gates to open or close because the ligand binds to the active site on the channel. The ligand-gated channels are involved in creating graded potentials by changing the electrochemical gradient and concentrations of ions from inside and outside the membrane.

  1. voltage gated Voltage-gated channels are located on the plasma membrane of axons of all neurons. These channels open in response to voltage stimulus or membrane potential changes. These gates are responsible for generating and the conduction of action potentials.
  2. mechanically gated Mechanically-gated channels are located on the plasma membrane of dendrites of some neurons such as touch, pressure and pain receptors. These gated channels open when responding to a mechanical stimulus such as touch, pressure or vibration. The channels open allowing ions to enter into the membrane and travel down the gradient sending and action potential to the brain which detects the stimulus.
  3. Neurotransmitters cause postsynaptic ion channels to open. Explain how this can lead to either a depolarizing graded potential or a hyperpolarizing graded potential. Neurotransmitter can cause either a depolarization or hyperpolarization on the postsynaptic neuron. This is because it depends on the receptors that the neurotransmitter is binding to which can excite or inhibit an action potential. Once the neurotransmitter binds to the receptor, ligand-gated channels are activated and open allowing ions to pass through the membrane. For example, if the Na+ channel opens, an influx of Na+ can cause depolarization. Whereas, if the Cl- or K+ channel opened, allows Cl- to move into the cell and K+ to move out causing the cell to hyperpolarize because the interior of the cell becomes more negative.

Chapter 8: The Central Nervous System

  1. Choose a cranial nerve and describe its functions. Is it a sensory, motor, or mixed nerve? What do you imagine might happen if this cranial nerve were damaged? The facial cranial nerve is considered mixed, meaning it contains axons of both motor and sensory neurons. Its function is to convey taste input from the front two-thirds of the tongue (sensory), stimulates secretion of tears and saliva (sensory) and controls facial muscles (motor). If the facial cranial nerve was damaged, facial paralysis would occur. An individual would not have control over their facial movements and would likely have a droopiness to their face. It would also cause a decreased ability to form tears and saliva as well as the sensory input from the tongue would weaken and the individual would have a diminished sense of taste.
  2. Imagine you have been hired by a pharmaceutical company to develop a drug to regulate a specific brain disorder. What is a major physiological roadblock to developing such a drug? How can you design a drug to bypass that roadblock so that the drug can be delivered to the brain where it is needed?