Introduction To Physiology: Homeostasis (PDF)

INTRODUCTION TO PHYSIOLOGY: HOMEOSTASIS Block: Foundations Block Director: James Proffitt, PhD Session Date: Monday, July 29, 2024 Time: 9:00 – 10:00 am Instructor: Zoe Cohen, PhD Department: Physiology Email: zcohen@email...

INTRODUCTION TO PHYSIOLOGY: HOMEOSTASIS Block: Foundations Block Director: James Proffitt, PhD Session Date: Monday, July 29, 2024 Time: 9:00 – 10:00 am Instructor: Zoe Cohen, PhD Department: Physiology Email: [email protected] INSTRUCTIONAL METHODS Primary Method: IM13: Lecture ☐ Flipped Session ☐ Clinical Correlation Resource Types: RE18: Written or Visual Media (or Digital Equivalent) INSTRUCTIONS Please review learning objectives and the notes before attending this session. READINGS N/A LEARNING OBJECTIVES 1. Define homeostasis. 2. Describe a homeostatic process in the human body. Give specific examples of how all the organs work together. 3. Describe how dysfunction in a single organ can lead to dysfunction of another organ. 4. List the steps associated in the loss of homeostasis in heat stroke. CURRICULAR CONNECTIONS Below are the competencies, educational program objectives (EPOs), disciplines and threads that most accurately describe the connection of this session to the curriculum. Related Related Competency\EPO Disciplines Threads COs LOs CO-01 LO #1 MK-02: The normal structure and Physiology N/A function of the body as a whole and of each of the major organ systems CO-01 LO #2 MK-02: The normal structure and Physiology N/A function of the body as a whole and of each of the major organ systems CO-01 LO #3 MK-05: The altered structure and Physiology N/A function (pathology & pathophysiology) of the body/organs in disease Block: Foundations | COHEN [1 of 10] INTRODUCTION TO PHYSIOLOGY: HOMEOSTASIS Related Related Competency\EPO Disciplines Threads COs LOs CO-01 LO #4 MK-05: The altered structure and Physiology N/A function (pathology & pathophysiology) of the body/organs in disease CONTEXT: This lecture on homeostasis aims to introduce the fundamental concept of functional interaction/interdependence among organ systems in the human body, as well as to illustrate how dysfunction of a single organ may lead to multiple organ dysfunction. In all blocks of the ArizonaMed curriculum, it will be critically important to have this concept in mind as you seek to understand the bases for inter-organ interaction and the consequences of dysfunction in a particular organ or organ system for other organ systems. WHAT IS PHYSIOLOGY?__________________________________ Physiology is the study of normal body function. It might not seem as “sexy” as a ischemic stroke, hypovolemic shock, or Goodpasteur’s disease (things you’ll learn about in your training here at UACOM), but without having a strong base of understanding HOW things should work, it’s much harder to diagnose what the issue is when things don’t work (as well as how to treat it). Because of this, Physiology will appear in every block during the pre-clerkship curriculum. Spend the time now learning how things should work, and disease and treatment become much easier! Block: Foundations | COHEN [2 of 10] INTRODUCTION TO PHYSIOLOGY: HOMEOSTASIS IMPORTANT PHYSIOLOGICAL FUNCTIONS: Feedback Loops: Feedback is defined as the ability of a system to change in a way to maintain homeostasis. Biological systems (including us) operate based on a series of inputs and outputs, each caused by and causing a certain event. Biological systems contain many types of regulatory circuits, both positive and negative. As in other contexts, positive and negative do not imply that the feedback causes good or bad effects. A negative feedback loop is one that tends to slow down a process, whereas the positive feedback loop tends to accelerate it. In a positive feedback mechanism, the output of the system stimulates the system in such a way as to further increase the output. Common terms that could describe positive feedback loops or cycles include “snowballing” and “chain reaction”. Without a counter-balancing or “shut- down” reaction or process, a positive feedback mechanism has the potential to produce a runaway process. The majority of positive feedback loops in healthy individuals have to do with gestation and birth of an infant. Most biological feedback systems are negative feedback systems. Negative feedback occurs when a system’s output acts to reduce or dampen the processes that lead to the output of that system, resulting in less output. In general, negative feedback loops allow systems to self- stabilize. Negative feedback is a vital control mechanism for the body’s homeostasis. Examples are everywhere, including blood pressure regulation, heart rate, temperature control…and many many more. Flow Down Gradients: Flow is the movement of “stuff” from one point in a system to another point in the system. 1. Molecules and ions in solution move from one point to somewhere else. 2. Fluids (blood, lymph) and gases (air) move from one point to another. 3. Heat moves from one place to another. Block: Foundations | COHEN [3 of 10] INTRODUCTION TO PHYSIOLOGY: HOMEOSTASIS Flow occurs because of the existence of a gradient between two points in a system. 1. Differences in concentration (concentration gradients) cause of molecules and ions in solution to move toward a region of lower concentration. 2. Differences in electrical potential (potential gradients) causes ions in solution to move. 3. Differences in pressure (pressure gradients) between two points in a system cause substances to move toward a region of lower pressure. 4. Differences in temperature (temperature gradients) between two points cause heat to flow. The magnitude of the flow is a direct function of the magnitude of the energy gradient that is present – the larger the gradient the greater the flow. More than one gradient may determine the magnitude and direction of the flow. 1. Osmotic (concentration gradient) and hydrostatic pressures together determine flow across capillary walls. 2. Concentration gradients and electrical gradients determine ion flow through channels in cell membranes of neurons and muscle cells. There is resistance or opposition to flow in all systems. 1. Resistance and flow are reciprocally related, the greater the resistance the smaller the flow 2. Resistance is determined by the physical properties of a system 3. Some resistances are variable and can be actively controlled 1. ion channels in a membrane can open and close (increasing resistance) 2. arterioles and bronchioles can constrict and dilate 3. piloerection can increase the resistance to heat flow in many mammals OVERVIEW OF HOMEOSTASIS: The foot bone is connected to the leg bone! ☺ Although this childhood song is anatomically and physiologically lacking, it does have one thing correct…Everything in the body is “connected” to everything else. This idea of connectedness is termed “homeostasis”. The Encyclopedia Britannica (online edition) defines homeostasis as “any self-regulating process by which biological systems tend to maintain stability while adjusting to conditions that are optimal for survival”. If homeostasis works, life goes on…if it doesn’t, death occurs. Block: Foundations | COHEN [4 of 10] INTRODUCTION TO PHYSIOLOGY: HOMEOSTASIS A good example of homeostasis in medicine is the control of body temperature. In humans, normal body temperatures hover around 37° C (98.6° F). However, various factors such as; exposure to hot or cold, hormonal changes, changes in metabolic rate, or disease states can cause body temperature to increase or decrease. Temperature regulation is controlled by the hypothalamus in the brain. When changes in temperature are sensed, compensatory mechanisms, which include shunting of blood to the skin or core, perspiration, or shivering happen. Control center: thermoregulatory center in brain Receptors: temp Effectors: sweat sensitive cells in glands activated skin and brain Stimulus: Body Temp Rises Stimulus: Body Temp Falls Receptors: temp Effectors: skeletal sensitive cells in muscles skin and brain Control center: thermoregulatory center in brain But what happens when this feedback loop is unsuccessful? In the body, the cardiovascular system supplies oxygen and nutrients to every cell in the body. Without this, the cells become non-functional. If we first look at how certain organs (specifically some of the organs introduced in this block) work together, we can understand the seriousness if homeostasis fails. The cardiovascular system consists of a pump (heart), a series of tubes (vessels) and the delivery substance (blood). The system works because of pressure differences between the left side of the heart and the right side of the heart. If the pump can’t generate pressure, the system is dysfunctional. Likewise, if there is low pressure within the vessels (due to increased diameter) or because there’s a decrease in blood volume, not enough nutrients or gases are making it to our organs. Heat related diseases are something we in Arizona should understand. Heat related issues fall along a continuum from Heat Rash (also known as “prickly heat”, which is caused by blockage of sweat glands) to Heat Cramps (loss of body salts), to Heat Exhaustion (increased body salt and fluid loss, which leads to headache, nausea, dizziness, weakness and irritability) and finally Block: Foundations | COHEN [5 of 10] INTRODUCTION TO PHYSIOLOGY: HOMEOSTASIS ending in Heat Stroke (the most serious form of heat related illness, where the body is no longer able to rid itself of excess heat and core temperature begins to rise, leading to central nervous system dysfunction, coma and possibly death). Let’s look briefly at many of the organs that are introduced in Foundations and how they work together. Skin: The skin has three main functions: protection, regulation and sensation. The skin provides protection from: mechanical impacts and pressure, variations in temperature, micro-organisms, radiation and chemicals. In terms of regulation, skin helps us regulate body temperature and fluid balance. In terms of sensation, the skin contains an extensive network of nerve cells that detect and relay changes in the environment. CV System: Our pump system that allows blood with nutrients to get to all cells within the body. The heart and vessels allow transport of nutrients, oxygen, and hormones to cells throughout the body as well as removal of metabolic wastes (carbon dioxide, nitrogenous wastes). The blood also contains the cells of the Immune System, which defend the body against foreign microbes and toxins, and platelets, which play a role in coagulation. The combination of blood and the vessels it moves through allows the cardiovascular system to play a role in temperature regulation. Respiratory System: The respiratory system is involved in breathing, also called pulmonary ventilation. In pulmonary ventilation, air is inhaled through the nasal and oral cavities (the nose and mouth). It moves through the pharynx, larynx, and trachea into the lungs. Then air is exhaled, flowing back through the same pathway. Changes to the volume and air pressure in the lungs trigger pulmonary ventilation. Inside the lungs, oxygen is exchanged for carbon dioxide waste through the process called external respiration. This respiratory process takes place through hundreds of millions of microscopic sacs called alveoli. Renal System: The function of the kidneys is to remove liquid waste from the blood in the form of urine; keep a stable balance of salts and other substances in the blood; and produce erythropoietin, a hormone that aids the formation of red blood cells. It also senses and plays a role in regulation of blood pressure. Spleen: The spleen plays multiple supporting roles in the body. It acts as a filter for blood as part of the immune system. Old red blood cells are removed from circulation in the spleen, and platelets and white blood cells are stored there. GI Tract: The large, muscular tube that extends from the mouth to the anus, where the movement of muscles, along with the release of hormones and enzymes, allows for the digestion of food. Also called the alimentary canal or digestive tract. __________________________________________________ Case study: A 38 year old male went for a hike up to Finger Rock in the Santa Catalina Mountains on August 5th 2015 (temp 106 F, Humidity 55%). After finishing the hike, he complained of dizziness, finally falling into an “apathic” state. Emergency Medical personnel were called and while being treated, the patient suffered a seizure before falling into a coma. Block: Foundations | COHEN [6 of 10] INTRODUCTION TO PHYSIOLOGY: HOMEOSTASIS What happened? Skin: Liquids help to cool us down by allowing the body to produce sweat. However, liquids are also necessary for bodily functions, such as keeping up blood pressure. You can lose large amounts of body fluid in the form of sweat without noticing any effects, but at a certain point the body will reserve the remaining fluid for vital functions and stop sweating. Sweat evaporates more rapidly in dry weather, cooling the body more efficiently than in humid weather. When working in humid conditions, the core temperature rises more rapidly. This is why weather forecasts add a humidity factor or heat index to represent how you will actually feel outdoors. CV System: In an effort to decrease heat, the vessels (specifically the arterioles) nearest the skin dilate…increasing heat dissipation. When this happens, there is less volume available to meet the needs of other organs. In addition, when sweating, there was a decrease in total blood volume due to fluid loss. The combination of vasodilation and decreased blood volume leads to decreased blood pressure (the driving force of blood though the CV system). The heart must then work harder to try and move blood through the body. However, the heart is also working with reduced delivery of oxygen and nutrients. When this happens, the contractile cells of the myocardium are unable to contract as forcefully, decreasing blood pressure and delivery of blood to all organs. There is also the chance of changes in heart rhythm (arrhythmias), further decreasing blood delivery. Respiratory System: Less blood enters the pulmonary system (both for supplying the structures of the lungs, and for gas transfer). Two things happen…first, the structures aren’t receiving oxygen and nutrients needed to maintain their integrity, which can allow pathogens to enter the blood stream. A person suffering from heat stroke will also increase respiratory rate, which can lead to respiratory alkalosis. Over time, the cells of the respiratory system start to die due to lack of oxygen and nutrients and there’s a switch to a metabolic acidosis Renal System: Renal dysfunction in heat stroke can be caused by direct thermal injury, volume depletion, or muscle cell breakdown (rhabodomyolysis). Dysfunctional kidneys lose the ability to filter substrates, which can lead to fluid retention, increased blood pressure, and changes in mental status. Spleen: If the cells of the spleen aren’t getting oxygen and nutrients, they will be unable to work in the role of a filter (especially a place to remove red cells), and a person can become Block: Foundations | COHEN [7 of 10] INTRODUCTION TO PHYSIOLOGY: HOMEOSTASIS jaundiced (due to increased circulating bilirubin from death of red cells not cleared from the system). The spleen also acts as a secondary lymphoid structure and loss of function can be associated with increased risk of infection. GI tract: Excessive heat exposure reduces intestinal integrity. Heat-stress causes blood to move to the periphery in an attempt to maximize radiant heat dissipation, and this blood redistribution is supported by vasoconstriction of the gastrointestinal tract. As a result, reduced blood and nutrient flow leads to hypoxia at the intestinal epithelium, which ultimately compromises intestinal integrity and function. What didn’t happen that should have? Questions to think about and discuss. 1. What would you predict his blood pressure was when EMTs arrived? What did they do about it? Would they give him fluids? Would they give him O2? 2. What would you guess his vital signs were: respiratory rate? shallow or deep? BP? Heart rate? Cardiac output? Temp—skin? core?? 3. What would have caused this person to have a seizure? 4. How would you counsel this patient/future patients to avoid this situation in the future? Controlled Hypothermia As you can see, the body continuously engages in coordinated physiological processes to maintain a stable temperature. In some cases, however, overriding this system can be useful, or even life-saving. Hypothermia is the clinical term for an abnormally low body temperature (hypo- = “below” or “under”). Controlled hypothermia is clinically induced hypothermia performed in order to reduce the metabolic rate of an organ or of a person’s entire body. Controlled hypothermia often is used, for example, during open-heart surgery because it decreases the metabolic needs of the brain, heart, and other organs, reducing the risk of damage to them. When controlled hypothermia is used clinically, the patient is given medication to prevent shivering. The body is then cooled to 25–32°C (79–89°F). The heart is stopped and an external heart-lung pump maintains circulation to the patient’s body. The heart is cooled further and is maintained at a temperature below 15°C (60°F) for the duration of the surgery. This very cold temperature helps the heart muscle to tolerate its lack of blood supply during the surgery. Some emergency department physicians use controlled hypothermia to reduce damage to the heart in patients who have suffered a cardiac arrest. In the emergency department, the physician induces coma and lowers the patient’s body temperature to approximately 91 degrees. This condition, which is maintained for 24 hours, slows the patient’s metabolic rate. Because the patient’s organs require less blood to function, the heart’s workload is reduced. Block: Foundations | COHEN [8 of 10] INTRODUCTION TO PHYSIOLOGY: HOMEOSTASIS This section is just FOR YOU!! I’ve been chatting with pre-med and medical students for years, and one area that has come up over and over is that there is a “new language” that needs to be learned. That’s true…luckily, much of that language is Latin! Here is a chart with some common Latin terms that will hopefully help! **This is NOT a definitive list…but a good place to start! Word Part Meaning Examples Meaning of example a-, an, non Without, Not Apnea, Anuria Not breathing, Without urine Ab-, ef- Away Abductor muscle, Muscle pulling away Efferent neuron from midline, carrying info away from brain Ad-, af- Toward Afferent neuron, Carrying info toward Adductor muscle brain, muscle pulling toward midline -alg Pain Neuralgia, fibromyalgia Nerve pain, muscle pain Ang(i)-, vaso Vessel Angiogenesis, Making new blood vasodilator vessel, increase radius of vessel Ante-, pre-, pro- Before Prenatal, antebrachial, Before birth, before the promonocyte upper arm, before the monocyte is mature Anti-, contra- Against, resisting Antibody, Resisting a foreign contraindicated body, against using Arthr(o), artic- Joint Arthritis, articulation Joint inflammation, joint -ase Enzyme Maltase, lipase Enzyme breaking down maltose, enzyme breaking down fats Aut(o)- Self Autoimmunity Self-immunity Bi-, di-, diplo- Two Bicuspid valve Heart valve with 2 leaflets Brady- Slow Bradycardia Slow heart rate Cephal-, -ceps Head Hydrocephalus, biceps Water in brain (in the fermoris head), 2-headed muscle by femur -cide Kill Spermicide Sperm killer Circ-, peri- Around Circumcision, Cut around (i.e. male periodontal foreskin), around the teeth -clast Break, destroy Osteoclast Cells that destroy bone cells -crine Secrete, release Endocrine gland Glands that secrete hormones Cyan- Blue Cyanosis Bluish tint to skin Dia-, per-, trans- Through, separate, Diarrhea, permeable, Flow though across transcutaneous (intestines), across a membrane, across skin Dys-, mal- Bad, painful, difficult Dyspnea, malnutrition Difficulty breathing, bad nutrition/diet Ectop- Displaced Ectopic pregnancy Displaces pregnancy -emia Blood Hyperglycemia High blood sugar En-, endo-, intra- Inside, within Endosteum, intraocular Space inside bone, inside the orbit of the eye Epi- Upon, over, above Epidermis Layer of skin over the dermis Block: Foundations | COHEN [9 of 10] INTRODUCTION TO PHYSIOLOGY: HOMEOSTASIS Equi- homo-, iso- Same, equal, balanced Homeostasis, isotonic Constant balance of body systems, equal solute Ex-, ecto- Outside Extracellular fluid Solute/fluid located outside cell -gram Something written Electrocardiogram Print out of electrical (ECG) activity of the heart -graph Writing apparatus Electrocardiograph Machine used to make an ECG Hem- Blood Hemothorax Blood that has leaked into chest cavity Hemi-, semi- Half Cerebral hemisphere One half of the brain Hist- Tissue Histology Study of tissues Hypo-, infra-, infer-, Under, below, less Hypotonic, Lesser solute sub- submandibular concentration, under the jaw -itis Inflammation Appendicitis Inflammation of the appendix Inter- Between Interstitial fluid Fluid between cells Lys, lyze Break apart, dissolve Hydrolysis, lysosome Breaking down, organelle that digests Med-, meso-, meta- Middle Mediastinum Middle space of chest cavity Micro-, -ole, -ule Small Microscope, arteriole, Apparatus to view small venule objects, small artery, small vein Mono-, Uni- One Monozygotic, unicellular Twins from same zygote (identical), 1- celled organism Morph, -plasty Shape Morphology, rhinoplasty Distinguishing by shape, nose shaping Mort, necro- Death Post mortem, necrotic After death, dead tissue tissue Neo- New Neonatal Newborn Olig- Little, few Oliguria Very little urine produced Ost- Bone Osteoblast, Maker of new bone osteomyelitis cells, bone infection -ostomy Make an opening Tracheostomy Make an opening in the trachea Para Beside Parathyroid glands Small glands embedded into the sides of the thyroid gland Path Disease Pathogenic bacteria Disease causing bacteria Phago Eat, feed Phagocyte Eating cell -phasia Speech Dysphagia Difficulty speaking Phobia, phobe Fear Hydrophobia Fear of water -plasia Growth, formation Hyperplasia Excessive growth Post After Post natal After birth Pseudo False Pseudounipolar neuron Neuron common in the eye Super, supra Above, over Superior vena cava, Veins bringing blood supraorbital from above the heart, over the eye Tachy Fast Tachycardia Faster than normal heart rate Block: Foundations | COHEN [10 of 10]