Homeostasis and Body heat (1).pdf

BIOLOGY 154 Form and Function of Animals This series of lectures will be given over 5 weeks. We will cover three learning themes 1) Homeostasis and body heat 2) Neural control and muscle contraction 3) Respiration, energy and muscle metabolism The re...

BIOLOGY 154 Form and Function of Animals This series of lectures will be given over 5 weeks. We will cover three learning themes 1) Homeostasis and body heat 2) Neural control and muscle contraction 3) Respiration, energy and muscle metabolism The relevant textbook page numbers are given in the pdf documents (Page numbers and study objectives on SUNLearn) for each learning theme. Presenter: Prescribed Text Book: Prof Theresa Wossler Russel et al. 2019. Biology [email protected] The Dynamic Science. 5th edition Why do elephants have big ears? Spend a few minutes thinking about this The ears account for one-sixth of the animal's surface area. If you said temperature regulation  This infrared picture shows just how much cooler the ears are having lost heat from them  Body plans (an animal’s shape and size) are constrained mainly due to its surface area to volume ratio (thus endothermic animals cannot get too big or too small) With increased complexity, comes specialised organ systems and extensive folding of external and internal surfaces (so as to increase the surface area relative to the volume). nucleus Materials are exchanged at the The surface area to surface, but used to supply cells that volume ratio gets smaller make up the volume. Thus, an as the organism/cell gets organism’s surface area must be large larger compared to its volume for exchange to be effective  Brings us to an important concept in biology Surface area to volume ratio: the comparison between the size of the outside of an object and the amount inside Understanding surface area to volume ratio: Video 1 in the Video repository on SUNLearn  Using figures A-D, complete Table 1 Table 1: Surface area to volume ratio calculations Figure Total # of cubes Surface area Volume Surface are to volume ratio A B C D  Physiology What other features can you think of that assist with thermoregulation in elephants? Air permeates the thin skin of the elephant's ears, thereby cooling blood as it passes though a web of vessels inside the ears before Morphology returning to the body. Elephants often spread their ears and face the wind to magnify this effect. Behaviour Elephants also cool down by increasing blood flow to highly vascularized skin patches, Morphology and biological function called “hot spots” from where heat is lost (physiology) are correlated  What differences Importance do you notice about of shape the jackal and Arctic fox? Think where they live Jackal Similarly, what is different between the jackrabbit and snowshoe hare? Arctic fox Rounder body shapes, small ears and shorter limbs reduces surface area to volume ratios = heat conservation Elongated bodies, longer limbs, large thin ears increases surface area to volume ratios = heat loss The body's surface = main site for heat exchange with the environment  Who will lose Importance of size heat slower? Think about it carefully. Remember these are both endotherms Why? You might ask yourself what is an endotherm? Endotherms use internally generated heat (mostly via metabolic processes) to maintain body temperature. Their body temperature tends to stay steady regardless of environment. Thermoregulation in elephants and penguins: Video 2 in the Video repository on SUNLearn  How small can you go? Pygmy shrew ~2g Hummingbird 2g Shrews and humming birds are the smallest of terrestrial endotherms. With a high surface area to volume ratio, they lose metabolic heat very quickly. Because they are endotherms, they have metabolisms that work overtime to keep their tiny bodies warm. To feed their metabolism (to maintain ~constant body heat) they eatCanadian hourly shrew or would starve to death. Metabolic demands met via torpor (evolutionary adaptation). Torpor is a state of slowed body functions (reduced metabolism) used to conserve energy and heat during the cold nights.  Daily energy budgets are difficult to maintain as body size decreases. Hummingbirds eat 2-3 times their body weight per day to fuel their metabolisms. During torpor, they consume up to 50 times less energy and become hypothermic. Hummingbird torpor is an evolutionary strategy that preserves their daily metabolic budgets It is important to remember that biological processes, Proximate Ultimate unlike other processes, (mechanistic) (evolutionary) are a result of evolution explanations explanations through natural selection. How does Why does There are TWO levels of it work? it work explanation for like that? biological phenomena Relationship of basal metabolic rate to body size Why does the elephant have a lower mass specific basal metabolic rate compared to the mouse?  So we have briefly looked at animal shapes and sizes and the importance of surface area to volume ratio. One aspect of this is having to regulate body temperature since body surfaces are the main site for heat exchange with the environment Why regulate body temperature? All living organisms depend on a complex series of chemical reactions that are reliant on temperature. Life is sustained through the regulation of body temperature. Let us look at a basic example of maintaining a relatively constant body temperature Body Body temperature temperature rises drops What would one call Body sweats this mechanism? more Negative feedback loop This brings us to a very important concept and that is: HOMEOSTASIS The ability of organisms to regulate the condition of their internal environment within narrow limits. Life is only possible within physiological limits.  Homeostasis Below Above optimum OPTIMUM optimum Homeostasis Maintaining relative constancy of the internal (fluid) environment Minimum level Maximum level What do we mean by the internal (fluid) environment?  What do we mean by the internal environment? Internal Environment Extracellular fluid = interstitial fluid + plasma Cells Intracellular fluid (ICF) cytoplasm INTERNAL ENVIRONMENT (Extracellular fluid) ECF (Tissue fluid)  Body compartments and exchange Compartments have barriers and the properties of these In the body, water moves barriers determines through semi-permeable the movement of membranes of cells and substances between from one compartment of compartments the body to another by a process called osmosis. The concentration of water and salts is the same inside and outside of the cells. If body cells lose or gain too much water by osmosis, they do not function efficiently.  Osmosis Passive movement of water from an area of low solute concentration (dilute) to an area of high solute concentration (less dilute) across a semi- Direction of movement permeable membrane Osmosis between 2 solutions Unequal solute Equal solute concentrations concentrations Original level H 2O of solutions Semipermeable membrane  No further net diffusion  Steady state exists  Osmosis between pure H2O and a solution Hydrostatic (fluid) pressure difference Tendency for water to diffuse by osmosis to the right arm is balanced by an opposing hydrostatic pressure to push water into left arm. Osmosis ceases. Opposing pressure necessary to completely stop osmosis is equal to the osmotic pressure of the solution.  Simplifying osmotic and hydrostatic pressures Osmotic pressure (the pulling pressure) of a solution is the measure of tendency of a solution to pull water into it by osmosis because of the relative concentration of non penetrating solute and water Hydrostatic pressure of a solution (the pushing pressure) is the pressure exerted by a stationary fluidic part of the solution on an object (semi permeable membrane in case of osmosis)  Osmosis and Tonicity Osmotic pressure is an important factor affecting biological cells. Osmoregulation is the homeostasis mechanism of an organism to reach balance in osmotic pressure. Body cells need to maintain osmotic pressure to function efficiently. For example, if a cell is put in a hypertonic solution, water escapes the cell and flows into the surrounding solution, causing the cell to shrink. Understanding osmosis and tonicity: Video 3 in the Video repository on SUNLearn Multicellular animals require a stable internal environment Interdependent relationship Maintain of cells, body systems and homeostasis Body Homeostasis systems Is essential for Homeostasis maintains optimal Make up survival of conditions for enzyme action throughout the body, as well as all cell functions. Homeostasis is essential for cell survival, each cell makes up part of a body system which maintains the internal environment shared by all cells  Three basic mechanisms used by animals to maintain homeostasis Environmental deviation span a few minutes to that of over many generations the lifespan of an individual - adaptations Response Physiology Morphology Behaviour These responses can be rapid, lasting a few minutes, or occur seasonally, and some may be selected over many generations (adaptations).  Animals in their environment & homeostasis Nervous System (NS) Internal environment Many homeostatic responses Control Small internal are regulated by the NS and Systems fluctuations endocrine system working together or independently. What are the consequences of the Large external evolution of homeostasis? fluctuations Endocrine System HOMEOSTASIS is a dynamic process responsible for maintaining a relatively “constant” internal environment (small fluctuations) even with large external fluctuations  Requirements for homeostasis 1) sensors/receptors  monitor a “controlled” condition i.e. temperature, and send inputs to the control centre) 2) control centres (integrators)  integrates incoming information and compares it to the set point (for temp = 37°C) and determines action. 3) Effectors (muscles/glands/behaviour)  information from the control centre elicits a response Negative feedback Loops = corrective action eg. Blood pressure / sugar levels / body temperature Homeostasis works on the principle of negative feedback Note: Positive feedback does not play a role in homeostasis Positive feedback loops = disturbance is amplified eg. Nerve action potentials / Blood clotting / contraction of uterus Uterine contractions during parturition (birthing process) 2 3 Hormonal output Neural input 1 4 5  Homeostasis and Negative Feedback Loops Response Return to Perturbing set point factor Effector Negative Causes changes feedback loop to compensate completed Stimulus for deviation – Deviation from set point Integrating Sensor center Constantly Compares monitors conditions to conditions set point  A typical example of Neural Negative Feedback control pilorelaxation piloerection Don’t forget there are also behavioural thermoregulation mechanisms: Hot: stretch out to increase surface area, shade etc. Cold: curl up to reduce surface area, huddle  How do you think we could improve homeostatic control? Imagine you had this system warming your home. How could you improve your temperature regulation of your home? Think about it for a while If you came up with adding an air conditioner together with the furnace then you would be correct = antagonistic effectors Having effectors with antagonistic actions allows for a finer degree of control Your blood glucose levels are maintained using anatgonists Insulin & glucagon are antagonists Antagonistic effectors act in opposite directions Example of endocrine negative feedback control