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Chapter 5

Chapter 5 Study Guide

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University of Toronto Scarborough
Biological Sciences

CHAPTER 5 Mass Balance and Homeostasis 1) law of mass balance says that if the amount of substance in the body is to remain constant, any gain must be offset by an equal loss. It is summarized by the following equation: Total amount (or load) of substance x in the body = intake + production excretion metabolism o To maintain constant level, output must equal input. o Materials enter the body by various routes or are produced through metabolism o Materials leave the body either by excretion or by metabolism o Excretion is defined as the elimination of material from the body, and it usually takes place through the urine, feces, lungs, or skin. Xenobiotics (foreigner), like drugs or artificial food additives, are excreted by the liver and kidneys o Metabolism converts the original nutrient to a different substance but in doing so creates a new mass balance disturbance by adding more of the metabolite ( any product created in a metabolic pathway) to the body Excretion Clears Substances from the Body 2) Clearance is the rate at which a molecule disappears from the body by excretion, metabolism, or both. The major organs that are involved are kidney, liver, and lungs. 3) Clearance is usually expressed as a volume of blood plasma cleared of substance x per unit of time. It is therefore only an indirect measure of the movement of substance x. o mass flow rate of intake, production, or output of x: mass flow (amount x/min) = concentration (amount x/vol) * volume flow (vol/min) a more direct measure applies to movement of substances from one compartment in the body to another Homeostasis Does Not Mean Equilibrium 5) homeostasis refers to the stability of the extracellular fluid 6) dynamic disequilibrium?? 7) Water is the only molecule that moves freely between most cells and the extracellular fluid 8) Osmotic equilibrium is a state in which the total amount of solute per volume of fluid is equal on the two sides of the cell membrane. Extracellular and intracellular compartments can reach this state due to the free movement of water 9) A chemical disequilibrium is a state in which the major solutes are more concentrated in one of the two body compartments (extra or intracellular) than in the other.( e.g., sodium and calcium are more concentrated in the extracellular fluid where K+ ions are more concentrated inside the cell) www.notesolution.com 10)The concentration differences of chemical disequilibrium are a hallmark of a living organism as only the continual input of energy keeps the body in this state. If solutes leak across the cell membrane dividing the intra and extracellular compartments, energy is required to return them to the compartments they left ( e.g., sodium-potassium needs to ATP to pump ions across cell membrane). When cells die and cannot use energy, they obey the second law of thermodynamics and return to a state of randomness that is marked by a loss of chemical disequilibrium. 11)The inside of cells is slightly negative relative to the extracellular fluid due to the few extra negative ions. This electrical difference creates a state of electrical disequilibrium - the osmotic equilibrium and the two disequilibria are dynamic steady states. The modifier steady indicates that materials are constantly moving back and forth between the two compartments, but in a steady state, there is no net movement of materials between the compartments Diffusion 12)selectively permeable lipid and protein composition of a given cell membrane determines which molecules will enter the cell and which will leave. If a membrane allows a substance to pass through it, the membrane is said to be permeable to that substance. If a membrane does not allow a substance to pass, the membrane is said to be impermeable to that substance 13)the size of the molecule and its lipid solubility are the two properties of a molecule that influence its movement (very small and those that are lipid soluble can cross directly through the phospholipid bilayer 14)passive transport does not require input of energy whereas active transport requires the input of energy from an outside source (ATP) 15)a molecule can move across a membrane through simple diffusion (molecule goes through lipid bilayer), facilitated diffusion, primary active transport, secondary active transport ( mediated transport requires a membrane protein), endocytosis, exocytosis and phagocytosis (uses a membrane bound vesicle) refer to Fig. 5-4 on pg 132 16)Diffusion is the movement of molecules from an area of higher concentration of the molecules to an area of lower concentration of the molecules 17)Seven properties of diffusion are: General Properties of diffusion o Diffusion uses the kinetic energy of molecular movement and does not require an outside energy source o Molecules diffuse from an area of higher concentration to an area of lower concentration o Diffusion continues until concentrations come to EQ. Molecular movement continues, however, after EQ has been reached www.notesolution.como Diffusion is faster - With higher concentration gradients - Over shorter distances ( if distance increased from 1 to 2, then the time will increase from 1^2 to 2^2) - At higher temperatures - For smaller molecules o Diffusion can take place in an open system or across a partition that separates two systems Simple Diffusion across a membrane o The rate of diffusion through a membrane is faster if %K0202-7,3088:7face area is larger The membrane is thinner The concentration gradient is larger The membrane is more permeable to the molecule o Membrane permeability to a molecule depends on %K024O0.:O08OL5L/84O:-LOL9\ %K024O0.:O088L]0 The lipid composition of the membrane - ion movement is influenced by electrical gradients due to the attraction of opposite charges and repulsion of like charges. They move in response to combined electrical and concentration gradients, or electrochemical gradients 18)Factors affecting rate of simple diffusion are: o The rate of diffusion depends on the ability of the diffusing molecule to dissolve in the lipid layer of the membrane. Molecules that are lipid-soluble (lipophilic) can tra
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