Plant Competition Essay

Submitted By danyel12
Words: 4052
Pages: 17

What we know…

• The body is an open system that exchanges heat and materials with the outside environment. • To maintain homeostasis the body utilizes the principle of mass balance.

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Mass Balance in the Body
Water and nutrients- food and drink- intestine Oxygen and other gases- lungs Lipid soluble molecules through skin
Intake (through intestine, lungs, skin)

Foreign substances such as drugs or artificial food additives – liver and kidneys Carbon dioxide- lungs
Excretion (by kidneys, liver, lungs, skin)


Metabolic production

Metabolism to a new substance


Input = Output
Law of Mass Balance
Intake or metabolic production Excretion or metabolic removal

Mass balance = Existing + body load

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Figure 5-2

Mass Balance maintained by clearance
• Clearance is the rate at which a molecule disappears from the body by excretion, metabolism or both. • Kidney – clears solutes from body • Liver – clears hormones, drugs • Clearance= volume of blood plasma cleared of substance per unit of time. • Indirect measure. • More direct measure – determining mass flow • Mass flow = concentration  volume flow • Eg. Person given IV infusion of glucose (50g/l) at 2ml/min. Mass flow of glucose into body = 50g glucose/1000ml solution x 2ml solution/min = 0.1g glucose/ min

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• • •

Stability of body’s internal environment. Stability of ECF = blood plasma + interstitial fluid. ECF homeostasis is easier to monitor than intracellular fluid compartment.

Copyright © 2009 Pearson Education, Inc.

Figure 5-3a

Homeostasis does not mean equilibrium
• Homeostasis  equilibrium • Osmotic disequilibrium: Water moves freely b/w cells and ECF, across semi-permeable (or differentially permeable or selectively permeable) membrane. Eg. dialysis tubing, cellulose acetate sausage casing. • Chemical disequilibrium: Certain solutes are more concentrated in one body compartment than in the other. • Electrical disequilibrium : Many solutes are ions. Body is overall electrically neutral. Few extra –ve ions in ICF vs few extra +ve ions in ECF. Inside of cells slightly negative relative to ECF. Ionic imbalance causes electrical disequilibrium.

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Figure 5-3b

Map of membrane transport

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Diffusion: Seven Properties
1. 2. 3. 4. 5. 6. 7. Passive process- does not require energy input from outside source. Movement of molecules from high concentration to low concentration. Net movement until concentration is equal. Rapid over short distances but much slower over long distances. Directly related to temperature. Higher temperature ≡ faster diffusion. Inversely related to molecular size. Can take place in an open system or across a partition that separates two systems.

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Fick’s Law of Diffusion
Extracellular fluid Membrane surface area Lipid solubility Molecular size Concentration outside cell

Membrane thickness
Composition of lipid layer

Concentration gradient

Intracellular fluid

Concentration inside cell

Mathematically relates the factors that influence the rate of simple diffusion across a membrane.

Fick's Law of Diffusion says: surface area • concentration gradient • membrane permeability membrane thickness

Rate of diffusion

Membrane permeability

Membrane permeability

lipid solubility molecular size

Changing the composition of the lipid layer can increase or decrease membrane permeability.
Copyright © 2009 Pearson Education, Inc.

Figure 5-6

Functions of Membrane Proteins
• • • • In the body simple diffusion is limited to lipophilic molecules. Majority of molecules are lipophobic or electrically charged. They cannot cross membranes by…