CHAPTER 5: MEMBRANES.
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Transcript of CHAPTER 5: MEMBRANES.
CHAPTER 5: MEMBRANES
Mass Balance and Homeostasis
Human body is an open systemExchanges heat and materials with external environment
Principle of MASS BALANCE is used to maintain Homeostasis
Law of Mass Balance:If the amount of a substance in the body is to remain constant,any gain must be offset by an equal loss
Example: Water loss (output) must be balanced by water intake (from external environment and from metabolic water production)
Copyright © 2010 Pearson Education, Inc.
Figure 5-1
Mass Balance and Homeostasis
Law of Mass Balance:If the amount of a substance in the body is to remain constant,any gain must be offset by an equal loss
Total amount (load) of substance X in body =Intake + production – excretion - metabolism
Mass Balance and Homeostasis
Applies to:
WaterOxygenCarbon DioxideSalts (electrolytes)Hydrogen ions (pH)
Copyright © 2010 Pearson Education, Inc.
Figure 5-2
Mass Balance and Homeostasis
Input:
Most substances enter the body from the outsideWater, nutrients, enter via digestive tract
Oxygen and other gases enter via lungs:
Some lipid-soluble molecules can enter through the skin
Mass Balance and Homeostasis
Output:
1. ExcretionThrough urine, feces, lungs, or skin
2. Metabolize the substance to a different one
Metabolite: a product created in a metabolic pathway
Clearance:The rate at which a molecule disappears from the body(via excretion or metabolism)
Mass Balance and Homeostasis
Clearance example:Volume of blood plasma cleared of the substance per unit of time
Mass Flow: a more direct way to measure this
Mass Flow = concentration x volume flow
Amount of substance/min = amount of substance/vol x vol/min
Mass Balance and Homeostasis
Mass Flow: example:A person is given an intravenous infusion of glucose solution (50 g glucose per liter), given at a rate of 2 ml per min
Mass flow is:
50 g glucose/1000 ml x 2 ml solution /min = 0.1 g glucose/min
Mass flow applies to entry, production, and removal of substancesAnd also to movement of substances from one functional compartment to another
Homeostasis and Equilibrium
Homeostasis: usually refers to stability of the internal environment
Usually refers to stability of the ECF (plasma, interstitial fluid)
Cells maintain a state of cellular homeostasisBut, lots harder to measure stability of ICF (inside environment of cells)
Homeostasis and Equilibrium
In a state of homeostasis, the composition of both body compartments is relatively stable
BUT
The composition of the compartments are different
Copyright © 2010 Pearson Education, Inc.
Figure 5-3a
Electrolytes
These dissociate (come apart) in liquidsand form ions (charged particles)
Acids: HCl (hydrochloric acid)Dissociates to form H+ and Cl-
Bases: NaOH (sodium hydroxide)KOH (potassium hydroxide)
Salts: NaCl (sodium chloride or table salt)KCl (potassium chloride)
Electrolytes areChemically reactive in metabolism
– Major cations• Na+, K+, Ca2+, H+
– Major anions• Cl-, HCO3
-, PO43-
Cation: positive ionAnion: negative ion
ElectrolytesMain functions in body:
1. Many are essential minerals
2. As the most numerous solutes, they control osmosis of water between body compartments
ElectrolytesMain functions in body:
3. They help maintain the acid-base balance required for normal cellular activities
4. They can carry an electric current:
This allows Action Potentials, graded potentials to happen; controls secretion of some hormones and neurotransmitters
Distribution of Electrolytes in Extracellular Fluid1. Interstitial fluid contains:
Na+ (most abundant positive ion)Cl- (most abundant negative ion)
H2CO3 (Bicarbonate ion; abundant)K+
Ca++
Mg++
2. Plasma contains:Same ions as interstitial fluid and Lots of protein anions
Distribution of Electrolytes3. Intracellular fluid (ICF) contains:
K+ (most abundant positive ion)
Protein ions; phosphate ions (HPO42-)
(most abundant negative ions)
H2CO3 (Bicarbonate ion; not as abundant as in ECF's)Cl-Na+
Mg++
Copyright © 2010 Pearson Education, Inc.
Figure 5-3b
Homeostasis and Equilibrium(p. 134-135)
4 phrases to learn:
Dynamic disequilibrium
Osmotic equilibrium
Chemical disequilibrium
Electrical disequilibrium
Homeostasis and Equilibrium(p. 134-135)
Dynamic disequilibriumECF and ICF contain different concentrations of various solutes, resulting in a state of dynamic disequilibrium
Osmotic equilibriumWater moves freely between ECF and ICF, so these can reach a state of osmotic equilibrium
Homeostasis and Equilibrium(p. 134-135)
Chemical disequilibriumCertain solutes are more concentrated in one compartment than in the other
Electrical disequilibriumBody as a whole is electrically neutral
But due to ion concentrations, ICF is slightly negative relative to ECF
Changes to the ionic imbalance create electrical signals (nerve cells, muscle cells)
Copyright © 2010 Pearson Education, Inc.
Figure 5-3b
Homeostasis and Equilibrium(p. 134-135)
“The goal of homeostasis is to maintain the dynamic steady states of the body's compartments
Dynamic:Materials are constantly moving back and forth between compartments
Steady state:No net movement of materials between the compartments
Membrane Transport(p. 136-158)
“Humans are large complex organisms and the movement of materials within and between compartments is necessary for communication”
Movement of materials across selectively permeable membranes requires a variety of transport mechanisms
(Cell membranes are selectively permeable)
Membrane Transport(p. 136-158)
Transport Mechanisms:
Some require energy in the form of ATP(Active transport)
Some do not require ATP (Passive transport)This kind uses energy of molecular motion
Copyright © 2010 Pearson Education, Inc.
Figure 5-4
Copyright © 2010 Pearson Education, Inc.
Figure 5-5