Mass Balance in the Body

(through intestine,lungs, skin)

(by kidneys, liver,lungs, skin)

BODYLOAD

Metabolicproduction

Metabolism toa new substance

Mass balance Existingbody load

Law of Mass Balance

+Intake ormetabolicproduction

Excretion ormetabolicremoval

= –

Intake Excretion

Homeostasis

Homeostasis

Mass Balance and Homeostasis

• Clearance – Rate at which a molecule disappears from the body– Mass flow = concentration volume flow

• Homeostasis equilibrium– Osmotic equilibrium– Chemical disequilibrium– Electrical disequilibrium

Map of Membrane Transport

• Diffusion is the net movement of particles from an area of higher particle concentration to an area of lower particle concentration.

• Net movement = flux• Both the size and direction of

movement is concentration-dependent.

Diffusion

Simple Diffusion

• Fick’s law of diffusion

Rate of diffusionsurface area • concentration gradient • membrane permeability

membrane thickness

Extracellular fluid

Membranesurface area

Intracellular fluid

Compositionof lipid layer

Lipidsolubility

Molecularsize

Concentrationoutside cell

Concentrationinside cell

Membranethickness

Concentrationgradient

Fick's Law of Diffusion says:

lipid solubility

molecular size Membrane permeability

Membrane permeability

Changing the composition of the lipid layer can increase or decrease membrane permeability.

Simple Diffusion

Two classes of compounds move by simple diffusion

1. Lipid soluble compounds

2. Small ions which move through protein channels

a. channels are selective

b. channels can be regulated

Membrane Transport Proteins

Channel Proteins: Gated• Usually closed• Often highly Selective (size, charge)• Chemical (e.g. intracellular messengers)• Temperature• Mechanical/tension• Electric (voltage) signals• Consist of subunits

• Ion channels:e.g. K+, Na+, Ca2+

Leak channels open all timee.g. allow water, ions movement

Gating of Channel Proteins

Active Transport

• Can transport against a concentration gradient

• Requires energy input (ATP to ADP, P)

• Two forms:• primary active transport

• secondary active transport

Primary Active Transport

ADP

ATPase is phosphorylated

with Pi from ATP.

ADP

2

ATP

ICF

ECF

3 Na+ fromICF bind

11

Protein changesconformation.

3 Na+ releasedinto ECF

32 K+ fromECF bind

4

2 K+ releasedinto ICF

5

Secondary Active Transport

• Mechanism of the SGLT Transporter

[Na+] low[glucose] high

SGLT protein

Lumen of intestineor kidney

Intracellular fluid

Glucose binding changescarrier conformation.

Na+ binds to carrier.

[Na+] high[glucose] low

Na+ binding createsa site for glucose.

Na+ released into cytosol. Glucose follows.

13

4

2

Energy Transfer in Living Cells

ATP

Secondary active transport

Primary active transport

Metabolism

The chemical bond energy is convertedinto high-energy bonds of ATP through the process of metabolism.

The energy in the high-energy phosphate

bond of ATP is used to move K+ and Na+

against their concentration gradients.This creates potential energy stored in the ion concentration gradients.

The energy of the Na+ gradient can be used to move other molecules across the cell membrane against their concentration gradients.

Energy is imported into the cell asenergy stored in chemical bonds

of nutrients such as glucose.Glucose

Pyruvate

CAcycle

Heat

H2O

CO2

ADP+Pi

O2

High [K+]Low [Na+]

Na+

Na+

Glycolysis

ETS

K+

K+

2 Cl–

Low [K+]High [Na+]

Glucose

ATP

ATP

ETS = Electron transport system = Citric acid cycleCA

cycle

KEY

Membrane Transport Proteins

Carrier Proteins: Proteins are Required for Carrier-mediated Transport

• Specificity

• Saturation

• Competition

Carrier-Mediated Transport Competition

Carrier-Mediated Transport Saturation

Phagocytosis: important in immune cells

Vesicular Transport

Polarized cell transporting epithelia

Transepithelial Transport of Glucose

Transcytosis

46-61% body weight is water

• How is water distributed in body?

Osmosis and Tonicity

• Net diffusion of water from an area of low solute concentration to an area of higher solute concentration when movement of solute is prevented by a membrane.

Copyright © 2009 Pearson Education, Inc.

Tonicity

• Tonicity depends on the relative concentrations of nonpenetrating solutes

Osmolarity

• Total number of osmotically active particles

• Osmolarity = molar conc x # particles of solute in solution

• (1 mM glucose) x 1 particle =1 mOs glucose

• (1 mM NaCl) x 2 particles = 2 mOs NaCl

Tonicity• Describes only number of non-penetrating

solutes

300 mOs

300 mM NaCl = 600 mOs NaClHypertonic solution

Water moves out; cell shrinks

Isotonic = same as cell; size stable

Hypotonic = less than cell; cells lyse

• NaCl, protein: non-penetrating

• Urea: penetrating

The cell membrane enables separation of electrical charge in the body

Resting membrane potential is the electrical gradient between ECF and ICF

Resting membrane potential is the electrical gradient between ECF and ICF

Resting Membrane Potential

Extracellular fluid0 mV

Intracellular fluid-70 mV

Terminology associated with changes in membrane potential

Equilibrium Potential

• Nernst Equation

Eion = 61 x log [ion]out

z [ion]in

Z is electrical charge on ion

• E for K+ = -90 mV• E for Na+ = +60 mV

Tonicity Problems

RBC in a solution, what will happen to the cell?

• 300 mOs NaCl ?

• 300 mOs NaCl + 100 mOs urea?

• 300 mOs NaCl + 100 mOs protein?

• 300 mOs NaCl + 300 mOs urea?

Kidney Dialysis

urea

NaCl, proteins NaCl, proteinsurea urea

Movement acrossMembranesMovement acrossMembranes