Metabolic System

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Metabolic System

• BME 602
• SDSMT/USD
• Spring 2007

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Reading Assignment

• Chapter 8

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Metabolic System Overview

• The body attempts to maintain energy homeostasis
• Input nutrients
• Digestion stores chemical energy for later use
• Output work and heat
• The effect of externally produced work varies
  greatly by individual

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Human Energy Machine

• Automobile Engine
• Cylinder an explosive combustion of a fuel-air
  mixture transforms chemically stored energy into
  physical kinetic energy and heat.
• Energy moves the pistons
• Gears transfer motion to the wheels
• Engine must be cooled
• Waste products are expelled
• Fuel and oxygen must be present

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Human Energy Machine

• Muscle fibers are both cylinders and pistons
• Bones and joints are gears
• While muscles perform work, heat and metabolic
  by-products are produced, which must be removed
• Nutrients must be oxidized to produce energy

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Energy Balance Equation

• I M H W /- S
• I, energy input via nutrients
• M, metabolic energy generated
• H, heat
• W, work performed
• S, energy storage in the body

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Efficiency

• Assuming no change in energy storage, we have
• I H W
• Efficiency (in ) 100 W / I 100 W / M
• Normal efficiency is about 5 of input is
  converted to work (that is transmitted to outside
  objects)
• Highly trained athletes might approach 25
• Most of the remainder is converted to heat

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Energy Liberation Overview

• Food and Drink Inputs
• Main energy carriers carbohydrates, fats,
  proteins
• Some breakdown thru mouth, saliva, stomach
• Nutrients are absorbed in the small intestine
  into blood or lymph
• Absorbed nutrients are either
• Stored as fat or glycogen
• Used immediately as energy
• At muscle sites, mitochondria supply energy
  needed to convert ADP to ATP, thus fueling
  muscular work

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Measuring units for work and power

• Energy (work)
• 4.2 J 1 cal
• 1 J 1 Nm 0.2389 cal 107 ergs
• 0.948 x 10-3 Btu 0.7376 ft lb
• 1 kcal 1 Cal 1000 cal
• Power
• 1 kcal/hr 1.163 W
• 1 W 1 J/s

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Estimated Energy Content of Foods

• See Table 8.1

Item kcal / 100g
Steak 210
Sugar 385
Potato chips 575
Cola 40
Big Mac 275
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Energy Transformation

• Exergonic or Exothermic
• Chemical reactions that liberate energy, mostly
  heat
• Generally happens when molecular bonds are broken
• Endergonic or Endothermic
• Chemical reactions that require energy input
• Generally happens when molecular bonds are formed

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Digestion

• Some digestive processes start in the mouth with
  chewing and saliva, with further churning and
  liquification in the stomach
• Most chemical digestion occurs in the duodenum
  (first 25 cm of the small intestine, which is 7 m
  long!)
• Circular muscles mix
• Longitudinal muscles propel

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Villi of Duodenum

• Inner surface of duodenum has many fingerlike
  projections (villi), thus dramatically increasing
  surface contact area
• Blood and lymph capillaries are imbedded in the
  surface of the villi, absorbing the digested food
• 90 of nutrients are extracted in small intestine

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Rechargeable Battery Analogy

• Batteries contain an amount of energy that can be
  used (thus discharged), then recharged for
  further use
• ATP is the battery in charged form
• Adenosine triphosphate
• ADP is the battery in discharged form
• Adenosine diphosphate

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Indirect Calorimetry Assessment by oxygen
consumption Energy conversion 5 kcal/L O2
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Anatomy Coloring Plates

• 3rd Edition
• 136-145

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Physiology Coloring Plates

• 2nd Edition
• 71, 77-79, 130, 133, 136-138