Composition of Human body

1. COMPOSITION OF THE HUMAN
BODY:
FLUIDS, ELECTROLYTES AND ACID-
BASE BALANCE
Dr. Matwa Christopher
BSc[Hons]-physio; MBChB; MMed-PRAS (UoN)

2. OBJECTIVES
 Students should understand the following at the
end of the presentation:
 Chemical & fluid composition of the body
 The normal concentrations of the body chemicals and
fluids
 The major two body compartments and distribution of
chemicals & fluids therein
 Factors affecting chemical and fluid distribution in body
compartments
 Regulation of chemical and fluid distribution

3. INTRODUCTION :
CHEMICAL LEVEL OF ORGANISMS
 Living material is composed of free elements, ions,
radicals, molecules and compounds.
 Four elements compose of over 95% of the body.
 Hydrogen (H) 10%,
 Oxygen (0) 65%,
 Carbon (c) 18 % and
 Nitrogen (N) 3 %.
 Additional elements common to the body include
calcium (Ca), Sodium (Na), Potassium (K)
Phosphorus (P), Sulfur (S) and Magnesium (Mn).
 These elements combine to form macromolecules
that make up the cells

4. BODY COMPOSITION
 In an average young adult male,
 60-70% is water
 15-20% is fat
 15-18% of the body weight is protein and related
substances
 5-7% is minerals, nucleic acids, radicals
% OF BODY WEIGHT
Material MALE FEMALE
Water
Protein
Lipids
Carbohydrates
Others (nucleic) acids, radicals
62
18
14
1
5
59
15
20
1
5

5. BODY FLUIDS AND COMPARTMENTS
 Water.
 The principal fluid medium of the cell
 Present in most cells, except for fat cells, in a
concentration of 70 to 85 per cent.
 Many cellular chemicals are dissolved in the water.
 Others are suspended in the water as solid particulates.
 Chemical reactions take place among the dissolved
chemicals or at the surfaces of the suspended particles
or membranes.
 Directly related to muscle mass (70% water)
 Inversely related to fat content (10% water)

6. TWO MAJOR COMPARTMENTS OF BODY WATER
 Intracellular fluid
 Cytosol
 40% of total body weight or
 2/3 of total body water
 Extracellular fluid
 Interstitial fluid, plasma, lymph, CSF, synovial fluid,
serous fluid, etc
 20% of total body weight or
 1/3 of total body water

8. CONT’D
Comparment % total body water
Cytosol 62.5
Plasma 7
Connective tissue 5
Interstitial fluid and lymph 18
Bone 5
Transcellular 2.5

9. CLINICAL IMPLICATION OF FLUID
COMPARTMENTS
 Dehydration
 Shock (hypovolemic)
 Electrolyte imbalances
 Hypokalemia
 Hyponatremia
 Hypocalcemia
 Infections
 Sepsis
 Shock (septic)

10. CONT’D
 Stabilizing ECF and ICF involves:
 1) Fluid Balance
 Must have equal gain (food & metabolism) and loss (urine &
perspiration) of water
 2) Electrolyte Balance
 Electrolytes = ions from dissociated compounds that will conduct
an electrical charge in solution
 Must have equal gain (absorption in GI) and loss (urine in kidney
and perspiration in skin)
 3) Acid-Base Balance
 The production of hydrogen ions by metabolism must be matched
by loss of these H+ ions at the kidney and lungs (carbonic acid)
 How is stabilization achieved?
 Homeostasis: the regulation of composition and volume of
both fluid divisions

11. FLUID FLOW
 Diffusion
 Movement of particles down a concentration gradient.
 Osmosis
 Movement of solvent molecules into a region of higher solute
concentration across a semipermeable membrane
impermeable to the solute
 Active transport
 Movement of particles up a concentration gradient ; requires
energy
 Movement of fluids due to:
 hydrostatic pressure
 Capillary filtration
 Interstitial hydrostatic pressure
 osmotic pressure
 Capillary colloidal osmotic pressure
 Tissue colloid osmotic pressure

12. FLUID BALANCE
 There is continuous flow between ICF and ECF and
the external environment:-
 The flow between ICF and ECF:-
 Hydrostatic pressure pushes water from the plasma into
the interstitial fluid
 Colloid osmotic pressure draws water from the interstitial
fluid to the plasma

13. FLUID BALANCE
 Fluid exchange between environment and ECF:-
 Water losses (2500mL/day)
 Insensible loss
 Cannot be controlled or measured
 Includes fecal, respiration, skin evaporations and perspiration
losses
 40-600mL/day
 Obligatory loss
 Minimal amount of urine needed to excrete metabolic wastes
 600mL/day
 Facultative or sensible loss
 Controlled and measured
 Urine loss
 1500mL/day

14. FLUID BALANCE
 Water Gains
 Must match water losses or dehydration will result
 1000 mL from drink,1200 mL from food and 300 mL
metabolic “waste”
 Systems of gain: GIT – intake
 Systems of loss:
 GIT – fecal (diarrhea)
 Renal – urine
 Integumentary, Respiratory – insensible
 Applies to electrolytes and acid/bases

15. ELECTROLYTES
 The electrolytes vary depending on the fluid division:
 ECF
 Principal cation = Na+
 Principal anions = Cl- , HCO3-
 ICF
 Principal cation = K+, Mg2+
 Principal anions = HPO4
2- and negatively charged proteins-
 Although different ions dominate, both fluid divisions
have the same osmotic concentrations.
 The ions cannot pass freely through cell membranes,
but the water can by osmosis, and will move to
equilibrium.
 Thus, solute/electrolyte concentrations of the fluid
divisions will directly impact water distribution

17. ELECTROLYTE BALANCE
 Sodium
 Major ECF ion
 Where sodium goes, water follows
 The total amount of Na+ in the ECF is due to a balance
between Na+ uptake in the digestive system and Na+
excretion in urine and perspiration.
 The overall sodium concentration in body fluids rarely
changes because water always moves to compensate
 Minor gains and losses of Na+ in the ECF are
compensated by water in the ICF and later adjusted by
hormonal activities:
 ECF volume too low → renin-angiotensin system is activated
to conserve water and Na+
 ECF volume too high → natriuretic peptides released: block
ADH and aldosterone resulting in water and Na+ loss

18. CONT’D
 Potassium
 Major ICF ion
 Amount in concentration determined by GIT absorption
and renal excretion in exchange with Na+
 The rate of tubular secretion of K+ in the kidney is
controlled by three factors:
 Changes in the K+ concentration of the ECF
 ↑ K+ in ECF = ↑ K+ secretion
 Changes in blood pH:- acidosis causes hyperkalemia
 at low pH, H+ shifts K+ out of cells into ECF
 In renal tubules, K+ at the exchange pump is ↓ as Na+ is
exchanged with H+ = ↓ K+ secretion (K+ accumulates)
 Aldosterone levels
 ↑ aldosterone = ↑ Na+ reabsorption and ↑ K+ secretion

19.  The most important factor in Acid –Bade balance is
the maintenance of hydrogen ion concentration of
ECF within the range that is optimal for survival of
the organism.
 Function of cells are very sensitive to changes in H+
ion concentration.
 Intracellular H+ ion concentration is dependent on
ECF H+ ion concentration
ACID – BASE BALANCE

20. CONT’D
 H+ ion concentration in blood is very low compared to
other cations thus:
 The normal plasma Na+ ion concentration is 145 meq/l,
 K+ is 5 meq/l and
 [H+] is 0.00004 meq/l.
 The pH therefore is a more sensible way of denoting
[H+] as it’s the negative logarithm of [H+].
 Negative logarithm of 0.00004 = pH = 7.4,
 NB a decrease of pH of one unit means a 10 fold increase in
H+ concentration i.e. from 7 to 6.
 pH of blood = True pH of plasma
 Plasma pH is in equilibrium with that of RBC because RBCs
contain hemoglobin which is one of the most important blood
buffers

21. PH AND BUFFERING
 Acid
 A substance that dissociates to release H+ ions
 Base
 A substance that dissociates to release OH- ions or absorbs H+ ions.
 The pH scale is used to measure the concentration of H+ ions in a
solution
 pH = potential of Hydrogen
 Water is neutral: H+ = OH-, pH 7
 An acid solution
 pH O - 7
 has more H+ than OH-
 A basic or alkaline solution
 pH 7 – 14
 has more OH- than H+
 Strong acids or bases dissociate completely in solution
 Weak acids or bases do not completely dissociate: many
molecules remain intact

22. CONT’D
 Normal pH of the ECF = 7.35 – 7.45.
 Above or below this range will disrupt cell
membranes and denature proteins
 Acidosis = ECF pH below 7.35
 Alkalosis = ECF pH above 7.45
 Acidosis is the more common problem since
metabolism generates acid waste products

23. CONT’D
 Types of Acids
 Volatile Acids
 Can leave solution and enter the atmosphere
 CO2 + H2O ↔ H2CO3- ↔ H+ + HCO3-
lungs blood
 Fixed Acids
 Remain in solution until they are excreted e.g. sulfuric acid,
phosphoric acid
 Organic Acids
 The products of metabolism
 These are usually metabolized into other wastes, but they can
build up under anaerobic conditions or starvation e.g. Lactic acid,
Ketone bodies

24. ACID/ ALKALINE SOURCES
 Sources of Hydrogen ion.
 Dietary – degradation of protein yield sulphates and phosphates
which hydrate them.
 SO4 + H+ + OH – H2 SO4
 PO4 + 3H – H3PO4
 H+ load from this source is 150 meq/day
 Other common sources of extra hydrogen ions include:
 Strenuous exercise
 lactic acid
 Diabetic ketoacidosis
 Acetoacetic and B-hydroxybutyric acid.
 Ingestion of acidifying salts i.e.
 NH4Cl
 CaCl2
 The net effect of these acids is to add HCl to blood
 Failure of kidneys due to kidney disease to excrete H+
 Has net effect of increasing H+ ion concentration in blood.

25. CONT’D
 Sources of Alkali
 Fruits are main source of Alkali because they contain K+
and Na+ salts of weak organic acids
 the anion of these salts are metabolized to CO2 leaving
NaHCO3 and KHCO3 in body.
 NaHCO3 and other alkalinizing salts are sometimes
ingested in large amounts e.g. baking soda.
 Commonest cause of Alkaloses is vomiting due to loss
of gastric HCL
 Increase in PCO2 result in respiratory acidosis and a
decrease mean respiratory alkalosis.
 When acidosis and alkalosis occur changes are produced in
the kidneys which then tend to compensate for acidosis or
alkalosis hence adjusting the pH towards normal

26. MECHANISM OF PH CONTROL
 Buffers
 Dissolved compounds that can remove H+ ions to
stabilize pH
 Usually buffers are a weak acid and its
corresponding salt
 Three major buffering systems:
 The Protein Buffer System
 The carbonic acid – bicarbonate buffer system
 Phosphate buffer system

27. PROTEIN BUFFER SYSTEM
 Proteins are used to regulate pH in the ECF and ICF
(most effective in the ICF)
 Amino acids can be used to accept or release H+ ions:
 At typical body pH, most carboxyl groups exist as COO- and
can accept H+ ions if the pH begins to drop
 Histidine and Cysteine remain as COOH at normal pH and
can donate H+ if the pH rises.
 All proteins can provide some degree of buffering with
their carboxyl terminal.
 Hemoglobin can have a great effect on blood pH
 The Hemoglobin (Hb) Buffering System
 Most effective in the ECF: blood
 In RBCs the enzyme carbonic anhydrase converts CO2 into
H2CO3 which then dissociates
 The H+ remains inside RBCs, but the HCO3- enters the
plasma where it can absorb excess H+

29. CARBONIC ACID – BICARBONATE BUFFER
SYSTEM
 The most important buffer for the ECF (free in plasma or
aided by Hb)
 Carbon dioxide and water form carbonic acid which
dissociates into hydrogen ions and bicarbonate ions
 The bicarbonate ions can be used to absorb excess H+ ions
in the ECF and then can be released as CO2 and H2O at the
lungs
 This buffering only works if:
 CO2 levels are normal
 Respiration is functioning normally
 Free bicarbonate ions are available
 Bicarbonate ions can be generated from
 CO2 + H2O or
 NaHCO3-
 but to have free HCO3-, H+ ions must be excreted at the kidney

30. PHOSPHATE BUFFER SYSTEM
 Phosphate is used to
buffer ICF and urine
 H2PO4 or Na2PO4 can
dissociate to generate
 HPO4
2-, which can
absorb H+
 As long as H+ is
excreted at the kidney

31. MAINTENANCE OF ACID – BASE
 Buffering will only temporarily solve the H+ problem:
permanent removal as CO2 at the lungs or through
secretion at the kidney is necessary to maintain pH near
neutral
 pH homeostasis:
 Respiratory Compensation
 Respiration rate is altered to control pH
 ↑ CO2 = ↓ pH
 ↓ CO2 = ↑ pH
 Renal Compensation
 The rate of H+ and HCO3- secretion or reabsorption can be
altered as necessary
 ↑ H+ = ↓ pH
 ↑ HCO3- = ↑ pH

32. RESPIRATORY ACIDOSIS AND ALKALOSIS
 Changes in arterial pCO2 from any cause will affect
the [H2CO3]/HCO-
3} ratio and hence the pH
 Rise in pCO2 means a rise in H2CO3 and resulting
in HCO-
3 and consequently a rise of [H+]. The
overall net effect is a fall in pH and vice versa
 Resp. acidosis
 Hypoventilation:
 in CNS depression, drugs, illnesses like mysthenia gravis
 Build up of CO2 hence reduced pH
 Resp. alkalosis
 Hyperventilation
 CNS disorders, drugs, increased ammonia, pregnancy
 Blow out of CO2 hence increase in pH

33. METABOLIC ACIDOSIS AND ALKALOSIS
 Metabolic acidosis
 When body is producing too much acid or renal failure
to excrete H+
 Anion gap classification
 Increased anion gap:
 Ketoacidosis
 Lactic acidosis
 Chronic renal failure
 Intoxication ie methanol
 Normal anion gap
 Intractable diarrhea
 Renal tubular acidosis
 intoxication

34. CONT’D
 Metabolic alkalosis
 Renal loss of H+
 Excessive retaining of HCO3-
 Hyperaldosteremia
 Alkalotic agents eg ie excessive antiacids

35. UNCOMPENSATED METABOLIC ACIDOSIS OR
ALKALOSIS
 Before renal mechanisms which are far much slower sets in,
the respiratory system has the very important duty of either
decreasing [H+] or adding up [H+] into the blood system.
 In metabolic alkalosis, H+ ions are depleted from blood
evoking respiratory response of inhibiting ventilation thus
resulting in CO2 build up in blood.
 In metabolic acidosis, the acid anions that replace HCO-
3 are
excreted in combination with a cation principally Na+
effectively maintaining electrical neutrality.
 Note, for each H+ lost in urine one Na+ + one HCO-
3 are
reabsorbed.
 The H+ in urine must be buffered to prevent decrease of pH to
below 4.5 which is injurious to cells.
 Urine H+ is buffered by
 HCO-
3 system which results H2O + CO2,
 HPO4 + H+ results in - H2PO4 and
 with NH3 to NH+
4

36. POTASSIUM METABOLISM AND ACID BASE
BALANCE
 K+ ion and H+ ion produce parallel effect in plasma,
 when there’s excess of H+ ion in plasma, K+ ion is
reabsorbed by renal tubule as H+ ion is lost.
 In case of excess of K+ ion, K+ ion is lost by renal tubule
as H+ ion is reabsorbed ,
 When H+ ion is low, K+ ion is lost as H+ ion is
reabsorbed and when H+ ion is in excess H+ ion is lost
as K+ ions is reabsorbed.

37. Thank YOU