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Body fluid compartment.ppt
1. BODY FLUID COMPARTMENTS &
COMPOSITION
Prof. BL Mtinangi MD, MSc PhD
Department of Physiology
Kampala International University (T)
Dar es Salaam
2. Homeostasis and Body Fluids
Maintaining the volume and composition of body fluids are
important
Body fluids are defined as dilute, watery solutions
containing dissolved chemicals inside or outside of the
cell
Intracellular Fluid (ICF)
Fluid within cells
Extracellular Fluid (ECF)
Fluid outside cells
Interstitial fluid is ECF between cells and tissues
3. BODY FLUID COMPARTMENTS
Total body water (TBW) = 42L in a70kg
male
Body water content depends on age and sex
TBW has two major compartments;
ECF (14L) and ICF (28L).
ECF = 14L (1/3 of TBW)
Subdivided into ISF and Intravascular fluid
(Plasma)
Interstitial = 10L Interstitial fluid (ISF)
Intravascular = 3.5L Intravascular fluid (IVF)
Tran cellular = < 0.5L
4. Body Fluid varies depending on body fat:
Infant: 73-80%
Male adult: 60%
Female adult: 40-50%
Effects of obesity
Old age 45%
Climate Level of physical
activity
7. COMPOSITION OF ICF ECF
ECF most abundant cation is
Na+, anion is Cl-
ICF most abundant cation is
K+, anion are proteins and
phosphates (HPO4
2-)
Na+ /K+ pumps play major role
in keeping K+ high inside cells
and Na+ high outside cell
10. Sodium - Na+
Most abundant ion in ECF
90% of extracellular cations
Plays pivotal role in fluid and electrolyte
balance because it account for almost half of
the osmolarity of ECF
Level in blood controlled by
Aldosternone – increases renal reabsorption
ADH – if sodium too low, ADH release stops
Atrial natriuretic peptide – increases renal
excretion
11. Chloride - Cl-
Most prevalent anions in ECF
Moves relatively easily between ECF and ICF
because most plasma membranes contain Cl- leakage
channels and antiporters
Can help balance levels of anions in different fluids
ie Chloride shift in RBCs
Regulated by
ADH – governs extent of water loss in urine
Processes that increase or decrease renal
reabsorption of Na+ also affect reabsorption of Cl-
12. Bicarbonate - HCO3
-
Second most prevalent extracellular anion
Concentration increases in blood passing through
systemic capillaries picking up carbon dioxide
Carbon dioxide combines with water to form
carbonic acid which dissociates
Drops in pulmonary capillaries when carbon
dioxide exhaled
Chloride shift helps maintain correct balance of
anions in ECF and ICF
Kidneys are main regulators of blood HCO3
-
Can form and release HCO3
- when low or excrete
excess
13. Calcium - Ca2+
Most abundant mineral in body
98% of calcium in adults in skeleton and teeth
In body fluids mainly an extracellular cation
Contributes to hardness of teeth and bones
Plays important roles in blood clotting,
neurotransmitter release, muscle tone, and
excitability of nervous and muscle tissue
Regulated by parathyroid hormone
Stimulates osteoclasts to release calcium from bone – resorption
Also enhances reabsorption from glomerular filtrate
Increases production of calcitrol to increase absorption for GI tract
Calcitonin lowers blood calcium levels
14. Phosphate
About 85% in adults present as calcium phosphate salts in
bone and teeth
Remaining 15% ionized – H2PO4
-, HPO4
2-, and PO4
3- are
important intracellular anions
HPO4
2- important buffer of H+ in body fluids and urine
Same hormones governing calcium homeostasis also
regulate HPO4
2- in blood
Parathyroid hormone – stimulates resorption of
bone by osteoclasts releasing calcium and
phosphate but inhibits reabsorption of
phosphate ions in kidneys
Calcitrol promotes absorption of phosphates and
calcium from GI tract
15. Magnesium
In adults, about 54% of total body magnesium
is part of bone as magnesium salts
Remaining 46% as Mg2+ in ICF (45%) or ECF
(1%)
Second most common intracellular cation
Cofactor for certain enzymes and sodium-
potassium pump
Essential for normal neuromuscular activity,
synaptic transmission, and myocardial function
Secretion of parathyroid hormone depends on
2+
16. Potassium - K+
Most abundant cations in ICF
Key role in establishing resting membrane
potential in neurons and muscle fibers
Also helps maintain normal ICF fluid
volume
Helps regulate pH of body fluids when
exchanged for H+
Controlled by aldosterone – stimulates
principal cells in renal collecting ducts to
secrete excess K+
17. Alterations in Water Movement
Edema
Fluid accumulation in interstitial
spaces
Due to any condition that leads to:
Net movement of fluid out of
capillaries into interstitial tissues
18. Potassium
Major intracellular cation
Needed for nerve, cardiac,
skeletal function
Excess excreted by kidneys
Imbalance can cause sudden
death
28. Buffer System
Immediate Buffer System
CO2 + H20 H2CO3 H+ +
HCO3
-
Excessive CO2 acidosis
Excessive HCO3
-
alkalosis
Simplified:
CO2 H+
29. Question...
Is the average pH of the blood lower
in:
a) arteries
b) veins
Veins!
Why?
Because veins pick up the
byproducts of cellular metabolism,
including…
CO2!