Body Fluids And Homeostasis

Front 1

Body Fluid Compartments

Back 1

In lean adults, body fluids constitute 55% of
female and 60% of male total body mass
– Intracellular fluid (ICF) inside cells
• About 2/3 of body fluid
– Extracellular fluid (ECF) outside cells
• Interstitial fluid between cell is 80% of ECF
• Plasma in blood is 20% of ECF

Front 2

Body Fluid diagram

Back 2

Front 3

Fluid Balance

Back 3

Body is in fluid balance (homeostasis) when required mounts of water and solutes are present and correctly proportioned among compartments

• Water is by far the largest component of body making up 45-75% of total body mass
• Process of filtration, reabsorption, diffusion, and osmosis, all continually exchange water and solutes among compartments

Front 4

Sources of Body Water Gain and Loss

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– Intake of water and electrolytes rarely proportional

– Kidneys excrete excess water through dilute urine or excess electrolytes through concentrated urine
• Body can gain water by
– Ingestion of liquids and moist foods
– Metabolic synthesis of water during cellular respiration and dehydration synthesis
• Body loses water through
– Kidneys (1500mL/day)
– Evaporation from skin (600mL/day)
– Exhalation from lungs (300mL/day)
– Feces (100mL/day)

Front 5

Electrolytes

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• Ions form when electrolytes dissolve (kidneys keep balance)
• 4 general functions
– Control osmosis of water between body fluid
compartments
– Help maintain the acid-base balance
– Carry electrical current
– Serve as cofactors

* sodium (Na+)
* potassium (K+)
* chloride (Cl-)
* calcium (Ca2+)
* magnesium (Mg2+)

Front 6

Water Gain and Loss diagram

Back 6

Front 7

Regulation of body water gain

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Front 8

Major hormone regulating water loss...

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Antidiuretic hormone (ADH)

Produced in the hypothalamus and released by the posterior pituitary gland, (ADH) controls the permeability of the collecting ducts to water. Increased levels of ADH result in greater reabsorption and decreased water excretion

Front 9

Movement of water

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Normally, cells neither shrink or swell because intracellular and interstitial fluids have the same osmolarity
• Increasing osmolarity of interstitial fluid draws water out of cells and cells shrink
• Decreasing osmolarity of interstitial fluid causes cells to swell

Front 10

Water intoxication

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drinking water faster than the kidneys can excrete it

Front 11

Concentrations in body fluids

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– Concentration of ions typically expressed in milliequivalents per liter (mEq/liter)
• Na+ or Cl- number of mEq/liter = mmol/liter
– Chief difference between 2 ECF compartments (plasma and interstitial fluid) is plasma contains many more protein anions
• Largely responsible for blood colloid osmotic pressure

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ICF differs considerably from ECF

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• ECF most abundant cation is Na+, anion is Cl -
• ICF most abundant cation is K+, anion are
proteins and phosphates (HPO42-)
• Na+ /K+ pumps play major role in keeping K+
high inside cells and Na + high outside cell

Front 13

Fluid exchange between ICF and ECF

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• Free movement of water
• Direction by hydrostatic pressure and osmotic
pressure balance determined by osmolality
• Water channels(aquaporins)
• Ionic movement determined by membrane
transporters

Front 14

Sodium Na +

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– 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

Front 15

Chloride Cl-

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– 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
• Chloride shift in RBCs

Front 16

Potassium K+

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– 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+

Front 17

Bicarbonate HCO 3 -

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– 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
– Chloride shift helps maintain correct balance of anions in ECF and ICF
– Kidneys are main regulators of blood HCO3-

Front 18

Calcium Ca 2+

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– 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

Front 19

Blood composition

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Front 20

Blood - Functions

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• Respiratory – Transport O2 from lungs to tissues – Transport CO2 from tissues to lungs
• Nutrition – Transport “food” from gut to cells
• Excretory – Transport waste from tissues to kidney (urea, uric acid, water)

• Regulatory – Water Content of Tissues
- Water exchanged through vessel walls to tissue
• Body Temperature
• Protective – Antibodies, antitoxins, white blood cells (WBC)
• Acid-base balance – pH 7.35~7.45
• Coagulation (clotting)

Front 21

Blood composition

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• Cells - 45% by volume
• Plasma - 55% by volume
• Cells – Red cells (erythrocytes):
• 5x106/mL

– White cells (leukocytes)
• 7x103/mL

– Platelets (thrombocytes)
• 3x105/mL

Front 22

Centrifuged Blood Sample

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Add anticoagulants (heparin, potassium
oxalate)

Front 23

Separation of Components

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Front 24

Plasma vs. serum

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Plasma is the liquid, cell-free part of blood, that has been treated with anti-coagulants.

Serum is the liquid part of blood AFTER coagulation, therefore devoid of clotting
factors as fibrinogen.

serum= plasma - fibrinogen

Front 25

Components of Plasma

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Water 90%
Plasma Proteins 6-8 %

Electrolytes (Na+ & Cl-) 1%

Nutrients (e.g. Glucose and amino acids) Hormones (e.g. Cortisol, thyroxine)

Wastes (e.g. Urea)

Blood gases (e.g. CO2, O2)

Front 26

Plasma proteins

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simple proteins and conjugated proteins

Front 27

Characteristics of plasma proteins

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1. They are synthesized in liver except

immunoglobulin.
2. Almost all plasma proteins are glycoproteins.
3. Many plasma proteins exhibit polymorphism -antitrypsin, transferrin, haptoglobin.
4. Each plasma protein has a characteristic halflife in the circulation.
5. Acute Phase Proteins, APP

Front 28

Homeostasis

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The maintenance of static or constant conditions in the internal environment

•For the body’s cells to survive and function properly, the composition and temperature of the fluids around the cells (“interstitial fluid”) must remain much the same.

•An organism is said to be in homeostasis when the internal environment contains:
-The optimal concentration of gases
-The optimal concentration of nutrients
-The optimal concentration of ions and water
-At the optimal temperature

Front 29

Negative Feedback

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response is negative to the initiating stimulus ...the control system initiates a series of changes that return the factor toward a certain mean value ... thus maintaining homeostasis.

Front 30

Negative Feedback diagram

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Front 31

Types of information necessary for
physiological systems

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• Set point—a reference point
• Feedback information—what is happening in
the system
• Error signal—any difference between the set
point and feedback information

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Regulatory systems

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• Obtain, integrate, and process information
• Issue commands to controlled systems
• Contain sensors to provide feedback
information that is compared to the set point

• Regulatory systems then issue commands
to effectors that effect changes in the
internal environment.
• Effectors are controlled systems
because they are controlled by regulatory
systems.

Front 33

Sensory information in regulatory systems

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• Negative feedback:
• Causes effectors to counteract the
influence that creates an error signal
• Positive feedback:
• Amplifies a response
• Increases deviation from a set point
• Feedforward information:
• Anticipates internal changes and
changes the set point.