body fluids. objectives outline the functions of water in the body. state how water content varies...
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Objectives• Outline the functions of water in the body.• State how water content varies with age and sex.• Differentiate between intracellular and extra-cellular
fluid.• Explain how water moves between fluid
compartments.• List the major sources of body water gains and losses.• State the function and stimuli of thirst.• Briefly explain how ADH regulates urine concentration.• Briefly describe the role of aldosterone in fluid
balance.
Functions of water
Water is the solvent used in the body:
to transport nutrients to cells
to remove waste products from cells
to act as a transport vehicle for blood gases O2
Functions of water
Water is also necessary ..
* for body structure (e.g. skin turgor)
* in temperature regulation
* as a medium for chemical reactions
* as a lubricant
* as a cushion and shock absorber
Body water and age and sexThe volume of total body water in a healthy adult male is
approximately 45 L (i.e.60% of their body is H2O)
Variations in water content with ageInfant Adult Older Adult
% H2O 80% % H2O 55%
Infants also ingest and excrete a greater volume of water in relation to their size ? why
Fluid Compartments and Fluid Exchange
2/3 body H2O 1/3 body H2O
Inside cells Outside cells
Intra-Cellular Fluid Extra-Cellular Fluid
(ICF) = 30L (ECF) = 15LInterstitial fluid 12LPlasma 3L
Also … Lymph
Cerebrospinal fluid
Body space fluid e.g.
Intra-ocular fluid
About 65% of Body Weight
Adult has 45 litres 45 litres of water in the body:of water in the body:
Total Body WaterTotal Body Water
Intracellular30 Litres
Extracellular15 litres
Tissue Fluid 12L Plasma 3L
Water gains and lossesGains Losses
Water 1300 ml urine 1700 ml
Food 1000 ml insensible losses ..
Metabolism 400 ml faeces 200 ml
lungs 300 ml
skin 500 ml
Total 2700 ml 2700 ml
Alterations in homeostasis
• If the water gained = water lost each day the body will be in water equilibrium
• If the water gained is less than water lost DEHYDRATION
What interventions may be necessary treatment of dehydration?
[Application to clinical practice: Dehydration]
What patients may be at risk of dehydration?
Have you ever been dehydrated and how did you feel?
[Application to clinical practice: Dehydration]
What are the signs and symptoms of dehydration?
What is minimum urine output/hr to maintain kidney function?
Whose role is it to ensure that patients are adequately hydrated?
Regulation of Intake
• The sensation of thirst ensures that water intake is adequate
• What patients may not be able to respond to the thirst sensation?
• The thirst centre is in the hypothalamus where there are nerve cells called osmoreceptors
Regulation of intake
Saliva Blood osmolarity
Dehydration
Mouth / throat dry Thirst centre stimulated
Sensation of thirst and desire to drink
Mucosa of mouth/ pharynx wetted
Distension of intestineOsmotic pressure
Initial quenching of thirst Major inhibition of thirst
Regulation of Fluid Volume
Increased Osmotic Decreased Pressure (blood) Flow of Saliva
THIRSTTHIRST
INCREASED INTAKE
INCREASED BLOOD VOLUME
DEHYDRATION
HypothalamusDry Mouth &
Throat
Regulation of Output
Fluid output adjusted by... • ADH • Aldosterone
(both regulate urine production)
• Anti Diuretic hormone (ADH)
• Increases re-absorption of water by the kidneys
Anti Diuretic Hormone
The hypothalamus synthesizes ADH which is transported to the posterior pituitary and stored there
Alcohol Inhibits release of ADH
Control of ADH secretion
• Changes in extra-cellular osmolality
• Detected by Osmoreceptors in hypothalamus
• ADH production and release will be increased or decreased
• What will the effect be of increased ADH?
• What will the effect be of decreased ADH?
Aldosterone
Aldosterone is a Mineralocorticoid produced by the Zona glomerulosa of the adrenal cortex
Function of aldosterone is to:• Stimulate kidneys to reabsorb Na+ and
secrete K+ sodium and water reabsorption
Aldosterone
Tissue fluid production
Arteriole end Venule end
Lymph vessel
Tissue Fluid
CapillaryHP = 35mmHg HP = 15mmHg
OP = 25mmHg
Hydrostatic pressure?
Osmotic pressure?
Structure of the capillary?