Body Fluids

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 O2O2

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 sex The 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 age InfantAdultOlder 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 H2O1/3 body H2O Inside cellsOutside cells Intra-Cellular Fluid Extra-Cellular Fluid (ICF) = 30L(ECF) = 15L Interstitial fluid 12L Plasma 3L Also … Lymph Cerebrospinal fluid Body space fluid e.g. Intra-ocular fluid

About 65% of Body Weight 45 litres of water in the body: Adult has 45 litres of water in the body: Total Body Water Intracellular 30 Litres Extracellular 15 litres Tissue Fluid 12L Plasma 3L

Water gains and losses GainsLosses Water1300 mlurine1700 ml Food1000 mlinsensible losses.. Metabolism 400 mlfaeces200 ml lungs300 ml skin 500 ml Total 2700 ml2700 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 intestine Osmotic pressure Initial quenching of thirstMajor inhibition of thirst

Regulation of Fluid Volume Increased Osmotic Decreased Pressure (blood) Flow of SalivaTHIRST INCREASED INTAKE INCREASED BLOOD VOLUME DEHYDRATION Hypothalamus Dry 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 hormone (a mineralocorticoid) produced by the adrenal cortex

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 Capillary HP = 35mmHg HP = 15mmHg OP = 25mmHg Hydrostatic pressure? Osmotic pressure? Structure of the capillary?