fluid balance presentation for hap 2012 (1)

8/13/2019 Fluid Balance Presentation for HAP 2012 (1)

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Learning Outcomes

1. Outline the functions of water in the body and identify themain fluid compartments of the body.

2. Describe how fluid is gained and lost by the body.

3. Explain the difference between hypertonic, hypotonic and

isotonic solutions and explain the importance of plasmaproteins in controlling the movement of water between

fluid compartments.

4. Describe the homeostatic mechanisms that regulate fluid

balance and consider fluid balance issues related to age.

GML/Renal System/IHB/2009 2


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2000 Lippincott Williams & Wilkins Fudamentals of Nursing 4th Edition adapted

The Primary Functions of Water in

the Body: Provide a medium for transporting nutrients to cells

and wastes from cells, and transporting of blood cells

and substances eg. hormones, enzymes, platelets,

Facilitate cellular metabolism and cellular functions

Act as a solvent for electrolytes.

Help maintain normal body temperature

Facilitate digestion and promote elimination

Act as a tissue lubricant


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Fluid Sources:

Ingested liquids= 1500mls daily

Water in food =1000mls/day

Water from metabolic oxidation= 500mls/day


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The total amount of water in a man of

average weight (70 kg) is approximately40

litres(or 57% of his total body weight)

In a newborn, this may be as high as 75% of

total body weight (progressively decreasing)

Obesity the % of water in the body,

sometimes to as low as 45%

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Body fluid is contained within the cells (intra-

cellular) and outside the cells (extra-cellular)

Intra-cellular =

Extra-cellular can be further

subdivided into:

25 litres (or of total)

Extra-cellular = 15 litres (or of total)

Plasma =

Interstitial =(3rdspace)

3 litres

12 litres


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The cells are generally impermeable to

sodium

Most sodium that enters into the cells is

removed by a pump on the cell membrane

which exchanges it for potassium


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Electrolytes:

Ion:an atom or molecule carrying an electric charge

Electrolytes:substances capable of breaking into

electrically charged ions when dissolved in solution

Sodium Potassium

Calcium

Magnesium

Chloride

Bicarbonate

Phosphate


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Fluid and Electrolyte Movement:

Osmosis:

Diffusion:

Active transport:

Filtration:

Review the

defini tion forthese terms in

your books

and complete

this slide.


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Osmosis


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Definitions

Hypotonicfluid containing fewer solutes(therefore more water) than the cells eg. distilledwater, 0.5% saline (in extreme dehydration)

Isotonicfluids having the same soluteconcentration as cells do eg. 5% dextrose, 0.9%salineno damage to cells

Hypertonicfluids containing more solutes ordissolved substances,sometimes given foroedema to attract the fluid out of tissue spaces and

back into the bloodstream and excess to beexcreted by kidneys


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Movement of Water When the blood flows from arterioles to capillaries

(which are narrower) the hydrostatic pressure isincreased because of the decreased diameter of thevessel

Plasma is filtered out of the blood into the

interstitial fluid which bathes the cells (tissue fluid) The return of this fluid back into the blood is

essential to maintain the blood volume and it is theproteins in the blood which provides the osmotic

pressure to pull the plasma (water) back into thecapillary at the venous end (draw a picture!)

This is an example of how the body relies onconcentration gradients for movement of substances


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Homeostasis of Fluid BalanceAnti-Diuretic Hormone (ADH)

Osmoreceptors in the hypothalamus of brain reactto changes in blood composition such asdehydration where blood volume decreased.

Impulses sent to posterior pituitary gland in brain,which produces ADH*

ADH acts on DCTs and collecting ducts causingmore water to be reabsorbed back into the bloodresults in a more concentrated urineresults in anincrease in blood volume and BP

* Alcohol inhibits production of ADH and causeslarge volumes of dilute urine to be formed cerebral dehydration results in hung over feeling!


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Anti-Diuretic Hormone

Reduced water intake or increased water loss causesincreased osmotic pressure(solute concentration) of blood

Hypothalamus

Posterior Pituitary Gland

Anti-Diuretic Hormone (ADH)

Kidney

Increased water reabsorption by increasing the permeabilityof the distal convoluted tubules/collecting ducts

Increased blood volume and BPsmall volume ofconcentrated urine


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Homeostasis of Fluid Balance

Renin-Angiotensin System

Decrease in BP and Blood Volume (BV)stimulates kidneys to releases rennin

Rennin brings about production of angiotensin ll

(via a series of reactions) Angiotensin ll causes vasoconstriction leading to

increased BP

Angiotensin ll also stimulates adrenal glands (on

top of kidneys) to secrete ALDOSTERONEwhich increases Na+ and H20 reabsorption and

increased blood volume


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Renin-Angiotension-Aldosterone System

Low BP or Kidneys

Low BV

Renin (enzyme)

Angiotensin ll

Vasoconstriction Aldosterone (adrenals)

(Increased BP) Na+and H2O

reabsorption

Maintain BP and Blood Volume

By Altering Fluid Balance2000 Lippincott Williams & Wilkins Fudamentals of Nursing 4th Edition adapted


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Homeostasis of Fluid BalanceAldosterone

Aldosterone is a hormone secreted by the adrenal

cortex when Na+levels fall or K+levels rise

Causes active reabsorption of Na+ and secretion

of K+in DCT and collecting ducts 80% of Na+is passively reabsorbed in the PCT

Aldosterone alsoincreases water reabsorption in

the tubules since water follows Na+ back into the

bloodstreamwater follows salt!

Fluid and electrolyte balance fine tuned in DCT &

collecting ducts


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Regulation of Blood pH

Blood pH is determined by the H+

ionconcentration

Bicarbonate ions (HCO3) buffer pH by mopping

up excess H+ ions and make the blood less acidic

HCO3 + H+H2CO3(carbonic acid)

Fewer H+ions in solution ALKALINE

Kidneys regulate pH by excreting or reabsorbing

HCO3 and limits its availability to bind with H+


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So...........

When blood is too acidic ie. Lots of free floatingH+, the nephrons of the kidney REABSORB more

bicarbonate (HCO3) which binds to the H+making the blood more alkaline

When the blood is too alkaline, more bicarbonate(HCO3) ions are excreted in urine so that there arenot enough bicarbonate for the H+ to bind to,

making the blood more acidic

What does acidosis and alkalosis mean?

fluid balance presentation for hap 2012 (1)

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