Kideney & body fluids

By

DR KHALED SALEH ALGARIRIOctober 2014

INTRODUCTION

•The main channels of excretion in the body are kidneys, skin, lungs, digestive tract and salivary glands .

•Kidneys and partly the skin excrete soluble substances and water from the blood (maintain homeostasis of water and electrolyte concentrations within the body).

•Lungs excretes CO2 and water vapour, ammonia, ketone bodies, alcohol, aromatic oils etc.

• Skins excretes water, salts, little urea etc.

• Liver excretes fatty substances through bile.

• Colon and salivary glands excretes heavy metals.

• The excretion of waste products done by the kidneys, that system will be called as Urinary system (or) renal system.

FUNCTIONS OF THE KIDNEY

Filtration of waste products from the blood.

Tubular reabsorption of useful substances from the filtrate.

Kidneys produce urine that contains metabolic waste products, including the nitrogenous compounds urea and uric acid, excess ions and some drugs.

Maintaining normal blood pressure by balancing electrolytes in the blood.

In average young adult male:

% of body weightBody composition

18%Protein, & related substances

15%Fat

7%Mineral

60%Water

BODY COMPOSITION

BODY FLUIDS

Water content in body is divided into 2 compartments:

1. Extracellular fluid (ECF)

- fluid outside the cells.

1/3 volume of fluids in body ( 33% of total body water).

- contains ions & nutrients needed for cellular life.

2. Intracellular fluid (ICF):

- fluid inside the cells.

2/3 volume of fluids in body ( 67% of total body water).

VOLUME OF BODY FLUIDS IN 70 kg MAN

TOTAL VOLUME

42 L

INTRA CELLUAR FLUID28 L(ROUGHLY 2/3 OF TBW)

EXTRA CELLULAR FLUID

14 L(ROUGHLY 1/3 OF TBW)

PLASMA4 L (ROUGHLY ¼ OF ECF)

Fluid Compartments 60% of body weight

Extracellular fluid

( 1/3)

33% of TBW 20% of body wt

Intracellular fluid

( 2/3)

67% of TBW 40% of body wt

Interstitial fluid75% of ECF

15% of body wt

Plasma

25% of ECF

5% of body wt

Transcellular fluid

CSFIntraocular

PleuralPeritonealPericardialSynovialDigestive secretions

BODY FLUID COMPARTMENTS

Composition of body fluids

Organic substancesGlucose

Amino acids

Fatty acids

Hormones

Enzymes

Inorganic substances Sodium

Potassium

Calcium

Magnesium

Chloride

Phophate

Sulphate

DIFFERENCES

ECF Most abundant cation -Na+,

Most abundant anion - Cl-

ICFMost abundant cation - K+

Anion are proteins andphosphates (HPO4

2-)

Na+ /K+ pumps play major role in keeping K+ high inside cells and Na+ high outside cell

TRANSPORT OF WATER AND FLUIDS

Filtration - the movement of water and solutes from an area of high hydrostatic pressure to an area of low hydrostatic pressure

Osmolality - reflects the concentration of fluid that affects the movement of water between fluid compartments by osmosis

Osmotic pressure - the amount of hydrostatic pressure required to stop the flow of water by osmosis

Active transport - movement of solutes across membranes; requires expenditure of energy

Active Transport

OSMOLARITY

Isotonic – same solute concentration, equal, no movement across membrane

Hypertonic/hyper-osmotic – greater concentration osmotic pressure water pulled into fluid to equalize

Hypotonic/hypo-osmotic – lesser concentration osmotic pressure water pulled out of fluid to equalize

Dehydration Fluid Overload

FLUID IMBALANCES

Fluid Deficit Fluid Excess

Isotonic – fluid and

electrolytes loss equally; decline in circulating blood volume

Hypertonic – fluid loss

exceeds loss of electrolytes

Hypotonic – electrolytes

loss exceeds loss of water

Isotonic – Only ECF is

expanded

Hypertonic – excessive

Na+ intake; fluid shifts from ICF to ECF

Hypotonic – water

intoxication; life threatening; fluid moves in ICF and all compartment expands

EXTRACELLULAR FLUID OSMOLALITY

Osmolality

Adding or removing water from a solution changes this

Increased osmolality

Triggers thirst and ADH secretion

Decreased osmolality

Inhibits thirst and ADH secretion

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Regulation of Body Fluid Characteristics

• The kidneys are the most important organs for regulating the characteristics of body fluids. This regulation is apparent in the control of (a) blood volume, (b) extracellular fluid volumeand (c) osmolarity of body fluids. Thirst also plays a vital role in controlling some characteristics of body fluids.

HORMONAL REGULATION OF BLOOD OSMOLALITY

REGULATION OF ECF VOLUME

Mechanisms

Neural

Renin-angiotensin-aldosterone

Atrial natriuretic hormone (ANH)

Antidiuretic hormone (ADH)

Increased ECF results in

Decreased aldosterone secretion

Increased ANH secretion

Decreased ADH secretion

Decreased sympathetic stimulation

Decreased ECF results in

Increased aldosterone secretion

Decreased ANH secretion

Increased ADH secretion

Increased sympathetic stimulation

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HORMONAL REGULATION OF BLOOD VOLUME

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HORMONAL REGULATION OF BLOOD VOLUME

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KIDNEY AND BODY FLUIDS99 % of water& Na is reabsorpred by tubules to maintain osmotic balance.

Kidney regulate volume of the body fluid by reabsoping

water and Na.

If more Na is excreted, this leads to water excretion and

dehydration.

If low Na is excreted, this leads to low water excretion and

fluid retention (hypervolemia), thus increase BP

- When low BP & low blood flow to kidney, kidney release

rennin which convert angiotensinogen to angiotensin1, lung

covert angiotensin I to angiotension II, Leads to

vasoconstriction, increase BP, increase renal perfusion.

Activates Adrenal cortex to releases Aladstrone

hormone increase renal reabsorption of water and Na,

thus increase BP, increase renal perfusion.

Aldastone activate pituitary gland to release

Antiduitretics hormones ( ADH) which stop diuretics,

this lead to low urine output, and high Na & water

retention thus increase BP, increase renal perfusion

KIDNEY AND BODY FLUIDS

REGULATION OF ECF VOLUME

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REGULATION OF WATER INTAKE