kideney & body fluids
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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
27-18
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
27-21
HORMONAL REGULATION OF BLOOD VOLUME
27-22
HORMONAL REGULATION OF BLOOD VOLUME
27-23
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
27-26
REGULATION OF WATER INTAKE