Pages 524-531

Blood composition depends on:1. Diet2. Cellular metabolism3. Urine output

How the kidneys manage blood composition:1. Excretion of nitrogenous wastes2. Water/electrolyte balance of the blood3. Ensuring proper blood pH

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The main fluid compartments that water occupies: 1. Intracellular Fluid (ICF) : fluid inside cells2. Extracellular Fluid (ICF) : fluid outside cells

1. interstitial fluid2. blood plasma, CSF, lymph, humors of the eye

Changes in electrolyte balance can influence blood volume/blood pressure, cellular activity

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Lungs Gastrointestinaltract

Kidneys

Bloodplasma

Interstitialfluid

Intracellularfluid in tissue cells

O2 CO2 Nutrients

O2 CO2 Nutrients

H2O,Ions

H2O

H2O,Ions

Ions

Nitrogenouswastes

Nitrogenouswastes

Electrolytes: charged particles (ions) that conduct an electrical current in aqueous solution allow reactions that require electrical charge to take

place Cell membrane stability Muscle contraction Nerve impulse

Body electrolytes include: Sodium (Na⁺) Potassium (K⁺) Calcium (Ca⁺⁺) Magnesium (Mg⁺⁺)

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Osmoreceptors: cells in the hypothalamus Activated by small changes in blood

composition Results in a dry mouth Reinforces the drive to drink water

What is a diuretic? A substance that causes your kidneys to eliminate more salt and water than it should

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Hormones regulate reabsorption of water and electrolytes by the kidneys Antidiuretic hormone (ADH)

Hypothalamus tells posterior pituitary to release ADH

prevents excessive water loss in the urine increases water reabsorption

Aldosterone (produced by adrenal cortex) increases sodium and water reabsorption; decreases potassium reabsorption

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Regulates blood pressure The juxtaglomerular (JG) apparatus of the

renal tubules sense drop in BP or solute concentration

Causes release of the enzyme renin into blood

Renin produces angiotensin II Acts directly on the blood vessels to

vasoconstrict Works to reduce filtrate volume

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Ideal blood pH: between 7.35 and 7.45 Kidneys : biggest impact in controlling

pH Other acid-base controlling systems

Blood buffers Respiration

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HCl H2CO3

H2CO3

H2CO3

H2CO3

H2CO3 HCO3−

HCO3−H+

H+

H+H+H+ H+

H+H+H+

Cl−

Cl− Cl−

Cl−

Cl− Cl−

Cl−

(a) A strong acidsuch as HCldissociatescompletelyinto its ions.

(b) A weak acid suchas H2CO3 doesnot dissociatecompletely.

The bicarbonate buffer system is a mixture of: sodium bicarbonate (NaHCO3)

carbonic acid (H2CO3)

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Bicarbonate ions (HCO3–):

react with strong acids to change them to weak acids

HCl + NaHCO3 H2CO3 + NaCl strong acid weak base weak acid salt

Carbonic acid :dissociates in the presence of a strong base to form a weak base and water

NaOH + H2CO3 NaHCO3 + H2O strong base weak acid weak base water

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As blood pH changes: respiratory rate can rise and fall to:

retain CO2 (decreasing the blood pH)

remove CO2 (increasing the blood pH)

CO2 + H2O H2CO3 H+ + HCO3−

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When blood pH rises: Bicarbonate ions are excreted Hydrogen ions are retained by kidney

tubules

When blood pH falls: Bicarbonate ions are reabsorbed Hydrogen ions are secreted

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