Fluid, Electrolyte, Acid-Base Balance

Functions of Water

• Temperature Regulation

• Protective cushion

• Lubricant

• Reactant

• Solvent

• Transportation of nutrients and removal of wastes

Fluid Compartments

• Intracellular Fluids (ICF)

• Extracellular Fluid (ECF)

  • Interstitial Fluid

  • Plasma

Nonelectrolytes

Substances that do not dissociate into ions in solution, such as glucose, urea, and lipids that do not conduct electricity.

Body Water content

• percentage of water in an adults total body weight

• Factors that influence this

  • Age

  • Diet

  • Gender

  • Body Composition: Muscle Mass and Fat Content

  • Health Conditions and Physical Activity

the amount of fat in the body (more fat = less water)

Percentage of Water in the body depends on…

approximately 60%

Percentage of water for males

approximately 50%

Percentage of water for females

approximately 73%

Percentage of water for newborns

approximately 45%

Percentage of water for elderly people

Intracellular fluid (ICF)

• fluid within cells or cytosol

• about 2/3 of the body’s total water content

• contains K+ and PO4 ions

extracellular fluid (ECF)

• fluid found outside of cells

• about 1/3 of body’s total water content

• plasma and interstitial fluid is this type of fluid

• contains Na+, Cl-, and HCO3-

Interstitial fluid

• a form of extracellular fluid that surrounds the cells

• largest fluid compartment

plasma

• a form of extracellular fluid that is the component of blood

• contains a higher protein content

Body fluid

refers to the water in the body and all of its dissolved substances

electrolytes

ions that are dissolved in body fluids to perform several different functions

number of positive and negative ions may not be equal, however the number of charges must be equal and balanced within the fluid compartment

Balance of Charge

Function of electrolytes

• cofactors for enzymes

• action potential in neurons and muscle cells

• important in the secretion and action of hormones and neurotransmitters

• muscle contractions

• maintains acid/base balance (pH balance)

• secondary active transport

40L of water and it remains constant (total body water)

Average adult contains about…

2300 mL of water through food

We take in about

200 mL

________ of body water is generated through cell metabolism

kidneys, lungs, skin, and GI tract

we lose water through the

1500mL of water

Kidneys lose

600 mL of water through insensible water loss

Skin lose

Insensible water loss

continuous, unnoticeable loss of water from the body

300 mL of water through insensible water loss

Lungs lose

100 mL of water

GI Tract lose

Mechanisms of fluid balance

• ADH

• Thirst mechanism

• Aldosterone

• Sympathetic Nervous System

Thirst Mechanism

the primary regulator of water intake that involves hormonal, neural, and voluntary behaviors

Why Dehydration leads to thirst (Thirst Mechanism)

• Impulses go from the dry mouth to the thirst center in the hypothalamus

• Plasma osmotic pressure increases because there is a lack of water, so the concentration of solutes increases resulting in the stimulation of osmoreceptors in the thirst center

• Decreased blood volume and pressure will stimulate the baroreceptors and cause the release of renin and production of angiotensin 2 which will also stimulate the thirst center.

Fluid Ingestion

• dryness of mouth and throat is relieved

• stretch receptors in the stomach and intestines send inhibitory signals to the thirst center

• normal fluid osmolarity and volume are restored, which relieves dehydration, and the thirst center will not be stimulated

Sympathetic Nervous System

stimulated by a decrease in blood volume so blood pressure as well. If BP is low, it activates mechanisms to conserve water and increase blood pressure. By the release of renin which will stimulate aldosterone.

ADH

A hormone produced by the posterior pituitary gland that promotes water reabsorption in the kidneys, helping to regulate body fluid balance and osmolarity.

It causes aquaporins (water channels) to form in the cell of the DCT and CD to enhance water reabsorption and reduce urine output, thus increasing blood volume and decreasing plasma osmolarity.

Aldosterone

a hormone produced by the adrenal cortex that regulates sodium and potassium levels in the body by promoting sodium reabsorption and potassium excretion in the kidneys, thus helping to control blood pressure and fluid balance.

Electrolyte Balance

concentration of electrolytes must be maintained within specific limits so controlling fluid movement between different compartments in the body.

Movement of fluid across the cell membrane differs from the movement of fluid between the interstitial compartment and plasma, which involves processes such as osmosis and hydrostatic pressure. This balance is crucial for proper cellular function and overall homeostasis.

Edema

the abnormal accumulation of fluid in the interstitial spaces that occurs to be a disturbance of water levels and occurs as a result of electrolyte imbalance

4 causes of edema

• decreased capillary colloid osmotic pressure

• increased capillary hydrostatic pressure

• increase capillary permeability

• lymphatic obstruction

6 important ions in the body

• Sodium (Na+)

• Potassium (K+)

• Calcium (Ca++)

• Magnesium (Mg++)

• Chloride (Cl-)

• Bicarbonate (HCO3-)

• Phosphate (PO43-)

Sodium (Na+)

• Normal Range: 136-145 mEq/L

• most significant osmotic effect in the ECF

• roles: stimulates nerve impulses and muscle contraction, regulates water movement, their changes determine fluid levels in other areas

Hypernatremia

high concentration of sodium in the ECF that causes cells to shrink because water follows solutes, so water is pulled out of the cell and into the ECF

Hyponatremia

low concentration of sodium in the ECF that causes cells to swell because water follows solutes so there is more solutes inside the cell than out of it so water flows into the cell causing it to swell.

Urine Regulation of Na+

Kidneys fine-tune concentration of Na+ in the plasma, and 85-95% of Na+ is reabsorbed into the plasma at the PCT and the loop of Henle.

Increase in blood volume is caused by

an increase in solutes specifically Na+

Increase in Blood pressure is caused by

an increase in solvents specifically H2O

Potassium (K+)

• most is found in the cell, but the concentration is measured in the plasma

• ends up in the ECF through dietary, and the cell membranes are more permeable to it compared to sodium, so more of it leaks out of the cell.

• Roles: responsible for ICF volume through osmosis, are leaky so they leave a negative charge in the cell, help maintain resting membrane potential, nerve impulse conduction, muscle contraction, and maintenance of normal cardiac rhythm. During Acid/Base balance H+ moves out of cells and these move in (vice versa) to help maintain electrical balance inside the cells.

Urinary Regulation of K+

• 90% is absorbed through the PCT and LOH

• if the levels of this is high aldosterone is secreted and the excess of this is secreted into the filtrate from the plasma within the DCT and Collecting Duct.

Hyperkalemia

high concentration of potassium in the blood. It causes health issues such as chronic kidney disease, and arrhythmias. A person with this condition may be on dialysis to filter potassium from the blood.

Hypokalemia

low concentration of potassium in the blood. It causes Cushing’s syndrome, Bartter’s syndrome, and Gitelman Syndrome

Calcium (Ca++)

• crucial to normal body function so small changes can be detrimental. It plays a key role in bone health, muscle contraction, nerve transmission, and blood clotting.

• Normal Range: 9-11 mg/dl

Hypercalcemia

high concentration of calcium in the blood, which can lead to symptoms such as nausea, vomiting, weakness, and serious complications like kidney stones, heart dysrhythmias, and can stop the heart altogether.

Hypocalcemia

• low concentration of calcium in the blood, which can cause muscle spasms, weakness, and other neurological symptoms. Such as tetanus and stoppage of breathing

• when this happens the parathyroid secretes PTH into the blood to increase calcium by increasing the activity of osteoclasts that will secrete calcium and phosphate into the blood and plasma. It will also stop the reabsorption of phosphate by the kidneys.

Arterial blood pH range

7.35-7.45

Venous blood pH range

7.35

Intracellular fluid (ICF) range

7

Extracellular Fluid (ECF) range:

7.35

Gastric Juice range

1.2-3.0

Intestinal Juices pH range

8.0

Urine pH range

4.5-8.0

Acids

proton donors that release H+ ions

Strong Acids

when added to water it dissociates into H+ and Cl- ions, so all the H+ ions are released

Weak Acid

does not completely dissociate

When a base is added to water

it will bind hydrogens into hydroxide ions (OH-)

Electrolytes in the plasma

can act as weak acids and bases

HCO3-, HPO4-, SO4- and anions or organic acids serve as

bases

H2PO4 is a

acid

Buffers

substances that help maintain pH levels by neutralizing acids or bases to help the body maintain pH.

it is a combination of weak acid and weak base pairs (conjugate acid/base pairs)

3 buffer systems

• H2CO3/HCO3 buffer system (carbonic acid/bicarbonate)

• H2PO4-/HPO4 buffer system (phosphate_

• Protein buffers

Protein Buffers

most abundant intracellular mechanism for regulating pH

Respiratory Control of pH

The body's method of regulating pH by adjusting the levels of carbon dioxide through respiration. By increasing or decreasing breathing rate, the concentration of carbonic acid in the blood can be controlled, thus influencing pH levels.

H+ ions are released which makes the plasma more acidic

If respiratory rate decreases

H+ ions are bonded with oxygen and make the plasma more alkaline

If respiratory rate increases

Renal Mechanisms

• tubules selectively reabsorb and secrete acids and bases to fine-tune the pH

• slowest but most powerful mechanism for acid/base balance

HCO3 is not reabsorb and is excreted through the urine

(Renal Mechanism) If the plasma pH is too high

1. HCO3 will be reabsorbed

2. HCO3- will be generated by the kidney tubule cell

3. H+ ions will be secreted into the filtrate

(Renal Mechanism) If the plasma pH is too low

Metabolic Alkalosis

• Too much bicarbonate in the blood, too little hydrogen ions in the blood

• Restlessness (Lethargy)

• Dysrhythmia (Tachycardia)

• Hypoventilation

• Confusion (Dizziness, Irritable)

• Nausea, Vomiting, Diarrhea

• Tremors, Muscle Cramps, Tingling of fingers and Toes

• Hypokalemia

Metabolic Acidosis

• Too little bicarbonate in the blood, too much hydrogen ions in the blood

• Headache

• Low BP

• Hyperkalemia

• Muscle Twitching

• Warm, Flushed Skin (Vasodilation)

• Nausea, Vomiting

• Low Muscle Tone, and Reflexes

• Hyperventilation

Respiratory Acidosis

• Too much carbonic acid due to the increase (retention) of carbon dioxide

• Can’t catch their breath

• Hypoventilation → Hypoxia

• low BP even with vasodilation

• Dyspnea

• Headache

• Hyperkalemia

• Dysrhythmias (increased potassium levels)

• Drowsiness, Dizziness, and Disorientation

• Muscle Weakness, Hyperreflexia

• Causes: decreases respiratory stimuli, COPD, Pneumonia, and Atelectasis

Respiratory Alkalosis

• too little carbonic acid due to the loss of carbon dioxide

• Hyperventilation

• Tachycardia

• Low BP

• Hypokalemia

• Numbness and tingling of extremities

• Hyper Reflexes and Muscle Cramping

• Seizures

• Increased anxiety and irritability

• Causes: hyperventilation, and mechanical ventilation

PTH (Parathyroid Hormone)

increase calcium and phosphate levels through the activity of osteoclasts and renal reabsorption.

Calcitonin

decreases calcium and phosphate levels through inhibiting osteoclast activity and promoting calcium excretion in the kidneys.

Hypercapnia

excess carbon dioxide in the blood, often leading to respiratory acidosis.

Hypocapnia

a condition of low carbon dioxide levels in the blood, which can lead to respiratory alkalosis.

Ketoacidosis

a serious complication of diabetes characterized by high levels of ketones and acidity in the blood, often resulting from insulin deficiency.

Dehydration

a condition resulting from excessive loss of body fluids, due to vomiting, diarrhea, sweating or inadequate water intake that leading to an imbalance in electrolytes, reduced blood volume, impaired nutrient transport and waste removal.

Hypotonic Hydration

a condition that occurs when there is an excess of water in the body relative to sodium levels, leading to dilution of sodium in the blood (hyponatremia) which causes cells to swell.

converting strong acids to weak acids

Acid-base buffer systems minimize pH changes by

respiratory acidosis

A person with emphysema (lung condition where the alveoli is damaged) can exhibit signs of 

carbon dioxide

The most important factor affecting the pH of body fluids is the concentration of

aldosterone secretion decreases

When the amount of sodium ions in the ECF increases

metabolic alkalosis

If you chronically consume antacids, you may be at risk for

Transcellular fluid

a form of extracellular fluid that is found within epithelial spaces, such as cerebrospinal fluid, synovial fluid, aqueous and vitreous humor, serous fluids, GI fluids, and even urine