Brewer Fluid, Electrolyte Acid-Base

What is the focus of this chapter?

Homeostatic mechanisms that regulate body fluids and are critical to cells.

How much fluid makes up total body composition? (percentage)

50-60%

What are minerals?

Inorganic substances that are dissolved within and form ions called electrolytes

Name the two components of fluid compartments

• Intracellular fluid (ICF)

• Extracellular fluid (ECF)

Describe intracellular fluid

• fluid inside a membrane

• water content varies most here

Why does water content vary in ICF?

This is because of variation in tissue types (muscle vs fat)

Why is ICF distinct with extracellular fluid? (ECF)

Due to plasma membrane transport

Describe ECF

• fluid not inside a membrane

• interstitial volume varies

How does the volume of blood vary between the sexes

Men have a higher volume of blood than women

Here’s a picture to help visualize ICF & ECF

What is meant by the term “fluid balance”

water content stable over time

• think in terms of gains and losses

How do we gain fluids in our body?

Primarily by absorption along GI tract

How do we specifically gain water?

As nutrients and ions are absorbed, an osmotic gradient is created causing passive absorption of water

How do we lose the fluids in our body?

• Mainly through urination, but other routes as well

• digestive secretions are reabsorbed similarly to ingested fluids

What percentage of urine accounts for the fluid being loss?

over 50%

Give an overview of what occurs when the body maintains fluid balance (in terms of gains and losses)

The source and method of elimination of water are equal

Describe what occurs with ECF and ICF when they are balanced

Although different compositions, they’re at osmotic equilibrium

How is loss of water from the ECF replaced?

replaced with water in ICF

Describe a fluid shift

occurs in minutes to hours and restores osmotic equilibrium

What happens when to the ECF and ICF when a person is dehydrated

• results in long term transfer that cannot replace ECF water loss

• homeostatic mechanism to increase ECF fluid volume will be employed

NOW LET’S STUDY MINERAL BALANCE

Describe mineral balance

equilibrium between ion absorption and excretion

Where does major ion absorption occur?

• Small intestine

• colon

Where does major ion excretion occur?

Kidneys

Which glands excrete ions and water variably

sweat glands

Where does ion reserve mainly occur?

Primarily in the skeleton (bone)

Which two ions are not stored in the bone?

Sodium and Potassium are not stored in the bone

• remains in solution

Describe the overall pathway food and minerals take in the body

Digestive

ECF

ICF

Bone

Excreted through sweat and kidneys

Ion absorption occurs in the ___________ while ion excretion occurs at the _______

• GI tract

• kidneys

What are the mechanisms in which sodium is absorbed/move through solution?

• channel mediated diffusion

• co transport

• active transport

Which electrolytes are absorbed through active transport (Hint* Sam & Cat make idiot people suffer)

• Sodium (can be)

• Calcium

• Magnesium

• Iron

• Phosphate

• Sulfate

Which electrolytes are important for normal membrane function

Sodium and potassium

Here’s a chart for some major functions of electrolytes

Moving on to WATER AND SODIUM BALANCE 🙂

Describe sodium balance

when sodium gains equal losses

Which type of fluid responds to changes in sodium

Relatively small changes in sodium are accommodated by changes in ECF volume

Homeostatic responses involve what two parts?

• ADH control of water loss/retention by kidneys and thirst

• Fluid exchange between ECF and ICF

When sodium gains exceed losses, the ECF volume __________

INCREASES

When sodium losses exceed gains, the volume of the ECF _____

DECREASES

Describe the overall process of restoring homeostasis when sodium levels in the plasma increase

1) Osmoreceptors in hypothalamus are stimulated

2) ADH secretion increases (restricts water loss and stimulates thirst)

3) Because ECF osmolarity increases, water shifts out of the ICF, increasing ECF volume and lowering ECF Na+ concentrations

4) Homeostasis restored- decreased levels of sodium in the ECF (which leads to normal)

Describe the overall process of restoring homeostasis when sodium levels in plasma decrease

1) Osmoreceptors in hypothalamus inhibited

2) ADH secretion decreases (thirst is suppressed and water losses at the kidneys increase)

3) water loss reduces ECF volume, concentrates ions

4) Homeostasis restored-increased sodium levels

If ECF volume increases, blood volume ________

increases

Exchange in sodium are accommodated by changes in…

• Blood pressure

• Blood volume

Describe hyponatremia

Not enough sodium in the blood

• low ECF sodium concentration

Hyponatremia is low sodium concentration of <__________ mEq/L

136 mEq/L

Why could hyponatremia occur?

can occur from overhydration or inadequate salt intake

Describe hypernatremia

high ECF sodium concentration

Hypernatremia is high sodium concentration of >__________ mEq/L

145 mEq/L

What could be a cause from hypernatremia

Commonly from dehydration

Sodium changes are accompanied by change in blood pressure and volume, knowing this, describe the mechanisms that occur when blood pressure and volume INCREASE

1) Natriuretic peptides released by cardiac muscle cells

2) This causes increased sodium and water loss in urine and reduced thirst

3) Inhibition of ADH, aldosterone, epinephrine, and norepinephrine release

4) These combined effects cause reduced blood volume and pressure

5) Homeostasis restored-ECF volume decreases

Sodium changes are accompanied by change in blood pressure and volume, knowing this, describe the mechanisms that occur when blood pressure and volume DECREASE

1) Increased renin secretion and angiotensin II activation, increased aldosterone release, and increased ADH release

2) Causes increased urinary sodium retention, decreased urinary water loss, increased thirst, and increased water intake

3) Homeostasis restored-ECF volume increases

Let’s move on to POTASSIUM IMBALANCE

Describe potassium balance

When potassium gain equals potassium loss

How does major gain of potassium occur?

Major gain is through the digestive tract absorption

How much potassium is gained per day through the GI tract?

Approximately 100mEq (1-9-5.8 g)/day

How is potassium lost?

Major loss is excretion by the kidneys

Describe potassium loss by the kidneys

Controlled by aldosterone regulating the sodium and potassium exchange pumps in the DCT and collecting duct of the nephron

What happens when the ECF pH gets low?

Can cause H+ to be substituted for K+

Is potassium highest in the ECF or ICF?

ICF due to Na+/K+ exchange pump

Compare the numbers of potassium in the ICF vs ECF

135 mEq/L in ICF vs 5 mEq/L in ECF

What two factors affect potassium balance?

The rate of potassium entry across the digestive epithelium and the rate of potassium loss into the urine

What percent of potassium is in the ICF compared to the ECF

98%

When the blood concentration of potassium falls below 2 mEq/L, this is referred to as…

Hypokalemia

What 2 things are hypokalemia caused by?

• Diuretics

• Aldosteronism

What is aldosteronism?

Excessive aldosterone secretion

• aldosterone is a steroid hormone produced by the adrenal glands which plays a role in regulating blood pressure and electrolyte balance

What are the symptoms of hypokalemia

muscular weakness, followed by paralysis (potentially lethal when affecting the heart)

When the blood concentration of potassium rises above 8 mEq/L, this is referred to as…

Hyperkalemia

Hyperkalemia is caused by

• chronically low pH

• Kidney failure

• drugs promoting diuresis by blocking Na+/K+

What are the symptoms of hyperkalemia?

Muscular spasm including heart arrythmias

SECTION 2: ACID BASE BALANCE

Describe acid base balance

when H+ production equals loss

What’s normal plasma pH?

7.35-745

Many _______ activities produce acids

metabolic

What are some metabolic activities that produce acids?

• Carbon dioxide —> carbonic acid from aerobic respiration

• Lactic acid from glycolysis

How is carbon dioxide eliminated?

Through the respiratory system

How is H+ lost and stored?

• Lost by H+ excretion from kidneys

• Buffers temporarily store H+

What are fixed acids?

Acids that do not leave solution and remain in body fluids until kidney secretion

Name some fixed acid examples and how they are generated

sulfuric and phosphoric acid

• generated during catabolism of amino acids, phospholipids, and nucleic acids

What are organic acids?

Acids that are part of cellular metabolism

Name some examples of organic acids

lactic acid and ketones

Organic acids are metabolized _________ so no _____________

rapidly, accumulation

What are volatile acids?

Acids that can leave the body by external respiration

What’s an example of a volatile acid?

Carbonic acid (H2CO3)

Describe acidemia

when the pH of blood decreases below 7.35. The physiological state that results is called acidosis.

Acidosis is more common due to acid producing __________ activities

metabolic

What are the effects of acidosis?

• CNS function deteriorates, may cause coma

• cardiac function contractions grow weak and irregular

• peripheral vasodilation causes BP to drop

Describe alkalemia

When the pH of blood increases above 7.45. The physiological state that results is called alkalosis

• can be dangerous but relatively rare

What’s an important factor affecting body pH and why?

The partial pressure of CO2

• because carbon dioxide combines with water to form carbonic acid; this is a reversible reaction that can buffer body pH

• adjustments in respiratory rate can affect body pH

Partial pressure of CO2 and pH have a ____________ relationship

inverse

Describe the inverse relationship between partial pressure of CO2 and pH

When CO2 levels rise, more carbonic acid forms, additional hydrogen ions and bicarbonate ions are released, and the pH goes down.

Describe the function of a buffer

• a substance that tends to oppose changes in the pH of a solution by removing or replacing hydrogen ions

• Buffers maintain blood pH within normal limits (7.35-7.45)

A buffer system typically consists of…

a weak acid (HY) and the anion (Y-)

What does adding H+ to a buffer solution do?

Results in the formation of additional molecules of the weak acid

What does removing H+ from a buffer solution do?

results in the dissociation of additional molecules of HY. This releases H+

Describe one limit of a buffer system

They can only temporarily affect pH (H+ not eliminated)

Name the three buffer systems

1. Phosphate buffer system

2. carbonic acid-bicarbonate buffer system

3. Protein buffer system

Describe the function of the phosphate buffer system

buffers pH of ICF and urine

Describe the carbonic acid-bicarbonate buffer system

• most important in the ECF

• fully reversible

• bicarbonate reserves contribute (from NaHCO3 in ECF)

Describe the protein buffer system

• contribute to the regulation of pH in the ECF and ICF

• usually operate under acidic conditions

• binding to carboxylic and amino group

Name 3 examples of a protein buffer system

• hemoglobin buffer system

• amino acid buffers (all proteins)

• plasma protein buffers