Exam 2 Applied Physiology

What age group has the highest percentage of total body water?

Infants

Decreases with age

What percentage of total body water does the intracellular and extracellular fluid compose?

Intracellular = 40% of body weight

Extracellular = 20% of body weight

Of the extracellular fluid, what percentage is interstitial and intravascular fluid?

Interstitial = 75%

Intravascular = 5%

Intracellular fluid

Water inside cells

Extracellular fluid

Plasma (intravascular) and interstitial fluid (surrounds cells)

Steady state (homeostasis) of water

Equal movements in both directions

No net shift in water

Cellular Swelling/Shrinking

Net shift between intracellular and extracellular compartments

Edema

Net shift between intravascular and interstitial fluid

Increased fluid in the interstitial space of the ECF

Osmotic forces

Water moves from low → high osmolality

Hydrostatic forces

Pressure exerted by a fluid in a compartment

Tonicity

Describes the relationship between two solutions (or compartments)

Hypertonic vs hypotonic

Molarity = ____ for our purposes

Molality

Plasma osmolality depends on what?

Sodium concentration since sodium is the primary cation in the ECF

\-Sodium can diffuse between intravascular and interstitial space

\-Normal plasma osmolality = 290mOsm

What happens to the osmolality if we change the volume of ECF?

Nothing (decrease volume does not change osmolality)

What happens when we change extracellular osmolality?

Change in intracellular volume

What organ maintains blood osmolality?

Kindney

Volume status

Function of both water and salt

Hydration status

Function of water

Hypovolemic

Less water AND less salt

Hypervolemic

more water AND more salt

Dehydrated

Salt concentration increases

ex: less water around same amount of salt

Input < output

Treatment: replace what was lost!

Overhydrated

Salt concentration decreases

ex: more water around same amount of salt

Treatment: fluid restriction or infuse sodium chloride slowly

Typical urine output

1\.5L per day

Proximal tubules

Obligate reabsorption of water

\-prevents water loss in urine

\-prevents circulatory collapse

Collecting ducts

optional reabsorption of water in dehydration

\-prevents water loss in urine

\-control hydration status

When the hypothalamus senses an increase in osmolality (increase in sodium) what happens?

Stimulates ADH release from posterior pituitary

Stimulates water absorption in the collecting duct

Increase osmolality → stimulate thirst

ADH signaling causes what changes in the collecting duct?

Aquaporin (water channels) are inserted into the luminal membrane

Increase water permeability of the collecting duct → increase water reabsorption

Preserve plasma osmolality

ADH is secreted with ___ osmolality

High

Diabetes Insipidus (DI)

Failure of ADH release from posterior pituitary or kidney is resistant to its effects

Primary polydipsia

Excessive thirst/water drinking

Capillary walls are permeable to what?

Water and electrolytes

What are capillary walls NOT permeable to?

Protein

Osmotic pressure of just the protein is referred to as what?

Oncotic pressure

\-contributes to total osmotic pressure of the solution

What pressure of intravascular and interstitial compartments oppose each other?

Hydrostatic and oncotic pressures

Edema causes

Increased capillary hydrostatic pressure

Decreased capillary oncotic pressure

Increased interstitial oncotic pressure

What cannot diffuse freely between ECF compartment and ICF compartment?

Electrolytes

What can diffuse freely between ECF compartment and ICF compartment?

Water

A change in tonicity of the ECF will result in what?

A water shift into/out of the ICF

What is the primary determinant of ECF tonicity?

Sodium concentration

What are the most common causes of fluid disorders?

Hypernatremia and hyponatremia

Darrow-Yannet Diagrams

Used to visualize changes in osmolality and volume

Volume expansion = fluid gain

Volume contraction = fluid loss

Increase osmolality = rectangles get taller

Decrease osmolality = rectangles get shorter

Steps to approach fluid disorders

1. Determine change in ECF volume first
2. Determine if there was a change in ECF tonicity
3. Determine final tonicity and volume of ECF

If fluid is gained, what happens to ECF volume

Always increases

If fluid is lost, what happens to ECF volume?

Always decreases

Increased ECF tonicity is due to what?

Water leaving ICF

Decreased ECF tonicity is due to what

Water entering ICF

Isotonic fluid loss

ECF volume contracts

No difference between ECF/ICF tonicity (no fluid shift)

Result = isotonic hypovolemia

Isotonic fluid loss examples

Diarrhea

Blood loss due to hemorrhage

Isotonic fluid gain

ECF volume expands

No difference between ECF/ICF tonicity (no fluid shift)

Result: isotonic hypervolemia

Isotonic fluid gain examples

Isotonic saline infusion

Blood transfusion

Hypertonic fluid loss

ECF contracts

Fluid shift from ECF to ICF until equal

Result: hypotonic hypovolemia

Hypertonic fluid loss examples

Loop diuretics

Addison’s disease

Hypertonic fluid gain

ECF volume expands

Fluid shift from ICF to ECF until equal

Result: hypertonic hypervolemia

Hypertonic fluid gain examples

Infusion of hypertonic saline

Primary aldosteronism

Hypotonic fluid loss

ECF volume contracts

Fluid shift from ICF to ECF until equal

Result: hypertonic hypovolemia

Hypotonic fluid loss examples

Sweating

Vomiting

Hypotonic fluid gain

ECF volume expands

Fluid shift ECF to ICF until equal

Result: hypotonic hypervolemia

Hypotonic fluid gain examples

half-normal saline infusion

The ____ reabsorbs >90% of filtered salt and water

Proximal tubule

The ___ reabsorb variable amounts of substances depending on the body’s requirements

Distal tubule and collecting duct

What is sodium uptake controlled by?

Aldosterone

Aldosterone effect on the collecting duct

Binds to mineralocorticoid receptor → epithelial sodium channel expression to increase → increase sodium potassium ATPase activity → increase reabsorption of sodium through collecting duct epithelial cells

What is a potent stimulus for aldosterone release?

Low blood pressure

Where is renin released from

Juxtaglomerular cells in the afferent arteriole of the glomerulus

What is renin release stimulated by?

Decrease in afferent arteriole pressure

Renin-Angiotensin-Aldosterone-System (RAAS)

Decrease BP → release renin from juxtaglomerular cells → renin converts angiotensinogen to angiotensin I → angiotensin II by ACE → vasoconstriction → raise BP → aldosterone release → enhance renal sodium retention

Addison’s disease

Adrenal insufficiency

\-no aldosterone produced → hyponatremia

Symptoms: hypotension

Hyperaldosteronism

Increased aldosterone secretion → hypernatremia

Symptoms: hypertension

What promotes urine excretion by inhibiting salt reabsorption in different parts of the nephron?

Diuretics

Leads to loss of sodium rich fluid → hyponatremia

What tonicity of solution is ideal to give someone that just exercised?

Hypotonic solution

ex: diluted gatorade, pedialyte, water

What tonicity of solution is ideal to give someone who is hemorrhaging?

Isotonic solution to maintain effective blood volume

What tonicity of solution is ideal to give someone who overdosed on a diuretic

Hypertonic fluid

Hyperkalemia and hypokalemia alters membrane potential and can alter ___

neuromuscular activity

What happens when potassium levels deviate outside normal range?

Life threatening cardiac arrhythmias and paralysis can occur

___ levels of potassium stimulates aldosterone production

high

Aldosterone stimulation of sodium potassium ATPase activity leads to increased what?

potassium secretion into the urine through ROMK channel

What promotes potassium sequestration into cells by stimulating sodium potassium ATPase?

insulin

Causes of hypokalemia

Anything that increases potassium secretion

pH is a measure of what

Hydrogen ion concentration

An increase in pH is due to

decreased hydrogen ion concentration

A decrease in pH is due to

increased hydrogen ion concentration

What cells secrete bicarbonate to neutralize stomach acid?

Duct cells of the pancreas

Normal blood pH

7\.35-7.45

What stabilizes pH?

Buffers

What is the most important buffer in the body?

Bicarbonate

Henderson-Hasselbach equation

Describes relationship between bicarbonate, CO2 and pH

pH is dependent on the ratio of bicarbonate and CO2

pH =\[HCO3-\]/\[CO2\]

Buffer system: Lungs

Breathing patterns influence CO2 elimination or retention and influence carbonic acid concentration

Buffer systems: kidney

controls acid/base excretion and can form new bicarbonate

Metabolic disturbances refers to changes in

bicarbonate (HCO3-)

Respiratory disturbances refers to a change in

Carbon dioxide (CO2)

Metabolic acidosis

Decrease/loss of bicarbonate OR increase of non-carbonic acid

compensation = decreased CO2 pressure (increased ventilation)

Respiratory acidosis

Increased CO2 pressure

Compensation = increase bicarbonate retention (increase H+ secretion)

Metabolic alkalosis

Increased bicarbonate or loss of acid (vomiting)

Compensation = increased CO2 pressure (decreased ventilation)

Respiratory alkalosis

Decreased CO2 pressure (hyperventilation)

Compensation = decreased bicarbonate reabsorption (decreased H+ secretion)

Right heart delivers blood where?

Deoxygenated blood to lungs

Left hear delivers blood where?

Oxygenated blood to body

3 layers of arteries

Tunica intima, tunica media, tunica adventitia

Tunica intima

Innermost

Interacts with blood

Endothelial cells

Tunica media

Muscular part of smooth muscle cells, collagen, elastin

\-allow vessel to expand/contract due to BP changes

Middle layer

Tunica adventitia

Outer layer

Nerves and capillaries supply muscular layer

Contains fibroblasts