fluid and electrolyte

capillary oncotic pressure

(pulling water into the capillary)

Capillary hydrostatic pressure

(pushing water out of capillary)

total intake of water

2,500 mL

Normal serum osmolarity

275 to 295 milliosmoles/liter (mOsm/L)

Antidiuretic hormone (ADH) is triggered by:

A drop in BP or blood volume A rise in blood osmolarity (increased concentration) Causes kidneys to reabsorb more water resulting in: higher vascular volume; and low output of concentrated urine

Cardiac peptides

Atrial Natriuetic Peptide (ANP) Brain Natriuetic Peptide (BNP)

Transcellular

CSF, GI, ocular, etc., can become pathological as in ascites "third space"

Starling forces- out:

Capillary hydrostatic pressure Interstitial oncotic pressure

ANP lowers blood volume and BP by:

Causing vasodilation by direct effect on blood vessels and suppression of renin-angiotensin system Decreasing aldosterone release by adrenal glands, causing increased urinary excretion of sodium and water Decreasing ADH release by pituitary gland, causing increased urinary excretion of water Increasing glomerular filtration rate, increasing rate of urine production and water excretion

Starling's Law of the Capillaries

Filtration (net fluid movement into or out of the capillary) is determined by the difference between the forces favoring filtration and those opposing it (tug of war) Interstitial hydrostatic pressure pushes water into the capillary and Interstitial oncotic pressure pulls water out of the capillary (this is very low pressure- little movement of water) Capillary hydrostatic pressure (pushing water out of capillary) and capillary oncotic pressure (pulling water into the capillary)

Age related considerations

Full term baby 80% water Older adult 40% water

Atrial Natriuetic Peptide (ANP)

Hormone released as a result of atrial stretch

Brain Natriuetic Peptide (BNP)

Hormone released with ventricles as a result of ventricular stretch

Movement of fluids

Hydrostatic pressure Osmotic pressure

ICF

Intracellular fluids

Renin-Angiotensin-Aldosterone System

Hypovolemia (low blood pressure) into kidney renin out of kidney angiotensin 1 angiotensin 2 -retention of Na+ by kidney via aldosterone -water retention by kidney (via Na+ uptake and vasopressin -salt appetite -increased drinking (via subfornical organ) -increased blood pressure

ISF

Interstitial fluids

IVF

Intravascular fluids

Fluid regulation body systems

Kidney Sodium (mainly) and other electrolyte levels Antidiuretic hormone (ADH) Stimulates water conservation and the thirst center Aldosterone Controls Na+ absorption and K+ loss along the descending convoluted tubules and Collecting duct Natriuretic peptides (ANP and BNP) Reduce thirst and block the release of ADH and aldosterone Baroreceptors Proteins and Starlings forces in the capillary

Oncotic pressure

Oncotic pressure, also called 'colloid osmotic pressure', is the 'pulling force', pulling fluids from the surrounding tissue into the capillaries. It's the result of a difference in the concentration of solutes in the fluid inside the capillaries as opposed to outside them.

Fluid and electrolyte movement

Osmosis - (osmotic/oncotic pressure) Diffusion Hydrostatic pressure Filtration Active transport

Starling Forces- in:

Plasma oncotic pressure Interstitial hydrostatic pressure

Aldosterone

Released and inhibited by feedback loop as part of renin-angiotensin-aldosterone system

Renal regulation of fluids

Renin activation of RAAS Solute concentration and dilution Protein conservation Acid-base balance Waste excretion

Antidiuretic hormone (ADH) is inhibited by

Rise in BP or blood volume Drop in blood osmolarity (decreased concentration) Causing the kidneys to excrete more water in the urine. Resulting in: Lower vascular volume; and High output of dilute urine

What is the major solute in plasma?

Sodium (so can estimate 2 x serum sodium = osmo)

Solution

The liquid

hydrostatic pressure

Think of hydrostatic pressure as the 'pushing force', pushing the fluid out of the capillaries. It's the result of the actual pressure of the fluid on the capillary walls.

TBW

Total Body Water

Urine Constituents output? contains? pH?

Urine output = 1-2 L/day Protein free Contains: Electrolytes Glucose Bicarbonate Urea Creatinine pH = 4.6-8.0 is normal

BNP lowers blood volume and BP by:

Vasodilating arteries and veins Decreasing release of aldosterone Causing diuresis with excretion of both sodium and water

As fluid leaves the capillaries as a result of hydrostatic pressure...

albumin and other large proteins cannot pass through the capillary walls. This results in a greater concentration of solutes inside the capillaries, and the oncotic pressure rises, pulling more water into the capillaries.

Water follows sodium d/t osmosis, thus

aldosterone has an indirect effect on water

Blood Urea Nitrogen (BUN) and Glucose

also contribute to osmolarity

Extracellular Fluid (ECF) volume depends cheifly upon

concentration of sodium ions

An increase in Na+ in plasma? Thus we will have:

fluid will be pulled from interstitial and intracellular compartments into plasma. hypervolemia (plasma) compartment hypovolemia or dehydration of the interstitial and intracellular compartments

Whenever the oncotic pressure is greater than the hydrostatic pressure

fluid will enter the capillaries.

Whenever hydrostatic pressure is greater than oncotic pressure...

fluid will leave the capillaries.

A decreases in Na+ in plasma? Thus we will have:

fluid will move from plasma into interstitial and intracellular compartment. hypovolemia (of plasma) compartment hypervolemia of interstitial and intracellular spaces

Neutral balance

input = output

Positive balance

input > output

Negative balance

input< output

Interstitial oncotic pressure

pulls water out of the capillary (this is very low pressure- little movement of water)

Interstitial hydrostatic pressure

pushes water into the capillary

Adrenal Gland hormone that conserves sodium (NA+) in the body by causing the kidneys to:

retain sodium; and excrete potassium (K+)

Fluid compartments

separated by semi permeable membranes

Solute

substance dissolved in a liquid

Osmolarity

the concentration of solute in a fluid (mostly sodium) per KILIGRAM of WATER