L8 | Fluid and Electrolyte Imbalances

______________ — volume of fluid within all cells

Intracellular Fluid (ICF)

___________ — all non-intracellular fluid (interstitial fluid [ISF], intravascular compartment [plasma], lymph and transcellular [other])

Extracellular fluid (ECF)

Total boyd water (TBW) = ________% of body weight in liters

60%

The amount of __________ in the body is a prime determinant of the ECF volume

sodium

Excess sodium is secreted by the ____________

kidneys

Solutes (NaCl, NaHCO₃) are confined to the ______________ compartment

ECF

What is the result of dietary salt overload?

-adds NaCl to the ECF compartment

-increases total solute concentration of the ECF (increases Osm_ECF)

What is the result of dietary water overload?

-decreases total solute concentration of the ECF (decreases Osm_ECF)

[Na⁺]_plasma indicates ________________

water balance

-not Na⁺ balance

[Na⁺]_ECF controls __________________

ECF/ICF water distribution

___________ describe the pressures that control fluid movement in and out of capillaries.

Starling Forces

________ and ________ are hydrostatic pressures that push fluid

-Capillary pressure (P_C)

-interstitial fluid pressure (P_if)

___________ and _________ are colloid osmotic pressures that pull fluid

-Plasma colloid ocmotic pressure (π_p)

-Interstitial fluid colloid osmotic pressure (π_if)

Which starling forces keep plasma fluid inside the capillary?

-Plasma colloid ocmotic pressure (π_p)

-interstitial fluid pressure (P_if)

Which starling forces keep plasma fluid inside the interstitial fluid?

-Capillary pressure (P_C)

-Interstitial fluid colloid osmotic pressure (π_if)

What occurs at the arterial end of the capillary?

-blood pressure is greater than colloid osmotic pressure

-fluid flows out of the capillary into the interstitial fluid

What occurs at the venular end of the capillary?

-blood pressure is less than colloid osmotic pressure

-fluid flows from the interstitial fluid into the capillary

True/Flase: The amount of fluid that is filtered at the arterial end equals the amount of fluid absorbed at the venular end

True

Edema is produced by an increase in ______________

interstitial fluid volume

Edema does not become evident until the interstitial fluid (ISF) has been increased by __________

3 liters

Why does edema occur?

Starling forces have a strong favoring of fluid filtration out of the capillary and into the interstitium

-fluid from capillary pushed or pulled into the interstitium.

What are the changes in starling forces that make edema happen?

_______ edema only occurs at the site of trauma

Localized

_______ edema is associated with diseases such as renal failure

Systemic

________ edema is where fluid pools in gravity-dependent areas, may be a sign of systemic edema, and is also known as pitting edema

Dependent

What are the four physiologic mechanisms that contribute to edema?

-increased capillary permeability

-decreased plasma oncotic pressure

-increased plasma hydrostratic pressure

-obstruction to lymph flow (lymphedema)

How does increased capillary permeability contribute to edema?

When capillary pores become enlarged or the integrity of the capillary wall is damaged, capillary permeability is increased → large Plasma proteins and other osmotically active particles leak into the interstitial spaces, increasing the tissue colloidal osmotic pressure and contributing to the accumulation of interstitial fluid.

-causes: burn injury

How does decreased capillary oncotic pressure contribute to edema?

May be caused by decreased plasma protein synthesis (liver disease), glomerular diseases, drainage from large, open wounds

-live typically synthesizes the plasma proteins, including albumin

-produce generalized edema

How does increased capillary hydrostatic pressure contribute to edema?

-localized edema — allergic or inflammatory conditions resulting from the release of histamine or other inflammatory mediators

-generalized edema — result of increased vascular volume, caused by venous obstruction, excessive salt intake, or water retention  due to congestive heart failure or renal failure

How does obstruction of lymphatic flow contribute to edema?

-Edema due to impaired lymph flow is commonly referred to as lymphedema

-May be caused by infection, surgical excision of lymph nodes or tumors

How do increased levels of antidiuretic hormone (ADH) decrease urine output?

ADH prevents diuresis by causing more water to be reabsorbed in the collecting ducts (CD) of the kidneys.  If more water is reabsorbed, there is less water left to eliminate as waste, decreasing urine output.

What does high osmolarity result in?

-increase in thirst

-increase in ADH secretion

What does low osmolarity result in?

-lack of thirst

-decreased ADH secretion

How is high osmolarity related to low osmolarity?

-low osmolarity balances high osmolarity

-high osmolarity causes increased thirst and ADH secretion, which increases water retention, which increases circulating fluid volume. This then causes low plasma osmolarity to decrease thirst and ADH secretion

_________ is excessive thirst

Polydipsia

__________ and _________ can cause inappropriate/false thirst

-Congestive heart failure

-Chronic kidney disease

__________ is the decreased ability to sense thirst

Hypodipsia

What causes hypodipsia?

Damage to brain cells (osmoreceptors) that are responsible for detecting the osmolarity of the extracellular fluid

Thirst is regulated by the _____________ in the ______________

osmoreceptors; hypothalamus

________ is where the kidneys pass an abnormally large volume of urine that is insipid (diluted & odorless)

Diabetes insipidus (DI)

What causes diabetes insipidus?

deficieny of or decreased response to ADH, which causes the inability to concentrate urine even during periods of water restriction which results in polyuria (increased urine production)

Identify this type of diabetes insipidus:

-lack of ADH production in the hypothalamus

-symptoms: polyuria (increased urine output), nocturia (urinating at night), polydipsia (excessive drinking)

Neurogenic

Identify this diabetes insipidus:

-kidneys do not respond to ADH, impairment of urine concentrating ability

-symtpoms: polyuria, nocturia, polydipsia

Nephrogenic

Identify this type of diabetes insipidus:

-dfect of or damage to thrist mechanism (hypothalamus)

Dipsogenic

Identify this type of diabetes insipidus:

-excess placental production of vasopressinase (increased breakdown of mother’s ADH)

Gestational

__________________ — body retains water instead of excreting in urine due to inappropriate elevated ADH

Syndrome of inappropriate ADH (SIADH)

What causes SIADH?

-failure of negative feedback, which leads to dilutional hyponatremia (low sodium concentration in plasma)

What are some potential causes of syndrome of inappropriate ADH (SIADH)?

-surgery

-intracranial (infection or head injury)

-alveolar

-drugs

-hormonal

How is syndrome of inappropriate ADH treated?

-fluid restriction

-diuretics

Why would retaining sodium cause high blood pressure?

The excess sodium is going to hold onto water. That sodium is in the extracellular compartment, which plasma is also located

-increase in volume = increase in pressure

It's a very hot day and a PT falls down the stairs on the way to see the doctor about their hepatitis and renal disease. Explain why they have edema in their sprained ankle and foot?

1.Hepatitis – decreased albumin production by diseased liver leads to decreased plasma oncotic pressure (∏_P)

2.Renal disease – proteinuria resulting from loss of protein in urine leads to decreased plasma oncotic pressure (∏_P)

3.Fall – inflammation and leaky capillaries leads to increased capillary hydrostatic pressure (P_c) and decreased plasma oncotic pressure (∏_P)

-all cause an increase in filtration of fluid from capillaries into the interstitial fluid which leads to edema