Volume depletion & dehydration Flashcards
Cell Membrane
Also known as the plasma membrane
Composed of lipids and proteins (phospholipid bilayer)
Functions:
Separate the interior of the cell from the outside environment
Provides protection to the cell
Allows for selective transport of molecules
Remember LIKE dissolves LIKE
Lipid soluble molecules pass thru the membrane (passive transport)
Water soluble molecules require a channel (proteins) to pass thru the membrane (active transport)
Cell Membrane transport
Diffusion- passive/facilitated
Requires no ATP
Movement of molecules from high to low concentration along an electrochemical gradient
Simple diffusion
Movement of small or lipophilic molecules (O2, CO2)
Through the membrane for lipid soluble molecules
Osmosis: movement of water molecules (depends on solute concentration)
Facilitated diffusion
Movement of large or charged molecules via a protein channel or a carrier protein that is structurally specific (ions, sucrose)
Cell Membrane Transport
active transport
Active
Required ATP
Movement from low concentration to high concentration (against the gradient)
Carrier
Primary(direct)active transport– direct use of metabolic energy (ATP hydrolysis) to mediate transport
Secondary(indirect)active transport– coupling the molecule with another moving along an electrochemical gradient
Vesicular
Endocytosis: into the cell
What are the 2 types of endocytosis?
Exocytosis: out of the cell
Volume status
Balance between water and solutes
Solutes → majority of which is Na
Volume depletion (hypovolemia)
Refers to extracellular cellular fluid loss; loss of both water and Na
↓ circulating volume
Caused by decreased oral Na intake and/orincreased volume losses
Dehydration
Refers to a total body water loss; loss of water across all compartments
↓ circulating volume; ↓ intracellular volume
Caused by decreased oral water intake
Volume depletion and dehydration are NOT the same!
Dehydration
etiology
due to decreased oral water in take:
Acute or critical illness
Decreased access to water
Altered thirst mechanisms in childhood or old age
Dementia
Volume depletion due to decreased oral Na intake:
Acute or critical illness
Eating disorders
Dementia
Volume depletion
etiology
Volume depletion due toincreased volume losses:
Bleeding
* GI losses:
Diarrhea
Vomiting
Drains (nasogastric tube)
* Renal:
Diabeticketoacidosis
Diuretic therapy
Diabetes insipidus
* Third-space losses:
Burns
Severepancreatitis
* Insensible losses:
Skin/mucous membranes (fever, excessive sweating)
dehydration
patho
Fluid shifts with illness/disease
Occur due todiffusion across asemipermeable membrane
Regulated by a difference inplasma osmolality between ECF andICF
Dehydration:
Water is lost, but not Na
Water is lost from ECF → ECFosmolality increases → water diffuses fromICF to ECF
Net effect: ECF hypertonicity andhypernatremia
Example: ↓ water intake or inadequate water replacement in critical illness
Volume depletion
Hypotonic loss of fluid
Water > Na
Hypotonicfluid is lost from ECF → ECFosmolalityincreases → water diffuses fromICFto ECF
Example: Increased insensible losses (fever or excessive sweating)
Volume Depletion
Isotonic loss of fluid
NA = water
Isotonicfluid is lost from ECF → ECFosmolalitydoes not change → no gradient fordiffusionwithICF
Plasmaosmolalityand serum Na do not change
Example: diarrhea, loss of whole blood
Volume Depletion
Hypertonic loss of fluid
Na > water
Fluid is lost from ECF → ECF contracts and ECFosmolalitydecreases → water shifts from ECF toICFviadiffusion
Example: loop diuretics, primary adrenal insufficiency
dehydration
S/Sx
Varies greatly depending on the severity - asymptomatic to potentially fatal hypovolemicshock
Symptoms of mild and moderateare often nonspecific:
Fatigue
Dizziness
Thirst
Musclecramps and/or headache
Decreased urination
Symptoms with severehypovolemia:
Severe dizziness
Cool extremities
Confusion/altered mental status
