Disposition Flashcards
What is the definition of diffusion?
The net movement of molecules from an area of high concentration to low concentration
Also referred to as moving ‘down a concentration gradient.’
What is transcellular diffusion?
Diffusion of toxicants through cells, requiring passage through cellular membranes
Often occurs when cells are tightly packed with little space between them.
What is paracellular diffusion?
Diffusion of toxicants in between cells
This process does not require passing through cellular membranes.
True or False: Toxicants can enter the bloodstream without diffusing through tissues.
False
Toxicants must diffuse through tissues before entering the bloodstream.
What is passive transport?
Movement of substances across membranes without energy input.
What is diffusion?
Movement of molecules from an area of higher concentration to an area of lower concentration.
How do most toxicants cross membranes?
Primarily through passive transport mechanisms.
How can small hydrophilic toxicants move through membranes?
They can move through aqueous pores, such as aquaporins.
How do small hydrophobic toxicants cross the lipid bilayer of membranes?
They diffuse across the lipid bilayer.
Toxicants vary in how _______ they are.
[lipophilic]
What does the rate of transport across membranes correlate with?
The lipid solubility of the substances.
What is filtration in the context of membrane transport?
The process where blood plasma is forced out of capillaries through pores due to pressure.
What types of molecules stay in the blood during filtration?
Big molecules like albumin and red blood cells.
In which part of the kidney is filtration an important process?
In the glomeruli.
What type of transport requires ATP?
Active transport
Active transport moves substances against their concentration gradients, requiring energy input.
What is the main characteristic of movement in active transport?
Movement against concentration gradients
This means substances move from areas of lower concentration to areas of higher concentration.
What is a limitation of transporters in active transport?
Transporters can be saturated
Saturation occurs when all available transporters are occupied, limiting the rate of transport.
What can cause competitive inhibition in transporter-mediated transport?
Chemical antagonists or compounds carried by the same transporter
Competitive inhibitors can block the transport of the primary substance by occupying the transporter.
What type of transport does not require energy?
Facilitated diffusion
Facilitated diffusion allows substances to cross membranes through specific transport proteins without the use of ATP.
Fill in the blank: Transporters in active transport can reach a maximum, indicating that they can be _______.
saturated
Saturation limits the effectiveness of transporters in moving substances.
True or False: Facilitated diffusion requires ATP to function.
False
Facilitated diffusion is a passive process that does not require energy input.
What are ATP-binding cassette (ABC) transporters?
A superfamily of genes involved in active transport
Examples include MDR1, MRP, BSEP, BCRP
What type of transport do ATP-binding cassette (ABC) transporters utilize?
Active transport
What is the general term for transporting larger compounds?
Solute carriers
What is facilitated diffusion?
A process that allows larger molecules to cross cell membranes without energy
Examples include OATP, OAT, OCT, PE
How can larger toxicants enter cells?
Through endocytosis
What is more common for large molecules entering cells?
Endocytosis
Name a few examples of proteinaceous toxins.
- Shiga toxin (Stx)
- Ricin
- Botulinum toxin
- Cholera toxin (Ctx)
What is receptor-mediated endocytosis?
A process where cells use receptors to recognize proteins and form a vesicle
What are the components of protein toxins often described as?
Heterodimers made of the toxin (α subunit) and multiple β subunits
What role do β subunits play in protein toxins?
They bind to membrane components, causing the cell to take in the toxin
