24 Questions
What is the approximate volume of plasma in the standard person?
2.75 L
What is the approximate volume fraction of formed elements in the blood?
0.45
What is the approximate length of the vasculature in the human body?
19,000 km
What is the approximate percentage of total body water in women?
60%
What happens to the volume of distribution (Vd) when there is stronger binding to tissue proteins and membranes?
It increases because this binding lowers the unbound fraction of drug in tissues (fUOi)
How does stronger binding to plasma proteins affect the volume of distribution (Vd)?
It decreases Vd because this binding lowers the unbound fraction of drug in plasma (fUP)
What does Equation 4 indicate about the volume of distribution (Vd) in relation to protein binding?
If binding occurs in tissues, it increases Vd; if binding occurs in plasma, it decreases Vd
What is the relationship between the volume of plasma (VP) and the corrected volumes of organs (VOCi) in the calculation of Vd?
Vd is the sum of VP and corrected volumes of organs (VOCi)
What is the impact of protein binding on drug metabolism and excretion?
Protein-bound drug molecules are prevented from metabolism and excretion
In the context of drug distribution, how does the drug amount in plasma (mg) relate to the amount in tissues (mg)?
The drug amounts in plasma and individual organs are in the same ratio as the volumes V and V
For the standard patient, if VP = 3 L, what is the ratio of drug amounts in plasma to the amount in tissues (mg)?
3:7
What is the primary role of protein binding in drug distribution?
Protein binding serves as a depot for drug molecules and attracts the molecules to the given compartment
What is the composition of blood in large veins?
Plasma, erythrocytes, and leukocytes
What is the average diameter of capillary cross-sections?
8 mm
Which component is part of capillary structure?
Endothelial layer
What is the function of glycocalyx in capillaries?
To enhance nutrient exchange
In which organ is capillary density high?
Lungs
How does the distance of living cells from capillaries impact drug absorption?
It increases drug absorption
What is the ratio used to define Volume of Distribution (Vd)?
Drug amount to drug concentration in plasma
Which factor influences the Volume of Distribution (Vd)?
Protein binding
In what circumstances can the Volume of Distribution (Vd) be equal to body volume?
When drug is evenly distributed in all tissues
What percentage of cardiac output do the lungs receive?
100%
How does capillary wall porosity affect permeability?
Higher porosity leads to higher permeability
What is the minimum value of Volume of Distribution (Vd)?
Volume of plasma
Study Notes
Capillaries: Structure and Function
- Blood contains 8 liters (3 liters in large veins) with 50% in large veins
- Blood composition includes plasma (rich in proteins such as albumin and lipoproteins), erythrocytes (5 million/μL), leukocytes (5 thousand/μL), and platelets (500 thousand/μL)
- Capillaries consist of an endothelial layer, basement membrane, and glycocalyx
- Capillary cross-sections have an average diameter of 8 mm, with minimum and maximum diameters of 4 mm and 40 mm, respectively
- Capillary walls can be continuous, fenestrated, or discontinuous (sinusoids) with varying porosities and permeabilities
- Capillary density varies among organs, with high density in lungs and low density in muscles and fat
- Distance of living cells from capillaries affects drug absorption and distribution
- The number of cell layers served by a capillary varies by organ and impacts drug penetration
- Blood flow through organs varies, with lungs receiving 100% of cardiac output and fat and muscle receiving 0.04% and 0.03%, respectively
- Volume of Distribution (Vd) is defined as the ratio of drug amount to drug concentration in plasma at any given moment
- Vd is influenced by membrane accumulation, protein binding, and organ volume, with the minimum value being the volume of plasma
- Vd can be equal to body volume in rare circumstances when certain conditions are met
Test your knowledge of capillaries with this quiz on their structure and function. Explore topics such as blood composition, capillary types, density in organs, drug absorption, and volume of distribution.
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