Absorption, Distribution,

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Chapter 5

• Absorption, Distribution,
• and Excretion of Toxicants

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Overview
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Cell Membranes

• Passive Transport
• Simple Diffusion
• Filtration
• Special Transport
• Active Transport
• Facilitated Diffusion
• Additional Transport Processes

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Schematic Model of a Biological Membrane
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Special Transport
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Absorption

• Absorption is the transfer of a chemical from the
  site of exposure, usually an external or internal
  body surface, into the systemic circulation.

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Absorption
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Absorption of Toxicants by the Gastrointestinal
Tract
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For Weak Acids and Bases

• Weak bases

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Absorption of Toxicants by the Gastrointestinal
Tract
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Absorption of Toxicants by the Lungs
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Absorption of Toxicants by the Lungs

• Gases and Vapors
• Aerosols and Particles

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Absorption of Toxicants Through the Skin
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Special Routes of Administration

• Intraperitoneal
• Subcutaneous
• Intramuscular
• Intravenous

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Distribution

• Volume of Distribution

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Total Body Water Compartments
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Distribution

• Storage of Toxicants in Tissues
• Plasma Proteins
• Liver and Kidney
• Fat cells
• Bone

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Plasma Proteins
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Blood Brain Barrier

• Less permeable than other sites in the body
• Capillary endothelial cells of CNS are tightly
  joined
• Cells have ATP dependent transporter multi-drug
  resistant protein
• Cells surrounded by glial cell processes
• Protein conc. In the interstitial fluid of CNS is
  lower than that in other body fluids

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BBB Permeability

• More permeable parts include
• Cortex
• Lateral nuclei of hypothalamus
• Area postrema
• Pineal body
• Poster lobe of hypophysis

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Placenta

• Functions of the Placenta
• Protection
• Provide nutrition
• Exchange of blood gases

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• Toxicants are removed from the systemic
  circulation by biotransformation, excretion, and
  storage at various sites in the body.

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Excretion

• is the removal of xenobiotics from the blood and
  their return to the external environment via
  urine, feces, or exhalation.

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Excretion

• Urinary Excretion
• Proximal tubule of the Kidney

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Urinary Excretion
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Fecal Excretion

• Nonabsorbed Ingesta
• Biliary Excretion
• Intestinal Excretion
• Intestinal Wall and Flora

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Biliary Excretion
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Exhalation

• Role of the Lungs

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Other Routes of Elimination

• Cerebrospinal fluid
• Breast Milk
• Sweat and Saliva

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Conclusion
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Question 1 Which of the following are processes
by which a toxicant may pass through a membrane?

• 1) Filtration
• 2) Active transport
• 3) Facilitated diffusion
• 4) Plasma proteins
• A) 1 and 3 only
• B) 1,2, and 3 only
• C) 2 and 3 only
• C) all of the above

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Question 2 Which of the following is not a
storage site of toxicants in tissues?

• A) Liver
• B) Kidney
• C) Fat
• D) Small intestine
• E) Bone