In vivo processes and transmembrane transport of drugs-2020 Medical and Health Pharmacy Knowledge

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1. The process of drugs in the body

From the time a drug enters the body to when it is excreted, it can be roughly divided into four processes: absorption, distribution, Metabolism and excretion

1. Absorption refers to the process of drug entering the blood circulation from the site of administration.

2. Distribution refers to the process by which drugs are transported to various tissues, organs or body fluids after entering the systemic circulation.

3. Metabolism refers to the process of changes in the chemical structure of drugs in the body.

4. Excretion refers to the process by which drugs and their metabolites are excreted from the body.

The processes of drug absorption, distribution and excretion are collectively called transport; the processes of distribution, metabolism and excretion are called disposal; the processes of metabolism and excretion are collectively called elimination. In addition to intravascular administration such as intravenous injection, there is an absorption process in non-intravascular administration (such as intramuscular injection, inhalation administration, transdermal administration, etc.).

2. Transmembrane transport of drugs: The phenomenon of substances passing through biological membranes is called transmembrane transport of substances. Transmembrane transport is an important process for drug absorption, distribution, and excretion.

(1) Passive transport

Passive transport is the transport of substances from a high concentration area to a low concentration area. It does not require a carrier and does not consume energy. The transport rate is directly proportional to the concentration difference on both sides of the membrane. Drugs mostly pass through biological membranes in this way. Passive transport includes filtration and simple diffusion.

1. Filtration: Also known as membrane pore transport, there are membrane pores on the cell membrane, and water-soluble small molecular substances are transported through the pores.

2. Simple diffusion: Most drugs pass through biological membranes in this way. The diffusion rate of the drug depends on the concentration gradient of the drug on both sides of the membrane, the lipid-water partition coefficient of the drug and the diffusion of the drug within the membrane. speed.

(2) Carrier transport

There are two methods: active transport and facilitated diffusion. The carrier's transport mode is generally saturable, competitive and specific.

1. Active transport: It is a transport method that reverses the concentration gradient and requires energy and carriers. Usually some essential substances for life (such as K+, Na+, I-, simple sugars, amino acids, water-soluble vitamins ) and ionic compounds with weak electrolytes such as organic acids and bases can be absorbed through active transport.

2. Facilitated diffusion: Also known as intermediary transport, the transport rate is much higher than passive diffusion. It is a transport method along the concentration gradient that does not require energy and requires a carrier. It is common in small intestinal epithelial cells and fat. Transport of highly polar substances such as nucleoside drugs, monosaccharides and amino acids in the cell membranes of cells and blood-brain barriers.

(3) Membrane motility transport

Biological membranes undergo active deformation through flow, taking certain substances into the cells or releasing them from the cells to the outside. This process is called membrane motility. transport. The ingestion of liquid by cells through membrane transport is called pinocytosis, the ingestion of particles or macromolecular substances is called phagocytosis, and the transport of macromolecular substances from inside the cell to the outside of the cell is called exocytosis. Membrane transport is an important absorption method for proteins and peptides.

Compatibility questions

[1~2]

A. Absorption of drugs B. Distribution of drugs

C. Metabolism of drugs D. Excretion of drugs

E. Elimination of drugs

1. The process of drugs entering the systemic circulation from the site of administration is ().

2. The process of drug transport from systemic circulation to tissues, organs or body fluids is ().

Answer 1.A. 2.B.

Multiple choice questions

3. Transport methods that require energy ()

A. Active transport B. Simple diffusion C. Facilitated diffusion D. Membrane Kinetic transport

Answer A.

4. The main absorption mode of protein ()

A. Active transport B. Simple diffusion C. Facilitated diffusion D. Membrane transport

Answer D .