![]() ![]() ![]() They consist of two layers of phospholipid molecules arranged like a sandwich, referred to as a "phospholipid bilayer." Each phospholipid molecule consists of a phosphate head and a lipid tail. Suppositories - used for medicines that may not be adequately absorbed after oral administration or that are intended for local therapy usual locations for suppositories are the rectum and vagina.Ĭell membranes (often referred to as plasma membranes) surround all body cells and are similar in structure.Conjunctival instillations (eye drops) - primarily for treating ocular conditions however, in some cases, considerable absorption can occur and cause systemic toxicity.Some materials enter the body via skin penetration as the result of accidents or weapons. Many medical devices are implanted for which minimal absorption is desired (such as artificial lens or tendons). Implants - pharmaceuticals may be implanted to permit slow, time-release (for example, hormones).Injections - primarily used for pharmaceuticals.Other routes of exposure – used primarily for specific medical purposes: Skin - important environmental and occupational exposure route many consumer and pharmaceutical products are applied directly to the skin.Respiratory tract - important for environmental and occupational exposure to air contaminants some pharmaceuticals (such as nasal or oral aerosol inhalers) use this route.Gastrointestinal (GI) tract - important for environmental exposure to contaminants from food and water the main route for many pharmaceuticals.The primary routes of exposure by which xenobiotics can gain entry into the body are: A substance may be categorized as relatively non-toxic by one route and highly toxic via another route. For example, very little DDT powder will penetrate the skin whereas a high percentage will be absorbed when it is swallowed.ĭue to such route-specific differences in absorption, xenobiotics are often ranked for hazard in accordance with the route of exposure.In some cases, a high percentage of a substance may not be absorbed from one route whereas a low amount may be absorbed via another route. The route of exposure influences how the concentration and properties of the substance vary. Chemical and physical properties of the substance. ![]() Concentration of the substance at the site of contact.Several factors affect the likelihood that a xenobiotic will be absorbed. For substances injected or implanted directly into the body, exposure dose is the same as the absorbed or internal dose.For skin, oral or respiratory exposure, the absorbed dose is only a fraction of the exposure dose (external dose).Illustration of an axon releasing dopamine by exocytosis.Absorption varies greatly by specific chemicals and the route of exposure. For a detailed animation of cellular secretion, see. Newly made membrane proteins and membrane lipids are moved on top the plasma membrane by exocytosis. Exocytosis occurs when a cell produces substances for export, such as a protein, or when the cell is getting rid of a waste product or a toxin. Pinocytosis is a type of endocytosis.Įxocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell, as shown in Figure below. Transmission electron microscope image of brain tissue that shows pinocytotic vesicles. When the channel is closed, the liquid is encircled within a pinocytic vesicle. Pinocytosis, or cellular drinking, occurs when the plasma membrane folds inward to form a channel allowing dissolved substances to enter the cell, as shown in Figure below.The plasma membrane engulfs the solid material, forming a phagocytic vesicle. Phagocytosis, or cellular eating, occurs when the dissolved materials enter the cell.At this point a membrane-bound sac, or vesicle, pinches off and moves the substance into the cytosol. The membrane folds over the substance and it becomes completely enclosed by the membrane. ![]() \)Įndocytosis is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane. ![]()
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