Absorption vascular system

Absorption Movement of substances into the blood vascular system or into the tissues of the organism. 

The absorption from the gastrointestinal tract is of particular importance because compounds so absorbed are transported directly to the liver via the hepatic-portal vascular system (figure 3,8). 

The processes whereby water passes back and forth across the capillary wall are called filtration and absorption. The flow of water depends upon the relative magnitude of hydraulic and osmotic pressures across the capillary wall and is described quantitatively by the Kedem Katchalsky equations (the particular form of the equations applied to capillary water transport is referred to as Starling s Law). Recently, the physical mechanism of Starling s Law has been re-assessed [54]. Overall, in the steady state there is an approximate balance between hydraulic and osmotic pressures which leads to a small net flow of water. Generally, more fluid is filtered than is reabsorbed the overflow is carried back to the vascular system by the lymphatic circulation. The lymphatic network is composed of a large number of small vessels, the terminal branches of which are closed. Flap valves (similar to those in veins) ensure unidirectional flow of lymph back to the central circulation. The smallest (terminal) vessels are very permeable, even to proteins that occasionally leak from systemic capillaries. Lymph flow is determined by interstitial fluid pressure and the lymphatic pump (oneway flap valves and skeletal muscle contraction). Control of interstitial fluid protein concentration is one of the most important functions of the lymphatic system. If more net fluid is filtered than can be removed by the lymphatics, the volume of interstitial fluid increases. 

The nasal tissue is highly vascularized and provides efficient systemic absorption. Compared with oral or subcutaneous administration, nasal administration enhances bioavailability and improves safety and efficacy. Chitosan enhances the absorption of proteins and peptide drugs across nasal and intestinal epithelia. Gogev et al. demonstrated that the soluble formulation of glycol chitosan has potential usefulness as an intranasal adjuvant for recombinant viral vector vaccines in cattle [276]. 

Two different circulatory systems, the bronchial and the pulmonary, supply the lungs with blood [133], The bronchial circulation is a part of the systemic circulation and is under high pressure. It receives about 1% of the cardiac output and supplies the conducting airways, pulmonary blood vessels and lymph nodes [133], It is important for the distribution of systemically administered drugs to the airways and to the absorption of inhaled drugs from the airways [18]. The pulmonary circulation comprises an extensive low-pressure vascular bed, which receives the entire cardiac output. It perfuses the alveolar capillaries to secure efficient gas exchange and supplies nutrients to the alveolar walls. Anastomoses between bronchial and pulmonary arterial circulations have been found in the walls of medium-sized bronchi and bronchioles [18, 65, 67],... 

A drug can be administered directly into the vascular compartment or by an alternative route, such as orally. It can usually be assumed that the entire dose administered by the intravenous route reaches the systemic circulation. After oral administration, only a proportion may reach the systemic circulation because of incomplete absorption or because absorbed drug may be metabolised in the mucosa of the gastrointestinal... 

Mecfianism of Action An ergotamine derivative, alpha-adrenergic blocker that directly stimulates vascular smooth muscle. May also have antagonist effects on sero-fonin. Therapeutic Effect Peripheral and cerebral vasoconstriction. Pharmacokinetics Slow, incomplete absorption from the gastrointestinal (GI) tract rate of absorption of intranasal route varies. Protein binding greaterthan 90%. Undergoes extensive first-pass metabolism in liver. Metabolized to active metabolite. Eliminated in feces via biliary system. Half-life 7-9 hr. 

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