title: Portal circulations and their relation to counter-current systems.
abstract: We have reviewed the distribution of portal circulations throughout the animal body; they are commoner than is generally supposed. Most portal circulations consist of two serial capillary beds connected by one or more larger vessels. We have called these 'convergent' portal circulations: examples are hepatic portal, placental, hypophysial, renal, ovarian and testicular circulations, as are parts of the lymphatic circulation. A second type of portal circulation, which is less common, consists of two serial capillary beds that are not connected by larger vessels. These we have called 'continuous' portal circulations: adrenal and pancreatic circulations are examples of this type. When a countercurrent concentrating mechanism exists in the body it is always part of the primary or secondary bed of a convergent portal circulation, though some convergent portal circulations are not associated with countercurrent mechanisms.
mesh_terms: D000311:Adrenal Glands / Q000098:blood supply; D000818:Animals; D002196:Capillaries / Q000502:physiology; D003377:Countercurrent Distribution; D005260:Female; D007668:Kidney / Q000098:blood supply; D008102:Liver Circulation; D008208:Lymphatic System / Q000098:blood supply; D008297:Male; D010053:Ovary / Q000098:blood supply; D010179:Pancreas / Q000098:blood supply; D010902:Pituitary Gland / Q000098:blood supply; D011168:Portal System / Q000502:physiology*; D013737:Testis / Q000098:blood supply; D014599:Uterus / Q000098:blood supply; D014680:Veins / Q000473:pathology