Figure 1718

Photomicrograph of the Rokitansky-Aschoff sinuses in the wall of the gallbladder. This photomicrograph shows deep invaginations of the mucosa extending into the muscularis externa. These invaginations are referred to as Rokitansky-Aschoff sinuses. X120.

the intercellular compartment of the epithelium. ATPase is located in the lateral plasma membranes of the epithelial cells. This active transport mechanism is essentially identical to that described in Chapter 16 for the entero-cytes of the small intestine and the absorptive cells of the colon.

Active transport of Na+, CI", and HC03" across the lateral plasma membrane into the intercellular (paracellular) compartment causes the concentration of electrolytes in the intercellular space to increase. The increased electrolyte concentration creates an osmotic gradient between the intercellular space and the cytoplasm and between the intercellular space and the lumen. Water moves from the cytoplasm and from the lumen into the intercellular space because of the osmotic gradient, i.e., it moves down its concentration gradient (see Fig. 17.17b). Although the intercellular space can distend to a degree often visible with the light microscope, this ability is limited. The movement of electrolytes and water into the space creates hydrostatic pressure that forces a nearly isotonic fluid out of the intercellular compartment into the subepithelial connective tissue (the lamina propria). The fluid that enters the lamina propria quickly passes into the numerous fenestrated capillaries and the venules that closely underlie the epithelium. Studies of fluid transport in the gallbladder first demonstrated the essential role of the intercellular compartment in transepithelial transport of an isotonic fluid from the lumen to the vasculature.

v pancreas Overview

The pancreas is an elongate gland described as having a head, body, and tail. The head is an expanded portion that lies in the C-shaped curve of the duodenum (Fig. 17.19). It is joined to the duodenum by connective tissue. The centrally located body of the pancreas crosses the midline of the human body, and the tail extends toward the hilum of the spleen. The pancreatic duct (of Wirsung) extends through the length of the gland and empties into the duo cystic duct jj gallbladder common hepatic duct bile duct accessory pancreatic duct (of Santorini)

pancreas cystic duct jj gallbladder common hepatic duct minor duodenal papilla major duodenal papilla

pancreas main pancreatic duct

(of Wirsung)

duodenum hepatopancreatic ampulla (of Vater)

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