Figure 1710

Electron micrograph showing the perisinusoidal space (of Disse). The perisinusoidal space (D) is located between the hepatocytes (H) and the sinusoid. A gap (large arrow) separates the endothelial cells (En) that line the sinusoid. Such gaps allow easy passage of small substances between the sinusoid and the perisinusoidal space. Numerous microvilli extend from the hepatocytes into the perisinusoidal space. These processes are long and frequently branch (small arrow). A red blood cell (RBC) is within the sinusoid, x 18,000.

site for hepatic vitamin A in the form of retinyl esters within cytoplasmic lipid droplets. Vitamin A is released from the hepatic stellate cell as retinol (alcohol form) bound to RBP. It is then transported from the liver to the retina, where its stereoisomer 11-cis retinal binds to the protein opsin to form rhodopsin, the visual pigment of rods and cones of the retina. For many years, fish liver oils

(e.g., cod liver oil) were medically and economically important nutritional sources of vitamin A.

In certain pathologic conditions, such as chronic inflammation or cirrhosis, hepatic stellate cells lose their lipid and vitamin A storage capability and differentiate into cells with characteristics of myofibroblasts. These cells appear to play a significant role in hepatic fibro-genesis; they synthesize and deposit type I and type III collagen within the perisinusoidal space, resulting in liver fibrosis. This collagen is continuous with the connective tissue of the portal space and the connective tissue surrounding the central vein. An increased amount of perisinusoidal fibrous stroma is an early sign of liver response to toxic substances. The cytoplasm of hepatic stellate cells contains contractile elements, such as desmin and smooth muscle a-actin filaments. During cell contraction, they increase the vascular resistance within the sinusoids by constricting the vascular channels, leading to portal hypertension. In addition, hepatic stellate cells play a role in remodeling the extracellular matrix during recovery from liver injury.

Lymphatic Pathway

Hepatic lymph originates in the perisinusoidal space

Plasma that remains in the perisinusoidal space drains to the periportal connective tissue where a small space, the space of Mall (see Fig. 17.11b), is described between the stroma of the portal canal and the outermost hepatocytes. From this collecting site, the fluid then enters lymphatic capillaries that travel with the other components of the portal triad.

The lymph moves in progressively larger vessels, in the same direction as the bile, i.e., from the level of the hepatocytes, toward the portal canals and eventually to the hilum of the liver. About 80% of the hepatic lymph follows this pathway and drains into the thoracic duct, forming the major portion of the thoracic duct lymph.

Hepatocytes

Hepatocytes make up the anastomosing cell plates of the liver lobule

Hepatocytes are large, polygonal cells measuring between 20 and 30 pm in each dimension. They constitute about 80% of the cell population of the liver.

ITepatocyte nuclei are large and spherical and occupy the center of the cell. Many cells in the adult liver are bin-ucleate; most cells in the adult liver are tetraploid (i.e., they contain the 4n amount of DNA). Heterochromatin is present as scattered clumps in the nucleoplasm and as a distinct band under the nuclear envelope. Two or more well-developed nucleoli are present in each nucleus.

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Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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