Well fibrosis is a process mediated by special cells called stellate cells, that sit between the sinusoid and hepatocyte, known as the perisinusoidal space.
Frequently affected organs include the liver, where the bacterial toxins damage liver sinusoids and hepatocytes, causing bilirubin to spill into the bloodstream - which clinically translates as jaundice.
As the central veins and sinusoids become compressed and push on the fluid inside, their pressure starts to build up, leading to intrasinusoidal (or portal) hypertension, which is this higher pressure in the portal veins.
Here's a pretty basic layout of the basic functional unit of the liver, you've got the portal vein and hepatic artery that combine into a sinusoid, which then goes into the central vein, and these are all lined with hepatocytes.