Intestinal epithelial cells form an outer protective layer. The cells have multifold functions including:
Nutrients absorption: Cells called enterocytes take up nutrients from digested food, including sugars, amino acids, fatty acids, vitamins, and minerals. Their tiny surface projections, called microvilli, provide a large area for absorption.
Protect the gut: Protecting the intestinal lining acts as a barrier between the contents of the gut and the rest of the body. Connections called tight junctions help control what can pass through the lining and prevent unwanted substances from entering easily.

The selection of the human kidney fibroblast model requires a quick judgement. Determine whether primary human kidney fibroblasts or immortalised fibroblast cell line is required for the experiment. Primary cells offer closer physiologically relevance with humans, but they have limited life span. However, with immortalized cells large scale experiments to gain reproducible data is possible.
To ensure consistency, reproducibility, and authenticity of the experimental outcome one must review the key features. This includes tissue origin, donor information, cellular morphology, passage number, culture medium, authentication, and mycoplasma testing. Globally, the suppliers of fibroblast and any animal cell culture related cells are procured from established repositories.

Human liver tissue for research is procured from donated human liver. It is obtained through established clinical or tissue-procurement networks rather than collected directly by a research laboratory.
The tissue collection process, that is, consented donors, surgical resections, transplant-related sources, or accredited tissue banks depends on the research objective and research design. The exact source can vary based on factors such as donor eligibility, tissue quality, availability, and the requirements of the study.
It is crucial to maintain ethical regulations to procure human liver tissue. This involves gaining informed consent and clearance from the relevant ethical committee.

The human liver is formed by distinct cell types. The cells that are broadly categorized as hepatocytes and non-hepatocyte liver cells. These cells are highly organized and responsible for performing adequate liver function.
Hepatocytes make up more than 70% of the liver cells. They are responsible for bile production that aids in digestion, absorption of nutrients, conversion of nutrients into energy, storage of vitamins and glycogen, and production of essential proteins like albumin. The core mechanism involves the breakdown of medicines, alcohol, and other substances that enter the body. They are also unique because they can divide and replace damaged cells, giving the liver its well-known ability to regenerate after injury.

Hepatocytes make up the liver and have subtypes based on their specific functions. There are two main types of hepatocytes, classified based on where they are located within the liver lobule: periportal hepatocytes and pericentral (centrilobular) hepatocytes. Between these two regions is Zone 2, which contains hepatocytes with features that fall somewhere in between.
Periportal hepatocytes: The cells are located closer to the portal vein and receive the highest supply of oxygen and nutrients. These cells are mainly responsible for energy-producing processes such as glucose production, fatty acid breakdown, cholesterol synthesis, and ammonia detoxification through the urea cycle.