Cells the extra-cellular fluid outside of the

Cells function in similar fashions to the organisms that they make up. They need to breathe, eat, drink, produce waste, etc. Cells have adapted ways in which to do these seemingly menial tasks, one of which, pinocytosis, we look at here.

What is Pinocytosis?

All cells need to carry out basic functions, like ‘eating’ and ‘drinking.

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Pinocytosis is literally translated from Greek as ‘cell drinking.’ It is one mechanism by which cells will take in fluids.Inside of cells we have the liquid portion called the cytoplasm, and each cell is surrounded by a semi-permeable cell membrane (which allows some things in and out) made of lipids (fats).

Through pinocytosis, a cell will suck in everything that is in the extra-cellular fluid outside of the cell, including solutes (dissolved particles). Only small amounts of material will enter the cell during this process, and a minimal amount of adenosine triphosphate (ATP, an energy molecule used by the cell) is necessary.When the cell takes in the fluid, it is stored in a tiny vesicle. A vesicle is a membrane-bound organelle that consists of just the membrane in a circular orientation around the fluid inside of it. The membrane of the vesicle is made from the same lipid layer that is the cell membrane.

How Does Pinocytosis Work?

So how does pinocytosis work? The process itself is rather simple in that it only really involves the cell membrane, the vesicle, and a lysosome. Let’s go over it step by step:1. The cell membrane will allow the fluid it wants to take in to push inwards, causing a divot in the membrane.

2. The fluid fills into the divot and the bend gets larger.3. Eventually, the membrane pinches it off, trapping the fluid inside the vesicle, which is now inside the cell.

This is similar to blowing up a balloon. You blow air into it, before you finally pinch it off and tie it, trapping the air inside.

Here we see pinocytosis occurring.

Notice the solute (dissolved materials) that are taken in along with the fluid.


Once the vesicle is formed around the fluid, it moves about until it links up with a lysosome. A lysosome is another organelle in a cell that carries acidic enzymes that help break down food and food particles. The lysosome attaches to the vesicle and helps break down what little solute and food material the vesicle caught.

Again, the amount of energy (ATP) that is generated here is small, and this process usually occurs as a way to clear up waste products created elsewhere.

Lesson Summary

The outside of a cell is covered and protected by a semi-permeable lipid membrane. The membrane helps keep the contents of the cell inside and foreign substances out.

Occasionally, the cell will want to take in fluid from the outside through pinocytosis. This process involves a small indent in the cellular membrane that allows the fluid to push into the cell. Eventually, enough fluid gets in and the cell membrane pinches off, leaving the fluid trapped in a vesicle.

This vesicle will link up with a lysosome, which carries with it enzymes that break down whatever solutes are in the vesicle. Remember, pinocytosis will not occur with large food particles but rather fluid that has solutes in it that were already broken down elsewhere.


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