What are human cells

The human cell - structure and function

Cells form the smallest (functional) unit in the human body. The human body consists of over 200 different cell types that combine to form larger structures (tissue, organs, organ systems). Cells are roughly divided into prokaryotes (cells without a real nucleus) and eukaryotes (cells with a real nucleus).

In the human organism, all cells have the same structure in principle, differ only in terms of their habitus (size) and lifespan of the cell. The lifespan of a cell ranges from a few days to twenty years (in the case of bone cells). The most important human cells are the sperm cells, nerve cells, sensory cells, skin cells, connective tissue cells, muscle cells and bone cells.

Functions of human cells

As mentioned at the beginning, the human cells form the smallest functional unit in the human body. Without this cell, the human organism would not be able to exist, as the vital metabolic processes take place in the cells (energy generation). A human cell does not only serve as an energy supplier for the human body, but can also absorb certain substances (glucose, oxygen) and release them again. In addition, most cells can divide and interact with other cells or organs through the cell membrane.

In addition, individual cells have other functions, for example the main task of nerve cells is to transmit “impulses” (or signals) between different organs. Blood cells, for example, have the job of transporting oxygen (and carbon dioxide) through the human body and supplying other cells with oxygen.

Structure of a typical human cell

Almost all human cells are made up of the nucleus, the cytoplasm and the cell membrane (but there are also human cells that do not have a nucleus, such as the red blood cells (also known as erythrocytes), which are found in the blood in the bone marrow, from “cell precursors” that contain cell nuclei. Therefore, the nucleated red blood cells in the blood can no longer divide).

The cell membrane envelops the cells and also gives the cell a certain shape and stability. The cell membrane is not permeable to all substances. Therefore the cell membrane “controls” which substances are exchanged between the cell and the “outside world”. This ability of the cell to be permeable only for certain substances is called permeability. The cell membrane consists of a lipid bilayer, a liquid bilayer of fats that are embedded in a structure made of proteins.

The cell membrane envelops the cytoplasm that is the skin component in human cells. The cytoplasm contains the so-called cytosol. The cytosol consists of up to 90% water and in dissolved form carbohydrates, mineral salts and amino acids. In addition to the cell nucleus, this cytoplasm also contains the so-called cell organelles, which make up around half the volume of the cytoplasm

The cell organelles in the human body

In addition to these cell components, the cell also contains other components, the so-called organelles.

  • The nucleus is a spherical object that is embedded in the cytoplasm of the cell. The cell nucleus is also known as the nucleolus. The cell nucleus is the carrier of the genetic code and contains deoxyribonucleic acids (DNA for short), i.e. the human genetic information. The cell nucleus is enveloped by what is known as the nuclear membrane.
  • The mitochondria are also important cell components for the human organism. Metabolic processes take place in the mitochondria, and the oxidation of (formerly) glucose releases energy in the form of adenosine triphosphate (ATP) (this process is part of the so-called respiratory chain). The ATP then serves as an energy supplier for the entire human organism. Therefore, mitochondria are often referred to as the power plants of the cells.
  • The ribosomes are also vital for humans. The so-called protein biosynthesis takes place on the ribosomes, which are embedded as a spherical object in the cytoplasm inside the cell. Here different amino acids are linked to form proteins. The linking sequence of the amino acids results from the genetic code of the human DNA.
  • The endoplasmic reticulum is still located in the cell as a cell organelle. With the endoplasmic reticulum, a distinction is made between the rough and the smooth endoplasmic reticulum. While there are ribosomes on the rough endoplasmic reticulum, there are no ribosomes on the smooth endoplasmic reticulum. Therefore, the smooth endoplasmic reticulum has the task of transporting the transport away from the ribosomes. Among other things, the smooth endoplasmic reticulum serves to transport nutrients from the rough endoplasmic reticulum to the Golgi apparatus.
  • In the Golgi apparatus, the proteins that were formed on the ribosomes as part of protein biosynthesis are stored there and proteins that are not yet finished are processed. An important task of the Golgi apparatus is to form so-called transport vesicles so that, for example, proteins can be transported in the cell. For this purpose, “protective sheaths” are formed around the proteins in the Golgi apparatus; without these vesicles, substances cannot be transported through the cell.

Difference between animal, human and plant cells

First of all, the “same thing”, animal, human and plant cells belong to the eukaryotes.

Animal and human cells (usually) consist of a cell membrane, a cell plasma and a cell nucleus. In addition to an animal or human cell, plant cells have a cell wall, a cell sap vacuole and chloroplasts. The plant cell has additional cell organelles that animal and human cells do not have.