About Human Cells

Overview

The human body holds more than 100 trillion cells, according to the National Institute of Child Health and Human Development. Human cells are small, too tiny to be seen without using a microscope, but they make up all of the organs and systems of the body. Every cell carries within it the entire genetic code of the human to whom it belongs, but the specific function or activity of a particular cell is controlled by which genes are turned on and off during development and throughout its life.

Structure

A human cell consists of a lipid cell membrane surrounding a fluid interior called cytoplasm containing numerous organelles and a nucleus that holds the genetic material of the cell. Cells interact with each other, passing signals in and out of the cell membrane. Different types of cells have specific structures that help them carry out different activities, such as the axons of brain and nerve cells, which send signals out across long distances to other cells.

Types

The human body contains many different types of cells, all carrying out different functions. Some are organized into tissues, such as liver or heart cells. Others operate independently, such as blood and immune defense cells. The functions of human cells can include movement, producing enzymes, conducting electrical impulses and destroying invaders.

Organelles

Organelles are the small structures inside a cell that carry out the work of the cell. Mitochondria, for example, convert glucose to energy inside the cell. The nucleus, the largest cell organelle, contains and protects the cell’s DNA. Other organelles include the endoplasmic reticulum, Golgi bodies, ribosomes, lysosomes and peroxisomes.

Replication

A human cell divides in two ways. When a cell needs to create new cells for use in the body itself, it goes through a process called mitosis, in which the genetic material of the cell is doubled, and the cell splits into two daughter cells that are identical to the parent cell. During human reproduction, special cells in the ovaries or testes undergo a different type of division called meiosis, in which the DNA doubles, then splits itself in half, creating gametes with half of the genetic material in each. These gametes are also known as eggs and sperm.

Diseases

Cellular diseases can affect any part of a human cell. Genetic diseases affect the DNA in the nucleus. Mitochondrial diseases strike the mitochondria, hampering its ability to produce energy. Cancer is an overgrowth of cells that occurs when the mechanisms keeping normal cell division in check become damaged or destroyed.

About this Author

Bridget Coila has been writing professionally since 1998 and specializes in health, nutrition, pregnancy and parenting topics. Some of her articles have appeared in “Oxygen,” “American Fitness” and on various websites. Coila has a Bachelor of Science in cell and molecular biology from the University of Cincinnati and over 10 years of medical research experience.