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Aug 14, 2020 · A cell is the smallest living thing in the human organism, and all living structures in the human body are made of cells. There are hundreds of different types of cells in the human body, which vary in shape (e.g. round, flat, long and thin, short and thick) and size (e.g. small granule cells of the cerebellum in the brain (4 micrometers), up to the huge oocytes (eggs) produced in the female ...
Belonging to the liver, they are cells rich in organelles, glycogen and fat. They are responsible for secreting bile substances. Basal cells. Located in the outermost part of the skin, they produce the scaly layers of tissue that form the border of the body with the outside. Odontoblasts.
- Overview
- Inside the cell
- Cell division
- Cell types
- Summary
A cell is the smallest living organism and the basic unit of life on earth. Together, trillions of cells make up the human body. Cells have three parts: the membrane, the nucleus, and the cytoplasm.
People can think of cells as tiny packages that contain minute factories, warehouses, transport systems, and power plants. They function on their own, creating their own energy and self-replicating — the cell is the smallest unit of life that can replicate. Cells are the basic units of life.
The body contains around 50—100 trillion cells, and they vary widely in size, number, structure, and use.
Cells also communicate with each other. Whether in plants, humans, or animals, they connect to create a solid, well formed organism. In humans, cells build tissues, tissues form organs, and organs work together to keep the body alive.
Experts estimate that there are around 200 cell types in the human body.
Cell types can look different, and carry out distinct roles within the body.
For instance, a sperm cell resembles a tadpole, a female egg cell is spherical, and nerve cells are essentially thin tubes.
Despite their differences, cells often share certain structures. These are known as organelles or mini-organs. Below are some of the most important:
Mitosis
Mitosis is how most of the cells in the body divide. The “parent” cell splits into two “daughter” cells. Both daughter cells have the same chromosomes as each other and the parent. People refer to them as diploid because they have two complete copies of the chromosomes.
Meiosis
In meiosis, the body produces sperm cells and egg cells. In males, meiosis occurs after puberty. Diploid cells within the testes undergo meiosis to produce haploid sperm cells with 23 chromosomes. A single diploid cell yields four haploidsperm cells. They contain one complete set of 23 chromosomes. In females, meiosis begins during the fetal stage, before the individual is born. It happens in stages. A series of diploid future egg cells enter meiosis. At the end of the first stage of meiosis the process stops, and the cells gather in the ovaries. At puberty, one female egg cell resumes meiosis each month. As meiosis completes, it yields a single haploid egg cell each monthly cycle. During human reproduction, the haploid sperm and haploid egg combine. This temporarily doubles the number of chromosomes. A small portion of each chromosome breaks off and reattaches to its partner chromosome before fertilization finishes.
Stem cells
Stem cells are cells that must choose what they are going to become. Some differentiate to become a certain cell type, and others divide to produce more stem cells. The embryo and some adult tissues, such as bone marrow, house them.
Bone cells
There are at least three main types of bone cells: •osteoclasts, which dissolve bone •osteoblasts, which form new bone •osteocytes, which help communicate with other bone cells
Blood cells
There are many types of blood cells, including: •red blood cells, which carry oxygen around the body •white blood cells, which are part of the immune system •platelets, which help blood clot to prevent blood loss after injury •neutrophils and basophils, and other types of white blood cells
There are various and fascinating cells. In one sense, cells are autonomous cities that function alone, producing their own energy and proteins. In another sense, they are part of the huge network of cells that creates tissues, organs, and us.
Apr 27, 2017 · There are countless different functions that cells must perform to obtain energy and reproduce. Depending on the cell, examples of these functions can include photosynthesis, breaking down sugar, locomotion, copying its own DNA, allowing certain substances to pass through the cell membrane while keeping others out, etc.
7.3 Summary. Cells of the human body show a lot of variation. Some cells are unattached to other cells and can move freely, while others are attached to each other and cannot move freely. Some cells can divide readily and form new cells, and others can divide only under exceptional circumstances.
- Christine Miller
- 2020
Oct 31, 2024 · Cells of humans typically have a mass 400,000 times larger than the mass of a single mycoplasma bacterium, but even human cells are only about 20 μm across. It would require a sheet of about 10,000 human cells to cover the head of a pin, and each human organism is composed of more than 30,000,000,000,000 cells.
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Dec 13, 2021 · Muscle tissue is made up of cells that have the unique ability to contract or become shorter. There are three major types of muscle tissue, as pictured in Figure 10.3.14 10.3. 14: skeletal, smooth, and cardiac muscle tissues. Skeletal muscles are striated, or striped in appearance, because of their internal structure.
