Making a Tissue of It
Tissues are collections of similar cells that define a specific layer of and relate an essential function to an organ. While the adult human body consists of over 200 different cell types, each human began his or her life as a single fertilized egg cell, which divided and gave rise to all the rest of their cells.
The Creation of Tissue
To understand how tissue fits in the organization of the human body, think of it as the level between cells and organs. Tissue is made up of cells and in turn it is used to make organs.
Stem cells and tissue
Stem cells are unspecialized cells that can, under certain conditions, take on specific cell, organ, and/or tissue functions. For example, under the right circumstances, a stem cell might be persuaded to become a neuron, helping to conduct electrical impulses throughout the body. In some tissues, stem cells work to repair damage, sort of like a corps of engineers.
Early in embryonic development, the newly (and rapidly!) dividing cells produce three distinct layers of cells from which all the cells of the body are derived. This process, called gastrulation, begins when a cluster of cells (called a blastula) organizes into layers. At first there is only an inner and an outer layer. These layers work together to produce a third middle layer. Organisms, such as humans, that have these three layers are called triploblastic.
These layers are called germ layers. Here the use of the word “germ” has nothing to do with disease-causing pathogens, but is related to the word “germination.” Germ layers form during the embryonic (“germination”) stage of human development, and they are the origin of all tissues and organs in the body (thus they “germinate” these structures). The layers are called:
· the ectoderm
· the mesoderm
· the endoderm
The ectoderm (ecto meaning “outside”) refers to the tissue that makes up your skin, which is the outer covering of the body. The ectoderm also creates the neural tube that eventually becomes home to your central nervous system.
The human body is often considered a tube within a tube. In this sense, the ectoderm produces the outside tube of skin and the endoderm (endo meaning “internal”) produces the tube on the inside. That tube is the digestive tract.
This leaves a lot of tissue and organs in between, which make up the mesoderm (meso meaning “middle”). Muscle, bone, blood, and connective tissue are all derived from this middle layer that is produced early in cell development.
Anatomy of a Word
organogenesis
Organogenesis is the name for the process by which the germ layers form all of the organs in the human body.
Your body has four main types of tissue:
· epithelial, which generally works to protect your body
· connective, which joins structures together
· muscle, which contracts
· nervous, which coordinates your body’s movements
How does the anatomy of a tissue relate to its physiology?
Think of anatomy as “form” or “structure” and physiology as “function.” They are linked together and can’t really be separated. For example, muscle tissue has the property of being able to contract (anatomy), so it is used to move the body around (physiology).
Histology is the study of tissues and how they work to allow the human body to function as a whole. Scientists often refer to the parenchyma of an organ, which is the tissue of the organ that performs its essential function, and the stroma, which is other tissue in the organ, such as a vein or a nerve, which does not perform the essential function. A true understanding of how an organ works (or why it may not be functioning correctly) requires attention to both the parenchyma and the stroma.