Tissues, organs, & organ systems (article) | Khan Academy
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle For the fungal structure of the same name, see Pileipellis. Functions of epithelial cells include secretion, selective absorption, protection, transcellular transport, and sensing. Epithelial 10 Further reading; 11 External links. Explain the structure and function of epithelial tissue; Distinguish between tight and projects through the cell membrane to link with the cadherin molecules of. Third, epithelial cells exhibit polarity with differences in structure and function between [link] summarizes the different categories of epithelial cell tissue cells.
The survival of the organism depends on the integrated activity of all the organ systems, often coordinated by the endocrine and nervous systems.
Introduction If you were a single-celled organism and you lived in a nutrient-rich place, staying alive would be pretty straightforward. For instance, if you were an amoeba living in a pond, you could absorb nutrients straight from your environment. The oxygen you would need for metabolism could diffuse in across your cell membrane, and carbon dioxide and other wastes could diffuse out. When the time came to reproduce, you could just divide yourself in two!
How, then, does the body nourish its cells and keep itself running? Let's take a closer look at how the organization of your amazing body makes this possible.
Multicellular organisms need specialized systems Most cells in large multicellular organisms don't directly exchange substances like nutrients and wastes with the external environment, instead, they are surrounded by an internal environment of extracellular fluid—literally, fluid outside of cells. The cells get oxygen and nutrients from this extracellular fluid and release waste products into it.
Humans and other complex organisms have specialized systems that maintain the internal environment, keeping it steady and able to provide for the needs of the cells. Different systems of the body carry out different functions.
For example, your digestive system is responsible for taking in and processing food, while your respiratory system—working with your circulatory system—is responsible for taking up oxygen and getting rid of carbon dioxide.
The muscular and skeletal systems are crucial for movement; the reproductive system handles reproduction; and the excretory system gets rid of metabolic waste. Because of their specialization, these different systems are dependent on each other. The cells that make up the digestive, muscular, skeletal, reproductive, and excretory systems all need oxygen from the respiratory system to function, and the cells of the respiratory system—as well as all the other systems—need nutrients and must get rid of metabolic wastes.
All the systems of the body work together to keep an organism up and running.
Epithelial Tissue | Anatomy & Physiology
Overview of body organization All living organisms are made up of one or more cells. Unicellular organisms, like amoebas, consist of only a single cell. Multicellular organisms, like people, are made up of many cells. Cells are considered the fundamental units of life. The cells in complex multicellular organisms like people are organized into tissues, groups of similar cells that work together on a specific task.
Organs are structures made up of two or more tissues organized to carry out a particular function, and groups of organs with related functions make up the different organ systems. At each level of organization—cells, tissues, organs, and organ systems—structure is closely related to function. For instance, the cells in the small intestine that absorb nutrients look very different from the muscle cells needed for body movement.
The structure of the heart reflects its job of pumping blood throughout the body, while the structure of the lungs maximizes the efficiency with which they can take up oxygen and release carbon dioxide. Types of tissues As we saw above, every organ is made up of two or more tissues, groups of similar cells that work together to perform a specific task. Humans—and other large multicellular animals—are made up of four basic tissue types: Epithelial tissue Epithelial tissue consists of tightly packed sheets of cells that cover surfaces—including the outside of the body—and line body cavities.
For instance, the outer layer of your skin is an epithelial tissue, and so is the lining of your small intestine. Epithelial cells are polarized, meaning that they have a top and a bottom side.
The apical, top, side of an epithelial cell faces the inside of a cavity or the outside of a structure and is usually exposed to fluid or air. The basal, bottom, side faces the underlying cells. For instance, the apical sides of intestinal cells have finger-like structures that increase surface area for absorbing nutrients. Epithelial cells are tightly packed, and this lets them act as barriers to the movement of fluids and potentially harmful microbes.
- Epithelial Tissue
- Tissues, organs, & organ systems
Often, the cells are joined by specialized junctions that hold them tightly together to reduce leaks. Connective tissue Connective tissue consists of cells suspended in an extracellular matrix. In most cases, the matrix is made up of protein fibers like collagen and fibrin in a solid, liquid, or jellylike ground substance.
Connective tissue supports and, as the name suggests, connects other tissues.
Loose connective tissue, show below, is the most common type of connective tissue. It's found throughout your body, and it supports organs and blood vessels and links epithelial tissues to the muscles underneath. Dense, or fibrous, connective tissue is found in tendons and ligaments, which connect muscles to bones and bones to each other, respectively. Specialized forms of connective tissue include adipose tissue—body fat—bone, cartilage, and bloodin which the extracellular matrix is a liquid called plasma.
Simple columnar epithelia are found in the female reproductive system and in the digestive tract. The cells in the fallopian tubes are ciliated and involved in the movement of the ovum towards the uterus. Those in the digestive tract are non-ciliated, and instead contain microvilli, which gives the epithelium the appearance of being brush-bordered.
Pseudostratified epithelia are formed of cells that have varying heights and therefore present the illusion of being stratified. However, every cell in this tissue makes contact with the basement membrane, thereby placing it among the simple epithelia.
Stratified Epithelium Stratified epithelia consist of more than one layer of cells and only one layer is in direct contact with the basement membrane. Similarly, only one layer of cells has the apical surface exposed to the lumen of the organ or to the external environment.
These tissues often have a protective role, and the extent of friction or abrasion often determines the number of layers of cells. Stratified squamous epithelia are found in skin, with many dead, keratinized cells providing protection against water and nutrient loss. Stratified cuboidal epithelia are found surrounding the ducts of many glands, including mammary glands in the breast and salivary glands in the mouth.
Stratified columnar epithelia are rare, found predominantly in some organs of the reproductive system, and in the conjunctiva of the eye.
Transitional epithelia are a special subset of stratified epithelia that consist of ovoid cells that can stretch based on the pressure of liquids inside the organ. They are exclusively found in the excretory system. Characteristics of Epithelial Tissue Epithelial tissues play the role of separating two structures from each other.
For instance, the epithelium in a blood vessel demarcates the cells of the blood from those forming the artery or vein. This allows two organs to remain in close proximity for their function while maintaining separate internal physiology. In order to accomplish this function, however, epithelial tissues need to be tightly attached to each other, forming a mostly impenetrable layer.
This is achieved by the presence of tight junctions between two epithelial cells. Tight junctions in cells are also known as occluding junctions because they prevent the flow of material through the interstitial space between two cells. These are structures formed from the close interaction between the extracellular domains of two sets of transmembrane proteins.