Tissues are made of cells that share morphological features to achieve specific functions within the body. They are 4 types of tissue in our body:
- Connective Tissue
- Epithelial Tissue
- Muscle Tissue
- Nervous Tissue
1. What Is a Connective Tissue?
Connective tissue provides structure, support, protection, and connection to other tissues and organs of the body .
1.1. What Are the 3 Types of Connective Tissue?
Connective tissue is made of fibers, gelatinous-like substances, and cells, and is divided into 3 types of tissues: loose connective tissue, dense connective tissue, and specialized connective tissue.
1.1.1. Where Is Loose Connective Tissue Found and What Is Its Function?
Loose connective tissue is found in almost every part of the body where it maintains organs in place.
It is made of an extracellular matrix and fibers of collagen, elastin, and reticulum.
- What Is Extracellular Matrix?
The extracellular matrix is found between the different cells of the body where it works as a structural scaffold and serves as membranous support where cells stand.
Glycoproteins are a type of protein involved in the interactions between and within cells.
Laminin is made of glycoproteins and collagen that form a membrane where the cells stand. This type of membrane is known as the basement membrane.
Fibronectin is a glycoprotein that works like a biological glue that connects the cells to the extracellular matrix through its interaction with proteins known as integrins found on the surface of cells.
Hydroxyapatite is also known as the bone mineral is made of calcium and phosphorus. It is mostly found in the bone and teeth connective tissues.
Enzymes are proteins that work as a catalyst through reactions that produce products necessary for the function of cells and tissues.
What Are Collagen Fibers?
Collagen is made by cells known as fibroblasts and is assembled into fibrils that make the collagen fibers.
Collagen fibers provide structural support for the cells of the extracellular matrix.
What Are Collagen Fibers?
What Are Elastin Fibers?
Elastin fibers are fibers that provide elasticity to the tissues.
What Are Reticular Fibers?
Reticular fibers are a type of collagen made by reticular cells. They form a supportive network for soft tissues such as the liver, bone marrow, and lymphatic system.
1.1.2. Where Is Dense Connective Tissue Found and What Is Its Function?
Dense Connective Tissue is what makes the tendons and ligaments. It also provides structure, support, protection, and connectivity.
Dense Connective Tissue is also made of extracellular matrix and fibers of collagen, elastin, and reticulum.
1.1.3. What Is Specialized Connective Tissue and What Is Its Function?
Blood is a bodily fluid that provides oxygen and nutrients to tissues and organs of the body. It also collects metabolic waste away from the cells. It is made of red blood cells and plasma.
The bone is a hard connective tissue (support and connect tissues) that contains a honey-comb shaped structure made of a mineralized matrix and bone cells.
Cartilage is a gelatinous-like substance that is found in body parts such as joints, rib cage, ears, nose, intervertebral discs, and bronchial tubes.
The Adipose tissue is a specialized tissue that stores fat and insulates the body.
2. What Is Epithelial Tissue?
Epithelial tissue or epithelium is made of one or more sheets of interconnected cells, known as epithelial cells, that cover the surface of organs and vessels and internal cavities of the body .
The epithelium is also part of the endocrine and exocrine glands that produce hormones and other substances and is the main component of the skin epidermis.
The epithelial cells have no blood vessels, and therefore, oxygen and nutrients are provided by the conjunctive tissue through basement membranes.
2.1. Epithelial Tissue Types
There are 8 different types of epithelial tissues according to their functions, morphologies, and localization in the body:
- Simple Squamous Epithelium
- Simple Cuboidal Epithelium
- Simple Columnar Epithelium
- Pseudostratified Columnar Epithelium
- Stratified Squamous tissue
- Stratified Cuboidal Epithelium
- Stratified Columnar Epithelium
- Transitional Epithelium
2.1.1. Where Is Simple Squamous Epithelium Found in the Body?
The simple squamous epithelium is permeable which allows the diffusion and filtration of small molecules.
2.1.1. Where Is Simple Cuboidal Epithelium Found in the Body?
The simple cuboidal epithelium is made of cuboidal (cube-like shape) epithelial cells found in the kidneys and small glands. It is involved in absorption and secretion.
2.1.1. Where Is Simple Columnar Epithelium Found in the Body?
The simple columnar epithelium is made of ciliated epithelial cells that are shaped like columns, and that is found in bronchi, digestive tissue, and uterus.
2.1.1. Where Is Pseudostratified Columnar Epithelium Found in the Body?
The pseudostratified columnar epithelium is also made of ciliated epithelial cells that are shaped like columns.
However, their nuclei are found in different areas within each cell which makes them different from the simple columnar epithelial cells that have the nucleus at the bottom of the cells.
The pseudostratified columnar epithelium is found in the upper respiratory tract where they secrete and move mucus along the tract through cilia.
2.1.1. Where Is Stratified Squamous Epithelium Found in the Body?
The stratified squamous epithelium is made of layers of flat epithelial cells found in the mouth, esophagus, and vagina where it protects against abrasion.
2.1.1. Where Is Stratified Cuboidal Epithelium Found in the Body?
The stratified cuboidal epithelium is made of layers of cuboid epithelial cells found in mammary glands, salivary glands, and sweat glands where it acts as a protective tissue.
2.1.1. Where Is Stratified Columnar Epithelium Found in the Body?
The stratified columnar epithelium is made of layers of non-ciliated column-shaped epithelial cells found in male urethra and ducts of some glands where they are involved in secretion and have a
2.1.1. Where Is Transitional Epithelium Found in the Body?
The transitional epithelium is made of layers of epithelial cells that have different shapes and that are found in the bladder, urethra, and ureters where they allow these organs to stretch.
3. What Is Muscle Tissue?
The muscle tissue is made of cells and contractile proteins that allow the contraction and relaxation of muscles.
There are 3 types of muscle tissues according to their functions and localization in the body:
- Skeletal Muscle Tissue
- Smooth Muscle Tissue
- Cardiac Muscle Tissue
3.1. What Is Skeletal Muscle Tissue?
The skeletal or striatal muscle is made of elongated cylindrical muscle cells known as muscle fibers (myofibers) that are attached to bones through tendons .
Examples of skeletal muscles are the muscles of the arms and legs.
Each muscle fiber is a bundle of fibers arranged in parallel, known as myofibrils, and that are surrounded by collagen.
Myofibrils can be made of thin filaments containing actin or thick filaments made of myosin.
The filaments are known as myofilaments which are arranged in such a way that it alternate light and dark bands, hence the striatal aspect of the muscle.
3.2. What Is Smooth Muscle Tissue?
The smooth muscle tissue is made of smooth muscle cells known as myocytes.
Myocytes are elongated cells with a wide middle and contain proteins such as actin and myosin responsible for their contraction and relaxation.
Smooth muscle tissue is found in organs such as the intestines, stomach, bladder, uterus, and blood vessels.
3.3. What Is Cardiac Muscle Tissue?
The cardiac muscle tissue is what makes the myocardium of the heart, a muscle that is found between the endocardium (inner layer) and the epicardium (outer layer).
The cardiac muscle tissue is made of cardiac cells known as cardiomyocytes that provide the contraction and relaxation of the heart.
Some of the cardiomyocytes, known as peacemaker cells, are responsible for maintaining heartbeats and are found in the atria of the heart.
4. What Is Nervous Tissue?
The nervous tissue is the tissue that makes the nervous system including the peripheral and central nervous systems .
The central nervous system (CNS) includes the brain and the spinal cord, while the peripheral nervous system (PNS) includes the branching nerves that are outside the brain and the spinal cord.
The nervous tissue is made of neurons that transmit nerves impulses and neuroglia cells that provide support to neurons.
4.1. What Are Neurons and Their Functions?
Neurons are highly specialized cells that transmit nerve impulses (action potentials).
They are made of a cell body, an axon, and an axon terminal.
The cell body contains cell projections known as dendrites.
The axon extends from the cell body and all the way to the axon terminals which are cell projections.
Axons are covered by a sheet made of a fatty substance known as myelin sheet that protects the axon and helps with the transmission of nerve impulses.
Neurons are interconnected through gaps, known as synapses, that are found between a dendrite of one neuron and an axon terminal of another neuron.
A neurotransmitter that is released in the synapse by the axon terminal of a neuron is captured by receptors that are specific to the neurotransmitter and that are found on the dendrite of the following neuron.
Once the dendrite of a neuron receives the neurotransmitter, there is a start of a nerve impulse (action potential) that is transmitted along the axon and all the way to the axon terminal where it is transferred to the next neuron.
This process of nerve transmission is known as neurotransmission.
Based on their function, neurons are classified as sensory, motor, or interneurons.
- What Are Sensory Neurons?
- What Are Motor Neurons?
Motor neurons or efferent neurons are neurons that transmit information from the nervous central nervous to different organs of the body to initiate an action (e.g., muscle).
- What Are Interneurons?
As their name indicates, interneurons are neurons that serve as neuronal bridges between neurons, such as between sensory or motor neurons and the central nervous system.
4.2. What Are Neuroglia Cells and Their Functions?
Neuroglia cells are not neurons but different types of cells that provide support to neurons and include microglia, astrocytes, oligodendrocytes, Schwann cells, and enteric glia .
- What are Microglia Cells?
Macroglia cells are macrophages that contribute to the immunity of the central nervous system.
- What Are Astrocytes?
Astrocytes or astroglia are star-shaped cells that have many functions such as providing nutrients to the nervous tissue, repair, and scarification of the brain and spinal cord, support of endothelial cells involved in the blood-brain barrier.
- What Are Oligodendrocytes?
Oligodendrocytes are cells that make the myelin sheet and provide insulation and support for neurons.
- What Are Schwann Cells?
Schwann cells are cells that make the myelin sheet and provide insulation and support for neurons in the peripheral nervous system.
- What Are Enteric Glia Cells?
Enteric glial cells are cells found in the enteric nervous system (gut nervous system) where they may play a role in neurotransmission .
In the central nervous system, the brain tissue can also be classified as grey matter and white matter
- What Is Grey Matter?
The grey matter is made of the neurons’ cell bodies, neurons’ unmyelinated axons, neurons’ dendrites, astrocytes, oligodendrocytes, synapses, and blood capillaries.
- What Is White Matter?
The white matter is mostly made of myelinated axons of neurons is found in a brain structure known as the corpus callosum which is a tract of fibers located under the cerebral cortex.
Tissues are what make the body, and therefore, taking care of our tissues through a healthy diet, exercise, and a healthy environment can only improve their function and health which will increase the potential of a healthier and longer life.