The Three Main Types Of Loose Connective Tissue
As the name implies, connective tissue serves a "connecting" function. It supports and binds other tissues in the body. Unlike epithelial which has cells that are closely packed together, connective tissue typically has cells scattered throughout an extracellular matrix of fibrous proteins and glycoproteins attached to a basement membrane.
Loose Connective Tissue
In vertebrates, the most common type of connective tissue is loose connective tissue.
It holds organs in place and attaches epithelial tissue to other underlying tissues.
Loose connective tissue is named based on the "weave" and type of its constituent fibres. There are three main types:
• Collagenous Fibres, Collagenous fibres are made of collagen and consist of bundles of fibrils …show more content…
that are coils of collagen molecules. • Elastic Fibres, Elastic fibres are made of the protein elastin and are stretchable. • Reticular Fibres, Reticular fibres join connective tissues to other tissues.
Dense Connective Tissue
Another type of connective tissue is dense or fibrous connective tissue, which is found in tendons and ligaments. These structures help attach muscles to bones and link bones together at joints. Dense connective tissue is composed of large amounts of closely packed collagenous fibres. Much of the dermis layer of the skin is composed of dense irregular connective tissue.
Specialized Connective Tissues
Adipose
Adipose tissue is a form of loose connective tissue that stores fat. Adipose lines organs and body cavities to protect organs and insulate the body against heat loss.
Adipose tissue also produces endocrine hormones.
Cartilage
Cartilage is a form of fibrous connective tissue that is composed of closely packed collagenous fibers in a rubbery gelatinous substance called chondrin. The skeletons of sharks and human embryos are composed of cartilage. Cartilage also provides flexible support for certain structures in adult humans including the nose, trachea, and ears.
Bone
Bone is a type of mineralized connective tissue that contains collagen and calcium phosphate, a mineral crystal. Calcium phosphate gives bone its firmness.
Blood
Interestingly enough, blood is considered to be a type of connective tissue. Even though it has a different function in comparison to other connective tissues it does have an extracellular matrix. The matrix consists of the plasma, while red blood cells, white blood cells, and platelets are suspended in the plasma.
Lymph
Lymph is another type of fluid connective tissue. This clear fluid originates from blood plasma that exits blood vessels at capillary beds. A component of the lymphatic system, lymph contains immune system cells that protect the body against pathogens.
Epithelial tissue Epithelial tissue is a sheet of cells that covers a body surface or lines a body cavity. Two forms occur in the human body:
1. Covering and lining epithelium-forms the outer layer of the skin; lines open cavities of the digestive and respiratory systems; covers the walls of organs of the closed ventral body cavity.
2. Glandular epithelium-surrounds glands within the body.
Characteristics of epithelium
Epithelial tissues have five main characteristics these are:
1. Polarity-all epithelia have an apical surface and a lower attached basal surface that differ in structure and function. For this reason, epithelia is described as exhibiting apical basal polarity. Most apical surfaces have microvilli (small extensions of the plasma membrane) that increase surface area. For instance, in epithelia that absorb or secrete substances, the microvilli are extremely dense giving the cells a fuzzy appearance called a brush border. Examples of this would include epithelia lining the intestine and kidney tubules. Other epithelia have motile cilia (hair like projections) that push substances along their free surface. Next to the basal surface is the basal lamina (thin supporting sheet). The basal lamina acts as a filter allowing and inhibiting certain molecules from passing into the epithelium.
2. Specialized contacts-epithelial cells fit close together and form continuous sheets (except in the case of glandular epithelia). They do this with tight junctions and desmosomes. Tight junctions form the closest contact between cells and help keep proteins in the apical region of the plasma membrane. Desmosomes connect the plasma membrane to intermediate filaments in the cytoplasm.
3. Supported by connective tissue-all epithelia are supported by connective tissue. For instance, deep to the basal lamina is reticular lamina (extracellular material containing collagen protein fibre) which forms the basement membrane. The basement membrane reinforces the epithelium and helps it resist stretching and tearing.
4. Avascular and innervated-even though epithelium is avascular (contains no blood vessels), it’s still innervated (supplied by nerve fibres).
5. Regeneration-epithelium have a high regenerative capacity and can reproduce rapidly as long as they receive adequate nutrition.
Classification of Epithelia Epithelium has two names. The first name indicates the number of cell layers, the second describes the shape of its cell. Based on the number of cell layers, epithelia can either be simple or stratified.
• Simple epithelia-consist of a single cell layer (found where absorption, secretion, and filtration occur).
• Stratified epithelia-are composed of two or more cell layers stacked on top of each other (typically found in high abrasion areas where protection is needed).
There are three ways to describe the shape and height of epithelial cells these are:
- squamous cells which are flat and scale-like
- cuboidal cells which are box like but the same height and width
- and there are also columnar cells which are tall and column shaped
Nervous tissue
Nervous tissue is found in the brain, spinal cord, and nerves.
It is responsible for coordinating and controlling many body activities. It stimulates muscle contraction, creates an awareness of the environment, and plays a major role in emotions, memory, and reasoning. To do all these things, cells in nervous tissue need to be able to communicate with each other by way of electrical nerve impulses. The cells in nervous tissue that generate and conduct impulses are called neurons or nerve cells. These cells have three principal parts: the dendrites, the cell body, and one axon. The main part of the cell, the part that carries on the general functions, is the cell body. Dendrites are extensions, or processes, of the cytoplasm that carry impulses to the cell body. An extension or process called an axon carries impulses away from the cell …show more content…
body.
Nervous tissue also includes cells that do not transmit impulses, but instead support the activities of the neurons. These are the glial cells (neuroglial cells), together termed the neuroglia. Supporting, or glia, cells bind neurons together and insulate the neurons. Some are phagocytic and protect against bacterial invasion, while others provide nutrients by binding blood vessels to the neurons.
Nervous tissue is composed of neurons, also called nerve cells, and neuroglial. Typically, nervous tissue is categorized into four types of tissue. In the central nervous system (CNS), the tissue types found are grey and white matter. In the peripheral nervous system (PNS), the tissue types are nerves and ganglia. The tissue is categorized by its neuronal and neuroglial components.
Neurons are cells with specialized features that allow them to receive and facilitate nerve impulses, or action potentials, across their membrane to the next neuron. They possess a large cell body (soma), with cell projections called dendrites and an axon. Dendrites are thin, branching projections that receive electrochemical signalling (neurotransmitters) to create a change in voltage in the cell. Axons are long projections that carry the action potential away from the cell body toward the next neuron. The bulb-like end of the axon, called the axon terminal, is separated from the dendrite of the following neuron by a small gap called a synapse. When the action potential travels to the axon terminal, neurotransmitters are released across the synapse and bind to the post-synaptic receptors, continuing the nerve impulse.
Neurons are classified both functionally and structurally.
Functional classification:
• Sensory neurons (afferent): Relay sensory information in the form of an action potential (nerve impulse) from the PNS to the CNS
• Motor neurons (efferent): Relay an action potential out of the CNS to the proper effector (muscles, glands)
• Interneurons: Cells that form connections between neurons and whose processes are limited to a single local area in the brain or spinal cord
Structural classification:
• Multipolar neurons: Have 3 or more processes coming off the soma (cell body).
They are the major neuron type in the CNS and include interneurons and motor neurons.
• Bipolar neurons: Sensory neurons that have two processes coming off the soma, one dendrite and one axon
• Pseudo unipolar neurons: Sensory neurons that have one process that splits into two branches, forming the axon and dendrite
• Unipolar brush cells: Are excitatory glutamatergic interneurons that have a single short dendrite terminating in a brush-like tuft of dendrioles. These are found in the granular layer of the cerebellum.
Neuroglia encompasses the non-neural cells in nervous tissue that provide various crucial supportive functions for neurons. They are smaller than neurons, and vary in structure according to their
function.
Neuroglial cells are classified as follows:
• Microglial cells: Microglia are macrophage cells that make up the primary immune system for the CNS. They are the smallest neuroglial cell.
• Astrocytes: Star-shaped macro glial cells with many processes found in the CNS. They are the most abundant cell type in the brain, and are intrinsic to a healthy CNS.
• Oligodendrocytes: CNS cells with very few processes. They form myelin on the axons of a neuron, which are lipid-based insulation that increases the speed at which the action potential, can travel down the axon.
• NG2 glia: CNS cells that are distinct from astrocytes, oligodendrocytes, and microglia, and serve as the developmental precursors of oligodendrocytes.
• Schwann cells: The PNS equivalent of oligodendrocytes, they help maintain axons and form myelin sheaths in the PNS.
• Satellite glial cell: Line the surface of neuron cell bodies in
• Ganglia (groups of nerve body cells bundled or connected together in the PNS).
• Enteric glia: Found in the enteric nervous system, within the gastrointestinal tract.
Loose Connective Tissue
In vertebrates, the most common type of connective tissue is loose connective tissue.
It holds organs in place and attaches epithelial tissue to other underlying tissues.
Loose connective tissue is named based on the "weave" and type of its constituent fibres. There are three main types:
• Collagenous Fibres, Collagenous fibres are made of collagen and consist of bundles of fibrils …show more content…
that are coils of collagen molecules. • Elastic Fibres, Elastic fibres are made of the protein elastin and are stretchable. • Reticular Fibres, Reticular fibres join connective tissues to other tissues.
Dense Connective Tissue
Another type of connective tissue is dense or fibrous connective tissue, which is found in tendons and ligaments. These structures help attach muscles to bones and link bones together at joints. Dense connective tissue is composed of large amounts of closely packed collagenous fibres. Much of the dermis layer of the skin is composed of dense irregular connective tissue.
Specialized Connective Tissues
Adipose
Adipose tissue is a form of loose connective tissue that stores fat. Adipose lines organs and body cavities to protect organs and insulate the body against heat loss.
Adipose tissue also produces endocrine hormones.
Cartilage
Cartilage is a form of fibrous connective tissue that is composed of closely packed collagenous fibers in a rubbery gelatinous substance called chondrin. The skeletons of sharks and human embryos are composed of cartilage. Cartilage also provides flexible support for certain structures in adult humans including the nose, trachea, and ears.
Bone
Bone is a type of mineralized connective tissue that contains collagen and calcium phosphate, a mineral crystal. Calcium phosphate gives bone its firmness.
Blood
Interestingly enough, blood is considered to be a type of connective tissue. Even though it has a different function in comparison to other connective tissues it does have an extracellular matrix. The matrix consists of the plasma, while red blood cells, white blood cells, and platelets are suspended in the plasma.
Lymph
Lymph is another type of fluid connective tissue. This clear fluid originates from blood plasma that exits blood vessels at capillary beds. A component of the lymphatic system, lymph contains immune system cells that protect the body against pathogens.
Epithelial tissue Epithelial tissue is a sheet of cells that covers a body surface or lines a body cavity. Two forms occur in the human body:
1. Covering and lining epithelium-forms the outer layer of the skin; lines open cavities of the digestive and respiratory systems; covers the walls of organs of the closed ventral body cavity.
2. Glandular epithelium-surrounds glands within the body.
Characteristics of epithelium
Epithelial tissues have five main characteristics these are:
1. Polarity-all epithelia have an apical surface and a lower attached basal surface that differ in structure and function. For this reason, epithelia is described as exhibiting apical basal polarity. Most apical surfaces have microvilli (small extensions of the plasma membrane) that increase surface area. For instance, in epithelia that absorb or secrete substances, the microvilli are extremely dense giving the cells a fuzzy appearance called a brush border. Examples of this would include epithelia lining the intestine and kidney tubules. Other epithelia have motile cilia (hair like projections) that push substances along their free surface. Next to the basal surface is the basal lamina (thin supporting sheet). The basal lamina acts as a filter allowing and inhibiting certain molecules from passing into the epithelium.
2. Specialized contacts-epithelial cells fit close together and form continuous sheets (except in the case of glandular epithelia). They do this with tight junctions and desmosomes. Tight junctions form the closest contact between cells and help keep proteins in the apical region of the plasma membrane. Desmosomes connect the plasma membrane to intermediate filaments in the cytoplasm.
3. Supported by connective tissue-all epithelia are supported by connective tissue. For instance, deep to the basal lamina is reticular lamina (extracellular material containing collagen protein fibre) which forms the basement membrane. The basement membrane reinforces the epithelium and helps it resist stretching and tearing.
4. Avascular and innervated-even though epithelium is avascular (contains no blood vessels), it’s still innervated (supplied by nerve fibres).
5. Regeneration-epithelium have a high regenerative capacity and can reproduce rapidly as long as they receive adequate nutrition.
Classification of Epithelia Epithelium has two names. The first name indicates the number of cell layers, the second describes the shape of its cell. Based on the number of cell layers, epithelia can either be simple or stratified.
• Simple epithelia-consist of a single cell layer (found where absorption, secretion, and filtration occur).
• Stratified epithelia-are composed of two or more cell layers stacked on top of each other (typically found in high abrasion areas where protection is needed).
There are three ways to describe the shape and height of epithelial cells these are:
- squamous cells which are flat and scale-like
- cuboidal cells which are box like but the same height and width
- and there are also columnar cells which are tall and column shaped
Nervous tissue
Nervous tissue is found in the brain, spinal cord, and nerves.
It is responsible for coordinating and controlling many body activities. It stimulates muscle contraction, creates an awareness of the environment, and plays a major role in emotions, memory, and reasoning. To do all these things, cells in nervous tissue need to be able to communicate with each other by way of electrical nerve impulses. The cells in nervous tissue that generate and conduct impulses are called neurons or nerve cells. These cells have three principal parts: the dendrites, the cell body, and one axon. The main part of the cell, the part that carries on the general functions, is the cell body. Dendrites are extensions, or processes, of the cytoplasm that carry impulses to the cell body. An extension or process called an axon carries impulses away from the cell …show more content…
body.
Nervous tissue also includes cells that do not transmit impulses, but instead support the activities of the neurons. These are the glial cells (neuroglial cells), together termed the neuroglia. Supporting, or glia, cells bind neurons together and insulate the neurons. Some are phagocytic and protect against bacterial invasion, while others provide nutrients by binding blood vessels to the neurons.
Nervous tissue is composed of neurons, also called nerve cells, and neuroglial. Typically, nervous tissue is categorized into four types of tissue. In the central nervous system (CNS), the tissue types found are grey and white matter. In the peripheral nervous system (PNS), the tissue types are nerves and ganglia. The tissue is categorized by its neuronal and neuroglial components.
Neurons are cells with specialized features that allow them to receive and facilitate nerve impulses, or action potentials, across their membrane to the next neuron. They possess a large cell body (soma), with cell projections called dendrites and an axon. Dendrites are thin, branching projections that receive electrochemical signalling (neurotransmitters) to create a change in voltage in the cell. Axons are long projections that carry the action potential away from the cell body toward the next neuron. The bulb-like end of the axon, called the axon terminal, is separated from the dendrite of the following neuron by a small gap called a synapse. When the action potential travels to the axon terminal, neurotransmitters are released across the synapse and bind to the post-synaptic receptors, continuing the nerve impulse.
Neurons are classified both functionally and structurally.
Functional classification:
• Sensory neurons (afferent): Relay sensory information in the form of an action potential (nerve impulse) from the PNS to the CNS
• Motor neurons (efferent): Relay an action potential out of the CNS to the proper effector (muscles, glands)
• Interneurons: Cells that form connections between neurons and whose processes are limited to a single local area in the brain or spinal cord
Structural classification:
• Multipolar neurons: Have 3 or more processes coming off the soma (cell body).
They are the major neuron type in the CNS and include interneurons and motor neurons.
• Bipolar neurons: Sensory neurons that have two processes coming off the soma, one dendrite and one axon
• Pseudo unipolar neurons: Sensory neurons that have one process that splits into two branches, forming the axon and dendrite
• Unipolar brush cells: Are excitatory glutamatergic interneurons that have a single short dendrite terminating in a brush-like tuft of dendrioles. These are found in the granular layer of the cerebellum.
Neuroglia encompasses the non-neural cells in nervous tissue that provide various crucial supportive functions for neurons. They are smaller than neurons, and vary in structure according to their
function.
Neuroglial cells are classified as follows:
• Microglial cells: Microglia are macrophage cells that make up the primary immune system for the CNS. They are the smallest neuroglial cell.
• Astrocytes: Star-shaped macro glial cells with many processes found in the CNS. They are the most abundant cell type in the brain, and are intrinsic to a healthy CNS.
• Oligodendrocytes: CNS cells with very few processes. They form myelin on the axons of a neuron, which are lipid-based insulation that increases the speed at which the action potential, can travel down the axon.
• NG2 glia: CNS cells that are distinct from astrocytes, oligodendrocytes, and microglia, and serve as the developmental precursors of oligodendrocytes.
• Schwann cells: The PNS equivalent of oligodendrocytes, they help maintain axons and form myelin sheaths in the PNS.
• Satellite glial cell: Line the surface of neuron cell bodies in
• Ganglia (groups of nerve body cells bundled or connected together in the PNS).
• Enteric glia: Found in the enteric nervous system, within the gastrointestinal tract.