Anatomy and Morphology of Animal Tissues

Introduction

A human body contains trillions of cells, and are the fundamental units of living organisms that give structure to the body. Cells communicate with each other through cell-cell adhesion or via extracellular matrix through cell adhesion molecules. A group of cells specialised in one or more similar functions is termed tissue. They form organs like skin, kidney, lungs, liver, and heart and an organ system comprises two or more organs that have the same functions. These all share their work and contribute to the survival of the entire body.

What are the different Types of Animal Tissue?

The animal tissues differ in their origin, structure, and functions and these are grouped into four types:

• Muscular tissues

• Nervous tissues

• Epithelial tissues

• Connective tissues

How are different Tissues derived?

All types of tissues are derived from three different germ layers. These germ layers are initially formed during embryonic development.

• Ectoderm (outer layer) develops into the epidermis and nervous system.

• Mesoderm (middle layer) develops into connective tissue and lines the cavities of the body.

• Endoderm (inner layer) develops into several internal organs such as the liver, pancreas, and lining the digestive tract, respiratory system, and reproductive system.

Images Coming soon

What is an Epithelial Tissue?

Epithelial tissue or epithelium covers and lines all the inner and outer surfaces of the body. The cells are closely packed together forming single or multi layers.

Type of Epithelial Tissues and Their Function

Types	Location	Function
Simple squamous	Blood vessels, capillary walls, air sacs, linings of lymph	Transport the selective material to pass through osmosis, diffusion, filtration, and absorption
Simple cuboidal	Lining of ducts, tubular linings of kidneys, surfaces of ovary	Absorption and secretion
Simple columnar	Linings of the respiratory tract, digestive tract and uterus	Mucous secretion, absorption and protection
Transitional epithelium	Inner linings of the ureter, urethra and urinary bladder	Prevent reabsorption of toxic materials
Pseudostratified columnar	Linings of respiratory passage	Secretion, movement of mucous and protection
Stratified squamous	Throat, linings of the mouth, vagina, and the outer surface of skin	Protection
Stratified cuboidal	Salivary glands, mammary glands, pancreas and sweat glands	Protection
Stratified columnar	Parts of the pharynx and male urethra	Secretion and protection

Characteristics of Epithelial Tissues

• Cells are compactly packed together without intercellular spaces between them and form a sheet.

• The cells are linked by gap junctions, tight junctions, and adherens junctions.

• These are non-vascular, that is the lack of blood supply, however, innervated (supply nerves to organs or parts of the body).

• The tissue has a high rate of regeneration.

• These do not have their blood supply, however, they get nourished by substances diffusing from the blood vessels of underlying tissues.

• The epithelial tissues are attached to connective tissues at basal surfaces forming basal membranes.

What is Muscular tissue?

These tissues are comparatively longer that possess the contractile ability to produce motion. These tissues are highly vascularized.

Types	Location	Function
Cardiac muscle	Heart	Continuous blood pumping
Skeletal muscle	Skeletal bone	Movement
Smooth muscle	Eyes, uterus, blood vessels, and digestive tract	Maintain blood flow and blood pressure

Characteristics of Muscular Tissues

• Muscular tissues respond to stimuli by contracting and producing motion.

• They can be stretched beyond their normal length.

• These tissues can return to their normal length after stretching, thus elastic in nature.

• They are adaptable to their environment.

What are Connective Tissues?

Connective tissue is a basic tissue that connects and supports the other tissues or organs of the body. These tissues can store fat and help the transportation of nutrients and other substances among the tissues and organs through diffusion.

What are the components of Connective Tissues?

The connective tissue is made up of cells and the extracellular matrix.

• The cells include mast cells, macrophages, plasma cells, adipocytes, chondrocytes, fibroblasts, osteoblasts, and osteocytes.

• The tissue fibre and ground substance are collectively called the extracellular matrix. The fibres include collagen, elastic, reticular, and fibrillin and the ground substances like glycoproteins, glycosaminoglycans, and proteoglycans.

Are Adipose tissues the same as Bones?

Adipose tissue is a special form of connective tissue that is generally composed of fat cells called adipocytes. These act as cushions for internal organs and insulate the body with the presence of fat. Bones are connective tissue and they have rich calcium and collagen, therefore they support the joints to form a skeletal structure of the body. However, the bone marrow adipose tissue in the bone marrow has fat deposition, which stimulates homeostasis and regeneration.

Types and Functions of Connective Tissues

Types	Location	Function
Loose connective tissues	Areolar and adipose	Binding of tissues, organs and movement
Dense connective tissues	Tendon and ligament	Provides a stable connection between tissues
Supportive connective tissues	Bone and cartilage	Absorb shock, provides shape, support and flexibility at the joints
Fluid connective tissues	Blood and lymph	Blood-Transportation of oxygen, blood clotting, invading germs Lymph- Carrier for nutrients and hormones, fight against infection.

What are Nervous tissues?

The central nervous system (CNS) and peripheral nervous system (PNS) are made up of nervous tissues. The neural or nervous tissue is responsible for controlling and coordinating the various activities in the body by transmitting nerve impulses. These are present in the spinal cord, the brain, and nerves that stimulate muscle contraction, and control emotions, memory, and reasoning.

Classification of Nervous tissues

Nervous tissue comprises neurons and neuroglial cells that support the nervous system by producing electrical signals called an action potential.

Neurons

Axon, dendrites, and cell bodies make up a neuron, and they are responsible for transmitting and receiving signals throughout the body.

Neurons are classified into the following types based on their structures:

• Bipolar neurons have two extensions including an axon and a dendrite.

• Unipolar neurons have only a single extension from the body (one axon).

• Multipolar neurons have one axon and many dendrites.

Neurons are classified into the following types based on their functions

• Sensory neurons are unipolar, and have short axons and long dendrites. It carries action potential from the sensory receptor to the direction of the CNS and brain, therefore they are also known as afferent neurons.

• Motor neurons are multipolar, that carry the action potential out of the CNS to cause muscle movement, therefore they are known as efferent neurons.

• Associated neurons are also multipolar, connecting the sensory and motor neurons that assist the brain learning, decision-making and regeneration of new neurons. They are also called interneurons.

Neuroglial cells

It is responsible for supporting and maintaining the nervous system. They are classified into the following types:

• Astrocytes control blood flow and the blood-brain barrier.

• Ependymal cells maintain brain metabolism, remove wastes from the brain, and involve cerebrospinal fluid homeostasis.

• Microglial cells defend against inflammation and infection in the brain.

• Oligodendrocytes produce myelin sheath on the axons of neurons.

Conclusion

A group of cells with similar functions are tissues and the animal tissues are classified based on their structure and function. Epithelial tissues are located on the upper surfaces of the skin, these have tightly packed cells with intercellular material. Squamous, cuboidal, columnar, stratified, transitional, and pseudostratified types of tissues come under epithelial tissues. Muscle tissues can contract the muscles to perform particular functions in the heart, skeleton, blood vessels, eyes, and digestive tract. Connective tissues support the arrangement of organs to facilitate the proper structure and function of internal organs of the body. It includes bone, cartilage, blood, lymph, tendon, ligament, areolar and adipose tissues. Nervous tissue comprises neurons and neuroglial cells that are situated in the brain and spinal cord to control the CNS and PNS.

FAQs

1. What are the types of epithelial tissues?

There are various epithelial tissues including the simple squamous, cuboidal, columnar, pseudostratified, stratified squamous, cuboidal, columnar, and transitional epithelium.

2. How is epithelial tissue developed?

The epithelial tissue is developed from the embryonic layers including ectoderm, endoderm, and mesoderm.

3. Which type of epithelial tissue is located in the respiratory passage?

The pseudostratified columnar epithelium is located in the respiratory passage to secrete and transport the mucous and protect the respiratory system.

4. What is the function of transitional epithelium?

Transitional epithelium is situated in the urinary bladder, urethra, and ureter to prevent the reabsorption of toxic substances.

5. How do epithelial cells protect the body?

The epithelial cells or tissues act as a barrier to protect the body by preventing the entry of microbes and dirt from the external environment.

References

Animal Tissues - Epithelium, Connective Tissues - PMF IAS. PMF IAS. (2022). Retrieved 30 May 2022, from https://www.pmfias.com

Difference Between Neurons and Neuroglia | Definition, Characteristics, Types, Function. Pediaa.Com. (2022). Retrieved 30 May 2022, from https://pediaa.com

Molnar, C., & Gair, J. (2022). 14.2 Animal Primary Tissues. Opentextbc.ca. Retrieved 30 May 2022, from https://opentextbc.ca

Images Coming soon