Tissue

Tissue Tissue is a cellular organizational level intermediate between cells and a complete organism. The study of tissue is known as histology or, in connection with disease, histopathology. Based on morphology, tissues can be grouped into four basic types.

A. Epithelium Epithelium lines both the outside (skin) and the inside cavities and lumen of bodies such as the skin, the airways, and the digestive tract. Many glands are also formed from epithelial tissue. It serves functions of protection, secretion, and absorption, and is separated from other tissues.

Classification Epithelial cells are classified as:

Squamous: All Squamous cells are flat cells with

an irregular shape. A one-cell layer of simple squamous epithelium forms the alveoli of the respiratory membrane, and the endothelium of capillaries. These cells are associated with the diffusion of water, electrolytes, and other substances.

Cuboidal:

As the name suggests, these cells have a shape similar to a cube, meaning its width is the same size as its height. The nuclei of these cells are usually located in the center. The cuboidal epithelium forms the smallest duct glands and many kidney tubules.

Columnar:

These cells are taller than they are wide. Simple columnar epithelium is made up of a single layer of cells that are longer than they are wide. The nucleus is also closer to the base of the cell. The small intestine is a tubular organ lined with this type of tissue. Unicellular glands called goblet cells are scattered throughout the simple columnar epithelial cells and secrete mucus. The free surface of the columnar cell has tiny hairlike projections called microvilli. They increase the surface area for absorption.

Transitional:

This is a specialized type of epithelium found lining organs that can stretch, such as the urothelium that lines the bladder and ureter of mammals. Since the cells can slide over each other, the appearance of this epithelium depends on whether the organ is distended or contracted: if distended, it appears as if there are only a few layers; when contracted, it appears as if there are several layers.

Stratification: Simple: There is a single layer of cells.

Stratified:

More than one layer of cells. The superficial layer is used to classify the layer. Only one layer touches the basal lamina. Stratified cells can usually withstand large amounts of stress.

Pseudostratified: There

is only a single layer of cells, with each cell touching the basal lamina directly. However, without careful observation, the location of the nuclei within the cells may give the impression that the epithelium is stratified. For example, the epithelium lining the bronchi in mammals is pseudostratified epithelium.

Specializations 1.

2.

Keratinized:

Cells contain keratin (a cytoskeletal protein). While keratinized epithelium occurs mainly in the skin. Ciliated: Additionally, the structure of the cilia found on ciliated epithelial cells.

The outermost layer of our skin is composed of dead stratified squamous, keratinized epithelial cells. Tissue that line the inside of the mouth, the esophagus, and part of the rectum are composed of nonkeratinized stratified squamous epithelium. Other sufaces that separate body cavities from the outside environment are lined by simple squamous, columnar, or pseudostatified epithelial cells.

Secretory epithelia There are two major classification of glands: endocrine glands and exocrine glands. Endocrine glands are glands that secrete their product directly onto a surface rather than through a duct. This group contains the glands of the Endocrine system

B. Connective tissue Connective tissue is comprised of cells separated by non-living material, which is called extracellular matrix. Connective tissue holds other tissues together such as in the formation of organs, and has the ability to stretch and contract passively. Bone and blood are examples of specialized connective tissues. 1.Involved in structure and support. 2.Derived from mesoderm, usually. 3.Characterized largely by the traits of nonliving tissue.

4.

Collagen is the main protein of connective tissue.

Classification The old classification system for connective tissue is proper versus specilized. There has been a new classifications system proposed, however, and it is as follows: Loose connective tissue 1.

Areolar

2.

Adipose

3.

Reticular

3.

Elastic

3.

Elastic

Dense connective tissue 1.

Regular

2.

Irregular

Cartilage 1.

Hyaline

2.

Fibrocartila ge

Other 1. 2.

Bone Blood

3.

Lymphatics

Connective tissue proper

Specialized connective tissues

Specialized connective tissues •

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Blood functions in transport. Its extracellular matrix is blood plasma, which transports dissolved nutrients, hormones, and carbon dioxide in the form of bicarbonate. The main cellular component is red blood cells. Bone makes up virtually the entire skeleton in adult vertebrates. Cartilage makes up virtually the entire skeleton in chondrichthyes. In most other vertebrates, it is found primarily in joints, where it provides cushioning. The extracellular matrix of cartilage is composed primarily of collagen. Adipose tissue contains adipocytes, used for cushioning, thermal insulation, lubrication (primarily in the pericardium) and energy storage. Reticular connective tissue is a network of reticular fibres (fine collagen, type III) that form a soft skeleton to support the lymphoid organs (lymph nodes, bone marrow, and spleen.)

Fiber types Fiber types as follows: •

Collagenous Fibers

• •

Elastic Fibers Reticular Fibers

C. Muscle Muscle cells form the active contractile tissue of the body known as muscle tissue. Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle tissue is separated into three distinct categories: 1. 2. 3.

visceral or smooth muscle: which is found in the inner linings of organs; skeletal muscle: which is found attached to bone providing for gross movement and cardiac muscle: which is found in the heart, allowing it to contract and pump blood throughout an organism.

Classification: There are three types of muscle. •

Skeletal muscle or "voluntary muscle" is anchored by tendons to bone and is used to affect skeletal movement such as locomotion and in maintaining posture. An average adult male is made up of 40–50% of skeletal muscle and an average adult

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female is made up of 30–40% (as a percentage of body mass). Smooth muscle or "involuntary muscle" is found within the walls of organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels. Unlike skeletal muscle, smooth muscle is not under conscious control. Cardiac muscle is also an "involuntary muscle" but is more akin in structure to skeletal muscle, and is found only in the

Skeletal Muscle

Smooth Muscles

Cardiac Muscles

heart.

D. Nervous tissue Cells comprising the central nervous system and peripheral nervous system are classified as neural tissue. In the central nervous system, neural tissue forms the brain, cranial nerves and spinal cord and, in the peripheral nervous

system, peripheral nerves inclusive of the motor neurons.

Structure of a Motor Neuron A motor neuron has many processes (cytoplasmic extensions), called dendrites, which enter a large, grey cell body at one end. A single process, the axon, leaves at the other end, extending towards the dendrites of the next neuron or to form a motor endplate in a muscle. Dendrites are usually short and divided while the axons are very long and does not branch freely.

Classification On the basis of their structure, neurons can also be classified into three main types: 1.Unipolar Neurons Sensory neurons have only a single process or fibre which divides close to the cell body into two main branches (axon and dendrite). Because of their structure they are often referred to as unipolar neurons. 2.Multipolar Neurons Motor neurons, which have numerous cell processes (an axon and many dendrites) are often referred to as multipolar neurons. Interneurons are also multipolar. 3.Bipolar Neurons

Bipolar neurons are spindle-shaped, with a dendrite at one end and an axon at the other . An example can be found in the light-sensitive retina of the eye.

Examples System circulatory digestive digestive digestive digestive

Tissue Epithelium Subtype blood vessels Simple squamouis endothelium ducts of submandibular Stratified columnar glands Stratified squamous, attached gingiva keratinized Stratified squamous, dorsum of tongue keratinized Stratified squamous, hard palate keratinized

digestive digestive digestive digestive digestive digestive digestive endocrine nervous lymphatic integumentary integumentary integumentary reproductive female reproductive female reproductive female reproductive female reproductive female reproductive female reproductive female reproductive female

Stratified squamous, nonkeratinised Simple columnar, nonstomach ciliated Simple columnar, non- intestinal small intestine ciliated epithelium Simple columnar, non- intestinal large intestine ciliated epithelium Stratified squamous, nonrectum keratinised Stratified squamous, anus keratinised Simple columnar, nongallbladder ciliated thyroid follicles Simple cuboidal ependyma Simple cuboidal lymph vessel Simple squamous endothelium skin - dead superficial Stratified squamous, layer keratinized sweat gland ducts Stratified cuboidal mesothelium of body Simple squamous mesothelium cavities germinal ovaries Simple cuboidal epithelium (female) Fallopian tubes Simple columnar, ciliated oesophagus

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uterus

Simple columnar, ciliated -

endometrium

Simple columnar

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cervix (endocervix)

Simple columnar

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cervix (ectocervix) vagina labia majora

reproductive - male tubuli recti reproductive - male rete testis reproductive - male ductuli efferentes reproductive - male epididymis

Stratified squamous, nonkeratinised Stratified squamous, nonkeratinised Stratified squamous, keratinised germinal Simple cuboidal epithelium (male) Simple cuboidal Pseudostratified columnar Pseudostratified -

reproductive - male vas deferens reproductive - male ejaculatory duct reproductive - male bulbourethral glands (gland) reproductive - male seminal vesicle (gland) respiratory respiratory respiratory respiratory respiratory sensory sensory urinary urinary urinary urinary urinary urinary urinary urinary urinary urinary urinary

columnar, with stereocilia Pseudostratified columnar Simple columnar Simple columnar

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Pseudostratified columnar -

Stratified squamous, nonkeratinised Pseudostratified respiratory larynx columnar, ciliated epithelium larynx - True Vocal Stratified squamous, nonCords keratinised Pseudostratified respiratory trachea columnar, ciliated epithelium respiratory bronchioles Simple cuboidal Stratified squamous, noncornea corneal epithelium keratinised olfactory nose Pseudostratified columnar epithelium kidney - proximal Simple columnar, ciliated convoluted tubule kidney - ascending thin Simple squamous limb kidney distal Simple columnar, nonconvoluted tubule ciliated kidney - collecting Simple cuboidal duct renal pelvis Transitional urothelium ureter Transitional urothelium urinary bladder Transitional urothelium prostatic urethra Transitional urothelium Pseudstratified columnar, membranous urethra non-ciliated Pseudostratified penile urethra columnar, non-ciliated external urethral Stratified squamous orifice oropharynx