Written by Elijah Dave M. Cordova

Histology is a fascinating field of study. It helps you understand how normal tissues appear. It teaches you how they function. It helps confirm the presence of several diseases. Histology allows you to trace the causes of diseases. It can also teach you how to treat them.

The term “histology” comes from two Greek words. “Histos” means tissue, and “-logos” is a field of study. Hence, it deals with the study of the tissues in the body. It studies how they constitute the different body organs. It focuses on how cells’ order and structure optimize the organs’ functions.

Recall the different levels of organization in organisms.

• Cells are the most basic structures that constitute life.
• Tissues comprise cells similar in function and form. They work together to perform the same functions.
• Organs are tissues that work together to do specific activities.
• Organ systems are many organs that work together to perform needed roles. These functions benefit the organism in normal conditions.

The interconnectedness of histology to other study fields is obvious here. Among these fields are the following:

• Biology
• Medicine
• Genetics
• Immunology

Histology grants a microlevel perspective on these subjects and more. Many students who prefer more generalized and applicable studies might find it boring. Yet, without it, these other studies would fail to make sense.

Through this article, you will get to learn more about histology. You will discover its main goals and concepts. You will appreciate its relationship with other fields in medicine. Moreover, you will realize the privilege that is the chance to learn this subject.

What are the basic concepts of histology?

Now that you know its importance, you might wonder how to start studying histology. It begins by learning what makes up tissues. Next, you will learn how to prepare tissue sections for examination. What follows is a discussion on the different microscopes you can use.

Cells and the extracellular matrix (ECM) make up tissues. Several macromolecules form the ECM. Among them are collagen fibrils which are the building blocks of tendons.

The ECM aids the cell and contains the fluid that serves three purposes.

1. It transports nutrients to the cells;
2. It provides mechanical support for the cells; and
3. It transports cell wastes and other secretory products.

Cells produce ECM components. These components, in turn, influence cells. This relationship causes intense interactions between these two components. These interactions create different types of tissues, each having unique features.

The minute size of the cells and ECM elicits the need for microscopes. Hence, the most common procedure in histology is the preparation of tissue sections. These are thin and translucent organ slices. The basic steps to prepare tissues for examination under light microscopy are here:

1. Fixation is placing tissue sections in fixatives. These are solutions with cross-link proteins that inactivate degradative enzymes. Hence, they preserve the tissue structures.

A buffered isotonic solution of 37% formaldehyde is a usual light microscopy fixative. Meanwhile, glutaraldehyde is a prevalent electron microscope fixative.

2. Dehydration is placing the sections through increasing concentrations of alcohol solutions. The final solution is 100% alcohol.

3. Clearing is removing the alcohol in the samples through organic solvents. These solvents are miscible in alcohol and embedding mediums. Common embedding mediums are paraffin and xylene.

4. Infiltration is placing the sample in melted paraffin. You perform this at 52°- 60°C.

5. Embedding is placing the paraffin-infiltrated tissue in a mold. It allows your samples to harden. It is often done at room temperature.

6. Trimming is slicing or sectioning the hardened sample. It does this through an instrument called a microtome. This microtome creates 3-10 μm thick tissue sections for light microscopy.

7. Staining (dyeing) makes tissues distinguishable from one another. Its necessity is due to most cells and ECM components being colorless.

Cell components with an anionic (negative) charge react well with basic dyes or stains. These components are basophilic. Examples include DNA and RNA.

Cationic (positive) substances react with acidic dyes. These substances are acidophilic. Examples are collagen and several cytoplasmic proteins.

Hematoxylin and eosin (H&E) are the most common staining dyes. The former is a basic dye, and the latter is acidic.

8. Mounting a glass coverslip on the slide is the last step. The coverslip must have a clear adhesive.

Slide preparation (steps 1 through 8) takes around 12 hours to 2½ days. Its duration depends on tissue size, staining method, and embedding medium.

There are two types of microscopes you can use in histology. They are as follows:

1. Light microscopy uses the interaction of light with tissue components.
   1. Bright-field microscopy identifies tissues through colors caused by staining. Students and pathologists use this the most.
   2. Fluorescence microscopy uses UV light to visualize fluorescent molecules alone. It allows fluorescent probe localization that is more specific than routine stains.
   3. Phase-contrast microscopy produces stain-less images. Hence, it allows you to observe living cells. It does this through refractive index differences among tissue components.
   4. Confocal microscopy scans samples at successive focal planes to generate images. It often uses a laser. Confocal microscopy produces a 3D reconstruction with the image.
2. Electron microscopy uses the interaction of electron beams with tissue components.
   1. Transmission electron microscopy (TEM) permits resolutions around 3 nm. It allows up to 400,000x magnification. You can add compounds with heavy metal ions to the fixatives here to improve resolution. You can also perform cryofracture and freeze etching. Here, you freeze the specimen in liquid nitrogen before cutting it.
   2. Scanning electron microscopy (SEM) produces black-and-white images. It presents a 3D view of the specimen.

Other ways of studying histology samples are the following:

1. Autoradiography uses radioactive precursors to localized synthesized cell components.
2. Cell and tissue culture is growing cells in vitro. You will often use the phase-contrast microscope here.
3. Enzyme histochemistry (cytochemistry) uses specific enzyme activities in samples. It yields visible products in specific enzyme locations. You will often use a cryostat here.
4. Immunohistochemistry visualizes specific molecules in samples. It uses antigen-antibody reactions with visible markers.
5. Hybridization techniques localize DNA sequences on chromosomes. They also detect specific RNA targets in cells. In situ hybridization (ISH) is a common hybridization technique.

What are the four types of tissue? Describe each.

You now know the basic concepts in histology. You may next wonder what kinds of tissues there are in our bodies. The epithelium and connective tissue are among them. The muscle and nervous tissues complete this list.

The epithelial cells (epithelium) have the following functions:

1. Absorption. It includes the gut (intestinal lining) and the stomach.
2. Filtration. An example is a kidney.
3. Protection. It involves the skin that protects us from the outside world.
4. Secretion. It includes the different glands in our bodies.

They have the following characteristics:

1. A free (apical) surface open to outside the body. It can also be in internal organ cavities in the body.
2. A fixed (basal) area connected to underlying connective tissue
3. Can have several nerves in them (innervated)
4. Excellent regeneration as seen in sunburn
5. Forms a protective barrier through close attachment to each other
6. No blood vessels

They, too, have the following classifications:

1. By cell arrangement.

a. Simple. They are single-cell layers often used for absorption and filtration.

b. Stratified. They have several layers often used for protection.

2. By shape.

a. Columnar. These are column-shaped and tall.

b. Cuboidal. These take the form of a cube.

c. Squamous. These are scale-like and flat.

Meanwhile, connective tissues have the following functions, elements, and classifications.

A. Functions

1. Cushioning and internal support for organs.

2. Protects and attaches body parts. Examples include tendons and ligaments.

3. Stores nutrients.

4. Strengthens the skin.

2. Elements

1. Cells.

2. Fibers provide elasticity, support, and strength.

3. Ground substance is a gel around the cells and fibers.

Classifications

1. Loose connective.
   1. Adipose. These have blood vessels and cells. They also store nutrients.
   2. Areolar connective. These are a loose arrangement of cells and fibers. They provide cushions to organs
   3. Reticular connective. These are delicate fiber-cell networks. They provide internal support to organs.
2. Dense connective

Dense regular connective. These include tendons and ligaments. They often have fibers and provide strength.

Dense irregular connective. These include the skin and organ capsules. They often have fibers going in all directions.

Next are the jobs and elements of nervous tissues.

A. Functions

1. Conducts impulses to and from organs through neurons.

B. Elements

1.Brain.

2.Nerves.

3.Spinal cord.

Last are the jobs and types of muscle tissues.

A. Functions

1. In charge of body movement.

2. Transports waste, food, and blood through the body organs.

3. Responsible for mechanical digestion.

Types

1. Cardiac muscle. It is the muscles that make up the heart. These muscles are involuntary and striated. They have intercalated discs that cause synchronous heart contractions.

2. Skeletal muscle. It includes all the body muscles. They are voluntary and striated. They connect to bones to aid movement. They, too, come in bundles.

3. Smooth muscle. It includes all blood vessels and organ walls. These muscles are involuntary and spindle-shaped. They push materials through organs.

What is the difference between histology and biopsy?

You now know the basic types of tissues. Let us now discuss the terms associated with histology. The first is a biopsy. A biopsy is a procedure of taking small tissue samples. It also refers to the tissue sample itself. Meanwhile, histology is a study field that uses biopsies in diagnosing diseases.

Biopsies often diagnose or rule out the following diseases:

1. Cancer.
2. Peptic ulcers.
3. Hepatitis.
4. Kidney diseases.

Also, among the types of biopsies are as follows:

1. Endoscopic biopsy. You can use it during an endoscopy which visualizes the upper GI tract. It uses an endoscope to remove tissues.

2. Excisional biopsy. You can use this in surgery to remove larger tissue sections.

3. Needle biopsy. It uses a hollow needle to get organ or skin tissue sections.

What is the difference between histology and pathology?

Next to a biopsy is pathology. Pathology is a branch in the field of medicine. It studies the nature and causes of diseases. It, too, investigates their development and effects. Histology has roots in biology. It involves the small tissue structures and their composition.

Histology can benefit the study of pathology. It helps explain how and why certain diseases afflict humans. Pathology can also benefit histology. Its study provides applications of what histologists identify under their microscopes.

What is the difference between biopsy and histopathology?

Last is the term histopathology. It combines histology and pathology. Histology studies tissues, and pathology studies diseases. Hence, histopathology studies tissues related to disease. A biopsy is the removal of tissue samples for clinical examination. It also refers to the actual tissue samples.

Biopsies are crucial to the field of histopathology. They help in diagnosing diseases from tissue samples.

Why should I study histology?

Histology is interesting. It allows you to see and appreciate the world in a different way. It gives you a thorough understanding of the microstructures that make you, you. Histology also sits at the crossroads of anatomy, pathology, and physiology.

Aside from this, there are other applications for histology:

1. Autopsies. Studying tissues from a deceased human or animal can help determine the cause of death.

2. Forensic investigations. Tissue sample studies can clarify several forensic issues. Hence, they can help solve crimes.

3. Veterinary diagnosis. Animal samples can suggest ways to treat and manage their conditions.

REFERENCES:

Ali, R. (n.d.). Introduction to Basic Histology. UO Babylon. Retrieved February 20, 2022 from uobabylon

Brown,    R.    (2021).    What    is    a    biopsy?    Rcpath.org.    pathology/news/fact-sheets/what-is-a-biopsy.html#:~:text=Histopathologists%20examine%20biopsies%20(tissue%20or,more% 20detail%20under%20the%20microscope.

Exploring Nature. (n.d.). from exploring nature. The 4 Basic Tissue Types in the Human Body

Histology vs. Pathology – What’s the difference? | Ask Difference. (2018). Askdifference.com.

Introduction to Histology – Applications & Importance – Anatomy Notes. (2020, January 14). Anatomy Notes. https://anatomynotes.org/histology/introduction-to-histology- applications-importance/

Mescher, A. (2018). Junqueira’s basic histology : text and atlas (15th ed.). Mcgraw Hill Education.

Thompson, V. (2014). Why Is the Study of Histology Important in Your Overall Understanding of Anatomy & Physiology? Education – Seattle PI. https://education.seattlepi.com/study- histology-important-overall-understanding-anatomy-physiology-5337.html

Written by Kheizaya Methuzela G. Aguirre

Histology includes studying tissues and cells under a microscope. Histologists perform this to diagnose and research disorders of the tissues. They make tissue diagnostics and assist doctors in patient care management.

People study histology to:

• Examine the contents of the tissue.
• In agriculture, they seek what chemicals are present in the soil.
• Perform autopsies in this field. It is to comprehend better some inexplicable deaths during autopsy and forensic investigations. Microscopic tissue analysis may reveal a cause of death in some circumstances.

Why is it called histology?

Histology is a study that deals with cell and tissue structure at the microscopic level.

Its name comes from the Greek term “histos,” which means tissue or columns. The other is “logia,” which refers to “study.”

Histology first appeared in a book written by Karl Meyer in 1819. It was where he combined the two Greek words. And it was then traced back to the 17th century by Marcello Malpighi.

He experimented with insects, botany, and embryology as a scientist. He was the first to use the silkworm as a model to study insect respiration.

He also further investigated the development of chick embryos than anybody else. His experiments are what made him a pioneer in the science of embryology.

But it was his delineation of pulmonary capillaries and alveoli that made him famous. Using only a single magnifying lens, Malpighi saw pulmonary capillaries in the frog.

He termed these capillaries as “nature’s microscope.” It allowed him to see things that are not present in big animals.

Although he uses these single lenses in most of his findings, he also utilized a new microscope. This new type is the compound microscope, which arose at the end of the 16th century. It allowed him to see chick embryo development.

Here are some human body structures named after Malpighi:

1. Malpighian corpuscles
2. Malpighian layer in the skin
3. Malpighian tubules of the insect’s excretory system

How is tissue classified?

Tissues refer to a collection of cells with similar structures and play a specific role. Histology focuses on tissues’ appearance, structure, and function under a microscope.

Below are the classifications of tissues based on their structural and functional similarity:

• Epithelium
• Connective
• Muscular
• Neurological systems

The fundamental tissue collaborates to assist the human body’s general health and maintenance. As a result, any change in tissue structure might result in harm or illness.

Epithelial tissue is the body’s outer cover, lines interior cavities, and forms glands. As its name indicates, connective tissue ties the body’s cells and organs together.

When the body stimulates muscle tissue, it contracts, allowing mobility. Nervous tissue is also reactive. It enables electrochemical signals to generate and propagate into nerve impulses. When this happens, it communicates to the different parts of the body.

What are examples of tissues?

In histology, we all know that there are four types of tissues:

• Epithelial
• Connective
• Muscle
• Nervous

• Each of these tissues has examples of their structure and biological function. Under the epithelial tissue, you have the following:

• Simple Squamous
• Simple Cuboidal
• Simple Columnar
• Transitional
• Stratified Squamous
• Stratified Cuboidal
• Stratified Columnar
• Pseudostratified Columnar

The simple squamous allows items to flow through diffusion and filtration. It also emits lubricating substances. It resides on the lining of the heart, blood vessels, and lymphatic vessels, as well as the air sacs of the lungs.

Simple cuboidal epithelium ingests and secretes. It is in ducts and secretory parts of tiny glands and kidney tubules.

Simple columnar consumes and releases mucus and enzymes. They are on ciliated tissues like lungs, uterine tubes, and uterus. The digestive tract bladder also contains smooth (nonciliated tissues).

Transitional epithelium allows for the expansion and stretching of the urinary organs. The bladder, urethra, and ureters are all lined with it.

Stratified squamous epithelial tissue is the skin protector against abrasion. The esophagus, mouth, and vaginal canal are all lined with this substance.

Stratified cuboidal is present in sweat, salivary, and mammary glands. All these mentioned glands have a protective epithelial layer.

The stratified columnar epithelium is an uncommon kind of epithelial tissue. It has quite a few layers of column-shaped cells. The conjunctiva, throat, anus, and male urethra are some places where it situates. It also occupies the embryo.

Pseudostratified columnar epithelia are tissues that constitute a single layer of cells. But, they appear to look like they are of many layers when seen in cross-section. These epithelial cells’ nuclei are at various levels, giving the appearance of stratification.

• Connective tissue is another type of tissue that functions as a linking role in the body. It works to support and bind other tissues.

Examples of specialized connective tissues are:

• Adipose
• Cartilage
• Bone
• Blood
• Lymph

Adipose tissue is a fat-storing connective tissue. It protects organs and insulates the body from heat loss by lining organs and cavities in the body. Hormones produced by this affect blood coagulation, insulin sensitivity, and fat accumulation.

Cartilage is a tissue composed of packed collagenous fibers encased in chondrin. This chondrin is a rubbery and gelatinous material. Sharks and human embryos have cartilage in their bones. It offers flexible support for tissues such as the nose, trachea, and ears in mature humans.

Collagen and calcium phosphate, a mineral crystal, are all seen in bone tissue. It is a mineralized connective tissue made up of calcium phosphate for hardness.

Scientists classify blood as a form of connective tissue. It originates from the mesoderm, the central germ layer of growing embryos. The blood also functions to connect different organ systems. It carries signal molecules between cells to supply them with nutrients.

Another form of fluid connective tissue is lymph. Blood plasma exits blood vessels at capillary beds, resulting in this transparent fluid. It contains immune system cells that defend the body from infections.

• And for the muscle tissues, below are the examples that you must know about it:
• Smooth muscle
• Skeletal muscle
• Cardiac muscle

Smooth muscle is present in the intestines, blood vessels, urinary and reproductive systems. It contracts, causing peristaltic movement and blood vessel obstruction in the alimentary canal.

From the word “skeleton,” skeletal muscle links to the bones of our arms and legs. Voluntary motions involve the skeleton. To move bones, they contract and relax.

Cardiac muscle is a kind of muscle found in the heart. It settles in the heart’s walls where its cardiac muscle tissues are. They contract to pump blood to every region of the body.

• Nerve cells and their associated neuroglia cells make up nervous tissue. These cells receive and send nerve impulses or action potentials from one nerve cell to the next.

Dendrites and axons are two types of cellular projections found in nerve cells. The electrochemical signals are all received by the dendrites (from another nerve cell). The action potential will then forward to the next nerve cell via the axons.

The axon terminal is a bulb-like terminus to the axon. This axon terminal releases neurotransmitters that go to the next nerve cell of the body. It is to finally pass the nerve impulse from one nerve cell to another.

Neuroglia cells lie in the nervous tissue like the nerve cells. These cells assist in the protection and nourishment of nerve cells. They also aid in the maintenance of homeostasis and the formation of myelin.

The nervous system comprises nervous tissue. Nervous tissue comes in a variety of forms. Grey matter and white matter exist in the central nervous system. There are ganglion tissues and nerve tissues in the peripheral nervous system.

Where are the 4 tissues located?

Tissues are a bunch of cells with the same shapes and functions. Different organs contain different types of tissues. Listed below are the following four fundamental kinds of tissues found in humans.

• Epithelial
• Connective
• Muscular
• Nerve tissue

Within each of the primary tissues, there may be many sub-tissues. Each of them has its designated place in the human body where it operates. that you should know about.

Most inner cavities line epithelial tissue, covering the body’s exterior. The roles of epithelial tissue incorporate protection, secretion, absorption, and filtration.

An example of this is the skin protecting the body from dirt, germs, and other hazardous organisms. These tissue cells come in various forms – thin, flat, cubic, or elongated cells are all possible.

Connective tissues locate between other tissues everywhere in the body. They help bind structures to form frameworks and support organs. They store fat, carry chemicals, and guard against disease throughout the body. Additionally, they also help rectify tissue impairment.

Your muscle tissues are on your body’s muscles. These shorten or contract to produce motion of your body parts. The tissue is cellular and well-furnished with blood.

The nervous tissues in our body are all found in the brain, spinal cord, and nerves. They are in charge of supporting the nervous system in handling many functions.

How long does it take to become a histologist?

A histologist is someone who prepares tissue samples for examination by a pathologist. Its job is to cut tissue samples from organs or tissues and stain them with dyes. You use dyes to enhance the visualization of tissues for microscopic tissue examination.

There are times that you are also tasked to complete these activities immediately. Activities like taking a sample of tissue from a patient during surgery. You will also work on this when doing rapid laboratory analysis.

Becoming a histologist is quite long and requires patience. You must have either an associate or bachelor’s degree and a license to practice in the state where you work.

You may also need to earn certification from ASCP. Yet, this depends on your employer’s recommended job qualities.

This sector requires two years of laboratory experience. Thus, it necessitates meticulous attention to detail and knowledge of the equipment needed. Training in the handling of valuables is also part of the profession.

Students wishing to pursue this field must:

• Get a high school diploma and two years of histopathological clinical laboratory experience.
• Get an associate or bachelor’s degree in histotechnology.
• Finish at least a year of clinical lab experience in histotechnology.
• Get a license by passing the national examination.

Is histology a hard class?

Histology is beneficial to medical students in a variety of ways. It aids them in comprehending the typical organ system’s cell and tissue architecture. Furthermore, it links structure to function by tying tissue structure to operate.

Histology is somehow complex because it needs excellent memorization and understanding skills. But at the same time, it is a fascinating field of study. It’s amazing how intricate the tissues are while still being so similar.

You will still find the fascinating aspect of it. There is no single branch of biology that is very easy, with all honesty.

All fields need a thorough understanding because the scientific world is expansive. Yet, you won’t regret learning new things because uncommon ones are always interesting.

References:

Anatomy and Physiology: Four Types of Tissues. (n.d). https://open.oregonstate.education/aandp/chapter/4-1-types-of- tissues/#:~:text=Tissues%20are%20organized%20into%20four,maintenance%20of%20th e%20human%20body.

Classification of Tissues. (n.d). https://www.vedantu.com/biology/classification-tissue Goldberg, Alexander. 2018, December 18. A Brief History of Histology.

Helmenstine, Anne Marie. 2019, March 24. What Histology Is and How It’s Used. thoughtco/histology

Stoppler, Melissa Conrad. 2021, March 29. Medical Definition of Histology. Medicinenet/histology

ZipRecruiter Marketplace Research Team. (n.d). What Is A Histologist and How to Become One. Ziprecruiter/histology

Written by Franzgayle T. Husain

The word histology comes from the Greek word “histo,” which means tissue, and “logos,” which means study. Hence, medical histology refers to the study of the structure of tissues. It examines tissues, cells, and organs from a morphological and molecular standpoint.

Before we delve more into histology, let us first understand the concept of cells and tissues.

Cells and Tissue

The human body is consists of trillions of cells that work various functions. It serves as the fundamental unit of life and is essential for the survival of individuals. When a group of cells has the same structure and function, they form tissues.

Tissues play a significant role in various activities of your body. Different types perform distinct functions, including secretion, movement, and strength. Classification of tissue forms four groups– nervous, Muscle, epithelial, and connective tissue. Once they get damaged by different diseases, it will put your life at risk.

Histology is the opposite of gross anatomy because it focuses more on the cellular level. Medical professionals study the role and anatomy of tissues under the microscope. They examine how it interacts with your body systems and how diseases affect them.

History of Histology

The scientist Marie François Xavier Bichat first did the study of tissues. He was the one who used the term tissue in an anatomical sense. He discovered different weaves and textures in the body and named them layers of tissues.

Bichat was able to discover these during his dissection for his anatomical studies. Bichat then created a classification of these issues based on their distinct textures. His workings made him the father of modern histology and descriptive anatomy.

What is histology used for?

All multicellular organisms possess tissues and organ systems. Thus, scientists examine cells to understand concepts and answer questions in many fields.

Medicine

In medicine, it is vital to understand the normal to identify the abnormal. Using histology allows you to detect any abnormalities in your tissues. Whenever there is a disruption of your cells, it affects your body’s activities. This explains why medical professionals conduct histological tests to diagnose certain diseases.

Agriculture

Examining plants in histological viewpoints helps in identifying chemicals present in the soil. These hazardous chemicals can put your plants at risk. But with histology, you can prevent potential dangers from diseases. Additionally, this can aid in deploying the best control methods in the longer term.

Autopsies

Microscopic tissue examination helps in explaining the cause of death of some patients. This is applicable when macroscopic studies fail to provide specific diagnostic pathology. Microanatomy may disclose information about a person’s environment after they die.

How is histology performed?

In every laboratory work, a specific person works on certain procedures. A histotechnologist examines preserved sections and smears of tissues. They stain these samples and place them under a microscope.

Histotechnologists make sure that a tissue section is of good quality. This allows various interpretations of any microscopic cellular changes. They preserve and process the sample’s structures by following these steps:

1. Fixation. Histotechnologists fix the sample as soon as it arrives in the laboratory. They put it in a liquid fixing agent like formalin. The formaldehyde solution penetrates your specimen, resulting in chemical and physical changes. This helps in preserving the tissue and protecting it from the following stages.

After fixation, the histotechnologist will trim and place your sample in labeled cassettes. Generally, this stage is the crucial part of preparing histological sections. Once there is a delay of fixation, your specimen may become damaged.

2.       Dehydration

Melted paraffin wax is hydrophobic. Thus, it is essential to remove the water first from the specimen. To do this, soak your sample in an increased concentration of alcohol solution. In this way, you can avoid distortion of tissue and remove water and formalin.

3.       Clearing

After dehydration, the specimen is immediately transferred to an intermediate solvent like xylene. This type of solvent is soluble in both ethanol and paraffin wax. Using this will remove the amount of fat present, allowing wax infiltration.

In this stage, the solvent xylene replaces the ethanol in the specimen. But the molten paraffin wax will take its place once the tissue becomes embedded.

4.       Infiltration

Now that the tissue has cleared, a histology wax can infiltrate your specimen. Wax, like paraffin, is liquid at 60°C. Thus, you must let it cool to solidify and allow thin sectioning.

5.       Embedding

Embedding happens after infiltration with wax. You must put the tissue in a mold that contains molten wax. Placing resin on it creates a big solid tissue block. This can be clamped into a microtone and sectioned once it has changed.

In embedding, you must ensure that the specimen is in the correct orientation in a mold. Any errors may result in damaged elements during microtomy.

6.       Section-cutting

Histotechnologists can now trim your tissue specimen into thin sections. They can put it in a microscope slide. They use an instrument called microtome to perform section cutting. It must be in thin sections in the form of a ribbon.

Each routine has its required thickness of your tissue. Most specimens for routine hematoxylin and eosin (H&E) are 3-5 μm in thickness. Meanwhile, specimens for amyloid deposits must be at 8-12 μm.

After cutting, you must transfer these sections to a warm water bath to allow them to float on the surface. You can now pick them up and place them under a microscopic slide.

7.       Staining

Most of your cells appear colorless and transparent, so you must stain them to produce contrast. Using histochemical stain provides a more precise visualization of your specimen. It makes the structures and features of your tissues more visible and easier to examine.

How does histology help diagnose an injury or disease?

Understanding the normal anatomy of your tissues is one way of detecting infection. Healthcare providers interpret the changes that arise caused by diseases. Each condition generates distinct changes of characteristics in your tissue structure. Thus, a histological examination can provide information that helps diagnose illness injuries.

Histopathology, a branch of histology, tackles tissues affected by diseases. Damage of cells and inflammation reactions indicates signs of viral infection. Pathologists look for any changes in your cells that might explain your conditions.

Your tissues contain evidence of a pathological process. Interpreting it provides crucial information for your diagnosis and treatment of your disease. Although some changes are vague, there are others that are obvious.

Cancer is a known disease that results from mutations in your cells’ genes. Histopathologists examine your cells from suspicious lumps in your body. They perform a biopsy to provide information about the type of cancer you might have. It is also one way to determine whether your cancer is malignant or benign.

You must remember that histopathology results are only one piece of the puzzle. Pathologists perform laboratory procedures to identify the virus and confirm the diagnosis. These procedures include immunohistochemistry (IHC), serology, and molecular biology.

What is the difference between cytology and histology?

Cytology and histology both study human cells and tissues. But they differ when it comes to the scope of their study. The former focuses on the structure of a single cell or a small group of cells found in body fluids. While the latter investigates the entire section of human tissue.

Cytology or otherwise known as cytopathology, examines your cells for diagnostic purposes. Medical professionals like pathologists observe any abnormalities in your cells. Hence, they use cytology tests to analyze cells for diagnosis. This explains why cytology is used for screening and diagnosing cancer.

Generally, there are two branches of cytology–exfoliative cytology and intervention cytology.

Exfoliative Cytology

Exfoliative cytology is when a pathologist examines cells shed by your body or scraped from the surface of your epithelial tissue. Smears that have been spontaneously shed or manually removed from epithelial and mucous surfaces may contain these exfoliated cells.

These are some exfoliative cytology that deals with manual tissue brushing.

• Gynecological samples
• Gastrointestinal tract samples
• Skin or mucus samples

There are three examples of exfoliative cytology that involve collecting tissues or fluids that your body sheds. These are:

• Respiratory samples
• Urinary samples
• Discharge or secretion samples

Intervention Cytology

Medical professionals intervene with your body to get cells for cytology tests. This means that they will perform procedures that involve piercing your skin to get samples of your cells. Hence why its name is “Intervention Cytology.”

Fine needle aspiration (FNA) is the most used method of intervention cytology. The FNA is helpful for evident lesions. A medical professional injects a needle into the lesion or on the area that draws out a fluid. They may do a fine-needle aspiration in the following parts of your body:

• subcutaneous soft tissue tumors
• thyroid
• lymph nodes,
• salivary glands
• breast.

What is the role of histology in medicine?

Tissues act as building blocks of your body. It forms your organs as it works together. Thus, histology will help you understand and predict the activities of your organs. This is important in the field of medicine, especially for diagnosing diseases. Medical students can also get a better knowledge of cellular biology.

Studying how these cells work provides different insights into the development of complex organs and your organ systems. The information you gain allows you to monitor how your body reacts when certain diseases or treatments affect you.

Diseases occur when there is a rupture of your cells due to infection. Some disorders involving infected connective tissue include lupus and rheumatoid arthritis. They arise when your collagen and elastin become swollen. This then caused harm to the proteins and body parts they connect.

Medical professionals use histology to study the development of these diseases. Observing their progress helps them to identify suitable treatments. This is also one way of comparing the efficacy of different medications and lifestyle choices on your body.

Furthermore, histological studies contribute to the advancement of medical science. Researchers use tissues to test discoveries and verify theories about drug medication. As for medical students, this widens their knowledge of cellular biology and pathology.

Is medical histology hard?

In research conducted by Garcia et al. (2019), they found that undergraduate biology students find it hard to study histology. The nature of the topic and its terminology made it difficult for them to comprehend. But for P. del Rio-Hortega (1933), histology is an exotic meal where you become addicted as you taste it repeatedly.

Medical schools integrate histology into their curriculum to provide information about biological tissues, animal growth, physiology, and tissue diseases. It also continues to deliver different findings in clinical medicine and advanced research.

Unfortunately, medical students find this complex due to insufficient time and attention. Students suggest that teachers should base their teaching on practical tasks. They must also add anatomy subjects and make histology education more engaging.

Learning histology is challenging, but constant reading will make you appreciate it more. One cannot know medicine well if they have no rich perspective on the tissue-level organization.

References

García, M., Victory, N., Navarro-Sempere, A., & Segovia, Y. (2019). Students’ Views on Difficulties in Learning Histology. Anatomical sciences education, 12(5), 541–549. https://doi.org/10.1002/ase.1838

Sorenson, R. L (2008). Atlas of Human Histology: A Guide to Microscopic Structure of Cells, Tissues, and Organs. Retrieved from https://histologyguide.com/about-us/sorenson-atlas-of-human-histology- chapters-1-and-14.pdf

Hussein IH, Raad M, Safa R, Jurjus R, and Jurjus A (2015). Once Upon a Microscopic Slide: The Story of Histology. J Cytol Histol 6:377. doi:10.4172/2157-7099.1000377

Open University. (n.d). Functions of tissues. Retrieved

from https://www.open.edu/openlearn/mod/oucontent/view.php?id=65376&section=1

Elliot, M. Miller, K. Pins, M. and Watson, Mark. (2004). What is a tissue? Retrieved

from https://www.roswellpark.org/sites/default/files/What_is_Tissue amp Why_is_it_Important.pdf

Wood, R. (1996). Sustainable agriculture: the role of plant pathology. Canadian Journal of Plant Pathology, 18(2), 141–144. https://doi.org/10.1080/07060669609500638

Lane, A. Buckley, G. McLaughlin, K. Whitehous, L. Knapp, S. and Cotoia, A. (2018). Histology. Retrieved from https://biologydictionary.net/histology/

Helmenstine, A. (2019). What Histology Is and How It’s Used. Retrieved

from https://www.thoughtco.com/histology-definition-and-introduction-4150176

Cleveland Clinic Organization. (2021). Cytology. Retrieved

from https://my.clevelandclinic.org/health/diagnostics/21714-cytology

Bruce-Gregorios, J. B. H., & Faldas, M. (2017). Histopathologic Techniques. Independently published.

Brown, R. (n.d). Histopathology. Retrieved from https://www.rcpath.org/discover-pathology/news/fact- sheets/histopathology.html

The Open University. (2016). Introduction to histopathology. Retrieved from https://www.open.edu/openlearn/mod/oucontent/view.php?printable=1&id=2312

Written by Elijah Dave M. Cordova

Neurotransmitters allow brain cells to communicate with each other. They enable the transfer of information across gaps among neurons. Among the major neurotransmitters in the CNS are acetylcholine and catecholamines. Serotonin and GABA (γ-aminobutyric acid) complete the list.

Before we go into each of them, let us first classify neurotransmitters.

1. Excitatory. They cause neuron firing of an action potential to a receiving neuron.
2. Inhibitory. It is the opposite of excitatory action. It inhibits the firing of action potentials across synapses.
3. Neurohormones. Neurons synthesize and secrete them into the bloodstream. Oxytocin and vasopressin are examples.
4. Neuromodulators. They influence other neurotransmitters and affect several neurons at once.

Acetylcholine (Ach) is a neuromodulator that affects your attention and memory. It also impacts how you learn things through integration. Ach cells originate in your brainstem and midbrain. They then travel to every area of the CNS through synapses.

In the Peripheral Nervous System (PNS), Ach is an excitatory neurotransmitter. Neuromuscular junctions often use Ach to send signals between your nerves and muscles. For example, acetylcholine signals parasympathetic smooth muscle movement.

Choline acetyltransferase catalyzes the production of acetylcholine. It separates the acetyl part of acetyl coenzyme A (acetyl-CoA). It then joins this acetyl part to choline to form the product.

Catecholamines are neurohormones crucial to maintaining homeostasis in your body. Your adrenal glands on top of your kidneys produce them. Dopamine is a catecholamine. So, too, are norepinephrine (NE) (i.e., noradrenaline (NA)) and epinephrine (adrenaline) catecholamines.

Dopamine is a neuromodulator across many brain regions. One of its main functions is in the prediction and learning of rewards. Axons of your midbrain house dopamine.

L-amino acid decarboxylase (i.e., DOPA decarboxylase) synthesizes dopamine from L-Dopa. It is a precursor chemical. This same enzyme also facilitates the synthesis of histamine and serotonin, another neurotransmitter.

Dopamine β-hydroxylase synthesizes noradrenaline from dopamine. Its cells originate from your brainstem. Its main function is regulating the sympathetic nervous system. It helps regulate your body systems based on specific situations.

You can think of it as what regulates your arousal to specific situations. In times of stress, norepinephrine increases your alertness or wakefulness. It is so that you can respond in a proper manner and ensure your survival.

Epinephrine is the hormonal equal to norepinephrine. They work together to form your “fight or flight” response which you need to survive.

During stress, norepinephrine constricts your blood vessels to raise your blood pressure. Meanwhile, epinephrine forces your heart to contract with much greater strength. Its actions increase blood pressure and cardiac output.

Your body releases noradrenaline to your blood circulation at a low dose. Your body releases adrenaline in stressful moments alone.

Serotonin uses the amino acid L-tryptophan in its synthesis. Hence, it is also known as 5- hydroxytryptamine (5-HT). Most of it is in the raphe nucleus of your brain stem. Serotonin also cannot pass through your blood-brain barrier. It performs its functions in your brain alone.

Serotonin, like dopamine, is a neuromodulator. Unlike adrenaline and noradrenaline, it does not have a specific function. Instead, it affects many brain regions and body systems in consequence. Serotonin affects your mood, sleep, circadian rhythms, and body temperature, among others.

GABA is a derivative of glutamate (glutamic acid), a non-essential amino acid. It is the main inhibitory neurotransmitter of your brain. This means it inhibits the transmission of messages along neural pathways. It makes sure that your brain does not send random messages.

The enzyme glutamic acid decarboxylase (GAD) synthesizes GABA from glutamic acid. It demands cofactor pyridoxal phosphate (derived from Vitamin B6) in its synthesis. As GABA increases in your brain, it inhibits the action of GAD. With this, it manages its own synthesis.

GABA-A and GABA-B are its two receptors. They act on both receiving and transmitting targets. They do this to fine-tune the responses of your CNS. GABA cells work through lateral inhibition. This mechanism ensures the highlighting of important information in your brain.

In essence, GABA blocks noise or irrelevant message transmission. GABA also promotes sleep but inhibits brain regions that promote awakening. Abnormalities in GABA contribute to anxiety disorders which unnecessary brain activity often causes.

What triggers neurotransmitter release?

You have now come to appreciate the role of neurotransmitters in your body. Now, we ask how they travel across synapses. The opening of voltage-gated calcium channels triggers the release of neurotransmitters. These neurotransmitters travel to your synapses.

Your brain cells have dendrites that receive information and axons that conduct information. A myelin sheath can protect your axons and speed up its message transmission. Degradation of this myelin sheath leads to multiple sclerosis. It leads to a lack of muscle control.

Nerve cells also have the soma or cell body. It contains all things your nerve cell needs. The information your dendrites receive may belong from the environment or other neurons. Most neurons have one axon and many dendrites. These are multipolar neurons.

Each axon terminates on the next neuron at a synapse. These synapses are less than a millionth of an inch apart. A synapse is a specialized structure for transferring information.

The tip of each axon is the axon terminal. This part of your neuron contains synaptic vesicles that house neurotransmitters. Meanwhile, the postsynaptic membrane of the target cell has receptors for those neurotransmitters.

Your axon terminal also contains voltage-gated calcium channels. An action potential travels from your dendrites to your axons. When an action potential reaches your axon terminal, it changes its membrane potential. This action potential also opens these voltage-gated calcium channels.

Now, calcium flows into your axon terminal through diffusion. This event increases the concentration of calcium in your axon terminal. This calcium causes the fusing of vesicle and axon terminal membrane proteins.

This fusion allows your neurotransmitters to communicate outside the neuron through the synapse. These neurotransmitters diffuse into the synapse and bind to target cell receptors. They fit the receptors like a key to a lock.

Three things affect this process.

The frequency of action potentials fired down your axon opens more calcium channels. More calcium would flow in the axon terminal. More synaptic vesicles would fuse with the membrane of your axons. Hence, more neurotransmitters would travel into the synapse.

The duration of action potentials fired down your axon means longer neurotransmitter release.

Third, the blockage of target cell receptors causes failure of message transmission. It can also show the presence of a disease. Myasthenia gravis is muscle weakness due to circulating antibodies that block acetylcholine receptors.

When the train of action potentials stops firing, your calcium channels will close. Calcium stops flowing into your axon. The fusion between your vesicles and axon membrane stops. Hence, there are no more neurotransmitters that travel down your synapses.

Where can you find vesicles of neurotransmitters?

Neurotransmitter vesicles are also known as synaptic vesicles. These vessels store neurotransmitters for transport across synapses. They are in the neuron region known as the axon hillock or axon terminal. This region is the release zone.

Synaptic vesicles contribute a great deal toward the transmission of neurotransmitters across neurons. They aid in facilitating the communication between the CNS and the rest of your body.

When an action potential travels down your axon terminal, it generates a set of reactions. This results in the release of neurotransmitters kept by your synaptic vesicles. These neurotransmitters travel through synapses to communicate with target cells.

Removal of neurotransmitters from the synapse entails either of the following:

1. Reuptake.

Here, uptake pumps take your neurotransmitters from the synapse. Then, your axon terminal membrane would close off. An example of this would be serotonin uptake pumps. Selective serotonin reuptake inhibitors (SSRIs) induce serotonin buildup in your body.

• Deactivating Enzymes.

These enzymes break down your neurotransmitters. An example of this would be acetylcholinesterase (AchE). It breaks down acetylcholine in your synapses. Inhibition of its action or production builds up acetylcholine in your synapse.

How does neurotransmission affect human behavior?

Everything psychological is biological. Our biological condition affects our ideas, impulses, and moods. Our neurons communicate with neurotransmitters. This communication leads to motion and emotion. They make us move and feel.

Endorphins make you feel good. They are like opium in that they associate with the control of pain and pleasure. Your systems would flood with endorphins after exercising or eating delicious food. Falling in love can make you feel good too.

Norepinephrine controls alertness and arousal as discussed in a previous section.

Glutamate, from which we derive GABA, is also a neurotransmitter. It helps manage memory. Having too much glutamate in your CNS could cause migraines or seizures. Hence, some people sensitive to glutamate avoid monosodium glutamate (MSG). It is an ingredient you can find in ramen.

Serotonin affects your feelings of hunger, your mood, and your sleep. We link depression to low amounts of serotonin. Some antidepressants like SSRIs treat depression by increasing serotonin levels in the brain.

Acetylcholine affects learning, memory, and muscle action. Deterioration of acetylcholine-producing neurons causes Alzheimer’s. It is a progressive neurological degradation due to brain degeneration.

Dopamine affects attention, emotion, and learning. It also impacts movement and pleasure. An excess of dopamine causes schizophrenia. It is a chronic psychiatric illness where you disassociate behavior, emotion, and thought. Excess dopamine also causes other addictive or impulsive behaviors.

Acetylcholine and dopamine neurotransmitters can be excitatory or inhibitory. It depends on the type of receptors they encounter.

Like neurotransmitters, hormones act on the brain. Some hormones are even identical to certain neurotransmitters. Hormones also affect our arousal, mood, and circadian rhythms. Besides this, they can impact physical growth and aid in sexual reproduction. They can also control your metabolism.

Neurotransmission occurs at high speeds. Hormones take their time and deliver slow communications through glands. Hence, hormones linger. This explains why it takes time to calm down after having a bout of severe stress or trauma.

Adrenaline works with noradrenaline for the fight or flight response.

Your endocrine and nervous systems work together to affect your behavior.

What neurotransmitter causes happiness?

Does happiness make you healthy? Does being healthy make you happy? We may go different ways here but we can agree that both are important. Hence, we now concern ourselves with what neurotransmitter causes happiness.

Seven neurotransmitters provide a general feeling of well-being. Adrenaline, dopamine and endocannabinoids are among them. So, too, do endorphin, GABA, oxytocin, and serotonin belong.

Adrenaline elicits an exhilarating feeling. It also creates a surge in energy. It makes you feel alive.

Dopamine drives behaviors driven by rewards and seeking pleasure. Several addictive drugs act on the dopamine system. These drugs block dopamine reuptake, leaving it in your synapses longer.

Endocannabinoids that include anandamide have similar effects to marijuana. They prevent anxiety and burnout. They contribute to the runner’s high you would get after sustained running.

Endorphins resemble opiates. They are painkillers in essence.

GABA creates a sense of calmness by inhibiting the firing of neurons. Benzodiazepines are anti-anxiety medications that work by increasing GABA.

Oxytocin is a neurohormone linked to feelings of intimacy and affection. Couples distant from each other for a long time have decreased oxytocin levels.

Serotonin affects your appetite, mood, social interaction, and performance. High serotonin levels mean increased self-esteem and feelings of worthiness.

Where is GABA neurotransmitter produced?

GABA is the brain’s main inhibitory neurotransmitter. It is also a major inhibitory neurotransmitter in the spinal cord. Glutamate decarboxylase uses Vitamin B6 (pyridoxine) to synthesize GABA from glutamate. GABA production happens in the brain and β-cells of the pancreas.

Several diseases exhibit GABA deficiencies:

1. Dystonia and spasticity.

Dystonia is involuntary muscle contraction. It causes repetitive and twisting motions. Spasticity refers to stiff muscles. A deficiency in GABA signaling can cause these two diseases.

• Hepatic encephalopathy.

It refers to impaired brain function due to advanced liver disease. Elevated ammonia levels can bind to a GABA complex and cause this disease.

• Huntington’s disease.

It is an inherited disease the causes the progressive degeneration of brain neurons. A lack of GABA exhibits this disease.

• Pyridoxine deficiency.

It is when your body does not have Vitamin B6 to produce GABA. Frequent seizures during infancy are common.

REFERENCES

Bergland, C. (2012). The Neurochemicals of Happiness. Psychology Today. https://www.psychologytoday.com/us/blog/the-athletes-way/201211/the-neurochemicals- happiness

Hank. (2014). The Chemical Mind: Crash Course Psychology #3 [YouTube Video]. In YouTube. https://www.youtube.com/watch?v=W4N-7AlzK7s

Jensen, M. B. (2014). Neurotransmitter release | Nervous system physiology | NCLEX-RN | Khan Academy [YouTube Video]. In YouTube. https://www.youtube.com/watch?v=Ac- Npt3vgCE

Pastore, R. (2020, May 7). What are the Main Neurotransmitters? PowerOnPowerOff. https://poweronpoweroff.com/blogs/guide/what-are-the-main-neurotransmitters