#Histology Epithelial Tissue Quiz

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70 Top Basic Histology Quiz Online Practice Test

Challenge yourself with our Histology Quiz and MCQs Questions to explore the fascinating world of tissues and cells. Put your knowledge to the histology practice quiz test now! Histology Quiz Topics Connective Tissue Histology Quiz Histology Quiz On Tissue Identification Endocrine Histology Quiz Digestive System Histology Quiz Histology Epithelial Tissue Quiz Histology Quiz…

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Quiz Review #2: The PAS/PASD Stain

bout that time again ay chaps. right oh. big ol wall of text under the cut, let’s get at it

Alright so sometimes in the course of a patient’s disease, they’re either going to have carbohydrates end up in tissues that aren’t meant to store them or have too few carbohydrates in places where they ought to be. A handy test for this is the Periodic Acid-Schiff test and/or the Periodic Acid Schiff with Diastase digestion. This isn’t to say that the PAS/D is a strict presence/absence test but it gets used that way fairly often depending on the case. 

First things first: What’s a carbohydrate? Well that’s a big chemistry question and if we wanted to deal with that mess we’d have gone to grad school. For the purposes of the HTL this post, carbohydrates are organic compounds such as sugars, starches, cellulose and polymers that are typically bound to proteins found in tissue. When we eat food, we break the complex sugars down into simple sugars such as glucose. What we don’t immediately use we store as glycogen. This glycogen *generally* should be found within liver and skeletal muscle tissue, specifically within the cytoplasm of those cells.

 Disease and uses- A healthy liver should be able to store glycogen up and release it as the body’s demand for it changes. We can use the PAS/D to look at how much glycogen the liver has and where that glycogen is within the liver.  Most of the disease you’ll see in medical histology regarding glycogen storage disorders are congenital and fatal. A good example is Pompe’s disease, in which the  patient has a mutation that causes them to be unable to convert glycogen back into glucose, causing an over-accumulation of glycogen within the skeletal muscle, cardiac muscle and liver; most people born with Pompe’s disease will die in less than a year. Other illnesses that effect glycogen storage are diabetes (low glycogen in the liver) and certain wasting disease. There are also some applications for differentiating tumor types on the oncology end of things; for instance you can use the PAS to differentiate secreting adenocarcinomas (should be PAS positive) from undifferentiated squamous cell carcinomas (should be PAS negative). I am told that these days we would use an immuno stain to answer this question but, you know, half of histology is actually Arcane Medical History so whatever. My favorite application of the PAS, however- one that could have saved my undergrad research project had I known what the hell I was doing but that’s another topic for another day- is its ability to stain for fungal cell walls. Fungal cell walls are made of chitin, a complex carbohydrate that stains nicely with PAS. Some of the techs in my current lab will automatically order PAS along with any silver stains they get on a suspected fungal case, just because it’s a nice way of double checking (especially if you’re looking at tissues with lots of argentaffin/argyrophil structures where the fungi could be obscured other things). 

Fixation- now if you’re in a hospital, chances are you’re just going to throw the tissue in question into a bucket for formalin and be done with it. And that’s not necessarily bad; tissue slated for PAS can be fixed in either aqueous or alcoholic solutions. Just remember that structurally, the carbohydrates you’re testing for are bound to the tissue proteins, so the faster you preserve those proteins the more honest and indicative the results of your PAS will be. If you know that this tissue is going to have to wait a while before going to processing, go for alcohol if you can. Formalin and most other aqueous fixatives will slowly leach glycogen from tissue because glycogen is water soluble. Of some note to pathologists, glycogen degrades rapidly postmortem, so get that liver out of there and into some sort of fixative asap of you’ll be missing that particular piece of the puzzle. The only real fixatives to avoid are those containing chromate, since these may over oxidize the tissue and result in a weak stain or cause resistance the diastase digestion in the PASD. 

Reagents and their purposes- Fairly straight forward. 

Periodic acid, aqueous, 0.5%. This will act as your oxidizer. It opens up ‘certain tissue elements’ (nice dodge, Frieda) and exposes aldehydes such as 1,2 glycol groups. At this concentration periodic acid probably will not burn you to death if you spill it on yourself but you should be extremely careful when preparing it from concentrate (under a hood, wearing goggles and gloves, full weenie regalia required, this is not fun stuff to get in your eyes). Remember: acid into water is the way that you oughta. Dispose of with lots of water down the sink. 

Schiff Reagent. This stuff is N A S T Y but you gotta use it. It binds to the aldehyde groups exposed by the periodic acid  and forms an intermediate colorless compound known as leucofuchsin. Schiff’s contains sodium metabisulfite, hydrochloric acid and basic fuchsin. Basic fuchsin is classified as a known carcinogen by OSHA so you need to make and use schiff’s under a fume hood whenever possible; most labs i have been in are not good about this and some even heat their shiff’s in a microwave, which causes techs to breath in even more vapors. Most labs need to dispose of used solution via a licensed waste hauler; do not flush down the sink. 

Sodium metabisulfite, aqueous, 10%. This will remove any excess schiff’s that’s hanging onto the tissue and prevent overstaining. At 10% it’s not horribly dangerous but it is a strong reducing agent and if you’re preparing it from powder you should do your mixing under the hood. dispose of down the sink with lots of water. 

Alum hematoxylin (counterstain). This is just hematoxylin that contains alcohol. Normal alcohol precautions apply (ie it’s slightly flammable and skin/eye irritant; normal ppe is fine). Dispose of down the sink. 

How it works, step by step:

First- are you doing a PAS or a PASD? If you’re doing a PAS, start at step 2. For a PASD, start here. You need some way to chop up the glycogen in your section, and that’s a job for an enzyme. Once upon a time we used malt disatase to do this, which is a mix of a bunch of different amylases. If possible, you should use alpha amylase because it’s the most specific enzyme for glycogen, aka your target. Now, if you’re anything like my lab, you have chill pathologists and cheap administrators, so what you gotta do is think real hard about sour candy and go ahead and just spit on the slide. I’m dead serious. You have perfectly good amylase in your spit, and on the off chance that you have free cells in your mouth the pathologist should be able to figure out what doesn’t belong to the patient tissue; it’s a thing that’s done. The first time I saw my instructor do it I almost walked out of the lab but. you know. When in Rome. We usually let ours digest for about 20 minutes, rinse real well in DI and then add the slides to the PAS group for the rest of the procedure.

oxidize your tissue with periodic acid. We use periodic acid because it’s not going to over-oxidize the aldehyde groups it creates when it opens the c-c bonds in the sugars. 

add schiff reagent. it will bind to the aldehyde groups creating an unstable, colorless compound (leucofuchsin) that resembles a partially opened ring. When you run warm water over the slide, the ring will close and this creates the colored reaction product (pink). 

rinse in sodium metabisulfate. some labs omit this step to save time/money and some labs do get good results just by rinsing for extra time in water but you’re better safe than sorry. Sodium metabisulfate should remove any excess schiff reagent. 

counterstain with hematoxylin. My instructor told me that some labs use fast green instead. I’ve never seen it done before but it strikes me as a good idea (who wants to look at a bunch of pink/purple on top of the schiff reaction? not me). 

Other important details:

Controls should be kidney (specifically the golmeruli and basement membranes) if you’re doing PAS and Liver if you’re doing PASD. 

Good results should show glycogen, neutral mucosubstances, epithelial sulfomucin and sialomucins, colloid, basment membranes and fungal cell walls. They will appear ‘bright rose’ (aka pink). 

A PAS and a PASD  of the same tissue  slides run in the same batch should be loose negative images of eachother; this is to say, the PAS will show the presence of glycogen in the section, while the PASD will show what the tissue looks like once that glycogen is digested away. This is not to say that a PASD is necesarily PAS negative, but rather that a PASD will show any PAS positive substances that are NOT glycogen. 

Before you use your schiff reagent you want to test it for freshness. Do this by pouring a small beaker (10ml should do) of formalin. Drip a few drops of schiff into the beaker. If it’s good to use, you’ll see a red to purple color. If it’s degraded, you’ll get a delayed reaction and an eventual dark purple to deep blue color. This a good test but remember: when it doubt, throw it out. It’s not worth having to repeat a day’s worth of PAS/Ds just because you don’t want to take ten minutes to make your reagents properly. 

Calling back to last week’s quiz on water quality, PAS procedures have been known to fail if the water you’re using to rinse is heavily chlorinated, since the chlorine can oxidize the schiff reagent and turn it back into basic fuchsin, giving you a false negative. I’m not sure what constitutes ‘heavily chlorinated’ but I figure you’d probably smell it and say, you know, maybe i shouldn’t put this precious sample into this nasty water and go talk to my supervisor before i ruin this poor sick person’s life. 

What-if list:

no PAS/D reaction occurs at all, including control- check your periodic acid. If oxidation fails, so does everything after it. 

faint of pale staining-you probably cut the tissue too thin. This is a little counter-intuitive but the thicker the section is, the less time you will need to stain it for in PAS/D. My theory is that staining time is strictly is a function of quantity of glycogen, and quantity of glycogen should go up with section thickness. There’s biochemistry afoot here but my ochem-failing-self is ill-equipped to suss this one out. have at it, you nerds. 

you still see glycogen on a PASD- give it more time in amylase and keep it around 37C. If you’re heating your slide too high you can degrade your enzymes (remember, most enzymes used in the clinical setting work at body temperature. Don’t go above that if you can help it). 

you have weird glycogen looking artifacts in places where glycogen 100% can’t be-should have used some kind of sulfurous rinse. this is what you get for cutting corners and being a cheapskate. are you happy now. look at your life, look at your choices. 

Alright that’s all for now. My instructor is traveling this week so I don’t know if I’ll have a quiz next monday but I’ll keep you posted. 

Peace!

-Reby

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New Post has been published on Biology Dictionary

New Post has been published on https://biologydictionary.net/thymus-gland/

Thymus Gland

Thymus Gland Definition

The thymus is an organ that is secretory in pre-pubescence, which earns its status as a gland. The thymus gland has an important role in immune function. One of its main secretions is the hormone thymosin. Thymosin stimulates the maturation of T cells, which are derivatives of the white blood cells that circulate our system. T cells “kill” or are cytotoxic to damaged cells. The damaged cells may be cancerous cells that have lost the ability to stop proliferating, or even cells infected with viruses. T cells will be able to bind the T receptor on the target cell’s surface that will initiate its eventual death. The T cell’s cytotoxicity comes from the cytokines it produces.

Despite the thymus’ essential role in immune health, the thymus gland is not active during our entire lifetime. In fact, it is only active until puberty and becomes non-functional in adulthood. But its actions are instrumental in preventing the body from having an autoimmune response, which is when the immune system cannot distinguish between itself and foreign agents. Chronic periods of fever, fatigue, and malaise mark the lives of patients with autoimmune diseases. Therefore, the thymus gland is closely tied to the lymphatic system as it is the body’s natural defense network. The network of vessels and tissues that make up the lymphatic system make it possible for the body to expel or “drain” toxins and waste from the body.

Thymus Gland Location

The thymus is a soft organ located behind the breastbone and between the lungs. In relation to the organs in the human body, the thymus is a two-lobed structure that lies almost on top of the heart and traces up along the trachea. The thymus gland is more or less triangular in shape and has two lobes that are encased in a fibrous exterior. Its thymic lobes are an opaque pink, and the most superficial layer is named the cortex. When the thymus is sliced for a histology study, it will reveal a deeper layer called the medulla. If the human chest were divided into four regions, the thymus would be located right in the center of the upper quadrants with both clavicles beside it.

The image depicts an anatomical illustration of the thymus gland, in relation to other important organs.

Thymus Gland Anatomy

The thymus gland is made up of a patchwork of epithelial tissue and lymphatic tissue. Likewise, the tissues will contain dendritic, or “antigen presenting,” cells that will signal off the killer T cells. Meanwhile macrophages will be present as well to eat away any cellular debris or to directly ingest foreign pathogens. The macrophage and dendritic cells really populate the thymus, which of course is crucial as they assist the thymus gland in performing its immune functions of discarding harmful waste and identifying diseased cells to destroy.

The thymus gland is active in childhood and reaches it maximum weight of around one ounce during puberty. However, after reaching this pinnacle, the thymus will become less and less active. This decline in activity will correspond to a decrease in size as well, until the thymus tissue is almost completely replaced by fat. This shrinking will take place after puberty and into adulthood.

Function of Thymus Gland

As previously alluded to, the main function of the thymus gland is to release thymosin hormone that will stimulate the maturation of T cells. All of our childhood, white blood cells or lymphocytes will come in contact with the thymus gland. This contact will transform them into T cells. Once the T cells have matured, they will migrate to the lymph nodes which are the stores of immune cells in the body. So, the thymus gland can be understood to be a recipient of immature T cells that were created in the bone marrow but have yet to reach full maturation. Once the thymus receives the cells, they will be trained to only attack foreign agents. The way this happens is through positive selection. Only the T cells that have properly responded to foreign antigens will be selected to survive and eventually migrate to the medulla. The T cells that do not make the cut will die by apoptosis in a healthy patient.

Once the surviving T cells have reached the medulla, the T cells will proceed to mature. The remaining T cells will go on to kill pathogens, will activate helper B cells that make antibodies against specific antigens, and will store the memories of previous infections and viruses so that the body can be better prepared to fight them off if they ever return.

Quiz

1. Which of the following best describes the location of the thymus gland? A. In front of the breastbone B. Between the lungs C. Behind the trachea D. Below the heart

Answer to Question #1

B is correct. Between the lungs is the best answer choice. The thymus gland is found snug in between the upper lobes of the two lungs, and in the human body almost lies on top of the heart.

2. The maturation of functional T cells requires which of the following natural processes? A. Evolution B. Bottleneck selection C. Positive selection D. Natural selection

Answer to Question #2

C is correct. As mentioned in the article, T cells will mature via positive selection which is when only the functional T cells that respond adequately to foreign antigens will survive and proliferate. The others will initiate apoptosis.

References

Inner Body (2017). “Thymus Gland.” InnerBody. Retrieved on 2017-07-01 from http://www.innerbody.com/image_endoov/lymp04-new.html

Sargins, Robert MD (2017). “An Overview of the Thymus.” Endocrine Web. Retrieved on 2017-07-01 from https://www.endocrineweb.com/endocrinology/overview-thymus

New Health Advisor (2017). “Functions and Disorders of Thymus Gland.” New Health Advisor. Retrieved on 2017-06-30 from http://www.newhealthadvisor.com/Thymus-Gland-Function.html

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New Post has been published on Biology Dictionary

New Post has been published on https://biologydictionary.net/carcinoma/

Carcinoma

Carcinoma Definition

Carcinoma is a term used to describe cancer derived from epithelial cells that line various tissues throughout the body. In addition, malignant tumors that have an unknown primary origin, but share histological characteristics with epithelial cells (e.g., stratification, pseudostratification, cytokeratin production, mucin, etc.) are also classified as carcinomas. Depending on the location, carcinomas can be surgically removed, or treated with conventional radiation or chemotherapy.

Types of Carcinoma

Carcinomas are classified based on the histological features that they exhibit. The following terms are used to describe the most common types of carcinomas.

Adenocarcinoma

Adenocarcinomas are carcinomas which are derived from glandular epithelial cells or exhibit glandular characteristics. Thus, the cells often exhibit structural and molecular features consistent with glandular tissue (see below). Adenocarcinomas are some of the most common types of cancer, of which the pancreas, breast, and cervix are the most frequently affected organs. This is largely attributed to the fact that breast, colorectal, and genital tissues are highly glandular.

Squamous Cell Carcinoma

Squamous cell carcinoma refers to carcinomas that are derived from the skin and exhibit features specific to squamous cell differentiation (see below). Some examples of these features include squamous pearls and keratinization. Squamous cell carcinomas are most frequently caused by prolonged exposure to direct sunlight without sun protection. Moreover, squamous cell carcinoma is more common in individuals with lighter colored skin. In addition, squamous cell carcinoma is associated with a higher risk of metastases and the symptoms are often highly variable or asymptomatic. Approximately 90% of all head and neck cancers are classified as squamous cell carcinoma.

Basal Cell Carcinoma

Basal cell carcinomas originate in the folliculo-sebaceous-apocrine region of the basal layer of the skin. As such, this type of carcinoma is one of the most common forms of skin cancer following exposure to direct sunlight. There are three specific types of basal cell carcinoma, which include superficial, nodular, and infiltrative basal cell carcinoma. This type of carcinoma accounts for approximately 70% of all non-melanoma related skin cancers.

Anaplastic Carcinoma

Anaplastic carcinomas are carcinomas that lack specific histological or morphological hallmarks of differentiated cells. In these types of cells, the nucleus to cytoplasm ratio is altered such that the nucleus is highly enlarged and hyperchromatic, indicative of an elevated proliferative potential. Moreover, the enlarged nuclei are often irregularly shaped and exhibit a complete loss in cellular polarity.

Large Cell Carcinoma

Large cell carcinomas are characterized by the absence of the histological hallmarks of other carcinomas and exhibit a large cytoplasm and a polygonal morphology. The most common etiology of large cell carcinoma is a history of cigarette smoking.

Small Cell Carcinoma<h/3>

Small cell carcinoma is exhibited by extremely small, round cells with little cytoplasm (see below). These cells are also polygonal or spindle-shaped. In addition, small cell carcinomas are extremely malignant, with rapid doubling times and a high tendency for metastases (approximately 70% of cases). The most common locations of small cell carcinoma include the lung and cervix. This type of carcinoma is highly associated with cigarette smokers, as small cell carcinoma is rarely observed in non-smokers.

Adenosquamous Carcinoma

Adenosquamous carcinomas are tumors which exhibit characteristics of both squamous cell carcinoma, each comprising a minimum of 10% of the total tumor volume. This type of cancer is most frequently observed in the lung, but is relatively uncommon, comprising between 1% and 5% of all lung cancers. In addition, there is a high linkage between adenosquamous carcinomas and a history of smoking.

Quiz

1. The histological analysis of a lung biopsy from a suspicious lesion of a smoker reveals cells smaller than lymphocytes, exhibiting minimal cytoplasm. This type of carcinoma is best described as: A. Squamous cell carcinoma B. Adenocarcinoma C. Adenosquamous carcinoma D. Small cell carcinoma

Answer to Question #1

D is correct. Small cell carcinoma is described as cells at least three times smaller than a lymphocyte with minimal cytoplasm. This type of carcinoma is commonly found in the lungs of smokers.

2. The histological analysis of a skin biopsy revealed malignant cells exhibiting keratinization. This type of carcinoma is most likely: A. Squamous cell carcinoma B. Adenocarcinoma C. Adenosquamous carcinoma D. Small cell carcinoma

Answer to Question #2

A is correct. Squamous cell carcinoma is a common form of skin cancer. Malignant squamous cell carcinomas exhibit the morphological characteristics of squamous epithelial cells (e.g., squamous pearls and keratinization).

References

Antonelli A and La Motta C. (2017). Novel therapeutic clues in thyroid carcinomas: The role of targeting cancer stem cells. Med Res Rev. doi: 10.1002/med.21448.

Datta P, Gupta V, Mohi GK, Chander J, Janmeja AK. (2017). Lactobacillus coryniformis Causing Pulmonary Infection in a Patient with Metastatic Small Cell Carcinoma: Case Report and Review of Literature on Lactobacillus Pleuro-Pulmonary Infections. J Clin Diagn Res. 11(2):DE01-DE05.

Filippiadis et al. (2017). Metastatic bone disease from breast cancer: a review of minimally invasive techniques for diagnosis and treatment. Eur J Orthop Surg Traumatol. doi: 10.1007/s00590-017-1986-9.

Rouanet M, Lebrin M, Gross F, Bournet B, Cordelier P, and Buscail L. (2017). Gene Therapy for Pancreatic Cancer: Specificity, Issues and Hopes. Int J Mol Sci. 18(6): E1231.

Stucky et al. (2017). Single-cell genomic analysis of head and neck squamous cell carcinoma. Oncotarget. doi: 10.18632/oncotarget.18021.