Getting Under Your Skin: Exploring Human Body Tissues

Dr. Stephen Flanagan

Welcome to the Flanatomy podcast. I’m your host, Dr. Stephen Flanagan. We’re diving into the wild world of anatomy with a side of crazy stories from my bizarre life. Let’s explore what makes you, you!

Keshia Rayna

And I’m Keshia Rayna, your co-host, keeping it one hundred and making sure Doc doesn’t get lost in his wild tales. I’m locked and loaded with my phone to fact-check and break down the nerdy stuff so y’all can vibe with the science. Back in my days running experiments in a human physiology lab, I lived under the microscope, analyzing tissue slides till I could ID cells blindfolded.

Dr. Stephen Flanagan

Grab your slides and scopes, ‘cause we’re zooming in on the body’s building blocks like they’re the stars of a tissue box blockbuster. A tissue is a group of cells with similar structure working together for a common anatomical role—think of them as the body’s construction crews, each with a unique look under the microscope. There are four basic types: epithelial, covering surfaces; connective, binding stuff together; muscle, built for structure; and nervous, wired for signaling. We’re keeping it anatomical, focusing on their microscope vibes, not their jobs. Keshia, in that physio lab, ever stare at a slide so long you saw cells in your coffee mug?

Keshia Rayna

Amazingly, this was a regular occurrence! I’d be hunched over a scope, spotting goblet cells, and one time I swore my latte foam looked like a kidney tubule—too many late nights! So, tissues are cell teams with distinct microscope looks. Where we starting?

Dr. Stephen Flanagan

Let’s jump into epithelial tissue, from Greek epi, upon, and thele, nipple, ‘cause it covers surfaces like a protective blanket. These cells have polarity—the apical surface faces out, toward a lumen or external environment, like the gut or skin; the basal surface anchors to a basement membrane, tying to connective tissue below. We’ll cover two forms: simple, one cell layer, and stratified, multiple layers, with cell shapes—squamous, cuboidal, columnar—popping differently under the scope. We’re primarily using H&E stains—hematoxylin and eosin—for slides. Hematoxylin stains nuclei dark blue or purple, highlighting DNA; eosin stains cytoplasm and extracellular bits pink or red, making structures stand out like a neon sign. Let’s start with simple squamous epithelium.

Keshia Rayna

H&E was my bread and butter in the lab—blue nuclei, pink cytoplasm. We should start with why this stain is the standard for histology slides.

Dr. Stephen Flanagan

Great point! H&E’s the go-to ‘cause it’s cheap, reliable, and gives killer contrast—nuclei pop dark, cytoplasm glows pink, so you can spot cell shapes and layers clearly. Simple squamous epithelium is a single layer of flat, scale-like cells. Under H&E at 400x, they look like a mosaic of fried eggs—super thin, pale pink cytoplasm, dark oval nuclei bulging in the center, almost translucent, like a delicate film. We use slides of lung alveoli or Bowman’s capsule in the kidney’s renal corpuscle ‘cause they’re ultra-thin, showcasing that flat structure perfectly. Alveoli are tiny air sacs with walls so thin you can see the squamous layer without clutter; Bowman’s capsule wraps the glomerulus, its thinness highlighting the flat cells. I was teaching a lab class once and I showed an alveoli slide one the overhead. I was using a microscope with a camera connected to the projector. I was too zoomed in. I was using the 100x objective lens, doing a little showboating, but I thought I’d lost the cells. Which is a pain because you have to clean the oil off the slide and start all the way back at the 4x objective lens and refocus everything. Fortunately, one of the students pointed out the nuclei at the very top of the screen and I just moved the stage adjustment knobs and found the cells.

Keshia Rayna

Classic Flan chaos! So, simple squamous looks like flat eggs, used in lungs or kidneys ‘cause they’re thin and clear.

Dr. Stephen Flanagan

Right, but the alveoli of the lungs in cross section leave these big open spaces. so there are these tight little lines of cells all over the slide like a map of the streets in a big city.

Keshia Rayna

I get it. that is a simple enough mistake. What’s next under the scope?

Dr. Stephen Flanagan

Simple cuboidal epithelium, one layer of cube-shaped cells, like a grid of tiny boxes. At 400x with H&E, they’re neat squares, nuclei round and centered like dark blueberries, cytoplasm a soft pink, forming tidy rows or rings. Kidney tubule slides are the go-to, same slide as Bowman’s capsule. To tell them apart, look for the renal corpuscle: it’s a round, chaotic blob—glomerulus capillaries like a pink, tangled knot, wrapped by the thin squamous capsule. Tubules are orderly, circular or oval rings, cuboidal cells like a pearl necklace of nuclei, clean and uniform. Kidney slides are perfect ‘cause tubules are packed in, showing that boxy shape clearly. In a lab I taught, a student called the corpuscle “the kidney’s messy meatball” to remember it—stuck with the whole class!

Keshia Rayna

Messy meatball? I’m stealing that for my old lab crew! Tubule slides were my zen—those neat rings are so satisfying. Next epithelium?

Dr. Stephen Flanagan

Simple columnar epithelium, tall, rectangular cells like a picket fence. At 400x with H&E, they’re elongated, nuclei oval and basal, like dark almonds near the bottom, cytoplasm pink, forming a tight, vertical wall. Small intestine slides show these lining villi, with goblet cells—big, pale, oval-ish patches, named for their goblet shape, like a wine glass, holding mucus for the gut. In H&E, goblets are lighter, almost ghostly, ‘cause they’re packed with mucus, not DNA, standing out among the columnar cells. They look like pale balloons in a pink forest. A student once said they looked like “gut snowmen,” and I couldn’t unsee it!

Keshia Rayna

Gut snowmen? Stop it! So, columnar’s tall in the intestine, goblets are pale ovals for mucus. What’s that ciliated one in the esophagus?

Dr. Stephen Flanagan

Probably the most fun phrase to say in all of anatomy! Ciliated pseudostratified columnar epithelium, say SOO-doh-STRAT-ih-fied, looks like multiple layers but is one, with nuclei at different heights, giving a “false” stratified look. At 400x with H&E, it’s a wavy fence of tall cells, nuclei scattered like dark seeds, cytoplasm pink, with hair-like cilia on the apical surface looking like a fuzzy fringe. Esophagus slides show this, packed with goblet cells for mucus, pale ovals dotting the scene. The ciliary escalator is the cilia’s coordinated wave, moving mucus like a conveyor belt. Under the scope, cilia shimmer like a tiny forest swaying, goblets like pale bubbles. Keshia, why don't you tell everyone what stratified squamous looks like.

Keshia Rayna

So, pseudostratified’s one layer, looks layered, with cilia and goblets. Then, Stratified squamous epithelium, is multiple layers of flat cells, the flattest are at the surface. In vaginal slides at 400x with H&E, you navigate to the epithelial boundary—where cells meet the blank slide edge. Basal layers are cuboidal, nuclei dark and round; upper layers flatten into thin, pink, pancake-like sheets, top ones almost translucent, like stacked tissue paper. It’s thick, protective, perfect for wear-and-tear spots. Finding that boundary feels like hunting the edge of a cell city—cells on one side, empty space on the other.

Dr. Stephen Flanagan

So, stratified squamous have stacked flat cells at the boundary. Which should we discuss net Keshia?

Keshia Rayna

Stratified cuboidal epithelium, rare, in sweat gland ducts on skin slides. At 400x with H&E, it’s two layers of cube-like cells, nuclei round like dark marbles, cytoplasm pink, forming tubular ducts that look like stacked boxes in a ring. Navigate to the skin’s deeper layers to spot these glands—neat, compact clusters. Stratified columnar epithelium, super rare, is in male urethra slides. At 400x, it’s multiple layers of tall cells, nuclei elongated like dark ovals, cytoplasm pink, looking like stacked columns in a tight formation. Finally, transitional epithelium, in urinary bladder slides. At 400x with H&E, basal layers are cuboidal, nuclei round; upper layers are bulbous, round cells, like pink balloons, stretching to dome-like shapes. Focus on basal layers for that cuboidal look, then upper layers for the bulbous vibe. A student called it “bubble wrap tissue” in lab, Keshia, and it’s now my favorite description!

Dr. Stephen Flanagan

Bubble wrap tissue? I’m stealing that! So, transitional’s stretchy, cuboidal to bulbous. Got any lab stories from your scope days, Kesh?

Keshia Rayna

Oh, yeah! Early in my research, I mixed up a bladder slide with a kidneys, The professor was like, “Kesh, those aren’t tubules!” I turned it into a game to spot the differences—saved the day, but my Prof gave me side-eye for weeks. Let’s shift to connective tissue.

Dr. Stephen Flanagan

Those histology professors can be so strict! All connective tissues share common features: cells, fibers (collagen, elastic, reticular), and an extracellular matrix—ground substance ranging from fluid to solid. The four classes are connective tissue proper (loose/dense), cartilage, bone, and blood. Each has unique cells, fibers, matrix, and structural roles. Keshia, do you think we should tell everyone what the matrix is?

Keshia Rayna

What’s the matrix, Doc?

Dr. Stephen Flanagan

It’s a sci-fi classic, starring Keanu Reeves as Neo, a hacker who learns the world’s a computer simulation—a digital prison where humans are plugged into a virtual reality by sentient machines harvesting their energy. Neo’s the prophesied “One,” guided by Morpheus and Trinity to break free, dodge bullets in slow-mo, and fight agents like Smith in a world where code bends reality. Keanu’s leather coat and those green digital rain sequences? Iconic! And there is a scene where this elevator door dances down a hallway in a fiery explosion, amazing!

Keshia Rayna

Well, that really spiraled off the rails! Not the movie Flan. The matrix of connective tissue is the extracellular ground substance—gel-like, fluid, or solid—that surrounds cells and fibers, giving the tissue its structure and support. It’s like the scaffolding holding everything together, from loose goo to hard bone. Back to reality, Doc—what’s the first connective tissue?

Dr. Stephen Flanagan

Ha, nice pivot! Lets mention all the connective tissues that are referred to as Connective tissue proper is a category of connective tissues that includes loose and dense types. The loose connective tissues have sparse fibers and open spaces. Areolar tissue, is a great example, found just under skin or between organs. it’s a wispy web—collagen fibers like pink, wavy threads, and sparse black reticular fibers scattered fibroblasts with flat, dark nuclei, and a clear, gel-like matrix. It’s like looking at tissue cotton candy. Next up is Adipose tissue, fat storage also under skin, shows big adipocytes at 400x—empty-looking, thin pink cytoplasm rims, nuclei like dark crescents pushed to the side, matrix clear, no fibers. It’s like a bubble wrap of fat cells. Reticular tissue, in lymph nodes, looks like a dark net—reticular fibers stained black, reticulocytes with dark nuclei, loose matrix like the stars in Dali's Starry Night. It is very important the you remember the names of the cells in each of these tissues: Areolar has fibroblasts, Adipose has adipocytes, Reticular tissue has reticulocytes. Then, it is also important to remember the fibers Adipose does not have visible fibers, but Reticular tissue has reticular fibers and Areolar has both collagen fibers and reticular fibers.

Keshia Rayna

Bubble wrap fat? My lab slides of adipose were like that! That is a good way to remember what your looking at. Sometimes when students do lab practicals they need little tricks like that to keep everything straight. What’s next?

Dr. Stephen Flanagan

Next up are the three types of dense connective tissue proper. first, Dense regular connective tissue, in tendons, with H&E shows tightly packed collagen fibers, parallel like pink cables, fibroblasts sparse with dark nuclei, dense matrix. Well... the collagen fibers should be pink... turns out they don't stain very well in tight like this so they fibers are always like a tan-ish, clear-ish color. I usually have to adjust the condenser a bit to make them visible. Second, is Dense irregular, in dermis deep to the skin, has random collagen fibers like tangled yarn, same cells, pink matrix. it is very pretty, like a swirled paint on the surface of water. It might be easy to mistake this tissue for smooth muscle. The last Dense connective tissue proper is Dense elastic, found in arteries, shows dark, wavy elastic fibers, fibroblasts, stretchy matrix. It is pink with jagged black reticular fibers stacked on top of each other... maybe like a barcode on pink paper.

Keshia Rayna

I love it! A pink barcode. Like something you might see at a candy shop! Ok, after connective tissue proper I am guessing you're going to want to discuss Cartilage? They are firm and flexible, with no blood vessels or nerves. Also, when you think cartilage, you should think water. Because, the ground substance is almost all water. Another nice thing is that with all these tissues the dominate cell type are called chondrocytes.

Dr. Stephen Flanagan

Perfect transition Kesh! Hyaline cartilage is always first up in the cartilage and it is my favorite tissue in the body! It comes from the Greek word hyalos, which means glass. But, it was described to me like glassy water.... so like a calm lake or pond with few ripples, and it kinda looks like that. You can find this tissue in the nose or trachea, our slides usually come from the trachea where hyaline cartilage forms a deep thin layer below the basment membrane. It looks glassy, of course, with a smooth, pale blue matrix, chondrocytes are in lacunae, like stars in a lake, collagen fibers present but invisible. Then there is Elastic cartilage, most easily found in the external ear. Elastic cartilage has dark elastic fibers like a springy net, and chondrocytes in lacunae. Lastly, Fibrocartilage, in intervertebral discs, shows thick, light pink, collagen bundles, less matrix, fibrous and pink with sparse blue dots representing the nuclei of chondrocytes.

Keshia Rayna

Glassy lakes? Poetic, Doc! Hyaline was my lab fave—those lacunae are cozy. Can we move on to bone tissue? It looks so interesting under a microscope! Compact bone, in bone shafts, looks like tree rings—osteons with central canals, osteocytes in lacunae like dark dots, hard pink matrix. You have to navigate to the thinner parts of the bone chip to see it though. Spongy bone, in bone ends, is porous at 100x, trabeculae like a lattice, osteocytes sparse. Very interesting.

Dr. Stephen Flanagan

You’re spot-on about bone—those slides are like a work of art! Last up is the blood. It is a little odd to think of blood as connective tissue but it is and plasma is the matrix. At 400x shows red blood cells (pink, no nuclei) and white blood cells (dark nuclei) in a clear plasma matrix.

Keshia Rayna

I think we should move on to membranes—mucous, in gut, with H&E membranes show epithelial layers (often columnar with goblets) over loose connective tissue, pink and layered. Serous, like pleura, is thin epithelium over connective tissue, looking delicate, pink matrix at 400x. Cutaneous, skin, is thick stratified squamous over dense connective tissue, pink and robust.

Dr. Stephen Flanagan

Perfect! And with the cutaneous skin, we have keratinized and non-keratinized versions. At 400x with H&E, keratinized cutaneous membrane, like on your palms, shows a thick stratified squamous epithelium, basal layers with cuboidal cells and dark nuclei, upper layers flattening into pink, flaky sheets packed with keratin—say KER-uh-tin—a tough protein making it look dense and scaly, like a pink desert with dark nuclear specks. Non-keratinized cutaneous membrane, like in the mouth, is also stratified squamous but softer, no keratin, so the top layers are moist, pink, and plump, nuclei still visible, looking like stacked, juicy pancakes. It’s a protective shield either way, but keratinized is the armored version!

Keshia Rayna

Finally! We can talk muscle tissue?!

Dr. Stephen Flanagan

No problem Kesh, it is a big favorite of mine as well! Skeletal muscle, with H&E shows long, cylindrical fibers, striated with alternating pink and dark bands, which is pretty trippy looking on the eyes! There should be multiple small dark nuclei on edges, like striped ropes. Keep in mind the cells are very wide, like most of the field of view. Cardiac muscle, in heart, at 400x is shorter, smaller, branched fibers, striated so still trippy, single central nuclei, intercalated discs like dark crossbars, looking like a pink lattice. A lot of the time we use the slide that is stained with just the Iron Hematoxylin because it shows the intercallated discs better so the slide will be completely blue. Smooth muscle, is non-striated, spindle-shaped cells, single oval nuclei, pale pink, like a smooth pink weave.

Keshia Rayna

Cardiac slides were my A&P lab obsession—those discs pop! They look like big think horizontal bars. Last up, nervous tissue?

Dr. Stephen Flanagan

That's right. Nervous tissue, motor neuron slides at 400x with H&E show big motor neurons—large, blue-stained cells, nuclei dark purple from hematoxylin ‘cause they’re DNA-heavy, cytoplasm pale blue. Smaller pink glial cells have less DNA, so they’re eosin-light. In spinal cord slides, neurons look like stars with long processes, glia like faint pink dots. The color difference is all about DNA—neurons have more, so they soak up hematoxylin like a sponge. A student called neurons “blue starfish” once, and I’ve used it ever since!

Keshia Rayna

Blue starfish? Love that! So, big blue neurons, small pink glia ‘cause of DNA. Alright, Doc, wrap it up!

Dr. Stephen Flanagan

Let’s close this like a perfect microscope focus—sharp and clear! Tissues are the body’s building blocks, from epithelial shields to connective scaffolds, muscle fibers to neuron stars. Under the scope, they’re a cellular art gallery, staining blue and pink with H&E. Keep those slides spinning, students, and you’ll ace anatomy! No tissue boxes needed for tears—you got this!

Keshia Rayna

Cellular art gallery? Yo, Doc, you’re serving microscope masterpieces! That’s tissues—epithelial covers, connective binds, muscles flex, neurons spark. See you next time everybody!