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Anatomy and Physiology: The Pitfalls of LDL Cholesterol

Posted by Courtney Smith on Fri, Nov 13, 2015 @ 12:10 PM

As I get older, I try to be conscientious of what I eat, but the problem is that I'm always craving mac & cheese and there's nothing I can do about it. Resisting the urge to shove a block of sharp cheddar down my gullet with a macaroni chaser is, as they say in "Star Trek," futile. No matter how much I fight it, I eventually cave. My doctor isn't impressed. "Stop eating things so high in cholesterol," she pleads, and I nod seriously and say, "I hear what you're saying, but let's be realistic."

And so it goes.

More and more, we're warned about foods that are high in "bad" cholesterol and the dangers of having high cholesterol, but what does it all mean? Read on to find out!


Cholesterol: What Is It and Why Do We Have It?

Cholesterol is a waxy substance that helps maintain the structure of all of your cells and performs certain tasks, like producing hormones and vitamin D, as well as helping you to digest your food.

Red blood cells flowing through an artery

On its own, cholesterol isn't inherently "bad." In fact, your body—particularly your liver—produces all the cholesterol it needs!

So, where does it all go wrong? Why do so many people have high cholesterol levels? Well, look no further than the foods you eat. Meat, butter, shellfish, cheese, and pastries all can be very high in cholesterol, which is a bummer because everyone knows that lobster mac & cheese is the best kind of mac & cheese on the planet. Obviously eating these things in moderation is fine, but too much of a good thing can be bad for you (except ice cream*).


The Good, the Bad, and the Ugly:
Two Types of Cholesterol

Like a Hollywood classic for which I'll probably be sued for naming, "good," "bad," and "ugly" characteristics can be applied to cholesterol.

Two types of proteins carry cholesterol through your bloodstream: low-density lipoproteins and high-density lipoproteins, and too much of one or not enough of the other isn't a good thing. It's important to try and maintain a healthy balance between them.

Cholesterol traveling with blood cells and other substances through an artery

HDL cholesterol is the "good" cholesterol, as it carries cholesterol from other parts of your body back to the liver, which then removes the cholesterol from your body.

LDL cholesterol is "bad" because a high level of it can lead to a buildup of it in your arteries.

A buildup of LDL cholesterol is "ugly" because it can lead to a bunch of issues. Actually, why don't we talk about those right now?


The Good, the Bad, and the Ugly 2:
Electric Heart Disease Boogaloo

Ah, coronary heart disease: the one threat that gets me on my feet and forces me to stay somewhat active. As we discussed previously, CHD is no joke.

What does heart disease have to do with cholesterol? A lot, actually. See, when there's a buildup of LDL in your artery walls, it narrows the amount of space through which blood travels. Add a buildup of other things, like calcium and fat, and you get plaque. When plaque accumulates in the arteries, it's known as atherosclerosis. When less blood flows, your organs don't get the amount of oxygen and nutrients they need. This can lead to stroke, heart attack, or even death.

An artery narrowed by plaque buildup, showing atherosclerosis

In CHD, the arterial walls of the heart become hard with plaque buildup and grow narrow, limiting oxygen to the heart. When there's a limited or lack of oxygen flow, tissues will die and heart attack can occur.

According to the Center for Disease Control, a whopping 73.5 million adults in the United States have a high LDL cholesterol level, which puts them at double the risk of heart disease than someone whose levels are normal. A high LDL cholesterol level usually doesn't come with symptoms, so many people have no idea if their blood cholesterol level is too high. Exercising, eating well, and not smoking will lower your risk of heart disease.

While it may be impossible for me to give up mac & cheese completely, I can certainly curb my intake. It won't be easy, but it's important. My very life may depend on it.

* I’ve been told that this is just wishful thinking on my part.


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Related posts

- Anatomy and Physiology: Stroke Is No Joke: Always Act FAST
- Learn Muscle Anatomy: Of Dads and Rotator Cuff Injuries
- Anatomy and Physiology: 7 Facts about Cardiovascular Disease

Further Reading:

1. CDC.gov

2. National Heart, Lung, and Blood Institute

3. Heart.org

Topics: anatomy and physiology

Anatomy and Physiology: Five Things About The Integumentary System

Posted by Courtney Smith on Tue, Oct 20, 2015 @ 03:30 PM

For all we talk about taking care of our organs, we always seem to leave out one of the most important and obvious. The integumentary system—which is comprised of your hair, nails, and skin—protects everything inside you, acting as a barrier to keep your bones, organs, and muscles safe and sound. It’s one of the many things about our anatomy we take for granted.

The integumentary system is a pretty amazing structure. So amazing, in fact, that it deserves its own post. Let’s take a look at it.

Integumentary skin


1. The integumentary system is one big, busy organ

That’s right! The integumentary system is the body’s largest organ, absorbing nutrients (from the sun and other sources), regulating internal body temperature (which is why you’re miserable on hot days, but not as miserable as you could be), and eliminating waste (sweat, anyone?).

It also has a very high cell turnover rate—in one year, you’ll shed over 8 pounds of dead skin! In fact, what you see on your body is dead skin waiting to be sloughed off while everything else is beneath the surface.



2. The skin is made up of several different types of cells

Each type of cell contributes to the skin in different ways. The epidermis, the outermost layer of skin, is made up of melanocytes, keratinocytes, Merkel cells, and Langerhans cells. At least two of those should look vaguely familiar to you.

Melanin is pigment, which absorbs ultraviolet rays and determines skin color. The more melanin you have, the darker your skin is.

Keratin is a fibrous protein that protects skin and tissue, and it also is the key structural material in hair and nails.



3. Your skin is divided into layers

Integumentary epidermis dermis hypodermis skin keratinocytes melanocytes

You know this one, though. But did you know that the skin is categorized by three layers, which are then broken down into sublayers?

The three main layers of the integumentary system are the epidermis (outermost layer), dermis (middle layer), and hypodermis (innermost layer).

We’ve gone over the epidermis already, but what about the other two layers? The dermis is a thick layer composed mainly of connective tissue rich in collagen and elastin. The dermis stores water, regulates body temperature and the production of vitamin D, cushions the body, and supplies blood to the epidermis.

The hypodermis is the subcutaneous layer and is composed of mainly adipose (fatty) tissue and collagen-rich connective tissue. It separates muscle from skin, stores fat, and conserves body heat.



4. Your fingers are primed to detect touch

epidermal cells meissners corpuscles touch skin integumentary

There’s a reason you use your hands to feel around in the dark, and it’s not just for balance! Special receptors (free nerve endings) called Meissner’s corpuscles are divvied up around your skin, but are concentrated in places more sensitive to touch, such as your fingers.


5. A special muscle causes goosebumps

Integumentary arrector pili dermis hypodermis skin keratinocytes melanocytes

We’ve all experienced goosebumps before—usually when you’re cold or afraid (or, in my case, when you watch the last 20 minutes of Close Encounters of the Third Kind). But have you ever given thought as to what causes goosebumps? What is in your skin that makes it pucker in such a way? The answer is small muscles known as arrector pili.

The arrector pili muscles (one for each hair) extend from the dermis and attach to each hair follicle, just above the bulb. Hair is sensitive to touch, changes in temperature and air, as well as in reaction to an emotion (e.g., hearing beautiful music, seeing something amazing, the last 20 minutes of Close Encounters, etc.), and the arrector pili muscles contract in response to these physical and emotional changes. When the muscles contract, the hairs stand on end.


The integumentary system has a low rate of permeability (a.k.a., it’s hard for things in the environment to penetrate it), which makes it the perfect protector for the rest of the body systems.


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Related posts

- Anatomy and Physiology: Stroke Is No Joke: Always Act FAST
- Anatomy and Physiology: The Pharynx and Epiglottis
- Anatomy and Physiology: 7 Facts about Cardiovascular Disease


1. Care for conditions from acne to wrinkles 

2. Advances in treating eczema and dermatitis

3. Dermatology pictures, Hardin Library for the Health Sciences, University of Iowa

4. A video that shows the development of skin cancer



Topics: anatomy and physiology

Camp Neuro: The STEM Summer Camp Everyone's Talking About

Posted by Courtney Smith on Tue, Sep 22, 2015 @ 03:00 PM

At my high school, Anatomy & Physiology was one of the hardest courses to pass. It was also the hardest course to join because of the sheer number of students who wanted to take it. If there had been a summer program geared toward A&P, the waiting list to get in would have been endless. But, like the after-school astronomy club I tried (and failed) to start, nothing of the sort was offered.

But that was over 10 years ago. School programs are changing. The internet has opened a myriad of doors and has helped people to connect and be vocal about various shared interests. Thanks to the power of the web, a new program is working its way up the ranks.

Camp Neuro is a week-long STEM summer camp run by local medical students and has cropped up in 18 cities nationwide over the last two years. Their mission is to give high school students interested in medicine or psychology an introduction to those fields, with a focus on the care and maintenance of the brain.

When you think “summer camp,” you no doubt jump to the image of kids throwing themselves into lakes and roasting marshmallows over a fire. Not at Camp Neuro, where by 9 a.m. the campers are wrist-deep in a pig brain or learning how to tie surgical knots.

Camp Neuro students in a workshop with medical professionals.
In the middle of a workshop. (Camp Neuro, Dallas–Ft. Worth, TX, 2015)

My sister works in the field of pediatric neurology, and if she ever found out about this she’d flip. She would’ve killed for something like this when she was in school.

Each day is filled with workshops, interesting A&P lectures, exercise, and special guest speakers from different fields—all of which give the campers a taste of real-world medicine careers, ranging from physical therapy to neurosurgery. A typical day looks something like this:

A typical day at Camp Neuro

We were able to talk with Sohail Kamrudin, a second-year medical student at the Texas College of Osteopathic Medicine, who was the Medical Student Director of Camp Neuro during its run in Dallas–Fort Worth this past July. He and his fellow team members used Visible Body’s brain model as a visual reference for the campers during lectures.

Cross-section of the human brain within the context of the skull

A cross-section of the brain (from Human Anatomy Atlas)

“Your app provided a great learning experience for our attendees,” Kamrudin said. “Seeing the brain from different angles really helped our campers understand it. We ended up building a brain from the brainstem up.”

Camp Neuro isn’t alone in its venture to invigorate enthusiasm for medicine and health. Its sister camp, Camp Cardiac, introduces the basics of cardiology to its campers through hands-on workshops and interaction with professionals. As of right now, there isn’t a Camp Respiratory or Camp Lymph, but who’s to say that won’t change, especially when you see testimonials like this:

“I LOVED my week at Camp Neuro. My only complaint is that it went by too quickly! :-) I learned so much, and made a lot of friends! I’m planning to apply to Camp Cardiac next summer!”
S.T. — Pasadena, CA

“My son said it was his best camp ever! I am blown away by how much they covered in only 1 week. He loved everything but his favorite part was the brain dissection. He also loved the counselors, as they were so positive and fun. Thank you so much for putting together such an amazing program for young people.”
P.L. — Silver Spring, MD

“Our son truly had an amazing time at Camp Neuro. The camp ended a couple of weeks ago and he’s still talking about experience. He is now seriously considering becoming a doctor. Thanks so much for everything!”
R.H. — New York, NY

So here’s to Camp Neuro and Camp Cardiac, paving the way for our future medical practitioners and educators, one pig dissection at a time.

Students of Camp Neuro, Dallas–Ft. Worth, TX, 2015
The medical professionals of the future. (Camp Neuro, Dallas–Ft. Worth, TX, 2015)


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Read further.

- Anatomy and Physiology: 5 Things about the Integumentary System
- Anatomy and Physiology: The Limbic System
- Anatomy and Physiology: 5 Cool Facts about the Middle and Inner Ear

Topics: teach kids anatomy

Learn Muscle Anatomy: Of Dads and Rotator Cuff Injuries

Posted by Courtney Smith on Wed, Jul 29, 2015 @ 11:04 AM

If my dad tells me about the hockey game that led to him tearing his rotator cuff one more time, I’m going to tear the rest of his arm off and beat him with it. I’d rather he’d relive his glory days a little less and focus more on being seen by a doctor for his rotator cuff issues. But because he never got adequate help with his rotator cuff tear when he was younger, I’m doomed to a lifetime of watching His Stubborness wince every time he scratches the back of his head.

Dads. Am I right?

What is the rotator cuff, though, and why does an injury to it have such an impact? Read on! If you’re my dad, read on and then please go see your doctor.


The rotator cuff is a group of muscles and tendons that surround the shoulder joint. These muscles keep the top of the upper arm in the shoulder socket by forming a "cuff" that not only holds the arm in place but helps it move in various directions.

The rotator cuff muscles hold the ball at the top of the humerus firmly in the glenoid fossa. The rotator cuff muscles are the supraspinatus, subscapularis, infraspinatus, and teres minor.







Subscapular fossa

Lesser tubercle
of the humerus

Medial rotation of the head of the humerus; prevents anterior displacement of the humerus


All of the supraspinatus fossa

Greater tubercle
of the humerus

Assists the deltoid in abducting the arm; stabilizes the glenohumeral joint


Infraspinatus fossa on the posterior surface of the scapula

Greater tubercle
of the humerus

Laterally rotates the upper limb; stabilizes the glenohumeral joint

Teres minor

Lateral border of the scapula

Greater tuberosity
of the humerus

Lateral (external) rotation of the humerus; helps protect and stabilize the shoulder joint


Rotator Cuff Injury

When my dad was in high school, he played on our hometown hockey team and ended up… in a fight? In a dogpile? A ninja battle? I don’t know, I feel like the story’s changed over the years. Regardless, he tore his rotator cuff while tending goal and, thanks to our family’s particular strain of stubbornness, never got it properly checked out. It’s been plaguing him ever since.


Tears are typically categorized in two ways: if they have partial thickness or full thickness, and if the tears are traumatic or degenerative. Gradual degeneration, like repetitive overheard motion of the shoulder (think of baseball pitchers), or sudden traumatic events (my dad at hockey) can tear one of the muscle tendons of the rotator cuff. It’s usually a torn supraspinatus that ends up causing the bulk of the issues.

Rotator cuff tears usually occur at the insertion point on the head of the humerus so that the tendon will no longer fully attach to the bone. Want to see it in all its gruesome action? You’re in luck! We’ve got a super short animation about it:



Symptoms of a rotator cuff injury include pain, decreased range of motion in the shoulder, and muscle weakness.

Treating a rotator cuff injury can range from easy (physical therapy being the most common) to invasive (surgery). I’ve been hounding my dad to have surgery on his shoulder for years, but he hasn’t budged yet. I’m not sure what he’s waiting for.

There are several types of surgery to treat the rotator cuff, including open tendon repair – in which a surgeon reattaches the tendon to the bone – and shoulder replacement – in which a surgeon installs the ball part of the artificial joint onto the shoulder blade and the socket part onto the arm bone (but this is reserved for only the most massive rotator cuff injuries coughdadcough).

Minor rotator cuff injuries will heal on their own with plenty of ice, rest, and daily shoulder exercises. If you do end up suffering a more involved injury, do literally the opposite of my dad and have it evaluated by a doctor. It may be one less story to tell at family gatherings, but you’ll be saving yourself a lifetime of pain.



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Topics: learn muscle anatomy

A Stroke Is No Joke: Always Act FAST

Posted by Courtney Smith on Wed, Jul 08, 2015 @ 03:22 PM

I’m about to get a bit personal here, so hold onto your butts.

When I was 14, my friend took me to her aunt’s house so we could swim in her pool. Her aunt was always so cool—super funny and smart, with elegant streaks of gray in her long hair—and I was happy to go. We swam for a while until her aunt called us in to help make lunch. My friend wanted melon balls to go with our salads and sandwiches, so we spent about 10 minutes mechanically scooping out little pink globules into porcelain dishes.

Then, my friend’s aunt paused. I’ll never forget the sound she made, a little boof of confusion, the noise a dog makes when it’s not committed to growling but musters up the effort. She frowned at the half-filled dish in front of her. From across the counter, I watched—horrified, rapt—as one side of her face kind of … melted. The hand holding the melon scoop twitched, as if she meant to lift it, and she began to mumble things I couldn’t understand. My friend immediately went to her side and helped her to the floor as she began to fall, and I called 9-1-1.

As the EMTs loaded my friend’s aunt into the ambulance, one of them came over and helped my friend call her mom. The EMT spoke to her mother and said calmly, “It was a stroke, ma’am. We’re taking her to Whidden Hospital; your daughter and her friend are going to ride with us. Can you meet us there?”

It was honestly one of the most terrifying experiences of my life up to that point; I can’t imagine what my friend’s aunt was feeling.

Pardon the rhyme, but a stroke is no joke. But what is a stroke, and why is it so important to act FAST when one occurs? Keep reading to find out.



While her aunt recovered, my friend would tell our curious and sympathetic classmates, “My aunt had a stroke.” And immediately that would shut them up. It was as if the stark, one-syllable word were an expletive, a harbinger whose wrath no one wanted to incur.

The thing is, there are different types of stroke, and those different types have different causes. They happen for a variety of reasons and they’re associated with as many risk factors.

Ischemic Stroke

My friend’s aunt had an ischemic stroke, which is the most common kind—in fact, 85% of strokes are ischemic. An ischemic stroke is caused when the blood supply to the brain is reduced (also called “ischemia”). Reduced blood flow to the brain causes cell death, which is as bad as it sounds.


The most common types:

  • Thrombotic ischemic stroke: A blood clot, or thrombus, forms in one of the brain arteries due to a build-up of plaque or other vascular conditions, and blocks the artery. This blockage causes reduced blood flow to the brain.
  • Embolic ischemic stroke: A blood clot forms elsewhere in the body (like the heart) and travels to the arteries of the brain, where it becomes lodged in a narrow vessel. This type of clot is called an embolus.

There is also something called a transient ischemic attack (TIA), which is a bit like a mini stroke. A blood clot forms and blocks an artery like in an ischemic stroke, but the blockage is temporary. Before the clot is able to move, it briefly reduces the blood supply to the brain. The symptoms of a TIA and a full ischemic stroke are similar, but brief, but a TIA greatly increases a person’s risk for a full-blown stroke.

Hemorrhagic Stroke

On the other side of the stroke spectrum are hemorrhagic strokes, in which a blood vessel in the brain ruptures or leaks. This can happen for a bunch of reasons, including hypertension, overmedicating with anticoagulants, and aneurysms.


There are two types:

  • Subarachnoid hemorrhagic stroke: A vessel in the brain bursts, causing blood to leak into the space between the brain and skull. When this occurs, it’s usually followed by an immediate, unbearable headache.
  • Intracerebral hemorrhagic stroke: A vessel in the brain bursts and spills blood into the brain tissue, causing cell damage or death.


I mentioned above that there are many contributing factors to stroke. Well, I wasn’t kidding. Risk factors associated with stroke range from family history, lifestyle, and present medical conditions.

Obesity, smoking, alcohol abuse, and drug use are all treatable risks for stroke. Conditions like hypertension (high blood pressure), diabetes, high cholesterol, and cardiovascular disease all contribute to stroke risk.

Those with a family history of stroke or heart attack are more likely to suffer a stroke than those without. Age and gender also play a part. People over the age of 55 have a higher risk. Men tend to suffer strokes more than women, but women—particularly older women—tend to die from them more than men.

Suffering a stroke can cause long-lasting, even permanent complications. Luckily, my friend’s aunt was able to get away with nothing more than memory loss of the incident, but others don’t come away from it so easily.

As I said, memory loss is one complication, but more severe ones include paralysis, pain or numbness, aphasia (or difficulty with speaking or understanding speech), and changes in behavior.



I remember seeing a poster about “Acting F. A. S. T.” in the hospital room my friend’s aunt recovered in, and since then I’ve never forgotten it. F. A. S. T. is an acronym for the warning signs of a stroke—I highly recommend you learn it.

Face drooping: During a stroke, the face can go numb or even droop. The person may have difficulty smiling or his or her smile may be uneven.

Arm weakness: One arm may go weak or numb. In this case, ask the person to lift both arms. If one arm drifts downward beyond his or her control it could be a sign of stroke.

Speech difficulty: A person suffering a stroke may slur words or be hard to understand. Ask the person to say a simple sentence, like, “The birds are singing.” If he or she can’t, it may be a sign of stroke.

Time to call 9-1-1: If you suspect someone is suffering a stroke, you need to call 9-1-1 right away, even if the symptoms disappear. Remember, a TIA’s symptoms are temporary; if someone suffers a TIA, their risk for a full-blown stroke increases exponentially.


 F.A.S.T. poster, courtesy of the American Stroke Association

For those of you wondering, my friend’s aunt made a full recovery. She still has no memory of the event, but that’s okay: I remember it enough for the both of us.

A stroke is no joke. If you suspect someone is having one, remember to act FAST (emphasis on the T).



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Related posts

- Anatomy and Physiology: 5 Things about the Integumentary System
- Anatomy and Physiology: The Pharynx and Epiglottis
- Anatomy and Physiology: 7 Facts about Cardiovascular Disease





Topics: anatomy and physiology

Serious as a Heart Attack: 7 Facts about Cardiovascular Disease

Posted by Courtney Smith on Fri, May 22, 2015 @ 02:47 PM

When you see a heart attack in a movie or TV show, it’s usually a dramatic event—clawed hands clutching a chest, groaning, and then a twisting fall to the floor. Which… well. Take that with a grain of salt. A heart attack is caused by a blockage, usually a build-up of plaque, in an artery that prevents blood flow and oxygen from reaching the heart. The longer the heart doesn't receive blood, the greater the damage to it. In many cases, people don’t even know they’re having a heart attack.

But despite what Hollywood tells you, a heart attack doesn’t exist in a vacuum—it’s the result of a bigger problem: heart disease. Even with a large presence in our society, not many people know the cold hard facts about heart disease, so I'm here to lay them down for you.



7 Facts about Cardiovascular Disease


1. Many people might think cancer is the number one cause of death for both men and women in the United States, but it in fact is number two, right behind heart disease. Heart disease is the cause of 611,000 deaths every year in the United States—that's 1 in every 4 deaths.


2. More than 735,000 people suffer a myocardial infarction (MI)—that’s the official name of for heart attack—every year in the United States. Of those people, 15% (110,250) of them will die from it.


3. Every 34 seconds, someone in the United States suffers a heart attack.


4. While most people know that chest pain is a sign of a heart attack (thanks, Hollywood), it's not the only one. Shortness of breath, fatigue, dizziness, nausea, and pain or discomfort in the back, jaw, neck, and arms are all possible indicators of MI.


5. It's a no-brainer that high cholesterol and blood pressure are contributing factors to heart disease, but additional factors include smoking, diabetes, and not getting enough exercise.


6. Since 1984, more women than men have died from heart disease, but only 1 in 5 women knows that heart disease is the greatest threat to her health. 38% of women die within a year of having a heart attack as compared to 19% of men.


7. According to the World Health Organization, childhood obesity has reached epidemic proportions. Obese children are at a significant risk for heart disease in their adult lives, as well as diabetes, atherosclerosis (build-up of fats and cholesterol in the artery walls), and high blood pressure.


Don’t let heart disease be the thing that does you in, my dear readers. Go out in a blaze of glory, maybe in an incident involving a jet pack or a giraffe herd. Take care of yourselves—I want y’all around for a long time!

Like what you read in this blog? Then go a step further:

Try Human Anatomy Atlas:

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Related Posts:

Anatomy & Physiology: The Anatomy of Vision
Anatomy & Physiology: Parts of a Human Cell
The Endocrine System: Hypothalamus and Pituitary 


-   Know the Signs and Symptoms of a Heart Attack. (2015, April 30). Retrieved May 22, 2015, from CDC.gov

-  Leading Causes of Death. (2015, February 6). Retrieved May 22, 2015, from CDC.gov

Childhood obesity and cardiovascular disease.Tracey Bridger. Paediatr Child Health. 2009 March; 14(3): 177–182.

Heart Disease Facts. (n.d.). Retrieved May 22, 2015, from The Heart Foundation

Facts about Heart Disease in Women. (n.d.). Retrieved May 22, 2015, from Illinois Department of Public Health

Topics: learn heart anatomy

The Lymphatic System: Innate and Adaptive Immunity

Posted by Professor Blythe Nilson on Mon, May 11, 2015 @ 02:20 PM

Today’s post is coming all the way from Canada’s western-most province. Blythe Nilson, Associate Professor in the Biology Department at the University of British Columbia—Okanagan campus, is about to school y’all in the lymphatic system. So pop some vitamin C, kick back, and read on.

Take it away, Professor!


The Lymphatic System

First, let’s quickly review the lymphatic system. The lymphatic system carries out the body’s immune responses by producing and distributing cells, such as lymphocytes and macrophages, that combat disease.

Lymph vessels, or lymphatics, drain fluid from all parts of the body and return it to the heart. They begin as narrow blind-ended vessels in tissues then merge with others as they travel toward the vena cavae, where they return the lymph into the circulatory system. Unlike the blood vessels, lymphatics are one-way.


The spleen is a soft, delicate organ that filters blood for pathogens, debris, or worn-out cells. The spleen is made up of compartments called follicles that are filled with lymphocytes and macrophages that can mount an immune response quickly if antigens are detected. The spleen destroys and recycles about 200 billion worn-out red blood cells every day.


The thymus is a soft, bilobed organ that lies between the heart and the sternum. It’s larger in young people because developing T-lymphocytes spend time there as they mature. Only competent T-cells are allowed to leave the thymus, which destroys any faulty ones. After puberty, the thymus is no longer needed; it atrophies and the lymphatic tissue is replaced by fatty tissue.

Lymph nodes are small, roundish organs that form along lymph vessels. As lymph passes from a lymph vessel through a node it slows down and percolates through millions of lymphocytes and macrophages. If a pathogen is detected the immune cells will multiply, causing the lymph node to swell.



Innate Immunity

As you may know, the body has several structures that serve as protective barriers against infection. These include the skin, respiratory and digestive tract mucous membranes, and other structures.

The term immunity refers to the many structures and responses the human body has for preventing pathogens from entering the body and for fighting them off if they do get in.

Immunity can be broadly divided into two categories: innate immunity and adaptive immunity. Innate immunity is the body’s general response to invading pathogens—it’s the same in everyone and reacts the same way each time. Essentially, we are born with innate immunity all ready to go.

Innate immunity includes physical barriers, such as the skin, and chemical responses, such as antimicrobials found in tears. It also includes physiological responses, such as fever and inflammation. These processes stimulate immune cells to take action, hinder pathogen growth, and prepare damaged tissues for repair. Specialized cells, like macrophages, can kill and digest bacteria and parasites, as well as secrete cytokines that can induce inflammation and mobilize other parts of the immune system.


An inflammatory response causes blood vessels to dilate, bringing more blood to the site and causing localized heat. The vessels also become leaky, allowing fluid and immune cells to leave the bloodstream and enter the infected tissue. The cardinal signs of inflammation are swelling, redness, and heat, and often there is pain and loss of function.


Adaptive Immunity

Now let’s have a look at the other arm of the immune system: adaptive immunity.

Adaptive immunity is the body’s way of mounting an immune response that is specific for each pathogen. B- and T-lymphocytes, or B- and T-cells are central to adaptive immunity. They are able to recognize each kind of invading pathogen and respond with a large, focused response tailored to that specific invader. What’s more, each time a new pathogen is found, the lymphocytes that recognized it will multiply and remain in your body so that if that pathogen ever returns, your immune response will be swift and massive.


Antibody-mediated immunity is triggered when  your B-cells recognize a pathogen. Of the trillions of B-cells in your body there are some with receptors specialized to recognize every pathogen you are likely to encounter. When a subset of B-cells is activated they produce antibodies, specialized proteins that are released into blood and tissues where they bind to pathogens, marking them for destruction by macrophages and other immune cells.

Cell-mediated immunity is carried out by T-cells when they recognize pathogens living inside your cells. Infected body cells display pieces of the pathogen on their surface that are recognized by T-cells. This activates the T-cells, causing them to recruit other cells of the immune system that will deal with the invaders, often by killing the infected cell!


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Related Posts:

Anatomy & Physiology: The Anatomy of Vision
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The Endocrine System: Hypothalamus and Pituitary 


Special thanks to Professor Nilson for contributing to the Visible Body Blog!

Topics: anatomy and physiology

Anatomy and Physiology: The Limbic System's Major Three

Posted by Courtney Smith on Fri, Mar 27, 2015 @ 02:25 PM

What is your earliest memory?

Mine is the sound of my older brother Steve muttering, "I don't know why you're laughing, we're going to get in trouble," and the rush of sand as he helped me pour a bucketful over my head. We were at my Yiayia's house in her sun-soaked backyard, sitting in the little turtle sandbox that was missing an eye (courtesy of my cousin Billy, I would learn years later while going through pictures). The bed of wildflowers nearby kept catching on Steve's shirt and smelled earthy-sweet. While the adults lounged about on the back deck, toasting my mother for keeping her too-curious child alive long enough to see a second birthday, Steve helplessly held the now empty yellow bucket in his hand while I cackled triumphantly to myself.

Sometimes when I'm lounging in my Yiayia's backyard (now hanging with the adults), I'll smell the wildflowers and bam. Suddenly I'm two years old again with sand in my hair and so very proud of the fact.

Long-term memory is still a mystery in a lot of ways, but we do know that the limbic system has a hand in processing and consolidating it. That's not all the limbic system does, however, and we're going to take a look at the role three of its major components play in the brain.


A Functional Classification:
The Limbic System Is, Well, a System

When one speaks aloud about the limbic system, it sounds as though they consider it to be a single structure. That's simply not true. While there’s some debate in the scientific community about which structures are part of the limbic system, there's a unanimous agreement about three of them: the amygdala, hippocampus, and cingulate gyrus. In addition, there’s also the dentate gyrus, parahippocampal gyrus, fornix, and other nuclei and septa.


The limbic system functions to facilitate memory storage and retrieval, establish emotional states, and link the conscious, intellectual functions of the cerebral cortex with the unconscious, autonomic functions of the brain stem.

While the sensory cortex, motor cortex, and association areas of the cerebral cortex allow you to perform certain tasks, the limbic system makes you want to do those tasks. It's your very own internal motivational speaker!


Amygdala: The (Not Actually) Missing Link

Amygdala is a fun thing to say, yes? Ah-meg-dala. It sounds like a city in Game of Thrones.

While small, the amygdala has the big job of acting as the link between a stimulus and how you react to that stimulus. By receiving processed information from the general senses (your eyes, your skin, your tongue, etc.), it’s able to mediate the proper emotional responses. For example, I'm allergic to chocolate, so smelling it invokes a response of disgust in me. For others, it would invoke a kinder response. In my friend's case, it would send her into a euphoria.


Output from the amygdala goes either to the hypothalamus or the prefrontal cortex. Output going to the hypothalamus influences visceral and somatic motor systems. Through these connections, an emotional response to something might make your hair stand on end, make your heart race, or even induce vomiting! Output going to the prefrontal cortex involves conscious responses, such as telling someone you love them or controlling your anger.  


Hippocampus: Memory Consolidator

Hippocampus sounds like something straight out of myth—which it is. In Greek mythology, the hippocamp(us) was a creature with the top half of a horse and the bottom half of a long, scaly eel or fish. Chances are, there was one swimming around the Great Lake at Hogwarts.

The actual anatomical structure is named for its resemblance to the curved tail of the seahorse-like creature. The hippocampus is found in the medial temporal lobe and consists mostly of gray matter. Not very pretty for a memory-forming center, all things considered.


Memories aren’t stored in the hippocampus, but rather cognitive and sensory experiences are organized into a unified, long-term memory. When you experience something, like touching something hot for the very first time, the hippocampus learns the sensory input in relation to the experience and then plays the memory back repeatedly to the cerebral cortex to form a long-term memory in a process called memory consolidation. Think of it as the hippocampus' way of teaching the cerebral cortex. Memory consolidation continues until a long-term memory is formed, which will be held in one of the various areas of the cortex (different memories are housed in different areas).


Cingulate Gyrus: The Limbic Big Boy

I love the cingulate gyri—they look like something Professor X would wear to help him look for new mutants. While it isn't known whether they can enhance one's telepathic ability to locate others with superhuman abilities, the cingulate gyri are known for other things that are just as cool (okay, maybe not).

Ever been so excited about something that your arms flail around, or so angry that your hands clench into fists? The cingulate gyrus, a large arch-shaped structure, plays a role in expressing emotions through gestures.


A gyrus is a convolution, or fold, in the brain that acts to increase surface area, which in turn increases the number of neurons, as well as gray matter. There are many gyri that interact with the limbic system and the brain as a whole. The precentral gyrus (posteriormost gyrus of the frontal lobe) contains the primary motor cortex and controls the precise movements of skeletal muscles. The postcentral gyrus (anteriormost gyrus of the parietal lobe) contains the primary somatosensory cortex and is responsible for spatial discrimination (recognizing the part of your body that’s being stimulated).


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Topics: anatomy and physiology

No dry-erase boards: An ER doctor discusses using our anatomy reference with his patients

Posted by Lori Levans on Mon, Mar 09, 2015 @ 11:16 AM

Meet Dr. Brennen Beatty. He’s an ER physician in Austin, TX.

In recent months, he’s changed the way he talks to patients about their diagnosis. The old way was to tell them what was going on and hope they understood what he was talking about. The new way? Show and tell them using Visible Body’s Human Anatomy Atlas, a visual anatomy reference.

When did you start using Human Anatomy Atlas?

I started using Visible Body’s Atlas on my iPhone just recently—and I’ve kicked myself for not using it earlier. I use Atlas to quickly help patients visualize and understand their diagnosis. This technology helps me improve patient experience, compliance with treatment plans, and my overall efficiency.

Do you find that most of your patients understand their own anatomy?

Not exactly. One out of five Americans are seen every year in the ER and the bulk of patients don’t understand their own anatomy and physiology. To help them understand, patients want to see something. We’re visual animals.

How do they react when you use Atlas?

When I show Atlas on my iPhone my patients become wide-eyed with understanding.


What did you do to help illustrate a point before using Atlas?

Previously I found myself constantly using the dry-erase board in the ER to draw crude anatomy. Or if there was a rolling laptop cart in the room, I’d Google an image. If a patient presented with vertigo and dizziness, for example, I’d call up a picture of the inner ear to explain that connection.


Your overall verdict?

With Atlas, I’m using modern, advanced technology to quickly help my patients visualize and understand their diagnosis. Plus, the learning curve is straight up; it’s easy to use.


Want to see how Dr. Beatty explains gallstones to a patient using Human Anatomy Atlas 7?



Topics: anatomy and physiology

Pregnant Pause: A look at ovulation, fertilization, and implantation

Posted by Courtney Smith on Wed, Feb 18, 2015 @ 01:09 PM

You know, I took a look back through all of the posts we've written over the last few years, and I noticed a glaring omission on our part. We've never once discussed pregnancy.

Part of the reason I think we've shied away from it is because everything else we talk about is equal opportunity—for the most part, everyone's body operates the same. It's only in the physiology of pregnancy and childbirth that we deviate from that. I am a firm believer, however, that knowledge can change the world, and so I think it's incredibly important that everyone—those who have the ability to have kids and those who don't—learn about pregnancy and how it changes the body.

Note: This blog post will be written using "perfect storm" circumstances. Remember: one can conceive pretty much at any time; biology isn't limited to certain weeks.

Weeks 1–2: Prime Time

When we talk about pregnancy, it's usually week to week. Seems annoyingly tedious, right? Wouldn't it be easier to keep track of things month to month? Nope!

Despite the fact that we refer to our pregnant friends and family as being "X months along," so many different things are happening week to week that there'd be far too much to fit into a monthly breakdown. In this "perfect" scenario, weeks 1 and 2 are counted even though one isn't pregnant. The first week starts on the last day of one's period.


A friend of mine once likened the body during ovulation (and the monthly cycle as a whole) to a very excited and unstable aunt. Picture it: she's painting the walls of the prospective nursery, setting up the crib, fixing decals of baby animals by the windows, and hanging a cloud mobile from the ceiling. She turns up the heat in the room and sometimes kicks the furniture a little when she gets too impatient.

Then, one of two things happens:

  1. The egg is fertilized! Huzzah! Our work is done.
  2. The egg wasn't fertilized. Well. It's time to burn the entire room to the ground.

Don't laugh. It's true. Periods are the worst.

Ovulation is the time during the cycle in which a mature egg is released from one of the ovaries and is sent down one of the fallopian tubes where it will wait to be fertilized. With the help of the hormone progesterone, the endometrium lining begins to thicken in preparation for fertilization—if the egg isn't fertilized, the lining is shed (a.k.a. burning the entire room to the ground).



You may be asking yourself, "What does that header even mean?" Well, I threw the famous Inception sound effect up there because “inception” rhymes with "conception," which is what we're going to be talking about. Inception has nothing to do with conception. Well, not really. Conception is a film that I'm writing starring Joseph Gordon-Levitt and my ovaries.

Week 3 is when conception happens. If you're wondering how that works, you're probably not old enough to be reading this.

During weeks 3 and 4, fertilization and implantation occur. Somewhere, the aunt in the nursery is throwing a party and putting the matches away, because there's going to be a baby!

When you hear “fertilize,” your mind probably goes to fertilizer, which is used to aid in the growth of plants. Fertilizer adds nutrients to help a seed grow, creating an environment perfect for the seed.


Fertilization is somewhat similar. Imagine an egg cell, or oocyte, is a seed. On its own, it really doesn't do much. It has the potential for life. But along comes a sperm cell, or spermatocyte, which penetrates the egg, much like the nutrients needed to kick-start the growth of a flower. The fused egg and sperm cells become a unique cell called a zygote.

Over the course of about 30 hours, the sperm cell's nucleus will fuse with that of the egg cell, combining their respective genetic material. About five days after fertilization, the zygote will divide into more cells and move down the uterus and implant into the endometrium as a collection of hundreds of cells, called a blastocyst, that continues to divide into more cells.


Week 4: Seriously, Though—
Don't Make Any Plans for the Next 9 Months

All right! Our crazy aunt is super happy and everything seems to be going swimmingly thus far. The blastocyst has implanted into the endometrium and is dividing, so now what? Well, this week marks the start of the embryonic period.

During week 4, the blastocyst will continue to divide until the cells branch into two groups: the first group includes the earliest baby cells, which will develop into the fetus, while the other group forms an environment that will protect and nourish the fetus—some of these cells will eventually develop into the placenta. When the placenta begins to develop, it sends a signal to the brain and endocrine system to start producing HCG (human chorionic gonadotropin), which is what pregnancy tests attempt to detect in blood (blood test) or urine (pee-on-a-stick test). When HCG is being produced, the body stops releasing eggs and the endometrium stays put.

However, the placenta isn't developed enough at this point to be the main provider of nutrients, so the blastocyst will be "fed" oxygen and other goodies by a microscopic circulatory system.

Stay tuned! We'll be tackling weeks 5–10 soon.


But don't stop there!

We've got an amazing new app coming soon, all about the anatomy & physiology of pregnancy! Be the first to know when it's available.

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