Lithograph of the Rotator Cuff group from Gray's Anatomy.

The Rotator Cuff is a group of four muscles that attach to the humerus and scapula to support the shoulder joint. The Glenohumeral joint (where the scapula and humerus meet, a.k.a. the shoulder) is a ball and socket style joint and due to the small surface area of each bone where they connect, it is the most moveable joint in the entire body. The Rotator Cuff along with deltoid, teres major and the coracobrachialis make up the 7 muscles responsible for the movement and stability in the shoulder.

The four muscles of the Rotator Cuff include the supraspinatus, the subscapularis, infraspinatus and teres minor all of which have their attachment and/or insertion points on the scapula bone and/or the humerus (the large bone connecting the shoulder to the elbow). The most commonly damaged muscles in the group are the supraspinatus and the infraspinatus.

A sudden, powerful movement of the shoulder joint can cause an acute tear. Bowlers, tennis players, boxers, and pitchers often suffer an acute tear. A chronic tear is caused by repetitive motion wearing down the muscle on or near the tendon. Chronic tears can lead to Impingement Syndrome; the condition where the inflammed muscles are squished under the acromial arch before they attach to the Humerus. Chronic tears occur most often in people over 40 years old.

Rotator Cuff tears have a 40-90% treatment success rate.

Smooth Muscle cells by Polarlys

The human body has three different kinds of muscle: smooth, skeletal and cardiac. Smooth muscle is the involuntary, non striated muscle that is found in your digestive tract, blood vessels, lymph system, bladder, respiratory system, uterus, skin – almost any part of the body you can think of that requires movement of some type that is automatically regulated without your conscious control. For example, smooth muscle lines your digestive tract and is responsible for moving the partially digested food through the small and large intestine by peristalsis, the systematic contraction and relaxation of muscle fibers that produces a squeezing effect. Peristalsis is what happens when you swallow food as well. Smooth muscle cells contain only one nucleus; whereas skeletal muscle cells contain multiple nuclei.

Skeletal muscle is under our conscious control and is involved in every movement the human body

Skeletal muscle structure by Raul654

makes; be it walking, talking, chewing, riding a bike, and so on. Skeletal muscle fibers are structurally different from smooth muscle in that they are striated – under a microscope, dark lines appear along their length. Each space between two striations in a skeletal muscle cell is called a sarcomere and is made up of actin and myosin proteins. When a muscle contracts or relaxes, actin and myosin fibers slide against one another becoming closer together or further apart. Thus the striations appear (if we could see this in action under a microscope) to come closer together or further apart.

Individual smooth muscle cells are fusiform in shape and flatten out in their relaxed state and fatten up in their contracted state. Individually, these cells have more elasticity than skeletal muscle cells.

Heart Muscle fibers by Dr.S. Girod, Anton Becker

Cardiac muscle cells are striated, involuntary cells found in the heart. They differ from skeletal and smooth muscle in many ways, but two are key: cardiac muscle fibers appear branched under the microscope, but still have a striated appearance and the chemical mechanisms that activate their contraction or relaxation are different from those of skeletal or smooth muscle.

Cow Pox pustules on a Cow's Udder

Both viruses and bacteria cause diseases in plants and animals. It’s important to note, though, the vast majority of bacteria are harmless to humans, and a great number of bacteria are essential to our survival. Viruses, bacteria, prions and fungus that cause disease are known as pathogens. Pathogens are simply infectious agents; as the word origin suggests in this case: “pathos” means suffering and “gen” means the generation of.  A virus is an interesting entity that hovers on the cusp of being life. It is basic genetic material boiled down to the most essential elements: genes, protein and sometimes, a lipid outer shell, built using the host’s cellular material. That’s it. Bacteria are prokayotic cells, of which there are many, many varieties. Prokaryotes lack a nucleus and have very few (if any) membrane bound organelles (cellular organs wrapped in their own individual coating).

A virus cannot multiply on its own; it needs to be inside a cell in order to divide. Typically, a virus is proliferated in the following manner: first, it attaches to the outer shell of a cell and either through diffusion or chemical messenger channels, is absorbed. Next, the protein covering protecting the viral DNA or RNA (there are both DNA and RNA viruses) dissolves, releasing the virus’ genetic material. The plant, animal, or fungi cell then combines its own DNA with the viral DNA and begins making copies. Since the viral DNA is actually combined with the host’s DNA, any host cell division will also make a copy of the virus. Viruses can also proliferate by cellular lysis: the host cell completely fills up with copies of the virus, causing the cell to burst and spew out viruses which can then infect other cells in the body. The perfect parasite!

Now the biggest, medically relevant difference between viruses and bacteria is how they are treated when infecting a body. Antibiotics only treat bacterial infections; not viral ones; like the Common Cold or Influenza. Your body needs to just batten down the hatches and kill the viral invaders on its own. It has only been very recently that drugs have been developed to treat a virus once it has become symptomatic: Tamiflu and Relenza are but a few. The main defense against viruses is still vaccines: altered forms of the virus introduced to the body to create an immunity “memory”. Our body then recognizes subsequent exposures to the same virus and can mobilize an immune attack accordingly. The etching at the right is Cow Pox, the much less dangerous form of a similar strain called Small Pox. It was discovered that those who were exposed to Cow Pox, did not succumb to Small Pox as the Cow Pox created an immunity memory.

Beta blockers are a class of drugs that are most commonly used to treat heart problems; short for Beta- adrenergic blocking agents. These drugs prevent epinephrine (adrenaline) and norepinephrine (noradrenaline) from binding to the beta cells located on your nerves resulting in slowed transmission of nerve impulses to the heart (Beta 1 receptors – there are three different beta receptors located on cells – 1, 2 and 3). Once nerve impulses are slowed, the heart requires less blood and oxygen to function, slowing heart rate and preventing blood vessel constriction. Under normal circumstances, when beta 1 cells are stimulated, heart rate increases, and your blood vessels constrict to allow more blood to flow to your skeletal muscles. This is an important adaptation in our bodies, readying them for fight or flight when faced with imminent danger; your heart beats faster, bringing a fresh supply of oxygen to your skeletal muscles, allowing you to run or fight; an evolutionary adaptation. At the same time, blood flow is redirected away from your digestive system as your body needs to worry about the immediate danger in front of it, not with everyday functioning; where you have trouble figuring out priorities, your body decides for you!

The problem with this system, and thus one of the reasons why Beta blockers are prescribed, is that if your heart muscle is damaged, or if you have arrhythmias, or one of many other heart conditions, any increase in workload puts  you at risk for sustaining further heart damage. Beta blockers have negative inotropic and chronotropic effects:

What is an Inotropic Effect?

Inotropic refers to the strength at which a muscle contracts. A negative inotrope decreases the strength of a muscle contraction and a positive inotrope increases the strength of a muscle contraction. Beta blockers are negative inotropes – if your heart doesn’t beat as “hard” it is less likely to break down. Drugs like Milrinone have the opposite effect; they increase the contractility of the heart and are used in some cases of congestive heart failure.

What is a Chronotropic Effect?

Chronotropic refers to the speed at which the heart beats. Negative chronotropic agents, such as beta blockers, decrease the hearts contraction rate.

In summary beta blockers work to decrease heart rate (beats per unit time) and the strength of the heart contraction protecting it from incurring further damage.

Shin splints is the general term given to pain experienced in the shin area of the leg and is not a specific diagnosis, but rather a convenient term to describe a number of possible physical processes at work; most commonly associated with the tibia. The tibia and fibula are the two leg bones between the knee and foot; the fibula is on the outside of the leg and much thinner than the tibia which sits on the inside of the leg. Pain in this area is most commonly caused by stress to the muscles, tendons or ligaments connected to the tibia. This stress can be caused by an increase in intensity or duration of exercise, or in athletes who endure a lot of shock to the legs; for example, marathon runners. Pain associated with this condition is called medial tibial stress syndrome, the attachment point on the tibia for the soleus and tibialis posterior muscles. This is half way between the knee and the foot on the inner surface of the tibia. In addition to marathon running, and dramatic exercise increases, the shape and locomotion of your foot can cause this syndrome. If you overpronate; your foot flattens out too much when standing upright, your foot will roll inwards placing stress on the muscles and tendons attaching to the tibia.

Another cause of shin splints is a stress fracture in the tibia.  Unlike acute fractures that happen with impact stress and are instantaneous – breaking a leg skiing or falling; or breaking a bone in a car accident – large, instant traumas, stress fractures are usually caused by low forces acting on a bone over a long period of time. Also known as fatigue fractures, these breaks occur in athletes who do a lot of running and jumping on hard surfaces; dancers and runners.

Undiagnosed shin pain can be caused by Compartment syndrome. If you look at a cross section of the muscles and bones below the knee, you will see different pockets with the various muscles that make up the lower leg – these pockets, or compartments can contain one or several different muscles wrapped in fascia. Think of fascia like connective tissue shrink wrap surrounding your muscles. If, in the course of training, one of these muscles becomes too big for its compartment, it will cause stress and pain in the surrounding tissue. This is one cause of compartment syndrome. Another cause is swelling or bleeding resulting from a traumatic event.

Permanent treatment usually involves surgery – splitting the fascia; followed by careful rehabilitation. Short term treatments involve rest, physiotherapy and possibly orthotics.

My standard disclaimer – I am not a doctor, nor should any of the above information be taken as medical advice. I provide the above for informational interest. If your reaction to the above is “huh”, or “interesting”, my job is done.

Your entire digestive system.

Your stomach is located at the end of your esophagus and is the terminus for swallowed food and drink. The stomach receives chewed food and continues to mechanically and chemically break it down into smaller pieces, creating more surface area for your small intestine to absorb nutrients.

Your stomach is an acidic environment with a low pH of between 1 and 3. Parietal cells in the wall of the stomach secrete hydrochloric acid (HCl). If your esophageal sphincter; basically the lid to your stomach; isn’t closed properly, HCl will creep into your esophagus resulting in heartburn. HCl has a few different jobs. One, is to kill bacteria or other potentially dangerous pathogens you may have unknowingly ingested with your food. Another is to convert pepsinogen into pepsin. Pepsinogen is released from chief cells in your stomach wall. HCl, chemically changes pepsinogen into pepsin and is essential because pepsin doesn’t function in an environment with a pH greater than 5. Pepsin begins protein digestion by breaking it down into peptide chains. Peptide chains are made up of amino acids. Your small intestine absorbs amino acids into your circulatory system for distribution to the rest of your body. It is important to note there is a layer of mucus protecting your stomach from being chemically broken down by pepsin and HCl.

Parietal cells of stomach wall

Parietal cells in your stomach wall also secrete intrinsic factor; a substance whose only job – as far as scientists know – is to facilitate the absorption of  vitamin B-12.  Intrinsic factor cannot do its job in the acidic environment of your stomach; it works best in a pH of 7 – close to water – but is used later in your ileum to absorb vitamin B-12 into your circulatory system after bile from your gallbladder has neutralized the acidic chyme (what your partially digested food is called when it enters your small intestine). B-12 is vital for your red blood cells to carry oxygen. People who lack intrinsic factor, cannot absorb vitamin B-12 and suffer from pernicious anemia.

Chymosin, or rennin, is secreted by the chief cells in your stomach wall and is responsible for the breakdown of a specific peptide bond: phenylalanine and methionine, through a complicated chemical process that I won’t detail here. Interestingly, rennin is the active ingredient in rennet which is used the cheese production; compelling some vegetarians into eating cheese without rennet.

Gastric lipase (“lip” means fat and “ase” means breakdown) is secreted by the chief cells to begin fat digestion in your stomach by hydrolyzing (“hydro” means water and “lyzing” means breaking apart; so the breaking apart of a molecule using water) fat molecules into fatty acid chains. Further fat digestion happens in the small intestine with the addition of pancreatic lipase.

G-cells in the wall of your stomach secrete gastrin, a hormone responsible for stimulating the release of HCl from the parietal cells. Gastrin is a chemical messenger that travels in your bloodstream and is released when your stomach is distended from having recently eaten, or when directed to be released by your brain in response to the sight or smell of food. Gastrin stimulates the release of HCl and pepsinogen. It enhances the strength of your stomach contractions to aid in mechanical digestion and causes the pyloric sphincter to relax or contract, controlling movement of chyme that moves into duodenum, the first segment of the small intestine. Your duodenum can only process a certain amount of chyme at a time, so your pyloric sphincter opens and closes to allow small packets of chyme to enter at regular intervals.

In summary, your stomach breaks your food into smaller pieces and mixes it with all of the above secretions in mechanical digestion. Parietal cells secrete hydrochloric acid and intrinsic factor. Chief cells secrete pepsinogen, chymosin and gastric lipase. Mucus cells secrete mucus to protect the stomach wall from the acidic chyme. Gastrin is the hormone responsible for mobilizing the whole process.

The colon is the biggest part of the large intestine. Your entire intestinal tract between your stomach and your anus includes your small intestine that is divided into the duodenum, the jejunum and the ileum. Your large intestine is made up of your cecum, ( in anatomical order) the ascending, transverse, descending and sigmoid colon, rectum and anus.

The cecum is the small sac that connects to the ileum of the small intestine to the ascending colon. Chyme is the mostly digested food matter that enters the cecum from the small intestine. 90% of digestion has already taken place. The colon has no digestive enzymes, but positive intestinal bacteria called gut flora and mucus are added to the chyme to form feces. At this point, your body will reclaim water and vitamins; essentially concentrating the feces before it exits the body. Note; when you have watery poop, your colon is not reabsorbing water and vitamins from the feces; the last step in digestion is being skipped. This is one of the reasons why it is so important to stay hydrated when you have diarrhea.

One type of gut flora - Candida albicans

Now, a word about dietary fiber. We are constantly reminded to eat lots of fiber for colon health. But why? The bacteria in your large intestine consume the largely undigested fiber for their own sustenance, and give off acetate, propionate and butyrate as waste products which the cell lining of the large intestine uses as nutrients. It really is amazing how efficient our bodies are; the 3 R’s to the extreme.

What can go wrong?

Colitis (“col” is colon and “itis” means inflammation), not matter what the cause is a swelling of the large intestinal wall. It can caused by autoimmune processes, idiopathic (of unknown cause), vascular (an interruption of blood flow to a portion of the intestine), infectious (as is the case with clostridium difficile and e coli), or caused by parasites.

Hereditary or other causes of colorectal cancer affect approximately 7% of U.S. citizens.

Crohn’s disease is an autoimmune disorder where the body attacks the colon wall, causing colitis.

Major elements of the urinary system

The urinary bladder, as it is referred to anatomically to distinguish it from meaning “pouch or flexible enclosure”, sits atop your pelvic floor: protective layers of muscles and connective tissues designed to hold you internal organs in place. The bladder is the final internal destination for urine that has been collected and concentrated by the kidney and transported via the ureters – one for each kidney.

The urinary bladder; like the design of many other internal surfaces of your body, like the small intestine and the stomach is lined with folds of tissue. In the stomach and bladder, these folds are called rugae and they stretch and flatten in response to increased pressure – if you have just eaten a big meal or haven’t urinated in a long time. Our wonderful bodies follow this design because internal bladder expansion takes the pressure off the surrounding pelvic and abdominal organs. In contrast, if the bladder filled outwards like a balloon, our pelvic and abdominal muscles would be continually squashed.

We start feeling the urge to pee when our bladder is about 25% full. For most people; this pretty easy to ignore. Nerves on and near our bladder, when stretched, trigger the parasympathetic nervous system (the rest and digest part of our nervous system as opposed to the sympathetic fight or flight part of our nervous system) to signal us to go pee. As the bladder stretches, the PNS becomes more insistent that we go pee. If the bladder reaches 100% capacity you will expel urine involuntarily. The flow of urine is controlled by two muscles; an internal involuntary muscle called the detrusor muscle and an external voluntary Kegel muscle.

OK, a brief aside to explain involuntary and voluntary muscle: involuntary muscles are controlled directly by our nervous system without conscious input from us. They are made up of smooth muscle fibres. Skeletal muscle, under our voluntary control is also regulated by our nervous system, but we are the ones sending the signals to the brain to move or not move. Skeletal muscle is striated. Microscopically, they look very different from each other. Smooth muscles are working away in your body all the time; like for example, in your small intestine as the smooth muscles push food along the digestive tract towards the large intestine (or colon) and out the anus.

Kegel muscle a.k.a. the Pubococcygeus muscle

It is our voluntary muscle we contract to “hold pee in” You can strengthen this muscle by doing Kegel exercises – for women, flexing the little ring of muscles, inside your vaginal opening. Doing about 25 flexes of this muscle every day well help to prevent urinary incontinence problems when you are older. Men also have a Kegel muscle that allows their penis to stay erect, and controls their ejaculation and of course, help with incontinence. Men can isolate and strengthen this muscle by stopping and starting the flow when urinating. This is the same for women.

What can go wrong? Well it all boils down to incontinence, but for many different reasons. If you have damaged nerves, you may not be able to receive the PNS’s signals urging you to urinate as is the case with some Parkinson’s and Multiple Sclerosis patients. Your detrusor muscle (involuntary) is controlled by the PNS. If your PNS is damaged, this muscle may not function properly, and the only protection you have is your external muscle; which is likely not strong enough to hold back small outputs of urine. Prostate cancer can damage pelvic nerves resulting in incontinence.

Sometimes (mostly in women), if you laugh, sneeze or cough, the pressure it creates overcomes both sets of muscles resulting in little spurts of urine coming out. This is called Stress Incontinence and happens mostly in older women – over the age of 60, but can happen younger; say if you have a genetic predisposition to urinary incontinence.

Overactive bladder is diagnosed when you have to pee 8 or more times a day, and are up 1 or 2 times a night. Based on this definition approximately 1 in 6 people in the U.S. have this problem. OAB can be treated with antimuscarinic drugs or through a really cool sounding procedure whereby physicians insert an electrode near the tibial nerve in your leg. An electrical impulse travels to your sacral plexus via your tibial nerve. Recall, that your tibia is a bone in your lower leg. Your sacral plexus is a bundle of nerve fibers responsible for controlling parts of your pelvis and lower extremities. The treatment takes place once a week for 12 weeks. Some patients need more or ongoing treatment. I myself have an overactive bladder, but it doesn’t badly interfere with my life – excepting 11 hour long bus rides in Central Turkey with only one bathroom stop; I have just lived with it without treatment. Please understand, I am not a medical professional and I am not advocating any procedure or treatment, but just seek to educate people about our bodies and how they work. Peace out.

Your thyroid is a butterfly-shaped organ that lies across the cartilage of your neck above the collar bone. The role of the thyroid is to  stimule metabolism and along with the parathyroid glands ( beside or near thyroid), controls the body’s circulating calcium levels.

The thyroid produces T3 and T4; triiodothyronine and thyroxine for those of you who like wordy words as well as calcitonin. As their name suggests, both T3 and T4 use iodine, and their numbers refer to how many iodine molecules are attached to the structure. Detailed and easy to understand information about the thyroid is hard elusive and I find myself having to refer to my anatomy and physiology textbooks to provide the best answer. Your thyroid has two different kinds of follicle cells – cells that secrete hormones: follicular cells and parafollicular cells. Your follicular cells produce T3 and T4.

Your pituitary gland is located in your brain and secretes, among other things Thyroid Stimulating Hormone (if it is a stimulating hormone, it comes from your pituitary gland). TSH tells your thyroid to make T3 and T4 which travel to every cell in your body and stimulate those cells to produce protein or increase oxygen usage.

The thyroid’s parafollicular cells produce calcitonin which decreases the amount of circulating calcium in your blood. To help you remember this, think “calcitonin tones down the body’s calcium.” Your body does this by storing the excess calcium in your bones, and interestingly, calcitonin contributes to us no longer feeling hungry. There are times also, when you need to increase the amount of circulating calcium. The parathyroid glands that sit atop the thyroid secrete parathyroid hormone to stimulate our bone cells to release calcium, by stimulating our kidney to reabsorb calcium in the process of urine concentration, and stimulates our small intestine to absorb more calcium from the food we eat via Vitamin D. Essentially, the small intestine asks the kidney for a usable form of Vitamin D which enhances the absorption of calcium by the microvilli in your small intestine. The production of parathyroid hormone is not dependent upon a feedback loop with the pituitary gland in your brain. Sensors on the parathyroid gland themselves can measure the amount of circulating calcium in the blood.

There are lots of different disorders associated with the thyroid, but almost all of them break down into too little or too much thyroid hormone. The cause can be linked to a problem with the thyroid itself, or a problem with the hypothalamus or pituitary gland in your brain. Whatever the case, symptoms are similar.

Hypothyroidism is a deficiency of thyroid hormone. Although, as I stated, there are many causes, the most common cause is iodine insufficiency  (the introduction of iodized table salt into our collective diet has helped with this problem). Since T3 and T4 are responsible for cellular metabolism, our body doesn’t metabolize our food properly, nor does it get the boost in energy that increased oxygen production supplies; leading to weight gain, tiredness, cold intolerance, muscle cramps, joint pain, carpal tunnel syndrome,decreased sweating, brittle hair and nails , constipation and a low heart rate. Hashimoto’s thyroiditis is an autoimmune disorder that causes hypothyroidism, and ironically, the drug treatment for hypER thyroidism can cause hypothyroidism.

Hyperthyroidism in an excess of thyroid hormone that lead increases metabolism beyond a healthy level. This results in stimulating the body’s sympathetic nervous system (the getting ready for fight system fueled by adrenaline). This exhibits as fast heart beat, palpitations, tremor, anxiety, diarrhea and weight loss – not a good diet plan. Grave’s disease is the most common presentation of hyperthyroidism.

The spleen sits just under your ribs in the upper, left portion of your abdomen and is responsible for filtering out old red blood cells, storing monocytes and collecting antibody covered bacteria and blood cells for removal from the body.

Red blood cells; the cells responsible for carrying oxygen to the body’s tissues, have a life span of about 4 months before the wear out. The monocytes in the spleen collect dying rbc’s and to recycle their constituents for use in the body. What can’t be recycled, is excreted by the kidneys and large intestine. Both urine and feces get their trademark colors, in part, from the waste products of red blood cells bilirubin and biliverdin. Monocytes are white blood cells that can either directly destroy dead red blood cells though a series of surface membrane chemical reactions or can differentiate into macrophages which resemble gobbling Pac-Men. Half of the body’s monocytes are stored in the spleen. Monocytes also travel through your body and migrate to damaged tissues when needed. Monocytes differentiate (mature) into macrophages to “eat up” dead cells, bacteria, or other waste products from damaged tissues.

Human Monocyte surrounded by red blood cells

The spleen’s monocytes are also responsible for eating up antibody coated bacteria and cells. Think of antibodies as little “please kill me” signs attached to the outside of cells. The body’s immune system has marked these antibody complexes for destruction. Monocytes will either ingest these complexes directly, or cause them to self destruct.

You can live without your spleen, but its absence will leave you more susceptible to infection. Splenectomy patients have a higher than average rate of death from pneumonia and a higher concentration of circulating monocytes – since their storage unit has been removed. Splenectomy patients also show a decreased response to some vaccinations. Without your spleen, you need to work harder to stay healthy to prevent disease.