ANATOMY & PHYSIOLOGY

A great deal of enzymatic digestion occurs in the small intestine, the products of which are very small nutrient molecules, small enough to be absorbed through the intestinal wall and into the bloodstream. For carbohydrates this means monosaccharides (simple, single-unit sugars like glucose). For proteins this means individual amino acids. For lipids this means fatty acids.

Ever wonder what happens in the two to four hours after you take a bite of that apple? Lon Kilgore delves into the sophisticated mechanical and chemical processes that take place in the stomach during digestion.

The stomach receives ingested and masticated food and drink from the esophagus. This material is then subjected to further mechanical and chemical degradative processes. New contents of the stomach spend about two to four hours being digested before they pass out of the stomach and into the small intestines. 

The esophagus is a muscular tube composed of four layers: the mucosa, submucosa, muscularis, and adventitia. This 7- to 10-inch tube helps carry food and drink downstream to the stomach. Additionally, sphincters at either end of the esophagus keep air from entering the digestive tract and digestive acid from escaping the stomach.

We don't often think about what happens when we swallow because the process is mostly reflexive, but here's why the feat is an anatomical wonder worth pausing over.

The tongue has roughly 10,000 taste buds, with receptor types specific to each of the five basic tastes regionally distributed. Taste buds also exist elsewhere. Chemoreceptors in the nose and sinuses help sommeliers, cicerones, and gourmands assess taste more fully. And although we associate taste with deriving pleasure from the foods we eat, it also has a more fundamental biological function: survival.

The lips, mouth, and tongue are the gateway to the body’s gastrointestinal system. As soon as you put food or a drink into your mouth, you begin the process of deriving nutrition and energy from it.

Understanding the anatomy and physiology of the gastrointestinal system allows us to know how eating supports exercise adaptation. It also provides us with an essential critical skill: the ability to determine which dietary approaches may actually work and which are baseless marketing claims that ignore how the body actually functions.

Asthma is a chronic inflammatory disease of the airway. During an asthma attack, the respiratory tract becomes narrowed. This may be a survival mechanism — a reduction in airflow to limit lung injury from harmful airborne materials — that has gone awry in some individuals. Lon Kilgore, Ph.D., explains what happens to the body’s respiratory system during an asthma attack and why coaches must become cognizant of how to safeguard athletes in the case of an episode.

Through breathing and gas exchange, our bodies manage to get oxygen into the blood and carbon dioxide out of the blood. How this is accomplished is conceptually simple but also exquisitely intricate and complex when considered in detail. Lon Kilgore, Ph.D., explains.

Ever wonder what's going on in your body when your plan to complete a WOD unbroken comes crashing down mid-workout? Lon Kilgore, Ph.D., explains how lung volume and breathing frequency change as the body moves from rest to work.

The lungs are less like balloons and more like giant warm marshmallows. They contain 1,000 miles of air-conducting tubes. The surface area of the tiny air sacs that make up the lungs is roughly the size of a tennis court. Here, Lon Kilgore, Ph.D., describes the anatomy of the lungs and explains how the respiratory system works to move oxygen from the atmosphere into the bloodstream.

As a key part of the respiratory system, the lungs help process a critical element of life and exercise: oxygen. The circulatory system then helps distribute oxygen throughout the body. To maintain this elegant system of supply and demand during sustained aerobic exercise, our ventilation rate increases by about 300 to 400%. If we push our exercise intensity, that rate can exceed baseline by more than 500%.

What happens during a heart attack? How long is the window before permanent damage begins to occur in the heart’s tissues? Here, Lon Kilgore, Ph.D., describes the series of events that follow a complete or partial blockage. He also discusses innovative research into how high-intensity exercise might harness the body’s healing processes to create an infarction-resistant heart.

Heart attack: Words no one wants to hear from a physician. Here's what happens when a person suffers a myocardial infarction.

Blood is made up of a solution of water and mineral ions and bioactive molecules called plasma. The solid portion of blood is made of cells, platelets, cell fragments, and very large molecules. The ratio of these two components, solid and liquid, is expressed as a percentage and is called the hematocrit. A higher hematocrit is associated with better endurance performance, but efforts to artificially elevate hematocrit can sometimes prove fatal.

When we teach about the heart, we differentiate between the structures and functions of its right and left sides. The major functional difference is that the right side of the heart delivers blood to the lungs and the left side delivers blood to the rest of the body. The right side’s purpose is pulmonary circulation, and the left side is responsible for systemic circulation.

Coronary circulation includes important arteries and veins that perfuse the heart. The blood inside the atria and ventricles does not directly support the heart muscle; the heart has to deliver and drain blood as it does for any other muscle.

Blood vessels are adaptable to stress. If there is hypoxic stress (low oxygen content present) that results in tissue hypoxemia (low oxygen in the tissue), a cascade of local hormonal and anabolic events occurs that produces new capillaries and new arterioles. This process is called angiogenesis and is considered to be an endurance-friendly anatomical adaptation, improving the body’s capacity to deliver oxygen to working skeletal muscle.

The flow of blood through the heart follows the same general pattern as the electrical conductive pathway if we begin tracing it from its entry into the right ventricle. However, the blood flow system includes both inflow and outflow.