Human Nutrition: The Anatomy of Digestion

If you’re new to the series, you can start here.

It is my inclination to launch into an entire, in-depth anatomy and physiology lesson, because that kind of thing makes me giddy, but I’ve stopped myself for both of our benefits. This would be a much longer post, if I explained digestion down to a cellular level. Instead, I’m just going to make a few key points, so neither of us gets lost in the remaining parts of this series. If you have questions, though, be sure to post them in the comments or email me.

You probably know that steak in steak-form doesn’t nourish you, and your body has to go through several processes to break it into a form it can use. This is, of course, all involuntarily controlled by nerve impulses, muscles, and hormones. The only time you might be aware of this is when you need an antacid, or you forgot to eat lunch, or you’re so full that you fall asleep right where you ate. I’m not sure exactly how important it is that you know how your digestive tract works in your everyday life, but you’re about to have a little more knowledge for your trivia night!

Nearly every system in your body plays some role in how your body absorbs and uses the foods and beverages you consume.

Metabolism is the entirety of chemical processes involved in maintaining life. Your metabolism is handled on a cellular level, and (sorry!) you have very little long-term control over your metabolism. We will talk more about this later, as we learn to determine basal metabolism, and dig deeper into designing sustainable diets.

There are 4 main types of tissue in the human body: epithelial, connective, muscle, and nerve. Epithelial cells cover the surfaces of the outside and inside of your body, forming the lining to your organs, absorbing nutrients, secreting fluids, and excreting waste. Connective tissue protects and supports your body, produces blood cells, and stores fat. Muscle tissue is designed to streamline movement, inside and outside your body. Nerve tissue is made for communication, and extends from your brain and spinal cord to the tips of your fingers and toes. Most of the time, these tissues work together to make your body do what it’s meant to do: help you live your best life.

Photo courtesy WikiMedia Commons.

All of those tissues mingling and cooperating make up the 11 different systems working together all the time to keep your body going: digestive, lymphatic/immune, cardiovascular, urinary, nervous, endocrine, integumentary, skeletal, muscular, respiratory, and reproductive. All of the things you eat are used by all of those systems. So, that means it’s incredibly important that these areas are properly nourished, and possibly equally important that you know what these systems do.

Digestive System

I hope it goes without much explaining that this is where the chemical and mechanical digestion processes happen. The digestive system is made up of your mouth, esophagus, stomach, intestines, liver, gallbladder, pancreas and rectum, so it’s also the primary place for absorption and elimination. It also helps the immune system because it destroys germs and creates a barrier that protects you from any weird items you may ingest.

Lymphatic/Immune System

No, they are not the same system, but they work so closely with one another that I’ll put them here. The immune system contains your white blood cells, thymus gland, spleen, and all of the lymph glands, vessels, nodes and tissues. The immune system is responsible for creating white blood cells and protecting from microbes. The lymphatic system maintains tissue fluid balance, helps with fat absorption, and removes foreign materials from your lymph and blood.

Cardiovascular System

When we talk about the cardiovascular system, we’re referring to your heart, blood, and vessels. This is where some of the nutrient magic happens: your blood carries hormones, nutrients, gases, and waste around your body.

Urinary System

Your urinary system involves your kidneys and urinary bladder. It regulates your blood pH balance, your body’s chemical balance, and the water balance. It also removes waste products from blood.

Nervous System

Your brain, nerves, sensory receptors, and spinal cord work together to identify and interpret your senses, control your movements, and your various brain functions intellectually and psychologically.

Endocrine System

Your endocrine system regulates growth, reproduction, metabolism, and other functions through your endocrine glands: pancreas, hypothalamus, pituitary, adrenal, and thyroid.

Integumentary System

This is a really long way of saying your hair, skin, and finger and toe nails. Your sweat glands are also a part of this. The integumentary system produces vitamin D, regulates body temperature, prevents water loss, and protects your muscular system from damage.

Skeletal System

Da Vinci's Anatomical Man

Courtesy WikiMedia Commons

This is your bones, ligaments, cartilage, and joints. It’s why you’re able to be in the position you are right now (I’m sitting) and not be just a giant pile of human. Your skeletal system makes your blood cells and stores minerals, but it’s also there to support the weight of your body and protect your organs.

Muscular System

There are 3 types of muscle that maintain your posture, allow you to move, produce body heat, keep your heart beating, and propel food in your digestive tract: cardiac, skeletal, and smooth.

Respiratory System

Every breath you take exchanges oxygen and carbon dioxide between the air around you and your blood. Your lungs and airways also help regulate the blood’s pH balance.

Reproductive System

This system is vital in sexual maturation and reproduction. Believe it or not, this system is just as important in your nutrition journey as the others. All of your nutrition choices will affect your reproductive system, too, even if you’ve already had or are never going to have children. Health here is also paramount.

That’s just a basic rundown of our internal systems. I wanted to give you only what’s necessary here to continue on this series. We will occasionally talk more about each system while we discuss what happens where, in reference to macro nutrients, micronutrients, eating disorders, and fitness.

So, about the digestive system

I told you all of that to tell you this: there are 3 major absorption points along your digestive tract. Not everything is absorbed in your stomach or small intestine. In fact, your stomach only absorbs a small amount of the water you drink, and about 20% of the alcohol you consume. It’s really there to begin the breaking-down process of the food you eat into a form the body can use. Your small intestine absorbs the remainder of the alcohol, and around 90% of the water you ingest. Also absorbed in the small intestine are fats, vitamins, most of the minerals, amino acids, glucose, and bile. Your large intestine absorbs the rest of the water you drink, along with potassium, sodium, a few of the fatty acids, and gases.




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About Terra Walker

Terra loves creating recipes, imparting wisdom, searching for an amazing cider, owning this website, and traveling the globe. You can catch up with Terra on the channels above, where she never uses third person, because she hates writing about herself that way.

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