We often tend to think of the gastrointestinal tract (also referred to as the GI tract or, more affectionately, the GIT) as a one-pony wonder – with digestion being its one functional “pony”.
But, while digestion of food into the “metabolic fuel that drives the machine” is definitely an important function, it is only one of many; the digestive tract’s plethora of functions intertwine it with Dog’s whole body.
As is true of any organ system that affects so many other parts of the body, when the GIT is well oiled and healthily purring along, we hardly notice it.
Were it not for that distinctive fragrance of the healthy GIT’s end product, we might not notice it at all. But woe betide the dog owner who is experiencing an out-of-sorts dog with an out of kilter GIT.
Bottom line: treat the GIT right … or you (and your carpet) will suffer the consequences.
GI Tract Basics
The GIT is an organ system responsible for transporting and digesting foods, absorbing nutrients and expelling waste and a host of other functions that link it to other bodily systems.
The GIT includes all structures between the mouth and the anus, forming a continuous passageway that includes the main organs of digestion: the stomach and the small and large intestines.
Most GIT specialists also include within the system the accessory organs of digestion: the teeth, tongue, salivary glands, esophagus, pancreas, liver and gallbladder.
While the basic anatomy and functional physiology of the GIT of all mammals are very similar, there are some differences between species.
For example, the dog’s salivary glands don’t contain amylase – which helps explain why dogs can get away with gulping their foods instead of chewing them well (as Grannie always admonished us to do, so we’d mix and digest our starches).
And the length of the dog’s small intestines, measuring roughly two and a half times the animal’s total body length, is said to be one of the shortest intestines of all mammals in the animal kingdom.
A Digestion Short Course
Specialized cells along the length of the GIT release digestive-regulating hormones.
These hormones – along with other stimuli, such as gastric and intestinal distention, the animal’s activity level, and the type of diet – stimulate and regulate enzyme release from the pancreas, liver and specialized cells along the GIT, and each class of enzyme then digests its designated food type into particles that can be absorbed and utilized.
Digestion basically takes the big chunks of swallowed food (proteins, complex carbohydrates and fats) and enzymatically disassembles them into nutritionally available biochemicals (amino acids, fatty acids, simple carbohydrates and sugars).
The usable nutrients are floated along the tract in a liquid called chyme and then absorbed through the gut wall either by simple diffusion across the thin intestinal wall or by biochemical processes activated within the cells and transported via the blood to other parts of the body.
From the small intestine, digested food moves into the large intestine (cecum) where little, if any, further digestion takes place. The cecum functions as a place where:
- Water, electrolytes and the products of bacterial action are absorbed
- The synthesis and absorption of some vitamins occurs (B vitamins including riboflavin, nicotinic acid, folic acid and biotin, and vitamin K)
- Remaining carbohydrates are fermented (releasing hydrogen, carbon dioxide and methane gasses)
- Remaining amino acids are digested into fragrant compounds such as hydrogen sulfide, indoles and skatoles
- Bilirubin (the product of old red cell breakdown in the liver) is excreted, giving feces their brown color
The end product of digestion is feces, which contain undigested materials ( fiber for example), expelled toxins, living and dead bacteria and other notables such as parasite eggs, the remains of the plastic bag Puppy ate yesterday and myriad other surprises!
5 Reasons Why Intestinal Health Matters
OK, that’s the old-hat stuff; let’s take a quick look at some of the more interesting GIT goodies – realizing that some of this info has so far only been worked out in rats or their human counterparts.
The “gut associated lymphoid tissue” (GALT) is the largest immune organ in the body, consisting of several aggregates of lymphoid tissues found throughout the lining of the gut wall.
It produces a variety of lymph cells and thus offers a variety of immune functions.
The GALT combines with other immune components within the gut including: the mucosal lining of the gut; the microbiome (like a mini ecosystem in the gut) and probiotics (the beneficial micro-organisms that live in the gut); and a wealth of antigens that have been produced by specialized cells lining the gut.
This GALT and associated entities may contribute up to 70 percent of the body’s total immune capability.
2. Healthy Gut, Healthy Life
The more we learn about the gut’s immune system in general, and especially its beneficial microbiome, the more we gain appreciation for its multitude of health-giving functions, in addition to the protective activities of its immune system.
Beneficial gut bugs are also known as probiotics. Probiotics are a part of the entire population of intestinal micro-organisms referred to as the microbiome.
A healthy balance of probiotics is necessary to ensure good health. Prebiotics are those substances that feed and sustain the probiotics. Prebiotics include a variety of fibers that are often found in vegetables and fruits.
Dysbiosis is a term describing a microbial imbalance, generally referring to conditions of the digestive tract. Dysbiosis has been associated with illnesses such as inflammatory bowel disease, obesity, cancer and colitis.
The intestinal immune system, and especially its probiotic component, has a direct connection to the animal’s mind.
A healthy GALT along with a healthy probiotic population helps maintain a healthy mind; it’s been shown that an unhealthy immune system may contribute to all sorts of mental problems including short term memory loss, depression, hyper-excitability and anxiety.
3. Leaky Gut Syndrome
Many of the problems that result from an unhealthy mix of intestinal bug flora (dysbiosis) come from leaky gut syndrome – a condition that allows unwanted stuff (toxins, allergens, partially digested food, etc.) to cross the intestinal wall where they’re absorbed into the blood stream.
A healthy intestine is a thin-walled hollow tube with long fingers (villi) projecting into its lumen. The cells along the villi are responsible for absorbing digested nutrients.
The intestinal wall is responsible for keeping the unwanted stuff out of Dog’s general circulation using several mechanisms:
- The inner surface of the intestine is lined with a thick barrier layer of mucoid material, and the beneficial probiotics provide the maintenance and upkeep of this layer
- Normally there is a tight junction between cells, which, acting as a gatekeeper, only opens up for those substances that the intestinal immune system deems to be appropriate and healthy
- The lining cells themselves can regulate what substances should or should not be absorbed – many substances require a biochemically active process within the cell to allow the substance to be absorbed
A leaky gut disrupts one or more of the protective mechanisms of the intestinal lining:
- The mucoid intestinal lining is removed
- Tight junctions between intestinal cells are opened
- The intestinal cells are either destroyed or they become dysfunctional to the point where they can no longer act to screen out substances that should not enter the blood stream
4. An Allergic Response
Leaky gut causes a generalized allergic response that may result in any of many disease states including:
- food allergies (in turn resulting in any number of conditions including: skin irritations, diarrhea or constipation, etc.)
- inflammatory bowel disease
- autoimmune issues
- joint conditions (arthritis, etc.)
- gluten intolerance
- thyroid disease
- liver dysfunction
- pancreatic insufficiency
- weight gain
- low energy and
- slow metabolism.
Leaky gut syndrome is usually provoked by exposure to substances that:
- Damage the integrity of the intestinal mucosa disrupt the healthy function of the intestinal cells
- Destroy the healthy balance of probiotics in the microbiome
Contributors to the creation of leaky gut include:
- Infectious agents (viral, bacterial, and protozoan)
- Non-steroidal anti-inflammatory drugs (NSAIDs such as Rimadyl, Metacam, Deramaxx, Previcox, etc.)
- Poor nutrition including processed and GMO foods
- Bacterial imbalance, often brought on by antibiotic use
- Toxic overload from exposure to herbicides, pesticides, household cleansers, excessive vaccines, etc.
- Excess, chronic stress
- Lack of exposure to the outdoors (vitamin D deficiency is a known factor in the pathology of inflammatory bowel disease, and there is an active vitamin D receptor in the gut)
- Lack of overall body fitness
5. Taste Receptors
New evidence indicates that taste receptors are not just located on the tongue; they occur throughout the body, including the nose and elsewhere along the airway, as well as in the heart, lungs, along the length of the intestinal tract and in other organs including the liver.
These taste receptors not only detect how a particular food tastes (bitter, sweet, salty, sour or savory, as examples); their other job is to detect potential toxins and to alert the immune system to their presence.
These sentinel taste receptors, by reacting to substances that come into the body, act as gatekeepers for the digestive system, providing information about the food Dog has just eaten. “Should I swallow this stuff or retch it back up onto the carpet?” asks the Dog’s taste buds.
Taste bud scientists have found that the human sentinel taste buds are generally categorized within the “bitter” category, with some 25 types of receptors that detect bitter compounds (referred to as T2Rs by the taste bud cognoscenti), and it’s these “bitter detectors” that are the true “worker-tasters” for alerting the immune system.
Interestingly, some people are genetically hard-wired as “super tasters,” meaning they have the genetic wherewithal to first detect and then produce a potent immune-mediated response against certain invading bacteria – bacteria that have activated their taste bud receptors in the lungs or intestinal tract.
Other people, “non-tasters,” don’t have this tough-guy genetic profile, and there are genetic variants all along the spectrum of tasters.
As you’d expect, the super tasters, with their healthier sentinel and immune-reacting systems intact, are generally healthier.
We have yet to see if all this applies to our dogs but one would suspect that it does, at least to some degree.
The many functions of the gastrointestinal tract make it a prime organ system for holistic care.
Today’s prescription for Every Dog (and Every Dog’s Human) …
Eat well, play hard, get outside, have fun and keep reinforcing your gut’s health with a mix of probiotics, fed with prebiotics.