I couldn't resist this image that is floating around on the web. I don't know who to give artistic credit to, but it just fit too well with this post. Don't let angry feet take you down. Treat your feet well because as you will learn below, their revenge can be very painful and debilitating.
Your feet are like the foundation under a house. If the foundation sags, so does the house. 
If you have ever tried to square the door frames in a house standing on a sagging foundation you know exactly what we mean. It is impossible and it won't last.
The same is the case with the body. Your chiropractor is trying to square you up structurally, but if your feet are wrong the adjustments just won't last. Your physical therapist is trying to strengthen your body, but suspended over a foundering foundation, the joints, muscles and ligaments will succumb to the forces of gravity. Muscles that would support good posture almost effortlessly are committed to constant strain just to keep you upright.
How is it that the feet have such a huge impact on the whole body? It is typically referred to as the kinetic chain, kind of like the old song 
"Toe bone's connected to the foot bone" etc. every bone in the body is connected with cartilage, ligaments, muscles and tendons, and as a result, we have an articulating system that has a lot in common with a gear box. Literally when you create a rotation in one end, it transmits through the whole body to the other end, and in the process, your posture changes for the better or worse, usually the latter. Since we are starting with the foundation, the feet, we call this the ascending posture pattern.
The basic postural influence from the feet through the ankles cause an internal or an external rotation of your legs. Although the knees may absorb a little of this rotational motion, most of it travels up to the hips, and the close connection in the hips is set up to follow the legs. If the leg rotates inward, the hip on that side will tilt forward. If the leg rotates externally, the hip will rotate posteriorly. The left and right hip is connected via the sacrum through the SI (sacroiliac joints) and you can imagine the problems rising up if your legs cause too much rotation in the hips. Pain—yes you got that right, and you have probably heard of SI joint pain. Very common among pregnant women when the ligament relaxes in preparation for child birth.
It would be nice if that's as far as the trouble travelled, but that's not the case. With one hip more forward rotated than the other, the upper body becomes rotated, usually away from the most forward rotated hip. Typically, both hips are usually forward rotated, one slightly more than the other, the whole base of the spine is tilted forward, and that has a big impact on the curves of your back. Your kyphotic curves (curve of your back looking from the side) will be exaggerated, creating more pressure on the spine in your lower back, and slumping your upper back and neck forward, often referred to as a Head Forward Posture. But because the differential forward rotation of your hips, you will also look like you have a leg length difference, so one hip will be higher than the other, and the opposite shoulder will hike up. That will make it look like you have scoliosis.
As you consider all these changes you begin to appreciate the importance of keeping the foundation in order, because if it is, the rest of your body will generally remain in good alignment. There are a few exceptions of course, one of which is what is called a descending posture pattern that starts from your head. Usually though, the ascending pattern is the most influential, so focussing on your feet is a good idea.
The feet have a unique connection to your body via your ankle. You may have heard of pronation and supination. That is the foot leaning inward (pronation) and leaning outward (supination).
If your feet pronate too much, your legs will be too internally rotated, and if they supinate too much, your legs will be too externally rotated, and if your feet are slightly different, one leg will act slightly different than the other, and you will get what is called a functional leg length difference which in real life tend to cause the same problems you would experience if one leg was actually structurally longer than the other.
That's how the feet are linked to your whole body from your feet to your jaw. This is great knowledge because if you experience back pain, shoulder or neck pain, or ankle and knee pain, your can often look to your feet to fix the problem.