Here are some excerpts from the Satipatthana Sutta. Although this has been translated from Pali and might not be completely accurate, I like how articulate, descriptive and factual he puts it. My 80 IQ summary is: This is what's in the body, and this is what happens to it! So better live in the moment before its all gone.
Enjoy!

The Reflection on the Repulsiveness of the Body

And further, monks, a monk reflects on this very body enveloped by the skin and full of manifold impurity, from the soles up, and from the top of the head-hairs down, thinking thus: "There are in this body hair of the head, hair of the body, nails, teeth, skin, flesh, sinews, bones, marrow, kidney, heart, liver, midriff, spleen, lungs, intestines, mesentery, gorge, feces, bile, phlegm, pus, blood, sweat, fat, tears, grease, saliva, nasal mucus, synovial fluid, urine."
Just as if there were a double-mouthed provision bag full of various kinds of grain such as hill paddy, paddy, green gram, cow-peas, sesamum, and husked rice, and a man with sound eyes, having opened that bag, were to take stock of the contents thus: "This is hill paddy, this is paddy, this is green gram, this is cow-pea, this is sesamum, this is husked rice." Just so, monks, a monk reflects on this very body enveloped by the skin and full of manifold impurity, from the soles up, and from the top of the head-hairs down, thinking thus: "There are in this body hair of the head, hair of the body, nails, teeth, skin, flesh, sinews, bones, marrow, kidney, heart, liver, midriff, spleen, lungs, intestines, mesentery, gorge, feces, bile, phlegm, pus, blood, sweat, fat, tears, grease, saliva, nasal mucus, synovial fluid, urine."

The Nine Cemetery Contemplations

And further, monks, as if a monk sees a body dead one, two, or three days; swollen, blue and festering, thrown in the charnel ground, he then applies this perception to his own body thus: "Verily, also my own body is of the same nature; such it will become and will not escape it."
Thus he lives contemplating the body in the body internally, or he lives contemplating the body in the body externally, or he lives contemplating the body in the body internally and externally. He lives contemplating origination-factors in the body, or he lives contemplating dissolution factors in the body, or he lives contemplating origination-and-dissolution-factors in the body. Or his mindfulness is established with the thought: "The body exists," to the extent necessary just for knowledge and mindfulness, and he lives detached, and clings to nothing in the world. Thus also, monks, a monk lives contemplating the body in the body.
And further, monks, as if a monk sees a body thrown in the charnel ground, being eaten by crows, hawks, vultures, dogs, jackals or by different kinds of worms, he then applies this perception to his own body thus: "Verily, also my own body is of the same nature; such it will become and will not escape it."
Thus he lives contemplating the body in the body...
And further, monks, as if a monk sees a body thrown in the charnel ground and reduced to a skeleton with some flesh and blood attached to it, held together by the tendons...
And further, monks, as if a monk sees a body thrown in the charnel ground and reduced to a skeleton blood-besmeared and without flesh, held together by the tendons...
And further, monks, as if a monk sees a body thrown in the charnel ground and reduced to a skeleton without flesh and blood, held together by the tendons...
And further, monks, as if a monk sees a body thrown in the charnel ground and reduced to disconnected bones, scattered in all directions_here a bone of the hand, there a bone of the foot, a shin bone, a thigh bone, the pelvis, spine and skull...
And further, monks, as if a monk sees a body thrown in the charnel ground, reduced to bleached bones of conchlike color...
And further, monks, as if a monk sees a body thrown in the charnel ground reduced to bones, more than a year-old, lying in a heap...
And further, monks, as if a monk sees a body thrown in the charnel ground, reduced to bones gone rotten and become dust, he then applies this perception to his own body thus: "Verily, also my own body is of the same nature; such it will become and will not escape it."