Digestion begins in mouth with mechanical chewing, assisted by enzymes, such as Amylase for starch break-down to glucose. Various carbohydrates begin the digestion process in the mouth due to this mechanical (chewing) process, as does initial (digestion) of proteins. Food moves through esophagus by way of PERISTALSIS (muscular contractions), as it does through the entire digestive tract. The base of esophagus is the Cardiac Sphincter, and the Pyloric Sphincter muscle prior to emptying into the Duodenum (first 12" small intestine) constricts the base of the stomach.

The stomach is a "holding tank" where most all digestion takes. It has a volume of between 2-4 liters (about 2-4 qts.), a low pH, between 1.5 and 2.5. This assists in chemical of food materials, as well as activating protein enzymes, such as PEPSIN. While the protein digestion in the mouth began by chewing, it is basically completed in the stomach by digestive enzymes. A mucus lining prevents digestion stomach wall tissue. Very little absorption takes place in stomach.



The SMALL INTESTINE is where most all absorption of digested food takes place. The first 12" of the Small Intestine is Duodenum, where fat digestion (emulsified) takes place; bile transported from the Gall Bladder (associated with Liver) through the COMMON BILE DUCT to Duodenum. Bile is important in fat digestion. Large finger-like projections, called VILLI (and MICRO VILLI) increase surface area of Small Intestine for food absorption. These are heavily vascularized (i.e., contain good blood supply) for absorption of digested materials. While the primary function of the Small Intestines is absorption, all final digestion of carbohydrates, proteins, and especially fats, takes in the small intestine.

The Large Intestine is primarily a "holding tank" of solid waste material. It is generally quite fluid (watery). Absorption of minerals (Calcium, Magnesium) as well as B-complex vitamins, and some amino acids takes place here. Bacteria in colon produce the B-complex vitamins, which also produce various useful amino acids.


The Lungs serve the function of gas exchange (water vapor, carbon, and oxygen). The air passes from the mouth cavity to the Trachea to the Bronchi, to the Bronchioles and finally into the lung tissue. Bronchioles become smaller and smaller and end in a like structure called the ALVEOLUS (ALVEOLI).

  Gas exchange takes place in the Alveolus (alveoli), at the level of small arteries and vein (capillaries) which are wrapped around the alveoli. Gas exchange takes place through a process of osmosis (at the capillary level) in the lungs, as well as in the body tissues.


Note: all arteries lead from heart; all veins lead to heart.

The Aorta is main blood supply to body; the Vena Cava is main vein blood from body parts, leads from body to heart (into Rt. atrium). Pathway of blood flow is from body parts to Vena Cava, to Rt. Atrium, to Rt. Ventricle, from the Rt. Ventricle through Pulmonary Artery (carrying deoxygenated blood), to the lungs where gas exchange takes place. From the lungs OXYGENATED blood flows back to the heart by way of the Pulmonary Vein into the Left Atrium, then to the Left Ventricle. From the Left Ventricle blood is pumped to the Aorta, and finally to the body parts. The Aorta is the largest artery in body and leads directly from heart.

High cholesterol and triglycerides (fatty like substances transported as part of the blood) contribute to formation of plaque on artery walls, leading to heart disease, high blood and strokes. Narrowing (reducing cross sectional area) of arteries is often observed in constrictions of coronary arteries leading to reduced blood supply and therefore reduced oxygen supply to heart muscle. In addition, this process may also be observed in constriction of carotid arteries, reducing blood and oxygen supply to brain--causing fainting spells, or decreased "brain" function, and may be an indicator of high blood pressure and potential for strokes. Both cholesterol and triglycerides are natural products of body metabolism, and are important for maintaining proper "materials" as building blocks of certain body structures.


For example, cholesterol levels in the blood is naturally produced in the liver and is used as part of cell membrane structure, as well as part of molecular structure of hormones. There is a strong correlation between cholesterol levels in the blood and fat content as part of diet, especially saturated fats. High triglycerides may also be due to a high fat diet, but in some people may be related to too many simple sugars as part of diet (i.e., too many "goodies").

Cholesterol is generally divided into two groups; HDL, or High Density Lipo-proteins, and LDL, or Low Density Lipo-proteins. HDLs are considered the "GOOD" kind of cholesterol, while LDLs are the "BAD" kind. LDLs are responsible for forming the plaque on the artery walls and reducing the cross sectional area. This plaque contributes significantly to increased blood pressure and risk for heart disease. Plaque is forming almost from birth and continues throughout life. Proper diet has been demonstrated in many studies to reduce risk of these heart/artery diseases. Low fat diets are important; medical/health care advisors have strongly suggested that a diet consisting of 30% fat is acceptable; however, more recent studies suggest (STRONGLY) that a diet of 10-15 % fat is more acceptable and beneficial to good heart/artery health. [NOTE: a side benefit is that low fat diets significantly reduce the risk of a variety of cancer and cancer related diseases] It is important to maintain a low fat diet, but also one which is composed primarily of monosaturated and polyunsaturated fats (i.e., mainly vegetable oils, like corn oil, olive oil, etc.).

HDLs have been found to be important, especially in helping to reduce the LDLs in the blood. The HDLs play a role in transporting the LDLs to the liver for destruction. In some cases, lowering of total cholesterol and increasing HDLs in the blood have even reduced the amount of plaque already formed. In other words, some evidence suggests that plaque formation on artery walls may be "reversible" to some degree.

RATIO OF TOTAL CHOLESTEROL/HDL is important. An acceptable ratio is 4.5 or less; an ideal ratio is 3.5 or less. Between 3.5 and 4.5 the risk is higher, and the formation of plaque (atherosclerosis) is slowly taking place. If one lives long enough, thickening and/or lesions the arteries WILL TAKE PLACE.


CHOLESTEROL: Desirable levels:
less than 200

Borderline high: 200-239
High (danger): greater than 240
HDLs: Acceptable--greater than 35
Increased Risk--less than 35

LDLs: Desirable levels--less than 130
Borderline high---130-159
High risk ---greater than 160

TRIGLYCERIDES: Desirable level--
less than 150

Borderline risk--150-200
High--greater than 200


TROPIC HORMONES - Produced by glands in the brain (such as the anterior pituitary) and transported to some other site such as endocrine glands, (i.e., Thyroid Gland) for action; these hormones are needed in only small quantities for impact.

  ADH (Anti-diuretic Hormone) and TSH (Thyroid Stimulating Hormone - it stimulates the Thyroid Gland to produce the hormone THYROXINE) are two of the TROPIC Hormones. There are numerous examples of steady-state conditions in human physiology. Two that will be used as examples here are: WATER BALANCE AND TEMPERATURE control.


Kidneys serve to filter metabolic waste material from blood plasma. They are well vascularized (good blood flow) and the functional unit which accomplishes this task is the NEPHRON. Filtration of water material, various dissolved minerals and of course water, takes place by OSMOSIS at the level of the GLOMERULUD and BOWMAN'S CAPSULE. Liquid waste, water and various waste materials are accumulated in the portion of the NEPHRON called the LOOP of HENLE (Henle's Loop). - See figures in text for the basic structure of the Nephron, and the manner in which capillaries surround the Loop of Henle.

Water re-absorption, along with certain minerals, such as Calcium and Potassium, takes place in the Loop of Henle. The TROPIC Hormone, ADH, produced by the Pituitary (actually the posterior lobe of the pituitary), controls the permeability of the membranes of Henle's Loop to water and minerals.

  ADH production is controlled by the HYPOTHALAMUS, which senses blood volume (actually blood pressure).

When blood volume is high, there is no need to conserve water, thus ADH is not active in stimulating the permeability of the LOOP. When blood volume is low (and thus water content in blood plasma), there is a need for water (body fluids), and thus ADH is produced by the by the pituitary. The ADH production, however, is under the control of the HYPOTHALAMUS gland, which sense blood pressures (blood plasma water content). When blood pressure is low, the HYPOTHALAMUS directs the pituitary to produce ADH, which in turn controls (stimulates) water re-absorption in the Loop of Henle.

Absorption of minerals, especially calcium is assisted by Aldosterone, a hormone produced by the Adrenal glands (these are associated with the Kidneys).


Calcium is important in diet as it significantly contributes to bone density. Loss of bone density, referred to as OSTEOPOROSIS, is a progressive process, especially after age 40-45. Gender (sex) is no protector--it occurs in both men and women. It is more critical in postmenopausal women, and progresses rapidly unless measures are taken to maintain high bone density throughout the aging process. Osteoporosis is a significant contributor to death by complications related to bone fractures--progressively more so in elderly people (both men and women). It compromises the health of some 24 million Americans at all ages and sex.


Peak bone density is achieved between ages 25-40. It will be maximized by an early diet high in calcium (i.e., milk products), sun exposure or Vitamin D consumption, and weight bearing exercise. Loss of bone density progresses more rapidly after about age 40-45 in all people; it can be slowed by maintaining a good diet of calcium rich foods and weigh bearing exercise.

A daily consumption of 1,000 to 1,500 mg calcium for women and 1,000 mg for men is required to maintain maximum bone density and to prevent significant bone density loss during the aging process. An 8 oz. glass of skim milk contains 300 mg. calcium; a cup of low-fat (or better yet) non-fat yogurt contains 400 mg. of calcium.



Blood temperature registered ("felt") by hypothalamus gland; Hypothalamus controls pituitary to produce hormone TSH (THYROID STIMULATING HORMONE); TSH stimulates THYROID TO PRODUCE THYROXINE. THYROXINE controls basic metabolism, (i.e., rate at which energy is utilized).


Recall that as energy - glucose (is oxidized or burned in tissues), two forms of energy are produced, ATP and body heat. It is the body heat that keeps us warm. See contrast of Ectotherms (cold-blooded animals ) vs. Endotherms (warm-blooded animals) and note discussion of HYPOTHALAMUS in text.

Hypothalamus serves as a thermostat to monitor blood temperature. When blood temp. is cold, it directs the pituitary (anterior lobe) to produce TSH. The primary source of heat in endotherms is the TSH-releasing factor associated with blood temperature.