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.
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.
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.
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).
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.
all arteries lead from heart; all veins lead to heart.
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.
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.
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").
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.).
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
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.
less than 200
Borderline high: 200-239
High (danger): greater
levels--less than 130
High risk ---greater
less than 150
High--greater than 200
(STEADY STATE) CONDITIONS IN HUMAN SYSTEMS
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.
(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.
FUNCTION - WATER BALANCE
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.
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.
production is controlled by the HYPOTHALAMUS, which senses blood volume
(actually blood pressure).
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.
of minerals, especially calcium is assisted by Aldosterone, a hormone
produced by the Adrenal glands (these are associated with the Kidneys).
OF CALCIUM IN DIET
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.
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.
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.
CONTROL - AN EXAMPLE OF FEED-BACK MECHANISMS
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).
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.
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.