Hello svdh
One of the sites given by pinkfreud in her answer stated:
"The large intestine is 4 ft. long and 2.5 in. in diameter... The
epithelial surface area of the large intestine is only 1/30 that of
the small intestine, because the large intestine is not convoluted and
lacks villi. The colon does have crypts of Lieberkühn and numerous
goblet cells."
Northwest Nazarene University: Digestive Physiology
http://courses.nnu.edu/bi362bf/newpage7.htm
Of course we also need to take account of the fact that the large
intestine is actually made up of the cecum, colon, rectum and anal
canal. http://www.eusimaging.com/organs/organs.html
The EPA estimate for colon surface area, quoted by pinkfreud, is given
in the following poster (Nb pdf format):
http://www.epa.gov/heasd/edrb/posters/pdf/196herb99.pdf
(look under “Parameters” find this estimate)
It is expressed as 3018 sq cm
There are 100 cm in 1 m
which gives
100 x 100 sq cm in 1 sq m = 10,000 sq cm
3018 sq cm is therefore 0.3 sq m.
Lets take the figures given in the first reference for the dimensions
of the complete large intestine. According to data on
http://www.geocities.com/medinotes/large_intestine.htm
the caecum, rectum and anal canal account for about 21-23 cm of the
total.
These data also give the following alternative estimates of dimensions
for the colon:
Ascending colon 12-20 cm, transverse colon 45 cm, descending colon
22-30 cm, sigmoid colon 40 cm. This gives a total length of 123-135
cm for the colon.
OK, using all these figures:
Length of large intestine = 4 ft = c. 122 (121.92) cm
Diameter = 2.5 inches
Circumference = diameter x pi = 2.5 x 3.14 inches = 7.85 inches
= c. 20 (19.94) cm
Area = length times circumference = 2440 sq cm – which is the apparent
surface area (making no allowances for thickness of the tissue)
Metric conversions used
http://www.sciencemadesimple.com/conversions.html
Another source gives an average length of 1.5 m for the large
intestine
www.uq.edu.au/~anvkippe/an105/digorgan.html
Using the same calculation, this would give an area of 3000 sq cm.
Taking the figures cited above from
http://www.geocities.com/medinotes/large_intestine.htm
gives a total length of 123-135 cm for the colon, which gives
estimated areas of 2460-2700 sq cm for the colon itself, plus 420-460
sq cm for other bits.
So, taking all the above sources into account, the possible range of
areas for the large intestine as a whole is about 2440-3160 sq. cm,
and the range of areas for the colon is c. 2000-2700 sq. cm.
OK, from these figures we can see that the EPA did not make allowances
for villi or microvilli in its calculations and probably took the
whole of the large intestine into account rather than just the colon.
As aceresearcher has pointed out, the colon does not have villi.
However, I did find the following reference. It refers to a species
of rat, but probably provides a rough estimate for humans as well,
since the title of the article claims to relate to mammals in general:
"A pilot experiment to determine the surface enlargement due to
microvilli is presented from material taken from the giant pouched
rat. This was performed by measuring video sequences of microvilli
taken from electron microscopy images. Cecal microvilli increase the
surface area 15-fold, while in the colon the increase is approximately
19- to 20-fold. "
From a paper in Advances in Anatomy, Embryology and Cell Biology,.
1997, Volume 138, nos. III-VIII, pages 1-90.
Intestinal absorptive surface in mammals of different sizes.
By Snipes RL., Institute of Anatomy and Cell Biology,
Justus-Liebig-University, Giessen, Germany.
URL to summary: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9308197&dopt=Abstract
Let us take these figures into consideration:
We are only working with estimates of length. Also, we are assuming a
constant diameter over the whole large intestine, which is probably
not exactly the case. This means that we can obtain a reasonable
estimate of total surface area with respect to order of magnitude, but
not an exact figure.
Taking the range of apparent surface areas for the colon to be
2000-2700 as calculated above, and multiplying them by a factor of 20
as suggested by Snipes, the true surface area of the colon can be
taken as being in the range 38000-54000 sq cm or 3.8-5.4 sq m.
Taking a further 420-460 sq cm apparent surface area for the other
parts of the large intestine, and assuming a 15-fold increase
(although we cannot be sure this is the case for the rectum and anal
canal, since Snipes only discusses the cecum), we can add another
6300-6900 sq cm, ie 0.63-0.69 sq. m to the above.
A reasonable overall estimate for the true surface area of the large
intestine is therefore 4.5-6.0 sq.m. with 3.8-5.4 sq m of that being
due to the colon itself.
I hope this answer meets with your satisfaction.
Search strategies on Google and on Medline
(http://www.ncbi.nlm.nih.gov/entrez/query.fcgi ): combinations of the
search terms: colon, “surface area”, dimensions, villi, microvilli. I
also took full account of the previous research done on this question
by pinkfreud. |