Download The Small Intestine, Large Intestine and Rectum

The Small Intestine and
Large Intestine
Review
Salivary Juice contains:
 1. Water
 2. Salivary amylase

Gastric Juice contains:
 1. Mucous
 2. HCl
 3. Pepsinogen

The Small Intestine
 Averages
about 6 metres in length
 Small diameter
 Why
is the small intestine so long?
 Time
and surface area for digestion to
occur
 The first 25 cm is called the duodenum
 Ducts from the gallbladder (bile) and
pancreas (pancreatic juice) enter the
duodenum
Bile
 Bile:
Emulsifies fat into droplets
that disperse in water
Pancreatic Juice
1.
2.
3.
4.
5.
6.
Water
Sodium bicarbonate
Lipase
Trypsin
Nuclease
Pancreatic Amylase
Pancreatic Juice
Source of Enzymes  Pancreas
 Lipids

Glycerol + fatty acids
(fat droplets) Lipase

Nucleic acids  Nucleotides
nuclease
Source of enzyme – also Sm. Intestine

Optimal pH: 8
Pancreatic Juice
Source of Enzymes  Pancreas
 Starch

maltose
pancreatic amylase


Protein

shorter polypeptides
Trypsin
Optimal pH: 8
Question

What is the optimal pH of the small
intestine and how is it achieved?
Optimal pH is 8
 The bile and pancreatic juice neutralizes
the pH of the chyme (stomach pH 2)

Question

It has been suggested that the surface
area of small intestines is analogous to
the surface area of a tennis court. How?
A: The wall of the small intestine contains finger-like
projections called villi (sing. villus)
Villi increase the surface area of the intestinal wall
which increases the amount of nutrients that can be
absorbed.
Villi

A villus has an outer
layer of epithelial cells
that contain thousands
of tiny extensions called
microvilli


Forms a brush border
where intestinal enzymes
are secreted
Greatly increase the
surface area available
for nutrient absorption
Villi
A villus contains blood capillaries and a
small lymphatic capillary called a lacteal
 Glucose and amino acids enter the
blood capillaries of a villus

 Hepatic

portal vein  liver
Glycerol and fatty acids are packages
as lipoproteins and enter the lacteal
 Lymphatic system
 After absorption, they
are carried to the
cells by the bloodstream
Small Intestine
Absorption occurs across the wall of
each villi and continues until the
nutrients are absorbed
 This occurs actively (with ATP) or
passively (without ATP)

Anatomy of the Small Intestine
Interstitial glands

Walls of the duodenum and small
intestine are lined with millions of
interstitial glands
 Produce
Interstitial juice which contains
 Peptidases
 Maltase
 Sucrase
 Lactase

Interstitial juice finishes the digestion of
protein and starch
Interstitial Juice

Source of enzymes – interstitial gland /small
intestine
Peptides

Amino acid
peptidase
Maltose
(dissacharide)
Optimal pH: 8

Glucose + Glucose
maltase (monosacharide)
Interstitial Juice

Source of enzymes – interstitial gland /small
intestine
Sucrose
(disaccharide)

Glucose + Fructose
sucrase (monosaccharide)
Lactose
(disaccharide)

Glucose + Galactose
lactase (monosaccharide)
Optimal pH: 8
The Large Intestine
Consists of the cecum, the colon, the
rectum and the anal canal
 Larger in diameter than small intestine

 But
shorter (1.5 meters)
Does not produce digestive enzymes,
but does absorb water, salts and some
vitamins
 Also stores indigestible waste until
defecation

The Cecum

Lies below the
junction of the small
intestine
 Has a small
projection called the
appendix
 What is the role of
the appendix?
A: Plays a role in fighting off infections in humans.
The Colon

Includes the
 ascending colon (right side),
 transverse colon (passes abdominal
cavity),
 descending colon (left side)
 sigmoid colon (enters the rectum)


Does not play a role in nutrient absorption
Absorbs water from waste before it is
eliminated
The Rectum

The last 20 cm of the large
intestine
 Opens at the anus, where
defecation of indigestible
material is expelled
 Main function is storage of
feces
 Components of feces:
 3/4 water
 1/4 solid
Question

Why is feces so smelly?
A: The rectum contains bacteria that act on
indigestible material resulting in an unpleasant odour
and also produce gas, which has a foul smell.
Intestinal Bacteria
99% of colon bacteria are obligate
anaerobes (poisoned by oxygen)
 Break down indigestible material and
produce vitamins that our bodies need
 Perform services for us!

Question

What are two common disorders that
are related to the large intestine?
A: Diarrhea and constipation
Diarrhea


Prolonged diarrhea can lead to dehydration due
to water loss and disturb heart contractions due
to ion imbalance
2 major causes of diarrhea:
 1. Infection of the lower intestinal tract
 Food poisoning from contaminated food
 Irritated intestinal wall
 Increase in peristalsis
 2. Nervous stimulation
 Stimulation of intestinal wall
Constipation



Feces are dry and hard
and defecation does not
occur regularly
To prevent constipation:
 Diet rich in water and
fibre
 Take laxatives
 Prevent water from
being absorbed and
expel the contents of
the colon
Chronic constipation due
to hemorrhoids, which are
large, inflamed blood
vessels of the anus
Photo References
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http://healthy-diet.maxupdates.tv/the-basics-of-the-human-digestivesystem/
http://www.cancer.umn.edu/cancerinfo/NCI/CDR350260.html
http://cureibszone.com/diarrhea
http://remedynatural-herbs.com/home-remedies-for-constipation
http://www.thenibble.com/reviews/news/2007-01.asp
http://www.nlm.nih.gov/medlineplus/ency/imagepages/1128.htm
http://www.smithinst.ac.uk/Projects/PG2004/CASEUnilever04/ProjectSummary
http://blog.beliefnet.com/chatteringmind/2006_07_01_chatteringmind_
archive.html
http://www.coloniccleansing.org/
http://www.nlm.nih.gov/medlineplus/ency/imagepages/9390.htm