Transcript Topic 6.1 2016 PP

Topic 6.1 – Digestion & Absorption
Digestion of Large Food Molecules
• Many of the food molecules that humans
consume are much too large to be absorbed by
the cells of the body, particularly the villi of the
small intestine where absorption of molecules
takes place.
• As you will recall from topic 2 on the biological
molecules, they are large molecules that need to
be broken down into simpler components. For
example, all complex carbohydrates are digested
or broken down into their smallest component,
glucose (sugar).
• All large molecules have to broken down into
molecules that are small enough to diffuse
across the plasma membranes of the body’s
cells.
Events in Digestion
• Ingestion – taking food in
• Digestion – a series of chemical reactions that break
down the ingested food into molecules that are small
enough to pass across plasma membranes.
• Absorption – uptake of small nutrient molecules by
the body’s cells.
• Transport & Assimilation –nutrients are delivered to
all cells in your body via the circulatory system. They
converted into fluid or solid parts of the organism or
used in biochemical reactions of cells in the tissues
of the body.
6.1 S1 Production of an annotated diagram of the digestive system
Accessory organs
A person
produces
over a litre of
saliva a day!
Salivary
glands
Alimentary canal (GI tract)
Oral cavity
Tongue
Pharynx
Esophagus
IN your
drawing book:
Annotate with
the functions
of each part
Stomach
Liver
Gallbladder
Pancreas
Small intestine
Colon
Appendix
Rectum
Anus
Large
intestine
Figure 22.6
The Stomach
• large j-shaped organ
attached to the esophagus
at one end and the small
intestine at the other.
• food is temporarily stored
while it mixes with gastric
juices consisting of pepsin,
hydrochloric acid and
mucus.
• It can hold about 1.5 L of
food (digested into semisolid mixture called chyme)
• Gastric ulcers
– Are erosions of
the stomach
lining
– Are often caused
by a bacterium
named
Helicobacter
pylori
Figure 22.11
6.1 U1 The contraction of circular and longitudinal muscle of the
small intestine mixes food with enzymes and moves it along the gut
-
Smooth muscle (short cells not
elongated)
-
Often has continuous force with
short period of vigorous
contraction
-
Peristalsis occurs here as well and
moves the food through the
intestines
-
Circular muscles behind the food
prevent the food from backing up
-
Longitudinal muscle contraction
(at site of food) move it along the
intestines
https://www.youtube.com/watch?v
=Ujr0UAbyPS4
-From esophagus to small intestine
peristalsis moves food forward
(vomiting is abdominal muscles)
- Moves slow through small intestine
(cm at a time) to give time for gastric
juice to mix with food leading to faster
absorption
6.1 U2 The pancreas secretes enzymes into the lumen
of the small intestine.
• Pancreas is composed of two
types of gland tissue: cells that
produce hormones (insulin &
glucagon) and cells that produce
digestive enzymes.
• Hormones made and released by
the stomach regulate the
production of enzymes by the
pancreas (responds to food
contents).
• Enteric nervous system plays a
role as well (stomach has a mind
of its own!)
• The pancreas contains ducts
which are small tubes which all
lead to the main pancreatic duct.
• Hydrolases released by the
pancreas include:
• Amylase (digests starches)
• Lipase (digests triglycerides and
phospholipids)
• Proteases (or endopeptidase –
digests proteins and peptides)
Source: [Frank, A., Deng, Sh. et al. 2004, Transplantation for type I diabetes: comparison of
vascularized whole-organ pancreas with isolated pancreatic islets. 240: 631-643.]
6.1 U3 Enzymes digest most macromolecules in food into
monomers in the small intestine.
• The pancreas secretes enzymes into the lumen of the small intestine
and the following chart summarizes the effect of the hydrolases:
Biological Molecule
Enzyme
Digested Form
Starch
amylase
maltose
Proteins &
polypeptides
protease
Shorter peptides
Phospholipids
phospholipase
Fatty acids, glycerol &
phosphate
Triglycerides
lipase
Fatty acids & glycerol
or fatty acids
monoglycerides
Amino acid
Protein
Hydrolase
(pepsin)
Sugar
Hydrolase
(amylase)
Fatty acid
Glycerol
Hydrolase (lipase)
(b) Hydrolases
Figure 22.4b
Enzymes and Digestion
• Digestion is completed in the small intestine by enzymes
produced in gland cells of the walls of the small intestine.
Molecule
Enzyme
Digested Form
DNA & RNA
Nucleases
Nucleotides
Maltose
Maltase
Glucose
Lactose
Lactase
Glucose & glalactose
Sucrose
Sucrase
Glucose & fructose
Peptides
Exopeptidases
dipeptides
Dipeptides
dipeptidases
Amino acids
Small Intestine
• The small intestine has
three different portion or
sections; the duodenum,
jejunum and ileum.
6.1 S2 Identification of tissue layers in transverse sections of the small
intestine viewed with a microscope or in a micrograph
First…without the
EM picture
Goblet
cells
Lymph vessel
also called
lacteal
Examine these!
E-epithelium
SM-submucosa
M-muscosa
IM- inner circular muscle
OM-outer longitudinal muscle
Now try and label the parts on the
diagram on page 281 of your text
Digestion and the Small Intestine
• Digestion of the macromolecules is completed in the small
intestine and the end products of nutrient digestion are also
absorbed here. Food spends hours here due to the length of
the small intestine and to allow for completion of digestion
and absorption. 90% of absorption takes place here.
• Once the food has been digested and the nutrients have been
absorbed the only thing left to empty into the large intestine
is waste products and water. Some substances such as
cellulose (main component of dietary fibre) remain
undigested because humans lack the enzymes required to
break it down.
6.1 U4 Villi increase the surface area of epithelium over which
absorption is carried out.
• The villi that line the small
intestine greatly increase the
surface area for absorption. They
contain capillaries and a lacteal for
the transport of nutrients.
• The villi are only one cell layer
thick so it is easy for nutrients to
diffuse across the cells. This layer
is called the epithelium layer.
• The surface area greatly influences
the rate of absorption. An adult
small intestine is about 7m in
length and 25-30 mm in width.
The inner surface is highly folded
and contains the villi which further
increase the surface area.
• Each villus measures between 0.5 and
1.5 mm in length and there are
approximately 40 villus per square mm
of small intestine making the surface
10x larger.
6.1 U5 Villi absorb monomers formed by digestion as well as
mineral ions and vitamins
•
Epithelium of the villi needs to protect the body (from harmful substances) but at
the same time be permeable to nutrients.
Nutrients absorbed are:
- glucose, fructose, amino acids
and other monosaccharides
- Any of the 20 amino acids used to
make proteins
- Fatty acids, monoglyceride and
glycerol
- Nucleotide (DNA/RNA) bases
Other absorbed
substances needed
(but no digesting
needed):
-Mineral ions (ie.
calcium, potassium,
sodium)
Other absorbed
substances not needed:
-harmful substances (liver
detoxifies)
-food color and flavour
chemicals
- vitamins (ie. Vitamin
-Small amounts of
C)
bacteria (wbc’s in liver
destroy)
6.1 U6 Different methods of membrane transport are required
to absorb different nutrients.
Large Intestine
• The large intestine, also
known as the colon
receives the waste
products of digestion from
the small intestine.
• The material that passes
into the colon contains
water and any unabsorbed
or undigested food.
• There is an ascending,
transverse and descending
portion of the colon.
Function of the Large Intestine
• The major function of the large intestine is the
absorption of water. Water is reabsorbed through the
walls of the colon along with any small molecules that
may be dissolved in the water.
• The colon also hosts a large number of naturally
occurring E. coli bacteria with whom we have a
symbiotic relationship. Our colon provides the bacteria
with nutrients, water and a warm environment and in
turn they synthesize vitamin K and keep our colon
healthy.
• Any food that remains undigested or unused by us or
the bacteria is eliminated by the body as feces.
6.1 A1 Processes occurring in the small intestine that result in
the digestion of starch and transport of the products of
digestion to the liver
• See assignment completed in class.
6.1 A2 Use of dialysis tubing to model absorption of digested
food in the intestine
• Read pages 287-88 in text to prepare for the
next lab day.