Transcript Delivery of Nutrients to Cells

Delivery of Nutrients to Cells
As discussed previously, digestive enzymes
break down large complex food molecules into
smaller useable molecules. The components of
these small molecules are required for the bodies
growth, development, metabolism and production
of enzymes and hormones. These small molecules
are soluble and are absorbed through the small
intestine directly into the blood stream.
The Small Intestine
The Small Intestine (cont.)
The inner lining of the small intestine
Is folded and covered in finger like
projections called villi. These are
further covered with more folds called
microvilli.
This folding increases the surface
area for absorption of nutrients
through the epithelial cell which line
the villi.
This structure is so efficient because
the epithelial cells are thin being only
one cell thick and found directly within
each villi is a blood capillary and
central lacteal (lymphatic vessel)
which are ready to absorb nutrient
molecules.
Absorption of Nutrients
Carbohydrate
Proteins
Fats/Lipids
Glucose
Amino Acids
Fatty Acids
Glucose and Amino acids are absorbed into the epithelial
cells and then pass directly into the blood capillary.
Fat products pass into the epithelial cells and then pass
into the central lacteal.
Calcium, iron and vitamin B12 are also absorbed through the
epithelium of the small intestine. B12 requires the presence of and
additional factor produced in the stomach to be absorbed. Intrinsic
factor is a polypeptide produced in the stomach. It encourages
endocytosis and therefore the vitamin is transported into the epithelium
of the small intestine.
Emulsifiers
An emulsion is when two normally
separate products or liquids
become mixed and form droplets
e.g. oil in water. An emulsifier is
something which maintains the
emulsion state. In the body, bile
salts act as emulsifiers.
Bile Salts
Bile salts are a steroid compound
produced in the liver and stored in
the gall bladder. They consist of a
water soluble (hydrophilic) head
and a lipid soluble (hydrophobic)
tail. If bile salts and lipid droplets
are shaken together the bile salts
arrange themselves around the
outside of the lipid droplet with
their tails on the inside of the lipid
droplet. As the hydrophilic heads
are negatively charged the
droplets repel each other and stay
apart. This process is called
emulsification.
Lipase
Lipase is a digestive enzyme
produced in the pancreas which in
the small intestine digests lipids
into monoglycerides and fatty
acids. As shown in our
experiment, bile salts increase the
action of lipase on fatty acids.
This occurs because the bile salts
have maintained an emulsion and
therefore increase the total
surface area and the total number
of substrate molecules for the
lipase to act on the lipids.
Micelles
After lipase has
digested lipids into
monoglycerides and
fatty acids and bile salts
have attached around
creating and maintaining an
emulsion, minute water
soluble molecules called
micelles are formed which
travel to the surface of the
intestinal epithelium
microvilli. (fig 22.6)
Absorption of Monoglycerides and
fatty Acids (fig 22.7)
Monoglyceride and Fatty Acid
Diffuse through cell membranes into Epithelium
Pass into Smooth Endoplasmic Reticulum and rebuilt into lipid
molecules
Coated with Lipoprotein and leave cell by exocytosis
Absorbed by lacteal
Enter lymphatic system
Enter blood stream
The Liver
The Livers Blood Supply (fig 22.8)
Hepatic Artery: Carries oxygenated blood to
the liver ( branched from aorta)
Hepatic Vein: Carries deoxygenated blood away
from the liver ( leads to vena cava)
Hepatic Portal Vein: Carries blood from another
source ( e.g. from the
intestine) to the liver which
then leads to the general
circulation.
The Liver and Metabolism
Carbohydrate: Regulation of Blood Glucose excess glucose converted to
glycogen by insulin and stored in the liver. When glucose is
required glucagon produced in the pancreas converts glycogen
back to glucose.
Lipid: Cholesterol required for cell membrane structure and synthesis of
steroids. Liver synthesises cholesterol if not enough obtained through
dietary intake. Excess cholesterol excreted by liver and passed out of body
as bile.
Protein: The liver synthesises three types of plasma proteins. Amino acids
required for this are absorbed from the blood stream by liver cells (table
22.1)
Albumins
Globulins
Fibrinogen
Fate of Absorbed Materials
Absorbed
material
Immediate
use
Fate of excess of
substance
Carbohydrates
(glucose)
Aerobic
Stored as glycogen in
respiration
muscle/liver or as fat in
(energy)
adipose
Lipids (fatty acids, Energy source
Stored in adipose
glycerol)
tissue
Proteins
(Amino acids)
Protein
synthesis
Energy source or urea
excreted in urine
Vitamins and
minerals
Enzyme
action
RBC’s etc
Some stored, some
excreted