Transcript Milk Synthesis

How is goat milk produced?
Alveoli are the milk producing structures of the
mammary gland. Each alveoli has a rich supply of
blood that brings the components to produce milk
to the cells. Alveoli are linked with Capillaries that
bring the components and Venuoles that remove
excess fluids. About 500 volumes of blood must pass
through the udder to maque 1 volume of milk.
The lining of each alveolus is composed of cells (Epithelial
cells) that surround a cavity called the lumen.
The Epithelial cells
The Epithelial cells act like factories, let’s explore it’s functions in milk production
As all cells, epithelial cells need energy to work.
One of the products by microbian
fermentation in the rumen is propionic
acid. It is absorbed into the blood and
transported to the liver where it is
converted to glucose. More than half of the
glucose that will get to the alveolus will be
used as a source of energy for the cells (
the other half will be used to crate lactose).
CH3CH2COOH

C6H12O6
The epithelial cells need to synthetise components of milk that are not present in blood such as lipids (fats),
some proteins and lactose (milk’s sugar). The cells control by the way the amount of each component in the
milk.
Lipogenesis is the process where
syntesis of milk fats is done. This
fats are manufactured from
precursors brought to the cells by
blood.
A fatty acid is a molecule that has a long or short of carbon atoms
whit this structure at the end. Where C=Carbon, O=Oxygen and
H=Hydrogen (here an example with an acetic acid).
Acetic acid (C2H4O2) and β –hydroxybutyric (C4H8O3) are also products of the rumen
fermentation and are the main precursors of milk fatty acids synthesis in the mammary
gland. In a complicated series of steps, the acids are combined to crate a long chain of
fatty acid called palmitic acid.
Palmitic acid has a 16
carbon atoms in it’s chain.
Palmitic acid can be used to synthetise fat or it can be
broken down into a shorter chain fatty acid such as
carpic acid. Wich is present in a big amount in goat milk
Carpic acid has 10 carbon atoms in it’s chain.
The percentage of fats in milk is influenced by nutrition and environment.
A fat is creted when 3 fatty acids attach to a glycerol molecule. The result
is called a triglyceride, the most commun kind of fat in milk. This is a long
chain triglyceride fat.
Glycerol
Fatty acids
Proteins are made from amino acids. The genes in
the nucleus of the cell direct the types of proteins
created. There are 20 different amino acids which
are the end product of intestinal digestion of
proteins. The amino acids are absorbed through the
intestinal wall and transported by the blood to the
liver which directs them to the body tissues as
needed.
In the nucleus, a
template of the DNA is
created, the Messanger
RNA. This copy of DNA
will get out of the
nucleus and counter the
different amino acids.
Each Messanger RNA
sequence has a different
code, the amino acids
will be fixed in different
ways and orders to form
chains, the proteins.
Let’s try to understand what really
happens with proteins.
Most of the protein in milk is casein. There are four kinds of casein protein:
-Two types of alpha casein (α1 & α2)
-a beta casein (β)
The four casein
-a kappa casein (κ)
forms agregate
Kappa casein is different. It
prevents Alpha and Beta casein
proteins from combining with
additional calcium. That’s why
individual micelles repel each
other.
But the Chymosin enzime, that we find in rennet, has the capability to
change the kappa casein protein. We obtain para-kappa-casein which is
no longer able to prevent calcium and phosphate from binding to the
casein proteins. Micelles clump thus together causing the milk to
coagulate. An important stem in cheese production.
In fluid milk, casein proteins form
small spheres called micelles Alpha
and Beta proteins are connected to
each other by phosphate and calcium.
β-lactoglobulin and α–lactalbumin proteins are also synthesized only in the mammary
gland. Other proteins and the immune globulins are sinthesized elsewhere in the body.
Lactose is the sugar of milk. It is
created only in the alveolar cells of
the udder by combining glucose and
galactose. Glucose is absorbed from
blood. Inside the cell some glucose is
converted into galactose.
In a few more steps,
Galactose and Glucose are
combined to form Lactose
Galactose is very similar to
glucose except for the orientation
of these molecules.
The alveolar cells have to regulate the amount of components that
come directly from the blood but are not changed in the cell, such
as water, vitamins and minerals.
Water flows through and
between cells by
diffusion.
The amount of minerals included in the
milk is also regulated by alveolar cells.
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Major minerals:
Calcium
Phosphorus
Chlorine
Magnesium
Sodium
Trace minerals (oligo-éléments):
Iron
Manganese
Copper
Zinc
Vitamins are synthesized in the
goat’s body or come directly from
feed sources.
 Vitamine A: Vitamine A precursor
comes from plant diet and is
converted into vitamine A in the
wall of small intestine.
 Vitamine D: comes from exposure
to the sun and from some plants.
 Vitamine E: comes from green
feed
 Vitamine K: is synthesized by
bacteria in rumenand intestines.
Both K and D are present in small
quantities in milk.
 B vitamine: is synthetized by
rumen bacteria. The bacteria is
broken down when it goes
through the intestine and the
vitamine can be used.
 Vitamine C: is naturally
synthesized by the goat.
The milk contains now all it’s elements and is ready to be expulsed
from the alveolus. It has the following composition:
During the manufacturing of milk, lumen fills with milk.
Each alveolus is surrounded by cells
called basket cells which act like
muscles.
When activated by the oxytocin hormone the basket cells contract pushing
the milk out of the alveoli into the collecting ducts.