Macro Structure of the
Mammary Gland
Macro-structure of the Cow Mammary
Gland
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Suspensory System
Teat Structure
Gland Structure
Blood Flow and Structures
Lymph Movement and Structures
Nerve System and Structures
Tissue Types and Organization of Secretory
Tissue
Cow’s Udder Suspensory Structure
• Intermammary groove separates left and right halves of the udder
• Udder can weigh anywhere from 7 to 165 pounds
– May support up to 80+ pounds of milk
– Rear quarters secrete 60% of the milk
– Udder continues to grow in size until cow is 6 years of age
• Well attached udder fits snugly against the abdominal wall in front
and on the sides
– Extends high between thighs in rear
• 3 major supporting structures
– Skin
– Median suspensory ligament
– Lateral suspensory ligament
Division of the Cow Udder
Division of Quarters
60%
40%
Seven Tissues that Provide Udder
Support
• Skin- Minor support
• Superficial fascia (This attaches the skin to the
underlying tissue)- Minor support
• Coarse areolar (This tissue forms a loose bond
between the dorsal surface of the front quarters
and the abdominal wall. This is part of what is
referred to as the fore quarter attachments when
evaluating dairy cattle. Help keep the fore
quarters attached to the body wall)- Minor
support
Tissues that Provide Udder Support
Cont.
• Subpelvic tendon (This tendon is not actually part of
the suspensory system, but it gives rise to the
superficial and the deep lateral suspensory ligaments.
It is attached to the pelvis at several points)
• Superficial layers of the lateral supensory ligaments
(These are mostly composed of fibrous tissue- with
minor elastic tissue, arising from the subpelvic tendon.
They extend downward from the pubic area and
spreads out over the external udder surface beneath
the skin and attaching to the areolar tissue.)
Tissues that Provide Udder Support
Cont.
• Deep lateral suspensory ligaments (The inner part of
the lateral suspensory ligament also arises from the
subpelvic tendon, but is thicker than the superficial
layer, and is mostly fibrous tissue. It extends down
over the udder almost enveloping it. The ligament
attaches to the convex lateral surfaces of the udder by
numerous lamellae which pass into the gland and
become part of the framework of the udder. The left
and right suspensory ligaments do not join under the
bottom of the udder and the fibrous nature of the
ligaments means they do not stretch as the gland fills
with milk. All the lateral ligaments together provide
substantial support for the udder.
Tissues that Provide Udder Support
Cont.
• Median suspensory ligament (This is the most
important part of the suspensory system in cattle.
It is composed of two adjacent heavy yellow
elastic sheets of tissue that arise from the
abdominal wall and that attach to the medial flat
surfaces of the two udder halves. The median
suspensory ligament has great tensile strength. It
is able to stretch somewhat as the gland fills with
milk. It is the center of gravity of the gland and
gives balance to the udder.
Support of the Bovine Mammary
Gland
Support of the Bovine Mammary Gland
Suspensory Ligaments of the Udder
Mammary Gland Support
The Cow Teat
• The teat is the only exit for the secretion of
the gland
• Usually only one teat drains one gland
• No hair, sweat glands or sebaceous glands are
found on the cow teat
• Front teats are usually larger than the rear
teats
• Teat size is heritable in cattle
Teat Structures
• Supernumerary teats (About 50% of cattle have these
“extra” teats. Some open into a normal gland but
many do not.)
• Streak canal (Functions as the only opening of the
gland to the external environment. It is a main barrier
to intramammary infection and is lined with a
epidermis that forms a keratin material that has
antibacterial properties. The canal is opened and
closed by the sphincter muscles surrounding the streak
canal. When a cow is milked the sphincter muscle
relax allowing the canal to open. The canal remains
open an hour or more after milking.)
Teat Structures
• Furstenburg’s rosette (Mucosal folds at the
internal end of the teat canal. May be
involved in the immune response of the teat)
• Cricoid rings/Annular folds (Region that
separates the teat cistern and the gland
cistern)
• Teat cistern (Cavity within the teat that is
located between the Annular folds and
Furstenburg’s rosette.)
Teat Structure
Detailed Structure of the Cow Teat
Cross Section of the Teat Canal
Involuting Teat Canal Cross Section
Basic Mammary Gland Structure
Structures within the Mammary Gland
• Alveoli is the basic milk producing unit
– Small bulb-shaped structure with hollow center
• Lined with epithelial cells that secrete milk
• Each cubic inch of udder tissue contains 1 million alveoli
• Each alveoli surrounded by network of capillaries and myoepithelial cell
– Contraction of myoepithelial cell stimulates milk ejection
• Groups of alveoli empty into a duct forming a unit called a lobule (150-220
alveoli)
– Several lobules create a lobe
• Ducts of lobe empty into a galatophore, which empties into the
gland cistern
• Ducts provide storage area for milk and a means for transporting it outside
– Lined by two layers of epithelium
Mammary Ducts
• Are the tubing that that move milk from the
alveoli to the teat for milk removal. The network
of ducts continually gets larger as they move
away from the aveolus. Tertiary ducts are the
small ducts that exit the alveolus. Intralobular
ducts transport milk within the lobule.
Interlobular ducts drain milk from multiple
lobules. Intralobar ducts drain regions of the
lobe and interlobar ducts drain multiple lobes.
However there is no uniformity in the system of
duct branching within the different structures of
the gland.
Gland Cistern
– Also called the udder cistern. It opens directly
into the teat cistern. Separated from the teat
cistern by the cricoid or annular fold. It can
hold up to 400 milliliters of milk and is the
collecting area for the largest mammary ducts.
The gland cistern is the start of all mammary
duct branching similar to the trunk of a tree.
Cartoon of Gland Structure
Gross Structure of the Goat Mammary
Gland
Blood Circulation in the Cow
• One gallon of milk requires 400-500 gallons of blood
being passed through udder
– Ratio may increase in low producing cows
• That is approximately 280 ml/second and corresponds
to about 8-10 % of total blood volume in the udder
• There is essentially no cross over of blood supply
between the udder halves
• Blood enters the udder through external pudic arteries
• Blood exiting udder from veins at the base of udder
blood can travel through two routes
– Via external pudic veins
– Via subcutaneous abdominal veins
Arterial Blood Supply to the Udder
Arterial Blood Supply
• Most of the blood is supplied to the udder by the two
external pudenal (external pudic) arteries, one for each half
of the udder. The arteries enter the mammary gland from
the abdominal cavity through the inguinal canal. As they
enter the mammary gland, the arteries form a sigmoid
flexure, which probably allows for the lowering of the
udder when it becomes filled with milk. The mammary
artery branches soon after it penetrates the mammary
gland into cranial mammary artery (supplies the front side
of the udder) and the caudal mammary artery (supplies the
rear part of the udder). Numerous branches from these
arteries provide oxygenated to all parts of the udder. The
arteries in the teat are part of these and are known as the
papillary arteries.
Arterial Blood Supply to the Udder
Venous Flow from the Udder
Venous Blood Flow
•The blood from each half of the udder leaves by two veins, the
external pudenal and the subcutaneous abdominal (milk vein) vein.
Veins leave the mammary gland anti-parallel to the arteries. Two
routes of venous blood carry CO2 back to the heart. Many papillary
veins course upward from the teat and join, making several large
mammary veins the venous circle. After the venous circle, blood can
leave the udder by one of two routes;
1- Two external pudic veins which will eventually join the vena cava to
deliver blood to the heart.
2- Two subcutaneous abdominal veins (milk veins). These are anterior
extension of the large mammary veins and run forward a long the
ventral abdominal wall just under the skin. They penetrate the thoracic
cavity at the milk well and eventually join the anterior vena cava.
Venous Flow from the Udder
Parallelism between the Arterial and
Venous System
Mammary Venous Circle
Cranial Mammary
Vein
Dissection of a Mammary Artery and
Vein
Lymphatic System
•Lymph is a colorless tissue fluid that is drained from tissue spaces by thinwalled lymph vessels. Lymph originates as a filtrate of the blood serum and is
similar in composition to serum except that lymph has no/very few red blood
cells and about ¼ the protein content. Lymph flows from the udder to the
thoracic duct and is eventually discharged into the blood system. The lymph
nodes of the udder and the other lymph nodes of the body are important for
disease resistance in the cow. The lymph nodes form lymphocytes which are
involved in immunity. In response to bacterial infection (e.g. mastitis), lymph
nodes increase their output of lymphocytes which are transported to the
udder to compact infection. Around the time of parturition, the filtration of
lymph out of the blood capillaries in the udder may exceed the drainage back
into the blood. This causes accumulation of fluid in the intercellular tissue
spaces. This disorder is known as udder edema. This is more serious in
firstcalf heifers and in older cows with pendulous udders.
Lymphatic System
• Lymph is clear, colorless
– contains less protein than blood plasma
– contains high concentration of lymphocytes (WBC’s)
which play a role in immune defense
– contains few RBC’s
– carries glucose, salts, fat
– dissipates heat
– carrier of fibrinogen (clotting protein)
Lymph Movement
•
Movement of lymph is passive:
– lymph moves through vessels by:
1. muscle movement (exercise, etc.)
2. breathing
3. heart beat
4. tissue massage
Lymphatic System Function
• Helps regulate proper fluid balance within udder and
combat infection
• Fluid drained from tissue only travels away from udder
– Blood capillary pressure
– Contraction of muscles surrounding the lymph vessels
– Valves that prevent backflow of lymph
– Mechanical action of breathing
• Lymph travels from udder to the thoracic duct and empties
into blood system
• Flow rates of lymph depend on physiological status of the
cow
• Fluid enters the lymph system through open-ended vessels
called lacteals
Lymphatic System of the Cow’s Udder
Functions of the Lymphatic System
Udder Edema
Udder Edema
• Edema:
– low pressure, passive system fed by a high
pressure vascular system!
• this situation results in pooling of interstitial
fluid if evacuation of lymph is impaired
Example: tissue trauma; increased mammary
blood flow at parturition
Removing/Preventing Udder Edema
• Preparturient milking may be helpful
– store colostrum from healthy cows to feed calves
• Frequent milkout to reduce mammary pressure
• Diuretics, corticoids to reduce swelling
• Mammary massage, icing, work fluid towards
supramammary lymph nodes
• Reduce salt intake
• Don’t feed too much, too early before calving
Neural System of the Mammary Gland
•
The efferent innervation of the mammary gland is entirely sympathetic in origin. Stimulation of
the nerves leading to the mammary gland causes a vasoconstriction of the blood vessels, which
has a significant impact on milk secretion because the blood flow to the mammary gland is
decreased. The efferent nerves innervate the muscle fibres within the connective tissue
surrounding the lobules, lobes, and the blood vessels. However, the nerves do not pierce the
alveoli. The efferent fibers nerves apparently play an important role in innervating the smooth
muscles within the tea, especially those around the teat streak to keep it closed between
milkings.
- Innervation of the udder is sparse compared with other tissues.
- Sensory (afferent) nerves are involved in milk ejection and found in the teats and skins.
- Similar to other skin glands, there is no parasympathetic innervation to the gland.
- Sympathetic nerves are associated with the arteries but not with alveoli.
- There is no innervation of the secretory system.
- Myoepithelial cells contract in response to oxytocin and not in response to direct innervation.
- Few nerves go to the interior of the udder.
Neural System of the Mammary Gland
• The primary functions of the sympathetic nerve
fibers to the udder are control of the blood supply to
the udder and innervation of smooth muscle
surrounding the milk collecting ducts and the
sphincter muscles within the teat. Stimulation of the
sympathetic nervous system causes a
vasoconstriction of the blood vessels and this has an
inhibiting effect on milk secretion.
Innervation of the Cow’s Udder
Tissue Types within the Mammary
Gland
• Fat Pad
– Fatty tissue that is the area that the mammary
gland develops into from puberty-lactogenesis
• Parenchyma
– Functional part of an organ (epithelial and
myoepithelial cells)
• Stroma
– Supporting tissue of an organ (fibroblasts,
connective tissue, blood vessels, etc.).
Mammary Fat Pad
Bovine Fat Pad
Mouse Fat Pad
Udder Structure Cartoon