Other systems in the mammary gland support nervous circulatory and lymphatic
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Other Systems in the Mammary Gland: Support, Nervous, Circulatory, and Lymphatic PowerPoint PPT Presentation

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Other Systems in the Mammary Gland: Support, Nervous, Circulatory, and Lymphatic. Melissa Hlavacek. Support Systems. Variation across species. Litter-bearing Species. No large suspensory ligaments Fibrous connective tissue and skin are the primary support

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Other Systems in the Mammary Gland: Support, Nervous, Circulatory, and Lymphatic

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Other Systems in the Mammary Gland: Support, Nervous, Circulatory, and Lymphatic

Melissa Hlavacek

Support Systems

  • Variation across species

Litter-bearing Species

  • No large suspensory ligaments

  • Fibrous connective tissue and skin are the primary support

  • Examples: pigs, dogs, cats, rodents

Humans and Litter-Bearing Species

  • Gland is on top of muscle tissue

  • Strong, fibrous connective tissue separates it from the muscle

  • Suspensory ligaments are either attached to the muscle or the connective tissue

  • In litter bearing species, each half is also separated from the other

    • Midline

  • Skin also provides protection and a little support

The Cow

  • Many different tissues…

    * Median suspensory ligament* Skin

    * Lateral suspensory ligament- Superficial fascia

    - Fine connective tissue- Subpelvic tendon

    - Coarse connective tissue

© The Babcock Institute

Connective Tissue & Skin

  • Fine connective tissue

    • Attaches skin to underlying tissue

  • Coarse connective tissue

    • Attaches front quarters to abdominal wall

  • Skin

    • Little support

    • Protection from pathogens

  • Front and rear are also separated by connective tissue

    • No internal crossover between any of the quarters

Median Suspensory Ligament

  • Primary support of the udder

  • Two adjacent heavy sheets of tissue

  • Mostly elastic, some fibrous tissue

  • Attaches to the abdominal wall

  • Divides the udder into halves (left and right)

    • Glands on each half are divided by sheets of tissue

© Biology of Lactation, Schmidt

Lateral Suspensory Ligaments

  • Like a “hammock” around the udder

    • From the pelvis to the median suspensory ligament

  • Mostly fibrous tissue

    • Collagen

  • Attaches to the alveolar tissue

    • Provides internal framework

  • Does not connect at the base of the udder

How much support is enough?

  • High producing Holstein cow

  • Empty Udder = 50 lb.

  • Milk = 60 lb.

  • 50 + 60 = 110 lb. !!!


  • Udder support can significantly affect milking ability and useful life

    • 10 – 25% heritable

  • Pendulous udders are more likely to suffer injury

    • Especially teats

    • Increased mastitis

    • Affect on offspring

Nervous System

  • Few nerves go into the gland

  • Like other skin glands…no parasympathetic innervation

Sensory Nerves

  • Skin and teats

  • Positive stimulation of teats and surrounding area initiates milk let-down reflex via oxytocin

    • Critical!

© Biology of Lactation, Schmidt

Sympathetic Nerves

  • Associated with arteries in the gland

    • Control blood flow to the gland

    • Carry oxytocin to the gland

    • Innervation of sphincters muscles in teats

    • Stress causes vasoconstriction decreasing milk secretion and let-down

  • There are no nerves to myoepithelial cells or alveolar cells

    • Contraction is regulated by oxytocin

Nervous System

  • In species such as pigs, nerve supply to the abdominal mammary glands is different than inguinal mammary glands.

Circulatory System

  • All milk precursors come from the blood

  • No crossover between each side of the mammary gland

  • Venous circle

    • Prevents pinching off of areas of venous outflow when animal is lying down


  • Elongation and proliferation of growing vessels

    • Angiogenesis

    • Vasculogenesis

  • Complex interactions between

    • Endothelial cells

    • Extracellular matrix

    • Specific stromal cells

  • Requires dramatic reorganization of surrounding tissue

    • Growth factors affect rates of endothelial cell proliferation and degree of vessel formation

      • VEGF-vascular endothelial growth factor

        • Major regulator

        • Maintains viability

        • Stimulates mitogenesis and chemotaxis

        • Changes permeability

    • Many growth factors in different isoforms

    • Enzymes alter surrounding tissue


    • Capillary beds

      • alveolus ‘hairnet’

    • Sphincters constricted

      • no blood flow

    • Sphincters open

      • blood flow to alveolus

    • Local control of blood flow

      • High pO2 = high blood flow

      • Need ATP

      • ATP needs oxygen

      • High pO2= high ATP

      • = sphincters constricted

    Terminal arteriole


    Large vein


    Post capillary venule

    Other local controllers of blood flow

    * Oxygen

    * Carbon Dioxide

    • Adenosine

    • Lactic Acid

    • pH

    • Hormones

    • Nitric Oxide

      • Alveolar cells each control their own blood and nutrient supply

    So how much blood is enough?

    500 Liters blood = 1 Liter milk

    1 truck of blood = 100 lbs. milk

    Hot area of research: mammary tumors

    Depends on angiogenesis for survival

    Killer of females and males


    • Mediates synthesis/secretion of local tissue growth factors

      • Direct effect?

    • Changes in angiogenesis of ovary, placenta, endometrium

    • Mammary gland is a reproductive organ

    • Other hormones?


    • What’s u-PA?

      • Activator of the zymogen plasminogen

      • Plasmin degrades extracellular proteins

      • Increases angiogenesis and mammary development

    • High concentrations of u-PA in breast cancer patients


    Hot spot

    Infra-red thermography

    Lymphatic System

    • Molecules go out of the capillaries but not all can get back in

      • Disrupt the normal osmotic pressure

    • Functions

      • Pick up extracellular fluids and bring back to the circulatory system

      • Transport of leukocytes

      • Transport of immune cells

    Lymphatic System

    • 2 Supramammary Lymph Nodes

      • Each above ½ the udder

      • Filter tissue fluids

      • Remove foreign material

      • Vaccination?

    1.6 L LYMPH = 1 LbMILK

    Udder Edema

    • Parturition

    • Accumulation of secretions

      • Pressure

      • Passive flow is hindered

    • Tight junctions do not function well

      • Fluid enters interstitial space

      • Alters osmolarity

      • Alters hydrostatic pressure

      • Less fluid is removed

    • Connective tissue spaces swell

    • Causes???

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