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

Melissa Hlavacek

support systems
Support Systems
  • Variation across species
litter bearing 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
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
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
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
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
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
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
Nervous System
  • Few nerves go into the gland
  • Like other skin glands…no parasympathetic innervation
sensory nerves
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
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 system1
Nervous System
  • In species such as pigs, nerve supply to the abdominal mammary glands is different than inguinal mammary glands.
circulatory system
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
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
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
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
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 system1
Lymphatic System
  • 2 Supramammary Lymph Nodes
    • Each above ½ the udder
    • Filter tissue fluids
    • Remove foreign material
    • Vaccination?
udder edema
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???