Lecture 13 - Lactation Part 1 Flashcards
Some of the components of milk…
Water, fat, protein, lactose, ash
Species with high fat in milk? High protein? High lactose? High water?
Fat = canines then swine
Protein = canines
Lactose = equine then swine
Water = equine
What monosaccharides make up lactose
Galactose + glucose
Components of ash
Calcium
Magnesium
Iron
Phosphorus
Parts of the teat
Teat cistern, streak canal
How is mammary gland structure species specific?
Different locations, number of glands, cisterns, teat canals
How many glands do cows have? Sheep? Pigs?
Cows = 4
Sheep = 2
Pigs = 12-14 <
What is the streak canal? Role?
Teat opening
Muscular sphincter
Keep milk in, bacteria out
The cow udder is divided into…
Quarters (four glands)
How many teat cisterns/streak canals in cows? Horse?
Cows = 4
Horses = 4 (two per half)
How many streak canals/teat cisterns per teat in dogs
Many, 5?
Extra, nonfunctional teats aka
supernumerary teats
What is good teat conformation
Moderate size
Central in each quarter
Tight sphincter
Rear teats usually shorter
Straight down (not out to sides)
What is teat hypoplasia? Dilated teats
Hypoplasia of hindquarters = back teats are small
Hypoplasia of forequarters = front teats are small
Dilated teats = saggy/long
Why is udder conformation important
Udder weight = 3 to 70 kg
~36 kg of milk
Grows until cow is 6 years
Three major supporting structures of the mammary gland
Skin (small amount)
Median suspensory ligament
Lateral suspensory ligament
What is the median suspensory ligament
Separates right and left halves of udder
Connects udder to abdominal wall
Elastic tissue which responds to weight of milk in udder
What is the lateral suspensory ligament
Inflexible
Surrounds the outer wall of the udder
Attached to the prepubic and subpubic tendons
What is the intermammary groove
Were median and lateral suspensory ligaments meet
Left x right halves
Indicates good attachment
Good lactating vs non-lactating udders
Lactating = strongly attached, teat size and shape is good, udder size
Non-lactating = fully collapsed, firm attachment, uniform teats
Bad udder abnormalities
Attachment failure
Udder size and shape is bad
Teat size, shape and placement is bad
What is the alveolus? Characteristics
Functional milk production unit
Bulb shaped
Hollow center
Lined with epithelial cells
Alveolus epithelial cells secrete…
Lipids, protein, lactose, water, minerals/vitamins
(synthesize and secrete milk)
Six components of the alveoli and duct system
Epithelial cells
Lumen
Myoepithelial cells
Basement membrane
Terminal duct
Capillary system
Role of the myoepithelial cells in the alveoli/duct system
Contact in response to oxytocin for milk ejection
Role of the capillary system in the alveoli/duct system
Supply milk precursors, deliver hormones, support blood supply
Role of the terminal duct and lumen in the alveoli and duct system
Lumen = collect milk components and water
Terminal duct = milk transport out of alveoli
Alveoli vs lobules vs lobes
alveoli < lobules < lobes
Alveoli = secretory ducts
Lobules = lactiferous ducts
Lobes = mammary ducts
Role and structure of ducts in the alveoli and duct system
Storage and transport
Two layers of epithelium
Myoepithelial cells arranged in longitudinal pattern
-contract for milk flow
What is the cricoid fold
Separates the gland cistern and the teat cistern
How much milk can the gland cistern hold
~ 400 mL
What separates the teat cistern from the streak canal
Folds of tissue called Furstenberg’s rosettes
How much milk can the teat cistern hold
30-45 mL
Mammogenesis, lactogenesis, galactogenesis
Mammogenesis = tissue growth and development
Lactogenesis = differentiation of alveolar cells into milk-producing and secreting cells
Galactogenesis = maintenance/enhancement of lactation
What is isometric growth? when does it occur
Mammary tissue growing same as rest of body
Up to 3-4 months, overfeeding
Hormones related to mammary growth from birth to puberty
Growth hormones
ACTH
Insulin-like growth factors
When does allometric growth start
Before first estrus
Estrogen causes…
Branching/elongation of ductal system
Increased vascularity
Two types of growth
Isometric: mammary tissue grows at same rate as rest of body
Allometric: grows faster than rest of body (45-95% of total growth)
What happens at late gestation (>4 months)
Alveolar development
Hormones involved in conception to parturition
Estrogen, progesterone, prolactin, growth hormone
When/how does lactogenesis occur
At parturition, progesterone levels fall, prolactin receptors are synthesized, prolactin stimulates synthesis of alpha-lactalbumin initiating milk secretion
What is preventing milk secretion in late gestation
High progesterone blocks prolactin receptor synthesis
Prolactin induces…
Lactogenesis
Roles of estradiol, cortisol
Estradiol = stimulates prolactin secretion from pituitary
Cortisol = Growth of RER and golgi apparatus
Role of progesterone
Mammary development, lactogenesis inhibition
Slide 45, 46
Mammary tissue development
Lactation curve
How does the milk ejection reflex occur (oxytoxin, prolactin)
Oxytocin and prolactin released from pituitary following stimulation of skin on teats
Stimulatory effects of oxytocin on udder
Increases pressure in alveolar lumen
Reduces resistance in small excretory ducts
Reduces resistance in teat canal
How does activation of the sympathetic nervous system inhibit milk let down
- reduces secretion of oxytocin
- inhibits response of myoepithelial cells to oxytocin
- elicits contract of smooth muscle cells in sphincter at tip of teat
- reduces blood flow to udder
How can we physically control milk secretion
- removal rate (stops if not removed >35h)
- gland storage capcity (larger udder = more alveolar tissue = more milk)
- intramammary pressure (full = stop producing)
How can we chemically control milk secretion
Feedback inhibitor of lactation (FIL) slows milk secretion (produced when pressure in alveoli)
What happens after milking
Prolactin released
Decrease in intramammary pressure
FIL is removed from alveoli
Slide 50
Involution/dry period
One gallon of milk requires how much blood to udder
400 gallons
Slide 54-59
Blood circulation to udder
Main routes of getting blood to/back from udder
Ventral perineal artery and vein
Cranial/caudal mammary artery and vein
Subcutaneous abdominal vein (only bacK)
Milk vein aka
Subcutaneous abdominal vein
Route blood takes to/from udder
Heart <-> caudal vena cava/aorta (leaving heart) <-> iliac veins/arteries <-> external pudic vein/artery <-> mammary veins/arteries
Lymph carries…
Glucose, salts, fat, fibrinogen
How is movement of lymph passive
Muscle movement, breathing, heart beat, tissue massage all moves lymph
Roles of the lymph system
- regulate proper fluid balance within udder
- immune function (lymphocytes)
- drains fluid from tissue away from udder
Route that lymph takes
From udder to thoracic duct, empties into blood system
Why does fluid drained from lymph tissue only travel away from the udder
- blood capillary pressure
- contraction of muscles around lymph vessels
- valves that prevent backflow
Lymphatic vs circulatory systems
Lymph = low pressure, passive system
Circ = high pressure, active system
What happens if lymph is impaired? Why would this happen
Pooling of interstitial fluid (edema?)
E.g. tissue trauma
Ways of preventing edema
- preparturient milking (store colostrum)
- frequent milking to reduce pressure
- diuretics
- mammary massage, icing
