Mammary gland development and gross anatomy

what is the significance of lactation? (4)

1. frees neonate from dependency of other foods

2. continues development outside of uterus

3. social development and bonding

4. natural form of contraception

why do mammals have a hard palate?

• to enable suckling of milk whilst simultaneously breathing, then swallowing

what is the embryological origin of the mammary gland?

• epidermis

describe what mammary gland are

• epithelial glands

where do mammary glands arise from?

• ventral surface, 2 lateral lines on ventral surface of developing foetus

what do we call the ventral, parallel lines on which the mammary glands develop?

• mammary ridges

where dow e find the mammary ridges

• from axillary region to inguinal canal

outline pre-natal mammogenesis

1. mammary ridges form - thickened epidermal tissue

2. run from axilla to inguinum, bilaterally

3. cause an invagination of the epidermis forming the primary mammary bud

how do secondary mammary buds form?

• primary bud pushes into the dermis

what do secondary buds finally become after having canalised?

• lactiferous ducts

describe the microanatomy of a mammary alveolus

1. lumen filled with milk

2. surrounded by secretory epithelium/spherical lumen

3. myoepithelial cells surround each alveolus and ducts

the contraction of what cells causes the propulsion of milk out of alveoli into the mammary ducts

• myoepithelial cells

what do we call a group of alveoli

• lobules

what do we call a group of lobules

• lobes

what surrounds each lobe?

• connective tissue

What can be identified here from top to bottom?

1. gland parenchyma

2. milk ducts coalescing

3. gland sinus - equid and bovid

4. annular fold

5. teat sinus

6. teat sphincter

7. teat/streak canal

what cell type do we find at the teat/streak canal

• stratified squameous epithelium

what 2 features are in teh equid and bovid teat that are made of bilayer cuboidal epithelium?

• gland sinus

• teat sinus

what is an important factor when considering how glands and teats connect

• a singular/multiple glands may drain into a gland sinus separate from others, into a separate teat sinus, teat canal and then orifice even if they’re in the same teat

• Number or sections is species dependent

What species does this schematic represent?

• mare

• sow

• camel

describe the dog number, location and teat canals of mammary glands

• abdominal, around 80-220 glands and 8-22 canals per gland per teat

describe the cat number, location and teat canals of mammary glands

• abdominal

• 40-48 (L+R)

• 5-6 canals per gland per teat

describe the sow number, location and teat canals of mammary glands

• abdominal

• 16-13 (L+R)

• 2 (per gland per teat)

describe the rat number, location and teat canals of mammary glands

• abdominal

• around 10

• 1 (per gland per teat)

describe the rabbit number, location and teat canals of mammary glands

• abdominal

• 80-100

• 8-10 per gland per teat

describe the goats, sheep number, location and teat canals of mammary glands

• inguinal

• 2

• 1 per gland per teat

describe the guinea pig number, location and teat canals of mammary glands

• inguinal

• 4

• 1 per gland per teat

describe the mare number, location and teat canals of mammary glands

• inguinal

• 4

• 2 per gland per teat

describe the camel number, location and teat canals of mammary glands

• inguinal

• 8

• 2 per gland per teat

describe the cow number, location and teat canals of mammary glands

• inguinal

• 4

• 1 per gland per teat

Describe this structure and the species it belongs to

• 1 canal per teat

• cow, ewe, goat

Describe this structure and the species it belongs to

• 2-3 ducts per teat

• mare, sow

describe this schematic and the species it belongs to

• 2 canals per teat

• camel

Describe this set up and state the species ti belongs to

• 5-6 ducts per teat

• bitch, queen

what structure do dogs and queens contain compared to a cow?

• lactiferous sinuses = smaller versions of gland sinus in teats with many ducts

how can a teat have more than 1 gland supplying it?

• one gland supplies one teat canal but each teat can have more than one teat canal

describe the suspensory system of the mammary tissue

• supported by a strong suspensory ligament, dvided into

1. medial suspensory ligament

2. lateral suspensory ligament

describe the medial suspensory ligament of the mammary suspensory system

• arises from symphyseal tendon

• highly elastic

what is the relevance of the medial suspensory ligament having a high elastin content?

• when it stretches e.g. due to engorged udder, the teats will appear to deviate laterally

describe the lateral suspensory ligaments

• run from symphysial tendon and external inguinal ring crus ventrally over lateral udder.

• inelastic connective tissue

describe mammary glands in marsupials

• within the pouch

how does the connection of a young marsupial to the teat differ from mammals

• marsupials form a direct deal around the teat

what is polythelia?

• supernumery teats - additional teats along the mammary ridge!

where do supernumery teats appear?

• along the mammary ridge ONLY

what controls mammogenesis

• hormones

describe the type of growth from birth to puberty

• isometric growth

describe the type of growth after puberty

• allometric growth

describe what takes place during allometric growth

• after puberty complete and rapid growth in the ducts due to prolactin and GH

• oestrogen causes ducts to branch

• progesterone cause alveolar development

what do we mean by the cycle of mammary function?

• function undergoes: mammogenesis, lactogenesis, weaning and involution (although never back to exact original size)

describe how involution occurs

• gradually - initiated by loss of young or senile.

how do lactation cycles affect the amount of milk produced?

• after involution after each cycle, the tissue volume doesn’t return back to the same original point therefore has a greater ability to produce milk during the next cycle

what change does oestrogen, GH and ddrenal steroids evoke in mammary glands?

• duct growth

what effect do oestrogen, progesterone, prolactin, GH and adrenal steroids have on mammary tissue?

• lobulo-alveolar growth

what effect do prolactin and adrenal steroids have on mammary glands

• milk secretion

how does mammary development during gestation compare for singletons vs twins?

• higher in twins than singletons

what hormone acts in synergy with oestrogen for mammry development during gestation?

• placental lactogen

Explain waht this graph is demonatratin

• during gestation there is development of mammary tissue, hwoever no milk production

  • after parturition due to hormonal changes, the tissue which has grown is able to suddenly activate and produce the milk required

what arteries supply the mammary glands?

• mammary arteries

what supplies thoracic mammary glands?

• branches of internal thoracic artery and pectoral artery

what vessels supply the abdominal mammary glands

• branches of cranial and caudal superficial epigastric aa

what vessel supplies inguinal mammary glands?

• branches of external pudenal artery

compare beef calf cow udder blood flow to dairy cow

• in the beef cow the caudal epigastric vein drains caudally and contains valves, the cranial epigastric vein drains cranially, all arteries have a joint vein to go with it

• in the dairy cow, the cranial and caudal epigastric veins drain cranially and don’t have valves in them, arterial blood flow to udder is too strong for joint venous drainage

what do we call the giant vein on the ventral abdominal cavity of the cow? what is it?

• the milk vein

• it’s the caudal and cr. epigastric vein draining cranially

where does the cranial epigastric vein enter into the body cavity?

• caudal to the sternum

what innervation does the bovine mammary gland have?

• somatic sensory afferent innervation → from skin

• sympathetic motor nerves along blood vessels

• 4 spinal nerves

what innervation deos the bovine mammary gland NOT HAVE

• no parasympathetic innervation

• no innervation of myoepithelial cells

describe the lymphatic drainage of mammary glands

• crainial glands lead to axillary + accessory axillary

• caudal → superficial inguinal nodes

describe the direction of drainage of the lymph nodes in mammary glands

• cranial or caudal, never both

why is recognising that lymphatic drainage is either cranial or caudal important?

• metastatic cancers will only drain in one direction, therefore need to know how far the tumour will have/could have spread and where from

describe the contents of colostrum

• more protein, fat, minerals and vitamins

• less lactose

• igG, IgM, IgA proteins

in which speices is the transfer of immunoglobulins in the milk essential and why?

• equidaea, bovidae, suidae

• epitheliochorial placenta limits the transfer that can happen in utero

what should the pH of milk be?

• 6.6-6.9

what mineral does milk noteably lack in?

• iron

in which species is milk iron content particularly relevant/

• piglets

describe the milk composition change over time

• lactose remains at relatively high levles throughout

• protein acts in a shallow u shape over time

• protein remains fairly constant over time until around month 11 when fat content becomes greater

what is the legal limit for cell count in milk?

• 400,000

what is the ideal cell count for milk?

• <200,000

why do we get increased cell count with inflammation?

• neutrophil invasion

what cells does milk contain?

• leucocytes

  • dislodged mammary epithelial cells

what regulates milk yield?

• demand of the neonate

why do we milk 2-3 times a day?

• to prevent milk inhibition due to lack of calf

waht hormone is used in some countries to sustain milk production, is this used in the UK?

• growth hormone - bovine somatotropin (BST)

• no

what cells synthesise milk?

• epithelial cells

why do the epithelial cells around milk lumen have many mitochondria?

• ATP synthesis for fatty acids and non-essential amino acids

what is the role of the RER in milk production?

• secretory protein synthesis

what is the role of the SER in milk synthesis?

• phospholipids and triglycerides

how is protein released into milk?

• granules by exocytosis - merocrine/eccrine secretion

how does lactose get into milk?

• secreted with protein

how does lipid get into the milk?

• secreted as membrane limited lipid droplets but incorporation into cell membrane

  • apocrine secretion

how does water get into milk?

• osmotic pressure

what is the triglyceride made from in milk?

• fatty acids in chylomicrons and LDL in the blood?

• glucose - non ruminants

• acetate and B-hydroxybutyrate in ruminants

why do dairy cows put on subcutaneous fat before parturition

• as body fat serves as a supply of fat in milk production - it acts as an energy reserve before lactation

how do we describe the metabolic state of the cow during lactation

• rheostasis

why is a cow in rheostasis during lactation?

• body adapts to the energy requirements the body needs for milk production

describe the changes in the cow during rheostasis

• reduced lipogenesis

• increased lipolysis

• decreased glucose uptake in tissues and adipose tissue incresed mammary uptake

• amino acid intake increases in mammary gland

what 3 hormones are involved in the changes during rheostasis during lactation?

• prolactin

• growth hormone

• insulin

state the 3 effects progesterone has on milk production during gestation

• blocks prolactin receptors - therefore no lactation

• increases arachidonic acid stores

• increases body fat stores

what hormonal changes at birth lead to lactation?

• fall in P4 (and rise in E2) → stops inhibition of prolactin

• mammary glands becoming sensitive to oxytocin

• rise in cortisol

what is the overall goal of hormonal changes which leads to lactation?

• reducing the effects of progesterone

describe the changes that take place when P4 is taken over by E2 during parturition

• arachidonic acid (store built up by P4) → PGF2a (P4 levels decrease)

• myometrium expresses oxytocin → uterine contractions

• prolactin inhibition is removed