Chapter 15 Chapter 15 Puerperium and LactationPuerperium and Lactation

AVS 222AVS 222

PuerperiumPuerperium• The period after parturition when reproductive

tract repairs itself and returns to its non-pregnant condition (Uterine involution)

• Become prepared for another pregnancy

• Begins immediately after parturition and recovery period varies among species

• Short and smooth recovery period is desirable

Events of PuerperiumEvents of Puerperium

1. Myometrium contraction and expulsion of lochia

2. Endometrial repair

3. cyclcity:

4. Elimination of bacterial contamination

Stage 1: Myometrium contraction and expulsion of lochia

Stage 2 & 3:Stage 2 & 3: Endometrial repair Endometrial repairResumption of ovarian function

– Necrosis of caruncular tissues

– Sloughing of the caruncular tissues

– Reorganization of uterine endometruim

– First postpartum ovulation

• Continuation of uterine contraction

• Rise in Estradiol and increase in leukocytes

• High degree of

Stage 4:Stage 4: Elimination of bacterial contamination

LactationLactation

The Mammary GlandThe Mammary Gland

• Exocrine gland; common to all mammals

• Function: nourish the neonate

- Food source: fat, protein, sugar (CHO),vitamins, minerals, water

- Protection: immunoglobulins

• Loosely considered part of the reproductive system:

Serves a “reproductive function”; nourishment of

the neonate = survival of species.

• Relies on same endocrine (hormonal) support for development and function.

Example: gonadal steroids, prolactin, etc.

The Mammary GlandThe Mammary Gland

Embryo Origin:

• The mammary gland is a skin gland

–

–

The Mammary GlandThe Mammary Gland

Secretory Tissues:

• Glandular; secreting tissue =

– Alveoli: – Duct system; lined by epithelial cells

– Lobules & lobes; clusters of alveolar tissuesupported by connective tissue

The Mammary GlandThe Mammary Gland

Alveolus:– basic secretory unit; lined by epithelial cellswhich synthesize and/or secrete:

• lipid - triglycerides & free fatty acids (FFA)

• protein -

• lactose –

• minerals & vitamins - Ca, P, K; Vits. A, B, C, D• water

The Mammary GlandThe Mammary Gland

Milk SynthesisMilk Synthesis

• Milk synthesis is dependent on:– no. secreting cells– – supply of milk precursor– – milking frequency•

No. secreting cells is dependent on:– genetics– endocrine support for mammogenesis– –

Example:What volume of blood would a 1400 lb. Holstein pump per day?

Blood Flow (cattle)

Blood ComponentsBlood Components

1400 lb. Cow ~ .9 liters/ heart stroke

Volume/day = .9 x 70 strokes/min = 63 liters/min

63 liters/min x 1440 min/day = 90,720 liters/day

= ~ 22,600 gal/day

Blood Flow (cattle)

• Volume of blood/ volume of milk synthesized =

(this is an approximation; actual ratio is

affected by stage of lactation, efficiency, etc.)

Blood ComponentsBlood Components

Steroid Hormones and MammogenesisSteroid Hormones and Mammogenesis

• Estrogens:– follicle, placenta,

• Progesterone:– corpus luteum, placenta,

• Corticoids:– adrenal cortex

• Estrogens (E2) (follicle, placenta)

1)

2)

3) synergize with progesterone & prolactin tostimulate protein synthesis and duct growth

Steroid Hormones and MammogenesisSteroid Hormones and Mammogenesis

• Progesterone (P4) (corpus luteum, placenta)

1) stimulates lobulo-alveolar growth– retards milk synthesis

2) retards synthesis of enzymes (a-lactalbumin) necessary for lactogenesis in the prepartum mammary gland

Steroid Hormones and MammogenesisSteroid Hormones and Mammogenesis

Lactogenesis; CortisolLactogenesis; Cortisol

• Action of cortisol:( from adrenal cortex)(dexamethasone is synthetic cort.)

1) synthesis stimulated by maternal, fetal ACTH

essential to lactogenesis (adrenalectomy > nolactogenesis)

2)

• Placental E2 + luteal P4 =

– duct development

– lobulo-alveolar development

– suppression of milk synthesis

(P4 suppresses

-lactalbumin; lactose synthesis

MammogenesisMammogenesis

(Mammary Growth and Development) (Mammary Growth and Development)

• Action of cortisol + PRL:

– increase PRL receptor synthesis

–

–

– increase protein transcription/translation

–

• cortisol is permissive to action of PRL

MammogenesisMammogenesis

(Mammary Growth and Development) (Mammary Growth and Development)

LactogenesisLactogenesis(Milk Synthesis)(Milk Synthesis)

• How does P4 retard milk synthesis in the nonlactating mammary gland?

• Blocks glucocorticoid (cortisol) receptors

• Cortisol + PRL stimulates synthesis of PRL receptors on mammary cells

P4 blocks induction of PRL receptors

• Retards synthesis of a-lactalbumin, casein mRNA

• Retards casein, a-alactalbumin, lactose synthesisthus, retards milk synthesis

Endocrine Glands SupportingEndocrine Glands SupportingMammary FunctionMammary Function

Posterior pituitary (protein hormones): Oxytocin

Synthesized in the hypothalmus

Ttransferred to post. pit.

Secreted into blood > acts on myoepithelial cells

Contraction of myoepithelial, smooth muscle

Endocrine Glands SupportingEndocrine Glands SupportingMammary FunctionMammary Function

• GH (STH, BST):

– increases milk yield

Action:

•

•

•

• increases gluconeogenesis

• increases blood glucose

• increases efficiency of

production (greater lbs. of

milk/ lb. DMI)

Endocrine Glands SupportingEndocrine Glands SupportingMammary FunctionMammary Function

Pancreas (islets of Langerhans; protein hormones)

(responsive to blood glucose concentration)

Glucagon (alpha cells):

• increases lipolysis

• increases glycogenolysis

• depresses cellular glucose uptake

• catabolic to adipose, muscle, liver tissue

• increases blood glucose concentration

• Lactogenesis = initiation of milk synthesis

– initiated in the E2/P4 “primed” mammary

gland when:

• corpus luteum regresses

• P4 declines

• cortisol increases

• PRL, GH increase

– these circumstances occur at parturition

Lactogenesis