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Biochemistry Y1 > Female Reproductive Tract > Flashcards

Female Reproductive Tract Flashcards

1
Q

Which 2 hormones important for reproduction are released by the hypothalamus and from where?

A

Gonadotrophin releasing hormone, GnRH

Prolactin inhibitory hormone/dopamine

Released from clusters of neurones called nuclei in the hypothalamus. GnRH released by preoptic and arcuate nuclei and dopamine released by arcuate nuclei.

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2
Q

How can GnRH be released?

A

Released into portal blood supply and transported to the anterior pituitary gland.

Release can be pulsatile or surge. Frequency changes throughout oestrous cycle.

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3
Q

What are the 3 hormones produced by the anterior pituitary gland that are involved in reproduction?

A

LH and FSH - glycoproteins, made up of an alpha and beta chain, secreted by gonadotrophs in response to GnRH. Stimulate oestrogen and progesterone.

PL, prolactin - a peptide secreted by lactotrophs.

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4
Q

What are the functions of FSH, LH and PL?

A

FSH - stimulates growth of follicles in the ovary before ovulation.

LH - triggers ovulation and maintains the corpus luteum for progesterone secretion.

PL - promotes lactation.

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5
Q

What 2 phases is the endocrine function of the ovaries split into?

A

Follicular – phase of the oestrus cycle where follicles in the ovary mature and are released in ovulation. The hormone mainly produced us oestrogen.

Luteal – the phase that follows ovulations, where the corpus luteum is formed. The hormone mainly produced is progesterone.

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6
Q

What is the effect of oestrogen and progesterone on GnRH pulses?

A

Oestrogen decreases the amplitude of pulses and progesterone decreases the frequency of pulses.

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7
Q

Describe GnRH release in the follicular phase.

A
  • Increase in frequency of GnRH pulses due to absence of progesterone
  • Increase LH and FSH
  • FSH promotes development and differentiation of follicle by increased oestrogen synthesis by the follicle
  • Increase in oestrogen leads to GnRH and LH surge in ovulation
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8
Q

Describe GnRH release in luteal phase.

A
  • Reduced frequency in GnRH pulses
  • Fall in FSH and LH secretion
  • Increased progesterone synthesis from corpus luteum
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9
Q

Describe the steps leading to ovulation.

A
  1. In the follicular phase, there is an increase of oestrogen release and a lack of progesterone.
  2. This decreases the amplitude and increases the frequency of GnRH pulses.
  3. Oestrogen dramatically increases at a point in the GnRH surge.
  4. Surge in GnRH leads to a surge in LH and FSH.
  5. As a result, ovulations occurs.
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10
Q

What is the positive feedback of oestrogen?

A

High levels of oestrogen causes a positive feedback of a surge of GnRH. This causes a surge of LH and ovulation.

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11
Q

What is the role of inhibin?

A

Mature follicles secrete a peptide hormone called inhibin, the release of which is stimulated by FSH. When inhibin is released, it has a negative feedback on FSH. It decreases the amount of FSH being released in order to increase the LH surge.

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12
Q

What causes this switch from positive to negative control of oestrogen?

A
  • Oestrogen acts on both alpha and beta receptors.
  • GnRH neurones in the hypothalamus posses receptors that are if the beta type, these are the neurones that mediate this negative feedback affect on the phase of the oestrus cycle where there are GnRH and LH pulses.
  • Positive feedback occurs via the alpha receptors, but GnRH neurones only have beta receptor types, so there must be an intermediate neurone that induces the surge release that have an aloha receptor type.
  • A candidate for this neurone within the hypothalamus is the kisspeptin neurones, which have alpha receptor types.
  • These kisspeptin neurones synapse onto GnRH neurones, causing the change from pulsatile to surge GnRH release.
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13
Q

Define oestrus cycle and oestrus.

A

Oestrous cycle – cyclic pattern of ovarian activity which facilitates the female for the possibility of becoming pregnant. These cycles develop in females during puberty.

Oestrus – time of ovulation. Oestrous refers to the behavioural changes associated with increased sexual receptivity/”heat”. These behavioural changes occur just before ovulation, so optimises the chance of successful fertilisation.

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14
Q

What is spontaneous oestrus cycle and an exmaple?

A

Spontaneous cycle don’t require physical or chemical cues from a male to bring about the hormonal activity associated with reproduction and females display continuous cycling of reproductive hormones.
Example: horse

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15
Q

What is induced oestrus cycle and examples?

A

Induced cycles refer to induced ovulators, in which animals ovulate in response to an externally derived stimulus during or just before mating, rather than ovulating cyclically. Example: cat and rabbit

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16
Q

What is monestrous oestrus cycle and an example?

A

Monoestrous show one cycle of heat per year. If they do not become pregnant, they present with a long luteal phase. They remain in anoestrous – a period of sexual acquiescence – until they next year.
Example: fox

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17
Q

What is dioestrous oestrus cycle and an example?

A

Dioestrous show two cycles of heat per year. If they do not become pregnant, they present with a long luteal phase. They remain in anoestrous – a period of sexual acquiescence – until they next year.
Example: dog

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18
Q

What is polyoetsrous oestrus cycle and examples?

A

Polyoestrous animals cycle continuously. They present with heat between regular periods of time during the year. Can become pregnant without regard to the season or the year.
Example: cow and pig

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19
Q

What is seasonal polyoestrus oestrus cycle and examples?

A

Seasonal polyoestrous cycles present several heat periods during the reproductive season and remain in anoestrous during their non-reproductive cycle. You can get seasonal breeders classified as short day breeders where they present oestrous cycles during Autumn, when daylight hours are decreasing.
Example: goat and ewes.

Can get log-day breeders, where they show oestrus mainly during spring when daylight hours increase.
Example: horse

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20
Q

Name the stages of the oestrus cycle.

A

Proestrous
Oestrous
Metoestrous
Dioestrous

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21
Q

Describe proestrous.

A
  1. When corpus luteum has degenerated to the onset of oestrus/beginning of behavioural changes of sexual behavioural changes/heat.
  2. Rapid follicle development, leading to ovulation and the onset of sexual receptivity.

Proestrus overlaps with the follicular phase, increasing oestrogen to prepare the system for potential implantation of a fertilised egg. So vascularity of the female reproductive tract increases and endometrial glands of the uterus will begin to grow in response to oestrogen.

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22
Q

Describe oestrous.

A

The time of sexual receptivity/heat.

Ovulations usually occurs at the end of oestrus.

Oestrus is also part of the follicular phase, where you have behavioural changes, including allowing the male to mount and fertilise the egg. LH surge also occurs for the switch from the negative feedback effect of oestrogen to the positive feedback effect of GnRH and LH secretion. This is when oestrogen levels then decrease.

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23
Q

Describe metoestrous.

A

The early post-ovulatory period, during which the corpus luteum begins to develop and oestrogen levels are low. Contractions of the uterus are subsiding. Endometrial glands continued to grow and become cold. FSH increase to trigger release of other follicles for ovulation.

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24
Q

Describe dioestrous.

A

The period of mature luteal activity.

Begins with ovulation and ends with the regression of the corpus luteum.

  • Diestrus corresponds to luteal phase where progesterone levels are high. At some point, FSH levels will increase and cause another ovulatory follicle to grow. Endometrial glands secrete fluids but the volume gradually decreases. Contractions of the uterus stop. Corpus luteum regresses at the end of this period if the female is not pregnant due to prostaglandin release.
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25
Q

Define oogenesis.

A

The production of the female gametes/ova.

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26
Q

Describe the process of oogenesis.

A
  1. Egg maturation begins in the foetus, pauses in the juvenile period, resumes during puberty and ends at fertilisation.
  2. In the foetus, egg cells divide by mitosis.
  3. Germ cells go on to develop primary oocytes.
  4. In the female, mitosis of the gametes ceases at this point and oocytes are in a phase of arrested development in prophase of the first meiotic division.
  5. Meiosis won’t resume until ovulation occurs.
  6. After puberty, meiosis recommences and the first division is complete, forming 2 unequally divided cells: a secondary oocyte with the most of the cellular material and the rest forming a polar body. Polar body usually dies.
  7. Secondary division of meiosis stops at metaphase II.
  8. At ovulation, this secondary oocyte is released and travels towards the uterus through the oviduct.
  9. If fertilised, it will contain the full chromosomal content and be diploid. These will divide by mitosis to form an embryo.
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27
Q

Define folliculogenesis and follicle.

A

Folliculogenesis – the development of the follicles, the oocytes and their supporting cells.

Follicle – a small pocket-like sac located inside the ovary. Is responsible for the monthly growth, maturation and release of an egg. Also stimulates the production of sex hormones.

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28
Q

Describe the process of folliculogenesis.

A
  1. Primordial follicle goes on to from the primary oocyte.
  2. The single layer of granulosa cells changes from flat to cube shaped.
  3. The zona pellucida is formed by the oocyte secreting glycoproteins. It separates the oocyte from the granulosa cells, but gap junctions keep their contact maintained, to allow for the transfer of nutrients.
  4. Mitotic division of granulosa cells and the production of more layers.
  5. Blood vessels invade the fibrous investment of the molecules to form the theca interna. This is then surrounded by fibroblasts.
  6. At the 4th layer, fluid begins to collect in vesicles in between the granulosa cells, composed of granulosa cell secretions containing mucopolysaccharides. Forms secondary follicle.
  7. Vesicles coalesce to form one single antrum, forming graafian follicle/tertiary follicle.
  8. The oocyte is located to one side and is surrounded by 2 or more layers of cells.
  9. After ovulations, the cumulus oophorus surround the oocyte and the remaining follicle forms the corpus luteum.
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29
Q

What are follicular waves and what are the species differences of these?

A

Synchronous growth of group of follicles. Discovered using high-resolution ultrasounds. There are huge species variations:

  • Cattle = 2-3 per cycle
  • Sheep = 4-5 per cycle
  • Pigs and horses = 1 per cycle
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30
Q

Describe the process leading to a follicular wave.

A
  1. There is recruitment of a number of follicles due to the increase in FSH.
  2. As these begin to grow, one becomes the selected follicle and becomes larger than all the others.
  3. This follicle continues to grow even those FSH concentration decreases and it is able to survive. Other follicles undergo atresia and die.
  4. Selected follicle can survive due to an increase of LH receptors on it, so is able to switch its dependence from FSH to LH.
  5. Continues growth until it is the dominant follicle. At this point, it releases inhibin. This has a negative feedback effect on the anterior pituitary which causes a suppression in FSH release. This prevents other follicles from developing.
  6. Oestrogen is not produced from this follicle so is not able to have a positive effect on the hypothalamus and induce a surge. Animal displays no oestrus behaviours and the dominant follicle will not be ovulated.
  7. Dominant follicle cannot survive forever in high LH and progesterone, as there is not FSH to support it. So it dies off or goes under atresia.
  8. This decreases inhibin secretion, allowing FSH levels to rise again.
  9. This continues for as many waves.
  10. Progesterone begins to decline and the follicle is able to ovulate. This is because decreased progesterone allows GnRH release to be increased.
  11. This increases LH and oestrogen release to cause LH surge for ovulation and oestrus behaviour.
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31
Q

What are sex steroids, how are they derived, what are they made by and what are the 3 main classes?

A

Sex steroids are what will determine whether an animal develops male or female characteristics.
They are all derived from a common sterol precursor, cholesterol.
Mainly produced by the ovaries and testes, but also by the placenta, the brain and adrenal gland.

  • Progestagens
  • Androgens
  • Oestrogens
32
Q

Describe the process of steroidogenesis in ‘Two-cell two-gonadotrophin theory’.

A
  1. Granulosa cells bind FSH.
  2. Thecal cells of the theca interna bind LH.
  3. As the follicles grow in response to stimulation from the gonadotrophins, they start to secrete increasing amounts of oestrogen.
  4. The two cells collaborate in the production of oestrogen.
  5. Granulosa cells express the enzyme aromatase, which converts an androgen precursor into oestrogen. However, they lack the enzymes to make the androgen precursor.
  6. Theca cells lack aromatase but are able to produce the androgen precursor, which is converted to oestrogen by the granulosa cells.
  7. In this way, the two cells work together to produce the steroids.
33
Q

What does the LH surge for ovulations trigger?

A
  • An increase in blood flow
  • An increases protease and collagenase activity in the follicle
  • An increases follicular fluid
  • A local ischemia, due to the increase in blood flow and force between the follicle and ovary
  • Thinning of the granulosa cell layer
  • Formation of a stigma, which resembles a raised blister in the cortical surface of the ovary, at the onset of ovulation, this blister is torn apart and watery fluid spurts out. This is followed by the oocyte, which gently oozes out with more viscous liquid surrounding it.
34
Q

What 4 regions is the oviduct divided into?

A
  • Uterine tubular junction
  • Isthmus
  • Ampulla – the site of fertilisation
  • Infundibulum – have fimbriae, finger-like projections which are lined with cilia
35
Q

Describe the movement of the egg in the oviduct.

A

Fimbriae cilia create movement of fluid that directs the egg into the oviduct. This movement is greatly aided by the cumulus oophorous surrounding the oocyte.

The isthmus, ampulla and infundibulum are all lined with ciliated, secretory epithelium. Movement up until the isthmus is mainly due to these cilia movements. But at the isthmus, muscular contractions aid the oocyte, particularly through the uterine-tubular junction.

36
Q

Describe the movement of the egg in the isthmus.

A

Fimbriae cilia create movement of fluid that directs the egg into the oviduct. This movement is greatly aided by the cumulus oophorous surrounding the oocyte. The isthmus, ampulla and infundibulum are all lined with ciliated, secretory epithelium. Movement up until the isthmus is mainly due to these cilia movements. But at the isthmus, muscular contractions aid the oocyte, particularly through the uterine-tubular junction.

37
Q

Describe the movement of the egg in the ampulla.

A

In the ampulla, the egg is held and fed by secretions from the epithelium and oocyte usually loses the cumulus oophorous here, occurring largely due to the muscular contractions.

Egg arrived in ampulla a few hours after ovulation and is held in place at ampulla-isthmus junction by a physiological sphincter until fertilisation. Is physiological instead of physical, as conditions must be correct: sphincter is closed when oestrogen is high and open when progesterone is high.

38
Q

How is the corpus luteum formed?

A
  1. Forms when the follicle collapses in on itself.
  2. The granulosa cells and the thecal cells of the theca interna form the corpus luteum.
  3. Blood vessels invade form the theca.
  4. There is switch of production of hormones going from oestrogen to progesterone.
  5. Granulosa cells stop dividing and are transformed into lutein cells in luteinisation. They are celled lutein cells due to yellow pigment.
39
Q

What is the corpus luteum?

A

Secretes progesterone and prepares the uterus for the initiation and maintenance of pregnancy. This also prevents GnRH secretion due to negative feedback effect on the hypothalamus, which prevents the LH surge and ovulation.

40
Q

What 2 cell types is progesterone produced by?

A
  • Thecal cells – small lutein cells that secrete progesterone and androgens
  • Large lutein cells – produce progesterone
41
Q

What is luteolysis?

A

If there’s no pregnancy, the corpus luteum undergoes luteolysis. Luteolysis involves:

  • Ischemia
  • Progressive cell death
  • Fall in progesterone output
  • Whitish scar tissue that remains in the corpus albicans
42
Q

Describe the mechanism of luteolysis.

A

Mechanisms of initiation of luteolysis varies between species. But one factor that is common to most mammals is that it is prostaglandin alpha/PGF2 alpha that is involved in the regression of the corpus luteum. This is synthesised by the uterine endometrium and is released into the uterine veins.

  • The ovarian artery is wrapped very tightly around this vein.
  • Counter current flow causes PGF2 alpha to be transferred from the uterine vein to the ovarian artery.
  • Ovarian artery delivers PGF2 alpha back to ethe ovary, where it destroys the corpus luteum by luteolysis.
43
Q

What stimulates PGF2 production?

A

Oxytocin release from the corpus luteum stimulates PGF2 alpha production.

Early on, this does not have an effect, due to the lack of oxytocin receptors on the endometrium.

44
Q

What is the effect of oestrogen and progesterone on the oviduct?

A

Oestrogen:

  • Increased secretion
  • Increased cilia
  • Increased muscle activity

Progesterone:

  • Reduced secretions
  • Cilia decline
  • Reduced muscle activity
45
Q

What is the effect of oestrogen and progesterone on the cervix?

A

Oestrogen:

  • Relaxation of cervix
  • Secretion thinner to allow penetration of sperm

Progesterone:

  • Cervix firmer
  • Secretions thicker, may form a plug to prevent penetration of sperm
46
Q

What is the effect of oestrogen and progesterone on mammary glands?

A

Oestrogen: prime glandular tissue

Progesterone: stimulates growth glandular tissue

47
Q

What is the effect of oestrogen on the uterus?

A
  • Increased myometrium activity
  • Increased size and number of glands
  • Increased watery secretions
  • Induces synthesis of progesterone receptors
48
Q

What is the effect of progesterone on the uterus?

A
  • Reduced myometrium activity
  • Further glandular growth
  • Increased thick glycoprotein/sugar/amino acid rich secretions
  • Development of spiral arteries
49
Q

Describe sperm transport through the cervix.

A
  • The cervix has connective tissue and muscular canal physical barrier and crypts in the wall, where sperm can hide.
  • Cervix secretes fluid to help prevent infection, the makeup of which, changes during the cycle.
  • Transport aided through the cervix by uterine muscular contractions that create negative pressure.
50
Q

Describe the fluid produced by the cervix during oestrogen and progesterone phase.

A

In oestrogen phase, fluid is watery, alkaline, hospitable to sperm and forms micelles, which act like channels to help guide sperm

In progesterone phase, fluid is thick, acidic and inhospitable to sperm, preventing newly deposited sperm to not enter the reproductive tract.

51
Q

Describe transport of sperm through the uterus.

A
  • Passage of sperm is mainly due to their own propulsion by flagella.
  • This is aided by currents of fluid set up by action of uterine cilia.
  • Passage through utero-tubal junction regulated by intermittent sphincter.
  • Once in isthmus of oviduct, sperm become immotile.
  • Sperm swim to isthmus-ampullary junction, attracted by chemoattractant from oocyte/cumulus oophorous mass.
52
Q

What must the sperm undergo before fertilisation? Describe this.

A

Capacitation.

  • Exposure of sperm to environment of female reproductive tract
  • Change macromolecular structure of sperm membrane – enabling acrosome reaction – allowing for channels in the membrane.
  • Undergoes activation, changing in the beating pattern of flagellum, from a wave-like activity to whiplash beatings.
53
Q

Outline the stages of fertilisation.

A
  1. Penetration of cumulus and zona pellucida triggered acrosome reaction
  2. Fusion of egg and sperm membranes to allow incorporation of sperm nucleus into ovum,
  3. Triggers activation of egg. Cortical granules in the egg cytoplasm fuse with plasma membrane to harden zona pellucida.
  4. Pairing of chromosomes in syngamy in a now fertilised state.
54
Q

How is pregnancy established?

A

Passage of embryo to uterus

Developmental changes during this period

Maintenance of corpus luteum – maternal recognition of pregnancy

Implantation

Hormone production of early embryo

55
Q

Why do embryos remain in the tubular entrance of the uterus?

A

Spacing essential for polytocous animals, such as pigs.

Prevents overcrowding and embryonic death.

56
Q

What are the 2 mechanisms of spacing in the uterus?

A
  1. Embryo secretes a factor, which induces contractions in the smooth muscle of myometrium.
  2. Refractory area, where the process of implantation creates a refractory area around it so no other embryos can implant around this area.
57
Q

How is luteolysis prevented after fertilisation?

A
  • Corpus luteum life is extended
  • Extended corpus luteum life needed by all species during early pregnancy
  • Life span of corpus luteum in pregnancy is species dependent
  • Factors produced by early embryo prevent luteolysis until placenta is established
58
Q

What does the embryo produce in cows and sheep to prevent luteolysis?

A

Interferon trophoblast, which decreases the synthesis of oxytocin receptors in teh uterus, reducing PGF2 alpha. Luteolysis is prevented and progesterone levels remain high.

59
Q

What does the embryo produce in pigs to prevent luteolysis?

A

Oestrogen, which acts n the uterus to redirect PGF2 alpha from entering the circulating and so preventing luteolysis.

60
Q

What does the embryo produce in cats to prevent luteolysis?

A

In cats, the corpus luteum is around 45 days after ovulation regardless of the presence of pregnancy, so early modification of luteal activity isn’t required to establish early pregnancy.

61
Q

What does the embryo produce in dogs to prevent luteolysis?

A

Dog does not extend the luteolysis is 7 days in a non-pregnancy animal.

62
Q

What does the embryo produce in primates to prevent luteolysis?

A

In primates, the substance produced to prevent luteolysis is chronic gonadotropin.

63
Q

What does the embryo produce in horses to prevent luteolysis?

A

In horses, the substance produced is equine chronic gonadotropin.

64
Q

State the 4 functions of the placenta.

A
  • Allow maternal and foetal blood supply to be close with one another.
  • Nutrients, gases and foetal waste ae exchanged
  • Serves as an immunological barrier to prevent rejection
  • Source of hormones
65
Q

What hormones are produced by the placenta?

A
  • Progesterone – stabilises uterus, development of mammary gland and HPA
  • Oestrogen – stimulates uterine and mammary growth and development
  • Relaxin – softening of tissues in cats, dogs and mares
  • CG – prolongs corpus luteum in mares
  • Placental lactogen – growth hormone activity in cows, goats and sheep
66
Q

What metabolic changes occur during pregnancy?

A
  • Uterine growth
  • Increased body fluids
  • Proliferation of liver and mammary gland
  • Increased lipid stores
67
Q

What is parturition?

A

Physiological process whereby mother delivers the foetus and the foetal membranes.

  • Is a complex process involving precise timings and interplay between maternal and foetal hormones.
  • Accompanied by physiological changes and behavioural signs.
68
Q

What causes cervical contractions?

A

The pituitary-adrenal axis develops late in gestation and leads to an increasing level in adrenal corticosteroid hormones from the foetal adrenal cortex.

This leads to the synthesis and release if prostaglandin F2 alpha from the uterus. This causes muscle relaxation of the cervix and contraction of myometrial layers of the uterus.

69
Q

Describe how mares get contractions and the hormonal changes necessary.

A
  • Relatively high levels of progesterone, relatively low levels of oestrogen and increasing levels of PGF2 alpha.
  • The reason that progesterone doesn’t drop despite the PGF2 alpha rise is that there is no corpus luteum present in the mare at around 150 days.
  • The increased PGF2 alpha levels are thought to increase the contractility of the uterus and that these early contractions position the foetus for delivery.
  • The presence of the foetus in the birth canal causes oxytocin to be released from the posterior pituitary gland.
  • The myometrium is exposed to relatively high levels of oestrogen throughout gestation makes the uterus very sensitive to circulating levels of oxytocin. So pGF2 is able to overcome regressive effects of progesterone on myometrial activity and cause contractions to occur.
  • The initial increase in myometrial activity in positioning the foetus in the birth canal puts pressure on the cervix.
  • This mechanical stimulus is sent to the brain via the dorsal horn of the spinal cord and projects up the brain to the hypothalamus to the posterior pituitary gland.
  • Cells in the posterior pituitary gland release oxytocin, and then oxytocin release is increased in positive feedback.
  • Positive feedback is enforced by the removal of the inhibitory effects of progesterone for species that decrease progesterone before birth.
  • Oestrogen also induces oxytocin receptor formation within the myometrium of the uterus.
  • PGF2 alpha also increases the sensitivity of the myometrium to oxytocin release, which enhances the rhythmic contractions of the uterine musculature during delivery.
70
Q

What are the stages of parturition?

A
  1. Positioning of the foetus and dilation of the cervix. PGF2 alpha release increasing myometrial activity is essential for this phase. The cervix open up further and the foetus passes into the cervical canal. Myometrial contractions become less important for the delivery of the foetus and is more due to increasing abdominal pressure, due to closure of the epiglottis and contraction of maternal abdominal muscles.
  2. Expulsion of the foetus.
  3. Expulsion of the placenta.
71
Q

Define mammogenesis, lactogenesis

A

Mammogenesis – prenatal events, growth of gland before and after puberty, developmental changes during pregnancy.

Lactogenesis – initiation of milk secretion.

Lactopoiesis/galactopoiesis – maintenance of milk secretion.

72
Q

What is the structure of a mammary gland?

A
  • Glandular tissue arranged into alveoli, which occur in clusters called lobules, and supporting tissue.
  • Functional milk secreting cells are surrounded by a single layer of epithelium. When full of milk, these glands are squashed flat, but columnar when not. Also covered by a layer of myoepithelial cells, which are surrounded by a rich network of capillaries.
  • Each alveolus empties into a small duct and into a larger duct and so on, which eventually opens out to the exterior as a teat/nipple.
73
Q

Describe lactogenesis.

A
  • Initiation of lactation is a sudden decline in oestrogen and progesterone.
  • Increased secretion of prolactin is a stimulus for lactation.
  • Epithelia cells secrete milk into alveoli.
  • Colostrum – higher in solids, protein, minerals, vitamins and immunoglobins.
  • Regular milk – water, protein, lactose, fat, minerals and vitamins.
74
Q

Describe the suckling stimuli/maintenance of lactation reflex.

A

Sucking stimulus is transmitted to the spinal cord and then acts on cells in the hypothalamus to decrease the secretion of prolactin inhibitory factor/dopamine. This acts on cells in the anterior pituitary gland to increase prolactin, which stimulates milk production. This is a neuroendocrine reflex.

75
Q

Describe the milk milk ejection reflex.

A

Stimulated by the action of oxytocin cells on the myoepithelial cells, which surround the epithelial cells and push milk out of the lumen of the alveoli into the duct. Suckling stimulus is transmitted to the spinal cord and acts on cells in the hypothalamus. Hypothalamus acts on the posterior pituitary gland to increase oxytocin release seconds after stimulus. Causes an increase in pressure within the mammary gland and within a minute of stimulation, milk is forced out of the alveoli and the ducts because of contraction of these myoepithelial cells due to oxytocin. This is milk let-down. In addition to mechanical stimulus, visual, auditory and olfactory stimuli can occur to stimulate oxytocin release. Is a neuroendocrine reflex.

76
Q

What are some similarities between milk ejection reflex and maintenance of lactation?

A
  • Initiated by mechanical stimulation of nipple in suckling

* Stimulation of sensory neurones, information conveyed to CNS via spinal cord

77
Q

What are the difference between the milk ejection reflex and maintenance of lactation?

A

Milk production requires prolactin and requires suckling.

Milk ejection requires oxytocin and is a conditioned reflex that can occur without mechanical stimulation of the nipple.

Biochemistry Y1 (10 decks)

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