The Reproductive System

Question 1

Fill in the labels on this diagram of the male gonads:

Answer 1

Question 2

What are the functions of each of the circled labels on the diagram?

What are the 3 structures that provide seminal fluid constituents?

Answer 2

Testicles - make the sperm

Epididymis - where the sperm mature, and get broken down if they are not ejaculated

Ductus / Vas deferens - tube from the testes taking the sperm, surrounded by spiral muscle (that contract to help the sperm along)

Prostate - a gland, into which the sperm enter from the vas deferens, and produced some of the sminal fluid constituents

Seminal vesicles - provide the seminal fluid together with the prostate and bulbourethral gland

Bulbourethral gland - provides some of the constituents of the seminal fluid, and important for the secretion of the sugary rich solution (the pre-ejaculate)

Prostate, seminal vesicles, bulbourethral gland = seminal fluid

Question 3

What 5 things does seminal fluid contain? And why?

Why is the seminal fluid important?

Answer 3

Fructose - nutrients for the sperm (as they travel far)

Citric acid - mutrients for the sperm (as they travel far), sterile

Bicarbonate - neutralise acidic environment of the vagina

Fibrinogen - thickening agent

Fibrinolytic enzymes - help sperm break through to find the egg

To support the sperm?

Question 4

What is the spermatic cord? Where is it found?

What are the main 5 of the 9 structures it contains?

Answer 4

Cord-like structure that suspends the testes in males, formed at the deep inguinal ring, passes through the inguinal canal and down to the testes

Contains: the testicular artery, panpinaform plexus of veins, autonomic and genitofemoral nerves, lymph vessels and vas deferens

Question 5

Why are the testes kept outside the body rather than inside?

Answer 5

To keep it 2-3 degrees cooler than the body temperature, which allows for sperm production and storage

Too hot = reduced fertility (due to impaired sperm production)

Question 6

What are the 3 muscles of the penis?

Which branches of the ANS is responsible for erection and ejaculation?

Answer 6

2x Corpora Cavernosa, 1x Corpora Spongiosum

PNS - erection (P-oint) - increases pressure in penis by blocking venous drainage

SNS - ejaculation (S-hoot)

(Point and Shoot)

Question 7

What is the lymphatic drainage system of the male gonads? Why is it important to study lymphatic drainage of organs?

What is the arterial blood supply to the testes?

What are the 3 layers of the capsule of the testes?

Which structure is separated by the septa and in which sperm is made?

Answer 7

Lymphatics ascend along the testicular vessels, and drain into the para-aortic lymph nodes - important in terms of spread of cancer

Testicular arteries from the aorta via the spermatic cord which suspends the testes

The 3 tunicas: tunica vasculosa - rich in blood supply. tunica albugnia - , tunica vaginalis (covers both, the testes and the apididymis)

Seminiferous tubules

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Question 8

Fill in the labels on this diagram using the names of the structures revised in the last flashcard:

In which structures is sperm made, where is it stored temporarily and where does it pass through to?

Answer 8

Sperm = made in the seminiferous tubules, stored temporarily in the rete testes, and pass through to the epididymis, and then through the vas deferens as well

Question 9

Which part of the testes is cut during a vasectomy?

Answer 9

Vas deferens is cut (on both sides with a minimal incision)

Question 10

Where are the ovaries found?

Which part of the female reproductive system (FRS) releases the egg and how does it travel to the uterus?

In which part of the FRS does fertilisation occur?

Answer 10

Inside the peritoneal cavity

Ovaries, egg travels via fallopian tube = relying on the spiral muscles and cilia found there to sweep the egg along into the uterus. Non-funcitoning cilia = ectopic pregnancy (v. dangerous, as it can rupture the fallopian tubes)

In the ampulla - the widest part of the fallopian tube

Question 11

How is the uterus suspended?

What is the name of the issue that occurs with uterus suspension in elderly women?

What is the name given to the top of the uterus? What are the linings of the uterus?

What causes menstruation in women?

Answer 11

By the tone of the pelvic floor muscles (levator ani and coccygeal muscles), and 3 ligaments (broad, round and uterosacral)

Uterine prolapse (uterus can invert and descend throught he vagina) - due to loss of pelvic floor muscle tone

uterine fundus; perimetrium = outside, myometrium = middle (muscle), endometrium = inner lining (special layer of epithelial cells)

Endometrial lining sheds once a month due to drop in progesterone = vasiconstriction of the arterioles in the endometrium = ischemia = necrosis = pain (period cramps)

Question 12

Where is the ureter in comparison to the cervix? Why is it important to note this?

Which parts of the FRS are sterile? And how is this maintained?

How does the progesterone birth control pill work?

How is low pH of the vagina formed / maintained?

Answer 12

1cm lateral to the cervix - important to note in terms fo spread of cervical cancer

All areas suprior to the cervix are sterile (no bacteria) - pH<4.5, sheds every month, thick cervical mucus blocking the cervical entry, narrow os (opening at the cervix)

Builds up cervical mucus at the enterance of the cervix to prevent sperm entering

Ostrogens stimulate vaginal epithelium to secrete glycogens which are then converted by bacteria (in the vagina) into acid

Question 13

What is the arterial blood supply for the FRS?

What is the lymphatic drainage system for the FRS?

How does the smear test work?

Answer 13

Ovaries = ovarian arteries from the aorta; Uterus / vagina = uterine arteries

Ovaries = lymphatic vessels drain into the para-aortic lymph nodes; uterus / vagina = lymphatic vessels drain into the iliac, sacral, aortic and inguinal lymph nodes

Cells are taken from the external os (opening of the cervix)

Question 14

What are the 2 main functions of the testes and ovaries (the gonads)?

What are germ cells? What are the names of the male and female germ cells?

Why are men always fertile?

Answer 14

Gametogenesis (production of gametes) and reproductive hormone production

Germ cells are from which the sperms or eggs are made - spermatogonia = male, oogonia = female

Men always have spermatogonia (pool of germ cells) throughout their life

Question 15

Describe this graph in terms of the female germ cell count and how it changes throughout their life:

Answer 15

6M per ovary before birth, where the oogonia form 1^o oocytes that then complete prophase and stop at that stage of meiosis; after birth = 2M germ cells remain (as many of the primary oocytes degenerate); so by puberty only half a million germ cells per ovary remain to complete meiosis

Question 16

How is sperm formed in the testes?

Answer 16

Spermatogenesis - begins at puberty:

Undergo mitosis to form the primary spermatocytes. Then undergo 2 rounds of meiotic division to produce 4 gametes with half the genetic information

Question 17

Fill in the labels on this microscopic slide image of the seminiferous tubules (in which sperm cells are made):

What are the functions of the different labels?

Answer 17

Tunica propia = basement membrane

Spermatogonium = cells found on the outside, that mature and move inwards to form the primary spermatocytes and eventually to eventually form the spermatids

Spermatids = exit via a duct to the rete testes

Sorteli = support sperm production, produce inhibin

Leydig cells = produce testosterone

Question 18

What are the 3 hormones the testes produce? And what are their functions?

Answer 18

1. Androgens - testosterone, dihydrotestosterone (more potent form), and androstenedione
2. Inhibin (secreted by sorteli cells) - stops pituitary from making / releasing LH or FSH
3. Oestrogens - (from androgen aromatisation) maintains bone density in men, important in plate fusion

Question 19

What is the name of the enzyme that converts testosterone to oestrogen?

What happens if men are missing that enzyme?

What are the functions of the sertoli cells? What receptors are found on the sertoli cells?

What is the function of AMH (anti-mullerian hormone) and ABP (androgen-binding protein)?

Answer 19

Aromatase converts testosterone to oestrogen

Very tall - due to growth plates not closing, severe osteoporosis (due to lack of bone density)

Has FSH receptors and has 2 main functions: Supprts developing germ cells by - assisting movement of germ cells to tubular lumen, transfering nutrients from capillaries to developing germ cells, phagocytosis of damaged germ cel ls; and hormone synthesis - inhibin & activin (-ve or +ve on FSH), anti-mullerian hormone (AMH), and androgen-binding protein (ABP)

AMH - inhibit development of fallopian tubes in male foetuses

ABP - transfers testosterone to the sperm making machinary in the seminiferous tubules

Question 20

What are the functions of the leydig cells?

Answer 20

When stimulated by LH, production of androgens (testosterone, androstenedione, dehydroepiandrosterone (DHEA))

These can be aromatised to oestrogens (using aromatase)

Look pale under the microscope due to the presence of large amounts of cholestrol

Contain LH receptors

Question 21

How are mature oocytes produced from the ovaries? (oogenesis)

What is released by the ovaries during menstruation?

Answer 21

Oogenesis - at the 2nd trimester of pregnancy for the foetus, all of the oogonia undergo one round of mitosis, and stop at the prophase of the first meiotic division (all primary oocytes formed)

Meiotic divisons resume during menarche i.e. when females begin their menstrual cycles

Each separation = uneven; forms a polar body at each meiotic division (has significantly less cytoplasm)

A secondary oocyte is released during menstuation

Ova are formed when sperm fuses with the secondary oocyte, and then they undergo their final differentiation steps

Question 22

So what are the key differences between spermatogenesis and oogenesis?

Answer 22

Question 23

What is folliculogenesis? How does this occur (go through steps 1-7)?

What are the scientific names given to the primary, secondary and mature follicles?

Why is the corpus luteum important?

Answer 23

Follicle development - the primordial follicle contains the primary oocyte at birth. These then get surrounded by granulosa and theca cells forming the primary (Preantral) follicle. Then, it matures to form a secondary (Antral) follicle, which contains an antrum (a fluid filled cavity) that contain the FSH and LH receptors. Afterwards, the mature (Graafian/Preovulatory) follicle is formed due to a surge in LH, half way through the menstrual cycle, which forms the secondary oocyte. The follicle then ruptures, releasing the secondary oocyte. The ruptured follicle degenerates into the corpus luteum

Primary = preantral, secondary = antral, mature = graafian/preovulatory

Where progesterone (and oestrogen) come from - prepares uterus for implantation (placenta takes over progesterone production after pregnancy)

Question 24

What is meant by the terms ovulatory and anovultary?

On average, 80-90% of menstruation is ovulatory, others are not. What are the 2 tests used clinically to determine whether the ovulation was ovulatory or anovulatory (used esp. to look into infertility)?

Answer 24

Ovulatory = oocyte released during the the menstruation cycle, anovulatory = oocyte not released

Hormone test - rise in progesterone (around day 21) for ovulatory menstruation as there would have been successful rupture of the follicle to form the corpus luteum); and / or an ultrasound to see the corpus luteum

Question 25

Looking at the mature follicle in more detail:

Which cells make the androgens?

What are the granulosa cells responsible for?

Answer 25

Theca cells

They aromatise the androgens made by the theca cells into oestrogens

Question 26

What are the 5 hormones made by the ovaries?

Answer 26

1. Oestrogens - 3 different forms (oestradiol, oestrone, oestriol)
2. Progestogens (progesterone)
3. Androgens (testosterone, androstenedione, DHEA, but not DHEAS as that is made by adrenal glands)
4. Relaxin - relaxes the cervix and pelvic ligaments in preparation for childbirth
5. Inhibin - negative feedback on FSH

Question 27

Fill in the table to summarise the functions of the gonads:

Answer 27

Question 28

What are the 2 main cell types of the ovary? Where are they found in the ovarian follicle? What are they responsible for?

What is a cause of PCOS? What are the 3 signs you need to be clinically diagnosed with PCOS?

Answer 28

Theca cells = outer part of the ovarian follicle, support folliculogenesis by providing structural and nutritional support of the gorwing follicle, and synthesise androgens when stimulated by LH

Granulosa cells = inner part of the ovarian follicle, involved in hormone synthesis - secrete inhibin and activin, FSH stimulates the granulosa cells to convert the androgens secreted by the theca cells into oestrogens; after ovulation, they turn into gransulose lutein cells that produce progesterone and relaxin

Overactivity of the theca cells producing high androgen levels; 3 things - polycystic ovaries on an ultrasound, clinical signs of high androgens such as excessive body hair / acne or high androgen levels on blood tests, and impaired menstrual cycles (i.e. oligo/a-menorrhoea)

Question 29

What is the enzyme that converts testosterone to oestrodial?

What is the precursor for all steroids?

Answer 29

Aromatase

Cholesterol

Question 30

Fill in the covered labels for all the different hypothalamic-pituitary gland axes:

Answer 30

Question 31

How many hormones made by the anterior and posterior pituitary respectively? And what are they?

Which glands are involved from start to end for the production of these hormone axes?

Answer 31

Anterior = 6, posterior = 2

Anterior = growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL)

Posterior = oxytocin, ADH

Hypothalamus, pituitary, target gland

Question 32

What is the most common cause of amenorrhoea?

What is the difference between primary and secondary hypothyroidism?

What is amenorrhoea?

What is the difference between primary and secondary amenorrhoea?

Answer 32

Hypothyroidism

Primary = the thyroid gland is the problem e.g. autoimmune condition that has destroyed the thyroid gland; secondary = the thyroid gland is fine, but there is little / no TSH production so the thyroid gland is not stimulated to produce thyroxine

No periods for 3-6 months

Primary amenorrhoea = never had periods (due to severe weight loss coming into puberty, tumour, etc.); secondary amenorrhoea = used to have periods, but now they have stopped (due to menopause, stress, severe unintended weight loss etc.)

Question 33

What is the Hypothalamic-Pituitary-Gonadal (HPG) axis?

What is the pattern of the testosterone / oestrogen levels throughout the day?

Answer 33

Kisspeptin neurons are found in the hypothalamus, which secrete kisspeptin

Kisspeptin binds to kisspeptin receptors found on the GnRH neurons (also found in the hypothalamus)

This stimulates the GnRH neurons to release GnRH into the local blood supply (portal circulation system)

GnRH is released in pulses (pulsatile fashion) - frequency and amplitude of pulses governs the downstream action

GnRH passes to the gonadotrophs, and stimulates them to release LH and FSH in a pulsatile fashion to the systemic circulation (so LH and FSH levels can be measured in blood tests)

LH and FSH then pass to the gonads, stimulating them to make prodominantly testosterone and oestrogen (and also progesterone, activin, inhibin)

These feedback directly on the pituitary or onto the kisspeptin neurons (positive or negative feedback)

Testosterone and oestrogen levels are higher in the morning than the evening (diurnal variation)

Question 34

What is hyperprolactinaemia? What may be a cause of hyperprolactinaemia?

What are some complications of hyperprolactinaemia?

Answer 34

Due to excessive prolactin secretion from lactotrophs, it results in high prolactin levels (may be caused by e.g. a tumour), which shuts down the reproductive axis resulting in amenorrhea (i.e. no periods for 3-6 months)

Prolactin binds to prolactin receptors on kisspeptin neurons, which inhibits kisspeptin release - so inhibits the release of the downstream hormones in the axis

Often results in osteoporosis (due to lack of oestrogen production), low libido, infertility, amenorrhea etc.

Question 35

What is a prolactinoma?

What line of questioning may be asked to a patient if suspecting a prolactinoma is causing hyperprolactinaemia?

Why might someone with a prolactinoma feel tired?

Answer 35

A tumour in the pituitary gland secreting too much prolactin - prolactin switches off GnRH and the rest of the axis

Have you noticed any changes in your vision? Have you been bumping into things a lot? (looking for the bilateral hemianopia)

Headaches and tiredness = generic; lactation outside of pregnancy = something wrong with prolactin (regulates milk production from the breast)

Tired = tumour could be squishing some of the normal cells that produce TSH / cortisol and thyroid hormones = responsible for energy levels

Question 36

What investigations could be performed to look for hyperprolactinaemia?

What would the results of these tests show for hyperprolactinaemia?

Answer 36

A blood test to look for: prolactin levels, LH and FSH levels, oestrogen levels [Cannot measure GnRH as levels are too low to measure in systemic circulation)

High prolactin levels + low LH/ FSH/ oestrogen levels

Question 37

What is the purpose of the menstrual cycle?

What are the 2 cycles the menstrual cycle is comprised of?

What are the 3 phases of each of these cycles?

Answer 37

Preparations for possible fertilisation of the secondary oocyte

The ovarian cycle and the uterine cycle

Ovarian cycle = follicular stage, ovulation, luteal phase

Uterine (endometrial) cycle = menstrual phase, proliferative phase, secretory phase

Question 38

Describe the stages of the menstrual cycle? How do the levels of the 4 hormones change along the menstruation cycle?

What is the name given to menstrual cycles that occur more than 35 days apart?

Which hormones thin out and thicken the cervical mucus?

Answer 38

Day 1 = follicular phase, drop in progesterone causes the arterioles in the endometrium lining to constrict resulting in ischemia so the lining degrades and sheds = first day of bleeding

Day 8 - day 14 = slow increase in LHG / FSH also causes increase in oestrogen to help egg maturation (oestrogen dominates the first half of the menstrual cycle), oestrogen currently has a negative feedback effect on LH secretion

Day 14 = ovulation occurs as there is a switch from the negative feedback caused by the oestrogen to a positive feedback, so there is an LH surge = helps final stages of maturation for the follicle so corpus luteum is formed

Day 14 - Day 28 = 2^nd half of the cycle, known as the luteal phase, is dominated by progesterone, progesterone causes the endometrium to be secretory so thickening of the cervical mucus protects the possible pregnancy. Towards the end of the cycle, when there is no pregnancy, the corpus luteum dies, which causes the drop in progesterone

Oligomenorrhea

Oestrogen (first half of cycle) = allows for thin cervical mucus so sperm can pass, but progesterone (second half of cycle) = thickens cervical mucus to protect possible implantation

Question 39

What drives the changes in hormones of the mentrual cycle?

If there is no pregnancy, how does the menstrual cycle restart?

What and why is there a change in body temperature after ovulation? What is this useful for?

Answer 39

Negative and positive feedback loops

The corpus luteum dies - progesterone comes back down, endometrium sheds = period

0.5 degree increase due to increasing levels of progesterone - used in home temperature kits by women to measure when their ovulation is

Question 40

What are the 7 basic principles of pregnancy?

Answer 40

1. Semen formation and voyage
2. Capacitation
3. Fertilisation (acrosome and corticol reaction)
4. Implantation (attachment and decidualisation)
5. Hormonal changes of pregnancy
6. Parturition (labour)
7. Lactation

Question 41

Fill in the labels on the picture, and recap how sperm in formed?

Answer 41

1. Seminal vesicle
2. Prostate (in red)
3. Bulbourethral gland
4. Cross section of the the seminiferous tubules - spermatogonia go through the seminiferous tubules, where there is some tubular fluid reabsorption due to oestrogen, which concentrates the seminal fluid; and nutrients and glycoproteins are added due to androgens

Question 42

Why does the sperm require the nutrients and protection of the seminal fluid?

What is the normal range of the sperm count? i.e. how many sperms in 1ml of semen?

Are all the sperm motile?

Answer 42

It travels a long distance to reach the secondary oocyte

15-120 million / ml

No

Question 43

How much seminal fluid is in an ejaculation?

What else does semen contain?

How many of the sperms get near the ovum?

Answer 43

2-5ml

Leucocytes - white blood cells to fight infection; also potential viruses e.g. Hep B / HIV

1/100 enter the cervix, 1/10,000 travel from the cervix to the ovum, 1/1M reach the ovum

Question 44

What is capacitation of sperm?

Fill in the labels of the different parts of the sperm, and their roles:

What are the changes?

Where does it take place?

Answer 44

Capacitation is the process by which the sperm achieves fertilising capability - only occurs in female reproductive tract

Acrosome = contains many of the enzymes to break through to the ovum; nucleus = haploid; remaining labels = machinery for movements

Loss of glycoprotein coat; changes in the surface membrane characteristics; and more whiplash of the tail (for travel)

Takes place in the ionic and proteolytic environment of the fallopian tube - as it is oestrogen and Ca²⁺ dependent

Question 45

What is the name given to the widest part of the fallopian tube?

What happens when the sperm reaches this?

Answer 45

Ampulla

Acrosome reaction - sperm binds to the ZP3 receptor (ZP stands for zona pellucida = glycoprotein outer layer of the ovum); progesterone stimulates Ca²⁺ influx in the sperm; acrosome releases hyaluronidase and proteolytic enzymes allowing the sperm to penetrate the ZP

Question 46

Where does fertilisation occur?

What reaction does fertilisation trigger?

What does fertilisation form?

Answer 46

In the widest part of the fallopian tube - the ampulla

Corticol reaction - stops more sperm from entering once one sperm has entered as cortical gransules are released to degrade the ZP so there are no more ZP3 receptors for sperm to bind onto to enter the ovum

A zygote

Question 47

How does the conceptus (i.e. zygote) develop?

How does the zygote travel from the ampulla to the uterus?

When does implantation occur?

Answer 47

The nuclei of the sperm and ovum fuse to form the zygote, which continues divsion as it travels down fallopian tube - takes about 3-4 days, and is driven by nutrients from the uterine secretions

Relies on the cilia, peristalsis (wave-like contractions) of the muscles to waft the zygote down to the uterus where it will implant

Implantation occurs between days 8-10

Question 48

What is the blastocyst comprised of?

Answer 48

Made up of the inner cell mass (that form the embryo), and surrounded by the trophoblast cells (that will eventually form the placenta)

Question 49

What are the 2 phases of the implantation? What do each of the phases do?

Which hormone does it require to drive the phases?

Answer 49

Attachment phase - outer trophoblast cells contact the the uterine surface epithelium;

then Decidualisation phase - changes in the underlying uterine stromal tissue

Progesterone (from the corpus luteum)

Question 50

What are the 2 main factors released by the endometrial lining that are important for the implantation and blastocyst attachment phase?

What are the 4 endometrial changes that occur during the decidualisation phase?

Answer 50

Leukemia inhibitory factor = stimulates adhesion of the blastocyst to the endometrial cells; and interleukin-11 = also released from the endometrial cells into the uterine fluid

Progesterone causes: glandular epithelial secretion of fluids; glycogen accumulates in the stromal cell cytoplasm; growth of capillaries for increased blood supply; and increased vascular permeability (leading to oedema)

Question 51

What are the 4 main hormones that play important roles throughout the pregnancy and what are their roles?

What are the hormone changes and effects during pregnancy?

What is measured in a pegnancy test?

Answer 51

hCG - comes from the placenta, stimulates LH receptors, which maintains the corpus luteum for longer, so progesterone is produced for longer, also inhibits maternal LH and FSH production; oestrogen; progesterone; and human placental lactogen - involved in altering female metabolism i.e. increases insulin resistance so more glucose available in the blood

hCG levels decrease after 40 days as the placenta takes over, to make all the other hormones; all other hormones continue to increase and drop after childbirth

hCG levels

Question 52

What is HPL?

Where is the progesterone and oestrogen made during the pregnancy?

Answer 52

Human placental lactogen - involved in making changes to maternal metabolism i.e. increased insulin resistance so more glucose available in the blood

First 40 days = corpus luteum, after day 40, placenta takes over

Question 53

What substrate does the placenta use to make oestrogen?

Answer 53

DHEAS (an androgen)

Question 54

What are some physiological changes in the maternal hormones? Fill in the tabel according to which hormone levels increase and decrease during pregnancy:

Why do some of the hormones decrease in secretion?

If a patient is pregnant, prolactin levels cannot be used as a biomarker of the prolactinoma. So what is used instead to monitor a prolactinoma in a pregnant lady?

Why is the HPG axis stopped due to the high prolactin levels?

Answer 54

Placenta version of GH is made; prolactin suppresses HPG axis; hCG takes over LH function so TSH production decreases

Cannot use prolactin level to judge size of prolactinoma as it goes up during pregnancy anyway. Visual fields checked in each trimester to monitor size of tumour (due to obstruction of optic nerves = bitemporal hemianopia)

Prolactin binds to kisspeptin neurons to prevent release of kisspeptin

Question 55

What is paturition and what is the name of the main hormone responsible for parturition?

Where does oxytocin come from?

How does it affect the uterus (during parturition)?

Which hormone controls milk production Vs which hormone controls milk ejection?

Answer 55

Labour - oxytocin

Posterior pituitary

There is an increase in the number of oxytocin receptors in the myometrium and endometrium cells of the uterus towards the end of pregnancy - cascade of changes leads to leads to dilation of the cervix, contraction for labour and milk ejection

Prolactin = production. oxytocin = ejection

Question 56

How is lactation controlled via the endocrine system?

Answer 56

1. Mechanical stimulation of the nipple and surrounding areas activates afferent (sensory) pathways
2. Signals from the afferent pathways stimulates changes in the ascending neurological pathway - so stimulates oxytocin-releasing neuron activity and inhibits dopamine release from dopaminergic neurons
3. Less dopmine release results in less inhibition of the lactotrophs in the anterior pituitary - lactotrophs secrete more prolactin
4. Increase in plasma prolactin increases milk secretion in mammary glands and increased oxytocin release increases milk ejection