V410 Exam I Flashcards
(145 cards)
1
Q
(L18) Reproductive hormones are classified as either species-specific or conserved in their structure. Which groups of hormones are species-specific?
A
The glycoproteins (FSH, LH, inhibins, AMH, and eCG) The polypeptide hormones (prolactin, GH)
2
Q
(L18) Species-specific hormones are clinically important for three reasons. What are they?
A
- The protein/glycoprotein hormones from one species cannot be used therapeutically in another since the expected effects may vary.
- Even if an effect can be elicited, the host’s immune system can mount a response against the foreign protein hormone.
- Diagnostic assays for protein hormones are also species-specific, preventing general use.
3
Q
(L18) Reproductive hormones are classified as either species specific or conserved in their structure. Which groups of hormones are conserved?
A
The small peptide hormones (GnRH, oxytocin)
The steroid hormones (testosterone, estrogen, progesterone)
The prostaglandins (PGF2-a)
4
Q
(L18) What is the basic structure of glycoprotein hormones?
A
Glycoprotein hormones are composed of an alpha and a beta chain. The alpha chain is shared between LH and FSH, whereas the beta chain confers specificity. Additionally, the level of glycosylated sites on the subunits grant an additional level of specificity.
5
Q
(L18) Compare equine CG and LH.
A
Equine chorionic gonadotropin (eCG) has the same exact alpha and beta subunits as equine LH. They differ in two ways - where they’re secreted and the extent of glycosylation of their subunits. eCG is secreted by the chorion of the fetus, while eLH is secreted by the anterior pituitary. Additionally, eCG is far more glycosylated than eLH, increasing its half-life.
6
Q
(L18) Biochemically, how are sex steroid hormones synthesized?
A
Steroid hormones are derivatives of cholesterol in which the 27 carbon structure has been cleaved into 21, 19, and 18 carbon structures. The 21 carbon hormone, pregnolone, is the precursor to the sex steroids (19 carbon androgens and 18 carbon estrogens) and 21 carbon gluco- and mineralocorticoids.
7
Q
(L18) Sex steroids and small peptide hormones are conserved across species, generally making them effective therapeutics. In what situation would small peptide hormones not be effective?
A
Chronic overexposure of receptors to these hormones downregulates these hormones, inhibiting LH and FSH release. This results in chemical castration. GnRH and oxytocin’s efficacy is determined by how their signal is received. Normally, pulsatile release of GnRH stimulates pulsatile release of LH and FSH from the anterior pituitary gland.
8
Q
(L18) Sex steroids and small peptide hormones are conserved across species, generally making them effective therapeutics. Generally, what occurs with chronic stimulation of sex steroid receptors?
A
Steroid receptors bind to nuclear receptors that do not exhibit downregulation when chronically stimulated. Unlike small peptide hormones, chronic steroid stimulation causes hyperplasia of the target tissue.
9
Q
(L18) Are diagnostic assays more effective for protein hormones or steroid hormones? Why?
A
Conserved steroid hormones.
10
Q
(L18) There’s a lot of variation in hormone concentrations within an individual and over time. What kind of test reduces this variability?
A
A response test minimizes the variability inherent to a single blood sample. With a response test, something like GnRH is administered, and there should be an expected increase in LH and testosterone soon after.
11
Q
(L18) Equine chorionic gonadotropin is a therapeutic stimulator of follicular growth when given to other species. Why?
A
eCG, because of its structure, binds to LH receptors in the horse. However, when administered to another species e.g. the dog, eCG binds to FSH receptors, not LH receptors. This induces stimulates follicular development.
12
Q
(L19) What are the 4 basic levels of sexual determination?
A
Chromosomal - XX or XY
Gonadal - ovaries or testes
Somatic - mullerian ducts/uterus/vagina or wolffian ducts/scrotum
Hypothalamic
13
Q
How could an XX or an XY individual have the gonads of the opposite sex?
A
Several genes have been identified e.g. SRY (the sex-determining region of the Y chromosome) and Fox L2 that appear to control gonadal differentiation. However, these genes have been identified as part of complex signaling cascades with other genes, and issues with any step along these pathways will disrupt normal gonadal development.
14
Q
(L19) The genital ridge contributes to gonad development. How?
A
Primordial germ cells from the yolk sac populate genital ridge’s cortex and medulla during embryological development. XY-associated signaling causes the cortex to regress, while the medulla remains to form the testes. XX-associated signaling does the opposite - the cortex survives while the medulla degenerates.
15
Q
(L19) How does the male internal genitalia develop?
A
The testes secrete two hormones associated with internal genitalia development - AMH from Sertoli cells and testosterone from Leydig cells. Testosterone binds to androgen receptors on mesonephric ducts/Wolffian ducts to stabilize them. AMH causes regression of the paramesonephric ducts/Mullerian ducts.
16
Q
(L19) How does the female internal genitalia develop?
A
The female internal genitalia develops in the absence of hormones because fetal ovaries are endocrinologically inactive. Wolffian ducts regress because there’s no signal for stabilization, while the Mullerian ducts persist because there’s no signal for regression.
17
Q
(L19) How does the male external genitalia develop?
A
Male external genitalia development depends on the conversion of testosterone into DHT by 5-alpha-reductase. DHT then stimulates the formation of the penis and scrotum.
18
Q
(L19) How does the female external genitalia develop?
A
Female external genitalia develop in the absence of DHT. The tissues that would form the penis and scrotum instead form the vagina and clitoris.
19
Q
(L19) How would an XX individual develop internal and/or external male genitalia?
A
Female fetuses express the same androgen receptors and 5-alpha-reductase as males do. Exposure to androgens or AMH masculinizes the female fetus. Testosterone will stabilize Wolffian ducts and AMH would cause regression of the Mullerian ducts. Even low levels of testosterone, when converted to the more potent DHT, would induce development of external male genitalia (in the absence of Wolffian ducts).
20
Q
(L19) What are true hermaphrodites?
A
True hermaphrodites express both type of gonadal tissue. This can manifest as either one of each type of gonad or an ovotestis.
21
Q
(L19) What are pseudohermaphrodites?
A
A pseudohermaphrodite expresses one gonad type but the internal/external genitalia of the other sex.
22
Q
(L19) What is true sex reversal?
A
A sex reversed individual will express one karyotype but the gonad type of the other sex.
23
Q
(L19) Describe what happens with androgen resistance syndrome.
A
Androgen resistance syndrome is defined as a dysfunctional gene that encodes the androgen receptor. The gene is found on the X chromosome, so a female carrier may potentially pass it onto some of her male offspring. Affected males will express gonads (as determined by their karyotype) but will have Mullerian ducts, no Wolffian ducts, and female external genitalia.
24
Q
(L19) What occurs with a 5-alpha-reductase deficiency?
A
Males, without enough 5-alpha-reductase, will express Wolffian ducts but will have external female genitalia.
25
(L19) Describe what happens with Persistent Mullerian Syndrome
In persisent Mullerian syndrome, there is an issue with either the synthesis of AMH by Sertoli cells or AMH receptors. Ultimately, the Mullerian ducts fail to regress (Wolffian duct and external genitalia development is unaffected).
26
(L20) What is the defining characteristic of a fibroelastic penis and which species have one?
A fibroelastic penis only lengthens when erect; there is not change in girth. This is because they have a very thick tunica albuginea, preventing growth. Cows, pigs, sheep, and goats have one.
27
(L20) What is the defining characteristic of a musculocavernous penis and which species have one?
A musculocavernous penis, when erect, lengthens and increases in girth. These penises have a relatively thin tunica albuginea. Dogs and horses have one.
28
(L20) What are the three general parts of a penis?
The root - where the crus penis, the origin of the penis' erectile tissue is
The body
The glans
29
(L20) What are some unique features to the canine penis?
The canine glans is divided into two structures - the bulbus glandis and the pars longa glandis. The bulbus glandis, when expanded, is what creates the copulatory tie.
30
(L20) What are some unique features of the equine penis?
The equine glans has a specialized glans - the corona glandis which gives rise to the fossa glandis. The fossa glandis is clinically significant because it needs to be regularly cleaned in geldings. The equine penis also has a third erectile tissue, which is continuous with the corpus spongiosum - the corpus spongiosum glandis. This tissue, when engorged, creates a vacuum that helps semen enter the female's uterus.
31
(L20) What are the erectile tissues of the penis?
The corpus cavernosum
The corpus spongiosum
The corpus spongiosum glandis in horses
32
(L20) How is erection achieved? Which nerves are associated?
1. Blood is shunted along the pudenal arteries and the corpus cavernosum.
2. Non-adrenergic non-cholinergic neurons (NANCs) release nitrous oxide (NO) onto sinusoids supplied by helicine arteries in the erectile tissue, allowing them to be engorged with blood.
3. Simultaneously, at the root of the penis, the venous supply of the corpus cavernosum is compressed against the ischium.
4. Erection is achieved with an increase in arterial flow and a decrease in venous flow.
33
(L20) What is emission and ejaculation?
Emission is the deposition of seminal fluid into the pelvic urethra. Ejaculation is movement of that fluid out of the penis. Both are mediated by the SNS.
34
(L20) What are the primary functions of the scrotum?
Protection
| Thermoregulation - spermatogenesis occurs at 2-3 degrees less than body temperature
35
(L20) What are the two tunics of the scrotum?
The parietal vaginal tunic
| The visceral vaginal tunic
36
(L20) How is blood cooled before it enters the testes?
Within the pampinoform plexus, the testicular artery is surrounded by veins moving blood in the opposite direction. The cooler venous blood cools the arterial blood before it enters the testes.
37
(L20) What is the main role of the epididymis?
The epididymis, and mainly the tail of the epididymis, temporarily stores sperm and allows cells to mature and attain mobility before being ejaculated.
38
(L20) What is the blood-testis barrier?
The blood testis barrier is formed by the basement membrane of the seminiferous tubules and the tight junctions between the Sertoli cells. It protects the haploid sperm cells within the lumen from immune cells.
39
(L21) How is the hypothalamus masculinized?
1. Testosterone secreted by the testes reaches the hypothalamus, where it's then converted to estradiol.
2. Estradiol changes the secretion pattern of GnRH so that it is released in pulses.
3. FSH, LH, and, subsequently, testosterone, are stimulated to be released in pulses as well.
40
(L21, 27) What is the female pattern of GnRH secretion in the hypothalamus?
In the absence of testosterone and estradiol, the hypothalamus releases large amounts of GnRH in periodic surges under the stimulation of a "surge center". Later, after puberty, a surge of GnRH and LH can be initiated by surge releases of estradiol from the ovaries.
41
(L21) How does nutrition affect the onset of puberty?
Puberty is associated with positive energy balance as an animal approaches its mature body weight. This is evident with flushing, where increasing the amount of available food can stimulate the early onset of puberty. However, chronic over- and under-nutrition has been shown to negatively impact the onset of puberty.
42
(L21) How does leptin affect the onset of puberty?
Leptin appears to be a permissive signal to the onset of puberty - too little of it may delay puberty, but excess amounts does not accelerate it. Leptin, released by adipose tissue, binds to estrogen receptors in the hypothalamus to stimulate GnRH release.
43
(L21) In general, how does seasonality affect puberty and GnRH release?
In seasonal breeders, changing day lengths appears to affect the secretion of melatonin by the pineal gland -with decreasing day length sensed by retinal receptors, there is increased melatonin secretion. Melatonin, in a not completely understood mechanism, increases GnRH secretion from the hypothalamus.
44
(L21) Which species are seasonal breeders?
Long Day Breeders = Cats, Horses (Spring)
| Short Day Breeders = Sheep, Goats (Fall)
45
(L21) Which species are not seasonal breeders?
Dogs, cattle, and pigs
46
(L21) What is the Whitten effect?
The introduction of a male into a group of peri-pubertal females will accelerate the onset of puberty. The Whitten effect exhibits how social or environmental cues can affect the onset of puberty.
47
(L22) What are the two hormonally active cell types in the testes and what do they produce? How do these hormones regulate testes function?
Leydig cells in the interstitum, under LH stimulation, secrete testosterone and estrogens. Testosterone, when converted to estradiol, feeds back to the hypothalamus to inhibit GnRH, and subsequently LH and FSH, secretion. Sertoli cells, under FSH stimulation, secrete AMH, inhibins, and androgen binding proteins. Inhibins feed back onto the anterior pituitary and selectively inhibits FSH secretion.
48
(L22) What is the role of androgen binding protein (ABP)?
ABPs released by the Sertoli cells maintain a high local concentration of testosterone within the seminiferous tubules. This is critical for spermatogenesis.
49
(L22) With a hemi-castration, what is expected to occur to the remaining testis?
Removal of one testis essentially halves the negative feedback exerted by the testes on the hypothalamus. The resulting increase in gonadotropins causes compensatory hypertrophy of the remaining testis, increasing testosterone secretion until negative feedback is re-established.
50
(L22) What happens to FSH and LH if a castrated animal is exposed to testosterone? To inhibin?
If a castrated male was exposed to testosterone, then LH and FSH should decrease due to increased negative feedback. On the other hand, if a castrated male was exposed to inhibins, only FSH would decrease.
51
(L22, 23) What are the effects of a Sertoli cell tumor?
A Sertoli cell tumor can produce excess estrogen and inhibin, which can suppress GnRH and FSH secretion from the hypothalamus. This is why animals with a Sertoli cell tumor often present with one enlarged and one atrophied testicle. Additionally, the excess estrogen can induce endocrine alopecia, gynecomastia, and metaplasia of the prostatic urothelium.
52
(L22) What effects on the testes are expected with chronic iatrogenic steroid use?
The excess anabolic steroids in the system increase negative feedback on the hypothalamus, suppressing GnRH, LH, and FSH secretion. Without gonadotropin support, even with high plasma [testosterone], testosterone synthesis in the testes and spermatogenesis are impaired.
53
(L22, 23) What is cryptorchidism? What are its ultimate effects in the dog?
Cryptorchidism is failure for either one or both testes to descend into the scrotum. Due to increased temperature, spermatogenesis is inhibited and cryptorchid dogs are more likely to develop Sertoli cell tumors.
54
(L22) How does trans-abdominal migration of the testis occur?
At this stage, the testicle is suspended within the body cavity by two structures - a suspensory ligament and the gubernaculum. As the fetus grows, the testicles descend to the inguinal ring via differential growth. This process is not hormonally regulated.
55
(L22) How does inguinal passage of the testis occur?
A testis passes through the inguinal canal into the scrotum through the regression of the gubernaculum. However, at this stage, gubernaculum regression is hormone-sensitive and exposure to estrogens or a lack of testosterone will disrupt this process. This is why most cryptorchid testes are found near the inguinal ring.
56
(L22) Which hormone is used to diagnose cryptorchidism? Why that hormone as opposed to other testicular hormones?
AMH is the diagnostic option of choice because it's secreted in high concentrations in younger animals and cryptorchids and it's consistently secreted throughout life without seasonal fluctuations. Testosterone is a poor indicator because pre-pubertal animals do not secrete it and its association with seasonality make interpreting a sample difficult.
57
(L23) There are 4 accessory sex glands. What are they? Which species have them?
Ampullae - in horses and ruminants
Vesicular glands - horses, ruminants, and pigs
Prostate - all domestic species
Bulbourethral gland - all domestic species except the dog
58
(L22, 23) There are several differentials for a sperm granuloma. What are they?
1. Segmental aplasia of the epididymis will result in obstruction of sperm flow and the development of a sperm granuloma.
2. Similarly, a compromised blood-testis barrier allows for an immune response against spermatocytes and the development of a sperm granuloma.
3. Chronic epididymitis may contribute to a sperm granuloma.
59
(L23) Which testicular structure is associated with testicular torsion?
The appendix testis
60
(L23) What is the difference between testicular hypoplasia and degeneration/atrophy?
Hypoplasia is a developmental issue. Hypoplastic testes will be accompanied by other hypoplastic structures e.g the epididymis and the vaginal tunics should be smooth. Testis atrophy may be associated with inflammation, may result in loss of spermatogenesis (if seminiferous tubules are affected), and the atrophied testicle will be associated with a normal epididymis and thickened/fibrotic vaginal tunics. Spermatogenesis can be reclaimed if the insult is resolved and the spermatogonia are spared.
61
(L23) What are the three most common testicular neoplasms in dogs?
Leydig cell tumor
Sertoli cell tumor
Seminoma
62
(L23) Which canine testicular neoplasm is most likely to have secondary effects due to hormone production?
Sertoli cell tumor
63
(L23) Describe a Leydig cell tumor grossly
A Leydig cell tumor grossly and histologically resembles adrenal tissue. It's soft to semi-firm, yellowish, and bulges on the cut surface.
64
(L23) Describe a Sertoli cell tumor grossly.
A Sertoli cell tumor is very firm because they readily produce a lot of fibrotic tissue. They're also white and don't bulge on cut surface.
65
(L23) What are the endocrine effects of a Leydig cell tumor?
None - Leydig cell tumors are endocrinologically silent
66
(L23) Describe a seminoma grossly.
Seminomas are soft and have a pearly opalescent quality when cut.
67
(L23) Which species commonly get seminomas?
Seminomas are the most common testicular tumor in stallions, in which they are often highly malignant. Metastatis can spread to the kidneys and spleen.
68
(L23) What is orchitis? What are some effects?
Orchitis is inflammation of the testes. It can result from an ascending, hematogenous, or percutaenous infection. With inflammation, there is heat and swelling which could negatively impact spermatogenesis. If the blood-testis barrier would be compromised, there is a risk of an immune response against spermatocytes. Chronically, there is a risk for fibrosis and infarctions.
69
(L23) What is a common pathogen associated with suppurative epididymitis?
Brucella
70
(L23) What is balanoposthitis?
Inflammation of the penis and prepuce.
71
(L23) What are some possible lesions involving the penis?
A persistent frenulum in cattle
A hematoma fracture of the penis
A true fracture of the os penis
72
(L23) What is a varicocele of the spermatic cord or the scrotum?
A varicocele is when vessels become varicose. This lesion contributes to thrombus formation and ischemic damage.
73
(L24) What are the findings of a breeding soundness exam (BSE) an estimate of?
A BSE provides an estimate of a male's fertility at a given point in time. The male is healthy on a physical, has normal semen parameters, has no venereal diseases, and normal mating ability and libido.
74
(L24) What are the two primary parameters when evaluating semen?
Sperm motility and sperm morphology
75
(L24) Sperm motility can be broken down into which categories?
Total motility and progressive motility, or the ability for sperm cell to move in a straight line. Progressive motility is important because only cells that can move forward can participate in fertilization.
76
(L25) Where would a prostate normally be located in ultrasound? What nearby structures can be used to identify the prostrate?
The prostrate is immediately caudal to the urinary bladder and be identified as the structure with the urethra running through the middle of it (in both longitudinal and transverse planes).
77
(L25) How large is a normal prostate?
~2-4 cm
78
(L25) What are some radiographic and ultrasonagrphic features of benign prostatic hyperplasia?
On U/S, a hyperplastic prostate will be symmetrically, bilaterally enlarged and often will not be accompanied by changes to architecture or echogenicity e.g. mineralization, hyperechoic surrounding mesentery. However, benign hyperplasia may be associated with hypoechic cysts in the parenchyma. On radiographs, the enlarged prostate may displace the colon dorsally, narrowing its lumen, and displacing the bladder cranially.
79
(L25) What is a paraprostatic cyst and how can it be identified radiographically?
A paraprostatic cyst is a fluid filled structure that arose from the prostate. It's one of the differentials for a lobular fluid-filled structure in the caudal abdomen, resembling a second bladder.
80
(L25) How can a pyelogram be used to assess the prostate?
A pyelogram highlights the kidneys, ureters, and bladder with contrast. If the bladder is abnormally displaced or the ureters are somehow impinged, there may be an issue with the prostate.
81
(L25) What is the primary reason for a small prostate radiographically or sonographically?
Neutering
82
(L25) What disease processes is prostate mineralization indicative of?
Neoplasia
Chronic inflammation
Fungal prostatitis
83
(L25) Prostatitis, prostatic neoplasia, and benign hyperplasia are all associated with prostatic enlargement and cysts. How else, sonographically, could you differentiate the aggressive processes from the benign one?
Chronic inflammation and neoplasia are associated with mineralization. Prostatitis can cause local peritonitis and fills the adjacent mesentery with fluid. Inflammation will also aggravate the surrounding fat.
84
(L25) How do the epididymis and rete testes appear sonographically?
The epididymis is a hypoechoic structure associated with the testis, while the rete testes is a hyperechoic line near the middle of the testicle.
85
(L26) Which uterine structures are peritoneal? Which are retroperitoneal?
The uterine horns, the oviduct, and the ovaries are within the peritoneal cavity. Thus, they're covered by a serosal layer. The vagina, the cervix, and the vestibule are retroperitoneal and are covered by an adventitial layer.
86
(L26) What are the structures of the broad ligament?
The mesosalpinx - a connection with the oviduct
The mesovarium - a connection with the ovaries
The mesometrium - a connection with the uterus itself
87
(L26) How is the broad ligament different in dogs than in cows and horses?
In dogs, the ovary is surrounded by the ovarian bursa, a fusion of the mesosalpinx and mesovarium. In other species, these are discrete structures.
88
(L26) What is the most common type of uterus shape in domestic mammals? How does this shape vary between species?
The most common uterus in domestic species is the bicornuate where there are two uterine horns. Dogs, pigs, and cats have very complex and developed uterine horns, while cattle and horses less so. In fact, equine uteri have a pronounced uterine body, where pregnancy will take place.
89
(L26) What are the layers of the uterus?
The endometrium
The myometrium
The perimetrium
90
(L26) What are the segments of the oviduct?
The infundibulum
The ampulla
The isthmus
91
(L26) What are the internal and external os of the cervix?
The cervix is essentially a muscular valve separating the vagina from the uterus. The inner side of the valve, on the uterine side, is called the internal os. The outer side of the valve on the vaginal side is the external os.
92
(L26) How is an ovary arranged at a cellular level? How is this arrangement different in horses?
An non-equid ovary consists of a cortex and a medulla that is entirely surrounded by a germinal epithelium and connective tissue (the tunica albuginea). In horses, however, the germinal epithelium has regressed so that it only forms a small part of the ovary's surface, forming an ovulation fossa. Additionally, the cortex and medulla have traded places.
93
(L26) What is the difference between folliculogenesis and oogenesis?
Folliculogenesis is the maturation of a follicle into the corpus luteum that allows the oocyte within in to develop and eventually ovulate. Oogenesis involves primordial germ cells, while folliculogenesis involves the primary follicle.
94
(L26) Outline the steps of folliculogenesis
1. Primary follicles, through the expansion of cell layers, eventually become secondary and Graafian follicles.
2. The granulosa cell layers of a primary and secondary follicle reach a point in which they start secreting fluid into the antrum.
3. At this stage, the granulosa cells become cumulus cells.
4. The cumulus cells in the layer directly adjacent to the oocyte form the corona radiata, which sends projections into the oocyte in order to coordinate additional follicular and oocyte development, and ultimately ovulation.
95
(L26) What is a corpus hemorrhagicum?
The corpus hemorrhagicum is formed immediately after ovulation, when blood from ruptured vessels fills the follicular antrum.
96
(L26) What is the relevance of luteal crowns or papillae in cattle versus horses?
In cows, since ovulation occurs at the germinal surface, 50% of corpus lutea form a characteristic bulge, or crown, on the ovarian surface. This can be palpated rectally as an indicator for active CLs.
In horses, CLs form within the ovary and crowns can't be palpated. Thus, assessing whether a mare has ovulated requires a different technique e.g. progesterone assay.
97
(L26) What is a corpus albicans?
The corpus albicans is what a corpus luteum becomes when it has completely regressed.
98
(L27) Describe proestrus and estrus in the canine female
Protestrus and estrus are easily identifiable in the dog because these periods can last days. The primary hormones are estradiol and progesterone (from the pre-luteal follicle). Under the effects of estradiol, during proestrus, there is increased blood flow to the reproductive tract, increased blood-tinged vaginal secretions, vaginal cornification, the female is attractive to males, relaxation of the cervix, and activation of the uterine neutrophils. In estrus, the female is finally receptive to males and a surge of estradiol induces ovulation.
99
(L27) Describe metestrus and diestrus in the canine female.
Metestrus is the period of initial development of the corpus luteum, while diestrus is the mature phase of the CL. The primary hormone is progesterone. Progesterone suppresses reproductive behavior and ovulation, makes the female less attractive to males, closes the cervix, and decreases vaginal secretions.
100
(L27) How does vaginal cytology change as a canine female cycles?
Coming out of anestrus, the vagina is predominantly populated by parabasal epithelial cells. Increasing concentrations of estradiol with the onset of proestrus and estrus induce vaginal cornification and keratinization. Thus, parabasal cells are replaced by cornified epithelial cells and anuclear squamous cells. Metestrus is characterized by the appearance of metestrual cells, epithelial cells that have engulfed neutrophils.
101
(L27) Explain how estradiol can provide both negative feedback and positive feedback on the HPA.
At low concentrations, such as during the onset of proestrus, estradiol exerts little negative feedback on the hypothalamus, inhibiting FSH and LH secretion from the anterior pituitary. However, as the follicles develop, the amount of estradiol reaches a point that exerts positive feedback on the surge center of the brain, causing a surge release of GnRH and LH. This surge induces ovulation. Furthermore, estradiol sensitizes the anterior pituitary to GnRH by upregulating expression of GnRH receptors, increasing the amount of LH released.
102
(L27) Cats and ferrets are inducible ovulators. What does that mean about their cyclicity and hormone release?
Inducible ovulators exhibit continual estrous cycles with rising levels of estradiol. However, an LH surge, and thereby ovulation, is only induced when there is physical stimulation of the vagina or cervix.
103
(L28) The ovary has two hormonally active cell types. What are they and what do they secrete?
Theca cells of the theca interna layer synthesize and secrete testosterone under the influence of estradiol (they are the equivalent of Leydig cells in testes). The granulosa cells are FSH responsive and convert the testosterone synthesized by theca cells into estrogens. They also secrete inhibins.
104
(L28) Ovulation is the release of the oocyte from the follicle. How is this mediated?
Ovulation is mediated by the theca cells of the follicle. When stimulated by LH, theca cells release proteases and collagenases that dissolve the walls of the follicle, releasing the oocyte.
105
(L28) Luteinization is the foundation for the formation of the corpus luteum. How is this mediated on a cellular and physiologic level?
Luteinization is a phenotypic change in which follicular granulosa cells downregulate the expression of FSH receptors and upregulate the expression of LH receptors. By becoming LH responsive, graulosa cells shift from synthesizing estrogens to progesterone.
106
(L28) Pre-ovulation progesterone secretion is unique to which domestic species? Why does this matter?
The dog
Since ovulation occurs 2-3 days after the LH surge, monitoring changes to progesterone is a good marker for predicting the onset of ovulation.
107
(L28, 29) Female dogs and cows both ovulate in response to a LH surge. What is different about the oocytes that they ovulate? Why is the difference important from a management standpoint?
Dogs ovulate a primary oocyte, or an oocyte that hasn't released its first polar body yet, while cows ovulate a secondary oocyte. Primary oocytes are not fertilizable. This is reflected in canine sperm maintaining a relatively longer degree of viability in the female reproductive tract than cattle. Timing ovulation with insemination is far more important in cattle for this reason.
108
(L28) How is diestrus different between pregnant and non-pregnant dogs?
There is no perceivable difference in progesterone secretion between pregnant and non-pregnant dogs. Generally, the only distinction is the early withdrawal of progesterone prior to whelping in pregnant females.
109
(L28) How is prolactin important to the luteal phase in pregnant dogs? How does prolactin impact parturition? What other effects does it have?
After 35 days, the corpus luteum becomes dependent on prolactin in order to maintain progesterone secretion. Inhibition of prolactin through a dopamine agonist will cause regression of the CL. Prolactin also induces whelping, where an increase accompanied by progesterone withdrawal induces parturition. Prolactin also stimulates the initiation and maintenance of lactation and parental behavior.
110
(L28) Pregnancy is associated with an increase in maternal cardiac output, heart rate, and stroke volume. How does the dam prevent hypertension?
Peripheral vascular resistance is decreased.
111
(L28) How is diabetes associated with pregnancy in dogs?
Progesterone causes the release of growth hormone from canine mammary tissue. GH has direct effects and indirect effects through IGF-1, which contributes to insulin resistance by blocking insulin signaling.
112
(L28) Define pseudopregnancy. How do hormones play a role?
Overt pseudopregnancy is when a dog exhibits behaviors associated with birth and lactation. Hormonally, pseudopregnancy is likely cased by a premature progesterone withdrawal and increased prolactin (a hormonal pattern seen in pregnant females).
113
(L28) What is ovarian remnant syndrome and why is it an issue?
ORS is when a small piece of ovary tissue is left after an ovariohysterectomy. Due to the removal of ovarian tissue and the alleviation of negative feedback, the H-P axis experiences increased gonadotropin secretion. However, increased LH and FSH can induce hyperplasia of remnant ovarian tissue, risking the re-establishment of cyclicity.
114
(L28) Which hormone is used to diagnose ovarian remnant syndrome?
AMH is used to diagnose ORS. AMH can also be a measure for how many follicles are active in an ovary.
115
(L28, 29) What is the difference between the luteal phases of a non-pregnant cow and a non-pregnant dog?
Cows are capable of luteolysis, which terminates their luteal phase early and allows them to re-enter estrus. Non-pregnant dogs don't undergo luteolysis, so their progesterone levels are similar to that of a pregnant dog.
116
(L29) Describe the concept of follicular waves in cattle.
Pre-antral follicular development occurs independent of gonadotropins. So, there will be 1-2 groups or waves of developing follicles that reach antral size during the luteal phase. However, without the LH surge to induce ovulation, these follicles undergo atresia. However, if a dominant follicle is timed with the end of the luteal phase, the next LH surge will induce ovulation.
117
(L29) What is the clinical significance of follicular waves in cattle?
The administration of FSH before oocytes undergo atresia can rescue the oocytes of a given wave or cohort. With super-ovulation, the eggs of a valuable female can be transplanted into other females.
118
(L29) Which hormone is responsible for luteolysis in cattle?
PGF2-a released by the endometrium 12-17 days after ovulation.
119
(L29) In cattle, how does PGF2-a reach the ovaries?
PGF2-a reaches the ovary through the close association between the uterine vein and the ovarian artery. The two vessels coil around one another and where they are close, the vessel walls are thin. This allows PGF2-a to diffuse down a concentration gradient into the ovary. This local containment of PGF2-a is important because, in cattle, most of systemic PGF-2a gets metabolized in the lungs.
120
(L29) Describe the loop between oxytocin and PGF2-a in inducing luteolysis.
PGF2-a is released by the endometrium and travels the ovary to induce luteolysis. However PGF2-a also increases the release of oxytocin by the CL. Oxytocin binds to receptors in the endometrium to upregulate PGF2-a.
121
(L29) PGF2-a can be an important tool in the management of breeding cattle. However, timing its use is important. Why?
The CL is not always sensitive to PGF2-a. Only administration of PGF2-a 5-6 days after ovulation will cause luteolysis.
122
(L29) Cows exhibit luteolysis. How is a pregnancy maintained?
Maternal recognition of pregnancy is the physiological prevention of luteolysis. The embryo, around day 15, releases interferon tau which locally inhibits the release of PGF2-a by blocking endometrial oxytocin receptors.
123
(L30) Describe the interaction between the bovine placenta and the corpus lutuem in terms of progesterone secretion.
The bovine placenta starts making progesterone after 150 days, which supports the pregnancy instead of the CL. This lasts until day 240, when the CL becomes dominant again. Removal of the CL before day 240 will cause early parturition.
124
(L30) Describe how the pre-partum burst of hormones faciliates parturition.
The fetal pituitary releases ACTH, increasing the secretion of fetal cortisol from the adrenal cortices. Cortisol stimulates PGF2-a, which induces luteolysis and progresterone withdrawal. Additionally, the fall in progesterone is accompanied by a rise in placental estradiol and pituitary oxytocin, causing coordinated myometrial contraction (via gap junctions).
125
(L30) What are the four effects of fetal cortisol related to birth?
Fetal cortisol stimulates progesterone withdrawal and luteolysis by upregulating endometrial PGF2-a and estradiol. It increases the secretion of surfactant in the fetal lungs and prepares the fetal gut for colostrum and maternal immune transfer. Finally, it promotes glycogen deposition in the liver, which serves as an energy source for the neonate.
126
(L30) How is placental estradiol involved in bovine parturition?
The release of cortisol from the fetus signals the onset of parturition because its associated with a rise in PGF2-a and estradiol. Estradiol increases myometrial contractions through myometrial gap junctions and upregulates endometrial secretion of PGF2-a. PGF2-a ultimately induces luteolysis and progesterone wtihdrawal. Estradiol also relaxes pelvic ligaments and increases myometrial oxytocin receptors.
127
(L30) What is the Ferguson reflex?
The Ferguson reflex involves the release of pituitary oxytocin in response to the fetus causing cervical dilation. The oxytocin stimulates myometrial contractions.
128
(L30) What are the two methods that membranogenesis can occur?
Firstly, the trophectoderm folds over the fetus and fuses to form the amnionic and chorionic membranes. Secondly, the amnion can form by cavitation.
129
(L31) Describe the formation of the chorio-allantois.
The allantoic sac forms from the fetus' hindgut. By day 15-21, the allantois eventually fuses with the overlying chorion, forming the chorio-allantois. The allantoic vessels then allows for gas exchange and waste removal for the chorio-allantois.
130
(L31) Besides the chorio-allantois, there is another type of early placenta. What is it and which species is it important in?
The chorio-vitelline placenta is the first placenta in all species, supplied by the yolk sac's vasculature. In livestock, its replaced by the more efficient chorio-allantois within two weeks. In mares, however, the chorio-vitelline placenta lasts up to two months.
131
(L31) Describe the epithelial-chorial placentation. What species is it important in?
Horses and cows have epithelial-chorial placentation. With this type of placentation, the maternal endometrium is intact and, thus, there are 6 cell layer separating maternal blood from fetal blood. These cell layers prevent the transmission of maternal antibodies to the fetus, necessitating colostrum for passive transfer.
132
(L31) Describe endothelial-chorial placentation. What species is it important in?
All carnivores posses endothelial-chorial placentation. In this type of placentation, the epithelium and connective tissue layers of the maternal endometrium are eroded and the chorio-allantois is adjacent to the maternal endothelium. Thus, there are 4 cell layers, allowing for the transfer of some maternal antibodies.
133
(L31) Describe hemochorial placentation. What species is it important in?
Humans and rodents have hemochorial placentation. With this type of placentation, there is erosion all the way through maternal blood vessels. The chorio-allantois then directly associated with maternal blood, allowing for extensive transplacental antibody transfer.
134
(L31) What are the 4 chorio-allantois morphologies?
Cotyledonary
Diffuse
Zonary
Discoid
135
(L31) Describe the main aspects of cotyledonary placentation. Which species is it important in?
Ruminants possess cotyledonary placentation. The areas of interdigitation between the fetal membranes and the endometrium are localized to placentomes, structures which the fetal cotyledon fuses with the maternal caruncle.
136
(L31) Describe the main aspects of diffuse placentation. Which species is it important in?
Horses and pigs have diffuse placentation. The placenta interdigitates with the maternal endometrium at many places that resemble cotyledons in ruminants, referred to as microcotyledons.
137
(L31) There are two cell types associated with the chorion. What are they?
The chorion has uninucleate trophoblast cells and multinucleate, invasive cells. These cells either destroy the endometrium (as in humans) or just migrate into it (as in horses and ruminants)
138
(L31) Describe the main aspects of zonary placentation. Which species is it important in?
Dogs and cats have zonary placentation, which forms a band of interdigitation around the fetus. At the edges of the zone of interdigitation, the extravasation of fetal blood creates biliverdin.
139
(L31) What are amniotic plaques?
Amniotic plaques are normal raised epithelial concretions on the amnion of ruminants.
140
(L31) What is adventitious placentation?
In ruminants, there are places of interdigitation between the fetal membrane and the endometrium outside of the placentomes, referred to as adventitious placentation.
141
(L31) What are hippomanes?
In the allantoic cavity of cattle and horses, detached cells form aggregations called hippomanes.
142
(L31) What is the equine cervical star?
Despite the diffuse placentation of the equine chorio-allantois, it does not interdigitate with where it meets the internal os of the cervix because there is no endometrium there.
143
(L31) What are endometrial cups in horses?
In horses, multinucleate trophoblast cells migrate and implant into the maternal endometrium to release eCG. However, since these are foreign cells, they are eventually rejected. The sloughed cells are absorbed by the fetal membranes, forming allantoic pouches.
144
(L31) What are necrotic tips in pigs?
The tips of the porcine placenta are necrosed. They're thought to prevent the fusion of adjacent fetuses in the womb.
145
(L31) What is the urachus?
The urachus is the connection between the allantoic cavity and the fetal bladder traveling within the umbilicus.
