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VM744: THERIOGENOLOGY > Graham Lectures > Flashcards

Graham Lectures Flashcards

1
Q

Compare steroid vs protein hormones

A

Steroid: tiny, nuclear receptor –> mRNA –> protein (slow)
Protein: huge, need membrane receptors (fast)

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2
Q

What 2 enzymes are responsible for converting testosterone? What are the products of the conversion?

A

T converted to estradiol via aromatase
T converted to dihydrotestosterone (DHT) via 5A-reductase

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3
Q

What hormone is responsible for converting the sexually dimorphic nucleus of the hypothalamus into a male brain?

A

Estradiol
(Testosterone can be converted to estradiol)

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4
Q

What is the role of alpha-fetoprotein in masculinization?

A

Placenta produces lots of estradiol (fetus receives some)
Liver makes alpha-fetoprotein that binds estradiol and carries it to the liver to get degraded
Neither M nor F fetuses get that estradiol
Because M produce testosterone via testes, testosterone goes to the brain and is converted to estradiol to become male

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5
Q

Label the following diagram of the cross section of a testis

A
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6
Q

What are the 3 parts of the male brain and what receptors are associated with each?

A

Libido: estrogen receptors
Male behaviors: testosterone receptors
Pulse generator: estrogen, testosterone, progesterone receptors - stimulates GnRH release

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7
Q

What occurs once kisspeptin is released?

A

GnRH is released, binding to receptor on gonadotroph in pituitary
FSH and LH are stimulated
(1) FSH binds to gonadotrophic cell in seminiferous tubule, causing division
(2) FSH binds to sertoli cell and produces androgen binding protein
LH binds to leydig cell causing testosterone production
Testoster
(1) Testosterone binds to androgen binding protein to increase testosterone dramatically
(2) Testosterone feeds back to libido and aggression centers
(3) Testosterone goes to other tissues (secondary sex characteristics)

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8
Q

Diagram the roles of hormones from the sexually dimorphic nucleus

A
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9
Q

How do anabolic steroids alter the hormone function of the sexually dimorphic nucleus?

A

Anabolic T cannot be converted to estradiol
(1) pulse generator stops making KISS
(2) GnRH levels drop
(3) FSH/LH levels drop
(4) Normal testosterone levels drop
(5) Spermatogenesis stops

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10
Q

How does testosterone feed back on the different parts of the sexually dimorphic nucleus?

A

(-) FB on kisspeptin = decreased GnRH
(+) FB on aggression
(+) FB on libido (by conversion to estradiol by aromatase)

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11
Q

How many days is spermatogenesis?

A

~60 days

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12
Q

How may days does it take sperm to travel through the epididymus?

A

~10 - 14 days

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13
Q

What hormone regulates GnRH levels?

A

Melatonin acts on pulse generator cells to regulate GnRH levels
[Pineal gland produces melatonin]

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14
Q

What regulates seasonal breeding?

A

Melatonin
Day length

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15
Q

Define: Long Day Breeders

A

Cycle/breeding when light is increasing
Horses
Melatonin inhibits KISS = decreased GnRH = no breeding

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16
Q

Define: Short Day Breeders

A

Cycle/breeding when light is decreasing
Cattle, sheep
Melatonin increases KISS = increased GnRH = stimulates breeding

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17
Q

What role does heat play in spermatogenesis?

A

Short term = abnormal cells, occurs during spermatogenesis
Long term = spermatogenesis ceases

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18
Q

What does sperm production look like with cryptorchids?

A

Spermatogenesis cannot occur when testes are within the abdominal cavity
Leydig cells are not affected so testosterone is still produced
Higher risk of testicular neoplasm

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19
Q

What are the 4 ways in which the testes are thermoregulated?

A

(1) Conduction from venous blood to to surface of skin
(2) Sweat glands in skin or scrotum allows for evaporative cooling
(3) Pampiniform plexus = countercurrent heat exchange
(4) Contraction/relaxation of tunica dartos and external cremaster muscles

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20
Q

How does illness/stress/fat impact spermatogenesis?

A

Fever negatively impacts spermatogenesis
Stress increases cortisol = decreases KISS
Fat accumulation in scrotum makes thermoregulation difficult
High ambient temperature makes thermoregulation difficult
Heat doesn’t really effect sperm that is already traveling through the epididymus so ~14 days to see negative effects

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21
Q

What are the main hormones involved in spermatogenesis?

A

FSH = stem cells (primary spermatogonia), sertoli cells (androgen binding protein)
LH = testosterone (with androgen binding protein in sertoli cell)

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22
Q

What do leydig cells produce?

A

Testosterone

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23
Q

Where is sperm produced?

A

Seminiferous tubules –> rete testis

24
Q

What are the steps of spermatocytogenesis?

A

A0 spermatogonia divide into 2 populations (due to FSH)
A0 cells become A1 cells that continue to go mitotic division (cohort, stuck together)
A0 cell population constantly maintained
A1 become primary spermatocytes, undergo meiosis 1
primary becomes secondary spermatocytes, undergo meiosis 2 producing spermatids

25
Q

What are the steps of spermiogenesis?

A

Spermatid –> spermatozoa
Sertoli cells make all necessary enzymes and proteins by means of ABP maintaining testosterone levels

26
Q

At what point of spermatogenesis are cells no longer recognized as self?

A

2n –> n
Meiosis I –> Meiosis II
Proteins on plasma membranes change

27
Q

How long do cohorts share their plasma membranes?

A

Until released into the lumen (all have identical proteins)

28
Q

What makes up the blood testes barrier?

A

2 sertoli cells + tight junction in between

29
Q

How can the blood testes barrier be disrupted?

A

Physical trauma
Tight junction disrupters (bisphenol A, cadmium)

30
Q

What is the pattern in which spermatogenesis occurs?

A

Occurs in waves
When there is a cell undergoing meiosis, there will be no other cells undergoing division
Every time you have a cell undergoing meiosis, you have a sperm cell that has just been released into the lumen

31
Q

How do problems with thermoregulation correlate with different sperm defects?

A

1st step = acrosomes = last problem to show up
2nd step = DNA condenses (vacuoles if problem)
3rd step = midpiece maturation = first problem that shows up (cytoplasmic droplet)

32
Q

Why do all cells in a singular seminiferous tubule look the same?

A

Need different sets of enzymes for cell types to progress and each seminiferous tubule has a different set
All sertoli cells are in the same stage because they are making the same enzymes to move each sperm cell to the next stage
With different stages, we are able to have sperm being released every day

33
Q

What is a sign that the testis is functioning properly in terms of spermatogenesis?

A

Elongated and non-elongated spermatids

34
Q

What is responsible for the different head shapes of sperm?

A

Protamines (supercondense head)

35
Q

What are the steps of sperm structure formation?

A
  1. Acrosome
  2. Nuclear changes
  3. Midpiece/droplet
36
Q

Acrosome

A

Contains enzymes that digest hole in zona pelucida and allow sperm to get to oocyte

37
Q

What nuclear changes occur in sperm formation?

A

Condense head
Remove histones, replace with protamines
Can no longer make proteins (sertoli cells produce enzymes to move from one cell to the next)

38
Q

What is a cytoplasmic droplet indicative of?

A

Issue with sperm production/development

39
Q

Nexin

A

Allows tail to bend cilia (connects microtubules)
No nexin during spermatogenesis (+ no ATP made yet) so sperm cant swim out of seminiferous tubules

40
Q

How are sperm moved out of the testes?

A

Sperm released into the seminiferous tubules are not motile
Moved out of the testis by the flow of fluids produced by the sertoli cells (40-50ml per day in bulls)

41
Q

What part of the male reproductive tract has cilia?

A

Efferent ducts

42
Q

Are sperm in the head of the epididymus fertile?

A

No!
Have no proteins to bind to the zona pelucida

43
Q

What cells are found in the head of the epididymus ? What changes occur in that section?

A

Cells: tall, long microvilli, thin layer of smooth muscle
Absorb 80% of fluid
Gain ability to swim (nexin, increased cAMP)
Insert calcium channels into membrane
Sugar attachment (glycocalyx)
Remove cholesterol
Time: 2-3 days

44
Q

What cells are found in the body of the epididymus? What changes occur in that section?

A

Cells: shorter, shorter microvilli, thin layer of smooth muscle
Absorb fluid (14%)
Translocate cytoplasmic droplet
Add R (zona pellucida)
Change protamines (allows DNA to decondense in oocyte)
Lose cholesterol
Time: 2-3 days

45
Q

What cells are found in the tail of the epididymus? What changes occur in that section?

A

Cells: shortest, short microvilli, lots of smooth muscle
Absorb some fluid
Remove cholesterol
Add fluid proteins (inhibit motility, inhibit capacitation, decrease pH)
Time: 4 - 14 days

46
Q

Where is mature sperm stored?

A

Tail of the epididymus

47
Q

Sperm in the ____ is fertile. Sperm in the ______ is not fertile.

A

Tail = fertile
Head/body = not fertile

48
Q

Increasing collection frequency will do what to sperm quality?

A

Increase

49
Q

What stimulates motility? What does it consist of?

A

Seminal plasma
Proteins: stim motility by increasing cAMP = ATP, inhibit capacitation, coat sperm
Sugars: energy source, osmolality
Salts: osmolality
pH buffers: motility

50
Q

Erection

A

Parasympathetic
Excitation –> T to E in libido center –> NO released on endothelial cells, corpus cavernosum, isquiocavernosum muscle (increased cGMP = increased blood flow) –> contraction of ischiocaverosus mm inhibits blood from leaving

51
Q

Ejaculation (symp or para, what happens)

A

Sympathetic
Stimulation –> urethralis, bulbospongiosis mm –> tail of epididymus –> ductus deferens –> accessory sex glands

52
Q

When is sperm motility required?

A

Transverse mucus of cervix
(Moved through uterus via contractions)
Must swim through utero-tubule junction
Motility needed to contact the oocyte

53
Q

Capacitation

A

Freshly ejaculated mammalian sperm cannot fertilize oocyte, need to undergo changes (capacitation)
Cholesterol loss = membrane stabilization
Increased cAMP = phosphorylation of proteins (pka)
PKc = protein tyrosine phsophorylation, increase lysolipids, membrane fusion, calcium
Intracellular pH increase
Calcium = protein function, membrane fusion
Potassium

54
Q

Acrosome reaction

A

Release of acrosomal enzymes which digest hole through zona pellucida

55
Q

What is the gold standard of semen collection?

A

Artificial vagina

VM744: THERIOGENOLOGY (31 decks)

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