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Reproduction (Physiology 2) > Spermatogenesis > Flashcards

Spermatogenesis Flashcards

1
Q

Where is sperm produced?

A

The testes produce and store sperm

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2
Q

Where in the testes is sperm stored?

A

Sperm stored in epididymis

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3
Q

How is sperm transported to the seminal vesicle?

A

During ejaculation, due to smooth muscle contraction of epididymis and vas deferens propels sperm up vas deferens where they connect to seminal vesicle

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4
Q

What is the role of the seminal vesicle?

A

Seminal vesicles produce semen containing enzymes for the sperm

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5
Q

Where in the genitourinary tract is the prostate located?

A

Prostate meets urethra below bladder

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6
Q

Where is the urethra located?

A

Urethra moves out the penis through the urethral opening

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7
Q

What are the 2 types of tissues that form the penis?

A

Corpus spongiosum

Corpus cavernosum

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8
Q

What do the testes produce?

A

Produce sperm and store it.

Produce hormones which regulate spermatogenesis

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9
Q

Where are the testes located?

A

Lie in scrotum: outside body cavity…. optimum temperature for sperm production 1.5-2.5oC below body

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10
Q

What is the significance of maintaining a cool temperature for the testes?

A

Overheating of testes reduces sperm count

Well-vascularised, well-innervated

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11
Q

What is the normal testicular volume?

A

Normal volume of testes approximately 15-25ml

measured by orchidometer

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12
Q

Describe the testicular structure

A

Tubules lead to an area on one side called rete.
Rete leads to epididymis and vas deferens.
Testis is 90% seminiferous tubules
600m long in each testis! Tubules are tightly coiled

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13
Q

What is the significance of the seminiferous tubules?

A

Site of spermatogenesis

Seminiferous tubules feed into epididymis and into vas deferens

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14
Q

Where among the testicular structures is sperm located during different stages of maturation?

A

Sperm move towards lumen as they develop and mature moving into epididymis when fully developed

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15
Q

Explain how the structure aids Sertoli cell function

A

Sertoli cells have tight junctions between them. The tight junctions form compartments for sertoli cells to secrete growth factors, signalling molecules, and hormones to control the environment in which sperm develops

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16
Q

What is spermatogonia?

A

Diploid cell produced during the early stages of sperm production

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17
Q

Where are spermatogonia found?

A

Germ cell on basement membrane capable of mitotic/meiotic division to produce spermatocytes or spermatogonia (by mitosis) - diploid

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18
Q

Which cells are the walls of the tubules composed of?

A

Walls of tubule made up of tall columnar endothelial cells Sertoli cells
Tight junctions between these form Adluminal compartment

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19
Q

What is the role of the tight junctions between sertoli cells?

A

Allows specific enclosed environment for spermatogenesis which is filled with secretions from Sertoli cells

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20
Q

What fills the spaces between tubules?

A

Spaces between the tubules are filled with blood and lymphatic vessels, Leydig cells and interstitial fluid

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21
Q

What surrounds the seminiferous tubules?

A

Seminiferous tubule surrounded by blood vessels, connective tissue and leydig cells. Leydig cells are male analogues of theca cells

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22
Q

What is produced by Leydig cells?

A

Leydig cells produce testosterone

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23
Q

Describe the inner structure of semniferous tubules

A

Inside seminiferous tubules contains basement membrane, sertoli cells, primary & secondary spermatocytes. Elongated spermatids are also present.

Developed mature sperm are in the lumen of the tubule

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24
Q

What occurs during S phase of meiosis?

A

During S phase chromosome is replicated

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25
Q

How are sister chromatids formed?

A

The replicated chromosomes stay attached to the originals forming identical sister chromatids

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26
Q

How are new chromosomes formed from homologous pairs?

A

Homologous chromosomes grow together in pairs and exchange genetic material
This gives rise to new chromosomes containing a mixture of maternal and paternal genes

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27
Q

How do sister chromatids end up differing in genes?

A

At this stage sister chromatids remain attached and differ from one another due to crossing over

28
Q

Describe the events occurring in Meiosis I

A

Cell division occurs creating two haploid daughter cells, but each chromosome is two sister chromatids and these are no longer identical due to crossing over

29
Q

What happens during Meiosis II?

A

Sister chromatids separate as cell divides giving haploid gametes

30
Q

What is the role of primary spermatocytes?

A

Move into adluminal compartment and duplicate their DNA to produce sister chromatids which exchange genetic material before entering meiosis I - 46XY diploid

31
Q

What are secondary spermatocytes?

A

Have undergone meiosis I to give 23X + 23Y haploid no. of chromosomes arranged as sister chromatids

32
Q

What are spermatids?

A

Meiosis II occurs to give 4 haploid spermatids, round spermatid → elongated spermatid differentiation

33
Q

What is spermatazoa?

A

Mature sperm extruded into the lumen

34
Q

How often does spermatogenesis occur?

A

New cycle every 16 days, the entire process takes approximately 74 days

35
Q

What are the stages of spermatogenesis?

A
  1. Mitotic proliferation of spermatogonia.
  2. Meiosis and development of spermatocytes.
  3. Spermiogenesis, elongation, loss of cytoplasm,
    movement of cellular contents
36
Q

Why is each cell division in spermatogenesis incomplete?

A

Each cell division from a spermatogonium to a spermatid is incomplete - the cells remain connected to one another by cytoplasmic bridges forming a syncytium allowing synchronous development

37
Q

What is the role of the syncytia?

A

Syncytia at various stages of development throughout seminiferous tubule giving continuous supply for synchronous development

38
Q

Compare Oogonia and Spermatogonia

A

Oogonia

  • Oogonia all laid down in foetus.
  • Begin meiosis to make oocyte
  • Cannot make more oocytes by mitosis
  • Limited supply

Spermatogonia

  • Spermatogonia laid down in foetus
  • Begin meiosis to make spermatocyte…OR
  • Divide mitotically to make more spermatogonia.
  • Lifetime supply
39
Q

How does the male and female HPG axis differ?

A

Female HPG axis is cyclical
Male HPG axis isn’t
Testis produce testosterone which feeds back to the hypothalamus and pituitary
LH and FSH also produced

40
Q

What do Leydig cells produce?

A

Leydig cells contain LH receptors and primarily convert cholesterol into androgens

41
Q

Describe the intratesticular testosterone levels

A

Intra-testicular testosterone levels are 100x those in plasma

42
Q

What role do androgens play in spermatogenesis?

A

Androgens cross over to and stimulate Sertoli cell function and thereby control spermatogenesis

43
Q

What is the role of Sertoli cells?

A

Sertoli cells contain FSH receptors and converts androgens to oestrogen

44
Q

What are the roles of LH and FSH in the male reproductive organs?

A

FSH establishes a quantitatively normal Sertoli cell population, whereas androgen initiates and maintains sperm production

45
Q

What drugs interfere with the negative feedback on the HPG axis?

A

Anabolic steroids → reduces FSH/LH from pituitary leading to testicular atrophy

46
Q

What causes an erection?

A

Vasodilation of the corpus cavernosum
Partial constriction of the venous return.

Autonomic nervous system causes coordinated smooth muscle contractions of vas deferens, glands and urethra.

47
Q

What part of the CNS is involved in an erection?

A

Parasympathetic control

48
Q

What controls the movement of sperm through the penis?

A

Sympathetic nervous system controls the movement of sperm into epididymis, vas deferens, penile urethra (emission)

49
Q

What part of the nervous system regulates ejaculation?

A

Somatic nervous system (perineal branch of the pudendal nerve from nerve roots S2–S4) causes expulsion of the glandular secretions
& evacuation of urethra

50
Q

Describe the blood flow during an erection

A

Arterial blood flow into penis dilates

Venous return is constricted giving an erection

51
Q

How much sperm is produced ~1 day?

A

300 million sperm produced per day on average

52
Q

How much sperm is expelled during ejaculation?

A

approximately 120 million in

average ejaculate

53
Q

What is the normal ejaculate volume?

A

Normal ejaculate volume is 1.5ml - 6ml

around one third to just over a teaspoon full

54
Q

Describe the sperm distribution in ejaculation

A

Initial portion of the ejaculate is most sperm rich.
99.9% lost before reaching ampulla of the uterine tube.
around 120,000 sperm get near to egg, only one enters

55
Q

Where is the seminal fluid produced?

A

Seminal fluid consists of secretions from:

seminal vesicles, prostate, bulbo-urethral gland combined with epididymal fluid

56
Q

What does the Bubo-urethral gland produce?

A

Produces a clear viscous secretion high in salt, known as pre-ejaculate

57
Q

What is the purpose of the fluid secreted by the bulbo-urethral gland?

A

This fluid helps to lubricate the urethra for spermatozoa to pass through, neutralizing traces of acidic urine.

58
Q

How much of the ejaculate is from the seminal vesicles?

A

Secretions (semen) comprise 50-70% of the ejaculate

59
Q

What does semen consist of?

A

Contains proteins, enzymes, fructose, mucus, vitamin C and prostaglandins
High fructose concentrations provide energy source.
High pH protects against acidic environment in vagina

60
Q

How much of the ejaculate is produced at the prostate?

A

Secretes milky or white fluid roughly 30% of the seminal fluid

61
Q

What does the prostate seminal fluid contain?

A

Protein content is less than 1% and includes proteolytic enzymes, prostatic acid phosphatase and prostate-specific antigen which are involved in liquefaction

High zinc concentration 500–1,000 times that in the blood is antibacterial

62
Q

Outline typical results of a semen analysis

A 
Volume			                1.5 – 6.0 ml
Sperm concentration		>15million/ml
Liquefaction			        <30 minutes
Motility				        >40%
Progressive motility		>32%
Vitality (live)			        >58%
Morphology (normal forms)	>4%
pH				                >7.2
Leucocytes			        <1 million/ml
63
Q

Describe the composition of a spermatozoon

A

Virtually no cytoplasm, carries DNA only, no ribosomes, mitochondria or cytoplasm derived paternally
Smallest cell in the body

64
Q

What is the role of the acrosome?

A

Acrosome provides acrosome reaction due to the large no. of enzymes in the sperm head

65
Q

What is the significance of the spermatozoon tail?

A

Base of the tail contains mitochondrial sheath with lots of mitochondria for energy (ATP)

Reproduction (Physiology 2) (12 decks)

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