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Cell Biology + Physiology > Male Testicular Function > Flashcards

Male Testicular Function Flashcards

1
Q

Spermatozoa / Sperm

A
  • Contains genetic material in nucleus
  • Contains mitochondria (energy)
  • Contains flagellum (movement to deliver genetics)
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2
Q

Processes that don’t occur in spermatozoa

A
  • No transcription - no new proteins synthesised
  • No endoplasmic reticulum
  • No cytoplasm so cytoplasmic reactions
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3
Q

Post-translational modifications in Sperm

A
  • Glycosylation
  • Phosphorylation
  • Disulfide cross-linking, Ubiquitination, Acetylation + Methylation

Changes to proteins on cell membrane surface

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4
Q

Sperm’s journey after ejaculation

A

(1) Cervix –> (2) Uterus –> (3) Isthmus –> (4) Oviduct (fertilisation) –> (5) Oocyte (egg cell)

Swims ~18cm in 30-60 minutes

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5
Q

What is Spermatogenesis?

A

Biological process of producing mature sperm and occurs in the male gonad

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6
Q

How does spermatogenesis work?

A
  1. Begins as a basic eukaryote with typical organelles (with acrosomal vesicle on the nucleus )
  2. Centrioles move to either end of cell
  3. From the centrioles, microtubules form the centriole
  4. Excess cytoplasm is pinched off and lost from around the nucleus + the acrosome grows

A specialised sperm cell

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7
Q

A Sperm Cell’s Journey

A

From the epididymis to through the vans deferens and arrives at the ampulla

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8
Q

Glands in the male reproductive organs

A

Seminal vesicle
Prostate
Bulbourethral gland

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9
Q

Purpose of the scrotum

A

Provides cooler environment compared to the body (35-36 degrees)
- aids sperm’s development due to sensitivity to high temperatures

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10
Q

Where spermatogenesis occurs + sperm maturation

A

Coiled seminiferous tubule (SFT) in the testis
- Primary spermatocyte (diploid) goes through meiosis to form secondary haploid spermatocytes
- Spermatids then mature to become spermatozoa (spermiogenesis)
- Sertoli cell supports process by providing necessary nutrients

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11
Q

When is spermatogenesis initiated?

A

At puberty - caused by initiation of pulsatile release of gonadotropin releasing hormone (GnRH)

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12
Q

How long does spermatogenesis take?

A

74 days

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13
Q

How much sperm does a human produce?

A

1000 per heartbeat = 100-200 million/day

95% is abnormally formed so only a small proportion are capable of fertilising an egg

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14
Q

In between seminiferous tubules - Interstitial cells

A

Leydig cells - androgen (mainly testosterone) producing cell

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15
Q

Sertoli Cells - Tight junctions

A
  • Tight junction with adjacent Sertoli cells maintain spermatogonial stem cell niche
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16
Q

Sertoli Cells - Blood testis barrier

A
  • Separate developing germ cells from the immune system
  • Provides a controlled chemical microenvironment for spermatogenesis
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17
Q

Sertoli cells - Adherens junction

A

Form intimate associations with germ cells (40-50)

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18
Q

What are Sertoli cells + what do they do?

A

Form a syncytium-like epithelial monolayer that germ cells are embedded
- Phagocytose cytoplasm of spermatozoa - spermiation
- Secrete fluid into lumen of SFT that lush spermatozoa into rete testis + epididymis post-differentiation
- Secrete Inhibin + Androgen Binding Proteins to regulate spermatogenesis

19
Q

What are spermatogonia?

A

Reservoir of self-renewing stem cells (maintain germ cell line) and remain in the basement of the seminiferous tubule as
undifferentiated spermatogonia
- Some type ‘As’ S will form type ‘A’ S + start the process of spermatogenesis

20
Q

Miotic Proliferation of Spermatogonia

A

Each type ‘A’ S goes through mitosis to form type ‘B’ S
- Will divide again to form primary spermatocytes that will go through meiosis
- Then move towards lumen + through blood-testis barrier
- Enters resting phase where chromosomes duplicate ready for meiosis

21
Q

Meiotic Divisions of Sperm

A

I: Primary spermatocyte divide to form secondary spermatocyte (diff arrangement of genetic material)

II: Secondary spermatocytes divide to form haploid spermatid (diff sections of genetic material resulting in variation)

1 primary S => 4 round spermatids

22
Q

Sperm developmemt

A

Spermatogonia (base) -> spermatocytes -> spermatids -> spermatozoa (lumen)

  • Spermatocytes + spermatids move into adluminal compartment disrupting junctions between Sertoli cells
23
Q

Spermiogenesis / Cytodifferentiation

A

Round spermatids elongate to form spermatozoa
Requires the formation of specialised sperm structures - acrosome, centriole, flagellum, mitochondria, nucleus

24
Q

What is the acrosome?

A
  • Formed from the golgi apparatus which migrates to one end of nucleus
  • Contains hydrolytic enzymes which are released when sperm binds to the zona pellucida of the egg to aid penetration and thus fertillisation
  • Found on the head of the cell + envelopes the nucleus
25
Q

What is the Flagellum?

A

Formed from the centrioles when they migrate to opposite end of nucleus to acrosome + form axoneme
- For sperm movement through the female tract + penetration of the egg vestments

26
Q

Mitochondria in sperm

A
  • Helically arranged around first part of flagellum - midpiece
  • Energy is needed for motility
27
Q

Nucleus in Sperm

A

Sex determination of offspring (X or Y)
- Sperm DNA is highly condensed (histones replaced with protamines) to protect genome during transport
- DNA is transcriptionally and translationally inactive

27
Q

Nuclear chromatin re-organisation in spermiogenesis

A
  • Somatic histones are replaced by testis-specific histone variants
  • Transition proteins incorporated in spermatid nuclei
  • Protamines replace transition proteins in the late spermatids to pack genome into highly condensed sperm nucleus - no transcription factors can reach it
28
Q

Cytoplasm in sperm

A
  • Sperm had little cytoplasm (egg has a huge C which ends up in fetus)
  • Excess C from spermiogenesis form residual body / cytoplasmic droplet which is phagocytosed by Sertoli cell
29
Q

Developing sperm cells form a syncytium

A

During mitosis + meiosis, cytokinesis is incomplete
Syncytia persists until final stage of spermatogenesis

  • Allows sharing of cytoplasmic components e.g. a Y sperm can supply essential proteins encoded by genes on X (axoneme + acrosome)
30
Q

What is Spermiation?

A

Last step of spermatogenesis
- Facilitated by Sertoli cell cytoskeleton
- Cytoplasmic bridges rupture (syncytium)
- Spermatid cytoplasm is absorbed by Sertoli cell
- Sperm is released into lumen of seminiferous tubule in testis

31
Q

Endocrine Control of Testicular Function - Hypothalamus-pituitary gonadal axis

A

Controlled by products released by testis somatic cells
- Within tubules - Sertoli cells
- Between tubules - Leydig cells

32
Q

Extra-Testicular Regulation (Puberty) - Hypothalamus

A

Releases Gnhr (gonadotropin-releasing hormone) which act on the anterior pituitary

32
Q

Extra-Testicular Regulation (Puberty) - Anterior Pituitary (Gonadotrophins) - LH (Luteinizing hormone)

A
  • Binds to LH receptors on Leydig cells as well as Sertoli cells
  • Induces Leydig cells to produce androgen (testosterone)
32
Q

Extra-Testicular Regulation (Puberty) - Anterior Pituitary (Gonadotrophins) - FSH (follicle-stimulating hormone)

A
  • Acts on testis (Sertoli cells) to maintain spermatogenesis
  • Binds to FSH receptor on Sertoli cells
  • Induce expression of androgen receptors on Sertoli cells to increase responsiveness to androgens
  • Stimulates production of Androgen Binding Protein + Inhibin by Sertoli cells
32
Q

Testicular Hormones’ Role - Androgen

A
  • Development of testis of embryo
  • Sexual function and characteristic (puberty)
  • Reproductive function (adult)
  • Produced by Leydig cells (between tubules)
  • Negative feedback on hypothalamus + anterior pituitary by repressing LH + FSH production
33
Q

Testicular Hormones’ Role - Androgen (mainly testosterone)

A
  • Carried by ABP (androgen binding protein) in testicular fluid
  • Converted to dihydrotestosterone (by 5alpha-reductase in Sertoli cells)
  • Binds + affect Sertoli cells’ function
34
Q

Testicular Hormones’ Role - Inhibin

A

Protein heterodimer hormone
- Produce by Sertoli cells
- Acts on pituitary gland
- Inhibit FSH production

35
Q

Role of Testicular Product - Androgen Binding Protein (ABP)

A
  • Product of Sertoli cells under testosterone stimulation
  • Binds and carries testosterone in testicular fluid of seminiferous tubules
  • Maintain high levels of testosterone 100x more conc. than blood ( T is lipid soluble so diffuse across membrane - binding prevents diffusion)
36
Q

Movement of sperm into seminiferous tubules and rete testis

A
  • Spermatozoa released from testis are immotile until they tranvers epididymis
  • No cilia but fluid secretions from Sertoli cells + smooth muscle like cells in testicular tunic lamina propria of SFTs
  • Periodic powerful contraction - peristalsis
37
Q

Epididymal (male tract) Maturation - Anatomy

A

Regions:
- Caput - close testis - motility
- Corpus - fertilising ability
- Vas deferens - storage

Each segment
- Display different expression of genes]
- Maintains luminal ions concentrations
- Essential to regulate steps of sperm maturation

38
Q

Epididymal Maturation
(sperm maturation during epididymal transit)

A

Sperm interact with epididymal epithelial cells – removal of the cytoplasmic droplet
- Retention of cytoplasmic droplets is associated with reduced fertility

Change sperm proteome – protein, lipid and sugar content
- Incorporated into the sperm cells

Change in sperm surface
- Removal and/or modification of external proteins, sugars and lipid sperm membrane

Intracellular signaling pathways activation during transit
- Addition or removal of protein phosphate groups - phosphorylation

39
Q

Ejaculation

A

Sperm (2-5%) + Seminal plasm = semen
- Seminal plasma is secreted by accessory sex glands (seminal vesicles, prostate)

Cell Biology + Physiology (11 decks)

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