The Role of Sperm Flashcards
Pituitary Hormone Effects:
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Conc vs Motility vs Morphology
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Spermatogenesis definition:
- mitotic divisions of
spermtogenia, the meiotic
divisions of spermatogonia
(diploid 2n DNA) to haploid
spermatids (1n DNA) and the
maturation to spermatozoa
*includes spermatocytogenesis
and spermiogenesis
Spermatocytogenesis
- meiotic stages of
spermatogenesis - spermatogonia (diploid 2n)
develop into primary
spermatocytes (diploid 4n), then
into secondary spermatocytes
(haploid 2n) and then into
spermatids (haploid 1n)
Spermiogenesis:
- maturation of spermatids
(haploid 1n) to mature
spermatozoa - no cell division involved
Spermiation:
- release of spermatozoa from
Sertoli cells
Sperm capacitation:
- physiological changes
spermatozoa must undergo in
order to have the ability to
penetrate and fertilize an egg
What are the two main products of the testis?
- spermatozoa
- hormones
Section of the Testis and Seminiferous Tubule:
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Compartments of the Testis:
- interstitial (inter-tubular)
compartment - seminiferous tubule
compartment
The epithelium of which compartment of the testis is sensitive to elevated temperature?
Seminferous epithelium
Testis: Compartments:
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Testis: Interstitial Compartment:
- highly vascularised
- contains Leydig cells clustered
around vessels - Leydig cells are responsive to LH
Leydig Cells:
- vascularised stroma contains
Leydig cells - function = synthesize
testosterone, may be involved in
testicular immune environment - 4-10mg testosterone daily
secreted
Leydig Cells
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Leydig Cells: Features:
- abundant smooth endoplasmic
reticulum (SER) - high mitochondria conc
- both associated with steroid
synthesis
Sertoli Cells:
- location
- cell type
- function (2)
- feature
- function
- located in germinal epithelium
- somatic cells of testis
- involved in testis formation and
spermatogenesis - progression of germ cells to
spermatozoa via direct contact - large cytoplasm an oval nucleus
with dark nucleolus - Androgen Binding Protein is
synthesised by sertoli cells where
80% secreted into luminal fluid,
20% into interstitial
compartment
Sertoli Cells:
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Sertoli cells are embryological equivalent to?
granulosa cells
Where does spermatogenesis take place?
Seminferous tubules
Anatomy of Seminferous Tubules:
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Spermatogenesis:
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What hormones are most important maintaining reproductive and sexual function?
androgens: testosterone and 5alpha-dihydrotestosterone
What is testosterone is synthesised from?
acetate and cholesterol
Role of androgens:
- expression of the male
phenotype - male sexual differentiation
- development, maintenance of
secondary male characteristics - initiation and maintenance of
spermatogenesis
Testosterone Pathway to epididymis
Testosterone passes from the interstitial compartment to the seminferous tubules (lipid solubles)
Converted to dihydrotestosterone by 5 alpha-reductase in Sertoli cells
Androgen Binding Protein binds testosterone and transports it from the seminferous tubule to the epididymis
Taken up by a receptor-mediated processes into the principal cells of the initial segment and caput epididymis
Pituitary Control of Androgens:
- productions of androgens and
spermatozoa related functionally - at puberty androgens rise and
spermatogenesis commences - LH stimulates Leydig cells to
produce androgens - FSH stimulates sertoli cells and is
required for spermatogenesis
Organisation of Seminiferous Tubules:
- each cell 30-80cm long
- 540m total length
- peripheral myoid cells, then
basement membrane, then
sertoli cells and spermatogenic
cells within the tubules - superficial to deep
- the myoid cells are a muscle
layer that surrounds the sertoli
cells
What prevents macromolecules and metabolites entering the fluid of the testis?
Physiological barrier formed by par and tight junction complexes between sertoli cells
creates a basal compartment and a separate adluminal compartment
this barrier is within the sertoli cell layer
Junctions
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Where is the barrier in location to the spermatogonia?
smooth muscle surrounding tubule, one layer of germ cells, then barrier than next layer of germ cells and sertoli cells
Mitotic proliferation occurs in which compartment of the seminferous tubule? (separated by junction barrier)
basal compartment
What occurs in the adluminal compartment of the seminferous tubules?
meiosis and differentiation
Three elements to spermatogenesis:
- mitotic proliferation -> many
cells - meiotic division -> genetic
diversity - cell modelling -> package
chromosomes for delivery to
oocyte
Spermatogenesis: Mitosis:
- prospermatogonia = germ cells
of immature testis - reactivated at puberty to
undergo rounds of mitosis in the
basal compartment of the tubule - Spermatogonia emerge
- undergo a series of divisions to
form a clone of cells - final round of divisions form a
clone which divides to form
resting primary spermatocytes - primary spermatocytes inhibit
cavities formed in sertoli cell
cytoplasm - nuclear division is completed,
cytoplasmic division is not - primary spermatocytes are
linked by cytoplasmic bridges
Spermatogenesis:
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Spermatogenesis: Meiosis:
- resting primary spermatocytes push
through Sertoli cell junctions into
adluminal compartment - enters meiotic prophase
- paired homologous chromosomes
form contacts at pachytene, break,
swap segments and rejoin - first meiotic division = genetic
diversity = two chromosome pairs - second meiotic division = two
unpaired chromosomes in each cell
What is most damaging for chromatid packaging?
ROS
Spermatogenesis: Packaging:
- cytoplasmic remodelling of spermatid
- tail for forward propulsion
- midpiece with mitochondria for
energy = mitochondrial sheath - cap region forms for sperm oocyte
fusion - acrosome forms to penetrate oocyte
Sperm Diagram:
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How long does it take for an immature germ cell to develop into a mature male gamete?
16 days
Where does spermatogenesis occur?
- Testes
- until sperm moves to the epididymis
and gains motility - no resting phase during
spermatogenesi
Spermatogenic Cycle:
What is the trigger that allows germ cells to differentiate into sperm cells?
Retinoic acid
Vitamin A
What triggers the end of mitosis of spermatogonia and begin meiosis?
2nd pulse of Retinoic acid
The final pulse of retinoic acid in spermatogenesis function?
spermiation
Every 16 days a new generation of sperm cells are formed and hence in the testes —— are formed
layers
so some cells will be 0 days old, some will be 16 days, 32 days
but different “slices” will have different days eg day 5, 21, 37
newest generation is at the periphery of the tubule
hence superficial is new
What is the spermatogenic cycle?
clock of retinoid acid pulsatile release every 16 days in humans
begins waves of germ cell differentiation
*time taken for reappearannce of the same stage within a given segment of the tubule
Spermatogenic Wave
Distance between the same stage in testes
different patches of testes will begin differentiation on different days hence all patches will not have all layers
The final stages of maturation of spermatozoa occurs where?
- spermatozoa wash into the rete
- through the vasa efferentia
- into the epididymis where the fluid is
absorbed and sperm is concetrated - in the rete they can twitch: by the
causa epidiymis they can swim/move - process is dependent on androgen
stimulation
What % of seminal fluid is from the seminal vesicles?
85%
prostate gland secretes majority
What does the seminal vesicles secrete?
Yellow, alkaline and viscous fluid that contains fructose, fibrinogen, prostaglandins, Vitamin C
What does the endocervix do?
- secretes mucous with cyclical
variation - macromolecular network of mucin
fibrils guiding spermatozoa - oestrogen stimulates watery mucous
- progesterone inhibits secretory
activity - sperm can penetrate from day 9,
peaks at day 14
What happens to 99% of sperm ejaculated in the vagina?
- stuck in cervical mucous/expelled
from the vagina entirely
What does the endocervic offer sperm?
- receptive at the time of ovulation
- protection from hostile vagina, and
from phagocytosis - supplementation of energy
requirements - sperm selection by differential
motility and morphology - short term reservoir within the
endocervical crypts - initiation of the next stage in sperm
maturation: capacitation
3 properties of cervical mucous?
- consistency: watery or viscous
- spinnbarkeit: elasticity
- Ferning: crystalisation on glass
service
What is capacitation?
- sperm recovered at ejaculation do
not fertilise ova immediately - *cholesterol must be lossed
- phospholipids from the inner
membrane - activation of phospholipases
- hyperactivity motility
Semen Analysis:
- concentration
- motility
- morphology
- volume: 1.5-6ml
Asternozoospermia
low motility (slow sperm)
Oligozoospermia
low concentration
Azoospermia
no sperm
Aspermia
no ejaculate
