spermatogenesis and testicular function Flashcards
what is spermatogenesis
the process whereby spermatozoa are formed. it consits of proliferation (mitosis), meiosis and differentiation
how long does spermatogenesis take
5-9 weeks depending on species
where does spermatogenesis take place
seminiferous tubule
what are the 3 phases of spermatogenesis
- proliferation
- mitotic divisions of spermatozoa
- ultimately a large number of B spermatogonia are produced - meiosis
- crossing over ensures genetic heterogeneity
- haploid spermatids produced - differentiation
- formation of cell capable of fertilisation
development of spermatagonia into mature spermatazoa completes which stages
- spermatagonia (stem cells)
- primary spermatocytes
- secondary spermatocytes
- spermatids
- mature spermatazoa
what are the phases of sperm differentiation
- golgi phase
- cap phase
- acrosomal phase
- maturation phase
what occurs during the golgi phase of spermatid differentiation
- vesicles of golgi fuse to form acrosomic vesicle
- centrioles move to base of nucleus (proximal anchors tail to nucleus, distal forms central flagellum)
what occurs during the cap phase of spermatid differentiation
- acrosome forms cap
- golgi apparatus migrates and disappears
- primative flagellum forms
what occurs during the acrosomal phase of spermatid differentiation
- acrosome spreads and nucleus elongates
- manchette tubules formed
- neck and annulus formed
what occurs during the maturation phase of spermatid differentiation
- manchette forms postnuclear cap
- mitochondria form spiral assembly to make middle pience
what are the features of spermatozoa in the head and tail
head:
- nucleus + acrosome + nuclear cap
- shape caries across species
- acrosome contains hydrolytic enzymes required for penetration of zona pellucida
tail:
- self powered flagellum
- composed of:
- captilum = part of middle piece that fits into post nucleus
- middle piece
- prinicple piece
- terminal piece
outline the cycle of the seminiferous epithelium
- Spermatogonia Proliferation (Mitotic Phase)
Type A Spermatogonia: These are the stem cells that undergo mitosis to either self-renew or produce Type B spermatogonia.
Type B Spermatogonia: These cells are committed to differentiation and will undergo further divisions to produce primary spermatocytes. - Primary Spermatocyte Formation
Type B spermatogonia enter meiosis I to become primary spermatocytes. These cells are diploid (2n) and will undergo meiosis to reduce their chromosome number. - Meiosis I: Formation of Secondary Spermatocytes
Primary Spermatocytes: Each primary spermatocyte undergoes the first meiotic division, resulting in two haploid (n) secondary spermatocytes. These cells have half the chromosome number but each chromosome consists of two chromatids. - Meiosis II: Formation of Spermatids
Secondary Spermatocytes: These undergo the second meiotic division, producing spermatids. Each secondary spermatocyte divides to form two spermatids, resulting in four spermatids from each primary spermatocyte.
Spermatids: These are immature sperm cells that are haploid and round in shape. - Spermiogenesis: Differentiation into Spermatozoa
Spermatid Differentiation: Spermatids undergo a series of morphological changes, a process known as spermiogenesis, to become mature spermatozoa (sperm cells). This includes:
Condensation of the nucleus.
Formation of the acrosome, which covers the nucleus and contains enzymes needed for fertilization.
Development of the flagellum (tail) for motility.
Shedding of excess cytoplasm. - Spermiation: Release into the Lumen
Mature Spermatozoa Release: The fully formed spermatozoa are released from the Sertoli cells into the lumen of the seminiferous tubules. This process is known as spermiation. - Transport to Epididymis
Spermatozoa Movement: The spermatozoa are transported from the seminiferous tubules to the epididymis, where they undergo further maturation and gain motility. - Cycle Duration
Cycle Duration: The entire cycle of the seminiferous epithelium takes approximately 64 days in humans, though this can vary slightly among individuals. - Regulation by Hormones
Hormonal Regulation: The process is tightly regulated by hormones, particularly follicle-stimulating hormone (FSH) and testosterone, which are essential for the initiation and maintenance of spermatogenesis.
spermatogenesis is dependent on the production of which hormones
- GnRH secretion from hypothalamus
- FSH and LH from anterior pituitary
- testosterone and oestrogen from gonad
what is meant by spermiogenesis
Nuclear Condensation:
The spermatid’s nucleus becomes smaller and more condensed. The chromatin tightly compacts, resulting in a more streamlined and hydrodynamic shape, which is critical for the sperm’s ability to swim effectively.
Acrosome Formation:
The Golgi apparatus in the spermatid reorganizes to form the acrosome, a cap-like structure that covers the anterior part of the nucleus. The acrosome contains enzymes that are essential for penetrating the egg’s outer layers during fertilization.
Flagellum Development:
A long, whip-like tail called the flagellum forms from the centrioles at the posterior end of the spermatid. The flagellum is crucial for the motility of the spermatozoon, enabling it to swim toward the egg.
Mitochondrial Reorganization:
Mitochondria in the spermatid gather around the proximal part of the flagellum, forming the midpiece of the spermatozoon. This arrangement provides the energy required for the flagellum’s movement.
Cytoplasmic Reduction:
Excess cytoplasm is shed as the spermatid becomes more streamlined. The residual body, which contains the excess cytoplasm and other cellular organelles, is usually phagocytosed by the surrounding Sertoli cells.
Formation of the Mature Spermatozoon:
By the end of spermiogenesis, the spermatid has been transformed into a mature spermatozoon, featuring a compact head (containing the nucleus and acrosome), a midpiece packed with mitochondria, and a long flagellum.
Outcome of Spermiogenesis:
The end product of spermiogenesis is a mature, motile spermatozoon that is capable of fertilizing an egg. This process does not involve cell division but rather the differentiation and specialization of the cell to fulfill its role in reproduction. After spermiogenesis, the spermatozoa are released into the lumen of the seminiferous tubules in a process called spermiation.
what is meant by spermiation
Spermiation is the final step in spermatogenesis, the process by which mature spermatozoa (sperm cells) are released from the Sertoli cells into the lumen of the seminiferous tubules. During spermiation:
Detachment: The mature spermatozoa, which have developed their characteristic structures (such as the acrosome, condensed nucleus, and flagellum), detach from the Sertoli cells that have been supporting and nourishing them throughout their development.
Release into Lumen: Once detached, the spermatozoa are released into the lumen of the seminiferous tubules. From there, they are transported out of the testes.
Transport to Epididymis: After spermiation, the spermatozoa move along the seminiferous tubules and enter the epididymis, where they undergo further maturation, including gaining motility and the ability to fertilize an egg.
