W3 - MALE REPRODUCTIVE PROCESSES Flashcards
1
Q
Describe sexual reproduction
A
- Spermatogenesis
- Allows genetic mixing in order to increase offspring fitness
- Testis, epididymis and accessory glands
- Different reproductive anatomy permits production and delivery of genes (via gametes)
2
Q
What are the reprodutive cells? Desribe their functions in the reproductive process
A
- Mixing of genes occurs via gametes
- Specialized meiotic cells
- Spermatozoa (sperm) and oocytes (eggs)
- Different structure reflects different functions in reproductive process
- Spermatozoa
- Compact, streamlined, highly motile (delivery vessel for DNA)
- Oocytes
- Large, nutrient/protein-rich cells (facilitate embryo development)
- Spermatozoa
3
Q
What is the primary function of the testes? Describe the path of sperm in the testes
A
- Lie within the scrotum
- Approximately 4cm long and 2.5cm wide
- Primary function
- Produce sperm
- Produce steroids (Androgens such as testosterone)
- Each testis is divided into lobules contains 1-4 tightly coiled seminiferous tubules (site of spermatogenesis)
- Sperm pass from the seminiferous tubules through the rete testis and into the efferent ducts of the epididymis
- In the epididymis, sperm undergo further maturation (Acquire motility and fertilization ability) and storage until ejaculation
4
Q
What is the function of interstial (leydig) cells? Explain
A
- Interstitial (Leydig) cells
- Produce androgens (testosterone) in response to LH from the anterior pituitary
- Only testicular cells to express high-affinity LH receptors on their surface
- Prolactin and inhibin also bind to the receptors and facilitate the stimulator action of LH on testosterone production
- Found adjacent to the seminiferous tubule (In the interstitial space)
5
Q
What is the function of sustentacular (sertoli) cells? Explain
A
- Sustentacular (sertoli) cells
- Amorphic shape - Generally wedged between cells
- Support spermatogenesis and nourish it from a germ cell to spermatozoa
- Sit on the basal membrane and also creates the blood-testis barrier
- Tight junctions between them prevent blood from passing between
- Devices the germ epithelium in the basal and abluminal compartments
- Function is controlled by FSH
- Produce inhibin, androgen-binding protein and anti-mullerian hormone
- Cytoplasm invaginates and encloses
- Basally located nucleus
- Cytoplasm is attached to the basal membrane and extends to the lumen
- Cytoplasm strands head towards the lumen
- Provides nourishment as well as receiving cytoplasm from spermatocytes
6
Q
What is the function of myoid cells? Explain
A
- Myoid cells
- Contract to move sperm and fluid through tubules
- Surround the sertoli cells
- Structural regulation of the forming testis cord, promotion of movement of mature sperm through the seminiferous tubules to export it (smooth muscle-like character)
7
Q
What is the function of spermatogonia, spermatocytes and spermatids? Explain
A
- Spermatogonia, spermatocyte and spermatid - Precursor sperm
- Spermatogonia
- Basement membrane
- Not much DNA condensation
- Some may be progressing to the abluminal compartment
- Between tight junctions and basement membranes
- Primary spermatocytes
- Move through the tight junctions into the abluminal compartment
- Undergo cell growth - Become larger
- Nucleus undergoes condensation in preparation for separation
- Generally, have a “spotted nuclei”
- Round spermatids
- Nucleus is condensed
- Elongated spermatid
- Round spermatid changes form
- Releases much of the cytoplasm
- Chromatin is much more condensed (stains more highly)
- Grows flagellum
- Spermatogonia
8
Q
Explain testicular blood flow and heat exchange
A
- Spermatogenesis requires a temperature approximately 4-6°C lower than body temperature
- Complex venous network (pampiniform plexus) wraps around the testicular artery in the spermatic cord
- Cools incoming arterial blood (37°C) before it enters the testis by heat exchange with outgoing venous blood (33°C)
9
Q
How is the blood testis barrier formed? What is its function?
A
- Formed by the sertoli cells and their tight junctions
- Makes it fluid impermeable
- Forms a barrier between the basal and abluminal compartments of the seminiferous tubule
- Prevents the ‘naive’ immune system from mounting a response to ‘foreign spermatozoa’
- Controls the composition of luminal fluid
10
Q
What are the regions, structure and function of the epididymis?
A
- Regions
- Caput (Head)
- Corpus (Body)
- Cauda (Tail)
- Structure
- Highly coiled duct approximately 6m
- Pseudo-stratified epithelia with stereocilia
- Function
- Sperm maturation (acquisition of motility and fertilizing ability)
- Sperm storage in cauda (tail) possible for several months
- Sperm are ejaculated from the caudal epididymis not the testes
11
Q
What is gametogenesis?
A
- Formation of gametes (sex cells)
- Spermatogenesis → Testes
- Oogenesis → Ovaries
- Involves halving of the chromosomes via meiosis
- Avoids polyploidy → Detrimental
- Diploid adult (2n = 46) divide 2 = Haploid gamete (n = 23)
- Haploid sperm (n = 23) + Haploid egg (n = 23) = Diploid zygote (2n = 46)
12
Q
What is spermatogenesis?
A
- The formation of sperm occurs in the seminiferous tubules of the testes and takes approximately 64 to 72 days
- Process involves both mitotic and meiotic cell divisions
13
Q
Explain the process of mitotic proliferation
A
- Mitosis is the equal division of a cell to produce two identical daughter cells with the same number of chromosomes
- The stem cell – spermatogonia – forms the basal layer of the germinal epithelium
- This divides into type A daughter cells (remain as a further stem cell), and type B (go on to form spermatozoa)
- The type B daughter cells move to the abluminal compartment and become primary spermatocytes
- They pass through the tight junctions between the sertoli cells and grow (DNA condenses)
- While nuclear division is complete, cytoplasmic division is incomplete – all cells derived from one spermatogonium are linked by a thin cytoplasmic bridge
- This persists throughout meiotic divisions (cell only breaks off in the last states)
14
Q
Explain the process of meiotic division
A
- Generates genetic diversity and halves the chromosome number
- Freshly created primary spermatocyte enters meiosis
- Process
- The cell goes into the S Phase - doubling the DNA and leaving the basal compartment, going into the abluminal compartment
- Prophase I - chromosomes pair up and recombination occurs (crossing of genetic material)
- This can take up to 24 days and is especially sensitive to damage
- Metaphase I - chromosomes line up at the equator on the meiotic spindle and the microtubules attach
- Anaphase I - microtubules shorten, pulling homologous chromosomes to opposite poles
- Telophase I and cytokinesis - chromosomes arrive at their poles
- Each cell has half the number of chromosomes, but the chromosome consists of a pair of chromatids
- The microtubules disappear and a new nuclear membrane is formed
- Meiosis II - secondary spermatocyte undergoes prophase II – the disappearance of nucleoli and envelope, shortening and thickening of chromatids
- The centrosomes move the polar regions and arrange spindle fibres for the 2nd division
- Metaphase II - the centromeres attach to the spindle and the chromosomes line up
- Anaphase II - the sister chromatids separate and move towards the spindle poles
- Telophase II - the spindle disassembles, decondenses and the chromosomes lengthen
- The nuclear envelope reforms, cell cleavage and cytokinesis occur
- These products are called early spermatids (round spermatids)
- Secondary spermatocytes and spermatids are difficult to distinguish from one another
- The nuclear envelope reforms, cell cleavage and cytokinesis occur
15
Q
What is cytodifferentiation?
A
- The packaging of the chromosomes for effective delivery to the oocyte
- Cytoplasmic remodelling - spermiogenesis
- The spermatids change shape from being round, to being elongated
- Histones are replaced by protamine’s
- The tail is generated for forward propulsion
- The midpiece forms, containing mitochondria
- Equatorial and postacrosomal cap regions form (important for sperm-oocyte fusion)
- Acrosome cap forms
- Cytoplasmic remodelling - spermiogenesis
- Nucleus contains the compact packaged haploid chromosomes
- Residual body acts as a “bin” for the cytoplasm excess, which is then phagocytosed by sertoli cells
- Centrioles - reduce to a central form structure linking the mid-piece to the head
- Completed with the formation of a spermatozoon (Found in the lumen)
- Thin cytoplasmic syncytium bridges rupture, releasing cells
- Cells are released into the lumen via spermiation
