The short but happy life of a sperm Flashcards
What are the two main products of the testes?Where are they made?
Spermatozoa
Hormones
*Manufactured in different compartments
Spermatogenesis occurs in the seminiferous tubule- vascularised stroma containing leydig cells
Testosterone synthesised from acetate and cholesterol by leydig cells
- mainly into blood vessels but also lymph
- some to seminiferous tubule (DHT which testosterone is converted to be 5a-reductase in sertoli cells)
State the anatomical structures within the testis
draw a pic and label
Spermatic cord Blood vessels Ductus deferens Epididymis - storage of sperm Ductus epididymis Seminiferous tubule Lobule Straight tubulr Rete testis- network of tubules Tunica albuginea- septa forming lobules Tunica vaginalis- parietal and visceral layer Efferent duct- connect to the epididymis
What is the function of androgens?
Maintain reproductive and sexual function
Required fro spermatogenesis
Describe pituitary control of spermatogenesis
- Production of androgens and spermatozoa related functionally
- At puberty : increase in androgens–> beginning of spermatogenesis
Hypophysectomy –> testes shrink and spermatogenesis arrests
- LH stimulates leydig cells to produce androgens
- FSH stimlates sertoli cells
Describe the seminiferoud tubule
- Contains sertoli cells and spermatogenic cells
Physiological barrier formed by gap and tight junctions between sertoli cells. This creates a basal compartment containing spermatogonia, whilst spermatocytes, spermatids and spermatozia are in seperate adluminal compartments - Surrounded my myoid cells and basement membranes
Consider spermatogenesis
Describe step 1
MITOSIS (to increase numbers)
Begin as spermatogonium (2n)
- germ cells of immature testis (prospermatogonia) are reactivated at puberty to undergo rounds of mitosis in the basal compartment of the tubule
- from this emerge cells called A1 spermatogoma whichi undergo a series of devisions to form lots of cells
End as primary spermatocytes (2n)
Consider spermatogenesis
Describe step 2
MEIOSIS (to generate genetic diversity)
Begin as primary spermatocytes (2n)
- Resting primary spermatocytes push through sertoli cell junctions into adluminal compartment
- enter meiotic prophase
- paired homologous chromosomes form contacts at pachytene, break and swap segments and rejoin (damage sensitive)
- results in seperation of homologous chromosomes to opposite ends of meiotic spindle, cytoplasm divides forming short lived secondary spermatocytes (2n)
These quickly divide to form haploid spermatoids (n)
Consider spermatogenesis
Describe step 3
Outline all the structures in a sperm and their functions
PACKAGING
- cytoplasmic remodelling of spermatoid
1. Acrosome - to penetrate oocyte (a small residualbody is the dustbin for unwanted cytoplasm, later eaten by sertoli cells)
2. Cap region forms for spem-oocyte fusion
3. Nucleus with packaged chromosome
4. Midpiece with mitochondria for energy
5. Tail for forward projection
Describe the spermatogenic cycle
One process of spermatogenesis occurs, new stem cells at the same location dont start generation of clones again for a few days
- The interval is constant around 16 days: the process by which the stem cell population control, or is controlled is unknown
- 64 days: time for completion of spermatogenesis –> 4 successive sets of clonal development (at 4 seperate stages of the process)/place/time
How is the spermatogenic cycle controlled?
Spatial and temporal organisation
- If all spermatogonia were activated simultaneously, mature spermatozia would be produced every 16 days –> episodic fertility. If activated randomly –> continuous production
In reality, small regions seem to activated together in wedges around the tubu;e
- If seminiferoud tubules are dissected longitudinally, adjacent synchronised clones of spermatogenesis are seen (“WAVE-LIKE”)
Where does the final stage of maturation of spermatozoa occur?
Spermatozia wash into the rete, thorugh the vasa efferentia and into the epididymis where fluis is absorbed and sperm concentrated
In the rete they can twitch, by the cauda epididymis they can swim. This process is dependent on androgen stimulation
What are the components of semen?
- Spermatozoa mixed with epididymis secretions and seminiferous secretions
- Cellular components: leukocytes (risk of HIV), spermatogenic cells, spermatozoa, epithelial cells from tract
- Secretions from prostate, seminal vesicles and bulbourethral glands at time of ejactulation
- Fluid components: nutrition (fructose, sorbitol), buffer (to protect against vaginal acidity, antioxidants (ascorbic acid, hypotaurine)
What does the endocervix do?
- Secrete musuc with cyclical variation
- Macromolecular network of mucin fibrils (guide spermatozoa)
- Oestrogen stimulates watery mucus
- Progesterone inhibits secretory activity
- Allows sperm penetration from day 9, pak at time of ovulation
What does the endocervix offer sperm?
- Receptive to sperm at ovulation time
- Protection from hostile vagina and from phagocytosis
- Supplementation of energy requirement
- Sperm selection by differential motility and morphology
- Short term reservoir within endocervical crypts
- Initiation of next stage in sperm maturation (CAPACITIATION)
What is capacitiation?
Stripping of glycoprotein from sperm surface which accumulates in the epididymis
- Sperm dont fertilise in vitro immediately, in uterus it does after it undergoes capacitiation
- This causes hyperactivity motility - ‘whiplash’ and makes sperm response to signals from oocyte
