Case 14- gametes and placenta Flashcards
Where the Sperm travels from
Sperm is produced within the seminiferous tubules of the testes. Sperm will travel from the Rete testes, through the Efferent ductules and into the Epididymis where they will mature. It then enters the ductus vas deferens which travels through the spermatic cord and into the inguinal canal. The ampulla of the ductus then joins with the seminal vesicle, this forms the ejaculatory duct which joins with the prostate. The Bulbourethral glands also connects to the urethra which goes through the penis.
The two processes of Spermatogenesis
Spermatocytogenesis and Spermiogenesis
The 4 stages of Spermatocytogenesis
Spermatogonia -> Primary Spermatocyte -> Secondary Spermatocyte -> Spermatids.
Spermatogonium
Primary spermatogonium are diploid. They undergo mitosis to maintain the stem cell population before meiosis starts. The role of Primary Spermatogonium type A is to replenish the population through mitosis, to maintain male fertility. Primary Spermatogonium type B eventually go on to form the mature sperm.
Process of Spermatocytogenesis
1) Primary Spermatogonium type B
2) Primary Spernmatocyte which are diploid. This undergoes Meiosis 1
3) Two Secondary Spermatocytes which are haploid. They undergo Meiosis 2
4) Four spermatids which are also haploid.
Sertoli cells structure
1) The Sertoli cells are bound together by tight junctions, forms an unbroken layer in the Seminiferous tubule.
2) Helps form the blood testes barrier.
3) The tight junctions divide the Sertoli cells into a Basal compartment and an Adluminal
compartment.
4) The Basal compartment contains the Spermatogonia, the Adluminal compartment contains the Primary Spermatocytes, the Secondary Spermatocytes and the Spermatids.
Role of Sertoli cells
- Guides sperm towards the lumen, forms and re-forms junctions, making contact with the sperm cells. Sperm cells are produced within the seminiferous tubules of the sertoli cells
- Blood testes barrier- formed from tight junctions, immunologically safe microenvironment.
- Secretes fluid- moves immobile sperm to epididymis
- Transfer of nutrients- to keep sperm alive
- Phagocytosis- gets rid of residual cytoplasm and dead sperm.
- Expresses FSH receptors and androgen receptors
- Produces ABP, inhibin, AMH and oestrogen
Spermiogenesis
The second process of sperm production, where spermatids are converted into Spermatozoa, through development and maturation
Process of Spermiogenesis
- The pieces of the Golgi body come together to form the Acrosome, which sits at the head of the nucleus
- The mitochondria arrange themselves in a parallel position around the tail
- A tail starts to form
- The mitochondria move to the start of the tail. The centriole is the midpiece of the sperm.
- The Sertoli cells remove the residual cytoplasm
- The resultant spermatozoa are not mature and are immobile.
- The Sertoli cells will flush the Spermatozoa to the Epididymis cells where they mature and become mobile.
Structure of sperm
The head of the sperm contains the DNA and the acrosome which contains the enzymes for penetrating the oocyte. The neck contains the centriole which is needed for the formation of the tail. The midpoint contains mitochondria which is the energy store for cell movement. The tail propels the sperm forward.
How often does sperm production take
64 days, occurs in waves. You need to wait 64 days before giving sperm sample
Semen composition
5-10% of semen is sperm, the rest is seminal plasma i.e. extracellular fluid
Is fluid secreted from the Epididymis
yes
Seminal vesicle
Contributes 60-70% of the final volume of the semen. The secretion from the seminal vesicle is a thick alkaline fluid which protects sperm from the acidic nature of the urethra and female reproductive tract, Secretes its fluid at the start of the ejaculatory duct
Components of the seminal vesicle secretions
- Fructose- energy source for the sperm
- Prostaglandins- lowers the female immune response to semen, improves sperm motility to the uterine tubes.
- Coagulation factors- coagulates semen to help deliver sperm as directly as possible to the cervix.
Ejaculatory duct
The duct of the seminal vesicle joins with the ampulla of the ductus deferens to form the ejaculatory duct. Within the prostate the ejaculatory duct joins the urethra
Prostatic secretions
Contributes 20% of the total volume of semen, secretes into the Prostatic urethra. It is a thin milky fluid which contains citric acid, zinc and proteolytic enzymes. It contains a Prostate specific antigen which liquifies the coagulated ejaculate once the sperm is at the cervix. The antigen only acts 20 minutes later and helps the sperm move through the uterine tubes.
Bulbourethral glands
Pea sized glands embedded within the external urethral sphincter. It sits between the pelvic floor and the urogenital triangle. It drains into the Spongy urethra. Within the deep perineal pouch. It secretes mucus/ lubricating secretions which is the final volume of sperm. Helps with the passage of sperm through the urethra.
Types of fluid that contribute to semen
Testes- sperm
Epididymis- epididymal fluid
Seminal vesicles- thick alkaline fluid with fructuse, prostaglandins and coagulation factors
Prostate- thin milky fluid containing citric acid, zinc and proteolytic enzymes
Bulbourethral glands- mucus/lubricating secretions
Typical sperm count
- Semen volume: 1.5ml or more
- pH: 7.2 or more
- Sperm concentration: 15 million spermatozoa per ml or more
- Total sperm number: 39 million spermatozoa per ejaculate or more
- Total motility (percentage of progressive motility and non‑progressive motility): 40% or more motile or 32% or more with progressive motility
- Sperm morphology (percentage of normal forms): 4% or more
- Vitality: 58% or more live spermatozoa
What develops as the embryonic pole
Chorionic frondosum, the amniotic membrane, chorion leave and decidua parietalis
How maternal blood enters the placenta
Blood enters through the spinal arteries in the wall of the uterus and moves into the intervillus space. The blood flow slows to allow adequate exchange. After bathing the villi the blood drains into larger maternal placental veins.
How foetal blood enters the placenta
Once the blood has obtained O2 and nutrients it flows back to the foetus through umbilical veins carrying oxygenated blood. Umbilical arteries which bring waste from the foetus carry deoxygenated blood which returns to the maternal system.
Adaptions of the Placenta
The maternal blood has high pO2 and low p CO2. The placenta has numerous villi that increase the surface area. The thickness of the synctiotrophoblast at the terminal villi is very thin aiding gaseous exchange.
The placenta is less efficient then the lungs in exchange- how does the conceptus receive sufficient oxygen?
- The difference of oxygen/carbon dioxide concentration in the feto-maternal system
- Fetal haemoglobin has a higher affinity for oxygen as 2-3 DPG is unable to bind to Fhb. The graph shifts to the left.
How are carbohydrates transferred across the placenta
Carbohydrate transfer is by facilitated diffusion via the carrier protein Glut. Glucose provides 90% of the energy requirements for the fetus, only sugar that can cross the placental membrane. Used in oxidative metabolism. Glucose uptake is not regulated by insulin, the fetus will take glucose if its available in the maternal blood stream. Excess fetal glucose is stored in the muscle, liver and placenta.
How do fats cross the placenta
Fats are broken down and transported to the maternal blood as free fatty acids bound to albumin or lipoproteins or proteins packed chylomicrons. Once broken down the lipids move either by simple diffusion or facilitated diffusion down the concentration gradient. They are:
• Basic constituent parts of the lipid membrane
• Act as fuel for oxidative metabolism
• Precursors for important compounds i.e. prostaglandins
How does the fetus store energy
Glycogen stores in the fetal liver are double that of an adult but this falls within hours of birth
How are amino acids transported across the placenta
Higher concentration of proteins in the fetus so secondary active transport is required. The movement of amino acids is coupled with the movement of sodium into the fetus. Role of amino acids:
• The formation of proteins and growth
• Energy store
• Fetal hepatocytes can modify maternal amino acids if there is a shortage of a particular type.
• Fetal hepatocytes can develop new amino acids via de novo synthesis.
How high molecular mass compounds move across the placenta
Unable to cross the villi. Microdroplets of the compound are engulfed in the cytoplasm of the synctiotrophoblast and transported within small vesicles to the fetal circulation. Process of pinocytosis. Used for immunoglobulins.
