Sex and Fertilisation Flashcards
1
Q
Describe the source and functions of the main constituents of semen
A
- Seminal vesicles
- 60% of volume
- Alkaline fluid
- Fructose, prostaglandins, clotting factors
- Prostate gland
- 25% volume
- Milky, slightly acidic fluid
- Proteolytic enzymes - breakdown clotting proteins
- Citric acid, acid phosphatase
- Bulbourethral glands (Cowper’s glands)
- Alkaline fluid
- Mucous that lubricates the end of the penis and urethral lining
- Sperm - 100-200 million
2
Q
Explain the autonomic control of sexual function
A
- Parasympathetic system stimulates erection
- Sympathetic system stimulates emission and ejaculation
3
Q
State the stages of the human sexual response
A
- Excitement phase - psychogenic and/or somatogenic stimuli
- Plateau phase
- Orgasm phase - ejaculation in male
- Resolution phase - return to haemodynamic norm followed by a refractory period in males
- Not present in females
4
Q
Explain the physiological process of erection
A
- Nerve stimulation (of pelvic plexus) causes sinusoidal relaxation, allowing the corpus cavernosum to relax
- Blood fills the corpus cavernosum spaces through arterial dilation
- The blood increases the pressure and causes the penis to expand and erect
- Tunica albuginea is compressed, causing venous compression as many veins run within
- Prevents blood outflow to sustain erection
- Does not enlarge corpus spongiosum and cause blood to enter as do not want to compress urethra
5
Q
Explain the role of nitric oxide in erection
A
- Post ganglionic fibres release ACh
- ACh binds to M3 receptor on endothelial cells
- Rise in [Ca], activation of NOS and formation of NO
- NO diffuses into vascular smooth muscle and causes relaxation (vasodilation)
- NO also released directly from cavernous nerves
6
Q
What are causes of erectile dysfunction
A
- Psychological - descending inhibition of spinal reflexes
- Tears in fibrous tissue of corpora cavernosa - tunica albuginea
- Vascular problems (arterial and venous)
- Drugs, alcohol
7
Q
How does viagra maintain erection
A
- Viagra slows rate at which cGMP is degraded
- cGMP aids smooth muscle relaxation and vasodilation
- Nitric oxide effect lasts longer
8
Q
Explain emission
A
- Movement of semen into prostatic urethra
- Contraction of smooth muscle in prostate, vas deferens and seminal vesicles
- Dry ejaculation - no emission
9
Q
Explain ejaculation
A
- Ejaculation - expulsion of semen
- Contraction of glands and ducts
- Bladder internal sphincter contracts - prevent retrograde ejaculation
- Rhythmic striatal muscle contractions - somatic
10
Q
Explain the changes in cervical mucus
A
- In the presence of just oestrogen, mucus is thin and stretchy
- Facilitate sperm entrance
- Fern test - fern like structure shows thin and stretchy mucus
- In the presence of oestrogen and progesterone, mucus is thick, sticky and forms a plug
- Limit entry of sperm from cervix to female reproductive tract
11
Q
Describe the process of sperm movement in the female
A
- Sperm are deposited at the external os of the cervix
- They swim through the body of the uterus and into the fallopian tubes
- Fertilize at ampulla
- Sperm transport based on own propulsion
- Oocyte transport based on beating cilia and peristalsis of fallopian tube
12
Q
Describe the process of capacitation
A
- Further maturation of sperm in female reproductive tract
- Sperm cell membrane changes to allow fusion with oocyte cell surface
- Removal of glycoproteins and cholesterol from sperm membrane
- Activation of sperm signalling pathways
- Tail movement changes from beat to whip-like action (B)
- Allows physical puncture of egg
- Now capable of undergoing the acrosome reaction (C)
13
Q
Explain the acrosome reaction
A
- Sperm pushes through corona radiata
- Binding of sperm surface receptor to ZP3 glycoprotein of zona pellucida
- Triggers acrosome reaction
- Requires multiple sperm to release hyaluronidase and break corona radiata and granulosa cells
- Digestion of zona pellucida to enter cytoplasm of oocyte
14
Q
Explain the process of fertilisation
A
- One sperm penetrates leading to fusion of ova and sperm membranes
- Cortical reaction - converts oocyte membrane to prevent further binding
- Blocks polyspermy
- Series of calcium waves are activated following fusion of oocyte and sperm membranes
- Resumption of meiosis II occurs
- Pronuclei move together and fuse
- Mitotic spindle forms leading to cleavage - first mitotic division
15
Q
What is a morula
A
- Cells in a solid ball
- Each cell at this stage of development is totipotent
- Has the capacity to become any cell type
