Sex and fertilisation Flashcards
(44 cards)
1
Q
Briefly outline spermatogenesis
A
- Occurs in seminiferous epithelium found in testis
- Controlled by HPG axis
- 100 million sperm produced per day
2
Q
What is the sperm’s journey through the epididymis?
A
- On entry, spermatozoa not capable of movement
- Once at tail of epididymis, they are capable of movement and have potential to fertilise
- Addition of secretory products to surface of sperm
- Maturation dependent on support of epididymis by androgens
3
Q
What makes up the semen?
A
- Spermatozoa and seminal plasma
4
Q
Where is seminal plasma derived from?
A
- Accessory glands of male reproductive tract
5
Q
What are the functions of seminal plasma?
A
- Transport medium
- Nutrition
- Buffering capacity
- Prostaglandins may stimulate muscular activity in female tract
6
Q
Which glands contribute to making seminal plasma?
A
- Seminal vesicles
- Prostate gland
- Bulbourethral glands (Cowper’s glands)
7
Q
What do seminal vesicles contribute to seminal plasma?
A
- 60% of volume
- Alkaline fluid - neutralises acid in male urethra and female
- Fructose, prostaglandins, clotting factors (semenogelin)
8
Q
What do bulbourethral (Cowper’s) glands contribute to seminal plasma?
A
- Very small volume
- Alkaline
- A mucous that lubricates end of penis and urethral lining
- (pre ejaculate)
9
Q
What does the prostate gland contribute to seminal plasma?
A
- 25% volume
- Milky, slightly acidic
- Proteolytic enzymes (keep semen fluid)
- Citric acid, acid phosphatase
10
Q
What should the normal sperm count be?
A
- 33-46 million
- Normally around 40 million
11
Q
How far does the sperm have to travel to meet the female gamete?
A
- 100 000 times its own length
12
Q
What is the normal site of fertilisation?
A
- Ampulla of uterine tube
13
Q
What are the phases of the human sexual response?
A
- Excitement phase - due to psychogenic and/or somatogenic stimuli
- Plateau phase
- Orgasm phase
- Resolution - return to haemodynamic norm followed by a refractory period in males
14
Q
Which nervous system causes erection in males?
A
- Parasympathetic
15
Q
What are the stimulants for erection?
A
- Psychogenic
- Tactile (sensory afferents of penis and perineum)
16
Q
What are the efferents for erection?
A
- Somatic and autonomic
- Pelvic nerve (PNS)
- Pudendal nerve (somatic)
- Causes haemodynamic changes
17
Q
What does erection involve?
A
- Straightening of coiled helicine arteries
- Allows blood to fill the corpus cavernosum
18
Q
Describe blood flow in the flaccid penis?
A
- Arterio-venous anastomoses allows blood to bypass corpus cavernosum
19
Q
Describe blood flow to the penis during erection
A
- Smooth muscle in helicine arteries relaxes and straightens
- Blood flows into corpus cavernosum
- Bulbospongiosus and ischiocavernosus muscles compress venous plexus
- This retains blood in the penis
20
Q
Which nerves provide parasympathetic innervation to the penis?
A
- Fibres from lumbar and sacral spinal levels
- Pelvic nerve and pelvic plexus
- Cavernous nerve to corpora and vasculature
21
Q
Outline the neurophysiology of erection
A
- Inhibition of sympathetic arterial vasoconstrictor nerves
- Activation of PNS
- Activation of non-adrenergic, non-cholinergic, autonomic nerves to arteries
- NO released
22
Q
What are the effects of NO on erection
A
- Post-ganglionic fibres release ACh
- ACh binds to M3 receptor on endothelial cells
- Causes a rise in Ca2+ concentration, activation of NOS and formation of NO
- NO diffuses into vascular smooth muscle and causes vasodilation
- This leads to erection
(NO is also released directly from nerves)
23
Q
What causes erectile dysfunction?
A
- Psychological (descending inhibition of spinal reflexes)
- Vascular - CVD, DM, HTN
- Anatomical
- Neurogenic - peripheral (polyneuropathy/DM) or central (spinal cord lesion/MS)
- Hormonal
- Drugs
24
Q
Which nervous system causes emission and ejaculation?
A
- Sympathetic
25
What happens in emission of semen?
- Movement of semen into prostatic urethra
- Contraction of smooth muscle in prostate, vas deferens and seminal vesicles
26
What happens in ejaculation?
- Expulsion of semen
27
What happens to facilitate ejaculation?
- Contraction of glands and ducts
- Bladder internal sphincter contracts
- Prevents retrograde ejaculation
- Rhythmic striatal muscle contractions of pelvic floor and perineal muscles (ischiocavernosus and bulbospongiosus)
28
How does the character of cervical mucus change over the course of the menstrual cycle?
- Oestrogen alone causes thin and stretchy mucus
- Oestrogen and progesterone forms thick and sticky mucus (forms a plug)
29
Outline capacitation of sperm?
- Further maturation of sperm in female productive tract (6-8 hours)
- Sperm cell membrane changes to allow fusion with oocyte cell surface
- Tail movement changes from beat to whip-like action
- Now capable of undergoing acrosome reaction
30
How long can sperm survive once they've left the body?
- 48-72 hours
31
How long do oocytes survive after ovulation?
- 6-24 hours
32
How long is the fertile period?
- Sperm deposition up to 3 days prior to ovulation or day of ovulation
33
How do oocytes move after ovulation?
- Beating cilia and peristalsis of uterine tube
34
What is the acrosome?
- Derived from golgi region of developing spermatid
- Contains enzymes
- Necessary for fertilisation
35
What is the acrosome reaction?
- Sperm pushes through corona radiata
- Binding of sperm surface receptor to ZP3 glycoprotein of zona pellucida
- Triggers acrosome reaction
- Digestion of zona pellucida
36
What is the cortical reaction?
- One sperm penetrates zona pellucida
- Plasma membranes fuse
- Blocks polyspermy
37
What does fertilisation trigger?
- Series of calcium waves activated
- Meiosis II continues
- Pronuclei move together
- Mitotic spindle forms leading to cleavage
38
Describe the cells of the morula
- Each cell is totipotent
39
Outline what happens in IVF
- Oocytes fertilised in vitro
- Divide to the 4 or 8 cell stage
- Morula is then transferred into uterus
40
What is Pre-implantation genetic diagnosis?
- Cell safely removed from morula
- Tested for serious heritable conditions
- Prior to transfer of embryo
41
What is the process of hatching?
- Occurs after formation of blastocyst
- Blastocyst hatches from zona pellucida
- Now can enlarger without constraint
- Can interact with uterine surface to implant
42
Outline the process of implantation
- Outer cell mass (trophoblast) interacts with endometrium
- Endometrium controls degree of invasion
43
What happens in ectopic implantation?
- Implantation occurs at sites other than endometrium lined uterine cavity
- Invasion not controlled
44
What causes placenta praevia?
- Implantation in lower uterine segment
