7. Conception & Contraception

Question 1

How many sperm are produced per ml

How many sperm are contained per ejaculate
What proportions are normal / have abnormal morphology

How long post-ejaculation does the ejaculate liquefy

Answer 1

20-200 million

> 40 million
60% swimming forward vigorously

Question 2

What does the secretions from seminal fluid contain & what are their functions

Answer 2

Alkaline fluid:
neutralises acid in male urethra & female reproductive tract

Fructose:
Energy for sperm

Prostaglandins

Clotting factors (Fibrinogen):
Holds sperm in place after ejaculation, before liquefaction

Question 3

What do the secretions from the prostate gland contain & what are their functions

Answer 3

Milky, slightly acidic fluid

Proteolytic enzymes:
Break down clotting factors, re-liquefying sperm in 10-20mins

Citric acid

Phosphatase

Question 4

What does the secretions from the bulbourethral (cowper’s) glands contain & what is their function

Answer 4

Alkaline fluid

Mucous:
Lubrication @ end of penis & urethral lining

Question 5

Where are sperms moved to just prior to ejaculation

How does this occur

Answer 5

Into prostatic urethra

Due to peristalsis of vas deferens& secretions of seminal vesicles

Question 6

Describe the mechanism of ejaculation:
How is it controlled
What occurs as a consequence

Answer 6

A spinal reflex

Sympathetic nervous system control (L1, L2):

Contraction of glands & ducts (smooth muscle)

Bladder & internal sphincter contracts (prevents entry of semen into bladder)

Rhythmical striatal muscle contractions (pelvic floor, Ischiocavernosus, bulbospongisus, hip & a all muscles)

Question 7

Describe the harmodynamic changes in erection

Answer 7

Inhibition of sympathetic arterial vasoconstrictor nerves

Activation of parasympathetic nervous system
(Pelvic nerve, her parasymp=vasodilation, release Ach @ M3 receptors, rise in Ca2+ = activation of NOS to form NO)

Activation of non-adrenergic, non-cholinergic nerves to arteries also releases NO

Central helical arteries in corpora cavernosa straighten, enlarging lumen

Bulbospongiosus & ischiocavernosus muscles compress veins egressing from corpora cavernosa
Impeding return of venous blood

Dilation of arteries & compression of veins = corpora cavernosa engorged with blood near arterial pressure
Erectile bodies turgid

Question 8

Describe how the release of nitrous oxide causes vasodilation

Answer 8

NO diffuses into & causes relaxation smooth mucs:
Increased NO = 
Formation cGMP = 
less Ca2+ taken up into stores = 
less actin/myosin cross bridges = 
smooth musc relaxed
Vasodilation

Question 9

Erectile dysfunction:
What is the epidemiology
What are the possible causes
What is the the possible treatment & how does it work

Answer 9

40% 40 year olds, 70% 70 year olds

Psychological
Tears in fibrous tissue of corpora cavernosa
Vascular (most common)
Blocking NO: alcohol, anti hypertensives, diabetes

Viagra: inhibits breakdown of cGMP, maintaining erection
(Less Ca intracellularly = less actin/myosin bridges = vasodilation)

Question 10

What physiological changes occur in the female to facilitate coitus

Answer 10

Vaginal lumbrication
Swelling & engorgement of external genitalia
Internal enlargement of vagina
Cervical mucus:
Oestrogen = abundant, clear, non-viscous
Progesterone + oestrogen = thick, sticky mucus plug

Question 11

Describe the process involved in sperm transport through the cervix & uterus

Answer 11

Immediately after ejaculation, semen coagulates
(clotting factors:fibrinogen)

10-20mins later, semen re-liquefies
(by enzymes on prostatic secretions)

Majority of sperm don’t enter cervix; lost be leakage

Those that do enter uterus travel 15-20cm to reach uterine tube within a few hours

Question 12

How is sperm transported

Answer 12

Own propulsive capacity

Fluid currents caused by action of ciliates cells in uterine tract

Question 13

Describe the process of capacitation

Answer 13

Further maturation of sperm in female reproductive tract (6-8hrs)

Sperm cell membrane changes to allow fusion with oocyte cell surface (removal of glycoprotein coat)

Tail movement changes from beating to whip like action

Sperm become responsive to signals from oocyte

Question 14

Describe the acrosomal reaction

Answer 14

(Acrosome = sperm outer shell)

Capacitated sperm comes into contact with oocyte zona pellucida

Membrane fuse = start of reaction

Acrosome swells & lubricates contents by exocytosis

Proteolytic enzymes & further binding facilitate penetration of zona pellucida by sperm (approx 15 mins)

Question 15

What are capacitation & acrosomal reaction both induced by

Answer 15

Influx of calcium

Rise in cAMP in spermatozoa

Question 16

What is:
Primary oocyte
First polar body
Secondary oocyte

Answer 16

Ovum = primary oocyte

completion of 1st meiotic division produces:
Secondary oocyte (haploid no of chromosomes & bulk of cytoplasm)
First polar body (remaining haploid no of chromosomes)

Question 17

Describe the structure of the secondary oocyte

Answer 17

Surrounded by follicular cells (cumulus) embedded in gelatinous matrix

Question 18

Describe the process of fertilisation of the ovum

Answer 18

Secondary oocyte arrives at ampulla; main site of fertilisation

Only 1 sperm penetrates cytoplasm of ovum
Egg completes meiosis II (pro nuclei: 2 sets chromosomes)
Nucleus fuses with nucleus of ovum = zygote (pronuclei fusion)

Within few hrs, zygote begins to divided mitotically: clevage (totipotency)

Forms ball of cells: morula, then hollow structure: blastocyst (loss totipotency)

Blastocyst moving down uterine tubes & after a day or so in unsterile cavity, attached to uterine endometrium: implantation (6 days after ovulation)

Question 19

Describe the structure of the blastocyst

Answer 19

Outer layer: trophoblast
Surrounds embryo
Sticky trophoblasts over inner cell mass adhere to endometrium & release hCG (can detect clinically)

Inner cell mass: becomes embryo

Question 20

Describe the main methods of contraception

Answer 20

Natural: abstinence, coitus interruptus, rhythm method

Vasectomy: divide vas deferens & prevent sperm entering ejaculate

Barrier methods: condoms, diaphragm, cap

Hormonal contraception (tablets, progesterone depot/implant) progesterone (thick mucus plug & -ve feedback to hypothalamus/pituitary)
Oestrogen (-vely feeds back on anterior pituitary)

Sterilisation: occlude Fallopian tubes

Intrauterine contraceptive device:
inert copper (interferes with endometrial enzymes, implantation, sperm transport into Fallopian tube)
Progesterone impregnated

Post-coital contraception: combined or progesterone only

Question 21

Define:
Infertility
Primary infertility
Secondary infertility

What proportion of couples does it affect

Answer 21

Failure to conceive within 1 year

Primary: no previous pregnancy

Secondary: previous pregnancy (successful or not)

Affects 15% of couples

Question 22

Describe the male causes of infertility

Answer 22

Abnormal sperm production
Obstruction of ducts
Hypothalamic/pituitary dysfunction

Question 23

What is a normal semen analysis

Answer 23

Volume >2ml
Sperm count > 20 million per ml
Motility >50%
Morphology > 50%

Question 24

What are the female causes of infertility

Answer 24

Anovulation:
Hypothalamic (e.g. Weight loss, exercise, stress)
Pituitary (e.g. Tumours, necrosis)
Ovarian (e.g. Ovarian failure, menopause, radio/chemotherapy)

Induction of ovulation:
Anti-oestrogen (reduce -ve feedback to hypothalamus/pituitary)
Gonadotrophins
GnRH agonists

Tubal occlusion:
E.g. Sterilisation, PID

PCOS:
Increased androgens, LH/FSH ratio, insulin resistance

Question 25

How might you differentiate between possible causes of female infertility

Answer 25

Hormonal levels:
LH
FSH
oestrogen

Question 26

Describe the management of infertility

Answer 26

Regular unprotected intercourse
Ovulating? Induce ovulation
Patent tubes?
Adequate sperm count?

Question 27

What is the normal volume of ejaculate fluid

Answer 27

2-4ml