Reproduction Flashcards

Question

What is the structure of a spermatozoon?

Answer 1

Head is pear-shaped front end – 4 to 5 microns long structure containing the nucleus, acrosome and basal body of the tail flagellum • nucleus contains haploid set of chromosomes • acrosome contains enzymes that penetrate the egg • basal body

Answer 2

Tail is divided into 3 regions – midpiece contains mitochondria around axoneme of the flagellum (produce ATP for flagellar movement) – principal piece is axoneme surrounded by fibers – endpiece is axoneme only and is very narrow tip of flagellum

Answer 3

Efferent ductless Epididymis Ductus (vas) deferens Ejaculatory duct

Answer 4

Efferent ductules – 12 small ciliated ducts collecting sperm from the rete testes and transporting it to the epididymis

Answer 5

Epididymis (head, body & tail) – 6 m long coiled duct adhering to the posterior of testis – site of sperm maturation & storage (fertile for 40 to 60 days)

Answer 6

Ductus (vas) deferens – muscular tube 45 cm long passing up from scrotum through inguinal canal to posterior surface of bladder – widens into a terminal ampulla

Answer 7

Ejaculatory duct – 2 cm duct formed from ductus deferens & seminal vesicle & passing through prostate to empty into urethra

Answer 8

Seminal vesicles Prostate gland • Bulbourethral glands

Answer 9

Seminal vesicles Prostate gland • Bulbourethral glands

Answer 10

• Other components of semen – fructose provide energy for sperm motility – fibrinogen – clotting enzymes convert fibrinogen to fibrin causing semen to clot – fibrinolysin liquefies semen within 30 minutes – prostaglandins stimulate female peristaltic contractions – spermine is a base stabilizing sperm pH at 7.2 to 7.6

Answer 11

Our cells contain 23 pairs of chromosomes – 22 pairs of autosomes – 1 pair of sex chromosomes (XY males: XX females) • males produce 50% Y carrying sperm and 50% X carrying • all eggs carry the X chromosome • Sex of the child is determined by the type of sperm that fertilizes the mother’s egg

Answer 12

-The process by which gametes are produced in the reproductive organs (gonads) of an organism. -Gametes are fundamental for sexual reproduction and genetic diversity.

Answer 13

Hypothalamus pituitary-gonad feedback loop FSH/LH Oestrogen and progesterone negative feedback

Answer 14

-The process by which gametes are produced in the reproductive organs (gonads) of an organism. -Gametes are fundamental for sexual reproduction and genetic diversity.

Answer 15

•Capacitation was first discovered by Chang and Austin independently (1950). •The final maturational stage of spermatozoa that takes place in the female genital tract, before spermatozoa gain the ability to fertilize oocyte. •It is one of the most investigated areas of andrology and one of the least understood areas of andrology.

Answer 16

Artificial Insemination (AI) •Embryo Transfer (ET) •In Vitro Fertilization (IVF) •Intra-Cytoplasmic Sperm Injection (ICSI) •Somatic Nuclear Transfer (Cloning) •Stem Cell Therapy (Regenerative Medicine) •IPS Cells (Induced pluripotent Stem Cells)

Answer 17

Oocyte activation is key and is triggered by a sperm protein called Phospholipase C zeta (PLCz). •This ‘activates’ the egg to release calcium from internal stores and this rise in calcium facilitates fertilisation. •Oocyte activation is essential for the transformation of the decondensed sperm nucleus in to pronucleus. •4-7 hours after gamete fusion the two sets of haploid chromosomes form the female and male pronucleus (23 chromosomes each) •Pronuclei are equal size and contain nucleoli •In IVF multinucleate oocytes can be identified - polyspermic

Answer 18

Male and Female pronucleus migrate to centre (cytoskeletal system plays important role) •Haploid chromosomes pair and replicate DNA in preparation for the first mitotic division •The pronuclear membranes breakdown •The mitotic metaphase spindle forms •46 Chromosomes organise at the spindle equator

Answer 19

Approx 24 hours after fertilisation the ooplasm divides in to two equal halves •If one or more of the PN fail to decondense and move in to one of the blastomeres, diploid or triploid mosaics may occur

Answer 20

maintains micro -environment for embryo until hatches at blastocyst stage)

Answer 21

Cleavages are timed from sperm entry by an oocyte program that also regulates ‘house keeping’ activities in embryos. •Successive cleavages result in an increase in cell number – essential to provide sufficient cells for differentiation.

Answer 22

Prior to 4-8 cell stage the developmental control depends on maternally-derived stores of RNA laid down during oogenesis. •Activation of the embryonic genome and start of embryonic transcription occurs in a 4-8 cell embryo. •Developmental arrest can occur.

Answer 23

Early cleavage stage embryos are ‘totipotent’ – the nuclei of individual blastomeres are each capable of forming an entire foetus.

Answer 24

Compaction Cells flatten •Maximise intracellular contacts •Tight junctions form •Polarisation of outer cells •Morula – 16 cells

Answer 25

Cavitation and differentiation Tight junctions occur between outer cells – forms the trophectoderm •Fluid filled cavity expands •Sodium pumped in which pulls water in by osmosis •Now >80 cells •50-66% comprise trophectoderm, rest is ICM •Pluripotent In a trophodectoderm - single epithelial layer Inner cell mass - pluripotent used for stem cell lines

Answer 26

Cavity expands •Diameter increases •ZP thins Expanded blastocyst

Answer 27

Hatching Blastocyst expansion and enzymatic factors cause the embryo to hatch from the ZP. •Essential for implantation •TE – extraembyronic •ICM - embryonic

Answer 28

Early preimplantation embryo –ATP turnover low –ATP / ADP ratio is high –Energy metabolism characterised by consumption of pyruvate –Glucose uptake and utilisation is low •Blastocyst stage –Metabolic activity rises sharply –ATP / ADP ratio falls, reflecting an increase demand for energy e.g for protein biosyntheses and ion pumping associated with blastocoel cavity. –Glucose is the predominant exogenous energy substrate

Answer 29

Genetic control - maternal vs embryonic Metabolic activity - low vs high Biosynthetic activity - low vs high Nutrient requirements exogenous - simple (low glucose, non-essential amino acids) vs complex - high glucose, essential and non-essential amino acids, vitamins

Answer 30

Supplied by –Cumulus cells –Fallopian Tube secretions e.g. calcium, sodium, chloride, glucose, proteins. –Uterine secretions e.g. iron, fat soluble vitamins, glucose •Concentrations of nutrients vary along the tract to provide the embryo requirements •Growth factors and cytokines –important in embryonic growth and differentiation –Insulin-like growth factor - IGF–I and IGF–II increase cell numbers in blastocyst –Leukaemia inhibitory factor (LIF) enhances embryo-endo interaction

Answer 31

Cellular differentiation – 10 days •After implantation embryogenesis continues with the next stage of gastrulation when the three germ layers of the embryo form in a process called histogenesis •The 3 germ layers form: ectoderm, mesoderm and endoderm (three overlapping flat discs) •It is from these three layers that all the structures and organs of the body will be derived

Answer 32

Endometrial cell changes to help absorption of uterine fluid – bring the blastocyst nearer to the endometrium and immobilises it. •Changes in thickness of endometrium and its blood supply development •Formation of the decidua Implantation window = 4 days (6-10 days postovulation)

Answer 33

Well defined starting point •Gradual process over several weeks •No universal agreement when process is completed

Answer 34

= Carnegie stage 5A Note the small size of the implantation site compared to the thickness of the endometrium. 1 day after initiation of implantation

Answer 35

After embryo hatched the embryonic and maternal cells enter into a complex dialogue •High degree of preparation and coordination required •Controlled cascade of trophoblast proliferation, differentiation, migration and invasion

Answer 36

The cross talk between endometrium and the developing embryo is mediated by substances including: –Hormones (sex steroids) –Cell adhesion molecules –Proteases –Cytokines, Growth Factors –Also genetics •5 genes up regulated during implantation window (Haouzi et al 2009)

Answer 37

Apposition •Attachment •Invasion

Answer 38

Unstable adhesion of the blastocyst to the uterine lining •Synchronisation of embryo and endometrium (decidua) •Hatched blastocyst orientates via embryonic pole (always attaches at the area above the ICM) •Receptive endometrium (implantation window day 19 – 22)

Answer 39

Stable/stronger adhesion •penetrate with protrusions of the trophoblast cells (microvilli) •Massive communication between the blastocyst and endometrium conveyed by receptor-ligand interactions •Apical surfaces of the endometrial epithelial cells express variety of adhesion molecules (integrin subunits) •Trophoblastic cells also express integrins •Attachment occurs through the mediation of bridging ligands that connect with integrins on their surfaces

Answer 40

Trophoblast protrusions continue to proliferate and penetrate the endometrium •cells differentiate to become syncytiotrophoblast •The trophoblast surrounding the ICM = cytotrophoblasts. •Highly invasive - trophoblast quickly expands and erodes into endometrial stroma. •Invasion is enzymatically mediated •Syncytiotrophoblast erodes endometrial blood vessels •Eventually syncytiotrophoblast comes into contact with maternal blood and form chorionic villi – in initiation of the formation of the placenta •Blood filled lacunae form (spaces filled with maternal blood). Exchange nutrients and waste products.

Answer 41

After first few days of implantation, the trophoblast changes character to become less invasive

Answer 42

Promotes placental formation •stromal cells adjacent to the blastocyst differentiate into metabolically active, secretory cells or Decidual Cells (under influence of progesterone) •Secretions include growth factors/proteins to support growth of implanting blastocyst in the initial stages before the placenta is fully developed. •Endometrial glands enlarge and local uterine wall becomes highly vascularised. •The decidual reaction is not required for implantation e.g. ectopic implantation can occur anywhere in the abdominal cavity.

Answer 43

Modifies the distribution of oestrogen receptors •Stimulates secretory activity •Stimulates stromal oedema •Increases volume of blood vessels •Primes decidual cells •Stabilises lysosomes •Might be an immunosuppresent •May stimulate growth factors and binding proteins •May regulate the formation of reactive oxygen species (reducing oxidative stress)

Answer 44

Embryo is antigenically different from the mother •At the same time as the decidual reaction, leukocytes in the endometrial stroma secrete interleukin-2 which prevents maternal recognition of the embryo as a foreign body during the early stages of implantation •uterine natural killer cells

Answer 45

Essential to sustain early pregnancy •ensures the corpus luteum continues to produce progesterone throughout the first trimester of pregnancy (prevents menstruation). •Interacts with the endometrium via specific receptors •Immunosuppressive – has highly negative charge, may repel the immune cells of the mother & protect the foetus.

Answer 46

hCG to double every 1.3 days in the first 10-12 days of a normal singleton pregnancy •A short doubling time signifies a healthy pregnancy •Slow rate of increase might indicate –Early abortion –Ectopic pregnancy –Delayed implantation –Inadequate trophoblast

Answer 47

Embryos are highly sensitive to the environment – essential to optimise conditions to enable successful program Day 0 - egg collection Day 1 Day 5/6 - embryo transfer cryopreservation

Answer 48

Embryos are highly sensitive to the environment – essential to optimise conditions to enable successful program Day 0 - egg collection Day 1 Day 5/6 - embryo transfer cryopreservation

Answer 49

Use a sequential culture medium – different composition at different stages Day 1-3 Water, salts &ions Pyruvate, lactate, protein and No/low Glucose Non essential amino acids Day 3+ Water, salts &ions Pyruvate, lactate, protein and Glucose Essential and non essential amino acids Vitamins

Answer 50

Use a sequential culture medium – different composition at different stages Day 1-3 Water, salts &ions Pyruvate, lactate, protein and No/low Glucose Non essential amino acids Day 3+ Water, salts &ions Pyruvate, lactate, protein and Glucose Essential and non essential amino acids Vitamins

Answer 51

One step (single culture) –Culture day 1-6 in same media one media –Let the embryo choose principal –useful in uninterrupted systems like time lapse –Why? Reduce stress, less disturbance, Increase embryo viability

Answer 52

Maternal Factors –Follicle environment –Oocyte maturity (hCG trigger 36hours before egg collection) •Embryonic factors –Cleavage rate, size of blastomeres, degree of fragmentation –Gross chromosome imbalance –Variations in embryo metabolism –Failure or abnormal formation of the blastocoel cavity

Answer 53

Laboratory Conditions –Exposure to light –Exposure to high oxygen concentrations –Changes in pH or osmolarity –Culture medium –Volatile organic compounds

Answer 54

•Select morphologically best embryo(s) to transfer on day 5. •If any remaining embryos - cryopreserve. •Need to be of good quality and correct stage of development to be frozen.

Answer 55

Evidence – blastocyst transfer •Enable better selection (embryonic genome activated) •Promotes synchronization with the endometrium. •Higher pregnancy and live birth rates for selected patient populations. Blake DA, et al Cochrane Database Syst Rev., 2007; (4): CD002118 Papanikoloau EG, et alHum Reprod., 2005; 20 911): 3198 -203 Styer A, et al Fertil. Steril. Epub 2007 Jul 17 •Recent systematic review and meta-analysis demonstrated a much improved live birth rate compared to the early cleavage stage when equal numbers of embryos were replaced Papanikolaou EG, et al Hum Reprod., 2008; 23 (1): 91 – 9

Answer 56

Implantation failure is mainly related to either maternal factors or embryonic causes. •Problem with the embryo - high proportion of embryos fail to implant –Aneuploidy (40% IVF fertilised eggs abnormal) •Interaction between embryo and uterus - insufficient trophoblast invasion – miscarriage •Insufficient invasion of maternal blood vessels •Pre-eclampsia, poor foetal growth, hypertension •Sperm problem – DNA fragmentation (abnormal genetic material). Increase miscarriage. Nutrition & lifestyle.

Answer 57

Recurrent implantation failure when: Failure to achieve a clinical pregnancy after transfer of at least 4 good quality embryos in at least 3 cycles •Under the age of 40

Answer 58

Poor ovarian function •Increased sperm DNA fragmentation •Uterine pathologies –Polyps/fibroids –Congenital anomalies –Intrauterine adhesions •Hydrosalpinges shown to significantly reduce implantation and preg rates - fluid toxic to embryos and affects endometrial receptivity. •Immunological factor (NK cells)

Answer 59

Lifestyle changes (smoking, BMI) •Sperm DNA fragmentation test •Improve embryo selection e.g. PGT-A •Hysteroscopy – remove anomalies •Fibroid / Polyps /Hydrosalpinges removal •Immunotherapy (intravenous immunoglobulin) – maybe only subgroup of women benefit.