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STRUCTURES - WEEK 2 > LEC 11: Embryology I - 08.25.14 > Flashcards

LEC 11: Embryology I - 08.25.14 Flashcards

1
Q

When does human development begin

A

Human development begins at fertilization (sperm fertilizes egg)

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2
Q

totipotent stem cells

A

ability of a single cell to divide and produce all of the differentiated cells in an organism (e.g. zygotes)

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3
Q

gametogenesis

A

process of formation and development of gametes (oocytes or sperm)

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4
Q

ploidy of gametes

A

sperm and oocyte are highly specialized sex cells; are haploid (half the necessary chromosomes)

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5
Q

oogenesis

A

formation of mature ovum during gametogenesis

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6
Q

spermatogenesis

A

formation of mature sperm during gametogenesis

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7
Q

clinical significance of meiosis during gametogenesis

A
  • germ cells only (to produce haploid gametes)
  • reductive division
    • diploid germ cells –> haploid gametes (sperms and oocytes)
  • contant chromosome number
    • variable number of copies
  • genetic variability
    • random assortment
    • recombination
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8
Q

overview of spermatogenesis

A
  • process by which spermatogonia are transformed into mature sperm
    • spermatogonia dormant in seminiferous tubules of testes until puberty
    • transformed into 1* spermatocytes
    • transformed into 2* spermatocytes
    • 4 spermatids undergo spermiogenesis

Result: 4 mature sperm (spermatozoa)

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9
Q

1st meiotic division of spermatogenesis

A
  • primary spermatocyte (46 XY) undergoes 1st meiosis
  • (2) secondary spermatocytes (23 X, 23 Y)
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10
Q

2nd meiotic division of spermatogenesis

A
  • secondary spermatocytes (23 X, 23 Y) undergo 2nd meiotic division
  • (4) spermatids (23 X, 23 X, 23 Y, 23 Y)
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11
Q

spermiogenesis

A
  • 4 spermatids from 2nd meiotic division undergo spermiogenesis
  • result is (4) mature sperm
  • spermiogenesis is last phase of spermatogenesis
    • rounded spermatid transformed into elongated sperm
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12
Q

Where does spermatogenesis occur, and where are mature sperm stored

A
  • spermatogenesis occurs sequentially in the testes
  • sperm then transfored from seminiferous tubules to epididymis
    • stored
    • become functionally mature during puberty
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13
Q

spermatozoa

A

mature sperm cell

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14
Q

How long does spermatogenesis take

A

approximately 2 months

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15
Q

Sertoli cells

A

line the seminiferous tubules and support/nuture germ cells; may be involved in regulating spermatogenesis

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16
Q

When do sperm become functionally mature

A

sperm are passively transported from seminiferous tubules (testes) to the epididymis, where they are stored and become functionally mature during puberty

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17
Q

location and description of epididymis

A

elongated coiled duct along the posterior border of the testes; continguous with the ductus deferens which transport sperm to the urethra

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18
Q

characteristics of spermiogenesis

A
  • loss of cytoplasm
  • development of the tail
  • formation of the acrosome
  • acrosome, derived from Golgi region of spermatid, contains enzymes released at beginning of fertilization
    • assist sperm in penetrating corona radiata and zona pellucida
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19
Q

Structure of mature sperm

A
  • head
    • haploid nucleus
    • partially covered by enzyme-filled acrosome
  • tail (motility to site of fertilization)
    • middle piece = full of mitochondria (ATP)
    • principal piece
    • endpiece

NB: Y chromosome is essential for normal spermatogenesis; microdeletions = defective spermatogenesis and infertility

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20
Q

oogenesis

A

process by which oogonia transformed into mature oocytes; begins before birth and is completed after puberty; ends with menopause

NB: timing differs for spermatogenesis and oogenesis

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21
Q

sequence of events in oogenesis

A

oogonium –> primary oocyte –> secondary oocyte / Polar Body I –> fertilized ovum / Polar Body II

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22
Q

oogonia

A
  • primordial female sex cells
  • fetal life proliferate via mitosis
  • enlarge to form primary oocytes before birth
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23
Q

folliculus

A

Latin, “small bag, shell, pod”

24
Q

What is the difference between a follicle and an oocyte

A
  • oocyte develops within a follicle in the ovary
  • follicle is a thin-walled structure containing fluid, with the egg attached to the wall
  • Usually, only one follicle develops per month
25
Q

primary oocytes (primordial follicles vs. primary follicles)

A

primary oocytes are surrounded by flattened follicular cells

  • before or at birth, primordial follicles
  • after birth, primary follicles
  • NO PRIMARY OOCYTES form after birth
  • primary oocyte is in suspended prophase from birth until puberty
    • dormant in ovarian follicles until puberty (years)
26
Q

primary oocytes (primary follicles)

A
  • during puberty, primary oocyte enlarges, follicular cells become columnar
  • follicle becomes surrounded by zona pellucida
  • NO PRIMARY OOCYTES form after birth
    • primary oocyte is in suspended prophase from birth until puberty
    • dormant in ovarian follicles until puberty (years)
27
Q

secondary follicle / secondary oocyte

A
  • Leading up to puberty, follicle matures, increases in size
  • oocyte completes 1st meiotic division before ovulation
  • this gives rise to secondary oocyte / polar body I
28
Q

ovulation and formation of fertilized ovum

A
  • at ovulation, nucleus of secondary oocyte begins 2nd meiotic division
    • arrests in metaphase
  • if sperm penetrates, 2nd meiotic division is completed
    • fertilized egg and 2nd polar body
29
Q

gametogenesis in men vs. women

A

MEN

  • begins at puberty
  • one germ cell results in 4 mature spermatazoa (23 X or 23 Y)

WOMEN

  • begins during embryogenesis
  • arrests until puberty
  • one germ cell results in 1 ovum and 2 polar bodies (23 X)
30
Q

zona pellucida

A

primary oocyte surrounded by a covering of amorphous acellular glycoprotein material

31
Q

corona radiata

A

layer of follicular cells around oocyte

32
Q

Uterus

A

thick walled, pear shaped muscular organ (body, cervix)

33
Q

endometrium

A

lining of uterus; during menstrual cycle at peak of development, lining is 4-5cm thick

NB: basal layer of endometrium has own blood supply, not sloughed off during menstruation; functional layers (compact, spongy) disintegrate and are shed during menses

34
Q

GRH

A

Gonadotropin Releasing Hormone

  • released by neurosecretory cells in hypothalamus
  • carried into anterior pituitary
  • stimulates release from anterior pituitary of FSH and LH
35
Q

FSH

A

Follicle Stimulating Hormone

  • stimulate development of ovarian follicles
  • stimulate production of estrogen by follicular cells
  • promotes growth of several primordial follicles into 5-12 primary follicles
  • ONLY 1 FOLLICLE USUALLY DEVELOPS into mature follicle and ruptures, expelling its oocyte
36
Q

LH

A

Luteinizing Hormone

  • trigger of ovulation
  • release of secondary oocyte
  • stimulates follicular cells and corpus luteum to produce progesterone, inducing growth of ovarian follicules and endometrium
37
Q

Ovulation

A
  • early in cycle, ~50 follicles recuited, only one is dominant follicle
  • primary follicle = zona pellucida
  • secondary follicle = antrum, proliferation of follicular cells
  • tertiary (mature) follicle = presses on surface of ovary
38
Q

corpus luteum

A
  • walls of ovarian follicle collapse to form folds
  • develop into grandular structure
  • secretes progesterone and some estrogen
39
Q

What triggers ovulation

A
  • LH surge (12-24 afterwards)
  • ovary expells secondary oocyte surrounded by zona pellucida and layers of follicular cells (corona radiata)
  • resumption of 1st meiotic division
40
Q

Female menstrual cycle

A
  • menstrual phase
  • proliferative phase
    • growth of ovarian follicles
    • controlled by estrogen
    • endometrium thickens
  • luteal phase
    • formation, functioning, growth of corpus luteum
    • progesterone stimulates epithelium –> glycogen-rich material
41
Q

What happens if no egg fertilization

A
  • Corpus luteum degenerates
  • estrogen and progesterone levels fall
  • secretory endometrium becomes ischemic (lose oxygen)
  • menstruation occurs
42
Q

What happens if fertilization occurs

A
  • clevage of zygote and formation of blastocyst
  • blastocyst impoants in endometrium about day 5-6
  • hCG (human chorionic gonadotropin), produced by syncytiotrophoblasts, keeps CL producing estrogen and progesterone
  • luteal phase continues and menstruation does not occur
43
Q

syncytiotrophoblasts

A
  • produces by hCG
  • keeps corpus luteum producing estrogen and progesterone
44
Q

How are oocytes transported

A
  • during ovulation, fimbriated end of tubule applied to ovary
  • sweeping action of fimbriae and fluid currents sweep secondary oocytes into infundibulum of uterine tube
  • oocyte passes into ampulla of tube (peristalsis of tube)

ovary –> fallopian tube (ampulla)

45
Q

How are sperm transported

A
  • sperm transported from epididymis to urethra through peristalsis of ductus
46
Q

When is meiosis arrested (oogenesis)

A

Meiosis is arrested at two points:

  • 1* oocyte arrests before birth in prophase; this arrest continues until puberty
    • division resumes shortly before ovulation for formation of 2* oocytes + 1st polar body
  • 2* oocyte arrests in metaphase during ovulation
    • if fertilization occurs: meiosis will resume
    • no fertilization: oocyte remains arrested
47
Q

syncytiotrophoblast (Greek roots)

A
  • syn *= “together”
  • cytio *= “of cells”
  • tropho *= “nutrition”
  • blast *= “bud”
48
Q

Where does fertilization usually occur

A

In the ampulla (ampullary region) of fallopian tube

49
Q

endometriosis

A

endometrial tissue that lines uterus is also appear and flourish outside the uterine cavity, most commonly on membrane that lines abdominal cavity (peritoneum)

50
Q

capacitation

A

phase in which ejaculated sperm are transformed so that they can fertilize an egg

  • freshly ejaculated sperm CANNOT fertilize an egg
    • glycoprotein coat and seminal proteins removed/digested from acrosome
    • membrane cholesterol/phospholipid ratio altered
    • increased motility
    • changes allow acrosome reaction to occur
51
Q

acrosome reaction

A

reaction that occurs in sperm during fertilization

  • when capacitated (changed) sperm comes into contact with corona radiata surrounding 2* oocyte, undergo complex molecular changes
  • point fusions occur between plasma membrane of sperm and external acrosomal membrane
  • enzymes **hyaluronidase **and acrosin released from acrosome to facilitate fertilization
52
Q

When and where does fertilization occur

A

~12-24 hours after ovulation occurs; typically in ampulla (ampullary region of fallopian tube)

53
Q

Phases of fertilization

A
  1. penetration of corona radiata
  2. penetration of zona pellucida
  3. fusion of sperm and egg plasma membranes
  4. zona reaction
  5. completion of meiosis II by 2* oocyte (was arrested at metaphase)
  6. breakdown of female/male pronucleii and aligment of chromosomes
  7. zygote
54
Q

zona reaction

A

once the sperm reaches the zona pellucida, there are changes in properties of the zona pellucida to make it impenetrable

55
Q

In Vitro Fertilization (IVF)

A
  • hormones given to woman to get multiple mature follicles
  • collection of oocytes from follicles during laparoscopy
  • place oocytes in petri dish with capacitated sperm; IVF occurs
  • cleavage of zygotes in culture medium until 4-to-8-cell stages reached
  • transfer of 1-2 cleaving embryos into uterine cavity
56
Q

ICSI

A

Intracytoplasmic sperm injection

  • injection of 1 sperm into 1 mature oocyte (specific)
  • used when IVF fails or when there are too few sperms available
57
Q

ectopic pregnancy

A

occurs when embryo implants anywhere outside uterus (most common is fallopian tube)

  • can be treated early with medication, but if not caught in time can pose serious complications and even death

STRUCTURES - WEEK 2 (10 decks)

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