Advanced A&P - Unit 1c: Reproduction

meosis

• at the beginning of the process each diploid has 2 sets of chromosomes (46) that are in the form of 23 homologous pairs

• chromosome pairs come together or synapse and crossing over occurs, resulting in mixing of genetic info

• 2nd division = 4 cells with half the # of chromosomes

compare meiosis and mitosis

• prior to both, DNA replication occurs

• nuclear membrane breaks down as DNA organizes into chromosomes

prophase I

homologous chromosomes pair up side by side and tightly intertwine (synapsis) crossing over occurs here

cross over

homologous chromosomes touch at various points and often times break in or more places and exchange parts

metaphase I

chromosome pairs lineup about midway between the poles of the developing spindle

anaphase I

homologous chromosome pairs separate, and each replicated member moves to one end of the spindle. each daughter cell receives only one replicated member of a homologous pair of chromosomes, overall halving the chromosome number

telophase I

original cell divides in two, forming two haploid cells with 23 individual (unpaired) homologous chromosomes, each with 2 chromatids

meiosis II

separates the chromatids

prophase II

chromosomes condense and reappear, still replicated

metaphase II

replicated chromosomes attach to the spindle fibers, aligned at the center of the cell

anaphase II

centromeres separate, freeing the chromatids to move to opposite poles of the spindle. former chromatids are now considered to be chromosomes (nonreplicated)

telophase II

each cell undergoing meiosis has the potential to produce 4 genetically different gametes

day 0-12

during which time in the reproductive cycle does the follicle mature into an antral follice?

events of spermatogenesis

1. during embryonic development, hormones stimulate the spermatogonia to undergo mitosis.

2. each cell division gives rise to two new cells; one type A cell (maintains supply of undifferentiated cells) and one type B cell (differentiates to become a primary spermatocyte).

3. (at puberty) primary spermatocyte divides by meiosis, forming two secondary spermatocytes.

4. each secondary spermatocyte divides to form two spermatids (four haploids in all).

5. spermatids mature into sperm cells.

spermatogenesis results in hundreds of gametes on a continual bases.

spermatogonia and spermatogenesis

of the cells undergoing spermatogenesis, which have 46 chromosomes?

24-48 hours

what is the timeframe sperm are most likely to fertilize an egg after ejaculation?

events of oogenesis

1. beginning at puberty, some primary oocytes are stimulated to continue meiosis; resulting cells are haploids.

2. primary oocyte divides, cytoplasm is unequally distributed; divides into a secondary oocyte (larger) and first polar body (smaller).

3. if fertilization occurs, the secondary oocyte completes the 2nd meiotic division and divides unequally to produce a tiny second polar body and a large ovum egg). If not fertilized within hours, it degenerates.

4. at the end of the 2nd meiotic division, the chromosomes from the sperm cell combine with those of the ovum producing a zygote.

menstrual cycle review

1. a dominant developing antral follicle fully matures in the ovary and by around day 14 of cycle,, mature antral follicle appears on surface of the ovary (follicular fluid accumulates).

2. around day 14 of follicular development, the ant. pituitary cells respond to the pulses of GnHR and release LH- in response to LH, primary oocyte within antral follicle completes meiosis I (secondary oocyte). LH also interacts with FSH, inducing complex actions leading to weakening and rupturing of bulging follicular wall —> this send the secondary oocyte out of ovary (THIS IS OVULATION).

space containing follicular fluid fills with blood which soon clots; remnants of the follicle within the ovary form temporary corpus luteum.

fertilization

union of secondary oocyte and a sperm cells in the upper part of the uterine tube

fertilization process

1. sperm cell penetrate the corona radiata.

2. the acrosome of the sperm releases proteolytic enzymes.

3. the sperm cell penetrates the zona pellucida.

4. the sperm cell membrane fuses with the oocyte membrane.

5. vesicles beneath the oocyte membrane release enzymes that harden the zona pellucida to prevent additional sperm from entering.

6. results in zygote.

occurrences in fertilization

• tiny second polar body is expelled from fertilized egg.

• pronuclei unite to complete fertilization.

• the sperm cell nucleus enters the oocyte and swells while the cytoplasm of the secondary oocyte divides unequally.

• meiosis is completed.

implantation

• usually occurs 7 days after implantation

• occurs in uterine lining; cells of trophoblast produce tiny, fingerlike extensions that grow into the endometrium. at the same time, growth of endometrium envelopes blastocyst until it is completely embedded in uterine wall.

• begins toward the end of the first week and completes during the second week of development.

blastocyst

early stage of prenatal development when the developing embryo is a hollow ball of cells

pre-embryonic stage

• period: fertilization-2nd week of development

• 30 hours after zygote is formed, it undergoes mitosis, giving rise to two new cells that divide to form four cells, then eight, etc.

period of cleavage

rapid cell divisions and distribution of zygote’s cytoplasm into progressively smaller cells

embryonic stage

• begins at 3rd week-end of 8th week

• includes process of organogenesis, primary germ layers

• most critical period of development because embryo implants in the uterine wall and all the essential external and internal body parts form

primary germ layers

• given rise from inner cell mass

• three layers of cells in the embryo that divide and differentiate into specific tissues and organs; ectoderm, endoderm, and mesoderm

ectoderm

develop into nervous system and integumentary system

endoderm

develops into linings of digestive and respiratory tract, urinary passageways, gallbladder, pancreas

mesoderm

develops into ct. tissues, bl. vessels, kidneys, and reproductive organs

fetal stage

begins at the end of the 8th week of prenatal development and lasts until birth

hCG hormonal change

maintains the corpus luteum, produces progesterone, helps prevent spontaneous abortions, inhibits the ant. pituitary gland’s release of FSH and LH and thus halting the normal menstrual cycle

placental progesterone and estrogens

maintains the last 5-6 months of pregnancy

placental lactogen

causes breast development in preparation for lactation

relaxin from corpus luteum & placenta

relaxes uterine sm. muscle and relaxes ligaments to allow pelvis to accommodate the passage of the fetus during birth

increased aldosterone

causes retention of sodium and water to increase maternal blood volume

increased PTH

causes an increase in blood calcium levels for fetal bone development

progesterone; estrogens

the placenta produces _____ which is converted to _____ by the developing adrenal glands of the embryo

placenta

formed from maternal and fetal tissues, keeps maternal and fetal blood separate but allows diffusion of oxygen and nutrients to the fetus and allows diffusion of fetal waste and CO2 away from fetus

mechanisms by which nutrients enter the embryo

active transport, diffusion, pinocytosis

fetal cardiovascular system

picks up oxygen in placenta

umbilical vein (1)

transports blood rich in oxygen & nutrients from placenta to the fetal body. This vein enters body thru umbilical ring & continues along ant. abdominal wall to the liver. half of this blood passes into liver the rest enters the ductus venosus

ductus venosus

bypasses liver and takes blood directly to inf. vena cava - this is the main source of oxygen for the fetus

foramen ovale

an opening between the R & L atriums; it allows blood in R atrium to go into L atrium, bypassing the lungs

ductus arteriosus

fetal blood vessel that allows blood in pulmonary trunk to go into aorta, bypassing lungs

umbilical arteries (2)

blood flows back to placenta to be re-oxygenated

post natal cardiovascular system

picks up blood from lungs

fetal blood flow circulation (brief version)

• umbilical vein

• ductus venosus

• inf. vena cava

• r atrium and heart

• abdominal aorta

• umbilical arteries

constrict, arteries closing first

following birth, the umbilical vessels _____, with the umbilical arteries closing first. foramen ovale also closes, and so does the ductus venosus.

parturition

process of birth

decrease; increase

as the placenta ages, progesterone _____, which stimulates prostaglandins to ______ which promotes uterine contractions

oxytocin

stimulates powerful uterine contractions