ANA 205 Embryology Flashcards
What is human development?
Human development is a continuous process that begins when an oocyte (ovum) from a female is fertilized by a sperm (spermatozoon) from a male
Oocyte
refers to the female germ or sex cell produced in the ovaries
Sperm
refers to the male germ cell or male sex cell produced in the testes (testicles)
Zygote
This cell results from the union of an oocyte and a sperm during fertilization
Gestational age
Is the age of the embryo or fetus from the presumed first day of the last normal menstrual period
Embryo
The developing human during its early stages of development
How long is the embryonic period?
56 days (8th week)
Fetal period
begins on day 57 and ends when the fetus is completely outside the mother
At what stage is the developing human recognized as a fetus?
After the embryonic period (8 weeks) and until birth, the developing human is called a fetus
Sexual reproduction
occurs when female and male gametes (oocyte and spermatozoon, respectively) unite at fertilization
N number
refers to the amount of DNA in a cell
Ploidy
no. of chromosomes in a cell
What is meiosis
A cell division that takes place in the germ cells generate male and female gametes
What is gametogenesis?
Gametogenesis is the production of gametes from haploid precursor cells
Polar Body
A body formed from the uneven (asymmetrical) cell division of the oocyte
Interphase
Stage before mitosis
Includes G1 S and G2 phase
Undergoes growth and DNA is synthesized (S phase)
G1 Growth and protein synthesis
G2 Some cell organelles are duplicated
S phase is the longest phase
Cells that spend the majority of their life in G1 phase are called
Permanent cells
action of the fimbriae on the oocyte during oocyte transport
- sweeping action of the fimbriae
- fluid currents produced by the cilia of the mucosal cells of the fimbriae ; the secondary oocyte migrates into the funnel-shaped infundibulum of the uterine tube
Action of oocyte after reaching the infundibulum
From the infundibulum, the secondary oocyte passes into the ampulla of the tube, mainly as the result of peristalsis-movements (alternate contraction and relaxation) of the wall of the tube
Where are sperm produced?
Sperms are produced in the testes
Where are sperm temporarily stored?
Epididymis
What aids the movement of the sperm in the ductus deferens?
peristaltic contractions of the thick muscular coat of the ductus deferens
The male accessory sex glands and use
seminal glands (vesicles), prostate, and bulbourethral glands secrete fluid surrounding sperm
How many sperm are ejaculated into the vagina during intercourse?
200 to 600 million
What is the enzyme produced by the seminal gland whilst the sperm is in the cervical canal?
vesiculase
Function of vesiculase
coagulates(hardens) some of the semen or ejaculate and forms a vaginal plug (barrier) that may prevent the backflow of semen into the vagina
Function of prostaglandins in the semen
helps to stimulate uterine motility at the time of intercourse and assist in the movement of sperms to the site of fertilization in the ampulla of the tube
Which energy source is secreted by the seminal gland for the sperm in semen?
Frutose
What is the volume of sperm or ejaculate during intercourse?
averages 3.5 mL, with a range of 2 to 6 mL
Average speed of sperm
2 to 3 mm per minute, but the speed varies with the pH of the environment
At what stages is the sperm immotile and motile?
They are nonmotile during storage in the epididymis, but become motile in the ejaculate
Effect of pH on sperm speed
They move slowly in the acid environment of the vagina,
but move more rapidly in the alkaline environment of the uterus
What is capacitation?
The removal of the glycoprotein coat and seminal plasma proteins from the plasma membrane overlying the acrosomal region of the sperm
What is the zona pellucida?
The zona is a glycoprotein shell surrounding the egg that facilitates and maintains sperm binding and induces the acrosome reaction
What allows the sperm to penetrate the zona pellucida
Acrosomal enzyme, acrosin
What is the glycoprotein involved in the acrosomal reaction
zona glycoprotein (ZP3/ zona protein 3)
What happens when the sperm comes in contact with the oocyte during fertilization?
As soon as the head of a sperm comes in contact with the oocyte surface, the permeability of the zona pellucida changes
When a sperm comes in contact with the oocyte surface, lysosomal enzymes are released from cortical granules lining the plasma membrane of the oocyte
Function of lysosomal enzymes during fertilization
prevent sperm penetration and
inactivate binding sites for spermatozoa on the zona pellucida surface
Normal sperm count for males
100 million sperms per milliliter of semen in the ejaculate of normal males
Sperm count for a fertile male
20 million sperms per milliliter, or 50 million in the total semen
Sperm count for a sterile male
with fewer than 10 million sperms per milliliter of semen
For potential fertility, _____ of sperms should be motile after 2 hours and some should be motile after 24 hours
50%
Causes of male infertility
Male infertility may result from;
a low sperm count
poor sperm motility
medications and drugs
endocrine disorders
exposure to environmental pollutants
cigarette smoking
abnormal sperms
taking too much alcohol
or obstruction of a genital duct such as in the ductus deferens
What is a vasectomy
The most effective method of permanent contraception in the male is vasectomy, or excision of a segment of each ductus (vas) deferens
This surgical procedure is reversible in more than 50% of cases
Following vasectomy, there are no sperms in the semen or ejaculate, but the volume is the same
What is dispermy?
several sperms begin to penetrate the corona radiata and zona pellucida, usually only one sperm penetrates the oocyte and fertilizes it
Two sperms may participate in fertilization during an abnormal process known as dispermy, resulting in a zygote with an extra set of chromosomes
How long does capacitation last
7 hours
What is required for the sperm to bind to the zona pellucida
ZP3/ zona protein
Gonad
An organ that produces gamete e.g ovary and testes
Cytodifferentiation
The developer of specialized cells from unspecialized precursor cells
Which arm of a chromosome is longer
q arm
p arm is shorter
Diploid
(of a cell or nucleus) containing two complete sets of chromosomes, one from each parent, 46 chromosomes
Haploid
(of a cell or nucleus) having a single set of unpaired chromosomes.
Synapsis in meiosis
Homologous chromosomes align themselves in pairs in prophase 1
Crossing over in meiosis
The interchange of chromatid segments between pairs homologous chromosomes in prophase 1
Chiasma
a chiasma is the point of contact, the physical link, between two chromatids belonging to homologous chromosomes
Disjunction (in meiosis 1)
The separation of 46 homologous duplicated chromosomes from each other (centromeres do not split) centromeres split in meiosis II
Causes of genetic variability
Mutation
Homologous recombination, crossing over
Parts of the tail of sperm
Middle piece (contains mitochondria which provides ATP necessary for activity)
Principle piece
End piece
Cleavage
A series of repeated mitotic divisions of the zygote resulting in the rapid increase in the number of embryonic cells known as blastomeres
What is the name of the nucleus of the mature Oocyte
Pronucleus
How long after fertilization do the blastomeres begin to divide
30 hours
What what cell stage does the blastomeres undergo compactation
8 cell stage
What is compactation
Blastomeres change their shape and tightly align themselves against each other to form a compact ball of cells
What is the name of the blastomere 3 days after fertilization
16 cell morula
Oogenesis
The sequence of events by which oogonia are transformed into mature oocytes
All primary oocytes are formed when in a baby girl
5th month
What keeps the meiotic process arrested in the meiosis of oocyte ?
Oocyte maturation inhibited (OMI)
The first polar body
A a small nonfunctional cell that soon degenerates
What ion stimulates the acrosome reaction?
Calcium ions
Describe the acrosomal reaction
The intact acrosome of the sperm binds with a zona glycoprotein (ZP3/ zona protein 3) on the zona pellucida
•Release of acrosomal enzymes (acrosin) allows sperm to penetrate the zona pellucida, thereby coming in contact with the plasma membrane of the oocyte
•As soon as the head of a sperm comes in contact with the oocyte surface, the permeability of the zona pellucida changes
•When a sperm comes in contact with the oocyte surface, lysosomal enzymes are released from cortical granules lining the plasma membrane of the oocyte
What are granulosa cells
Granulosa cells are a type of cell in your ovaries that produce hormones including estrogen and progesterone.
What is spermatogenesis
Spermatogenesis is the sequence of events by which spermatogonia are transformed into mature sperm
Process of Spermatogenesis
Spermatogonia, which have been dormant in the seminiferous tubules of the testes since the fetal period, begin to increase in number at puberty
• After several mitotic divisions, the spermatogonia grow and undergo changes
•Spermatogonia are transformed into primary spermatocytes, the largest germ cells in the seminiferous tubules.
•Each primary spermatocyte subsequently undergoes 1st meiotic division (reduction division) to form two haploid secondary spermatocytes, which are approximately half the size of primary spermatocytes
Secondary spermatocytes then undergo a second meiotic division to form four haploid spermatids
• these haploid spermatids are approximately half the size of secondary spermatocytes.
• The spermatids are gradually transformed into four mature sperm by a process known as spermiogenesis
• The entire process of spermatogenesis, which includes spermiogenesis, takes approximately 2 months
•When spermiogenesis is complete, the sperms enter the lumina of the seminiferous tubules
•Sertoli cells lining the seminiferous tubules support and nurture the germ cells and may be involved in the regulation of spermatogenesis
Sperms are transported passively from the seminiferous tubules to the epididymis, where they are stored and become functionally mature
Describe the process of ooogenesis (prenatal maturation)
1.During early fetal developments oogonia proliferates by mitosis
- Oogonia enlarge to form primary oocytes before birth
As the oocytes formed flattened follicular cells around them forming a primordial follicle - Primary oocyte enlarges during puberty, the follicular epithelial cells become cuboidal in shape then columnar forming a primary follicle
- The primary oocyte is soon surrounded by a covering, the zona pellucida
NB: primary oocyte begin the first meiotic division before birth but completion of prophase does not occur until adolescence, the surrounding follicular cells secrete oocyte maturation inhibitor (OMI) which keeps the meiotic process arrested
Functions of the ovaries
They produce oocytes
They also produce estrogen and progesterone
Estrogen and progesterone are hormones responsible for the;
development of secondary sex characteristics
regulation of pregnancy
The Ovarian cycle includes 3 main changes
- development of follicles
- ovulation
- Formation of the corpus luteum
Stages of follicle development in the ovarian cycle
i. Growth and differentiation of primary oocyte
ii. Proliferation of follicular cells
iii. Formation of zona pellucida
iv. Development of the theca folliculi
Describe the proliferation of follicular cells in the ovarian cycle
Before puberty, oogonia are converted into primordial follicle which is frozen in prophase I of meiosis I
As primordial follicles begin to grow, surrounding follicular cells change from flat to cuboidal in shape and then columnar, forming a primary follicle (stimulated by androgens)
Describe the production of the zona pellucidA
Formation of zona pellucida
the follicular (granulosa) cells and the oocyte secrete a layer of glycoproteins on the surface of the oocyte, forming the zona pellucida
Ovary
Almond shaped reproductive gland located close to the lateral pelvic walls on each side of the uterus
Ovulation is triggered when LH reaches its peak at
12-36 hours prior to ovulation
What is the stigma?
A small a vascular spot inside the cystic swelling on the surface of the ovary
The surge in LH does what to the stigma?
Causes the stigma to balloon out, forming a vesicle
The stigma then ruptures, expelling the secondary oocytes with the follicular fluid
What causes the expulsion of the oocyte during ovulation?
Intrafollicular pressure and possible contraction of smooth muscle in the theca externa after stimulation by prostaglandins
What is mittleschmerz?
Middle pain caused near the middle of the menstrual cycle
Signs of ovulation
- Change in cervical mucus
- Increased libido, sex urge
- Tenderness of the breast
- Swollen vagina or vulva
- slight drop in basal body temperature followed by an increase after ovulation
Anovulation
A woman unable to ovulate due to low conc. of gonadotropins
Describe the development of the theca follici in the ovarian cycle
Development of theca folliculi
As the primary follicle continues to grow, the adjacent (surounding) connective tissue organizes into a capsule, called the theca folliculi
Continuous growth causes cells of the theca folliculi to differentiate into:
an inner layer of secretory cells, called the theca interna
and an outer fibrous capsule, called the theca externa
How does the secondary follicle become the graffian follicle
As development continues, fluid-filled spaces appear between follicular (granulosa) cells
The fluid filled space is crescent-shaped, but with time, it enlarges which coalesce to form a single large cavity, the antrum, which contains follicular fluid
When a large cavity called antrum forms, the ovarian follicle is refered to as a vesicular or secondary follicle
The primary oocyte is pushed to one side of the follicle, where it is surrounded by a mound of follicular cells, the cumulus oophorus, that projects into the antrum
The secondary/ vesicular follicular continues to grow and become matured having a diameter of about 25mm or more
At maturity, it is called the mature vesicular/ mature secondary or Graafian follicle
What prevents the degeneration of the corpus luteum
human chorionic gonadotropin
The corpus luteum of pregnancy remains functionally active for how long?
throughout the first 20 weeks of pregnancy
What is the corpus luteum of menstruation?
If the oocyte is not fertilized, the corpus luteum involutes and degenerates 10 to 12 days after ovulation
It is then called a corpus luteum of menstruation
Corpus luteum secretes;
Mainly progesterone and
some estrogen
Purpose of progesterone and estrogen in implantation
progesterone and estrogen, cause the endometrial glands to secrete and prepare the endometrium for implantation of the blastocyst
How is the corpus luteum formed?
Shortly after ovulation, the walls of the ovarian follicle and theca folliculi collapse and are thrown into folds, under LH influence, they develop into a glandular structure known as the corpus luteum
what is corpus albicans?
White scar tissue of degenerated corpus luteum of menstruation
Dimensions of the uterus
Length = approx 7-8 cm
width = approx 5-7cm at its superior part
thickness= approx 2-3 cm
Parts of the uterus
Body, the expanded superior 2/3
Cervix, the cylindrical inferior 1/3
Describe the body of the uterus
The body of the uterus narrows from the fundus (the rounded, superior part of the body) to the isthmus
Note: the isthmus is the 1cm long constricted region between the body and cervix
Describe the cervix of the uterus
is its tapered vaginal end that is nearly cylindrical in shape
It has a lumen called the cervical canal
the cervical canal, has constricted openings at each end
At the upper constricted end is the internal os, while at the lower constricted end is the external os
The internal os communicates with
the cavity of the uterine body
The external os communicates with
the vagina
What are the walls of the body of the uterus?
The walls of the body of the uterus
consist of three layers
Perimetrium, the thin external layer
Myometrium, the thick smooth muscle layer
Endometrium, the thin internal layer
Where does capacitation of sperm take place?
The uterus
how do cortical granules prevent polyspermy?
The cortical secretory granules release an enzyme that hydrolyses the ZP3 receptor on the zona pellucida and so prevents other sperm from binding and undergoing the acrosome reaction, thus establishing the block to polyspermy
how do cortical granules prevent polyspermy?
The cortical secretory granules release an enzyme that hydrolyses the ZP3 receptor on the zona pellucida and so prevents other sperm from binding and undergoing the acrosome reaction, thus establishing the block to polyspermy
Causes of male infertility
Low sperm count
Medications a drugs
Poor sperm motility
cigarette smoking
alcoholism
Obstruction of the genital duct
Exposure to environmental pollutants
Endocrine disorders
What is the menstrual cycle
The monthly series of changes that occur in the inner layer of the uterus
What are the range of days the menstrual cycle lasts and what determines the variation?
In 90% of women, the length of the cycles ranges between 23 and 35 days
Almost all these variations result from alterations in the duration of the proliferative phase of the menstrual cycle
Phases of the Menstrual Cycle
- Menstrual phase
- Proliferative phase
- Luteal phase
- Ischemic phase (only occurs if the oocyte is not fertilized)
Describe the Menstrual Phase of the menstrual cycle
Usually lasts 4 to 5 days
The functional layer of the uterine wall is sloughed off and discarded with the menstrual flow-menses (monthly bleeding)
The blood discharged through the vagina is combined with small pieces of endometrial tissue
After menstruation, the eroded endometrium is thin
Describe the Proliferative Phase of the menstrual cycle
Also known as the follicular /estrogenic phase
lasting approximately 9 days
coincides with growth of ovarian follicles and is controlled by estrogen secreted by these follicles
estrogen then stimulates the anterior pituitary gland to release FSH and LH which mature the follicles
There is a 2-3 fold increase in the thickness of the endometrium and in its water content
Early during this phase, the surface epithelium reforms and covers the endometrium
uterine glands increase in number and length
the spiral arteries elongate
Describe the Luteal Phase of the menstrual cycle?
also called the secretory/ progesterone phase
lasting approximately 13 days
coincides with the formation, functioning, and growth of the corpus luteum
The progesterone produced by the corpus luteum stimulates the glandular epithelium to secrete a glycogen-rich material
The uterine glands become wide, tortuous, and saccular, and the endometrium thickens because of;
the influence of progesterone and estrogen from the corpus luteum
and because of increased fluid in the connective tissue
As the spiral arteries grow into the superficial compact layer, they become increasingly coiled
The venous network becomes complex and large lacunae (venous spaces develop)
Direct arteriovenous anastomoses are prominent features of this stage
Describe the Luteal Phase of the menstrual cycle?
also called the secretory/ progesterone phase
lasting approximately 13 days
coincides with the formation, functioning, and growth of the corpus luteum
The progesterone produced by the corpus luteum stimulates the glandular epithelium to secrete a glycogen-rich material
The uterine glands become wide, tortuous, and saccular, and the endometrium thickens because of;
the influence of progesterone and estrogen from the corpus luteum
and because of increased fluid in the connective tissue
As the spiral arteries grow into the superficial compact layer, they become increasingly coiled
The venous network becomes complex and large lacunae (venous spaces) develop
Direct arteriovenous anastomoses are prominent features of this stage
Describe the ischemic phase of menstrual
If fertilization does not occur:
The corpus luteum degenerates
Estrogen and progesterone levels fall and the secretory endometrium enters an ischemic phase
Menstruation occurs
Ischemic Phase
occurs when the oocyte is not fertilized
Ischemia (reduced blood supply) occurs as a result of constriction of spiral arteries giving the endometrium a pale appearance
There is decreased secretion of hormones, primarily progesterone, by the degenerating corpus luteum
a loss of interstitial fluid
shrinking of the endometrium
This results in venous stasis and patchy ischemic necrosis (death) in the superficial tissues
Eventually, rupture of damaged vessel walls follows and blood seeps into the surrounding connective tissue
Small pools of blood form and break through the endometrial surface, resulting in bleeding into the uterine lumen and from the vagina
What stimulates ovulation?
Around mid-cycle (14 days in an “average” 28-day menstrual cycle) the ovarian follicle undergoes a sudden growth spurt under the influence of the FSH and the LH.
This growth spurt produces a cystic swelling or bulge on the surface of the ovary.
A small avascular spot, called STIGMA, soon appears in the swelling.
The production of LH is usually stimulated by which hormone (positive feedback loop)?
Estrogen
diameter of a secondary follicle
about 25mm or more
growing follicle produce what, and what is the function of this?
Estrogen, prepares endometrium for the implantation of the blastocyst (pregnancy)
What is the interval for fertilization (how long does ovulation last)?
12-24 hrs
What are the walls of the body of the uterus?
Perimetrium, the thin external layer
Myometrium, the thick smooth muscle layer
Endometrium, the thin internal layer
Layers of the endometrium
i. A thin superficial layer called the compact layer
ii. A thick middle layer called the spongy layer
ii. A thin deep layer called the basal layer
a. The basal layer of the endometrium has its own blood supply and is not sloughed off during menstruation
b. The compact and spongy layers collectively are called the functional layer
c. This functional layer disintegrate and are shed during menstruation and after parturition (delivery of a baby)
What makes up the functional layer of the endometrium?
compact and spongy layers
Which layers are shed during menstruation?
This functional layer disintegrate and are shed during menstruation and after parturition (delivery of a baby)
parts of the uterine tube
infundibulum
ampulla
isthmus
uterine part
Function of uterine tube
carries oocytes from the ovaries and sperms entering from the uterus to reach the fertilization site in the ampulla of the uterine tube
conveys the cleaving zygote to the uterine cavity
