Embryology

Question 1

What is the function of human chorionic gonadotropin (hCG)?

Answer 1

Human chorionic gonadotropin interacts with the LHCG receptor of the ovary and promotes the maintenance of the corpus luteum during the beginning of pregnancy. This allows the corpus luteum to secrete the hormone progesterone during the first trimester. Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can sustain the growing fetus.

Produced in the human placenta by the syncytiotrophoblast.

Question 2

What is a somite?

Answer 2

Somites are bilaterally paired blocks of paraxial mesoderm that form along the head-to-tail axis of the developing embryo in segmented animals. In vertebrates, somites subdivide into the sclerotomes, myotomes and dermatomes that give rise to the vertebrae of the vertebral column, rib cage, and part of the occipital bone; skeletal muscle, cartilage, tendons, and skin (of the back)

Question 3

Zona pellucida: structure and function

Answer 3

The zona pellucida (plural zonae pellucidae, also egg coat or pellucid zone) is a glycoprotein layer surrounding the plasma membrane of mammalian oocytes. It is a vital constitutive part of the oocyte.

This structure binds spermatozoa, and is required to initiate the acrosome reaction. ZP3 is then involved in the induction of the acrosome reaction, whereby a spermatozoon releases the contents of the acrosomal vesicle.

In humans, five days after the fertilization, the blastocyst performs zona hatching; the zona pellucida degenerates and decomposes, to be replaced by the underlying layer of trophoblastic cells.

The zona pellucida is essential for oocyte death and fertilization.

Question 4

Ectopic pregnancy

Answer 4

Ectopic pregnancy, also known as eccyesis or tubal pregnancy, is a complication of pregnancy in which the embryo attaches outside the uterus

Question 5

In female: What does the gubernaculum becomme?

Answer 5

Ovarian ligament + Round ligament of the uterus.

The round ligament of the uterus originates at the uterine horns, in the parametrium. The round ligament enters the pelvis via the deep inguinal ring, passes through the inguinal canal and continues on to the labia majora where its fibers spread and mix with the tissue of the mons pubis. The function of the round ligament is maintenance of the anteversion of the uterus (a position where the fundus of the uterus is turned forward at the junction of cervix and vagina) during pregnancy. The round ligament develops from the gubernaculum which attaches the gonad to the labioscrotal swellings in the embryo.

The ovarian ligament (aka utero-ovarian ligament) is a fibrous ligament that connects the ovary to the lateral surface of the uterus. Embryologically, each ovary (which forms from the gonadal ridge) is connected to a band of mesoderm, the gubernaculum. This strip of mesoderm remains in connection with the ovary throughout its development, and eventually spans this distance by attachment within the labium majus. During the latter parts of urogenital development, the gubernaculum forms a long fibrous band of connective tissue stretching from the ovary to the uterus, and then continuing into the labium majus. This connective tissue span, the remnant of the gubernaculum is separated into two parts anatomically in the adult; the length between the ovary and the uterus termed the ovarian ligament, and the longer stretch between the uterus and the labium majus, the round ligament of uterus.

Question 6

Sulcus limitans is the border between?

Answer 6

Basal and alar plate

Question 7

Primordial kidney derives from? and are separated into which 3 parts?

Answer 7

Intermediate mesoderm

Pronephros
Mesonephros
Metanephros

Question 8

Mesonephric duct/Wollfian duct forms what in male and female?

Answer 8

Wolffian structures are male urogenital structures that include the epididymis, vas deferens, rete testies, and seminal vesicles that differentiate from this structure.

In both the male and the female the Wolffian duct develops into the trigone of urinary bladder, a part of the bladder wall. However, further development differentiates between the sexes in the development of the urinary and reproductive organs.

Question 9

The ureteric bud (metanephrogenic diverticulum) it the orign of?

Answer 9

Uretric bud -> Uretric duct

Ureter, renal pelvis, major and minor calyx and collecting duct.

The ureteric bud, also known as the metanephrogenic diverticulum, is a protrusion from the mesonephric duct during the development of the urinary and reproductive organs.

The ureteric bud starts close to where the Wolffian duct opens into the cloaca, and grows dorsalward and rostralward along the posterior abdominal wall, where its blind extremity expands and subsequently divides into several buds, which form the rudiments of the renal pelvis and renal calyces; by continued growth and subdivision it gives rise to the collecting duct system of the kidney. The other, more superficial, portion of the diverticulum, on the other hand, becomes the ureter.

Question 10

Metanephric mesoderm to differentiate into? Which structures does it form?

Answer 10

The metanephrogenic blastema or metanephric blastema (or metanephric mesenchyme, or metanephric mesoderm) is one of the two embryological structures that give rise to the kidney, the other being the ureteric bud.

Metanephric mesoderm to differentiate into metanephric vesicles

The S-shaped renal tubules differentiate into the connecting tubule, distal convoluted tubule, loop of Henle, proximal convoluted tubule, and Bowman capsule

Question 11

What is the position of the kidney in after formation in the embryo and in the adult?

Answer 11

The fetal metanephros is located at vertebral level S1–S2, whereas the definitive adult kidney is
located at vertebral level T12–L3.

Question 12

The urinary bladder are derived from?

Answer 12

Urogenital sinus which connect with the allantois (form urachus in the medial umbilical ligament).

The mesonephric duct (with its utetric bud) becomme inforporated in the posterior wall and forms the trigone of the bladder.

The transitional epithelium of the urinary bladder is derived form endoderm!

Question 13

Female and male utethra development

Answer 13

Female: Lower portion of the urogenital sinus. Develops from endofermal outgrowths into the sorrounding mesoderm to form the urethral glands and paraurethral glands of Skene (same as prostate in male). The female urethra ends at navicular fossa, which empties into the vestibule of the vagina, which also forms from the urogenital sinus.

Question 14

What is the cause of the failure of ascending of the kidneys?

Answer 14

The inferior mesenteric artery obstruct it. No clinical finding.

Question 15

What derives from the ventral part of the cloaca?

Answer 15

Urogenital sinus

Anal canal on its posterior surface

Question 16

What is the other name of the mesonephric and paramesonephric duct?

Answer 16

Wolffian and Mullarian duct, respectively

Question 17

What induce the diferentiation and regression of th wolffian and mullarian duct respectively?

Answer 17

Testosterone and anti-mullarian hormone produced in the testies. This causes the formation of male internal genetalia. If these hormones are not pressnes, female internal organs develop.

Question 18

Development of the male urethra

Answer 18

Endodermal origin. Associated glands are formed by endodermal outgrown (e.g. cowpers gland (bulbourethral gland) and urethral gland of Littre.

Distal part of the penile urethra is formed from an ingrowth of surface ectoderm called the glandular plate. The glandular plate joins the proximal penile urethra and becomes canalized to form the navicular fossa. Ectodermal septa appear lateral to the navicular fossa and become canalized to form the foreskin. The stratified squamous epithelium lining of the distal penile urethra is derived from ectoderm.

Question 19

Development of female urethra.

Answer 19

Lower portion of urogenital sinus. Endodermal orign. Outgrows from endoderm form urethral glands and paraurethral glands of Skene (which are homologous to the prostate gland in the male).

The female urethra ends at navicular fossa, which empties into the vestibule of the vagina, which
also forms from the urogenital sinus.

The vestibule of the vagina develops endodermal outgrowths into the surrounding mesoderm to form the lesser vestibular glands and greater vestibular glands of Bartholin (which are homologous to the bulbourethral glands of Cowper in the male).

The greater vestibular glands of Bartholin open on each side of the vaginal orifice.

Question 20

Development of the suprarenal glands

Answer 20

Cortex:
Mesoderm from intermediate mesoderm. Two episodes of migration: The cortex forms from two episodes of mesoderm proliferation that occur between the root of the dorsal mesentery and the gonad. The first episode forms the inner fetal cortex. The second episode forms the outer adult cortex, by which mesoderm proliferation occurs at the periphery of the fetal cortex.

Medulla:
The medulla forms when neural crest cells aggregate at the medial aspect of the fetal cortex and eventually become surrounded by the fetal and adult cortex. The neural crest cells differentiate into chromaffin cells,

Question 21

Whats are the two parts of the placenta?

Answer 21

Decidua basalis and chorion frondosum

Question 22

What are the name of the decidua around the non-maternal site of the featus and the non-placental parts of the uterus?

Answer 22

Chorion laeve

Decidua parietalis

Question 23

Which 2 structures give rise to the kidney?

Answer 23

Uteric bud and metanephric blastema (from metanephric mesoderm)234tyr

Question 24

What is the name of the septum that divides cloaca into two parts? What does this parts becomme?

Answer 24

Urorectal septum

Dorsal part -> Anus and rectum
Ventral part -> Urogenital sinus -> urinary bladder + lower urogenital tract

Urorectal septum forms the peroneal body

Question 25

What does the paramesonephric duct give in female?

Answer 25

Fallopian tube, uterine tube and upper 1/3 of the vagina

Urogenital sinus gives the lower 2/3 of the vagina + the bulbourethral glands

aka, mullarian duct

Question 26

What is the gene that is important in the development of male sexual organs?

Answer 26

SRY gene, found on the Y chromosome

Question 27

What is the important hormones in the development of internal and external male sexual organs

Answer 27

Internal: Testosterone
External: DHT

Question 28

Stages in the development of the gonads

Answer 28

1: Primordial germ cells from the yolk sac migrate to the genital ridge/gonadal ridge
2: Epithelium of the genital ridge proliferate and cells penetrate the underlying mesenchyme -> Primary sex cords
3 Some primordial germ cells become sorrounded by cells of the primary sex cords

In male:

1: Testes cords forms (after the stimulation of testis-determining factor protein, which helps to develop and nourish the Sertoli cells.
2: The cords of the central mass run together toward the future hilum and form a network which ultimately becomes the rete testis. On the other hand, the seminiferous tubules are developed from the cords distal to the hilum, and between them connective-tissue septa extend. Via the rete testis, the seminiferous tubules become connected with outgrowths from the mesonephros, which form the efferent ducts of the testis.
3: A thick fibrous CT, the tunica albuginea, sepatates the testis cords from the surface epithelium
4: Sertoli cells derive from the surface ectoderm of the gland. Leydig cells derive from orginal mesenchyme of the gonadal ridge, lie between the testis cords
5: Wolfian duct/mesonephric duct meet the testies and froms ductus efferentis testies, epididymis, vas deferens, and seminal vesicle.

Female:

1: Primary sex cords -> irregular cell clusters
2: Medullary cells disappears and are replaced with vascular stroma -> Ovarian medulla
3: Surface epithelium profilirate and form cortical cords
4: These cells form isolated cell clusters surrounding eachh oogonium -> Folilicular cells (primordial follicle)
5: Medullary cords regress

Question 29

Extraembryonic mesoderm comes from?

Answer 29

Hypoblast -> Embryonic umbilical vesicle

Some from epiblast (?)

Question 30

Dura mater and leptomeninx orign from?

Answer 30

Dura from mesenchyme

Leptomeninx from neural crest

Question 31

Viteline arteries gives rise to?

Answer 31

Celiac artery, SMA

Question 32

What it he special name for ductus arteriosus, where is it located and what does it becomme?

Answer 32

Botalli`s duct, is a blood vessel connecting the pulmonary artery to the proximal descending aorta. It allows most of the blood from the right ventricle to bypass the fetus’s fluid-filled non-functioning lungs. Upon closure at birth, it becomes the ligamentum arteriosum. There are two other fetal shunts, the ductus venosus and the foramen ovale.

Question 33

What happens when the dorsal mesocardium regress?

Answer 33

It forms the transverse sinus of the heart

Question 34

Valve of foramen ovale is formed by?

Answer 34

Septum primum

Question 35

Inferior mesenteric artery is derived from?

Answer 35

Umbilical artery

Question 36

What forms the inferior vena cava?

Answer 36

Right sacrocardial vein + renal segment of IVC (right subcardial vein) + hepatic segment of IVC (from portal system + left umbilical vein)

Question 37

Lungs, trachea and larynx orign from?

Answer 37

Endoderm

Cartilage, muscle and connective tissue from splanchnic layer of lateral plate mesoderm

Question 38

What are the sequens of events from just the endodermal lyning to the formation of a lung bud

(Extra events are mentioned)

Answer 38

1: Respiratory diverticulum (between the 3rd and 4th arch)
2: Trachoesophageal ridge:
3: When this ridge fuse to form the tracheoesophageal septum -> Esophagus and tracha with a lungbud is made
4: Lung buds -> Bronchial buds

The respiratory primordia connects to the pharynx via the laryngeal orifice

5: As the lung grow caudaly it fills the space of the pericardoperitoneal canal.
6: Later, the pericardoperitoneal canal divides into a peritoneal and pericardial cavity and form the primitive pleural cavity
7: The mesoderm that surrounds the lung becomes the viceral layer while the parietal layer if formed by the somatic layer of lateral plate mesoderm. In between lies the pleural cavity
8: The lung divide in a dichotomus fashion (10 lobes on the right side and ?? on the left side) - bronchiopulmonary segments.
9: Maturation of lung alveoli is not compleate before post-natal life

The featus is not able to breath before the 7th month

Question 39

Cartilage and muscle for the larynx come from?

Answer 39

4th and 6th arch

Question 40

What are the names of the two foldings of the embryo?

Answer 40

Lateral and cephalocaudal folding