Embryology
What is the Meckel's diverticulum, describe its location and developmental origin?
• The outpocketing of the ileum located about 40-60 cm from the ileocecal valve on the antimesenteric border of the ileum. One of the possible remnants of the vitelline duct.
What is the neural plate? What is meant by neural induction?
• Thickening of the ectoderm, primordium of the nervous system. The notochord has an inductive influence on the ectoderm, resulting in the formation of the neural plate.
Which veins can be first distinguished in the embryo?
• Three pairs of major veins: vitelline or omphalomesenteric veins, umbilical veins, cardinal veins.
Which organs develop from the cloaca?
• Urinary bladder except the trigone, urethra, prostate, lower part of vagina, rectum, upper part of the anal canal
Which parts of the pancreas develop from the ventral and from the dorsal pancreatic bud? How the duct system is formed?
• Ventral: uncinate process and the inf. part of the head of the pancreas. • Dorsal: the remaining parts of the gland. • Main pancreatic duct is formed by the distal part of the dorsal pancreatic bud and the entire ventral pancreatic bud. The accessory duct develops from the proximal part of the dorsal pancreatic bud.
Which veins open into the sinus venosus?
• Vitelline or omphalomesenteric vein, umbilical vein, common cardinal vein: at both sides.
Which of the aortic arches persist and what do they give rise to?
1. 3rd: • common carotid artery and the first part of the int. carotid artery. 2. 4th: • left: part of the arch of the aorta • right: prox. segment of right subclavian artery 3. 6th: • right: prox. segment of the right pulmonary artery • left: ductus arteriosus, prox. segment of left pulmonary artery.
Make a schematic drawing of the early blastocyst and label its major parts!
1. Blastocyst cavity 2. Outer cell mass or trophoblast 3. Inner cell mass or embryoblast
Describe the parts of the full term placenta!
1. Fetal portion: chorionic plate, chorion villi. 2. Maternal portion: decidua basalis.
Draw the superior aspect of the calvaria of newborn, and label the fontanels, sutures and the bones!
1. Frontal bone 2. Occipital bone 3. Parietal bone 4. Anterior (or frontal) fontanel 5. Posterior (or occipital) fontanel 6. Coronal suture 7. Sagittal suture 8. Lambdoid suture
Name the phases of fertilisation and describe the reactions of the fertilised oocyte.
1. Penetration of the corona radiata 2. Penetration of zona pellucida 3. Fusion of oocyte - sperm cell membranes 4. The spermatozoon (except for the cell membrane) enters the cytoplasm of the oocyte. • Reactions of the egg: cortical and zonal reaction; resumption of the second meiotic division; metabolic activation of the egg.
Make a simple drawing to demonstrate the primitive gut in a 4-week-old embryo! Label parts!
1. Pharyngeal gut, 2. tracheobronchial diverticulum, 3. esophagus, 4. stomach, 5. pancreas, 6. liver, 7. gallbladder, 8. vitelline duct, 9. allantois, 10. cloaca, 11. primitive intestinal loop, 12. hindgut, 13. cloacal and 14. buccopharyngeal membrane.
Make a schematic drawing illustrating the dorsal view of a 16-day old embryo! Label parts!
1. Prochordal plate 2. Notochordal process 3. Primitive streak 4. Primitive node 5. Future cloacal membrane 6. Ectoderm
Define the term of cotyledon!
• The compartments of the placenta, partially separated by the decidual septa, each cotyledon consists of one or more stem villi surrounded by maternal blood.
What is the fate of matured ovarian follicle?
1. Release of the oocyte by rupture of the follicle: ovulation 2. The collapsed wall of the follicle surrounds a central clot of retained blood and follicular fluid. This is the corpus hemorrhagicum. From the granulosa cells the granulosa luteal, and from the theca interna cells the theca luteal cells develop respectively. 3. In case of pregnancy, the corpus luteum further develops and forms the persisting corpus luteum, otherwise it degenerates and becomes the corpus albicans. 4. Matured, but undischarged follicles undergo degeneration resulting in atretic follicles.
List the components of the extraembryonic mesoderm.
1. Somatopleuric mesoderm 2. Splanchnopleuric mesoderm 3. Connecting stalk 4. Chorionic mesoderm
Name those parts of the drawing, which are indicated by arrow.
1. Syncytiotrophoblast with lacunae 2. Cytotrophoblast 3. Amnionic cavity 4. Epiblast (Ectoderm) 5. Hypoblast (Endoderm) 6. Exocoelomic cavity (primitive yolk sac) 7. Exocoelomic (Heuser's) membrane
List the functions of placenta !
1. Transport and exchange of gases, nutrients, waste products, 2. Transport of antibodies to fetus, 3. Endocrine function, 4. Mechanical protection, 5. Barrier for some germs and drugs.
Which is the first permanent tooth, and when does it appears ?
• The first molar, at the age of 6-7 years
Name the layers of the chorionic plate!
1. amnionic epithelium 2. central mesoderm 3. chorionic mesoderm 4. trophoblasts (syncytio-, and cyto-)
Make a schematic drawing illustrating the transverse section of the trilaminar germ disc at the cephalic part of an 18-day-old embryo! Label parts
1. mesoderm 2. notochord 3. ectoderm. 4. entoderm 1. yolk sac
Define the term genital ridges and describe their formation in the embryo!
• A pair of longitudinal ridges on the celomic epithelium at the medial aspect of the mesonephric ridges. Proliferation of the celomic epithelium and a condensation of the underlying mesenchyme form them.
From which germ disk does the blood, lens of eye, epithelium of kidney tubules, and thymus develops?
a) Blood - mesoderm b) Lens of eye - ectoderm c) Kidney tubules - mesoderm d) Thymus - endoderm
Explain the following malformations: a) patent ductus arteriosus and b) coarctation of aorta.
a) Ductus arteriosus: communication between the aorta and left pulmonary artery. It gets obliterated functionally shortly after birth, and morphologically during the 1-3 postembryonic months. If it is not closed: patent ductus arteriosus. b) the aortic lumen below the origin of the left subclavian artery is narrowed.
From which structures do a) the parenchyma and b) the stroma of the liver develop? What is the principal function of the liver in the fetus?
a) Epithelium of the distal end of the foregut derived from endoderm. b) Septum transversum. • Hemopoietic function, bile formation.
a.) From which sources does the kidney develop? List the structural elements of the kidney developing from them! b) From which structure does the ureter develop?
a) Metanephric mesoderm: nephron; Ureteric bud: collecting system. b) Ureteric bud.
List the most common types of twin formation and characterize the relationship of placentas and the fetal membranes of the twins!
a) Monozygotic or identical twins: i) with separate placenta, amnion and chorion. ii) common placenta and chorion, separate amnionic cavities. iii) common placenta, chorion and amnionic cavity. b) Dizygotic or fraternal twins: i) separate placenta, separate chorion, separate amnion. ii) separate placenta and amnion, fused chorion.
List and characterize the different developmental stages of the placental villi!
a) Primary villi : cyto- and syncytiotrophoblast cells b) Secondary villi: cyto- and syncytiotrophoblast cells + extraembryonic mesoderm in the centre of villi c) Early tertiary villi: blood vessels in the mesoderm layer + the layers of the secondary villi. d) Late tertiary villi: the cytotrophoblast partially disappears, and the syncytium and the endothelial wall of the blood vessels may be in direct contact. Villi form richly arborizing tree-like structure.
Characterize the pseudoglandular and the canalicular phases, and the terminal sac period in the development of the lung!
a) Pseudoglandular phase: (five to 17 weeks) the developing lung resembles an exocrine gland up to the 7th prenatal month. b) Canalicular phase: the bronchioli continuously divide into more and smaller canals and the vascular supply increases steadily. c) Terminal sac period: (from the beginning of the 7th prenatal month) cuboidal lining of bronchioli changes into thin flat cells: the alveolar epithelial cells, which are intimately associated with blood capillaries.
From which germ disk does the bone, hypophysis, chief cells of the parathyroid glands and the thyroid glands develop?
a) bone - mesoderm b) hypophysis - ectoderm c) chief cells of the parathyroid gland - placod plate d) thyroid gland - endoderm
How does the truncus arteriosus divide into aorta and pulmonary trunk?
• A pair of opposing ridges appears in the cephalic part of the truncus arteriosus. After complete fusion, the ridges form a septum: the aorticopulmonary septum, dividing the truncus into an aortic and pulmonary channel.
What are the fetal membranes?
• Amnion, chorion, decidua parietalis and capsularis
Define the word "proctodeum"!
• An external depression opposite to the anal membrane formed by the mesenchymal swellings.
Define the term "dorsal mesentery" and describe its extension!
• A double layer of peritoneum that encloses the gastrointestinal tract. It extends from the lower end of the esophagus to the cloacal region of the hindgut and connects the gastrointestinal tract to the posterior abdominal wall.
What is the respiratory distress syndrome?
• An insufficient amount of surfactant is secreted. As a result of this malfunction the surface tension of air-water interface increases, so the risk that the alveoli which collapse during expiration will not open in inspiration also increases. In case of alveolar collapse the lung is not capable of gas exchange.
Define the fontanels of the newborn skull! Describe their positions related to the bones of the skull!
• Anterior, posterior, anterolateral or sphenoid, posterolateral or mastoid fontanels. 1. Anterior: where the two parietal and frontal bones meet. 2. Posterior: where the occipital and two parietal bones meet. 3. Anterolateral: where the parietal, frontal, temporal and sphenoid bones meet 4. Posterolateral: where the occipital, parietal, temporal bones meet.
Define the approximate date of ovulation and describe the hormonal background!
• Around midcycle (14 days) under the influence of FSH and LH, triggered by a surge of LH production.
When does the mesentery of the jejunoileal loops become separated from the mesocolon transversum?
• Around the 6th embryonic week, when the caudal limb of ansa umbilicalis moves to the right side of the abdominal cavity and the dorsal mesentery twists (90° counter-clockwise) around the origin of the superior mesenteric artery.
What is meant by the "physiological umbilical herniation" which occurs during the 6th week of embryonic development?
• As a result of the rapid growth of the primary intestinal loop and the simultaneous expansion of the liver the abdominal cavity temporarily becomes too small to contain all the intestinal loops, so they enter the extraembryonic celom in the umbilical cord temporarily.
What is the notochord and the primitive pit? Indicate its place in a schematic drawing showing the midsagittal section of the 16-day-old embryo!
• At the cephalic end of the primitive streak the primitive node develops. The primitive pit develops from the primitive node by cell-invagination. These cells migrate straightforward towards the cephalic end, and form a tube - like process: the notochordal or head process. The canal of the head process is the cranial extension of the primitive pit. The dorsal wall of the notochordal process proliferates and forms the definitive notochord. 1. amnionic cavity 2. ectoderm (epiblast) 3. primitive pit 4. prochordal plate 5. notochordal process 6. primitive streak 7. allantois 8. yolk sac
Define the term "aortic arches" in the embryo?
• Branches of the rostral extensions of the truncus arteriosus referred to as ascending aorta located in each branchial arch.
Name the parts of the heart tube which can be identified after the formation of cardiac tube!
• Bulbus cordis, ventricle, atrium, sinus venosus.
What is meant by cleavage and blastocyst formation?
• Cleavage: Formation of morula and then the blastocyst by mitotic divisions of fertilized ovum. • Blastocyst formation: fluid begins to penetrate into the intercellular spaces of the inner cell mass. The spaces become confluent and a single cavity, the blastocele is formed: the blastocyst.
What are the main changes that occur at the vascular system at birth?
• Closure of the umbilical arteries and vein • Closure of ductus venosus. • Closure of the ductus arteriosus. • Closure of the oval foramen.
What is the ductus venosus and what role does it play in the embryonic circulation?
• Communication between the former left umbilical vein and right hepatocardiac channel. The ductus venosus bypasses the sinusoidal plexus of the liver.
What is the difference in the composition of the primitive and matured umbilical cord?
• Contents of primitive cord: the connecting stalk that contains allantois, umbilical vessels consisting of two arteries and two veins, yolk sac stalk accompanied by the vitelline vessels. • Contents of the matured cord: two umbilical arteries, one umbilical vein, Wharton's jelly.
What is the difference between syncytiotro-phoblast and cytotrophoblast?
• Cytotrophoblast: mononucleated cells that form the inner layer of trophoblast (Langhans cell layer). • Syncytiotrophoblast: outer multinucleated zone of trophoblast without distinct cell boundaries.
Define the term of decidua! Name its parts in relation to the implanted embryo!
• Decidua: Functional layer of the gravid endometrium. 1. Decidua basalis: between the chorion frondosum and myometrium. Primordium of placenta materna. 2. Decidua capsularis: over the abembryonic pole. 3. Decidua parietalis: rest of the decidua, except the basalis and capsularis.
What is meant by the "ovarian cycle"?
• Development of follicles, ovulation, formation and subsequent regression of corpus luteum.
Name and characterize the most common malformation of the thoracic diaphragm! Describe also the mechanism of malformations!
• Diaphragmatic hernia: caused by failure of the pleuroperitoneal membrane(s) to close the pleuroperitoneal canal(s). The peritoneal and pleural cavities are continuous with each other along the posterior body wall. • Parasternal hernia: a small muscular part of the anterior portion of the diaphragm fails to develop. • Esophpageal hernia: is due to a congenital shortness of the esophagus.
What are the derivatives of the hindgut?
• Distal third of the transverse colon, descending colon, sigmoid, rectum, upper part of the anal canal, urinary bladder, urethra, lower part of vagina, prostate.
List the major parts of the dorsal mesentery!
• Dorsal mesogastrium, dorsal mesoduodenum, mesentery proper, dorsal mesocolon.
Which malformation of the heart is called "probe patency"?
• Due to the incomplete fusion of the septum primum and septum secundum a narrow oblique cleft remains between the two atria
List the separating layers between fetal and maternal blood in the early and the matured placenta!
• Early: syncytiotrophoblast, cytotrophoblast, trophoblast basement membrane, connective tissue, capillary basement membrane, endothelium • Late: syncytiotrophoblast, trophoblast basement membrane, capillary basement membrane, and endothelium. Some connective tissue may be present between the two basement membranes.
Describe the processes that make the spermatozoa capable of fertilising the oocyte!
• Epididymal maturation: changes in metabolism, acquiring the capability for movement. • Capacitation: a glycoprotein coat and seminal plasma proteins are removed from the plasma membrane that overlies the acrosomal region of the spermatozoa. • Acrosomal reaction: Release of enzymes from the acrosome: a) hyaluronidase; b) proteolitic enzymes.
Which parts of the mesonephros persist in the adult? List their derivatives in male and female!
• Excretory tubules of mesonephros and mesonephric duct (Wolffian duct). • In male: ductuli efferentes testis, ductus epididymidis, ductus deferens, seminal vesicle, and ejaculatory duct. In female: epoophoron, paroophoron. In both sexes: trigone of urinary bladder, ureteric bud (Kupffer's duct).
What is the difference between the extraembryonic and intraembryonic mesoderm? Where do they originate from?
• Extraembryonic mesoderm: derives from the trophoblast and form a fine, loose connective tissue, which is located outside the embryo. • Intraembryonic mesoderm: the third germ layer between the epiblast and hypoblast layers. Origin: epiblast.
How do the shape and position of the stomach primordium change during development?
• First it runs in the long axis of the embryo, as a fusiform dilatation of the foregut. • Later it rotates clockwise causing its left side to face anteriorly, and its right side posteriorly. • During the rotation, the original posterior wall of the stomach grows faster than the ant. portion and this results in the formation of the lesser and greater curvatures. • The cephalic and caudal ends of the stomach are originally located in the midline, but during further growth the caudal part moves to the right and upward and the cephalic portion to the left and slightly downward.
What is meant by the a) cephalo-caudal and b) lateral foldings of the embryo?
• Folding of a flat trilaminar embryonic disc into a somewhat cylindrical embryo. a) Cephalo-caudal fold: Cranially, the developing forebrain grows beyond the buccopharyngeal membrane and overhangs the developing heart. Caudally the tail region projects over the cloacal membrane. b) Lateral/transverse folds: Each lateral body wall folds towards the median plane in a ventral direction.
From which structure does the corpus luteum develop, and what does it secrete ?
• From corpus hemorrhagicum, by proliferation of theca interna, and granulosa sells. • Progesteron and oesrtogen
From which structures do the semilunar valves develop?
• From swelling of the mesenchyme of the pulmonary and aortic channels: 1. Right truncus swelling (right bulbar ridge) 2. Left truncus swelling (left bulbus ridge) 3. Minor truncus swellings (2) or dorsal and ventral swellings.
What are the derivatives of the dorsal mesogastrium?
• Gastrophrenic ligament, gastrolienal ligament, phrenicolienal ligament, lienorenal ligament, greater omentum.
Describe the malformation called "spina bifida"!
• Imperfect fusion or nonunion of the vertebral arches.
What is the location of the cardiogenic area in the presomite embryo?
• In the splanchnic mesoderm in front of the neural plate on both sides of the embryo.
Which parts of the intestinal canal develop from the primary intestinal loop and which artery supplies them?
• Jejunum, ileum, cecum, appendix, ascending colon, proximal two-thirds of the transverse colon, Meckel's diverticulum. • Superior mesenteric artery.
Which structures separate the pericardial and pleural cavities from each other?
• Left and right pleuropericardial folds
What are the derivatives of the left and right horn of the sinus venosus?
• Left: oblique vein of the left atrium and coronary sinus. • Right: smooth - walled part of the right atrium.
What are the derivatives of the ventral mesentery?
• Lesser omentum, falciform ligament.
What are the derivatives of the septum spurium of the embryonic heart?
• Limbus of fossa ovalis. Valve of coronary sinus, valve of inferior vena cava.
What are the derivatives of the midgut?
• Lower part of duodenum, jejunum, ileum, cecum, vermiform appendix, ascending colon, prox. 2/3 of transverse colon.
Which bones develop from the viscerocranium?
• Maxilla, mandible, zygomatic bone, squamous and tympanic parts of temporal bone, styloid process of temporal bone, nasal bone, lacrimal bone, vomer, hyoid bone, inf. concha, medial plate of the pterygoid process of the sphenoid bone, palatine bone.
Which septa are formed in the ventricles and truncus arteriosus?
• Muscular interventricular septum. • Membranous interventricular septum • Aorticopulmonary septum.
What is the developmental abnormality that leads to the malformation called "congenital cystic kidney"?
• The collecting and excretory tubules fail to join. Accumulation of urine in the convoluted tubules results in the cyst formation.
Where is the preferred site of implantation? List few abnormal implantation sites!
• Normal: Along the posterior. and anterior. wall of the body of the uterus, between the openings of the glands. • Abnormal: close to the internal os of the uterus; outside the uterus (extrauterine or ectopic pregnancy): any place of the abdominal cavity, ovary, uterine tube.
Which bones develop from the chondrocranium?
• Occipital bone (except the upper portion of squamous part), petrous and mastoid parts of temporal bone, sphenoid bone (except the medial plate of the pterygoid process), ethmoid bone.
What are the derivatives of the paraxial, intermediate and the lateral plate of mesoderm?
• Paraxial mesoderm: breaks up into blocks of somites, and somitomers at the cephalic region. The somites differentiate into sclerotom, dermatome, myotome. • Intermediate: in the cervical and upper thoracic region it gives rise to the nephrotomes. Caudally the nephrogenic cord develops from it. • Lateral plate: somatic or parietal mesoderm layer, splanchnic or visceral mesoderm layer, intraembryonic celomic cavity.
What is the connecting stalk and how does it develop further?
• Part of the extraembryonic mesoderm containing the allantois, vitelline duct, as well as the umbilical and vitelline vessels. • Later the amnion envelops the connecting stalk and the yolk sac stalk with their vessels, forming the primitive umbilical cord.
Into which parts can the intraembryonic celomic cavity be divided in the 4th embryonic week?
• Pericardial cavity, pleuroperitoneal canal, peritoneal cavity.
What are the derivatives of the foregut?
• Pharyngeal gut, tracheobronchial diverticulum, esophagus, stomach, upper part of duodenum, gall bladder, pancreas, liver.
What is the "placode" and what are its derivatives?
• Placode: thickenings of the surface ectoderm at the head region of the embryo. a) Hypophyseal placode (I): Rathke's pouch. (adenohypophysis) b) Nasal placode (2): olfactory epithelium. c) Lens placode (2): lens of eye d) Trigeminal placode (2): semilunar ggl. e) Acoustic placode (2): sensory epithelium of vestibular and cochlear receptors, ganglions. f) Epibranchial placode (2): sensory epithelium of taste buds. g) Branchial: placode (2): sensory ganglia of VIIth, IXth, Xth cranial nerves.
Name the stages of development of the ovarian follicle in sequence! Make a drawing of the Graafian follicle, and label the major parts!
• Primordial, primary, secondary (growing), tertiary or vesicular follicle. 1. Theca externa 2. Theca interna 3. Follicular antrum with fluid 4. Cumulus oophorus 5. Corona radiata 6. Membrana granulosa 7. Oocyte 8. Zona pellucida
List the hormones that are produced by the placenta!
• Progesteron, estrogenic hormones, human chorionic gonadotropins (hCG),human chorionic somatotropin (hCS), human chorionic thyreotropin (hCT), relaxin, human chorionic adreno-corticotropin (hCACTH).
Which kidney systems are formed during the intrauterine life in the human?
• Pronephros, mesonephros, metanephros.
What do the rotation and the retraction of the herniated intestinal loops during development mean?
• Rotation: Parallel with the growth in length, the primary intestinal loop rotates around an axis formed by the superior mesenteric artery. This rotation occurs in counterclockwise direction. • Retraction : At the end of the 3rd month, the herniated intestinal loops begin to return to the abdominal cavity due to expansion (growth) of abdominal cavity.
What is the role of syncytiotrophoblast during implantation?
• Secretion of proteolytic enzymes which erode the endometrial epithelium and the stroma of the endometrium, so that the blastula can penetrate, and get implanted in the endometrium.
Name the septa and their openings, which separate the common atrium during the development of the heart.
• Septum primum: ostium primum and ostium secundum. • Septum secundum: oval foramen.
From which structures does the diaphragm develop?
• Septum transversum, pleuroperitoneal membranes, dorsal mesentery of esophagus, muscular component of the lateral and dorsal body wall.
Describe the sequence of oogenesis.
• Sequence: 1. oogonium, 2. profase of 1st meiotic division: primary oocyte, 3. completion of 1st meiotic division: secondary oocyte and first polar body 4. completion of the second meiotic division: second polar body and definitive oocyte, 5. third and fourth polar bodies.
Define the term "spermiogenesis". Describe the spermatogenesis in sequence. Draw a mature spermium and label parts!
• Spermiogenesis: formation of spermatozoa from spermatid. • sequence of spermatogenesis: spermatogonium, primary spermatocyte, secondary spermatocyte, spermatid. 1. Head 2. Neck 3. Middle piece 4. Principal piece 5. End piece
How does the endometrium change during the menstrual cycle?
• Stages of the menstrual cycle: 1. Menstrual phase: rupture of blood vessels and detachment of the functional layer of the endometrium. 2. Regeneration phase: regeneration of the functional layer 3. Proliferative phase (follicular or estrogenic stage): gradual growth of the endometrium. 4. Secretory (luteal ) phase: development of the compact and spongy layers in the functional layer. Secretory activity of glands, decidual reaction of stroma cells, formation of coiled arteries within the endometrium, edema in the stroma. 5. Regression: temporary contraction of coiled arteries resulting in ischaemia of the endometrium. Consecutive dilatation of vessels followed by hyperemia of the endometrium.
From which branchial arches does the larynx develop?
• The cartilages and muscles of the larynx develop from the mesenchyme of the 4th, 5th and 6th pharyngeal arches.
What is meant by the rearrangement of the sclerotomes in development of the vertebral column?
• The caudal half of each cranial sclerotom proliferates, proceeds into the subjacent tissue and joins the cephalic part of the subjacent sclerotom. The fused halves of the adjacent sclerotomes with the incorporated intervertebral tissue form the cartilaginous vertebral body that becomes intersegmental in origin.
How does the trigone of the urinary bladder develop?
• The caudal portion of the mesonephric ducts gradually becomes incorporated into the wall of the urinary bladder. Later the mesodermal lining of the trigone is replaced by endodermal epithelium.
From which veins does the portal vein develop and how?
• Vitelline veins. • Before entering the sinus venosus, the vitelline veins form a plexus around the duodenum and pass through the septum transversum. The liver cords growing into the septum interrupt the course of the veins and an extensive vascular network of hepatic sinusoid is formed. The anastomoting network around the duodenum develops into a single vessel: portal vein.
When, where and in which form does the primordium of the respiratory system appear first?
• When the embryo is approximately 4-week-old the primordium of the respiratory system appears first as a groove on the ventral wall of the foregut (Laryngotracheal groove).
Which cells of spermatogenesis are isolated from the blood-born antigens by the blood-testis barrier?
• late primary spermatocytes • Secondary spermatocytes • Spermatids • Sperm cells (spermatozoa)
Which milk tooth erupts first and when ?
• the lower medial incisor, approximately at 6-7 months.
Describe the configuration of milk teeth of one quadrate of a child!
• two incisors, one canine, two molars
What are the names of the blood vessels of mature umbilical cord? Which of them transport oxigenated blood?
• two umbilical arteries, • one umblical vein. The vein transports oxigenated blood.
List signs of maturity of a newborn!
• weight : above 2500 gr, • nipples are protruding out from the skin, • nails extend beyond finger tips, • testes are in scrotum, • labia majora covers labia minora, • forehead-hair border evident.