Embryology Flashcards
Embryology definition
It is the science that deals with the study of the intra-uterine development of the human body till birth
Embryo
From 2nd to 8th week
Foetus
From 9th week to 9th month
Teratology definition
It is the science that deals with the study of abnormal foetal development causing congenintal malformations.
Gametogenesis in males and females
Males —> Spermatogenesis
females —> oogenesis
Purpose of gametogenesis
To reduce number of chromosomes from a diploid number to a haploid number
To alter the shape of the germ cell to make it more specialized to its function
Spermatogenesis site, conditions, onset, end, period and hormonal control
It is the process of formation of sperms Seminiferous tubules which are the structural unit of the testis Lower than normal body temperature (35) Starts at age of puberty and doen't end takes about 64 days Controlled by FSH
Stages of spermatogenesis
Spermatogonia to primary spermatocyte (by mititic division)
Primary spermatocyte to secondary spermtocyte (by first meiotic division)
Secondary spermtocyte to spermatids (by second meiotic division)(mitotic)
spermatids to sperms through differentiation and maturation
Abnormalities of the sperms
Abnormalities in shape
Abnormality in motility
Abnormality in sperm count ::: Oligospermia (<20 million/ml)
Necrospermia (dead sperms)
Azospermia (0 sperms)
Enumerate length & parts of mature sperm
Sperm is about 50u and consists of head, neck, middle piece and tail
Mention characters of seminal fluid
Geryish, offensive, alkaline watery medium.
Rich in vitamin C and fructose
About 2-4 ml per time
Enumerate source of seminal fluid & its hormonal control
Contains spermatozoa and secretions from the prostate, seminal vesicles and bulbo-urethral glands.
Stimulated by LH
Define fertilization & mention its site
It is the process of invasion and fusion of the mature sperm with the fully formed ovum to produce a zygote
It occurs in the wide lateral 1/3 of the uterine tube (ampulla)
Enumerate mechanism of transport of sperms
The spermatozoa pass rapidly from the vagina into the uterus
Undulating movement of their tails acting as propellers
Contraction of the muscles of the uterus and tube producing suckling action
Enumerate mechanism of transport of ovum
The sweeping movement of the fimbriae of the uterine tube with carry the ovum in a stram of peritoneal fluid
Activity of the cilia of the uterine tube
Muscular contraction of the tubal wall
Define capacitation & its mechanism
Preperation of freshly ejaculated sperms to be aable to penetrate the ovum
MECHANISM
Removal of the surface coating glycoprotein coat derived from seminal fluid
Unmasking of the glycosyltransferase on the sperm cell membrane
Enumerate acrosomal contents and their function
The acrosome contains enzymes
Hyalurinidase: assists in penetration of corona radiata
Zonalysin and trypsin-like substances: needed for digestion of zona pellucida
Acrosin: attached to the inner surface of the acrosomal membrane and helps the sperm cross the zona pellucia
Oogenesis site, conditions, onset, end, period and hormonal control
It is the process of formation of mature ova
Coretx of the ovary
Normal body temperature
Starts during fetal life and continues after puberty
ends at menopause
Stimulating factor is FSH
Enumerate results of fertilization
Formation of zygote
Restoration of diploid number of chromosomes.
Determination of sex and heriditary characteristcs
Cleavage of zygote
Mention the significance of zona pellucida
Once a sperm penetrates, zonal reactions prevents further penetration of other sperms
Keeps dividing cells together during migration
Prevents adhesion to the uterine tube epithelium
Define cleavage & enumerate its stages by time
A series of repeated mitotic divisions resulting in an increase in number of cells after fertilization
2 cell stage —> 30 hours after fertilization
4 cell stage —> 40 hours after fertilization
8 cell stage —> 2-3 days after fertilization
16 cell stage —> 3-4 days after fertilization (called morula)
Mention the events occur in first week
Fertilisation
Cleavage
Implantation
Mention normal site of implantation
Upper part of the posterior wall of the uterus near the fundus in the median plane
Mention the abnormal sites of implantation
Inside the uterus
-Inside the cervix
-At internal os
-Lower down in the body of the uterus
-Placenta previa lateralis
-Placenta previa marginalis
- Placenta previa centralis
Outside the uterus (Ectopic pregnancy)
-Abdominal pregnancy
-Tubal pregnancy
-Ovarian pregnancyMention the events occur in second week of fertilization
2 embryonic layers: Epiblast and hypoblast
2 cavities: Amniotic cavity and yolk sac
2 trophoblast layers: Cytotrophoblast and syncytiotrophoblast
2 zones of extra-embryonic mesoderm: Visceral and parietal mesoderms seperated by extraembryonic coelom (later called the chorionic cavity)
Mention events occur in 11th & 12th days
The balstocyst is now completely embeded in the endometrium. the endometrium is now called the decidua.
The syncytiotrophoblast erodes the decidua and communication between maternal blood sinusoids and lacunae starts the utero-placental circulation
Primamry mesoderm is formed and divided into 2 visceral and parietal mesoderms
Mention the origin of extra embryonic mesoderm and its division
Extra-embryonic mesoderm is derived from the hypoblast
It is divided into visceral mesoderm and parietal mesoderm seperated by the chorionic cavity
Define gastrulation and mention its time
The transformation of the bilaminar embryonic disc to a trilaminar embryonic disc
From the 14th to the 19th
Define primitive streak and mention its function, fate & anomalies.
By the 15th day, a thickened dark line appears caudally in the midline of the dorsum of the embryonic disc. It results from the rapid multiplication and migration of epiblast cells towards the centre.
Function: It actively forms the intra-embryonic mesoderm until about 4th week
Significance: determine the direction of the embryo and formation of notochord
Fate: After formation of the intra-embryonic mesoderm, it dimishes to become an insignificant structure in the sacrococcygeal region.
Anomalies: If it doesn’t disappear, it gives rise to teratoma
Mention the function and fate of notochord
The notochord is the structure around which the vertebral column forms.
It degenerates when the verterbral bodies are formed but remains as the nucleus pulposus
It acts as the primary inducer for the formtion of the neural plate
may give rise to a tumor called chordoma
Define neurulation, its onset & its functions
Onset: 19th day
Overgrowth of the ectodrem cells abovethe notochord results in formation of neural plate
The neural plate edges are raised and forms the neural folds and the neural groove.
The 2 edges fuse together and forms the neural tube and at the site of the union 2 neural crests are formed
functions: The cranial part of the tube forms the brain and the caudal part forms the spinal cord.
Mention 4 derivatives of neural crest
Melanocytes Cells of suprarenal medulla Autonomic ganglion cells Dorsal root ganglion cells Cranial sensory ganglion cells Neurolemmal cells
Enumerate number of somites and its differentiation
The total number of somites is 42-44 pairs.
Each somite is defferentiated:
-Ventromedial(Sclerotome) which forms the axial skeleton
-Dorsolateral (Dermomyotome) which is differntiated furthur to
-Myotome that forms the striated skeletal muscles
- Dermatome which forms the dermis of the skin
Mention the divisions of lateral plate mesoderm and their derivatives
The lateral plate is divided into:
- Intra-embryonic somatic mesoderm that forms the muscles of the thoracic and abdominal walls
- Intra-embryonic splanchnic mesoderm forms the smooth muscles of the thoracic and abdominal viscera
- The intera-embryonic coelum develops the body cavities:
- Pleural cavity
- Pericardium
- Peritoneum
Enumerate 4 derivatives of the ectoderm
The centra nervous system
The peripheral nervous system
The sensory epithelia of the nose, ear and eyes
The epidermis of the skin including the hai and nails
Pituitary gland
The subcutaneous and sweat glands
Enumerate 4 derivatives of the endoderm
Initially, epithelial linning of primitive gut
Epithelial linning of respiratory tract
Epithelial linning of urinary bladder and urethera
Epithelial linning of tympanic cavity and auditory tube
The parenchyma of the thyroid, parathyroid, liver and pancreas
The reticular stroma of tonsils and the thymus
Enumerate 4 derivatives of the mesoderm
Paraxial mesoderm forms the skeletal muscles, the axial skeleton and the dermis of the skin
The intermediate mesoderm forms the urogenital system (kidney, ureter), adrenal cortex, gonads, Vagina, uterus and uterine tubes
Mention directions of folding & their causes
Cephalo-caudal direction: caused by rapid growth of neural tube
Lateral direction: Caused by rapid growth of somites
Enumerate results of folding
Formation of head bulge
Formation of primitive mouth (stomodium) which is a depression between the head bulge and the thoracic bulge
Formation of the thoracic bulge (pericardial bulge)
Formation of gut tube (future GIT) and definitive yolk sac
Formation of the vitello-intestinal duct
Expansion of the amniotic cavity.
Formation of the cloaca
Mention sources of amniotic fluid
- In early stages: from the amnioblasts
- later: when the kidney develops, urine is added to the amnion
- Some may be formed as a transudation from the placenta
Enumerate functions of amniotic fluid
Permits symmetrical external growth of the embryo
Prevents adherence of the amnion to the embryo
Cushions the embryo against injuries
Halps to maintain an even temperature around the fetus
Enables the fetus to move freely
Aids in musoskeletal development
Helps to dilate the cervix during labour and sterilize the vagina
Mention anomalies of amniotic fluid
If the amnion doesn’t ruptue, the fetus is born inside the amniotic sac
Premature rupture of the amniotic membrane
Oligo-hydramnios: The amount of fluid is less than 400cc. Caused by renal agenesis or obstruction of the urethra
Poly-hydramnios: The amount of fluid exceeds 1.5-2 liters. Can be caused by
-In multiple pregnancies
-Idiopathic (35%)
-Maternal diabeties (25%)
-Anencephaly
-Esophageal atresia
Mention functions of yolk sac
Nutrition of blastula at early stage of development (2-3 week)
Formation of blood cells at early stage of development (3-6 week)
Shares in formation of gut at 4th week
Shares in formation of intestinal mucosa from the roof of yolk sac
Shares in the formation of gonads by the primordial germ cells that appears at the 3rd week
Define allantois and its fate
It is a finger like process arising from the secondary yolk sac to the connecting stalk
FATE:
During formation of urinary bladder, it changes to form a blind tube called the urachus that connects the urinary bladder to the umblicus
After birth, it changes to form a fibrous band called median umblical ligament that suspends the urinary bladder to the umblicus
Mention abnormalities of allantois
Urachal fistula
Urachal sinus
Urachal cyst
Enumerate contents of umbilical cord
2 Umblical arteries 1 Umblical vein Vitello-intestinal duct Definitive yolk sac Allamtois in its proximal part Intestinal loop between 6 weeks to 3 months (physiological hernia)
Mention anomalies of umbilical cord
Anomalies in its length Anomalies of shape (knots) Anomalies in number Anomalies in the site (Physiological umblical hernia) Anomalies in attatchement to the placenta -Normal in the centre -To the edge : battledore placenta -To the membrane: placenta velamentosa
Define connecting stalk and its fate
Define decidua and mention its parts
Decidua is the endometrium after the implantation of the blastula Its parts: -Decidua basalis -Desidua capsularis -Desidua parietalis
Define chorion and enumerate types (degrees) of chorionic villi
The chorion is the wall of the chorionic vesicle
it is formed of 3 layers, the syncytiotrophoblast, the cytotrophoblast and the extra-embryonic mesoderm
The chorionic vili start as primary vili the secondary vili then teritiary vili
Compare between placenta barrier before and after the 4th month
Before 4 months:
- Syncytiotrophoblast
- Cytotrophoblast
- Extra-embryonic somatic mesoderm
- Endothelium lining of capilaries
After 4 months:
- Syncytiotrophoblast
- Endothelium of capilaries
Enumerate function of placenta
Nutrition Respiration Hormone production Barrier Transmission of maternal antibodies
Mention anomalies of placenta
Anomalies in position:
-Placenta previa lateralis
-Placenta previa marginalis
- Placenta previa centralis
Anomalies in attatchment to the umblical cord
Anomalies in number
-Placenta succenturiate
-Placenta dipatita
-Placenta tripatita
-Placenta fenestrata
-Placenta membranaceaMention 4 types of equal conjoined twins
Craniopagus Thoracopagus Pyopagus Cranio-thoracopagus Union of trunk Rump-to-rump
Define unequal conjoined twins
One of the twins is large, called the host
The other twin is small, called the parasite
Superfoetation definition
Implantation of an extra blastocyst in a pregnant uterus
Superfecundation definition
Fertilization of more than one ovum by sperms from different males
