Embryology Flashcards
What does the lung bud form from?
The respiratory diverticulum - an out pouching of the foregut
What are the five stages of respiratory tract development?
- Embryonic
- Pseudo-glandular
- Canicular
- Saccular
- Alveolar
What happens in the embryonic phase of respiratory tract development and when does it occur?
0-5 weeks
Lungs and trachea develop
What happens in the pseudo-glandular phase of respiratory tract development and when does it occur?
5-16 weeks
Branching of the trachea
What happens in the canicular phase of respiratory tract development and when does it occur?
16-26 weeks
Respiratory bronchioles form
What happens in the saccular phase of respiratory tract development and when does it occur?
26w - birth
Terminal sacs form
What happens in the alveolar phase of respiratory tract development and when does it occur?
8m-childhood
Alveoli mature
Describe the first breath.
Fluid removed from the lungs
Adrenaline - increases surfactant release
Air inhaled
O2 vasodilates the pulmonary vessels
Umbilical arteries and ductus arteriousus constricts.. Foreamen ovale closes.
What separates the lung bud from the oesophagus in the embryo?
Transoesophageal septum
From what layer of the tri-laminar disc is the pleura derived from?
Mesoderm
From what layer of the tri-laminar disc is the respiratory tract derived from?
Endoderm
Do the lungs function in the embryo?
NO! They are of no use. Gas exchange occurs via the placenta.
What is the PaO2 equal to in the foetus?
3.2 KPa (equivalent to 31,000 feet)
In what direction does blood shunt in the foetus?
Right to Left: due to high vascular resistance in the lungs
meaning the pressure is higher in the right of the heart (supplies the lungs) than the left, thus blood will shunt through to the left via the foramen ovale
When is surfactant first produced?
At 34 weeks of gestation and production increased rapidly 2 weeks prior to birth.
Surfactant deficiency in premature babies can result in respiratory distress syndrome of the newborn. What are the implications of this?
Since low surfactant decreases lung compliance means that the baby can only inspire by the most strenuous of effort which may ultimately result in complete exhaustion, inability to breather, lung collapse and death
What does the ductus arteriosus do?
Shunts blood from aorta to left pulmonary artery
What does the ductus venosus do?
Shunts blood from umbilical vein to IVC
What does the foreamen ovale do?
Shunts oxygenated blood from RA to LA
Where does the foregut begin and end in the embryo?
Oropharyngeal membrane to the liver bud
Where does the midgut begin and end in the embryo?
Liver bud to 2/3 along TC
Where does the hindgut begin and end in the embryo?
Distal 1/3 of TC to cloacal membrane
Why are the foregut, midgut and hindgut divisions different in the adult compared to in the embryo?
It changes due to the formation of the ampulla of vater.
Are the pharyngeal clefts formed in the endoderm or ectoderm?
Ectoderm.
Are the pharyngeal pouches formed in the endoderm or ectoderm?
Endoderm.
How many pharyngeal arches are there?
5 (4 pharyngeal clefts and pouches).
What does the first pharyngeal arch form?
Muscles for mastication. Innervation: Cn 5.
What does the second pharyngeal arch form?
Muscles for facial expression. Innervation: Cn 7.
What does the third pharyngeal arch form?
Stylopharyngeus muscle. Innervation: Cn 9.
What does the fourth pharyngeal arch form?
Cricothyroid muscle. Innervation: External branch of superior laryngeal nerve (Cn 10).
What does the sixth pharyngeal arch form?
Intrinsic muscles of the Larynx. Innervation: Recurrent laryngeal nerve (Cn 10).
What are the 5 stages of midgut development?
- Elongation.
- Herniation.
- Rotation.
- Retraction.
- Fixation.
What connects the midgut to the yolk sac?
The Vitelline duct.
What happens in the elongation stage of midgut development?
Rapid elongation forms the primary intestinal loop. The proximal part of the loop forms the small intestine and the distal part forms the large intestine up to 2/3 TC.
What happens in the herniation stage of midgut development?
The rapid growth of the intestinal loop means it is pushed into the extra embryonic cavity in the umbilical cord.
What happens in the rotation stage of midgut development?
The elongated intestinal loop rotates 270 degrees anticlockwise.
What happens in the retraction stage of midgut development?
In the 10th week the herniated midgut returns into the expanded abdominal cavity. Th jejunum is first to return.
What happens in fixation of midgut organs?
This is when some regions of the gut lose their dorsal mesentery. These regions become retroperitoneal.
What does the dorsal mesentery become?
The greater omentum
What does the ventral mesentery become?
The lesser omentum
Most of the cardiovascular system is derived from cells situated in which germ cell layer?
Mesoderm
Through which two processes does the circulatory system develop?
Angiogenesis and vasculogenesis
On which day of embryogenesis does angiogenesis and vasculogenesis commence?
Day 18
Briefly describe foetal circulation
Maternal circulation - umbilical vein (oxygenated blood) - ductus venosus - IVC - RA - LA/RV - aorta - umbilical artery (deoxygenated blood) - maternal circulation.
What does the first heart field produce?
The left ventricle.
What does the second heart field produce?
The right ventricle, atria and outflow tracts.
What are the 3 stages of heart formation?
- Formation of primitive heart tube
- Cardiac looping
- Cardiac septation
Briefly describe the formation of the primitive heart tube
Day 19 = two endocardial tubes form which will fuse to form a single primitive heart tube
Day 22 = the heart is a single tube and it begins to beat
Describe what happens in cardiac looping.
Day 23 = heart tube begins to fold
Nodes secrete nodal, this circulates to the left due to ciliary movement. Nodal causes a cascade of transcription factors that transduce looping.
Day 28 = complete
What does the bulbus cordis form?
Right ventricle
What does the primitive ventricle form?
Left ventricle
What does the primitive atrium form?
Left atrium and anterior part of right atrium
What does the sinus venosus form?
Posterior part of the right atrium, coronary sinus and vena cava
What does the truncus arteriosus form?
Pulmonary trunk and aorta
What do the 1st and 2nd aortic arches form?
Minor vessels of the head and neck
What does the 3rd aortic arch form?
Common carotid arteries
What does the left and right 4th aortic arch form?
Left = Aortic arch Right = part of right subclavian artery
What does the left and right 5th aortic arch form?
There are no 5th arches!!!!!!
What does the left and right 6th aortic arch form?
Left: left pulmonary artery and ductus arteriosus
Right: right pulmonary artery
What does the 7th segmental aortic arch form?
L & R subclavian arteries
What does the left and right dorsal aortae form?
Left: descending thoracic aorta
Right: part of right subclavian artery
During embryonic life, what structure is responsible for the excretion of waste products?
The placenta
Give four functions of the placenta
- Gas exchange - carries oxygenated blood to the foetus
- Provides nutrition to growing foetus
- Endocrine and immune support
- Waste disposal
What is the structure of the umbilical cord?
2 umbilical arteries and 1 umbilical vein
What is the difference between the maternal and the foetal surfaces of the placenta?
Maternal - cobblestone appearance, villous tree structures = umbilical support
Foetal - smooth surface due to amniotic fluid
Describe oogenesis
- Oogonia undergo mitotic division in utero
- The oogonia develop into primary oocytes and begin mitotic division by replicating DNA
- They do not complete meiosis 1 in the foetus = mitotic arrest
- At puberty, there is renewed activity in the ovaries and oocytes destined for ovulation complete meiosis 1
- Meiosis 2 occurs if the secondary oocyte is fertilised, this will produce one ovum
What is a block to polyspermy?
A sperm has fertilised the egg the egg needs to prevent further sperm from fertilising it. It releases cortical granules that harden the zona pellucida and block sperm binding sites
What are the main stages of pre-implantation?
Syngamy - day 1 Cleavage - day 2-3 Compaction - day 4 Cavitation and expansion - day 5 Hatching - day 6-8 Implantation
Under what influence does male development take place?
Y chromosome = encodes SRY gene
Promotes testis determining factor
Genital ridge develops into testes
Leydig cells secrete testosterone
Mesonephric duct development
Sertoli cells secrete mullerian-inhibiting factor
Degeneration of the paramesonephric ducts
In the embryo, where do primordial germ cells originate?
The epiblast
At what week are the primitive male and female gonads identical?
Week 6
Where in the embryo do stem cells come from?
The inner cell mass
From what part of the tri-laminar disc are the bladder and urethra formed?
The endoderm
When in the menstrual cycle does implantation occur?
21st day
What are the six stages of implantation
APPOSITION ATTACHEMENT DIFFERENTIATION OF TROPHOBLAST INVASION DECIDUAL REACTION MATERNAL RECOGNITION
How many days after fertilisation does the apposition stage of implantation take place?
9 days after
When does the embryo reach the uterus?
Day 5/6
From which layer of the tri-laminar disc is the primitive gut tube derived from?
Endoderm and visceral mesoderm
When does the hepatic diverticulum form?
3rd week
What has developed from the hepatic diverticulum by the 5th week?
Bile duct, liver, cystic diverticulum, dorsal and ventral pancreatic ducts.
When does bile secretion begin?
12th week
Where does the liver develop and what does it divide the site into?
In the ventral mesentery and divides into the lesser omentum and falciform ligament
Where does the pancreas develop?
In the dorsal and ventral mesentery
What does the ventral bud go on to form?
Uncinate process and head of pancreas
What does the dorsal bud form?
Neck, body and tail
When do the islets of Langerhans develop?
3rd month
When does insulin secretion begin?
5th month
What is trapped when the ventral bud rotates behind the duodenum and fuses with the dorsal bud?
Superior mesenteric artery and vein
What are primordial germ cells?
Precursors of gametes which are diploid cells. Originate in the epiblast (2nd week) move through to the primitive streak to the wall of the yolk sac (4th week). Finally migrate towards the gonads where they differentiate into mother cells (spermatogonia and oogonia)
What is cleavage? Where does it occur?
One of the early growth phases defined as a series of mitotic divisions of the zygote. Occurs in the uterine tube.
What is a morula?
A 16 cell blastomere - formed three days after fertilisation
When does the zona pellucida degenerate to allow the implantation of the embryo?
Day 5
What are blastomeres without a zona pellucida called?
Blastocyst
What is a blastula? How many layers does it consist of?
A blastomere that has reached 128 cells
- Embryoblast - gives origin to the developing of the embryo
- Trophoblast - gives origin to the foetal membranes (placenta, yolk sac and amnion)
- Blastocele
What does the bilaminar germ disc differentiate into in the second week of development?
- Dorsal epiblast - layer of columnar cells
2. Ventral hypoblast - layer of cuboidal cells
What does the trophoblast become in the second week of development?
- Outer syncytiotrophoblast
2. Inner cytotrophoblast
What two cavities form in the second week of development?
- Amniotic cavity (dorsal)
2. Yolk sac (ventral)
What process is completed at the end of the second week of development?
Implantation
What is implantation?
Attachment of the blastocyst to the functional layer of the endometrium at the upper part of the body of the uterus.
If implantation occurs anywhere else other than the body of the uterus, what is it called?
Placenta previa
At the end of implantation, what is the endometrium of the uterus called?
Decidua
When does the embryonic period begin?
At the 3rd week of development
What is the 3rd week of development known as?
The weak of gastrulation = establishment of the trilaminar disc
What leads to the appearance of the primitive streak?
Proliferation of the epiblast (ectoderm)
What does the hypoblast give rise to?
Endoderm
What does the epiblast give rise to?
Endoderm, mesoderm, ectoderm
Where do the hypoblast and epiblast fuse?
Fuse caudally at the cloacal membrane (future anus)
The solid cord of cells extending from the primitive node to the precordal plate is known as…..
The notochord
What is neuralation?
The process of formation of the embryonic nervous system.
Which layer thickens in the mid-line in the 3rd week to form the neural plate?
Ectoderm
The ectoderm undergoes mitosis to form a midline groove, what is this known as?
The neural groove
What do neural crest cells develop into?
Sensory (dorsal root) ganglia Bony skull Meninges Dermis Adrenal medulla Schwann cells CN 10, 9, 7, 5
What does the ectoderm form?
Epidermis of the skin Epithelial lining of mouth and rectum Cornea and lens of eye Nervous system Adrenal medulla Hair cells Epithelium of pineal and pituitary glands Tooth enamel
What does the mesoderm form?
Notochord
Skeletal, muscular excretory, circulatory, reproductive and lymphatic systems
Dermis of skin
Adrenal cortex
What does the endoderm form?
Epithelial lining of the digestive tract and respiratory system
Lining of the urethra, urinary bladder and reproductive system
Liver, pancreas, thymus
Thyroid gland and parathyroid gland
When should the neural tube fuse?
By the end of the 4th week
Which parts of the respiratory system are derived from the endoderm?
Epithelial lining of trachea, larynx, bronchi and alveoli
Which parts of the respiratory system are derived from the mesoderm?
Cartilages, muscle, connective tissue and visceral pleura
Respiratory embryology: what occurs in the 4th week?
Formation of lung buds (initially appear as respiratory diverticulum)
Respiratory embryology: what occurs in the 5th week?
Development of L & R bronchi
Respiratory embryology: what occurs in the 16th week?
Terminal bronchioles give way to terminal sacs
Respiratory embryology: what occurs in the 24th week?
Alveolar sac formation, type 1&2 pneumocytes
When is surfactant first produced?
34th week - production rapidly increases 2 weeks before brith
When does the pseudoglandular phase of respiratory development occur? What happens in this phase?
5-16 weeks: branching to form terminal bronchioles
When does the canicular phase of respiratory development occur? What happens in this phase?
16-26 weeks: each terminal bronchiole divides into 2 respiratory bronchioles
When does the terminal sac phase of respiratory development occur? What happens in this phase?
26 weeks: terminal sacs (primitive alveoli form)
When does the alveolar phase of respiratory development occur? What happens in this phase?
8 months - childhood: alveoli mature, more respiratory bronchioles and alveoli
What does the prosencephalon divide into?
Telencephalon
Diencephalon
What does the Rhombencephalon divide into?
Metencephalon
Mylencephalon
What structures in the adult brain are formed from the Telencephalon?
The cerebral hemispheres and lateral ventricles
What structures in the adult brain are formed from the diencephalon?
Thalamus, hypothalamus and third ventricle
What structures in the adult brain are formed from the mesencephalon?
Midbrain, colliculi and cerebral aqueduct
What structures in the adult brain are formed from the metencephalon?
Pons, cerebellum and upper part of fourth ventricle
What structures in the adult brain are formed from the mylencephalon?
Medulla oblongata and lower part of fourth ventricle
At what week of development do the 3 primary vesicles become 5 secondary brain vesicles?
7th week
What vitamins are needed for the fusion of the neural tube?
Folic acid (B9) and B12
What type of sensation is present at 19 weeks?
C fibre connection = noxious/painful stimuli
What type of sensation is present in an embryo of 24 weeks?
Connections from thalamus to the cortex
When does the dorsal root ganglion connect to the spinal cord? Does it result in nociceptive pain?
From 8 weeks, does not result in nociceptive pain.
Embryologically, what is the ventricular system derived from?
The lumen of the neural tube
