Embryology Flashcards
What is the appendix of the testis derived from?
Paramesonephric (Mullerian) duct
What is the ligamentum arteriosum derived from?
Ligamentum Arteriosum = small ligament attaching aorta to pulmonary artery
Ductus arteriosus
What is the ductus arteriosus derived from?
6th aortic arch (left)
When does the anterior pituitary form in the foetus?
Week 5
Complete mole vs Partial mole
Complete: empty egg fertilised by one or two normal sperm: 46XX or 46XY
Diffuse swelling of villous tissue and diffuse trophoblastic hyperplasia in the absence of embryonic tissue
Partial: normal haploid egg fertilised by two or three sperm: 69XXY, 69XXX, 69XYY
Focal swelling of villous tissue and focal trophoblastic hyperplasia in the presence of embryonic tissue
Highest risk time to use warfarin?
6-9 weeks
What remnant of the upper mesonephric duct is commonly seen at laparoscopy?
Epoophoron- remnant of caudal mesonephric duct found next to ovary and Fallopian tube (homologue of male epididymis)- located in lateral part of mesosalpinx.
May give rise to local para-ovarian cyst/ adenoma
What is a Gartner’s cyst?
Remnants of mesonephric duct that are located along anterior and lateral parts of the vaginal wall
What do oocytes develop from?
Primordial germ cells
What is the allantois derived from?
Endoderm & splanchnic mesoderm
Origin of ureteric bud?
Mesonephric duct
What do the ovaries originate from?
The gonads begin as genital ridges – a pair of longitudinal ridges derived from intermediate mesoderm and overlying epithelium.
What are the pharyngeal arches?
In the developing embryo, there are six pharyngeal arches. They arise in the fourth week of development as out-pocketings of mesoderm on both sides of the pharynx.
Each pharyngeal arch has a branch of the aorta, a cranial nerve and a cartilage bar associated with it.
What does cleft palate result from?
Failure of development of the 1st pharyngeal arch: failure of fusion of palatal shelves in the midline.
Derivatives of 2nd pharyngeal arch?
Facial nerve
Muscles of facial expression (buccinator, stapedius, stylohyoid, posterior belly of digastric, platysma)
Temporal styloid process, lesser horn of hyoid bone, stylohyoid ligament, stapes, reacher’s cartilage
Stapedial artery
What is the proximal internal carotid artery derived from?
3rd pharyngeal arch
Derivatives of 1st pharyngeal arch
Trigeminal nerve (V2 and V3)
Muscles of mastication (mylohyoid, anterior belly of digastric, tensor veil palatine, tensor tympani).
Malleus and Incus of middle ear, maxilla, mandible, zygoma and sphenomandibular ligament
External carotid artery
Maxillary artery
Derivatives of 3rd pharyngeal arch?
Glossopharyngeal nerve
Stylopharyngeus muscle
Greater horn (lower part) of hyoid bone
Common carotid artery, internal carotid artery
Derivatives of 4th pharyngeal arch?
Vagus nerve
Superior laryngeal nerve
Pharyngeal/ cricothyroid muscles
Thyroid cartilage, Cricoid cartilage
Subclavian artery
Derivatives of 6th pharyngeal arch?
Vagus nerve
Recurrent laryngeal nerve
Muscles of larynx & oesophagus (except cricothyroid)
Aytenoid cartilages
Cricoid cartilage
Cuneiform cartilage
Corniculate cartilage
Pulmonary artery
Ductus arteriosus
Pharyngeal pouches & their derivatives
1st: tubotympanic recess, middle ear, auditory tube, tubal tonsil
2nd: palatine tonsil
3rd: DORSAL- inferior parathyroid glands, VENTRAL- thymus gland
4th: DORSAL- superior parathyroid glands, VENTRAL- ultimobranchial body
5th: Ultimobranchial body (fuses with lateral lobe of thyroid gland), parafollicular cells (produce calcitonin)
How many days after fertilisation does the blastocyst hatch from the zona pellucida?
5-7
What germ cell layer does the GIT develop from?
Endoderm.
GIT forms via gastrulation from the endoderm of the trilaminar embryo around week 3
What germ layer does the kidney develop from?
Intermediate mesoderm
What structures develop from the endoderm/ mesoderm/ ectoderm?
Endoderm
- Stomach
- Intestines (mucosal layers)
- Colon (mucosal layers)
- Liver
- Pancreas
- Bladder
- Epithelial parts of trachea
- Lungs
- Pharynx
- Thyroid
- Parathyroid
Mesoderm
- Muscle (smooth and striated)
- Bone
- Cartilage
- Connective tissue
- Adipose tissue
- Lymphatic system
- Dermis
- Genitourinary system
- Serous membranes
Intermediate mesoderm
- Kidneys
- Gonads
Paraxial mesoderm
- Cartilage
- Skeletal muscle
- Dermis
- Somites
Lateral plate mesoderm
- Circulatory system (inc heart) and
- Spleen
- Gut wall
Ectoderm
- Epidermis
- Hair
- Nails
- Lens
- Cornea
- Sebaceous glands
- Tooth enamel
- Epithelium of the mouth and nose.
From Neural Crest of Ectoderm
- Peripheral nervous system
- Adrenal medulla
- Melanocytes
- Facial cartilage
- Dentin of teeth.
From Neural tube of Ectoderm
- Brain
- Spinal cord
- Posterior pituitary
- Motor neurons
- Retina
- Anterior pituitary
During formation of the mid, fore and hind guts the initial gut tube undegoes rotation. How can this be described?
It rotates 270 degrees anticlockwise
Mechanism of closure of ductus arteriosus
Baby takes first breath and inflates lungs –> Increased arterial pO2, increased bradykinin (produced by lungs) and decreased prostaglandin E2
Oxygen causes constriction of DA, decreased vascular resistance also drops pressure in lumen, aiding closure. Bradykinin stimulates smooth muscle constriction of ductus.
Prostaglandin is metabolised in the lungs, so falls rapidly within 3h of birth
Spermatogenesis
Spermatogonium undergoes growth/ maturation to produce primary spermatocyte.
Primary spermatocyte undergoes meiosis I to produce secondary spermatocytes (diploid)
Secondary spermatocytes undergo meiosis II to produce spermatids (haploid)
Spermatids undergo differentiation to produce spermatozoa
Oogenesis
Oogonium undergoes growth/ maturation to produce primary oocyte
Primary oocyte undergoes meiosis I to produce a secondary oocyte and first polar body
Secondary oocyte undergoes meiosis II to produce ootid and second polar body
Ootid undergoes differentiation to produce ovum
Oogonium = diploid, x2 DNA pairs, 46 chromatids
Primary = diploid, x4 DNA pairs, 2x 46 chromatids
Seconday= haploid, x2 DNA pairs, 46 chromatids
Ootid/ ovum= haploid, 1 DNA pair, 23 chromatids
Which structure becomes the definitive adult kidney?
Metanephros
How many days after fertilisation does implantation typically occur?
7-9
What causes a bicornuate uterus?
Abnormal fusion and reabsorption of the paramesonephric ducts
What does mullerian agenesis typically result in & what is the syndrome called?
Failure to form a uterus
Mullein Agenesis = rokitansky-kuster-hauser syndrome
15% of cases of primary amenorrhoea
Prevalence 1 in 5000
Karyotype 46XX
Crossed fused etopia results in what structural abnormality?
Horseshoe kidney
How many oocytes present in the ovaries at birth/ puberty/ 20 week foetus?
Birth: 1-2 million
Puberty: 300,000
20 week foetus: 6-7 million
> 99% breakdown in a process called atresia
What are Ladd’s bands?
In intestinal malrotation fibrous bands fix the caecum in the right upper quadrant. These bands are called Ladd’s bands.
How many days following fertilisation does the morula/ blastocyst form?
Morula: 4
Blastocyst: 5
(Morula precedes blastocyst)
Feto-maternal circulation, what are the three shunts?
Foramen ovale: shunt between right and left atria of fetal heart. Blood enters RA and flows to LA, bypassing the pulmonary circulation. It then passes into the aorta.
Ductus arteriosus: connects aorta with the pulmonary artery, further shunting blood away from the lungs and into the aorta (some blood from RA enters RV and PA, but this then passes through ductus arteriosus rather than entering pulmonary circulation)
Ductus venosus: shunts oxygenate blood from the placenta away from the semi functional liver and towards the heart.
Oxygenated blood arrives from umbilical vein, passes though the DV into the IVC, which then enters RA –> LA (through foramen ovale) etc
What is the corpus luteum and what does it secrete?
Temporary endocrine structure.
Secretes progesterone (17a hydroxyprogesterone) and estradiol + inhibin A
If fertilisation doesn’t occur, the corpus luteum stops secreting progesterone and degenerates into a corpus albicans.
If fertilisation occurs hCG signals the corpus to continue progesterone production and it is then termed the corpus luteum graviditatis
How is a patent ductus arteriosus closed (pre-term vs term)
Pre-term: NSAIDs e.g. indomethacin or ibuprofen
Term: surgical closure
At what gestation does meconium first appear in the fetal terminal ileum?
10-16 weeks
Embryological origin of the dome of the bladder
Yolk sac
Which hernia occurs due to abnormal involution of umbilical vein?
Gastroschisis (to the right of the umbilicus)
From which germ cell layer do the autonomic ganglia develop?
Neural crest
