ANHB2212 Major Concepts from Lectures

What is fertilisation?

Fusion of sperm and oocyte to form a zygote.

Where does fertilisation usually occur?

Ampulla of the uterine tube.

What is cleavage?

Rapid mitotic divisions of the zygote without major growth in overall size.

What is a morula?

A solid ball of embryonic cells formed after cleavage divisions.

What is a blastocyst?

A fluid-filled embryonic structure with an embryoblast, trophoblast and blastocyst cavity.

What does the embryoblast form?

The embryo proper.

What does the trophoblast contribute to?

Placenta and extraembryonic support structures.

What is implantation?

Attachment and invasion of the blastocyst into the uterine endometrium.

What are the two trophoblast layers?

Cytotrophoblast and syncytiotrophoblast.

Which trophoblast layer invades the endometrium?

Syncytiotrophoblast.

What is the bilaminar embryonic disc?

A two-layered embryonic disc made of epiblast and hypoblast.

What are the two layers of the bilaminar disc?

Epiblast and hypoblast.

Which bilaminar layer gives rise to the embryo proper?

Epiblast.

What is gastrulation?

Formation of the three germ layers: ectoderm, mesoderm and endoderm.

What structure appears during gastrulation?

Primitive streak.

Why is the primitive streak important?

It establishes body axes and allows epiblast cells to migrate to form germ layers.

What are the three germ layers?

Ectoderm, mesoderm and endoderm.

What is the notochord?

A midline axial mesodermal structure important for signalling and patterning.

What does the notochord induce?

Neural plate/neural tube formation and somite development.

What is the adult remnant of the notochord?

Nucleus pulposus of the intervertebral disc.

What is neurulation?

Formation of the neural tube from the neural plate.

What does the neural tube become?

Brain and spinal cord.

What are neural crest cells?

Migratory cells from neural fold margins that form many PNS and craniofacial structures.

Give two neural crest derivatives.

Dorsal root ganglia, Schwann cells, melanocytes, adrenal medulla, autonomic ganglia, enteric ganglia, craniofacial connective tissue.

What can failure of anterior neuropore closure cause?

Anencephaly.

What can failure of posterior neuropore closure cause?

Spina bifida.

What is embryonic folding?

Transformation of a flat disc into a three-dimensional body form.

What are the two major types of folding?

Craniocaudal folding and lateral folding.

What does lateral folding help form?

Ventral body wall and gut tube.

What does craniocaudal folding reposition?

Heart, septum transversum and future mouth/anus regions.

What does the intraembryonic coelom become?

Pericardial, pleural and peritoneal cavities.

What does ectoderm generally form?

Nervous system, epidermis and neural crest derivatives.

What does mesoderm generally form?

Muscle, bone, connective tissue, blood vessels, kidneys, gonads and serous membranes.

What does endoderm generally form?

Epithelial lining of gut, respiratory tract, bladder and glandular organs.

Germ layer of epidermis?

Surface ectoderm.

Germ layer of CNS?

Neuroectoderm.

Germ layer of spinal cord?

Neural tube/neuroectoderm.

Germ layer of PNS ganglia?

Neural crest.

Germ layer of Schwann cells?

Neural crest.

Germ layer of melanocytes?

Neural crest.

Germ layer of adrenal medulla?

Neural crest.

Germ layer of adrenal cortex?

Mesoderm.

Germ layer of skeletal muscle?

Mesoderm, especially paraxial mesoderm/myotome.

Germ layer of vertebrae?

Paraxial mesoderm/sclerotome.

Germ layer of ribs?

Paraxial mesoderm/sclerotome.

Germ layer of dermis of the back?

Paraxial mesoderm/dermatome.

Germ layer of kidney?

Intermediate mesoderm.

Germ layer of gonads?

Intermediate mesoderm.

Germ layer of gut epithelium?

Endoderm.

Germ layer of respiratory epithelium?

Endoderm.

Germ layer of liver parenchyma?

Endoderm.

Germ layer of pancreas parenchyma?

Endoderm.

Germ layer of blood vessels/endothelium?

Mesoderm.

Germ layer of cardiac muscle?

Mesoderm.

Germ layer of smooth muscle of gut wall?

Splanchnic mesoderm.

What does paraxial mesoderm form?

Somites → vertebrae, ribs, skeletal muscle, dermis, tendons.

What does intermediate mesoderm form?

Urogenital system.

What does lateral plate mesoderm form?

Body wall, limbs, serous membranes, cardiovascular structures and gut wall support tissues.

What does somatic lateral plate mesoderm form?

Body wall, limb skeleton/connective tissue and parietal serous membranes.

What does splanchnic lateral plate mesoderm form?

Visceral serous membranes, gut wall connective tissue/muscle and cardiovascular structures.

What is the placenta?

A fetal-maternal organ for exchange of gases, nutrients, wastes and hormones.

Does maternal blood normally mix directly with fetal blood?

No. Exchange occurs across the placental barrier.

What are chorionic villi?

Fetal projections that increase surface area for maternal-fetal exchange.

What crosses from mother to fetus?

Oxygen, nutrients, antibodies, some hormones, drugs and toxins.

What crosses from fetus to mother?

Carbon dioxide, urea, uric acid, creatinine and bilirubin.

How many arteries are in the normal umbilical cord?

Two.

How many veins are in the normal umbilical cord?

One.

What do umbilical arteries carry?

Deoxygenated blood from fetus to placenta.

What does the umbilical vein carry?

Oxygenated, nutrient-rich blood from placenta to fetus.

Why is the umbilical vein unusual?

It carries oxygenated blood.

What is Wharton’s jelly?

Gelatinous connective tissue protecting umbilical vessels.

What are the three fetal circulatory shunts?

Ductus venosus, foramen ovale and ductus arteriosus.

What does the ductus venosus connect?

Umbilical vein to IVC via liver venous pathway.

What is the function of ductus venosus?

Bypasses much of the liver.

Adult remnant of ductus venosus?

Ligamentum venosum.

What does the foramen ovale connect?

Right atrium to left atrium.

Function of foramen ovale?

Bypasses fetal pulmonary circulation.

Adult remnant of foramen ovale?

Fossa ovalis.

What does the ductus arteriosus connect?

Pulmonary trunk to aorta.

Function of ductus arteriosus?

Diverts blood away from high-resistance fetal lungs.

Adult remnant of ductus arteriosus?

Ligamentum arteriosum.

Adult remnant of umbilical vein?

Ligamentum teres hepatis.

Adult remnants of umbilical arteries?

Medial umbilical ligaments.

Adult remnant of urachus?

Median umbilical ligament.

What happens to pulmonary vascular resistance after birth?

It decreases.

What happens to left atrial pressure after birth?

It increases due to increased pulmonary venous return.

What causes functional closure of the foramen ovale?

Left atrial pressure becomes greater than right atrial pressure.

Why are fetal lungs not the main site of gas exchange?

They are fluid-filled and pulmonary resistance is high; placenta performs gas exchange.

What is a major clue that a specimen is fetal?

Large head relative to body size.

Why does fetal skeleton look different from adult skeleton?

More cartilage, less mineralisation and visible growth plates/ossification centres.

Why is the fetal liver proportionally large?

It has major developmental and hematopoietic functions.

Why are fetal lungs small/immature?

They are not used for air breathing before birth.

Why may fetal kidneys appear lobulated?

Renal development is incomplete and lobulation can be visible.

What should you look for first in a fetal sagittal section?

Midline structures: brain, spinal cord, vertebral column, heart, diaphragm, liver, gut, bladder.

What should you identify in a fetal thoracic transverse section?

Vertebral body, spinal cord, ribs, heart, lungs and body cavities.

What body cavity contains the fetal heart?

Pericardial cavity.

What body cavities contain the fetal lungs?

Pleural cavities.

What separates thoracic and abdominal cavities?

Diaphragm.

What fetal structure connects fetus to placenta?

Umbilical cord.

What fetal organ often dominates the upper abdomen?

Liver.