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Embryology SDL 5
VCOM 2014
26
Anatomy
Graduate
09/29/2010

Additional Anatomy Flashcards

 


 

Cards

Term
Intraembryonic space
Definition

- Is open and continuous with the extraembryonic coelom and forms a U shape around the sides and head of the embryonic disk

- Is isolated from the extraembryonic coeloic space by the growing body wall

Term
Body wall
Definition

As the embryo folds laterally, the edges of the embryonic disk composed of parietal mesoderm and ectoderm are brought together to form the outside body wall

- Fusion of the body wall at the ventral midline encloses the coelomic space within the embryo

- Parietal (somatic) mesoderm will form the body wall and the thin membranous lining of the coelom (future body cavity) called the serosa

Term

Body cavities

 

Gut

Definition

- As the embryo folds in the craniocaudal direction, the connection to the yolk sac narrows and forms the foregut and hind gut as distinct tubes

- The midgut is open to the yolk sac, which is covered by visceral mesoderm. With time, the yolk sac decreases in size and is incorporated into the midgut. The gut is now suspended in the coelomic cavity covered entirely by viseral mesoderm

Term
Visceral mesoderm layer
Definition

- The visceral mesoderm layer covers the foregut and hindgut tubes as they form

- Visceral mesoderm forms the serosal layer covering the viscera, the mesenteries, and the muscles and connective tissue of the gut

Term
Intraembryonic coelom
Definition

-Embryo folding in the cranial region causes the base of the original U shape intraembryonic coelom to fold under the two arms of the U. This base region will form the pericardial cavity

- The proximal portion of the arms, now directed dorsocaudally will become paired periocardio-peritoneal canals (eventually pleural cavities)

- The distal portions of the arm are brought together on the ventral side of the embryo as the body wall folds (forming the peritoneal "abdominal" cavity

- The intraembryonic coelom remains open to the extraembryonic coelom in the developing umbilicus until after the 11th week

 

Term
Division of the Intraembryonic Coelom
Definition

Late in the 4th week it divides into 3 regions:

- pericardial cavity

- two pericardio-peritoneal canals (eventual pleural cavities)

- peritoneal cavity

Term
Pleuropericardial fold
Definition

A ridge of tissue which forms on the lateral wall of each pericardio-peritoneal canal between the heart and developing lungs

The two pleuropericardial folds grow medially to separate the two pleural cavities from the pericardial cavity

- The folds will form the fibrous pericardium (the outer layer of the pericardial cavity) surrounding the heart

- By the 7th week, the folds fuse in the midline with undifferentiated mesoderm around teh esophagus in in the primordial mediastinum

Term
Second division of the coelomic space
Definition

Is created from 2 structures, the pleuroperitoneal fold and the septum transversum

- The septum transversum originates as thick mesoderm cranial to the heart in the embryonic disc. As the embryo folds it becomes located immediately caudal to the heart

- A second ridge of tissue forms in the wall of each pericardio-peritoneal canal calle the pleuroperitoneal folds

- These folds elongate and thin to form the pleuroperitoneal membranes which join with the spetum transversum to form the diaphragm

Term
Formation of the Diaphragm
Definition

- The diaphragm is a muscular separation between the thoracic and abdominal cavities.

- It is composed of a number of different embryological components that fuse to form the definitive diaphragm

- The main component comes from the septum transversum

Term
Septum Transversum
Definition

Grows from the ventral body wall dorsally forming the central tendon of the diaphragm as it separates the pericardial and peritoneal cavities

- During the 6th week, the pleuroperitoneal folds fuse with the spetum transversum

- Mesoderm around the esophagus then fuses with the septum transversum and pleuroperitoneal membranes to form the complete diaphragm

Term
Diaphragm
Definition

- During the 9th to 12th weeks, muscle ingrowth from the body wall contributes to the periphery of the diaphragm

- Muscle ingrowth from the body wall and central tendon comprise the majority of the diaphragm

- There are openings in the diaphragm to allow passage of the esophagus, aorta, and vena cava

Term
Innervation of the diaphragm
Definition

- Begins during the 4th week when the septum transversum is located in the cervical region adjacent to the 3-5th cervical somites

- Myoblast and associated nerve fibers (2-5 spinal nerves) from these somites invade the septum forming the phrenic nerve

- As the embryo grows, the diaphragm assumes a thoracic position but is still innervated by these cervical nerves

- The periphery of the diaphragm is innervated by thoracic nerves

Term
Malformation of the diaphragm
Definition

Congenital diaphragmatic hernia

- occurs when one of the pleuorperitoneal folds fails to form of fuse with the other components of the diaphragm

- This abnormality occurs predominately on the left side

- Depending on the size of the defect, the intestines, stomach, and even liver may be found in the thoracic cavity

- Fetal lung development is limited on the affected side

- Newborns often present with respiratory distress due to the compromised lung

Term
Malformations of the body wall
Definition

If the body wall fails to close properly, the thoracic or abdominal caviteis may remain open and visceral components may be located outside the body wall

 

Term
Defect in closure of the thoracic cavity
Definition
Results in ectopia cordis, with the heart located outside the body wall
Term
Defect in abdominal cavity closure
Definition

Results in gastroschisis where loops of intestine and sometimes other organs are located outside the body fre in the amniotic cavity

The opening is usually to the right of the umbilicus

Gastroschisis is increasing in prevalence particularly in younger mothers

Term
Omphalocele
Definition

A defect that presents similar to gastroschisis but has a different developmental origin.

In normal development, intestinal growth outpaces growth of the abdominal cavity and the displaced intestinal loops are held for a number of weeks within the umbilical cord

As the abdomical cavity expands, the intestines return to the abdominal cavity. If the intestines fail to move back out of the umbilical cord, an omphalocele results

Term
Differenct between gastroschisis and ompalocele
Definition

The intestinal loops are not covered by the amnion, they are free in the amniotic cavity with gastroschisis

 

In ompahlocele the intestines are both covered by amnion and are withing the umbilical cord

Term

Staging Embryonic Development

 

Classification based on embryological events

Definition

Preimplantation: week 1

Bilaminar Disk: week 2

Trilaminar Disk: week 3

The Embryonic Period: 3rd-8th week

The Fetal Period: 9th week to birth

Term

Staging Embryonic Development

 

Classification base on time

Definition

- Month: Gestation divided into 9 months. Used most often by the general public. Not very accurate as many events occur each month

- Embryonic (or Fertilization) Age: Time is measured from fertilization onward and is counted in days or weeks. Most accurate way to describe development and is used by embryologist

- Gestational Age: Method widely used clinically due to ease of measurement. It estimates embryonic age based on the woman's last menstrual period

Term

Staging Embryonic Development

 

Classification based on morphologic characteristics

(Carnegie Stages)

Definition

The Carnegie system uses standardized morphological features that can be observed and used to accurately stage and compare developmental progression

 

- It is based on clearly observable or measurable physical features


Term
The 4th week
Definition

Days 21-28          Carnegie stage 9-12        Embryo length (mm) 3-4

- during the 4th week the embryo folds

- body cavities and GI system form

- cranial and caudal neuropores close (brain develops and enlarges)

- Pharyngeal arches form

- The heart is prominent on ventral aspect of embryo and pumps blood

- Limb buds

- Otic pits, which become the ears

- Lens placodes form, marking the future eye

Term
The 5th week
Definition

Day 28-35          Carnegie Stage 13-15          Embryo length (mm) 4-7

- the head enlarges due to rapid development of the brain and face

- the nasoplacodes form and develop into a nasal pit surrounded by nasal prominences which become the nostril and nose

- 1st pharyngeal arch has divided into the maxillary and mandibular prominences (future upper and lower jaw)

- Germ cells migrate to the future gonad

- the kidney begins to form

- the lungs begin to develop as an outgrowth from the foregut

Term
The 6th week
Definition

Days 35-42          Carnegie Stage 15-17          Embryo length (mm) 7-11

- the head continues to enlarge

- the upper lip and nose forms from facial prominences

- the upper limbs begin to regionalize and develop handplates with the first indication of digits

- the lower limbs develop footplates

- the developing intestines loop into the extraembryonic coelom within the umbilical cord as the abdominal cavity is not large enough

- The intestines remain outside the abdominal cavity until the 10th wk

Term
The 7th week
Definition

Day 42-49          Carnegie Stage 17-19          Embryo length (mm) 11-18

-Ossification begins in the long bones of limbs

- the trunk and neck straighten

- eyelids begin to form

- the abdomen enlarges mainly due to growth of the liver

- the yolk sac regresses to a small omphaloenteric duct

Term
The 8th week
Definition

Day 49-56          Carnegie stage 20-23          Embryo length (mm) 18-31

-Fingers and toes are visible

- the caudal eminence a tail like structure disappears by the end of the 8th week

- the head is still large but the trunk and limbs undergo rapid growth

- the neck is established

- external genitalia are present but cannot determin gender

- Eyelids fuse, covering eye

- the kidney begins to function late in the 8th week

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