Unit Ii Anatomy Lecture 12

Front 1

What type of diaphragmatic hernia is thought to be due to congenital shortness of the esophagus?

Back 1

Esophageal Hiatal Hernia
Congenital Diaphragmatic hernia

Front 2

What is the frequency of a esophageal hiatal hernia?

Back 2

1 in 2000 of newborns
Increases with age
Women affected more

Front 3

Why is polyhdramnios often associated with TEFs?

Back 3

In some types of tracheoesophageal fistulas, amniotic fluid does not pass to the stomach and intestines
Gastric contents and/or amniotic fluid may enter the trachea through the fistula
Fluid cannot pass to the intestine for absorption and transfer through the placenta

Front 4

What treatments are used to stimulate surfactant production of Type II cells or development of the cells?

Back 4

Mammalian-derived (artificial) surfactant
Glucocorticoids (corticosteroids-betamethasone) to stimulate surfactant production
Oxygen therapy

Front 5

How many alveoli are present at birth?

Back 5

50-250 million
1/8 to 1/6 of adult number
Remaining alveoli formed during first 10 years of life

Front 6

What other types of defects would you expect from a baby born with TEF?

Back 6

Cardiac abnormalities
Vertebral anomalies
Anal atresia
Cardiac defects
Esophageal atresia
Renal problems
Limb defects

Front 7

Can diaphragmatic defects in CHD be repaired by surgery before birth?

Back 7

Yes but with great risk to mother and fetus

Front 8

What is the mortality rate of CDH?

Back 8

75%

Front 9

Why do most newborns with CDH die?

Back 9

Pulmonary insufficiency
Pulmonary hypoplasia and dysfunction

Front 10

What stimulates the infact to start breathing at birth?

Back 10

Seems to be reflex response to sensory stimuli of air and touching
Changes in blood gasses, O2 tension, pH, and CO2 are also stimuli

Front 11

What is the rate of death of newborns with RDS?

Back 11

20%

Front 12

What are functions of amniotic fluid?

Back 12

Cushion (absorbs jolt), symmetrical growth, barrier to infection, permits normal fetal lung development, permits fetal movement, and prevents adherence of fetus/embryo to amnion

Front 13

Describe the respiratory system at 4 weeks

Back 13

Appears as outgrowth of ventral wall of foregut

Front 14

What is the origin of the epithelial lining of the larynx, trachea, bronchi, and lungs?

Back 14

Endodermal

Front 15

What is the origin of the connective tissue, cartilage, and smooth muscle components?

Back 15

Splanchnic mesoderm surrounding the foregut

Front 16

Describe separation of the respiratory system from the foregut

Back 16

Respiratory diverticulum is later separated from foregut by two longitudinal ridges which later fuse to separate the foregut into a dorsal portion, the esophagus, and a ventral portion, the larynx, trachea, bronchi and lungs
Opening of the laryngotracheal tube into pharynx becomes inlet of larynx or laryngeal auditis

Front 17

Describe the development of the larynx

Back 17

1) Epithelium of larynx is of endodermal origin. Cartilages are derived from cartilages in fourth and sixth pairs of brachial arches
2) Mesenchyme proliferates rapidly at cranial end of laryngotracheal tube, producing paired arytenoid swellings
3) Remainder of laryngeal cartilages- thyroid, cricoid, corniculate, and cuneiform also develop from mesenchyme. Epithelium proliferates rapidly, resulting in temporary occlusion of the laryngeal lumen but during tenth week recanalization occurs. Laryngeal ventricles are formed, bounded by false and true vocal cords
4) Epiglottis develops from caudal part of hypobranchial eminence, prominence produced by proliferation of mesenchyme in ventral ends of third and fourth branchial arches
5) Laryngeal muscles develop from myoblasts in fourth and sixth branchial arches. Superior laryngeal nerve innervates derivatives of fourth branchial arch, and recurrent laryngeal nerve derivatives of sixth branchial arch

Front 18

Describe the development of the trachea and tracheoesophageal fistula

Back 18

1) Endoderm distal to larynx gives rise to epithelium and glands of the of the trachea and lungs. The cartilage, connective tissue, and muscles of the trachea are derived from surrounding splanchnic mesoderm
2) Communication or fistula connecting trachea and esophagus occurs about one in every 2500 births
3) TEF is usually associated with esophageal atresia; in all cases, there is an abnormal communication between trachea and esophagus
4) TEF is most common malformation of lower respiratory tract. It results from incomplete division of cranial part of foregut into respiratory and digestive portions during fourth week. Incomplete fusion of TE ridges (folds) results in a defective TE septum and an abnormal communication between trachea and esophagus

Front 19

Describe development of the lung buds

Back 19

The bulb-shaped lung bud at the caudal end of the laryngotracheal tube soon divides into two knob-like lung buds which grow laterally into the pericardioperitoneal canals, the primordium of the pleural cavities
Together with the surronding splanchnic mesenchyme, the lung buds differentiate into the bronchi and their ramifications in the lungs

Front 20

Describe lung development from about the fifth week until birth

Back 20

Early in the 5th week, each lung bud enlarges to form the primordium of a principal or primary bronchus
Primary bronchi subdivide into secondary bronchi
Each secondary bronchus subsequently undergoes progressive branching
Tertiary or segmental bronchi; ten in right lung and ten on left, begin to form by 10th week
Each segmental bronchus with its surrounding mass of mesenchyme is the primordium of a bronchopulmonary segment
By 6 months, about 17 generations or subdivisions have formed and respiratory bronchioles have developed
An additional 6-7 order of branches develop after birth
As lungs develop, they acquire a layer of visceral pleura from splanchnic mesenchyme, and come to lie close to heart
Thoracic body wall becomes lined by a layer of parietal pleura, derived from somatic mesoderm

Front 21

What are the four stages of lung development?

Back 21

1) Pseudoglandular period
2) Canalicular period
3) Terminal sac period
4) Alveolar period

Front 22

Describe the pseudoglandular period of lung development

Back 22

5-16 weeks; by 16 weeks all major elements of lung have formed, except those involved with gas exchange; respiration is not possible

Front 23

Describe the canalicular period of lung development

Back 23

16-26 weeks; respiratory bronchioles have formed and some thin-walled terminal sacs (well-vascularized)
Fetus born toward end may survive in ICU, most likely will due due to respiratory immaturity

Front 24

Describe the terminal sac period of lung development

Back 24

26 weeks-birth; many more terminal sacs develop and their epithelium becomes thin
Squamous epithelial cells of endodermal origin appear (also called type I alveolar cells or pneumocytes)
Among these cells are secretory epithelial cells or type II pneumocytes which secrete surfactant, which spreads out over terminal sac walls
Role of surfactant is to conteract surface tension forces and facilitate expansion of terminal sacs
During 7th month after fertilization, sufficient terminal sacs and surfactant are present to permit survival of a prematurely born infant
Adequate pulmonary vasculature and suficient surfactant are the most critical factors in the survival of premature infants

Front 25

Describe the alveolar period of lung development

Back 25

Epithelial lining of terminal sac attenuates to an extremely thin squamous epithelium
Before birth, alveoli are still considered immature and appear as small bulges on walls of terminal sacs and respiratory bronchioles
Characteristic mature alveoli do not form for some time after birth
Alveolocapillary membrane is sufficiently thin to allow gas exchange
After birth, alveoli enlarge slightly but increase in lung size is mainly result of increase in alveoli number
About 95% of alveoli develop after birth
Developing lungs at birth are about half-filled with fluid derived from amniotic cavity, lungs, and tracheal glands
Aeration of lungs at birth the rapid replacement of intra-alveolar fluid with air

Front 26

Describe respiratory distress syndrome (RDS)

Back 26

Infants born prematurely are most susceptible
Shortly after birth, develop rapid, labored breathing
Deficiency of pulmonary surfactant causes hyaline membrane disease which causes RDS
Alveoli collapse during expiration
Amount of surfactant increases during terminal stages of pregnancy, especially last two weeks

Front 27

What are the four structures that the diaphragm develops from?

Back 27

1) Septum transversum
2) Pleuroperitoneal membranes
3) Dorsal mesentary of esophagus
4) Dorsal mesentary of body wall

Front 28

Describe the septum transversum

Back 28

Transverse septum, composed of mesoderm, forms central tendon of diaphragm
First identifiable at end of third week as a mass of mesoderm cranial to pericardial cavity
After head folds ventrally during 4th week, septum transversum appears as a thick, incomplete partition between pericardial and abdominal cavities
Fuses with mesenchyme ventral to esophagus (primitive mediastinum) and with pleuroperitoneal membranes

Front 29

Describe the pleuroperitoneal membranes

Back 29

Fuse with dorsal mesentery of esophagus and septum transversum
Completes partition and forms primitive diaphragm
Represent relatively small portion of infant's diaphragm

Front 30

Describe the dorsal mesentary of the esophagus

Back 30

Constitutes median portion of diaphragm
Crura of diaphragm develop from myoblasts that frow into dorsal mesentery of esophagus

Front 31

Describe the body wall

Back 31

During 9th-12th week, lungs and pleural cavities enlarge and burrow into lateral body walls
During this excavation, tissue is split in two layers- outer layer that becomes part of definitive abdominal wall and inner layer that contributes muscle to peripheral portions of diaphragm, external to parts derived from pleuroperitoneal membranes
Further extension of pleural cavities into body walls forms right and left costodiaphragmatic recesses and establishes characteristic dome-shaped configeration of adult diaphragm

Front 32

Describe the positional changes and innervation of the diaphragm in the 4th week

Back 32

Septum transversum lies opposite the third, fourth, and fifth cervical somites

Front 33

Describe the positional changes and innervation of the diaphragm in the 5th week

Back 33

Myoblasts form myotome of somites and migrate into developing diaphragm and bring their nerves with them from cervical region
Phrenic nerve that supplies diaphragm come from cervical roots 3, 4, and 5
Phrenic nerves in embryos pass to septum transversum via pleuro-pericardial membranes

Front 34

Describe the positional changes and innervation of the diaphragm in the 6th week

Back 34

Developing diaphragm is at level of thoracic somites because of rapid growth in dorsal part of embryo

Front 35

Describe the positional changes and innervation of the diaphragm in the 8th week

Back 35

Dorsal part of diaphragm lies at level of first lumbar vertebrae

Front 36

Describe motor and sensory innervation of the diaphragm

Back 36

As parts of diaphragm fuse, mesenchyme of septum transversum extends into other parts and forms myoblasts that differentiate into muscle of diaphragm
Motor nerve supply of diaphragm is phrenic nerves
Sensory innervation is also phrenic, but also some lower intercostal nerves

Front 37

What is the most common congenital malformation?

Back 37

Congenital diaphragmatic hernia (CDH)
Results from defective formation and/or fusion of pleuroperitoneal membrane with other parts of diaphragm
Occurs about 1:2000 newborns and leads to herniation of abdominal content into thoracic cavity