Module 1D: Development Of The Cardiopulmonary System

Question 1

When is the formation of Bilaminar Embryonic (Germ) Discuss?

Answer 1

Early 2nd week

Question 2

What are the 2 layers the embryo last differentiates?

Answer 2

• Epiblast: high columnar cells adjacent to the amniotic cavity (blue)
• Hypoblast: small cuboidal cells adjacent to the blastocyst cavity (yellow)

Question 3

What is the small cavity that appears within the epiblast?

Answer 3

Amniotic cavity

Question 4

When does the formation of trophoblastic lacunae and Heuser’s membrane appear?

Answer 4

Mid 2nd week

Question 5

What is gastrulation?

Answer 5

formation of the 3 germ layers and the primitive streak during the 3rd week of development

Question 6

When does the gastrulation process begin?

Answer 6

Formation of the promative streak on the caudal end of the embryo in the epiblast

Question 7

What is neuralation?

Answer 7

A. Position of the neural plate in relation to the nonneural ectoderm, the mesoderm, and the endoderm.
B. Folding of the neural plate to form the neural groove.
C. Dorsal closure of the neural folds to form the neural tube and neural crest.
D. Maturation of the neural tube and its position relative to the axial mesodermal structure, notochord, and somites (derived from the paraxial mesoderm)

Question 8

What happens during the development during the embryonic period?

Answer 8

The fate of the mesodermal germ layer
1) Paraxial mesoderm formation/differentiation of:
• Somatomeres
• Somites
2) Intermediate mesoderm
3) Lateral plate mesoderm
• Early blood and blood vessel formation

Question 9

The mesoderm between the paraxial and the
lateral plate is called the __________ ___________.
More laterally, the mesoderm layer remains thin
Lateral and is known as the _________ _______ __________ - plate intracellular cavities present which disappear mesoderm gradually

Answer 9

Intermediate mesoderm

Lateral plate mesoderm

Question 10

What are the 3 germ layers structures called?

Answer 10

Trilaminar germ disc

Question 11

What does the lateral plate mesoderm divide into?

Answer 11

Somatic/Parietal mesoderm (covering the Amnion)

Visceral/Splanchnic mesoderm (covering the yolk sac)

Question 12

What arises from the lateral plate mesoderm divide into?

Answer 12

Blood vessels form in two ways:
Vasculogenesis
- Vessels arise from blood islands
- Islands of mesoderm cells that are induced to form (Hemangioblasts)

Angiogenesis
- Which entails sprouting from existing vessels

Question 13

What does the Mesenchymal cells in the Visceral/Splanchnic mesoderm differentiate into?

Answer 13

Hemangioblast

Question 14

What is the cranial migration of cardiogenic mesoblasts?

Answer 14

Part of the invaginating epiblast during gastrulation that is differentiating and migrates further through the mesodermal layer, settling between visceral/splanchnic mesoderm and the endoderm - Primary heart field- PHF

Question 15

What is the shaped oropharyngeal membrane and neural plate?

Answer 15

The central region of the horseshoe- shaped cardiogenic area is initially cranial to both the oropharyngeal membrane and the neural plate

Question 16

What does the intraembryonic cavity over the PHF later develops into?

Answer 16

Pericardial cavity

Question 17

What are the 3 stages of the heart formation?

Answer 17

I. Formation of the primitive heart tube
II. Cardiac looping
III. Cardiac septation

Question 18

Describe the formation of the heart tube (cardiac tube).

Answer 18

With time, the islands will form 2 tubes called endocardial tubes

Later, the Left & Right endocardial tubes - fuse together to become the primitive heart tube

Question 19

What is The second source of cells for heart formation is the cells residing in splanchnic mesoderm, ventral to the pharynx called?

Answer 19

Secondary heart field (SHF)

Question 20

Where does the primary heart field originate from? Where does it reside?

Answer 20

This originates from the epiblast- comes to reside in the splanchnic mesoderm just above the endoderm- PHF cells make the myocardium of most of the heart.

Question 21

Where does the secondary heart field originate from? Where does it reside?

Answer 21

This layer originates from the splanchnic mesoderm- it gives rise to the dorsal mesocardium. It also forms the myocardium of the blood inflow and outflow channels of the heart.

Question 22

Summarize the primary heart field.

Answer 22

• Mesoderm - Lateral Plate -
Visceral plate mesoderm
• Differentiate - Hemangioblasts - Blood
Islands - primitive blood cells,
and vessels
• Sandwiched anteriorly between Visceral
mesothelium and Endoderm
• Primitive endothelial vessels fuse form Endocardial tubes
• Cranial and caudal folding - endocardial tubes fuse - Primitive Heart tube

Question 23

Summarize Secondary Heart Field.

Answer 23

Secondary Heart Field (PHF) derived from:
• Mesoderm - Lateral Plate - Visceral plate mesoderm dorsal to PHF
• Forms Dorsal mesocardium attaching the heart tube to the dorsal wall of the pericardial cavity
1. Helps suspend heart tube in the pericardial
cavity
2. Adds more cells to the developing mass of the
heart tube
• Increasing mass of cells from SHF enables
elongation of the heart tube
• Elongation - eventual Cardiac Looping

Question 24

What is the secretion of the myocardium layer of extracellular matrix called? Why is it important?

Answer 24

Cardiac jelly (Collagen, GAGs, glycoproteins) which important for regulating cell shape, migration, proliferation, and differentiation of the heart cells

Question 25

What are the 3 layers of the heart tube?

Answer 25

1. Endocardium- originated from endoderm 2. Myocardium- originated from PHF and SHF 3. Epicardium- originated from dorsal mesocardium- SHF

Question 26

Describe the lengthening process for cardiac looping.

Answer 26

Secondary heart field cells are added to the cranial end, causing elongation of the heart tube This lengthening process is essential for: 1) Formation of part of the right ventricle and the outflow tract region (that forms part of the aorta and pulmonary artery) 2) The looping process

Question 27

How does the cardiac looping process work?

Answer 27

- The cephalic portion of the tube bends ventrally, moving caudally to its right - The caudal portion shifts dorsally, cranially to its left

Question 28

What is the primary pacemaker? Where is it located?

Answer 28

Sinoatrial (SA) Node: Forms in the right atrium near the sinus venosus, establishing the primary pacemaker.

Question 29

Where do the purkinje fibers develop from?

Answer 29

Evolve from ventricular myocardium to enable rapid impulse transmission.

Question 30

What is the timing of contractions? When do they start int he development stage?

Answer 30

Electrical activity starts the 4th week, with maturation of conduction pathways as heart chambers develop.

Question 31

What are the two methods of septum formation in the heart?

Answer 31

1.Cushion Tissue Fusion: forms from mesenchymal cells, dividing chambers by merging at specific locations to create septa (e.g., atrioventricular septa). 2.Tissue Growth and Fusion: A septum grows from the heart wall toward the opposite side and fuses to divide the chamber (e.g., interatrial septum). These mechanisms ensure the proper partitioning of the heart into four chambers and the establishment of pulmonary and systemic circulations.

Question 32

What does the endocardial cushion protrusions assist in formation of?

Answer 32

• the Septum Intermedium (fibrous portion of the atrioventricular septum) • the openings of the aortic and pulmonary channels • the atrioventricular valves (Tricuspid and Bicuspid)

Question 33

What does the cushion tissue fusion involve?

Answer 33

Involves two actively growing masses of tissue - approaching each other until they fuse, dividing the lumen into two separate (atrial and ventricular) chambers

Question 34

What does the tissue growth and fusion involve?

Answer 34

Involves a single tissue mass that actively grows until it reaches the opposite side of the lumen (Fig. C). Example: Interventricular/interatrial septa (septum primum and septum secundum) and cardiac outflow

Question 35

What is the interatrial septa?

Answer 35

• Divide the primitive atrium into right and left atria. • They form the foramen ovale, enabling fetal blood to bypass the lungs. • After birth, the septa fuse (forming Fossa ovale) separating oxygenated and deoxygenated blood.

Question 36

What is the patent foramen ovale (PFO)?

Answer 36

• A flap-like opening persists if the foramen ovale fails to seal completely after birth, allowing intermittent right-to-left shunting. • ASDs can lead to increased pulmonary blood flow, right atrial and ventricular enlargement, and, if untreated, pulmonary hypertension or heart failure.

Question 37

What are the changes in the vascular system at birth caused by?

Answer 37

1) Cessation of placental blood flow 2) Beginning of respiration

Question 38

Why does the closure of the foramen ovale happen?

Answer 38

The ductus arteriosus closes by muscular contraction of its wall - the amount of blood channeled to the lungs increases rapidly. This results in an increase in blood returning from the lungs, increasing the pressure in the left atrium.

Question 39

How long does full closure of the foramen ovale require?

Answer 39

After 6 months

Question 40

What happens when a baby cries during the first few days of life?

Answer 40

During the first few days of life, this closure is reversible. Crying of the baby creates a shunt from right to left atria, which accounts for cyanotic periods in the newborn.

Question 41

What are the changes that occur to the arteries at birth?

Answer 41

• Closure of the umbilical arteries - By contraction of the smooth musculature in their walls due to thermal and mechanical stimuli • Closure of the ductus arteriosus - by contraction of its muscular wall occurs almost immediately after birth Complete anatomical obliteration of ductus arteriosus by proliferation of the intima is thought to take 1 to 3 months • Closure of the Ductus Venosus : This was a fetal blood vessel that connects the umbilical vein to the inferior vena cava, a major vein leading to the heart. This shunt allows oxygenated blood from the placenta to bypass the fetal liver and travel directly to the heart. After birth, the ductus venosus closes and becomes a fibrous remnant called the ligamentum venosum. Becomes the ligamentum venosum, redirecting blood through the liver. Umbilical Arteries and Vein : • The umbilical arteries become the medial umbilical ligaments. • The umbilical vein forms the ligamentum teres of the liver.

Question 42

What is the function of umbilical arteries? What is the postnatal structure? What are the changes after birth?

Answer 42

Carry deoxygenated blood from fetus to placenta Medial umbilical ligaments (distal) Part of internal iliac arteries (proximal) Constrict after birth; distal portions become ligaments Proximal parts remain patent to supply bladder

Question 43

What is the function of umbilical veins? What is the postnatal structure? What are the changes after birth?

Answer 43

Carries oxygenated blood from placenta to fetus Ligamentum teres hepatis (round ligament of liver) Closes and fibroses postnatally

Question 44

What is the function of ductus venosus? What is the postnatal structure? What are the changes after birth?

Answer 44

Shunts blood from umbilical vein to IVC, bypassing liver Ligamentum venosum Closes shortly after birth

Question 45

What is the function of Ductus Arteriosus? What is the postnatal structure? What are the changes after birth?

Answer 45

Shunts blood from pulmonary artery to aorta (bypasses lungs) Ligamentum arteriosum Functional closure within hours; anatomical closure

Question 46

What is the function of Foramen Ovale? What is the postnatal structure? What are the changes after birth?

Answer 46

Shunts blood from right atrium to left atrium (bypasses lungs) Fossa ovalis Closes functionally at birth due to pressure changes

Question 47

What are the two mechanisms that blood vessels development?

Answer 47

1. Vasculogenesis in which vessels arise from angioblasts 2. Angiogenesis whereby vessels sprout from existing vessels

Question 48

What are the major vessels including the dorsal aorta and cardinal veins formed by?

Answer 48

Vasculogenesis

Question 49

What is the role of the respiratory system?

Answer 49

• All parts of the respiratory system function as air distributors except alveoli, tiny alveolar ducts that serve as gas exchangers • The respiratory system also filters, warms, and humidifies the air we breathe • Help produce sounds and phonation for speech • Special sensory epithelium makes the sense of smell (olfaction) possible • important role in the regulation, or homeostasis, of pH in the body.

Question 50

Describe the brochial tree

Answer 50

• After the primary bronchi enter the lungs, they branch into secondary, or lobar, bronchi that enter each lobe • The left primary bronchus divides into two secondary bronchi, entering the superior and inferior lobes of that lung • The right lung has three secondary bronchi that enter the superior, middle, and inferior lobes • Right bronchus has slightly larger diameter and more vertical orientation

Question 51

What does the development of the brachial (pharyngeal) apparatus shape into?

Answer 51

The head and neck anatomy in vertebrate embryos

Question 52

Describe the laryngeal development.

Answer 52

1. The larynx is located at the cranial end of the trachea. The surrounding mesenchyme from the fourth and sixth pharyngeal arches contributes to the cartilages (thyroid, cricoid, and arytenoid) and muscles of the larynx. 2. The epithelium of the larynx is derived from the endoderm of the respiratory diverticulum. 3. The laryngeal orifice (opening) forms between the pharynx and the developing trachea.

Question 53

What are the tissues involved in lung-bud formation?

Answer 53

1) Endoderm of gut forms the epithelial lining of larynx, trachea, bronchi and lung 2) Visceral mesoderm (surrounding the foregut) forms the cartilage, muscular, and connective tissue of the lungs

Question 54

When does lung bud (respiratory diverticulum) appear?

Answer 54

Appears in a 4 weeks old embryo - as an outgrowth from ventral wall of the foregut

Question 55

What are some developmental anomalies of the respiratory system?

Answer 55

• Esophageal atresia (EA) • Tracheoesophageal fistula (TEF)

Question 56

What is the sequence that the lungs form into?

Answer 56

Lung Bud - 2 bronchial (2 Bronchial Buds grow into) - Right & Left Bronchial main buds Right Bronchial main buds bronchi - 3 secondary bronchi (3 lobes) - 10 tertiary bronchi Left main bronchi - 2 secondary bronchi (2 lobes) - 8 tertiary bronchi

Question 57

Describe the development of the pleural cavity.

Answer 57

• Visceral mesoderm present outside of the lung - develops into visceral pleura • Parietal mesoderm layer present on the inside of the body wall - develops into parietal pleura • The space in between the 2 pleura, becomes the Pleural cavity • When the lung buds grow and branch, they push into the pleural cavity that is present around them.

Question 58

What is involved the branching of the lung bud that is regulated by the cellular interaction between the endoderm of the lung buds and the surrounding visceral mesoderm?

Answer 58

FGF (fibroblast growth factor)

Question 59

Where is the tracheal bifurcation at birth?

Answer 59

4th thoracic vertebra

Question 60

Describe the maturation of the lungs. 1. Embryonic 2. Pseudoglandular 3. Canalicular 4. Saccular 5. Terminal Sac/ Alveolar

Answer 60

Lung maturation is a complex, stage-dependent process that ensures the lungs are structurally and functionally prepared for efficient gas exchange at birth. It progresses through five key stages: 1.Embryonic (Weeks 4–7): The lungs begin to form as small buds from the throat area. 2.Pseudoglandular (Weeks 5–17): The airways branch and grow, but no structures for breathing are developed yet. 3.Canalicular (Weeks 16–25): Small airways and early air sacs form; blood vessels start to grow nearby for future gas exchange. 4.Saccular (Weeks 24–birth): Air sacs (saccules) grow larger and thinner, preparing for breathing. 5.Terminal Sac/Alveolar (Week 36–8 years): Final air sacs (alveoli) form and increase in number, allowing the lungs to mature and fully support normal breathing.

Question 61

What are the histological changes in the lung development for the pseudoglandular period?

Answer 61

Pseudoglandular period -Weeks 5 to 17 • Resemble exocrine glands • By week 16 all elements of lungs have formed But no gas exchange surfaces have formed - respiration is not possible

Question 62

What are the histological changes in the lung development for the canalicular period?

Answer 62

Canalicular period - Weeks 16 to 25 • Lumens of bronchi and bronchioles enlarge • By week 24, each has formed two respiratory bronchioles, each of which has split into three to six primordial alveolar ducts • Respiration is possible because the tissue is well vascularized, and there exist some thin- walled terminal sacs; respiration is still very immature Canalicular phase (until the end of 7th month): • Bronchioles divide into smaller canals, vascular supplies increases • Terminal bronchioles divide into respiratory bronchioles (which further divide into 3-6 alveolar ducts) • By the end of the 7th month, alveolar sacs are also present - premature infant may survive

Question 63

What are the histological changes in the lung development for the Terminal Saccular period?

Answer 63

Terminal Saccular period - Weeks 24 to birth • Many terminal sacs develop; their epithelium is very thin, and type I pneumocytes. Capillaries begin to bulge into the terminal sacs, establishing the blood-air barrier, which permits gas exchange • Type II pneumocytes appear during this stage and begin producing surfactant, but usually are not enough until later fetal life Terminal sac/Alveolar period - Late fetal period to 8- 10 years of age • At 32 weeks, terminal sacs analogous to alveoli are present with an alveolocapillary membrane sufficiently thin to allow for gas exchange • Sufficient amounts of surfactant are present • Between the third and eighth years, the adult complement of approximately 300 million alveoli has developed

Question 64

Describe the changes in the alveolar sacs during the last 2 months of fetal life.

Answer 64

Changes in the alveolar sacs during the last 2 months of fetal life/ Terminal sac phase • Terminal sacs increase in number • Type I alveolar cells become thinner, and capillaries adhere to the alveolar sacs • Blood–air barrier is formed • Type II alveolar cells were produced at the end of the 6th month of gestation, and actively produce surfactant inside the lung • Before birth, the lungs contain 1. Chloride-rich fluid 2. Protein 3. Mucus 4. Surfactant from the type II alveolar epithelial cells

Question 65

What is the role of surfactant?

Answer 65

• The surface of the water that lines the small alveoli tends to contract because of its high surface tension • This would result in collapsing the entire alveolus • Surfactant disrupts some of the attractive forces and thus reduces surface tension and the risk of alveolar collapse. (Patton, A&P 9e, 2016)

Question 66

What is the Law of LaPlace?

Answer 66

• Alveolar pressure (P A) is directly proportional to surface tension (T) and inversely proportional to the radius (r) of the alveolus • Smaller alveoli have more pressure inside than larger ones, if surface tension is the same. • Without surfactant, the pressure gradient would cause air to flow from the small alveoli to the larger alveoli, thus triggering collapse of the smaller alveoli (Patton, A&P 9e, 2016)

Question 67

What are the changes with the lungs during birth?

Answer 67

1) Fetal breathing movements begin before birth- aspiration of amniotic fluid- conditioning the respiratory muscles. 2) When respiration begins, fluid in the lung is rapidly resorbed 3) surfactant remains- deposited as a thin coat on alveolar cell membranes

Question 68

What are the changes of the lungs after birth?

Answer 68

• Alveoli size increases by a little bit. • After birth, the bronchial tree primarily grows due to an increase in the number of respiratory bronchioles and alveoli • Only 1/6 of the adult number of alveoli are present at birth. The remaining alveoli are formed during the first 10 years of postnatal life