Unit 2.L1-Development of Limbs, Integumentary System, Body Cavities, Mesenteries & Diaphragm Flashcards
(165 cards)
1
Q
What are the 4 cellular processes that promote Limb formation?
A
- Cell divison promotes the growth of limb
- Cell migration causes cells to reach their correct location
- Cell Differentiation produces specialized cells, such as muscle cells
- Apoptosis eliminates cells in between fingers
2
Q
By Day 26 & Day 28 respectively what appears and from where?
A
By Day 24, upper limb buds & Day 26 lower limb buds appears from the somatic lateral mesoderm.
3
Q
What appears from the somatic lateral mesoderm by Day 26, Day 28?
A
- Day 24→Upper limb buds
- Day 26→Lower limb buds
4
Q
What does the upper and lower limb buds contain? (2)
A
The bud has a mesenchyme core & outer epithelial ectoderm (comes from epiblast)
5
Q
What migrates into the buds from the somites?
A
The muscle cells migrate into the bud from the somites.
6
Q
What is present underneath the tip of the limb buds and what is its function?
A
Progress zone (PZ) (underneath the tip of the bud) has dividing & proliferating mesenchyme, which elongates the limb buds
7
Q
What lays above the progress zone (PZ) and what is its function?
A
The epithelial Apical Ectodermal Ridge(AER) (lays above the progress zone) and initiates limb bud formation
8
Q
Where does the Upper limb buds appear and what grows faster compared to it?
A
Upper limb buds appear low as the cranial half grows faster
9
Q
Upper limb buds form opposite to what?
A
Upper limb buds form opposite to the caudal cervical segments
10
Q
Lower limbs form opposite to what?
A
Lower limb buds form opposite to the lumbar/upper sacral segments
11
Q
What are the 2 developmental fields/organizing centers that are formed in the early limb? And include their locations
A
- Apical Ectodermal Ridge (AER) at the limb bud tip (anterior)
- Zone of Polarizing Activity(ZPA) with 2 PZ (Progress Zones) at the posterior by aggregation/condensation of mesenchymal cells
Limb patterning is regulated by positioning information
12
Q
What is the location and function of the Apical Ectodermal Ridge (AER)?
1 of 2 developmental fields/oganizing area
A
The AER at the distal border, induces proliferation of the underlying undifferentiated mesenchyme, elongating the limb bud
13
Q
What is function of the Zone of Polarizing Activiy (ZPA)?
A
When this zone of proliferating cells (proliferating/progress zone; PZ) begin differentiation and condense into the cartilage precursors, initiation of limb bones begin
14
Q
What are the 2 Progress zones of the Zone of Polarizing Activity (ZPA)?
A
- The proximal PZ
- The distal PZ (tip)
15
Q
What does the Promixal PZ differenitate into?
Part of the Zone of Polarizing Activity (ZPA)
A
The proximal PZ differentiate into blood vessels & cartilage bone models
16
Q
What does the distal PZ (tip) differentiate/flatten into?
Part of the Zone of Polarizing Activitiy (ZPA)
A
The distal PZ (tip) of the limb buds flatten into hand plates and foot plates
17
Q
Upper limbs develop __________ than lower limbs
A
earlier
18
Q
By Day 44 of hand formation, what condenses and what does it form?
Day 32-56, Wk 5-8
A
By Day 44, mesenchyme in the hand plates condense to form digital rays, forming fingers in the hand plates.
19
Q
How are fingers in the the hand plate formed?
A
Mesenchyme in the hand plate condensing to form digital rays
Footplate develops in the same way
20
Q
By day 48 of foot development, what condenses and what does it form?
A
By Day 48, mesenchyme in the foot plates condense to form digital rays, forming toes in the foot plates.
21
Q
What is present at the tip of each digital ray (formed in the hand and foot plate) and what does it become?
A
At the tip of each digital ray, the AER induces the mesenchyme to become bone primordia (phalanges)
22
Q
What induces mesenchyme (at the tip of each digital ray) to become bone primordia (phalanges)?
A
Apical Ectodermal Ridge (AER)
23
Q
What happens to the mesenchyme between the digital rays and what is formed?
A
The mesenchyme between the digital rays apoptose and separate digits. This form fingers and toes by eighth week
Apoptose: death of cells that is normal
24
Q
When are fingers and toes formed by in the developing fetus?
A
By the eight week
25
What forms bone models?
Mesenchymal cellular condensation
26
What occurs to the bones model in the 5th week, 6th week, 7th week and 12th week of development?
* 5th week: What centers appear?
* 6th week: What is the limb skeleton made of?
* 7th week: What begins in the primary ossification centers?
* 12th week: What is present in all long bones?
* **5th week:** **Chondrification centers** appear.
* **6th week (Day 42)**: The limb skeleton is **cartilaginous**
* **7th week**: **Osteogenesis of long bones** begins in the primary ossification centers.
* **12th week: Ossification centers** are present in **all long bones**
27
What occurs with the fingers and toes by day 52?
* The **fingers separate** toes begin to separate.
* Feet are **fan shaped but toes have not separated**.
28
What occurs to the fingers and toes by day 56? And what other features are visible?
* Digits of the hands and **feet are separated**.
* **Elbows , Knees and distinct digits** visible.
## Footnote
Rotation occurs during this time
29
How do the Upper limbs rotate? and where do the elbows point?
| By day 56
* Upper limbs **rotate laterally** by 90 degrees
* **Elbows** come to **point dorsally & point Caudally**
30
How do Lower limbs rotate? And where do the knees point?
| By day 56
* Lower limbs **rotate medially** by 90 degrees
* Knees come to **face ventrally & point Cranially**
31
Development of what by the 5th week provides innervation of the limb?
Development of the Dermatomal Patterns & Cutaneous Innervation of Limbs
##Footnote##
From the Pre-axial mesoderm
32
What grows into the dorsal and ventral masses of the limb buds?
| 5th week
**Motor axons** & later **Sensory axons** (from the spinal cord) grow into the dorsal & ventral muscle masses of the limb buds
33
What type of cells do neural crest cells give rise to? and what does it form?
| 5th week
Neural crest cells give rise to **Schwann cells**, myelin sheath surround motor/sensory nerve fibers in the limbs and form the **Neurolemma (aka Sheath of Schwann)**
34
Where does every dermatome originate from? And has an areas of skin innervated by what?
| 5th week
Every dermatome originates from a **single somite** & has area of skin innervated by a **single spinal nerve & its spinal ganglion**
35
The dorsal dermatome is also called the? and which somites are present in the upper and lower limb?
| 5th week
* **Preaxial border**
* Upper Limb: Cervical somites C3-C6; Lower Limb: Lumbar somites L2-L4
36
The ventral dermatome is also called the? and which somites are present in the upper and lower limbs?
| 5th week
* **Postaxial border**
* Upper Limb: Cerivcal and Thoracic somites C7-T2
* Lower Limb: Lumbar and Sacral somite L5-S3
37
What seperates the preaxial and postaxial borders in the upper and lower limbs?
| 5th week
Ventral axial line
38
What is caused by medial rotation of the lower limb?
| 5th wk
**Original ventral surface** of the lower limb **goes to the back** of the **adult limb**
39
Where does L5 and L2 (somites) of the lower limb rotate towards?
| 5th wk
L5 and L2: Rotated towards the **posterior aspect**
40
Where does S1, S2, and S3 (somites) of the lower limb move to?
| 5th wk
S1, S2, S3: Moves to the **center at the ventral axis**
41
Where does the developing blood supply to the upper limb start from?
Dorsal aorta
42
What does the dorsal aorta become before it enters the upper limb bud?
Intersegemental arteries
43
Where do intersegmental arteries go and what arteries do they become?
Intersegmental Arteries enter the upper limb bud and **bifurcates into the Primary axial artery** which becomes the **Branchial artery** (proximal arm)
44
What are the 4 branches of the brancial artery (proximal arm)?
1. Ulnar
2. Radial
3. Medial
4. Anterior Interosseous arteries
45
What does the Ulnar and Radial branches of the branchial artery form?
Palmer arches
46
Where does the developing blood supply to the lower limb start from?
Dorsal Aorta
## Footnote
(Umbilical, Common/External Iliac arteries)
47
What other important vessels that formed in the upper limbs? (2)
* Deep Superficial palmar arch
* Fine Capillary Network in limb mescenhyme & hand plate
48
What does the Dorsal Aorta bifurcate into in the Lower limbs? What does it give rise to?
The **common Iliac artery** which gives rise to the:
1. **Primary axial artery**
2. **External Iliac artery**
49
Which artery does the primary axial artery give rise to in the lower limb buds?
**Deep artery of the thigh (profunda femoris)**
50
Which arteries does the External Iliac artery of the lower limb give rise to? (2)
**Femoral artery→Popliteal artery**
51
Which arteries does the Popliteal artery (from the ext. iliac artery) in the lower limbs give rise to? (3)
1. **Fibular artery**
2. **Anterior tibial artery**
3. **Posterior tibial artery**
* Lateral Planter Artery
* Medical Planter Artery
52
What are the foot & toe capillaries and where do they arise from?
* **Lateral Planter Artery**
* **Medial Planter Artery**
* Arise from the Posterior tibial artery
53
When do limb defects occur in fetuses and how often?
* **D24 -36**: Limb defects occur during the **most critical period** of limb development.
* Common: **1:500 neonates**
## Footnote
Causes include genetics, environmental (tabacoo, alcohol)
54
# Birth Defect of the Limbs
What is Quadruple Amelia and what causes it?
* Quadruple Amelia means **all four limbs** are missing
* Cause was **Thalidomide** (teratogen) that is most **potent at 3-5 week stage**
## Footnote
* Amelia: Absense of limbs
* Thalidomide a medication from Europe that helped treat morning sickness
55
# Birth Defect of the Limbs
What is Meromelia?
Partial limb formation
56
# Birth Defect of the Limbs
What is Sironomelia (Mermaid Syndrome)? and is cause known?
* **Caudal dysgenesis**: lower limbs fused; appears like a **mermaid's tail**
* Exact cause unknown; sporadic!
57
# Birth Defect of the Limbs
What are some examples (5) of split hand/foot malformations (SMFMs) and what is the cause?
* Bifurcated (forked) hand
* Cleft foot
* Absence of one or more central digits
* Fingers missing
* Toes missing
* Cause: **Failure of development** of **one or more digital rays**
58
# Birth Defect of the Limbs
What is Brachydactyl and what type of genetic trait is it? What clinical manifestation is seen?
* **Shortness** of the **digits** (fingers or toes) due to reduction in the length of the phalanges
* **Dominant** inherited trait
* Shortness of body or overall short stature
59
# Birth Defect of the Limbs
What is Polydactylyl and what type of gentetic trait is it?
* Shows **more than five digits** on the **hands or feet**.
* Extra digits are called **“supernumerary digits”**
* **Dominant** inherited trait.
60
# Birth Defect of the Limbs
What are the extra digits caused by Polydactylyl called?
Supernumerary digits
61
# Birth Defect of the Limbs
What are the two types of Syndactyly?
1. **Cutaneous Syndactylyl**
2. **Osseous Syndactylyl**
62
# Birth Defect of the Limbs
What is Cutaneous Syndacytyl? Where is it more frequent? And what causes it?
* **Simple webbing** between digits is called “cutaneous syndactyly” . It is seen **more frequently in the foot** than in the hand.
* Cause: Failure of the webs to degenerate between two or more digits due to **blockade of cell apoptosis**; thus, the digits do not separate
63
# Birth Defect of the Limbs
What is Osseous Syndactyly and what causes it? Where is it seen frequently?
* Fusion of bones (**synostosis**).
* Cause: Notches between the digital rays fail to develop & **digits do not separate**. Seen **frequently between the third and fourth fingers** and between the **second and third toes**
64
* What is Talipes equinovarus aka Clubfoot?
* How common is it and what is the cause?
* Explain the characteristics present (What is the position of the foot and what does it cause? Where is the sole of the foot turned? The foot is what? How is it seen in 50% of the cases? Who gets affected more?)
* What is the treatment?
* Talipes equinovarus (Latin talus (ankle) + pes (foot)) or clubfoot is a common birth defect with **musculoskeletal deformation**
* 1:1000 births
* Cause: **Multifactorial inheritance**
**Characteristics**
* Abnormal position of the foot **does not allow normal weight bearing**
* The **sole of the foot** is **turned medially**
* The foot is **inverted (incurving)**
* Seen **bilaterally in 50%** of cases
* Occurs **twice** as frequently in **males**
* Treatment: **Casting or taping & physiotherapy**
65
Limb buds appear _______ of gestation as ________ on the __________.
Limb buds appear **24-28th day** of gestation as **slight bulges** on the **ventrolateral body wall**
66
Upper limbs develop _______ of lower limbs from ___________ and _________.
Upper limb buds develop **2 days ahead** of lower limb buds from **mesoderm + ectoderm.**
67
The limb buds elongate by ________ of the __________.
The limb buds **elongate** by **proliferation** of the **mesenchyme**
68
_________ degenerates tissues in the ________ between the digital rays.
**Cell apoptosis** degenerates tissues in the **notches** between the digital rays
69
_______ are derived from mesenchyme (myogenic precursor cells;myoblast) originating in the ___________. ________ convert to ________ to form mature muscles.
**Limb muscles** are derived from mesenchyme (myogenic precursor cells; myoblast) originating in the **somites**. **Myoblast** convert to **myotubes** to form mature muscles.
70
Myoblasts migrate and form ___________ and _________ muscle masses. __________ grow into these muscle masses.
Myoblasts migrate and form **dorsal and ventral** muscle masses. **Nerves grow** into these muscle masses.
71
Blood vessel in the limb buds arise from the ____________.
Intersegmental arteries
72
Many birth defects of the limb have ___________; may arise as a result of interaction of _____________.
Most birth defects of the limbs have **hereditary influence**; many arise as a result of interaction of **genetic & environmental factors (multifactorial inheritance)**
73
What is the Integumentary System?
The Skin & Its appendages the protect humans
74
How many layers does the skin has and where were they dervied?
Skin has two layers derived from two different germ layers:
1. **Epidermis**: Superficial epithelial tissue derived from surface **ectoderm**
2. **Dermis**: Deeper layer of connective tissue derived from **mesoderm**
75
During the 4-5th week of development what is the epithelium of the surface ectoderm of the skin? what does it form?
The surface ectoderm of the skin is made of **simple cuboidal epithelium** and forms the **primordium of the epidermis**
76
During the 7th week, What begins to happen to the simple cuboidal epithelial cells and what do they form?
The simple cuboidal epithelial cells start to **proliferate** and form **TWO layers** of **squamous epithelium**
77
What are the 2 layers of the squamous epithelium? What occurs in each layer?
* **The 1st layer**: **The periderm**→ **keratinization**→**Desquamation** (shedding)→**Complete Exfoliation of peridermal cells** forming part of **vernix caseosa**
* **The 2nd layer**: **The basal layer cells**: replace the periderm and forms the **“future stratum germinativum”**
78
What layer of skin is formed at 11 weeks and what does it contain and where is it located?
An **intermediate layer**, containing **several cell layers**, is interposed between the **basal cells (future stratum germinativum) and the periderm**
79
Where do cells of the intermediate layers invade and what do they form?
Cells from this intermediate layer invade the **dermis to form epidermal ridges**, which form **future fingerprints on digits**
80
What can be used for diagnosis of Chromosomal defects? (eg. Down Syndrome)
**Abnormal and unique epidermal ridge pattern** is used for diagnosis
81
During the early fetal period, what is the epidermis invaded with? where are they derived from?
During the early fetal period the epidermis is invaded by **melanoblasts**, which are the cells **derived from the neural crest cells in mesoderm**
82
Where do melanoblast move to and what do they differentiate into?
Melanoblasts move to **dermoepidermal junction** and differentiate into **melanocytes (pigment-producing cells)** between day 40-50 (late embryonic stage)
83
What is involved in the differentiation of Melanoblasts into Melanocytes?
* The formation of **pigment granules (grain-like particles containing “Melanin” in “Melanosomes”)**
84
What are the unique type of melanin carried by the melanoblast/melanocytes and what is the outcome for each?
* Eumelanins→Black/brown heads
* Pheomelanins→Red heads
## Footnote
Some individuals can synthesis both
Phemelanins are more prone to skin cancer
85
Where do Melanocytes reside and how does this affect skin color?
* **Melanocytes reside in epidermis with their dendrites**
* Dendrites carry melanosomes which secrete out the melanin which is taken up by kerationcytes into the epidermis/epithelial cells on top
## Footnote
How melanosomes are distrubuted determines skin color not how much is present
86
What disappers and forms on the skin by the 21st week?
* Periderm disappears
* Multiple layers of the epidermis are formed by differing stages of keratinization
87
What are the 5 layers of the epidermis?
1. **Stratum corneum** (Horney top layer; dead corneocytes)
2. **Stratum lucidum** (Smooth layer; Eleidin a product of Keratohyalin)
3. **Stratum granulosum** (Granular layer)
4. **Stratum spinosum** (Spinous polyhedral or prickle cell layer)
5. **Stratum basale** (Stratum germinativum cell layer)
## Footnote
NOTE: **At birth all adult epidermis layers are present**
88
What gives rise to two disctinct types of the epidermis and what are they?
Continuous **inductive interactions** with the **dermis** gives rise to the **two distinct type of epidermis depending on its thickness**
1. Thick skin
2. Thin skin
89
* Where does thick skin cover and what is present/not present there?
* Where does thin skin cover and what is present/not present there?
**Thick Skin**
* Covers the **palms** of the hands and **soles** of the feet.
* Has **sweat glands only**
* NO hair follicles or hair
* NO arrector muscles of hairs
* NO sebaceous glands
**Thin Skin**
* Covers most of the rest of the body
* It contains hair follicles, arrector muscles of hairs, sebaceous glands, and sweat glands.
90
What type of cells is the dermis derived from?
The dermis is derived from the **mesenchyme** (mesoderm/dermatomes) underlying the surface ectoderm (epidermis)
91
What are the two origins of the skin mesenchyme of the dermis?
1. Most from **Somatic layer of the Lateral mesoderm**
2. Some from **Dermatomes of the somites (fibroblasts)**
92
* What type of tissue fibers are being produced by the mesenchymal cells at the 11th week?
* What is the dermis made up of at birth?
* **At 11th week**: the mesenchymal cells begin to produce **collagenous and elastic connective tissue fibers**
* **At birth**: **the dermis is made up of 2-layers** (two mesodermal layers)
1. **The papillary layer**
2. **The reticular layer**
93
What does the dermis (specifically the papillary layer) form and where?
Between the **descending epidermal ridges**, the dermis (**the papillary layer**) **interdigitate upward** and forms the **dermal papillae** (finger prints)
94
What develops and what invades the dermal papillae?
* **Sensory nerve endings** develop and **invade** into these papillae.
* **Capillary loops of blood vessels** also simultaneously **invade the dermis** and provide nourishment
95
At 5-6 weeks what develops concerning hair?
**Hair bud** develops by 5-6 weeks, but the **hair is visible** only later by **20th week**
96
How are hair buds developed? (Epidermal cells proliferate inwards, giving rise to what? And invades what? )
What happens to the hair buds at 16 weeks?
* What does the root of the hair bud become? What does it form?
* What does the hair bud get filled by?
* Where does the hair shaft grow from?
* After 14 wks: Epidermal cells **proliferate inwards**, giving rise to hair buds that **invade into the underlying dermis**
* 16 wks: The **root of the hair bud** becomes **cup-shaped, forming a hair bulb with a hair shaft**
* 16 wks: The hair bulb gets filled by **mesenchymal “hair papilla”** (some melanocytes are also present)
* 16 wks: The **hair shaft grows** from the **central epithelial cells** of the hair bulb.
97
Where does the hair shaft invade at the 20th week?
20 wks: The **hair shaft invades upwards** into the **epidermis** and protrudes **out of the skin**
98
What does the peripheral cells of the hair bulb form?
The peripheral cells of the hair bulb form the **epidermal(secondary epithelial layer)/dermal (muscle layer) root sheath**
## Footnote
* Epidermal root sheath forms INTO the mesodermal cells
* Dermal root sheat forms FROM the mesodermal cells
99
What do the cells of the epithelial sheath form?
Laterally, the cells of the epithelial root sheath proliferate to form a **sebaceous gland bud (Sebum)**
## Footnote
Formed in the same gland that hair is growing
100
What is formed from the mesenchymal cells that differenitate into the dermal sheath?
The **arrector pili muscle** (for goose bumps, sebum) differentiates from the surrounding mesenchyme.
## Footnote
The more the arrector pilli contracts the more oil will come out
101
What cells migrate into the hair bulb and what is there function?
* **Melanoblasts** migrate into the hair bulb and differentiate into **melanocytes** to provide hair color
* **Capillaries/blood vessels** come in to provide the hair bulb with **nourishments**
## Footnote
Some epithelial cells and mesenchymal stem cells present near the bulb get nourished all the time
102
When and how do sweat glands develop in the skin? What do they start as?
* Sweat glands develop by ~20th wk.
* Starts as **solid growth of epidermal cells** invading the dermis by 16th wk
103
For the Sweat Glands:
* The terminal parts coils and forms what?
* The central cells degenerates and forms what?
* The peripheral cells differeniate into what?
* Its **terminal part coils** & forms **“body of the gland”** by 20th wk
* The **central cells degenerate** to form the **lumen of the gland (sweat duct)**
* The **peripheral epithelial cells differentiate** into:
1. **Secretory cells (sweat)**
2. **Contractile myoepithelial cell**
## Footnote
Contractile myoepithelial cell contract as sweat comes out (Sympathetic)
104
What are mammary glands?
Mammary glands are modified & **highly specialized types of sweat glands**
105
By the 4th week, where do Mammary Crests (ridge) develop? Where do they eventually proliferate at?
* By 4th wk **Mammary Crests** (ridges) develop along **each side of the ventral surface** of the embryo.
* Mammary Crests spans the **axillary region (armpit) to the inguinal region**
* Eventually, the **Crest regress** in most locations & **proliferate around pectoral muscles**
106
What gives rise to the lactiferous ducts of the mammary glands?
The **down-growth** of epidermis/epithelial tissue continues to proliferate into **16-24 solid out-buddings** which give rise to the **lactiferous ducts (milk)**
107
What does the fibrous connective tissue form in the mammary gland?
| Surrounding meschyme
Fat or adipose tissue of the mammary gland
108
How is the mammary pit formed? And what happens to it after birth?
* **Epithelial lactiferous ducts** at first open into a **small mammary pit**.
* **After birth**, **the nipples rise** from the **mammary pits** because of **proliferation/pushing** of the surrounding **connective tissue mesenchyme below the “Areola"**, which surrounds the nipples.
## Footnote
The depressed nipple is d/t apoptosis
109
When and how do fingernails and toenails develop?
* 10th Wk: **Toenails and fingernails** develop as **thickened areas of the epidermis (nail fields)** at the **tips of the digits**
* By 32 weeks the fingernails formed
* By 36 weeks the toenail formed
110
Where does the nail field extend and what eventually grows over it and what does it form?
* The **nail fields** extend to the **dorsal surface** and is surrounded by the **lateral nail folds**
* Cells from the **proximal nail fold** grow over the nail field and form **keratinized nail plate, the primordium of the nail**, which grows toward the tip of the finger.
111
What are the 2 parts of the Keratinized Nail Plate?
1. **Eponychium** (corneal layer of *epidermis*; **proximal cuticle**)
2. **Hyponychium** (skin under the free margin of the nail)
112
What are the five adult cavities? And how are the seperated?
**Dorsal Cavity**
1. **Cranial Cavity**
2. **Vertebral Cavity**
**Ventral Cavity**
3. **Thoracic Cavity**
4. **Abdominal Cavity**
5. **Pelvic Cavity**
## Footnote
* Thoracic cavity: one pericardial; two pleural cavities
* Abdomino-pelvic cavity: one larger peritoneal cavity
113
How and when is the Intraembryonic cavity formed? (What is formed in the lateral mesoderm? What is formed by merging the vacuoles? What does the flat embryo split into and what is it surrounded by?)
* Day 20: **Vacuoles** formed in the **lateral mesoderm**
* Day 21: **U- or Horse shoe-shaped body cavity** forms by **merging of vacuoles** in the lateral mesoderm in the **flat trilaminar disc** (3-Somite stage).
* **“FLAT EMBRYO”** splits →**U-shaped cavity (Intraembryonic Coelom)** surrounded by **two layers**:
1. **Somatopleure layer (Parietal layer;body wall)**
2. **Splanchnopleure layer (Visceral layer; organs)**
114
What is formed by merging the vacuoles that formed in the lateral mesoderm?
**U- or Horse shoe-shaped body cavity** forms by **merging of vacuoles** in the lateral mesoderm in the **flat trilaminar disc** (3-Somite stage).
115
When the "Flat Embryo" (flat trilaminar disc) splits what is formed?
**U-shaped cavity (Intraembryonic Coelom)** surrounded by **two layers**:
1. **Somatopleure layer (Parietal layer;body wall)**
2. **Splanchnopleure layer (Visceral layer; organs)**
116
What are the two layers of the developing body cavity? And what do they cover/line?
* **Visceral (serous) layer** – *Covers organs* (Sphanchnopleure)
* **Parietal (serous) layer** – *Lines the body wall* (Somatopluere)
## Footnote
* Visceral: Inner membrane
* Parietial: Outer membrane
116
What is the Pericardio-peritoneal canal?
Connection between the pericardial coelom and peritoneal coelom (cavity)
117
What are serous membranes? And what is its function?
* Single mesothelial cell layer (inner/outer)
* Functions to **preclude adhesions** among organs so that organs can grow & move freely to be **positioned & sculpted**
118
What are the Throacic membranes lining the cavity?
* Visceral pleura
* Parietal pleura
* Visceral pericardium
* Parietal pericardium
## Footnote
* Pleura: lungs
* Pericardium: heart
119
What are the Abdominopelvic membranes lining the cavity?
* Visceral peritoneum
* Parietal peritoneum
* Visceral perineum
* Parietal perineum
## Footnote
* Peritoneum: abdominal organs
* Perineum: geneto-anal organs
120
What does the "cranial bend" and lateral extensions ("limbs") of the intraembryonic coelom each form?
* The **“cranial bend”** in the intraembryonic coelom forms **future pericardial cavity**
* The (lateral extensions; **“limbs”**) forms the future **pleural and peritoneal cavities**
| Day 21-22
## Footnote
Continuity of Intraembryonic & Extra embryonic cavity at lateral edges
121
How is the Pericardial cavity formed is the early heart?
Early heart growing and pushing into the 2 layer coelom (u-tube) which forms the visceral and parietal pericardium, between them is the formation of the pericardium (pericardial) cavity
122
What makes up the extraembryonic splanchnopluere and somatopleure?
* **Splanchnopleure**=Endoderm+splanchnic mesoderm
* **Somatopleure**=Trophectoderm+somatic mesoderm
123
What action brings the "limbs" of the coelom together? On what side of the embryo?
**Horizontal folding** brings the **“limbs”** of the coelom together on the **ventral side** of the embryo.
124
What is the coelom lined with and where is it derived from?
* The coelom is **lined by the mesothelium (serous membrane)**
* Derived from the **somatic mesoderm (parietal layer)** and the **splanchnic mesoderm (visceral layer)**
125
What does the junction of the somatic (parietal) and sphlanchic (visceral) layers of the mesoderm form dorsally and ventrally?
* Dorsally→**Dorsal Mesentery**
* Ventrally→**Ventral Mesentery**
126
What is reduced when the dorsal and ventral mensentaries are being formed?
Reduced communication between the intra-embryonic & extra-embryonic coeloms
127
The somatic mesoderm forms what?
The **somatic mesoderm** forms the **parietal-peritoneum lining the abdominal wall**
128
The splanchnic mesoderm forms what?
The **splanchnic mesoderm** forms the **visceral-peritoneum** covering the organs
129
Which mesentary disappears and what is formed?
**Disappearance** of the **ventral mesentery** & **formation of the ventral body wall**
130
What moves dorsally and begins to split the thoraic and abdominal cavities?
**Septum transversum** moves dorsally and begins to **split the thoracic and abdominal cavities**
131
What action brings the pericardial cavity to the ventral side of the foregut?
**Cranial folding** brings the **pericardial cavity** to the **ventral** side of the foregut
132
**The Pericardioperitoneal Canals**:
* Arises from?
* Passes where?
* Lies where?
* Caudally, opens into what?
* **Arise from the dorsal wall** of the pericardial cavity
* Pass on **each side of the foregut**
* Lie **dorsal to septum transversum**
* Caudally, open into the **peritoneal cavity**
133
What pathway does the dorsal mesentery eventually form?
Pathway for blood vessels, nerves and lymphatics to reach the gut tube
134
Dorsal mesentary forms a pathway for blood vessels the the gut. Which artery provide blood to the 3 sections of the gut?
| End of 4th week
1. **Celiac arterial trunk (foregut)**
2. **Superior mesenteric artery (midgut)**
3. **Inferior mesenteric artery (hindgut)**
| 5 week embryo
135
# Embryonic cavities in a 5 week embryo
What is attached to the midgut? What remains seperated?
* Umbilical cord is attached to the mid-gut.
* Peritoneal cavities remain separated.
136
# Embryonic cavities in a 5 week embryo
What is the state of the peritoneal cavity in the hingut?
Peritoneal cavity is continuous
137
What folds are formed?What canal is formed and what incompletely divides the cavity into two at Day 28? What does incomplete division allow for?
* **Pleuropericardial folds** are formed.
* **Pericardio-peritoneal canals forms** as the **septum transversum incompletely** divides the cavity into two:
1. **Thoracic cavity**
2. **Abdominal (peritoneal) cavity**
* **Incomplete division** allows formation of **continuous Pericardio- peritoneal canals bilaterally**
## Footnote
Formation of the Pleuropericardial folds & Pericardioperitoneal canals
138
What seperates the thoracic cavity? And what two distinct cavities are evident?
| At 35 days (end of 5 weeks)
* **Pleuropericardial folds** separate the thoracic cavity
* Two distinct cavities are evident:
1. **Pericardial cavity**
2. **Pleural cavities**
139
What does the Pleuropericaridal folds carry? How does the position of the heart change and what fuses? And what does the pleuropericardial folds eventually form?
| At 35 days (end of 5 weeks)
* The Pleuropericardial folds carry the **phrenic nerves & common cardinal veins**
* The position of the **heart changes inferiorly** & the folds fuse.
* The pleuropericardial folds then forms the **fibrous pericardium**
140
* The LUNGS grow __________ & expands the _____________
* The heart moves _____________
* The LUNGS grow **inferiorly** & expands the **pleural cavities**
* The HEART moves **inferiorly**
141
What is isolated when the Pleuropericardial fold fuse to form fibrous pericardium?
Pleuropericardial folds fuse to form fibrous pericardium, isolating the **pericardial cavity**
142
What canals and cavity are continous by week 5?
The pericardio-peritoneal canals & the pericardial cavity are continuous
143
6 weeks: Lung ________ & the pleural cavities ________ into the body wall & splits the __________
6 weeks: Lung **grows** & the pleural cavities **expand** into the body wall & splits the **somatic mesoderm**
144
7 weeks: Pleural cavities expand ________ around the ________. ___________ fuse medially, ventral to __________.
7 weeks: Pleural cavities expand **ventrally** around the **heart**. **Pleuropericardial folds** fuse medially, ventral to **esophagus**
145
8 weeks: Lungs/pleural cavities expand and split mesoderm further into what? (2)
1. **Inner fibrous pericardium** protecting/isolating the heart
2. **Outer thoracic wall** protects the lungs/pleural cavity
146
What is the primordial mediastinum and where does it extend?
| 8 wks
Primordial mediastinum (mesenchymal mass), extends from the sternum to the vertebral column.
147
What are the four components that the diaphragm develops from?
1. Septum transversum
2. Dorsal mesentery of esophagus
3. Pleuroperitoneal folds
4. Muscular ingrowth from lateral body walls
148
What is the state of the developing diaphragm in:
* 5 weeks:
* 6 weeks:
* 12 weeks:
* 5 weeks: Unfused pleuroperitoneal folds
* 6 weeks: **Migration of myoblasts** fuse the pleuro-peritoneal folds with **septum transversum** & **esophageal mesentery**
* 12-weeks: Muscular ingrowth from the body wall (4th component).
149
In the neonate diaphragm what does the septum transversum form? And what thickens?
* Septum transversum forms the **Central tendon of diaphragm**
* **Muscular ingrowth thickens**
150
What is the crura of the diaphragm and where does it extend?
Crura of the diaphragm: **Two tendinous structures** (**left right & crus**; leg like structure), extends below the diaphragm to the vertebral column
151
After the fusion of the 4 components of the diaphragm what invades the other parts forming the diaphragm and what does it give rise to?
After the fusion of the 4 components of the diaphragm, **the myoblasts from the pleuroperitineal folds and the lateral body wall** invade into the other parts forming the diaphragm & give rise to the **muscles of the diaphragm**
152
What innervates the muscles of the diaphragm?
During development the **phrenic nerve** descends from **spinal nerves (C3, C4, C5)** & **passes through the pleuropericardial membranes/folds** and **innervates the muscles of diaphragm**
153
What is Congential diaphragmatic hernia (CDH)? Where does it occur and what clincial manifestations are common?
| Also called Posterolateral Defect of Diaphragm
* CDH occurs commonly through a **posterolateral defect** in diaphragm (1: 2200 neonates)
* Occurs mostly on left side.
* **Left lung hypoplasia** is common
* **Herniation** of abdominal contents
154
What causes Eventration of the Diaphragm?
Because of **defective musculature** development of the **diaphragm** the **abdominal viscera are displaced** in the thorax **within a pouch of diaphragmatic tissue**
155
What is Congential Hiatal Hernia?
**Herniation** of part of the **fetal stomach** may occur through an excessively large esophageal hiatus
156
The __________ splits to form the __________. (Day 21)
The **lateral mesoderm** splits to form the **intraembryonic coelom** (Day 21)
157
_____________ circles ________ to form a ________ in the ____________ by day 28
**Intraembryonic coelom** circles **cranially** to form a **U-shaped cavity** in the **cardiogenic mesoderm** by day 28
158
Cranially, the coelom forms the ___________ and laterally, future ________ and ___________ cavities.
Cranially, the coelom forms the **pericardial cavity** and laterally, future **pleural** and **peritoneal** cavities.
159
___________ parts of the Intraembryonic coelom move _______ towards the _________ aspects and merge to form the _________.
**Lateral** parts of the intraembryonic coelom move **medially** towards the **ventral** aspect and merge to form the **peritoneal cavity**
160
The ________ of mesoderm enclose the ________ and suspends it from the _________ by a ____________ (made of splanchnic & somatic layer)
The **splanchnic layer** of mesoderm encloses the **primordial gut** and suspends it from the **dorsal body** wall by a **double-layered dorsal mesentery** (made of splanchnic & somatic layer)
161
Fusion of the __________ during formation of the _________, seperates the ________ from the _________.
Fusion of the **caudal pleuroperitoneal folds** during formation of the **diaphragm** separates the **pleural cavities** from the **peritoneal cavity**
162
The diaphragm develops from:
(i)
(ii)
(iii)
(iv)
The diaphragm develops from the **(i) septum transversum, (ii) mesentery of the esophagus, (iii) pleuroperitoneal folds & (iv) muscular outgrowth from the body wall**
163
The diaphrgam divides the body cavity into ______ and _______.
The diaphragm divides the body cavity into **thoracic** and **peritoneal cavities**
164
A birth defect (opening) in the pleuroperitoneal membrane on the left side causes what?
CDH (Congential diaphragmatic hernia)
