Human Structure & Development 212
COELOMIC CAVITIES
Structure and development
THIS WEEKS LAB:
The thoracic Cavity
READINGS
eg. Cartmill and Hylander: The thorax
Stern: Thorax
Grants Method: The thorax
or - Moores:- The thorax
or any other regional anatomy textbook - similar sections
IN THIS LECTURE I WILL COVER:
Lateral plate mesoderm and the coelomic cavity
Somatopleure
Visceropleure
Definition and adult structure of serous cavities
Pericardial cavity
Pleural cavity
Peritoneal cavity
Intra-embryonic coelom and lateral plate mesoderm
Partitioning of the coelom
Embryonic folding
Development of the Diaphragm
Peritoneal cavity
Foregut, Midgut and Hindgut
The Intra-embryonic coelom
Definition and Adult Derivatives
The coelom is a space which develops within the mesoderm.
The extra-embryonic coelom develops within the extra-embryonic
mesoderm during week 2
The intra-embryonic coelom
1. Develops within the intra-embryonic mesoderm during week 3
2. Divides the lateral plate mesoderm into two layers:
A. Somatopleure - associated with the ectoderm
B. Visceropleure - associated with the endoderm
Accordingly derivatives of
the Intra-embryonic
coelom are spaces which
separate the body walls
(somatopleure) from the
viscera (visceropleure)
Derivatives of the intraembryonic coelom: (Serous cavities)
Pericardium - surrounds the heart
Pleura
- surrounds the lungs
Peritoneum - surrounds the abdominal organs
The Intra-embryonic coelom
Arrangement of Serous Cavities
Structure of Serous Membranes
Organs are surounded by their serous cavity
(They don’t lie inside a serous cavity)
The serous cavities are lined by a serous membrane:
Pericardium lines the Pericardial cavity
Pleura lines the Pleural cavity
Peritoneum lines the Peritoneal cavity
Serous membranes (peritoneum, pleura and pericardium) are thin sheets
of connective tissue coated on one side with a simple squamous
“mesothelium”
The mesothelium exudes a thin film of serous fluid so that side is a
non-stick surface.
The connective tissue side and it adheres to adjacent tissues
Organs develop adjacent to the coelom and invaginate the cavity
As they grow “into” the cavity they become coated by a layer of serous
membrane (“visceral layer coats the organ”).
The serous cavity surrounds the organ.
The parietal layer
lines the body
cavity.
It is further
subdivided and
named according
to the parts it
covers:
*eg. Costal pleura
lines the rib cage.
*eg. Diaphragmatic pleura coats the diaphragm (thorax side).
*eg. Diaphragmatic peritoneum coats the diaphragm (Abdomen side).
Zygosis
We shall see later that there are some occasions when peritoneum does stick to
itself.
A) Normal process in the development of “secondarily retroperitoneal organs”
B) Pathological process in response to injury or infection (adhesions)
The visceral and parietal layers are parts of the same serous membrane
enclosing the cavity
Mesenteries
Some books refer to a “connecting layer” which are also known as
mesenteries
Development of the Serous Cavities
The coelom begins as a horseshoe shaped cavity
The ends of the horseshoe are initially continuous with the extraembryonic coelom.
The arch of the horseshoe passes
1. :In front of the oral membrane
2.
3. Behind the cardiogenic area (developing heart) and behind the
septum transversum (developing diaphragm)
Development of the pericardial cavity
Heart
Week 4 - Folding of the embryo (and the coelom) partitions the Coelom
into Pericardium and left and right pleuro-peritoneal canals.
Coelom
When the head fold occurs:
* The septum transversum and the developing heart and brought into their
proper positions and the thorax is formed:
· The coelom is folded
too.........
Becomes:
Pericardium and two
Pleuroperitoneal canals
Development of the pleural cavity
Lungs
*The foregut (oesophagus) runs down behind the developing heart
*It has the pleuroperitoneal canals on either side
*The foregut gives rise to the lung buds which grow out into the left
and right pleuroperitoneal canals
*The Septum transversum (Developing diaphragm) receives its nerve
supply (phrenic nerve) from cervical nerves (C34&5).
*When folding occurs the phrenic nerve is dragged down through the
thorax
*The phrenic nerve comes to lie between the pericardium and the
pleuro-peritoneal canals - helps to separate these parts
Development of the peritoneal cavity
Gut tube
Initially the peritoneal cavity is in left and right parts.
The gut has a dorsal and ventral mesentery
The liver develops in the ventral mesentery of the foregut
And the foregut retains both ventral and dorsal mesenteries
Diaphragm (separates the thorax
and abdomen)
The pleuroperitoneal canals are partitioned (into pleural and peritoneal
cavities) by the growth of the diaphragm:
1. Septum transversum (centrally)
2. Pleuroperitoneal folds (posteriorly)
3. Ingrowth of the body wall (laterally)
The midgut and hindgut lose their ventral mesentery
So the left and right sides become a single cavity.