Transcript Topic 15

BIOL 370 – Developmental Biology
Topic #15
Lateral Plate Mesoderm and Endoderm
Lange
Figure 12.1 Mesodermal development in frog and chick embryos
Notice here how if the
chicken is removed from the
large yolk (c ), that it will
develop in a circular pattern
like the frog.
Figure 12.2 Overview of heart development
Heart development
comparing chick and
mouse.
Heart field formation is a major step in heart development.
The first heart field forms a primary aspect of the left ventricle,
whereas the second heart field forms the primary portions of the
right ventricle and the two atria in organisms with a four
chambered heart.
Figure 12.3 Model of inductive interactions involving the BMP and Wnt pathways that form the
boundaries of the cardiogenic mesoderm
In this model, please note how the lateral plate mesoderm has two regions with
two different, but related outcomes. The anterior will become the heart whereas
the posterior will become the blood & vessels. Also notice how Wnt, Noggin,
and BMP affect development.
Figure 12.4 Formation of chick heart from splanchnic lateral plate mesoderm
• The endocardium is the
innermost layer of tissue that
lines the chambers of the heart.
• Its cells are similar to the
endothelial cells that line blood
vessels.
• The endocardium also provides
protection to the valves and heart
chambers.
Figure 12.5 Migration of heart primordia
• In (a) we see what is called
cardia bifida which is a period
where the embryo has “two”
hearts because there is no
interconnection (this is a
chicken).
• (b) & (c) show zebrafish, but (c)
is a mutant form called miles
apart (for obvious reasons)
• (d) & (e) show mouse with (d)
showing heart fusion and (e)
showing a Foxp4 deficient
mouse
MCPs are multipotent cardiovascular progenitors. They develop into:
• endocardium - the innermost layer of tissue that lines the chambers of the
heart
• endothelium - the thin layer of cells that lines the interior surface of blood
vessels and lymphatic vessels
• smooth muscle
• cardiomyocytes (cardiac muscle cells)
Figure 12.8 Cardiac looping and chamber formation (Part 1)
Human heart formation and looping occurs
during the 3rd to 4th week after fertilization.
*** Also notice how the aortic sac tissues at
day 21 become both the aortic sac and
pulmonary arteries by birth as we talked about
in the prior chapter.
Figure 12.8 Cardiac looping and chamber formation (Part 2)
• Notice how significant a change has occurred between stage 9 and
stage 10 chick embryo (b & c)
• (d & e) both show the mouse heart and show through selective
staining how specificity of the atria and ventricles have already
occurred (due to differences in their myosin proteins)
Figure 12.9 Formation of the chambers and valves of the heart
Three examples of congenital heart defects
Narrowed
aorta
Occurs in
about 1 in every
500 births
(a) Ventricular septal defect.
The superior part of the interventricular septum fails to form;
thus, blood mixes between
the two ventricles, but because
the left ventricle is stronger,
more blood is shunted from
left to right.
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Occurs in
about 1 in every
1500 births
Occurs in
about 1 in every
2000 births
(b) Coarctation of the aorta.
(c) Tetralogy of Fallot. Multiple defects
A part of the aorta is narrowed,
(tetra = four): Pulmonary trunk too
increasing the workload on
narrow and pulmonary valve
the left ventricle.
stenosed, resulting in a hypertrophied
right ventricle; ventricular septal
defect; aorta opens from both
ventricles; wall of right ventricle
thickened from overwork.
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Figure 12.10 Embryonic circulatory systems
Lungs and intestines are not functional in
the adult sense at embryonic stages.
Placental nourishment (including oxygen)
necessitate some interesting differences:
• Vitelline veins serve to bring
nourshment in shell encased eggs (like
in birds and reptiles)
• Placental veins (umbilical vein) brings
nourishment in mammals
• The allantoic artery in shell encased
bird and reptile eggs will carry wastes
away from the embryo
• Placental artery (umbilical artery)
carries wastes away from the embryo
in mammals
Levels of protein structure.
Amino acid
Amino acid
Amino acid
Amino acid
Amino acid
(a) Primary structure:
The sequence of
amino acids forms the
polypeptide chain.
(b) Secondary structure:
The primary chain forms
spirals (-helices) and
sheets (-sheets).
-Helix: The primary chain is coiled
to form a spiral structure, which is
stabilized by hydrogen bonds.
-Sheet: The primary chain “zig-zags” back
and forth forming a “pleated” sheet. Adjacent
strands are held together by hydrogen bonds.
(c) Tertiary structure:
Superimposed on secondary structure.
-Helices and/or -sheets are folded up
to form a compact globular molecule
held together by intramolecular bonds.
(d) Quaternary structure:
Two or more polypeptide chains, each
with its own tertiary structure, combine
to form a functional protein.
Tertiary structure of prealbumin
(transthyretin), a protein that
transports the thyroid hormone
thyroxine in serum and cerebrospinal fluid.
Quaternary structure of a
functional prealbumin molecule.
Two identical prealbumin subunits
join head to tail to form the dimer.
An example of the progression in complexity of structure in proteins with the final
quaternary structure being that of hemoglobin.
Figure 12.11 Adult and fetal hemoglobin molecules differ in their globin subunits
When you examine
fetal hemoglobin, you
see that the protein
differences (fetal has
the y form and the adult
has the B form) lead the
fetal RBCs to have a
higher oxygen
saturation at any state of
oxygen pressure.
Why is this of value?
Note that BPG (bisphosphoglycergic acid) is a molecule which is lower in fetal
hemoglobin than in materinal hemoglobin.
This lower interaction gives the higher affinity for fetal hemoglobin.
Figure 12.12 Redirection of human blood flow at birth
•
The ductus arteriosus is
squeezed shut due to pressure
changes from the expanding
lungs
•
The embryological foramen
ovale (not to be confused with
the one in the adult skull) of
the heart also closes due to the
pressure changes.
Figure 12.13 Aortic arches of the human embryo
Aortic arches at day 29 further develop into the leading arteries
associated with the aorta and by day 56.
Some Major Blood Vessels in the Human Body
The lymphatic system
Regional
lymph nodes:
Cervical
nodes
Axillary
nodes
Entrance of
right lymphatic
duct into right
subclavian vein
Internal
jugular vein
Entrance of
thoracic
duct into left
subclavian vein
Thoracic duct
Aorta
Cisterna chyli
Lymphatic
collecting
vessels
Inguinal
nodes
(a)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Distribution and special structural features of lymphatic capillaries
Venous
system
Heart
Arterial
system
Venule
Loose connective
tissue around capillaries
Arteriole
Lymph duct
Lymph trunk
Lymph node
Lymphatic
system
Lymphatic
collecting
vessels,
with
valves
Lymphatic
capillary
Tissue fluid
Tissue cell
(a)
Blood
capillaries
Blood
Lymphatic
capillaries capillary
Filaments
anchored to
connective
tissue
Endothelial
cell
Flaplike
minivalve
Fibroblast in loose
connective tissue
(b)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Figure 12.14 Vasculogenesis and angiogenesis
• Vasculogeneis development of new (oiginal) blood vessels
• Angiogeneisis the process through which new blood vessels form from preexisting vessels
Her most famous work:
“Studies on the origin of blood vessels
and of red corpuscles as seen in the living
blastoderm of the chick during the second
day of incubation”
Journal: Contributions to Embryology
Volume 9, 213-262, 1920
Florence Rena Sabin – much
of her work involved the
discovery of the pathways of
blood vessel and lymphatic
vessel genesis
Figure 12.15 Vasculogenesis (Part 1)
Vasculogenesis – notice how
there is blood island formation
where primitive blood cells are
being made which are derived
from undifferentiated
mechenchyme. This is very
different than in RBC
production in the neonate or
adult.
Figure 12.16 The lumen, or central space, in the vascular tubes is formed by the fusion of
intracellular vacuoles
Lumen formation in vessels:
• Vacuole accumulation occurs in
lumen cells (endocytosis)
• Vacuoles merge forming
“megavacuoles”
• Continued fusion leads eventually
to the lumen being formed.
Figure 12.17 VEGF and its receptors in mouse embryos
The VEGF mutant lacks blood vessel
development with the yolk sac, and
therefore is miscarried.
Figure 12.18 Roles of ephrin and Eph receptors during angiogenesis
Eph receptors predominate venous vessels, whereas ephrin-b2
receptors predominate arterial vessels. To encourage angiogenic
modeling of capillaries, there is some (as yet unclear) ephrin/Eph
interaction that allows formation of these capillary connections.
Figure 12.20 Blood vessel formation in the chick blastoderm
One theory explaining blood vessel formation involves the use of VEGF
(vascular endothelial growth factor) which may occur as a gradient promoting
vessel formation in areas with higher concentration.
Figure 12.22 VEGF-C is critical for the formation of lymphatic vessels
A “C” form of VEGF (VEGFC) is the growth factor for the
formation of lymph vessels.
Notice the pronounced edema
in the mouse embryo that is
VEGF-C deficient.
Figure 12.23 Sources of blood cells to adult bone marrow
Hematopoiesis – the formation of blood
cells is primarily in the red bone marrow in
the adult, but embryologically it can occur
in diverse places including the liver, the
yolk sac and placenta.
Hematopoietic stem cells near and around
osteoblast cells can differentiate into
various blood cell components.
Figure 12.24 A model for the origin of mammalian blood and lymphoid cells
Erythropoiesis: genesis of red blood cells
Stem cell
Hemocytoblast
Committed cell
Proerythroblast
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Developmental pathway
Phase 1
Phase 2
Phase 3
Ribosome synthesis Hemoglobin accumulation Ejection of nucleus
Early
erythroblast
Late
erythroblast
Normoblast
Reticulocyte Erythrocyte
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Leukocyte formation
Hemocytoblast
Stem cells
Lymphoid stem cell
Myeloid stem cell
Committed
cells
Developmental
pathway
Myeloblast
Myeloblast
Promyelocyte Promyelocyte
Myeloblast
Promyelocyte Promonocyte
Eosinophilic
myelocyte
Basophilic
myelocyte
Neutrophilic
myelocyte
Eosinophilic
band cells
Basophilic
band cells
Neutrophilic
band cells
Eosinophils
(a)
Basophils
(b)
Granular leukocytes
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Neutrophils
(c)
Lymphoblast
Prolymphocyte
Monocytes
Lymphocytes
(e)
Agranular
Some
leukocytes
become
Some become
Plasma cells
Macrophages (tissues)
(d)
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Genesis of platelets
Stem cell
Developmental pathway
Hemocytoblast
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Megakaryoblast
Promegakaryocyte
Megakaryocyte
Platelets
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Figure 12.26 Endodermal folding during early human development
Notice the differential cuts and
how they show organization of
the structures that can be
visualized in 3D.
Figure 12.27 Formation of glandular primordia from the pharyngeal pouches
Notice how pharyngeal arches develop into:
• 1  tympanic cavity
• 2  tonsils
• 3  parathyroid gland (dorsal) and (ventral) the thymus
• 4  more parathyroid gland.
•
Note that the thyroid is not part of any pharyngeal arch.
Figure 12.28 Regional specification of the gut endoderm and splanchnic mesoderm through
reciprocal interactions (Part 1)
• cSox2 • Pdx1  pancreatic and
duodenal homeobox 1
• Hox  homeobox
• cdxC  caudal gene C
• cdxA  caudal gene A
Figure 12.29 Pancreatic development in humans
Figure 12.33 Partitioning of the foregut into the esophagus and respiratory diverticulum during the
third and fourth weeks of human gestation
Figure 12.34 Wnt signaling is critical for separation of the trachea and early differentiation of the
lung
Figure 12.35 The immune system relays a signal from the embryonic lung
End.