Development of the heart & gut Flashcards
Describe Specification of the heart primordia
the heart primordia is an aggregation of angioblastic cells in the cardiogenic region; it is the first indication of heart development in the third week of embryonic development
- they are born in the primitive streak
All cells of the future heart are generated from which two cardiogenic mesodermal clusters?
cardiogenic mesoderm
Describe the process of heart formation in the dog
After migration, cardiac precursors form a simple tube. From the tube, the heart undergoes differential growth into a four chambered structure while it is pumping blood throughout the embryo and into extra-embryonic membranes. Major vessels form and the heart initiates a peristaltic pumping action during the third week in the dog
Re. heart formation; failure of midline migration results in …?
Mutations of which gene?
cardia bifida
mutations of Fox P4
What is heart looping? Describe the process of heart looping… (try and remember 3-part diagram - page 11)
Looping inverts future atria to sit anterior to future ventricles
- Initial formation is as a two-chambered tube: 1 atrium, 1 ventricle
- Heart looping converts the AP polarity of the heart tube to the L/R specified structure of the adult heart
- 1st bend is to the right! creates ‘s’ shape at 45 degree angle
Process: drawing…
Development of the cardiac conduction system (was mentioned in the exam revision lecture but wasn’t in lecture objectives!)
Pacemaker cells:
•First formed in caudal part of left cardiac tube.
•Subsequent centre formed in the right horn of the sinus venosus.
•Become incorporated into right atrium – SinoAtrial node.
•Prior to formation of the separate chambers, entire cardiac tube contracts as a single unit
Understand the difference between vasculogenesis and angiogenesis, how extension and pruning define the adult vascular system
Two distinct mechanisms, vasculogenesis and angiogenesis implement the formation of the vascular network in the embryo. Vasculogenesis gives rise to the heart and the first primitive vascular plexus inside the embryo and in its surrounding membranes, as the yolk sac circulation. Angiogenesis is responsible for the remodeling and expansion of this network
Describe the transition from fetal to neonatal circulation
FETAL CIRCULATION: blood from placenta is returned by two large umbilical veins
- ductus arteriosis is OPEN -> diverts blood from pulmonary artery to aorta to placenta
- no blood return from pulmonary vein so need to fill left ventricle from another route
- foramen ovale is OPEN (between L & R atria)
NEONATE CIRCULATION: pressure in left side of heart increases at 1st breath -> CLOSURE OF FORAMEN OVALE -> SEPARATES SYSTEMIC & PULMONARY CIRCULATION
- DUCTUS ARTERIOSUS CLOSES separating connection between aorta & pulmonary artery
Learning objectives:
• Know the components of the mammalian digestive system and associated derivatives.
• Know how the simply gut tube develops to form the regionalised gut
• Know how the simple stomach and rumen are formed during fetal development
…
Early gut tube formation…
- derived from the endoderm and is a ventrally located tube of endoderm surrounded by splanchnic mesoderm
Consists of three regions
–Foregut
–Hindgut
–Midgut – connected to yolk sac via yolk stalk
The tube that form the gut originates from two sites: the anterior intestinal portal and the caudal intestinal portal
These tubes extend to the midline to fuse to form the gut tube proper
Ininially the gut tubes is closed
At the anterior end this is called the stomodeum
At the posterior end this is called the proctodeum
Both ends of the tube will break open forming the oral and rectal openings respectively
Re. gut components and their derivatives… the FOREGUT forms which components & derivatives…?
components: oesophagus, stomach, cranial duodenum
derivatives: liver & pancreas
Re. gut components and their derivatives… the MIDGUT forms which components & derivatives…?
components: caudal duodenum, jejunum, ileum, colon (ascending)
derivatives: connection to yolk sac
Re. gut components and their derivatives… the HINDGUT forms which components & derivatives…?
components: colon (descending) birds: cloaca
derivatives: rectum
Formation of the simple stomach
- The dorsal portion of the stomach proliferates more rapidly than the ventral part
- Results in a curvature of the stomach giving rise to the dorsal (greater) curvature and ventral (lesser) curvature of the adult stomach
- Stomach then rotates in two directions: 90o clockwise in a cranio-caudal axis and then 45 degrees clockwise around a dorsoventral axis
- The left hand (cranial) components then develop into the cardia and fundus
- The middle portion becomes the corpus and pylorus
- Differentiation of the stomach mucosa then occurs with species specific differences… carnivores; mucosa is glandular. In pigs/horses; mucosa is non-glandular
Drawing…
Describe Development of the Intestine…
- Midgut region intestine suspended by dorsal mesentery
- Attachment to yolk sac lost – loop allowed considerable movement
- Caecum formed – small/large intestine
- Mesoduodenum fixes cranial point
- Rapid elongation and passes out of body cavity
