Organ-System Development

*** Collecting part of the kidney (From collecting tubules up to urethra) develops from the ureteric bud (i.e. mesonephric duct)
*** Secretory part of kidney (Nephron) develops from metanephros.


Derivatives of mesonephric duct: 
a. Ureteric bud: It gives rise to collecting part of the kidney-
   • Collecting tubule & collecting duct
   • Minor calyx
   • Major calyx
   • Renal pelvis
   • Ureter
b. Trigone of urinary bladder
c. Male genital ducts:
   • Prostate & part of prostatic urethra
   • Seminal vesicle
   • Epididymis
   • Vas deferens
   • Ejaculatory duct

Septum transversum gives rise to central tendon of the diaphragm & fibrous pericardium.

Anus below the pectinate line develops from proctoderm

Prostatic utricle & appendix of testes are fates of Mullerian duct in male

Factors responsible for descent of testis:
1. Gubernaculum testis (main factor)
2. Differential growth of the posterior abdominal wall
3. Intraabdominal pressure
4. Intraabdominal temperature
5. Uncurling of the fetal curves
6. Arched fibres of internal oblique
7. Male sex hormones (fetal testosterone)

(Ref: medical examination review anatomy P:213)

Explanation: The septum primum and the endocardial cushions fuse to close the foramen primum. Subsequently, perforations in the upper part of the septum primum coalesce to form septum secondum. It is this foramen that closes postnatally when the left atrial pressure equals right atrial pressure.

Metanephros Gives rise to nephrons i.e. secretory/excretory part of the kidneys
• Bowman’s capsule
• Glomerulus
• PCT
• Loop of Henle
• DCT

Explanation: An ostium secondum defects is a large opening between the atria that can be caused either by excessive resorption of the septum primum or inadequate development of the septum secondum. Depending on the size of the defect, there can be shunting of blood between the atria.

Explanation: The foramen cecum on the tongue is the point from which the thyroid gland evaginated and began its journey down into the neck It lies at the apex of the V shape terminal sulcus, which divides the tongue into anterior two-thirds, from the lateral lingual swellings and tuberculum imper and posterior one-third, from the copula.

During the relative ascent of the kidneys in fetal development, the kidneys rotate 90 degrees medially so that the renal hilus is normally orientated in a medial direction.

• Immunological competence of the fetus begins to develop at around 3 months. By this time the fetus makes all the components of the complement
• Maternal IgG begins to be transported from the mother to the fetus at approx 14 weeks (3.5 months)
• Newborns begin to produce their own antibody, but adult levels are not reached until the age of 3 years

Anus below the pectinate line develops from proctoderm

Meckel's diverticulum is a remnant of Vitello intestinal duct

Explanation-
Lesser omentum, Falciform ligament, Coronary ligament from ventral mesogastrium.

Septum transversum gives rise to central tendon of the diaphragm & fibrous pericardium.

Explanation: The portal vein forms when an anastomotic network around the duodenum forms one vessel. This anastomotic network is from the veins of the gut,the vitelline veins.

Pons & Cerebellum are formed from metencephalon

Explanation: also transverse mesocolon, sigmoid mesocolon.

Septum transversum gives rise to central tendon of the diaphragm & fibrous pericardium.