Histology of Spleen

Spleen consist of
1) Capsule : Connective tissue covering of spleen consisting of collagen and elastin

2) Trabeculae : Holds capsule with inner splenic pulps

3) White pulp :

• Consist of B & T lymphocytes around central arteries.
• Blood moves out from central artery and reaches to marginal zone.
• @ marginal zone antigen presenting cells are present which process and present antigen from blood>>>this stimulates B & T lymphocytes

(Imagine Very thirsty couple(B/T lymphocytes) are present praying around Well(central artery) filled with plenty of water but with bacteria within.Impure water in well is purified by Antigen presenting cells in marginal zone and then provided to hungry couple.Getting water they are activated)

4) Red pulp : consist of 

• leaky Vascular sinuses : blood cells are engulfed here.Remaining debris is engulfed by phagocytic lining
• Splenic cords of bilroth

HISTOLOGY OF THYMUS GLAND

• Simila to spleen consist of capsule,trabeculae,cortex and medulla
• Cortex has free lymphocytes and no lymphatic nodules
• Medulla has epithelial reticular cells,hassal corpuscles
• Starts involuting after puberty

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Development of veins

There are 3 pairs of veins at 5th week of intrauterine life
1)Vitelline vein(visceral)
2)Umbilical vein(visceral)
3)cardinal vein(somatic)

Vitelline Vein :

• Also known as Omphalo-mesentric veins
• Drains yolk sac to sinus venosus in heart
• However before entering into sinus venosus it forms plexus around duodenum which later forms PORTAL Vein.
• This plexus enters liver and divides in multiple veins to end in hepatic sinusoids.
• This sinusoids are drained into sinus venosus by hepatocardinal channels.
• Left hepato cardinal channels and distal portion left vitelline vein disappears gradually.
• Remaining proximal portion of left vitelline vein forms HEPATIC VEIN
• Right hepatocardinal channels forms hepatic part of INFERIOR VENA CAVA
• Right vitelline vein forms SUPERIOR MESENTRIC VEIN

Umbilical vein

(will discuss fate of U.artery too)

• Initially 2 arteries and 2 veins in umbilival cord
• @ 4 months of intraiterine life,Right umbilical vein disappears so remains 2 arteries and 1 vein
• Left umbilical vein communicates with hepatocardinal channels via ductus venosus
• Left umbilical vein changes to ligamentum teres
• Ductus venosus changes to ligamentum venosum
• Proximal portion of umbilical arteries form superior vesical artery and distal portion forms medial umbilical ligament

Cardinal Vein

• Drains embryo proper

Formation of SUPERIOR VENA CAVA

• from right anterior cardinal vein
• and right common cardinal vein

Formation of INFERIOR VENA CAVA

• Hepatic part - Right hepatocardinal veins
• Prerenal part - right subcardinal vein
• Renal part - right subcardinal-supracardinal anastomosis
• Post renal part - right posterior cardinal vein

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