Vitelline veins the developing liver and broken up by it into a plexus of small capillary-like vessels termed sinusoids. The vitelline veins give rise to Inferior mesenteric vein, Ciliac trunk The branches conveying the blood to the plexus are named the venae advehentes, and become the branches of the portal vein. The vessels draining the plexus into the sinus venosus are termed the venae revehentes, and form the future hepatic veins. Ultimately the left vena revehens no longer communicates directly with the sinus venosus, but opens into the right vena revehens. The persistent part of the upper venous ring, above the opening
Headache pain receptors and can thus sense pain. These include the extracranial arteries, middle meningeal artery, large veins, venous sinuses, cranial and spinal nerves, head and neck muscles, the meninges, falx cerebri, parts of the brainstem, eyes, ears, teeth and lining of the mouth. Pial arteries, rather than pial veins are responsible for pain production. Headaches often result from traction to or irritation of the meninges and blood vessels. The nociceptors may be stimulated by head trauma or tumors and cause headaches. Blood vessel spasms, dilated blood vessels, inflammation or infection of meninges and muscular tension can also stimulate nociceptors and