Friday, November 16, 2018

Palpebral arteries

The palpebral arteries are the terminal orbital branches of the ophthalmic artery, which in turn arises from the internal carotid. There are two; lateral and medial, which provide the upper and lower eyelid with oxygen-rich blood.

After having branched from the ophthalmic, the lateral and medial palpebral arteries anastomose with each other forming an arterial circle that runs through the upper and lower eyelid.

Below, the palpebral arteries at the end of the ophthalmic

Branches of the middle cerebral artery (summary)

Most of the branches of the middle cerebral artery are external and supply a large cortical area where important centers of motor, sensory and intellectual functions are located. The first branches are lenticulostriate or anterolateral ganglionic ones (four or five), which supply the basal ganglia, being the only deep and internal arteries that come off the middle cerebral. The other ones are external: external inferior frontal, ascending frontal (supplying the primary motor or pre-rolandic), ascending parietal (supplying the sensorial or post-rolandic area), parietotemporal, and temporal artery.

Below, diagram of the branches of middle cerebral artery

Wednesday, November 14, 2018

Two different veins

Although most veins in the human body drain carbon-dioxide-rich blood from tissues and organs in the periphery into the right atrium of the heart, there are two types of veins which not only carry a different kind of blood but also in a direction other than into the right atrium of this pumping organ as ordinary veins do. They are the portal and the pulmonary veins. We can say these are special veins that have a dissimilar function.

The portal vein carries blood straight into the liver; and not in the direction of the right side of the heart. It arises from the union of its two main tributaries, which are the superior mesenteric and the splenic vein, which in turn receives blood from the inferior mesenteric. Since the superior and inferior mesenteric veins drain both the small and large intestines respectively, the portal vein carries blood rich in nutrients, which are the products of digestion of the food we eat. Once in the liver, these nutrients are further processed metabolically by hepatocytes; for example, excess glucose is transformed into glycogen and stored as such and amino acids and glycerol, which derives from saturated fat, are converted into glucose through a process called neoglucogenesis, etc. But the liver is drained by the hepatic veins into the inferior vena cava, which are ordinary veins that transport deoxygenated (carbon-dioxide-rich) blood into the right atrium.

Contrary to all the other ordinary veins, the pulmonary carries oxygen-rich blood from the lungs into the left atrium, which is in the upper left side of the heart. In this case, the pulmonary vein not only conveys a different type of blood but also carries it in the opposite direction and into a different cavity of the heart, to be pumped by the left ventricle to the rest of the body.

Saturday, November 10, 2018

Blood Supply To The Orbit

The blood supply to the orbit and eyeball is carried out by the ophthalmic artery and its branches. The ophthalmic arises from the internal carotid, entering into the orbit through the optic canal alongside the optic nerve. Once in the orbit and running superiorly to this nerve, it gives off the lacrimal artery, which runs forward laterally to supply the lacrimal gland. The short posterior ciliary artery arises from the lacrimal long before it gets to the gland.

As the ophthalmic turns left and travels over and across the optic nerve, the central retinal artery branches from it and gets into the center of the optic nerve, running forwards inside it to supply the retina. Once the ophthalmic has gone over across the optic nerve, it gives off the long posterior ciliary artery, which, along with the short posterior ciliary, provides the choroid with oxygen-rich blood. At this point, the ophthalmic also gives off the muscular branches that supply the muscles of the eyeball.

After the ophthalmic has run over to the internal lateral side of the orbit, the supraorbital, posterior ethmoidal and anterior ethmoidal arise from it. The supraorbital artery supplies the frontal bone and upper eyelid, while the posterior and anterior ethmoidal irrigate the nasal cavity. Finally, at its terminal end, the ophthalmic branches into the palpebral, frontal and nasal arteries, which carry oxygenated blood to the eyelids, lower frontal bone region, and the anterior nasal bone respectively.

Down below, diagram of arteries supplying the human orbit (from Gray's Anatomy)

Posterior ethmoidal artery

The posterior ethmoidal artery is an oxygen-rich blood vessel which comes off as a smaller branch of the ophthalmic artery in the orbit region. From its point of origin, it runs sideways and downwards through the posterior ethmoidal canal into the nasal cavity. Function: it supplies the upper and back part of the nasal cavity, while the anterior ethmoidal supplies the anterior third part of the that cavity.

Thursday, October 11, 2018

Blood supply to the neck

Every part (gland, muscle, vertebra) of the human neck is supplied by several smaller branches that come off from different larger arteries, all of them arising from the aortic arch. The thyroid gland receives oxygen-rich blood from the superior thyroid artery, which comes off the external carotid artery (coming from the common carotid), and the inferior thyroid, which originates from the thyroid cervical trunk, which in turn comes off the subclavian.

The cervical vertebrae are supplied by the transverse cervical, superficial cervical, and deep cervical branches which arise from the vertebral artery, which in turn also originates from the subclavian. While the larynx is nourished by the superior laryngeal artery, which is a branch of the superior thyroid artery.

The sternocleidomastoid muscle is supplied by the branches that originate from the occipital and the superior thyroid arteries, both of which branch from the external carotid artery. The sternohyoid muscle is also supplied by the superior thyroid muscle. The omohyoid muscle receives blood from the sternocleidomastoid branch of the superior thyroid artery. The trapezius is supplied by superficial branches of the transverse cervical artery. The splenius by muscular branches of the aorta.

Wednesday, October 10, 2018

Muscles of the pharynx

The human pharynx has two types of muscles: constrictor muscles and longitudinal muscles. They are supplied by pharyngeal branches of ascending pharyngeal artery.

Constrictor muscles

They are the superior, middle, and inferior constrictor muscles. Function: all three constrict the pharynx. Innervation: they are supplied by the vagus nerve (CN X).

1) The superior constrictor arises from the pterygomandibular raphe and the mandible adjacent bone, and inserts itself on the pharyngeal raphe.

2) The middle constrictor originates from the upper margin of hyoid bone greater horn, and attaches to the pharyngeal raphe.

3) The inferior constrictor muscle arises from the cricoid cartilages and the outer surfaces of pharynx, inserting itself into the pharyngeal raphe in the wall of pharynx posterior portion. Function: chokes lower part of pharynx when swallowing.
Longitudinal muscles

They are also three and are named according to the origin.

1) The stylopharyngeus arises from the styloid process of temporal bone and inserts in the pharyngeal wall. Function: it raises the pharynx. Innervation: it is supplied by the glossopharyngeal nerve (CN IX).

2) The salpingopharyngeus originates from the pharyngotympanic tube cartilaginous part, and inserts itself in the pharyngeal wall. Innervation: vagus nerve (CN X). Function: it lifts the pharynx and larynx during deglutition (swallowing).

3) The palatopharyngeus emerges from the upper surface of palatine aponeurosis. Innervation: vagus nerve.