Lacrimal Excretory System- Human
Tears are produced in the lacrimal gland (#1 in diagram to the left)exit the ocular surface via the puncta at the medial portion of the eyelids (#2 Diagram left). Each punctum is a small, round, or transversely oval aperture situated on a slight elevation. The puncta can be seen to be roughly in line with the openings of the Meibomian glands, the nearest of which is only 0.5 to 1 mm away.
Each puncta empties into a canaliculus (Diagram left #3)which has at first a vertical and then a horizontal portion.
In the photo below, the puncta and canaliculi are lined by stratified squamous epithelium (
Photomicrograph below #'s 1 and 2). Click to enlarge the photograph. The puncta are positioned between conjunctiva (Photo below 3) and skin (Photo below #4) at the border of the eyelid.
The lacrimal sac is placed in the lacrimal fossa (formed by the lacrimal bone and the frontal process of the maxilla) which lies in the anterior part of the medial wall of the orbit. The sac is closed above(Diagram above #4) and open below, where it is continuous with the naso-lacrimal duct (Diagram above #5). The lacrimal sac and duct are both lined by two layers of epithelium, the superficial of which is columnar, the deeper flattened. The bases of the columnar cells pass through the deeper layer to reach the basement membrane. Unlike the pseudostratied columnar respiratory epithelium of the sinuses and nose, the superficial layer is not ciliated, but contains goblet cells and mucous glands.