Chapter 14- Ocular anatomy and physiology part 1 (1) Flashcards
When light rays strike the surface of the eye, what is the first thing they encounter?
The tear film
What is a tear film?
A thin layer of fluid
What are the functions of the tear film?
1- Lubricates the eye
2- Barrier to foreign bodies and antigens (protection)
3- Ensuring a smooth refractive surface for vision
What is the tear film composed of?
Mucus, serous, sebaceous substances arranged in layers.
Tear film secretions occur from where?
Exocrine glands, located within epithelial tissue.
What exocrine glands are involved with tear film?
1- Outer lipid layer (sebaceous)
2- Central aqueous layer (serous)
3- Inner mucin layer (mucous)
What are the roles of the outer lipid layer (sebaceous)?
1- Minimises evaporation
2- Limits contamination from particles and microorganisms
What is the outer lipid layer secreted primarily by?
It is secreted primarily by meibomian (tarsal) glands
Where are the meibomian (tarsal) glands located?
Located within tarsal plates of upper and lower eyelids.
What is a tarsal plate?
Regions of dense connective tissue located deep in the upper and lower eyelid.
What type of gland is a meibomian (tarsal) gland?
A simple, multicellular exocrine gland.
What does the tarsal plate open on to?
They open onto the ocular surface via pores at the eyelid margin.
What are the roles of the central aqueous layer (serous)?
1- Washing away foreign bodies and contaminations
2- Nourish the avascular cornea
What is the central aqueous layer secreted by?
Secreted primarily by the lacrimal gland.
Where is the lacrimal gland located?
Above the upper eyelid
What type of gland is the lacrimal gland?
Compound multicellular exocrine gland
What are the roles of the inner mucin layer (mucous)?
1- Forms a glycocalyx over the ocular epithelium that prevents pathogen adhesion
2- Reduces friction during blinking
What is the inner mucin layer secreted by?
Secreted by goblet cells
Where are these goblet cells located?
Located in the conjunctiva
What is the conjunctiva?
A mucous membrane covering the inner surface of the eyelid and the exposed surface of the eyeball up to the limbus.
What type of gland is the goblet cell?
This is a unicellular exocrine gland
How does the orbicularis oculi operate around the eye?
The orbicularis oculi runs in circular bands around the eye
What is the function of the orbicularis oculi?
Involved in the closing of the eyelid
Where is the orbicularis oculi situated?
Part of the muscle lies within the face and part within the eyelid.
What happens when the orbicularis oculi muscle contracts?
The tears are drawn from the tear film.
Where is the levator palpebrae superioris situated and what does it do?
Runs along the top of the eyeball and sends tendons down into the eyelid.
The contraction of the levator palpebrae superioris does what?
Its contraction raises the upper eyelid
