Key Concepts in Anatomy & Physiology: Sensory Systems, Hormones, and Blood Vessels

Eye Anatomy and Physiology

Photoreceptors in the Eye

The human eye contains specialized cells called photoreceptors that detect light and enable vision.

• Rods: Photoreceptors involved in dim light vision; highly sensitive to low light but do not detect color.

• Cones: (Additional info) Responsible for color vision and function best in bright light.

Regulation of Light Entry

The iris is the structure that controls the amount of light entering the eye by adjusting the size of the pupil.

• Iris: Colored part of the eye; contains muscles that constrict or dilate the pupil.

Equilibrium and Sensory Structures

Equilibrium is maintained by structures in the inner ear, including the maculae, which contain receptor hair cells.

• Maculae: Sensory regions in the vestibular system that detect changes in head position.

• Eardrum: (Tympanic membrane) Part of the external ear that vibrates in response to sound waves.

Hormones and Their Functions

Leptin

Leptin is a hormone primarily produced by adipose (fat) tissue and is involved in regulating appetite.

• Function: Signals the brain to reduce food intake and increase energy expenditure.

Growth Hormone

Growth hormone targets bones and skeletal muscles, stimulating growth and cell reproduction.

• Source: Anterior pituitary gland.

• Effects: Promotes protein synthesis and increases fat breakdown.

Atrial Natriuretic Peptide (ANP)

Atrial natriuretic peptide is a hormone produced by the heart that helps regulate blood pressure and fluid balance.

• Function: Causes vasodilation and promotes sodium excretion by the kidneys.

Taste and Sensory Terminology

Gustatory Sense

The layman's term for the sense of taste is gustatory.

• Gustatory cells: Specialized epithelial cells in taste buds responsible for detecting taste stimuli.

Blood Vessels and Circulation

Types of Blood Vessels

Arteries are blood vessels that carry blood away from the heart to various tissues.

• Arteries: Thick-walled vessels; withstand high pressure.

• Veins: (Additional info) Carry blood toward the heart; have thinner walls and valves.

Arterial Tunics

Blood vessels have three layers, or tunics, that provide structure and function.

• Tunica intima: Innermost layer; consists of endothelium.

• Tunica media: Middle layer; contains smooth muscle and elastic fibers; responsible for maintaining blood pressure.

• Tunica externa: (Additional info) Outermost layer; provides structural support.

Classes of Arteries

Arteries are classified based on their size and function.

• Elastic arteries: Largest arteries; have the highest blood pressure and contain many elastic fibers to accommodate pressure changes.

• Muscular arteries: (Additional info) Distribute blood to specific organs; have more smooth muscle.

Capillaries

Capillaries are the smallest blood vessels and consist of only one tunic, the tunica intima.

• Function: Site of exchange of gases, nutrients, and waste between blood and tissues.

Clinical Terms

Meningitis

Meningitis refers to inflammation of the meninges, the protective membranes covering the brain and spinal cord.

• Symptoms: Headache, fever, neck stiffness.

• Causes: Bacterial or viral infection.

Conjunctiva

The conjunctiva is a mucous membrane that lines the eyelid and covers the white part of the eyeball.

• Function: Protects and lubricates the eye.

Summary Table: Blood Vessel Structure

Vessel Type	Main Tunics Present	Function
Artery	Tunica intima, media, externa	Carry blood away from heart; withstand high pressure
Capillary	Tunica intima only	Exchange of gases and nutrients
Vein	Tunica intima, media, externa	Carry blood toward heart; lower pressure

Key Equations

• Blood Pressure Equation:

$\text{Blood Pressure} = \text{Cardiac Output} \times \text{Peripheral Resistance}$

• Leptin Regulation: (Additional info) Leptin levels are proportional to body fat mass.