The word “fundus” is a common medical term whose meaning shifts dramatically depending on the organ described. It is a general anatomical designation referring to a specific section of a hollow organ, often its largest or most distant part. The term names a functional region within a structure, making its purpose dependent on its biological context.
Understanding the Anatomical Term
The general definition of a fundus is the part of a hollow organ farthest away from its opening (os). This area is typically described as the bottom, base, or rear wall, even if its orientation places it at the top of the organ. The fundus is a region, not a standalone structure, and its name derives from the Latin word for “bottom” or “base.”
This concept applies to several major body systems, where the fundus plays a distinct mechanical or storage role. Organs that possess a defined fundus include the uterus, stomach, gallbladder, urinary bladder, and eye. Understanding the location of the fundus within these organs provides insight into their function, from digestion and vision to reproductive health.
Location and Significance of the Uterine Fundus
The fundus of the uterus is the dome-shaped, superior portion of the organ, situated opposite the cervix. This area is the thickest and most muscular part of the uterine wall. During pregnancy, the uterine fundus grows significantly to accommodate the developing fetus, and its muscular composition is important during labor.
The fundus is the primary site of muscle contraction during childbirth. Waves of muscle action begin here and move downward to push the baby toward the cervix and birth canal. Its location also serves to protect the fetus from external trauma and infection during gestation. The position and size of the uterine fundus is a measure of a healthy pregnancy.
Medical professionals use the fundal height measurement as a non-invasive method to track fetal growth and estimate gestational age, typically starting around 20 weeks. The measurement is taken using a flexible tape measure to calculate the distance in centimeters from the top of the pubic bone (symphysis pubis) to the top of the uterine fundus.
After approximately 24 weeks of gestation, the fundal height in centimeters is expected to roughly match the number of weeks pregnant, plus or minus 2 to 3 centimeters. For example, 28 centimeters suggests a pregnancy of around 28 weeks. Discrepancies in this measurement can signal potential issues requiring further investigation, usually via ultrasound.
A fundal height measurement significantly larger than expected may indicate a multiple gestation pregnancy (e.g., twins) or an excess of amniotic fluid (polyhydramnios). Conversely, a smaller measurement could suggest fetal growth restriction or too little amniotic fluid (oligohydramnios). Factors like a full bladder, fibroids, or fetal position can also temporarily affect the measurement’s accuracy.
Fundi in Other Key Organs
The fundus of the stomach is the rounded, superior section located above the opening where the esophagus enters (the cardia). This area collects gas that is a byproduct of digestion. It also temporarily holds undigested food before it is mixed with the stomach’s acidic chyme.
The ocular fundus refers to the back interior surface of the eye, which can be viewed directly through the pupil. This surface includes the retina (the light-sensitive layer) and the optic disc, where the optic nerve exits the eyeball. It is a uniquely visible part of the central nervous system’s vasculature and nerve tissue.
The non-invasive examination of this region, called fundoscopy (or ophthalmoscopy), allows clinicians to detect eye conditions and systemic diseases. Changes in the retinal blood vessels can be early indicators of conditions like diabetes (diabetic retinopathy) or high blood pressure.
The fundus of the gallbladder is the rounded, broad end of the pear-shaped organ, projecting beyond the lower edge of the liver. Its primary function is to store and concentrate bile produced by the liver, ready for release into the small intestine to aid in fat digestion. Similarly, the fundus of the urinary bladder is the posterior wall forming its base, located farthest from the urethral opening.