Nikon D80 has a 10.0MP APS-C
(23.6 x 15.8 mm ) sized CCD sensor . On the other hand, Pentax K-500 has a 16.0MP APS-C
(23.7 x 15.7 mm ) sized CMOS sensor and features PRIME M processor.
Pentax K-500's sensor provides 6MP more than Nikon D80's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the D80 and K-500 sensor size comparison.
Nikon D80 and Pentax K-500 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. It scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Nikon D80 and Pentax K-500 sensors have been tested by DxO and the results show that K-500 has a better overall score of 79, 18 points higher compared to D80's score of 61.