It depends on the life stage that the star is in. Currently, in the mid-life stage, the sun is still fusing hydrogen into helium, so the maximum here is helium; however, far in the future when the star is nearing its final days, it can fuse atoms into elements as heavy as iron and nickel.
There is a valve at the meeting point between each ureter and the bladder prevents the back flow of urine from the urinary bladder to the kidney
