A list of the organs inside our body.

器官 (きかん, kikan) – organ (of body, plant, etc.)

脳 (のう, nou) – brain

心臓 (しんぞう, shinzou) – heart

肝臓 (かんぞう, kanzou) – liver

腎臓 (じんぞう, jinzou) – kidney

肺 (はい, hai) – lung

胃 (い, i) – stomach

腸 (ちょう, chou) – guts; bowels; intestines

大腸 (だいちょう, daichou) – large intestine; large bowel; colon

小腸 (しょうちょう, shouchou) – small intestine

盲腸 (もうちょう, mouchou) – appendix

直腸 (ちょくちょう, chokuchou) – rectum

膵臓 (すいぞう, suizou) – pancreas

脾臓 (ひぞう, hizou) – spleen

胆嚢 (たんのう, tannou) – gall bladder

淋巴節 (りんぱせつ, rinpasetsu) – lymph node

膀胱 (ぼうこう, boukou) – urinary bladder

皮膚 (ひふ, hifu) – skin

血液 (けつえき, ketsueki) – blood
The word 血 (ち, chi) can be used on it’s own to mean the same.

血管 (けっかん, kekkan) – blood vessel; vein

静脈 (じょうみゃく, jyoumyaku) – vein

動脈 (どうみゃく, doumyaku) – artery

筋肉 (きんにく, kinniku) – muscle

骨 (ほね, hone) – bone

骨髄 (こつずい, kotsusui) – bone marrow; medulla

骨格 (こっかく, kokkaku) – skeleton; skeletal structure; build; frame; physique

背骨 (せぼね, sehone) – spine; backbone; spinal column

Definitions from jisho.org.