The digestive tract breaks down food mechanically and chemically, absorbing nutrients primarily in the small intestine and water in the large intestine. Common conditions include gastroesophageal reflux disease (GERD), in which stomach acid frequently backflows into the esophagus; peptic ulcers (sores in the stomach or duodenum most often caused by H. pylori infection or NSAID use); inflammatory bowel diseases (Crohn's disease, which can affect any part of the gastrointestinal tract with patchy deep inflammation, and ulcerative colitis, which causes continuous superficial inflammation of the colon and rectum); irritable bowel syndrome (a functional disorder causing pain, bloating, and altered bowel habits); celiac disease (autoimmune damage to intestinal villi triggered by gluten); and lactose intolerance (inability to digest milk sugar due to lactase deficiency). Other significant disorders include appendicitis, gallstones, pancreatitis, hepatitis (inflammation of the liver caused by viruses A, B, C, D, or E), cirrhosis (irreversible liver scarring), and fatty liver disease. Diagnostic and screening procedures include colonoscopy (recommended starting at age 45), upper endoscopy, and ultrasound.
The urinary system filters blood and maintains fluid and electrolyte balance. A urinary tract infection (UTI), most often caused by E. coli and more common in women, produces frequent and burning urination, cloudy urine, and pelvic pain; treatment requires antibiotics. Kidney stones (usually calcium oxalate) cause severe flank pain and hematuria. Chronic kidney disease (CKD), staged by glomerular filtration rate (GFR), is commonly caused by diabetes and hypertension and may progress to end-stage renal disease requiring dialysis (hemodialysis or peritoneal dialysis) or kidney transplant. Other important concepts include the nephrotic syndrome (heavy protein loss, edema, hyperlipidemia), nephritic syndrome (hematuria, hypertension, RBC casts), acute kidney injury (sudden decline in kidney function), polycystic kidney disease, and renal artery stenosis.
The reproductive system produces hormones and supports conception and childbirth. Common conditions include uterine fibroids (benign smooth muscle growths), endometriosis (uterine-lining tissue growing outside the uterus), polycystic ovary syndrome (PCOS, an endocrine disorder with irregular periods and excess androgens), and pelvic inflammatory disease. Pregnancy complications include preeclampsia (hypertension and proteinuria after 20 weeks), gestational diabetes, ectopic pregnancy (implantation outside the uterus, usually in a fallopian tube), and miscarriage. Cervical cancer, almost always caused by persistent high-risk HPV infection, can be prevented by HPV vaccination and detected early by Pap smear screening. Breast cancer is the most common cancer in women; risk factors include age, family history (BRCA mutations), and hormonal influences, and screening is performed by mammography. In men, benign prostatic hyperplasia (BPH) causes urinary symptoms in older men and is treated with alpha-blockers and 5-alpha reductase inhibitors, while prostate cancer is the most common male cancer and testicular cancer, though rare, affects young men and is highly curable. Sexually transmitted infections (chlamydia, gonorrhea, syphilis, HIV, HPV) are prevented by barrier protection, vaccination, and screening.