- Acute Flaccid Myelitis
- Alzheimer’s Disease
- Arteriovenous Malformations
- Attention Deficit Hyperactivity Disorder
- Back Pain
- Brain Aneurysm
- Brain Tumors
- Carpal Tunnel Syndrome
- Childhood Brain Tumors
- Delirium
- Dementia
- Hemorrhagic Stroke
- Ischemic Stroke
- Memory
- Meningitis
- Mild Cognitive Impairment
- Movement Disorders
- Multiple Sclerosis
- Neuroblastoma
- Neuromuscular Disorders
- Parkinson’s Disease
- Polio and Post-Polio Syndrome
- Speech and Language Problems in Children
- Stroke
- Transient Ischemic Attack
- Tremor
- Walking Problems
- West Nile Virus
- A1C
- Blood Glucose
- Diabetes
- Diabetes and Pregnancy
- Diabetes Complications
- Diabetes in Children and Teens
- Diabetes Medicines
- Diabetes Type 1
- Diabetes Type 2
- Diabetic Diet
- Diabetic Eye Problems
- Diabetic Foot
- Diabetic Heart Disease
- Diabetic Kidney Problems
- Diabetic Nerve Problems
- How to Prevent Diabetes
- Hyperglycemia
- Metabolic Syndrome
- Prediabetes
- Abortion
- Breast Cancer
- Breast Diseases
- Breast Reconstruction
- Breastfeeding
- Cervical Cancer
- Cervical Cancer Screening
- Cesarean Delivery
- Childbirth
- Ectopic Pregnancy
- Endometriosis
- Female Infertility
- Health Problems in Pregnancy
- High Blood Pressure in Pregnancy
- HIV and Pregnancy
- Hormone Replacement Therapy
- HPV
- Hysterectomy
- Infections and Pregnancy
- Mammography
- Mastectomy
- Menopause
- Menstruation
- Miscarriage
- Ovarian Cancer
- Ovarian Cysts
- Ovarian Disorders
- Pelvic Floor Disorders
- Pelvic Inflammatory Disease
- Pelvic Pain
- Period Pain
- Polycystic Ovary Syndrome
- Pregnancy
- Pregnancy and Drug Use
- Pregnancy and Opioids
- Premenstrual Syndrome
- Prenatal Care
- Prenatal Testing
- Primary Ovarian Insufficiency
- Sexual Problems in Women
- Stillbirth
- Teenage Pregnancy
- Trichomoniasis
- Tubal Ligation
- Uterine Cancer
- Uterine Diseases
- Uterine Fibroids
- Vaginal Bleeding
- Vaginal Cancer
- Vaginal Diseases
- Vaginitis
- Vulvar Cancer
- Vulvar Disorders
- Yeast Infections
- Alcohol
- Calcium
- Child Nutrition
- Cholesterol
- Cholesterol Levels: What You Need to Know
- Cholesterol Medicines
- DASH Eating Plan
- Eating Disorders
- Food Allergy
- HDL: The “Good” Cholesterol
- High Cholesterol in Children and Teens
- How to Lower Cholesterol
- How to Lower Cholesterol with Diet
- Infant and Newborn Nutrition
- LDL: The “Bad” Cholesterol
- Malabsorption Syndromes
- Nutrition for Older Adults
- Pregnancy and Nutrition
- Toddler Nutrition
- Triglycerides
- VLDL Cholesterol
- Alpha-1 Antitrypsin Deficiency
- Ataxia Telangiectasia
- Brain Malformations
- Cerebral Palsy
- Charcot-Marie-Tooth Disease
- Chiari Malformation
- Cleft Lip and Palate
- Color Blindness
- Congenital Heart Defects
- Craniofacial Abnormalities
- Cystic Fibrosis
- Ehlers-Danlos Syndrome
- Fetal Alcohol Spectrum Disorders
- Friedreich Ataxia
- Genetic Counseling
- Hemophilia
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- Hydrocephalus
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- Neurofibromatosis
- Newborn Screening
- Osteogenesis Imperfecta
- Prader-Willi Syndrome
- Pregnancy and Medicines
- Rett Syndrome
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- Tay-Sachs Disease
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- Acute Lymphocytic Leukemia
- Allergy
- Animal Bites
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- Asthma in Children
- Childhood Leukemia
- Childhood Vaccines
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- COVID-19 Vaccines
- Cryptosporidiosis
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- Eosinophilic Esophagitis
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- HIV and Infections
- HIV in Women
- Hodgkin Lymphoma
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- Pemphigus
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- Scleroderma
- Sjogren’s Syndrome
- Tonsillitis
- Vaccines
- Viral Infections
- Adhesions
- Ankle Injuries and Disorders
- Arm Injuries and Disorders
- Back Injuries
- Brachial Plexus Injuries
- Burns
- Chest Injuries and Disorders
- Concussion
- CPR
- Dislocated Shoulder
- Dislocations
- Elbow Injuries and Disorders
- Eye Injuries
- Facial Injuries and Disorders
- Finger Injuries and Disorders
- Foot Injuries and Disorders
- Fractures
- Hand Injuries and Disorders
- Heel Injuries and Disorders
- Hip Injuries and Disorders
- Inhalation Injuries
- Insect Bites and Stings
- Jaw Injuries and Disorders
- Knee Injuries and Disorders
- Leg Injuries and Disorders
- Mosquito Bites
- Neck Injuries and Disorders
- Rotator Cuff Injuries
- Shoulder Injuries and Disorders
- Spinal Cord Injuries
- Sprains and Strains
- Tick Bites
- Toe Injuries and Disorders
- Traumatic Brain Injury
- Wrist Injuries and Disorders
- Acute Bronchitis
- Bird Flu
- Chronic Bronchitis
- COPD
- COVID-19 (Coronavirus Disease 2019)
- Croup
- E-Cigarettes
- Fistulas
- Flu
- Granulomatosis with Polyangiitis
- H1N1 Flu (Swine Flu)
- Legionnaires’ Disease
- Lung Cancer
- Mesothelioma
- Pneumonia
- Pulmonary Hypertension
- Respiratory Syncytial Virus Infections
- Sleep Apnea
- Smoking
- Tuberculosis
- Whooping Cough
- Anatomy
- Assisted Reproductive Technology
- Birth Control
- Chlamydia Infections
- Circumcision
- Erectile Dysfunction
- Genital Herpes
- Genital Warts
- Gonorrhea
- Herpes Simplex
- Infertility
- Male Infertility
- Penis Disorders
- Prostate Cancer
- Prostate Cancer Screening
- Prostate Diseases
- Reproductive Hazards
- Sexual Health
- Sexual Problems in Men
- Sexually Transmitted Diseases
- Syphilis
- Testicular Cancer
- Testicular Disorders
- Vasectomy
- Abdominal Pain
- Bad Breath
- Bleeding
- Breathing Problems
- Bruises
- Chest Pain
- Choking
- Chronic Pain
- Constipation
- Cough
- Diarrhea
- Dizziness and Vertigo
- Edema
- Fainting
- Fever
- Frostbite
- Gas
- Gastrointestinal Bleeding
- Headache
- Heartburn
- Heat Illness
- Hives
- Hypothermia
- Indigestion
- Itching
- Jaundice
- Nausea and Vomiting
- Pain
- Rare Diseases
- Raynaud’s Disease
- Sciatica
- Speech and Communication Disorders
- Stuttering
Blood
Summary
Your blood is made up of liquid and solids. The liquid part, called plasma, is made of water, salts, and protein. Over half of your blood is plasma. The solid part of your blood contains red blood cells, white blood cells, and platelets.
Red blood cells (RBC) deliver oxygen from your lungs to your tissues and organs. White blood cells (WBC) fight infection and are part of your immune system. Platelets help blood to clot when you have a cut or wound. Bone marrow, the spongy material inside your bones, makes new blood cells. Blood cells constantly die and your body makes new ones. Red blood cells live about 120 days, and platelets live about 6 days. Some white blood cells live less than a day, but others live much longer.
There are four blood types: A, B, AB, or O. Also, blood is either Rh-positive or Rh-negative. So if you have type A blood, it’s either A positive or A negative. Which type you are is important if you need a blood transfusion. And your Rh factor could be important if you become pregnant – an incompatibility between your type and the baby’s could create problems.
Blood tests such as blood count tests help doctors check for certain diseases and conditions. They also help check the function of your organs and show how well treatments are working. Problems with your blood may include bleeding disorders, excessive clotting and platelet disorders. If you lose too much blood, you may need a transfusion.
NIH: National Heart, Lung, and Blood Institute
National Heart, Lung, and Blood Institute
Encyclopedia
- Arterial stick Medical Encyclopedia
- Blood typing Medical Encyclopedia
- Capillary sample Medical Encyclopedia
- Cord blood testing Medical Encyclopedia
- Red blood cell production Medical Encyclopedia
- Venipuncture Medical Encyclopedia
Reference Desk
- Biology of Blood Merck & Co., Inc.
- Hematology Glossary American Society of Hematology
Teenagers
- Blood Nemours Foundation
- Blood Types Nemours Foundation
Start Here
- Blood (For Parents) Nemours Foundation
- Blood Basics American Society of Hematology
- Blood Donation FAQs America’s Blood Centers
- Blood Tests National Heart, Lung, and Blood Institute
Specifics
- Blood Types (For Parents) Nemours Foundation
- Facts About Blood and Blood Types American Red Cross
Clinical Trials
- ClinicalTrials.gov: Blood Cells National Institutes of Health
Related Issues
- Cord Blood Testing and Banking National Library of Medicine
- Diversity in Blood Types American Red Cross
Find an Expert
- Find a Hematologist American Society of Hematology
- National Heart, Lung, and Blood Institute National Heart, Lung, and Blood Institute
Games
- Play the Blood Typing Game Nobel Foundation
Journal Articles
Diagnosis and Tests
- What You Need to Know About Blood Testing National Library of Medicine
Children
- What’s Blood? Nemours Foundation