There are far more organs and organ systems in animals than in plants. All animal organs are covered or lined with epithelial tissue, held in place and manipulated by connective and muscular tissues, and controlled by nervous tissue. But beyond those similarities, each organ is a discrete structure with a unique arrangement of tissues and specialized functions.

Organs
The organization and intricate interrelationships of organs in humans provides a good overview of the internal organization found in many animals.

Major organs of the human body include the brain, spinal cord, heart, lungs, esophagus, stomach, small and large intestine, liver, kidneys, and bladder, to name just a few. These (and others) are organized into systems which carry out the tasks needed to maintain the body and produce offspring.

Organ Systems
There are 11 organ systems in the human body. Although each has distinctive functions, their work is intimately interconnected and their activities frequently overlap.

System: Skeletal
Function: supports the body and protects internal organs
Components: bones, cartilage, tendons, ligaments

System: Muscular
Function: produces movement and provides mobility, drives the movement of materials through other systems
Components: skeletal, cardiac, smooth muscles

System: Nervous
Function: receives and transmits electrical signals, controls body activities
Components: brain, spinal cord, peripheral nerves

System: Digestive
Function: processes food and absorbs nutrients
Components: mouth, esophagus, stomach, small intestine, large intestine, liver

System: Circulatory
Function: transports nutrients, gases, chemical compounds through the body, and carries away metabolic wastes
Components: heart, blood vessels, blood

System: Respiratory
Function: conducts gas exchange between the atmosphere and the blood, absorbs oxygen and releases carbon dioxide
Components: nose, trachea, lungs

System: Lymphatic (Immune)
Function: attacks pathogens, removes fluids and wastes from cells
Components: lymph, lymph nodes, macrophages, antibodies

System: Urinary (Excretory)
Function: removes metabolic wastes from blood and expels them from the body in urine
Components: kidneys, ureters, bladder, urethra

System: Reproductive
Function: produces and brings together eggs and sperm, supports embryonic and fetal development
Components: ovaries, oviducts, uterus, vagina, breasts, testes, seminal vesicles, penis

System: Integumentary
Function: protects the body, helps maintain temperature and control water loss
Components: skin, hair, nails, sweat glands, sebaceous glands

System: Endocrine
Function: produces and regulates hormones which direct physiologic activity
Components: hypothalamus, pituitary gland, thyroid, pancreas, adrenal glands