TEAS Science: Human Body Systems and Organ Functions Complete Review

Human anatomy and physiology is the single most heavily tested topic on the TEAS Science section. Of the 50 Science questions, approximately 18-22 focus on body systems, organ functions, and the physiological processes that keep the body running. If you can master these systems, you are securing nearly half the points available in the Science section.

The TEAS does not expect you to know anatomy at the level of a medical student. It tests your understanding of what each system does, which organs belong to it, how the major processes work, and how systems interact with each other. This review covers all 11 body systems with the specific details that appear most frequently on the exam.

Cardiovascular System

The cardiovascular system pumps blood throughout the body, delivering oxygen and nutrients to cells and carrying away carbon dioxide and waste products. The heart is the central organ — a four-chambered muscular pump divided into right and left sides. The right side receives deoxygenated blood from the body and sends it to the lungs, while the left side receives oxygenated blood from the lungs and pumps it to the entire body.

• Key organs: Heart, arteries, veins, capillaries
• Blood flow path: Right atrium → Right ventricle → Pulmonary arteries → Lungs → Pulmonary veins → Left atrium → Left ventricle → Aorta → Body
• Arteries carry blood AWAY from the heart (remember A for Away). Veins carry blood TO the heart.
• Capillaries are the tiny vessels where gas exchange actually occurs between blood and tissues
• The SA node (sinoatrial node) is the heart's natural pacemaker, initiating each heartbeat

Respiratory System

The respiratory system brings oxygen into the body and removes carbon dioxide. Air enters through the nose or mouth, travels through the pharynx and larynx, down the trachea, through the bronchi and bronchioles, and finally reaches the alveoli — tiny air sacs in the lungs where gas exchange occurs. Oxygen diffuses from the alveoli into the blood, and carbon dioxide diffuses from the blood into the alveoli to be exhaled.

• Key organs: Nose, pharynx, larynx, trachea, bronchi, bronchioles, lungs, alveoli, diaphragm
• The diaphragm is the dome-shaped muscle that drives breathing — when it contracts and flattens, the lungs expand and air rushes in (inhalation). When it relaxes, the lungs compress and air is pushed out (exhalation).
• Gas exchange happens by diffusion across the thin walls of alveoli and capillaries
• The epiglottis prevents food from entering the trachea during swallowing
• Oxygen is transported in blood primarily bound to hemoglobin in red blood cells

Digestive System

The digestive system breaks down food into nutrients the body can absorb and use for energy, growth, and repair. Digestion begins in the mouth with mechanical breakdown (chewing) and chemical breakdown (salivary amylase starts digesting starch). Food travels through the esophagus to the stomach, where hydrochloric acid and pepsin break down proteins. The small intestine is where most nutrient absorption occurs, and the large intestine absorbs water and forms solid waste.

• Key organs: Mouth, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine, liver, gallbladder, pancreas
• The liver produces bile, which is stored in the gallbladder and released into the duodenum to emulsify fats
• The pancreas produces digestive enzymes (lipase, protease, amylase) and bicarbonate to neutralize stomach acid
• The small intestine has villi and microvilli that dramatically increase surface area for absorption
• Peristalsis — involuntary wave-like muscle contractions — moves food through the entire digestive tract

Nervous System

The nervous system controls and coordinates all body activities by transmitting electrical signals. It is divided into two main parts: the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which includes all the nerves that extend throughout the body.

• CNS: Brain (cerebrum, cerebellum, brainstem) and spinal cord
• PNS: Cranial nerves, spinal nerves; further divided into somatic (voluntary) and autonomic (involuntary) divisions
• The autonomic nervous system has two branches: sympathetic (fight-or-flight response) and parasympathetic (rest-and-digest)
• Neurons transmit signals via electrical impulses along axons and chemical signals (neurotransmitters) across synapses
• The cerebrum handles higher functions like thinking, memory, and voluntary movement; the cerebellum coordinates balance and motor control; the brainstem controls vital involuntary functions like breathing and heart rate

Musculoskeletal System

The skeletal and muscular systems work together to provide structure, support, protection, and movement. The adult human skeleton has 206 bones that protect internal organs, produce blood cells in bone marrow, and store minerals like calcium and phosphorus. Muscles attach to bones via tendons and contract to produce movement at joints.

• Three types of muscle: skeletal (voluntary, striated), cardiac (involuntary, striated, found only in the heart), smooth (involuntary, non-striated, found in organ walls)
• Joints are classified by movement: ball-and-socket (shoulder, hip), hinge (knee, elbow), pivot (neck), gliding (wrists)
• Ligaments connect bone to bone; tendons connect muscle to bone (remember: L comes before T in the alphabet, like 'bone-to-bone' comes before 'muscle-to-bone')
• Bone marrow produces red blood cells, white blood cells, and platelets
• Cartilage cushions joints and provides flexible support in areas like the nose and ears

Endocrine System

The endocrine system uses hormones — chemical messengers released into the bloodstream — to regulate body processes over longer time periods compared to the nervous system's rapid electrical signals. Glands produce hormones that control metabolism, growth, reproduction, mood, and the body's response to stress.

• Key glands and their hormones: Pituitary (growth hormone, TSH, FSH, LH), Thyroid (thyroxine — regulates metabolism), Adrenal (cortisol — stress response, adrenaline — fight-or-flight), Pancreas (insulin — lowers blood sugar, glucagon — raises blood sugar)
• The pituitary gland is called the 'master gland' because it controls other endocrine glands
• The hypothalamus links the nervous system to the endocrine system and controls the pituitary
• Insulin and glucagon work as antagonistic hormones to maintain blood sugar homeostasis
• The thyroid gland requires iodine to produce its hormones

Urinary System

The urinary system filters blood, removes waste products, and maintains water and electrolyte balance. The kidneys are the primary organs, filtering approximately 180 liters of blood per day but producing only about 1-2 liters of urine. Each kidney contains about one million nephrons — the functional units where filtration occurs.

• Key organs: Kidneys, ureters, bladder, urethra
• The nephron filters blood through the glomerulus, then reabsorbs useful substances (water, glucose, amino acids) in the tubules
• The kidneys regulate blood pH, blood pressure (via the renin-angiotensin system), and electrolyte levels
• ADH (antidiuretic hormone) signals the kidneys to reabsorb more water when the body is dehydrated
• Urine flows from kidneys → ureters → bladder → urethra

Immune and Lymphatic System

The immune system defends the body against pathogens — bacteria, viruses, fungi, and parasites. It works through two main mechanisms: innate (non-specific) immunity, which provides immediate general defense through barriers like skin and mucous membranes plus cells like phagocytes, and adaptive (specific) immunity, which creates targeted responses using lymphocytes (B cells and T cells).

• Key components: White blood cells (leukocytes), lymph nodes, spleen, thymus, bone marrow, tonsils
• B cells produce antibodies that target specific antigens. T cells directly attack infected cells (killer T cells) or coordinate immune response (helper T cells)
• The lymphatic system transports lymph fluid, filters pathogens through lymph nodes, and returns fluid to the bloodstream
• Vaccines work by exposing the immune system to a harmless form of a pathogen so it creates memory cells for faster future response
• Inflammation is part of the innate immune response — redness, swelling, heat, and pain signal increased blood flow to an injured area

Integumentary System

The integumentary system — skin, hair, nails, and glands — is the body's largest organ system and serves as the first line of defense against the outside world. Skin has three layers: the epidermis (outer protective layer), dermis (contains blood vessels, nerves, glands, and hair follicles), and hypodermis (fat layer for insulation and cushioning).

• Functions: Protection from pathogens, UV radiation, and physical injury; temperature regulation through sweating and blood vessel dilation; sensation via nerve receptors; vitamin D synthesis
• Melanocytes in the epidermis produce melanin, which protects against UV damage
• Sweat glands help regulate body temperature through evaporative cooling
• Sebaceous glands produce oil (sebum) that moisturizes skin and hair
• The skin plays a crucial role in homeostasis by regulating body temperature and water loss

Reproductive System

The reproductive system enables the production of offspring. In males, the testes produce sperm and testosterone. In females, the ovaries produce eggs (ova) and the hormones estrogen and progesterone. The TEAS focuses primarily on the menstrual cycle, fertilization, and basic embryonic development.

• Male: Testes produce sperm through spermatogenesis; sperm travel through vas deferens, combine with seminal fluid, and exit through the urethra
• Female: Ovaries release one egg per menstrual cycle (ovulation, around day 14); if fertilized, the embryo implants in the uterine wall; if not, the uterine lining is shed (menstruation)
• Fertilization typically occurs in the fallopian tube
• Estrogen and progesterone regulate the menstrual cycle and support pregnancy
• Human gestation lasts approximately 40 weeks, divided into three trimesters

How Body Systems Work Together

The TEAS loves to test connections between systems. Understanding how systems interact is often what separates good scores from great ones. Here are the most commonly tested interactions:

• Respiratory + Cardiovascular: The lungs oxygenate blood; the heart pumps it to tissues. Without both working together, cells cannot get oxygen.
• Digestive + Cardiovascular: Nutrients absorbed in the small intestine enter the bloodstream and are carried to cells throughout the body.
• Nervous + Endocrine: The hypothalamus bridges both systems. The nervous system provides rapid responses; the endocrine system provides sustained hormonal regulation.
• Muscular + Skeletal: Muscles pull on bones to create movement. Without bones, muscles would have nothing to anchor to; without muscles, bones could not move.
• Urinary + Cardiovascular: The kidneys filter blood to remove waste and regulate blood pressure and volume.
• Immune + Integumentary: Skin provides the physical barrier; when breached, the immune system responds to fight infection.

High-Yield Study Tips for Body Systems

To maximize your score on body systems questions, focus your study on these high-return strategies:

• Create a one-page summary for each system listing: organs, primary function, key process, one disease/disorder, and connections to other systems
• Use mnemonics for sequences you need to memorize (like blood flow through the heart or the digestive pathway)
• Focus on understanding WHY things happen, not just memorizing facts — the TEAS tests comprehension, not recall
• Practice identifying which system is being described when given a function or symptom
• Pay special attention to homeostasis — how the body maintains stable internal conditions through feedback loops

Body systems are the backbone of the TEAS Science section. By understanding each system individually and then connecting them together, you build the kind of integrated knowledge that the test rewards. Use this review as your foundation, then practice with questions to reinforce what you have learned.