Human Anatomy and Physiology

The One Thing

The human body is an integrated hierarchy of cells, tissues, organs, and organ systems whose structures are specialized for particular functions. These systems depend on one another and are coordinated to maintain homeostasis and sustain life.

Reactions, Processes and Experiments

Key Terms

• Cell: The basic structural and functional unit of the human body.
• Tissue: A group of similar cells performing a particular function.
• Organ: A structure made of different tissues that performs a specific function.
• Organ system: A group of organs working together to carry out major body functions.
• Epithelial tissue: Tissue that covers body surfaces, lines internal organs, and may form glands.
• Connective tissue: Tissue that supports, binds, protects, or connects body parts; examples include bone, cartilage, blood, and fat.
• Muscular tissue: Tissue that contracts and produces movement.
• Nervous tissue: Tissue specialized to receive and transmit electrical messages.
• Digestive system: The system that breaks food into simpler soluble substances, absorbs nutrients, and removes undigested matter.
• Mouth: The beginning of the alimentary canal, where food is chewed and mixed with saliva.
• Stomach: A muscular organ that churns food and begins the digestion of proteins using gastric juice.
• Small intestine: The main site of digestion and absorption of digested nutrients.
• Villi: Tiny finger-like projections in the small intestine that increase the surface area for absorption.
• Liver: A large gland that produces bile, stores nutrients, and helps process absorbed substances.
• Respiratory system: The system responsible for taking in oxygen and removing carbon dioxide.
• Alveoli: Tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged between air and blood.
• Breathing: The physical movement of air into and out of the lungs.
• Respiration: The chemical process by which cells release energy from food, usually using oxygen.
• Aerobic respiration: The breakdown of glucose in the presence of oxygen, releasing energy, carbon dioxide, and water.
• Circulatory system: The system consisting mainly of the heart, blood, and blood vessels that transports substances around the body.
• Heart: A muscular organ that pumps blood through the pulmonary and systemic circuits.
• Arteries: Blood vessels that generally carry blood away from the heart under high pressure.
• Veins: Blood vessels that generally carry blood toward the heart and contain valves to prevent backflow.
• Capillaries: Very narrow vessels with thin walls where exchange of gases, nutrients, and wastes occurs.
• Red blood cells: Blood cells containing haemoglobin that transport oxygen.
• White blood cells: Blood cells that help defend the body against disease-causing organisms.
• Platelets: Small cell fragments that help clot blood and prevent excessive bleeding.
• Lymph: A fluid that helps return excess tissue fluid to the blood and supports immunity.
• Excretory system: The system that removes metabolic wastes and helps regulate water and salt balance.
• Kidney: An organ that filters blood, forms urine, and regulates water and mineral levels.
• Nephron: The microscopic structural and functional unit of the kidney.
• Urine: A fluid containing water, urea, and excess salts removed from the blood by the kidneys.
• Nervous system: The system that detects stimuli, processes information, and coordinates rapid responses.
• Neuron: A nerve cell specialized to transmit electrical impulses.
• Central nervous system: The brain and spinal cord, which control and coordinate body activities.
• Reflex action: A quick, automatic response to a stimulus, usually coordinated through the spinal cord.
• Endocrine system: A system of glands that releases hormones into the blood to regulate body functions.
• Hormone: A chemical messenger produced by an endocrine gland and carried by the blood to a target organ.
• Skeletal system: The framework of bones and cartilage that supports, protects, and helps move the body.
• Joint: The place where two or more bones meet.
• Ligament: A strong band of connective tissue joining bone to bone.
• Tendon: A strong connective tissue structure joining muscle to bone.
• Muscular system: The system of muscles that produces movement, maintains posture, and generates heat.
• Antagonistic muscles: A pair of muscles that work in opposite ways, such as the biceps and triceps.
• Reproductive system: The system responsible for producing gametes and enabling reproduction.
• Homeostasis: The maintenance of a fairly constant internal environment despite external changes.
• Metabolism: The sum of all chemical reactions occurring in the body.

Easily Confused

• Breathing and respiration: Breathing is the physical movement of air into and out of the lungs, whereas respiration is the chemical release of energy from food in cells.
• Bile and digestive enzymes: Bile emulsifies fats but does not digest them chemically; enzymes chemically digest food.
• Arteries and veins: Arteries generally carry blood away from the heart under high pressure, whereas veins generally carry blood toward the heart and contain valves.
• Pulmonary and systemic circulation: Pulmonary circulation carries blood between the heart and lungs; systemic circulation carries blood between the heart and the rest of the body.
• Nervous and endocrine coordination: Nervous control is generally rapid and short-lived, whereas hormonal control is generally slower and longer-lasting.
• Ligaments and tendons: Ligaments join bone to bone, whereas tendons join muscle to bone.
• Ultrafiltration and selective reabsorption: Ultrafiltration separates substances from the blood in the kidney; selective reabsorption returns useful substances to the blood.
• Excretion and egestion: Excretion removes metabolic wastes, whereas the digestive system removes undigested matter.
• Structure and function: Alveoli have thin walls for rapid gas exchange, while villi have a large surface area for efficient absorption.
• BMI and overall health: BMI is calculated using body mass and height, but health cannot be judged by BMI alone.

What Gets Asked

• Identify the levels of organization: Questions may require the sequence cell → tissue → organ → organ system → organism. Reversing the order or omitting a level loses marks.
• Describe digestive pathways and functions: Questions may ask for the alimentary canal sequence or the roles of salivary amylase, the stomach, bile, the small intestine, and villi. A common error is stating that bile chemically digests fats; it emulsifies them.
• Explain gas exchange and respiration: Questions may require the role of alveoli or the equation glucose + oxygen → carbon dioxide + water + energy. Breathing should not be confused with respiration.
• Trace blood through the heart: The specified sequence from the venae cavae to the aorta may be examined. The right side pumps deoxygenated blood to the lungs, whereas the left side pumps oxygenated blood to the body.
• Explain excretion and urine formation: Questions may ask about the kidneys, nephrons, or ultrafiltration, selective reabsorption, and tubular secretion. The roles of the kidneys, lungs, skin, and liver should not be conflated.
• Compare coordination and movement: Questions may examine reflex arcs, hormones, or antagonistic muscles. Nervous impulses are generally rapid and short-lived, hormones are slower and longer-lasting, and muscles work by contraction rather than pushing.