Human Anatomy and Physiology

The One Thing

Human life depends on the coordinated activity of interconnected organ systems. Respiratory, circulatory, excretory, nervous, endocrine, and reproductive systems work together through transport, regulation, waste removal, and reproduction to maintain homeostasis and sustain life.

Reactions, Processes and Experiments

Key Terms

• 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.
• Inhalation: Breathing in; the diaphragm contracts and moves downward while the ribs move upward and outward.
• Exhalation: Breathing out; the diaphragm relaxes and moves upward while the ribs move downward and inward.
• Diffusion: Movement of particles from a region of higher concentration to a region of lower concentration.
• Circulatory system: The heart, blood, and blood vessels, which transport substances throughout the body.
• Heart: A muscular organ that pumps blood through pulmonary and systemic circulations.
• Pulmonary circulation: The flow of deoxygenated blood from the right ventricle to the lungs and oxygenated blood back to the left atrium.
• Systemic circulation: The flow of oxygenated blood from the left ventricle to body tissues and deoxygenated blood back to the right atrium.
• Arteries: Blood vessels that generally carry blood away from the heart and have thick, elastic walls.
• Veins: Blood vessels that generally carry blood towards the heart and contain valves to prevent backflow.
• Capillaries: Very thin blood vessels where gases, nutrients, and wastes are exchanged between blood and tissues.
• Red blood cells: Cells containing haemoglobin that transport oxygen and some carbon dioxide.
• White blood cells: Cells that protect the body against pathogens and other foreign substances.
• Platelets: Small cell fragments that help blood clot and prevent excessive bleeding.
• Plasma: The liquid part of blood that transports dissolved substances, hormones, nutrients, and wastes.
• Double circulation: A circulatory arrangement in which blood passes through the heart twice during one complete journey through the body.
• Excretory system: The system that removes metabolic wastes and helps regulate water and salt balance.
• Kidney: An organ that filters blood, forms urine, and maintains water, salt, and acid-base balance.
• Nephron: The structural and functional unit of the kidney.
• Ultrafiltration: Pressure-driven filtration of water and small dissolved substances from blood into the nephron capsule.
• Selective reabsorption: Return of useful substances such as glucose, amino acids, salts, and much water from the kidney tubule to the blood.
• Tubular secretion: Movement of additional wastes and excess ions from blood into the kidney tubule.
• Urine: Fluid containing nitrogenous wastes, excess salts, and excess water that is eliminated by the kidneys.
• Nervous system: The system that receives information, processes it, and produces rapid responses through electrical impulses.
• Neuron: The basic structural and functional unit of the nervous system.
• Receptor: A specialised cell or sense organ that detects a stimulus.
• Reflex action: A rapid, automatic response to a stimulus that usually occurs through a reflex arc.
• Central nervous system: The brain and spinal cord, which process information and coordinate responses.
• Peripheral nervous system: The nerves connecting the central nervous system with receptors, muscles, and glands.
• Synapse: The small junction between two neurons or between a neuron and an effector across which signals are transmitted.
• Endocrine system: A system of ductless glands that releases hormones directly into the blood.
• Hormone: A chemical messenger produced by an endocrine gland that affects specific target organs or tissues.
• Pituitary gland: A major endocrine gland that controls several other glands and influences growth and reproduction.
• Thyroid gland: A gland that produces hormones regulating metabolic rate and growth.
• Adrenal glands: Glands producing hormones involved in stress responses, salt balance, and metabolism.
• Pancreas: An organ producing digestive enzymes and hormones such as insulin and glucagon for blood glucose regulation.
• Insulin: A hormone that lowers blood glucose by promoting its uptake and storage.
• Reproductive system: Organs that produce gametes and reproductive hormones and support fertilisation and development.
• Testes: Male reproductive organs that produce sperm and secrete testosterone.
• Ovaries: Female reproductive organs that produce ova and secrete oestrogen and progesterone.
• Ovulation: Release of a mature ovum from an ovary.
• Fertilisation: Fusion of a sperm and an ovum to form a diploid zygote.
• Menstrual cycle: Recurring changes in the female reproductive system that prepare for possible pregnancy.
• Placenta: A temporary organ through which nutrients and oxygen pass from the mother to the foetus and wastes pass in the opposite direction.
• Homeostasis: Maintenance of a relatively stable internal environment despite external changes.
• Aerobic respiration: The process in which glucose reacts with oxygen to release energy, producing carbon dioxide and water.
• Stimulus: A detectable change in the internal or external environment.
• Effector: A muscle or gland that produces a response.
• Cerebrum: The brain region associated with conscious thought, memory, intelligence, sensory interpretation, and voluntary actions.
• Cerebellum: The brain region that coordinates muscular activity and helps maintain posture and balance.
• Medulla oblongata: The brain region controlling involuntary activities such as breathing, heartbeat, swallowing, and blood pressure.
• Testes: Male reproductive organs containing seminiferous tubules, where sperm are produced.
• Oviducts: Female reproductive tubes in which fertilisation usually occurs.
• Uterus: The organ whose lining receives the implanted embryo and supports development.
• Placenta: The temporary exchange organ between mother and foetus.
• Gamete: A reproductive cell containing 23 chromosomes.
• Zygote: The diploid cell formed by fertilisation.
• Embryo: The early developing stage formed after repeated division of the zygote.
• Foetus: The later developmental stage following the embryo.
• Negative feedback: A regulatory mechanism in which a response opposes a change and returns internal conditions towards normal.

Easily Confused

• Inhalation and exhalation: Inhalation involves diaphragm contraction and downward movement; exhalation involves diaphragm relaxation and upward movement.
• Pulmonary and systemic circulation: Pulmonary circulation is between the heart and lungs; systemic circulation is between the heart and body tissues.
• Arteries and veins: Arteries generally carry blood away from the heart and have thick, elastic walls; veins generally carry blood towards the heart and contain valves.
• Ultrafiltration and selective reabsorption: Ultrafiltration moves water and small dissolved substances from blood into the nephron capsule; selective reabsorption returns useful substances to the blood.
• Nervous and hormonal control: Nervous control is generally rapid and short-lived; hormonal control is usually slower and longer-lasting.
• Insulin and glucagon: Insulin decreases blood glucose, whereas glucagon increases it.
• Ovulation and fertilisation: Ovulation is the release of an ovum from an ovary; fertilisation is the fusion of a sperm and an ovum.
• Fertilisation and implantation: Fertilisation usually occurs in the oviduct; implantation occurs in the lining of the uterus.
• Oestrogen and progesterone: Oestrogen helps develop female secondary sexual characteristics and rebuild the uterine lining; progesterone helps maintain the uterine lining.
• Body cells and gametes: A normal human body cell contains 46 chromosomes, whereas a normal gamete contains 23.
• Cerebrum, cerebellum, and medulla oblongata: The cerebrum controls conscious and voluntary functions, the cerebellum coordinates movement and balance, and the medulla oblongata controls involuntary activities.
• Excretion and reproduction: Excretion removes metabolic wastes, whereas reproduction produces gametes and enables the formation and development of new individuals.

What Gets Asked

• Explain gas exchange at the alveoli: Questions require diffusion and the adaptations of alveoli—large surface area, thin moist walls, and rich capillary supply. Omitting the structural adaptations loses marks.
• Trace blood through the heart: The required sequence is venae cavae -> right atrium -> tricuspid valve -> right ventricle -> pulmonary artery -> lungs -> pulmonary veins -> left atrium -> bicuspid valve -> left ventricle -> aorta. Confusing the tricuspid and bicuspid valves or reversing pulmonary and systemic circulation costs marks.
• Calculate cardiac output: Use Cardiac output = heart rate x stroke volume. The quantities must be multiplied rather than added.
• Describe urine formation: State the sequence ultrafiltration -> selective reabsorption -> tubular secretion. These processes should not be treated as interchangeable.
• Describe a reflex arc: Use the sequence receptor -> sensory neuron -> relay neuron in the spinal cord -> motor neuron -> effector. Leaving out the relay neuron or reversing sensory and motor neurons loses marks.
• Compare nervous and hormonal coordination: Nervous control is generally rapid and short-lived, whereas hormonal control is usually slower and longer-lasting. Reversing these characteristics is a common error.
• Explain reproduction and chromosome numbers: Include haploid gametes, fertilisation, the diploid zygote, embryo and foetal development, and the figures of 46 chromosomes in body cells and 23 in gametes. Confusing fertilisation in the oviduct with implantation in the uterine lining loses marks.