Romania Clasa a XI-a Biology (human anatomy and physiology)
Chapters: 5
1. Structure of the human body
Body organisation
- Human Body Systems – Your body is organised in levels: cells make tissues, tissues make organs, organs make organ systems, and all systems together make you, the organism. Each system has a main job: skeletal (frame), muscular (movement), circulatory (transport), respiratory (gas exchange), digestive (food), excretory (waste), nervous and endocrine (control), immune (defence), integumentary (skin, hair, nails) and reproductive. No system works alone: during exercise the muscles, heart, lungs and nerves all change together to keep the inside of the body steady (homeostasis).
2. Relation functions
Nervous system · Sense organs (analysers) · Endocrine glands · Movement
- Neural Control and Coordination – Coordination means organs working together. The nervous system does this fast, using neurons. A neuron has a cell body, dendrites and an axon; many axons have a myelin sheath with nodes of Ranvier. The central nervous system (brain and spinal cord) processes information; the peripheral nervous system (nerves) carries it. The PNS has a somatic part (skeletal muscles) and an autonomic part (sympathetic and parasympathetic) for internal organs, the visceral system. At rest the axon is polarised: inside −, outside +, about −70 mV. A stimulus lets Na+ rush in, creating an action potential that travels along the axon. At a synapse, neurotransmitters carry the signal to the next neuron.
- Sense Organs – Sense organs let us pick up changes around us (stimuli). The eye senses light, the ear sound and balance, the nose smell, the tongue taste, and the skin touch, pressure, heat, cold and pain. Each has receptor cells that turn the stimulus into nerve signals. The signal goes along a sensory nerve to the brain or spinal cord, which sends an order to a muscle: the response.
- Chemical Coordination and Integration – Hormones are chemical messengers made in tiny amounts by ductless (endocrine) glands. They travel in blood and act on target cells that have the right receptor. The hypothalamus controls the pituitary, which controls many other glands; negative feedback keeps levels steady. Main glands: pineal, pituitary, thyroid, parathyroid, thymus, adrenal, pancreas (islets), testis and ovary. The heart, kidney and gut also make hormones. Protein hormones act through membrane receptors and second messengers like cAMP; steroid and thyroid hormones enter the cell and change gene expression. Too little (hypo-secretion) or too much (hyper-secretion) of a hormone causes disorders like dwarfism, gigantism, goitre, diabetes, Addison's disease and Cushing's syndrome.
- Locomotion and Movement – Movement is a change in position of a body part; locomotion is moving the whole body from place to place. Cells move in three ways: amoeboid, ciliary and flagellar. Humans use muscular movement. Muscles are skeletal, visceral or cardiac. A skeletal muscle is made of fibres, each packed with myofibrils made of repeating sarcomeres of actin and myosin. A nerve signal releases Ca2+, myosin heads pull actin using ATP, and the sarcomere shortens (sliding filament theory). The skeleton has 206 bones. Joints can be fibrous, cartilaginous or synovial (ball and socket, hinge, pivot, gliding, saddle). Disorders include myasthenia gravis, tetany, muscular dystrophy, arthritis, osteoporosis and gout.
3. Nutrition functions
Digestion and absorption · Circulation · Respiration · Excretion · Metabolism
- Human Digestive System and Heterotrophic Nutrition – Heterotrophs take ready-made food from other living things. Humans are holozoic: we eat whole food and break it down in a long tube, the alimentary canal. Teeth, saliva, stomach acid, enzymes, bile and pancreatic juice cut big food molecules into small ones that villi in the small intestine absorb into blood.
- Body Fluids and Circulation – Blood and lymph are the body's transport fluids. Blood is plasma (about 55%) plus formed elements: RBCs, WBCs and platelets. Blood groups (ABO, Rh) depend on antigens on RBCs. A clot forms when fibrinogen turns into fibrin threads. The human heart has four chambers and pumps blood through two loops: to the lungs and to the body (double circulation). The SA node starts each beat; one beat is a cardiac cycle of about 0.8 s, recorded as an ECG with P, QRS and T waves. Cardiac output = stroke volume × heart rate ≈ 5 L/min.
- Breathing and Exchange of Gases – Breathing moves air in and out of the lungs. Air travels nose → trachea → bronchi → bronchioles → alveoli. We breathe in when the diaphragm and outer rib muscles contract and make the chest bigger, so pressure inside falls. In the alveoli, oxygen moves into blood and carbon dioxide moves out, always from higher partial pressure to lower. Blood carries O2 mostly on haemoglobin and CO2 mostly as bicarbonate. A centre in the brain sets the rhythm. Lung volumes like tidal volume and vital capacity can be added and measured.
- Excretory Products and their Elimination – Animals must remove nitrogen waste. Ammonia is most toxic and needs lots of water; urea is less toxic; uric acid needs least water. Humans are ureotelic. Each kidney has about a million nephrons. Urine forms in three steps: glomerular filtration (about 125 mL/min, 180 L/day), reabsorption (about 99% taken back) and secretion. The loop of Henle and vasa recta make the medulla salty by a counter-current mechanism, so urine can be concentrated. ADH, the renin-angiotensin-aldosterone system and ANF control water and salt. Lungs, liver, skin and sweat also help. Failed kidneys need dialysis or a transplant.
- Metabolism: How Cells Build, Break and Use Energy – Metabolism is the full set of chemical reactions inside a living thing. Breaking big molecules into small ones is catabolism; it gives out energy. Building big molecules from small ones is anabolism; it uses energy. ATP carries the energy between the two, like a rechargeable battery. Each reaction is sped up by its own enzyme, and the reactions link into chains called metabolic pathways.
4. Reproduction
Reproductive system and health
- Human Reproduction – Humans reproduce sexually and are viviparous (the baby grows inside the mother). Testes make sperm in seminiferous tubules; ovaries make ova in follicles. Gametogenesis uses meiosis: 1 spermatogonium gives 4 sperm, but 1 oogonium gives just 1 ovum plus polar bodies. The menstrual cycle (about 28 days) is run by FSH, LH, oestrogen and progesterone; an LH surge near day 14 causes ovulation. Fertilisation in the ampulla makes a zygote, which divides into a morula and a blastocyst that implants in the uterus. The placenta feeds the fetus; birth comes after about 9 months, followed by lactation.
5. The organism as a whole
Homeostasis
- Homeostasis – Homeostasis is how the body keeps its internal environment (blood and tissue fluid) steady even when the outside world changes. It controls body temperature (about 37 °C), blood glucose (about 4–6 mmol/L), water and salt, and blood pH (about 7.4). It mostly uses negative feedback: a receptor senses a change, a control centre decides, and an effector brings the level back to its set point.