Poland Liceum ogólnokształcące, klasa II Biology

1. V. Human structure and physiology

Body organisation and homeostasis · Nutrition and digestion · Liver, diet and digestive health · Immunity · Breathing · Circulation · Excretion and osmoregulation · Hormonal regulation · Nervous regulation · Senses, sleep and brain health · Movement · Skin and thermoregulation · Reproduction and development

• 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.
• 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.
• Nutrition – Nutrition is how we get and use the substances in food. The body needs six groups of nutrients: carbohydrates and fats (mainly energy), proteins (growth and repair), vitamins and minerals (small amounts to keep the body working), and water, plus fibre for healthy digestion. Carbohydrate and protein give about 17 kJ per gram, fat about 37 kJ per gram. A balanced diet gives all nutrients in the right amounts, and energy in should roughly equal energy out.
• The Immune System: How Your Body Fights Germs – Germs (pathogens) cause infectious disease. The body has three lines of defence: barriers (skin, mucus, acid), a fast general (innate) response (inflammation, fever, phagocytes) and a slow, specific (adaptive) response (B cells make antibodies, T cells kill infected cells). Memory cells make the second attack fast. Vaccines create memory safely. Immunity can go wrong: allergy, autoimmune disease, immunodeficiency (e.g. HIV).
• Respiration: Aerobic, Anaerobic and the Human Lungs – Respiration is the breakdown of food, usually glucose, inside cells to release energy, stored as ATP. With oxygen (aerobic) glucose is fully broken into carbon dioxide and water and gives much energy; without oxygen (anaerobic) it gives little energy and makes ethanol (yeast) or lactic acid (muscles). Our lungs bring oxygen to the blood through millions of alveoli.
• Transportation in Humans: Heart, Blood Vessels, Blood and Lymph – The heart is a four-chambered muscular pump. Blood passes through it twice in one full round: once to the lungs to pick up oxygen, and once to the rest of the body. This is double circulation. Arteries carry blood away from the heart, veins bring it back and capillaries do the exchange. Blood (plasma, RBCs, WBCs, platelets) and lymph together carry food, gases, hormones and wastes.
• 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.
• 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.
• 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.
• 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.
• Human Skin: Layers, Jobs and Sun Safety – Skin is the largest organ of the body. It has three layers: the epidermis (outer, waterproof, holds melanin), the dermis (blood vessels, nerves, glands, hair roots) and a fat layer underneath. It protects, senses touch and pain, controls body temperature with sweat and blood flow, and makes vitamin D in sunlight. Too much UV light harms skin cells, speeds ageing and can cause skin cancer such as melanoma.
• 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.