6th Grade Chapter 12.1: Transporting Materials

Body Organization and Homeostasis * Cells function as the basic unit of life, forming tissues, organs, and organ systems. * Homeostasis is the maintenance of steady internal conditions during external changes. * The body uses stored energy and releases excess as thermal energy; sweat ($\text{perspiration}$) helps maintain temperature homeostasis. # Digestive and Excretory Systems * Digestion breaks down food, while excretion removes unused substances. * Mouth: Chewing and saliva with enzymes ($\text{proteins that speed reactions}$) begin chemical breakdown. * Stomach: A flexible baglike organ that uses enzymes to further break down food. * Small Intestine: Performs digestion and absorption; uses bile from the liver and enzymes from the pancreas. * Large Intestine/Colon: Absorbs water from remaining waste material. * Excretory System: Collects and eliminates wastes ($CO_{2}$, urea, feces, salt) to prevent toxicity. * Kidneys: Remove urea by producing urine, which travels through the ureter to the bladder and leaves via the urethra. * The hypothalamus regulates fluid homeostasis by controlling hormone secretion to retain or excrete water. # Nutrition and Energy * Nutrients: Parts of food used for growth and survival, including proteins, fats, carbohydrates, vitamins, and minerals. * Calorie: The amount of energy required to raise the temperature of $1\,kg$ of water by $1^\circ\text{C}$. # Respiratory System and Gas Exchange * Breathing exchanges gases between the body and the environment via the nose, mouth, pharynx, trachea, bronchi, and lungs. * Alveoli: Over $100~\text{million}$ tiny cell groups per lung where oxygen and carbon dioxide exchange with capillaries. * Diaphragm: A thin muscle that contracts to pull air in and relaxes to push air out. # Circulatory System and Blood * The heart pumps blood through a system of vessels more than $1,000$ times daily. * Vessels: Arteries carry blood away from the heart; veins carry blood back to the heart; capillaries are sites of chemical exchange. * Total vessel length in the body exceeds $95,000\,km$. * Blood Composition: Plasma ($55\%$, transports substances), Red Blood Cells ($43\%$, carry $O_{2}$ and $CO_{2}$), White Blood Cells ($1\%$, fight infection), and Platelets ($1\%$, clot wounds). * Sickle Cell Disease: Results in crescent-shaped red blood cells that hinder transport. # Lymphatic System and Immunity * Functions include removing extra fluid around organs ($\text{maintaining fluid homeostasis}$), making white blood cells, and transporting fats. * Body Composition: Approximately $65\%$ of the human body is water. * Organs: Spleen ($\text{stores blood for emergencies}$), thymus, bone marrow, and over $500$ lymph nodes. * Lymphocytes: A specific type of white blood cell made in the thymus, spleen, or bone marrow to defend against infection.