Biology Chapter on Body Organization and Functions

Levels of Organization

• The human body is organized in a hierarchical structure: cell → tissue → organ → organ system → organism.
• Cells are the fundamental units of life and perform basic functions like energy production.
• Tissues are groups of similar cells with a specific function (e.g., epithelial, connective, muscle, nervous).
• Organs are complex structures made of various tissues performing specific tasks (e.g., heart, lungs).
• Organ systems are groups of organs working together for a common cause (e.g., digestive, respiratory).
• An organism is a complete living being capable of growth and reproduction.

Blood and Gas Transport

• Blood transports oxygen and carbon dioxide.
• Hemoglobin, found in red blood cells, carries oxygen from lungs to cells for energy.
• Blood carries carbon dioxide from the cells back to the lungs for release.
• Carbon dioxide is the main waste gas exhaled.

Heart Valves

• Heart valves prevent blood backflow, ensuring one-way blood flow.
• Key valves include the tricuspid, pulmonary, mitral, and aortic valves, each with a specific location.

Nervous System and Digestion

• The nervous system, through the brain, controls digestive processes.
• Signals regulate enzyme secretion and muscle contractions in the stomach and intestines.
• Stress can impact digestion due to nervous system interference.

Stomach Digestion

• Enzymes (e.g., pepsin) break down proteins into amino acids.
• Hydrochloric acid (HCl) lowers pH to activate enzymes and kill bacteria.

Nutrient Absorption

• The small intestine absorbs nutrients through villi and microvilli.
• Absorbed nutrients include carbohydrates (glucose), proteins (amino acids), and fats (fatty acids and glycerol).
• The large intestine absorbs water and salts, preparing waste for elimination.

Metabolic Waste

• The body removes various metabolic wastes.
• Carbon dioxide is removed via the lungs.
• Urea is filtered from the blood by the kidneys and excreted in urine.
• Other wastes include lactic acid, excess salts, and water, also removed through sweat.

Skin and Excretion

• The skin eliminates sweat containing water, salts, and urea.
• It is a crucial barrier and regulates temperature; however, primary excretion is handled by kidneys, lungs, and liver.

Stomach Muscles

• The stomach uses smooth muscle for churning and mixing food with digestive juices.
• Stomach muscle action is involuntary, controlled by the autonomic nervous system.

Nervous System Division

• The central nervous system (CNS) comprises the brain and spinal cord; it processes information.
• The peripheral nervous system (PNS) connects the CNS to various body parts like muscles, organs, and skin.

Gas Exchange in Lungs

• Gas exchange occurs in the alveoli, tiny air sacs in the lungs.
• Oxygen diffuses into the blood from alveoli.
• Carbon dioxide diffuses from the blood into alveoli for exhalation.

Skeletal System

• Adults have 206 bones.
• Bones are categorized into axial (80) and appendicular (126) skeletons.
• Axial skeleton includes the skull, spine, and rib cage, which provide structural support.

Systems During Exercise

• Several systems work together during physical activity—running.
• The skeletal system provides the framework.
• The muscular system propels movement.
• The circulatory, respiratory, and other systems support these.