Biology Levels of Organization and Systems

Study Notes

Atoms are the fundamental building blocks of matter.
Molecules are formed by the combination of atoms.
Cells are the basic units of structure and function in living things.
Tissues are groups of similar cells that work together to perform a specific function.
Organs are structures made of two or more different tissues that perform a specific function.
An organ system is a group of organs that work together to perform a specific function.
An organism is a complete individual living thing.

The digestive system is responsible for the ingestion, digestion, and elimination of food.
Digestion takes place within the digestive tract, starting at the mouth and ending at the anus.
Digestion involves mechanical and chemical processes.

Epithelial tissue covers body surfaces and lines cavities.
Connective tissue binds and supports body parts.
Muscular tissue moves the body and its parts.
Nervous tissue receives stimuli, processes information, and conducts nerve impulses.

The body systems work interdependently in order to function.
The integumentary system includes skin, nails, hair, and other structures that protect the body.
The circulatory system transports blood, nutrients, gases, and wastes, and helps control homeostasis.
The lymphatic and immune systems control fluid balance and defend against infectious disease.
The digestive system ingests, digests, and absorbs nutrients, and eliminates waste.
The respiratory system maintains breathing and exchanges gases between lungs and tissues.
The urinary system excretes metabolic wastes and helps control fluid and pH balance.
The nervous system receives sensory input, integrates information, and initiates motor output.
The musculoskeletal system supports and protects the body, moves body parts, stores minerals, produces blood cells, and maintains posture.
The endocrine system produces hormones that coordinate organ systems and regulate stress, fluids, pH, and metabolism.
The reproductive system produces gametes and nurtures and gives birth to offspring.

The digestive tract begins with the mouth and ends with the anus.
Mechanical digestion involves chewing, churning, and mixing food in the stomach.
Chemical digestion involves enzymes breaking down macromolecules into smaller organic molecules.
The mouth receives food, initiating starch digestion.
The pharynx is a passageway for air and food. Swallowing involves the soft palate and epiglottis.
The esophagus moves food to the stomach by peristalsis.
The stomach mechanically and chemically digests food, and moves it into the small intestine.
The small intestine completes digestion and absorbs nutrients into the blood.
The large intestine absorbs water, salts, and some vitamins, and stores indigestible material. Defecation is the expulsion of feces.

The pancreas produces pancreatic juice (to neutralize stomach acid and digestive enzymes), and has endocrine functions with hormones like insulin and glucagon that regulate blood glucose.
The liver produces bile (to emulsify fat) and performs detoxification, protein synthesis, and blood glucose regulation. The liver has about 100,000 lobules as structural and functional units.
The gallbladder stores and concentrates bile from the liver, releasing it into the small intestine as needed; bile emulsifies fat.

Digestive enzymes speed up the breakdown of carbohydrates, proteins, and fats into smaller units for absorption.
Different enzymes function best at specific pH levels.

Digestive secretions (enzymes) are controlled by the nervous system and hormones (e.g., gastrin, secretin, CCK).
Hormones are released in response to the presence of nutrients.

Stomach ulcers are caused by infection with Helicobacter pylori or by other factors.
Intestinal disorders like diarrhea (acute or chronic) and constipation.
Polyps and colon cancer can arise from the digestive tract lining.
Pancreatic disorders include conditions like pancreatitis and pancreatic cancer.
Diabetes mellitus.
Liver disorders include hepatitis and cirrhosis.
Gallstones can block bile ducts, and jaundice may result.