Human Body Systems

• Humans are multicellular organisms composed of millions of cells, which are the body's functional units.
• Cells require raw materials to perform their functions.
• Similar cells performing the same job form tissues (e.g., skin cells form skin tissue).
• Tissues are grouped to form organs, such as the stomach or brain.
• Organs consist of at least two tissue types working together.
• Systems are groups of organs working together for a specific job.

Body Systems Jobs

• Digestive system processes food for the body's use.
• Respiratory system takes in oxygen.
• Circulatory system transports food and oxygen to cells.
• Excretory system removes wastes.
• Skeletal/muscular system supports the body and enables movement.

The Digestive System

• Food consists of complex chemicals and must be digested into simple, soluble nutrients.
• Nutrients provide energy, growth, and repair.
• Digestion is the process of breaking down food into a usable form.
• The digestive system includes the digestive tract and other organs.
• The digestive tract is a pathway from the mouth to the anus.
• Organs alongside the digestive tract produce chemicals that aid digestion.
• Mechanical digestion physically breaks food into smaller pieces, involving slicing, tearing, and crushing.
• No new substances are created in mechanical digestion.
• Chemical digestion involves saliva and gastric juice to break down food into simpler chemicals.
• New, smaller chemicals are produced during chemical digestion for absorption.

The Mouth

• Digestion begins in the mouth with teeth performing mechanical digestion.
• Incisors bite off pieces, and premolars and molars grind the food.
• Saliva, produced by salivary glands, initiates chemical digestion.
• Saliva contains chemicals that convert starch into glucose.
• Saliva moistens food, turning it into a bolus for easy swallowing.

The Oesophagus

• The oesophagus (foodpipe) is a muscular tube connecting the mouth to the stomach.
• Peristalsis, the rhythmic contraction and relaxation of oesophagus muscles, moves food down.
• The epiglottis prevents food from entering the windpipe during swallowing.
• Sphincters are rings of muscle along the digestive tract.
• The first sphincter separates the oesophagus from the stomach.
• The second sphincter separates the stomach from the small intestine.

The Stomach

• The stomach stores and further digests food for one to six hours.
• Muscular walls churn food, mechanically digesting it and mixing it with gastric juice.
• Gastric juice, produced in the stomach wall, contains hydrochloric acid, mucus, and digestive juices.
• Hydrochloric acid kills bacteria.
• Mucus protects the stomach lining.
• Digestive juices start protein digestion.

The Small Intestine

• The small intestine is the longest part of the digestive tract, approximately 6 meters long with a 3 cm diameter.
• The pyloric sphincter controls the release of digested food from the stomach into the small intestine.

The Duodenum

• The duodenum is the first section of the small intestine.
• Tubes from the pancreas and liver connect to the duodenum, carrying digestive chemicals.
• Muscular walls continue to churn food, mixing it with digestive chemicals.
• The mixture changes the remaining food into forms usable by the body.

The Pancreas and Liver

• The pancreas produces pancreatic juice, which digests fats, protein, and carbohydrates.
• The liver, the largest internal organ, performs over 500 chemical processes, including removing toxins from the blood.
• The liver acts as a short-term store for glucose and produces bile.
• Bile breaks down large fat pieces into smaller, easily digestible pieces.

The Ileum

• The ileum is the lower part of the small intestine.
• The ileum is where digested food is absorbed into the body.
• Villi, microscopic 'fingers', line the ileum to increase the surface area for absorption.
• Capillaries within villi facilitate nutrient absorption into the bloodstream.
• Nutrients absorbed include fatty acids, glycerol, amino acids, and glucose.
• Fatty acids and glycerol come from the digestion of fats.
• Amino acids come from the digestion of proteins.
• Glucose comes from the digestion of carbohydrates.
• Glucose is the body's main energy source.

The Large Intestine

• The final section of the digestive tract is the large intestine.
• The large intestine is 1.5 metres long and 6 to 7 cm in diameter.
• Water and remaining nutrients are reabsorbed into the body in the large intestine.
• Waste forms faeces (stools).
• The anus, a sphincter muscle, expels faeces.
• Bacteria makes up about one-third of the solid material in faeces.

Digestive Disorders: Vomiting

• Vomiting is a quick way to eliminate unwanted bacteria.
• Stress or infections can cause stomach and small intestine muscles to contract.
• The stomach's contents are forced up the oesophagus and out of the mouth.
• Vomit consists of partially digested food, stomach acid, and bile.

Digestive Disorders: Diarrhoea

• Diarrhoea is a quick way to eliminate harmful bacteria and viruses.
• Inflammation of the small intestine lining prevents water absorption from faeces.
• Faeces contain excess water, risking dehydration.

Digestive Disorders: Heartburn

• Heartburn is a burning sensation rising from the stomach to the oesophagus.
• Pressure on the stomach wall pushes contents back up.
• The oesophagus lacks mucus protection, so acid attacks its lining.

Digestive Disorders: Appendicitis

• The appendix is a dead-end tube connected to the large intestine.
• Blockage leads to inflammation and swelling, causing pain.
• Treatment involves removing the appendix to prevent rupture and severe infection.