The Digestive System Group of organs working together to convert food into energy and basic nutrients to feed the body Carbohydrates, proteins, fats, vitamins, minerals

Digestive System – 4 Stages StageDescriptionLocation(s) in Human Body IngestionFood enters digestive systemMouth Digestion Mechanical Chemical Food is physically broken down into small pieces Digestive enzymes break food pieces into smaller, microscopic molecules Mouth, stomach Mouth, stomach, small intestine AbsorptionWater and digested food enter the bloodstream from digestive system Small intestine (food), large intestine (water) ExcretionUndigested food leaves the system in the form of feces Anus

Gastrointestinal Tract Long tube that begins at the mouth and ends at the anus Mouth→ Pharynx→ Esophagus→ Stomach→ Small Intestine→ Large Intestine→ Rectum→ Anus Also called the alimentary canal

Accessory Organs Play a direct role in digestion but are not a part of the GI tract Salivary Glands (parotid, submandibular, sublingual) – Secrete saliva, which contains enzymes that initiate breakdown of carbohydrates Liver – Produces bile to help emulsify fats in the small intestine Gall Bladder – Stores bile that the liver produces Pancreas – Secrete bicarbonate ions to help buffer acid concentration of chyme – Secretes digestive enzymes

Mechanical Digestion Mouth, teeth, tongue, stomach Food enters the mouth via ingestion Food is prepared for chemical digestion by chewing, mixing, churning Tongue pushes food back to prepare for swallowing Bolus – Mass of food that has been chewed at the point of swallowing

Propulsion Process of moving food through the GI tract Swallowing Peristalsis – Smooth muscle contraction and relaxation – Esophagus, stomach Sphincter (valves) – Circular muscle that controls movement of food throughout the GI tract

Heartburn Faulty sphincter Gastric juice coming up from stomach causing damage to the esophagus Causes – Smoking, alcohol, ibuprofen, aspirin, caffeine, large meals Treatment – Zantac, Gaviscon, Pepcid, Pepto Bismol, Prilosec, Acidopholous Can Lead to GERD – Gastroesophageal reflux disease

Chemical Digestion (Enzymes) Salivary Glands – Secrete amylase – breakdown carbohydrates Stomach – Secrete pepsin – breakdown protein Pancreas – Secrete trypsin – breakdown protein – Secrete lipase – breakdown fat Small Intestine – Secrete lactase – breakdown lactose

Stomach Bolus enters the stomach through the esophageal sphincter Gastric juice HCl – kills or inhibits bacteria and provides acidic pH of 2 Enzymes – chemical digestion Mucus – protects lining of stomach from acidic environment Bolus is converted into chyme by gastric juice

Helicobacter pylori Bacteria that is found in the stomach Causes gastritis, gastric ulcers by preventing mucus from forming Also linked to stomach cancers

Small Intestine Site of nutrient absorption Villi – increase surface area for absorption – Fingerlike projections that protrude from small intestine – Each villi contain a network of capillaries and microvilli – Nutrients are transported into capillaries via diffusion

Large Intestine Absorbs water from remaining indigestible food matter Transmits waste matter from body Houses over 700 species of bacteria – Digest polysaccharides – Produce vitamin K and biotin (B vitamin)

Excretory System (Kidneys) Removes waste Balances blood pH Maintain body’s water balance Blood is supplied to kidney via renal artery Blood re-enters circulatory system via renal vein

Nephrons Functional unit of the kidney ( per kidney) Regulate water balance Conduct excretion

Urinary Bladder Renal pelvis connects the kidney to the ureter which fills the bladder Holds ~300mL- 400mL of urine before exiting the urethra

Filtration Fluid and dissolved substances enter the nephron from blood Smaller molecules pass through Blood, platelets stay in bloodstream 1400L of blood pass through kidneys every day ~1.5L is excreted as urine daily

Reabsorption Water, glucose, some ions (Na⁺, Cl⁻) and other useful substances return to blood from nephron

Secretion Toxins and unwanted ions (H⁺) are secreted from the blood and into nephron for removal as urine

Malnutrition Insufficient, excessive, or imbalanced consumption of nutrients Gravest single threat to global public health Iodine – used to produce hormones that regulate thyroid gland Deficiency – Impaired mental abilities – Goiter – swelling of thyroid Vitamin A – Immune system uses to help fight infection Deficiency – Impaired vision Zinc – Healing of wounds, growth and repair of tissue, metabolism of macromolecules, alcohol Deficiency – Retarded growth, recurrent infections