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 Stage Description Location(s) in

Human BodyIngestion Food enters digestive system Mouth

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

Absorption Water and digested food enter the bloodstream from digestive system

Small intestine (food), large intestine (water)

Excretion Undigested 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 – Mesenteric arteries supply blood to small intestine

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 (~1 000 000 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• Active and Passive transport across membrane

Secretion • Toxins and unwanted ions (H⁺) are secreted from

the blood and into nephron for removal as urine

Kidney Stones• Small, hard deposits that form

inside the kidney• Crystallization of calcium when

urine becomes supersaturated • Symptoms– Excruciating pain, nausea,

vomiting• Causes – Dehydration, high protein diet,

refined sugars• Treatment – Pass through urinary tract– Ureteroscopy

Renal Dialysis • Process used to remove waste and excess water from the

blood• Artificial replacement for people who experience kidney failure• Works on principles of diffusion across a semi-permeable

membrane

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