DIGESTIVE SYSTEM

Peritoneum: Membrane of the abdominal cavity Parietal Peritoneum covers the abdominal wall Visceral Peritoneum covers the inner organs Branching from the peritoneum: – Lesser omentum—attaches the liver to the lesser curvature of stomach – Greater omentum: (Apron) Contains fat to insulate, cushion, and protect abdominal organs

The Digestive System Functions Ingestion—taking in food Digestion—breaking food down both physically and/or chemically Absorption—movement of nutrients into the bloodstream Defecation—rids the body of indigestible waste

Organs of the Digestive System Two main groups of organs – Alimentary canal (gastrointestinal or GI tract)— continuous coiled hollow tube from mouth to anus – Accessory digestive organs (aid in digestion but food does not pass through)

Organs of the Alimentary Canal Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus

Accessory Digestive Organs Teeth Salivary glands Pancreas Liver Gallbladder

Mouth (Oral Cavity) Anatomy Lips (labia)—protect the anterior opening Cheeks—form the lateral walls Hard palate—forms the anterior roof Soft palate—forms the posterior roof Uvula—fleshy projection of the soft palate

Mouth Physiology Mastication (chewing) of food Mixing masticated food with saliva Initiation of swallowing by the tongue Allows for the sense of taste

Salivary glands They make as much as a quart of saliva each day. Saliva helps with – swallowing – protects your teeth against bacteria – aids in the digestion of food.

Enzymes found in saliva Amylase – breaks down startches Lysozyme – breaks down cell walls of bacteria (also secreted in eyes and nose) Lipase – starts the breakdown of fats, specifically triglycerides

Pharynx Anatomy Nasopharynx—not part of the digestive system Oropharynx—posterior to oral cavity Laryngopharynx—below the oropharynx and connected to the esophagus

Pharynx Physiology Serves as a passageway for air and food from mouth to esophogus Food is propelled to the esophagus by two muscle layers – Longitudinal inner layer – Circular outer layer Food movement is by alternating contractions of the muscle layers (peristalsis)

Esophagus Anatomy and Physiology Anatomy – About 10 inches long – Runs from pharynx to stomach through the diaphragm Physiology – Conducts food by peristalsis (slow rhythmic squeezing) – Passageway for food only (respiratory system branches off after the pharynx)

Layers of Alimentary Canal Organs  Mucosa  Innermost, moist membrane, smooth muscle layer  Submucosa  Just beneath the mucosa, contains blood vessels and nerve endings Muscularis externa— smooth muscle – Inner circular layer and outer longitudinal layer Serosa—outer membrane

Stomach Anatomy Located on the left side of the abdominal cavity Food enters at the cardioesophageal sphincter – Food empties into the small intestine at the pyloric sphincter (valve)

Stomach Physiology Temporary storage tank for food Site of food breakdown – HCl acid Chemical breakdown of protein begins by the enzyme pepsin Delivers chyme (processed food) to the small intestine

Small Intestine The body’s major digestive organ Muscular tube extending from the pyloric sphincter to the ileocecal valve Site of nutrient absorption into the blood Suspended from the posterior abdominal wall by the mesentery ( a membrane within the small intestine)

Subdivisions of the Small Intestine Duodenum – Attached directly to the stomach Jejunum – Attaches anteriorly to the duodenum Ileum – End portion of the small intestine extends from jejunum to large intestine

Chemical Digestion in the Small Intestine Chemical digestion begins in the small intestine – Bile, formed by the liver, enters via the bile duct breaks down fats – Enzymes in the small intestine are secreted by the pancreas and the intestinal cells *Peptidases (breaks proteins into amino acids *Sucrase breaks down sucrose sugar *Lactase breaks down lactose in milk *Maltase breaks down maltose into glucose Amylase breaks down starch Nucleases break down nucleic acids

Small Intestine Anatomy Three structural modifications that increase surface area – Microvilli—tiny projections of the plasma membrane (create a brush border appearance) – Villi—fingerlike structures formed by the mucosa – Circular folds (plicae circulares)—deep folds of mucosa and submucosa

Small Intestine Anatomy Structural modifications that increase surface area – Microvilli—tiny projections of the plasma membrane (create a brush border appearance) – Villi—fingerlike structures formed by the mucosa

Large Intestine Larger in diameter, but shorter in length, than the small intestine Frames the internal abdomen

Large Intestine Anatomy No villi present Goblet cells produce alkaline (high pH)mucus which lubricates the passage of feces Muscularis externa layer is reduced to three bands of muscle called teniae coli These bands cause the wall to pucker into haustra (pocketlike sacs)

Large Intestine Anatomy Cecum—saclike first part of the large intestine Appendix (you can live without an appendix) – Accumulation of lymphatic (immune system) tissue that sometimes becomes inflamed (appendicitis) – Hangs from the cecum – Nursery for important digestive bacteria

Large Intestine Anatomy Colon – Ascending—travels up right side of abdomen – Transverse—travels across the abdominal cavity – Descending—travels down the left side – Sigmoid—enters the pelvis Rectum and anal canal—also in pelvis

Large Intestine Anatomy No villi present Goblet cells produce alkaline mucus which lubricates the passage of feces Anus—opening of the large intestine – Double sphincter – These sphincters are normally closed except during defecation

Liver Produces bile so the small intestine can break down fats and proteins Makes blood cells Helps in creating blood clot factor Carbs are stored in the liver as glycogen – when no glucose is available and energy is needed this is released Stores vitamins A,D,E,K and iron Removes hormones like estrogen and drugs and alcohol Has immune cells that destroy pathogens that enter the liver from the gut. Makes albumin – a protein for transporting hormones

Gall bladder Stores bile for release into the intestines

Pancreas Secretes many enzymes that act in the small intestine Part of the endocrine system – maintain homeostasis by producing insulin (to allow the uptake of glucose into cells) and glucagon (when too little glucose available it takes stored glycogen from the liver and breaks it down)When glycogen runs out, muscles will be broken down.