Human Anatomy Chapter 23 The Digestive System

Composition of Saliva

- 97-99.5% water, slightly acidic - Electrolytes- Na, K, CI, PO,HCO - Salivary amylase and lingual lipase - Mucin - Metabolic wastes- Urea and Uric acid - Lysozyme, IgA, defensins

Blood Supply: Splanchnic Circulation

- Branches of aorta serving digestive organs ~Hepatic, splenic, and left gastric arteries ~Inferior and superior mesenteric arteries - Hepatic portal circulartion ~ Drains nutrient- rich blood from digestive organs ~ Delivers it to the liver for processing

Mucosa #1

- Lines Lumen - Functions- different layers perform 1 or all 3 - Secretes mucus, digestive enzymes, and hormones - Absorbs end products of digestion - Protections against infectious disease

Peritoneum and Peritoneal Cavity #2

- Mesentery- Double layer of peritoneum - Routes for blood vessels, lymphatics, and nerves - Holds organs in place; stores fat - Retroperitoneal organs posterior to peritoneum (kidneys) - Intraperitoneal (Peritoneal) Organs surrounded by peritoneum (stomach)

Functional Anatomy: Mouth

- Oral (buccal) Cavity ~ Bounded by lips, cheeks, palate, and tongue ~ Oral orifice is anterior opening ~ Lined with stratified squamous epithelium ~ Only part involved in ingestion

Peritoneum and Peritoneal Cavity #1

- Peritoneum- Serous membrane of abdominal cavity ~ Visceral peritoneum on external surface of most digestive organs ~ Parietal peritoneum lines body wall - Peritoneal cavity ~Between two peritoneums ~Fluid lubricates mobile organs

Tongue

- Skeletal Muscle - Functions include ~ Repositioning and mixing food during chewing ~ Formation of bolus ~ Intiation of swallowing, speech, and taste - Intrinsic muscles change shape of tongue - Extrinsic muscle alter tongue's position

Digestive System #1

- Two groups of organs 1) Alimentary canal (gastrointestinal GI tract) ~mouth to anus ~Digest food and absorbs fragments ~mouth, pharynx, esophagus, stomach, small intestine, and large intestine

Serosa

- Visceral peritneum - Areolar connective tissue covered with meothelium in most organs

GI Tract Regulatory Mechanisms

1) Mechanoreceptors and chemoreceptors - Respond to stretch, changes in osmolarity and pH, and presence of substrate and end products of digestion - Initiate reflexes that ~Activate or inhibit digestive glands ~Stimulate smooth muscle to mix and move lumen contents

Digestive System #2

2) Accessory digestive organs - Teeth, tongue, gallbladder - Digestive glands ~ Salivary glands ~ Liver ~Pancreas

Mucosa #2

Epithelium - Simple columnar epithelium and mucus secreting cells (most of tract) - Mucus - Protects digestive organs from enzymes - Eases food passage - May secrete enzymes and hormones

Histology of the Alimentary Canal

Four basic layers (tunics) - Mucosa - Submucosa - Muscularis externa - Serosa

Salivary Glands

Function of saliva - Cleanses Mouth - Dissolves food chemicals for taste - Moistens food; compacts into bolus - Begins breakdown of starch with enzymes

Musularis Externa

Mucularis externa - Responsible for segmentation and peristalsis - Inner circular and outer longitudinal layers ~Circular layer thicken in some areas---> Sphincters

Homeostatic Imbalance

Peritonitis - Inflammation of peritoneum - Causes by e.g., piercing abdominal wound, perforating ulcer, ruptured appendix - Peritoneum coverings stick together, localizing infection - Dangerous lethal if widespread - Treated with debris removal and antibiotics

Digestive Processes

Six essential activities 1) Ingestion- Take food in (mouth) 2) Propulsion- Move food through alimentary canal/peristalsis (esophagus) 3) Mechanical Breakdown- Physical prep for digestion (chewing, churning in stomach) 4) Digestion- Catabolic breakdown by enzymes (Cavity of alimentary canal) 5) Absorption- Passage of products to blood or lymph (small intestine) 6) Defecation- Eliminates what is left (anus)

Submucosa

Submucosa - Areolar connective tissue - Blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus