DIGESTIVE_SYSTEM

Composed of four layers:
- Mucosa: Mucous epithelium (simple columnar).
- Submucosa: Connective tissue layer.
- Muscularis: Contains two to three layers of smooth muscle for movement.
- Serosa: Serous membrane covering abdominal organs and forming mesenteries.

Roof: Formed by hard palate (maxillary and palatine bones) and the soft palate (arch-shaped muscle).
Floor: Formed by the tongue and its muscles.
- Papillae: Small elevations on tongue, home to taste buds.
- Uvula: Downward projection of the soft palate.
- Lingual Frenulum: Connects the tongue to the floor of the mouth.

Types of Teeth:
- Incisors: Central and lateral.
- Canines: Cuspids.
- Pre-molars: Bicuspids.
- Molars: Tricuspids.
Temporary Set: 20 teeth (deciduous or milk teeth); first tooth appears around 6 months, complete by 2 years.
Permanent Set: 32 teeth; first permanent tooth at around 6 years, complete by ages 17-24.
Structure of a Tooth: Includes crown (visible part covered by enamel), neck, and root (embedded in the jaw).
Pulp: Soft material in the central cavity containing nerves and blood vessels.

Nasopharynx: Located above soft palate; contains tonsils and opening for auditory tube. Prevented from receiving food by elevation of the soft palate.
Oropharynx: Between soft palate and epiglottis, contains palatine tonsils.
Laryngopharynx: Behind the larynx, connects to the esophagus.

A muscular tube (food pipe) that connects pharynx to stomach, located inferior to the diaphragm.

Size: Expands after meals, initially about the size of a large sausage.
Parts:
- Cardiac End: Esophagus opening into stomach.
- Fundus: Dome-shaped section above esophageal opening.
- Body: The main part of the stomach below the fundus.
- Pylorus: The lower part of the stomach, has a pyloric sphincter muscle.
Wall: Contains smooth muscle for churning movements (peristalsis).
Lining: Mucous membrane with microscopic glands secreting gastric juice and hydrochloric acid.
Rugae: Folds in the mucous membrane when the stomach is empty.
Chief Cells: Secrete pepsinogen; Parietal Cells: Secrete hydrochloric acid.

Size: Approximately 7 meters (20 feet) long, 2 cm in diameter.
Extends from stomach to beginning of large intestine (cecum).
Main site for digestion and absorption.
Divisions:
- Duodenum: Receives bile and pancreatic juice.
- Jejunum.
- Ileum.
Wall: Smooth muscle for peristalsis, lined with mucous membrane secreting intestinal juice.
- Villi: Finger-shaped projections for absorption into blood and lymph.

Size & Location: Largest gland, fills upper right abdominal cavity, extends into the left side.
Function: Secretes bile.
Ducts:
- Hepatic Duct: Drains bile from liver.
- Cystic Duct: Bile transport to/from gallbladder.
- Common Bile Duct: Formed from hepatic and cystic ducts, drains bile into duodenum.

Location: Behind the stomach.
Functions:
- Secretes pancreatic juice into the pancreatic ducts.
- Pancreatic islets secrete glucagon and insulin into the blood.

Divisions: Cecum, vermiform appendix, colon (ascending, transverse, descending, sigmoid), rectum, anal canal.
Appendix: Blind tube off cecum, no significant digestive role.
Rectum & anal canal open to the exterior at the anus.
Special Features:
- Taeniae Coli: Thickened smooth muscularis.
- Haustra: Puckering caused by taeniae coli.
- Epiploic Appendages: Fat-filled pouches of visceral peritoneum.

Definitions: Serous membrane lining the abdominal cavity and covering abdominal organs.
- Parietal Layer: Lines the abdominal cavity.
- Visceral Layer: Covers the abdominal organs.
- Peritoneal Space: Lies between parietal and visceral layers.
Extensions:
- Mesentery: Attaches small intestine to posterior abdominal wall.
- Greater Omentum: Hangs down from the stomach and transverse colon over the intestines.

Definition: Changing food to be absorbed and utilized by cells.
- Mechanical Digestion: Involves chewing, swallowing, and peristalsis to break food into small particles and mix with digestive juices.
- Chemical Digestion: Breaks down large food molecules into smaller compounds via digestive enzymes.
- Chyme: Partially digested food from the stomach.

Definition: Movement of digested food from the intestine into the blood or lymph.
- Portal Vein: Carries blood from the digestive tract to the liver.
- Most food and water absorbed in the small intestine; some water absorbed in the large intestine.

Main Intraperitoneal Organs: Stomach, liver, spleen, small intestine, transverse colon, sigmoid colon, cecum (partially), and appendix.
Taste Buds Innervation: By cranial nerves VII, IX, X.
Parotid Gland: Largest salivary gland.
Layer Order of Digestive Tube: Mucosa, submucosa, muscular layer, serosa.
Deciduous Teeth: Usually 20 in a set.
Gastric Glands Components: Parietal cells, chief cells, G cells.
Pyloric Canal: Opens into the duodenum.
Chief Cells: Secrete pepsinogen, converted to pepsin by gastric acids.
Parietal Cells: Secrete hydrochloric acid and intrinsic factor.
Ileum: The longest portion of the small intestine.
Gallbladder Function: Storage and modification of bile.
Renal Papillae: Empty urine into minor calyx.
Nephron Structure: Includes renal corpuscles and renal tubules.
Glomerulus: A tuft of capillaries in renal corpuscles.
External Urethral Sphincter Supply: Voluntary control by pudendal nerve.
Male Urethra Structure Order: Prostatic urethra → membranous urethra → spongy urethra.
Prepuce: Fold of skin covering the glans penis.
Interstitial Endocrine Cells: Produce testosterone in the testes.
Corpus Luteum: Secretes progestins.
Milk Production: Stimulated by hormones including prolactin, growth hormone, and human placental lactogen.