Chapter 22: The Digestive System Flashcards
Alimentary Canal
Gastrointestinal (GI) tract
Alimentary Canal Structural Components: Digestive Organs
Mouth Pharynx Esophagus Stomach Small and Large Intestines Anus
Alimentary Canal Structural Components: Accessory Digestive Organs
Teeth Tongue Salivary Glands Liver Gall Bladder Pancreas
Digestive Process
- Ingestion: intake food
- Propulsion: movement of food by swallowing and peristalsis
- Mechanical Digestion: chewing, churning and segmentation (local rhythmic constrictions) food
- Absorption: transport of digested products from lumen into blood and lymph capillaries
- Defecation: elimination of undigested food substances
Abdominal Regions
- Abdominal organs will move
- Abdominal regions aid in locating organs
- Hypochondriac
- Epigastric
- Hypogastric
Hypochondriac
deep to the ribs
Epigastric
superior to the belly
Hypogastric
inferior to the belly
Peritoneal Cavity and Peritoneum
Peritoneum: which will cover and line abdominopelvic cavity
Layers:
- Visceral peritoneum: covers external surface or digestive organs
- Pariteal Peritoneum: lines the walls of cavity
- Space contains serous fluid to allow organs to move against one another
Mesentereies
- Double layer of peritoneum; serous membranes fused together
- Will extend to digestive organs from body wall to hold organs in place
- Fat storage
- Support vessels and nerves to reach organs
Ventral Mesenteries
- Falciform Ligament: anterior of liver to anterior abdominal wall and diaphragm
- Lesser omentum (fatty skin)-runs from liver fissure to lesser curvature
Dorsal Mesenteries
Greater momentum (fatty skin) - cover intestines
Mouth Functions
ingest, mechanical digest and chemically digest
Boundaries of the Mouth
- Anterior-lips
- Posterior-fauces of oropharynx
- Lateral-cheecks
- Interior-tongue
- Superior-palates
Structures of the Mouth
- Vestibule: space external to teeth
- Oral cavity proper: space internal to teeth
Salivary Glands Produce:
Saliva
Functions of Saliva
- moistens mouth
- dissolves food chemically-starches
- binds food together to blue
- neutralizes acids produced by oral bacteria to prevent tooth decay
- bactericidal enzymes
Glands
paired compound tubuloalveloar glands
- Parotid: “near ear”
- Submandibular: medial surface of mandibular body
- Sublingual: inferior to tongue
The Pharynx
- bolus leaves mouth enters oropharynx and laryngopharynx
- pharynx is continous with esophagus
Esophagus
food to stomach
- Lumen collapses when no food is present
- Passes through diaphragm: esophageal hiatus
- Joins stomach at cardiac orifice where the cardiac sphincter closes off lumen to prevent regurgitation
The Stomach Functions
- temporary storage for food
- chum food into chin paste
- starts breakdown of food proteins by secreting pepsin which functions only under acidic conditions
- absorbs water, electrolytes and some drugs
Food remains in stomach for about 4 hours
Structures of the Stomach
- Cardiac Region (Cardia): near the heart
- Fundus
- Body
- Pyloric Region: Pylorus and Pyloric Sphincter: conducts chyme into small intestine
- Rugae: “wrinkles” accounts for distensibility of stomach; allows for expansion
Microscopic Anatomy of the Stomach
Mucosa Layer: Gastric pits which open into gastric glands
3 types of secretory cells in gastric glands
1) Mucous neck cells: mucus lining of stomach
2) Parietal (Oxyntic) Cells: hydrochloric acid
3) Chief (Zymogenic) Cells: pepsinogen which is cleaved to form pepsin
The Small Intestine
- Time=3-6 hours
- Longest part of alimentary canal
- Site of most enzymatic digestion and almost all absorption of nutrients
- Most digestive enzymes are secreted by pancreas not small intestine
- Churning and peristalsis shuffle chyme to maximize absorption
- Runs from pyloric sphincter to first part of large intestine
Small Intestine- Duodenum
-receives digestive enzymes from pancreas and bile duct
STRUCTURES:
- hepatopancreatic ampulla: bulb that collects secretions from bile/liver and pancreas
- major duodenal papilla: entry
Jejunum
Empty (40% of SI)-absorption
Ileum
Twisted (60% of SI)- absorption
Villi
like projections of mucosa specialized for absorption in small intestine
Layers of Villi
Absorption cells
-Enterocytes: simple columnar epithelial cells
-Goblet Cells: secrete mucus to lubricate chime and provides protective surface
Lacteal: blood and lymph capillaries
Smooth Muscle within villi to move during digestion
The Large Intestine
- Time: 12-24 hours
- Food breakdown occurs
- BreLast major organ of alimentary canal
- Little additional akdown that occurs is bacterial
- Main function is to absorb water and electrolytes resulting in semi-solid feces
- Mass peristaltic movements: slow sluggish and weak movements propel
Structures of the Large Intestine
Cecum “blind sac”- beginning of large intestine
-ileocecal valve: prevents reflux of feces
Verniform appendix “worm-shaped”-blind tube that opens on poster medial wall of cecum
-Lymphoid tissue to collect neutralize pathogens
-Colon
Colon
- Ascending colon
- Right colon (hepatic) flexure
- Transverse Colon
- Left colon (splenic) flexure
- Descending colon
- Sigmoidal colon (s shaped)
structures of the Large Intestine
- rectum
- anal canal
Rectum
Straight: joins sigmoid colon; descends and retroperitoneally along inferior portion of sacrum
- no tenaie coli; has longitudinal muscle
- rectal valves: transverse fold of rectum that prevent feces from being passed with flatus (gas)
Anal Canal
Passes through elevator ani muscle and lies external to abdominopelvic cavity
2 SPHINCTERS
- External anal Sphincter: will contract voluntarily to inhibit defecation
- Internal Anal Sphincter: will contract involuntarily to inhibit infection
- Both will prevent fecal leakage from anus between defecations and will exhibit defecation from emotional stress
Special Features of Large Intestine
TENIAE COLI: “Colon Ribbons”- thickenings of longitudinal muscle layer to maintain muscle tone
HAUSTRA: “draw up”- puckered sacs caused by teenier coli
EPIPLOIC (OMENTAL) APPENDAGES: “Membrane covered”- fat filled pouches of visceral peritoneum; unknown functions
Gallbladder
- Muscular Sac resting on the visceral surface of right hepatic lobe
- Functions to store and concentrate bile
- When fatty chyme enters duodenum, a hormone cholecytoskinin is released from enterodendocrine cells of duodenum-cause bile duct sphincters to relax and bile is expelled
Cystic Duct
Pancreas
- Exocrine and endocrine gland
- Produced most of the enzymes that will digest food in the small intestine
Structures:
- Head
- Body
- Tail
- Main pancreatic duct: drains most of the
Acinar (Acini) glands
are responsible for synthesizing, storing, and secreting pancreatic digestive enzymes
Acinar (Acini) cells
compose glands
Zygomen granules
Enzymes are stored in their inactive form in intracellular granules
