Digestive System Flashcards
How are the digestive system organs divided?
- Alimentary canal: GI tract/gut
o Muscular tube from mouth to anus
o Digests and absorbs food - Accessory Digestive Organs
o Produce secretions to digest food
o Teeth, tongue, salivary glands, gallbladder, liver, pancreas
What happens/where during the digestive process?
- Ingestion + propulsion –> mechanical breakdown –> chemical digestion –> absorption –> defecation
Explain each digestive process
- Propulsion
o Swallowing
o Peristalsis – involuntary; contraction/relaxation of organ walls - Mechanical breakdown
o Chewing
o Mixing
o Churning
o Segmentation – constriction of small intestine + digestive juices - Chemical Digestion – breakdown into chemical blocks with enzymes
- Absorption – end products (vitamins, minerals, and water) from lumen through mucosal cells into blood or lymph
- Defecation – get rid of indigestible solid wastes
What controls digestive activity? What do the receptors respond to?
via mechano and chemoreceptors
- Mechano and chemoreceptors respond to:
o Stretching of organ from food
o Presence of substrates and end products
o Osmolarity
o pH - receptors initiate reflexes that:
o activate or inhibit glands
o stim smooth muscle to mix contents and move them
What relationship does the GI have with the Peritoneum?
- Peritoneum – serous membrane of ab cavity
o Visceral – external of digestive organs
o Parietal – lines entire body wall - Peritoneal cavity – fluid filled space between the two
o Lubes - Mesentery – double layer of Peritoneum
o Extends organs from body wall
o Vascular and nerve supplier to visceral
o Holds organs in place
o Stores fat - Peritoneal Organs – surrounded by peritoneum: stomach
- Retroperitoneal organs – outside the peritoneum: pancreas, duodenum, large intestine
What provides blood to the digestive system?
- Splanchnic Circulation – arteries branch off aorta to serve digestive organs
o Celiac trunk branches supply stomach and liver
o Mesenteric arteries – supply small and large intestines - Hepatic portal
o Collects nutrient rich venous blood from: stomach, small/large intestines –> liver for metabolic processing and storage via hepatic portal vein
What are the 4 layers of the alimentary canal?
- Mucosa
o Secretes mucous, digestive enzymes, absorbs end products into blood, protects bad bacteria - Submucosa
o Supply blood vessels and nerve fibers - Muscularis externa
o Smooth muscle = segmentation and peristalsis (sphincters) - Serosa
o Holds everything together; visceral peritoneum
What structures make up the oral cavity?
- Buccal cavity – stratified squamous epithelium with keratinization for protection
- Teeth – mastication
- Palate –
o hard palate – anterior; rigid bone for chewing
o soft palate – posterior; skeletal muscles closing nasopharynx during swallowing + uvula - tongue – skeletal muscle
o mixes food with saliva to compact mass (Bolus)
o papillae either contain taste buds or provide friction
What are the different salivary glands?
- Major salivary glands – produce most saliva presence of food and though of food
o Parotid glands
Mumps – inflammation caused by virus and common in childhood
o Submandibular glands
o Sublingual glands - Within glands, saliva is secreted from?
o Serous cells – watery secretion with enzymes
o Mucous – mucus
What is the purpose of saliva and what is it made up of?
- Functions
o Cleaning
o Dissolve foods
o Moisten food into bolus
o Contain enzymes for chemical breakdown of starch - What is it made of?
o Electrolytes
o Digestive enzymes:
Salivary amylase – breaks down starch
Lingual lipase – breaks lipids
o Protein: mucin, lysosome, defensin, lgA
What makes up the Pharynx?
- Throat
- Oropharynx –> laryngopharynx
- Squamous epithelium and mucus
- Two skeletal muscles – propel food into esophagus
What makes up the esophagus?
- Muscular tube from laryngopharynx to stomach
o Change from skeletal to smooth - Upper esophageal sphincter gastroesophageal sphincter
- Joins stomach at cardiac orifice
- What does mucus do?
o In gastroesophageal sphincter protects esophagus from reflux of stomach acid
What happens during Deglutition (swallowing)?
- Highly coordinated with tongue + soft palate + etc
- Buccal Phase
o Mouth and voluntary
o Tongue pressed against roof, bolus is forced into oropharynx
o Swallowing past uvula is involuntary - Pharyngeal-esophageal phase
o Involuntary
o All routes sealed except digestive tract
o Peristalsis moves food
What digestive processes are the Mouth and its accessory organs involved in?
- Ingestion
- Mechanical breakdown
- Chemical digestion
- Propulsion
What is the stomach and what occurs there?
- Smooth muscle storage tank
- Chemical breakdown of proteins + food converted chyme
- 50ml when empty or 4L when full
- Vomiting (emesis) – stretching or irritant
- Collapses into folds when empty (rugae) – sound
What structures exist within the stomach?
- Cardia – opening
- Fundus – dome at top
- Body – midportion
- Pyloric part – distal region
o Pyloric antrum + canal - Pyloric sphincter – end duodenum
What are the different layers of the stomach?
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
What makes up the epithelial lining?
- Surface mucous cells – alkaline coat to protect stomach
- Gastric pits – gastric juice
What are the different types of stomach gland cells?
- Mucous neck cells – acidic mucus
- Parietal – secret HCL and intrinsic factor
- Chief cell – pepsinogen – protein producing enzyme
- Enteroendocrine cells – secretes chemical messengers
o Gastrin (G cells) – stimulate parietal cells to HCL(hydrochloric acid) secretion + small intestine contraction
o Somatostatin – D cells that influence digestive organs
Stomach – inhibits gastric secretion
Pancreas – inhibits secretion of insulin and glucagon
How does the mucosal barrier of the stomach lining work?
- Mucosal barrier to prevent gastric juice from eating itself
o Bicarbonate rich mucus
o Epithelial cells + tight junctions
o Epithelial lining is rebirthed every 3-6 days - Gastric ulcer – erosion
What structures of the stomach wall enhance digestion?
- Muscular layer
- Mucosa epithelial lining = stomach gland cells
How does the stomach regulate gastric secretion?
o Phase 1 Cephalic (reflex) – before food is eaten
Few mins
Pavlonian + smelling/seeing food
Stimulation –> sight and thought + taste and smell
Inhibit –> loss of appetite + depression
o Phase 2 Gastric Phase – food enters stomach
2/3 gastric juice released
Stimulation –> stretching + food chemicals
Inhibit –>excess acidity + emotional stress
o Phase 3 Intestinal
Short stim –> inhibit gastric secretion
Enterogastric reflex – declines gastric secretory to protect small intestine
Stimulation –> partially digested food
Inhibit –> presence of chyme + food
What is the enteric nervous system?
- Controls digestion
- Communicates with CNS, para with Vagus nerve and sympa with collateral ganglia
- Separate with reflex activity
o Motor neurons controls peristalsis and churning
o Neurons control secretion of enzymes
How does Gastric contractile activity work?
- Peristalsis waves pylorus at 3/min
o Controlled by cells of Cajal (pacemaker)
o Propulsion grinding retropulsion
What is the essential stomach function?
- Intrinsic factor – absorption of B12 for red blood cell production
What makes up the small intestine?
- Pyloric sphincter to ileocecal valve
o Duodenum
Where food transfers from stomach
Hepatopancreatic ampulla – bile duct and pancreatic duct empty into duo
o Jejunum
8’
o Ileum
12’
Thick mesentery for both
What exists within the small intestine (micro)
- Absorbs nutrients
- Circular folds – deep mucosa/sub
o Force chyme to spiral through lumen slowing movement - Villi – small extensions
o Epithelium = absorptive cells – electrolytes and nutrients
o Intestinal crypts – secrete intestinal juice and enteroendocrine cells that make enterogastrones - Microvilli – tiny extensions of absorptive
o Brush border enzymes to digest carbs and small proteins
How is it made and what makes up intestinal juice?
- Intestinal glands secrete 1-2 L daily
- Slightly alkaline, largely water + mucus
- Enzyme poor and in response to irritation of mucosa
What makes up the liver?
- 4 lobes
- Hepatic artery, hepatic portal vein enter liver via porta hepatis
What is bile?
- Stored in gallbladder
- Alkaline solution – bile salts, phospholipids (aid digestion), bile pigments, cholesterol, neutral fats, electrolytes
What are bile salts?
- Cholesterol
o Emulsify fat
o Facilitate fat and cholesterol absorption - Key bile is bilirubin – waste product of heme
What does the gallbladder do?
- Stores bile
- Releases bile via cystic duct
- Gallstone – crystalized cholesterol
How does bile leave the liver?
- R/L hepatic ducts common hepatic duct
- Common hepatic duct cystic duct common bile duct
- Common bile + main pancreatic duct duodenum at hepatopancreatic ampulla
What is the exocrine function of the pancreas?
- Secrete pancreatic juice via main pancreatic duct duodenum
What makes up pancreatic juice?
- Water solution = enzymes + electrolytes (neutralizes acidity in stomach)
- Pancreatic proteases are active in duodenum
- Pan enzymes are secreted actively but need bile
o Pancreatic amylase (carbs)
o Lipase
o Nuclease
What are the three unique features of the large intestine?
- Teniae coli – 3 bands of longitudinal smooth muscle
- Haustra – pocket sacs cased by teniae coli
- Epiploic appendages – fat filled pouches
What are the five subdivisions of the large intestine?
- Cecum
o Appendix – plays role in immunity and gut bacteria - Appendix
- Colon
- Rectum
- Anal canal
How does bacteria work in the large intestine?
- Gets in from small intestine –> cecum or anus
- Synthesize B and K vitamins
- Ferment indigestible carbs –>flatus (dimethyl sulfide)
How are carbs digested?
- Small intestine
o Pancreatic amylase + brush border enzymes
How are proteins digested?
- Stomach – pepsin
- Small intestine
o Pancreatic proteases
o Brush border enzymes
How are fats digested?
- Mouth – lingual lipase
- Stomach – gastric lipase
- Small intestine
o Emulsifications via bile salts
o Pancreatic lipase
How are nucleic acids digested?
- Small intestine
o Pancreatic ribonuclease
o Brush border enzymes
