Week 5 Flashcards
what is propulsion?
food movement initiated by swallowing and continued by peristalsis (muscle contractions push food through)
list the 4 layers of the gastrointestinal tract
mucosa, submucosa, muscularis externa, serosa
what does the mucosa and submucosa consist of?
mucosa- innermost epithelial layer covered by mucus, contains blood vessels, lymphatics, nerves, and mucus glands
submucosa- dense, irregular connective tissue, houses blood vessels, lymphatics, nerves, secretes substances aiding in digestion and absorption
what is the role of the muscularis externa layer and its two layers?
responsible for peristalsis and mechanical breakdown
two layers of smooth muscle:
- inner layer: circular muscle fibres
- outer layer: longitudinal muscle fibres
nerve fibres in between these layers regulate muscle activity
what is the function of the serosa layer and what are its components?
outermost layer, minimises friction between organs and body wall
also known as peritoneum in abdominopelvic cavity
- parietal peritoneum lines body wall
- visceral peritoneum wraps around organs
- mesentery (double peritoneum layer) connects parietal and visceral peritoneum
- peritoneal cavity (between parietal and visceral peritoneum) is filled with fluid, minimises friction
what is the function of the oral cavity?
involved in ingestion, mechanical breakdown, chemical breakdown, and propulsion
what is the function of the nasal cavity?
passageway for air
uvula prevents food from entering nasal passage
what are the functions of salivary glands and what are their 3 types?
accessory organ for chemical breakdown, salivary amylase breaks down complex carbs, lingual lipase starts fat breakdown
3 pairs: parotid, submandibular, sublingual
what are the functions of the pharynx and its components?
connects mouth and nasal cavity to trachea and oesophagus, respiration and digestion
- nasopharynx connects to oropharynx
- oropharynx is a passage for food, liquids, air
- laryngopharynx includes glottis, connects to oesophagus
- epiglottis prevents food/liquid from entering trachea during swallowing
what is the function of the oesophagus?
connects pharynx to stomach, uses peristalsis to push food into stomach
what are the 4 major regions of the stomach and the 3 muscle layers of the stomach wall
major regions: cardia, fungus, body, pyloric region
layers: longitudinal muscle, circular layer, oblique layer (additional layer compared to rest of tract, allows churning and stretching)
what two organs does the pylorus and pyloric sphincter connect?
stomach to small intestine, contains smooth muscle ring that must relax to allow food passage
what are the components and functions of the stomach lining?
composed of simple columnar epithelium
millions of gastric pits leading to gastric glands
- secretes gastric juices (parasympathetic response)
- triggered by sight, smell, taste, initiating digestive process
- lined by mucus secreting cells: parietal, chief, enteroendocrine
parietal cells secrete Hal and intrinsic factor (for B12 absorption)
chief cells secrete inactive enzyme pepsinogen
enteroendocrine cells produce gastrin hormone (amplifies production of gastric juice)
why does the stomach have a low pH of 1.5 to 2.5?
kills bacteria, activates pepsin from pepsinogen
describe the stomach action
- mucus lining protects stomach from erosion by HCl and enzymes like pepsin
- food entering stomach mixes with acidic gastric juice to form chyme, stirred by muscular wall
- pepsin breaks down proteins into amino acid chains
- intrinsic factor enables vitamin B12 absorption
- secretion of gastric juice stimulated by gastrin and vagus nerve impulses
- relaxation of pyloric sphincter allows chyme into small intestine
what are the three segments of the small intestine and their function
the small intestine- chemical breakdown, nutrient absorption (long but skinny)
duodenum- first segment, receives secretions from liver/gallbladder/pancreas
jejunum- middle segment
ileum- last segment
all segments involved in digestion, absorption, and peristalsis
what adaptations increase surface area in the small intestine?
villi contain lacteals and blood capillaries for absorption
microvilli are on epithelial cells of villi (brush border)
describe the small intestine action
- chyme in duodenum mixes with bile (emulsifies fat) and pancreatic juice
- carbs and proteins nearly fully broken down
absorption:
- occurs in all segments, enhanced by intestinal folds, villi, microvilli
- monosaccharides (like glucose) and amino acids actively transported into epithelial cells, then move into blood capillaries within villus, then nutrient rich blood goes to liver via portal vein
- free fatty acids and monoglycerides enter epithelial cells, repackaged into chylomicrons, enter lacteals (lymphatic capillaries that transport fat), fat-soluble vitamins absorbed with lipids
- water is absorbed (soluble vitamins also absorbed)
what are the components of pancreatic juice and their functions?
bicarbonate- neutralizes acidic chyme
pancreatic amylase- breaks down starches to short sugar chains (2 sugar molecules)
pancreatic lipase- breaks down lipids to fatty acids and monoglycerides
inactive pancreatic proteases- activated in duodenum
what is bile and its function?
watery solution containing bile salts, produced by the liver , emulsifies fats (increases SA) and aids in fat breakdown by lipases, stored in gallbladder and released after meals containing fat
what are the functions of the liver?
- maintains blood concentrations of glucose, lipids, amino acids
- nutrient conversion (carb -> lipid, amino acid -> glucose)
- synthesis and production of glycogen, cholesterol, plasma proteins, clotting factors
- storage of iron, lipids, fat-soluble vitamins
- absorption and inactivation of toxins, hormones, immunoglobins, drugs
describe the functions of the pancreas
accessory organ, both endocrine and exocrine gland
digestive (exocrine)- produces and secretes pancreatic juice into duodenum
metabolic (endocrine)- produces hormones insulin and glucagon, secreted into bloodstream
what are the 4 segments and functions of the large intestine?
wide but short, segments: cecum, colon (ascending, transverse, descending), rectum, anal canal
functions:
- propulsion and elimination of waste
- limited absorption of water, electrolytes, some vitamins
- bacterial colonies present (smelly gas, produces some vitamins B and K)
