Flashcards in Chapter 9 - Digestive System Deck (71)
What is digestion?
The breakdown of food into organic molecules:
Lipids into fatty acids and glycerol
Starch and carbs into monosaccharides
Proteins into amino acids
Mechanical digestion - what is it, and what ISNT it?
Physically breaking down large pieces of food - it is NOT chemical breakdown
Chemical digestion - what is it, and some examples
The enzymatic cleavage of chemical bonds
Ie, the peptide bonds of proteins, or the glycosidic bonds of starches
The order of what structures food travels through:
What additional structures help provide enzymes and lubrication to aid in digestion?
What is the enteric nervous system?
Millions of neurons that govern the GI system
These are present in the walls of the digestive tracts and trigger PERISTALSIS (rhythmic contractions of the gut to help move food along)
What controls the enteric nervous system?
It is largely autonomic, but it can function independently of the brain and spinal cord.
PARASYMPATHETIC: stimulates digestion, increased secretions, promotes peristalsis
SYMPATHETIC: inhibits the above activities
What is intracelullar digestion?
What is extracellular digestion?
Intracelullar: the oxidation of glucose and fatty acids for energy
Extracellular: obtaining nutrients from food in the lumen of the alimentary canal
What role do ADH (aka vasopressin) and ALDOSTERONE play in feeding behavior?
They trigger the sensation of thirst, encouraging the behavior of fluid consumption.
What substances trigger the feeling of HUNGER?
Glucagon (secreted by the pancreas)
Ghrelin (secreted by the stomach and pancreas)
What substances trigger SATIETY?
Cholecystokinin (peptide hormone secreted by GI tract)
What 3 substances account for chemical digestion in the oral cavity?
Salivary amylase "ptyalin" (starch into smaller sugars such as maltose and dextrin)
Lipase (breaks down lipids)
What are the 3 portions of the pharynx?
Laryngopharynx (above vocal cords)
What structures does the esophagus connect?
The pharynx and the stomach
Different muscle composition of the esophagus:
Top third: skeletal muscle
Middle third: mix
Bottom third: smooth muscle
Aka top: somatic/voluntary
Bottom: autonomic/involuntary control
Where does peristalsis start?
At the smooth muscle (lower third) of the esophagus
What is emesis?
the reverse of peristalsis
Where is swallowing initiated?
In the muscles of the oropharynx (upper esophageal sphincter)
What is the cardiac sphincter?
The lower esophageal sphincter
(Empties into the cardia of the stomach)
**weakness in this sphincter leads to gastroesophageal reflux disease (GERD) = "heartburn"
What are the THREE main sources of energy?
Stomach as an organ
(What is it made of?)
(Where is it?)
(What substances does it use to digest food?)
Holds about 2 L's
Made of muscle; thick mucosa
Upper left quadrant of the abdominal cavity, under the diaphragm
Uses hydrochloride acid and enzymes
Four main anatomical divisons of the stomach
Fundus - gastric glands
Body - gastric glands
Antrum - pyloric glands
Pylorus -pyloric glands
How does NSAIDs impact the stomach?
They MAY disrupt mucus production which leaves the mucosa unprotected and probe to irritation.
Gastritis, or gastric ulcers may result
How are gastric glands innervated?
What cell types do they have? (3)
Respond to signals from the vagus nerve (PARASYMPATHETIC nerve) which is activated by sight/smell/taste of food
What do mucous cells do?
bicarbonate-rich mucous that protects mucosa
What do chief cells and parietal cells do?
Chief cells make PEPSINOGEN (which is inactive - Pepsin is active)
And parietal cells make hydrochloric acid
These combine to make GASTRIC JUICE
What is special about PEPSIN?
An enzyme that breaks down proteins
It is activated by the ACIDIC environment - most active at a low pH
(Other enzymes mostly active at physiological pH)
What do the pyloric glands do?
They have G-cells that secrete GASTRIN
What is GASTRIN?
Induced parietal cells to secrete more HCl and stomach to contract and mix it's contents.