Chapter 9- The Digestive System Flashcards
2 types of digestion
- intracellular- metabolism, oxidation of glucose and fatty acids for energy.
- extracelluar- process by which nutrients are obtained from food (occurs in lumen on alimentary canal- mouth to anus)
sphincters
circular smooth muscles around the canal that can contract to allow compartmentalization of function. sections off the alimentary canal (mouth to anus)
mechanical vs. chemical digestion
m- physical breakdown of large food particles into smaller ones.
c- enzymatic cleavage of chemical bonds
absorption
transport of products of digestion from digestive tract into the circulatory system for distribution to the body’s tissues and cells.
digestive tract order
oral cavity–> pharynx–> esophagus–> stomach–> small intestine–> large intestine–> rectum
other helper organs include: salivary glands, pancreas, liver, gallbladder
enteric nervous system
collection of 1hundredmillion neurons that governs the function of the GI system. neurons are present in walls of digestive tract and trigger peristalsis (rhythmic contractions of gut to move materials through system)
what hormone triggers the sensation of thirst?
ADH and aldosterone (encourage behavior of fluid consumption)
ghrelin
secreted by stomach and pancreas (stimulates feelings of hunger)
leptin and cholecystokinin
stimulate feelings of satiety (feeling full)
mastication
chewing
salivary amylase
aka: ptyalin. hydrolyzes starch into smaller sugars. (found in saliva)
lipase
catalyzes hydrolysis of lipids (found in saliva)
3 parts of pharynx
- nasopharynx- behind nasal cavity
- oropharynx- back of mouth
- laryngopharynx- above vocal cords
emesis
reversal of peristalsis, vomiting
upper esophageal sphincter
swallowing is initiated here (muscles of the oropharynx)
lower esophageal sphincter
cardiac sphincter. relaxes and opens to allow the passage of food into the stomach
4 main anatomical divisions of stomach
1/2. fundus/ body, which have mainly gastric glands
3/4. antrum/ pylorus, which contain mostly pyloric glands
gastric glands
respond to signals from the vagus nerve of the parasympathetic nervous system. 3 types of cells here: mucous, chief, and parietal
mucous cells of gastric glands
produce bicarbonate-rich mucus that protects the muscular wall from harsh stomach environment
chief cells and parietal cells of gastric glands
gastric juice is a combo of secretions from these two.
chief- secrete pepsinogen
parietal- secrete H+ions in form of HCl, intrinsic factor
pepsin
digests proteins by cleaning peptide bonds near aromatic amino acids resulting in short peptide fragments. activated by acidic environment
intrinsic factor
glycoprotein secreted by parietal cells. absorption of vitamin B12
stomach secretes 6 products
HCl (kill microbes, denatures proteins), Pepsinogen (cleaved to pepsin then digests proteins), mucus (protects mucosa), bicarbonate (protects mucosa), water (dissolves/dilutes ingested material), intrinsic factor (B12 absorption)
pyloric gland
contain G cells that secrete gastrin (peptide hormone that induces parietal cells in the stomach to secrete more HCl and signals stomach to contract to mix its contents)
chyme
digestion of solid food in stomach results in this acidic semifluid mixture
2 substances absorbed directly from stomach
alcohol and aspirin
3 segments of small intestine (in order)
- duodenum (major chemical digestion and minor absorption)
- jejunum (absorption)
- ileum (absorption)
pyloric sphincter
sphincter between stomach and duodenum
brush-border enzymes
present on luminal surface of cells lining duodenum and break down dimers and trimers of biomolecules into absorbable monomers
what is secreted from the duodenum?
- enteropeptidase (involved in activation of other digestive enzymes from accessory organs of digestion)
- other hormones like secretin and cholecystokinin (CCK) into the bloodstream
disaccharidases and what they digest
- maltase (maltose)
- isomaltase (isomaltose)
- sucrase (sucrose)- found on duodenal cells
- lactase (lactose)
peptidases
break down proteins (peptides)
aminopeptidase
peptidase secreted by duodenum that removes N-terminal amino acid from a peptide (aminopeptidase secretion)
dipeptidases
cleave the peptide bonds of dipeptides to release free amino acids (unlike carbohydrates, larger peptides can be absorbed across the small intestine wall)
enteropeptidase
enzyme critical for activation of trypsinogen (pancreatic protease) to trypsin (initiates activation cascade, also activates procarboxypeptidases A and B)– activates pancreatic juices!!!
secretin
peptide hormone that causes pancreatic enzymes to be released into the duodenum/ regulates pH by reducing HCl secretion from parietal cells and increasing bicarbonate secretion from pancreas
what type of hormone is secretin
slows motility through digestive tract which allows increased time for digestive enzymes to act on chyme (especially fats)
cholecystokinin (CCK)
secreted in response to entry of amino acids and fat into duodenum. this stimulates the release of both bile and pancreatic juices while promoting satiety in the brain
bile/ bile salts
complex fluid composed of bile salts, pigments, and cholesterol. bile salts mechanically digest fats and facilitate chemical digestion of lipids. bile salts emulsify fat and cholesterol into micelles to make them accessible to pancreatic lipase
what two products does proper fat digestion depend on?
bile (mechanical) and lipase (chemical)
pancreatic juices
complex mixture of several enzymes in a bicarbonate-rich alkaline solution (enzymes here are basic, about 8.5 pH)
pancreas function
endocrine: release insulin, glucagon, and somatostatin for proper sugar levels
exocrine: acinar cells (pancreatic juice formation)
pancreatic amylase
carbohydrate digestion
pancreatic peptidases
trypsinogen, chymotrypsinogen, carboxypeptidases A and B are released in zymogen form then activated for protein digestion
pancreatic lipase
capable of breaking down fats into free fatty acids and glycerol
how are pancreatic juices released in the body?
transferred to duodenum via duct system with the major and minor duodenal papillae.
2 structures of liver for communicating with digestive system
- bile ducts (connects liver-produces bile- with both gallbladder-stores bile- and small intestine-bile secreted here)
liver
processing of nutrients, production of urea, detoxification of chemicals, production of bile, and synthesis of albumin and clotting factors.
bilirubin
major pigment in bile. byproduct of the breakdown of hemoglobin. travels to liver where it is conjugated (attached to protein) and secreted into bile for excretion.
jaundice
yellowing of skin that occurs when liver is damaged so it cannot process/excrete bilirubin
albumin
a protein that maintains plasma oncotic pressure and also serves as a carrier for many drugs and hormones as well as clotting factors used during blood coagulation
gall bladder
stores and concentrates bile. upon release of CCK the gallbladder releases bile into the biliary tree (bile duct system)
segments of small intestine in order
- duodenum
- jejunum
- Ileum
(2/3)- absorption of nutrients
main purpose of large intestine
absorb water
villi
small projections from epithelial lining with microvilli as well that line the small intestine to increase surface area for absorption
whats inside of the villi of the small intestine?
- capillary bed- absorption of water-soluble nutrients
2. lacteal- a lymphatic channel that takes up fats for transport to lymphatic system
everything requires facilitated secondary transport to go from small intestine to blood except for what and why?
fats b/c they are nonpolar, so they can pass through
chylomicrons
insoluble packages of triglycerides and esterfied cholesterol molecules. these enter lymphatic circulation through lacteals which converge to form the thoracic duct
4 fat-soluble vitamins
A, D, E, and K and the rest are water-soluble (B and C)
where do fat-soluble vitamins go?
dissolve directly into chylomicrons to enter the body
2 ways water is absorbed into the bloodstream?
transcellularly (across cell membrane) and paracellularly (squeezing between cells) to reach the blood
large intestine sections
- cecum
- colon
- rectum
cecum
accepts fluid exiting small intestine through ileocecal valve and is site of appendix.
colon
absorb water and salts (NaCl). forms feces
rectum
storage site for feces (indigestible material, water, bacteria)
anus
opening with 2 sphincters (internal- autonomic involuntary control and external- somatic voluntary control)
vitamin K production
bacteria in gut produces this. its necessary for clotting factors
what absorbs the most water?
small intestine even tho the main purpose of the large intestine is water absorption
hyperkalemia
buildup of K in the blood
hyperammonemia
buildup of ammonia in the blood
