digestive system Flashcards
what is gastroenterology?
the study of the digestive tract and the diagnosis and treatment of its disorders
what is the digestive system?
an organ system that processes food, extracts nutrients, and eliminates residue
what are the 5 stages of digestion/
- ingestion: selective intake of food
- digestion: mechanical and chemical breakdown of food into a form usable by the food
- absorption: uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and lymph
- compaction: absorbing water and consolidating the indigestible residue into feces
- defecation: elimination of feces
what is mechanical digestion?
physical breakdown of the food into smaller particles
what is chemical digestion?
series of hydrolysis reactions that break dietary macromolecules (polymers) into their monomers (residues)
what is the digestive tract?
- 30 ft long muscular tube extending from the mouth to the anus
- mouth, pharynx, esophagus, stomach, small intestine, and large intestine
- The gastrointestinal tract is the stomach and intestines
what are the Accessory organs?
- teeth, tongue, salivary glands, liver, gallbladder, and pancreas
what are the layers of the digestive tract?
- Mucosa: epithelium (simple columnar), lamina propria (loose connective tissue), muscularis mucosae (thin layer of smooth muscle) MALT
- submucosa (loose connective tissue)
- Muscularis externa: inner circular layer (contains sphincters), outer longitudinal layer (motility that propels food and residue)
- Serosa: areolar tissue, mesothelium (areolar tissue w/simple squamous mesothelium) - reduces friction
what is adventitia?
fibrous connective tissue layer that binds and blends the pharynx, most of the esophagus, and the rectum into adjacent connective tissue of other organs
what is the Enteric Nervous system?
nervous network in the esophagus, stomach, and intestines that regulates digestive tract motility, secretion, and blood flow
what two networks of neurons make up the enteric nervous system?
- Submucosal plexus: in the submucosa (controls glandular secretions of the mucosa, controls movements of muscularis mucosae)
- Myenteric plexus: parasympathetic ganglia and nerve fibers between the two layers of the muscularis external (control peristalsis)
what is a mesenteries?
connective tissue sheets that suspend the stomach and intestines from the abdominal wall
what is parietal peritoneum?
a serous membrane that lines the wall of the abdominal cavity
what is the lesser omentum?
a ventral mesentery that extends from the lesser curvature of the stomach to the liver
what is the greater omentum?
hangs from the greater curvature of the stomach and covers the small intestine and apron
what is the mesocolon?
an extension of the mesentery that anchors the colon to the abdominal wall
what is intraperitoneal?
when an organ is enclosed by the mesentery on both sides
- considered within the peritoneal cavity
- stomach, liver, and parts of small and large intestine
what is retroperitoneal?
when an organ lies against the posterior body wall and is covered by peritoneum on its anterior side only
- considered to be outside the peritoneal cavity
- duodenum, pancreas, and parts of the large intestine
what are motility and secretion of the digestive tract controlled by?
- Neural control: short (myenteric) reflexes: stretch or chemical stimulation acts through myenteric plexus
- Hormones: chemical messengers secreted into bloodstream
- paracrine secretions: chemical messengers that diffuse through the tissue fluids to nearby target cells
what is long (vagovagal) reflexes?
parasympathetic stimulation fo digestive motility and secretion
what is peristalsis?
adjacent segment of alimentary tract organs alternately contract and relax, which moves food along the tract distally
what is segmentation?
nonadjacent segments of alimentary tract organs alternately contract and relax, moving the food forward then backward
what tissue type lines the mouth?
stratifies squamous epithelium
- keratinized in gums and hard palate
- nonkeratinized in floor of mouth, soft palate and cheeks
what is the tongue? main function?
muscular bulky but agile and sensitive organ
- manipulate, sense food, taste/texture
what tissue type makes up the tongue?
nonkeratinized stratified squamous
what is the hard palate?
anterior portion that is supported by the palatine processes of the maxillae and the palatine bone
what are the parts of the tongue?
- lingual papillae: bumps that are taste buds
- body: anterior 2/3
- root: posterior 1/3
- lingual frenulum: attaches body of tongue to floor of mouth
what is the uvula?
conical medial projection visible at the rear of the mouth
what is the palate?
separates oral cavity from nasal cavity
what is the soft palate?
- posterior with a more spongy texture
- skeletal muscle and glandular tissue
what does it mean to masticate?
chew; makes it easier to swallow food
how many of each teeth do we have?
- 32 total
- 2 incisors
- 1 canine
- 2 premolars
- 3 molars
what are the regions of the tooth?
- crown: above gum
- root: below gum in bone
- nech: where crown, root and gum meet
what are the layers of the tooth?
- dentin: hard yellowish tissue (regenerates)
- enamel: covers crown and neck (no regenerate)
- cementum: cover root (no regenerate)
- root canal: space in a root leading to pulp cavity in the crown
what is salivary amylase?
enzyme that begins starch digestion
what is saliva made of?
hypotonic sol: 99% water
- phosphate and bicarbonnates
- ph: 6.8 - 7
moistens mouth and dissolves molecules
what is lingual lipase?
enzyme that is activated by stomach acid and digests fat after food is swallowed
what is salivation activated by?
medulla oblongata and pons respond to signals generated by the presence of food
- parasympathetic: stimulate the glands to produce an abundance of thin, enzyme-rich saliva
- sympathetic: inhibits the glands, thus producing less and thicker, saliva with more mucus
what is a bolus?
ass swallowed as a result of saliva behind food particles into a soft, slippery, easily swallowed mass
what does the pharynx do?
connects the oral cavity to the esophagus and the nasal cavity to the larynx
- forms pharyngeal constrictors
what does the esophagus do?
contains lower esophageal sphincter: food pauses here because of constriction
- prevents stomach contents from regurgitating into the esophagus
- nonkeratinized stratified squamous
what is the action of swallowing?
deglutition: a complex action involving over 22 muscles in the mouth, pharynx, and esophagus
- swallowing center: medulla oblongata
what are the three phases of swallowing
- oral: the tongue forms and food bolus and pushes to laryngopharynx (vol)
- pharyngeal: palate, tongue, vocal cords and nasal cavities and airway while pharyngeal constrictors push the bolus into esophagus (invol)
- esophageal: peristalsis drives the bold downward and relaxation of the lower esophageal sphincter admits it into the stomach
what does the stomach do?
mechanically breaks up food, liquifies it and begins chemical digestion of protein and fat
what is chyme?
soupy or pasty mixture of semi-digested food in the stomach
where does the stomach receive its info from?
- parasympathetic fiber from vagus nerve
- sympathetic fibers from celiac ganglia (solar plexus
what are the 4 regions of the stomach?
- cardial
- fondus
- body
- pyloric part
what are the muscular layers of the stomach?
- longitudinal
- circular
- oblique
what is gastric juice?
mixture of water, hydrochloric acid and pepsin
what cells are in the stomach mucosa?
- mucous cells: secrete mucus
- regenerative cells: base of pit, replace old with new
- parietal cells: upper half, secrete HCl, intrinsic factor and secrete ghrelin
- chief cells: secrete gastric lipase and pepsinogen
- enteroendocrine cells: secrete hormone and paracrine messengers
what does HCl do in the stomach?
- activates pepsin and lingual lipase
- breaks up connective tissues and plant cell walls
- destroys most ingested pathogens
what is a peptic ulcer?
- acid-resistant bacteria Helicobacter pylori, which can be treated with antibiotics and Pepto-Bismol
- pepsin and hydrochloric acid erode the stomach wall.
what does gastic lipase do?
- produced by chief cells
- digest dietary fats
what does intrinsic factor do?
- secreted by parietal cells
- essential to absorb vitamin B
what are the 2 main functions of the contraction of gastric smooth muscle?
- ingested food is crushed, ground, and mixed, liquefying it to form what is called chyme.
- chyme is forced through the pyloric canal into the small intestine, a process called gastric emptying
when do digestion and absorption occur?
after chyme has passed into the small intestine
what are the protective mechanisms in the stomach?
- mucus coat: thick, highly alkaline mucus resists the action of acid and enzymes
- tight junction: prevent gastric juice from seeping between them and digesting deeper tissue
- epithelial cell replacement: cells live only 3-6 days, replaced by cell division
what are the 3 phases of gastric activity?
- Cephalic phase: stomach being controlled by the brain
- Gastric phase: stomach controlling itself
- Intestinal phase: stomach being controlled by small intestine
What does the small intestine recieve?
chyme from stomach
secretions from liver and pancreas
anatomy of the liver?
reddish brown gland located immediately inferior to the diaphragm
- largest gland
- produces and secretes bils
what are hepatocytes?
they absorb things from the blood
- glucose, amino acids, iron, vitamins
they break down stored glycogen and release it to the blood
what do Hepatocytes remove and degrade?
hormones, toxins, bile pigments, and drugs
what do the hepatocytes secrete into the blood?
albumins, lipoproteins, clotting factors, angiotensinogen
what does the gallbladder do?
serves to store and concentrate bile by absorbing water and electrolytes
what is bile?
yellow-green fluid containing minerals, cholesterol, neutral fats, phospholipids, bile pigments, and bile acids (steroids from cholesterol)
what is the pancreas?
Is spongy retroperitoneal gland posterior to the greater curvature of stomach
what is the portion of the pancreas?
- endocrine: pancreatic islets that secrete insulin and glucagon
- exocrine: acini cells: 99% of the pancreas that secretes 1,200 to 1,500ml of pancreatic juice per day
what is pancreatic juice?
alkaline mixture of water, enzymes, zymogens, sodium bicarbonate, and other electrolytes
what are pancreatic zymogens?
- trypsinogen
- chymotrypsinogen
- procarboxypeptidase
what stimuli are responsible for regulating secretion?
- Ach: stimulates the pancreas to secrete enzymes during the cephalic phase of gastric control
- CCK: secreted by the mucosa of the duodenum in response to the arrival of fats in the small intestine
- Secretin: released from duodenum in response to acidic chyme arriving from the stomach
What occurs in the small intestine?
nearly all chemical digestion and nutrient absorption
- coiled mass filling most of the abdominal cavity inferior to the stomach and liver
what are the 3 regions of the small intestine?
- Duodenum: receives stomach contents, stomach acid is neutralized here, fats are broken, pepsin inactivated
- Jejunum: most digestion and nutrient absorption
- ileum: MALTs present, ileocecal junction and ileocecal valve
what tissue type is the lumen lined with?
simple columnar epithelium
what are circular folds?
promotes more thorough mixing and nutrient absorption
- only involve mucose and submucosa
- they increase surface area by a factor of 2 to 3
what is villi?
finger-like projections w/absorptive cells and goblet cells
-they increase surface area by a factor of 10
what is microvilli?
form a fuzzy brush border on the apical surface of each absorptive cell
-increase the surface area by a factor of 20
what are brush border enzymes?
contained in the plasma membrane of microvilli
- carry out final stages of enzymatic digestion
what are the 3 functions of contractions of the small intestine?
- To mix chyme with intestinal juice, bile, & pancreatic juice
– To neutralize acid
– Digest nutrients more effectively - To churn chyme and bring it in contact with the mucosa
for contact digestion and nutrient absorption - To move residue toward large intestine
what is lactose intolerance?
when lactose passes undigested into large intestine
- increases osmolarity of intestinal contents
- causes water retention in the colon and diarrhea
what are lipases?
fat digestion enzymes
what are the fat-soluble vitamins?
A,D,E, and K
What are the water-soluble vitamins?
vitamin B complex and C
What do minerals do in digestion?
- they are absorbed all along the small intestine
- exchanged for bicarbonates reversing the chloride-bicarbonate exchange that occurs in the stomach
- iron absorbed by active transport
what does water do in the digestive system?
receives about 9L of water a day
what does the ascending colon do?
right colic (hepatic) flexure
what does the appendix do?
it attaches to lower end of cecum
- densely populated with lymphocytes
what does the descending colon do?
frame the small intestine
what does the transverse colon do?
left colic (splenic) flexure
what is the sigmoid colon?
is S-shaped portion leading down into pelvic cavity
what is the rectum?
portion ending at anal canal
What are the muscularis externa of the colon?
- Taenia coli: longitudinal fibers concentrated in 3 thickened, ribbon-like strips
- Haustra: pouches in the colon caused by the muscle tone of the Taeniae coli
- internal anal sphincter: smooth muscle of muscularis external
- external anal sphincter: skeletal muscle of the pelvic diaphragm
where is mucosa located?
anal canal has nonkeratinized stratified squamous epithelium in its lower half for abrasion resistance
- simple columnar epithelium
what are intestinal crypts?
glands sunken deeps into lamina propria with a high density of mucus-secreting goblet cells
what are Haustral contractions?
distension of a haustrum stimulates it to contract
- occur every 30 minutes
what are mass movements?
stronger contractions that occur one to three times a day
- triggered by gastrocolic and duodenocolic reflexes
what is a gut microbiome?
bacteria digest cellulose, pectin, and other carbohydrates for which our cells lack enzymes
- help in the synthesis of vitamins B and K
what is a Flatus?
intestinal gas
