Gastrointestinal System Flashcards
function of abdominal muscles
support the viscera by compressing the abdominal cavity, stabilize the vertebral column, and help in respiration, urination, defecation, and childbirth
abdominal muscles include
external oblique, internal oblique, transverse abdominis, and rectus abdominis
Linea alba
runs in between the rectus abdominis muscles in the abdomen
layers of the GI tract
beginning externally - serosa, muscularis, submucosa, and the mucosa
mucosa contains
epithelium, glands that secrete GLP-1 and cholecystokinin (CCK), the lamina propria which contains blood vessels and lymphoid tissue (mucosa-associated lymphoid tissue - MALT), and smooth muscle
submucosa contains
connective tissue, Meissner’s plexus with autonomic neurons, and Peyer’s patches
muscularis contains
skeletal/voluntary muscle within the mouth, pharynx, superior esophagus, and external anal sphincter and smooth muscle everywhere else with an inner circular layer and an outer longitudinal layer, also contains myenteric plexus of autonomic innervation
serosa
connective tissue that lines the surface of the organ
peritoneum
the serous membrane that encases the bowel which carries vasculature, nerves, and lymphatics and consists of 2 layers, the visceral and parietal layers, with a small space (peritoneal cavity) between them that is filled with fluid (the visceral layer lines the organs and the parietal layer attaches to the abdominal wall providing support and protection of visceral organs)
retroperitoneal organs
pancreas, kidneys, and aorta
omentum
composed of two parts, the greater and lesser omentum, where the lesser omentum arises from the lesser curvature of the stomach and extends to the liver and the greater omentum arises from the greater curvature of the stomach and forms a large sheet that lies over the intestines and converges into the parietal peritoneum
GI tract overall functions
mechanical breakdown of nutrients, further chemical breakdown, absorption, and excretion of unneeded elements/wastes, and immune protection
phases of swallowing
oral phase = voluntary, pharyngeal phase = voluntary, and esophageal phase = involuntary
mastication
voluntary process of chewing causing the mechanical breakdown of food with teeth using the temporalis and masseter facial muscles, salivary amylase begins the breakdown of complex carbohydrates and lingual lipase begins the breakdown of fats
function of incisor teeth
to cut food
function of premolars
to crush and tear food
function of canine teeth
to tear and grasp food
function of molars
chew and grind food
dental caries (cavities)
tooth decay caused by bacteria (mainly strep mutans) in dental plaque which begins as a soft film of bacteria, dead cells, and food debris
number of taste buds on the tongue
3,000 - 10,000 taste buds on average (each contain 100 taste cells), number decreases with age
sense of taste
the chemical binds to a taste hair receptor causing depolarization of the cell, generating an action potential
posterior aspect of tongue innervation
glossopharyngeal nerve and vagus nerve (at the base/pharynx)
gustatory cortex
the area within the brain (anterior insula-frontal operculum) where taste signals are processed following synapse within the hypothalamus
salivary gland function
stimulated by parasympathetic nervous system and secrete 1 liter of saliva per day which mostly consists of water but also contains sodium, mucus, bicarbonate, chloride, potassium, and salivary amylase
pH of saliva
7.4
superior constrictor muscle of the pharynx function
prevents movement of food bolus into the nasal cavity along with uvula
pharyngeal phase of swallowing
occurs when the food bolus reaches the oropharynx sending sensory signals from CN IX (glossopharyngeal) to the swallowing center in the medulla which responds by sending efferent signals to the pharynx to initiate the swallowing reflex which involves blockage of the airway by the epiglottis and relaxation of the UES
esophageal phase of swallowing
the involuntary portion of swallowing that takes 5-10 seconds and stimulates peristalsis through the esophagus, UES (cricopharyngeal muscle) closes and LES (gastroesophageal sphincter) opens resulting in bolus reaching the stomach, the epiglottis then reopens and the LES closes to prevent backflow of stomach contents
esophagus
measures 25 cm in length from the oropharynx to the stomach, contains UES and LES, lower esophagus innervated by the vagus nerve and upper esophagus has mixed innervation, peristalsis of inner circular and outer longitudinal musculature is initiated by stretch receptors
enteric innervation
includes plexuses within different layers such as the Meissner submucosal plexus, the Auerbach myenteric plexus, and the subserosal plexus which regulate motility, reflexes, blood flow, and absorption
stomach function
acts as a short-term food storage reservoir and is the location where chemical and enzymatic digestion is initiated, secretes intrinsic factor (absorption of B12), pacemaker cells cause rhythmic depolarization going toward the pylorus to mix the food which liquifies it into chyme that is then slowly released into the duodenum for further processing, microbes are killed, proteins are broken down, and bile is triggered to be released, the stomach is impermeable to water but will absorb ETOH and NSAIDs (rate of absorption depends on food ingested)
cephalic phase of gastric acid secretion
accounts for 30% of gastric acid secretion and is a response to seeing, smelling, and anticipation of PO intake which stimulates the medulla, vagus nerve, and submucosal plexus to increase HCl secretion, hypoglycemia increases acid response
gastric phase of gastric acid secretion
accounts for 60% of gastric acid secretion which is stimulated by food hitting the stomach which increases pH and causes distention triggering stretch receptors and chemoreceptors in the stomach leading to myenteric and vasovagal reflexes causing increase in HCl secretion
intestinal phase of gastric acid secretion
accounts for 10% of gastric acid secretion which is triggered by the initial movement of food into the small intestines causing distention and stimulating more HCl secretion, cholecystokinin (CCK) will decrease motility and emptying and somatostatin will slow the release of gastric acid
primary area of gastric acid secretion
gastric pits
types of cells within the stomach
goblet cells, parietal cells, chief cells, D cells, and G cells
gastric goblet cells produce
mucous which protects stomach lining
gastric parietal cells produce
hydrochloric/gastric acid and intrinsic factor
gastric chief cells produce
pepsinogen which is a pepsin (protease) precursor
gastric D cells produce
somatostatin which inhibits gastric acid secretion
gastric G cells produce
gastrin which stimulates gastric acid secretion
pH of pepsin
2
chyme
a mixture of gastric acid and mechanically broken down food
hydrochloric acid (HCl) function
breaks down proteins into amino acids and establishes an acidic environment that is inhospitable to bacteria, parietal cells secrete ~ 3-4 liters/day
gastric emptying
takes around 3 hours on average but will vary depending on the type of food ingested, mechanical and chemical breakdown of food will decrease food to 1 mm size particles, the stomach can hold about 1.5 liters of food/fluid
stimulation of bile and pancreatic enzyme secretion
stimulated by secretin which is released by the duodenum causing bile release from the liver/gallbladder combined with pancreatic enzymes through the sphincter of Oddi
small intestine
includes duodenum, jejunum, and ileum which is about 20 feet long and is the primary site of chemical digestion and nutrient absorption (90% nutritional absorption), contains a vast absorptive surface (brush border with microvilli) where each section differs functionally
duodenum function
separated from the jejunum at the Treitz ligament, accepts chyme from the stomach and readily absorbs water, thiamine (B1), and iron (via intestinal transferrin in proximal duodenum) which enter the portal venous system
ileum function
has the largest lumen, is the longest, and most distal section of the small intestine, and functions to absorb water, nutrients, magnesium, phosphate, vitamin B12 (in the distal ileum), and bile salts (terminal ileum)
jejunum function
the section between the duodenum and the ileum which functions to absorb water, thiamine (B1), magnesium, phosphate, amino acids, sodium, potassium, ETOH, and fats
cells within the small intestine
enterocytes are the most abundant and contain microvilli for absorption, scattered goblet cells that secrete mucus, and occasional enteroendocrine cells
movement through the small intestine
food causes distention which stimulates sensory autonomic neurons and mechanical digestion via segmentations created by contractions of circular inner musculature (occur more frequently in 1-4 cm segments to mix chyme and enzymes), peristalsis pushes chyme forward and is created by contractions of the longitudinal outer layer of musculature (occurs more slowly in 10 cm sections)
amount of water absorbed in small intestine
92% of the water that is ingested and secreted by the GI tract
amount of water absorbed in large intestine
6-7% of the water that is ingested and secreted by GI tract
Brunner’s glands
mucus-secreting glands within the duodenal submucosa which have excretory ducts that drain into the crypts of Lieberkuhn
Peyer’s patches
part of the gut-associated lymphoid tissue (GALT) that contains lymph nodes and forms large follicles that extend through the lamina propria and submucosa mostly within the ileum, create antimicrobial peptides and IgA which help maintain a happy relationship with the gut microbiome and have primarily B cells (also macrophages, T cells, and mast cells)
differences in microvilli throughout small intestine
the villi are leaflike and wide in the duodenum, have a fingerlike shape and are long in the jejunum, and are fingerlike but shorter in the ileum
ileocecal valve
sphincter between the end of the ileum and the cecum of the large intestine which opens with pressure within the ileum and shuts with pressure or contents within the cecum
cecum
a pouch at the beginning of the ascending large intestine
large intestine
1.5 meters long where it begins at the cecum and leads to the ascending colon, the hepatic flexure, the transverse colon, the splenic flexure, the descending colon, the sigmoid colon, the rectum, and the anus
liver
largest solid organ which weighs about 2% of total body weight and typically measures 10-12.5 cm in height and 20-23 cm wide, protected by ribs 7-11 and crosses midline into LUQ and epigastric region, broken into 4 lobes - right (largest) and left lobes which are separated by the falciform ligament (which is attached to the anterior abdominal wall) and caudate and quadrate lobes posteriorly which are part of the right lobe, covered by visceral peritoneum with a bare area posteriorly
Couinaud classification
functionally divides the liver into 9 sections which contain branches of portal vein, hepatic artery, and bile duct that separate them, these sections can be removed surgically without causing problems for the remaining parenchyma
porta hepatis
where the hepatic artery, portal vein, and left/right hepatic duct enter
Glisson capsule
encases the liver and contains neurovascular supply for the liver - irritation to this capsule can cause pain
ligamentum teres (round ligament)
remnant of umbilical vein which extends inferiorly off of the falciform ligament and attaches to the umbilicus
coronary ligament
extends superiorly off the falciform ligament to support superior to the diaphragm
blood supply to liver
the common hepatic artery which comes off the celiac axis/trunk and leads to the proper hepatic artery dividing into right and left hepatic arteries
amount of blood filtered by the liver
400-500 mL/minute from the arterial system and 1000-1200 mL/minute from the venous system
liver lobule
the functional unit of the liver which are made up of hepatocytes that are the functional unit for protein production (able to regenerate) and sinusoids
sinusoids
capillaries between hepatocytes within the liver lobule that receive both arterial and venous blood and are very permeable to nutrients and chemicals metabolized in hepatocytes, they drain into the central vein followed by the hepatic vein and then the IVC
Kupffer cells
specialized macrophages that line the walls of sinusoids in the liver and perform many key functions including blood monitoring, liver defense against invaders, and secrete anti-inflammatory cytokines
liver functions
- forms and secretes 700-1200 mL of bile per day which is made in hepatocytes and drained by the bile canaliculi
- produces plasma proteins including albumin, transferrin, ferritin, cholesterol, and lipoproteins
- converts excess glucose into glycogen to be stored and vice versa
- produces glucose through gluconeogenesis
- regulates blood levels of amino acids
- stores iron (ferritin) and breaks down hemoglobin
- converts poisonous ammonia (from protein breakdown) to urea by adding CO2 which is excreted in the kidneys
- clears the blood of drugs and toxic substances
- produces most blood clotting and clot breakdown factors and regulates clotting
- helps to create platelets by release of thrombopoietin - TPO
- removes or metabolizes hormones into inactive or active forms (which can accumulate in liver dysfunction)
- produces immune factors (complement proteins and C-reactive peptide) and removes bacteria from the bloodstream
- produces angiotensinogen which participates in the RAAS
- clears bilirubin from the body through bile and intestinal excretion
- activates vitamin D
bile function
composed of bile salts (acids), phospholipids, cholesterol, bilirubin, electrolytes, IgA antibodies and H2O which helps small intestine to emulsify and absorb fats, bile is alkaline
gallbladder function
stores and concentrates bile which is released when triggered by cholecystokinin (CCK) from the duodenum into the bloodstream (begins 30 minutes after eating), the smooth muscle layer of the gallbladder contracts causing bile to flow through the cystic duct to the common bile duct, through the ampulla of Vater and sphincter of Oddi, and into the duodenum
portal triad includes
a branch of the bile duct, branch of the hepatic portal vein, and branch of the hepatic artery
process of bilirubin formation
old/damaged RBCs (120 days) are broken down in the liver/spleen by macrophages (Kupffer cells) leading to hemoglobin breakdown where heme is separated from iron and converted first into biliverdin and then bilirubin to be sent into plasma, iron is stored in ferritin in the liver to be utilized during erythropoiesis
unconjugated (indirect) bilirubin
a waste product formed when RBCs are broken down by the spleen and heme is metabolized in the bloodstream to biliverdin through enzymatic reactions which then forms unconjugated bilirubin which is lipid-soluble and must be bound to albumin to be transported to the liver
conjugated (direct) bilirubin
upon reaching the liver, an enzyme combines unconjugated bilirubin with glucuronic acid which then becomes conjugated bilirubin which is water-soluble, conjugated bilirubin is converted by bacterial proteases to urobilinogen which is then excreted in feces as bile or in urine through the kidneys
process of bile formation
in the liver, hepatocytes break down cholesterol to create primary bile acids and amino acids conjugate with bile acids to form bile salts (bile), while some bile is stored in the gallbladder for release with a fatty meal, bile salts in the duodenum and jejunum break down fats and allow fat transport - 15-30% of bile salts are excreted in stool and 65-85% enter circulation with protein binding for re-transport to the liver
effect of insulin on the liver
in the fed state, insulin is released as an unbound protein into the bloodstream and enters the liver where it inhibits glycogenolysis and stimulates glycogenesis by increasing the activity of glycogen synthase, it also stimulates lipogenesis (fat storage), when glucose levels drop insulin levels fall and glycogenesis and glucose uptake is inhibited, enzymatic phosphorylation will cause glycogen to be broken down into glucose to keep glucose levels normal
effect of insulin on skeletal muscle and adipose tissue
in muscle, insulin increases amino acid influx, protein synthesis, and glycogenesis whereas in adipose tissue it stimulates lipogenesis and inhibits lipolysis (fat breakdown)
effect of glucagon on the liver
in the fasting state, glucagon is released from the pancreas into the bloodstream and enters the liver where it stimulates glycogenolysis to raise blood glucose levels and can also stimulate gluconeogenesis to form glucose from other molecules such as amino acids (produces ammonia), lactic acid, and fatty acids
systemic effects of glucagon
increases cardiac contraction, increases renal blood flow, increases bile excretion, inhibits gastric acid secretion, and rises during exercise (possibly to prevent hypoglycemia)
crystalloid solution
fluid made of small molecules including salts and electrolytes
colloid solution
fluid made of macromolecules including proteins (albumin), starches, gelatins, and dextrans
albumin function
makes up 50% of all plasma proteins and is required for the transport of hormones, fats, nutrients, and medications, and helps maintain intravascular volume (osmotic/oncotic pressure)
clotting factors made by the liver
all clotting factors of the intrinsic and extrinsic pathways besides factor VIII (although some is made in the liver in sinusoidal endothelial cells) including factor I (fibrinogen - precursor to fibrin), vitamin K-dependent clotting factors - II (thrombin), VII, IX, and X, and protein C & S, clotting factors are formed as the inactive form in the liver, the liver also produces factors that break down clots including plasminogen and antithrombin
important proteins within blood
albumins (osmotic pressure), fibrinogen (clotting), ferritin (iron storage), transferrin (iron transfer), enzymes, antibodies, and hormones
importance of Ca2+ within blood
assists with clot formation and multiple other processes including cardiac and muscle contraction, nervous system excitability, and bone density
pancreas
composed of head, neck, body, and tail where the head is attached to the duodenum and opens into it via the ampulla of Vater allowing the release of exocrine contents into GI tract, pancreatic duct begins in the tail and runs the length of the organ, the neck lies next to the stomach pylorus and the tail lies anterior to the kidney
blood supply to head of pancreas
superior mesenteric artery (SMA)
blood supply to the body/tail of pancreas
branches off of the splenic artery
exocrine pancreas function
when acidic chyme enters the duodenum, cholecystokinin (CCK) and secretin are released into the bloodstream which stimulates the acinar (exocrine) cells of the pancreas to release pancreatic juice rich in bicarbonate ions and digestive enzymes which assist with breaking down fats, carbohydrates, and proteins and helps to neutralize the sudden acidity from the stomach contents
pH of stomach
2
pH of duodenum
6
pH of ileum
7.4
enzyme released from pancreas that helps with fat breakdown
lipase - forms small micelles around fat with a hydrophilic outer layer that allows for diffusion
enzyme released from pancreas that helps with carbohydrate breakdown
amylase
enzymes released from pancreas that help with protein breakdown
trypsin (activates proteases) and chymotrypsin
large intestine/colon
begins at the cecum which contains the ileocecal valve and is the site for remaining undigested food sent from the small intestine, contains haustra which allow for segmental contraction/movement and teniae coli which run longitudinally beginning at the cecum, has rugae internally
internal anal sphincter
made of circular involuntary smooth muscle and innervated by the autonomic nervous system where sympathetic stimulation causes contraction and parasympathetic causes relaxation
large intestine function
point at which chyme is considered feces, responsible for the absorption of the remaining water from stool which occurs within haustral saccules, absorption of ions including sodium and potassium and acids/bases, storage and elimination of waste, and production of vitamins B and K, contains > 400 bacterial species