GI part one

pharynx, esophagus, stomach, small and large intestine

pharynx, esophagus, stomach, small and large intestine

Main organs of the GI tract

salivary glands, pancreas, liver, gallbladder

Accessory organs of the GI tract

motility, digestion, absorption, secretion

Major functions of the GI tract

chemical and mechanical

What are the mechanisms that dissolve and break down large food particles into smaller particles?

Amylase

What breaks down polysaccharides?

Lipase

What breaks down triglycerides?

proteases

What breaks down proteins?

into lymph (lacteals)

Where are fat and fat soluble nutrients absorbed?

Hepatic portal veins

Everything except lipophilic nutrients are absorbed through the….

Peristalsis

one-way contractions moving in wave-like fashion along the GI tract

increased surface area

Why is the surface of the GI tract highly convoluted?

epithelial layer

Where can you find endocrine and exocrine cells in the GI tract?

secreting hormones into the blood important in regulating aspects of digestion and appetite

What is the role of enteroendocrine cells?

epithelium, lamina propria, muscularis mucusa

What makes up the mucosa layer in the GI tract?

Lamina propria

loose connective tissue, small blood vessels, neurons, lymphatic vessels

Muscularis mucosa

Thin layer of smooth muscle involved in small movements of the mucosal surface

Submucosa plexus, major blood and lymphatic vessels

What makes up the submucosa?

submucosal plexus

network of neurons that extend to epithelium, largely influences gland and secretory functions

circular muscle, myenteric plexus, longitudinal muscle

What makes up the muscularis externa?

Muscularis externa

What provides forces for moving and mixing GI contents?

Circular muscle

What muscle is the main proponent of squeezing and propulsion?

Myenteric plexus

What is between muscular layers, innervated by sympathetic and parasympathetic neurons, and regulates smooth muscle activity and motility?

longitudinal muscle

Thinner outer layer of muscle that shortens the tube, main proponent of perstalsis

serosa

What is the last layer of the GI tract wall?

adhesions in the serosa

A patient presents to the ER for abdominal pain, upon a abdominal CT scan, you discover a small bowel obstruction. What is most likely the offender?

mechanically break food into smaller pierces, mixes food with saliva, molds food into bolus, starts positive digestive feedback through taste/baro/chemo-receptors

Functions of the mouth

mucus, water, bicarbonate, amylase, lipase, lysozymes

What are the components of saliva?

starts voluntary (skeletal) which creates an afferent signal to the medulla, efferent fibers activate pharynx, esophagus, and respiratory muscles, involuntary (smooth)

Swallowing reflex

soft palate rising when swallowing

How is food prevented from entering the nasal cavity?

Loss of voluntary and some involuntary swallowing mechanism

Why is it important to have airway maintenance in a sedated patient?

relaxation of the UES, peristalsis move bolus inferiorly, LES relaxes, bolus enters stomach

What happens after food enters the esophagus?

esophagus

muscular tube passing through the thoracic cavity into the abdonminal cavity

Upper and lower esophageal sphincters (UES, LES)

What prevents unwanted movement of air inward and stomach contents outward

gastroesophageal reflux

Impaired LES tone or increased intra-abdominal pressures from too much food can result in

prior to bolus arrival, feedforward

When does the stomach relax and this is an example of what type of mechanism?

when mixed with gastric secretions

When does the bolus become chyme?

fragments of proteins and polysaccarides, droplets of fat, free ions, water

Chyme is made up of

minimal water absorption

What does the stomach absorb?

mucus, bicarb

Cells at the tubular gland opening secrete

HCL and intrinsic factor

Parietal cells secrete

pepsinogen

Chief cells secrete

converted to pepsin by the low pH of the stomach

How is pepsinogen activated

histamine (H2 receptors)

Enterochromaffin like cells secrete

Somatostatin

D cells secrete

gastrin

G cells secrete

Duodenum, jejunum, iluem

What are the three sections of the small intestine?

mid-jejunum

A majority of ALL digestion and absorption is completed by ____________.

circular folds covered in villi which are covered with absorptive microvilli

Describe the surface of the small intestine

goblet cells

What secretes the protective mucus in the small intestine?

The center of each villus

Where can you find lacteal?

enteroendocrine cells

What controls the speed of movement of chyme through the small intestine

Hepatocytes (liver)

makes the bile

gallbladder

stores and concentrates the bile

galbladder contraction, sphincter of Oddi

Digestion stimulates ___________ and __________.

bile salts, phospholipids, bicarb, cholesterol, bile pigments, metabolic end products and trace metals

Components of bile

bile salts

Made from cholesterol, most important component of bile, recycled

Hepatic first pass phenomenon

all blood vessels involved in absorption from the GI tract flow through the liver prior to going system wide

Bicarb, trypsinogen, amylase, lipase, ribonuclease, deoxyribonuclease, chymotrypsin, elastase, CCK, secretin

What are the exocrine secretions of the pancreas in the GI tract

Break down peptide bonds to form fragments

Role of trypsin, chymotrypsin, elastase

Splits off terminal amino acids

role of carboxypeptidase

CCK (cholecystokinin)

stimulated by fatty and amino acids in small intestine; stimulates pancreatic enzymes secretion, gallbladder contraction, sphincter of Oddi relaxation and INHIBITS H+ secrete and motility of the stomach

fatty and amino acid absorption

What is the negative feedback for CCK?

stimulated by low pH in small intestines

Secretin stimulated is

stimulate bicarb; inhibits H+ secretion and motility of stomach

What is the role of secretin

contracts during colon distention to prevent backwards movement of bacteria and stool

What is the function of the ileocecal valve?

external anal sphincter

Which is the VOLUNTARY muscle of the rectum

internal anal sphincter

What is the INVOLUNTARY muscle of the rectum

active transport of salt and glucose

How does the large intestine absorb water?

vitamin K, short-chain fatty acids, flatus

What are the products of microbiome fermentation?

K, bicarb

What does the large intestine secrete?

stomach 3 layers, intestines 2 layers

The circular muscle has a different number of layers depending on the organ. What two organs have this muscle and how many layers do they have?

neutralizes the acid and moves it back down with peristalsis

It is normal for some stomach contents to travel back up through the LES. How does the esophagus correct this?

impaired LES tone, increase in intra-abdominal pressure, hiatal hernia (superior sliding of LES above diaphragm)

What are three conditions that can cause heart burn?

sphincter of Oddi, small intestine, controls amount of liver and pancreatic products allowed into GI tract

Pancreatic and hepatic exocrine gland ducts converge at ________ before entering the _______. What does this help control?

prevents recycling of bile salts

How does dietary fiber reduce blood cholesterol?

CCK

What hormone is used in HIDA scans?

reservoir for healthy bacteria

The appendix may have what function?

3-4 x per day, a meal, activated by parasympathetic and inhibited by sympathetic

How often does mass movement occur in the large intestine? What usually triggers it? What nerve types activate it and inhibit it?

distention of rectum walls initiate neural defecation reflex, sigmoid colon increases motility, internal anal sphincter relaxes, external anal sphincter contracts initially and then relaxes due to increasing pressure

Describe what happens during defecation? (rectum, sigmoid, internal anal sphincter, external anal sphincter)