HUMAN SYSTEMS GASTROINTESTINAL

What are the three salivary glands?

Parotid, submandibular, sublingual.

What are the four regions of the stomach from top to bottom?

Cardia/fundus, body, and antrum.

What is the pylorus?

Sphincter dividing stomach and duodenum.

When does bolus become chyme?

When it reaches the stomach and becomes more liquid.

Where is there more motility in the stomach?

In the Caudad.

What are the main functions of the small intestine?

Finish digestion, absorption.

What is main function of the colon?

Absorb water and electrolytes, store feces.

What are the GI sphincters under voluntary control?

External anal sphincter and upper esophageal sphincter.

What does the Sphincter of Oddi separate?

The bile duct and duodenum.

What are three components of the mucosa?

Epithelium, lamina propria, muscularis mucosa.

Where are the blood vessels that absorb products of digestion located?

Lamina propria.

What are the main function functions of the epithelium?

Nutrient absorption, secretions.

What is the submucosa?

CT layer with lots of blood and lymphatic vessels.

What is main function of the muscularis mucosae?

Local movements, create folds to increase surface area.

What do the circular and longitudinal layers do?

Coordinate peristalsis, form sphincters (circular muscle).

What are the two layers of the enteric nervous system?

Submucosal and myenteric plexus.

What is the serosa? What does it do?

Covers muscle layers.

Where are villi found?

In the small intestine.

Where are crypts found?

Small intestine and colon.

When does sensory information from the GI tract get sent to higher brain centers?

When it's pain.

What does the ENS regulate?

GI motility and secretion.

When is the parasympathetic nervous system active?

During rest and digestion, innervating ENS.

What does the sympathetic nervous system do to the ENS and smooth muscle?

Inhibits their activity.

What neurotransmitters are released from the myenteric plexus neurons?

Nitric oxide and ATP (inhibitory), ACh and substance P (excitatory).

What does the myenteric plexus modulate?

Motility.

What does the submucosal plexus modulate?

Secretion, absorption and muscularis mucosae contraction.

Where does parasympathetic innervation originate?

The vagus and pelvic nerves.

Where does sympathetic innervation originate?

The thoraco-lumbar spinal cord.

What cells release hormones in the GI tract? How do they know to do so?

Enteroendocrine cells (EEC). They are electrically excitable and detect sensory stimuli.

What do neurocrines act upon?

Enteric and autonomic afferent neurons.

What cells secrete gastrin?

G-cells.

What stimuli excite G-cells?

Nutrients (protein), stomach distention, vagal stimulation, and GRP.

What stimuli inhibits G-cells?

Increased acidity of the stomach (via somatostatin secretion).

What does gastrin stimulate?

Growth of gastric mucosa, increased gastric motility, increased acid secretion by parietal cells, and increased histamine secretion from enterochrommafin-like cells.

What stimulates CCK release from I-cells?

Fatty acids and amino acids in the small intestine.

Where are I-cells found?

Duodenum and jejunum.

What does CCK bind to?

CCK1 and Gastrin/CCK2 receptors.

What are the effects induced by CCK?

Contraction of the gallbladder, relaxation of the sphincter of Oddi, inhibits gastric emptying, increases bicarbonate and enzyme secretion from the pancreas, stimulates pancreatic growth, stimulates somatostatin release from D-cells (inhibiting gastric acid secretion).

Why does gastrin bind CCK2 over CCK in parietal and ECL cells?

5-10 times more gastrin than CCK.

When is secretin secreted?

When chyme enters the duodenum.

What is secretin homologous to?

Glucagon.

What cells secrete secretin?

S-cells of the duodenum.

What is secretin's main function?

Neutralize acidity in the intestine (stimulates bicarbonate secretion and inhibits gastric acid secretion).

What do K-cells secrete?

GIP.

What does L cells secrete?

GLP-1.

What does GLP-1 and GIP do?

Decrease blood glucose level through pancreas (inhibiting alpha-cells, stimulating beta-cells). Also signals for satiety.

Which peptides increase appetite?

Ghrelin through neuropeptide Y.

Which peptides increase satiety?

Leptin (from adipose), GLP-1, PYY, PP, and amylin.

When is motilin secreted?

During the fasted state.

What does motilin (from M-cells) stimulate?

MMC, gastric/gallbladder emptying in the GI tract, increased hunger, and pancreatic insulin secretion.

What does histamine (ECL cells) stimulate?

Gastric acid secretion.

What does serotonin (EC-cells) regulate?

Gastric motility and secretion.

What contractions and relaxations occur behind the food bolus in peristalsis?

Contractions of circular muscle and relaxations of longitudinal muscle relaxation.

What contractions and relaxations occur ahead of the food bolus in peristalsis?

Contractions of longitudinal muscle and relaxations of circular muscle.

What is peristalsis controlled by?

The enteric nervous system.

Is substance P excitatory or inhibitory?

Excitatory.

What is segmentation?

Local constriction of intestine that mixes food with digestive juices, without net forward movement.

What are GI motility patterns generated by?

ICCs (pacemakers), enteric motor neurons (modulate ICC activity), and smooth muscles (effectors).

What facilitates the spread of depolarization among smooth muscle cells?

Gap junctions.

Which parts of the GI musculature are skeletal?

Pharynx, UES, upper 1/3 of esophagus, and external anal sphincter.

What are slow waves?

Spontaneous depolarizations in GI smooth muscle elicited by ICC.

What increases the strength of contraction?

Larger amplitude slow waves, resulting in action potentials.

What are the specific frequencies of slow waves?

12/min in the duodenum, 8/min in the ileum, and 3/min in the stomach.

How does hormonal or neural stimulation modulate slow waves?

Increases/decreases amplitude but not frequency.

What are the pathophysiologies associated with ICCs?

Loss = chronic constipation, achalsia (inability to relax sphincters), and pyloric stenosis (failure of pylorus to relax).

What is the chewing reflex pathway?

Food in the mouth stimulates oral/periodontal mechanoreceptors and subsequent jaw opening reflex (lower jaw inhibition). Stretch spindles in masseter activate and initiates rebound contraction to chew.

What is the oral phase of swallowing?

Voluntary tongue pushing of bolus into the pharynx.

What is the pharyngeal phase of swallowing?

Involuntary reflexes (from swallowing center through cranial nerves V, IX, X) to inhibit respiration and close cavities.

What is the esophageal phase of swallowing?

Primary peristalsis continues from pharynx all the way to stomach, with the UES closed and LES open.

What is the purpose of secondary peristaltic contraction?

Clears the esophagus of remaining food.

Summarize swallowing.

Coordinated muscle contraction to build pressure to push the bolus downwards.

What is dysphagia?

Difficulty swallowing due to structural or neuromuscular issues.

What is GERD?

Acid reflux, inability to contract the LES properly.

What muscle in the stomach is responsible for churning?

Oblique layer.

How long does gastric emptying take?

1-4 hours.

What is the vagovagal relaxation reflex?

Gastric stretch stimulates inhibition/relaxation smooth muscle in the fundus via the medulla.

What are the four steps of gastric motility?

Propulsion, churning, retropulsion (caudad contraction with sphincter closed), and emptying (intermittent antrum contraction).

What stimulates the gastrocolic and gastroileal reflexes?

Gastric distention.

What is the main players in gastric emptying?

Duodenal inhibitory factors.

What stays open during MMC?

Pylorus.

What is the role of the MMC?

"Housekeeping".

How long after a meal does MMC take place?

1-2 hours.

What is gastroparesis?

Impaired gastric emptying.

What causes the net forward movement of chyme in the small intestine?

Segmentation concentrated earlier in the tract compared to later.

What does the gastroileal reflex induce?

Relaxation of the ileocecal valve and closing upon cecum distension.

Where does the majority of absorption occur in the colon?

Ascending portion.

Where does the majority of waste storage occur in the colon?

Descending portion.

What are taeniae coli?

Three ribbon-like bands of longitudinal muscle running the length of the colon.

What are haustrations?

Mixing movements in the colon that serve as main propulsive movement in cecum and ascending colon. Pockets are haustra.

How often do mass movements occur?

1-3 times a day.

What are the main triggers of mass movements?

Gastrocolic reflex, colon distention, irritants, and parasites.

What two systems are responsible for the defecation reflex?

Enteric and parasympathetic (sacral region).

What nerve relaxes the external anal sphincter?

Pudendal nerve.

What is defecation reflex stimulated by?

Gastrocolic and ileocecal reflex.

What is the sequence of events in vomiting?

Deep inhalation/hypersalivation, strong contraction of antrum with flaccid fundus, LES/esophagus relaxation with glottis closing, diaphragm/abdominal contraction.

Where is the control of vomiting?

Central vomiting center (medulla).

What are the trigger effectors for the vomiting center?

Chemoreceptor trigger zone (leaky BBB), baroreceptors, pain receptors, labyrinths via vestibular nuclei, and higher brain areas.

What do small buccal glands secrete?

Mucus.

What glands secrete serous fluid?

Parotic.

What are the enzymes in saliva?

Salivary amylase and lingual lipase, Kallikrein (from bradykinin).