Snf Test 4 - Gi Physiology

Front 1

What are the components the GI tract?

Back 1

GI Tract
Digestive Tract
Alimentary Canal
Gut

Front 2

What are the major functions of the GI tract?

Back 2

Digestion
Excretion
Supplies water, electrolytes, and nutrients

Front 3

What is a common problem of the GI tract that affects the oral cavity?

Back 3

Enamel Erosion

Front 4

What are the processes of ingestion?

Back 4

Mastication
Swallowing

Front 5

What is motility?

Back 5

Concerted movement of food through the alimentary tract

Front 6

What are the secretory function of the GI tract?

Back 6

Secretion of digestive enzymes, mucus, acid, bicarbonate, fluids

Front 7

What is digestion?

Back 7

Metabolism of carbohydrates, proteins and fats

Front 8

What is absorption?

Back 8

Removal of water, electrolytes, and nutrients

Front 9

What is elimination?

Back 9

Removal of undigested material

Front 10

What is the first step in digestion?

Back 10

Ingestion.
Involves mastication (chewing)
-Incisor:cutting
-Molars: grinding
-Breaks apart undigestible cellulose
-Increases surface area -decreases particle size
-Mixes food with saliva

Front 11

How much saliva is produced each day and what is it composed of?

What percentage of saliva produced come from the parotid and submandibular salivary glands?

Back 11

800-1500 ml/day
pH 6-7

Composed of Two types of secretion:
1. Serous - watery secretion contains an alpha amylase (ptyalin) for digesting starch
2. Mucous - contains mucin - lubrication

90% from parotid and submandibular salivary glands

Front 12

What are the proteins found in saliva?

Back 12

-Alpha-amylase
-Immunoglobulins (sIgA, IgG, IgM)
-Antibacterial proteins - lysosyme, lactoferrin, sialoperoxidase
-Glycoproteins

Front 13

What are the functions of saliva?

Back 13

-Lubrication and binding
-Solubilizes dry food
-Initiates starch digestion
-Maintain oral hygiene

Front 14

What are the three ways saliva helps maintain oral hygiene?

Back 14

1. Flush bacteria and food that support bacterial growth
2. Kill bacteria - contains proteolytic enzymes (lysozyme etc) and thiocyanate ions that are bactericidal
3. Destroying bacteria via binding/processing to antibodies

Front 15

What are the stages of saliva formation and where does each occur?

Back 15

1. Primary secretion - Acini
2. Secretion modified - Salivary ducts

Front 16

What is the tonicity of primary secretion and how is it powered?

Back 16

Primary secretion is nearly isotonic; levels of Na+, K+, Cl- and HCO3- are similar to plasma

Primary secretion is powered by the Na+/K+ pump that creates a gradient for Na+ and Cl-

Front 17

What are the steps in stage two of saliva secretion or ductal modification?

Back 17

1. Sodium ions are actively reabsorbed via a Na+ATPase pump
2. Potassium ions are actively secreted in exchange for Na+

Na+ reabsorption >>K+ secretion
Cl- is passively reabsorbed
HCO3- is secreted

Front 18

What is the net result of ductal modification with resepct to Na+, Cl-, K+, HCO3?

Back 18

Na+ = 0.1 x plasma
Cl- = 0.15 x plasma
K+ = 7 x plasma
HCO3 = 3 x plasma

Front 19

What increases the rate of secretion and by how much?

Back 19

Taste and tactile stimuli, 8-20X

Front 20

What happens to the ions as the flow rate of saliva increases?

Back 20

Ions approach plasma values because less time is available for modification

HCO3 remains elevated because salivary agonists stimulate its secretion.

Front 21

What is the predominant nervous regulation of salivary secretion and where is it controlled?

Back 21

Predominantly parasympathetic
Controlled from the brain stem

Front 22

What will a failure of parasympathetic stimulation of salivary secretion result in?

What can restore salivary flow in some cases?

Back 22

Xerostomia

In some cases, the muscarinic agonist, pilocarpine can restore salivary flow

Front 23

What are the three phases of swallowing?

Back 23

1. Oral phase - only voluntary portion of swallowing
2. Pharyngeal phase
3. Esophageal stage

Front 24

What occurs in the oral phase of swallowing?

Back 24

Voluntary
Moves food upward and back into pharynx

Front 25

What occurs in the pharyngeal phase of swallowing?

Back 25

- Food bolus stimulates touch receptors
- Impulses initiate a series of automatic pharyngeal muscle contractions
- Trachea closes, esophagus opens, and a fast peristaltic wave is initiated (all within 2 sec)

Front 26

What occurs in the esophageal stage of swallowing?

Back 26

-Primary and secondary peristaltic wave pushes food to stomach
-Between swallows: High pressure at sphincters
-During swallows:
*UES (upper esophageal sphincter) relaxes - low pressure
*Peristaltic wave - (high pressure)
*LES (lower esophageal sphincter) and fundus relax - receptive relaxation (low pressure)

Front 27

What is the function of the upper esophageal sphincter?

Back 27

Keeps air from entering esophagus

Front 28

What is the function of the lower esophageal sphincter (LES)?

Back 28

Prevents acid reflux into esophagus

Front 29

What is Gastroesophageal Reflux Disease (GERD)?

Back 29

-Heartburn/acid indigestion (1/10 people)
-Backwash of stomach acid
-Can lead to:
*stricture of esophagus (scar tissue)
*asthma (aspiration)
*chronic sinus infection (reflux into throat)
*Barret's esophagus

Front 30

What is motility with respect to the GI tract?

Back 30

Concerted movement of food through the alimentary tract - Purpose is to MIX and PROPEL the food

Front 31

What are the two types of muscles found in the muscularis externa of the GI tract and where are they found specificly?

Back 31

Circular muscle - around the gut

Longitudinal muscle - down the GI tract

Front 32

What are the components of the enteric nervous system?

Back 32

Meissner's plexus: large areas of smooth muscle that contract as a single unit

Myenteric nerve plexus: Integrates motor and secretory activities. Can function independent of the ANS.

Front 33

What are the two types of movement involved in GI motility>

Back 33

Propulsive (peristalsis)
Mixing

Front 34

How is GI motility initiated, what is required and what results in mixing?

Back 34

- Distension of the intestinal tract (stimulus) causes a contractile ring to appear which moves forward a few cm.
-Myenteric plexus is required
-Peristalsis plus local contraction causes mixing

Front 35

What are the 3 types of GI reflexes?

Back 35

1. Reflexes that occur entirely within the gut wall ENS
2. Reflexes from the gut to the sympathetic ganglia and then back to the gut
3. Reflexes from the gut to the spinal cord or brain stem and back to the gut

Front 36

What are the functions of the reflexes that occur entirely within the gut wall ENS?

Back 36

-Control secretion
-Peristalsis
-Mixing contractions

Front 37

What is the function of reflexes from the gut to the sympathetic ganglion and then back to the gut?

Back 37

Long distances to other GI areas
-Stomach causes evacuation of colon
-Colon and small intestine inhibit stomach motility

Front 38

What is the location and function of the Myenteric plexus?

Back 38

Location: Esophagus to anus

Function: Controls GI motility, controls muscle activity length of GI tract

Front 39

What are stimulatory influences and inhibitory influences of the myenteric plexus?

Back 39

Stimulatory Influences
-Increase tonic contraction
-Increase contraction frequency/intensity (Increase propulsion)

Inhibitory influences
-Decreased sphincter tone (relax) - pyloric sphincter, ileocecal sphincter

Front 40

What is the location and function of the submucosal plexus?

Back 40

Location: Mucosal layer

Function: Local Control
-Secretion
-Absorption
-Contraction of submucosal muscle

Front 41

How are the afferent sensory nerves stimulated and what results?

Back 41

Sensory nerves are stimulated by:
-Irritation of gut mucosa
-Distension of the gut
-Specific chemical substances in the gut

Cause excitation or inhibition of intestinal movement or secretions

Front 42

How does the sympathetic system affect the motility of the GI tract?

Back 42

Decrease motility (movement) of the large intestine

Front 43

How does the parasympathetic system affect the motility of the GI tract?

Back 43

-Increases intestinal and gland activity
-Relaxes sphincter muscles in the GI

Front 44

What are the two types of electrical waves that occur in the smooth muscle of the GI?

Back 44

1. Slow waves
2. Spike potentials

Front 45

What are slow waves?

Back 45

-Rhythmical changes in membrane potential cause by variations in sodium conductance
-Not action potentials
-Undulating changes in resting potential of membrane (change 5-15 millivolts)
-Frequency differs along GI tract (~3-12/min)
-Establishes rhythm of contraction
-Slow waves established by pacemaker cells (interstitial cells of Cajal)

Front 46

What are spike potentials?

Back 46

-Action potentials
-Occur when the resting potential becomes greater than -40 millivolts

Front 47

What is depolarization and what causes it in the GI tract?

Back 47

Muscle fibers become more excitable

Stretching, acetylcholine, parasympathetic nerves, some hormones

Front 48

what is hyperpolarization and what causes it in the GI tract?

Back 48

Muscle fibers less excitable

Norepinephrine, epinephrine

Front 49

What are the actions and functions of the fundus and body in gastric motility?

Back 49

-Receptive relaxation - relaxes to accomodate food (up to 1.5L)
-Weak mixing waves: Fragment food mix with secretions

Front 50

What are the actions and functions of the antrum in gastric motility?

Back 50

-Vigorous contractions, mixes food to form a semifluid mixture called chyme
-Retropulsion: pyloric muscle contracts pushing chyme back towards body
-Propels chyme into duodenum (antral pump, pyloric pump) at a rate suitable for proprer digestion and absorption

Front 51

How is gastric emptying regulated?

Back 51

-Chyme must enter duodenum at proper rate
-pH must be optimal for enzyme function
-Slow enough for nutrient absorption

Front 52

What are the 4 conditions that favor gastric emptying?

Back 52

1. Increased tone of body of stomach
2. Forceful peristaltic contractions
3. Decreased tone of pylorus
4. Absence of segmental contractions in intestine

Front 53

What are the secretory functions of the GI tract?

Back 53

Secretion of digestive enzymes, mucus, acid, bicarbonate, fluids

Front 54

How are the daily secretion of GI juices regulated?

Back 54

Highly regulated
-Presence of food
-Type of food
-Quantity needed
-local
-autonomic stimulation
-hormonal-regulate volume and character

Front 55

How much saliva, gastric secretions, bile, pancreatic juices, intestinal secretions are produced each day and what is their pH?

Back 55

-Saliva: 1500 ml/day, pH 6-7
-Gastric secretions: 2000 ml/day, pH 1-3.5
-Bile: 500 ml/day, pH 7.8
-Intestinal secretions: 1500 ml/day, pH 7.5-8.9

Front 56

What are the basic mechanisms of secretion?

Back 56

1. secrete substance
2. Move substance to target

REGULATED SECRETION

Front 57

What is the function of mucus secretion and are its characteristics?

Back 57

Functions: To lubricate and protect the gut wall
Composition: Water, electrolytes, glycoproteins

-Sticky - sticks to gut wall; sticks/coats food
-Thick - coats wall and prevents contact with mucosa
-Slippery - food particles slide along epithelium
-Stable - resistant to digestion by I enzymes
-Buffer - glycoproteins are amphoteric (ie can buffer acids/base) Contains bicarbonatate ions which neutralizes acids

Front 58

What are the 3 phases of gastric secretion?

Back 58

1. Cephalic phase via vagus: sight, smell, taste

2. Gastric phase: Local nervous secretory reflexes, Vagal reflexes, Gastrin-histamine stimulation; 70% of secretions occur in this phase

3. Intestinal phase: Nervous mechanisms, Hormonal mechanisms; Presence of food in upper portion stimulates gastric juices

Front 59

What are the two types of glands in the stomach?

Back 59

1. Gastric
2. Pyloric

Front 60

What do the gastric glands secrete?

Back 60

HCl
pepsinogen, gastric lipase
intrinsic factor
mucus

Front 61

What do the pyloric glands secrete?

Back 61

Gastrin
Mucus

Front 62

What are the 3 types of cells found in the gastric glands and what do they secrete?

Back 62

1. Mucous neck cells: Secrete mucus

2. Parietal cells: Secrete HCl and intrinisic factor

3. Chief cells: secrete pepsinogen and gastric lipase

Front 63

What are the two cell types of the pyloric gland and what do they secrete?

Back 63

1. G cells: release gastrin

2. Mucus neck cells: secrete mucous

Front 64

where are gastric and pyloric glands found and what percentage of the stomach do they compose?

Back 64

Gastric - upper portion of stomach, 80%

Pyloric - lower portion of stomach, 20%

Front 65

Where is HCl formed in the gastric glands and what are these cells enriched with?

Back 65

HCl is formed at the villus-like membranes of the canaliculi which are continuous with the lumen

Gastric glands are enriched with mitochondria

Front 66

How does the production of HCl affect the amounts of tubulovesicles and microvilli?

Back 66

During active HCl production:
-Microveilli increase
-Tubulovesicular system decreases

Front 67

What are the steps in HCl secretion by the gastric glands?

Back 67

-Metabolism drives the formation of carbonic acid
-Protons are pumped by H+, K+ - ATPase
-Cl- enters the cell in exchange for HCO3 (antiporter)
-Cl- enters the canalicular fluid via an ion channel - H+,K+ ATPase OF "PROTON PUMP" IN CANNALICULAR MEMBRANE IS KEY PLAYER

Front 68

What drug inhibits H+K+ - ATPase and is used to treat ulcers and gastric reflux disorders?

Back 68

Omperazole

Front 69

What are 3 things that stimulate acid secretion?

Back 69

1. Acetylcholine: cholinergic nerve terminals near parietal cells

2. Histamine: enterochromaffin-like (ECL) cells in the gastric mucosa and diffuses to the parietal cells

3. Gastrin: G cells in the mucosa of the gastric antrum and the duodenum and reaches parietal cells via the bloodstream

Front 70

What are 3 things that inhibit acid secretion?

Back 70

1. Somatostatin
2. Prostaglandin
3. Gastric Inhibitory Peptide (GIP)

Seomatostatin acts on G cells and ECL cells, inhibiting their release of gastrin and histamine, respectively

Prostaglandins and GIP act directly on parietal cells

Front 71

How do amino acids and Ach regulate HCl production?

Back 71

Stimulate G cells; release gastrin

Front 72

How does gastrin regulate HCl production?

Back 72

Stimulates ECL cells and parietal cells

Stimulates D cells to release somatostatin that is inhibitory
(D cells = gastric/duodenal mucosa and pancreas)

Front 73

What is gastric intrinsic factor?

Back 73

A glycoprotein necessary for the absorption of vitamin B12
Secreted by parietal cells

Front 74

Where does vitamin B12 bind to intrinsic factor for absorption?

Back 74

Duodenum

Front 75

What are problems that can lead to a lack of intrinsic factor with consequent deficiency of vitamin?

Back 75

Chronic gastritis
Parietal cells destroyed
No HCl and intrinsic factor

can lead to pernicious anemia

Front 76

What do chief cells secrete?

Back 76

Pepsinogen gastric lipase

Front 77

Induced motion

Back 77

the feeling of motion that a stationary person feels if the environment around you moves.

Front 78

How do peptic ulcers arise?

Back 78

Damaging effects of acid and pepsin overcome ability of mucosa to protect itself
-Gastric ulcers - decreased ability of mucosa to protect itself
-Duodenal ulcers - exposure to increased amounts of acid and pepsin

Front 79

Where is Helibacter pylori found?

Back 79

found in 95% of patients with DU and 100% of patients with GU (when alcohol, aspirin, NSAIDS are eliminated)

Gram negative bacterium
High urease activity - high NH4+ activity - NH4+ damages epithelial cells

Front 80

Where are Brunner's glands found and what do they secrete?

Back 80

Small intestine

Secrete alkaline mucus
Stimulated by tactile stimuli or irritating stimuli of the mucosa, vagal stimulation, secretin

Front 81

Where are the crypts of lieberkuhn found and what do they secrete?

Back 81

Small intestine and large intestine - in the large intestine the crypts of lieberkuhn have no villi or enzymes

Secrete intestinal digestive juices