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Physiology Module 4 > Digestive > Flashcards

Digestive Flashcards

1
Q

Functions of Digestive System

A

Supply body with
Water
Electrolytes
Vitamins
Nutrients

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2
Q

Processes of Digestive System

A

Movement
Secretion
Digestion
Absorption

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3
Q

List the functions of the digestive system

A

the function of the digestive system is to supply the body with water , electrolytes , vitamins , and nutrients . This is conducted through the processes of motility , digestion, secretion and absorption . Food travels through the body beginning in the mouth , pharynx , then down the esophagus . It then enters the stomach , small intestine /duodenum. jejunum , ileum), large intestine (ascending , transverse, descending, sigmoid colon) to the rectum and lastly the anus. Accessory organs include salivary glands ,liver , pancreas , and gal bladder

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4
Q

Tissue Layers of GI Tract

A

Mucosa
Submucosa
Smooth muscle
Circular layer
Longitudinal layer
Serosa

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5
Q

Give the layers of the gastrointestinal (GI) tract and explain their functions.

A

The mucosa is the innermost layer of the GI tract , facing the lumen. Mucosa is several epithelial cells thick in the beginning of the
trait to handle abrasion , and 1 cell thick later in the trait, designed for absorption.
The mucosa also has a thin muscle layer to help in
changing shape.
The submuwsa_ contains lots of vasculature ,nerves , lymph ,
and glands to aid in secretion and blood supply to the intestines.
Layers of smooth muscle assist in peristalsis :
-
The circular layer runs in circles around the submucosa
-
The longitudinal layer is the more superficial layer and runs in long lines
the serosa is the most superficial layer, consisting of connective tissue.

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6
Q

Accessory Organs
of Digestive System

A

Salivary glands
Pancreas
Liver
Gall bladder

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7
Q

GI Smooth Muscle

A

Unitary (single unit) smooth muscle
Functions as a syncytium (gap junctions)
Electrical Activity
Slow waves
Fixed frequency
Interstitial Cells of Cajal (pacemakers)
Variable amplitude
Affected by nervous/hormonal stimuli
Spike Potentials
True action potentials
When threshold reached

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8
Q

Spike Potentials

A

Contraction due to Ca++ levels
Enters through calcium – sodium channels
Slow to open & close
Long action potential duration
Frequency influenced by neural/hormonal stimuli
Increased frequency -> increased contraction

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9
Q

Endocrine (hormones)

A

All GI hormones are peptides
Released into blood → act on distant target cell

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10
Q

Paracrines

A

Some are peptides (somatostatin), some are not (histamine)
Endocrine cells release → diffuse to target cells
Can act on endocrine cells (+ or -)

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11
Q

Neurocrines (neurotransmitters)

A

Some are peptides (VIP), some are not (Ach, NE)
Nerves release → diffuse to target cells

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12
Q

Parasympathetic

A

Vagus nerve
Sacral/pelvic nerves
Generally excitatory (Ach)
More innervation near mouth/anus

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13
Q

Neural Control of GI Function

A

Enteric Nervous System
Myenteric plexus
(Auerbach’s plexus)
GI movements
Submucosal plexus (Meissner’s plexus)
GI secretion & local blood flow
Can function independently or be influenced by autonomic system
NT: excitatory and inhibitory

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14
Q

Sympathetic

A

T5-L2 (NE)
Innervation throughout GI tract
Generally inhibitory (NE)
Inhibition mostly by inhibiting ENS neurons

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15
Q

Sensory Nerves from Gut

A

80% of fibers in vagus nerve are afferent
Other afferents, too
Can be excitatory or inhibitory
Stimulated by
Irritation of mucosa
Distention of GI tract
Chemicals

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16
Q

Local: ENS reflexes

A

Secretion, mixing, peristalsis

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17
Q

Long Loop: Gut to prevertebral sympathetic ganglia & back

A

Gastrocolic reflex
Enterogastric reflex
Colonoileal reflex

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18
Q

Long Loop: Gut to CNS & back

A

Stomach/duodenum to control secretion
Pain reflexes
Defecation reflexes

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19
Q

Integration of Control

A

Nervous and endocrine systems work together
Neurons stimulate hormone release
Hormones stimulate neural activity
Simultaneous effects

Stimuli for both can be internal or external

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20
Q

Peristalsis

A

propulsive movements
Stimulated by distention
Myenteric plexus

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21
Q

Segmentation

A

mixing movements

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22
Q

Splanchnic Circulation

A

Blood to
GI tract
Spleen
Pancreas
Liver
25-30% of CO

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23
Q

Control of Gut Blood Flow

A

Blood flow proportional to local activity
Meal → ↑ blood flow (2-3 fold) for 3-6 hr
Causes of activity-induced blood flow
Vasodilating hormones
gastrin, secretin, CCK
Low oxygen
Nervous control of blood flow
PNS - ↑ gut activity → ↑ blood flow
SNS - Directly ↓ blood flow

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24
Q

GI Movements

A

Mastication (chewing)
Deglutition (swallowing)
Esophageal motility
Gastric motility
Small intestine motility
Large intestine motility

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25
Mastication (Chewing)
Purpose of Chewing Breaks apart indigestible cellulose Increases surface area by decreasing particle size Mixes food with saliva Begins digestion of starches (α-amylase) Begins digestion of lipids (lingual lipase) Lubricates food for swallowing Control of chewing Nervous (cranial nerve/brain stem) Mastication reflex
26
Deglutition (Swallowing)
Stages of Deglutition Voluntary Initiates swallowing process Pharyngeal Passage of food through pharynx into esophagus Reflex controlled Esophageal Passage of food from pharynx to stomach Reflex controlled
27
Esophageal Motility
Muscle composition Upper 1/3 is skeletal muscle Lower 2/3 is smooth muscle Peristalsis Primary peristalsis Continuation of swallowing reflex Secondary peristalsis In response to distention ENS and brainstem control
28
Gastric Motor Functions
Store food until processing complete Mix food with gastric secretions to form chyme Empty chyme into small intestine at appropriate rate
29
Storage Function of Stomach
Food entering causes stretch Leads to vagovagal reflex Relaxation of muscle tone to accommodate more food
30
Stomach Tissue Modifications
Smooth muscle 3 layers Circular Longitudinal Oblique Rugae Allow for expansion
31
Mixing/Propulsion in Stomach
Most of stomach Mixing (constrictor) waves due to slow waves Can have contraction just from slow waves Don’t need spike potentials Antrum Peristalsis Few ml get into duodenum through pyloric sphincter Retropulsion of remainder
32
Regulation of Gastric Emptying
Signals from stomach & duodenum Gastric factors that promote emptying Food volume Gastrin
33
Regulation of Gastric Emptying
Gastric factors that inhibit emptying Reflexes from food in duodenum Prevent too much chyme in duodenum Controlled by 3 routes that inhibit stomach contraction & increase pyloric sphincter tone ENS Duodenum to stomach Vagus afferents to brainstem Sympathetic Extrinsic afferent nerves to sympathetic inhibitory efferents Gastric factors that inhibit emptying Due to Duodenal distention Irritation of duodenal mucosa Low pH in duodenum High osmolality of chyme in duodenum Chyme from proteins & fats
34
Small Intestine Motility
Spike waves required for contraction Mixing contractions/Segmentation Due to slow waves Surface of small intestine contains ridges that move food through small intestine in circular motion (and slower than if smooth) Propulsive movements/Peristalsis Enhanced by Gastroenteric reflex (distention of stomach) Gastrin, CCK, insulin, motilin, serotonin Inhibited by Secretin, glucagon, epinephrine
35
Large Intestine Motility
Mixing Movements (Haustrations) Like segmentation in sm. intestine Propulsive Movements (Mass Movements) Modified peristalsis from cecum to sigmoid 1-3X/day for most people, for 10-30’ Large areas contract as a unit & propel feces When feces reaches rectum: defecation reflex Initiated by gastrocolic and duodenocolic reflexes
36
Defecation Control
Intrinsic Can be local, entirely within ENS using myenteric plexus to initiate peristalsis Spinal Control Higher CNS can also control
37
Defecation Reflex – Spinal/Parasympathetic
Stimulus Stretch Receptor Stretch receptors Afferent nerves Integrating center Spinal cord Efferent Sacral Parasympathetic Somatic (Pudendal) Target Smooth muscle of descending colon, sigmoid, rectum, anus External anal sphincter Response Intense peristalsis Relaxation of external sphincter - VOLUNTARY
38
Migrating Motor Complex
Housekeeping function” Sweeps undigested residue toward colon to maintain low bacterial counts in upper intestine Periods of intense, rapid peristaltic contractions ~90 min to go from stomach to colon Mediated by motilin and ENS
39
Secretion
Digestive enzymes From all along tract In response to food presence/type Regulatory peptides and modulators Mucus From mucous glands
40
Secretory Gland Types
Single cell (produce mucus) Mucous glands, mucous cells, goblet cells Pits Crypts of Leiberkühn Tubular glands Oxyntic gland that secretes acid Complex glands Many throughout tract Salivary, pancreas
41
Control of Secretion
ENS In response to Distention Tactile stimulation Chemical irritation ANS Parasympathetic – increases most secretion Sympathetic – dual effect, but decreases most secretion Causes vasoconstriction
42
Mechanism of Secretion
Secrete organic substances Secrete water and electrolytes to carry substances
43
Functions of Mouth
Secretion – saliva Motility – chewing, swallowing Digestion Mechanical digestion Chemical digestion Immune Saliva Tonsils (Minimal absorption of ions and very small things sublingually)
44
Saliva
Secreted into mouth by salivary glands Functions Lubricate food Digest food Immune function Contents include α- amylase (digests starches) Mucus (lubricates) Ions Enzymes (destroy bacteria) Also secreted into oral cavity Lingual lipase (digests lipids)
45
Pharynx/Esophagus
From mouth, bolus of food goes into pharynx, followed by esophagus Most secretion here is mucus to help lubricate food & protect mucosa
46
Functions of Stomach
Store food Motility – already discussed Liquefy food into chyme Release chyme into small intestine slowly Secretion (modified mucosa w/deep glands) HCl, pepsinogen, gastric lipase, mucus, bicarbonate, gastrin, histamine Digestion – limited to proteins (fats minimal) Limited absorption (lipid-soluble)
47
Mucus and Bicarbonate
Secreted by mucous cells Tonic secretion and in response to irritation Protect stomach lining from acid
48
Gastrin
Secreted by G cells In response to Ach, AAs, and peptides Causes acid production (by stimulating ECL and parietal cells)
49
Histamine
Secreted by ECL cells (enterochromaffin-like) In response to Ach, gastrin Causes acid production (by stimulating parietal cells)
50
Pepsinogen
Secreted by chief cells In response to gastrin, acid When converted to pepsin, helps digest proteins
51
Gastric lipase
Secreted by chief cells In response to gastrin, acid Digests lipids
52
Gastric acid
Secreted by parietal cells In response to Ach, gastrin, histamine Activates pepsinogen into pepsin Kills bacteria
53
Intrinsic factor
Secreted by parietal cells In response to Ach, gastrin, histamine Allows for absorption of vitamin B12 in the small intestine
54
Somatostatin
Secreted by D cells In response to acid Inhibits acid secretion by inhibiting G cells from producing gastrin ECL cells from producing histamine Parietal cells from producing HCL
55
Gastric (oxyntic) Glands
Neck cells Mucus Chief Cells (peptic cells) Pepsinogen Parietal cells HCl Intrinsic factor
56
Pyloric Gland
G-cells Gastrin Mucous neck cells Mucus Pepsinogen (small amounts)
57
Phases of Acid Secretion and Digestive Regulation
Cephalic Phase Gastric Phase Intestinal Phase
58
Acid Secretion
Basal secretion ~10% of response after meal
59
Cephalic Phase
Seeing, smelling, thinking about, and/or tasting food Stimuli Central pathway (thought) Hypoglycemia Chemoreceptors (smell/taste) Mechanoreceptors ~30% of acid response (after a meal)
60
Gastric Phase
When food enters stomach Stimuli Distention (local and vagovagal) Increased pH Peptides/amino acids ~60% of acid response after a meal
61
Intestinal Phase
When food enters small intestine Stimuli Distention Peptides/amino acids ~10% of acid response after a meal
62
Acid Response to a Meal
Duration of gastric acid response to meal is a function of Intra-gastric pH Nature of chyme entering duodenum Acid secretion before a meal is suppressed due to low pH Acid stimulates somatostatin release (which decreases gastrin secretion) Acid has direct effect to suppress parietal cell secretion
63
Stomach is Protected from Acid
Mucus layer protects stomach epithelium Bicarbonate keeps pH at stomach mucosa ~pH 7.0 Lumen is ~pH 2.0 pH gradient between epithelium and lumen
64
Pancreatic Secretion
Exocrine To handle chyme Digestive enzymes Bicarbonate Endocrine Metabolic hormones Insulin Glucagon
65
Pancreatic Digestive Enzymes
Help digest Proteins Carbohydrates Lipids
66
Pancreatic Enzymes for Protein Digestion
Trypsin Proteins to polypeptides Chymotrypsin Proteins to polypeptides Carboxypolypeptidase Polypeptides into amino acids
67
Pancreatic Enzymes for Carbohydrate Digestion
Pancreatic amylase Complex carbohydrates into disaccharides
68
Pancreatic enzymes are stored and secreted in
inactive forms called zymogens Not activated until enterokinase from intestinal cell converts trypsinogen to trypsin
69
Trypsin converts
Chymotrypsinogen into chymotrypsin Procarboxypeptidase into carboxypeptidase Procolipase into colipase Prophospholipase into phospholipase
70
Pancreatic Bicarbonate Secretion
Neutralizes acidic chyme Creates optimal pH (7-8) for digestive enzymes
71
Regulation of Pancreatic Secretion
Released throughout phases (mostly intestinal phase) Digestive enzymes In response to protein/fat content of chyme Bicarbonate In response to acid of chyme
72
Bile Secretion of the Liver
Helps digest fats Emulsification Aids absorption Helps excrete wastes Gall bladder stores & concentrates bile CCK stimulates gall bladder contraction
73
Small Intestine Secretions
Mucus Brunner’s glands of duodenum Protects mucosa Stimulated by Ach and irritation Inhibited by NE “Digestive Juices” Crypts of Leiberkühn throughout small intestine Most regulation by local ENS reflexes
74
Crypts of Leiberkühn
Secrete watery fluid Active secretion of Cl- Active secretion of HCO3- Electrical drag of Na+ Osmotic movement of H2O
75
Large Intestine Secretions
Also contains crypts of Leiberkühn Mucus Some bicarbonate Stimulated by ENS reflexes (irritation) Parasympathetic activation

Physiology Module 4 (2 decks)

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