Digestive 1 Flashcards
Functions of the G.I. tract
Motility
Secretions
Digestion
Absorption
Storage and elimination
Immune barrier 
Function of GI tract: Motility
Push ingested food from the mouth toward the rectum and mixes and reduces the size of the food
 Function of GI tract: secretions
From the salivary glands, pancreas, and liver etc.
(Fluid, electrolytes, enzymes, mucus etc) 
Function of GI tract: digestion
Breakdown of food into absorbable molecules
 Function of GI tract: absorption
Nutrients, electrolytes, water etc. are absorbed from the intestinal lumen into the bloodstream
Function of GI tract: Storage and elimination
Temporary storage and subsequent elimination of indigestible food molecules
Function of GI tract: immune barrier
Prevent pathological organisms and toxins
Role of mouth and oropharynx
Top food, lubrication, initiate carbohydrate/fat digestion, and pushing the food into esophagus
Where does carbohydrate and fat digestion first occur
In mouth and oropharynx
Role of esophagus
Pushes food down to the stomach
Role of the stomach
Temporarily stores food, initiate digestion by churning and by secreting proteases and acid
Role of small intestine
Continues digestion, primary site for nutrient absorption
Where is the primary site for nutrient absorption
Small intestine
Role of large intestine
Reabsorbs fluids/electrolytes , Stores fecal matter before expulsion 
Role of pancreas
Secretes digestive enzymes into duodenum , Secretes bicarbonate to neutralize gastric acid
Role of liver
Secretes bile and stores it in the gallbladder for future delivery to Duodenum during a meal 
Role of bile
Contains bile acids, which play a key role in digestion of fats
What are the four layers of the wall of the G.I. tract
- Mucosa
- Submucosa
- Mascularis
- Serosa
Wall of GI tract: Mucosa
What is it and what does it consist of
It’s the lumen (has direct contact with food)
Consists of 3 things/layers:
- epithelial cells : for absorption and secretion
- lamina propria: connective tissue, blood and lymph vessels
- muscularis mucosa : smooth muscle cells (changes surface area)
Wall of GI tract: submucosa
What is it and what does it consist of
Connective tissue
Consists of:
- blood vessels
- glands
- submucosal plexus (nerves)
Wall of GI tract: mascularis
What is it responsible for, and what does it consist of
Responsible for motility
Consists of:
- inner circular smooth muscle
- outer longitudinal smooth muscle
- myenteric plexus
Wall of GI tract: serosa
What is it and what is its role
Outer most layer for support and protection 
The enteric nervous system is made up of
- Submucosal plexus (Meissner’s plexus)
 - Myenteric plexus
The submucosal plexus (Meissner’s plexus) is between
Submucosa and circular muscle
The myenteric plexus is between
Circular muscle and longitudinal muscle
Innervation of G.I. tract is done by two components
Extrinsic components :
1. Sympathetic
2. Parasympathetic
Intrinsic components:
3. Enteric nervous system
- myenteric plexus
- subcosal plexus
Which nervous system Overall innervates the G.I. tract
Autonomic nervous system
Effect of sympathetic stimulation on G.I. tract
Decreased G.I. activity
Effect of parasympathetic stimulation on G.I. tract
Increase G.I. activity
What is considered the “mini-brain of the gut”
Enteric nervous system
Effects of stimulation of myenteric plexus on GI tract
Increase in motor activity (motility)
Effect of stimulation of submucosal plexus on G.I. tract
Control secretion and blood flow
Nerves and neurons involved in parasympathetic innervation of G.I. tract
( long preganglionic fibers that synapse IN or near target)
- Vagus nerve: innervates UPPER G.I. tract
2. Pelvic nerve: innervates LOWER G.I. tract
- Cholinergics neurons: release acetylcholine
- peptidergic neurons: Release substance P and VIP 
Fibers of Sympathetic innervation of G.I. tract
Short preganglionic fibers:
- synapse outside of G.I. tract
Postganglionic nerve fibers (adrenergic- release NE)
- synapse on ganglia in myenteric and submucosal plexus
Or
- directly innervate smooth muscle, endocrine, or secretory cells.
Actions of acetylcholine
Contraction of smooth muscle
Relaxation of sphincters
Increase salivary secretion
Increase gastric secretion
Increase pancreatic secretions
Actions of norepinephrine
Relaxation of smooth muscle
Contraction of sphincters
Increase salivary secretion
Actions of VIP
Relaxation of smooth muscle
Increase intestinal secretion
Increase pancreatic secretion
Actions of GRP
Increase gastric secretion
Actions of enkephalins
Contraction of smooth muscle
Decrease intestinal secretion
Action of neuropeptide Y
Relaxation of smooth muscle
Decrease intestinal secretion
Action of substance P
Contraction of smooth muscle
Increase salivary secretion
Ingestion of food involves two processes
- Mastication (chewing)
- Deglutition (swallowing)
What is mastication
Mechanical grinding/shearing of food to increase total surface area
Mixes food with saliva, lubrication to facilitate swallowing
Carbohydrates are digested by amylase 
What are the three phases of deglutition/swallowing
- Oral phase
- Pharyngeal phase
- Esophageal phase 
What initiates swallowing reflex
When pressure receptors in walls of pharynx are stimulated by food or drink
Swallowing is coordinated by
Swallowing center in brain stem (medulla oblongata)
Which nerves carry information between the G.I. tract and the medulla
Vagus
Glossopharyngeal
Oral phase of swallowing
VOLUNTARY
Elevation of bolus by tongue against hard palate to push it into pharynx
Pharyngeal phase of swallowing
- respiration is inhibited
- closure of nasopharynx
- epiglottis closes larynx
- peristaltic wave is initiated
- opening of upper esophageal sphincter UES
Esophageal phase of swallowing
Bolus is pushed down the esophagus by PRIMARY peristalsis.
But if this fails clearing the bolus, SECONDARY peristalsis is initiated
What is peristalsis
A wave like contraction of muscles of esophagus that pushes food down towards the stomach via the lower esophageal sphincter LES
Primary peristaltic contraction creates an area of _________ pressure behind the bolus.
High
Movement of the bolus occurs because
- Circular smooth muscle contracts behind, and relaxes in front of bolus
- Longitudinal muscle contraction causes tube shortening
- gravity
If lower esophageal sphincter is weak or not fully closed , what can occur?
Gastric reflux (heartburn)
Explain receptive relaxation of the stomach‘s
- Food moves down esophagus by peristalsis
- LES opens before arrival of food
- Stomach relaxes before arrival of food
- Filling of the stomach INCREASES relaxation of smooth muscles of stomach
Receptive relaxation REDUCES pressure and INCREASES volume of stomach
How much food can the stomach accommodate
1.5 L
Relaxation of both LES and stomach occur through …….
VAGAL fibers secreting VIP
(VIP relaxes smooth muscles)
Effect of vagotomy on receptive relaxation
Vagotomy (removing a part of the vagus nerve) will ELIMINATE receptive relaxation because the vagus nerve can no longer stimulate that relaxation
Structure of the stomach
Fundus
Body
Antrum
The Fundus and body of the stomach are responsible for
Storage
The antrum of the stomach is responsible for
Mixing and emptying
Function of the stomach
Storage of food
Mixing of food
Emptying of food into small intestine
The process of mixing food in the stomach is called
Retropulsion
Gastric exocrine secretions
- HCL
- Pepsinogen
- Intrinsic factor
- Mucus
What cells secrete HCL
Parietal (oxyntic) cells
Functions of HCL
- keeps stomach free of microorganisms
- converts pepsinogen (inactive) into pepsin (active enzyme
- lowers pH (acidic) to below 2
Which cells secrete pepsinogen ?
Chief cells
Function of pepsinogen
Digestion of proteins
(when it is converted to pepsin at below pH3 by HCL)
Which cells secrete intrinsic factor
Parietal cells
Function of intrinsic factor
- absorption of vitamin B12 in ileum
- the ONLY essential component of gastric juice
Where is vitamin B12 absorbed
Ileum
What is the only essential component in gastric juice
Intrinsic factor
Which cells secrete mucus
Mucus neck cells
Function of mucus
- protects gastric mucosa from mechanical and chemical (HCL) destruction by releasing bicarbonate
- lubricates gastric contents
What are the endocrine gastric secretions
- Gastrin
- Somatostatin
What cells secrete gastrin
G cells
Function of gastrin
- stimulates acid secretion by parietal cells
(So increases HCL and pepsin)
(Reaches parietal cells via endocrine mechanism)
Which cells secrete somatostatin
D cells
Function of somatostatin
Inhibits G cells from producing gastrin
(Therefore no gastrin, no HCL, no pepsin)
Paracrine gastric secretion
Histamine
Which cells secrete histamine
Enterochromaffin-like cells (ECL)
Function of histamine
- stimulates acid secretion by parietal cells
- stimulates enzyme secretion by chief cells
( so increase HCL and pepsinogen and pepsin)
What part of the stomach has parietal cells
Body
What do parietal cells secrete
HCl
Intrinsic factor
What part of the stomach has chief cells
Body
What do chief cells produce
Pepsinogen 
What part of the stomach has G cells
Antrum
What do G cells produce
Gastrin
Which part of the stomach has mucous cells
Antrum
What do mucus cells produce
Mucus
(In the table it also says pepsinogen) 
Activation of pepsin
Parietal cells produce HCl.
Chief cells produce pepsinogen.
Pepsinogen (inactive enzyme) is then converted into pepsin (active enzyme) by HCl.
Pepsin breaks down ingested protein to short peptides
How does the stomach protect itself from digestion
- Chief cells are extremely impermeable to HCl
- A layer of alkaline HCO3- mucus covers the mucosa, neutralizing the acid
- Mucosa cells are tightly fused to each other = no leakage of HCL
- Rapid rate of cell division in the mucosa
- Pepsin is secreted in inactive form (pepsinogen)
What is the longest part of the G.I. tract
Small intestine
What parts of the small intestine are the primary site of absorption of carbohydrates, lipids, amino acids, calcium and iron
Duodenum and jejunum 
Which part of the small intestine is the main site for absorption of bile salts, vitamin B 12, water and electrolytes
Ileum 
What structures of the small intestine increase surface area
Plicae circulares
Villi 
What does Villi contain
Columnar epithelial cells
Goblet cells
What are goblet cells
Mucus secreting cells
Lamina propria forms the connective tissue core of each villus. What does it consist of ?
Lymphocytes
Blood capillaries
Central lacteals (lymphatic vessels)
Absorbed monosaccharides and amino acids from the small intestine enter the _________________, while the absorbed fat enters the ________________.
Blood capillaries
Central lacteals
What two cells are present in the intestinal crypt and what is their function
- Paneth cells : Secrete antibacterial molecules, and protect intestine from inflammation
- Stem cells : replenish cells of intestinal mucosa
Intestinal enzymes: Disaccharidase
Sucrase : digest sucrose ➡️ glucose + fructose
Maltase: digests maltose ➡️ glucose + glucose
Lactase : digests lactose ➡️ glucose + galactose
Deficiency in what enzyme causes lactose intolerance
Lactase
Intestinal enzymes: peptidase
Aminopeptidase: Produces free amino acids, dipeptide, tripeptides
Enterokinase: activates trypsin
Deficiency in what enzyme causes protein malnutrition
Enterokinase
Intestinal enzymes: phosphatase
Ca2+, Mg2+ ATPase : Absorption of dietary calcium
Alkaline phosphatase: removes phosphate groups from organic molecules
BOTH are regulated by vitamin D
Brush border enzymes:
Are attached to cell membrane of microvilli (not secreted into lumen)
They hydrolyze disaccharides, polypeptide, and other substrates
Intestinal contractions and motility :
- Segmentation: mixes chyme and expose it to pancreatic enzymes and secretions
- Peristalsis: pushes chyme along small intestine toward large intestine 
The dominant mixing movement in small intestine is called
Rhythmic segmentation 
_____________ Are unique pacemaker cells which produce SLOW waves that depolarize adjacent muscle cells and determine the rate at which action potentials and contractions occur
Interstitial cells of cajal (ICC)
The effect of ANS on rhythmic segmentation is ______________
Modulatory
(Meaning it can increase or decrease the slow waves produced by the ICC , but the ANS does not produce these waves)
Effect of sympathetic stimulation on contraction intensity in small intestine
Decreases it (inhibits slow waves)
Effects of parasympathetic stimulation on contraction intensity in small intestine
Increases it
Propulsive movement in small intestine is called
Peristalsis
Where is peristalsis faster in the small intestine
Proximal part > distal part
Describe Orad and Caudad states during intestinal peristalsis
Orad : behind bolus
- circular contract
- longitudinal relax
Caudad: in front of bolus
- circular relax
- longitudinal contract
Presence of bullets and small intestine causes local Distention, and this activates ______________.
Myenteric plexus
(b/w circular and longitudinal muscles)
Similar to rhythmic segmentation, peristalsis is also under the control of __________, while the _________ only has a modulatory effect.
ENS
ANS
Mixing movements in the small intestine is called
Haustrations
Haustrations are characterized by contractions of :
Inner circular muscles
Propulsive movement in large intestine are of two types:
Mass peristalsis
Reverse peristalsis
Difference between mass peristalsis and reverse peristalsis
Mass peristalsis = strong peristalsis
- directed aborally (away from mouth)
- occurs several times a day in cecum and entire colon
Reverse peristalsis
- orally directed (towards mouth)
- gives more time to the fecal matter to expose of water absorption 
Functions of the liver
Detoxification of blood
Carbohydrates metabolism
Lipid metabolism
Protein synthesis
Secretion of bile
What does bile contain
Bile salts
Urobilinogen
Cholesterol
Lecithin
Bilirubin
Electrolytes
Bicarbonate
What is the principal digestive function of the liver
Bile secretion
Enterohepatic circulation
Bile from the liver and gallbladder are taken to the small intestine through a common bile duct. The bile emulsifies and digests fat. Then 90% of the bile secreted is reabsorbed into the hepatic portal vein back to the liver
The bile secreted by the liver is stored and concentrated in the ______________.
Gall bladder
Functions of gallbladder
Pancreas secretions are both ___________ and ____________
Endocrine
Exocrine
Endocrine secretions of the pancreas occur in which region
Islets of Langerhans
What are the two endocrine hormones secreted by the pancreas
Insulin and glucagon
Exocrine secretion of the pancreas produces
Pancreatic juice
Pancreatic juice is secreted by which cell
Acini cells
What does pancreatic juice contain
Water and electrolytes
Bicarbonate : neutralization of acid
Digestive enzymes 
What are the digestive enzymes in pancreatic juice
(Hint: L DART)
Lipase
Deoxyribonuclease
Amylase
Ribonuclease
Trypsin
Etc
Regulation of the digestive system
Neural mechanisms:
- ANS
Sympathetic: inhibits GI activity
Parasympathetic : stimulates GI activity
- ENS
Myenteric: controls contractions
Submucosal: controls secretions and blood flow
Hormones (endocrine):
- secretin (small intestine)
- gastrin (stomach)
- CCK (small intestine)
Reflexes in the intestine
- Enterogastric reflex
- Gasdtroilial reflex
- Ileogastric reflex
What is enterogastric reflex
Signals from small intestine inhibit gastric emptying
What is gastroilial reflex
Increase gastric activity causes increased motility of ileum and movement of chyme through ileocecal valve 
What is ileogastric reflex
When ileum is distended, this decreases the motility and emptying of the stomach
Regulation of pancreatic secretion is done by 
Hormones ( secretin and CCK)
Regulation of pancreatic secretion by secretin
Released from intestinal mucosa when ACIDIC food enters intestine
Secretin goes into bloodstream > pancreas > secretion of bicarbonate = neutralization
Dysfunction of secretin’s regulation of pancreatic secretion will lead to
Duodenal ulcer
Regulation of pancreatic secretion by CCK
CCK is released when FATTY food enters intestine
CCK is secreted by I cells of duodenal and jejunal mucosa
CCK goes into bloodstream > pancreas > releases digestive enzymes to digest the fat , proteins and carbs
Actions of CCK
- Contraction of gall bladder
- Secretion of pancreatic enzymes
- Secretion of pancreatic bicarbonates
- Growth of exocrine pancreas and gallbladder
- Inhibition of gastric emptying (ensures adequate digestion time)
Both ___________ and __________ stimulate secretion of bile by the liver
Secretin
CCK
___________ is a major stimulator of gallbladder contraction
CCK
Which nerve is involved with gallbladder contraction and bile release into duodenum
Vagus (Acetylcholine)
