Physiology Flashcards
Which part of the digestive tract contains striated muscle?
Pharynx,
Upper 1⁄2 Oesophagus
External Anal Sphincter
What are the 3 important features for splanchnic circulation?
Large blood flow
Large reservoir function
Perfuses a diversity of organs
What percentage of blood is funneled to the liver by the Hepatic portal vein?
70% - deoxygenated blood
In which part of the digestive tract is a serosa missing?
Oesophagus & Distal rectum
What percentage of blood is coming from the Hepatic artery to the liver?
30%
What percentage of the nerve fibres in the Vagus are afferents?
75%
Where do motor neuronal cell bodies in the cranial division reside and what do the project via?
They reside in the medulla oblongata and project via the Vagus nerve
At what level is the Enteric nervous system present in the hierarchy of neural organization ?
Level 1
Fill in the blanks.” Motor neuronal cell bodies in the sacral s.c. project in the _________ to colon , rectum and internal sphincter.”
Pelvic nerve
What substance is released by parasympathetic Motor neuronal cell bodies in the sacral s.c. ?
Acetylcholine
What substance is released by the sympathetic postganglionic neurone when they synapse on other neurone of the ENS, blood vessels, mucosa and sphincters?
Nor-epinephrine
What are the two nerve networks by which the enteric nervous system works by?
Submucous plexus- Meissner’s plexus
Myenteric Plexus - Auerbach’s plexus
Where is the Myenteric plexus found?
Between the middle circular and outer longitudinal layers.
Where is the submucosal plexus found?
Between the submucosa & muscularis propria
What are the types of Neurones found in the Enteric Nervous system?
Sensory neurons - respond to stretch , tonicity and chemicals
Motor neurons- Innervate smooth muscles to elicit movement
Secretory neurons - Regulate endocrine and exocrine secretions.
Interneurones- innervate both plexuses
What substances are released that causes excitatory nerves to innervate muscles?
Acetylcholine (Ach) and Substance P ( SubP)
What substances are released that causes inhibitory nerves to innervate the muscles?
Nitric Oxide (NO) and Vasoactive intestinal polypeptide(VIP)
What is the function of the Submucousal plexus ( Meissner’s plexus)?
It has an exocrine & endocrine function
What is the function of the Myenteric plexus?
It controls peristalsis and other motor activities
Which substances are involved with Paracrine secretions for the GI tract ?
Histamine
Somatostatin
What substances are involved in Neurocrine secretions for the GI tract?
Vasoactive intestinal polypeptide(VIP)
Gastrin releasing peptide ( GRP)
Enkephalins
Gastrin, CCK, Secretin , GIP (Glucose- dependent intsulinotropic peptide), motilin and ghrelin are what type of secretory substances?
Endocrine secretions
Where is Ghrelin secreted from and what is its function?
It is secreted by epithelia in body of stomach and is a hormone that regulates food intake.
What are Neurocrines?
These are peptide released from nerve endings in the gut in response to a stimulus.
What stimulates or inhibits the release of endocrines or paracrines?
NEUROCRINES (duhh)
What are endocrines?
These are hormones released in response to a specific stimulus
What are paracrines?
These are substances which acts as local mediators on cells in its immediate environments.
Fill in the blanks. “ Paracrines are release from _______.”
Endocrine cells
What are the control centres that help in the regulation of chewing?
Brain stem ( medulla oblangata- vagus efferents)
Cerebral Cortex
Hypothalamus
Amygdala
What is the nerve that innervates the muscles of chewing?
Trigeminal nerve ( CN V)
What are the processes in the Chewing reflex?
- Once food is present in the mouth the REFLEX INHIBITION takes place on the muscles of mastication occurs and the lower jaw drops. This happens as there is no action potentials passing through efferent fibres.
- STRETCH REFLEX of the jaw muscles, there is a rebound contraction to raise the lower jaw. This allows for ..
- CLOSURE OF THE TEETH - Food is compressed against the linings of the mouth and there’s is reflex inhibition of the muscles of mastication occurring again
What are the structures by which swallowing mechanism are triggered by?
Afferent impulses from the trigeminal, glossopharyngeal, vagus nerves, hypoglossal nerves , pharynx and facial nerves.
What happens after the afferent fibres from nerves triggers the swallowing mechanism?
- These impulses are integrated in the nucleus of the tractus solitarius, the nucleus ambiguus and the dorsal motor nucleus of vagus.
- Then, the efferent fibers pass to the pharyngeal musculature and the tongue via the vagus, trigeminal, facial nerves , hypoglossal nerves and the nerves of the nucleus ambiguous .
What are the structures that make up the Dorsal Vagal Complex?
Dorsal motor nerve of Vagus
Nuclei of nucleus ambiguous
Tractus solitarius
Area postrema
Where does the Dorsal Vagal Complex reside?
Medulla oblongata
True or False? The Swallowing mechanism has 3 stages and 2 phases.
FALSE ! It has 2 STAGES and 3 PHASES
(2 S/ 3 P)
What are the two stages that occur for the swallowing mechanism?
Voluntary Stage
Involuntary Stage
What is another name for the Voluntary stage?
Buccal phase of Swallowing
What happens during the voluntary stage of the swallowing mechanism?
- Food is squeezed and rolled posteriorly by the tongue
- The tongue is elevated against the palate.
- The tongue then retracts and pushes bolus upward and backwards against hard palate towards soft palate and into the oropharynx.
- In the soft palate, the mechanical presence of bolus is sensed and the Involuntary stage is initiated.
What are the two phases in the involuntary stage of the swallowing mechanism?
Pharyngeal phase
Oesophageal phase
How long is the pharyngeal phase?
Less than 1 sec ( <1 sec)
How long is the oesophageal phase?
8-10 seconds
What is the normal pH of saliva ?
6.8-7 ( may increase to 8 as salivary production increases)
True or False? Duct cells produce the Primary secretion of saliva.
FALSE!! Acini cells do this.
What is the main purpose of duct cells in relation to salivary secretion?
They modify the secretion into a secondary secretion.
What is the name given to the functional unit of a salivary gland?
Salivon
What are the function of the myoepithelial cells which line the acinar cells?
Contraction of the myoepithelial cells serve to:
1. Expel formed saliva from the acinus into ducts.
- Prevent distention of acini and back flow.
- Lower resistance to flow through intercalated ducts
What is the amount of salivary secretions produced each day?
1500 ml/day
Which salivary gland produces the most saliva ?
Submandibular (70%)
What type of enzyme produced in saliva is used in starch digestion and what type of secretions is it found in?
Ptyalin ( alpha- amylase) , it’s found in serous secretions.
Which ions are actively secreted during primary secretions from acini?
Chloride Ions
True or False? Primary secretions are described as Hypotonic while Secondary secretions are described as Isotonic .
FALSE!!! Primary secretions are ISOTONIC
Secondary secretions of HYPOTONIC
” PI - Private Investigator”
“ SH- Secondary highschool”
What happens to the saliva secretion if there is inhibition of the Na +/ K+ / 2 Cl - co- transporter?
The saliva secretion DECREASES by about 65%
What are the main transporters in the duct cells that modify the primary secretion of saliva?
- Basolateral & apical Cl- channels
- Luminal Cl-/HCO3- exchangers
- Basolateral Na+/K+ ATPase creates the Na+ gradient
- Apical Na+ and K+ channel
- Basolateral Na+/HCO3- must be present to concentrate HCO3-
How else can HCO3 enter lumen from ductal cell?
Cystic Fibrosis Transmembrane conductance regulator (CFTR) chloride channel
What is the energy source for the CFTR channel?
cAMP
Fill in the blanks. The net result of a Secondary Secretion results in a ____________ in luminal Na+ and Cl - while there is a _________ in luminal K+ and HCO3- .
There is a DECREASE in Na + and Cl-
There is an INCREASE in K+ and HCO3 -
What happens during low rates of flow of saliva secretion?
The sodium and chloride content decreases while Potassium INCREASES significantly . This is because the duct cells can do its thanggg and work properly to produce the HYPOTONIC secondary secretion.
True or False? At low rates of flow of saliva secretion the saliva is Hypotonic and rich in K+ and HCO3-
TRUE!!
What happens to water during Primary secretion of saliva?
Water moves DOWN the osmotic gradient causing an Isotonic secretion.
What happens at High Rates of flow for saliva?
Na+ Cl - content INCREASES
Less time for secretion of K+
HCO3 - remains relatively high ( due to salivary agaonist.
SALIVA APPROACHES ISOTONICITY , rich in NaCl.
True or False, At both high and low rates of flow of salivary secretion the HCO3 content is high?
TRUE!!
True or False? The primary secretion of saliva produced is isotonic and has the same Na+, K+, Cl–, and HCO3– concentrations as plasma.
TRUE!!
In what type of salivary ducts does modification of secretions occur?
In LARGER(striated) duct NOT intercalated ducts
What is the name of the hormone that increases Sodium reabsorption and increases Potassium content of saliva?
Aldosterone
What are some of the enzymes contained in saliva?
Pytalin ( alpha amylase)
Muramidase
Lingual lipase
Which enzyme is responsible for fat digestion?
Lingual lipase
Which enzyme is a lysozyme that lyses an acid for some bacteria ex staphylococcus?
Muramidase - lyses muramic acid
Fill in the blanks. “ Relaxation of the Lower oesophageal sphincter is ______”
Neurally mediated
What is the term given to when food enters the stomach, the fundus and upper portion of the body relax and accommodate the food with little if any increase in pressure?
Receptive Relaxation
What is the relative constant Intragastric pressure ?
5 mmHg
What is the normal frequency for slow waves of the stomach?
Every 3-4 mins
What is the normal duration for slow waves in the stomach?
12-20 seconds
What is the name given to the pacemaker cells found in the Stomach?
Intestinal Cells of Cajal (ICC)
Where are the pacemaker cells of the stomach normally located?
At the junction of the fundus and body
True or False? Slow waves initiate contraction ONLY when the plateau potential exceeds threshold.
TRUE!!
Where are spike potentials normally seen in the stomach?
Pyloric antrum
Which diseases can arise as a result of a Gastrectomy?
Iron deficiency anaemia
Vitamin B 12 deficiency ( Megaloblastic anaemia)
What are symptoms that will occur after a patient has a gastrectomy?
“Dumping Syndrome” - tachycardia, sweating, nausea . This will occur because of Rapid gastric emptying.
Hypoglycemia
Hypovolemia
Hypotension
What parts of the stomach is classified to be apart of the Proximal Motor Unit?
Cardia, Fundus & Body
What parts of the stomach is classified to be apart of the Distal Motor Unit?
Body, Antrum, Pylorus & “ Antral Pump”
True or False? The Distal Motor Unit of stomach can be known as the Receptacle or Reservoir for incoming food.
FALSE!! The proximal unit is known as this because it accommodates ingested materials.
By what structure is the Distal Motor unit innervated by?
Vagal Excitatory Ach fibres
Fill in the blanks. “ ___________ set the frequency of slow waves.”
Pacemaker cells
What structure is known as the main regulator for intragastric pressure?
Proximal Motor Unit
Fill in the blanks. “ __________ determine the duration and strength of phasic contractions of the antral pump.
Gastric slow waves
Where does Gastric Filling occur?
In the Proximal Motor Unit
What is the term given to the constant stretch of Smooth muscles resulting in a decreased tension?
Adaptive Relaxation
What is Laplace’s Law?
The pressure is proportional to tension over the radius.
P = 2T/R
What is Retropulsion?
This occurs when food lying in the core of the stomach ( which is greater then 7mm in diameter) is forced back into the stomach.
The grinding and mixing of food is termed as?
Trituration
Which phase of Gastric Secretions can be classified as Neuro-humorally mediated?
Gastric phase
True or False? The Cephalic phase of the stomach is neurally regulated while the Intestinal phase is Humorally regulated.
TRUE!!
What is the average amount of Gastric Juice produced per day?
2-2.5 L
What is the normal pH of Gastric Juice?
1-2
What are some substances contained in Gastric Juices?
Pepsins I & II ( Endopeptidaes)
Mucus
Gastric lipases
Intrinsic Factor
Gelatinase
Water
H+ ions
What type of cells are found in Gastric (Oxyntic) Glands?
Surface epithelial cells
Mucous neck cells
Peptic ( Chief cells)
Parietal cells ( Oxyntic cells)
What substance are produced by peptic/chief cells?
Pepsinogens ( inactive)
Gastric lipase
Fill in te blanks. “ Pepsinogens are split by ______ to form active forms - pepsin I (Ph2) and pepsin II (pH3)
Hyrdrochloric Acid ( Hcl)
What substance is produced by Oxyntic cells?
Hcl & Intrinsic factor
What type of cells are found throughout the base of Gastric glands and what substance do they produce?
Enterochromaffin - like cells( ECL)
They produce histamine in response to gastrin
What is the name of the structure that produces GI hormones ?
Amine Precursor Uptake & Decarboxylation (APUD) system - found in base of gastric glands also.
What type of cells are found in the pyloric glands present in the antrum?
G- cells
D- cells
True or False? G - cells produce Gastrin while D- Cells produce Somatostatin.
TRUE!!
What is the name of the cells in the stomach that produces mucous?
Mucous neck cells & Surface epithelial cells
What type of cells produce bicarbonate ?
Surface epithelial cells
What is the name given to the structure that stabilises the mucous - bicarbonate ( HCO3) layer in Stomach?
Trefoil peptides
Where are parietal cells and chief cells found in the stomach?
In the fundus and body of stomach
What is the main component of gastric juice?
Gastric acid
What is the pH of Gastric acid?
0.87
At rest , where are proton pumps located?
They are sequestered within the parietal cell in a series of membrane compartments known as TUBULOVESICLES.
What happens to the tubulovesicles when the parietal cells become active?
These vesicles fuse with invaginations of the apical membrane known as canaliculi, thereby amplifying the apical membrane area and positioning the proton pumps to begin acid secretion
True or False? Hcl is secreted into the tubulovesicles via proton pumps during the active phase of parietal cell.
FALSE!! Hcl is secreted into the caniculli during the active phase of the parietal cells.
True or False? In the active Parietal cell, There is a paucity (little) of tubulovesicles , long microvilli and numerous mitochondria.
TRUE!!
What are the characteristics of a non- secreting parietal cell?
Many tubulovesicles present
Caniculli are internalized
Devoid of microvilli
What are the main receptors found on the parietal cell and to what substances do they bind with?
CCK-B ——-> Gastrin
H2 ————> Histamine
M3 ———–> Acetylcholine
What happens when Gastrin & Acetylcholine binds to its respective receptors on the parietal cell?
They promote secretion by elevating cytosolic free calcium concentrations ( Ca 2+)
GA –>C
What happens when Histamine binds to its respective receptor on the parietal cell?
Histamine promotes secretion by increasing intracellular cyclic adenosine 3′,5′- monophosphate (cAMP)
What are sources of H+ ions for the parietal cells?
- Cytochrome Oxidase system - pumps H+ in caniculli.
- Dissociation of water
- Dissociation of carbonic acid
What is the name of the enzyme that aids in the formation of carbonic acid?
Carbonic anhydrase
What are sources of bicarbonate (HCO3 )?
1) Hydroxyl (OH) when buffered by carbonic acid will produce bicarbonate.
2) Splitting of Carbonic Acid
True or False? Chloride Drift is a passive process.
FALSE!! It is an active process ( energy dependent ) because Cl- moves down its electrochemical gradient through channels in the apical membrane.
Which phase of the regulation of Gastric secretion is the shortest phase?
Cephalic phase - 30% of secretions
Which phase of the regulation of Gastric secretion is the longest phase?
Intestinal phase - 4hrs
Which phase gives the basal secretion of 1-5 mEq/hr ( about 10%)
Interdigestive Phase
Which phase of Regulation of Gastric secretion is done through direct vagal stimulation?
Cephalic phase
What are the stimuli that will activate the Cephalic phase?
Thought of food
Smell
Taste
Chewing
Swallowing
Direct Vagal stimulation during the cephalic phase produces what substances that will initiate a secretory response?
Gastrin-releasing peptide (GRP) and Acetylcholine
What is the stimuli that will activate the Gastric Phase?
1)Gastric Distention - the physical presence of the meal distends the stomach and activates stretch receptors.
2) Products of protein digestion.
What is the response to stimuli in the Gastric phase of the Stomach?
1) Increase release of gastrin
2) It provokes a “vago-vagal” reflex
3) Local intramural reflexes that further amplify secretion during the gastric phase.
What is the stimuli that will activate the Intestinal Phase?
1) Protein digestion products in duodenum.
2) Distention
What is the response to stimuli in the Intestinal phase?
1) Increase amino acids in blood
2) Intestinal endocrine cell
What stimulates the release of Histamine from ECL cells?
Gastrin
True or False? PGE2 INHIBITS acid secretion.
TRUE!!
Which phase of regulation of gastric secretions is mainly an inhibitory phase to acid secretion ?
Intestinal Phase
True or False? Histamine is a hormone.
FALSE!! Histamine is NOT a hormone, its a paracrine secretion.
What cells produces Secretin?
S- cells
Which enzyme produced by the Exocrine pancreas is always produced in the active form?
Anti-Trypsin
True or False? In relation to the Exocrine pancreas - In humans, HCO3- and Cl- are secreted into the cell lumen.
TRUE!!
In the exocrine pancreas, what is the name of the substance that activates opening of CFTR channels in response to Secretin stimulation?
cAMP
True or False? The cystic fibrosis transmembrane conductance regulator (CFTR ) is present in acinar cells but not duct cells.
FALSE!! In humans it is present in DUCT cells not acinar cells.
Fill in the blanks. “ In the exocrine pancreas , the rate of HCO3- secretion is dependent on __________.”
Dependent on the availability of luminal Cl-
Fill in the blanks. “ In the exocrine pancreas, the availability of luminal Cl- is dependent on _______.”
The opening of the apical Cl- CFTR channels.
What is the Two-component theory ?
- Acini secrete low volume of Na+ & Cl-
- Duct cells secrete large volume of Na+ & HCO3-
At low secretion rates of pancreatic juice , what happens?
At low rates of secretion, the Cl− concentration of the juice is therefore relatively high due to low secretion of HCO3- by duct cells or high substitution of ions . This results in a Na + & Cl - solution.
What is the name of the substance found in saliva which chelates iron and thus prevents the multiplication of organisms that require it for growth?
Lactoferrin
” Ferrin —> ferrous —> has to do with iron duhh”
What is the optimum pH of salivary amylase and at what pH does it become denatured?
Optimum pH -7
Becomes denatured at a pH of 4 .
What happens to the carbohydrate digestion if salivary amylase is absent?
There is no defect in carbohydrate digestion because the pancreatic enzyme is secreted in amounts sufficient to digest all the starch present.
True or False? Lipid lipase is the enzyme found in saliva which plays a role in the hydrolysis of dietary lipid.
FALSE!! LINGUAL lipase does this !!
Ntn don’t name lipid lipase lol
What is the embryological origin of Salivary glands?
Ectoderm
Fill in the blanks. “The intercalated ducts are lined by ______ cells while striated ducts are lined by _______ cells.”
- Intercalated ducts- Myoepithelial cells
Striated ducts- Columnar cells
What happens as saliva traverses the striated duct?
Sodium (Na+) is actively reabsorbed from the juice, and potassium (K+) is transported into it.
Fill in the blanks. In the salivary gland, the parasympathetic preganglionic fibers are delivered by ______________ to the _______________.
Delivered by the Facial & Glossopharyngeal nerves to the Autonomic ganglion.
Where does the sympathetic preganglionic nerves of the salivary gland originate from?
Cervical ganglion
What happens to the Osmolality of salivary secretion as the secretory rate of the salivon is increased?
The osmolality of saliva also increases as secretory rate increases
True or False? In Primary secretions of the saliva , the levels of Na+ , K+, Cl- and probably HCO3- are similar to that of plasma.
TRUE!!
Fill in the blanks. Saliva is _________ at all rates of secretion.
Hypo-osmotic
True or False? HCO3 remains high in low secretory rates of saliva but remains low in high secretory rates of saliva.
FALSE!! It remains high in both high and low secretory rates of saliva.
What is the Primary ion secreted by the acini cells?
Cl-
What is the name of the drug that inhibits the Na+/H+ exchanger in Cell 2 of the acinar cell of the salivary gland?
Amiloride
What is the name of the drug that inhibits the secretory mechanism for Cl− in the acinar cell of the salivary gland?
Ouabain
What is the gastric mucosa divided into?
Oxyntic gland area (secretes acid) and the pyloric gland area ( gastrin secreting)
In the resting parietal cell, where is the H+ /k+ ATP-ase pump found?
In the membranes of the tubulovesicles
Fill in the blanks. “In Gastric filling, ______________ underlie the peristaltic contractions .”
Basic Electrical Rhythm (BER) or Gastric Slow Waves
What are the two types of Primary Bile acids formed by the hepatocytes?
Cholic acid
Chenodeoxycholic acid
What are the two types of Secondary bile acids formed by the hepatocytes?
Deoxycholic acid ( soluble)
Lithocholic acid( insoluble)
Fill in the blanks. “Mixing waves are achieved by ______ while propulsive waves are achieved by ______.”
Mixing waves- Segmentation
Propulsive waves- Peristalsis
What are prolonged contractions that isolate segments and fosters absorption?
Tonic contractions
Where does Slow waves or BER NOT occur ?
In the oesophagus & Proximal stomach
How are slow waves conducted ?
Aborally
They are slow oscillatory waves .
Fill in the blanks. “ BER or Slow waves are initiated by _______.”
Interstitial cells of Cajal
What is the rate of slow waves in the duodenum?
12 waves per minute
What is the rate of slow waves in the Terminal Ileum?
8 waves per minute
What is the rate of slow waves in the Stomach?
3-4 waves per minute
True or False? The BER or slow waves decreases in colon.
FALSE!! It increases in the colon
True or False? Slow waves DO NOT initiate muscle contractions.
TRUE!! - They coordinate contractions
True or False? Epinephrine DECREASES the intensity of spike potentials when body is under stress.
TRUE!!
In the small intestine, Depolarization occurs due to what?
Ca2+ influx via L- type channels
In the small intestine, Repolarization occurs due to what?
K+ efflux & inactivation of Ca2+ channels
Fill in the blanks. “ A plateu phase occurs by a balance between _____ &_______.”
Calcium (Ca2+ )INFLUX &
Potassium (K+)EFFLUX
What substances can increase the intensity of Spike potentials?
- Acetylcholine
- Gastrin
- CCK
What does it mean when no spikes or action potential appears at the crest of the slow waves for the small intestine?
Contractions are absent
True or False? “When Action potentials are present, small amplitudes of contractions occur with each slow wave.”
FALSE!! When action potentials (spikes) are present, LARGE amplitudes of contractions occur with each slow wave.”
When is Peristalsis initiated in the small intestines?
It is initiated by the stretching of the gut wall.
In Peristalsis of the Intestines, what substance is released by local stretch receptors?
5-HT (Serotonin )
Fill in the blanks. “ Cholinergic neurons via a _________ direction activate enteric neurons to release _____ &_______ that causes smooth muscle contraction .”
Cholinergic neurons via a RETROGRADE direction activate enteric neurons to release SUBSTANCE P & ACETYLCHOLINE that causes smooth muscle CONTRACTION .”
Fill in the blanks. “ Cholinergic neurons via a _________ direction activate enteric neurons to release _____ &_______ to cause relaxation ahead of the stimulus .”
Cholinergic neurons via a ANTEROGRADE direction activate enteric neurons to release NITRIC OXIDE (NO) & VASOACTIVE INTESTINAL PEPTIDE (VIP) to cause RELAXATION ahead of the stimulus .”
True or False? Peristalsis is weaker than Segmentation contractions.
FALSE!! Segmentation Contractions are weak jelly backs.
When does Segmentation contraction occurs?
It occurs when a contraction is not coordinated with activity above and below the content .
What is the function of Peristalsis in the colon ?
It propels contents from Caecum towards rectum intermittently .
What is the Extrinsic innervation of the small intestines?
Extrinsic innervation is supplied by the vagus nerve and by nerve fibers from the celiac and superior mesenteric ganglia (parasympathetic)
Contractions in the small intestines occur for what duration?
Multiple intervals of 5 seconds
Who first discovered the Law of the Intestines?
Bayliss and Starling
What is the Law of the Intestines ( Peristaltic reflex) ?
Peristalsis occurs when the stimulation of the gut produces excitation above and relaxation below in orderly sequence.
- Contents of the gut move the material in an aboral direction and if they occur sequentially, they can propel a bolus the entire length of the gut in a short time.
During what phase of the slow waves does Spike potential activity occurs in the small intestine?
They occur only during the DEPOLARIZATION PHASE of the slow wave
True or False? In the small intestines , slow wave frequency sets the maximum frequency of contractions at any one site.
TRUE!!
Fill in the blanks. “ Digestion is assisted by ______ & _________”
Hcl & Bile
What is Digestion?
It is the orderly process that involves the chemical breakdown of food by enzymes.
Where are the main enzyme secretions that aid in digestion from?
- Glandular cells in the mouth
- Chief cells of stomach
- Exocrine pancreas
- Apical membrane of the enterocytes
What is Absorption ?
It is the process by which molecules are transported into the epithelial cells of the GI tract , then to the blood and lymph draining that region of the GI tract.
Where is. the main Absorptive area of the GIT?
Duodenum & Jejunm
What is Luminal (Cavital) Digestion?
Luminal Digestion involves enzymes secreted by salivary glands, stomach & pancreas.
What is Membrane Digestion ?
This is significant digestion due to hydrolysis by enzymes (synthesized by epithelial cells ) at the intestinal brush border.
What is the optimum pH of Ptyalin?
6.7
What are the chief dietary forms of Carbohydrates ?
- Polysaccharides
- Disaccharides
- Monosaccharides
What are examples of Polysaccharides?
- Starches
- Glycogen
- Cellulose ( Beta-1,4 links)
What are examples of Disaccharides?
Sucrose (25%)
Lactose (5%)
What are examples of Monosaccharides?
Glucose
Fructose
What are the two polysaccharides that are found in starch?
Amylopetin (80-90%)
Amylose ( alpha 1,4-links)
Which enzyme catalyses the hydrolysis of Alpha - 1,4 links of Starch?
Ptyalin ( alpha -1,4 amylase)
What branches of a Starch compound cannot be hydrolysed by the Alpha - amylases?
- Alpha-1,6 branching links
- Spare terminal –1,4 links
- Spare alpha–1,4 links next to branching points
What are the products formed when Alpha amylase cannot hydrolase specific parts of the Starch molecule?
Oligosaccharides
- Maltose
- Maltotriose
- Alpha - limit dextrins
Where are microvilli found in the small intestines?
On the apical surface of columnar epithelial cells.
What are the function of Paneth cells?
These cells secrete several agents that destroy bacteria (lysozymes and defensins) or produce inflammatory responses (tumor necrosis factor-α [TNF-α]).
What is the cell turn-over time for epithelial cells in the GIT ?
3 to 6 days
What is Contact digestion?
Contact digestion connotes activity by exogenous enzymes that become adsorbed on the epithelial surface.
What is an example of a membrane- bound enzyme?
Oligosaccharidases
True or False? The half-life of membrane-bound enzymes is shorter than that of the epithelial cells.
TRUE!!
Where is Vitamin B12 and Bile salts mainly absorbed?
In the Terminal Ileum
What is the major form of carbohydrate in the diet?
Amylopectin (plant-starch)
Fill in the blanks. “ _______ &_______ are dimers of Glucose.
Maltose & Trehalose
What is the name of the substance that activates salivary & pancreatic amylase?
Chloride (Cl - )
Where does Hydrolysis of Amylase occurs?
- In the lumen
- Surface epithelial cells
What is the name of the enzyme that hydrolyses the products of amylase along with other dietary sugars?
Brush border carbohydrases
What are the brush border enzymes?
M- Maltase
I -Isomaltase
L- Lactase
T- Trehalase
S- Sucrase
Fill in the blanks. “ In the stomach , Before Ptyalin is inactivated , 30-40% of Starch is hydrolysed to form _____ & 2% is hydrolysed to form _______.”
30-40% - Hydrolysed to form Maltose
2% - Hydrolysed to Isomaltose
What is the function of the Brush border enzymes in the Small intestines?
They split disaccharides & trisaccharides into MONOSACCHARIDES
What are the ONLY products of Sugar digestion?
Glucose
Galactose
Fructose
What is the rate-limiting step in sugar assimilation?
The absorption of free hexoses following hydrolysis
Which Carbohydrates are not digested in the Small intestines?
Cellulose & Hemicellulose
By what process is Fructose absorbed in the blood stream?
Facilitated Diffusion
What is the name of the transporter in which Fructose enters the enterocyte?
GLUT-5
Where is the GLUT-5 transporter located?
On the apical surface of the enterocyte
What is the name of the transporter in which Fructose enters the bloodstream?
GLUT - 2
Where is the GLUT-2 transporter located?
On the basolateral membrane of the enterocyte
What is the name of the transporter in which Glucose and Galactose enters the bloodstream?
GLUT -2
How is Glucose and Galactose absorbed into the enterocyte?
Via a Na+-dependent carrier system (SGLT-1)
By what process is Glucose and Galactose transported into the Interstitium?
Facilitated diffusion via GLUT -2 transporter.
By what process is Fructose transported into the Interstitium?
Facilitated diffusion via GLUT -2 transporter.
True or False? The GLUT-5 transporter is Na+ dependent.
FALSE !! It is Na+ INDEPENDENT.
True or False? Carbohydrates remaining in the intestinal lumen decreases the osmotic pressure of the luminal contents because of defects in digestion and absorption.
FALSE!! Carbohydrates remaining in the intestinal lumen INCREASES the osmotic pressure of the luminal contents because of defects in digestion and absorption
What is the name of the condition given to individuals who have an Intolerance of sucrose and isomaltose and is mostly found in children?
Sucrose intolerance due to congenital sucrase-isomaltase deficiency (CSID)
What is the most common congenital disaccharidase deficiency?
Lactase deficiency
In persons who are Glucose and Galactose intolerant , what transporter is absent?
These patients the SGLT-1 transporter is ABSENT.
How can one survive if they are glucose and galactose intolerant?
The patients thrive and show no symptoms when they are fed FRUCTOSE, this is because GLUT-5 transporter is present.
True or False? SGLT -1 transporter has a greater affinity for Galactose than glucose.
TRUE!!
- SGLT has L & T in its name and so does gaLacTose so it loves it more. The word Glucose doesn’t have T in it.
When is Active transport of Glucose & Galactose inhibited?
When there is a FALL in the luminal Na+ to LESS than 90 mMol/L.
What is the name of the substance that activates Trysinogen to Trypsin?
Enterokinase
What is the name of the transporter that transports short - chain amino acids ( glycine,alanine, serine, proline) INTO the cell along with H+?
Proton-dependent amino acid transporters—PAT proteins
Which part of the small intestine has a greater capacity to absorb di-peptides and tri-peptides?
Proximal Intestines
Which part of the small intestine has a greater capacity to absorb single amino acids?
Distal intestines
True or False? In Protein Digestion , tetrapeptides, pentapeptides, and hexapeptides are poorly absorbed.
TRUE!!
Fill in the blanks. “ Di -peptides and Tri-peptides are transported into enterocytes via _______.”
Peptide transporter (Pep T1) that requires H+
True or False? In protein digestion, transport systems have a higher affinity for L-isomers?
TRUE!!
Fill in the blanks. “ Glycine prefers ______ groups while cysteine prefers _______.”
Glycine prefers Imino groups
Cysteine prefers Basic groups
What is the name of the transporter in which H+/peptide co- transporter (PEPT1) is functionally coupled with ?
Na+/H+ exchanger, NHE3, in the same membrane.
What is the name of the enzyme that hydrolyzes the peptides in the enterocytes?
Cytoplasmic peptidases
What is Cystinuria ?
This is a congenital defect in the transport of basic amino acids and results in Kidney stones.
What is Hartnup diseases?
This is a Congenital defect in the mechanism that transports neutral amino acids. Ex. Loss of trytophan , Deficiciency of vitamin b complex- Niacinimide (Pellagra)
What are examples of the Neutral amino acids?
Valine, Alanine, Cystine
Arginine and lysine are what type of amino acids?
Basic amino acids
What are examples of acidic amino acids?
Glutamic acid, Aspartic acid
Where is Pepsin I found?
In the body of the stomach
Where is Pepsin II found ?
In the Antrum of the stomach
What are examples of Endopeptidases?
Trypsin,
Chymotrypsin,
Elastase
What are examples of Exopeptidases?
Carboxypeptidase, Aminopeptidase, Dipeptidase
Bile flows towards periphery _____________ to flow of blood.
Countercurrent
What’s the benefit of the countercurrent flow?
- improves liver’s efficiency in extracting substances
- minimizes concentration difference between substances in blood & bile
Hepatocytes remove substances from the blood and secrete them into biliary canaliculi. T or F?
True
