Physiology Flashcards
The large intestine is the principal site of dietary nutrient reabsorption. True/False?
False
Small intestine is the principle site of dietary nutrient absorption
What are the main functions of the large intestine?
Reabsorbs fluid + electrolytes
Stores faecal matter
The exocrine and endocrine “parts” of the pancreas are both part of the GI system. True/False?
False
Only the exocrine pancreas is part of the GI system
Name some accessory structures of the GI tract
Salivary glands
Pancreas
Liver
Gall bladder
Which muscle - smooth or skeletal - is predominant in the motility of the GI tract?
Smooth muscle
Which parts of the GI tract are under skeletal muscle control?
Mouth + pharynx
Upper oesophagus
External anal sphincter
Name two polysaccharides
Starch
Glycogen
Name two disaccharides
Sucrose
Lactose
Name three monosaccharides
Glucose
Fructose
Galactose
What are proteins broken down into?
Amino acids
Dipeptides
Tripeptides
The apical membrane of an enterocyte faces the lumen. True/False?
True
Which membrane of an enterocyte faces the blood?
Basolateral membrane
What are the 4 main layers of the GI tract wall, from innermost to outermost?
Mucosa
Submucosa
Muscularis externa
Serosa
What is the function of epithelial cells in the mucosa?
Absorption
What is the importance/function of the muscularis mucosa?
Can change shape/SA to facilitate absorption
What does contraction of circular muscle do to the lumen of the digestive tract?
Makes it narrower and longer
What does contraction of longitudinal muscle do to the lumen of the digestive tract?
Makes it shorter and fatter
What is the function of gap junctions between adjacent smooth muscle cells?
Enable slow wave of contraction to spread across smooth muscle sheet
Which cells drive slow wave electrical activity?
Interstitial cells of Cajal (ICCs)
What type of cells are ICCs?
Pacemaker cells
What must happen for ICCs to produce contraction?
Slow wave amplitude must reach threshold to trigger an action potential
The upstroke of the AP generated by ICCs is mediated by Na+ influx. True/False?
False
Mediated by Ca++ influx through Ca++ channels
The force of contraction in the GI tract is related to the number of action potentials discharged from ICCs. True/False?
True
The more APs fired, the greater the force of contraction
What determines the basal electrical rhythm of the digestive tract?
Slow wave electrical activity
All slow waves trigger contraction. True/False?
False
Threshold must be reached first
What is the net direction of luminal contents in the small intestine? Why?
Aboral direction
Fduodenum greater than Fileum
What is the net direction of luminal contents in the large intestine? Why?
Oral direction
Fdistalcolon greater than Fproximalcolon in order to allow some reabsorption to take place
What connects myenteric and submucosal plexi?
Interganglionic fibre tracts
What is the nervous system of the gut called?
Enteric nervous system
The parasympathetic system plays a bigger role in the enteric nervous system than the sympathetic system. True/False?
True
Parasympathetic outflow is thoraco-lumbar. True/False?
False
Cranio-sacral
Which nerve provides parasympathetic cranial outflow?
Vagus nerve
Which nerve provides parasympathetic sacral outflow?
Pelvic nerves
Post-ganglionic neurones are essentially intrinsic to the ENS. True/False?
True
Name a local nerve reflex of the GI tract
Peristalsis
Name a short nerve reflex of the GI tract
Intestino-intestinal reflex
What is the intestino-intestinal reflex?
Overdistention in one area of the intestine causes relaxation in the rest of the intestine
Name a long nerve reflex of the GI tract
Gastroileal reflex
What is the gastroileal reflex?
Stomach signals increase motility of the ileum - open the ileocaecal valve to empty chyme to prepare ileum to receive fresh chyme from the stomach
What happens to the propulsive (oral) segment in peristalsis?
Circular muscle contracts
Longitudinal muscle relaxes
What happens to the receiving (aboral) segment in peristalsis?
Circular muscle relaxes
Longitudinal muscle contracts
Which substances mediate contraction of circular/longitudinal muscle?
ACh
Substance P
Which substances mediate relaxation of circular/longitudinal muscle?
VIP
NO
What is the process of segmentation called in the large intestine?
Haustration
The upper oesophageal sphincter is controlled by smooth muscle. True/False?
False
Skeletal muscle
The lower oesophageal sphincter is controlled by smooth muscle. True/False?
True
Which anal sphincter - internal or external - is controlled by skeletal muscle?
External anal sphincter
Which receptors are stimulated when food reaches the pharynx? What do they do?
Pharyngeal pressure receptors send afferent impulses to the swallowing centre in the medulla
In swallowing, what happens to the larynx? Why?
Elevates to prevent food from entering the trachea
In peristalsis, circular fibres in front of the bolus contract. True/False?
False
Circular muscle behind the bolus contracts
What happens if food becomes lodged in the oesophagus?
Secondary peristaltic wave, more forceful than the first, is triggered locally
What are the 3 major pairs of salivary glands and their locations?
Parotids - over the masseter below ears
Submandibular - lower edge of mandible
Sublingual - under tongue
Sublingual salivary gland contribute towards 70% of saliva. True/False?
False
Submandibular gland contributes 70% of saliva
How much saliva is contributed to by the parotid glands?
25%
What are the antibacterial components of saliva?
Lysozyme
Lactoferrin
Immunoglobulins
What is xerostomia?
Dry mouth syndrome due to inadequate production of saliva
Primary saliva secretion occurs from where?
Acinus
Secondary saliva secretion occurs from where?
Duct cells
What does the primary saliva secretion consist of?
Na, K, Cl and HCO3
How is the primary saliva secretion modified by duct cells?
Remove Na and Cl
Add some K and HCO3
Diluted as no H2O movement
NaCl content of saliva is lower than that of the plasma. True/False?
True
Glucose content of saliva is higher than that of the plasma. True/False?
False
No glucose in saliva
When flow rate is high, HCO3 content of the saliva increases. True/False?
True
How does the simple (unconditioned) reflex stimulate salivary glands to increase saliva production?
Pressure receptors in mouth activate in presence of food and sent afferent impulses to salivary centre in the medulla
How does the conditioned reflex stimulate salivary glands to increase saliva production?
Think/smell/see food activates cerebral cortex which activates salivary centre in the medulla
Which nerves carry parasympathetic innervation of saliva production control?
Facial nerve
Glossopharyngeal nerve
What is the effect of parasympathetic stimulation upon saliva production?
Large volume
Watery
Enzyme rich
What is the effect of sympathetic stimulation upon saliva production?
Low volume
Thick
Mucus rich
What are the 4 main anatomical areas of the stomach?
Fundus
Body
Antrum
Pylorus
Where does most mixing/churning of food take place in the stomach?
Antrum
What is the substance produced when food mixes with gastric secretions?
Chyme
Name a substance which can be absorbed by the stomach
Ethanol
Thickness of smooth muscle lining decreases distally in the stomach. True/False?
False
Increasing thickness distally (antrum thickness greater than fundus thickness)
What occurs in Retropulsion?
Peristaltic wave forces chyme against closed pyloric sphincter, so chyme bounces back and undergoes more mixing
Name 2 gastric factors promoting gastric emptying
Volume of chyme (larger volume increases motility due to distention)
Consistency of chyme (thinner liquid facilitates emptying)
Which 2 duodenal factors delay gastric emptying?
Enterogastric reflex
Release of enterogastrones
What is the enterogastric reflex?
Duodenum signals to stomach that it has enough chyme so slow down emptying/peristaltic contraction
What is the effect of enterogastrones on gastric emptying?
CCK and secretin release from duodenum inhibit stomach contraction
Where is the pyloric gland area located?
Antrum
Where is the oxyntic mucosa area located?
Fundus and Body
Which cells are contained in the pyloric gland area?
D cells
G cells
What do D cells secrete?
Somatostatin
What do G cells secrete?
Gastrin
Which cells are contained in the oxyntic mucosa?
Parietal cells
Enterochromaffin-like cells
Chief cells
What do ECL cells secrete?
Histamine
What do parietal cells secrete?
HCl
Intrinsic factor
What do chief cells secrete?
Pepsinogen
What does autocatalytic mean with regards to pepsinogen and pepsin?
Pepsin formation triggers further pepsin formation from pepsinogen
What is the role of intrinsic factor in the oxyntic mucosa?
Binds vitamin B12
What is the role of histamine in the oxyntic mucosa?
Stimulates HCl secretion
What is the role of gastrin in the pyloric gland area?
Stimulates HCl secretion
What is the role of somatostatin in the pyloric gland area?
Inhibits HCl secretion
In the gastric parietal cell, present in the gastric pit of the ____ ____, CO2 and H2O combine under the enzyme ____ ____ which dissociates to form _ and ___.
___ is transported out of the cell via an antiporter in exchange for __, which is driven out into the canaliculus.
_ is secreted into the canaliculus via the ___ ___, and combines with __ to form ___.
In the gastric parietal cell, present in the gastric pit of the oxyntic mucosa, CO2 and H2O combine under the enzyme carbonic anhydrase which dissociates to form H+ and HCO3.
HCO3 is transported out of the cell via an antiporter in exchange for Cl, which is driven out into the canaliculus.
H+ is secreted into the canaliculus via the proton pump, and combines with Cl to form HCl.
What are Secretagogues?
Substances promoting secretion of HCl (gastrin, ACh, histamine)
In response to Secretagogues, where do proton pumps move from and to in the parietal cell?
Move from inactive tubulovesicles in the cytoplasm to being active in the apical membrane
What are the 3 phases of gastric secretion?
Cephalic
Gastric
Intestinal
What is involved in the cephalic phase?
Stomach is prepared to receive food by conditioned reflex, chewing or swallowing, leading to gastric secretion through ACh and GRP
What is involved in the gastric phase?
Distention due to food causes mechanoreceptors to augment secretion
What is involved in the intestinal phase?
Gastric secretion is halted through secretin, CCK and somatostatin as the stomach empties
What is the importance of the mucus gel layer on the surface of mucous secreting cells?
Prevents pepsin/HCl reaching the apical surface of the cells and damaging the cells
What are the two forms of starch?
Amylose
Amylopectin
Amylose and amylopectin are branched chain molecules. True/False?
False
Amylose isn’t but amylopectin is branched
Which type of bond links glucose monomers in amylose?
alpha-1,4
Which type of bonds link glucose monomers in amylopectin?
alpha-1,4
alpha-1,6 for branched chain
Glycogen is a branched chain polysaccharide. True/False?
True
Which type of bond links glucose monomers in glycogen?
alpha-1,4
alpha-1,6
Name two oligosaccharides (disaccharides)
Lactose
Sucrose
Which monomers make up sucrose?
Glucose and fructose
Which monomers make up lactose?
Glucose and galactose
Which enzyme carries out luminal digestion of starch?
alpha-amylase
What is starch broken down into in luminal digestion?
Oligosaccharides - e.g. maltose
Which enzymes carry out brush border digestion of maltose, lactose and sucrose?
Maltase
Lactase
Sucrase-isomaltase
What are oligosaccharides such as lactose, maltose and sucrose broken down into in brush border digestion?
Monosaccharides - e.g. glucose, fructose, galactose
Alpha-amylase breaks down all alpha-1,4 glucose linkages. True/False?
False
Only breaks down linear internal links - not terminal links, hence no production of glucose
Lactase can only break down lactose. True/False?
True
How is isomaltase unique?
It is the only enzyme that can split the branching of alpha-1,6 linkages
What is lactose intolerance?
Inability to digest lactose, caused by lactase insufficiency
Absorption of monosaccharides involves entry via the basolateral membrane and exit via the apical membrane. True/False?
False
Other way around!
What is meant by secondary active transport?
Transport either via cotransport or antiport
What are oligopeptides?
Dipeptides
Tripeptides
Some tetrapeptides
[products of protein digestion]
What denatures proteins in the stomach?
HCl
Which enzyme cleaves protein into peptides in the stomach?
Pepsin
Is pepsin essential for protein digestion?
No
What are the active enzymes that digest protein in the duodenum?
Trypsin Chymotrypsin Elastase Procaroxypeptidase A Procaroxypeptidase B
Where does most fat digestion take place?
Small intestine
Which enzyme cleaves off fatty acids from triglycerides in the stomach?
Gastric lipase
What is the main lipid digesting enzyme in the duodenum?
Pancreatic lipase
What do bile salts do to large lipid droplets?
Emulsify them into smaller droplets with a larger SA to increase affinity for lipase
Which enzyme acts as a cofactor for lipase to help it gain access to the triglyceride chain?
Colipase
Digestion of triglyceride by pancreatic lipase produces glycerol + 3 fatty acids. True/False?
False
Produces monoglyceride + 2 fatty acids
What is a mixed micelle?
Emulsified fat globule containing monoglyceride, fatty acids, phospholipid, bile salt and cholesterol
How are short and medium -chain fatty acids absorbed into capillaries?
Exit basolateral membrane via diffusion
What happens to long-chain fatty acids and monoglycerides once in the enterocyte?
Resynthesised to triglyceride in the ER and incorporated into chylomicrons
What coats the cholesterol ester-triglyceride complex to form a chylomicron?
Apolipoprotein (apo-B48)
How does the chylomicron exit the enterocyte? Where does it go?
Exocytosis into the lymphatic system
Which enzyme metabolises chylomicrons?
Lipoprotein lipase
What carries the free fatty acids and glycerol released by chylomicron degradation?
Albumin
What does a chylomicron remnant consist of?
Cholesterol and phospholipid
Which protein allows cholesterol absorption?
NPC1L1 protein
How does the scaffold containing cholesterol bound to NPC1L1 move around the cell?
Via myosin runners
When calcium concn is low, it is absorbed via Ca channels. Which vitamin increases expression for these channels?
Vitamin D
Ferric iron can be absorbed by the enterocyte. True/False?
False
Must be converted to ferrous iron (Fe2)
Ferrous iron can be absorbed via a cotransporter. Which ion is coupled with its transport?
H+
i.e. H+ dependent cotransport of iron
What is the other mechanism (other than receptor transport) by which iron can be absorbed by the enterocyte?
Through haem - haem is taken up and degraded by haem oxidase
What is the storage form of iron called?
Ferratin
What are the ranges for normal BMI?
18.5-25
What are the ranges for BMI classed as overweight?
25-29
What are the ranges for BMI classed as obese?
30-39
What are the ranges for BMI classed as morbidly obese?
Greater than 40
How is obesity “a disease of the brain”?
The brain sees new fat/weight as normal, and attempts to lose weight are seen as a threat to survival, so the new weight is defended
Lesioning ventromedial hypothalamus causes leanness. True/False?
False
Lesioning ventromedial hypothalamus causes obesity
Which lesioning part of the hypothalamus causes leanness?
Lateral part
Define satiation
Feeling of fullness during/following a meal
Define satiety
Period from end of one meal to beginning of next
What effects do satiation signals have during a meal?
Increased signals limit meal size, i.e. you can’t eat anymore
What is ghrelin?
A hunger signal - levels increase before a meal and decrease after a meal
Which 2 hormones report the “fat status” of fat stores to the brain?
Leptin
Insulin
Levels of leptin and insulin increase in the blood as more fat is stored. True/False?
True
Reduced leptin mimics starvation. True/False?
True
Name a drug that can be prescribed to tackle obesity
Orlistat
How does Orlistat work?
Inhibits pancreatic lipase to decrease triglyceride absorption
Vomiting is due to stomach contraction. True/False?
False
Stomach, oesophagus + sphincters are relaxed
Which centre coordinates vomiting in the brainstem?
Vomiting centre (VC) in the medulla oblongata
Does nausea always cause vomiting?
No
Toxic materials stimulate enterochromaffin cells to release which mediator of vomiting?
5-HT (serotonin)
Which 3 stimulants stimulate the CTZ in the brainstem to act on the VC to initiate vomiting?
Toxins
Mechanical activity/disease
Motion sickness
What effects do vagal efferents have on the oesophagus, stomach and small intestine in the vomiting reflex?
Oesophagus shortens
Stomach relaxes
Small intestine retrograde contraction
Place the parts of the small intestine in order from shortest to longest
Duodenum (0.25m)
Jejunum (2.5m)
Ileum (3m)
Which 3 components increase the SA of the small intestine?
Circular folds
Villi
Microvilli
Where is gastrin secreted from?
G cells of stomach + duodenum
Where is CCK secreted from?
I cells of duodenum + jejunum
Where is secretin secreted from?
S cells of duodenum
Where is motilin secreted from?
M cells of duodenum + jejunum
Where is ghrelin secreted from?
Gr cells of stomach, small intestine + pancreas
Distention, gastrin, CCK, secretin + parasympathetic activity all enhance the secretion of intestinal juice. True/False?
True
What is the migrating motor complex in the small intestine?
Strong peristaltic contraction spanning from stomach to end of ileum which clears debris and mucus between meals (housekeeper - migrating “mother” complex!)
Gastrin and CCK trigger the migrating motor complex. True/False?
False
Motilin triggers it; CCK and gastrin inhibit it
The exocrine pancreas secretes digestive enzymes from ____ cells and aqueous salt from ____ cells, collectively called pancreatic juice
The exocrine pancreas secretes digestive enzymes from acinar cells and aqueous salt from duct cells
What does the aqueous salt solution released from pancreatic duct cells do?
Neutralises acidic chyme in the duodenum
In the duodenum, proton is lost/added to blood and bicarbonate is lost/added to lumen; in the stomach, proton is lost/added to lumen and bicarbonate lost/added to blood
In the duodenum, proton is lost to blood and bicarbonate is added to lumen; in the stomach, proton is added to lumen and bicarbonate lost to blood
Acid/chyme in duodenum stimulates/inhibits the release of secretin, which stimulates/inhibits release of intestinal juice from pancreas
Acid/chyme in duodenum stimulates the release of secretin, which stimulates release of intestinal juice from pancreas
Fat and protein in the duodenum stimulates/inhibits the release of CCK, which stimulates/inhibits release of intestinal juice from pancreas
Fat and protein in the duodenum stimulates the release of CCK, which stimulates release of intestinal juice from pancreas
Describe haustration
Intermittent contraction of circular muscle in proximal colon at slow rate to allow contents to move but leave enough opportunity for reabsorption
Which nerve conveys efferents to cause either relaxation or contraction of the external anal sphincter?
Pudendal nerve
Reabsorption of water is largely driven by the reabsorption of which salt?
Sodium
Which mechanism is the most major in Na reabsorption in the post-prandial period in the jejunum?
Na-glucose and Na-amino acid cotransport
What is the effect of cAMP, cGMP and Ca2+ on NaCl absorption?
Reduce NaCl absorption
Where do epithelial Na channels (ENaC) mediate Na absorption?
Distal colon
Where does blood from the hepatic artery and hepatic portal vein meet and mix in the liver?
Sinusoids (fenestrated capillaries that enable blood to leak out into space of Disse)
The liver is made up of hexagonal lobules. List the vessels and ducts contained in each lobule
Central vein (branch of hepatic vein) Portal triad (hepatic portal branch + hepatic artery branch + bile duct)
What is the direction of blood flow in a liver lobule?
Inwardly through sinusoids towards the central vein
What is the direction of bile flow in a liver lobule?
Outwardly through canaliculi towards the bile duct
Canaliculi are formed by the basolateral membrane. True/False?
False
Canaliculi are formed by the apical membrane
Which membrane faces the space of Disse?
Basolateral membrane
Which 3 types of cell are located in the sinusoidal spaces?
Endothelial cells
Kuppfer cells
Stellate (Ito) cells
What is the function of endothelial cells in the sinusoidal space?
Fenestrated structure allows passage of solute, but not cells
What is the function of Kuppfer cells in the sinusoidal space?
Macrophages that remove bacterial matter and dead RBCs
What is the function of Stellate (Ito) cells in the sinusoidal space?
Store vitamin A within the space of Disse
May deposit collagen, beginning liver cirrhosis
Most bile is secreted by bile duct cells. True/False?
False
Most is secreted by the liver
Most of the bile entering the duodenum is reabsorbed in the terminal ileum. True/False?
True
