Physiology Flashcards
Function of the mouth and oropharynx
- chops and lubricates food, starts carbohydrate digestion
Function of the oesophagus
-propels food to stomach
Function of the stomach
- stores/churns food, continues carbohydrate,
- initiates protein digestion,
- regulates delivery of chyme to duodenum
Function of the small intestine
-principal site of digestion and absorption of nutrients
Function of the Large intestine
-Colon reabsorbs fluids and electrolytes, stores faecal matter before delivery to rectum
Function of the rectum and anus
- regulated expulsion of faeces
Name the accessory structures of the GI tract
- salivary glands
- pancreas
- the liver and gall bladder
What does aboral mean?
- contents of GI track travel towards the anus
What is the name given to the movement in the opposite direction of aboral?
- oral movement
Define chyme
-the pulpy acidic fluid which passes from the stomach to the small intestine, consisting of gastric juices and partly digested food.
What are the 4 main structures/linings of the Digestive tract?
- mucosa
- submucosa
- muscular externa
- serosa
What are the 4 major functions of the alimentary canal?
- motility
- secretion
- digestion
- absorption
What happens to the lumen of the GI tract when the circular muscle contracts?
- lumen becomes narrower and longer
What happens to the lumen of the GI tract when the longitudinal muscle contracts?
- intestine becomes shorter and fatter
What junctions are couple to smooth muscle in GI tract?
- gap junctions
- allows all of the smooth muscle cells to contract in a synchronous wave
what creates spontaneous activity in smooth muscle cells in the Gi tract?
- specialised pacemaker cells
- intrinsic (enteric)
- extrinsic (autonomic)
What is the importance of the interstitial cells of cajal (ICCs)
- pacemaker cells
- located between muscle layers
- drive slow waves that occur in smooth muscle cells
- Determines the frequency, direction and velocity of rhythmic contractions
Explain the relationship between thresholds and contraction in the intestines.
- contraction only occurs if the slow wave amplitude is sufficient to reach a threshold
- force is related to number of action potentials discharged
What 3 factors effect the threshold requirements?
- neuronal stimuli
- Hormonal stimuli
- Mechanical stimuli
Where are the post-ganglionic parasympathetic cells located?
- within the walls of the enteric nervous system
What is the excitatory influences of parasympathetic nerves?
- increased gastric secretion
- increased blood flow
- smooth muscle contraction
The sympathetic influence on GI tract is functionally less important than parasympathetic?
true/false?
- true
When is the preganglionic fibres of the sympathetic nerves located in the GI tract?
- prevertebral ganglia
Excitatory influences the sympathetic nerves on the GI tract?
- increased sphincter tone
Name an example of a local reflex nerve in the GI tract?
- peristalsis
How is BMI calculated?
= weight (kg) /square of height (m)
Consequences of obesity?
- stroke
- respiratory disease
- heart disease
- osteoarthritis
- demential
- fatty liver
- diabetes
- cancer
Why is it hard to loose weight once you have gained it?
- Long-term obesity induces brain re-programming
- Your brain views the extra weight (fat) as
normal & dieting as threat to body survival
3 CNS influences on energy balance and body weight?
- behaviour
- ANS activity
- Neuroendocrine system
Define Satiation
sensation of fullness generated during a meal
Define Satiety
period of time between termination of one meal and
the initiation of next
Define Adiposity
the state of being obese
What regulates output from the brain in regards to obesity?
- hypothalamus
Examples of satiation signals?
- cholecystokinin
- peptide YY
- Glucagon-like peptide 1
- oxyntomodulin
- obestatin
What is ghrelin
- a hunger signal
- Increase in levels before meals and decreases after
What are the 2 hormones that report fat status to the brain?
- leptin (made from fat cells)
- insulin (made from pancreatic beta cells)
What is hormone function in regards to obesity?
- inform brain (hypothalamus) to alter energy balance - eat less and increase energy burn
Reducing leptin does what____
- mimics starvation
- causing unrestrained appetite
Biological roles of leptin?
- food intake/energy expenditure/fat depostion
- peripheral glucose homeostasis
- maintenance of immune system
- bone formation
What is an over the counter obesity drug and how does it work?
- Orlistat
- reduces fat absorption
Define peristalsis
- a wave of relaxation followed by a contraction, usually in an aboral direction in the gut
Define segmentation in the GI tract
- segmentation - mixing or churning movements
- rhythmic contractions of the circular muscle layer
Define colonic mass movement
- powerful sweeping contraction that forces faeces into the rectum
What occurs in the stomach?
- starting point of digestion of proteins
- continues carbohydrate digestion
- Mixing of food with gastric secretions to produce a semi-liquid liquid chyme
What are the 2 portions of the stomach and what is its role
- Orad stomach –> stores food
- Caudad stomach –> propel semi-digested food
There is slow wave activity in the orad region of the stomach.
True or false
- FALSE
- there is no slow wave activity
- food is static
- continious weak tonic contractions
Why is it important that food is static in the orad region of the stomach?
- allows for carbohydrate partial digestion by salivary amylase
What occurs in the caudad region of the stomach?
- slow waves occur continuously
- propelling contents towards pylorus to the duodenum
What controls the stomach emptying
- strength of antral wave, or pump, determines escape of chyme through pyloric sphincter
- proportional to the amount of chyme in the stomach
- the consistency of the chyme
What are examples of stimuli within the duodenum that drive neuronal and hormone responses?
- fat
- acid
- hypertonicity
- distension
What are the 3 parts of the small intestine?
- duodenum
- jejunum
- ileum
What is received at the small intestine?
- chyme from the stomach
- pancreatic juice from the pancreas
- bile from the liver and gall bladder
The name of the process by which chyme is mixed with digestive juices in the small intestine?
- segmentation
- occurs after a meal
How is the small intestine adapted for absorption?
- circular folds of kerckring
- villi
- microvilli
- all increase the surface area
How many contractions per minute does the duodenum have?
- 12 per minute
- 9 Per minute in the ileum
What are migrating motor complex (MMC)?
- Occurs between meals
- strong peristaltic contraction
- clears the small intestine of debris
- inhibited by feeding and vagal activity
Gastrin is secreted by the small intestine into blood, what is it?
- from g cells of gastric Antrum and duodenum
- stimulated H+ Secretion by gastric parietal cells
Cholecystokinin (cck) is released from the small intestine into the blood, what is it?
- from I cells of the duodenum and jejunum
- released in response to mnoglycerides, fatty acids and amino acids
- stimulates the release of bile
- inhibits gastric emptying
Secretion of the small intestine lack digestive enzymes but contains_____
- mucus
- aqueous salts for enzymatic digestion
What controls the secretions of the small intestine?
- distension
- gastrin
- CCK
- parasympathetic nerve - increases
- sympathetic nerve - decreases
What are the endocrine secretions of the pancreas?
- insulin and glucagon
- secreted to blood
What are the exocrine secretions of the pancreas?
- digestive enzymes
- secreted to the duodenum
What do the pancreatic duct cell secrete?
- alkaline fluid
- release into the duodenum
- neutralises acidic chyme entering the duodenum
What are the three phases of control of pancreatic secretion?
- cephalic
- gastric
- intestinal
what must carbohydrates be converted to, to allow absorption?
- carbohydrates must be converted to monosaccharides for absorption
Oligosaccharides are ____ membrane proteins?
- integral membrane proteins
How many substrates does lactase have?
- has one substrate
- breaks lactose to glucose and galactose
Absorption of glucose and galactose are absorbed by _______ mediated by ______
- absorbed by secondary active transport mediated by SGLT1
Fructose is absorbed by______ mediated by____
- facilitated diffusion
- mediated by GLUT5
Exit for all monosaccharides in the duodenum is mediated by____
- facilitated diffusion
- by GLUT2
What is the large intestine compromised of?
- caecum and appendix
- colon
- rectum
- anal canal and anus
What are the divisions of the colon?
- ascending
- transverse
- descending
- sigmoid
Which part of the large intestine has thickened smooth muscle?
- internal anal sphincter
What is the name of the ‘sac-like’ bulges in the large intestine and what causes them?
- haustra
- activity of the taeniae coli and circular muscle
What is the function of the caecum and appendix?
- no specialised function in humans
how is entry permitted into the caecum?
- gastroileal reflex in response to gastrin and CCK
What is obstructed during appendicitis?
- appendiceal orifice
What are the primary functions of the colon?
- absorption (Na+, Cl- and H20)
- absorption (fatty acids)
- secretion
- to store colonic contents
- periodically eliminate faces
Why does the large intestine absorb fatty acids?
- carbohydrates not absorbed by the small intestine are fermented by colonic flora to short chain fatty acids
The colon has villi to increase surface area
True or false?
- FALSE
- the colon lacks vili, instead it has colonic folds and crypts, microvilli to increases area
What are the 3 sources of motility in the large intestine?
- haustratration
- peristaltic propulsive movements
- defaecation
What is haustration?
- movement of haustra
- activity of the taeniae coli and circular muscle
Explain mass movement
- simultaneous contraction of large section of the circular muscle of the ascending and transverse colon
- triggered by a meal
Explain defaecation
- mass movement - rectum fills with faecal matter
- activation of rectal stretch receptors
- activation of afferents to brain/spinal cord
- relaxation or contraction of skeletal muscle of external anal spnicter
Gas released by the anus comes from where?
- swallowed air
- bacteria in the colon which attacks forms of carbohydrates that are indigestible to humans
- gas that is not absorbed by the large intestine
Name drugs that can be used in IBS?
- Linaclotide (peptide drug)
- amitriptyline
Name drugs that can be used in IBD?
- Glucocorticoids
- aminosalicylates
What are ingested lipids compromised of?
- fats/oils
- phospholipids
- cholesterol
- fatty acids
What must fats be converted to?
- emulsion of small oil droplets suspended in water
What causes emulsification?
- mouth
- stomach (gastric curing)
- small intestine (segmentation and peristalsis, mixing with pancreatic and biliary secretions)
How are emulsion droplets stabilised?
- addition of a coat of amphiphilic molecules that form a surface layer on the droplets
What are TAGs?
- triacylglyerol
- 1 glycerol molecule
- 3 fatty acids
How are TAGs digested?
- as they are extremely hydrophobic they are hydrolysed by water and gastric lipase
- form diacylglyerol and free fatty acid
Where does the lingual phase of digestion occur?
- the mouth
Short and medium chain fatty acids are absorbed by the stomach, but long chain fatty acids are not
True or false?
- true
Where does the intestinal phase of digestion occur?
- duodenum
- by pancreatic (TAG) lipases
Where is pancreatic lipase secreted from in response to what?
- secreted from acinar cells
- in response to CCK
Gastric lipase breaks triacylglyercol to what?
- diacylglycerol + free fatty acid
Pancreatic lipase breaks triacylglyerol to what?
- 2-monoacylglyerol + 2 free fatty acids
What is the role and characteristics of bile salts?
- released in the duodenum in bile from the gall bladder in response to CCK
- Help emulsify large lipid droplets to small droplets
- amphipathic
- increase the surface area for attack by pancreatic lipase - but block for TAG
What does a failure to secrete bile salts result in?
- lipid malabsorption
- secondary vitamin deficiency
What is colipase?
- amphipathic polypeptide
- binds to bile salts and lipase allowing access by the latter to try and di- acylglycerols
What is procolipase activated by? and what does it become?
- activate by: trypsin
- becomes : colipase
How do small/medium fatty acid chains enter the enterocyte?
- fatty acid translocases
- transport proteins
What happens to the long chain fatty acids and monoglycerides during lipid absorption?
- resynthesized to triglycerides
- incorporated into chylomicrons
How is cholesterol absorbed?
- NPC1L1 proteins
Where are newly formed chylomicrons sent?
- to the lymph
What is calcium absorption regulated by?
- 1,25-dihydroxyvitamin D3
- aka calcitriol
What would a deficiency in iron cause?
- microcytic anaemia
What would happen due to an excess of iron?
- toxic
- accumulation in the liver, pancreas and heart
What state is most dietary iron?
- Fe3+
- oxidised form
What form of iron can be absorbed across the apical membrane of the duodenal enterocytes?
- reduced form
- Fe2+
What does Fe2+ bind to in the stomach?
- gastroferrin
What oxidises Fe2+
Hephaestin
What is the main transport protein of iron in the body?
- transferrin
How is vitamin B12 obtained from the diet?
- ingested bound to protein
- stomach releases the b12
- haptocorin secreted in saliva binds to the b12
- digested by pancreatic proteases
- b12 absorbed by terminal ileum
How are fat soluble vitamins absorbed?
- they are incorporated into mixed micelles with other lipids and bile acids in the lumen of the small intestine
- enter the enterocyte largely by diffusion.
What digestion occurs in the stomach?
- continuation of carbohydrate digestion (salivary amylase)
- start of protein digestion (pepsin and HCl)
Explain retropulsion?
- mixes gastric contents reducing chyme to small particles to pass through the pylorus
What are the duodenal factors that influence stomach emptying?
- neuronal responses –> enterogastric reflex
- hormonal responses –> release of enterogastrones (cck)
D cells secrete?
- somatostatin
G cell secrete?
- gastrin
Enterochromaffin-like cells secrete?
- histamine
Function of HCl?
- activates pepsinogen to pepsin
- kills microorganisms
- denatures proteins
What is an intrinsic factor for?
- binds vitamin B12
What is gastroferrin
- binds Fe2+
What does histamine do?
- increases HCl secretion
Explain HCl secretion by parietal cells?
- CO2 enters parietal cells from basolateral end
- combines with water to produce H2CO3
- H2CO3 –> HCO3- + H+
- HCO3 leaves cell and CL- enters
- H+ leaves through proton pump and K+ enters
- K+ leaves through K channel
- Cl- leaves through Cl- channel
- Cl and H+ Combine in stomach lumen
What are the 3 phases of gastric acid secretion?
- cephalic phase (head)
- gastric phase
- intestinal phase
Absorption of water is a ________ process?
- passive process
Absroption of water is driven by the transport of ______
- solutes
Define diarrhoea in terms of fluid loss?
- loss of fluid and solutes in excess of 500ml/day
Where does Na+/H+ transport occur?
- ileum and proximal colon
Where does Na+/glucose co-transport occur?
- jejunum
CFTR closed = ____ secretions
-little
What causes diarrhoea?
- impaired absorption of Na+
- no absorption of solutes
- hypermobility
What does nausea involve?
- pallor
- sweating
- salivation
- perisalsis in opposite direction
Define retching?
- rhythmic reverse peristalsis of the stomach and oesophagus
- dry - no efflux of vomitis
Define vomiting?
- forecful expulsion of gastric contents out of the mouth
Explain the pathway of vomiting
- forceful inspiration, closure of rima glottiddis
- relaxation of LOS
- Contraction of diaphragm
- opening of UOS
- ejection of gastric contents
Where is the vomiting centre located?
- medulla of the brainstem
What are the consequences of severe vomiting?
- dehydration
- loss of electolytes
- hypokakaemia
- rare –> mallory weiss tear
Ondanestron is what class of anti-emetic drug?
- 5-HT3 receptor antagonist
- supress chemo side effects
Hyosine is what class of anti-emetic drug?
muscarininc acetylcholie receptor antagonist
- used for motionsickness
Cyclizine is what class of anti-emetic drug?
- histamine H1 receptor antagonist
- motionsickness
- can cause drowsiness
Domperiadone is what class of anti-emetic drug?
- used fr drug induced vomiting
- not effective for motionsickness
