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Physiology Flashcards

1
Q

Function of mouth and oropharynx?

A

Chops and lubricates food, starts carbohydrate digestion, propels food to oesophagus

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2
Q

Function of oesophagus?

A

Propels food towards the stomach

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3
Q

Function of stomach?

A

Stores/churns food, continues carbohydrate, initiates protein digestion, regulates delivery of chyme (fluid that is passed from stomach to intestine, acidic and uneven) to duodenum

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4
Q

Function of small intestine?

A

Principal site of digestion and absorption of nutrients

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5
Q

Function of the large intestine?

A

Colon reabsorbs fluids and electrolytes, stores faecal matter before delivery to rectum. No absorption occurs here.

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6
Q

Function of rectum and anus?

A

Regulated expulsion of faeces

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7
Q

4 layer generalised structure of the GI wall?

A
  1. Mucosa
  2. Submucosa
  3. Muscularis Externa
  4. Serosa
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8
Q

What layer is the submucous (Meissner’s) plexus contained within?

A

The submucosa

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9
Q

What layer is the myenteric (Auerbach’s) plexus contained within?

A

Muscularis externa

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10
Q

GI motility is mostly due to activity of _____1______
Circular muscle contraction results in _____2_______
Longitudinal muscle contraction results in ______3______
Muscularis mucosae contraction results in _______4_________

A

1 smooth muscle
2 lumen becomes narrower and longer (it is squeezed against pressure so by narrowing it, it becomes longer)
3 intestine becomes shorter and fatter (by shortening it, it becomes fatter)
4 change in absorptive and secretory area of mucosa (folding), mixing activity. All contents are evenly mixed and exposed to epithelium.

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11
Q

In the stomach, small, and large intestine spontaneous electrical activity occurs as __1___ waves - rhythmic patterns of membrane depolarization and repolarization that spread from cell to cell via __2___ junctions

A

1 slow

2 gap

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12
Q

Spontaneous activity across the coupled GI cells is driven by specialised pacemaker cells called ________ which are largely located __________

A

interstitial cells of Cajal (ICCs)

between the circular and longitudinal muscle layers

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13
Q

Smooth muscle in the GI tract is _______ which means _______

A

single unit smooth muscle
the electrical excitation spreads from cell to cell (not all are directly innervated though) and the contraction happens at the same time as a wave.

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14
Q

Slow wave activity happens all the time- fed or starving state however _______________________________

A

Depolarising slow waves do not necessarily result in contraction

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15
Q

Contraction in the intestines occurs only if ___________________1______________________
____2______ of slow wave is ultimately what influences whether contraction will happen.

A

1) the slow wave amplitude is sufficient to reach a threshold to trigger smooth muscle cell calcium action potentials (spikes)
2) Starting point

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16
Q

3 things that can influence whether slow wave aptitude reaches threshold?

A

Neuronal stimuli
Hormonal stimuli
Mechanical stimuli

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17
Q

Parasympathetic nerve supply of the GI system is by _____1______ and _______2_______

Preganglionic fibres releasing Ach synapse with ganglion cells within ______3_____

Excitatory influences result in increased __________________4____________________________

Inhibitory influences result in relaxation ____________________5______________________

A

1) Vagus nerves
2) Sacral nerves S2-4
3) the enteric nervous system
4) gastric, pancreatic and small intestinal secretion, blood flow and smooth muscle contraction
5) of some sphincters, receptive relaxation of stomach

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18
Q

Sympathetic nerve supply of the GI system is by _______1_________

Preganglionic fibres (releasing ACh) synapse in the _____2_______

Postganglionic fibres (releasing NA) innervate mainly _____3_____

Excitatory influences ____4_____

Inhibitory influences ______5_________

A

1) thoracolumbar region
2) directly onto cells
3) enteric neurons
4) Increase sphincter tone
5) Decrease motility, secretion and blood flow

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19
Q

The enteric nervous system is

A

a division of the autonomic nervous system that governs the GI tract

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20
Q

Explain what happens in peristalsis

A

Behind the food bollus the circular muscle contracts and the longitudinal muscle relaxes

In front of the food bollus the circular muscle relaxes and the longitudinal muscle contracts

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21
Q

What is segmentation?

A

rhythmic contractions of the circular muscle layer that mix and divide luminal contents. The position of the contractions varies so food is propelled forward and backwards with no overall direction of movement. This finely chops up the chyme and delays any forward movement allowing time for both digestion and absorption. This occurs in the small intestine in the fed state and in the large intestine where it is called haustration.

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22
Q

What is colonic mass movement?

A

A powerful sweeping contraction that forces faeces into the rectum – occurs a few times a day often after a meal.

Propels faeces in to the rectum (normally nearly empty) triggering the defaecation reflex in response to rectal stretch

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23
Q

What is migrating motor complex?

A

A powerful sweeping contraction from stomach to terminal ileum

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24
Q

Explain tonic contractions

A

These are sustained contractions:

  • low pressure - organs with a major storage function (e.g. stomach)
  • high pressure - sphincters
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25
How many sphincters are there? What is there order from mouth to anus?
``` 6 Upper oesophageal sphincter Lower oesophageal sphincter Pyloric sphincter Ileocaecal valve Internal (smooth muscle) and External (skeletal muscle) anal sphincters where internal sits within external bu both are at same level. ```
26
Function of upper oesophageal sphincter?
This is skeletal muscle and it relaxes to allow swallowing and closes during inspiration
27
Function of the lower oesophageal sphincter?
Relaxes to permit entry of food to the stomach and closes to prevent reflux of gastric contents to the oesophagus
28
Function of Pyloric sphincter?
Regulates gastric emptying, usually prevents duodenal gastric reflux
29
Function of Ileocaecal valve?
Regulates flow from ileum to caecum- distension of ileum opens, distension of proximal colon closes
30
Why is it difficult to lose weight once it is gained?
Increased body fat alters brain function. Long term obesity induces brain re-programming. Your brain views the extra weight as normal and dieting as threat to body survival.
31
The site of integration of feeding behaviour is the ____1_____ The neural centre responsible is the _______2______ The three basic concepts that underly this control mechanism are _________3___________
1 brain 2 hypothalamus 3 satiety signalling, adiposity negative feedback signalling and food reward
32
Definition of satiation
Sensation of fullness generated during a meal
33
Definition of satiety
Period of time between termination of one meal and the initiation of next
34
Definition of adiposity
The state of being obese
35
Five examples of satiation signals are...
``` Cholecystokinin (CCK) Peptide YY (PYY3-36) Glucagon-like peptide 1 (GLP-1) Oxyntomodulin (OXM) Obestatin ```
36
What is the hunger signal?
Ghrelin
37
Long term control of weight is by two hormones, describe these.
Leptin - made & released from fat cells Insulin - made & released from pancreatic cells Levels in blood increase as more fat is stored In the brain they tell the brain to alter energy balance and eat less and increase energy burn. In the obese state this malfunctions
38
If you have reduced leptin what happens?
The body mimics starvation- you have no appetite control- you are constantly hungry
39
Does injecting individuals with leptin work to reduce their weight?
Injecting lectin works in individuals who lack leptin | However, the vast majority of obese individuals have high levels of leptin and they have increased leptin resistanc.
40
The stomach is a ____1__ shaped bag that relaxes receptively driven _____2___ to accommodate food from the oesophagus
1) J | 2) vagus
41
What are the 2 mechanical regions of the stomach?
Orad- fundas and proximal body | Caudad- distal and antrum
42
In the orad region of the stomach there is no ____1____ activity instead contractions are due to the _____2_____ The result is intermittent propulsion of products to the _____3_____ and stomach size _____4______
1) slow wave 2) thin musculature 3) caudad region 4) decreases as it empties
43
What does the minimal mixing of products in the orad region of the stomach allow?
Carbohydrate partial digestion by salivary amylase
44
In the caudad region ____1___ occur continuously but not all reach threshold. Velocity of contraction ___2____ towards the junction overtaking the movement of ____3___ which results in ______4_____ of chyme allowing _______5_________
1) slow waves 2) increases 3) chyme 4) retropulsion 5) mixing of gastric products
45
Strength of antral wave determines escape of chyme through pyloric sphincter this is governed by ?
Gastric and duodenal factors
46
The rate of emptying of the stomach is proportional to ....
the volume of chyme in the stomach
47
The duodenum must be ready to receive chyme, how can it delay stomach emptying?
Neuronal response: the enterogastric reflex – decreases antral activity by signals from intrinsic nerve plexuses and the ANS Hormonal response – release of enterogastrones [e.g cholecystokinin CCK)] from duodenum inhibits stomach contraction
48
What are the 2 secretory regions of the stomach?
the oxyntic gland area (proximal stomach including the fundus and body) the pylorlic gland area (distal stomach, designated the antrum)
49
What do D cells secrete? | What is its purpose?
Somatostatin | inhibits HCl secretion
50
What do Enterochromaffin-like cells secrete? | What is its purpose?
Histamine | stimulates HCl secretion
51
What do G cells secrete? | What is its purpose?
Gastrin | stimulates HCl secretion
52
What do chief cells secrete? | What is its purpose?
Pepsinogen | inactive precursor of the peptidase, pepsin. Note: pepsin once formed activates pepsinogen (autocatalytic)
53
What do parietal cells secrete? | What is the purpose of these secretions?
HCl activates pepsinogen to pepsin denatures protein kills most (not all) micro-organisms ingested with food Intrinsic factor and Gastroferrin bind vitamin B12 and Fe2+ respectively, facilitating subsequent absorption
54
What is the only absolutely essential function of the stomach?
produce intrinsic factor- it aids the absorption of vitamin B12. If there is no intrinsic factor is vitamin B12 cannot be absorbed, will get a type of anaemia.
55
What are the three phases of gastric acid secretion and inhibition?
Cephalic phase Gastric phase Intestinal phase
56
Describe the cephalic phase that results in gastric acid secretion
(‘in the head’) – before food reaches the stomach preparing it stomach to receive food. This is driven directly and indirectly by the CNS and vagus nerves (CN X).
57
Describe the gastric phase that results in gastric acid secretion
Occurs when food is in stomach. It involves both physical and chemical mechanisms. Distension of the stomach due to the food activates reflexes that cause acid secretion.
58
Describe the cephalic phase that results in gastric acid inhibition
Vagal nerve activity decreases upon cessation of eating and following stomach emptying
59
Describe the gastric phase that results in gastric acid inhibition
``` antral pH falls when food exits stomach (due to decreased buffering of gastric HCl) – release of somatostatin from D cells recommences, decreasing gastrin secretion prostaglandin E2 (PGE2) continually secreted by the gastric mucosa acts locally to reduce histamine- and gastrin-mediated HCl secretion ```
60
Why doesn't the stomach digest itself?
It has a sticky protective mucus layer that prevents protons from reaching the surface but even if they do they are neutralised by bicarbonate contained within the layer.
61
How does perastalsis in the interdigestive or fasting state occur?
Migrating motor complex
62
Describe the migrating motor complex
occurs between meals every 90 – 120 min strong peristaltic contraction slowly passing length of the intestine clears small intestine of debris, mucus and sloughed epithelial cells between meals – ‘housekeeper function’
63
What is the migrating motor complex inhibited by?
feeding and vagal activity
64
Seven hormonal secretions of the small intestine?
``` gastrin secretin cholecystokinin GIP glucagon like peptide 1 motlilin ghrelin ```
65
What does secretin from the small intestine promote and what is it released from?
from S cells of duodenum, released in response to H+ and fatty acids in lumen promotes secretion of pancreatic and biliary HCO3-
66
What does motilin from the small intestine promote and what is it released from?
from M cells of duodenum and jejunum, secreted during fasting state initiates the migrating motor complex
67
Succus (juice) of the small intestine varies throughout what things does the secretion usually contain?
mucus – for protection/lubrication (from goblet cells) | aqueous salt - for enzymatic digestion (mostly from the crypts of Lieberkühn)
68
Pancreatic endocrine secretions?
insulin and glucagon into the blood
69
Pancreatic exocrine secretions?
digestive enzymes (acinar cells), aqueous NaHCO3- solution (duct cells) – secreted to the duodenum collectively as pancreatic juice
70
Duct cells secrete 1 – 2 litre of _____1______into the duodenum per day This neutralises acidic ___2___ entering the duodenum provides optimum ___3__ for pancreatic enzyme function protects the mucosa from ____4_____
1) alkaline (HCO3- - rich) fluid 2) chyme 3) pH 4) erosion by acid
71
What must all carbohydrate be converted to for absorption?
Monosaccharides glucose, galactose or fructose
72
Describe the role of alpha amylase in carbohydrate absorption
breaks down linear internal α-1,4 linkages but not terminal α-1,4 linkages. Hence, no production of glucose cannot cleave α-1,6 linkages at branch points (in amylopectin) or α-1,4 linkages adjacent to branch points products are thus linear glucose oligomers (maltotriose, maltose) and α-limit dextrins.
73
What do Oligosaccharidases do?
Break down oligosaccharides into monosacharrides
74
Four examples of Oligosaccharidases?
Lactase Maltase Sucrase Isomaltase
75
Where does digestion of glucose, galactose and fructose take place? ie the products of carbohydrate digestion?
Duodenum and Jejenum
76
Glucose and galactose are absorbed by ______1____ and fructose is absorbed by _____2_______Exit for all monosaccharides is mediated by facilitated diffusion by __3___
1) secondary active transport (SGLT1) 2) facilitated diffusion (GLUT-5). 3) GLUT-2
77
Explain the mode of operation for SGLT1
1. 2 Na+ binds: 2. Affinity for glucose increases, glucose binds: 3. Na+ and glucose translocate from extracellular to intracellular: 4. 2 Na+ dissociate, affinity for glucose falls: 5. Glucose dissociates: 6. Cycle is repeated The transporter is also permeable to water and each cycle thousands of water molecules are moved from the lumen and into the enterocytes and ultimately back into the rest of the body.
78
Protein must (after the first six months of life) be digested to ___1___ and amino acids for efficient absorption ___2__ major pathways exist
1) oligopeptides | 2) four
79
Initial digestion of proteins in the stomach involves...
denaturation by HCl | cleavage into peptides by pepsin
80
Digestion of proteins in the duodenum involves...
5 pancreatic enzymes some are exopeptidases that break peptide bonds from end-pieces of terminal amino acids and some are endopeptidases that break peptide bonds of nonterminal amino acids (i.e. within the molecule).
81
Where can additional break down of oligopeptides take place after digestion in duodenum and stomach
At the brush border or in cytoplasm of enterocytes
82
Amino acids are transported across the apical membrane via a variety of amino acid transporters. Oligopeptides are transported across the apical membrane by the _______1________ (IMPORTANT KNOWLEDGE) Oligopeptides with the cytoplasm are hydrolysed to amino acids by ____2_____ within the enterocyte Amino acids exit the enterocyte across the basolateral membrane by several, _______3______
1) H+/oligopeptide co-transporter, PepT1 2) peptidases 3) Na+-independent. transporters
83
For digestion an absorption what must lipids be converted from and too?
Must be converted from solid fat and oil masses into an emulsion of small oil droplets suspended in water
84
What enzyme aids the breakdown of TAGs?
Lipases
85
In the stomach what stimulates release of gastric lipase?
secreted in response to gastrin from chief cells
86
What stimulates secretion of pancreatic lipase?
CCK | Note CCK also stimulates bile flow
87
Describe the role of bile salts, where are they released from and into, why?
Bile salts released into the duodenum in bile from the gall bladder in response to CCK act as detergents to help emulsify large lipid droplets to small droplets
88
Where are the final products of lipid digestion stored in and released from?
Mixed Micelles
89
3 ways different lipids are absorbed?
Short chain and medium fatty acids diffuse through the enterocyte, exit through the basolateral membrane and enter the villus capillaries Long chain fatty acids and monoglycerides are resynthesized to triglycerides in the endoplasmic reticulum and are subsequently incorporated into chylomicrons Cholesterol is transported by endocytosis
90
Ca2+ absorption can occur by two mechanisms- passive and active. With [Ca2+] in chyme < 5 mM absorption is mainly ___1_____
1) active
91
It is __1___ iron form that can be absorbed and this binds to ___2____ in the stomach Reduction of Fe3+ is done by ________3_________
1 Fe2+ 2 gastroferrin 3 HCl, vitamin C or brush border cytochrome b ferric reductase
92
Fat soluble vitamins? What is needed for these to be absorbed?
bile secretion | intact intestinal mucosa
93
In the large intestine electrolyte absorption which drives the absorption of water is mediated by ____1_____ Ion secretion is mediated by _______2______
1) surface epithelial cells (colonocytes) | 2) crypt cells
94
The large intestine is divided into a series of saccule called ______ and these are not static The process of _____ is a very slow form of segmentation this allows time for _______
haustra haustration fluid and electrolyte reabsorption
95
3 patterns of motility in the large intestine?
Haustration (non-propulsive segmentation) Peristaltic propulsive movements (mass movement) Defaecation (periodic egestion)
96
The internal anal sphincter is controlled by ____1______ fibres which relax involuntarily. The external anal sphincter is controlled by a ____2______ nerve supply When the rectum is distended activation of rectal stretch receptors occur and the ____3______ reflex is initiated and relaxes the ___4____ sphincter. If defecation is not desired, ________5________ can delay it.
1) parasympathetic fibres 2) somatic 3) rectosphincteric 4) internal 5) voluntary contraction of the external sphincter
97
Four things commensal bacteria do in the large intestine?
increase intestinal immunity by competition with pathogenic microbes promote motility and help maintain mucosal integrity synthesise vitamin K2 and free fatty acids (from carbohydrate) that are absorbed activate some drugs (e.g. used in treatment of IBD)
98
Medical word for vomiting?
emesis
99
Where is vomiting co-ordinated?
Vomiting centre in the medulla oblongata of the brain stem
100
Explain the overall events in vomiting
Suspension of intestinal slow wave activity Retrograde contractions from ileum to stomach Suspension of breathing (closed glottis - prevents aspiration) Relaxation of LOS- contraction of diaphragm and abdominal muscles compresses stomach Ejection of gastric contents through open UOS Repeats of the cycle
101
What areas of the brain apart from the vomiting centre also receive info in vomiting
CTZ - chemoreceptor trigger zone within the area postrema (AP) NTS – nucleus tractus solitarius
102
Role of 5HT3 receptor in vomiting
Systemic toxins or toxic materials in the gut lumen stimulate vomiting by this pathway Enterochromaffin cells in the mucosa are stimulated by this stimuli and these cause depolarization of sensory afferent terminals in mucosa via the 5Ht3 receptors. This then allows action potential to be discharged to brain where it can be coordinated by vomiting centre in medulla
103
Absorbed toxic materials and drugs in blood stimulate vomiting through
CTZ within the AP of brainstem (as it lacks an effective blood brain barrier)
104
Mechanical stimuli in the pharynx or pathology within in the GI tract stimulates vomiting through
Vagal afferents to brainstem (CTZ and NTS
105
Motion sickness stimulates vomiting through
Vestibular nuclei
106
Stimuli within the CNS stimulate vomiting through
Cerebral cortex, limbic system
107
Water ingested and secreted is normally in balance with the water ____1____ To maintain this balance some water is therefore secreted in the faeces along with ________2_________
1) absorbed | 2) bacteria, cellulose and bilirubin
108
Intestinal fluid movement is always coupled to ___1___ movement. Reabsorption of __2__ provides a (local) osmotic force for reabsorption of __3___
1) solute 2) Na+ 3) water
109
________1_________are the major mechanisms of postprandial Na+ absorption in the jejunum. These are both examples of ____2____ active transport and ultimately results in the lumen being more negative which therefore allows parallel absorption of __3__.
1) Na+/glucose and Na+/amino acid cotransport 2) secondary 3) Cl
110
___________ in the jejunum- stimulated by alkaline environment of the lumen and is mainly involved in keeping the pH constant.
Na+/H+ exchange
111
___________ exchange in parallel occurs in the ileum and proximal colon and is the primary mechanism of Na+ absorption in the interdigestive period, but does not contribute greatly to postprandial (after eating a meal) absorption
Na+/H+ and CI-/HCO3-
112
______________ Occurs in the colon (distal particularly) and is regulated by aldosterone
Epithelial Na+ channels (ENaC)
113
Cl secretion occurs from ____ cells rather than villus.
crypt
114
What ion secretion is important in many diarrhoeas?
Cl-
115
_________ is involved in Cl secretion on the apical membrane Normally there is little secretion of Cl- occurs because apical CFTR is ______________
CFTR | either closed, or not present
116
CFTR can be indirectly activated by
bacterial enterotoxins hormones and neurotransmitters some immune cell products some laxatives
117
Activation of CFTR is a result of secondary messenger molecules which are
``` o cAMP (e.g. cholera toxin, VIP, histamine) o cGMP (e.g. heat stable enterotoxin, guanylin) o Ca2+ (e.g. acetylcholine, bradykinin, 5-HT) ```
118
Diarrhoea is defined as....
loss of fluid and solutes from the GI tract in excess of 500 ml per day
119
Four main causes of diarrhoea
impaired absorption of salts, excessive secretions, non-absorbable solutes or hypermotility.
120
Only a small fraction (5%) of bile salts entering the duodenum is lost in the faeces; most is reabsorbed by _____1_____ in the _____2______ and undergoes ______3_______
1) active transport 2) terminal ileum 3) enterohepatic recyling

Gastroenterology (28 decks)

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