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1st year GI > PHYSIOLOGY > Flashcards

PHYSIOLOGY Flashcards

1
Q

what is the alimentary canal

A

series of hollow organs running from mouth to anus (oral to aboral) that are separated by sphincters, controlling movement

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2
Q

what is the function of mouth and pharynx

A

chops and lubricates food, starts carbohydrate digestion, delivers food to oesophagus

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3
Q

what is the function of the oesophagus

A

propels food to the stomach

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4
Q

what is the function of the stomach

A

stores and churns food continues carbohydrate, initiates protein, digestion regulates delivery of chyme to duodenum

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5
Q

what is the function of the small intestine

A

(duodenum, jejunum and ilium) principal site of digestion and absorption of nutrients

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6
Q

what is the function of the large intestine

A

(caecum, appendix and colon). Colon reabsorbs fluids and electrolytes, stores faecal matter before delivery to recutum

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7
Q

what is the function of the rectum anal canal and anus

A

regulated expulsion of faeces

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8
Q

what are accessory structures to the alimentary canal

A

salivary glands, the pancreas, the liver and gall bladder (hepatobiliary system)

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9
Q

what are the generalised structures of the digestive tract wall (4)

A
  1. mucosa
  2. submucosa
  3. muscularis externa
  4. serosa
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10
Q

what are the 3 layers in the mucosa

A
  1. mucous membrane
  2. lamina propria
  3. muscularis mucosae
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11
Q

what are the structures in the submucosa

A
  • connective tissue
  • larger blood and lymph vessels
  • glands
  • submucosa plexus (neurone network)
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12
Q

what are the structures in the muscularis externa

A
  • circular muscle layer
  • myenteric plexus (neurone network)
  • longitudinal muscle layer
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13
Q

what are the 4 major functions of the alimentary canal

A
  • motility
  • secretion
  • digestion
  • absorption
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14
Q

what does the function of motility entail

A

mechanical activity mostly involving smooth muscle (skeletal at mouth, pharynx, upper oesophagus and external anal sphincter)

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15
Q

what does the function of secretion entail

A

into the lumen of the digestive tract occurs from itself and accessory structures in response to the presence of food, hormonal and neural signals. Required for digestion, protection and lubrication

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16
Q

what does the function of digestion entail

A

chemical breakdown by enzymatic hydrolysis of complex food stuffs to smaller, absorbable units

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17
Q

what does the function of absorption entail

A

transfer of the absorbable products of digestion from the digestive tract to the blood or lymph

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18
Q

what does circular muscle contraction cause

A

lumen becomes narrower and longer

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19
Q

what does longitudinal contraction cause

A

intestine becomes shorter and fatter

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20
Q

what happens when the muscularis mucosae contracts

A

change in absorptive and secretory area of mucosa (folding), mixing activity

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21
Q

what are the function of gap junctions between smooth muscle cells in the GI tract

A

Electrically couple adjacent cells (allow slow wave of depolarisation to spread across muscle sheet).
- synchronous wave (ie single unit smooth muscle)

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22
Q

what are Interstitial cells of Cajal (ICC)

A

Pacemaker cells located largely between the circular and longitudinal muscle layers. They form gap junctions with each other and smooth muscle cells electrically coupling them. Slow waves in ICC drive slow waves in the smooth muscle cells coupled to them. Some ICCs form a bridge between nerve endings and smooth muscle cells.

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23
Q

when does contraction in the intestines only occur

A

Contraction in the intestines occurs only if the small wave amplitude is sufficient to reach a threshold to trigger smooth muscle cell calcium action potentials

  • Depolarising slow waves do not necessarily result in smooth muscle contraction
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24
Q

what are slow waves

A

Slow waves, also known as the basic electrical rhythm (BER), vary in frequency along the length of the GI tract eg stomach, 3 min-1, small intestine, 8-12 min-1

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25
Q

whether a slow wave amplitude reaches threshold depends on: (3)

A
  • neuronal stimuli
  • hormonal stimuli
  • mechanical stimuli

(generally act to depolarise smooth muscle cells rather than influence slow waves directly - depolarisation shifts slow wave peak to threshold)

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26
Q

explain the autonomic innervation of the GI tract by the parasympathetic system

A

pre ganglionic fibres (releasing ACh) synapse with ganglion cells within the enteric nervous system

  • excretory influences = increased gastric, pancreatic and small intestinal secretion, blood floe and smooth muscle contraction
  • inhibitory influences = relaxation of some sphincters, receptive relaxation of stomach during feeding
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27
Q

explain the autonomic innervation of the GI tract by the sympathetic system

A

pre ganglionic fibres (releasing ACh) synapse in the pre vertebral ganglia. Post ganglionic fibres ( releasing noradrenaline) innervate mainly enteric neurones but also other structures

  • excretory influences = increased sphincter tone
  • inhibitory influences = decreased motility, secretion and blood flow
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28
Q

what is the enteric nervous system

A

The enteric nervous system (ENS) is a large division of the peripheral nervous system (PNS) that can control gastrointestinal behaviour independently of central nervous system (CNS) input

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29
Q

what does the myenteric (Aurbachs) plexus regulate

A

mainly regulates motility and sphincters

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30
Q

what does submucosus (Meissners ) plexus

A

mainly modulates epithelia and blood vessels

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31
Q

what neurones coordinate muscular, secretive and absorptive activities in the GI tract

A

sensory neurones , interneurones, effector neurones

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32
Q

what is peristalsis

A

A wave of relaxation, followed by contraction, that normally proceeds a short distance along the gut in an aboral direction - triggered by distension of the gut wall

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33
Q

what is the effect of altered activity of interneurones and hence motoneurons on the longitudinal and circular muscle in the propulsive segment and the receiving segment

A
  • (oral) Longitudinal muscle relaxed (release of VIP and NO from inhibitory motoneurons). Circular muscles contract ( release of ACh and substance P from excretory motoneurons)
  • (aboral) Longitudinal muscle contrasts ( release of ACh and substance P from excretory motor neurone). Circular muscle relaxes (release of VIP and NO from inhibitory motor neurone)
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34
Q

what is segmentation

A

mixing or churning movements- rhythmic contractions of the circular muscle layer that mix and divide luminal contents. It occurs in the small intestine ( in the fed state) and in the large intestine (where is it called haustartio)

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35
Q

what is colonic mass movement

A

powerful sweeping contraction that forces faeces into the rectum - occurs a few times a day

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36
Q

what is the migration motor complex

A

powerful sweeping contraction from stomach to terminal ilium

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37
Q

what are tonic contractions

A
  • Low pressure - organs with a major storage function

- High pressure - sphincters

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38
Q

how many sphincters are in the GI tract

A

6 excluding the sphincter of odd

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39
Q

what do sphincters do

A

act as one way valves by maintaining a positive resting pressure relative to two adjacent structures

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40
Q

name the sphincters

A 
Upper oesophageal sphincter 
Lower oesophageal sphincter 
Pyloric sphincter 
Ileocaecal valve
Internal and external anal sphincter
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41
Q

what are the functions of each of the sphincters

A
  • UOS = skeletal muscle relaxes to allow swallowing or closes during inspiration
  • LOS relaxes to permit entry of food to the stomach or closes to prevent reflux of gastric contents to the oesophagus
  • Pyloric sphincter = regulates gastric emptying and usually prevents duodenal gastric reflux
  • Ilieocaecal valve = regulates flow from ilium to caecum or distension of ilium opens, distension of proximal colon closes
  • Internal (smooth muscle) and external (skeletal muscle) anal sphincters = are regulated by the defection reflex
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42
Q

what is glycogenesis

A

synthesis of glycogen from glucose

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43
Q

what is glycogenolysis

A

breakdown of glycogen to form glucose catalysed by glycogen phosphorylase

  • Rate limiting step of glycogenolysis. One glucose molecule is cleaved off the ends of glycogen at a time
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44
Q

what is gluconegenesis

A

de novo synthesis of glucose from metabolic precursors (lactate, amino acids, glycerol)

-It is not the verse of glycolysis due to the need to overcome energetically unfavourable steps, catalysed by a unique set of enzymes

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45
Q

what is the function of hexokinase in glycolysis

A

primer for glucose phosphorylation

46
Q

what is the function of phosphoglucomutase in glycolysis

A

Targets glucose away from glycolysis and towards glycogen synthesis. It changes the position of the phosphate from 6 to 1

47
Q

What is the function of UDP glucose pyrophosphorylase in glycolysis

A

Binds the UDP to the glucose

Simple precursors are first converted to activated intermediates

UDP glucose can be thought of an activated form of glucose. ATP and acetyl-CoA are activated forms of phosphate and acetate respectively

48
Q

what is the function of glycogen synthase in glycolysis

A

attaches UDP glucose as a primed molecule to glycogen

49
Q

what is the function of glycogen syntheses

A

synthesises glycogen from UDP glucose. Adds one glucose molecule to glycogen at a time. Can only extend the chains of glycogen ie cannot start new molecules. Cannot introduce branches. Rate limiting enzyme of glycolysis

50
Q

what are the 4 liver enzymes required for gluconeogenesis

A
  • Glucose-6-phosphate
  • Fructose-1,6-bisphospahte
  • PEP carboxykinase
  • Pyruvate carboxylase
51
Q

what is the cori cycle

A

Lactate is a precursor if gluconegenesis. Blood transports lactate to the lover. The liver converts lactate back ti glucose. Glucose released into bloodstream. Buys time and shifts metabolic burden form muscle to other organ

52
Q

what is the structure of a triglyceride

A

glycerol and 3 fatty acids

53
Q

what are the main natural fatty acids

A

Palmitic acid 16:0
Stearic acid 18:0
Oleic acid 18:1

54
Q

what are the main products of fat digestion

A

Glycerol, fatty acids and monoglycerides

55
Q

where is fat absorbed

A

Absorbed into mucosal cells of intestine. Short and medium length fatty acids enter portal blood. Longer chains FAs and monoglycerides are resynthesises to triglycerides

56
Q

what is lipolysis

A

breakdown of lipids. Fat is stored in adipose tissue

57
Q

before fatty acids can be oxidised to generate energy what do they have to be converted to

A

CoA derivatives

58
Q

what is the carnitine shuttle

A

The carnitine shuttle represents a mechanism by which long-chain fatty acids, which are impermeable to the mitochondrial membranes, are transported into the mitochondrial matrix for the purpose β-oxidation and energy production.

59
Q

what is beta oxidation (in mitochondrial matrix)

A

Beta oxidation is a metabolic process involving multiple steps by which fatty acid molecules are broken down to produce energy. More specifically, beta oxidation consists in breaking down long fatty acids that have been converted to acyl-CoA chains into progressively smaller fatty acyl-CoA chains.

60
Q

what are ketone bodies

A

(three related compounds produced during the metabolism of fats, two of which are used as a source of energy instead of glucose during a period of fasting or very low carbohydrate intake) They are formed in the mitochondria from acetyl-CoA from b oxidation. Diffuse into the blood stream and to peripheral tissues. Important molecules of energy metabolism for heart muscle and renal cortex- convert back to acetyl-CoA, which enters the TCA cycle.

61
Q

what cells cover the oral cavity, oropharynx and larngopharynx

A

stratified squamous epithelium which is generally not keratinised

62
Q

what cells are on the anterior 2/3 of the tongue

A

stratified squamous epithelium, thin on ventural surface, thick and with papillae of the dorsal surface

63
Q

what cells are on the posterior 1/3 of the tongue

A

covered by smooth stratified squamous epithelium which, except for the circumvallate papillae, lacks papillae but does have substantial lymphoid aggregates in the submucosa

64
Q

what are the 4 types of papillae on the tongue

A

Fungiform, Circumvallate, Foliate, Filiform

65
Q

what are the 4 main layers from the digestive tract from the oesophagus to the anal canal

A
  1. Mucosa: 3 parts
    - Epithelium (sits on basal lamina)
    - Lamina Propria (loose connective tissue)
    - Muscularis mucosa (thin layer of smooth muscle)
  2. Submucosa (dense irregular connective tissue)
  3. Muscularis externa ( 2 thick layers of smooth muscle, an inner circular layer and an outer longnitudinal layer)
  4. Serosa or Adventitia (Outer layer of connective tissue that either suspends the digestive tract or attaches it to other organs)
66
Q

what is the gastro-oesophageal; junction

A

abrupt transition from stratified squamous epithelium of oesophagus to the simple columnar epithelium of the cardia of the stomach

67
Q

where would you find parietal cells and stem cells of the gastric gland

A

isthmus

68
Q

where do you find neck mucous cells and parietal cells

A

neck

69
Q

where do you find mostly chief cells with a few parietal cells and enteroendocrine cells

A

funds (base)

70
Q

what is the function of chief cells

A

digestive enzyme secreting cell

71
Q

what is the function of parietal cell

A

hydrochloric acid producing cell

72
Q

what are the different stomach regions

A
  • Cardia: deep gastric pits that branch into loosely packed, tortuous glands
  • Body: shallow gastric pits with long straight gastric glands
  • Pylorus: Deep gastric pits with branched, coiled gastric glands at a higher density than in the cardia
73
Q

what are the 3 segments of the small intestine

A
  1. Duodenum = 25cm long
  2. Jejunum = 2m long
  3. Ilium = 2.75m long
74
Q

compare the small intestine regions

A
  1. Duodenum contains Brunners glands in the submucosa
  2. Jejunum. Tallest villi, located on permenant circular folds of the mucosa and submucosa, the place circulars. Lymphoid follicles infrequent
  3. Ileum is characterised by shorter villi and aggregates of lymphoid follicles callers Peyer’s patches found in the submucosa and often extending into the lamina propria
75
Q

what are enterocytes

A

the most numerous cells, they are tall columnar cells with a brush boarder and are the principle absorptive cell

76
Q

what are goblet cells

A

produce mucin to protect epithelium and lubricate passage of material

77
Q

what are paneth cells

A

found at the base of the crypts of lieberkuhn, there have a defensive function and have a role in regulating bacterial flora (secrete lysozyme and definsins)

78
Q

what are enteroendocrine (neuroendocrine) cells

A

produce hormones that contribute to the control of secretion and motility

79
Q

what are stem cells

A

found at the base of the crypts of lieberkuhn, they divide to replenish the epithelium

80
Q

what occurs in the duodenum

A

Receives acidic, partly digested semifluid material called chyme from the stomach. It has glands located within the submucosa called Brunners glands and when stimulated by the presence of chyme they produce a thin, alkaline mucous to neutralise the chyme

81
Q

what are Peyers patches

A

the numerous areas of lymphoid tissue in the wall of the small intestine which are involved in the development of immunity to antigens present there.

82
Q

what are the 2 main types of cells in the large intestine epithelium

A
  • Absorptive cells for the removal of salts and thereby water
  • Goblet cells for the secretion of mucus to lubricate the colon
83
Q

what is the appendix

A

A blind ending hollow extension of the cecum

84
Q

what is the structure of the appendix

A

the structure of the appendix is similar to the rest of the colon, but the crypts are far less abundant sonf there is typically a circular arrangement of lymphoid tissue in the submucosa and often the lamina propria

85
Q

what cells are along the long anal canal

A

continuous with the keratinised stratified squamous epithelium of the surrounding skin

86
Q

what is the digestive tracts own nervous system

A

Enteric nervous system.

87
Q

where does the enteric nervous system receive input from

A

autonomic nervous system, but is capable of coordinating gut motility locally

88
Q

what is a neuron living outside the brain and spinal chord called

A

ganglion

89
Q

what cell composes the parenchyma of the liver and pancreas

A

glandular epithelial cells

90
Q

what is the structure of the liver

A

Made up of segments called lobules. Each lobule is approximately hexagonal and has a branch of the hepatic vein called the centrolobular even at its centre and portal triads at each corner

91
Q

what are portal triads

A

Branches of the vessels which enter at the aorta hepatis, that is the hepatic artery and hepatic portal vein. There is a third tube called the bile duct

92
Q

what are the main cells of the liver

A

hepatocytes

93
Q

what is the space of Disse

A

The sinusoids are lined by endothelial cells and there is a narrow space between these lining cells and the hepatocytes. The space is called the space of Disse

94
Q

what are hepatic stellate cells

A

They are scattered in the space of Disse. They are modifies fibroblasts and make connective tissue. They also store vitamin A within fat droplets in their cytoplasm. In some pathological conditions they transform into myofibroblasts and produce scar tissue in the liver

95
Q

what are Kupffer cells

A

They are resident macrophages scattered within the sinusoids. These cells remove particulate matter from the blood and help remove worn out RBCs

96
Q

what is bile

A

bile is an alkaline solution containing water, ions, phospholipids, bilirubin and bile salts.

97
Q

what is bilirubin

A

A pigment which results from the breakdown of haemoglobin in the spleen, and when excreted in the bile, is the principal cause of the brown colour of feces

98
Q

what are bile salts needed for

A

They are necessary for emulsification of fats in the digestive tract.

99
Q

how is bile produced

A

All hepatocytes produce bile in the liver

100
Q

what are bile canaliculi

A

they are small channels formed by tight junctions in the cell membranes of adjacent hepatocytes

101
Q

what does the exocrine pancreas produce

A

Digestive juices, lipase to break down lipids, nucleases to breakdown DNA and RNA, amylase to breakdown starch. These enter the duodenum via the pancreatic duct

The cells in the exocrine pancreas are very basophilic because they contain large amounts of RER in the basal part. In the apical part its very eosinophilic due to the presence of zymogen granules

102
Q

what does the endocrine pancreases do

A

the endocrine pancreas consists of small scattered islands of tissue called islets of langerhans which produce a number of hormones including insulin and glucagon

103
Q

what is the function of the enzymes produced from the exocrine pancreas

A

the enzymes produced are produced as proenzymes. Once the pancreatic secretion arrives at the duodenum an enteropeptidase converts the inactive proteolytic enzyme trypsinogen into the active form trypsin

104
Q

what is trypsinogen

A

an inactive substance recreated by the pancreas, from which the digestive enzyme trypsin is formed in the duodenum

105
Q

what is trypsin

A

enzyme that helps digest protein

106
Q

what is the structure and function of the gall bladder

A

the gall bladder is a muscular sac which is lined by columnar epithelium backed by lamina propria of loose connective tissue rich in blood vessels and lymphatic vessels, a coat of smooth muscle and an outer collagenous layer of adventitia. The gall bladder stores bile and modifies the bile within it. It has a folded mucosa when empty

107
Q

what hormone causes contraction of the gall bladder

A

cholecystokinin

108
Q

what is cholecystitis

A

Inflammation of the gall bladder is not uncommon. Here gall stones have obstructed the cystic duct leading expansion of the gall bladder, thickening of the muscle layers and inflammation

109
Q

what is the absorption of water in the GI tract largely driven by

A

absorption of Na+

110
Q

what are the principle mechanisms in the absorption of water in the GI tract

A
  • Na+/glucose co transport
  • Na+/ amino acid co-transport
  • Na+/H+ exchange
  • Parallel Na+/H+ and Cl-/HCO3- exchange
  • Epithelial Na+ channels (ENaC )

1st year GI (16 decks)

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