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GIT Flashcards

1
Q

Type of Cells in Mouth, oesophagus, anal canal

A

stratified squamous

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2
Q

Type of Cells in Stomach, small + large intestine

A

simple columnar

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3
Q

Lamina propria

A

Loose connective tissue (glands, blood/lymph vessels)

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4
Q

enteric nervous system (ENS)

A

Submucosal (Meissners) + Myenteric plexuses

between circular and longitudinal muscles of muscularis externae

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5
Q

What drains the gut?

A

Hepatic Portal Vein

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6
Q

What drains the liver?

A

Hepatic Vein

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7
Q

Where and which enzyme is responsible for fat digestion?

A

Small intestine by pancreatic lipase

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8
Q

water-soluble enzyme

A

Lipase

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9
Q

Micelles

A

Absorption in small intestine enhanced
Micelles smaller to emulsion droplets
Micelle = bile salt + monoglycerides + FA + phospholipids
Polar portions of molecules at micelle surface
non-polar portions (FA Chains) form micelle core

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10
Q

What does bile contain and what is its function?

A

Bile salts + phospholipids secreted in bile
amphiphatic molecules whose non-polar portions associate with non-polar interior of lipid droplet leaving polar portions exposed at water surface.

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11
Q

Chylomicrons

A

Extracellular fat droplets
Contain phospholipids, cholesterol; fat-soluble vitamins

Transport lipids absorbed from the intestine to muscle tissue

Pass into lacteals between endothelial cells (cannot pass through capillary basement membrane)

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12
Q

Fat-soluble vitamins

Water-soluble vitamins

A

A, D, E, K

B group, C and folic acid
Passive diffusion or carrier-mediated transport.

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13
Q

Vitamin B12

A

Binds to intrinsic factor in stomach to form complex which is absorbed in distal ileum.

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14
Q

B12 deficiency

A

pernicious anaemia

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15
Q

Iron

A

10% of daily ingested iron absorbed across intestine into blood

transported across brush border membrane (via DMT1) into duodenal enterocytes

Iron ions incorporated into ferritin (protein)
(protein-iron complex intracellular iron store)

Unbound iron transported across serosal membrane blood. Iron in blood binds to transferrin

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16
Q

Hyperaemia

A

increased ferritin levels

more iron bound in enterocytes

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17
Q

Anaemia

A

decreased ferritin levels

more iron released to blood

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18
Q

Saliva Contains

A

Water: Softens, moistens, dilutes particles. Solvent

Mucins: Protein. Mucins + water = mucus.
Viscous solution - lubricant function

Amylase: Catalyses breakdown of polysaccharide (starch, glycogen) into disaccharide (maltose) + glucose

Electrolytes: Tonicity/pH

Lysozyme: Bacteriocidal - cleaves polysaccharide component of bacterial cell wall

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19
Q

Salivary Secretion

Parasympathetic

Sympathetic

A

Parasympathetic
Cranial nerves VII (facial) & IX (glossopharyngeal)
Stimulation and profuse watery salivary secretion

Sympathetic
Stimulation - small volume – viscous
High Mucus and Amylase

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20
Q 
High mucus (protein) content 
High amylase content
A

(a1 adrenoceptors)

b2 adrenoceptors

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21
Q

Receptive relaxation of stomach

A

Initiated following relaxation of LOS (Lower Oesophageal Sphincter) + entry of bolus into stomach
Vagal reflexes = relaxation of thin, elastic smooth muscle of gastric fundus and body

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22
Q

Stomach Functions

A

Temporary store of ingested material
Dissolve food particles and initiate digestive process
Control delivery of contents to small intestine
Sterilise ingested material
Produce intrinsic factor (Vitamin B12 absorption)

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23
Q

Mucous neck cells

A

mucus

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24
Q

Chief cells

A

pepsinogens

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25
Parietal cells
HCl | Intrinsic factor
26
Stop Eating
Decrease Vagal Activity Increase HCL (pepsinpogen to pepsin) Decrease pH Decrease Gastrin (Stomach) Splanchnic reflex Secretin release (Small Intestine) - release of bicarbonate from pancreatic ducts - inhibits secretion of gastric acid decreasing parietal cell secretions and therefore HCL
27
Fat in duodenum
GIP Gastric inhibitory polypeptide release - insulin | Decrease Gastrin and Parietal (HCl) secretion
28
Smell. Taste Food | Gastric acid secretion processes
Increase Vagus Stimulation - ACh - Parietal cells - Neurocrine (vagus reflexes) - distention of stomach G cells - Gastrin - Parietal cells Endocrine (gastrin) - peptides in lumen Gastrin/ACh - ECLcells - Histamine - Parietal cells - Paracrine (histamine)
29
Hormones released from gland cells in response to acid, hypertonic solutions, fatty acids or monoglycerides in duodenum
``` Secretin, cholecystokinin (CCK), GIP Inhibit gastric acid secretion Increase Pancreatic Secretion Reduce gastric emptying (inhibit motility/contract pyloric sphincter) ```
30
Pepsinogen
(zymogen = inactive precursor of pepsin) secreted by Chief cells
31
Defaecation Reflex
parasympathetic control – via pelvic splanchnic nerves Contraction of rectum Relaxation of internal and contraction of external anal sphincters Increased peristaltic activity in colon
32
Enterotoxigenic Bacteria
Vibrio cholerae, Escherichia coli Produce protein enterotoxins which activate intestinal chloride secretion from crypt cells Elevate - cAMP, cGMP, calcium + H2O secretion swamps absorption in villus cells
33
Secretory Diarrhoea Treatment
Give sodium / glucose solution | Oral rehydration therapy (ORS)
34
Functions of Duodenum Jejunum Ileum
Gastric acid neutralisation; Digestion; Iron absorption Nutrient absorption - 95% NaCl/H2O absorption - chyme dehydration
35
Villus cell Crypt cell in small intestine
Absorbs: NaCl, Monosaccharides, Amino acids, Peptides, Fats Vitamins, Minerals, Water Secretes: Cl & Water (From epithelial cells lining crypts of Lieberkuhn)
36
H2O secretion in small intestine importance
H2O secreted passively (osmotically) as a consequence of active secretion of chloride into intestinal lumen Maintains lumenal contents in liquid state Promotes mixing of nutrients with digestive enzymes Aids nutrient presentation to absorbing surface Dilutes and washes away potentially injurious substances
37
Peristalsis
Following Segmentation and absorption of nutrients Migrating Motility Complex (MMC) Motilin (hormone) involved in initiation 1) Moves undigested material into large intestine 2) Limit bacterial colonisation of small intestine As one MMC ends (terminal ileum) another begins Arrival of food in stomach, cessation of MMC and initiation of segmentation
38
Segmentation
Most common during meal 1) Contraction + relaxation of short intestinal segments 2) Moves chyme into adjacent areas of relaxation 3) Relaxed areas contract and push chyme back 4) Provides mixing with digestive enzymes 5) Brings chyme into contact with absorbing surface Initiated by depolarisation generated by pacemaker cells in longitudinal muscle layer Intestinal basic electrical rhythm (BER) produces oscillations in membrane potential
39
Functions of the Pancreas
Endocrine - a and b cells secrete insulin and glycagon, somatostatin into bloodstream (pancreatic islets; islets of Langerhans) Exocrine - Acinar Cells secrete digestive enzymes - main pancreatic duct - common bile duct
40
Secretin
``` S cells in duodenum released in response to acid and fat in duodenum Increases Pancreatic HCO3- secretion, Biliary Secretion Decreases Gastric Acid Secretion ```
41
Gastric inhibitory polypeptide (GIP) | Glucose-dependent insulinotropic peptide
Increase Insulin | Decrease Gastric H+ Secretion
42
Brunnners Glands
HCO3- secretion in duodenum from pancreas or liver duct cells due to secretin release
43
D-xylose absorption test
Distinguishes GI mucosal damage from other causes of malabsorption
44
Manometry
Peristaltic Movements
45
A liver sinusoid capillary / discontinuous capillary
Discontinuous endothelium that serves as a location for *mixing of the oxygen-rich blood from the hepatic artery and the nutrient-rich blood from the portal vein.
46
Triacyclycerol contents before and after digestion
Glycerol and 3 Stearic Acids Monoglyceride and 2 Fatty Acids
47
Emulsification
Mechanical - smooth muscle contraction mixes lumenal contents. - dividing large lipid droplets into smaller droplets - increased surface area, accessibility to lipase action Emulsifying agent - prevents small droplets reforming into large droplets. Bile salts + phospholipids secreted in bile
48
Fundus Body Antrum Functions
Storage Storage, Mucus HCl, Pepsinogen, Intrinsic factor Mixing/Grinding Gastrin
49
Gastric Mucus
Produced by surface epithelial cells + mucus neck cells Protects mucosal surface from mechanical injury Neutral pH (HCO3) - Protects against gastric acid corrosion and pepsin digestion
50
Chewing
Voluntary Somatic nerves - skeletal muscles of mouth/jaw Reflex Contraction of jaw muscles - pressure of food against gums, hard palate and tongue - mechanoreceptors - inhibition of jaw muscles - reduced pressure - contraction
51
Swallowing
``` Oral Phase (voluntary) Bolus pushed to back of mouth by tongue ``` Pharyngeal Phase Presence of bolus - sequence of reflex contractions of pharyngeal muscles Co-ordinated by swallowing centre (medulla) Soft palate reflected backward and upward (closes off nasopharynx) As bolus approaches oesophagus… Upper oseophageal sphincter (UOS) relaxes and epiglottis covers opening to larynx ``` Once food has entered oesophagus… UOS contracts (prevents food reflux) ```
52
Acinar cells contain digestive enzymes stored as inactive zymogen granules. Function and how are they converted to an active form?
Prevents autodigestion of pancreas Enterokinase (bound to brush border of duodenal enterocytes) converts trypsinogen to trypsin Trypsin converts all other zymogens to active form
53
``` Proteases Nucleases Elastases Phospholipases Lipases ``` α-Amylase
``` Cleave peptide bonds Hydrolyse DNA/RNA Collagen digestion Phospholipids to fatty acids Triglycerides to fatty acids+ glycerol ``` Starch to maltose + glucose
54
Bare area
small area on diaphragmatic surface of liver surrounded by coronary ligament Only part of liver not covered by connective tissue capsule and visceral peritoneum
55
Septa
divide liver into hexagonal lobules Central veins at centre of each lobule Portal Triad at the corner of each lobule
56
Portal triad
hepatic portal vein, hepatic artery, hepatic duct
57
Hepatic cords
Radiate out from central veins and are Composed of hepatocytes Spaces between hepatic cords = hepatic Sinusoids (blood channels) Bile canaliculus lies between cells within each cord
58
Hepatocytes
bile synthesis nutrient storage (glycogen, fat, vits (B12,A,D,E,K), Cu, Fe) nutrient interconversion detoxification
59
Bile components
(1) Bile acids (2) Lecithin (3) Cholesterol solubilise Fat (4) Bile Pigments Bilirubin (from haemoglobin) (5) Toxic Metals Detoxified in liver (6) Bicarbonate Neutralisation of acid chyme (1) - (5) secreted by hepatocytes HCO3 secreted by duct cells
60
Bile Pigments
Breakdown products of haemoglobin from old/damaged erythrocytes Bilirubin (predominant bile pigment) - extracted from blood by hepatocytes and secreted into bile  yellow bile Bilirubin modified by bacterial enzymes, brown pigments  brown faeces Reabsorbed bilirubin excreted in urine  yellow urine
61
Bile Acids
Synthesised in liver from cholesterol (0.5g/day) Before secretion, bile acids conjugated with glycine or taurine to Bile Salts (Increased solubility) Secreted bile salts recycled via enterohepatic circulation
62
Sphincter of Oddi
Controls release of bile and pancreatic juice into duodenum When contracted (closed) - bile forced back into gallbladder
63
Fat in duodenum and CCK functions
``` Fat in duodenum releases CCK CCK - (A) Sphincter of Oddi relaxes (B) Gallbladder contracts Discharge of bile into duodenum - fat solubilisation CCK - Pancreatic enzyme secretion - Bile secretion ```
64
H2O secretion important for normal digestive process:
Maintains lumenal contents in liquid state Promotes mixing of nutrients with digestive enzymes Aids nutrient presentation to absorbing surface Dilutes and washes away potentially injurious substances
65
Gastroileal Reflex
Gastric emptying - segmentation activity in ileum Opening of ileocaecal valve (sphincter) Entry of chyme into large intestine Distension of colon Reflex contraction of ileocaecal sphincter (prevents backflux into small intestine)
66
Colon Functions
Absorption - Actively transports Na from lumen to blood Osmotic absorption of water Dehydration of chyme - solid faecal pellets
67
Bacterial fermentation of undigested carbohydrate ??
Short chain fatty acids (energy source in ruminants) Vitamin K (blood clotting) Gas (flatus) - nitrogen, CO2, hydrogen, methane, hydrogen sulphide
68
Defaecation Reflex
Under parasympathetic control – via pelvic splanchnic nerves (no sympathetic influence) Contraction of rectum Relaxation of internal and contraction of external anal sphincters Increased peristaltic activity in colon Increased Pressure on external anal sphincter - relaxes under voluntary control - expulsion of faeces
69
Enterotoxigenic Bacteria
eg Vibrio cholerae, Escherichia coli Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells Increase H2O secretion which swamps absorptive capacity of villus cells causing profuse watery diarrhoea Act by elevating intracellular second messengers: cAMP, cGMP, calcium Enterotoxins don’t damage villus cells Give sodium/glucose solution to Drive H2O absorption and allow rehydration

Revision Year 2 (14 decks)

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