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digestive system Flashcards

1
Q

nutrients in food

A

-macromolecules [proteins, CHO, lipids, nucleic acids]
-micronutrients [vitamins, minerals/trace elements]
-water

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2
Q

digestive system 6 functions

A

-ingestion
-secretion [release of water, digestive enzymes and acids, salts and buffers into the GI tract]
-mixing and propulsion [alternating contraction and relaxation of smooth muscle, moves contents down GI tract]
-digestion [breakdown of food, polymers into monomers, enables passage through epithelium]
-absorption [food enters blood or lymph]
-defecation

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3
Q

GI tract structure

A

-one continuous tract 5-7m long
-same four layers throughout: mucosa, submucosa, muscularis, serosa
[muscularis contains smooth muscle in two orientations, stomach contains a third muscle layer [inner oblique]]

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4
Q

mucosa

A

-lines GI tract -innermost layer
-moist due to glandular secretions
-divided into surface epithelium and lamina propria
-thin smooth muscle layer [muscularis mucosae]

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5
Q

submucosa

A

-2nd layer of GI tracts
-connective tissue
-extensive vascularisation, nervous supply and lymphatics

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6
Q

muscularis [externa]

A

-muscle layer divided into circular and longitudinal muscle
-moves food and fluid through tract by ‘peristalsis’

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7
Q

serosa

A

-outermost layer of GI tract
-thin connective tissue surrounds tract and extends to form mesentery that anchors tract to abdominal wall
-adventitia replaces serosa on oesophagus

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8
Q

swallowing - voluntary and involuntary phases

A

1-voluntary phase: tongue pushes the bolus posteriorly toward the oropharynx
2-pharyngeal phase: bolus enters the oropharynx, the soft palate and epiglottis seal off nasopharynx and larynx respectively
3- oesophageal phase: peristaltic waves move the bolus down oesophagus to the stomach

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9
Q

peristalsis

A

-circular muscle contract behind bolus and relax ahead
-longitudinal muscles ahead of bolus contract to shorten the segment
-sequence pushes bolus through tract

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10
Q

stomach 4 key functions

A

-accommodation of ingested food
-secretion of gastric juice
-mixing food, saliva and gastric juice using peristaltic mixing waves to form chyme
-secretion of hormone gastrin

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11
Q

stomach structure

A

-about the size of a large sausage when empty [can distend hugely to accommodate a meal]
-divided into four sections: fundus, cardia, body, pylorus
-lower oesophageal sphincter permits entry of food and fluid into stomach
-pyloric sphincter controls exit into
duodenum
-large folds of mucosa evident when stomach is empty [rugae] which permit distension when food/fluid enter stomach
-surface epithelium contains gastric pits, within these lie gastric glands

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12
Q

churning mechanism in stomach

A

1- stomachs smooth muscle contracts and propels a small amount of chyme through the pyloric sphincter. rest is propelled backwards
2- stomachs peristaltic waves churn the remaining chyme
3- remaining chyme is again propelled towards pyloric sphincter. more chyme is forced through as the process repeats

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13
Q

small intestine functions

A

-mix chyme with pancreatic juice and bile
-complete chemical digestion of nutrients
-absorb nutrients and water [90%]

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14
Q

small intestine sections

A

-duodenum - 25cm long C shaped tract extending from pyloric sphincter, receives chyme together with digestive secretions from liver and pancreas
-jejunum - 1 m long, site of most chemical digestion and nutrient absorption
-ileum - longest segment 2m long, absorb pile salts, vit B12 and any remaining nutrients, ends with ileocecal valve -sphincter muscle controlling flow into large intestine

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15
Q

small intestine internal structure

A

-folds on internal lining called plicae
-intestinal villi cover mucosa
-each villus is covered with epithelial cells with their own microvilli [known as brush border, increased surface area from 3300cm2 to 2million cm2]

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16
Q

enterocytes and the brush border

A

-each enterocyte [intestinal lining cell] possesses microvilli on their apical surface
-enzymes associated with brush border complete the chemical digestion process

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17
Q

large intestine

A

-1.5 m long
-four regions: caecum, colon, rectum, anus
-colon divided into: ascending, transverse, descending, sigmoid
-attached via mesocolon to posterior abdominal wall
-mucosa contains absorptive cells primarily for water absorption, goblet cells produce mucus for lubrication
-both contained in tubular glands called crypts of Lieberkühn

18
Q

3 major pairs of major salivary glands

A

-parotid
-sublingual
-submandibular

19
Q

components of saliva

A

-water [99.5%]
-amylase [CHO-digesting enzyme]
-lipase [lipid-digesting enzyme]
-IgA [immunoglobulin -immune function]
-lysozyme [antibacterial enzyme]
-following ions: sodium, potassium, chloride, bicarb, phosphate
-urea and uric acid [nitrogenous waste products]
-antioxidants

20
Q

gastric glands

A

-parietal cells [secrete hydrochloric acid and intrinsic factor
-chief cells [secrete pepsinogen and gastric lipase
-G cells [produce and release gastrin]
all creates gastric juice

21
Q

hydrochloric acid

A

-released by parietal cells
-kills most micro-org
-denatures proteins and break down plant cell walls
-activates pepsinogen to form pepsin
-promotes flow of bile and pancreatic juice

22
Q

intrinsic factor and pepsinogen

A

-intrinsic factors released by parietal cells
-required for the later absorption of vit B12
-pepsinogen released by chief cells
-coverts to the protease pepsin inside stomach

23
Q

gastric lipase

A

-released by chief cells
-breaks down triglycerides into fatty acids and glycerol
-optimum functional pH of 3-6

24
Q

gastrin

A

-released by G cells
-stimulated HCL secretion by parietal cells
-stimulates chief cells to secrete pepsinogen
-causes lower oesophageal sphincter to contract
-increases gastric motility
-causes pyloric sphincter to relax

25
digestion and absorption in stomach
-chyme is mixed mainly in body and pylorus regions of stomach -pepsin begins protein breakdown -gastric lipase breaks down triglycerides -stomach empties via pyloric sphincter around 2/4 hours after eating -most materials not absorbed through stomach due to mucus lining, cell structure and available time [alcohol and aspirins]
26
bile and gall bladder
-1 litre of bile is produced by hepatocytes each day - excess stored in gall bladder -bile is both a digestive aid and an excretory product
27
bile consists of
-water -bile salts that aid emulsification -cholesterol -lecithin -bile pigment bilirubin from breakdown of haem
28
exocrine pancreas
-pancreas exocrine function is to produce pancreatic juice [delivered via pancreatic duct to duodenum] -contains digestive enzymes and buffers [amylase, lipase, nucleases and proteases/peptidases, bicarb ions] -responsible for chemical digestion and raises pH of chyme
29
villus cells include
-absorptive cells with microvilli -goblet cells that secrete mucus -enteroendocrine cells -Paneth cells - immune function
30
secretin
-enteroendocrine cell hormones -release stimulated by gastric acid -reduces secretion of HCL in stomach -increases release of bicarb ions in pancreatic juice [neutralises gastric acid in small intestine]
31
gastric inhibitory polypeptide
-GIP -enteroendocrine cell hormones -reduces secretion of stomach acid -induces insulin secretion [glucose-dependent insulinotropic peptide
32
cholecystokinin
-CCK -enteroendocrine cell hormones -release is stimulated by fatty acids and AA entering the duodenum -inhibits stomach emptying -increases release of pancreatic digestive enzymes and bile -stimulates gut motility -suppresses hunger
33
intestinal absorption
-passage of material through the small intestine takes around 5 hours -90% of absorption occurs in small intestine -nutrients pass into enterocytes [epithelial cells] of intestinal villi -transferred to blood and lymph for distribution [AA and monosaccharides into blood cap, most fats into lymphatic cap [lacteals] in the form of chylomicrons]
34
intestinal absorption CHO and proteins
-CHO -absorbed as monosaccharides -proteins -absorbed into enterocytes as either AA, dipeptides or tripeptides, transferred to blood only as AA
35
intestinal absorption lipids
-pass into epithelial cells -large numbers of triglycerides are packed into chylomicrons and pass into lacteals in villi and into blood via lymphatic system
36
large intestine function
-any remaining chyme that enters the large intestine is subjected to haustral churning -the haustra are the bubble-shaped segmented pouches of the large intestine -chyme enters and causes a haustrum to distend -this then squeezes its contents along to the next haustrum -peristalsis also aids in this movement
37
large intestine digestion
-no digestive enzymes are secreted by the large intestine -resident bacteria ferment any undigested CHO [produce hydrogen, CO2 and methane gases etc] -AA and bilirubin also broken down [indole, skatole and stercobilin give faeces on a brown colour -bacteria synth vit K and some vit B [our major source of vit K]
38
large intestine absorption
-water is absorbed from chyme to make it semi-solid and now known as faeces -vit K absorbed [required for normal blood clotting cascade -vit B produced by bacteria and absorbed include B1,2,5,7,9and12 -sodium and chloride ions also absorbed
39
enteric nervous system
-myenteric plexus [found between the longitudinal and circular smooth muscle layers of the muscularis, primarily responsible for gut motility via activation of smooth muscle fibres] -submucosal plexus [found within mucosa, control the secretory cells of organs] -sensory neurons include chemoreceptors and mechanoreceptors
40
autonomic nervous system
-Vagus nerves provide parasympathetic connection to most of the GI tract -connected to the ENS -can directly activate smooth muscle and glandular activity in the GI tract -sympathetic nerves also connect with the ENS [causes a decrease in secretory action and motility in the GI tract, coupled with a reduction in blood flow]

biomed (9 decks)

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