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Phys > Week 11 - Gastrointestinal > Flashcards

Week 11 - Gastrointestinal Flashcards

1
Q

Digestive organs

A
  • Continupus tube which runs from mouth to anus
    Organs:
    Mouth, pharynx, oesophagus, stomach, small intestine (duidenum, jejunum & ileum), large intestine (caecum, ascending, transverse, descending & sigmoid colon), rectum and anus
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2
Q

Accessory digestive organs

A
  • Not part of alimentary canal but assists digestion

- Organs: teeth, tongue, salivary glands, liver, gallbladder and pancreas

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3
Q

Gastrointestinal System - Functions

A
  • critical role in fluid, electrolyte & acid-base homeostasis by taking in water and electrolytes via diet and delivering them to blood
  • Ingested vitamins and minerals and used to produce hormones
  • Excretion of metabolic wastes
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4
Q

Mastication

A
  • (chewing)

- mechanical & chemical breakdown

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5
Q

Ingestion

A

Swallowing & proplusion

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6
Q

Digestion

A
  • Mechanical & chemical breakdown of food particles into pieces that can pass through cell membranes
  • SECRETIONS from endocrine & exocrine organs aid digestive processes
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7
Q

Absorption

A

Transfer of nutrints from gut to blood circulation

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8
Q

Excretion

A

(defaecation)

Explusion of undigested material

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9
Q

Tissue layers

A
  1. Mucosa
  2. Submucosa
  3. Muscularis externa
  4. Serosa/ Adventitia
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10
Q

Mucosa

A

Lines lumen
Composed of:
- Epithelium (mostly simple columnar & mucus-secreting cells)
- Lamina propria (loose connective tissue w/ capillaries for nourishment & absorption)
- Muscularis mucosae (two layers of smooth muscle in circular and longitudinal directions)

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11
Q

Submucosa

A
  • Dense connective tissue w/ glands, blood/lymph vessels

- ContainsclustersofnervesknownasSUBMUCOUSAL PLEXUSwhich regulatescontrolssecretionandbloodflow

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12
Q

Muscularis Externa

A
  • Thick, muscular layer composed f smooth muscle arranged in circular & longitudinal layers
  • Responsible for segmentation & peristalsis; also contains MYENETRIC PLEXUS (neural network) - controls mobility
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13
Q

Serosa (or adventitia)

A
  • Outer layer made of simple squamous emithelium & loosely arranged connective tissue
  • Both structures support digestive organs & anchor them to surrounding structures
  • Serosa is the name for external coverings of organs within the peritoneal cavity. Adventitia is coverings outside the peritoneal cavity
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14
Q

Motility

A

Movement of alimentary canal - key process in every region of canal which takes several forms including swallowing, churning and defaecation

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15
Q

Peristalsis

A

Propulsive(forwardmotion),caused by alternating contractions of longitudinal and circular smooth muscle

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16
Q

Segmentation

A

Mixing contractions of circular smooth muscle of nonadjacent segments of GI tract moving the food FORWARDS THEN BACKWARDS. food mixing occurs

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17
Q

Neural regulation of GI functions - Sympathetic

A

Fight or Flight

  • main innervation via the thoracic and splenic nerve plexus
  • effects on GIT: decreases secretion & mobility, increases sphincter closure
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18
Q

Neural regulation of GI functions - Parasympathetic

A

Rest and Digest

  • main innervation via the vagus nerve, but some input from the facial, glossopharyngeal & sacral nerves
  • effects on GIT: increases secreation & motility, decreases sphincter closure
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19
Q

Submucosal nerve plexus

A

Regulate glands and smooth muscle in the mucosa

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20
Q

Myenteric nerve plexus

A

Controls digestive tract mobility (segmentation and peristalsis)

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21
Q

Enteric nervous system (gut-brain)

A

Linked to CNS but is able to control digestive activities independently

  • SENSORY neurons detect chemical and mechanical changes of digestive tract
  • MOTOR neurons stimulate or inhibit smooth muscle contraction and gland secretion in digestive system
  • INTERNEURONS connect sensory and motor neurons
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22
Q

Gastrin

A

secreted by G cells (stomach) and enteroendocrine cells (duodenum

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23
Q

Secretin

A

released when chyme arrives in

duodenum

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24
Q

GIP

A

Gastric inhibitory peptide

- released when fats and carbohydrates enter the SI

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25
Q

CCK

A

CHOLECYSTOKININ

secreted when chyme arrives in deudenum

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26
Q

VIP

A

VASOACTIVE INTESTINAL PEPTIDE

dialites intestinal capillaries and facillitates nutrient absorption

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27
Q

cephalic phase

A

Anticipation of food

  • CNS → ANS long reflex
  • Enetric → cells short reflex
  • GI motility
  • GI secretions
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28
Q

oral phase

A

digestion

  • grind, mix & liquefy
  • saiva: water, enzymes, muscus & lysozyme
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29
Q

saliva

A

contains enzyme SALIVARY AMYLASE →initiates chemical breakdown of carbohydrates

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30
Q

salivary glands

A
  1. Submandicular (65-70%)
  2. Parotid (25-30%)
  3. Sublingual (5%)
31
Q

saliva - composition

A
  • primarily water
  • can contain electrolytes, enzymes, antibodies, buffers (bicarbonate ions) and variable amounts of mucus depending of origination of saliva
32
Q

Saliva - functions

A
  • moistening, lubricating and cleansing oral mucosa
  • lysozyme and lgA DETER growth of pathogenic bacteris in oral cavity
  • mechanical digestion, achieved by moistening and helping to mix ingested food into a BOLUS to be swallowed
  • chemical digestion, achieved by actions of salivary amylase
  • many food molecules dissolve in water of saliva → stimulate taste receptors on tongue
33
Q

regulation of saliva secretion

A
  • triggered by taste, smell, sight or thought of food

- stimulated by the Parasympathetic NS via CN VII (facial nerve & CNIX (glossophangeal nerve)

34
Q

Swallowing

A
  • specialised type of proplusion that pushes a bolus of food from oral cavity though pharynx, esophagus into the stomach
  • first voluntary phase is controlled by the cerebral cortex
  • final two phases ( pharyngeal and esophageal) are regulated by medulla and enteric nervous system
35
Q

esophagus

A

muscular tube that connects pharynx to stomach.

lining contains esophageal glands which secrete mucus to lubricate bolus as it moves to stomach

36
Q

Esophagus sphincters

A

Upper esophageal sphincter
- helps the process of swallowing
Lower gastroesophageal sphincter
- controld movement of food into stomach

37
Q

Stomach regions

A
  1. Cardia → region where esophagus empties into stomach
  2. Fundus → dome-shaped top of stomach
  3. Body → largest portion of stomach
  4. Pyloric antrum → inferiior portion of stomach
  5. Pylorus → Terminal portion of stomach
38
Q

Mucous neck cells & goblet cells

A

secrete a mucus that lines and protects cells of stomach

39
Q

Enteroendocrine cells ( G CELLS)

A

secrete hormones and paracrine messengers

40
Q

Chief cells

A

secrete gastric lipase and pepsinogen

41
Q

Parietal cells

A

secrete HCl acid, intrinsic factor and ghrelin

42
Q

Pepsinogen

A

(secreted form chief cells)

  • breaks down protein chains into smaller peptide fragments
  • most effective in the very acidic environment
43
Q

Acid secretion from stomach

A

(secreted by parietal cells)

  • helps kill microbes
  • denatures proteins from food making enzymatic proteolysis easier
  • converts pepsinogen (inactive enzyme) into pepsin to initiate chemical break down of protein
  • inactives salivary amylase
44
Q

Cephalic phase

A
  • starts with sight, smell, taste, thought of food

- parasympathetic activation leads to stimulation of gastric secretion and motility (CN X - vagus)

45
Q

Gastric phase

A
  • activated via stretch receptors and chemoreceptors (monitor pH_ in the stomach after the food comes in
  • outcomes: increased peristalsis (mixing), release of gastrin, increased gastric secretion
46
Q

intestinal phase

A
  • enterogastric reflex and hormones (enterogastrones- secretin cholecytokinin and vasoactive intestinal peptide) decrease stomach secretion, motility & emptying
47
Q

Stomach- receptive function

A
  • Stomach can expand from 50ml at rest to about 1500 ml → smooth muscle relaxation + rugae results in limited inc. in internal pressure
48
Q

Stomach - churning function

A
  • Initiated and controlled by gastric pacemaker cells that control rate of peristalic waves ~/min
49
Q

Stomach - emptying function

A
  • Emptying rates based on amount and composition of chymr in duodenum (pH, conc/diluted)
50
Q

Small intestine

A
  • 6m x 2.5cm

- mixes and propels contents into large intestine and enterocytes produce multiple digestive enzymes, hormones and mucus

51
Q

duodenum

A

(first 25cm)

  • receives stomach contents, pancreatic juice & bile
  • neutralizes stomach acids, emulsifies fats, pepsin inactivated by pH inc
  • [amcreatic enzymes aid digestion
52
Q

jejunum

A

(next 2.5m)

  • has large circular fods; thick, muscular walls
  • most digestion and nutrient absorption occurs here
53
Q

Ileum

A

(last 3.6m)

  • terminates at the portion of large intestine → CECUM
  • ILEOCECAL VALVE → sphincter that controls movement & prevents backflow of bacteria from large intestine
54
Q

small intestine cells- secretory cells

A

Produces intestinal juice

  • 1-2L secreted daily in response to distension or irritation of mucosa
  • slightly alkaline; isotonic w/ blood plasma
  • largely water
  • enzymes released from brush border
  • contains mucus
  • facilitates transports and absorptio of nutrients
55
Q

chemical digestion

A

enzymes from pancreas and small intestine chemically break down food
- carbohydrates → monosaccharides
- proteins → amino acid and small peptides
- lipids → mono glycerides and fatty acids
RNA & DNA → phosphate sugars and nucleic acid

56
Q

Pancreas

A
  • glands with both endocrine (through insulin and glucagon) & exocrine functions (pancreatic juice)
  • main pancreatic duct merges w/ ducts from liver and gallbladder
  • most small ducts merge & drain into main pancreatic duct, although some secrete into smaller ACCESSORY PANCREATIC DUCT
57
Q

Pancreatic juice

A

composed of water, salts and bicarbonate (hydrocarbonate) ions
- pancreatic juice is alkaline → neutralises acidic gastric juice in chyme, stops the action of pepsin; creates the proper pH for pancreatic and intestinal digestive enzymes

58
Q

pancreatic juice- digestive enzymes

A

pancreatic amylase → carbohydrate starch breakdown

  • trypsin, chymotryspin and procarboxypeptidase → protein breakdown
  • pancreatic lipase → most tryglyceride breakdown
  • deoxyriboneuclase & ribonuclease → nucleic acid breakdown
59
Q

Regulation of pancreatic juice secretion

A

Cholecytokinin → produced by duodenum in response to presence of lipids and partially digested proteis in duodenum
Secretin → released by duodenal cells in response to acid and lipids in duodenum; secretin primarily triggers duct cells to secrete bicarbonate ions

60
Q

regulation of pancreatic hormones

A

pancreatic islets contain cells that produce hormones GLUCAGON and INSULIN which are released directly into the bloodstream

61
Q

Liver

A
  • located inferior to the diaphragm
  • digestive functio to make bile
  • bile is manufactured by the liver but stored in the gallbladder which lies underneath the liver
62
Q

Blood flow from GI tract to liver

A

Liver receives blood from:

  • hepatic portal vein bringing nutrient-rich blood from stomach & intestines
  • hepatic artery bringing oxygen-rich blood

Blood from both portal vein and hepatic arteries mixes in liver so that absorbed nutrient can be stored and processed

blood then leaves the liver via a single hepatic vein → IVC

63
Q

Liver functions- after meal

A
  • removes glucose, amino acids, iron, vitamins, nutrients from the blood
  • removes and degrades hormones, toxins, bile pigments and drugs
  • secretes albumin, lipoproteins clotton factors angiotensionogen and others into the blood
64
Q

Liver functions - between meals:

A
  • break down stored glycogen and releases glucose into the circulation
  • kupffer cells (hepatic macrophages) remove bacteria and debris from the blood
65
Q

Bile - composition

A

Water, ions, bile acids, cholesterole, lecithin (phospholipid), bile pigments (cojugated bilirubin)

  • pigments in bile give it a green/yellow colour. bile pigments not reabsorbed by the GI tract are broken down in the large intestine to produce a brown pigment stercobilin
66
Q

Bile - function

A
  • Emulsification of large lipid globules by bile acids (mechanical digestion) breaking them down into small lipid droplets so that of lipase enzymes can perform chem digestion
  • helps remove products including cholesterole, waste producs and toxins → not reabsorbed by small or large intestines → pass into feces
67
Q

Gallbladder

A
  • stores bilem, concentrates it (removes water) and releases it
  • bile release stimulated by CCK → contraction of smooth muscle causing gallbladder to release bile into cystic duct
68
Q

bile secretion - regulation

A

Liver produces bile continually but secretion occurs in response to gallbladder contraction and sphincter relaxation at hepatopancreatic ampulla

  • accomplished by CCK and vagus nerve
  • other factors influence bile secretion, including hormone secretin; stimulates bile production and release by hepatocytes
  • strong stimuli of bile secretion is the presence of bile in the duodenum
69
Q

Large intestine - segmentation

A

0 circular muscle of each hastrum contracts repeatedly; swirls material
- aids in water and electrolyte absorption; primarily controlled by locan neurons of ENS; triggered by stretch

70
Q

Mass movement (m,ass peristalsis)

A
  • during a mass movement, multiple hastura undergo peristalsis;propels their contents toward distal large intestine
  • mass movement occur three- four times per day and appear to be triggered by food comsumption; iniates refleces controlled by ENS
71
Q

Large intestine - processes

A
  • absorption of water and electroyyes by ABSORPTIVE CELLS
  • production and secretion of mucus by GOBLET CELLS
  • Mechanical digestion → slow peristaltic waves for churning and mixing of the content
  • chemical processes → bacterial fermentation of undigested carbohydrates (into CO2 and CH3), undigested proteins (into simpler substances) and bilirunin from bile into other pigments
  • Defacation → removal of waste and undigested products
72
Q

Bacterial Flora

A
  • metabolise undigested materials via bacteria fermentation
  • produce vitamins such as Vit.K necessary for blood clotting
  • deter growth of harmful bacteria
  • stimulate immune system
73
Q

rectum

A
  • horizontal folds called rectal valves; allow passage of flatus (gas) w/o risking simultaneous passage of feces
  • rectum ends at anal canal, last portion of large intestine
  • involuntary internal anal sphincter supplied by parasympathetic motor neurons
  • voluntary external anal sphincter → skeletal muscle; supplied by somatic motor neurons controlled by cerebral cortex
74
Q

Defecation regulation

A
  • short reflex : via the myenteric plexus causes muscularis to contract and internal sphincter to relax →relatively weak
  • long reflex : involves spinal cord
    → parasympathetic motor fibres induce intensifying peristalsis in descending and sigmoidal colon and rectum; also relaxes internal sphincter
  • occurs only if external anal sphincter is voluntary relaxed
  • abdominal contractions increase abdominal pressure during valsalva maneuver

Phys (14 decks)

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