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
2
Q
Accessory digestive organs
A
- Not part of alimentary canal but assists digestion
- Organs: teeth, tongue, salivary glands, liver, gallbladder and pancreas
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
4
Q
Mastication
A
- (chewing)
- mechanical & chemical breakdown
5
Q
Ingestion
A
Swallowing & proplusion
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
7
Q
Absorption
A
Transfer of nutrints from gut to blood circulation
8
Q
Excretion
A
(defaecation)
Explusion of undigested material
9
Q
Tissue layers
A
- Mucosa
- Submucosa
- Muscularis externa
- Serosa/ Adventitia
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)
11
Q
Submucosa
A
- Dense connective tissue w/ glands, blood/lymph vessels
- ContainsclustersofnervesknownasSUBMUCOUSAL PLEXUSwhich regulatescontrolssecretionandbloodflow
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
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
14
Q
Motility
A
Movement of alimentary canal - key process in every region of canal which takes several forms including swallowing, churning and defaecation
15
Q
Peristalsis
A
Propulsive(forwardmotion),caused by alternating contractions of longitudinal and circular smooth muscle
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
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
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
19
Q
Submucosal nerve plexus
A
Regulate glands and smooth muscle in the mucosa
20
Q
Myenteric nerve plexus
A
Controls digestive tract mobility (segmentation and peristalsis)
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
22
Q
Gastrin
A
secreted by G cells (stomach) and enteroendocrine cells (duodenum
23
Q
Secretin
A
released when chyme arrives in
duodenum
24
Q
GIP
A
Gastric inhibitory peptide
- released when fats and carbohydrates enter the SI
25
CCK
CHOLECYSTOKININ
| secreted when chyme arrives in deudenum
26
VIP
VASOACTIVE INTESTINAL PEPTIDE
| dialites intestinal capillaries and facillitates nutrient absorption
27
cephalic phase
Anticipation of food
- CNS → ANS long reflex
- Enetric → cells short reflex
- GI motility
- GI secretions
28
oral phase
digestion
- grind, mix & liquefy
- saiva: water, enzymes, muscus & lysozyme
29
saliva
contains enzyme SALIVARY AMYLASE →initiates chemical breakdown of carbohydrates
30
salivary glands
1. Submandicular (65-70%)
2. Parotid (25-30%)
3. Sublingual (5%)
31
saliva - composition
- primarily water
- can contain electrolytes, enzymes, antibodies, buffers (bicarbonate ions) and variable amounts of mucus depending of origination of saliva
32
Saliva - functions
- 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
regulation of saliva secretion
- triggered by taste, smell, sight or thought of food
| - stimulated by the Parasympathetic NS via CN VII (facial nerve & CNIX (glossophangeal nerve)
34
Swallowing
- 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
esophagus
muscular tube that connects pharynx to stomach.
| lining contains esophageal glands which secrete mucus to lubricate bolus as it moves to stomach
36
Esophagus sphincters
Upper esophageal sphincter
- helps the process of swallowing
Lower gastroesophageal sphincter
- controld movement of food into stomach
37
Stomach regions
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
Mucous neck cells & goblet cells
secrete a mucus that lines and protects cells of stomach
39
Enteroendocrine cells ( G CELLS)
secrete hormones and paracrine messengers
40
Chief cells
secrete gastric lipase and pepsinogen
41
Parietal cells
secrete HCl acid, intrinsic factor and ghrelin
42
Pepsinogen
(secreted form chief cells)
- breaks down protein chains into smaller peptide fragments
- most effective in the very acidic environment
43
Acid secretion from stomach
(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
Cephalic phase
- starts with sight, smell, taste, thought of food
| - parasympathetic activation leads to stimulation of gastric secretion and motility (CN X - vagus)
45
Gastric phase
- 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
intestinal phase
- enterogastric reflex and hormones (enterogastrones- secretin cholecytokinin and vasoactive intestinal peptide) decrease stomach secretion, motility & emptying
47
Stomach- receptive function
- Stomach can expand from 50ml at rest to about 1500 ml → smooth muscle relaxation + rugae results in limited inc. in internal pressure
48
Stomach - churning function
- Initiated and controlled by gastric pacemaker cells that control rate of peristalic waves ~/min
49
Stomach - emptying function
- Emptying rates based on amount and composition of chymr in duodenum (pH, conc/diluted)
50
Small intestine
- 6m x 2.5cm
| - mixes and propels contents into large intestine and enterocytes produce multiple digestive enzymes, hormones and mucus
51
duodenum
(first 25cm)
- receives stomach contents, pancreatic juice & bile
- neutralizes stomach acids, emulsifies fats, pepsin inactivated by pH inc
- [amcreatic enzymes aid digestion
52
jejunum
(next 2.5m)
- has large circular fods; thick, muscular walls
- most digestion and nutrient absorption occurs here
53
Ileum
(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
small intestine cells- secretory cells
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
chemical digestion
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
Pancreas
- 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
Pancreatic juice
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
pancreatic juice- digestive enzymes
pancreatic amylase → carbohydrate starch breakdown
- trypsin, chymotryspin and procarboxypeptidase → protein breakdown
- pancreatic lipase → most tryglyceride breakdown
- deoxyriboneuclase & ribonuclease → nucleic acid breakdown
59
Regulation of pancreatic juice secretion
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
regulation of pancreatic hormones
pancreatic islets contain cells that produce hormones GLUCAGON and INSULIN which are released directly into the bloodstream
61
Liver
- 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
Blood flow from GI tract to liver
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
Liver functions- after meal
- 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
Liver functions - between meals:
- break down stored glycogen and releases glucose into the circulation
- kupffer cells (hepatic macrophages) remove bacteria and debris from the blood
65
Bile - composition
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
Bile - function
- 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
Gallbladder
- 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
bile secretion - regulation
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
Large intestine - segmentation
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
Mass movement (m,ass peristalsis)
- 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
Large intestine - processes
- 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
Bacterial Flora
- 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
rectum
- 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
Defecation regulation
- 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
