GI physiology Flashcards
Grand tour of alimentary canal
what are the 4 main processes of the digestive system?
- Digestion
- Secretion
- Absorption
- Motility
Grand tour of alimentary canal
Is the lumen part of the inside or outside of the body?
Lumen is technically outside of body. Continuous tube from mouth to anus.
Grand tour of alimentary canal
What is gastric motility?
Movement of material from mouth to anus
Grand tour of alimentary canal
Explain Gastric motility
- Peristaltic contractions originate in the upper fundus, move to pyloric sphincter
- Moves gastric chyme forward → gastric emptying into duodenum
Grand tour of alimentary canal
Explain GI Absorption of nutrients and locations
○ Digested nutrients absorbed by GI mucosal cells into blood/lymph (liver will filter out before entering blood etc)
Grand tour of alimentary canal
name the Accessory Organs
Gallbladder, liver, pancreas
Grand tour of alimentary canal
In relation to GI explain what the liver does
Hepatocytes produce bile which emilsifies lipid globules, aids in abdorption
Stores glucose in form of glycogen
Grand tour of alimentary canal
in relation to GI explain the function of Gallbladder
Storage and concentrated Bile; releases bile into small intestine in reponse to hormonal stimulus
Grand tour of alimentary canal
In relation to GI explain the function of the pancreas
Exocrine function: acini secrete various digestive enzymes; “pancreatic juice;” e.g. secretin, cholecystokinin (CCK)
Endocrine function: islets produce glucagon, insulin to maintain normal glucose levels; somatostatin, pancreatic polypeptide production
Grand tour of alimentary canal
Explain the function of the mouth
Foodstuffs are broken down by chewing; saliva is added as a lubricant
Grand tour of alimentary canal
Explain the function of the oesophagus
Acts as a conduit between the mouth and the stomach
Grand tour of alimentary canal
Explain the function of the stomach
for Digestion of proteins; foodstuffs reduced to liquid form
for storage
for sterilisation hydrochloric acid and kills microorganisms.
Grand tour of alimentary canal
What is the function of the pancreas in the alimentary system?
Production of digestive enzymes for digestion of fats, carbohydrates and proteins
Grand tour of alimentary canal
What is the function of the small intestine?
Final stages of chemical digestion and nutrient absorption
Grand tour of alimentary canal
What is the function of the large intestine?
Water absorption
Bacterial fermentation
Formation of faeces
Grand tour of alimentary canal
Name the four layers of the alimentary canal?
Mucosa
Submucosa
Muscularis external
Serosa/ adventitia
Grand tour of alimentary canal
What type of epithelium is found in the mouth, oesophagus and anal canal?
Stratified squamous
Grand tour of alimentary canal
What are the layers of mucosa?
epithelium
lamina propria
muscularis mucosa
Grand tour of alimentary canal
What type of epithelium is found in the stomach and intestines?
simple columnar
Grand tour of alimentary canal
What is the function of the epithelium in the alimentary canal?
Synthesis and secretion of digestive enzymes, hormones, mucus
Absorbs products of digestion
Grand tour of alimentary canal
What is the lamina propria?
loose connective tissue
Grand tour of alimentary canal
What is the muscularis mucosae?
thin layer of smooth muscle
Grand tour of alimentary canal
What does the submucosa contain?
Neurones
Blood vessels
Lymphatic vessels
Grand tour of alimentary canal
Where are the submucosal glands found?
Oesophagus
Duodenum
Grand tour of alimentary canal
What do the neurones in the submucosa form?
Parasympathetic submucosal plexus
Grand tour of alimentary canal
Describe the submucosa layer
Thick, irregular connective tissue
Grand tour of alimentary canal
What is the serosa?
Connective tissue outer layer
Grand tour of alimentary canal
What is the difference between serosa and adventitia
Adventitia is outside peritoneal cavity
Serosa is inside peritoneal cavity
Grand tour of alimentary canal
What does serosa surround?
Stomach
Small intestine
Large intestine
Grand tour of alimentary canal
What does the adventitia attach?
Oesophagus and rectum to surrounding structures
Grand tour of alimentary canal
What is the muscularis externa?
Two concentric thick laters of smooth muscle
Grand tour of alimentary canal
What type of muscle in the inner layer of muscularis externa?
Circular muscle
Grand tour of alimentary canal
What type of muscle in the outer layer of muscularis externa?
Longitudinal muscle
Grand tour of alimentary canal
Where is the myenteric plexus located?
Between the inner circular and outer longitudinal muscular layers
Grand tour of alimentary canal
What is the function of muscularis externa?
peristalsis and segmentation
Grand tour of alimentary canal
What is the enteric nervous system made up of?
submucosal plexus and myenteric plexus
Grand tour of alimentary canal
What is the function of the enteric nervous system?
Independent control of gut function
Grand tour of alimentary canal
What provides autonomic control of the alimentary canal?
Long parasympathetic and short ENS reflexes
Grand tour of alimentary canal
What provides parasympathetic control of the alimentary canal?
Vagus nerve
Grand tour of alimentary canal
What nerves control salivation?
Facial (7th)
Glossopharyngeal (4)
Grand tour of alimentary canal
What provides sympathetic control of the alimentary canal?
Splanchnic nerve
Splachnic = Sympathetic
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What does the celiac trunk supply?
Stomach
Small intestine
Pancreas
Liver
Grand tour of alimentary canal
What does the superior mesenteric artery supply?
Small intestine
Caecum
Ascending colon
Transverse colon
Grand tour of alimentary canal
What does the inferior mesenteric artery supply?
Descending colony
Sigmoid colon
Rectum
Grand tour of alimentary canal
What provides venous drainage from the stomach?
Gastric veins
Grand tour of alimentary canal
What provides venous drainage from the pancreas?
Splenic vein
Grand tour of alimentary canal
What does all venous drainage from GI tract travel via?
Hepatic portal vein
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what is splenic artery branch of
Coeliac trunk behind pancreas
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portal triad
Common hepatic duct, portal vein hepatic artery
in lesser omentum.
Grand tour of alimentary canal
Name the monosaccharides
glucose, fructose, galactose
What are monosaccharides?
Hexose sugars
simplest carbohydrates (simplest sugars)
prefix indicates number of carbons: suffix –ose, indicates a saccharide
What are disaccharides?
two monomers linked by glycosidic bond
What are disaccharides broken down by?
Brush boarder enzymes in small intestine epithelial cells (enterocytes)
What is lactose made of?
glucose and galactose
What is sucrose made of?
glucose and fructose
What is maltose made of?
glucose and glucose
Name the polysaccharides
starch, glycogen, cellulose
What is starch?
storage form of glucose in plants
What are glucose monomers in starch linked by?
Alpha-1,4 glycosidic bonds
What makes glucose chains branched?
Amylopectin
70%-80% of starch)
Similar structure as amylose but branched
Glycosidic (α-4) bonds join glucose in the chains but branches
What links glucose in straight chains?
Alpha-amylose
How is stratch hydrolysed and where
Hydrolysed by amylases (saliva, pancreas)
Describe the structure of cellulose
Unbranched linear changes of glucose monomers
What links the cellulose chains?
B-1,4 glycosidic bonds
What are the glucose monomers in glycogen linked by?
Alpha 1,4 glycosidic bonds
What digests polysaccharides?
Alpha amylase
Mouth:
Begins carbohydrate digestion
Enzyme: salivary amylase hydrolyses (α1→ 4) bonds of starch
Starts starch digestion → Dextrins, maltose, maltotriose
Can we absorb disaccharides?
No
What does SGLT1 transport?
glucose and sodium
What does SGLT1 absorb?
Galactose
SGLT1 also helps get WATER into body
What channel does glucose move out the cell?
Glut-2
absorbed into enterocytes via sodium ion cotransport (secondary active transport) → GLUT2 transporter extrudes glucose, galactose across basolateral membrane into blood in apical membrane → GLUT2 transporter extrudes fructose across basolateral membrane into blood;
How does fructose enter the cell?
(GLUT5)
absorbed into enterocytes via facilitated diffusion by GLUT5 transporter in apical membrane → GLUT2 transporter extrudes fructose across basolateral membrane into blood; fructose absorption cannot occur against electrochemical gradient. Moved down concentration gradient (↑ in gut lumen ↓ in blood)
What are proteins?
polymers of amino acids linked by peptide bonds
What are peptides?
Small proteins, 3-10 amino acids in length
What is the addition of CHO to a protein called?
Glycoproteins
What is the addition of a lipid to a protein called?
Lipoprotein
What are proteases?
Enzymes which hydrolyse peptide bonds and reduce proteins
What does endopeptidase do?
digests internal peptide bonds
What does exopeptidase do?
Digests terminal peptide bonds
Proteases (endopeptidases, exopeptidases
Endopeptidases: tripsin, chymotrypsin, pepsin; hydrolyse interior peptide bonds
Digest large polypeptides/peptide
Name the types of exopeptides?
Aminopeptidase
Carboxypeptidase
What do amino acids travel through the cell via?
SAAT1 with sodium
What does PEPT1 transport?
Hhydrogen
Dipeptide
PepT1 (hydrogen dependent) in bacteria transports around 70% protein in diet.
Penicillin tripeptide is transported via PepT1.
What happens to the hydrogen that enters the cell with the dipeptide?
Exits via NHE3 to allow sodium to enter cell
What is most of the ingested fat in the form of?
Triacylgycerol
(triglycerides)
Esters of fatty acids and glycerol. (Esters - neutral uncharged lipids)
Water insoluble large lipid droplets
Dietary fuel and insulation.
What is all fat digested by? Where?
Pancreatic enzymes (pancreatic lipase, cholesterol ester hydrolyse, phospholipase A2) colipase finish digestion in small intestine. Lipase = water-soluble
Promote emulsification (dispersion) by bile salts & peristalsis (mixing) amphipathic (charged polar and non-polar non-charged) stop reaggregation,
Site of digestion: small intestine by pancreatic enzyme
Why is fat digestion so slow?
As digestion can only take place at surface of droplet
emulsify dietary lipids from large lipid droplets into smaller droplets → create ↑ surface area for pancreatic enzymes.
Nonpolar- lipid interior
Polar - water at surface, repels other droplets.
What is emulsification?
Dividing large lipid droplets into smaller droplets
(dispersion) by bile salts & peristalsis (mixing)
What does emulsification do?
Increase surface area and accessibility of lipase action
mulsify dietary lipids from large lipid droplets into smaller droplets → create ↑ surface area for pancreatic enzymes.
Nonpolar- lipid interior
Polar - water at surface, repels other droplets.
What does emulsification require?
Mechanical disruption
Emulsifying agent
What produces mechanical disruption for emulsification?
Smooth muscle contraction grinds and mixes lumeneal contents
What produces mechanical disruption for emulsification?
Smooth muscle contraction grinds and mixes lumeneal contents
Why is an emulsifying agent needed in the formulation of an emulsion?
Prevents small droplets reforming into large droplets
Give examples of emulsifying agents
Bile salts and phospholipids secreted in bile
Amphiaphatic molecules
What do polar portions do in terms of emulsification?
Repel other small lipid droplets and prevent reforming into large droplets
What is absorption of lipase digestion enhanced by?
Formation of micelles
What are micelles made of?
Bile salts
Monoglycerides
Fatty acids
Phospholipids
Where are the polar portions of molecules found on micelle?
Surface
What part of the micelle do non polar portions form?
Core
Describe micelle breakdown
Release of small amounts of free fatty acids and monoglycerides into solution resulting in diffusion across plasma membrane of absorbing cells
What does the dynamic equilibrium between fatty acids and monoglycerides in solution and in micelles retain?
Most of fat digestion products in solution while constantly replenishing supply of free molecules for absorption
What does the dynamic equilibrium between fatty acids and monoglycerides in solution and in micelles retain?
Most of fat digestion products in solution while constantly replenishing supply of free molecules for absorption
What happens to epithelial cels, fatty acids and monoglycerides when the enter the smooth endoplasmic reticulum?
They are reformed to triacylglycerolsThey are reformed to triacylglycerols
What are triacylglycerols droplets coated with?
Amphiphatic protein for emulsification
What are triacylglycerols droplets transported though?
Cell in vesicles from sER membrane
What are triacylglycerols droplets processed though?
Golgi apparatus and exocytosed into Extracellular fluid at serosa membrane
What are chylomicrons?
Extracellular fat droplets
Where do chylomicrons pass into?
Lacteals between endothelial cells
What are lacteals?
Finger like projections
What are the two classes of vitamins?
fat soluble and water soluble
What are the fat soluble vitamins?
A, D, E, K
What are the water soluble vitamins?
B, C and folic acid
What are the water-soluble vitamins absorbed by?
Passive diffusion or carrier- mediated transport
What are the water soluble vitamins absorbed by?
Passive diffusion or carrier- mediated transport
What is vitamin b12?
vitamin - large charged molecule (can not across membrane)
What does vitamin b12 bind to?
binds to intrinsic factor in stomach form complex → absorbed via specific transport mechanism in distal ileum
What is the vitamin B12 intrinsic factor complex absorbed via?
Specific transport mechanism in distal ileium
What does B12 deficiency lead to?
pernicious anemia
What is iron transported across?
Brush border membrane via DMT1 into duodenal enterocytes
What does iron in blood bind to?
Transferrin
What are iron ions incorporated into?
Ferritin
What is hyperaemia?
Increased ferritin levels so more iron bound in enterocytes
What is anaemia?
Decreased ferritin levels so more iron released to blood
What is ferritin expression regulated depending on?
Body’s irons status
The process of chewing is for…
Prolong taste experience
Defence against respiratory failure
food broken down into smaller pieces is easier to digest.
When mixed with saliva, allows the body to extract the greatest possible amount of nutrients
How is chewing voluntary controlled?
Somatic nerves innervate skeletal muscles of the mouth/ jaw
Describe the chewing reflex
- Contraction of jaw muscles causing pressure of food against gums
- Hard palate and tongue stimulates mechanoreceptors stimulation inhibition of jaw muscles reducing pressure
What glands secrete saliva?
parotid, submandibular, sublingual
What is in saliva?
Water - mucosal integrity
Mucins - lubrication, digestion, pellicle formation
Alpha- amylase - initiates digestion in stomach
Electrolytes - moistens food
Lysozyme - cell membrane hydrolysis
What is the function of water in saliva?
Softens, moistens and dilutes particles
What is the function of mucins in saliva?
lubrication
What is the major protein component of saliva?
Mucins
What is the function of alpha-amylase in saliva?
Catalyses breakdown of polysaccharides into disaccharide and glucose