Physiology Flashcards
4 functions of the digestive system
Digestion
Absorption
Secretion
Motility
Four layers of the GI tract
Mucosa
Submucosa
Muscularis externa
Serosa/adventitia
3 layers of mucosa
Epithelium
Lamina propria
Muscularis mucosae
2 types of epithelium and where they are found
Stratified squamous - mouth, oesophagus, anal canal
Simple columnar - stomach, small and large intestines
Submucosa
Thick irregular connective tissue
Serosa
Connective tissue layer surrounding intraperitoneal organs
Adventitia
Connective tissue layer surrounding retroperitoneal organs
Two laters of muscularis externa
Inner - circular
Outer - longitudinal
What make up the ENS?
Submucosal plexus
Myenteric plexus
Parasympathetic control is via which nerve?
Vagus nerve
Sympathetic control is via which nerve?
Splanchnic nerve
Effect of parasympathetic control
Increase secretion and motility
Effect of sympathetic control
Decrease secretion and motility
Arterial supply
Splenic
Celiac trunk
Superior and inferior mesenteric
Venous drainage
Gastric
Splenic
Superior and inferior mesenteric
Hepatic portal vein
Where does all venous drainage of the GI pass before returning to the heart?
Liver
3 monosaccharides absorbed by the body
Glucose, galactose and fructose
Monosaccharides that make up laltose
Glucose and galactose
Monosaccharides that make up sucrose
Glucose and fructose
Monosaccharides that make up maltose
Glucose and glucose
3 types of polysaccharides
Starch, cellulose and glycogen
Bond type in starch
Alpha-1,4 glycosidic bonds
Plant glucose storage type
Starch and cellulose
Bond type in cellulose
Beta-1,4 glycosidic bonds
How is cellulose broken down in vertebrates
Bacteria in colon expresses cellulase that hydrolysis cellulose
Animals glucose storage type
Glycogen
Bond type in glycogen
Alpha-1,4 glycosidic bonds
2 types of membranes in SI epithelial cells
Basolateral membrane - sides and bottom
Apical membrane - surface (brush border)
Transporters involved in glucose and galactose absorption
SGLT-1 - sodium glucose coupled transporter
Na/KATPase
GLUT-2
Transporters involved in fructose absorption
GLUT-5
GLUT-2
Enzymes that break down proteins and peptides
Proteases and peptidases
Endopeptidases
Act on interior amino acids of proteins
Exopeptidases
Act on terminal amino acids of proteins (amino and carboxy)
Transporters involved in amino acid absorption
SAAT1 - sodium amino acid coupled transporter
Na/KATPase
Amino acid carrier
Transporters involved in di/tripeptide absorption
PepT1 - hydrogen di/tripeptide coupled transporter
NHE3
Na/KATPase
Unknown di/tripeptide transporter
Fat is found in the form of
Triacylglycerol
Triacylglycerol is broken down by
Lipase
Triacylglycerol is broken down into
Monoglyceride + 2 fatty acids
Function of emulsifying agent
Prevents small droplets of fat reforming into large droplets of fat
Emulsification
Breaking down large droplets of fat into smaller droplets
Why does emulsification of fat globules occur?
To increase surface area for lipase to act on
Chylomicrons contains
Phospholipids, cholesterol and fat-soluble vitamins
Chylomicrons
Extracellular fat droplets
Water soluble vitamins
B group
C
Folic acid
Fat soluble vitamins
A, D, E, K
How is vitamin B12 absorbed
Binding to intrinsic factor
Vitamin B12 deficiency leads to
Pernicious anaemia
Iron is transported into duodenal enterocytes via?
DMT1
Ferittin
Intracellular iron store
Transferrin
What free iron binds to in the blood
3 salivary glands
Parotid, submandibular, sublingual
Components of saliva
Water Mucin Alpha-amylase Electrolytes Lysosome
Parasympathetic nerves control salivary secretion
Cranial nerves 7 (facial) & 9 (glossopharyngeal)
Effect of parasympathetic control on salivary secretion
Profuse watery saliva secretion
Effect of sympathetic control on salivary secretion
Viscous salivary secretion of small volume
3 layers of stomach muscularis external
Oblique, circular, longitudinal
Mucous neck cells secrete
Mucous
Chief cells secrete
Pepsinogen
Parietal cells secrete
HCl & intrinsic factor
4 controls of gastric epithelial proton pump activity
Increase - gastrin, histamine, acetylcholine
Decrease - Prostaglandins
3 mechanisms of control of gastric secretion
Neurocrine (vagus/local reflexes)
Endocrine (gastrin)
Paracrine (histamine)
Enterogastrones
Secretin, CCK, GIP (gastric inhibitory peptide)
Enterogastrones are release in response to
Acid, hypertonic solutions, fatty acids or monoglycerides in the duodenum
Function of enterogastrones
To prevent further acid build up in duodenum
Pepsinogen
Zymogen - inactive precursor for pepsin
Pepsinogen is activated by
Low pH (<3)
What controls the peristaltic rhythm of the stomach?
Pacemaker cells
What stimulates bicarbonate production in duodenum?
Presence of acid in duodenum
What control the secretion of bicarbonate in the duodenum?
Secretin
Vagal and ENS reflexes
What controls gastric motility?
Gastrin
Vagal and ENS reflexes
What inhibits gastric motility?
Chyme in duodenum
Endocrine portion of pancreas
Islets of Langerhans
Exocrine portion of pancreas
Acinar cells
Endocrine portion of pancreas secretes to
Circulatory system
Exocrine portion of pancreases secretes to
Lumen
Exocrine portion of pancreas responsible for
Digestion
Acinar cells secrete
Digestive enzymes
Duct cells secrete
Bicarbonate
Enterokinase is found at
Brush border of duodenal enterocytes
Function of enterokinase
Convert trypsinogen to trypsin
Pancreatic digestive enzymes
Proteases Nucleases Elastases Phospholipases Lipases Alpha-amylase
Secretion of zymogens from acinar cells stimulated by
CCK
CCK released is response to
Fat/amino acids in duodenum
Portal triad of liver consists of
Hepatic portal vein, hepatic artery, hepatic duct
What are the central veins of hexagonal liver lobules?
Hepatic veins
Components of bile
Bile acids, lecithin, cholesterol, bile pigments, toxic metals, bicarbonate
Main bile pigment
Bilirubin
Bile acid is synthesised from
Cholesterol
Bile acid is conjugated with
Taurine and glycine
Bile acid in conjugated to from
Bile salts
Why is bile acid conjugated?
To increase solubility
Gallbladder wall layers
Mucosa, muscularis, serosa (no submucosa)
Function of gallbladder
Store and concentrate bile
What controls bile secretion?
CCK
Function of CCK
Control bile secretion & pancreatic enzyme secretion
Crypt cells secrete
Chlorine & water
2 types of motility in SI
Segmentation & peristalsis
Effect of parasympathetic nerves on segmentation
Increases contraction
Effect of sympathetic nerves on segmentation
Decrease contraction
Hormone that initiated peristalsis in SI
Motilin
Teniae coli
3 bands that run the length of colon
Haustra
Pouches of colon formed by contraction of teniae coli
Anatomical cause of constipation
Distention of rectum
Symptoms of constipation
Headache
Nausea
Loss of appetite
Abdominal distention
Causes of diarrhoea
Food Stress Viruses Toxins Pathogenic bacteria Protozoans
Examples of enterotoxigenic bacteria
E. coli
Vibrio cholerae
Enterotoxigenic bacteria results in
Increased water in lumen and so profuse water diarrhoea
Enterotoxigenic bacteria act by elevating
cAMP
cGMP
calcium