GI Physiology Flashcards
How is protein digested to amino acids?
Protein + trypsin and pepsin= peptides in gastric juices (pepsinogen -> pepsin)
trypsinogen in pancreatic juices converted to trypsin at basic pH in SI
Peptides + peptidases = amino acids
Peptidases produced by SI
AA’s actively transported into epithelial cells
How are lipids digested?
Lipids combine with bile salts in duodenum forming fat droplets
Lipase digests triglycerides to monoglycerides and fatty acids
They diffuse into epithelial cells where they combine with proteins forming lipoproteins - chylomicrons and enter lacteal
How are carbohydrates digested?
maltose -> glucose
sucrose -> glucose and fructose
lactose -> glucose and galactose
polysaccharides broken down by amylase to maltose
What are the 3 layers of mucosa
Mucous membrane
Lamina propria
Muscularis mucosa
How is digestive function controlled
Autonomic smooth muscle
Intrinsic nerve plexuses
Extrinsic nerves
GI hormones
How does Autonomic smooth muscle Control digestion?
Self-induced electrical activity
Needs to reach threshold to induce contraction (eg: food present)
How does Intrinsic nerve plexuses Control digestion?
Enteric nervous system
Sensory neurons respond to stimuli
Excitatory and inhibitory neurones modulate motility or secretions of hormones.
Acetylcholine promotes smooth muscle contraction.
Nitric oxide & vasoactive intestinal peptide relax smooth muscle.
How does Extrinsic nerves Control digestion?
Sympathetic and parasympathetic nerves influence motility and secretion by modifying activity of intrinsic nerve plexuses.
Sympathetic slows down
Parasympathetic promotes motility and secretion
Also coordinates activity between diff. regions
What are some GI hormones in the stomach
Ghrelin
gastrin
What are some GI hormones in the duodenum
Cholecystokinin
secretin
GIP
Motilin
What are some GI hormones in the pancreas
Insulin
glucagon
amylin
What are some GI hormones in the colon
GLP-1
GLP-2
oxyntomodulin
PYY3-36
How is the Oesophagus related to function?
Straight muscle tube
Sphincters at each end
Peristaltic waves push food through
How is the Stomach related to function?
3 sections: fundus, body and antrum
secretes HCl to digest
Mixing moments convert food to chyme
Pyloric sphincter- barrier between stomach and SI
What is filling of the stomach mediated by?
Vagus nerve
What factors affect gastric emptying?
Amount of chyme in stomach
Fat in duodenum-> slows
Acid-> un-neutralised acid slows
Hypertonicity-> slows when contents osmolarity rises
Distension-> too much already in duodenum slows
What is the natural response for gastric emptying?
mediated thru intrinsic nerve plexuses and autonomic nerves
the enterogastric reflex
What is the hormonal response for gastric emptying?
Release of hormones from duodenal mucosa - enterogastrones (inhibit emptying):
Secretin
cholecystokinin (CCK)
What are the 3 types of gastric exocrine secretory cells?
Mucous cells- lines enzymes pits and entrance of glands
Chief cells- secrete pepsinogen
Parietal cells- secretes HCl and intrinsic factor
What does a Gastric pit look like
Like a crab claw but on the side