GI Physiology Flashcards by Judy Martin

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

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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

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How are carbohydrates digested?

maltose -> glucose
sucrose -> glucose and fructose
lactose -> glucose and galactose

polysaccharides broken down by amylase to maltose

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What are the 3 layers of mucosa

Mucous membrane
Lamina propria
Muscularis mucosa

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How is digestive function controlled

Autonomic smooth muscle
Intrinsic nerve plexuses
Extrinsic nerves
GI hormones

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How does Autonomic smooth muscle Control digestion?

Self-induced electrical activity
Needs to reach threshold to induce contraction (eg: food present)

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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.

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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

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What are some GI hormones in the stomach

Ghrelin
gastrin

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What are some GI hormones in the duodenum

Cholecystokinin
secretin
GIP
Motilin

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What are some GI hormones in the pancreas

Insulin
glucagon
amylin

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What are some GI hormones in the colon

GLP-1
GLP-2
oxyntomodulin
PYY3-36

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How is the Oesophagus related to function?

Straight muscle tube
Sphincters at each end
Peristaltic waves push food through

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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

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What is filling of the stomach mediated by?

Vagus nerve

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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

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What is the natural response for gastric emptying?

mediated thru intrinsic nerve plexuses and autonomic nerves
the enterogastric reflex

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What is the hormonal response for gastric emptying?

Release of hormones from duodenal mucosa - enterogastrones (inhibit emptying):
Secretin
cholecystokinin (CCK)

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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

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What does a Gastric pit look like

Like a crab claw but on the side

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What are the functions of HCl

activates pepsinogen to pepsin
Denatures protein by uncoiling
Kills mocroorganisms

What is the gastric mucosal barriers role? how does it work?

Allows stomach to contain acid without hurting itself
Membranes impermeable to H+
Cells joint by tight junctions
Mucus coating
HCO3- rich mucus serves as barrier that neutralizes acid near mucosa

What is in gastric juice

Pepsinogen
mucus
intrinsic factor

What’s digested and absorbed in the stomach?

Digest- carbs and protein
Absorb- alcohol and aspirin or other weak acids

What nerve controls digestion? what type of nervous system is it related to?

Vagus nerve parasympathetic

Pancreas-> what is the endocrine function?

Islets of Langerhans

Pancreas-> what is the Exocrine function?

Secretes pancreatic juice which contains: Pancreatic enzymes secreted by acinar cells Aqueous alkaline sol. actively secreted by duct cells - rich in NaHCO3 which neutralising HCl.

What does secretin stimulate?

Release of NaHCO3 from pancreatic duct cells

What enzymes digest proteins?

Trypsinogen - trypsin Chymotrypsinogens - chymotrypsin Procarboxypeptidase - carboxypeptidase

What causes increased secretion of pancreatic digestive enzymes into the duodenal lumen?

Fats and proteins in duodenal lumen causes increased Cholecystokinin (CCK) release from duodenal mucosa, causes pancreatic acinar cells to increase secretion of digestive enzymes into the lumen

What does gastrin do?

Stimulates HCl and pepsinogen

What does somatostatin do

Inhibits HCl, pepsinogen and gastrin

What does secretin do?

presence of acid, Stimulates NaHCO3 secretion

What does CCK do?

Presence of fat and protein, stimulates pancreatic enzyme release

What does the liver do when it comes to digestion?

Release bile salts

What are bile salts made of

Lecithin Cholesterol Bile

What are the 3 parts of the Small intestine

Duodenum Jejunum Ileum

what are the 2 ways the small intestine has motility

segmentation migrating motility complex

What is the mesentery proper

Keeps the small intestine together

What is segmentation in the small intestine?

Ring like contractions Mixes and propels chyme thru SI Initiated by pacemaker cells in SI which provide basic electrical rhythm

What is the migrating motility complex in the small intestine?

Sweeps intestines clean

What is digested in the SI lumen

Fat

What makes up the large intestine

Colon Cecum Appendix Rectum

What is the taeniae coli

Longitudinal bands of muscle in the large intestine

What is the haustra

Pouches or sacs in large intestine

What is the haustral contraction

Main motility of large intestine

Whats secreted in the large intestine

Alkaline mucus

Whats absorbed in the large intestine

Salt and water. Vit.k synthesized by bacteria

Explain the release, inhibition and function of: Gastrin

release: protein in stomach Inhibited by: accumulation of acid in stomach Function: Increase secretin of HCl and pepsinogen Enhances gastric motility and ileal motility Induces mass movements in colon helps maintain digestive tract lining

Explain the release, inhibition and function of: secretin

release: Presence of acid in duodenum Inhibited by: x Function: Inhibits gastric emptying to prevent further acid from entering duodenum until acid already neutralized Inhibits gastric secretion to decrease acid production Stimulates pancreatic duct cells to produce NaHCO3 Stimulates Liver to secrete NaCO3 rich bile

Explain the function of: CCK- cholecystokinin

Function: Inhibits gastric motility and secretions Stimulates pancreatic acinar cells to increase secretion of pancreatic enzymes Causes contraction of gallbladder Regulator of food intake

Explain the function of: GLP

Function: Glucose dependent insulinotrophic peptide Stimulates insulin release by pancreas Stimulated by presence of glucose in GI tract