GI Lecture 2 Flashcards by Mary Miller

2 types of secretions in alimentary tract

-Where

Digestive enzymes (mouth->ileum)

Mucus (in ALL parts of alimentary tract)

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Types of glands (4)

1-single cell mucous gland (local)
2-Pits/invaginations of epithelium in mucosa that contain specialized secretory cells
3-Deep tubular glands (stomach and upper SI)
4-Complex glands/accessory glands=help with digestion and uses duct system

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Mechanisms for secretion (2)

Mechanical stimulation (food present)

Same as gut molitiy= gut distention, chemical irritation… ect. Reflexes via ENS

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ANS PANS and SANS influence with secretion

PANS=almost always stimulates secretion via CN 9 and 10

SANS= moderately or inhibits secretion

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Mucus

What makes up mucus
Purpose

Made up of water, glycoproteins, and electrolytes

Coats food to allow it to go down tract easily and also prevent it from touching GI walls. Also resists digestive enzymes and has small buffer ability.

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Salivary glands (4) and glandular tissue
-What products are secreted

Parotid= serous/water
Sublingual=mixed (serous/mucous) and single duct
Mandibular=mixed

Glandular tissue secretes a lot of mucus and found in tongue. In carnivores, ZYGOMATIC gland does this,

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Fxns of saliva (6)

moistens food for mastication
lubricates food for deglutition
begins process of digestion CHO
Antibacterial properties (AB and lysozymes)
Evaporative coolin (cats/dogs)
Supports rumen fxn as buffer

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Digestive enzymes in saliva (2)

Salivary amylase (digests CHO) present in omnivores usually absent in carnivores and ruminants

Lingunal lipase helps fat digestion and disappears with age

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Stimulation of saliva production

PANS (CN 7 and 9)
SANS (carnivores drooling)
Mastication
Tastebud activation

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Is endocrine regulation used in saliva secretion?

Little to none

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Secretory process of saliva

Primary secretion from
Changes in content/rate

Primary secretion=acini

Changes in content due to absorption/secretion in duct. If high flow rate, acini fluid. If slow flow rate, duct has gretaer chance to change composition of product secreted

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Ruminant salivation

Secrete 100-200 L/day and need to replenish lost electrolytes

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Gastric secretions

Where are secreting cells
Types of tubular glands

Entire stomach has mucus secreting cells

Oxyntic (acid forming) gland-secretes HCl and pepsinogen and in proximal pt of stomch

Pyloric glands secrete mostly mucus and some pepsinogen and in distal pt of stomach

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3 types of secretory cells and products

Mucus neck cells (mucus + pepsinogen)

Peptic/Chief cells (PEPSINOGEN)

Parietal/Oxyntic (HCl and intrinsic factor)

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How parietal/oxyntic cells secrete H+

-Drug that can inhibit

Cell takes water and carbon dioxide and makes bicarbonate to go out into ECM and uses K+/H+ pump (ATP used) to pump H+ in lumen gastric cell to be SECRETED

-Omeprasol can inhibit H+ pump

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Primary protease in stomach?

Made by
Active form

Pepsinogen
Made by peptic glands
-Active form at low pH or when activated by other active pepsinogen.
-Inactive pH above 5

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Pyloric glands

Most prevalent cell
Secertes

Contains mostly mucus cells (few chief/no oxyntic)

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HCl secretion

Via
Controlled by
Operates in relation w/

Oxyntic cell deep in gastric gland
Under control of endocrine and nervous regulation
Operates w/eneterochromaffin (secretes histamine

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Enterochromaffin cells

Secrete
Stimuli

Secrete histamine proportional to HCl release.

Stimuli is gastrin from stomach directly via vagus release of Achl

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Pepsinogen secretion

Via
2 signals

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Chief cells

1-Via Achl from vagus or ENS
2-Via acid in stomach
–>Pepsinogen secretion proportional to acid secretion

(-) Feedback w/xs acidity

-What happens

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3 is optimal pH for digestive enzymes, if below 3 then 2 things happen:
1-Gastrin secretion blocked
2-Nervous reflex inhibits gastric secretions

Phases of gastric secretion

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1-Cephalic (food before eating)
2-Gastric (food in mouth)
3-Intestinal (food in SI)

Cephalic stage

Gastric %
What happens

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20% gastric secretions

Vagus n stimulates due to sight, smells

Gastric stage

Gastric %
What happens

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70%

Vagovagal and local enteric reflex

Inestinal phase | -Gastric %

10%

Intestinal inhibition - When - Stimuli

During intestinal stage -Reverse enterogastric reflex via ENS and same inhibitory influences as gut motility (distention, low pH, rotein breakdown products, irritation of mucosa, hyper/hypo osmotic chyme)

Pancreatic secretions - Made where - How does it deliver

Digestive enzymes made in acinar Delivers products by joining hepatic duct and emptying into SI at sphincter of Oddi OR pancreatic duct empties directly into SI solo

Pancreatic digestive enzymes - Major - Minor

Major (most abundant)= trypsin Chymotrypsin Carboxypolypeptidase Minor Elastase Nuclease

Chymotrypsin

Pancreatic digestive enzyme | Proteins-->polypeptides

Carboxypolypeptidase

Pancreatic digestive enzyme | polypeptides-->AA

Pancreatic amylase | -Digests

CHO and complex CHO but NOT cellulose

Fat digestion in pancreas (3 enzymes)

Pancreatic lipase (neutral fat-->FA and monoglycerides) Cholestrol esterase (hydrolyzes cholestrol esters) Phospholipase (splits FA from phsopholpids)

How to activate trypsinogen (pancreatic enzyme)

Chyme has to be present so enterokinase can be secreted. Enterokinase activates trypsinogen. Activated trypsinogen can activate trypsinogen. (auto-catalyze_

How to activate chymotrypsinogen and procarboxypeptidase

Active trypsin

Trypsin inhibitor | -made via

Acinar cells | prevents trypsinogen activation while in cells of acini and duct system

Regulation of pancreatc secretion (3)

Achl (from vagus and ENS) CCK (released from "I" cells when food/fat detected in SI and acinar cells stimulated and results in 70-80% enzyme secretion Secretin (released when acid enters SI and present in "s" cells and stimulates HCO3- and Cl to be made.

Secretin actions in pancreas

Results in Co2 absorbed in blood and NaCl to protect SI from low pH and allowing pancreatic enzymes to work in protected environment.

CCK and Achl and Secretin relationship in pancreas

CCK and Achl work together for prodcution of pancreatic enzymes and stimulate acinar cells Secretin used for delivery and NOT making digestive enzymes but NaCl/HCO3 All 3 needed to work together

Phases of pancreatic secretion

Cephalic 20% pancreatic secretions (nervous signals) Gastric 5-10 % (nervous signals) Intestnial 75 % Chyme enters SI in response to CCK and secretin

Special circumstances with pancreas - Omnivore/NR herbivore - Horse - Exocrine pancreatic insuffiency

- Omnivores/non ruminant herbivores: pancreas provides large volumes of buffered fluid for any fermentation occurring in LI - Horses: low enzyme concentration, low HCO3 in fluid and ileum exchanges Cl- for HCO3- - Exocrine pancreatic insufficiency: too much trypsin…digests pancreas and unable to digest and get nutrients. Affects insulin production.

3 bile fxns for digestions

Predominately involved in fat digestion Aids in absorption of digested fat products through intestinal mucosa Helps with some excretory processes

What makes bile?

Hepatocytes and duct cells (stimulated by secretin)

After bile is made, where does it go?

Gall bladder until needed. Bile becomes more concentrated in storage.

T/F Liver can make bile continuously

What makes up bile?

Bile acids/salts (modified cholesterol, bilirubin, lecithin)

What stimulates bile releasal? | What doesn't?

Stimulated by presence of fat products in SI and mediated by CCK. CCk relaxes sphincter of Oddi and contractions of gallb;adder -->CCK is most potent stimulator -->Achl from vagus and ENS stimulate weakly

Secretin affect on liver secretion

Stimulates production of serous bicarbonate rich fluid to help neutralize gastric acid in duodenum. Less effective than pancreatic secretion, generally Liver secretion is more important in sheep

Specific digestive functions of bile (3)

Emulsifaction of fats Transport fat products to intestinal mucosa Activate pancreatic lipase

How does bile help transport fat products to intestinal mucosa?

Micelle is formed (tiny droplets of fat surrounded by bile salt) Bile salts make micelles soluble in chyme Provide for absorption of these products Prevents reassembly of triglycerides

GI Lecture 2 Flashcards

(49 cards)