2 - Small Intestine and Pancreatic Secretions Flashcards

1
Q

Objectives: Describe different types of contractions in the small intestines

Segmentation

Peristaltic

Migrating myoelectric complex

A
  • Segmentation Contraction - Most common
    • Smooth muscle of isolated segments contract; propel food toward colon
    • Proximal Intestine Frequency > Distal Intestine Frequency
    • Mixes chyme with digestive juices
  • Peristaltic
    • Propels chyme down small intestine; occurs only over short distances
  • Migrating Myoelectric Complex (like stomach)
    • ~ 90 min
    • Clears remaining chyme
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2
Q

Objectives: Describe how flow rate affects the ionic composition of pancreatic juice

Na

Cl

K

HCO3

A
  • Na - Stays the same
  • Cl - Decreases
  • K - Stays the same
  • HCO3 - Increases
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3
Q

Objectives: Explain how the aqueous component of pancreatic juice is formed

Rates of secretion tonicity compared to plasma?

HCO3? Cl? K?

Rate dependent changes?

A
  • At all rates of secretion, juice isotonic with plasma
  • [HCO3-] higher than plasma
  • [Cl-] lower than in plasma
  • [K+] ~ plasma
  • At lowest flow rates: Juice = Na / Cl
  • At highest flow rates: Juice = Na / HCO3

AS FLOW RATE INCREASES, Na, K STAY THE SAME, HCO3 INCREAES, AND Cl DECREASES

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4
Q

Objectives: Explain how the aqueous component of pancreatic juice is formed

Ductile / Centroacinar Modifications

H+

HCO3

Cl

Na

Water

A
  • Acinus produces small volume of initial pancreatic juice, mainly Na, Cl
  • Ductile and Centroacinar cells modify via:
    • Secrete HCO3-
    • Absorb Cl-
  • H+ transported out of cell by NHE-1 antiporter
    • Venous blood around pancrease has lower pH
  • HCO3 co-transported into cell by NBC
    • Exchanged for Cl at lumen
    • Rate of secretion depends on Cl in lumen
  • Cl enters lumen through apical channels
    • CFTR channels mutates in cystic fibrosis
  • Na enters cell in exchange for H+
    • Tx out of cell by Na K ATPase
      • Keeps [Na] low
      • K exits through chnnel
  • Water moves into lumen along osmotic gradient as pancreatic ducts are water-permeable
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5
Q

Objective: Explain how pancreatic secretion is regulated

Regulation is phase dependent:

Cephalic and Gastric

Intestinal Phase (majority)

Potentiation

A
  • Cephalic and Gastric Phase
    • ACh acts on acinar and ductile cells
    • Vagovagal reflex, stimulates secretion
      • Stomach distension
    • CCK releasing peptide and monitor peptide released in response to nerve input on I-cells
  • Intestinal Phase (majority)
    • Stimulated by acid/fat/protein in duodenum
    • Acid releases secretin from S-cells
      • Secretin acts on ductule cells to increase HCO3 secretion which neutralizes acid
    • CCK - Increase enzyme secretion
      • Released from I cells in duodenum
    • CCK and ACh potentiate action of secretin on ductal cell secretion
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6
Q

Objectives: Explain how Cystic Fibrosis and Pancreatitis affect pancreatic function

Cystic Fibrosis

A
  • Cause:
    • Defect in Cl- channels
  • Effect:
    • Reduces secretion of aqueous and enymatic components; lack of aqueous secretion leads to concentration of pancreatic juice, which blocks secretion of enzymation component
  • Result:
    • Malabsorption and Steatorrhea
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7
Q

Objectives: Explain how Cystic Fibrosis and Pancreatitis affect pancreatic function

Pancreatitis

A
  • Forms:
    • Chronic
    • Acute
  • Causes:
    • Chronic Alcoholism
    • Gallstones
    • High TAGs
    • Smoking
  • Acute Symptoms:
    • Abdominal pain, swollen/tender abdomen
    • Nausea, Vomiting, Diarrhea, Fever
  • Result:
    • Activated enzymes digest pancreatic tissue
    • Serum Amylase / Lipase ELEVATED
  • Chronic:
    • Alcohol Abuse
    • High protein concentration in pancreatic juice
      • ​Reduced secretion of water, bicarbonate
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8
Q

What are the different cell types of the small intestine?

Enterocytes

Goblet Cells

Crypt Cells

A
  • Enterocytes
    • Epithelial; microvilli protrude from surface
    • Digestion, Absorption, Secretion
  • Goblet Cells
  • Crypt Cells
    • Proliferative Cells - form enterocytes / goblet cells
    • Secrete fluids and electrolytes
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9
Q

Objectives: Describe different types of contractions in the small intestines

Control:

Peristaltic Reflex/Rush

Intestinointestinal Reflex

Gastroileal Reflex

Gastrocolic Reflex

Ileus

A
  • Peristaltic Reflex/Rush
    • Initiated by chyme in intestine; causing distension/irritation
    • Sever infectious diarrhea
  • Intestinointestinal Reflex
    • Over distension of one segment inhibits contractile activity in rest of intestine
    • Prevents further adding contents to a full space
  • Gastroileal Reflex
    • Gastric secretion and emptying triggers increases peristalsis in ileum
    • Relaxes ileocecal sphincter and movement of ileal contents into colon
  • Gastrocolic Reflex
    • When you eat you have to poop.
  • Ileus
    • Loss (reduction) in contractile activity of intestines in absence of blockage
    • Irritation of peritoneum
    • Cause: Surgery, illness, electrolyte imbalance
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10
Q

Describe the different pancreatic cell types

Acinar - what do they produce?

Centroacinare and Duct cells - purpose?

A
  • Acinar cells produce:
    • Peptidases - digest protein
    • Lipases - digest fat
    • Amylase - digest carbs
  • Centroacinare and Duct cells secrete pancreatic juice
    • High HCO3- neutralizes gastric acid in duodenum
    • Raises pH for optimal enzymatic digestion of nutrients
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11
Q

How are the enzymatic components of pancreatic secretions stored and released?

Lipase

Amylase

Proteases

A
  • Lipase / Amylase secreted in active form
    • ​Fats, Carbs
  • Proteases (Trypsin, Chymotrypsin) secreted in inactive form
    • ​Proteins
    • Activated in small intestine
    • Trypsin inhibitor secreted to protect pancreas from autodigestion
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12
Q
A
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