2 - Small Intestine and Pancreatic Secretions Flashcards
Objectives: Describe different types of contractions in the small intestines
Segmentation
Peristaltic
Migrating myoelectric complex
- 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
Objectives: Describe how flow rate affects the ionic composition of pancreatic juice
Na
Cl
K
HCO3
- Na - Stays the same
- Cl - Decreases
- K - Stays the same
- HCO3 - Increases
Objectives: Explain how the aqueous component of pancreatic juice is formed
Rates of secretion tonicity compared to plasma?
HCO3? Cl? K?
Rate dependent changes?
- 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
Objectives: Explain how the aqueous component of pancreatic juice is formed
Ductile / Centroacinar Modifications
H+
HCO3
Cl
Na
Water
- 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
- Tx out of cell by Na K ATPase
- Water moves into lumen along osmotic gradient as pancreatic ducts are water-permeable
Objective: Explain how pancreatic secretion is regulated
Regulation is phase dependent:
Cephalic and Gastric
Intestinal Phase (majority)
Potentiation
- 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
Objectives: Explain how Cystic Fibrosis and Pancreatitis affect pancreatic function
Cystic Fibrosis
- 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
Objectives: Explain how Cystic Fibrosis and Pancreatitis affect pancreatic function
Pancreatitis
- 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
What are the different cell types of the small intestine?
Enterocytes
Goblet Cells
Crypt Cells
- Enterocytes
- Epithelial; microvilli protrude from surface
- Digestion, Absorption, Secretion
- Goblet Cells
- Crypt Cells
- Proliferative Cells - form enterocytes / goblet cells
- Secrete fluids and electrolytes
Objectives: Describe different types of contractions in the small intestines
Control:
Peristaltic Reflex/Rush
Intestinointestinal Reflex
Gastroileal Reflex
Gastrocolic Reflex
Ileus
- 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
Describe the different pancreatic cell types
Acinar - what do they produce?
Centroacinare and Duct cells - purpose?
- 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
How are the enzymatic components of pancreatic secretions stored and released?
Lipase
Amylase
Proteases
- 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