Physiology

Question 1

Functions of the stomach?

Answer 1

1. Temporary storage: 1-2 liters

Receptive relaxation: regulation is thru NANC vago-vagal reflex and possibly VIP and NO, enteric innervation to proximal stomach is largely inhibitory

2. Mixing of contents: semi liquid called CHYME mixed by the distal stomach
3. Propulsion into duodenum: regulated by pyloric sphincter
4. Gastric emptying

Question 2

What happens in the proximal part of the stomach?

Answer 2

• Low stable RMP (~50mV)
• Partially contracted at RMP
• Length-tension relationship
• Primary enteric innervation is INHIBITORY (NANC)
• Predominant type of activity: variations in tone

Question 3

What happens in the distal part of the stomach?

Answer 3

• Propagated contraction resulting from a series of enteric reflexes in response to local distension
• The MAGNITUDE of the stimulus (along with interaction of neural and hormonal factors) determines the AMPLITUDE of the peristaltic wave
• The ELECTRICAL CHARACTERISTICS OF THE SMOOTH MUSCLE determines the FREQUENCY, DIRECTION and VELOCITY of the wave
• Slow waves = ECA (electric control activity) or BER (basic electric rhythm)
• Spikes at the peak of BER = electrical response activity (ERA)
• This is coordinated by the interstitial cells of Cajal (stomach pacemaker)

Question 4

What happens at the pyloric sphincter?

Answer 4

At the end of a peristalsis, the pyloric sphincter actually contracts and allows only small molecules of enter the duodenum. The liquids pass way faster.

Regulation:

• Vagus nerve (proximal innvervates proximal stomach and distal innervates the distal)
• Distension, pH < 3.5, osmolarity (fat >> proteins > carbs) will regulate antral peristalsis

Question 5

By what is composed the mixed gastric juice?

Answer 5

• Volume: 1.5-2 L/d
• Ions: Isotonic fluids with Na+, K+, Cl- and H+ (precipitates soluble proteins, denatures proteins, activates pepsin and provides optimal pH for its activity)
• pH = 1-2
• Pepsinogen (converter to pepsin by HCL, autocatalysis and breaks protein to polypeptides)
• Intrinsic factor: glycoprotein and absorption of B12
• Gelatinase and lipase
• Mucin: mucin-bicarb layer, gastric mucosal barrier, effective blood glow, rapid cell turnover
• Prostaglandins (cyto-protection) increase mucin and bicarb secretion, increases blood flow and decreases acid production

Question 6

Cardiac and pyloric tubular glands secrete what?

Answer 6

alkaline mucin-rich fluid

Question 7

Parietal (oxyntic) cells secrete what?

Answer 7

1. secretes acids after a meal (changes phase)
2. glycoprotein (B12 absorption)

Question 8

Chief cells secrete what?

Answer 8

pepsinogen converter to pepsin by HCL

Question 9

Surface epithelial cells secrete what?

Answer 9

bicarb and mucus

Question 10

What are the 3 regulatory postprandial state?

Answer 10

1. Cephalic (psychic and gustatory) – 30%

Parietal, peptic and mucoses secretions + vasodilation

Mediated by vagus, vagotomy abolishes cephalic phase s

1. Gastric 60%

Due to food in the stomach

Local enteric, neuro (vagal) and hormonal (gastrin +, histamine - and somatostatin -) regulation

1. Intestinal 10%

Secretagogues in duodenum Inhibit acid secretion via neuro and hormonal pathways

Question 11

Major regulatory factors of the stomach pH?

Answer 11

• gastrin (+)
• somatostatin (-)
• histamine (potentialize +)
• vagus (+/-)

Question 12

Digestive enzymes secreted by the pancreas?

Answer 12

1. Amylase: polysaccharides ®disaccharides
2. Protease: proteins and activation of proenzymes into enzymes such as trypsinogen ® trypsin (which will also activate other proenzymes into enzymes)
3. Lipase: fats

Question 13

What are the 2 structures that contribute to the exocrine function of the pancreas?

Answer 13

1. Acinar cell: ENZYMES

Has zymogens (inactive pancreatic enzymes); when enzymes are produced, they are formed as zymogens (cannot be active in pancreas because they will digest the pancreas), and they become active enzymes in the duodenum

1. Centroacinar duct cells: ALKALINE FLUID

Are filled with mitochondria for energy

Question 14

Regulation of the pancreas?

Answer 14

1. Neuronal mechanism (vagal nerve)
2. Hormonal mechanism:
   - Secretin: will increase pH (decrease acidity)
   - CCK: triggered by fat and protein to release pancreatic enzymes via vagal nerve

Question 15

Pancreatic exocrine insufficiency causes?

Answer 15

• Chronic Pancreatitis: slow chronic fibrosis due to ductal obstruction, ATROPHY
• Cystic Fibrosis: CFTR gene mutation (Na⁺/ CL^-+ HCO₃^- transport problem)
• Bowel or pancreatic resection: affects CCK and secretin synthesis
• Pancreatic duct obstruction: cancer
• Shwachman-Diamon Syndrome: autosomal recessive, bone problems, short stature, can be secondary to CF

Question 16

Clinical manifestations of pancreatic disease?

Answer 16

• Asymptomatic
• Fat soluble deficiency: A, D, E, K
• Mild symptoms such as bloating and flatulence with normal stool
• Moderate to severe symptoms: maldigestion of fat and protein leading to weight loss
• Overt steatorrhea (fat caca) only when 90% of the glands have been damaged (very late in the process), associated with chronic diarrhea, giardiasis and celiac disease

Question 17

Diagnosis of pancreatic disease?

Answer 17

• Lab (vitamins and tryprinogen)
• Imaging
• Fecal Elastase-1/Fecal chymotrypsin
• Direct pancreatic function tests (GOLD STANDARD): stimulation of pancreas + duodenal fluid collection (secretin, CCK tests)