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PHYSIOLOGY EXAM 3 > GI Day 1 > Flashcards

GI Day 1 Flashcards

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1
Q

What are the functions of sphincters?

A

Seperate portions of the GI tract; there are internal and external.

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2
Q

How many sphincters are there in the GI?

A

6 + sphincter of oddi; Upper esophageal, lower esophageal, pyloric, ileocecel, internal and external anal.

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3
Q

What consists of the mucosa layer?

A

Epithelium: contains cells with microvilli to increase surface area for absorption.

Lamina propria: Connective tissue layer supporting the epithelium.

Muscularis mucosa: Thin muscles layer aiding in slight movement and dislodging food particles.

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3
Q

What does the Sphincter of Oddi do?

A

Regulates pancreatic and bile secretions into the duodenum.

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3
Q

Layers of the GI tract

A
  1. Mucosa (Inntermost)
  2. Submucosa
  3. Muscularis Propria
  4. Serosa (Outermost layer)
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4
Q

Submucosa layer?

A

contains blood vessles and nerves essential for GI tract functions and nutrient absoprtion

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5
Q

Muscularis propria

A

Two main muscle layers:
- Circular muscle (helps with segmentation contractions)
- Myenteric plexus
- Longitudinal muscle (aids in peristalsis moving food down the GI tract)

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6
Q

Serosa layer?

A

Outermost layer
- Mesothelium or peritoneum with visceral and parietal layers; filled with fluid to reduce friction.

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7
Q

Splanchnic circulation

A

Supplies blood to the GI tract:
- Recieving 25% of cardiac output between meals (not at it’s highest level of function).
Function:
- Feeds GI tract cells
- Absorbs nutrients

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8
Q

Hepatic portal system

A

A portion of the splanchic circulation (just the part between the GI tract and liver). *Contains dual-capillary bed system enabling nutrient processing by the liver

First Capillary bed: in the small intestine absorbs nutrients and oxygen.
Portal vein: transports absorbed nutrients to the liver
Second capillary bed: In the liver allows nutrients processing and detoxification before returning to general circulation - drains into the inferior vena cava.

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9
Q

Enteric Nervous system (ENS)

A

Independent nervous system within GI tract (similar to PNS)
Functions:
-Corrdinates activity of digestive tract (food moving at the same pace).
- Motor neurons, sensory neurons and interneurons
- Controls muscle contractions and other functions within the GI tract (
- Vagus nerve (cranial nerve 10) provides additional modulation from the brain.

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10
Q

Absorptive structure: Circular folds

A

Visible ridges in the intestines to increase surface area

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11
Q

Absorptive structure: Villi/Villus

A

Finger-like projections on folds that further enhance absorptive surface

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12
Q

Absorptive structure: Microvilli

A

Tiny projections on the cells lining the villi, forming the brush boarder to aid in digestion

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13
Q

Absorptive structure: Components of Villi

A

Capillaries: Absorb water-soluble nutrients
Lacteals: Part of the lymphatic system, absorbing lipids
Goblet cells: Produce mucus to protect the GI tract lining

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14
Q

Salivary Glands (Secrection amt, innervation, stimulation)

A

Secrete 1-1.5 L of saliva daily; for digestion and oral hygiene
Innervation: Facial nerve (VII) and Glossopharyngeal nerve (IX) activate salivation.

CNS inputs and presence of food in the mouth (touch receptors to activate and stimulate production).

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15
Q

Absorptive structure:Interestinal crypt

A

Contain holes and spots between cells, stem cells to replace cells in the lining. ?

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16
Q

Saliva Contents

A

Amylase: Enzyme breaking down carbohydrates
Lysozyme and immuniglobin A: Antibacterial angents (destroys)
Mucins: Form mucus upon activation (slows things down and thickens secretions)
Bicarbonate: Neutralizes acids to maintain oral pH (alkaline)

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17
Q

Regions of stomach

A

Fundus: upper part
Body: Main central part
Antrum: Lower part near the pyloric sphincter
Pyloric region: Near the exit to the small intestine

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18
Q

Gastic Cells: Parietal cells

A

Secrete hydrochloric acid (HCl) - to digest proteins and activate enzymes

Produce intrinsic factor needed for Vitamin B12 absorption in the ileum.

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19
Q

Gastic Cells: Chief Cells

A

Secrete pepsinogen, converted by HCl to pepsin for protein digestion

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20
Q

Gastic Cells: Goblet Cells

A

Produce mucus to protect the stomach lining from acidic conditions

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21
Q

Chief Cells: Location, function, Secretion

A

Location: Stomach

Secretion: Pepsinogen (Inactive enzyme do that it doesn’t wear down own tissue unless its needed).

Function: Activated to pepsin in the acidic environment of the stomach, adding in *protein digestion

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22
Q

Gastric secretions - stimuli

A
  1. Gastrin relase (into the blood stream)
    - Triggered by proteins or breakdown in stomach
    - This stimulates the ECL to release histamine
  2. Histamine
    - histamine stimulates parietal cells to secrete HCl.
  3. ACh from enteric nerve endings
    - Stimulates Chief cells to secrete pepsinogen.
  4. Somatostatin (Inhibitory Mechanism)
    - Released by D cells
    - Acts as inhibitor of gastric secretions, counteracting the stimulatory actions of gastrin, histamine, and ACh.
  5. Parietal cell receptors
    - Parietl cells have 3 receptors (Gastrin, ACh, Histamine). See other card
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23
Enterochromaffin-like cells (ECL)- Location, function, Secretion
Secretion: Histamine Function: Stimulates parietl cells to release HCl for protein digestion.
24
Mucus Neck Cell or Surface cells - Location, function, Secretion
Location: Stomach lining Secretion: Mucus Function: Protects stomach lining from acidic environemnt, preventing damage. **Note: Mucous neck cells serve as stem cells, replenishing the stomach lining as it constantly renews due to high acidity.
25
G Cells - Location, function, Secretion
Location: Antrum of the stomach Secretion: Gastrin (Hormone) Function: Stimulates parietal cells (HCl secretion), Chief cells (Pepsinogen), and ECL cells (Histamine). **Gastrtin increases stomach motility and mucusal growth.
26
Function of Parietal cells
Have 3 different receptors for 3 different stimuli. - Gastrin and Ach: leads to Ca++ influx. - Histamine: Triggers a cyclic AMP (cAMP) pathway, simular to the G protien, prompts active H+ ion (acid) secretion - Hydrogen pumps: Parietal cells use ATP-driven pumps to maintain high [H+], essential for creating stomach acidity. *this is why there are so many Mictochondria!!
27
Duodenum (Location, function, Secretion)
Location: Right after the stomach Function: Primary site for bile and pancreatic juice Bile from the liver (stored in gallbladder) and pancreatic enzyme aid in macronutrient digestion (Bile=lipids). About 1L/day of fluid in the small instestine.
28
Pancreatic Juice
Produced by **acini cells** in pancreas. About 1.5 L/day, containing **bicarbonate** (to neutralize chyme, pH ~8) and digestive **enzymes** for proteins, fats, and carbs. (Inactive while in duct or else it would destory tissue).
29
Pancreatic juice stimuli
Enzymes are released in inactive forms, becomes active in the lumen. Primary stimuli: - Secretin: Triggers the release of bicarbonate-rich fluid - CCK (Cholecystokinin): Promotes secretion of enzyme-rich juice and bile release.
30
Stimuli for pancreatic secretion pathway
Secretin --> secretion of HCO3- juice Cholecystokinin (CCK) --> secretion of enzyme rich juice
31
Acute Pancreatitis
Can be caused by pre-mature activation of phospholipase A2 which can destory cell membranes
32
Bile (Production, Function, Composition)
Production: Liver hepatocytes (~0.5 liters/day). Function: Emulsifies fats for digestion and excretes cholesterol and lipid waste. **high fiber can lower cholesterol because its needed to make bile Composition: - Bile acids (amphiphathic (polar and non-polar)), facilitate lipid transport in GI tract by forming micelles (surround fat and carry) - Bile pigments (e.g., bilirubin and biliverdin ): by-products of hemoglobin breakdown make it yellow - Alkaline nature: Assists in neutralizing stomach acid in the small intestine - increased pH.
33
Gastrin (Source, Stimuli, Actions)
Source: G cells in the stomach antrum. Stimuli: Presence of proteins and ENS activation Actions: Increases HCl and pepsinogen secretions; supports gastric mucosa growth
34
CCK - Cholecystokinin (Source, Stimuli, Actions)
Source: I cells in the upper small intestine Stimuli: Presence of proteins and fatty acids in the small intestine Actions: Promotes enzyme secretion from the pancreas, gallbladder contraction, and relaxation of the sphincter of oddi, allowing bile and enzymes into the duodenum.
35
Secretin (Source, Stimuli, Actions)
Source: S cells in the upper small intestine Stimuli: Acidic chyme entering the small intestine Actions: Stimulates release of bicarbonate-rich pancreatic juice to neutralize acid; regulates pH in small intestine. Contracts the pyloric sphincter to slow down gastric emptying, allowing more time for digestion in the small intestine.
36
Endocrine System Effects
Hormones are throughout the GI tract and can act as **endocrine** (system-wide effects) or **paracrine** (local effects), aiding in digestive coordination without a centralized gland structure.
37
Micelles
Formed by bile acids, these structure carry lipids through the watery environment of the GI tract facilitate absorption.
38
Calcium Influx
Common signal mechanism in GI cells, promoting vesicle transport and secretion.
39
HCl Acid Production
Involves the H+ transport, heavily reliant on ATP, which explains the high mitochonrial density in parietal cells.
40
GIP - Gastric Inhibitory Peptide (Category, Source, Stimuli, Actions)
Category: Incretin Source: K cells in the small intestine Stimuli: Presence of glucose and fats in the duodenum Actions: - Stimulates insulin release from pancreas "incretin response" - Works with GLP-1 (another incretin) in regulating insulin and appetite, which is relevant in Type 2 diabetes.
41
VIP - Vasoactive intestional peptide
Category: Neurotransmittor and hormone Source: Enteric Neurons Actions: - Increases water content in feces and relaxes smooth muscles in sphincters. - Aids in **smooth movement** through the GI tract
42
Motilin: (Source, Stimuli, Actions)
Source: MO cell in the small intestine (mostly in the duodenum). Actions: -Stimulates smooth muscle contractions **between meals** (helps with GI tract "housekeeping"). - Important in moving remaining food particles and bacteria towards the colon in the fasted state.
43
Somatostatin (Source, Stimuli, Actions)
Source: D cells in the stomach, pancreas, and intestines Stimuli: - Acid entering small intestine Actions: Inhibits multiple GI hormones (gastrin, VIP, GIP, secretin and motlin) acting as **regulatory hormone** - Helps slow gastric emptying, ensuring time for nutrient processing
44
Peptide YY - PYY (Source, Stimuli, Actions)
Source: Jejunum (small intestine) Stimuli: Presence of fat in the intestines Actions: - slows gastric motility to regulate the rate of chyme entering the intestines. - Inhibits gastric acid secretions
45
Ghrelin (Source, Stimuli, Actions)
Source: Stomach Stimuli: Fasting state; increases before meals Actions: Known as the "hunger hormone" stimulates appetite and growth hormone release.
46
Fluid Secretion Amt.
Ingested = 2 L Endogenous 7 L Total = 9 L (salivary glands = 1.5 L, Stomach = 2.5 L, Bile = 0.5 L, Pancrease 1.5 L, Intestine = 1.0 L) Fluid reabsorption is important to prevent dehydration = 8.8 L is reabsorbed.
47
Sodium Absorption
Water absorption is dependent on Na+ absorption. Na+ is absorbed via: - Secondary transport with glucose - Exchange with H+ - Coupled with Cl- - Epithelial Na+ Channels (ENaC same as kidneys)
48
Cholera
Diarrhea - can be extreme - Major reduction in NaCl absorption - Increased Cl- secretion - Resulting in hyperosmotic lumen - Stool volumes up to 20 L/day - Can be life threatening (water can't stay in the body it following the Na+ out).
49
Food Poisoning/what drugs
Inflammation disrupts absorption, leading to osmotic diarrhea. Can result in hypokalemia due to K+ secretion in the colon. Drugs can be used to slow intestinal motility, can help with more absorption and decrease diarrhea.
50
Constipation
Due to lack of fiber or lack of water in stool; magnesium sulfate can be used to draw water into the intestines by increasing osmotic pressure in lumen.
51
Whare are Carbohydrates digested?
- Begins with the mouth, with salivary amylase - Continues in the sm. intestines with pancreatic amylase breaking down polysaccharides - Brush border enzymes (e.g., maltase, sucrase) convert disaccharides into absorbable monosccarides
52
Digestion - by region
Mouth: Chewing (mechanical digestion); salivary** amylase** starts with carbohydrate breakdown. Stomach: Churning mixes food; HCl and pepsin chemically digest proteins. Small intestine: Primary site of digestion and nutrient absorption.
53
How are Carbohyrates absorbed?
Glucose and galatose: Absorbed via secondary co-transport with Na+/K pump SGLT 1 Na⁺move down their concentration gradient into the cell, and this energy helps **glucose move against its concentration gradient** into the cell along with sodium. This cotransport means that **SGLT-1 requires both Na⁺ and glucose to work efficiently.** Goes into the blood stream bia GLUT 2 Fructose: Absorbed through facilitated diffusion via GLUT 5 and then into the blood stream GLUT2
54
Where are proteins digested?
- Starts in the stomach with pepsin (low pH to activate), breaking proteins into smaller polypeptides. Cleaves some peptide bonds, stops in small intestine due to higher pH. Pancreatic Proteases:
55
Where are proteins absorbed?
Amino acids and small peptides are absorbed via **active transport** and secondary active transport (with Na+).
56
Fats:
57
Steatorrhea (Definition, Cause)
Definition: Fatty, Bulky clay colored stool due to dat malabsorption Causes: - Lipase deficiency (primary cause) - Bile Reabsorption issues in the ileum. - Too much acid secretion in stomach, which makes the enzymes ineffective if pH is too low - can't activate lipases. - Lack of pancreatic release of alkaline secretions
58
Short gut syndrome
Can present after removal of a portion of the small intestines (if 50% is removed) causing malabsorption
59
Celiac disease
Auto immune disease defense against gluten inflammation, loss of cilia and flattening of villi. Commone among those with other autoimmune diseases/condidiont (e.g., diabetes). **All malabsorption causes an impairment of absoprtion of vitamins and nutrients
60
Short Chain Fatty Acids in the Colon
- They are 2-5 carbon weak acids - Produced in the colon and aborbed Fibers -> gut microbia -> butyrate propionate acetate (SCFAs) -> various health benefits (see image on slide 31). - Trophic effect on colon - Absorbed via exchange with H+ to help with acid base balance - Promote absorption of Na+ (cotransport) - Reduce risk of CVD, Diabetes, colon cnaver, decrease inflammation - Energy source for cells of the colon
61
Water absortion in GI
Sodium is crucial for water reabsorption; sodium reabsorption creates an osmotic gradient, pulling water into the bloodstream. Conditions like diarrhea can arise from Na+ absorption issues, while diseases like cholera exacerbate water loss due to chloride secretions, leading to life-threatening dehydration.
61
Absorption of Minerals
Minerals deemed essential for life: - Iron; RBCs - Cobalt; vitamin B12 to avoid megaloblastic anemia - Iodine; thyriod function - Zinc; skin, immune system, dwarfism - Copper: anemia and bone health - Chromium; insuliin resistance - Fluorine; dental health - Na+ and K+; but very hard to exclude from diet Calcium: discussed previously for bone/muscle health Iron: Most dietary iron is Fe3+ but needs to be reduced to Ferric (Fe2+) to be absorbed. Once in the blood -> converted back to Fe3+ Carried in the blood bound transferrin protein.
62
Water-Soluble Vitamins
Most are water-soluble vitamins (B and C). are absorbed in the duodenum. Co-transports with Na+ - seven water soluable vitamins (excluding B 12 and folate) are absorbed with Na+ transport.
63
Vitamin B 12 and intrinctic factor:
Vitamin B 12 requires intrinicst factor (produced by parietal cells in the stomach) for absorption. B 12 is absorbed in the ileum, the last part of the small intestine.
64
Fat soluble vitamins
Vitamin (A, D, E and K) require bile to be absorbed. very large doses of fat coluble vitamins are toxic.
65
Summary of absorption locations in the GI tract
Duodenum: Primary for absorption site for water-soluable vitamins. Ileum: Absorption of vitamin B 12 (with intrinstic factor) and some reabsoption of bile acids Colon: Absorption of SCFAs produced by the gut bacteria.

PHYSIOLOGY EXAM 3 (2 decks)

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