DENT2155 - Intestinal Fluid and Electrolyte Transport

The Gut excretes around ____ mL of Fluid per day.

100 mL

The Gut absorbs around ____ mL of Fluid per day.

8900 mL

Absorbs almost 99% of Fluids

Almost ____ mL of Fluid absorbed by the Gut comes from Endogenous Secretions.

7000

Water moves across the Gut Wall via ____.

Osmosis

Ions like Na+, K+, and Ca2+ are ____ across the Gut Wall.

actively transported

Secretory Cells in the Crypt secrete ____.

Cl-

Villi of Enterocytes absorb ____.

Na+

What are the types of Junctions holding Intestinal Cells together?

- Tight Junctions

- Adherens Junctions

- Desmosomes

- Gap Junctions

- Hemidesmosomes

Tight Junctions

Specialized connections between adjacent Cells that create a barrier to control the movement of substances between them

Adherens Junctions

Cell-Cell adhesion structures that connect the Actin Cytoskeleton of neighboring Cells

Desmosomes

Cell-Cell adhesion structures that connect the Microfilament structure of neighboring Cells

Gap Junctions

Specialized Cell-Cell connections that allow direct communication between neighboring Cells by letting small molecules and ions pass from one Cell Cytoplasm to another

Hemidesmosomes

Cell-ECM connection using the Microfilament structure of the Cell

Disruption of Cell Junctions in the Small Intestine leads to ____.

Leaky Gut

The Tissue Permeability of the Jejunum is ____.

Leaky

The Tissue Permeability of the Ileum is ____.

Moderately Leaky

The Tissue Permeability of the Colon is ____.

Tight

What are the 3 Pathways of Water Absorption in the GI Tract?

- Na+ Coupled Absorption

- Na+ and Cl- Absorption (Small intestine and Colon)

- Na+ Absorption (Colon)

Na+ Coupled Absorption

Apical

(1) SGLT1 cotransports Na+ and Glucose into the Enterocyte

Basolateral

(2) GLUT2 pushes Glucose into the Bloodstream

(3) Na+/K+ Pump pushes Na+ out

(4) Cl- follows electrical gradient and travels paracellularly to pair with Na+

(5) Water follows NaCl

Na+ and Cl- Absorption

Apical

(1) Na+/H+ Exchanger pulls Na+ into Enterocyte

(2) Cl-/HCO3- Exchanger pulls Cl- in

Basolateral

(3) Na+/K+ Pump pushes Na+ out

(4) K+/Cl- Cotransporter pushes K+ and Cl- out

(5) Water follows NaCl

Occurs in the Small Intestine and Colon

Na+ Absorption

Apical

(1) ENaC pulls Na+ into Enterocyte

Basolateral

(2) Na+/K+ Pump pushes Na+ out

(3) Cl- follows electrical gradient and travels paracellularly to pair with Na+

(4) Water follows NaCl

Occurs in the Colon

What is the 1 Pathway of Water Secretion in the GI Tract?

Cl- Secretion (Small Intestine and Colon)

Cl- Secretion

Basolateral

(1) Na+/K+ Pump creates a Na+ gradient

(2) Na+/K+/Cl- Cotransporter pulls Na+, K+, and Cl- into the Acinar Cell

Apical

(3) Cl- Channel pushes Cl- into the Pancreatic Lumen

(4) Na+ follows electrical gradient and travels paracellularly to pair with Cl- in the Lumen

(5) Water follows NaCl

Fluid/Electrolyte Balance is disturbed by ____ and ____.

Vomiting/Diarrhea

What can trigger the Vomiting Reflex?

- Stomach Inflammation

- Dizziness

- Intracranial Pressure

- Pain

- Medications

- Pregnancy

- Smell

Be familiar with; Don't Memorize

Chemoreceptor Trigger Zone

Senses the CSF and relays it to the Nucleus tractus solitarius + Vomiting Center

Nucleus tractus solitarius

Brain Stem Vomiting Center

What stimulates the Nucleus tractus solitarius?

- Chemoreceptor Trigger Zone

- Gastric Irritation

- Gag Reflex

- Surgery

What stimulates the Brain Stem Vomiting Center?

- Chemoreceptor Trigger Zone

- Nucleus tractus solitarius

- Cerebellum (via Vertigo/Motion Sickness)

Vomiting Reflex

(1) Hypersalivation

(2) Reverse Peristalsis clears upper content from Small Intestine into Stomach

(3) Glottis closes to prevent Aspiration

(4) Abdominal Wall contracts, increasing intra-Abdominal Pressure

(5) Lower Esophageal Sphincter (LES) and Esophagus relax

(6) Gastric Contents eject

Vomiting leads to loss of what 4 contents?

- H+

- Cl-

- K+

- Fluid

Loss of H+ can lead to ____.

increased pH and Metabolic Alkalosis

Loss of K+ can lead to ____.

Hypokalemia

Loss of Fluid can lead to ____.

RAAS stimulation and loss of even more K+

What can cause Diarrhea?

- Inability to Absorb

- Increased Motility

- Secretory Agents

- Inflammation

Cholera

Acute Intestinal infection caused by ingestion of contaminated water or food

Cholera Mechanism of Vomiting

(1) Cholera releases A + B Toxin

(2) B Toxin binds to Ganglioside GM1

(3) A Toxin travels into the Cytosol and binds Gsa

(4) Gsa stimulates Adenylate Cyclase which increases cAMP

(5) cAMP increases Cl- Secretion

In Secretory Diarrhea, there is an increase in ____ and decrease in ____.

Cl- Secretion/Nutrient Absorption (Na+)

Diarrhea leads to loss of what 2 contents?

- HCO3-

- Fluid

Loss of HCO3- can lead to ____.

decreased pH and Metabolic Acidosis

Loss of Fluid can lead to ____.

RAAS stimulation and loss of K+

Diarrhea leads to an increase in ____.

Cl- Uptake

Secretion in the GI Tract is affected by what 4 factors?

- Hormones/NTs

- Immune System

- Toxins

- Laxatives

Absorption in the GI Tract is affected by what 5 factors?

- NTs

- Mineralocorticoids

- Glucocorticoids

- Somatostatin

- Opiates

Roles of Intestinal Epithelium

- Digestion (Brush Border)

- Absorption

- Protection (Mucus, pH, GALT)

- Secretion

DAPS