1.4 Nutrient Absorption

Enterocytes

Cells that line the inner surface of the small intestine

• form a physical barrier and absorptive surface between the gut lumen and the body

How is the lipid bilayer formed?

• One end points towards the lumen

• On the outside, there are hydrophilic R groups

• In the middle, there is a glycerol backbone

• Inside, there are fatty acids (hydrophobic tails)

• Then repeat

• One end is the cytosolic side of the lipid bilayer, which is the inner layer of a cell membrane that faces the watery fluid (cytosol) inside the cell

Types of diffusion

• Passive diffusion

• Facilitated diffusion

• Active transport

Passive diffusion (Draw and explain)

• With the concentration gradient (higher concentration in lumen; lower concentration in cytosol)

• Requires no energy

• Requires no transporter

Facilitated diffusion (draw and explain)

• With the concentration gradient (higher concentration in lumen; lower concentration in cytosol)

• Requires no energy

• Has a transporter

Active transport (draw and explain)

• Can go against the concentration gradient (higher concentration in the cytosol; lower concentration in the lumen)

• Has a transporter

• ATP/Energy

Where does diffusion occur?

All happen at the lipid bilayer

Sodium Potassium Pump

Results in a high concentration of sodium and a low concentration of potassium outside the cell

What is another name for the Sodium Potassium Pump?

Na+K+ATPase

How many sodium’s are pumped out of the cell?

3

How many potassium’s are pumped into the cell?

2

What energy does the Sodium Potassium pump require

Requires 1 ATP

• Turns ATP (adenosine triphosphate) into ADP (adenosine diphosphate)

What is the charge inside of a cell?

Negative

What is the charge outside of the cell?

Positive

Electrochemical gradient

As molecules move in and out, the charge inside the cell can become more positive or negative

Basolateral membrane

Part of a cell membrane that faces away from the inside of the organ/cavity and toward the blood or surrounding tissue.

Apical membrane

The apical membrane is the part of a cell membrane that faces the inside of a hollow organ or the outside environment

• faces the lumen

SGLT1

Sodium glucose transporter #1

Function of sodium-glucose transporter #1

The sodium-glucose transporter (SGLT) helps intestinal cells absorb glucose from food into the cell.

• It uses sodium (Na⁺) to “pull” glucose into the cell.

  • Sodium moves into the cell.

  • Glucose gets brought into the cell along with it.

  • Then glucose can leave the cell on the basolateral side and enter the blood.

Is there a high or low concentration of sodium in the lumen? Where does this concentration come from?

There is a high concentration of sodium in the lumen

• Sodium comes from the pancreas and Brunner’s gland

What kind of transport does SGLT1 use?

Indirect active transport

• NOT using ATP directly, but ATP is used for the sodium-potassium pump

  • A Na⁺/K⁺ pump uses ATP to pump sodium out of the cell.

  • This creates a high Na⁺ concentration outside the cell.

  • Na⁺ wants to move back into the cell.

  • SGLT lets Na⁺ move into the cell, and glucose comes along with it, even if glucose is moving against its gradient.

GluT2

Glucose Transporter 2

Glucose Transporter 2

A glucose transporter that helps glucose leave an intestinal cell and enter the blood.

• SGLT1: brings glucose into the intestinal cell (with sodium)

• GLUT2: lets glucose out of the intestinal cell and into the blood

What kind of diffusion does GluT2 use?

Facilitated diffusion

What kind of diffusion does the sodium-potassium pump use?

Active transport

Indirect Active Transport

uses the energy from one molecule moving down its concentration gradient to move another molecule against its concentration gradient

Aerobic Respiration

autoenzymatic digestion; involves oxygen

Anaerobic Respiration

fermentation; alloenzymatic digestion; no oxygen involved