Embed Size (px)
Citation preview
Absorption in the small intestine
Active and passive transport working together
The Small Intestine
Food beingDigested`
Products of digestionTravel along here
Features of microvilli
Use p63 to list the FOUR features of microvilli that accelerate the rate of diffusion of materials from the lumen of the intestine.
How big are the microvilli compared to the villi? (do not confuse the two)
Electron micrograph of an Epithelial cell from the intestine
6µm1mm
Blood vessel (arteriole)
A Villus
Sub-mucosa Crypts
HISTOLOGY OF THE ILEUM
How is the concentration gradient from the lumen of the intestine to
the capillaries maintained?
• What are the TWO main ways that a concentration gradient is maintained?
IN LUMEN
MICROVILLI
IN BLOOD
• Apart from having a huge surface area, what other organelles are present in large numbers in the cells lining the small intestine…. And why? Mitochondria - to provide energy for active transportMitochondria - to provide energy for active transport
1) Blood flow to remove diffused substances2) Muscle contraction of ileum to mix contents of lumen
For the most part, glucose from digested carbohydrates is at a higher concentration in the lumen than in the epithelial cells or the blood, so it
moves into the blood by facilitated diffusion
Capillary
Epithelial Cells lining the lumen of the small intestine
Lumen of the small intestine
Why do ileum cells contain lots of these?
Capillary
Epithelial Cells lining the lumen of the small intestine
Lumen of the small intestine
However, when most of the glucose has been absorbed by facilitated diffusion, how does the last bit get absorbed?
Uptake of the last Glucose from the ileum into the bloodstream
THREE transport processes are involved:-
1. Active transport of sodium into blood
2. Cotransport of glucose and sodium from lumen into ileum epithelial cells
3. Facilitated diffusion of glucose into blood
Capillary
Epithelial Cells lining the lumen of the small intestine
Lumen of the small intestine
Low [sodium]
High [sodium]
High [glucose]
Low [glucose]
High [sodium]
Low [glucose]
Capillary
Epithelial Cells lining the lumen of the small intestine
Lumen of the small intestine
Low [sodium]
High [sodium]
Type of transport here?
High [glucose]
Low [glucose]
High [sodium]
Low [glucose]
1
Potassium ions
Capillary
Epithelial Cells lining the lumen of the small intestine
Lumen of the small intestine
Low [sodium]
High [sodium]
High [glucose]
Low [glucose]
High [sodium]
Low [glucose]
Potassium ions
K+ Na+1) Sodium-potassium pump (Active transport)
Sodium-potassium pump (Active transport)
• The sodium-potassium pump (Na+-K+ ATPase) is an example of countertransport in which two kinds of particles are transported at the same time in opposite directions by the same mechanism.
• Sodium ions are actively transported from the epithelial cell (low Na+ conc.) into the blood (high Na+ conc.) in exchange for potassium ions.
• This maintains the diffusion gradient for sodium ions from the lumen (high Na+ conc.) into the epithelial cell (low Na+ conc.)
How is the Sodium ion concentration gradient maintained into the epithelial cell?
LUMEN ofintestine
EPITHELIAL CELL
TOBlood stream
Na+ Na+
Na+Na+
Na+Na+
1)
Na+
Na+Na+
Na+
Na+Na+
Na+
Na+Na+
Na+
Na+Na+
Maintaining the concentration gradient for absorption
Capillary
Epithelial Cells lining the lumen of the small intestine
Lumen of the small intestine
K+ Na+1) Sodium-potassium pump (Active transport)
Low [Glucose]
Low [Glucose]
High [sodium]
Low [sodium]
High [sodium]
Na+
High [glucose]
3) Cotransport of glucose with sodium ions ( = passive)
2) LOW Sodium concentration maintained HERE
Cotransport of glucose (with sodium)
from lumen of ileum
involves more than one type of particle being transported in the same direction at the same time by the same mechanism
Occurs from the lumen into the epithelial cell, absorbing a sodium ion and glucose molecule together : COTRANSPORT down a concentration gradient for SODIUM… but AGAINST for glucose
Animation link
2)
Maintaining the concentration gradient for absorption
Capillary
Epithelial Cells lining the lumen of the small intestine
Lumen of the small intestine
K+ Na+1) Sodium-potassium pump (Active transport)
Low [Glucose]
Low [Glucose]
High [sodium]
Low [sodium]
High [sodium]
Na+
High [glucose]4) Facilitated diffusion of glucose
3) Cotransport of glucose with sodium ions ( = passive)
2) LOW Sodium concentration maintained HERE
• Homework:
• Summary Qs page 64
• Page 71 Question 2 (exam-style question)
Homework
• Answer summary questions on page 64.
Use the information about Oral Rehydration solutions (ORS) to plan an experiment for the next lesson.
Three A4 sheets!
• Collect 3 sheets of A4 paper of different colours.• At the top of each put a heading:- ‘Lumen of the
ileum’ / ‘Epithelial cell lining the ileum’ / ‘inside the capillary’
• As we go through the powerpoint, use beads (3 different colours) to represent glucose, sodium and potassium molecules.
• Draw membranes / carrier proteins on the card as appropriate and add labels to describe what is happening at each point.
Lumen of the ileum Epithelial cell of villi lining the lumen
Blood capillary
Transport of Glucose
