Absorption in the small intestine Active and passive transport working together

The Small Intestine Food being Digested` Products of digestion Travel along here

Features of microvilli Electron micrograph of an Epithelial cell from the intestine 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) 6µm 1mm

HISTOLOGY OF THE ILEUM Sub-mucosa Crypts Blood vessel (arteriole) A Villus

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? 1) Blood flow to remove diffused substances 2) Muscle contraction of ileum to mix contents of lumen 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 transport

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 Lumen of the small intestine Why do ileum cells contain lots of these? Epithelial Cells lining the lumen of the small intestine Capillary

Lumen of the small intestine However, when most of the glucose has been absorbed by facilitated diffusion, how does the last bit get absorbed? Lumen of the small intestine Epithelial Cells lining the lumen of the small intestine Capillary

Uptake of the last Glucose from the ileum into the bloodstream THREE transport processes are involved:- Active transport of sodium into blood Cotransport of glucose and sodium from lumen into ileum epithelial cells Facilitated diffusion of glucose into blood

Lumen of the small intestine High [sodium] Low [glucose] High [glucose] Low [sodium] Epithelial Cells lining the lumen of the small intestine Low [glucose] Capillary High [sodium]

1 Lumen of the small intestine High [sodium] Low [glucose] High [glucose] Low [sodium] 1 Type of transport here? Potassium ions Epithelial Cells lining the lumen of the small intestine Low [glucose] Capillary High [sodium]

Lumen of the small intestine High [sodium] Low [glucose] High [glucose] Low [sodium] K+ Na+ 1) Sodium-potassium pump (Active transport) Potassium ions Epithelial Cells lining the lumen of the small intestine Low [glucose] Capillary High [sodium]

Sodium-potassium pump (Active transport) How is the Sodium ion concentration gradient maintained into the epithelial cell? Sodium-potassium pump (Active transport) Na+ Na+ Na+ Na+ LUMEN of intestine TO Blood stream Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ EPITHELIAL CELL Na+ Na+ Na+ 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.) 1)

Maintaining the concentration gradient for absorption Low [Glucose] High [sodium] Na+ 3) Cotransport of glucose with sodium ions ( = passive) Lumen of the small intestine Epithelial Cells lining the lumen of the small intestine 2) LOW Sodium concentration maintained HERE High [glucose] Low [sodium] K+ Na+ 1) Sodium-potassium pump (Active transport) Low [Glucose] Capillary High [sodium]

Cotransport of glucose (with sodium) from lumen of ileum Animation link 2) 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

Maintaining the concentration gradient for absorption Low [Glucose] High [sodium] Na+ 3) Cotransport of glucose with sodium ions ( = passive) Lumen of the small intestine Epithelial Cells lining the lumen of the small intestine 2) LOW Sodium concentration maintained HERE High [glucose] Low [sodium] 4) Facilitated diffusion of glucose K+ Na+ 1) Sodium-potassium pump (Active transport) Low [Glucose] Capillary High [sodium]

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.

Transport of Glucose Lumen of the ileum Epithelial cell of villi lining the lumen Blood capillary