Bulk Fluid Handling and the Large Intestine 5 Flashcards
LEARNING OBJECTIVES:
*Balancing secretion and absorption
*Water and ion movement in the gut
*Colon and rectum anatomy
*Colonic motility
*Constipation, diarrhoea, ORT
How is water moved in the gut - what is it secondary to?
Movement of water across intestinal epithelium: small and large intestine is secondary to ions and other solutes, particularly sodium and chloride ions this is KEY
What happens in the SI: duodenum, jejunum and ileum - broadly?
Duodenum - add secretions
Jejunum - digest/absorb
Ileum - specialised absorption
What is the movement dependent on?
Leakest and tightest parts of cells is where?
Tight junctions between cells on DT lining vary on how connective cells are throughout DT
Leakest upper part of SI such as duodenum
Become tighter as you move down into LI
Volume entering the colon from the small intestine per day and the volume absorbed by the colon per day?
500mL and 350mL
Large intestine structure?
Small intestine ends at this ileum via ileocecal valve into LI
This moves into blind ended pouch called the cecum
Location of appendix is at this cecum
Right hand side is the colon where it ascends: the ascending colon and turns into the transverse colon and this bend is called the: flexure (hepatic as next to liver)
Then into the descending colon on the left and we have another flexure (the splencic flexure)
Coming down turns into the sigmoid colon as it is S shaped
Then straightens up to form the rectum
Where are digestive juices derived from?
Where is most absorbed and why?
Digestive juices are derived from plasma such as salivary/pancreatic, etc so about 7L of materials of endogenous produced and 2+1/2L outside the body gives us 9+1/2 L and the large amount of this is absorbed in the small intestine to maintain plasma
Explain the major ion transport processes in the jejunum: but also takes place in duodenum
- Where is the lumen, basolateral and interstitial space located on the diagram?
- Where is the ATP pump located and what does this do?
- Key here is?
- Carbohydrates: monosaccharides - how does absorption happen?
- What else is seen here in regards to amino acid transport?
- Why is it key that these sodium ions are being influxed from the lumen?
- What happens to charge as we move these out and what does this increase?
What is the KEY POINT?
- Lumen side on the left at the top and basolateral side on bottom and the space is the interstitial space into the villi in the capillary network into the blood
- Na^+/K^+ ATP pump is located in jejenum in epithelium cells in the basolateral membrane and pumps 2 sodium ions out in exchange for 3 potassium ions in and that creates an overall electronegativity on the inside of the membrane
- Key thing here it does here is concentrate chloride ions in the interstitial space
- When we look at carbohydrates - monosaccharides absorption this happens via the sodium glucose transporter where sodium ions are carried down this electrochemical gradient and brings in different monosaccharides: simple sugars.
- Seen here as well for a symporter here for amino acid transporter
- Into the cell, also facilitated by a sodium/hydrogen ion exchanger when looking at amino acid absorption.
Key point is that sodium ions are influxing from the lumen across the cell and are concentrated here in the interstitial spaces - active transport of sodium ions into here, which is why they are in red boxes in diagram. - As we move Na^+ ions out of lumen it creates an electronegativity in lumen as these positive charges are being shunted outside, as this electrical gradient facilitates movement of Cl^- ions into space. Increases osmotic pressure in space facilitating movement of water through the cells
KEY POINT => water follows ions osmotically
What is Paracellular movement?
Where is this seen?
Movement between cells of ions and solutes
Upper parts of small intestine
Transcellular movement?
As we move down further, junctions becoming tighter and this refers to movement that goes through various symporters and antiporters: carbohydrates and amino acids - moving ions and solutes across lumen and basolateral membrane
Colonic motility - Specifications
1. What is the tenia coli?
2. Haustra?
- 3 longitudinal bands of muscle - they are shorter now than the underlying circular muscle thus they collect the inner circular muscle into little pouches and these pouches are called:
- Haustra - pouches or sacs
Within the major ion transport processes in the jejunum what is there net absorption of?
Na^+ and Cl^-
Ion + H20 transport - the jejunum:
Once water moves into these interstitial spaces what happens?
=>Once water moves into these spaces it increases hydrostatic pressure which is fluid pressure and flushes water into capillaries into the blood
What happens then in the ileum (lower part of SI) in regards to water and ion transport?
Sodium/potassium pump, same sodium and glucose transporter, moving sodium into the lumen and same sodium hydrogen exchanger as jejunum
=> Bottom line is moving sodium out into the space
Creates lumenal electronegativity thus facilitating the movement of these chloride ions also into space and net absorption of these ions and then water follows osmotically
Epithelial cells in colon are called?
Colonocytes
