Small Intestine Flashcards
What are the three regions of the small intestine?
Duodenum, jejunum, and ileum.
Why is absorption in the small intestine selective?
Occurs via specific transporter proteins by diffusion and secondary active transport.
What are the two phases of digestion in the small intestine?
- Luminal - enzymes secreted by salivary glands / pancreas.
- Membranous - enzymes attached to epithelial surface of intestinal cells.
How is the surface area of the small intestine increased?
Mucosal folds, villi, microvilli
What are the four types of intestinal epithelial cell?
Goblet cells, enteroendocrine cells, paneth cells and enterocytes
Describe the role of goblet cells.
Secrete mucous for lubrication & protection of mucosa.
Describe the role of enteroendocrine cells.
Control digestive function via sensory mechanisms and release of hormones.
Describe the role of paneth cells.
Possibly involved in defense against microbial penetration.
Describe the role of enterocytes (majority of cells).
Responsible for absorption via transporter proteins.
What are the two main types of motility in the small intestine?
Segmentation and peristalsis.
What is the role of segmentation in the small intestine?
Segmentation involves localised contractions that mix chyme with digestive juices, aiding digestion and maximising contact with absorptive surfaces.
What is the role of peristalsis in the small intestine?
Peristalsis involves wave-like contractions that move chyme forward along the small intestine.
How does the SI empty?
Ileo-colic sphincter relaxes - empties into colon.
How is small intestine motility regulated?
Controlled by interstitial cells of Cajal = pacemaker cells
Describe carbohydrate digestion in the luminal digestive phase.
Stach/amylose (amylase) –> maltose
Amylase digestion continues in small intestine with pancreatic amylase
Describe carbohydrate digestion in the membranous digestive phase.
Maltose (maltase) –> glucose + glucose
Sucrose (sucrase) –> glucose + fructose
Lactose (lactase) –> glucose + galactose
Describe the process of glucose and galactose absorption.
- Secondary active transport
- Na+ & glucose / galactose bind to transporter (SGLT1) on luminal side
- Conformational change in transporter moves Na+ & glucose / galactose into cell and release them into cytosol
- High levels of Na+ in digestive juice maintain luminal concentration of Na+ high
- Concentration of glucose / galactose in cytosol high so diffuse down concentration gradient into blood stream via facilitative transporter GLUT2
Describe the process of fructose absorption.
Fructose absorbed down concentration gradient by facilitative transporter (GLUT5) –> diffuse out of cytosol down concentration gradient into blood stream via GLUT2.
Where are monosaccharides transferred after absorption into the blood?
Transferred to liver via hepatic portal vein –> stored as glycogen or continue in circulation to be metabolised for energy.
Describe lactose intolerance.
- In absence of lactase, lactose accumulates in gut lumen.
- Osmotic force –> decreased water absorption (diarrhoea)
- Once reaches large intestine fermented –> lactic acid decreases pH
- Gas products cause distention resulting in pain / discomfort
How are amino acids transported into enterocytes?
Enterocytes via Na+ co-transport similar to monosaccharides (secondary active transport).
How are di/tri-peptides transported into enterocytes?
Via H+ co-transport
Draw a table to compare carbohydrate and protein digestion.
Look at notes/chat GPT
Describe protein digestion in neonates.
Allowed to absorb intact antibodies:
1. Epithelial cells of intestine are permeable to intact protein
2. Stomach produces negligible amounts of HCl
3. Pancreatic enzyme secretion is low
4. Colostrum contains trypsin inhibitors
