4A: Anatomy, Physiology and Path of the Small Intestine Flashcards
Describe the small intestine
- Constitutes the first 10-12 inches
- Begins at the pyloric valve, arcs around the pancreas and passes to the left, and ends at a sharp bend called the DUODENOJEJUNAL FLEXURE (JUNCTION)
Where does the duodenum receive what?
he stomach contents, pancreatic juice and bile
What happens in the duodenum?
Stomach acid is neutralized, fats are broken up by bile acids, pepsin is inactivated by the elevated pH and pancreatic enzymes take over the job chemical digestion.
Describe the jejunum
-8 feet long and extends from the duodenum to the ileum
Describe the ileum
About 12 feet in length and joins the large intestine at the ileocecal valve.
What needs to happen in order for absorption of nutrients, electrolytes, and water in the small intestine to occur?
There needs to be a maximal surface area which is accomplished thru PLICAE CIRCULARES, VILLI, and MICROVILLI
What does the surface absorptive cell contain?
A layer of closely packed microvilli, enzymes (brush border) and transporters
What is a GOBLET CELL?
Mucous producers
What is a Eneteroendocrine cell?
Secretes CCK, secretin, GIP (DNES cells; APUD cells..ugh)
What do regenerative cells do?
Divide to replace themselves and other types of epithelial cells
What do Paneth cells secrete?
Secrete the antibacterial enzymes lysozyme and other antibacterial agents
What are some enzymes of disaccharides?
sucrose, lactose, and maltose
What is sucrose made up of?
glucose and fructose
What is lactose made up of?
Galactose and glucose
What is maltose made up of?
glucose and glucose
What are the MOST common examples of polysaccharides?
1) Glycogen 2) starch 3) cellulose
What does Pancreatic amylase do?
degrades polysaccharides into disaccharides & oligosaccharides
What are disaccharides degraded by?
A group of brush border enzymes called disaccharidases
What breaks down starch and glycogen?
Salivary amylase
Partially converted starch (and partially digested glycogen) is converted to Lactose, alpha-dextrins, maltotriose, maltose, and sucrose by what?
Pancreatic amylase
What are the products of lactose digestion
Glucose and Galactose
What is the product of alpha-dextrins digestion?
Glucose
What is the product of Maltotriose?
Glucose
What is the product of Maltose?
Glucose
What is the product of Sucrose?
Glucose and Fructose
Glucose and galactose are absorbed by what mechanism?
Via secondary active transport through a Na+ dependent cotransporter known as SGLT1
What facilitates absorption of Glucose and Galactose against their gradients?
A high luminal concentration of Na+
Fructose enters the brush border by facilitated diffusion via what?
Glucose transporter 5 (GLUT 5) that does not require Na+
All monosaccharides are transported out of the enterocytes and into the capillaries by __________________
Also by what kind of diffusion ?
GLUT 2
**Facilitated diffusion
What is the difference between normal lactose digestion and lactose intolerance?
- With normal digestion Lactase breaks down lactose and normal stool is produced.
- With lactose intolerance Bacteria ferment lactose and produce gases, organic acids, other osmotically active molecules
The stomach does a good job denaturing proteins but is not effective at what?
Cleaving off individual amino acids (PEPSIN does some of this)
Cleaving off amino acids occurs mainly at the ?
Brush border with amino peptidases and with the active pancreatic enzymes (proteases)
Once the digestion of proteins is complete, most amino acids or small peptides are transported via the same co-transport mechanism utilized by?
Glucose
Some amino acids do not require this sodium co-transport mechanism but instead are transported by?
The same way that fructose is moved, i.e by facilitated diffusion
