The digestive system-4 Flashcards
Site where most digestion and absorption take place
Small intestine
Three segments of the small intestine:
Duodenum
Jejunum
Ileum
Motility of the small intestine?
- Segmentation
- Migrating motility complex
- Primary method of motility in small intestine
- Consists of ringlike contractions along length of small intestine
- Within seconds, contracted segments relax and previously relaxed areas contract
- Action mixes chyme throughout small intestine lumen
Segmentation
Explain segmentation
- Initiated by pacemaker cells in small intestine which produce basic electrical rhythm (BER)
- muscle responsiveness is influenced by distension of intestine, gastrin, and extrinsic nerve activity
Functions:
> Mixing chyme with digestive juices secreted into small
intestine lumen.
> Exposing all chyme to absorptive surfaces of small intestine
mucosa
> Migrating motility complex- Sweeps intestines clean
between meals
True or false
Juice secreted by small intestine contains digestive enzymes
False
where do enzymes ( synthesized by small intestine) act?
within the brush-border membrane of epithelial cells
enzymes secreted by the small intestine
- Enterokinase
- Disaccharidases
- Aminopeptidases
How does digestion occur in the small intestine?
- Pancreatic enzymes continue carbohydrate and protein
digestion - Brush-border enzymes complete digestion of carbohydrates
and protein - Fat is digested entirely within small intestine lumen by
pancreatic lipase
Most occurs in duodenum and jejunum
Absorption
Adaptations that increase small intestine’s surface area
> Inner surface has permanent circular folds
Microscopic finger-like projections called villi
Brush border (microvilli) arise from luminal surface of epithelial
cells
How often is the lining of the small intestine replaced?
about every three days
Products of fat digestion undergo ___________ that enable them to be ________________
transformations
passively absorbed
Primarily a drying and storage organ
Large intestine
the large intestine consists of:
Colon
Cecum
Appendix
Rectum
Contents received from the small intestine consists of:
indigestible food residues, unabsorbed biliary components, and remaining fluid
Extracts more water and salt from contents
Feces = _____________________
Colon
what remains to be eliminated
Longitudinal bands of muscle in the large intestine
Taeniae coli
Pouches or sacs ( in large intestine)
Actively change location as a result of contraction of circular smooth muscle layer
Haustra
- Main motility of the large intestine
- Initiated by autonomous rhythmicity of colonic smooth muscle cells
Haustral contractions
Mass movements
Massive contractions which moves colonic contents into distal part of large intestine
Gastrocolic reflex
- Mediated from stomach to colon by gastrin and by autonomic nerves
- Most evident after first meal of the day
- Often followed by urge to defecate
Defecation reflex
- Initiated when stretch receptors in rectal wall are stimulated by
distension - Causes internal anal sphincter to relax and rectum and sigmoid
colon to contract more vigorously - If external anal sphincter (skeletal muscle under voluntary
control) is also relaxed, defecation occurs
