Unit 15: Digestive System II Flashcards
The colon absorbs
Water+electrolytes
Stores and Concentrates
Feces
Sodium Absorption in the Colon
Absorbed via active transport mechanisms
Water Absorption in the Colon
Water follows via osmosis and takes place in the first half of the colon
Large Intestine Secretes
Mucous to protect its lining form chemical damage + mechanical damage + lubricate forming feces
Ions secreted into the colon
K+
Bicarbonate
Small amount of digestion in the colon
Occurs when undigested polysaccharides are metabolized by bacteria into free fatty acids that are absorbed via passive diffusion
The bacteria in the colon produced
Gas and vitamin K+ for blood coagulation
Careful regulation of _______ and _______ _____ through ______ and ______ mechanisms
motility and hormone secretion through neural and hormonal mechanism
Hormonal Mechanisms of Regulation
Release of chemicals from intestinal cells in response to direct mechanical stimulation from food in the stomach + intestine
hormones can be released in response to neural activation
Neural Control Mechanisms
Involves the enteric neurons system are divisions of the ANS
ANS
SYN
PSYN
Both can influence the digestive tract
_ _ _ performs this by altering the ______ of _______ in the _________ nervous system.
ANS performs this by altering the activity of nerves in the enteric nervous system
These nerve cells will then affect smooth muscle in the
Walls of the digestive tract
enzyme-secreting cells
endocrine cells
blood vessels of the tract
Long reflex loop
Travel from the CNS
Input from the higher brain centers
Stimulus: Sight + Smell of food which is detected by their respective sensors
Signals form the brain are sent through the PSYN to the enteric nervous system to alter the digestive function: enzyme release + gastric motility
Short reflex loop
Travels locally within the digestive system
begins by mechanical digestion (stretching) of the digestive tract + chemical changes (pH; osmolarity) w/ in the tract
these changes are detected by sensors of the enteric nervous system that initiate a reflex
reflex activates effector organs
Effector organs
Secretory cells
smooth muscle in the walls of the tract
causes the release of enzymes; alters gastric motility
PSYN
Increase gastric motility
causes secretion secretion
Production of water saliva
SYN
Decreased motility + secretion
Thick viscous saliva + dry mouth
Gastrointestinal motility
muscular contraction of the stomach + intestine that mix up food + propel it through the digestive tract
Digestion of fatty foods
Long+complex process
if prematurely released from the stomach into the intestine the fats + lipids may not be completely digested
chyme must be released by the stomach in leveled amounts in order to maximize the digestive + absorption process
Surrounding the digestive tract
Are specialized smooth muscle cells, interstitial cells
Interstitial Cells
spontaneously alter their membrane potential producing Basal electric rhythms
BER
Slow waves that travel down the digestive tract
BERs don’t cause the muscles to contract because they don’t reach threshold
Low waves travel from smooth muscle cell to smooth muscle cell through gap junctions
Frequency of these BERs
Stomach: 3 waves/min
Duodenum: 12 waves/min
As long as BER stays below the threshold of the smooth muscle cells
no contraction along the digestive tract
If peak of the slow waves reaches threshold
the smooth muscles will contract
To Reach threshold
additional stimulus in the form of mechanical, nervous, hormonal input is required
additional signals will cause BERs to reach threshold and fire action potentials: causing muscle contraction of the smooth muscle walls
contraction travel down the intestine
in a wave-like fashion
Hormones of the Intestine
Hormones regulate gastric motility + secretion of enzymes
secretion is released in response to the presence of acid in the intestine
CCK is released in the presence of fats
Cholecystokinin (CCK) is released in the presence of fats
- slows emptying of the stomach
- stimulates pancreas to release digestive enzymes
- causes gallbladder to contract to release bile
Glucose-dependent insulinotropic peptide
secreted in response to glucose + AAs
stimulates release of insulin from the pancreas
inhibits emptying of the stomach
Food
Causes release of hormones
Effect of Hormones
Causes release of particular pancreatic enzymes to break down food
Decreases motility + slows emptying of the stomach into the intestine
Type of food determines the type of hormones released
Hormone releases enzymes suited to digest the food
Gastric Hormones
- Stomach secretes gastrin
- secreted by G-cells located in the antrum of the stomach in response to the presence of proteins + mechanical distention from food + stimulation of PSYN
Gastrin causes secretion of HCl
HCl is secreted by ____ cells in the stomach
Parietal
amount of HCl secreted by these cells varies during the eating-digestive process
can be secreted before you start eating
Cephalic Stage: Gastric secretion initiated in response to
- sight
- smell
- taste
- chewing
- anticipatory response to the act of eating + involves the activation of the enteric nervous system through the long reflex loop
Stimulation of the PSYN triggers (stomach)
- PSYN activates the enteric nervous system
- parietal cells release HCl
- G-cells release gastrin
- motility of the stomach increases
Gastric Stage
- stomach
- gastric phase of acid secretion begins
- stimulus
- presence of food in the stomach distends the walls
- presence of AAs (chemical stimulus)from the breakdown of proteins
- Short reflex loop: - enteric nervous system
- HCl, gastrin, pepsinogen, increase gastric motility
Intestinal Stage
- Intestine
- most of digestive + absorptive processes take place here
- stimulus
- presence of fat, glucose, acidic chyme
- decreased motility + inhibit secretions in the stomach
- performed by the enteric neurons system
- secretin
- CCK
- glucose-dependent
- performed by the enteric neurons system
