Chapter 23 Digestive System Flashcards
Basic Digestive Functions
- Ingestion
- Propulsion (movement through anything of GI tract) (ex: peristalsis)
- Mechanical digestion (physical breakdown of food from solid –> liquid)
- Chemical digestion- use of enzymes + other chemicals to breakdown food into monomers (ex: protein -> amino acids)
- Absorption- passage of materials from the GI tract into blood
- Defecation- get rid of things we did not completely digest
The Digestive System has its own…
Enteric Nervous System (ENS)
-which can integrate some digestive processes
(long short reflex)
Short Reflex
a response that doesn’t involve integration by the CNS
(figures it out on its own)
ex: as soon as food enters the stomach, it knows its food chemicals so it does not need brain + spinal cord for help
Long Reflex
a response that’s the product of CNS integration
uses CNS
Deglutition
(swallowing)
- Buccal phase- (voluntary) tongue moves food in pharynx
- Pharyngeal Esophagus phase- (involuntary) pharyngeal constrictor muscle ( 3 muscles in throat) propel food into esophagus
Stomach Physiology: Mechanical Activities
performed by muscularis externa
- Filling
- Mechanical Digestion
Stomach Physiology: Mechanical Activities; Filling
a. Receptive Relaxation- stomach expands as food enters the esophagus
b. Adaptive Relaxation- stomach continues to expand as it receives food
Stomach Physiology: Mechanical Activities; Mechanical Digestion
- every 15-20 seconds, peristaltic waves travel from the fundus —> pylorus
- blends food into Chyme (substance that you regurgitate)
- moves 3-5 ml of chyme into duodenum with each wave
- This rate of contraction is set by Pacemaker Cells (cells that spontaneously depolarize, all on their own head toward threshold)
Stomach Physiology: Production + Release of Gastric Juice (Mucosa)
performed by cells of Gastric Glands ex: 1. Mucus Cells 2. Parietal Cells 3. Chief Cells 4. G Cells
Production + Release of Gastric Juice: Gastric Gland: Mucus Cell
release mucus to protect stomach lining
Production + Release of Gastric Juice: Gastric Gland: Parietal Cells
release HCl (hydrochloric acid) that keeps stomach at (pH2)(acidic) and also releases intrinsic factor (need to absorb vitamin B12)
Production + Release of Gastric Juice: Gastric Gland: Chief Cells
release the protein Pepsinogen
(pH2)
pepsinogen—> Pepsin (an enzyme that performs protein digestion; breakdown of protein)
- also release Gastric Lipase
(ex: Lipids(fats))
Production + Release of Gastric Juice: Gastric Gland: G Cells
release hormone Gastrin
- gastrin stimulates gastric gland cells (tells other cells to produce more of what they’re doing/ making)
- gastrin helps pacemaker cells reach threshold
Phases of Gastric Juice Secretion
- Cephalic
- Gastric phase
- Intestinal
Phase of Gastric Juice Secretion: 1. Cephalic
sight, smell, taste, thought of food
-cerebral cortex (makes you consciously aware)
l (tells hypothalamus food is nearby)
hypothalamus
l x(vagus nerve)
stimulation of gastric juice production (prepares for meal)
Phase of Gastric Juice Secretion: Gastric Phase
(what happens when stomach actually gets food)
1. Food enters the stomach
2. G cells detect food chemicals
3. G cells release gastrin
4. stimulation of gastric juice production
or
1. food enters stomach
2. mechanoreceptors detect food
3. hypothalamus
4. stimulation of gastric juice production (by vagus nerve (x) from hypothalamus)
Phase of Gastric Juice Secretion: Intestinal
- as food enters duodenum, duodenum uses Intestinal Gastrin to stimulate stomach
- once duodenum is distended (filled) by Chyme, the stomach is inhibited (stopped) via Enterogastric Reflex
- hypothalamus closes pyloric sphincter
- duodenum inhibits stomach with Secretin and CCK (makes you feel full)
Small Intestine
Duodenum: -receiving bile from gallbladder/ liver -receives pancreatic juice (these secretions perform lots of chemical digestion) Jejunum Ileum
Small Intestine Physiology
- Chemical Digestion
- Absorption
- Mechanical Digestion
- Propulsion
Small Intestine Physiology: Chemical Digestion
-small intestine secretes lots of Brush Border Enzymes (BBE), which are designed to complete the final stages of chemical digestion
ex: dipeptide –> amino acids
disaccharide –> monosaccharide
protein (pepsin, pancreatic juice)–> dipeptide —-> BBE amino acid
carbs (salivary amylase, pancreatic juice)—> disaccharide—–> BBE monosaccharide
-lots of surface area for releasing BBE’s
Small Intestine Physiology: Absorption
(taking nutrients from GI tract + bringing it into the bloodstream)
- these adaptations give small intestine lots of internal surface area
- Plicae (like Rugae in stomach)
- Villi (finger-like extensions on Plicae)
- Microvilli (on top of Villi)
Small Intestine Physiology: Mechanical Digestion
(segmentation)
-contractions of alternating segments of small intestine
Small Intestine Physiology: Propulsion
- Food Enters Stomach
- Hypothalamus
use vagus (X) nerve - peristalsis in small intestine moves food into large intestine through ileocecal valve
(Gastrointestinal Reflex (long reflex))
Liver
(Checks the blood before entering the general circulation)
- receives nutrient-rich blood directly from GI tract (as soon as food gets absorbed, the blood takes a tour through the liver)
- Hepatocytes (liver cells) do the following to the blood:
1. identify + destroy microorganisms (with the help of kupffler cells)
2. destroy toxins + drugs
3. process nutrients
4. make bile
Liver: Hepatocytes do what to the blood?
- Identify + destroy microorganisms (with the help of kupffler cells)
- Detoxify toxins + drugs
- Process nutrients
- store glucose as glycogen (to store for emergency)
- use amino acids to make plasma proteins - Make bile; helps in the digestion of fats
- help digestive enzymes adhere to fats
Gallbladder
-stores bile
-releases bile in response to CCK
(tells gallbladder to use bile to help empty when feeling full)
Pancreas
releases pancreatic juice into duodenum
this juice contains:
-alkaline solution (basic)(to neutralize acids)
(released in response to the chemical SECRETIN)
(tells pancreas to put solution to help make less acidic)
-Digestive Enzymes
Amylases–> carbs
Lipases–> lipids (especially fats)
Proteases–> proteins
Nucleases–> nucleic acids (DNA, RNA)
Large Intestine (colon) Physiology
- Chemical Digestion
- Absorption
- Mechanical Activities
Large Intestine Physiology: Chemical Digestion
-mostly “fibrous” carbohydrates like cellulose (partial digestion)
Large Intestine Physiology: Absorption
- small amounts of carbohydrates
- Water- exact amount depends on how hydrated the body is
- less well hydrated–> the more water
Large Intestine Physiology: Mechanical Activities
A. haustral contractions (pouch-like structures on intestine)
B. mass movement (mass peristalsis)
-occur 3-4 times a day (as part of Gastrocolic Reflex:)
1. food enters stomach–>hypothalamus–> fecal matter moved into sigmoid colon
C. defecation reflex
-distension of sigmoid colon makes it contract (and dilates anal canal)
(stuff gets shoved into sigmoid colon–> Gastrocolic reflex –> anal canal
