Chapter 24 - Digestive System Flashcards
2 Parts of Digestive System
- Alimentary canal (Gastrointestinal tract)
2. Accessory organs
Order of alimentary canal
- Mouth
- Pharynx
- Esophagus
- Stomach
- Small intestine
- Large intestine
Accessory organs
usually next to or inside tube; usually secrete chemicals that aid in digestion;
- tongue, teeth, salivary glands
- liver, gall bladder pancreas
6 Digestive Processes
- Ingestion
- Mechanical digestion
- Chemical digestion
- Propulsion
- Absorption
- Elimination
Mechanical digestion
physically tearing apart food into smaller pieces; chewing (mastication), churning (of stomach), segmentation
Chemical digestion
secretes digestive enzymes (to break down proteins); hydrolysis
Propulsion
pushing of food down alimentary canal (30 ft); ex. swallowing (deglutition); peristalsis - pushes food along small intestines
Absorption
process of taking in of nutrients into blood vessels or lymphatic vessels; now in body & now we can use
4 Tissue layers of Alimentary canal (technically digestion takes place outside of body)
- Mucosa
a. Epithelial
b. lamina propria
c. muscularis mucosae - Submucosa
- Muscularis externa
a. circular layer of smooth muscle
b. longitudinal layer of smooth muscle - Serosa
Lumen
hollow space in center of tube; where digestion takes place
Mucosa (layer of alimentary canal)
inner most layer; mucous membrane; opening to outside;
function: secretion, absorption, dislodges food
Epithelial (part of mucosa layer)
lines body cavities;
function: secretion
Lamina propria (part of mucosa layer)
areolar CT; richly vascularized; when associated w/mucous membrane, this CT is always called lamina propria;
function: blood vessels responsible for absorption
Muscularis mucosae (part of mucosa layer)
thin layer of smooth muscle;
function: dislodges food
Submucosa (layer of alimentary canal)
CT that surrounds mucosa; blood vessels, lymphatic vessels (carries food), nerves; submucosal nerve plexus located here
Submucosal nerve plexus
runs almost down whole canal;
function: responsible for stimulating gland secretions of the mucosa
Muscularis externa (layer of alimentary canal)
thickest layers of smooth muscles; main layer that produces movement of canal–peristalsis (kind of propulsion) & segmentation (mechanical digestion)
Myenteric nerve plexus
sandwiched between circular layer of s.m. & longitudinal layer of s.m.;
function: causing movements
Serosa (layer of alimentary canal)
serous membrane lining abdominal cavity; outermost layer; protective covering; visceral peritoneum
2 Controls of Enteric Nervous System (“brain of the gut”)
- Intrinsic control of digestion
2. Extrinsic control
Intrinsic control of digestion
exhibits control from inside of canal; submucosal & myenteric nerve plexuses form ENS; 100 million neurons-same size as spinal cord; more local
Extrinsic control of digestion
from outside of digestive system by ANS (hypothalamus);
parasympathetic stimulates digestive track motility & secretion;
sympathetic inhibits all digestive tracts movements & secretions from outside;
more extensive affecting whole digestive system
Peritoneal Folds
- Greater omentum
- Lesser omentum
- Mesentery
Greater omentum (peritoneal folds)
adipose tissue; nutrient storage
Lesser omentum (peritoneal folds)
stomach & duodenum attachment to liver; hepatic portal veins
Mesentery (peritoneal folds)
attaches small intestines to posterior body wall; fan-shaped fold associated w/small intestines; only place for blood vessels, nerves & lymphatic vessels to enter & leave digestive system
Hepatic portal veins
carries nutrients to liver; Liver-detoxification; portal - carries blood from one organ to another organ
Deglutition
swallowing; form of propulsion; involves voluntary & involuntary muscles; uses 4 cranial nerves & lots of muscles; uvula - by reflex this blocks food from going thru nasal passages
Peristalsis
uses muscularis externa to contract & squeeze food of circular layer; continuous contraction behind food; how food gets pushed down canal
Stomach
widest part of canal; function: storage & churning of food
Unique anatomy of Stomach
- Muscularis Externa - oblique layer - gross anatomy
- Rugae - gross anatomy
- Gastric Gland - microscopic anatomy
Muscularis externa (of stomach)
3rd layer only in stomach besides circular & longitudinal layer;
oblique layer - so stomach can churn in 3 different directions
Rugae (stomach)
fan-like folds; only appears when stomach is empty or near empty; stomach can hold a gallon of food or drink
Gastric Gland (stomach)
gland built into mucosa;
functions: 1. secrets HCl (hydrochloric acid) - ph of lumen is acidic;
2. Kills bacteria
3. Intrinsic factor - needed for vitamin B12 absorption (w/out it–severely anemic)
4. Pepsinogen - inactive enzyme; as protective measure
Function of HCl
denatures proteins (changes shape of proteins)
Zymogens
inactive enzyme; converted into pepsin (which begins to breakdown proteins;
Pepsinogen (inacitve)–HCl–pepsin in lumen (active)
Protections of the Stomach
- Zymogen Produced
- Goblet Cells - secrete mucus so acid doesn’t break down cells
- Tight Junctions
- High Turnover - lining of stomach gets replaced every 2 -3 days
- Gastric Gland impermeable to HCl - once HCl is released, it can’t harm cells
Small Intestines
function: chemical digestion of all nutrients completed; absorption of all nutrients completed; main place where chem digestion & absorption takes place; most important part of alimentary canal; narrowest part of canal (about 20 ft long)
Circular folds (plica circularis)
circular rings located w/in lining of s. i.;
function: to increase surface area for absorption to occur quick
Villi
located on circular folds of s.i.;
function: increases surface area more for absorption; blood vessels & lymphatic vessels main absorptive structure in s.i.; very bumpy
Microvilli
highly folded plasma membrane in absorptive cells of villi (of s.i.); increases surface are even more!; digestive enzymes are built into microvilli
Brush border enzymes
not secreted; built into lining of s.i.; digestion finished by these enzymes
3 Sections of Small Intestine
- Duodenum - 1st 10 inches
- Jejunum - middle section; 8 ft
- Ileum - last 12 ft
Duodenum
mixing region - chyme from stomach goes into duodenum; bile, gall bladder; pancreas;
weakness - chyme
Bile
from liver; emulsification of fats–helps break down globs of fat
Gall bladder
smooth muscle; stores & concentrates bile; when bile is not needed immediately, it comes here to be stored
Pancreas
most important accessory organ; gland: makes almost all enzymes that break down proteins, carbs & nucleic acids; digestive enzymes come from pancreas
Brunner’s gland
protects duodenum from chyme (which is very acidic);
functions: 1. secretes a slightly basic secretion; neutralizes the acids; neutralizes the chyme; to protect s.i. so it’s not harmed;
2. produces thick mucus to coat duodenum from acids
Jejunum
main chem digestion & absorption part
Ileum
absorption of vit B12 & bile salts (part of bile emulsifying fats); responsible for Peyer’s Patches
Peyer’s Patches
MALT (Mucosa Associated Lymphatic Tissue); houses immune cells & destroys microorganisms that get into this part; protection of s.i.
Large Intestine
Main function: absorption of water: only part of canal where solid waste is eliminated; fiber & other things can’t be broken down by digestive system; wider but not too long (about 5 ft)
2 Structures found only in L.I.
- Teniae coli
2. Haustra
Teniae coli
band of smooth muscle in l.i.; longitudinal layer of muscularis externa; does NOT completely surround circular layer as it does everywhere else; only part that is not covered;
Haustra
sac-like structures in l.i.; haustral contractions - slower than peristalsis; squeezes as much water as possible
Bacterial flora
not a structure; garden of bacteria located in lumen; helpful bacteria; makes B vitamins & vitamin K (needed for blood clotting)
Carbohydrate digestion
begins in mouth;
enzyme: amylase;
brush border enzymes finishes job
Protein digestion
begins in stomach; HCl denatures proteins; HCl unravels protein & prepares it for chemical digestion;
enzyme: pepsin (stomach);
enzymes made in pancreas: trypsin, chymotrypsin, carboxypeptidase;
brush border enzymes
Lipid digestion
bile salts emulsify fats;
enzyme: lipase
Nucleic acid digestion
enzymes: deoxyribonuclease (breaks down DNA); ribonuclease (breaks down RNA);
brush border enzymes
Digestive Processes involving Mouth
Ingestion;
Mechanical digestion - mastication;
Chemical digestion of carbs;
Propulsion - deglutition
Digestive Processes involving Pharynx
Propulsion - deglutition
Digestive Processes involving Esophagus
Propulsion - peristalsis
Digestive Processes involving Stomach
Mechanical digestion - peristalsis;
Chemical digestion of proteins (1 nutrient);
Propulsion - peristalsis;
Absorption of alcohol, some drugs, water
Digestive Processes involving Small Intestine
Mechanical digestion - segmentation;
Chemical digestion of nutrients completed;
Propulsion - peristalsis;
Absorption of nutrients completed
Digestive Processes involving Large Intestine
Propulsion - haustral contractions;
Absorption of water & some vitamins;
Elimination
Unique Anatomy of Stomach
Oblique layer of muscularis externa;
Rugae;
Gastric gland
Unique Anatomy of Small Intestine
Circular folds, villi, microvilli;
Brunner’s glands in duodenum;
Peyer’s patches in ileum
Unique Anatomy of Large Intestine
Teniae coli;
Haustra
Accessory Organs of Mouth
salivary glands, tongue, teeth
Accessory Organs of Small Intestine
Pancreas - produces digestive enzymes;
Live - produces bile;
Gall bladder - stores bile
