Chapter 18 The Digestive System Flashcards
MOTILITY is
Movement of food through the gastrointestinal (GI) tract via:
Ingestion
mastication
deglutition
contraction of smooth muscles: peristalsis, segmental contractions
SECRETION is
Release of exocrine and endocrine secretions into lumen of GI tract for digestion
DIGESTION is
Chemical/mechanical breakdown of food from macromolecules to smaller molecules, for absorption
ABSORPTION is
Transport of digested end products into blood/lymph
STORAGE AND ELIMINATION is
Temporary storage followed by elimination of indigestible food molecules
IMMUNE BARRIER is
Immune system cells in connective tissue outside of intestinal epithelium AND physical barrier to pathological organisms and toxins due to tight junctions in epithelial lining of intestine.
How does digestion occur by
hydrolysis reactions
Gastrointestinal (GI) Tract/Alimentary Canal is made up of
Mouth pharynx esophagus stomach small intestine large intestine
Accessory Organs and Tissues are made up of
What do they do
Teeth tongue salivary glands liver gallbladder pancreas
Secrete substances into the tract via connecting ducts
What does the mouth produce
Salivary amylase
Lipase
Water
What does the stomach produce
HCL
Pepsinogen
Mucus
Intrinsic Factor
What does the Small intestine produce
What do they do
Bile
Bicarbonate
Enzymes
Absorb nutrients
What does the large intestine do
Absorb water/vitamins
What are the 4 layers of the gut wall
Mucosa
Submucosa
Muscularis
Serosa
What is the first layer (innermost)
What does it do
What is unique about it and what does this do
MUCOSA:
Absorption and secretion
Mucus secretion
Muscularis mucosae (FOLDS):
Folds increase surface area for absorption
Produces movement of villi
What is the second layer
What does it have
SUBMUCOSA:
Connective tissue that serves mucosa
Blood/lymph vessels
Submucosal plexus: neuronal innervation for muscularis mucosae
What is the third layer
What is its main function
What is different between its outside and inside
MUSCULARIS EXTERNA:
Involved in segmental and peristaltic contractions, to move food through tract, and pulverize and mix it with digestive enzymes
Inner circular layer of smooth muscle
Myenteric plexus: neurons for entire GI tract
Outer longitudinal layer of smooth muscle
What is the fourth layer (Outermost)
SEROSA:
Connective tissue covered with epithelium
What lines the lumen in the gut
Absorptive cells
Where are the neural and muscular components in the gut
below the lumen
Blood and lymph vasculature are abundant to transport absorbed nutrients
True
What do the villi do
Increase the surface area for absorption of nutrients
What is Mastication
chewing of food in mouth
What does salivary amylase digest
Starch (carbohydrate)
What is Deglutition
Swallowing
What does food and drink stimulate
What does this result in
pressure receptors in the pharynx
afferent input to the medulla and efferent output to muscles in pharynx and esophagus
What is a bolus
mix of food with saliva
What prevents food from entering the nasal passages
Soft palate
What closes off the opening to the larynx
Glottis
What prevents food from entering the trachea
Epiglottis
What relaxes to allow food to descend into the esophagus
esophageal sphincter
What is Peristalsis
wavelike muscular contraction that pushes bolus to the stomach
What allows for the bolus to be pushed down the esophagus to the stomach
What happens just before reaching the stomach
Circular smooth muscle contracting behind bolus and relaxing in front
The lower esophageal sphincter muscle relaxes
What is Chyme
Partially digested food with gastric juices
What does the stomach do (5)
- Stores food
- Kills bacteria with acidity of gastric juice
- Starts digestion of proteins (not carbs or fats)
- Peristaltic waves mix and propel the chyme
- Moves chyme to the small intestine, where most digestion and absorption occur
What does the inner surface of the stomach contain
Folds called gastric rugae
What 4 things do specialised cells in the stomach produce
Mucus fluid
Enzyme precursors
Hydrochloric acid
Hormones
What secretes mucus in the stomach
Mucous neck cells
What secretes Pepsinogen in the stomach
Chief (zymogenic) cells
What secretes Hydrochloric acid in the stomach
Parietal cells
What secretes Histamine and serotonin in the stomach
Enterochromaffin like cells
What secretes gastrin
G cells
What secretes somatostatin
D cells
What secretes intrinsic factor
Gastric mucosa
What does intrinsic factor do
Allows for intestinal absorption of vitamin B12
What does ghrelin do
regulates hunger
What is gastric juice
Secretions of gastric cells + water
What does acid production by parietal cells depend on
Carbonic acid
Secretion of hydrogen into the stomach (active transport by H/K atpase pumps)
What happens when carbonic acid dissociates in the stomach
Bicarbonate secreted into the bloodstream
Exchanged for Cl via facilitated diffusion
What stimulates the secretion of HCl
What inhibtis secretion of HCl
Gastrin
ACh
Histamine
Somatostatin
What stimulates gastrin
Presence of partially digested proteins in stomach
How does Gastrin effect secretion of HCl (3)
Binds to receptors on parietal cells
Stimulates ECL cells to secrete histamine
Paracrine stimulation of parietal cells secretes HCl
What happens when gastric juice is acidic (3)
Activates pepsin
Optimizes activity of pepsin
Accelerates digestion of proteins
What protects the lining of the stomach
mucus layer containing bicarbonate
What converts pepsinogen to pepsin
HCl aciditiy
What does pepsin actually do
accelerates the digestion of proteins
What does the mucosa in the small intestine contain
Goblet cells for secreting mucus and lymphocytes
Folds called Villi
Microvilli on villi which increase the surface area for food absorption
What do microvilli also have
digestive enzymes
The small intestines is where there is digestion of… (3)
Carbohydrates
Lipids
Proteins
The villi in the small intestine project where
into the lumen - increases surface area for absorption
What are brush border enzymes
Enzymes on the plasma membrane of microvilli
What is the main contraction in the SI and why
Segmentation
Mixes and moves chyme
Controlled by enteric nervous system
The large intestine has no… (2)
Villi or digestion
The large intestine absorbs…
Electrolytes
Water
Vitamins
What is haustra
Pouches on outer surface of LI
What is the main activity in the LI
Active transport of sodium
And
Absorption of water
To concentrate the feces
Microbes in the LI produce… (2)
Vitamin K for blood clotting
B vitamins
How does defecation occur
Longitudinal rectal muscles contract
Increases rectal pressure
Internal and external sphincters relax
Contraction of abdominal and pelvic muscles
Gallbladder function
storage of bile from liver
Pancreas function
pancreatic juice (exocrine) for digestion
What are the 5 major functions of the liver
Detoxication of blood Carbohydrate metabolism Lipid Metabolism Protein synthesis Secretion of bile
What separates hepatocytes in the liver
Sinusoids
What is the passage of blood in the liver (4)
Blood enters a liver lobule through the portal triad
Passes through hepatic sinusoids
Leaves the lobule through a central vein
The central veins converge to form hepatic veins that take venous blood from the liver
What are the main components of bile
bile pigment bile salts lecithin bicarbonate ions cholesterol trace metals
What is the bile pigment
Bilirubin - breakdown of heme
Characteristics of Bilirubin
Not water soluble = carried in blood attached to albumin
Liver converts to water soluble from that can be secreted into bile
Bilirubin that is excreted in feces and urine is excreted as
Urobilinogen
Bile salts are…
They form…
Cholesterol based
Micelles
Emulsification is the
breakdown of large fat globules by bile salts into smaller globules, for digestion by lipase enzymes
The major pathway of cholesterol breakdown is activated when
cholesterol is used to produce bile salts
Where in the liver is bile produced
Where is it then secreted to
Hepatocytes
Bile caniculi
The caniculi are drained by…
Bile ducts at end of each lobule
Where do the bile ducts transport the bile
What then stimulates bile to move into the SI
into the gall bladder
Cholecystokinin (CCK)
How does bile enter the SI
Via the common bile duct
What happens to the cholesterol based bile salts along the intestine
Reabsorbed into the liver
What is unique about bile salt structure
Has one polar and one no polar end
What do the nonpolar ends of bile acid do
Emusify fats in water
What forms in bile acids
Micelles which are readily broken down
`What are the endocrine functions in the pancreas
Insulin
Glucagon
Secreted into the blood
What are the exocrine functions of the pancreas
Pancreatic juice
Secreted through pancreatic duct into duodenum of SI
What is pancreatic juice made up of
Bicarbonate and 20 enzymes
What does Amylase digest
Starch
What does Trypsin digest
Protein
What does Lipase digest
Triglycerides
The Exocrine cells in the pancreas produce what type of enzymes
they travel via the
Digestive enzymes
Pancreatic duct
When do digestive enzymes become active
In the SI
What are zymogens
Inactive enzyme precursors
Gastric motility and secretion is a ______ process
This process results in the presence of
automatic
Chyme
The GI tract is both an
Endocrine gland
And
Target for hormones
The regulation of GI processes can be controlled by
Hormonal (endocrine cells)
Neural (enteric nervous system)
What are the 3 phases of GI control
Cephalic phase
Gastric phase
Intestinal phase
What happens in the Cephalic phase (3)
Gastric secretion stimulated by sight, smell, taste, chewing, talking about food; continues into first 30 minutes of meal
Vagus nerves stimulate chief cells to secrete pepsinogen, parietal cells to secrete HCl, and G cells to secrete gastrin
Gastrin stimulates ECL cells to secrete histamine, which stimulates parietal cells to secret HCl
What happens in the gastric phase (9)
Focus on what cells secrete what and what acidity inhibits
Starts when food enters stomach
Casues: distension, acidity, AAs, peptides
Presence of AAs and peptides
Stimulates chief cells to secrete pepsinogen and G cells to secrete gastrin
Stimulates secretion of histamine from ECL cells to stimulate HCL from parietal cells
Acidity inhibits gastrin secretion
via somatostatin secreted by D cells when pH decreases.
Somatostatin also inhibits acid secretion by parietal cells
Distension
What happens in the Intestinal phase
What are the inhibitory hormones secreted by SI
Inhibition of gastric activity and motility by vagus nerves when chyme enters SI = time to digest and absorb food
gastric inhibitory peptide (GIP)
somatostatin
cholecystokinin (CCK)
glucagon-like peptide-1 (GLP-1).
The myenteric plexus is
the outer network
entire length of GI tract
The Submucosal plexus is
The inner network
Only in SI and LI
What is the sensory stimulus that activates interneurons
What does this then stimulate
Chyme
Motor neurons = smooth muscle contraction
Intestinal Reflexes affect what
Motility
What does Paracrine Regulation affect
Contraction
Absorption
Secretion
What is Cholecystokinin (CCK)
Protein and fat in chyme stimulate secretion of CCK by duodenum
What does the Cholecystokinin stimulate
secretion of pancreatic juice enzymesto digest protein and fat
What does Chyme stimulate in the SI
What does it inhibit
Gastric phase and reflex secretion of pancreatic juice and bile
Inhibits entry of additional chyme into SI, to allow digestion
What stimulates secretion of Secretin
What does it then stimulate
Reduced pH in SI (due to acidic chyme)
Secretion bicarbonate and water secretion from pancreas
The secretion of bile is
but…
Continuous
Does increase with meal
What causes bile volume to increase
Secretin and CCK stimulate liver to secrete bicarbonate into bile
What causes more bile to be delivered to the duodenum from the contracting gallbladder
Chyme in duodenum
CCK secretion in response to fat in chyme
During a meal, the arrival of bile in the duodenum causes what to happen
Liver to secrete more bile
Salivary amylase digests from…
mouth to upper stomach
Pancreatic amylase digests in…
Results in..
SI
Results in Disacc, trisacc, oligosacc
Brush border amylases hydrolyze in
Results in..
SI
hydrolyse into their components monosaccharides
How are carbohydrates absorbed
Via secondary active transport coupled to Na into SI
Then via facilitated diffusion in membrane
When Na is absorbed what follows
CL follows passively
Water then follows NaCl for absorption into blood
How do AAs enter the cells of the SI
via secondary active transport coupled to Na
Where are Dipeptides and tripeptides transported into
How…
What happens to them when they get there
epithelial cells of SI
via a different carrier
hydrolyzed into AAs in the cytoplasm
Lipids in chyme stimulate what into the SI
This results in
Bile
Emulsification
Digestion of lipid droplets in SI is by
Pancreatic lipase
Aided by colipase - bind lipases with lipid droplet
What does Phospholipase A digest
Phospholipids into fatty acids + lysolecithin
What is more polar undigested lipids or digested lipids
Digested lipids
Where do digested lipids then enter
Micelles of bile salts
Digestion of triglycerides releases what
What happens to the products
fatty acids and monoglycerides
Assoicate with micelles of bile salts, then secreted by liver
What are chylomicrons
Resynthesize triglycerides and phospholipids, cholesterol combine with protein
Where do free fatty acids and monoglycerides go after they leave micelles
SI cells
By what process are chylomicrons secreted by
exocytosis into lymphatic vessels, then into blood
What happens to Chylomicrons in the blood
Are modified to release triglycerides for energy, fat storage and cholesterol
Chylomicrons =
Triglycerides + protein
What is an ulcer
Erosion due to a failure of protective mechanisms in the stomach, esophagus, or duodenum
