Chapter 24 - Digestive System Flashcards
Digestive Process
Ingesiton, secretion, motility, digestion, absorption, defecation
Two parts of the digestive system
GI Tract, Accessory digsetive organs
Path of food through the GI tract
Oral cavity, esophagus, stomach, small intestine, large intestine, rectum, anus
GI tract
Runs from the mouth to the anus
accessory digestive glands
salivary glands, gall bladder, liver, pancreas, rectum, anus
These never come in contact w food, instead they produce or store secretions that aid in chemical digestion
Serous membrane of the abdominal cavity
The serous membrane of the abdominal cavity. It has two layers: visceral peritoneum (covers abdominal organs) and parietal peritoneum
Serous fluid
Serous fluid between these layers prevents friction and adhesion.
Falciform Ligament
Peritoneal fold that attaches the liver to the anterior abdominal wall and diaphragm.
GREATER OMENTUM
overs the folds of the small
intestine. Contains much adipose tissue (beer belly).
Contain many lymph nodes (part of the immune system
LESSER OMENTUM
connects the stomach
and duodenum to the liver. Pathway for
blood vessels entering the liver
MESOCOLON
binds the
large intestine to the posterior
abdominal wall. Contains
blood and lymphatic vessels.
MESENTERY
binds the small
intestine to the posterior wall. It
contains lots of adipose tissue and
contributes extensively to the
large abdomen in obese
individuals. Contains multiple
blood and lymphatic vessels, as
well as lymph nodes.
all the folds of the peritoneum
falciform ligament, greater omentum, lesser omentum, mesentery, mesocolon
peritoneum
largest serous membrane of the body;
Peritonitis
Inflammation of the peritoneum
Most often due to infection by microorganisms
◦ life-threatening
◦ could be due to surgery
◦ could be due to perforation of intestine
Can be due to rubbing of inflamed peritoneal surfaces
◦ not life-threatening, but still painful
LAYERS OF THE GI TRACT
deep to superficial, are the mucosa, submucosa, muscular layer, and serosa.
Mucosa Layer of GI Tract
Innermost layer consisting of epithelium (varies by region), lamina propria (areolar connective tissue with blood vessels, nerves, glands, immune cells), and muscularis mucosae (thin smooth muscle layer).
Submucosa Layer of GI Tract
Layer of areolar connective tissue surrounding the mucosa, containing large blood vessels, lymphatic vessels, and in some regions exocrine glands that secrete buffers and enzymes.
Muscularis Layer of GI Tract
Layer dominated by smooth muscle cells arranged in inner circular and outer longitudinal layers, essential for mechanical processing and movement of materials along the digestive tract.
SEROSA
AKA visceral peritoneum that covers organs along most portions of the
digestive tract; attaches the
digestive tract to adjacent
structures;
Enteric Nervous System
The ‘brain of the gut’ that can function independently. Includes the myenteric plexus (controls GI tract motility) and submucosal plexus (controls secretions of organs into GI tract).
Autonomic nervous system
View pg 21
Regulate neurons of the ENS
◦ Parasympathetic (CN X; sacral
nerves) – increase ENS activity
◦ Sympathetic (thoracic and upper
lumbar nerves – decrease ENS
Salivary Glands
Sublingual glands: deep to
the tongue in the floor of the
mouth, secrete mucus that
serves as a buffer
Submandibular glands:
medial in inferior to the
mandible, secrete salivary
amylase and mucus
Parotid glands:
inferior/anterior to the ears,
b/w skin and masseter,
secrete watery liquid with
salivary amylase
Sublingual glands
deep to
the tongue in the floor of the
mouth, secrete mucus that
serves as a buffer
Submandibular glands:
medial in inferior to the
mandible, secrete salivary
amylase and mucus
Parotid glands:
inferior/anterior to the ears,
b/w skin and masseter,
secrete watery liquid with
salivary amylase
Functions of Saliva
*Wet food for easier swallowing
*Dissolves food for tasting
*Chemical digestion of starch (salivary amylase)
*Chloride ions activate salivary amylase
*Enzyme (lysozyme) → helps destroy bacteria
*IgA = antibodies that prevent attachment of microbes to epithelium
- Also has lingual lipase but isnt used until stomach
Digestion in the Mouth
Mechanical digestion
Chemical digestion
◦ Lingual lipase
Digestion in the Mouth: Mechanical digestion
(mastication or chewing)
◦ breaks into pieces
◦ mixes with saliva so enzymes can access food molecules
◦ forms a bolus
Digestion in the Mouth: Chemical digestion
◦ Salivary amylase
◦ begins starch digestion (pH 6.5 or 7.0 in mouth)
◦ inactivated by gastric juices (pH 2.5)
Digestion in the Mouth:◦ Lingual lipase
◦ Lingual lipase
◦ Although it is secreted in the mouth, it begins the digestion of triglycerides
in the stomach
Deglutition process
- Bolus is forced into
the oropharynx by
tongue movement - Soft palate
moves up,
blocking the
nasal cavity - Epiglottis blocks the
trachea, preventing
food from entering - Food moves
from the pharynx
to the esophagus
DEGLUTITION (swallowing)
It consists of voluntary and involuntary stages
Voluntary stage begins when the bolus is forced into the oropharynx by tongue
movement
Receptors in oropharynx stimulate deglutition center in brain
Soft palate moves up, blocking the nasal cavity and epiglottis blocks the trachea – prevents food entry (involuntary)
Food moves from the pharynx to the esophagus
Esophagus
The esophagus squeezes food along to the
stomach
Peristalsis in the esophagus moves food
boluses into the stomach.
Cardiac sphincter (lower esophageal
sphincter) regulates passage of food through
the esophagus and into the stomach.
Peristalsis
a progression of coordinated contractions and relaxations of the circular and longitudinal layers of the muscular layer
lower esophageal
sphincter
regulates passage of food through
the esophagus and into the stomach.
Layers of the
esophageal wall
Same layers of the GI tract EXCEPT serosa. Instead adventitia; Attaches esophagus to surrounding
structures
mucosa and submucosa form large folds that allow for expansion during the passage of the bolus. Tone in the wall keep the lumen closed except when u swallow
superior part contains skeletal muscle fibres
lower portion contains smooth muscle tissue
Pharynx
when food is first swallowed it enters here
Gastroesophageal reflux disease (GERD)
When the lower esophageal sphincter fails to close adequately after food has
entered the stomach
stomach content (acidic) can reflux (go back up) into the inferior portion of the
esophagus
causes burning sensation (heartburn)
Stomach
stomach churns the food with gastric juice to form a mixture called acid chime (a thin liquid).
Openings of the stomach
cardiac sphincter and pyloric sphincter.
◦ The pyloric sphincter opens to allow
the passage of chyme into the small
intestine.
Emptying of the stomach into the small intestine occurs ~3ml at a time
Regions of the Stomach
Fundus
Cardia
Body
Pylorus
Layers of the Muscularis
Externa
strengthens the stomach
wall and assists in the
mixing and churning
activities essential to the
formation of chyme
rugae
folds in stomach that stretch and expand stomach
to accommodate incoming food
pyloric sphincter
Empties as small squirts of
chyme to leave the stomach
stomach Mucosa
Produces an alkaline carpet of mucus
that covers the interior surfaces of the
stomach and protects epithelial cells
against the acid and enzymes in the
gastric lumen
Lymphatic vessel
Artery and vein
Myenteric plexus
Surface mucosa cells
secretes mucus
Mucous neck cell
secretes mucus
parietal cell
secretes HCL as stomach needs to be acidic to activate pepsinogen and intrinsic factor, needed for absorption of vitamin B12
chief cell
secretes pepsinogen and gastric lipase
G cell
secretes the hormone gastrin into the bloodstream
gastric juice
The secretions of the mucous, parietal, and chief cells form gastric juice
gastrin
stimulate
additional secretion of
gastric juice
It plays a vital role in digesting proteins by activating pepsin.
The acidic environment created by gastric juice is crucial for digestion.
Apart from aiding digestion, gastric juice also absorbs Vitamin B12.
How is HCL secreted into the stomachs lumen?
see notes and pg 47
Protein digestion in the stomach
-HCL denatures protein molecules
-HCL turn pepsinogen into pepsin which breaks peptide bonds btwn A.A
Fat digestion
Gastric and lingual lipase spit triglycerides
Peptic ulcer disease
Ulcer (craterlike lesion in a membrane) exposed to
gastric juices can cause bleeding (sometimes severe)
Causes of peptic ulcers
3 causes:
* infection with Helicobacter pylori: bacteria that survives the high pH of the stomach and destroys the mucus layer.
- use of non-steroidal anti-inflammatory
drugs (NSAIDs) - hypersecretion of HCl (in certain tumors
Where does most chemical digestion occur?
Small intestine
Pancreas
Secrete enzymes that digest;
◦ starch
◦ fats
◦ nucleic acids
◦ proteins
Sodium Bicarbonate helps activate these enzymes when they enter the duodenum since they convert the acid chyme to an alkaline ph
Liver
Hepatocytes multifunction call that;
*Role in lipid homeostasis (cholesterol synth.,
lipoprotein synth., break down fatty acids to
generate ATP)
*Synthesis of bile salts from cholesterol; Fats
emulsification
*Role in glucose homeostasis
*Detoxify toxic substances and excrete drugs into bile
*Storage of vitamins (A, B12, D, E, K) and minerals
(iron, copper)
*Phagocytosis of worn out red and white blood cells
and bacteria
Gallbladder
Pear-shaped sac that stores
bile until needed for digestion
Vitamin A
precursor for retinal in eyesight
Vitamin b12
vital for mitosis
Vitamin D
Bone health and winter blues
path of bile into the duodenum
hepatocytes in the liver produce bile and enter the Right hepatic duct and left hepatic duct. These ducts combine to form the common hepatic duct. Then join the cystic duct from the bladder to form the common bile duct. Common bile duct join w the pancreatic duct which secretes pancreatic juices to form the hepatopancreatic ampulla. There the substances are empties into the duodenum when sphincter allows.
Gall bladder
stores and concentrates bile.
Bile
bile salts emulsify fats and help absorption of lipids in duodenum of small intestine. Bile mechanically breaks down fats into smaller droplets.
Gallstones
if bile contains insufficient bile salts or excessive cholesterol, cholesterol may
crystallize to form gallstones
partially or completely block ducts
blood supply to liver
The liver receives a double supply of blood
– Oxygenated blood from the hepatic artery goes to the hepatic sunusoids
– Deoxygenated blood from hepatic portal
vein; goes to the hepatic sinusoids, then the central vein, then the hepatic veins, then the inferior vena cava, then the right atrium of heart
What does the liver do with deoxygenated blood
liver sinusoids and
hepatocytes regulate solute and nutrient levels and
absorb or secrete molecules such as plasma proteins that are in the blood.
Phagocytic cells engulf pathogens and dead rbc. Also store iron lipids and heavy metal that were absorbed by the GI tract.
The blood is then goes to the central vein, then hepatic veins, them empties into the inferior vena cava.
Path of blood and bile in the liver
- Blood enters the liver sinusoids (highly
permeable capillaries) from small branches of
the hepatic portal vein and hepatic artery. - As blood flows through liver sinusoids,
hepatocytes regulate solute and nutrient levels and
absorb or secrete molecules such as plasma proteins. - Phagocytic cells, stellate reticuloendothelial
cells (Kupffer cells), engulf pathogens, cell debris,
and damaged blood cells. They are also store iron,
lipids, and heavy metals (tin or mercury) that are
absorbed by the GI. - The central vein collects blood from the sinusoids of
the lobule. All central veins merge to form the hepatic
veins, which then empty into the inferior vena cava. - Hepatocytes secrete bile into narrow
spaces called bile canaliculi. They extend
outward, away from the central vein. - Bile canaliculi carry bile to bile ducts in the
nearest portal triad. Bile plays an important role
in the digestion of fats in the small intestine.
hepatitis
inflammation of the liver that can be caused by:
◦ viruses
◦ drugs
◦ chemicals (including alcohol)
can lead to cirrhosis
◦ liver loses its functions because liver cells die and the tissue gets replaced by
scar tissue
◦ remember, scar tissue cannot perform same function
rbc cycle when in the liver
- A macrophage phagocytizes aged rbc. this releases iron, globin, and bilirubin.
2.iron and globin are recycled. The bilirubin is secreted into bile - the bilirubin is broken down in the intestine creating the products; stercobilin (makes feces brown) and urobilinogen (makes pee yellow)
small intestine
major organ of chemical digestion and nutrient absorption
Duodenum
Begins at the pyloric sphincter and merges with jejunum.
duodenal glands secrete alkaline mucus that neutralizes acid chyme
Mixes contents and secretions from pancreas and liver
Jejunum:
Digestion of most nutrients
Increased surface area (folds,
villi, microvilli) for optimal
absorption of nutrients
Ileum
absorption of bile salts and some vitamins (B12)
Joins to the large intestine at the ileocecal sphincter
Lymphoid nodules
are part of the
immune system
Why and how does the small intestine have so much surface area
Small intestine has a large surface area for absorption.
◦ Folds of the intestinal lining, villi, and microvilli all contribute to the large
surface area
Intestinal villus (plicae circulares
folds of the mucosa and submucosa– cannot stretch out like rugae in stomach
villi
Finger-like projections of mucosa– lamina propria contains blood and
lymph capillaries– lined with simple columnar epithelium
microvilli
Finger-like projections of
the plasma membrane on
individual cells
Layers of the small intestine
Muscularis is formed of two layers of smooth
muscle: outer longitudinal, inner circular
Serosa = CT and epithelial layer – forms portion
of visceral peritoneum
Solitary lymphatic nodules (Peyer’s patches) are
found in the lamina propria of the ileum
Cells of the Small
Intestine epithelium
microvilli - absorptive cell
goblet cell - mucus
enteroendocrine - secretes hormones secretin cholecystokinin or GIP
Paneth cell - secretes lysozyme and is capable of phagocytosis
intestinal Juice and Brush Border Enzymes
Intestinal juice
◦ water and mucus, slightly alkaline
◦ provides a liquid medium to aid for absorption
◦ intestinal enzymes (brush border enzymes) break down foods at the cell
membrane
Movements in the Small Intestine
Segmentation
◦ major movement of the small intestine
◦ localized contraction in areas containing food
◦ Serves for mixing, not moving food along
Peristalsis
◦ propels the chyme onward through the
intestinal tract
Digestion of Carbohydrates
turn into monosaccharides
Mouth - salivary amylase breaks down
polysaccharides (glycogen, starch) to
oligosaccharides and disaccharides
small intestine
-continues
breaking down glycogen and
starch to smaller oligosaccharides
-brush border enzymes → -dextrinase,
maltase, sucrase and lactase act on
oligosaccharides and produce monosaccharides
(fructose, glucose and galactose)
Digestion of Proteins
into single amino acids/dipeptides
stomach - HCl denatures proteins- pepsin turns proteins into peptides
small intestine
- proteolitic enzymes (trypsin, carboxypeptidase,
chymotrypsin, elastase) split peptide bonds
between specific amino acids (creates peptides)
-brush border enzymes break down
peptides to single amino acids/dipeptides
Digestion of Lipids
into fatty acids & monoglycerides
stomach -
-Lingual lipase (secreted in mouth, active
in stomach) and gastric lipase (stomach)
digest triglycerides to diglycerides,
monoglycerides and fatty acids
small intestine
-emulsification of fat globules
by bile (mechanical digestion)
- pancreatic lipase splits triglycerides
into fatty acids & monoglycerides
Digestion of Nucleic Acids
into pentose,
phosphate & nitrogenous bases
small intestine
-nucleic acid digestion only
happens in the small intestine
Pancreatic juice contains 2 nucleases: -ribonuclease which digests RNA
into nucleotide-deoxyribonuclease which digests
DNA into nucleotide
Nucleotides are further digested
by brush border enzymes: -nucleosidase and phosphatase
digest nucleotides into pentose,
phosphate & nitrogenous bases
Absorption of nutrients
Nutrients pass into epithelial cells of villi in the jejunum of the small intestine
Fatty acids and glycerol are recombined into fats and transported into lymph
Other absorbed nutrients such
as amino acids and sugars pass
into the blood, which then flows
directly to the liver
Absorption of Lipids
Small fatty acids enter and exit cells by simple diffusion
Larger lipids exit the lumen only within micelles (bile salts coating)
◦ Lipid-soluble vitamins get packaged along in micelles
◦ lipids enter cells by simple diffusion leaving bile salts behind
◦ Bile salts reabsorbed into blood & recycled into bile by liver
Inside epithelial cells, fats are rebuilt and coated with protein to form chylomicrons
Chylomicrons leave intestinal cells by exocytosis into a lacteal (lymphatic capillary)
◦ travel in lymphatic system to reach subclavian veins
◦ removed from the blood by the liver and adipose tissue
Absorption of Water
> 9 liters of fluid enters GI tract each day
Small intestine reabsorbs > 8 liters
Large intestine reabsorbs 90% of that last liter
Reabsorption is by osmosis through cells into
capillaries in villi
Digestion in Large Intestine
Undigested material passes to the large intestine or colon.
*No enzymes are secreted - only mucus
*Absorption of some ions (Na+ and Cl-) and vitamins
*Absorption of water (90% in small intestine, ~10% in large intestine)
*Bacteria
* ferment undigested carbohydrates; produces carbon dioxide and methane gas
* ferment undigested proteins into simpler substances → odor
* turn bilirubin into simpler substances → color
* produce vitamin K and B in colon
rectum
rectum stores feces until they can be eliminated.
Feces
= dead epithelial cells, undigested food such as cellulose,
bacteria (live & dead
There are two sphincters:
- Involuntary
Opens from the large intestine to the rectum. - Voluntary
Opens into the anus.
Movements in Large Intestine
Haustral churning:
◦ When the distension of a haustrum reaches a certain point, the walls
contract and squeeze the contents into the next haustrum
Peristalsis:
◦ Peristalsis will slowly move feces along
Mass peristalsis:
◦ Strong peristaltic wave begins at the middle of the transverse colon, quickly
driving the content into the rectum
Defecation
a reflex
* mass peristalsis causes filling of the rectum
* stretching of the rectal wall initiates the
defecation reflex
* The internal anal sphincter (involuntary)
relaxes
* the external anal sphincter can be
voluntarily controlled (except in infants) to
allow or postpone defecation
* voluntary contractions of the diaphragm
and abdominal muscles aid in defecation
