Lecture 5 - Digestive System Flashcards
What is Digestion?
The breakdown of ingested food
Absorption of nutrients into the blood
Concentration and removal of waste products
What is Metabolism?
Production of cellular energy (ATP)
Regulation of Cellular Activities
What are the two main functional groups of organs of the Digestive System?
Alimentary Canal (continuous hollow tube)
Accessory Digestive Organs
What are the structures of the Alimentary Canal?
Mouth, Pharnyx, Esophagus, Stomach, Small Intestine, Large Intestine, Anus
What is the tongue covered in?
Many backward facing projections called filiform papillae, which sense pressure
What can a species of frog hear with?
Its mouth
What are the accessory organs?
Salivary glands, Liver, Gall Bladder and Pancreas
What are the functions of the Salivary Glands?
Lubrication/Binding
Solubilization of Dry Food
Oral Hygiene - flushes away debris
Begins Starch Digestion (salivary amylases)
Alkaline Buffering
Evaporative Cooling
What is Mastification?
Chewing food - adding salivary amylase
What are the types of teeth?
Incisors, Canines, Premolars, and Molars
What do Incisors do?
Rip, cut
What do canines do?
Tear, pierce
What do pre-molars do?
Grind, shear
What do Molars do?
Grind
What is the hardest structure in the body?
The teeth
What is the total number of primary “baby” teeth?
20
What is the total number of permanent teeth?
32
Where does Deglutition (swallowing) occur?
Oral, Pharyngeal, esophageal
What does Deglutition require?
25 pairs of muscles in the mouth, pharynx, larynx upper esophagus
What are mouth, pharynx, and upper esophagus muscles innervated by?
Somatic motor neurons
What are the middle and lower esophagus muscles innervated by?
Autonomic motor neurons
What is the esophagus?
Connects pharynx to stomach: a muscular tube that is 25 cm long
What is Peristalsis?
Food moves by a wave like muscular contraction
What does Peristalsis do in the esophagus?
Peristaltic contraction and movement of bolus into the stomach
What does the Esophagus pass through?
The diaphragm
How does the esophagus mobilize food?
By peristalsis
Where does the smooth muscle layer?
In the wall of the stomach, the length of the organ and around the organ
What direction do smooth muscle layers run in?
An oblique direction
What do these muscles act?
To mix and mechanically break up food in the stomach.
What is the gross anatomy of the stomach?
Circular muscles, longitudinal muscles, and oblique muscles.
What are circular, longitudinal and oblique fibres arranged?
Perpendiculary to provide complex motility
What do the mucosal regions of the stomach contain?
Gastric pits and gastric glands
What are Gastric Pits?
The openings of the gastric glands
What are the Gastric Glands?
They consist of several types of cells (mucous cells, chief cells, parietal cells)
What does each cell type produce?
A specific secretion
What do mucous cells secrete?
Mucus
What do parietal cells secrete?
HCl, intrinsic factor (B12 - essential for life)
What do Chief cells (zymogenic) cells secrete?
Pepsinogen
What can erosions of the mucosa lead to?
Peptic ulcers (i.e, the stomach digests itself)
What can cause peptic ulcers?
The bacteria Helicobacter pylori
What does Helicobacter infect?
The GI tract of ~50% of adults worldwide.
What do Pepsinogen/HCl do?
In the presence of HCL, the inactive enzyme pepsinogen is activated to the pepsin form, which can digest proteins into smaller polypeptides.
What are the regions of the small intestine?
Duodenum
Jejunum
Ileum
What is the Duodenum?
The first 25 cm
Mucous secretion, receives pancreatic secretions and bile from liver
What is the Jejunum?
1 m in length
Numerous folds and villi
What is the Ileum?
Last 2m
Fewer folds/villi than jejunum
Absorbs primarily bile salts, water, electrolytes
What does the Ileum contain?
Peyer’s Patches (Aggregates of lymph nodes)
Where does the Ileum empty?
Into the large intestine via the Ilieocecal valve
What are the Microvilli formed by?
Foldings at the apical surface of each epithelial cell membrane
What are Villi covered in?
Columnar Epithelial cells
What do Goblet cells do?
Secrete mucous
What happens to epithelial cells at the tip of the villi?
Continuously sloughed off and replaced by new cells coming from the Intestinal Crypts (crypts of Lieberkuhn)
What are Paneth cells?
At the base of the crypts and secrete antibacterial molecules (lysozyme, antimicrobial peptides) to protect the intestine from inflammation
What are microvilli not?
Villi zoomed in!!!
(Common misconception}
What is the study on time-restricted diets?
Mice ate the same number of calories, however the obese mouse had food available 24 hours and the normal weight mouse only had food available 8 hours per day
What did the mouse eating 24 hours per day have?
4x more body fat even though they had the same number of calories
What did Access to food 24 hours per day cause?
Increased fat, increased glucose intolerance, increased leptin resistance, increased liver pathology, increased inflammation, and decreased motor control
What does the alkaline bile from live do to neutralize?
Releases chyme to neutralize the small intestine
What is the bacterial colony in the large intestine made up of?
Many species of bacteria and plays a role in digestive processes
What does the good bacteria do?
Put out pathogenic bacteria
What happens when pathogenic bacteria takes over the colon?
What happens when pathogenic bacteria takes over?
The colon reacts by eliminating colon content and sloughing off the colon epithelium - diarrhea
What is a small component of the colon?
The appendix
What is it thought that the appendix contains?
A reservoir of “good bacteria” that can re-colonize the colon following diarrhea and expulsion of the colon content
What does the appendix contain?
Like the tonsils it contains lymph vessels
What is the appendix subjected to and what does this cause?
Inflammation which causes appendicitis - pain in the lower right quadrant of the abdomen
What does a ruptured appendix cause?
Inflammation in the peritoneal cavity - peritonitis
What is the intestinal micriobiota?
10 times more numerous than human cells in the body
What does intestinal microbiota originate at?
Birth (gut microbiome starts forming)
What affects what grows in the gut?
Diet
What is serotonin altered with?
Stress, anxiety, and depression
What did a study of a germ free mouse model show?
The absence of bacteria during early life significantly affected sermonic concentrations in the brain in adulthood
What are the Accessory organs of Digestion?
Pancres, Liver, Gallbladder
What is the liver made up of?
Hepatic cells lining large capillaries called sinusoids
What also sinusoids lined by?
Endothelial cells
What do sinusoids contain?
Kupffer cells (Phagocytes)
What does the liver have?
God regenerative capabilities - if 2/3rds of a rodent’s liver are surgically removed, the remaining tissue with regenerate to its original mass In one week
What are the 2 blood inputs of the liver?
Portal Vein (coming from intestines, major source of blood supply to liver), and also hepatic artery (blood from heart to liver)
What are endocrine functions of the liver?
Where the enzymes and hormones of the liver do their thing and outputs get sent into the hepatic vein, going back to the heart so the nutrients loaded into there can get pumped through the whole body
What are the two exocrine functions of the liver?
Right and left hepatic ducts that come out from liver, which makes bile
Where is bile stored?
In the gallbladder
What do the right and left hepatic ducts do?
Meet up with the cystic duct from the gall bladder which stores bile and together they form the common bile duct which then goes into intestines
What is a derivative of the Heme group converted into and what is the pathway of it?
Bilirubin and carried in the blood on albumin proteins, taken up by the liver, mixed with glucoronic acid and now is water soluble and can be secrete into bile to intestine, converted by bacteria into urobilingen, and removed in faces
What can some urobiliogen do?
Re-enter circulation and be excreted by kidneys
What is the Gall-Bladder?
Sac-like organ attached to the inferior surface of the liver.
What does the gallbladder store?
Bile from the liver
What is a common complication of the gallbladder?
Gallstones
What are gall stones?
Mineral deposits that produce painful symptoms by obstructing the bile ducts
How are Gallstones removed?
Surgery - sometimes oral ingestion of bile acids, or fragmentation by huih energy shock waves.
What do pancreatic juices contain?
20 different digestive enzymes including amylase, trypsin, and lipase
What is Amylase?
Digests starch
What is Trypsin?
Digests proteins
What is Lipase?
Digests triglycerides
What does digestion in the pancreas require?
Pancreatic enzymes PLUS brush border enzymes
What is the inactive form of trypsin activated by?
The brush border enzymes; trypsin is a protease that can then activate other pancreatic enzymes
What is the Pancreas both of?
An endocrine gland and and digestive organ
How is the pancreas an endocrine gland?
Makes hormones (insulin, glucagon, and somatostatin)
