Session 9: Digestive System Flashcards
The alimentary canal consists of what?
Mouth, tongue, pharynx, esophagus, stomach, small intestine, colon of the large intestine, appendix, rectum, anus
What are the accessory organs of the digestive system?
Salivary glands, Liver, Gall bladder, Pancreas
What is the mesentery?
The double fold of the peritoneum that attaches the intestines to the wall of the abdomen
What are the four layers of the gut wall?
The mucosa (innermost) The submucosa The external muscle layers (muscularis externae) The serosa (outermost)
The mucosa of the gut wall lines the lumen and is made up of what three layers?
Epithelium
Lamina propria
Muscularis mucosae
What structures are often present in the lamina propria of the gut mucosa?
Peyer’s patches
The submucosa of the gut contains what important features?
Layer of connective tissue Glands Arteries Veins Nerves
The external muscle layers of the gut wall contain what?
How are these seen histologically?
2 layers of smooth muscle:
1) Outer longitudinal layer (cells with cigar-shaped nuclei)
2) Inner circular layer (cells with central nuclei)
Which layer of the gut wall is responsible for the successive peristaltic waves required to move luminal contents along the gut?
Muscularis externa (External muscle layers)
The outermost layer of the gut wall is known as what?
The serosa (a serous membrane)
The serosa of the gut wall is made up of what layers?
Connective tissue
Mesothelium (simple squamous epithelium)
The mesentery contains what?
Arteries
Veins
Nerves
List some of the major functions of the GI tract
Port of entry for food into the body Mechanically disrupt food Temporarily store food Chemically digest food Kill pathogens Move food along the tract Absorb nutrients from the resultant solution Eliminate residual waste
What is digestion?
The conversion of what we eat, by physical and chemical disruption into a solution from which we can absorb our nutrients
The solution brought about by chemical and physical disruption from which we absorb our nutrients is relatively _________, _______ in pH and __________
sterile
neutral
isotonic
Saliva starts digestion with the aid of which enzymes?
Amylase and lipase
What two features of saliva are bacteriostatic?
IgA
Lysozyme
What features of saliva helps to protect our teeth?
High in calcium
Alkaline
How does the digestive system contribute to physical disruption of food?
By the action of teeth, tongue and muscles of mastication (chewing)
During mastication, the mouth forms a _____ which enters the oesophagus
bolus
Which section of the oesophagus is under voluntary control?
Upper third
The lower section of the oesophagus is under ___________ control
involuntary
The upper end of the oesophagus contains some ________ _______ muscle as well as smooth muscle
Striated skeletal
The lower end of the oesophagus contains only which types of muscle?
Smooth
What mechanism is used to transport bolus to the stomach?
Rapid peristaltic transport
How long does it take for the bolus to travel from the mouth to the stomach?
8-9 seconds
Where does the fastest of the GI transport take place?
On entry (oesophagus) On exit (rectum/acus)
The oesophagus is made up of what four layers?
It is lacking what layer that is found in the gut wall?
Mucosa Submucosa Muscularis externa Adventitia There is no serosa, not intraperetaneal
What are the name of the two major nerve centres of the digestive system?
Myenteric plexus
Submucosal plexus
The stomach undergoes receptive relaxation, what is meant by this?
The walls relax so that pressure in the stomach does not increase as it swells (up to a point)
The stomach secretes what to break down tissues and disinfect?
Acid and proteolytic enzymes
How does the stomach protect its epithelium?
By secreting mucus onto its surface
The stomach produces hypertonic chyme, what is meant by hypertonic in this case?
The osmotic pressure of chyme increases and it therefore wants to draw in fluid from the rest of the body
What is chyme?
Broken down, partially digested stomach contents
Where is the chyme delivered to?
The duodenum
The stomach is lined with simple columnar epithelium with openings to various what?
Gastric pits
What extend down into the gastric pits?
Long, straight tubular gastric glands
Shallow gastric pits are lined with what cells?
Where are these cells infrequently found?
Surface mucous cells
Tubular gastric glands
The mucous secreted by gastric pits is released in response to what?
Distention
Stomach contents
Acid secretion from gastric glands
Secreted mucus is resistant to what?
Pepsin
What can cause damage to the mucous cells?
How are these damaged cells replaced?
Alcohol and aspirin
By mitosis in deeper cells in the neck of the gastric pit
Secreted mucus contains what which neutralises the effect of H+ ions?
Bicarbonate ions (HCO3-)
What is the isthmus?
The region of the gastric gland in which stem cells divide to populate the gland by upward or downward migration
What do parietal cells secrete?
H+ ions into the lumen
HCO3- ions into nearby capillaries which move it to surface mucous cells