Digestive system-6 Flashcards
What are 3 unique features of the large intestine? What are the 2 subdivisions of the colon? What is the definition of appendicitis?
▪ Teniae coli: three bands of longitudinal smooth muscle in muscularis
▪ Haustra: pocketlike sacs caused by tone of teniae coli
▪ Epiploic appendages: fat-filled pouches of visceral peritoneum
- Cecum: first part of large intestine
- Appendix: masses of lymphoid tissue
▪ Part of MALT of immune system
▪ Bacterial storehouse capable of recolonizing gut when necessary
▪ Twisted shape of appendix makes it susceptible to blockages
Appendicitis: acute inflammation of appendix; usually results from a blockage by feces that
traps infectious bacteria
What are the 4 regions of the colon? How many rectal valves are there and what are their purpose? What is the anal canal and what are it’s two sphincters?
▪ Ascending colon: travels up right side of abdominal cavity to level of right kidney
– Ends in right-angle turn - right colic (hepatic) flexure
▪ Transverse colon: travels across abdominal cavity
– Ends in another right-angle turn, left colic (splenic) flexure
▪ Descending colon: travels down left side of abdominal cavity
▪ Sigmoid colon: S-shaped portion that travels through pelvis
three rectal valves stop feces from being passed with gas (flatus)
last segment of large intestine that opens to body exterior at anus
Has two sphincters
▪ Internal anal sphincter: smooth muscle
▪ External anal sphincter: skeletal muscle
What are mesocolons? Which 3 organs are retroperitoneal?
Intraperitoneal regions are anchored to posterior abdominal wall by mesentery sheets called mesocolons
Cecum, appendix, and rectum are all retroperitoneal
What is the mucosa of the large intestine made of? What does the large intestine not contain? What type of cells do the abundant deep crypts have?
▪Large intestine contains thicker mucosa made up of simple columnar epithelium except in
anal canal, where it becomes stratified squamous epithelium to withstand abrasion
▪ Does not contain circular folds, villi, or digestive secretions
▪ Contains abundant deep crypts with many mucus-producing goblet cells
What are anal columns? What are anal sinuses? What is the pectinate line and what are the 2 ways it’s innervated?
▪ Mucosa of anal canal hangs in long ridges or folds referred to as anal columns
▪ Anal sinuses: recesses located between anal columns; secrete mucus to aid in
emptying
▪ Pectinate line: horizontal line that parallels the inferior margins of the anal sinuses
– Visceral sensory nerves innervate area superior to this line
• Region insensitive to pain
– Somatic nerves innervate inferior to this line
• Region sensitive to pain
How many different types of bacteria in the large intestine and how do they enter? What are the 3 metabolic functions of the bacteria?
▪ consist of 1000+ different types of bacteria (outnumber our cells 10:1
▪ enter from small intestine or anus to colonize colon
- Fermentation
• Ferment indigestible carbohydrates and mucin
• Release irritating acids and gases (~500 ml/day) - Vitamin synthesis
• Synthesize B complex & some vitamin K needed by liver to produce clotting factors - Keep pathogenic bacteria in check
– Beneficial bacteria outnumber and suppress pathogenic bacteria
– Immune system destroys any bacteria that try to breach mucosal barrier
• Epithelial cells recruit dendritic cells to mucosa to sample microbial antigens
and present to T cells of MALT, triggering production of IgA that restricts
microbes
What are 3 major things that the gut bacteria affects? What is the main cause of natibiotic-associated diarrhea? What is a possible treatment?
- Body weight
- Susceptibility to various diseases (including diabetes, atherosclerosis, fatty liver disease)
- Our moods
▪ Clostridium difficile, an anaerobic bacterium that many carry in intestine, is most common cause
• When other bacteria are wiped out by antibiotics, C. difficile can flourish and cause pseudomembranous colitis (inflammation of colon)
• May lead to bowel perforation and sepsis
▪ C. difficile infections are resistant to many antibiotics and difficult to treat
– New treatments include fecal transplants to replace healthy bacteria to suppress C. difficile
How long does residue remain in the large intestine? What are the 2 major functions? What are the 2 main ways of motility in the large intestine? What do the descending colon and sigmoid colon do?
12-24 hours
Major functions of large intestine: propulsion of feces to anus & defecation
▪ Haustral contractions: most contractions of colon, haustra sequentially contract in response to distension
-Slow segmenting movements, mostly in ascending and transverse colon
▪ Gastrocolic reflex: initiated by presence of food in stomach/duodenum
-Results in mass movements: slow, powerful peristaltic waves that are activated three to four times per day
Descending colon & sigmoid colon act as storage reservoir
What are the 6 key stages of the defecation process?
▪ Mass movements force feces toward rectum
▪ Distension initiates spinal defecation reflex
▪ Parasympathetic signals
-Stimulate contraction of sigmoid colon and rectum
-Relax internal anal sphincter
▪ Conscious control allows relaxation of external anal sphincter
▪ Muscles of rectum contract to expel feces
▪ Assisted by Valsalva’s maneuver
-Closing of glottis, contraction of diaphragm and abdominal wall muscles cause
increased intra-abdominal pressure
-Levator ani muscle contracts, causing anal canal to be lifted superiorly and
allowing feces to leave body
What are the 2 major consequences of a low fiber diet? What is IBS and what is a major contributing cause?
▪ Low-fiber diet can cause colon to narrow & cause strong contractions → increase pressure on walls can lead to diverticula: herniations of mucosa
▪ Diverticulosis: presence of diverticula
• Common in sigmoid colon
• Affects half of people > 70 yrs
▪ Diverticulitis
• Inflamed diverticula that may rupture and leak into peritoneal cavity
▪ Functional GI disorder
▪ Recurring abdominal pain, stool changes, bloating, flatulence, nausea, depression
▪ Stress is a common precipitating factor
• Stress management is important in treatment
What is the definition of diarrhea? What are the 2 main causes? What are 2 potential consequences of prolonged diarrhea? What is the definition of constipation and what are its 4 main causes?
▪ watery stool that results when colon does not have sufficient time to absorb remaining water
– Causes include irritation of colon by bacteria or jostling of digestive viscera (occurs in marathon runners)
– Prolonged diarrhea→ dehydration & electrolyte imbalance (acidosis and loss of potassium)
▪ food remains in colon for extended periods of time and toomuch water is absorbed
‒ Stool becomes hard and difficult to pass
‒ Causes: insufficient fiber or fluid in the diet, improper bowel habits, lack of exercise, or laxative abuse
