digestive part C

Question 1

what is the small intestine structure?

Answer 1

• The Small intestine is the major organ of digestion and absorption
• 2–4 m long (7–13 f t) from pyloric sphincter to ileocecal valve, point at which it joins the large intestine
• Small diameter of 2.5–4 c m (1.0–1.6 inches)

Question 2

what is a duodenum?

Answer 2

– Duodenum: mostly retroperitoneal; ~25.0 c m (10.0 in) long; curves around head of pancreas
 Has most features
– Jejunum: ~2.5 m (8 f t) long; attached posteriorly by mesentery
– Ileum: ~3.6 m (12 f t) long; attached posteriorly by mesentery; joins the large intestine at ileocecal valve

Question 3

what is the blood supply in the small intestine?

Answer 3

– Superior mesenteric artery brings blood supply
– Veins (carrying nutrient-rich blood) drain into superior mesenteric veins, then into hepatic portal vein, and finally into liver

Question 4

what is the nerve supply in the small intestine?

Answer 4

– Parasympathetic innervation via vagus nerve, and sympathetic innervation from thoracic splanchnic nerves

Question 5

what are the modifications of the small intestine for absorption?

Answer 5

– Small intestine’s length and other structural modifications provide huge surface area for nutrient absorption
 Surface area is increased 600 × to ~200m2 (size of a tennis court)
– Modifications include:
 Circular folds
 Villi
 Microvilli
– Circular folds
 Permanent folds (~1 c m deep) that force chyme to slowly spiral through lumen, allowing more time for nutrient absorption
– Villi
 Fingerlike projections of mucosa (~1 m m high) with a core that contains dense capillary bed and lymphatic capillary called a lacteal for absorption
– Microvilli
 Cytoplasmic extensions of mucosal cell that give fuzzy appearance called the brush border that contains membrane-bound enzymes brush border enzymes, used for final carbohydrate and protein digestion

Question 6

what is the histology of the small intestine?

Answer 6

– Modifications of mucosa and submucosa of the small intestine reflect its function in digestion
– Intestinal crypts: tubular glands scattered between villi
– Five main types of cells found in villi and crypts

Question 7

what are enterocytes?

Answer 7

make up bulk of epithelium
– Simple columnar absorptive cells bound by tight junctions and contain many microvilli
– Function
* Villi: absorb nutrients and electrolytes
* Crypts: produce intestinal juice, watery mixture of mucus that acts as carrier fluid for chyme

Question 8

what is goblet cells?

Answer 8

mucus-secreting cells found in epithelia of villi and crypts

Question 9

what is enteroendocrine cells?

Answer 9

source of enterogastrones (e.g.: C C K and secretin)
– Found scattered in villi but some in crypts

Question 10

what are pentad cells?

Answer 10

found deep in crypts, specialized secretory cells that fortify the small intestine’s defenses
– Secrete antimicrobial agents (defensins and lysozyme) that can destroy bacteria
 Stem cells that continuously divide to produce other cell types
– Villus epithelium renewed every 2–4 days
– Mucosa-associated lymphoid tissue protects intestine against microorganisms and includes:
 Individual lymphoid follicles

Question 11

what are Peyer’s patches?

Answer 11

 Peyer’s patches (aggregated lymphoid nodules), located in lamina propria
– Found in great numbers in distal part of the small intestine, where bacterial numbers increase
 Lamina propria also contains large numbers of plasma cells that secrete I g A
– Submucosa consists of areolar tissue
 Duodenal glands of duodenum secrete alkaline mucus to neutralize acidic chime

Question 12

Homeostasis imbalance for small intestine

Answer 12

• Chemotherapy targets rapidly dividing cells, such as cancer cells
• Negative side effect is that it also targets rapidly dividing G I tract epithelium
• Reason why many patients undergoing chemotherapy have symptoms of nausea, vomiting, and diarrhea

Question 13

what is intestinal juice?

Answer 13

• 1–2 L secreted daily in response to distension or irritation of mucosa
• Major stimulus for production is hypertonic or acidic chyme
• Slightly alkaline and isotonic with blood plasma
• Consists largely of water but also contains mucus
  – Mucus is secreted by duodenal glands and goblet cells of mucosa

Question 14

what is the digestive process in the small intestine?

Answer 14

• Chyme from stomach contains partially digested carbohydrates and proteins and undigested fats
• Takes 3–6 hours in the small intestine to absorb all nutrients and most water

Question 15

what is t source of enzymes for digestion?

Answer 15

– Substances such as bile, bicarbonate, and digestive enzymes (not brush border enzymes) are imported from liver and pancreas
– Brush border enzymes bound to plasma membrane perform final digestion of chyme

Question 16

how t regulate chyme entry?

Answer 16

– Chyme entering duodenum is usually hypertonic; therefore, chyme delivery has to be slow to prevent osmotic loss of water from blood
– Low p H of chyme has to be adjusted upward
– Chyme has to be mixed with bile and pancreatic juice to continue digestion
– Enterogastric reflex and enterogastrones control movement of food into duodenum to prevent it from being overwhelmed

Question 17

what is the motility of the small intestine?

Answer 17

– After a meal
 Segmentation is most common motion of the small intestine
– Initiated by intrinsic pacemaker cells
– Mixes/moves contents toward ileocecal valve
– Intensity is altered by long and short reflexes and hormones
* Parasympathetic increases motility; sympathetic decreases it
– Between meals
 Peristalsis increases, initiated by rise in hormone motilin in late intestinal phase (every 90–120 minutes)
 Each wave starts distal to previous wave; referred to as migrating motor complex (M M C)
 Meal remnants, bacteria, and debris are moved toward the large intestine
 Complete trip from duodenum to ileum takes ~2 hours
* Ileocecal valve control
– Ileocecal sphincter relaxes and admits chyme into the large intestine when:
 Gastroileal reflex enhances force of segmentation in ileum
 Gastrin increases motility of ileum
– Ileocecal valve flaps close when chyme exerts backward pressure
 Prevents regurgitation into ileum

Question 18

what is the structure of large intestine?

Answer 18

has three unique features not seen elsewhere:
– 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

Question 19

what are the subdivisions of the large intestine?

Answer 19

– Cecum: first part of large intestine
– Appendix: masses of lymphoid tissue
 Part of M A L T of immune system
 Bacterial storehouse capable of recolonizing gut when necessary
 Twisted shape of appendix makes it susceptible to blockages
– Colon: has several regions, most of which are retroperitoneal (except for transverse and sigmoid regions)
 Ascending colon: travels up right side of abdominal cavity to level of right kidney
– Ends in right-angle turn called right colic (hepatic) flexure
 Transverse colon: travels across abdominal cavity
– Ends in another right-angle turn, left colic (splenic) flexure
– Colon:
 Descending colon: travels down left side of abdominal cavity
 Sigmoid colon: S-shaped portion that travels through pelvis
– Rectum: three rectal valves stop feces from being passed with gas (flatus)
– Anal canal: 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

Question 20

what is the relationship of the large intestine to the peritoneum?

Answer 20

– Cecum, appendix, and rectum are all retroperitoneal
– Colon is also retroperitoneal, except for its transverse and sigmoid parts
– Intraperitoneal regions are anchored to posterior abdominal wall by mesentery sheets called mesocolons

Question 21

what is the homeostatic imbalance of large intestine?

Answer 21

• Appendicitis: acute inflammation of appendix; usually results from a blockage by feces that traps infectious bacteria
  – Most common in adolescence when entrance to appendix is at widest
• Venous drainage can be impaired, leading to ischemia and necrosis (tissue death)
• Ruptured appendix can cause peritonitis
• Symptoms: pain in umbilical region, moving to lower right abdominal quadrant
  – loss of appetite, nausea, and vomiting are also seen
• Treatment: surgical removal (appendectomy), or in some cases, with antibiotics.

Question 22

what are anal recesses?

Answer 22

located between anal columns; secrete mucus to aid in emptying

Question 23

what is a pectinate line?

Answer 23

the horizontal line that parallels anal sinuses

Question 24

what is bacterial flora?

Answer 24

consist of 1000+ different types of bacteria
– Outnumber our own cells 10 to 1
* Enter from small intestine or anus to colonize colon

Question 25

what is metabolic functions?

Answer 25

– Fermentation  Ferment indigestible carbohydrates and mucin  Release irritating acids and gases (~500 ml/day) – Vitamin synthesis  Synthesize B complex and some vitamin K needed by liver to produce clotting factors * Keeping 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 M A L T, triggering production of I g A that restricts microbes

Question 26

what is gut bacteria and health?

Answer 26

Gut bacteria and health – Mounting evidence supports findings that the kinds and proportions of gut bacteria can influence:  Body weight  Susceptibility to various diseases (including diabetes, atherosclerosis, fatty liver disease)  Our moods – Manipulating gut bacteria may become a routine health-care strategy in future

Question 27

what is Clostridium difficile?

Answer 27

an anaerobic bacterium that many carry in intestine, is most common cause

Question 28

what is Haustral contractions?

Answer 28

most contractions of colon, where haustra sequentially contract in response to distension  Slow segmenting movements, mostly in ascending and transverse colon

Question 29

what is Gastrocolic reflex?

Answer 29

initiated by the presence of food in stomach  Results in mass movements: slow, powerful peristaltic waves that are activated three to four times per day – Descending colon and sigmoid colon act as storage reservoir

Question 30

what is defecation?

Answer 30

– 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

Question 31

defecation pt2

Answer 31

– 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

Question 32

what is ileostomy?

Answer 32

a procedure that brings back the ileum through the abdominal wall if a colon is removed