Motility and secretion II

Functional unit of the liver

lobule

Hepatic portal circulation

• between two capillary beds

• Blood from intestines flows into liver first

Majority of the blood flow to the liver is from?

• hepatic portal vein: 70-80%

• 25% is from hepatic artery (oxygenated)

sinusoids in liver

leaky, discontionous, has gaps that allow for blood flow to be exposed to hepatocytes

very permeable and fenestrated

kupffer cell

fixed macrophages that remove damaged RBCs and other materials

Stellate cells

• vitamin A function (stores)

• maintains ECM

• Secretes GFs, cytokines

• More fibrotic liver = stellate cell

• Bile is formed by __

• Bile is stored by __

• Released through __ into the _

• liver

• gallbladder, removes water to concentrate bile

• sphincter, duodenum

Bile composition (5)

• Bile salts: travel to terminal ileum of SI and get recycled (reabsorbed)

• Phospholipid: detergent action

• Bicarbonate: neutralizes acid

• Cholesterol: bile eliminates

• Billirubin: product of heme metabolism

Function of bile salts

• Emuslfication of fats

• Non-polar and polar sides allow for a suspension of fat droplets

• In duodenum: solubilize ingested fat and fat soluble vitamins, facilitating digestion and absorption (by increasing surface area in droplet)

sphincter of oddi

• sphincter that opens into duodenum

• opens in response to CCK

Composition of pancreatic juice

• Bicarbonate (neutralizes acid)

• proteases: breaks down protein

• Pancreatic amylases: break down carbs

• Pancreatic lipase: break down fats

main source of digestive enzymes

pancreas

Pancreatic juice:

• During cephalic and gastric phases

• Intestinal phase:

• Cephalic and gastric: low pancreatic secretions

• Intestinal phase: high pancreatic secretions

size of the small intestine

• duodenum: 10 inches

• Jejunum: 8 feet

• Illeum: 12 feet

the pancreas is a mainly __

exocrine

Motility of small intestine

• segmentation (mixing): exposes chyme to wall of intestine for absorption

• Peristalisis: movement of contents along path of intestine (absorptive state)

• Power propulsion: rapid, long distance periastalsis

  • Pathological (clears it out)

    • Diarrhea: normal

    • Vomiting: oral direction

Migrating motor complex

SMALL INTESTINE:

• occurs in post-absorptive state: housekeeping function (sleep)

• Propagating wave of contraction that moves from antrum to ileum in 90-120 min

• MMC removes things that are not digestable (like a swallowed penny)

secretions of small intestine

Crypts of Lieberkuhn

• Goblet cells

  • mucus: important for movement and protection (lubrication)

• bicarbonate: acid neutralization

• Epithelial stem cells: high turnover rate

  • replace epithelial lining

• Paneth cells: secrete antimicrobial peptides

what cells are important for defense in small intestien

Paneth cells: antimicrobial peptides

Ascending colon: time? Comes in thru?

Short transit time, rapid movement

Ileosphecal sphincter

Transverse colon: function and time?

• Longest amount of time (24-48 hours)

• Storage and dehydration of contents

  • Recovers water

Descending Colon and Sigmoid colon: time? Leads to?

• Short transit time

• Leads to rectum and anus for defecation

Motility of Large intestine

• Haustrations: mixing movement

  • Pronounced areas of contractions

• Power propulsion: urges contents along for defecation

• Gastrocolic reflex: food in stomach can cause urge to defecate and moves content along, prevalent in small children

Why does the large instestine have a longer transit time in transverse colon?

to allow for storage / retainment of water

Defecation in large intestine

• rectal distention triggers mechanoreceptors

• Defecation reflex:

  • contraction of rectum

  • relaxation of internal anal sphincter

  • Periastalsis in sigmoid colon

    • External anal sphincter is voluntary

Without defecation reflex?

Fecal impaction

Secretions of large intestine

• Mucus: throughout the GI: protection and lubrication

• Bicarbonate: microbial fermentation can produce acid and bicarbonate neutralizes the low pH

highest population of bacteria in body

colon

Reabsorption in colon

Water and electrolyes (Na, Cl)

Gas (flatus)

• nitrogen from swallowed air

• CO2, methane, hydrogen, hydrogen sulfide from bacterial fermentation of undigested polysaccharides