intestines

3 parts of small intestine in order

Duodenum

Jejunum

ileum

Duodenum

10 in
first portion of SI,curves around pancreas head

Jejunum

8 ft

posteriorly attached via mesentery

Ileum

12 ft

posteriorly attached via mesentery; joins with the large intestine via ileocecal valve

what allows Ileocecal sphincter to relax/open

Gastroileal reflex enhances force of segmentation in ileum

Gastrin increases motility of ileum

Nerve supply to small intestine

parasympathetic via vagus nerve

sympathetic via thoracic splanchnic nerves

Functions of small intestine

mix together chyme and pancreatic juices/bile for absorption

Finishes digestion of carbohydrates, lipids and protein;

digestion of nucleic acids begins and finishes here

~90% of water and nutrient absorption

functions Circular folds in small I

slow down the path of chyme and cause it to spiral through lumen (more absorption time)

functions Villi in small I

mucosal projections containing capillary core and lymphatic lacteal capillary both for absorption

functions microvilli in small I

cytoplasmic extensions of the mucosal cells; give SI its brush border containing enzymes that complete final breakdown of carbohydrates
and proteins

Intestinal crypts

glands scattered between villi

5 cell types in villi and crypts of SI

Enterocytes (mostly)

Goblet cells- mucus
Enteroendocrine cells- source of CCK and secretin

Paneth cells

how often SI epithelium replaced

2-4 days

Paneth cells

found deep in crypts;secrete antimicrobial agents like defensins and lysozyme,

where MALT is found

lamina propria-also contains plasma cells secreting IgA

major stimulus for intestinal juice production

hypertonic or acidic chyme

intestinal juice & brush border enzymes

1–2 L secreted daily in response to distension or irritation of mucosa

Slightly alkaline and isotonic with blood plasma

Consists largely of water but also contains mucus

Fat-soluble vitamins (A, D, E, and K) absorption

small intestine

carried by micelles; diffuse into absorptive cells

Water-soluble vitamins (C and B) absorption

small intestine

absoroped by diffusion or by passive or active transporters

Vitamin B12 absorption

small intestine

binds with intrinsic factor and is absorbed by endocytosis

vitamin K and B absorption

absorbed in LARGE intestine

Iron and calcium absorption site

absorbed in duodenum

what 2 electrolytes are absorbed as needed

Iron and calcium

Ionic iron is stored

in mucosal cells with ferritin

transported by transferrin by blood when needed

three unique features of large intestine

teniae coli
Haustra

Epiploic appendages

teniae coli

three bands of longitudinal smooth muscle in muscularis of large intestine

Haustra

pocketlike sacs caused by tone of teniae coli of large intestine

Epiploic appendages

fat-filled pouches of visceral peritoneum

5 parts of large intestine

Cecum (1st)

Appendix

Colon

Rectum

Anal canal

Ascending colon

Ends in right-angle turn called right colic (hepatic) flexure

Transverse colon

Ends in another right-angle turn, left colic (splenic) flexure

parts of large intestine that are retroperitoneal

Cecum, appendix, and rectum

ascending, descending colon

Intraperitoneal regions are anchored to

posterior abdominal wall by mesentery sheets called mesocolons

Appendicitis cause

sually results from a blockage by feces that traps infectious bacteria

Pectinate line

horizontal line that parallels anal sinuses

Haustral churning

Distension reaches a certain point and the walls of the haustra contract to
squeeze contents onward

Mass peristalsis

A strong peristaltic wave that begins in the transverse colon and quickly drives the contents of the colon into the
rectum

The last stages of digestion occur through

bacterial action

Defecation Reflex

Rectal wall distends and stretch receptors send sensory nerve impulses to the sacral spinal cord

Diverticulosis

presence of diverticula
• Common in sigmoid colon
• Affects half of people > 70 years

Diverticulitis