gastrointestinal anatomy

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Gastrointestinal Anatomy

Fakhrurrazy


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Fig. 3.2 Organs and Systems


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Digestive System

Alimentary canal- mouth to anus

Functions

Movement

Secretion

Digestion

Absorption

Elimination

Nutrient production (by bacteria)


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Phases of Digestion: Overview

Figure 21-11: Overview of functions in different regions of the digestive system


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Processes of the Digestive System

Ingestion Motility: mixing &

propelling

Digestion:

enzymatic hydrolysis Secretion: enzymes,

water, mucus, buffers,etc.

Absorption: watersoluble vs. fat soluble

ExcretionFigure 21-1: Processes of the digestive system

How is hydrolysis different from energy metabolism?


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Digestive Anatomy

Figure 21-2a: ANATOMY SUMMARY: The Digestive System

Describe the 4-layer basic plan in thewall of the Alimentary Canal.


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Digestive Anatomy: HistologicalCompare histology in the stomach to that of the

small intestine (next slide). How are the

anatomical differences related to functional

differences in these organs?

Pg. 677Parietal cells secrete H+

Mucus neck cells

Parietal cells

Chief cells

G-cells

What keeps the body from

becoming too basic as a result? Histology of the Stomach


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Digestive Anatomy: Histological

Figure 21-2e: ANATOMY SUMMARY: The Digestive System

Where is the basolateral border on this cell?


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Fig. 3.8


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Digestion and the Mouth

Cooking Mastication Saliva

Enzymes to help breakdown simple sugars Mucus to lubricate the food for easier swallowing Lysozyme to kill bacteria

Tongue Taste receptors

(Flavor is enhanced with the olfactory cells) Enzymes to help breakdown fatty acids

Epiglottis


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The Swallowing Process


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Functions of the Sphincters

Cardiac or lower esophageal sphincter Prevents reflux of stomach content to cause heartburn

and ulcers

Pyloric sphincter Controls the amount of stomach content into the

small intestine

Sphincter of Oddi Controls the amount of bile into the small intestine

Ileocecal sphincter Prevents large intestine content (bacteria) back up into

the small intestine


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The Stomach

Lower esophageal sphincter and pyloric sphincter

Capacity of ~4 cups

Secretion of hydrochloric acid and enzymes

Destroys ingested proteins

Holds food for 2-4 hours

Results in the formation of chyme

Mucus layer prevents autodigestion Secretion of the intrinsic factor


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Physiology of the Stomach


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What stimulates acid production?

Stimulated by

Gastrin

Stomach distention

Histamine Thoughts of food (nerve input)

Food itself

Prevents autodigestion

Stop secretion when pH is ~2

Thick mucus layer

Animation of acid production
http://hopkins-gi.org/multimedia/database/intro_247_Parietal.swfhttp://hopkins-gi.org/multimedia/database/intro_247_Parietal.swf


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Stomach Acid

Destroys activity of protein

Converts pepsinogen to pepsin

Partially digests dietary protein Assists in calcium absorption


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The Small Intestine


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The Small Intestine

Duodenum

~10 inches in length

Primary site of digestion

Jejunum ~4 feet in length

Some digestion

Ileum ~5 feet in length

Little digestion


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Movement Along the Intestine

Peristalsis

A ring of contraction propelling material along the

GI tract

Segmentation

A back-and-forth action that breaks apart food

Mass movement

Peristaltic wave that contracts over a large area of

the large intestine to help eliminate waste


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Movement


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Motility: Smooth Muscle Contractions

Tonic contractions(esp. sphincters)

Phasic contractions

Slow wave potentials

Peristalsis

(move products) Segmentation

(mixing)

Figure 21-4: Contractions in the GI tract

How does this differ from SA node function?

Digestive Secretions:


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Digestive Secretions:(7 L / day from tissues into lumen)

Salivary glands,pancreas, liver,

stomach, intestine

Water Enzymes

Mucus

Ions: H+, Na+, HCO3-,etc.

Hormones

Figure 21-5: Daily mass balance in the digestive system


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Digestive Enzymes

Enzymes speed up chemical reactions

Enzymes lower the amount of energy

needed for the action to proceed Each enzyme acts on specific substance

Enzyme release and activation are

controlled by nerves and hormones

Enzymes are only released when needed


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Physiology of the Small Intestine

The wall is folded

Villi projections are located on the folds

Absorptive cells (enterocytes) are located on

the villi

Microvilli is located on the villi

Glycocalyx is located on the microvilli Increases intestinal surface area 600 x


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The Small Intestine


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Intestinal Mucosa

Absorptive cells

Produced in crypts

Migration and maturation from the crypts to thetips of the villi

Degradation of cells at the tips of the villi bydigestive enzymes

Newly formed cells constantly migrate to replace

dying ones (< 6 days) High turnover causes the cells to deteriorate

during nutrient deficiency


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In the Small Intestine

Bile acid from the liver via the gallbladder

Bicarbonate ions from the pancreas

Muscle contractions to mix the food with

digestive juices

Food remains 3-10 hours in the small intestine

~95% of digestion takes place here


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Site of Absorption


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Types of Absorption

Passive Intestinal wall is permeable to the nutrient Going from higher to lower concentration No energy expended

Facilitated A carrier shuttles substances into the absorptive cells Going from higher to lower concentration No energy expended

Active Uses a carrier and ATP

Endocytosis Phagocytosis and pinocytosis


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Types of Absorption


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Enterohepatic Circulation

Bile circulation

Liver gallbladdersmall intestine portal vein

liver

~98% of bile is recycled


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The Large Intestine

Little digestion occurs

Indigestible food stuff

Absorption of 85-90% of the water,some minerals, vitamins

Formation of feces for elimination


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A SummaryORGAN FUNCTIONS

Mouth Chewing

Digestion of starch

Esophagus Passage way

Stomach Food Storage

Acid kills bacteriaSome protein digestion

Small Intestine Final digestion

Absorption

Large Intestine Absorption of water, mineralsAnus Elimination

Liver Production of bile

Gallbladder Store and release bile

Pancreas Enzymes and bicarbonate


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GI Problems


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Ulcers

Helicobacter pylori

Heavy use of aspirin

Excessive acid production in the stomach

Symptoms

Pain 2 hours after eating

Treatment

Antibiotics Antacid


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Heartburn

Gastroesophageal reflux disease

Gnawing pain in the upper chest

Acid from the stomach to the esophagus

Treatment Smaller meals

Less fatty meals

Stop smoking

Do not lie down after eating

Avoid offending foods


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Constipation

Slows movement of fecal matter

Increases fluid reabsorption; hardening of the feces

Causes:

Results from ignoring normal urge Antacids, calcium and iron supplements

Treatment

Plenty of dietary fiber and fluids

Laxatives


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Hemorrhoids

Swollen veins of the rectum and anus

Causes:

Added stress and pressure to the vessels

Treatment

Check with physician

Warm compresses to reduce pain

Adequate fiber and fluid


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Irritable Bowl Syndrome

Visible abdominal distension

Crohns disease

No cure

Eliminate specific foods

gastrointestinal anatomy

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