Digestive system (Nutrition)

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Advanced nutrition and Metabolism
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What is digestion and absorption

Digestion: The process of breaking down food into components small enough for absorption

During the process of absorption, nutrients that come from the food (including carbohydrates, proteins, fats, vitamins, and minerals) pass through channels in the intestinal wall and into the bloodstream. The blood works to distribute these nutrients to the rest of the body. The waste parts of food that the body can't use are passed out of the body as feces.


3 parts of absorption

1. uptake of substances by the intestinal epithelial cell

2. metabolism within the cell

3. exit from the serosal side to the blood circulation or the lymphatic system


1.Oral Cavity

mechanical digestion

pH of saliva, saliva contains

The mouth and pharynx (or throat) constitute the oral cavity.

mechanical digestion: teeth, tongue, jaws

pH 6-7.4; saliva is 99.5% water, which helps dissolve foods.

Saliva containing: water, electrolytes, mucus, enzymes (alpha amylase - hydrolyzes internal a1-4 bonds within starch), antibactrerial and antiviral compounds



covers larynx opening while swallowing to prevent choking



What is bolus?

peristalsis forces food (now called a bolus) through the esophagus

Bolus= food+saliva

To swallow food, the esophageal sphincter relaxes, allowing the esophagus to open. Food then passes to the esophagus. Simultaneously, the larynx moves upward, inducing the epiglottis to shift over the glottis. Once food in the esophagus, the larynx shifts downward to allow the glottis to reopen.



A progressive wavelike motion that moves the bolus through the esophagus into the stomach.

Usually it takes less than 10 seconds.


Lower esophageal sphincter or

Cardiac sphincter

why it is important?

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lower esophageal sphincter prevents vomiting.

On swallowing, the gastroesophageal sphincter pressure drops. This drop in pressure relaxes the sphincter so that the food may pass from the esophagus into the stomach.

Keeping this sphincter closed is important, because it prevents gastroesophageal reflux: the movement of substances from the stomach back into esophagus.




what can relax or decrease the sphincter pressure?

A person experiencing the gastroesophageal reflux feels burning sensation in the midchest, a condition referred to as heartburn.

Gastric acid is irritant to the esophageal mucosa.

*smoking, chocolate, high-fat foods, alcohol promote relaxation of the cardiac sphincter and increase the likelihood of acid reflux to esophagus.

Gastroesophageal reflux disease (GERD) is a disorder marked by reflux of gastric contents (acid chyme) from stomach to esophagus.


What is GERD?

what can increase the sphincter pressure?

what are factors that could exacerbate the heartburn?

what stimulates the gastric secretion?

Gastroesophageal reflux disease (GERD) is a disorder marked by reflux of gastric contents (acid chyme) from stomach to esophagus.

*protein may help by increasing sphincter pressure

*overweight, tight clothing, large meals, pregnancy exacerbate heartburn

*Calcium, coffee, tea, alcohol stimulate stomach acid secretion.

*Citrus products are to directly irritate an inflamed esophagus.


The Stomach

made up of

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The stomach extends from gastroesophageal sphincter to the duodenum.

*made up of antrum/fundus/body

*mechanical and chemical digestion


Show main regions of the stomach





How stomach mixes food?

The stomach begins mixing the food with gastric juices and enzymes using circular, longitudinal, and oblique or diagonal smooth muscles of the stomach.


The gastric gland and its secretion in the body of the stomach

several cell types, which secrete different substances may be found within a gastric gland.

Mucus cells- bicarbonate and mucus

Pariental (oxyntic) cells, hydrochloric acid and intrinsic factors

Chief (peptic or zymogenic cells) - pepsinogens

Endocrene cells - variety of hormones


Hydrochloric acid secreted from ______

secreted from Gastric parietal cells


Why do we need a secretion of intrinsic factor from Parietal (oxyntic) cells?

Intrinsic factors needed for the absorption of B12


pH of the gastric juice

The high concentration of HCl acid in the gastric juice is responsible for its low pH, about 2.

The lower the pH, the more acid in the solution is.


Can we lower the pH of the gastric by drinking the orange juice?


pH of the orange juice is higher than that of the gastric juice.


Pepsin made by ____

Function of pepsin activation of pepsin

activation of pepsin/how low ph acts on activation of the pepsin

pepsin is made by chief cells

functions as proteolytic enzyme (protease) in the stomach.

An enzyme that hydrolyzes proteins.

Pepsin is derived from pepsinogens (inactive).

Pepsinogens can be converted to active enzyme in an acid environment (pH<5) or in the presence of previously formes pepsin


Secretion of pepsin or any acid is stimulated by ____

Secretion of acid also stimulated by acetylcholine.

*Pepsinogens are secreted in granules into the gastric lumen from chief cells when they are stimulated by acetilcholine, acid, or both.


a-amylase in the stomach active?

what is the function of a-amylase and where it is originated?

Originated from salivary glands in the mouth

this enzyme hydrolyzes starch (a1-4 bonds in starch) retains some activity in the stomach until it is incativated by the low pH of gastric juice.


Mucus secreted by ___ also found in gastric juice.

mucus from the neck (mucus) cells (protection and lubrication) – stimulated by gastrin and prostaglandins

lubricates the ingested gastrointestinal contents and coats and protects the gastric mucosa from mechanical and chemical damage.


Regulation of gastric secretion

what is gastrin and how it is released?

Gastrin is a peptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility.

It is released by G cells in the pyloric antrum of the stomach, duodenum, and the pancreas.

Stimulated by presence of food.

Gastrin also stimulates histamine release


Gastrin stimulates release of histamine


Gastrin stimulates pepsinogen release from chief cells


Gastrin inhibits neck cells to produce mucus to form a mucosal barrier


True True False

overall, gastrin stimulate release of

Histamine, Pesinogen, Neck cells to produce mucus, HCl


Name potent compounds that stimulate release of hydrochloric acid by parietal cells




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Peptic Ulcers

What is it? Cause? Possible treatment

A break in the inner lining of the stomach, first part of the small intestine or sometimes the lower esophagus

Result when normal defense and repair system that protect the mucosa of the gastrointestinal tract are disrupted.

Most common cause Helicobacter Pylori infection.

Also, chronic use of Alcohol, Aspirin, drugs that affect the stomach lining can promote the development of ulcers.

Drugs that prevent histamine binding to the H2 receptor on parietal cells used for treatment such that acid release is diminished.

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Peptic Ulcers

Treatment of symptoms

medications to reduce acid secretion;lyfestyle; antacids

An antacid is a substance which neutralizes stomach acidity and is used to relieve heartburn, indigestion or an upset stomach.


Hormones that act on stomach

What are hormones that inhibit gastric motility?

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Secretin and Gastrin inhibitory peptide (GIP) decrease or inhibit gastric motility (contractions of gastric smooth muscles)


What is GIP / functions

Gastric inhibitory polypeptide

Gastroihibitory peptide

Inhibit gastric motility, also inhibits gastric acid secretion.


Which nutrients are absorbed in the stomach?

F, I, ethanol, water


Pyloric Sphincter

Slowly allows the chyme (name of broken down food) into SI


The small intestine made up from 3 parts....

What is the ph of the duodenum?

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made up of duodenum, jejunem, ileum - ±10–16 ft

The pancreas secretes the bicarbonate ions through bile juice in the small intestines. These bicarbonates neutralize the acidic pH of the food from stomach and create an alkaline pH, thus maintain the required pH in small intestines.


How SI maximize its ability to absorb nutrients?

- Large circular folds of mucosa, called folds of Kreckring, that protrude into the lumen of the small intestine. (Submucosa and mucosa are in the folds of

- fingerlike projections, called villi.Each villus is made of absorptive cells called enterocytes. Each villus contains capillary network and lymphatic vessels.

- Microvilli, hairlike extensions of the plasma membrane of the enterocytes that make up the villi.


What is glycocalyx?

The microvilli posses a surface coat, or glycocalyx, together these make up the brush border of the enterocytes.

It lines the luminal side of the intestine.



Components of mucosa layer of the SI?

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Mucosa layer has villi, microvilli (with capillaries and
lymphatics), crypts of Lieberkuhn (with Paneth cells
and goblet cells)


Function and location of Crypts of Lieberkuhn cells

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Lie between the villi.

Epithelial cells in these crypts continuously undergo mitosis. The new cells migrate upward and out of the crypts toward the tips of the villi, function as absorptive enterocytes.

Intestinal cell turnover is rapid, 3-5 days.

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Cells in the crypts include Paneth and Globlet cells

what is their function?

Paneth cells secrete antimicrobial peptides - defencins

Goblet cells secrete both cystene-rich proteins with anifungal activity and mucus.


Goblet cells secrete antimicrobial compounds only


Paneth cells secrete mucin


Goblet cells secrete mucins and antimicrobial compounds

Paneth cells secrete antimicrobial compounds


How many layers of SI wall present?

SI wall contains 4 layers – serosa, muscularis,
submucosa, mucosa

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What are functions of SI wall layers – serosa, muscularis,
submucosa, mucosa?

Mucosa layer has villi, microvilli (with capillaries and
lymphatics), crypts of Lieberkuhn (with Paneth cells
and goblet cells)

Submucosa contains the submucosal plexus which
controls secretions (e.g. hormones) and blood flow

• Muscularis contains the myenteric plexus which
controls peristalsis and GI motility


How duodenum protected against the gastric acidity?

By secretion from the Brunner's glands and from pancreas.

Bicarbonate and fluid also secreted from Crypts of Lieberkuhn.

The pancreatic secretions released into the duodenum are rich in bicarbonate, which helps to neurtilize the acid released from stomach.


What is Brunner gland?

Brunner's glands are located in the mucosa and submucosa of the first few cm of the duodenum. The mucous-containing secretions are viscous and alkaline, with pH of 8.2-9.3. The mucus itself rich in glycoproteins and helps protect the epithelial mucosa from damage.


Where Brunner gland is secreted?

Brunner glands secrete mucus in the first part of the SI.


Bicarbonate and fluid also secreted from Crypts of Lieberkuhn



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Immune system protection of GI tract

what are GALT and MALT?

The lymphoid tissue found primarily in the mucosa and submucosa is called mucosa-accociated lymphoid tissue (MALT).

The lymphoid tissue found primarily in non-mucosal layer GALT gut-associated lymphoid tissue

GALT and MALT are composed of multiple cell types Peyer’s Patches, lymphocytes, M cells, macrophages, IgA, natural killers. This is a very important part of the immune system in the SI.



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GALT - gut-associated lymphoid tissue

GALT and MALT are composed of multiple cell types Peyer’s Patches, lymphocytes, M cells, macrophages, IgA, natural killers. This is a very important part of the immune system in the SI.


What are M cells?

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M cells pass or transport foreign antigens to the MALT lymphocytes, which turn mount (strengthen) an immune response.


What is pH of SI?

pH=7.5-8.0 in SI


What is Gastroparesis?

Common cause/Symptoms/Treatment

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chronic disorder of gastric motility that is characterized by delayed emptying of the stomach

common cause is diabetes – due to nerve damage or poor blood flow to gut

•other causes – nerve damage due to stomach surgery, infection, anorexia nervosa or bulimia; medications or disorders that affect smooth muscle or nervous system


Diabetes and nerve damage is a common cause of Gastroparesis?




What diet/treatment should an individual with gastroparesis follow?

smaller more frequent meals

liquid diet (soups)

reduced fat because it slows digestion

Avoid carbonated drinks, alcohol and smoking

medications that decrease nausea

medications that increase muscle contractions


Symptoms of gastroparesis

pain in the upper abdomen

nausea, vomiting, weight loss

postprandial fullness