NHM 365 - Module 2

What is the life span of enterocytes in the GI tract?

Approximately 72 hours

What type of mechanisms result in movement within the GI tract?

Neural mechanisms

What is the primary method of digestion in the GI tract?

By enzymes

What percentage of the diet is typically absorbed in the GI tract?

90% to 97%

What are the appendage organs associated with the GI tract?

Pancreas, liver, and biliary tree

What is the process of transforming food into a transportable mass called?

Bolus formation

What are the two types of breakdown that occur in the mouth?

Mechanical (chewing) and chemical (starch breakdown)

How much saliva do the three pairs of salivary glands produce daily?

1-1.5 liters

What is the role of lingual lipase in the mouth?

Minimal fat digestion

What enzyme begins starch breakdown in the mouth?

Ptyalin (salivary amylase)

What is the process of swallowing called?

Deglutition

What is the name of the movement that moves the bolus to the stomach?

Peristalsis

What kind of digestion happens in the stomach?

Mechanical and chemical to break down large molecules

Describe digestion in the stomach

Wavelike contractions mix food with gastric secretions: Gastrin, HCl, intrinsic factor, pepsinogen, gastric lipase, mucus

What reduces the number of microorganisms in the stomach (protective and immunological effect)?

Acid

What hormone is released from the stomach mucosa when food enters the stomach?

Gastrin

What does gastrin stimulate parietal cells to secrete?

Hydrochloric acid (HCL)

How do stretch receptors of enteric neurons contribute to digestion in the stomach?

They stimulate muscle contraction to mix food with HCL.

What is the result of mixing food with hydrochloric acid in the stomach?

Proteins are denatured.

What important glycoprotein do parietal cells secrete, and what is its function?

Intrinsic factor; it is important for vitamin B-12 absorption in the small intestine.

Which cells secrete pepsinogen in the stomach?

Chief cells

How is pepsinogen activated?

It is activated by hydrochloric acid (HCL) into pepsin.

What is the function of pepsin?

Pepsin catalyzes the hydrolysis of peptide bonds (protein digestion).

What enzyme do chief cells secrete that contributes to fat digestion in the stomach?

Gastric lipase

Does significant fat digestion occur in the stomach?

No, very little fat digestion occurs in the stomach.

What is the mixture in the stomach called after digestion?

Chyme

What is the typical emptying time for the stomach?

1-4 hours

Which type of food empties the stomach the most rapidly?

Liquids and carbohydrates (CHO)

Which type of food takes the longest to empty from the stomach?

Solids, fats, or foods containing large particles, such as fiber, gristle, or connective tissue

How long does it typically take for a solid, mixed meal to empty from the stomach?

2 to 3 hours

What factors can affect stomach emptying time?

Composition of the meal

What controls the flow of material into and out of the stomach?

Sphincters

What connects the pharynx to the stomach?

Esophagus

What is the function of the upper esophageal sphincter?

It is closed except when swallowing.

What does the lower esophageal sphincter (LES) do?

It closes the entrance to the stomach and prevents reflux of acidic chyme back into the esophagus.

Which substances decrease the pressure of the lower esophageal sphincter (LES)?

Alcohol, fat, peppermint, spearmint, chocolate, caffeine.

What is the function of the pylorus (pyloric valve)?

Closes exit from the stomach and prevents reflux of small intestine back into stomach.

What can happen if the pylorus malfunctions?

It can spasm and cause very painful sensations.

What can excessively stimulate sphincters in the digestive process?

Stress can excessively stimulate sphincters, causing spasm.

Where does chemical digestion and absorption occur the most?

Small intestine

What is the primary site of chemical digestion and absorption of nutrients in the human body?

Small intestine

What increases the surface area of the small intestine?

Length, folds, villi, and microvilli

What facilitates the activities of the small intestine?

Secretions from the pancreas, biliary tree, and liver

What are the segments of the small intestine?

Duodenum, Jejunum, Ileum

How long is the duodenum?

Approximately 25 cm long

What begins in the duodenum?

Chemical digestion

What is the primary function of the jejunum?

Absorption

How long is the jejunum?

Approximately 2.5 meters long

What is the primary function of the ileum?

Absorption

How long is the ileum?

Approximately 3.6 meters long

What does the pancreas secrete into the small intestine?

Digestive enzymes

What does the liver produce?

Bile

Where is bile stored?

In the gallbladder

What does the gallbladder release into the small intestine?

Bile

What is the role of bile in digestion?

Aids in fat digestion

What is the principal site of nutrient absorption in the digestive tract?

The small intestine, primarily the jejunum.

Why does the small intestine have a high capacity for absorption?

Because it has a huge surface area.

What are villi?

A capillary bed and a lacteal.

What are microvilli?

Tiny projections of the plasma membrane that form the brush border of the small intestine.

What forms the brush border in the small intestine?

Microvilli.

Where are bile salts reabsorbed?

In the terminal ileum

What is the process called when bile salts are recycled back to the liver?

Enterohepatic Circulation

What does Vitamin B-12 combine with for absorption in the ileum?

Intrinsic factor

How is most water absorbed in the small intestine?

By osmosis

How long does it take for food to travel the length of the small intestine?

3-10 hours

What happens to digestive enzyme activity in patients kept NPO for more than 3 days?

It decreases

What may patients experience when re-fed after being NPO for more than 3 days?

Food intolerance

What is the name of the sphincter between the small and large intestines?

Ileocecal valve

What are the two mechanisms of absorption?

Diffusion and Active Transport

What is diffusion in the context of nutrient absorption?

Random movement of nutrients through mucosal cells to the bloodstream.

What drives simple diffusion?

A concentration gradient.

What is facilitated diffusion?

Involves a carrier protein to move molecules too large to diffuse easily.

What is required for active transport?

Input of energy to move nutrients across the membrane.

What can cause competition for absorption in active transport?

Some nutrients share the same carrier protein.

What is the primary function of the large intestine?

Absorption of remaining water and electrolytes, colonic salvage, and removal of solid waste.

How long is the large intestine?

1.5 meters long.

What are the main parts of the large intestine?

Cecum, colon, and rectum.

What is the composition of fecal matter?

Approximately 75% water and 25% solid organic matter.

What are the components of solid organic matter in fecal matter?

1/3 dead bacteria, 20-40% inorganic materials and fats, 2-3% protein, and the rest undigested fiber and sloughed cells.

What vitamins are synthesized by colonic bacteria?

Vitamin K, B12, thiamin, riboflavin

What do colonic bacteria produce?

Gases and organic acids

Where does most fermentation of non-digestible carbohydrates occur in the large intestine?

Ascending colon

What is gut microbiota?

Symbiotic bacteria and other microbes naturally occurring in the large intestine that prevent pathogenic bacteria from colonizing

What do bacteria ferment to produce short chain fatty acids (SCFAs)?

Certain carbohydrates

What do short chain fatty acids (SCFAs) nourish?

Colonocytes

What are some beneficial effects of the gut microbiome?

Overall health benefits

What are probiotics?

Live microorganisms that are intended to have health benefits.

What are prebiotics?

CHO like inulin or FOS that aren't digested but are fermented by bacteria.

What are synbiotics?

Functional foods that provide both probiotics and prebiotics.

What hormone is released by 'g' cells in the stomach?

Gastrin

What does gastrin stimulate?

Gastric secretions and motility

What initiates the secretion of gastrin?

Distension of the antrum of the stomach, impulses from the vagus nerve, and presence of secretogues

What inhibits the secretion of gastrin?

High acidity

What hormone is released by cells in the proximal small intestine?

Secretin

What does secretin do in relation to gastrin?

Opposes the action and secretion of gastrin

What does secretin stimulate the pancreas to release?

Bicarbonate and water into the duodenum

What initiates the secretion of secretin?

Gastric acid and digestive products in the duodenum

What is Cholecystokinin (CCK) and what triggers its release?

Cholecystokinin (CCK) is released by cells in the small intestine in response to the presence of HCl and food, especially fat.

What are the functions of Cholecystokinin (CCK)?

Cholecystokinin (CCK) stimulates pancreatic enzyme release, gallbladder contraction, and increases satiety.

What is Motilin and what triggers its release?

Motilin is released by cells in the upper small intestine in response to bile and pancreatic secretions.