Digestion & Absorption

NCLEX

You're watching a preview. 300,000+ students are watching the full lesson.

Master

Previous Lesson

Next Lesson

Included In This Lesson

Outline

Transcript

Additional Lessons

NURSING.com students have a 99.25% NCLEX pass rate.

Outline

Overview

Digestion: process of breaking down foods into absorbable components in the gastrointestinal (GI) tract.
1. Mechanical: breakdown of food through physical actions such as chewing and muscle contractions
2. Chemical: breakdown of food with acids and enzymes
Gastrointestinal tract
1. Mouth
  1. Chewing begins breaking down the food into smaller pieces and mixes it with saliva.
  2. The saliva released contains water, electrolytes, mucus and a few enzymes.
  3. The saliva moistens the food so it mixes better as the food is broken into smaller pieces and is easier to swallow.
  4. Salivary amylase begins breakdown of starches.
  5. Bolus (moist food mass) is swallowed and enters the esophagus.
2. Esophagus
  1. Hollow muscular tube connecting the mouth and the stomach
  2. Epiglottis: small flap located in the throat, behind the tongue and in front of the larynx.
  3. Usually in upright position at rest allowing air to pass into the larynx and lungs.
  4. When a person swallows the epiglottis folds back to cover the entrance of the larynx so food and liquid do not enter the windpipe and lungs.
  5. After swallowing the epiglottis returns to its original upright position.
  6. The esophagus uses peristalsis, involuntary muscle contractions, behind the bolus, to push the bolus of food down the esophagus to the stomach.
3. Lower Esophageal Sphincter (LES)
  1. Located at bottom of esophagus
  2. LES relaxes and allows food into stomach.
  3. LES then closes to prevent backflow of hydrochloric acid (HCl) and acidic chyme from stomach into the esophagus.
4. Stomach
  1. Gastrin
    1. hormone that stimulates digestion through secretion of HCl and increases gastric motility and emptying.
  2. Hydrochloric acid (HCl)
    1. Activates the enzyme pepsin
    2. Starts protein digestion
    3. Acidic environment reduces microorganisms ingested from food.
  3. Pepsin
    1. Digestive enzyme that breaks down proteins (including collagen) to smaller chained polypeptides.
  4. Gastric lipase
    1. Breaks a relatively small amount of triglycerides into short chain fatty acids (SCFA).
  5. Intrinsic factor
    1. Helps with Vitamin B12 absorption
  6. Chyme
    1. Ball of food (previously called bolus) now called chyme
    2. a semi-liquid mixture of partially digested food and digestive juices.
5. Pyloric sphincter
  1. Located between the stomach and small intestine (SI).
  2. Controls the rate of stomach contents entering the SI.
  3. Peristaltic contractions push the chyme toward the lower part of the stomach.
  4. The pyloric sphincter relaxes and opens briefly then closes
    1. allows small amounts of the stomach contents to enter the small intestine
    2. prevents the chyme from going back up in the stomach.
6. Small intestine (SI) – duodenum, jejunum, ileum
  1. Hormones
    1. Secretin: produced in the duodenum in response to acidic chyme and slows gastric emptying.
    2. Cholecystokinin (CCK): produced in the duodenum cells in response to chyme with high fat or protein in it. Stimulates pancreas to release enzymes and the gallbladder to contract and release bile.
    3. Gastric Inhibitory Peptide (GIP): released in duodenum, slows gastric emptying.
  2. Enzymes+
    1. Trypsin – activated from inactive precursor trypsinogen in the duodenum, breaks down proteins
    2. Chymotrypsin – activated from inactive precursor chymotrypsinogen in the duodenum, breaks down proteins
    3. Carboxypeptidase – a protease that takes off the terminal amino acid group from a protein
    4. Pancreatic lipase – breaks triglycerides into di- and monoglycerides
    5. Pancreatic amylase – breaks down starches into smaller chains
    6. Brush border enzymes – further break down chyme to more absorbable particles.
      1. Examples: maltase, lactase, sucrase, peptidase
    7. Sodium bicarbonate – raises pH and neutralizes acidic chyme
  3. Structure of SI wall
    1. Mucosal folds – increases surface area and assist in movement of chyme
    2. Villi – fingerlike projections that increase surface area
    3. Microvilli (brush border) – increase surface area and assist with further digestion
  4. Absorption of nutrients
    1. Majority of macro (protein, carbohydrate and fat) and micronutrient (vitamin and mineral) absorption occurs in SI
  5. Ileocecal valave – prevents backflow of fecal matter into ileum
7. Large intestine (LI) cecum, colon, rectum
  1. Absorption of remaining water and electrolytes
  2. Bacterial fermentation of fiber and resistant starches (No digestive enzymes – chemical digestion done by bacteria)
  3. Vitamin K and biotin synthesis by gut bacteria
  4. Feces formation
8. Accessory organs
  1. Liver
    1. Bile production
    2. Processes nutrients absorbed by the SI
    3. Stores glucose (glycogen)
  2. Gall bladder
    1. Store and concentrate bile
  3. Pancreas
    1. Exocrine glands produce trypsin, chymotrypsin, amylase, lipase
Examples of improper absorption
1. Celiac disease
  1. Autoimmune condition
  2. Gluten damages villi of SI – prevents proper absorption of nutrients
2. Lactose intolerance
  1. People who don’t produce adequate levels of lactase (enzyme that digests lactose)
  2. Gas, bloating and diarrhea common symptoms

Unlock the Complete Study System

Used by 300,000+ nursing students. 99.25% NCLEX pass rate.

200% NCLEX Pass Guarantee.
No Contract. Cancel Anytime.

Transcript

Today we are going to be talking about digestion and absorption.

Digestion is the process of breaking down foods into absorbable components in the gastrointestinal (GI) tract. Mechanical digestion is the breakdown of food through physical actions such as chewing and muscle contractions. Chemical digestion is the breakdown of food with acids and enzymes.

The main organs in the GI tract, in the order they occur are the mouth, esophagus, stomach, SI and LI.

The mouth is where digestion begins. Chewing begins breaking down the food into smaller pieces and mixes it with saliva. Saliva contains water, electrolytes, mucus and a few enzymes, such as salivary amylase. The saliva moistens the food so it mixes better as the food is broken into smaller pieces and is easier to swallow. This moist food mass is called bolus and swallowed and enters the esophagus.

The esophagus is a hollow muscular tube connecting the mouth and the stomach. The epiglottis is a small flap located in the throat, behind the tongue and in front of the larynx. It is usually in an upright position at rest allowing air to pass into the larynx and lungs. When a person swallows the epiglottis folds back to cover the entrance of the larynx so food and liquid do not enter the windpipe and lungs. After swallowing the epiglottis returns to its original upright position. The esophagus uses peristalsis, involuntary muscle contractions, behind the bolus, to push the bolus of food down the esophagus to the stomach. The Lower Esophageal Sphincter (LES) is located at the bottom of the esophagus. It relaxes and allows food into the stomach. It then closes to prevent backflow of acidic chyme from stomach into the esophagus.

Gastrin is a hormone in the stomach that stimulates digestion through secretion of HCl and increases gastric motility and emptying. Hydrochloric acid (HCl) activates the enzyme pepsin and starts protein digestion. The acidic environment reduces microorganisms ingested from food. Pepsin ia a digestive enzyme that breaks down proteins (including collagen) to smaller chained polypeptides.

Gastric lipase is an enzyme that breaks down a relatively small amount of triglycerides into short chain fatty acids (SCFA). Intrinsic factor is a protein that helps with Vitamin B12 absorption. The ball of food (previously called bolus) is now called chyme. It is a semi-liquid mixture of partially digested food and digestive juices. The pyloric sphincter is located between the stomach and small intestine (SI). It controls the rate of the food entering the SI from the stomach.

Some hormones in the SI include secretin which is produced in the duodenum in response to acidic chyme and slows gastric emptying. Cholecystokinin (CCK) is produced in the duodenum cells in response to chyme with high fat or protein in it. It stimulates pancreas to release enzymes and the gallbladder to contract and release bile. Gastric Inhibitory Peptide is released in the duodenum and slows gastric emptying.

Trypsin is activated from inactive precursor trypsinogen in the duodenum, breaks down proteins.
Chymotrypsin is activated from inactive precursor chymotrypsinogen in the duodenum, breaks down proteins. Carboxypeptidase is a protease that takes off the terminal amino acid group from a protein.

Both pancreatic lipase and pancreatic amylase are enzymes produced by the pancreas. Pancreatic lipase breaks triglycerides into di- and monoglycerides. Pancreatic amylase breaks down starches into smaller chains. Brush border enzymes in the microvilli further break down chyme to more absorbable particles. One example is lactase. Sodium bicarbonate is also produced by the pancreas. It is a compound that isn’t an enzyme that raises the pH and neutralizes the acidic chyme.

Mucosal folds increase the surface area and assist in movement of chyme. Villi are fingerlike projections that increase surface area. Microvilli (brush border) – increases the surface area further and assists with digestion and absorption. The majority of macro and micronutrient absorption occurs in SI. The ileocecal sphincter is located between the SI and the LI. It prevents backflow of fecal matter into ileum.

The last organ of the GI tract is the large intestine. In addition to the absorption of remaining water and electrolytes, there is bacterial fermentation of fiber and resistant starches. There are no digestive enzymes in the LI. Chemical digestion done by bacteria. There is also Vitamin K and biotin synthesis by gut bacteria. Lastly, the LI is where feces are formed.

The liver is an accessory organ in digestion. A few roles include bile production, processing of nutrients absorbed by the SI, and glucose storage in the form of glycogen.

As already mentioned, the pancreas produces trypsin, chymotrypsin, amylase, and lipase. The gallbladder stores and and concentrates the bile made by the liver.

Examples of improper absorption include Celiac disease, an autoimmune condition when gluten damages villi of SI, causing decreased surface area of the villi which prevents proper absorption of nutrients. Lactose intolerance is when there is insufficient levels of lactase, the enzyme that breaks down lactose. This causes gas, bloating and diarrhea as common symptoms.

In summary, mechanical digestion is the breakdown of food through physical actions such as chewing and muscle contractions. Chemical digestion is the breakdown of food with acids and enzymes. The GI tract organs are the mouth, esophagus, stomach, SI, and LI. Accessory organs include the liver, gallbladder, and pancreas. A few examples of improper absorption are Celiac disease and and lactose intolerance.

Digestion & Absorption

You're watching a preview. 300,000+ students are watching the full lesson.

Included In This Lesson

NURSING.com students have a 99.25% NCLEX pass rate.

Outline

Overview

Unlock the Complete Study System

Used by 300,000+ nursing students. 99.25% NCLEX pass rate.

Transcript

Study Faster with Full Video Transcripts

Nursing School Doesn't Have To Be So Hard

Go from discouraged and stressed to motivated and passionate

NCLEX

Study Plan Lessons

Welcome Back