Digestion and Absorption Flashcards
To bring essential nutrients into the internal environment so that they are available to each cell of the body
Primary function of the Digestive System
(2) Mechanisms used to accomplish the primary function of the Digestive System
Ingestion
Digestion
Occurs when food is taken in
Ingestion
The breakdown of complex nutrients into simple nutrients
Digestion
Required to physically break down large chunks of food material & move food along the digestive tract
Motility of the Gastrointestinal (GI) Wall
Mechanism of Digestion
Facilitates chemical digestion
Secretion
Mechanism of Digestion
Movement of nutrients through the GI mucosa into the internal environment
Absorption
Mechanism of Digestion
Excretion of material that is not absorbed
Elimination
Mechanism of Digestion
Coordination of the various functions of the Digestive System
Regulation
Mechanism of Digestion
- Begins in the mouth; Changes ingested food from large particles into minute particles, facilitating chemical digestion
- Churns contents of the GI lumen to mix with digestive juices & ensure contact with the surface of the intestinal mucosa, facilitating absorption
- Propels food along the alimentary tract, eliminating digestive waste from the body
Mechanical Digestion
Mouth to Oropharynx
Voluntarily controlled
Oral Stage
Deglutition
Oropharynx to Esophagus
Involuntary movement
Combination of contractions & gravity moves bolus into Esophagus
Pharyngeal Stage
Deglutition
Esophagus to Stomach
Involuntary movement
Esophageal Stage
Deglutition
In an alternating fashion ____ and ____ can occur together.
Peristalsis
Segmentation
Wavelike ripple of the muscle layer of a hollow organ
Peristalsis
Mixing movement
Digestive reflexes cause a forward & backward movement with a single segment of the GI tract
Segmentation
- Food in the stomach is churned & mixed with gastric juices to form chyme
- Chyme is ejected about every 20 seconds into the duodenum
- Emptying the stomach takes 2 to 6 hours
Gastric Motility
Controlled by hormonal & nervous mechanisms
Gastric emptying
- Mixes chyme with digestive juices from the pancreas, liver, & intestinal mucosa
- Peristalsis rate picks up as chyme approaches the end of the jejunum, moving it through the small intestine into the large intestine
- After chyme leaves the stomach, it passes through the small intestine & takes approximately 5 hours
Intestinal Motility
Chemical changes result from
Hydrolysis
- Operate in lumen of digestive tract, outside of any body cells
- Specific in their action
- Function optimally at a specific pH
Digestive enzymes : Extracellular organic (protein) catalysts
(Chemical Digestion)
Enzymes are continually being destroyed or eliminated from the body & must continually be synthesized
Properties of Digestive Enzymes
Most digestive enzymes are synthesized as
Inactive Proenzymes
We eat 6 main types of chemical substances :
Carbohydrates, Proteins, Fats, Vitamins, Mineral Salts & Water
ONLY THE 1ST 3 MUST BE CHEMICALLY DIGESTED TO BE ABSORBED
Properties of Digestive Enzymes
Secreted by salivary glands
Saliva
Secretion
Lubricates food with water & facilitates mixing
Mucus
Secretion
An enzyme that begins digestion of starches
Amylase
Secretion
Secreted by gastric glands
Gastric Juice
A protease that begins the digestion of proteins
Pepsin
- Secreted by parietal cells
- Decreases the pH of chyme for activation & optimum function of pepsin
Hydrochloric Acid (HCl)
- Secreted by parietal cells
- Protects vitamin B12 & later facilitates its absorption
Intrinsic Factor
Protect & facilitate mixing of chyme
Mucus & Water
Secreted by acinar & duct cells of the pancreas
Pancreatic Juice
Such as Trypsin & Chymotrypsin
Enzymes that digest proteins & polypeptides
Proteases
Enzymes that digest emulsified fats
Lipases
Enzymes that digest nucleic acids such as DNA & RNA
Nucleases
An enzyme that digests starches
Amylase
- Only reflux mechanisms control the secretion of saliva
- Chemical & mechanical stimuli come from the presence of food in the mouth
- Olfactory & visual stimuli come from the smell & sight of food
Salivary Secretion
- Cephalic Phase
- Gastric Phase
- Intestinal Phase
Control of Gastric Secretion
Stimulated by several hormones released by intestinal mucosa
Pancreatic Secretion
- Causes increased exocrine secretion from the pancreas
- Opposes gastrin, thus inhibiting gastric HCl secretion
- Stimulates contraction of the gallbladder so that bile is ejected into the duodenum
CCK (Cholecystokinin)
Bile is secreted continually by the
Liver
Little is known about how it is regulated
Intestinal secretion
Most absorption occurs in the
Small intestine
Passage of substances through the intestinal mucosa into the blood or lymph
Process
Some substances, such as water, absorption occurs by simple diffusion or
Osmosis
How sodium is transported
Secondary active transport
How glucose is transported
Sodium cotransport (Coupled transport)
Moves nutrient particles through cells
Transcellular Absorption
Moves particles between cells
Paracellular Absorption
Nutrients that are absorbed into the blood (such as monosaccharides & amino acids) first travel to the liver via
The Portal System
Expulsion of feces from the digestive tract
Defecation
Contents of the lower part of the colon & rectum move at a slower than normal rate
Constipation
Result of increased motility of the small intestine, which causes decreased absorption of water & electrolytes & a watery stool
Diarrhea
