Chapter 13 - The Digestive System Flashcards
How do humans obtain their energy?
Since humans are heterotrophic, we cannot synthesize our own nutrients
- We must consume food to provide out bodies with raw material for energy, repair, and growth
How do we obtain energy?
1) Ingestion: Eating
2) Digestion: Breakdown
3) Absorption: Molecules into the bloodstream available to cells
What are 2 types of digestion?
1) Intracellular: Occurs within the cell
2) Extracellular: Occurs outside of the cell
What does the digestive tract consist of?
Begins with the oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, and the anus
What are accessory organs?
Salivary glands, pancreas, liver, gallbladder, etc.
What occurs in the oral cavity?
Digestion:
1) Mechanical = Chewing (mastication)
2) Chemical = Enzymatic break down
- Ex. Saliva lubricates food and the enzyme salivary amylase hydrolyses starch to maltose
What is a bolus?
Food that has been moistened and chewed enough to be swallowed
What is the esophagus? What does its role serve? How is it closed off from the stomach?
Muscular tube leading from the mouth to the stomach
- Food moves down in rhythmic waves of involuntary muscle contraction (peristalsis)
- Closed off from stomach by lower esophageal (cardiac) sphincter
Describe the esophagus in relation to its position and pressure:
Located in thoracic cavity with a negative pressure relative to the environment and the abdominal cavity has positive pressure
- Without normal defence mechanisms, continual reflux would occur
What are 3 physiological changes related to reflux?
1) May occur after spontaneous transient lower esophageal sphincter relaxations not associated with swallowing
2) GERD - decreased lower esophageal sphincter pressure that leads to increased passage of stomach contents into the esophagus
3) Resting pressure of lower esophageal sphincter normal range from 15-35mmHg above gastric baseline pressure
Where is the stomach located and what does it do?
It is a large, muscular organ located in the upper abdomen that stores and partially digests food
What is the wall of the stomach lined with?
Gastric muscosa (muscous membrane) that contains gastric glands - Secrets mucus to protect stomach lining from highly acidic juices (pH 2)
What are chief cells?
They are located in gastric glands of the stomach that synthesize pepsinogen
- They are converted to pepsin when in contact with stomach acid and break down proteins
What are parietal cells?
Present within gastric glands of the stomach which synthesize and release HCl
- Alters pH of stomach and kills bacteria
- Intrinsic factor necessary for B12 absorption
What is chyme? Where does it travel to?
Stomach churning and enzymatic activity produces acidic, semi-fluid mixture of partially digested food
- Passes into first segment of small intestine (duodenum) through the pyloric sphincter
What occurs in the small intestine? What is the small intestine composed of? Describe the process:
Chemical digestion is completed here
- Highly adapted for absorption
- 6m long
- Villi
Composed of:
1) Duodenum
2) Jejunum
3) Ileum
Process:
- Amino acids, etc. pass through villi into the capillary system
- Blood enters portal system of liver which is detoxified and stripped of nutrients
- Fatty acids pass through lacteals and reconverted to triglycerides in the liver
Where does most digestion occur in the small intestine?
Duodenum
- Secretions of intestinal glands, pancreas, liver, and gallbladder mix with acidic chyme entering the stomach
What does intestine mucosa secrete?
Lipases, aminopeptidases, and disaccarides
What are the digestion hormones?
1) Gastrin: Produced in G-cells of duodenum which stimulates histamine and pepsinogen secretion and increased gastric blood flow
- Stimulates parietal cells to produce HCl which denatures proteins and activates digestive enzymes
2) Intrinsic Factor: Secretion of parietal cells that facilitate absorption of vitamin B12 across intestinal lining
3) Cholecystokinin (CCK): Produced and stored in the I-cells of duodenal and jejunal mucosa
- Involved in stimulation of pancreatic enzyme and somatostatin secretion as well as gallbladder contraction
- Hunger suppressant
4) Secretin: Synthesized and stored in the S-cells of upper intestine; stimulates secretion of bicarbonate containing substances from the pancreas and inhibits gastric emptying and gastric acid production
How does the liver aid in digestion?
Produces bile that is stored in the gallbladder before being released into the small intestine
- Bile has no enzymes; it emulsifies fats, breaking down globules into droplets
- This exposes a greater surface area of fat to the action of pancreatic lipase
- Without bile = no fat digestion
What is another functions of the liver?
Storage of glycogen, conversion of ammonia to year, protein synthesis, detoxification, and cholesterol metabolism
What is the function of the pancreas? What is its optimal pH?
Produces enzymes:
- Amylase for carbohydrate digestion
- Trypsin for protein digestion
- Lipase of fat digestion
Optimal pH:
- High (basic)
What happens when the pancreas releases chymotrypsin and enterokinase?
Enterokinase cleaves trypsinogen to trypsin
- Trypsin cleaves and activates other zymogens (enzyme precursors)
-
What does the pancreas secrete?
Bicarbonate-rich juice which neutralizes acidic chyme arriving from the stomach in the duodenum
What is the large intestines role?
Absorbs salts and water not already absorbed by small intestine
- 1.5m
- Rectum = storage for feces before elimination through anus
