Chapter 49 Digestive System Flashcards by Sameer Desai

What are the four steps of the GI tract?

1) Ingestion
2) Digestion
3) Absorption
4) Elimination

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What is ingestion?

Food is taken in through the mouth and swallowed to move through the GI tract

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What is digestion and what are the types?

Digestion is the breakdown of complex biomolecules into smaller ones
a) Mechanical Digestion: broken down by teeth
b) Chemical Digestion: broken down my enzymes and biomolecules (bile)

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What is absorption?

Food particles become small enough and are absorbed by epithelial cells

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What is elimination?

indigestible parts are removed and needed substances are reabsorbed (water and bile acids)

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What is the progression of the digestive system?

1) Mouth
2) Pharynx
3) Esophagus
4) Stomach
5) Small Intestine
6) Large Intestine
7) Rectum
8) Anus

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What are the accessory organs of the digestive system?

1) Salivary glands
2) Liver
3) Gallbladder
4) Pancreas
5) Appendix

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What does concentric mean?
What are the four concentric layers that line the gut (lumen)?

Wrapped around one another
1) Mucosa
2) Submucosa
3) Muscularis
4) Peritoneum

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What is the function of the mucosa and where is it located?

innermost epithelial cell layer
secretes digestive enzymes and hormones for digestion
secretes mucus to protect the gut
absorbs digested particles
Villi/Microvilli increase surface area and help with absorption

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What is the function of the submucosa?

supports overlying epithelium
contains blood vessels that supply GI tract with oxygen and nutrients
transports nutrients to rest of body
has nervous tissue with sensory and secretory functions

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What is the function of the muscularis?

made up of smooth muscle arranged circularly or longitudinally
contraction moves food (via peristalsis)
muscular sphincters can stop food
nervous tissue helps control contractions (acts independent of CNS)

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What is the function of the peritoneum and where is it located?

outermost layer of epithelial cell and attaches the GI to the rest of the body
has epithelial tissue which secretes fluid to reduce friction of organs in the body cavity

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What is the function of the enteric nervous system?

Nerve nets in submucosa and between smooth muscle make up the enteric nervous system
The nerves only form synapses with other nerves in the same enteric network.
Responsible for communication in the gut
CNS can influence this system, but it is autonomous

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What is the structure of the mouth and two mechanisms for breakdown of food?

1) Mechanical Breakdown: food broken down via teeth
a) Incisors: used for cutting, chopping, or gnawing
b) Canines: for stabbing, gripping, ripping
c) Molars: shearing, crushing, grinding
*Tongue is a skeletal muscle
2) Chemical Breakdown: food broken down via saliva
- Salivary Amylase: starch/carbohydrates –> glucose
- Results in a clump of food called a bolus

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What movements occurs in the pharynx?

Pharynx is the throat
Pharynx –> esophagus (via swallowing)
No digestion occurs here

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What is the function of the epiglottis?

Epiglottis prevents food from going into the trachea (part of the pharynx)
The epiglottis is the covering for the glottis (opening of windpipe)

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What is the function of the esophagus?

Muscular tube which food moves through to the stomach
Food is moved via peristaltic contractions
No digestion occurs here

How does peristalsis work?

Waves of muscular contractions move food toward stomach
When food reaches the smooth muscle in esophagus, the esophagus contracts and pushes the food toward the stomach

**the upper esophagus is skeletal muscle; the rest is smooth muscle

How does digestion in the stomach work and what are the parts in the stomach that facilitate it?

Esophagus empties food into the J-shaped stomach
Peristaltic waves push food through the stomach (churning/motility)
Sphincters (2 muscular rings) control movement into and out of the stomach

What are the two sphincters in the stomach and their functions?

1) Lower Esophageal Sphincter: (esophagus and stomach)
- relaxes and stomach fills with food
- contracts when stomach is full (limits input)
2) Pyloric Sphincter: (stomach and small intestine)
- relaxes as stomach fills with food
- contracts as strong peristaltic waves move food through it
- only a limited amount can enter intestine at once (4 hours)

What are the functions of the stomach?

1) Stores food
- stretches to accommodate food
2) Mixes food + acid = chyme
- Chyme is a semi-solid paste from bolus and gastric juices
3) Continues digestive processes
- Fat digestion begins here
- Carbohydrate and protein digestion continues here

**Only items absorbed in the stomach are alcohol, aspirin, and caffeine

What are the three main gastric secretions of the stomach?

1) Hydrochloric Acid (HCl) from parietal cells
- hydrolyzes chemical bonds & activates pepsinogen
- pH around 1 (acidic) which kills microorganisms and denatures proteins and requires stomach lining to be replaced every 3 days
2) Pepsinogen from chief cells
- converted to pepsin (digests protein) by low pH
3) Mucus
- lubricates stomach lining protecting it from acid

What enzyme is found in the stomach and how do the ions move?

Carbonic anhydrase catalyzes the dissociation of carbonic acid
- H+ is exchanged for K+ in gastric pit lumens
- H+ is constantly returned to the stomach

What is heartburn caused by and how can it be solved?

Heartburn occurs when the lower esophageal sphincter relaxes and excess acids flow up into your esophagus
Tums (antacid) weaken the stomach acid as they contain CaCO3, MgOH, AlOH, NaCO3
Drugs like Prilosec and Nexum (proton pump inhibitors) block H+ pumps in the stomach that produce acid

What are the parts and functions of the small intestine?

1) Duodenum (most digestion occurs here) - beginning of small intestine - site of secretion of pancreatic juices and bile - gets hit by gastric juices (common in peptic ulcers) 2) Jejunum: (absorption) - upper 40% of small intestine above duodenum 3) Ileum: (absorption) - lower part of small intestine

What moves food between the small and large intestine?

Ileocaecal Sphincter

What are the purposes of the small intestine?

1) Primary site of absorption 2) Site where accessory organs secrete products (liver, gallbladder, pancreas) 3) Site where lipid digestion begins 4) Where most digestion is completed

What structures in the small intestine help with absorption and how?

Villi: highly folded tissue Microvilli: epithelial cells with projections - Increase surface area for absorption

What do the cells lining the small intestine release?

1) Disaccharidase - disaccharides --> monosaccharides (carbs) 2) Peptidase - protein fragments --> amino acids 3) Nucleases - DNA/RNA --> nucleotides 4) Choleocystokinin (CCK): hormones released from intestinal mucosal cells - stimulates release of bile and pancreatic juices

What does the pancreas do and what does it produce?

The pancreas secretes digestive juices into the small intestine (duodenum) via the pancreatic duct. a) Bicarbonate: to reduce the acidity of gastric juices b) Enzymes: (functions best at neutral or slightly basic pH) 1) Pancreatic Amylase: polysaccharides --> disaccharides 2) Trypsin & Chymotrypsin: proteins --> protein fragments 3) Peptidase: protein fragments --> amino acids 4) Nucleases: DNA/RNA --> nucleotides 5) Lipase: triglycerides --> free fatty acids and glycerol **no digestion in the pancreas**

What do the liver and gallbladder do?

- synthesizes bile salts from cholesterol and secretes them as bile - bile stored in gallbladder - contains phospholipids and bilirubin - bile breaks down fats into micelles

What organs are present in the large intestine and what are their functions?

1) Cecum (pouch at beginning of large intestine) 2) Ascending Colon 3) Transverse Colon 4) Descending Colon 5) Anal Sphincter (allows for defecation) 6) Appendix - at beginning of large intestine - no known digestive function - may have role in immunity (good bacteria)

What are the functions of the large intestines?

1) absorbs almost all water 2) absorption of bile acids to be recycled 3) concentrates and stores fecal material (unwanted/undigestible waste)

What are the three ways that food in stomach is regulated?

1) Gastrin 2) Cholecystokinin 3) Secretin

How does gastrin function?

- Released as a stretching of the stomach from mucosal cells into blood Stimulates: 1) release of HCl and Pepsin (digestion) 2) Increased stomach contractions (churning) *HCl has negative feedback, low pH = low gastrin

How does cholecystokinin(CCK) function?

- Released from small intestine mucosa when fat/lipid enters duodenum Stimulates: - release of bile by gallbladder and pancreatic enzymes **CCK has negative feedback, decreases churning

How does secretin function?

- Released by duodenum mucosa when chyme reaches small intestine Stimulates: - Release of pancreatic bicarbonate which neutralizes HCl **Secretin has negative feedback, decreases churning

What is energy?

capacity to do work

What is a calorie? What is a kilocalorie?

A calorie is the amount of heat needed to raise 1 gram of water by 1 degree Celsius - 1 kcal = 1000 calories - 1 Cal = 1 kcal

What are the basal expenditures for male and females?

Female: 1300-1500 cal/day Male: 1600-1800 cal/day **Exercise increases this number