Module 2 - Digestion Flashcards by lily diep

What are the two groups of organs of the digestive system? Which organs are included in each group?

GASTROINTESTINAL (digestive) TRACT
mouth, pharynx, esophagus, stomach, small and large intestine
ACCESSORY ORGANS
teeth, salivary glands, liver, gallbladder, pancreas

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What is the function of the digestive system?

the function of the digestive system is the digestion and absorption of food. Digestion is the breakdown of food into small molecules, which are then absorbed into the body

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What are the 6 major digestive processes? ISPDAD

Ingestion
Secretion 
Propulsion (peristalsis)
Digestion (chemical &amp; mechanical breakdown)
Absorption
Defacation

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What is mechanical breakdown?

movements that reduce particle size i.e teeth grinding, stomach churning, intestinal segmentation

PRECEDES chemical digestion to make it more efficient

increases surface area of food to increase access by digestive enzymes

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What is chemical digestion?

the break down of large macromolecules into smaller molecules using enzymes

Proteins (PROTEASES) amino acids
carbs/starch(AMYLASES)simple sugars i.e glucose
fats/triglycerides(LIPASES)monoglycerides and fatty acids

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What are the 4 gastrointestinal tract wall layers?

mucosa - innermost epithelium and muscle layer
submucosa - areolar CT layer containing blood vessels, glands and the submucosal nerve plexus
muscularis - longitudinal and circular (oblique muscle in stomach) myenteric nerve plexus
serosa outer (=visceral peritoneum)

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What is the peritoneum? what is it composed of?

the largest serous membrane of the body

composed of:

visceral layer: adheres to organs of the abdominal cavity (forms the serosa of the digestive tract)

parietal layer: attaches to the wall of the abdominal cavity

omentum: peritoneum covering small intestines and colon, contains lymph nodes and stores fat
mesentery: peritoneum that holds small intestines in place

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What is the mouth (oral cavity) formed by?

formed by:

cheeks
hard palate (maxilla and palatine bones)
soft palate (muscle tissues)
tongue (skeletal muscle)

extends from the mouth opening to the oropharynx

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What are the salivary glands? How many pairs are there and what are they called?

exocrine glands that lie outside the mouth and secrete saliva through ducts into the oral cavity

There are 3 pairs and they are the PAROTID, SUBMANDIBULAR, SUBLINGUAL

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What is saliva and what are the 5 different components? how is it regulated?

there is about 1000-1500mL produced a day

water (99%) - moistens mucous membranes; softens food for swallong
mucus: lubricates the mucous membranes, binds food into a bolus
salivary amylase: enzme that starts carbohydrate digestion
lysozyme: kills bacteria
bicarbonate: buffers (reduces acidity of) acidic food

release is regulated by the AUTONOMIC NERVOUS SYSTEM (in response to touch, smell or thought of food)

parasympathetic nerves stimulates saliva release for swallowing and speech
sympathetic nerves inhibit saliva release during stress and during sleep (dry mouth)

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What are the two digestive processes in the mouth and how do they work?

mechanical digestion

mastication (chewing) involves the teeth and tongue
food is maneuvered by the tongue, ground by the teeth, mixed with saliva, and shaped into a “bolus” (round ball) for swallowing

chemical digestion
-salivary amylase –> starts carbohydrate breakdown in the mouth

Starches (large chains of glucose) are converted into disaccharides (maltose), trisaccharides, and short chains (5-20) glucoses called dextrins

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What is the esophagus and what is the function?

a muscular tube (skeletal and smooth muscle)

lies posterior to the trachea

connects the pharynx to the stomach

passes through the diaphragm

NO digestive or absorptive function

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How does swallowing work? and what are the 3 phases?

passage of food from mouth to stomach takes about 4-8 seconds; liquids take ~1 second

three stages:
1. voluntary phase - the bolus of the food is moved to the back of the mouth by the movement of the tongue

pharyngeal phase - as food moves through the pharynx: breathing stops, the nasopharynx is blocked by the soft palate and uvula, the larynx is blocked by the epiglottis
esophageal phase - food moves through the esophagus by peristalsis = alternating waves of muscular contraction and relaxation, squeezes food from one part of the system to the next

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how does peristalsis work?

circular muscle above contracts to push the bolus downwards
longitudinal muscle below contracts to shorten and widen the esophagus
the wave of contraction continues as the bolus moves into the new section

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What is the stomach and what is its function? What are the 4 main regions? What are the two sphincters and what are their functions?

J-shaped enlargement of the GI tract

4 main regions: cardia, body, fundus, pylorus

temporary storage for food

3 muscle layers: circular, longitudinal and oblique

sphincters:

formed by a ring of a smooth muscle
lower esophageal sphincter - regulates entry of food into the stomach and prevents esophageal reflux
pyloric sphincter - regulates movement of stomach contents into the intestines

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What are the 5 different types of gastric gland cells and what are their functions?

surface mucous cell (secretes mucous)

mucous neck cell (secretes mucus)

parietal cell (secretes hydrochloric acid and intrinsic factor)

chief cell (secretes pepsinogen and gastric lipase)

G cell (secretes the hormone gastrin)

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What are the 6 gastric gland secretions and what are their functions?

PEPSINOGEN - an inactive enzyme that is converted to PEPSIN once released into the stomach (breaks down proteins)

HYDROCHLORIC ACID - converts pepsinogen to pepsin; kills microorganisms

INTRINSIC FACTOR - required for the absorption of vitamin B12 - important in the manufacture of erythrocytes

MUCOUS - protects the stomach wall from gastric acid

GASTRIN - a HORMONE that stimulates (1) HCL and pepsinogen release, (2) gastric motility and (3) relaxes the pyloric sphincter to promote stomach emptying

GASTRIC LIPASE - enzyme for fat (triglyceride) breakdown into diglycerides and fatty acids

What are the two ways of digestion in the stomach and how do they work?

entry of food into the stomach (distention, pH change) stimulates:

MECHANICAL DIGESTION

muscle contractions mix food with gastric juice to produce chyme - a semi-liquid paste of partially digested food
peristaltic waves push a small amount of chyme through the pyloric sphincter into the duodenum

CHEMICAL DIGESTION

start of protein breakdown
stomach acid (HCl) denatures food proteins, i.e it unravels the protein structures
pepsin breaks down proteins into shorter chains, called peptides, by hydrolyzing peptide bonds. It is optimized to work at about a pH 2 (acidic conditions)
gastric lipase aids digestion of triglycerides

What does the small intestine include (3 items) and what are its functions?

includes the duodenum (25 cm)
jejunum (1m)
ileum (2m)

2-4 hours after eating, most stomach contents have entered the small intestine

Functions of the small intestine:

completion of chemical digestion
requires: slow wall movements (mechanical digestion) and enzymes, optimized to work at a pH8 (alkali conditions)
90% of nutrient absorption happens here

How does mechanical digestion work, what does it require?

segmentation –> alternating contractions of circular muscle that mix contents with digestive juices, but do not move them forward

followed by peristalsis once most of the meal is absorbed

a peristaltic wave starts in the stomach and reaches the distal end of the ileum in 90-120 minutes and then another wave starts in the stomach

How does chemical digestion work, what does it require?

enzymes from the pancreas and intestinal epithelial (brush border) cells
bile (contains bile salts for the efficient digestion of fats)
alkaline pH (for enzyme function)

What is the importance of bile in lipid digestion?

bile is a yellow/green substance produced by the liver and stored in the gallbladder
it contains bile salts which have detergent-like properties that emulsify lipids
emulsification simply means turning large fat droplets into many more smaller droplets
emulsification accelerates the rate at which the enzyme LIPASE (in pancreatic juice) can chemically breakdown triglycerides into diglycerides and monoglycerides ready for absorption

What does the small intestine absorb?

monosachharides (simple sugars - glucose, galactose, fructose)
amino acids, dipeptides and tripeptides
fatty acids and monoglycerides
ions and water
bile salts
fat soluble vitamins A, D, E, K
vitamin b12

What is the absorption in the small intestine dependent on? What 3 things affect this?

absorption in the small intestine is surface area dependent

circular folds - folds that cause chyme to spiral and mix
villi - projections of the mucosa
microvilli - projections of individual columnar epithelial cells (also called the “brush border”)

absorption requires specific transport mechanisms

glucose and galactose --> secondary active transport with Na+ --> monosaccharides fructose --> facilitated diffusion ---> monosaccharides amino acids --> active transport or secondary active transport with Na+ --> amino acids --> diffusion dipeptides and tripeptides --> secondary active transport with H+ --> diffusion small short-chain fatty acids --> simple diffusion --> diffusion --> triglyceride to blood capillary of a villus --> to hepatic portal vein ---> to liver _______ALL ABOVE TO LIVER_______________ micelle - large short chain and long chain fatty acids and monoglycerides --> simple diffusion --> triglyceride -->to lacteal of a villus --> lymphatic system --> blood

How does the transport of absorbed lipids work?

- large fats form chylomicrons for transport - enter lymphatic vessels (called lacteals) in the villus - carried via the lymph to the circulation (via thoracic duct to left subclavian vein)

How does the transport of other nutrients work?

- all other nutrients enter blood capillaries in the villus | - carried first to the liver via the hepatic portal vein then on to the general circulation

What is the pancreas and where is it located?

it lies behind the stomach and within the curve of the duodenum - composed of acinar cells (exocrine cells) - comprise 99% of pancreatic cells - secrete digestive juice into the pancreatic duct --> duodenum

What do pancreatic secretions contain?

1. enzymes (i.e pancreatic amylase, lipase, proteases, etc.) 2. bicarbonate (increases pH in the duodenum (neutralizes gastric acid) - protects duodenal wall - activates pancreatic enzymes - inactivates pepsin (from the stomach)

Where is the liver located?

it is located below the diaphragm mainly on the right side RUQ divided into left and right lobes receives nutrient rich blood from the small intestine via the hepatic portal vein receives oxygen rich blood from the heart via the hepatic artery

The liver has dual blood flow

blood supply feeding liver cells with oxygen and removing CO2 and nutrients coming from gut for processing by the liver

what are the 6 functions of the liver?

1. production of bile containing bile salts 2. carbohydrate, fat and protein metabolism 3. processing and the inactivation of drugs and hormones 4. excretion of bilirubin (in bile) 5. storage of vitamins and minerals 6. activation of vitamin D

What is the galbladder and what is its function?

a muscular sac that hangs from the lower front margin of the liver - functions to store and concentrate bile produced in the liver - releases pulses of bile in response to fat digestion

What is bile?

- contains water, bile salts, cholesterol, bilirubin and electrolytes - released from the gallbladder when fats enter the duodenum - the common bile duct joins with the pancreatic duct --> enzymes and bile enter the duodenum together - bile salts break down fat globules into smaller droplets which therefore have increased surface area (=emulsification) this then accelerates the rate of fat digestion by pancreatic lipase

What are gallstones? how do they form?

also known as cholelithiasis - lumps of hardened bile - can form anywhere in the biliary tree - risk factors: high blood cholesterol, age, twice as common in females, obesity, diet, lots of saturated fat and refined sugar

Clinical manifestations of cholelithiasis

frequently asymptomatic abdominal pain and jaundice = yellowing of the skin an sclera -pain occurs 30 mins to several hours after eating a fatty meal: caused by the lodging of one or more gallstones in the cystic and or common duct -treatment may include endoscopic removal of gallstones -jaundice indicates that the stone is lodged in the common bile duct since bile backs up into the liver, increasing bilirubin levels in the blood -lodging of a stone in the cystic duct will cause cholecystitis = inflammation of the gallbladder

What is the large intestine and what are the 7 parts of it?

- extends from the ileocecal sphincter to the anus includes: - cecum - ascending colon - transverse colon - descending colon - sigmoid colon - rectum - anal canal

What is the large intestine structure?

- glands dip down into the mucosa --> mainly mucous production - no villi or circular folds (reduced absorption)

What are the 3 functions of the large intestine?

1. bacterial digestion - produce vitamin K and some B vitamins - ferment remaining carbohydrates (flatulence) - decompose bilirubin (gives feces brown color) 2. production of mucous for lubrication of intestine contents 3. water and ion absorption

CARBOHYDRATE DIGESTION

starch and disaccharides

PROTEIN DIGESTION

proteins

LIPID (FAT) DIGESTION

unemulsified triglycerides