bio 224 exam 3

digestive system

functions of the digestive system (6 items)

• ingestion- eating/drinking something

• mechanical digestion- does not change what the substance is, but just breaks it into smaller pieces.

  • Increases the surface area of food so chemical digestion occurs faster.

  • Includes chewing (also known as mastication), grinding, & churning

• chemical digestion- breaking chemical bonds. Makes big molecules into smaller molecules. This actually changes what the substance is

• secretion- the job of the accessory organs. Don’t move, but spit on food as it passes by

• absorption- the movement of nutrient molecules thru the digestive wall into the blood or lymph

• excretion/defecation- getting rid of the waste that couldn’t be absorbed or used

digestive organs & their mucosa (5 items)

(hint: there are mainly 2 types of mucosa for these organs, just know what differentiates the last 3 organs from each other!)

Food passes thru these

• oral cavity (strat. squam epi.)

• esophagus (strat. squam epi.)

• stomach (simp. col. epi / gastric pits)

• small intestine (simp. col. epi / plicae / villi / microvilli)

• large intestine (simp. col. epi / goblet cells everywhere)

accessory organs (3 items)

These don’t touch the food but secrete on it as it passes by

• salivary glands

• liver

• pancreas

layers of the digestive wall (from inner to outer) (4 layers)

• includes definitions of MALT, Peristalsis, Myenteric plexus, & mesenteries

• Mucosa- lots of epithelium & touches the food. Modified by the organ (mucosal modifications)

  • has MALT (mucosa associated lymphoid tissue), which is a lymphoid nodule

• Submucosa- areolar conn. tissue. Has blood, lymphatic vessels, & glands

• Muscularis externa: smooth muscle

  • has longitudinal layer & circular layer

  • Peristalsis- circular & longitudinal contractions. This is how we move food thru these organs.

  • Myenteric plexus- division of the ANS (works on its own). Aids in control of digestion by controlling the smooth muscle

• Serosa- serous membrane. abdomen (peritoneum). These sheets of serous membrane help hold the organs in place

  • Mesenteries- layers of serous membrane

peritonitis

inflammation of peritoneum. Common cause of death after abdominal surgery

oral cavity (what 3 parts does it include?)

• Includes…

  • hard palate- has bone & allows us to breathe while chewing

  • soft palate- has no bone

  • Uvula- end of the soft palate

Substances that make up teeth (3 substances)

• Define odontoblasts

• enamel- crystalized calcium phosphate. Noncellular & made of dead cells, so it can’t repair itself

• dentin- like bone but harder (more hydroxyapatite). NONCELLULAR

  • Odontoblasts- cells that make dentin. Nucleus in pulp cavity with the “arms” in dentin

• cementum- like mortar (dry glue) between bricks. anchors the tooth

Types of teeth (from front to back) (3 types)

• incisors- the teeth we cut with.

• canines- the “tearing” teeth. Strongly rooted into gums in order to tear with them

• molars- grinding/chewing teeth

  • 3rd molars (wisdom teeth)- can cause issues if not removed for most people (depends on the size of teeth or size of mouth)

The mucosa of the oral cavity is what type of tissue?

stratified squamous epithelium

vestibule

the area between the lips & teeth

bolus

the chewed up food that you swallow

Swallowing (aka deglutition) (location & phases)

• Takes place between the oral cavity & esophagus

• Phases of swallowing (it’s based on where the food is located)

  • Voluntary phase- can be controlled. Use the tongue to shove bolus to pharynx. (Voluntary because you can still spit out the bolus)

  • Pharyngeal phase- move the bolus into the esophagus

  • Esophageal phase- has peristaltic waves. Longest phase due to the long tube (the esophagus)

Esophagus

• Has smooth musc. & its mucosa is strat. squam. epi

• 10 inches long with the top third (3 inches) having skeletal muscle

  • this allows us to cough stuff out after entering the esophageal phase

• Known as the “bolus transport tube” as it takes abt 10 seconds for the bolus to travel to the stomach

chyme

a more liquid form of bolus. Allows for more surface area. This is what bolus becomes when it enters the stomach

Stomach

• know its function, the sphincters, what’s special about its muscularis externa, & rugae

• Function: changes bolus into chyme

  • bolus enters the stomach & leaves as chyme

• Smooth muscle sphincters:

  • Gastroesophageal (cardiac) sphincter- guards the entrance into the stomach

  • Pyloric sphincter- guards the exit from the stomach

• The stomach’s muscularis externa has an extra layer known as the inner oblique area.

  • this is the only digestive organ with this extra layer

• Rugae- folds in the organ’s wall that allow it to expand up to about 1 liter (on average for a normal stomach)

  • Can expand more thru training, as seen with competitive eaters

Stomach’s regions

• Fundus- the top, dome-shaped part

• Cardia region- where the bolus comes in

• Body region- the largest, main area of the stomach

• Pylorus- end of stomach

Stomach’s mucosa

• Know the gastric pit & each type of glandular cell

• Stomach’s mucosa is simple columnar epithelium

• Gastric pit- permanent pits (inward projections). Very deep & narrow. The stomach is the only one w/ gastric pits

  • different from rugae bc rugae is much larger

• Glandular cells- what the cells turn into at the bottom part of the gastric pit

  • parietal cells- make stomach acid (HCl)

  • chief cells- make digestive enzyme, pepsinogen

  • endocrine cells- make hormones

GERD

• gastroesophageal reflux disease.

• Stomach contents leak backwards into the esophagus

• Includes stomach acid from parietal cells

small intestine & its mucosa

• List the sections, its length, function, & the definition of plicae

• largest digestive organ (despite the name…)

  • “small” comes from this having a 1” diameter

• mucosa: simple columnar epithelium

• Sections:

  • duodenum - abt 1 ft long

  • jejunum - abt 8 ft long

  • ileum - abt 12 ft long (remember e for eat to not confuse it with the ilium bone)

• This organ is about 21 ft long while relaxed & 15-16ft long while still alive (bc different sections are contracted)

• Plicae- circular, permanent folds inside the small intestine. This is the part that looks wavy on the inside of the small intestine. (think of this as the wavy carpet)

  • Villi- small, finger-like projections on plicae. Think of this as the carpet fibers

    • Inside, villi have a cardiovascular capillary & lacteal (lymphatic capillary) for absorption

  • Microvilli- small, finger-like projections on simple columnar epithelium

• This organ deals with ABSORPTION

• has large surface area (thanks to folds & villi & microvilli) to do absorption as quickly as possible

What are the accessory organs to the small intestine?

liver & pancreas

Where are the liver, pancreas, & gallbladder located?

• Near the small intestine. They’re accessory to the duodenum

• In order from superior to inferior:

  • Liver

  • Gallbladder

  • Pancreas

Large intestine

• Know its length, function, mucosa, & structures (4 total)

• 2.5” diameter & 5 ft long

• Function: change chyme into feces by pulling water out of chyme. DEHYDRATES THE CHYME

  • If done too quickly, results in diarrhea (too much water remaining in feces) (watery feces)

  • If done too slowly, results in constipation (too much water removed from feces)

• Mucosa: simple columnar epithelium with LOTS OF GOBLET CELLS “gobs of goblets”

• Ileocecal valve- found in lower-right quadrant of abdomen. Sphincter guards the exit from ileum & entrance into colon (large intestine)

  • Cecum- the “dead end pouch”

    • if chyme moves up, it continues along the digestive tract. If it moves down, it reaches a dead end into the cecum

    • Some organisms have multiple of this, but we only have one.

  • Appendix- hangs off of the cecum

    • function is mainly unknown since it can be cut out with basically no issues

    • If inflamed, it can swell & rupture (extremely dangerous!)

• Taeniae coli- 3 striped on large intestine. Longitudinal muscle that helps move chyme (becomes harder to move as it becomes dry)

  • Pulling causes puckered appearance & forms pouches called haustrum

appendicitis

• inflammation of the appendix. Can swell & rupture. 50% chance of death when this occurs

• Treatment= cut it out

Path of chyme through the large intestine (5 parts)

as chyme moves on this path, it becomes more dry & harder to move

• ascending colon

• transverse colon

• descending colon

• sigmoid colon

• rectum

enzymes

• these are proteins

• These are “divas” because they’re picky about how they function (ex. need specific temperature & pH to function)

  • Some enzymes require coenzymes/vitamins in order to function properly

  • Other examples of what they may require are proenzymes & the presence of metals (ex. Fe or Zn)

• We need enzymes to break polymers into monomers because we can only absorb monomers!!

  • Enzymes perform chemical digestion by using water to split polymers

• If we don’t have a specific enzyme for a food molecule, then we can’t do anything with it.

  • This is why we can only break down some polysaccharides, proteins, etc.

    • ex. we can’t break down a plant’s cell wall because we don’t have enzymes for it

vitamins

these are coenzymes. Some enzymes require vitamins/coenzymes to be present in order to function

Hydrolysis

• lyse something by adding water to it.

  • this is NOT dissolving!!!

• This is carried out by hydrolase enzymes (our digestive enzymes)

Digestive enzymes that deal with CARBOHYDRATES (3 total)

• Name?

• Where is it made?

• Where does it work?

• What’s the reaction it makes happen?

• Salivary amylase- salivary glands; oral cavity; breaks polysaccharides into smaller polysaccharides

• Pancreatic amylase- pancreatic juice; small intestine; breaks polysaccharides into smaller polysaccharides

• Maltase, sucrase, lactase- intestinal brush border (microvilli); small intestine; breaks smaller polysaccharides into monosaccharides

Digestive enzymes that deal with PROTEINS (5 total)

• Name?

• Where is it made?

• Where does it work?

• What’s the reaction it makes happen?

• Pepsin- chief cells of gastric cells (secreted as prescursor pepsinogen); stomach; changes proteins into polypeptides & smaller polypeptides

  • this is the 1st enzyme to make polypeptides into smaller polypeptides

• Trypsin- pancreatic juice; small intestine; changes small polypeptides into smaller polypeptides (activates itself & other pancreatic enzymes)

• Chymotrypsin- pancreatic juice; small intestine; changes small polypeptides into smaller polypeptides

• Carboxypeptidase- pancreatic juice; small intestine; changes small polypeptides into smaller polypeptides

• Dipeptidase & tripeptidase- intestinal brush border (microvilli); small intestine; breaks small polypeptides into amino acids

Digestive enzymes that deal with LIPIDS (2 total)

• Name?

• Where is it made?

• Where does it work?

• What’s the reaction it makes happen?

• Gastric lipase- gastric glands; stomach; breaks triglycerides into free fatty acids & diglycerides

• Pancreatic lipase- pancreatic juice; small intestine; breaks triglycerides into free fatty acids & monoglycerides

Digestive enzymes that deal with NUCLEIC ACIDS (DNA/RNA) (1 total)

• Name?

• Where is it made?

• Where does it work?

• What’s the reaction it makes happen?

• Nucleases- pancreatic juice; small intestine; breaks nucleic acids into nitrogenous bases & simple sugars

Digestive enzymes in the ORAL CAVITY

• CARBS

  • polysaccharides —salivary amylase→ smaller polysaccharides

• PROTEINS

  • none

• LIPIDS

  • none

• NUCLEIC ACIDS

  • none

Digestive enzymes in the ESOPHAGUS

trick question! none for the esophagus :)

Digestive enzymes in the STOMACH (hint: only 2)

• CARBS

  • none

• PROTEINS

  • proteins —pepsin→ polypeptides & smaller polypeptides

• LIPIDS

  • triglycerides —gastric lipase→ free fatty acids & diglycerides

• NUCLEIC ACIDS

  • none

Digestive enzymes in the SMALL INTESTINE (hint: there are 7)

• CARBS

  • some polysaccharides —pancreatic amylase→ smaller polysaccharides

  • maltose, sucrose, & lactose —maltase, sucrase, & lactase→ monosaccharides

• PROTEINS

  • small polypeptides —trypsin, chymotrypsin, & carboxypeptidase→ smaller peptides

  • dipeptides & tripeptides —dipeptidase & tripeptidase→ amino acids

• LIPIDS

  • triglycerides —pancreatic lipase→ free fatty acids & monoglycerides

• NUCLEIC ACIDS

  • none

Digestive enzymes in the LARGE INTESTINE

trick question! none for the large intestine :)

How do we make stomach acid?

• Parietal cells in the gastric pit produce HCl (stomach acid). These pump out H⁺ (hydrogen ions)

  • Stomach acid is made to change pepsinogen to pepsin

• Parietal cells get this H⁺ thru this equation:

  • CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃^-

    • the H⁺ gets pumped out & helps lower pH to 1.5 or 2 to activate pepsin

The problem with lipids (includes definition of emulsified & micelle)

• The issue is that lipids can’t be efficiently digested/hydrolyzed until they have been emulsified

  • emulsified= forced to be in little globs (separated)

• Remember, lipids are “snobs” because they only get along with other lipids

  • Once you stop forcing lipids to be separated, they’ll get together again

• We use bile or bile salts (from the liver) to emulsify lipids

  • remember, liver is accessory to the small intestine

• Micelle- a lipid droplet surrounded by bile salts

Dual roles of the liver

• Makes bile salts

  • to emulsify lipids

• Detoxifies blood

  • hepatic portal vein- collects blood from abdominal, digestive organs & goes to the liver.

    • done to get rid of toxins before sending blood back to general circulation.

  • tissue in liver is set up with hexagon-shaped cells with a central vein in the middle

    • Has a trio of vessels on each corner (known as the portal triad)

      • hepatic arteriole- carries blood up

      • hepatic portal vein- carries blood up

      • bile duct- carries bile down

    • hepatic portal blood & arterial blood will meet & mix on their way to the central vein. Clears out toxins as they pass thru hepatic sinusoids since they’re beside hepatocytes

Dual roles of the pancreas

• Make & deliver enzymes

• Neutralize the acidic chyme

  • In other words, inc. its pH

  • duodenum can’t handle the low pH from stomach acid

  • uses bicarbonates & shoots it down the duct to neutralize the acidic chyme

    • Uses same chemical equation as the one to disguise CO₂ & make stomach acid

  • Pancreatic acini cells make the enzymes & bicarbonates

Control of some basic digestive processes (what is it controlled by?)

Controlled by…

• Nervous system (ANS Myenteric)

• Endocrine system (hormones)

3 phases of digestion (gastric/stomach secretion)

• Cephalic phase- takes place in the head. “food is on the way.” Prepares you for food

  • Triggered by sight, smell, or taste of food (it’s not in your stomach!)

  • Endocrine cells release gastrin to produce more stomach acid & more stomach churning

• Gastric phase- takes place in the stomach. “food is here”

  • Activated when the bolus arrives in the stomach

  • MORE GASTRIN!!

• Intestinal phase- takes place in the intestines. “food is leaving”

  • starts when the chyme enters the duodenum

  • Releases 3 hormones:

    • Secretin- stimulates secretion from pancreas & liver

    • Gastric Inhibitory Peptide (GIP)- inhibits acid secretion. slows down stomach activity

    • CCK (cholecystokinin)- stimulates secretion from pancreas & liver

      • when CCK hits the gallbladder, it will squeeze the gallbladder (the gallbladder holds bile)

absorption of carbs, proteins, & lipids (includes the definition of a chylomicron)

• To get absorbed, must move from chyme to blood or lymph

  • carbs & proteins: moves into blood. done by pumping monomers into the intestinal cell, then they diffuse out

  • Lipids: moves into lymph. Gets into intestinal cell by having micelle separate since bile salts are large proteins that can’t enter the intestinal cell. Bile salts stay left behind

    • Lipids enter intestinal cell easily because the cell membrane is made of lipids

    • These free lipids attach back together inside the intestinal cell

    • Throws new proteins (not bile salts) to surround the lipid to form a chylomicron. Gets spit out by exocytosis to enter lacteal

Absorption sites for various chemicals

Absorption occurs in areas other than the small intestine, but not much.

• Stomach absorbs…

  • around 20% ethanol (as long as there aren’t many lipids present)

  • a few drugs

• Large intestine absorbs…

  • water

  • potassium

  • sodium

  • a few vitamins or coenzymes

Defecation

• Know the definitions for feces & distention

• Feces- chyme after pulling out water, nutrients, etc

• Distention- feces pushing against the wall once it reaches the rectum

  • Causes reflex where the rectum & end of the colon contract (do peristalsis) & internal anal sphincter relaxes

    • internal anal sphincter is smooth muscle (involuntary)

  • External anal sphincter is skeletal muscle (voluntary)

Action of digestive hormones (site of production: stomach)

• Gastrin- inc. acid secretion

• Histamine- inc. acid secretion

• Serotonin- stimulates gastric motility

• Somatostatin- dec. acid secretion

Action of digestive hormones (site of production: intestines)

• Cholecystokinin (CCK)- stimulate secretion from pancreas & liver; cause the gallbladder to release bile

• Gastric inhibitory peptide- inhibits acid secretion

• Intestinal gastrin- stimulates acid secretion

• Motilin- stimulates migrating motor complex of the small intestine

• Secretin- stimulates secretion from pancreas & liver

• Vasoactive intestinal peptide- increase acid secretion; stimulate secretion from pancreas; inc. intestinal blood flow

emesis

Stomach contents move backwards. also known as vomiting.

peptic ulcers

an open sore on the inner lining of the stomach & the upper part of the small intestine

fecal transplant

transferring feces from a healthy donor to introduce them into a patient’s gastrointestinal tract. This is done to help introduce healthy bacteria, which can help control C. diff.

hepatitis

inflammation of the liver

cirrhosis

liver disease. It’s permanent scarring that damages the liver.

colitis

inflammation of the large intestine (colon)

pancreatitis

inflammation of the pancreas

pyloric stenosis

• a hardened pyloric sphincter, the stomach’s exit

• This narrows the exit, making it difficult for food to move into the intestines