digestive

what are the 4 main feeding mechanisms for animals?

filter feeding, substrate feeding, fluid feeding, and bulk feeding

what does intracellular digestion mean?

digestion within the cell

how is food broken down in intracellular digestion?

Food is usually phagocytized,
and fuses with food vacuoles
and lysosomes to break down nutrients

What does extracellular digestion mean?

digestion outside the cells

what are a network of fat and connective tissue that serve as the digestive system through structural support, fat storage, and by providing a framework through which blood supply, nerves, and the lymphatics can reach various locations

mesenteries

What is the monomer for starch?

glucose

What is the monomer for proteins?

amino acids

What is the monomer for fats?

fatty acids

What is the monomer for nucleic acid?

nucleotides

All digestive enzymes cleave ______ bonds.

specific

salivary amylase breaks down which molecules?

starch into maltose by breaking starch's a-glycosidic bonds.

What creates a bolus which is swallowed, and also increases the surface area of food, thus exposing it to more enzymes

chewing

What is the area where food and air passages cross?

pharynx

what is a flap of tissue that blocks the trachea so only solid and liquid enter the esophagus

epiglottis

How does food move from the esophagus to the stomach?

peristalsis

Of what does gastric juice consist?

digestive enzymes and HCl

Through what opening does food enter the stomach?

lower esophageal/cardiac sphincter

Where are the secretory cells of the stomach located?

gastric pits

The stomach contains accordion-like folds that allow for how much storage?

2-4 liters

food + water + gastric juice + mixing = what?

chyme (a creamy medium)

What is the process of physical breakdown in the stomach?

muscles are activated to break down food; HCl denatures proteins and kills bacteria

What are caused by failure of mucosal lining to protect stomach tissue?

peptic ulcers

What are stomach conditions that can induce a peptic ulcer?

- excess stomach acid
- H. pylori (antibiotics to treat)

Through what opening does chyme enter the small intestines?

the pyloric sphincter

What cells in the stomach secrete mucous?

mucous cells

What is the function of the secreted mucous in the stomach?

lubricates and protects stomach's epithelial lining from acid environment

What substance is composed of mainly sticky glycoproteins and electrolytes?

mucous

What cells in the stomach secrete pepsinogen?

chief cells

What is the zymogen precursor to pepsin?

pepsinogen

What activates the zymogen, pepsinogen, to pepsin?

low pH of stomach (acidity)

What substances does pepsin help digest?

proteins

What cells in the stomach secrete HCl?

parietal cells

What cells in the stomach secrete intrinsic factor?

parietal cells

What substance assists the ileum's B-12 absorption?

intrinsic factor

What cells in the stomach possess many mitochondria for energy to establish proton gradient?

parietal cells

(Note: proton gradient
needed for HCl secretion)

What cells in the stomach secrete gastrin?

G cells

What is a large peptide hormone which is absorbed into blood and stimulates parietal cell to secrete HCl?

gastrin

Which cell types in the stomach are stimulated to increase secretion in response to increased acetylcholine levels?

all cell types

What substance do gastrin and histamine increase secretion of in the stomach?

HCl

What are the neuroendocrine cells in the digestive tract?

ECL cells

gastrin stimulates which cells to release histamine?

ECL cells

(Note: in turn stimulates parietal cells to produce gastric acid)

A full stomach's pH is what?

2

(Note: extremely acidic)

Why does the stomach have a low pH?

beneficial for killing ingested bacteria, and is the optimal pH for pepsin!

Folds in the stomach are called what?

Rugal folds/rugae

What is the function of the rugae?

increase surface area of the stomach lumen

Protein digestion begins where?

stomach

Where does protein digestion take place?

intestines

What are the 3 portions of the small intestine?

1. Duodenum
2. Jejunum
3.Ileum

Which portion of the small intestines continues breakdown of starches and proteins as well as remaining food types (fats and nucleotides)

Duodenum

Which portion of the small intestines is the middle portion concerned with the absorption of nutrients?

Jejunum

Which portion of the small intestines is concerned with the absorption of nutrients, and is the longest portion?

Ileum

Which portion of the small intestines contains Peyer's patches?

Ileum

What are Peyer's patches?

large aggregates of lymphoid tissue

Where does 90% of digestion and absorption occur for the digestive system?

small intestines

how are the small and large intestines connected?

ileocecal valve

The wall of the small intestines has finger-like projections called what?

villi

(Note: increase surface area!)

Each villi have a lymph vessel called what?

lacteal

each lacteal in the villi of the small intestines is surrounded by what?

capillary network

(Note: function for nutrient absorption)

What are the even smaller protrusions on villi named?

microvilli

(Note: allow for even
greater surface area)

Which cells in the small intestines secrete mucus to lubricate and protect from mechanical or chemical damage?

goblet cells

What is the duodenum's pH?

~ 6

Why is the duodenum's pH (~6) higher than the stomach's pH (~2)?

bicarbonate ions secreted by pancreas

(Note: act as buffer)

proteases, disaccharidases, lipases, nucleotidases, phosphatases, and nucleosidases are known as what?

proteolytic enzymes

What organ secretes bicarbonate and acts as an exocrine gland in the digestive system?

pancreas

From where does the pancreas release major enzymes?

- acinar cells produce
- pancreatic ducts secrete

Into which portion of the small intestines does the pancreas secrete?

duodenum

What are the key enzymes of the pancreas?

trypsin, chymotrypsin, lipase, pancreatic amylase, and deoxy/ribonucleases

When enzymes are produced by the pancreas, what aggregate do they get secreted into?

pancreatic juice

(Note: alkaline solution because of bicarbonate ions secreted by the pancreas)

Why does the pancreas secrete bicarbonate?

acidic chyme needs to be neutralized to allow enzymes to get activated

In what form do the key enzymes of the pancreas exist?

zymogens/proenzymes (inactive)

What is the first key enzyme of the pancreas to get activated?

trypsin

(Note: activated trypsin activates the other enzymes)

What organ produces bile in the digestive system?

liver

What enzymes activate trypsin in the duodenum?

enterokinases

(Note: located in the brush border of the duodenum)

What does bile contain?

bile salts (like sodium bicarbonate)

(Note: to help emulsify fats)

Where is bile stored?

gallbladder

How does bile get from the gallbladder to the duodenum?

- cystic duct (which merges with
the hepatic duct of the liver)
- common bile duct (which then
merges with the pancreatic duct)
- duodenum

What is the area called where the common bile duct and pancreatic duct meet to secrete into the duodenum?

sphincter of oddi

What is the process of bile secretion called?

biliary flow

What does the emulsification of fat accomplish?

breaks fat into small particles (without chemically modifying it) which exposes a greater surface area for lipase to work on

Where do amino acids and sugars go when they are absorbed by the small intestines?

capillaries

Where do fatty acids and glycerol go when they are absorbed by the small intestines?

lymphatic system (later to bloodstream)

By what mechanism does chyme move through the small intestines?

peristalsis

(segmentation mixes chyme with digestive juices)

Where in the digestive system is where water and salts are reabsorbed to form feces?

large intestine (colon)

How long is the large intestine?

~1.5 m

What are the 4 parts of the large intestine?

ascending, transverse, descending, and sigmoid

What is the major function of the large intestine?

water and electrolyte reabsorption

Where is feces stored?

end of large intestines in the rectum

Where is feces excreted through?

the anus

What does malfunction of the large intestine often lead to?

diarrhea

What is a healthy breakdown of the parts of feces?

75% water and solid mass which contains...
- 30% dead cells
- 10-20% fat
- 10-20% organic matter
- 2-3% protein
- 30% roughage (cellulose)/ undigested matter (sloughed cells)

What is at the beginning of the large intestines (before ascending colon)?

cecum

(Note: aid in cellulose digestion for herbivores)

What is the offshoot of the cecum with unknown function called?

appendix

What is a symbiont in large intestines which provide us with main source of vitamin K?

Bacteria (like E. Coli) a symbiont in large intestine = main source of vitamin K (also produce Vitamin B12, thiamin, riboflavin)

Bacteria (like E. Coli)

Besides vitamin K, what do bacteria like E. Coli produce in the large intestines?

- vitamin B-12
- thiamin
- riboflavin

What hormone is produced by the stomach lining when food reaches or upon sensing of food?

gastrin

What hormone is a local peptide hormone from the small intestine, produced by cells lining duodenum in response to HCl?

secretin

What hormone stimulates pancreas to produce bicarbonate (neutralizes the chyme)?

secretin

What hormone is secreted by small intestine in response to fat digestates?

cholecystokinin (cck)

What hormone stimulates gallbladder to release bile and pancreas to release its enzymes?

cholecystokinin (cck)

What hormone decreases motility of stomach, giving more time for duodenum to digest fat

cholecystokinin (cck)