Chapter 17- Digestion Flashcards
Heterotropic
Animals
Unable to synthesize their own nutrients
Intracellular digestion
Occurs within the cell, usually in membrane bound vesicles
Extracellular digestion
Digestive process that occurs outside of the cell, within a lumen or a tract
In unicellular organisms, food capture is effected primarily by:
Phagocytosis
When do food vacuoles form?
Immediately after digestion
How does ingestion occur in amoeba
Pseudopods surround and engulf food (phagocytosis) and enclose it in food vacuoles.
digestion in amoeba
Contain digestive enzymes fuse with food vacuole in amoeba and release their digestive enzymes that act upon the nutrients- resulting simpler molecules diffuse into the cytoplasm
Excretion in amoeba
Eliminated from the vacuole
Ingestion in paramecium
Cilia sweep food into the oral groove and cytopharynx- a food vacuole forms around the lower end of the cytopharynx, which breaks off and goes to the anterior of the cell
Digestion in paramecium
Enzymes are secreted into the vacuole and the products diffuse into the cytoplasm
Excretion in paramecium
Solid wastes are expelled at the anal pore.
Physical breakdown
Multicellular organisms– in mouth and churning in digestive tract
Chemical breakdown in invertebrates
Accomplished by enzymatic hydrolysis
Digestion in cnidarians
Both intra and extracellular
Use tentacles to ingest and release particles into cup-like sac
Enzyme secreted into cavity from endodermal cells
Digestion mostly extracellular- but once food is reduced to small fragmets, the gastrodermal cells engulf nutrients and digestion is completed intracellularly.
Undig. food expelled through mouth
Digestion in annelids
One way tract- mouth to anus
Specializedparts
Mouth, pharynx, esophagus, crop (stores food), gizzard (grinds food), intestine (increase surface area- hypholosole) and anus
Soluble food passes thorough walls of small intestine to the blood thru diffusion
Digestion in arthropods
Similar to earthworm. Jaws for chewing and salivary glands to improve food digestion
Human digestive tranct
Oral cavity pharynx esophagus stomach small intestine large intestine the anus
Accessory organs of the digestive tract
Salivary glands,pancreas, liver, gall badder
Oral cavity in human
Mechanical (mastication) and chemical digestion of food begins
Chemical- saliva lubricates food and contains amylase (ptyalin)- hydrolyzes starch to maltose.
Esophagus
Muscular tube leading from the moth to the stomach
Perstalsis
How food is moved down the esophagus
Rhythmic waves of involuntary muscular contractions
Where does the body of the esophagus lie?
Within the thoracic cavity, which is negatively pressured on inhalation.
Abdominal cavity positive pressure gradient
GERD
occurs when pressure gradient favor a continual gastric materials into the esophagus.
Gastroesophageal reflux
How may GERD occur
Spontaneous lower esophageal sphincter relax- not associated with swallowing
Resting pressure of lower esophageal sphincter goes owe gastric baseline pressure
What is the stomach and where is it located
A large muscular organ located in the upper abdomen
What does the stomach do?
Stores partially digested food
What are the walls of the stomach lined by?
Gastric mucosa- which contain glands that secrete mucus
What does mucus in the stomach do?
Protects the stomach lining from the harshly acidic juices present in the stomach.
Glands in the gastic mucosa also secrete
Pepsin, a protein hydrolyzing enzyme, and HCl, which kills bacteria and breaks down food and also activates proteins
Chief cells
Synthesize pepsinogen
Parietal cells
Synthesize and release HCl and intrinsic factor
Churning of the stomach produces:
an acidic semifluid mixture and partially digested food known as chyme0 which passes into the first segment of the small intestine, the duidenum, thorugh the pyloric sphincter
Chemical digestion is completed in
The small intestine
The small intestine is divided into
duodenum
jejunum
ileum
The small intestine is highly adapted to:
Absorption
Villi
Fingerlike projection that increase the surface area of the small intestine that extend out of the intestinal wall.
What do the villi contain?
Capillaries and lacteals
Amino acids and monosaccharides pass through the villi walls into the:
capillary suystem
Large fatty acids and glycerold pass into the
Lacteals and are then reconverted into fats
What nutrients are actively absorbed and which ones are passively absorbed?
Actively- glucose and amino acids
Passively- rest of them
Where does most of the digestion occur in the small intestine?
the duodenum, where secretions of the intestinal glands, pancreas, liver, and gall bladder mix together with the acidic chyme entering from the stomach.
Lipase
Secreted by the intesinal mucosa- for fat digestion
Aminopeptidases
Secreted by the intesinal mucosa- for polypeptide digestion
Disaccharideases
Secreted by the intesinal mucosa- for maltose, lactose and sucrose digestion
Lactase
Disaccharidase- breaks down lactose or milk sugar
present in infants
Parietal cell secrete
HCl and intrinsic factor
Gastrin
Produced in the G cells of the duodenum, stimulates HCl, histamine, and pepsinogen secretion as well as increase gastric blood flow.
What happens after gastrin stimulates parietal cells
Release of HCl, which denatures proteins and activates digestive enzymes
Intrinsic factor
absorption of vitamin B12
Cholecystokinin
Produced in the I cells of the duodenal and jejunal mucosa
Involved in stimulation of pancreatic enzymes stores in the S cells of the upper intestine
Stimulates the secretion of bicarbonate-containing substances from the pancreas and inhibits gastric emptying and gastric acid production
Liver
produces bile
gall bladder
stores bile before releasing it to the small intestine
What does bile do?
does NOT contain enzymes, it emulsified fats, breaking down large globules into small droplets.
Why is fat emulsified?
It exposes fats to a greater surface area to the action of pancreatic lipase.
If there is not bile
Then fats cannot by digested
Other functions of the liver:
Storage of glycogen, conversion of ammonia to urea, protein synthesis, detoxification and cholesterol metabolism.
Pancreas
Produces amylase, trypsin and lipase
Releases chymotrypsin and enterokinase, which cleaves chymotrypsin to make trypsin
What does trypsin do
cleaves and activates other zymogens
How does the pancreas neutralize acidic chyme?
It secretes a bicarbonate-rich juice
Large intestine
Absorbs salts and water not already absorbed by small intestine.
Rectum
Stores feces before elimination though anus
Plants and digestion
Have no digestion system
Intracellular digestion in plants
Stores insoluble polymers, starches, lipid, and proteins in the cell
Starch
Found in seeds, stems and root
principal storage food
Is a glucose polysaccharide
When nutrients are required in plants,what happens?
Hydrolysis (enzyme) break down storage polymers into simpler molecules
Extracellular digestion in plants
Used by fungi
Rhizoids
In bread mold
Saprophyte lives on dead organic material that secretes material int othe bread
Digestion produces simple and soluble products that are absorbed by diffusion.
Fungi
Heterotrophic- get nutrients from the environment