Digestion

What are the four stages of food processing?

1. ingestion

2. digestion

3. absorption

4. elimination

What are the three types of ingestion?

1. filter feeding

2. fluid feeding

3. bulk feeding

What type of ingestion do humans do?

bulk feeding

What are the two ways in which digestion is carried out?

1. mechanical

2. chemical

mechanical digestion

taking big pieces of food and breaking them down into small pieces of food

ex: chewing

chemical digestion

molecules are being broken down
ex: enzymes that carry out hydrolysis

What are the two possible locations of digestion?

intracellular or extracellular

Unicellular, porifera, and cnidaria organisms undergo (intra/extra)cellular digestion.

intracellular digestion

Bilateria organisms undergo (intra/extra)cellular digestion.

extracellular digestion

What are the two main parts of the digestive system?

1. alimentary canal

2. accessory organs

alimentary canal

one-way tube with 2 openings (mouth & anus);

continuous with the outside;

has compartments

sphincters

smooth muscle valves between one compartment and another

What are the accessory organs of the digestive system?

• tongue

• salivary glands (3 major pairs)

• pancreas

• liver

• gallbladder

peristalsis

waves of smooth muscle contraction & relaxation that moves food

make the digestion of nutrients graphic organizer

In what way is the nervous system triggered before ingestion?

salivary secretion

The tongue forms a ____, or mass of food, and moves it for swallowing.

bolus

What is the path of a bolus?

oral cavity →
pharynx →
esophageal sphincter →
esophagus →
cardiac sphincter →
stomach

stomach wall

elastic & has folds

Gastric glands secrete…

gastric juice

What are the three cells that make up the gastric glands?

1. chief cells

2. parietal cells

3. mucous cells

What do chief cells produce?

pepsinogen

What do parietal cells produce?

HCl (pH ~ 2)

What do mucous cells produce?

mucus

What is the mechanical function of the stomach?

churning

What is the chemical function of the stomach?

HCl converts pepsinogen into pepsin

What is the main digestive enzyme of the stomach?

pepsin (an endopeptidase)

What breaks specific internal peptide bonds into smaller polypeptides (not amino acids)?

pepsin

The chyme that leaves the stomach is a mixture of…

• partially digested carbohydrates

• smaller polypeptides

• undigested material

What is the pH of chyme?

2

Chyme leaves the stomach through the…

pyloric sphincter

How long is the small intestine?

~ 6 meters long

Why is the small intestine called the “small” intestine?

small diameter

What are the 3 divisions of the small intestine?

1. duodenum

2. jejunum

3. ileum

Villi & microvilli increase…

surface area

villi and microvilli

projections of tissue;

exchange surface

What are the functions of the small intestine?

• mechanical digestion of fats

• chemical digestion

• absorption of nutrients & water

Fats are hydrophobic or hydrophilic?

hydrophobic

Why don’t the enzymes work on fats?

because the enzymes are hydrophilic

Where is bile produced?

liver

Where is bile stored?

gallbladder

Bile is released through the…

bile duct

After bile is released through the bile duct, where does it go?

into the duodenum of the small intestine

What do bile salts do?

emulsify fats;

large masses of fats → smaller droplets of fat

The emulsion of fats increases…

surface area

Why is the use of bile in digestion mechanical and not chemical?

bile does not use enzymes (chemical) to break down the fat molecules into their chemical building blocks, it physically (mechanical) divides them into smaller physical pieces

How does the small intestine mechanically digest fats?

bile

How does the small intestine chemically digest foods?

• pancreatic juice

• intestinal epithelium

Pancreatic juice moves through a duct into the…

duodenum of the small intestine

What is in pancreatic juice?

• bicarbonates

• several enzymes

aminopeptidases

enzymes that cleave single amino acids at the amino end

carboxypeptidases

enzymes that cleave single amino acids at the carboxyl end

What does the intestinal epithelium have in it?

enzymes

dipeptidases

hydrolyze dipeptides

Where does nutrient absorption occur in the small intestine?

intestinal villi

Why are intestinal villi an exchange surface?

nutrients use it to go from intestinal lumen to the bloodstream

What three processes are involved in the absorption of water and nutrients in the small intestine?

1. simple diffusion

2. facilitated diffusion

3. active transport

SEQ & draw the breakdown and absorption of lipids

What organ gets first access to nutrients from the small intestine?

liver

Through what structure does the liver get first access to nutrients from the small intestine?

hepatic portal vein

What are the three main functions of the liver?

1. convert glucose → glycogen

2. synthesize protein

3. inactivate toxins

At the end of the small intestine, most nutrients are…

absorbed

What is left at the end of digestion in the small intestine?

• undigested material

• indigestible material

• dead cells & bacteria

• bile salts

Why is the large intestine called the “large” intestine?

large diameter

What are the 4 divisions of the large intestine?

1. ascending colon

2. transverse colon

3. descending colon

4. sigmoid colon

What are the functions of the large intestine?

• water absorption

• host bacteria that produce vitamin K, B₁, B₂, B₁₂

• elimination of digestive waste as feces