Digestive Chemicals

Nutrient Breakdown

- carbohydrates → glucose
- protein → amino acids
- fats → fatty acids + glycerol
- nucleic acids → nucleotides

Mouth Exocrine Function

- pH = 7, temperature = 37oC
- salivary glands secrete
enzyme salivary amylase
- digestion of starch → maltose

Stomach Exocrine Function

-pH = 2, temperature = 37oC
- gastric juice = enzyme pepsinogen + HCl (acid) + mucus
- pepsinogen + HCl = enzyme pepsin (3D shape activated by acid)
- digestion of proteins → dipeptides/polypeptides
- secretions of mucus from lining protect against
corrosive effects of HCl (ulcers)
- lining regenerates every 3 days

Stomach Endocrine Function

- hormone gastrin secreted
in response to protein in stomach
- causes secretion of gastric juice

Pancreas Exocrine Function

- pancreatic juice = bicarbonate (NaHCO3) (basic)
- enzymes secreted by pancreas act in duodenum,
- enzyme pancreatic amylase digests starch → maltose
- enzyme trypsin digests protein → peptides
- enzyme lipase digests lipids → fatty acids + glycerol
- enzyme nuclease digests DNA and RNA → nucleotides
*centroacinar cells secrete bicarbonate
*basophilic cells secrete enzymes

Insulin Hormone

- ↑[blood glucose] triggers blood glucose uptake by target cells
(energy production) & stimulates liver to build glycogen from glucose
- destruction of cells producing insulin = diabetes I
- lack of insulin receptors on target cells = diabetes II

Glucagon Hormone

- opposite to insulin, ↓[blood glucose] stimulates liver to
release glucose by converting stored glycogen into glucose
hormones secreted by cells in
"islets of Langerhan"

Liver Exocrine Function

- secretes bile, a yellow/green basic fluid produced in liver
subunits (hepatocytes)
- composed of: water, cholesterol, pigment,
acids, phospholipids, bicarbonate, all
conjugated (held together) with salt
- bile salts have hydrophobic/hydrophilic
ends, form micelles around triglycerides
to separate them from larger lipid globules
- bile emulsifies (breaks down) fat which creates
large surface area for pancreatic enzyme lipase to work

Small Intestine Exocrine Function

- once enzymes secreted by pancreas into duodenum have
done their job, need more enzymes to complete digestion
- ileum pH = 8, temperature = 37oC
- enzymes secreted through interstitial
glands that sit on top of mucosal cells

maltase

digests maltose → glucose

peptidase

digests peptides → amino acids

nucleosidase

digests nucleotides → bases, sugars, phosphates

Small Intestine Endocrine Function

hormones secreted by cells in mucosal layer of duodenum

secretin

- released in response to acidic chyme
arriving from stomach
- causes pancreas to secrete bicarbonate
into duodenum

cholesystokinin (CCK):

- released in response to chyme rich in fatty acids,
cholesterol, amino acids arriving in duodenum
- causes pancreas to secrete enzymes, liver to secrete bile
into duodenum

enterogastrones
(general term):

oppose gastrin, inhibit stomach
peristalsis + gastric juice secretion

Large Intestine Bacteria

- anaerobic...die in presence of oxygen (ex. E. coli)
- break down indigestible material
- produce vitamins (K), amino acids, growth factors
- vitamins/nutrients absorbed by colon, used by body