CHAPTER 51 ~ Nutrition, Digestion, Absorption Flashcards
amino acids that humans need from Grains
Tryptophan, Methionine, Valine, Threonine, Phenylalanine, Leucine
amino acids that humans need from Legumes
Valine, Threonine, Phenylalanine, Leucine, Isoleucine, Lysine
human infants need what 4 extra amino acids?
histidine, tyrosine, cysteine, and arginine
why ingested proteins not just simply used “as is”?
macromolecules cannot be absorbed by epithelial cells lining gut; protein structure and function highly specific to species, so wouldn’t be compatible with humans’, and because foreign proteins would be attacked by immune system
Tissue Layers of the gut
1st: mucosa
2nd: submucosa
external to submucosa = two muscle layers, circular and longitudinal –>nerve net in between layers
serosa (visceral peritoneum)
1st layer Mucosa
delicate epithelial cells; secrete mucus to lubricate and protect walls of gut; some secrete HCl in stomach; absorb nutrients in some regions.
2nd layer Submucosa
blood and lymph vessels that carry absorbed nutrients to the rest of the body; network of nerves responsible for secretory and sensory functions
circular muscle layer
constricts the gut
longitudinal muscle layer
shortens length of gut
enteric nervous system
nerve nets b/n smooth muscle and in submucosa, neurons reside entirely inside the gut, and do not contribute synapses or neurons to CNS.
small intestine consists of…
duodenum, jejunum, and ileum
goblet cells
are among microvilli and secret lubricating mucus
hydrolytic enzymes
break down protein, carbs, and fat molecules into their monomers
Carbohydrase
hydrolyzes carbs
proteases
hydrolyze proteins
Lipase
hydrolyze fats
Nucleases
hydrolyze nucleic acids
salivary glands
secrete mucus and amylase
amylase
hydrolyzes bonds between the glucose monomers that make up starch - digests it into maltose (secreted by serous cells)
functions of saliva
- lubrication and binding (binding of food into “bolus”)
- coats oral cavity & esophagus = protect
- solubizes dry food
- important for oral hygiene (washes away food and contains lysozyme to lyse bact.)
- initiates starch digestion
serous cells
secrete amylase
swallowing:
soft palate pulled up while vocal chords pulled together to close larynx = larynx covered by epiglottis, esophageal sphincter relaxes to allow bolus to enter.
peristalsis
undulating movement of the GI tract that permits food to be moved along caused by alternating contractions of circular and longitudinal smooth muscle layers
stomach acid
HCl (pH 1-3)
- secretes 2-3 liters gastric fluid/day
- kills microorganisms
- hydrolize acid-labile substances
- activates pepsin
pepsin
endopeptidase –> major enzyme produced by stomach
- secreted by enzyme-secreting or “zymogenic” cell as a zymogen called pepsinogen.
- activated by low pH of stomach acid, once activated, newly formed pepsin can activate other pepsin molecules through autocatalysis.
zymogen
inactive enzyme precursor
how does HCl activate pepsin?
low pH activates pepsinogen by cleaving away a sequence of amino acids that masks the active site of the enzyme.
ulcers caused by
bacteria helicobacter pylori
side effects of untreated ulcers
indigestion, heartburn, gastric bleeding and stomach cancer
chyme
mixture of food and gastric juice in the stomach
what can be absorbed directly across stomach wall?
alcohol, aspirin, ad caffeine
Small Intestine
digestion of carbs and proteins CONTINUES, while digestion of fats and absorption of nutrients BEGINS.
Duodenum
(25 cm) = site of most digestion
Jejunum
2.5 m. along with ileum, is responsible for 90% of absorption of nutrients
Ileum
3.5 m. along with Jejunum, is responsible for 90% of absorption of nutrients
Liver
produces and secretes bile (made from bile salts from cholesterol) –> flows to small intestine through hepatic duct
bile
an emulsifier; disperses fat droplets into micelles –> increase surface area of fats that are exposed to lipases
micelles
stabilized tiny droplets of fat that can no longer aggregate due to bile salts
chylomicrons
largest lipoproteins, synthesized in mucosal cells of intestine; transport fats from intestine to adipose tissue (enter blood through thoracic ducts at base of the neck)
Lipoproteins
transport fats in aqueous circulatory system –> move fats from sites of storage to sites of use
High-Density Lipoprotein (HDL)
remove cholesterol from tissues –> carry it to liver for use in bile production = “good” cholesterol, high in fit people
Low-Density Lipoprotein (LDL)
transport cholesterol around body for storage and use in biosynthesis - 50% cholesterol = bad lipoproteins
Very Low-Density Lipoprotein (VLDL)
transport mostly triglycerides from liver to adipose tissue around body. “ugly” b/c excessive fat deposition and high risk for cardio disease
high LDL to HDL ration means
high risk for atherosclerotic heart disease
Pancreas
exocrine tissues of pancreas release a variety of digestive enzymes into the intestines.
- Trypsinogen (activated to trypsin)
- Bicarbonate secretion
Trypsinogen
zymogen released by the exocrine Pancreas; activated in duodenum by enterokinase into Trypsin. Active trypsin can activate other trypsinogens through autocatalysis. (if trypsin activated accidentally while still in pancreas, can cause pancreatitis!!)
Pancreatitis
accidental digestion of the pancreas via enzymes –> destroys both it’s exocrine and endocrine functions
Bicarbonate secretion (HCO3-)
neutralizes acidic chyme that enters intestine from stomach –> intestinal digestive enzymes function better at neutral/slightly alkaline pH levels
membrane-bound peptidases (on microvilli):
final digestion takes place here; cleave peptides into tri-, dipeptides, and individual amino acids
Colon
absorbs water, nutrients, and ions to produce semisolid feces
prolonged intake of antibiotics =
vitamin deficiency because they kill intestinal bacteria that help with vitamin uptake
