packet 22 Flashcards
5 feet long by 2½ inches in diameter
Ascending & descending colon are retroperitoneal
Cecum & appendix
Rectum = last 8 inches of GI tract anterior to the sacrum & coccyx
Anal canal = last 1 inch of GI tract
internal sphincter—-smooth muscle & involuntary
external sphincter—-skeletal muscle & voluntary control
large intestine
mechanical digestion in large intestine
smooth muscle peristaltic waves --haustral churning- --gastroilial reflex --gastrocolic reflex
mechanical digestion
smooth muscle
relaxed pouches are filled from below by muscular contractions (elevator
haustral churning
when stomach is full, gastrin hormone relaxes ileocecal sphincter so small intestine will empty and make room
gastroilial reflex
when stomach fills, a strong peristaltic wave moves contents of transverse colon into rectum
gastrocolic reflex
No enzymes are secreted only mucous
Bacteria ferment
undigested carbohydrates into carbon dioxide & methane gas
undigested proteins into simpler substances (indoles)—-odor
turn bilirubin into simpler substances that produce color
Bacteria produce vitamin K and B in colon
chemical digestion in large intestine
Some electrolytes—Na+ and Cl-
After 3 to 10 hours, 90% of H2O has been removed from chyme
Feces are semisolid by time reaches transverse colon
Feces = dead epithelial cells, undigested food such as cellulose, bacteria (live & dead)
absorption and feces formation in large intestine
Gastrocolic reflex moves feces into rectum
Stretch receptors signal sacral spinal cord
Parasympathetic nerves contract muscles of rectum & relax internal anal sphincter
External sphincter is voluntarily controlled
defecation
chyme passes too quickly through intestine
H20 not reabsorbed
diarrhea
-decreased intestinal motility
too much water is reabsorbed
remedy = fiber, exercise and water
constipation
dietary fiber
insoluble fiber
soluble fiber
woody parts of plants (wheat bran, vegie skins)
speeds up transit time & reduces colon cancer
insoluble fiber
gel-like consistency = beans, oats, citrus white parts, apples
lowers blood cholesterol by preventing reabsorption of bile salts so liver has to use cholesterol to make more
soluble fiber
1 source of energy
2 essential nutrients
3 stored for future use
Metabolism is all the chemical
function of food
metabolic adaptations
absorptive state
post-absorptive state
nutrients entering the bloodstream
glucose readily available for ATP production
4 hours for absorption of each meal so absorptive state lasts for 12 hours/day
absorptive state
absorption of nutrients from GI tract is complete
body must meet its needs without outside nutrients
late morning, late afternoon & most of the evening
maintaining a steady blood glucose level is critical
post-absorptive states
Body cells use glucose for ATP production
about 50% of absorbed glucose
Storage of excess fuels occur in hepatocytes, adipocytes & skeletal muscle
most glucose entering liver cells is converted to glycogen (10%) or triglycerides (40%)
dietary lipids are stored in adipose tissue
amino acids are deaminated to enter Krebs cycle or are converted to glucose or fatty acids
amino acids not taken up by hepatocytes used by other cells for synthesis of proteins
metabolism during absorptive state
Beta cells of pancreas release insulin
Insulin’s functions
increases anabolism & synthesis of storage molecules
decreases catabolic or breakdown reactions
promotes entry of glucose & amino acids into cells
stimulates phosphorylation of glucose
enhances synthesis of triglycerides
stimulates protein synthesis along with thyroid & growth hormone
regulation of metabolism during absorptive state
Maintaining normal blood glucose level (70 to 110 mg/100 ml of blood) is major challenge
glucose enters blood from 3 major sources
glycogen breakdown in liver produces glucose
glycerol from adipose converted by liver into glucose
gluconeogenesis using amino acids produces glucose
alternative fuel sources are
fatty acids from fat tissue fed into Krebs as acetyl CoA
lactic acid produced anaerobically during exercise
oxidation of ketone bodies by heart & kidney
Most body tissue switch to utilizing fatty acids, except brain still need glucose
Metabolism During Postabsorptive State
As blood glucose level declines, pancreatic alpha cells release glucagon
glucagon stimulates gluconeogenesis & glycogenolysis within the liver
Hypothalamus detects low blood sugar
sympathetic neurons release norepinephrine and adrenal medulla releases norepinephrine & epinephrine
stimulates glycogen breakdown & lipolysis
raises glucose & free fatty acid blood levels
Regulation of Metabolism During Postabsorptive State
Fasting means going without food for hours/days
Starvation means weeks or months
can survive 2 months or more if drink enough water
amount of adipose tissue is determining factor
Nutritional needs
nervous tissue & RBC need glucose so amino acids will be broken down for gluconeogenesis
blood glucose stabilizes at 65 mg/100 mL
lipolysis releases glycerol used in gluconeogenesis
increase in formation of ketone bodies by liver cells due to catabolism of fatty acids
by 40 days, ketones supply 2/3’s of brains fuel for ATP
Metabolism During Fasting & Starvation
Catabolic reactions breakdown complex organic compounds
providing energy (exergonic)
glycolysis, Krebs cycle and electron transport
Anabolic reactions synthesize complex molecules from small molecules
requiring energy (endergonic)
Exchange of energy requires use of ATP (adenosine triphosphate) molecule.
Catabolism and Anabolism
Each cell has about 1 billion ATP molecules that last for less than one minute
Over half of the energy released from ATP is converted to heat
ATP Molecule & Energy
Energy is found in the bonds between atoms
Oxidation is a decrease in the energy content of a molecule
Reduction is the increase in the energy content of a molecule
Oxidation-reduction reactions are always coupled within the body
whenever a substance is oxidized, another is almost simultaneously reduced.
energy tranfer
Phosphorylation is
bond attaching 3rd phosphate group contains stored energy
Mechanisms of phosphorylation
within animals
substrate-level phosphorylation in cytosol
oxidative phosphorylation in mitochondria
THERE ARE MULTIPLE MONOSACHHARIDES THAT WE CAN USE IN OUR BODY, BUT DURING CELLULAR RESPIRATION, GLUCOSE IS USED PREFERENTIALLY TO MAKE ATP
mechanisms of ATP generation
ADP + P = ATP
Liver glycogen runs low if fasting, starving or not eating carbohydrates forcing formation from other substances
lactic acid, glycerol & certain amino acids (60% of available)
Stimulated by cortisol (adrenal) & glucagon (pancreas)
cortisol stimulates breakdown of proteins freeing amino acids
thyroid mobilizes triglycerides from adipose tissue
Gluconeogenesis
