Lecture 22 Flashcards
Large intestine: Smooth muscle =
mechanical digestion
Mechanical: Peristaltic waves:
haustral churning
gastroilial reflex
gastrocolic reflex
haustral churning-
relaxed pouches are filled from below by muscular contractions
gastroilial reflex =
when stomach is full, gastrin hormone relaxes ileocecal sphincter so small intestine will empty and make room
gastrocolic reflex =
when stomach fills, a strong peristaltic wave moves contents of transverse colon into rectum
Chemical Digestion in Large Intestine:
- No enzymes are secreted only mucous
- Bacteria ferment
- Bacteria produce vitamin K and B in colon
Bacteria ferment: 1st step
- undigested carbohydrates into carbon dioxide & methane gas
Bacteria ferment: 2nd step
- undigested proteins into simpler substances (indoles)—-odor
Bacteria ferment: 3rd step
- turn bilirubin into simpler substances that produce color
Absorption in the Large Intestine:
- Some electrolytes—Na+ and Cl-
2. 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
Defecation: What moves feces into the rectum?
Gastrocolic reflex
Defecation: What signals the sacral spinal cord?
stretch receptors
Defecation: What contracts muscles of the rectum and relax the internal anal sphincter?
parasympathetic nerves
Defecation: What is voluntarily controlled?
external sphincter
Diarrhea =
chyme passes too quickly through intestine
H2O not absorbed
Constipation–
decreased intestinal motility
too much water reabsorbed
Dietary fiber- Insoluble fiber:
- woody parts of plants
- speeds up transit time & reduces colon cancer
Dietary fiber- Soluble fiber:
- gel-like consistency = beans, oats, citrus white parts, apples
- lowers blood cholesterol
How does soluble fiber lower blood cholesterol?
by preventing reabsorption of bile salts so liver has to use cholesterol to make more
Functions of food:
source of energy
essential nutrients
stored for future use
Metabolism is
all the chemical reactions of the body
Absorptive state:
- nutrients entering the bloodstream
- glucose readily available for ATP production
- 4 hours for absorption of each meal
Postabsorptive state:
- absorption of nutrients from GI tract is complete
- body must meet its needs without outside nutrients
- maintaining a steady blood glucose level is critical
Body cells use glucose for
ATP production
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
Beta cells of pancreas release
insulin
Insulin’s functions:
- increases anabolism & synthesis of storage molecules
- decreases catabolic
- promotes entry of glucose & amino acids into cells
- stimulates phosphorylation of glucose
- enhances synthesis of triglycerides
- stimulates protein synthesis along with thyroid & growth hormone
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
- lactic acid
- oxidation of ketone bodies by heart & kidney
Most body tissue switch to
utilizing fatty acids, except brain still need glucose
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
adrenal medulla releases
norepinephrine & epinephrine
determining factor of starvation;
amount of adipose tissue
Nutritional needs:
- nervous tissue & RBC need glucose
2. increase in formation of ketone bodies by liver cells
Catabolic reactions breakdown
complex organic compounds
-providing energy
Anabolic reactions synthesize
complex molecules from small molecules
-requiring energy
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
Energy is found in the
bonds between atoms
Oxidation is a
decrease in the energy content
Reduction is the
increase in the energy content
Oxidation-reduction reactions are always coupled within
the body
Phosphorylation is
ADP + P = ATP
3rd phosphate group
Mechanisms of phosphorylation:
within animals
Gluconeogenesis:
Liver glycogen runs low if fasting, starving forcing formation from other substances
Gluconeogenesis stimulated by
cortisol (adrenal) & glucagon (pancreas)
