Digestive system and excretion Flashcards
What would happen to lipids without micilles?
Lipids would simply float on the surface chyme (like oil on water) and can't be absorbed.
Differences between emulsification droplets and micelles
Although they are similar in structure to emulsification droplets, they are smaller and can fit between the microvilli for more efficient absorption.
Absorption in small intestine vs.
-Almost all absorption occurs in the small intestine.
-The stomach absorbs only a few fat-soluble drugs (e.g. aspirin, alcohol).
-The large intestine absorbs some vitamins, electrolytes, and water.
Carbohydrates (polysaccharides, oligosaccharides, disaccharides) are hydrolyzed to ___1___ by ___2___ and ___3___. Proteins (polypeptides, oligopeptides, dipeptides) are hydrolyzed to ___4___ by ___5___ and ___6___.
3. brush border carbohydrases
4. amino acids
6. brush border proteases
___1___ and ___2___ cross the apical
membrane of absorptive cells by ___3___
transport (specifically cotransport with ___4___).
2. amino acids
3. secondary active
___1___ and ___2___ diffuse through
the cytosol across the cell to the basal membrane. They cross the basal membrane by ___3___ and enter the interstitial fluid. They enter the blood by ___4___ through ___5___ between the endothelial cells of capillaries in the ___6___.
2. Amino Acids
3. Facilitated diffusion
5. intercellular clefts
6. lamina propria
Trace monosaccharides and amino acids from systemic capillaries in the small intestine to the heart.
systematic capillaries in the sm. intestine
small venous tributaries
superior mesenteric v.
hepatic portal v.
Lipid substances leave the micelles and cross the apical membrane of absorptive cells by ___1___.
Upon entering absorptive cells, the lipids are...
2.Immediately processed, so their
intracellular concentrations are kept low.)
Within the smooth ER, ___1___ and ___2___ are recombined to form ___3___. The newly synthesized ___3___ are then combined with ___4___, and
___5___, ___6___ (including lecithin) and ___7___ to form lipoproteins called ___8___. Transport vesicles carry the ___8___ to the __19____.
2. fatty acids
4. cholesterol esters
5. amphipathic cholesterol
9. golgi apparatus
The ___1___ packages the chylomicrons into secretory vesicles. ___2___ migrate to and merge with the basal membrane to release their
___3___ to the interstitial fluid.
2. secretory vesicles
From the interstitial fluid, the chylomicrons enter the lymph through the valves in the walls of the lacteals and are transported by the lymphatic system to the blood. Why is this?
Chylomicrons are too big to cross the walls of the blood capillaries.
Trace chylomicrons from lacteals to the liver.
lacteal-> collecting lymphatics-> intestinal trunk -> cisterna chyli-> thoracic duct->l. subclavian v. -> brachiocephalic v.-> superior vena cava-> r. atrium-> tricuspid-> r. ventricle->pulmonary valve -> pulmonary trunk and arteries-> lungs-> pulmonary vv.-> bicuspid-> l. ventricle-> aortic valve-> aorta-> celiac trunk-> hepatic a.
Functions of the liver
1. Metabolizes and/or stores the nutrients transported from the small intestine via the hepatic portal system.
2. Synthesizes all lipoproteins, except chylomicrons.
3.Synthesizes Cholesterol and triglycerides, Bile salts and lecithin, Plasma proteins (except gamma globins) and calcitriol(the active form of vitamin D).
4. Stores glycogen, certain vitamins (A, B12, D, E, and K) and minerals (e.g.iron from the breakdown of Hb).
5. Metabolizes drugs
glycogenesis vs. glycogenolysis
production of glucose from non carbohydrates
Why are lipoproteins important?
Lipoproteins provide delivery and transport services so that lipids can be available when
cells need them or removed from circulation when they are not needed.
How are lipoproteins named?
Lipoproteins are named according to their density, which varies with the ratio of lipids(which have a low density)to proteins (which have a high density)
Very low-density lipoproteins (VLDL)
transport triglycerides synthesized in the liver to adipocytes for storage.
Low-density lipoproteins (LDL)
deliver cholesterol to body cells for use in repair of cell membranes and to endocrine glands for the synthesis of steroid hormones(e.g. estrogen, testosterone).
High-density lipotroteins (HDL)
remove excess cholesterol from body cells and the blood and transport it to the liver for elimination in the bile.
Chylomicrons definition and function
Chylomicrons are lipoproteins synthesized in the
absorptive cells of the small intestine and transport dietary(ingested) lipids to adipocytes tissue for storage.
Large Intestine function
The large intestine absorbs water (as well as some vitamins and electrolytes)from the liquid chyme and reduces it to semisolid feces.
When the feces pass too quickly through the large intestine, less water than normal is absorbed.
When the feces pass too slowly through the
large intestine, more water than normal is absorbed .
1. Mucus to lubricate the feces.
3. Dietary fiber – plant polysaccharides (e.g. cellulose and pectin) for which we lack digestive enzymes.
Function of bacteria in feces
-Synthesize B vitamins and most of the vitamin K necessary for the liver to synthesize clotting proteins.
-Break down bilirubin to stercobilin, which is responsible for fecal color.
-Metabolize any remaining proteins to indole and skatole, which are responsible for fecal odor.
-Metabolize any remaining carbohydrates to hydrogen, carbon dioxide,and methane gases (flatulence).
Dietary fiber function in feces
Fiber aids the passage of feces by:
1) absorbing water and making the feces softer, and 2) by adding bulk to the feces.
Benefits of fiber in feces
-Prevents diverticula (sac-like outpouchings of the colon wall) that can become inflamed (diverticulitis)because easy passage of feces decreases pressure exerted on the colon wall.
-Lowers the risk of colon cancer.
-Lowers the risk of CAD b/c fiber binds cholesterol and prevents its re-absorption.
-Helps regulate blood sugar b/c fiber slows the rate of carbohydrate digestion and absorption.
Valsalva’s maneuver (straining) involves closing the glottis during exhalation and contracting the abdominal muscles to increase abdominal pressure, which promotes defecation.
Although it helps to move hard to pass feces out the anus, straining restricts venous return and can lead to hemorrhoids (varicose veins in the anal canal).
Why does fiber lower the risk of colon cancer?
Fiber absorbs toxins and carries them out of the digestive tract. Also, the more rapid passage of feces reduces the length of time the wall is exposed to toxins.
Why do people with lactose intolerance experience diarrhea and flatulence when eating dairy products?
1. Lactose passes undigested into lg. intestine--> 2. Increased osmotic pressure of intestinal contents->
3.Water moves into intestinal contents by osmosis->
5. Bacteria metabolize undigested lactose-->
6. Flatulence and cramping
How does defecation occur?
1. Distension, or stretch, of the rectal walls due to movement of feces into the rectum stimulates stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons
2.A spinal reflex is initiated in which parasympathetic motor (efferent) fibers stimulate contraction of the rectal walls and relaxation of the internal anal sphincter.
3. If it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so that feces can pass