Lecture 24 on the endocrine system, absorption, liver function.docx

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Biochemistry and Cellular and Molecular Biology
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BCMB 230

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Absorption -proteins are broken down to polypeptides Only absorb amino acids -get water, simple sugar absorption in the stomach -limited absorption in the stomach -don't have protein absorption -we have limited carbohydrate absorption Small intestine absorption -glucose -maintain high glucose levels in the plasma -secondary active transport (driven by sodium absorption) -AminoAcids -keep in high levels in the plasma [not as high as glucose] -can't use active transport -Fructose -not present in plasma in high levels -facilitated diffusion is used because of low levels -Fatty acids/monoglycerides Figure 15.12 -mechanical digestion breaks it up into fat droplets -gets into small intestine and then bile from the liver further mechanically digests it into emulsion droplets [smaller] (bigger surface area(?)) -expose it to lipase from the pancreas [breaks it up into fatty acids and monoglycerides] -ampiphatic molecules- have polar component so they can come together to form little droplets -micelle- ampiphatic molecules; can freely move around the cell -can freely move through plasma membrane into cells -in order to maintain the gradient [no transporters because the membrane is permeable to them] -break the fats down and then make them fats again -Epithelial cells of the intestines- within Endoplasmic reticulum, we synthesize triglyceride -this maintains a gradient for monoglycerides and fatty acids so we can keep getting them out of the intestine and into the cell -exocytosis= moves proteins out of the cell along with triglycerides -Chylomicron [droplets]= can't transport across membrane readily -want to move something from interstitial fluid- use blood to transport -move to adipose cells beneath skin 4 different droplets: ** be able to distinguish -Chylomicrons -micelles -fat droplets -emulsion droplets Lymphatic System [another transporting system]- Figure 12.47 -series of vessels like capillaries and veins of circulatory system -capillary- small, thin walled; very permeable -basic lymphatic vessels- very vein like [have valves] -lymph capillaries are more permeable than vascular capillaries -large pores are valved- material can get in but not back out -chylomicrons- in interstitial fluid of intestines but they can go into lymph capillaries -now we can circulate them wherever we want in the body -lymph will dump into veinous part of the body [at the base of the neck] Latiles- lymphs in the digestive system [milky looking] *to get chylomicrons to adipose sites or cell that need fatty acids for energy- need to break it down in the blood vessel -lots of enzyme activity -goes from lymphatic system to circulatory system where it is broken down and distributed to cells that need it ** all this is because we don't have a transport to get fatty acids across the membrane Control the digestive system -movement -smooth muscles cause this -we can control smooth muscle (using autonomic nervous system, hormones, pacemakers, etc) -peristalsis- use pacemaker to set rate/rhythm -can modify movement with nerves and hormones -grandular secretion -regulated by sympathetic nervous system or hormones -digestion -directly or indirectly control digestion -can use muscles to chew food [direct] -our stomach wants to digest the food [indirect] -ex) we can control the movement -absorption -the movement and secretion maximized digestion, which maximizes absorption -absorbs everything [stores excess] Two nervous systems that work in digestive system- Figure 15.3 -Digestive system has its own processing center/brain -can control nerve reflexes that don't use Central nervous system wall of digestive system: -plexus- complex network of nerves -enteric nervous system- made up of plexi -long and short neural reflexes -reflexes that go to brain[particularly hypothalamus] and help to control movement and secretion short reflex- action potentials never goes to CNS -only place we see this [in intestine] -only stay within the wall of the intestine -short reflex in the gut -long reflex in head 15.14 GI tract -intestinal hormones- inhibit stomach and promote important things for the intestine --secretion of enzymes
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