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Lecture 2

BIOL103 WEEK 2 HOMEWORK.docx

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Department
Biology
Course
BIOL 103
Professor
Virginia K Walker
Semester
Winter

Description
BIOL103 WEEK 2 HOMEWORK ABSORPTION SMALL INTESTINE -nearly all digestion and absorption of food + water occurs in the first quarter -hydrolytic enzymes break down molecules of organic nutrients into monomers -enzymes are on the lumen surface of the intestinal lining cells or secreted by pancreas -monomers absorbed across epithelial cells and enter blood -vitamins and minerals not digested, absorbed in s. intestine -water absorbed by osmosis from s. intestine in response to movement of nutrients gradient -large SA due to infoldings and specializations along length (villi and microvilli --> brush border) -large SA ^ chance of food particle meeting a digestive enzyme andn being absorbed -lacteal blood vesselin the centre of villi -->most too bulky to enter capillaries; fats absorbed through larger, wider lacteals of lymphatic system -->materials absorbed by lacteals enters circulatory system -->other nutrients absorbed directly into capillaries-->veins -duodenum, jejunum, ileum -herbivores have longer small intestine than carnivores (added time for plant material to be digested/absorbed) -less nutritious foods=longer s. intestine LARGE INTESTINE -cecum forms a small pouch, extends into the appendix -colon (ascending, transverse, and descending) -sigmoid colon (terminal portion of descending) empties into rectum, ending at the anus -chyme enters the cecum through a sphincter, which relaxes and opens after a meal -larger diameter, but smaller SA than s. intestine -l. intestine temporarily stores undigested material; concentrates it be absorbing salts and water -defecation: when contractions of rectum and relaxation of sphincter muscles expels feces through anus -absorbtion of products formed by bacteria living here (eg. small amounts of vitamins) -->other bacterial products: gas CARBS -starch digestion begins in the mouth, by salivary amylase -acid in stomach destroys amylase, preventing further digestion from saliva -starch digestion resumes in s. intestine by pancreatic amylase; mostly completed in s. intestine -->products via amylase are maltose -maltose, sucrose, and lactose broken down into fructose, glucose, and galactose by enzymes on brush border of s. intestine -monosacch. moved across epithelial membrane into blood -->fructose enters epith. cells via facilitated diffusion -->glucose and galactose enter epith. cells via secondary active transport coupled to sodium -monosacch. leave epith. cells and enter blood via facilitated diffusion transporters -->transepithelial transport: transport of substances from the lumen to blood, across epith. cell layer PROTEINS -broken down into peptides in the stomach by pepsin and in the small intestine by trypsin and chymotrypsin (latter 2 secreted by pancreas as zymogens: inactive precursors of enzymes, prevents enzyme from digesting pancreas itself) -once zymogen enters the s. intestine, it is enzymatically cleaved into the active molecules -trypsin activates zymogen form of chymotrypsin -peptide fragments further digested into amino acids by proteases on luminal membranes of epith. cells -amino acids enter epith. cells by secondary active transport coupled to sodium -leaves epith. cells and enters blood via facilitated diffusion carrier -mostly completed in upper portion of the small intestine FATS -most ingested fats in the form of triglycerides -digestion occurs entirely in s. intestine by pancreatic lipase: catalyses splitting of bonds linking fatty acids to glycerol--> 2 fatty acids + monoglyceride -poor water solubility; digestion of fats can only take place at the surface layer of a lipid glob -to ^ rate of digestion, fat is emulsified: disrupts large lipid droplets into smaller droplets (^ SA and exposure to lipase) -emulsification requires mechanical disruption -->caused by muscular contractions of stomach and s. intestine -->bile serves as an emulsifying agent (amphipathic) -absorption of poorly soluble products of lipase rxn facilitated by formation of micelles: bile salts, phospholipids, fatty acids, monoglycerides, core of fat-soluble vitamins and cholesterol -micelle continually breaks down/reforms near epith. membrane; individual molecules released into sol'n and diffuse across epith. membrane -fatty acids and monoglycerides enter epith. cells, triglycerides released on other side of epith. cell into interstitial fluid -->in epith. cell, resynthesized into triglycerides -->occurs in S.E.R. -->resynthesized triglycerides aggregate into chylomicrons -->released by exocytosis from epith. cell and passes into lacteal of intestinal villi, emptying into veins VITAMINS + MINERALS + WATER -not digested, absorbed in their complete form -water-soluble vitamins absorbed by diffusion or active transport -fat-soluble vitamins absorbed as fats would be -malabsorption: any interference w/ secretion of bile that decreases the absorption of fat-soluble vitamins --> leads to vitamin and mineral deficiency -small amounts of water absorbed from chyme in stomach -epith. cell membranes of s. intestine very permeable to water; water flows via osmotic gradient set by solutes EXCRETORY SYSTEM (Ch 47) -maintenance of body water levels is important (and ratio of water to salt in body) Elimination of Nitrogenous Waste -proteins in food and RNA broken down to smaller components- products are nitrogenous wastes: molecules w/ N from NH2 amino groups -toxic in high [ ] -eliminated in the form of ammonia and ammonium ions, urea, or uric acid (depending on species + environment) -only certain species (sharks, ray, skates) can survive with high [N waste] in blood and bodily fluids NH3 and NH4+ ions: most toxic; disrupts pH, ion electrochem. gradients, and redox rxns -animals that excrete this usually live in water -excreted across skin (invertebrates) or via gills and kidneys (fish) -b/c it's so toxic, aquatic animals excrete it as quickly as it's formed Urea: all mammals, most amphibians, some fish + reptiles +invertebrates -urea is less toxic than ammonia, doesn't require large V of water for excretion -animals can tolerate some accumulation of urea in blood, tissues, and bodily fluids -conserves water, removes need to constantly excrete, reduces chance of toxicity -converting ammonia--> urea uses moderate amount of ATP Uric acid: birds, insects, and most reptiles; also excrete purines (nitrogenous compounds) -less toxic than urea, but are more costly in terms of ATP to produce -poor solubility in water, not excreted in watery urine -mixed w/ other salts and waste into semisolid excretion -E usage requires is balanced w/ water conservation eg. Freshwater fish -b/c freshwater has very little [salt], salt gradient could move salts from fish's body into water -could move water into the fish -freshwater fish lose salt and gain water when ventilating gills; can cause dangerous decrease in [blood salt] -solution: kidneys adapted to produce lots of dilute urine to eliminate water; specialized gill cells actively transport Na+ and Cl- from lake water into fish's capillaries (important salt ions recaptured form the lake water) eg. Saltwater fish -tends to gain salts and lose water across gills (seawater has higher osmolarity than their bodies) -gain of salts and loss of water partly offset by kidneys-->produces very little urine with high [salt] to retain water -to prevent dehydration, saltwater fish drink water-->but, seawater is very salty -->the ingested salt is eliminated: gill cells pump salt of fish's blood and into surrounding water -drinks water to place water lost through gills by osmosis; uses E to move excess salt swallowed out of body EXCRETION 1. Filtration -organ acts like a filter, removing some water and small solutes from blood and interstitial fluid, while leaving behind blood cells and large solutes (eg. proteins) -eg. mammalian kidney: plasma of blood under pressure through capillaries into kidney tubules -filtrate: material that passes through filter and enters excretory system of organ 2. Reabsorption -some of the material in the filtrate is recaptured back into the blood -to filter blood and remove soluble wastes, salts, sugars, a.acids and needed molecules are also filtered in the process-->reclaimed at this stage -requires active transport pumps or other transport systems -urine: remaining part of filtrate 3. Secretion -sometimes solutes excreted from body in higher quantities than those found in the filtrate -some solutes actively transported from the interstitial fluid surrounding tubule cells into tubule lumen -supplements the amount of a solute that would normally be removed by filtration alone -often a way in which excretory organs eliminate really toxic compounds from the body; very effective -additional unwanted solutes actively removed from blood and interstitial fluids and directly enter the lumen of the excretory tubule 4. Excretion -urine is excreted -liver: metabolized + filters out toxins; converts toxic ammonia to urea -kidney: filters urea from blood from liver into urine MAMMALIAN KIDNEY -urine formed in each kidney collects in renal pelvis; flows through the ureters into bladder; eliminated via urethra -renal cortex: outer kidney -primary site of flood filtration -renal medulla: inner region -urine is concentrated by reabsorption of water back into blood NEPHRON consists of... 1.renal corpuscle: initial filtering component -contains a cluster of capillaries called glomerulus: has tiny holes in its walls that allow rapid flow of plasma out of capillary -supplied w/ pressurized blood from afferent arteriole -glomerulus protrudes into fluid-filled space called Bowman's capsule: filters plasma and blood 2. collecting duct: narrow tubule that extends out form the renal corpuscle -tubule made up of single layer of epithelial cells -proximal convoluted: Bowman's capsule drains into this first portion -particular solutes reabsorbed from filtrate (eg. Na+, K+, Cl-, glc, a.acids that passed through) -some ions diffuse
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