biol 2300-2.pdf

BIOL 2300 GENERAL PHYSIOLOGY REVIEW OF MACROMOLECULES OF LIFE AND THEIR METABOLIC PATHWAYS  MACROMOLECULES Carbohydrates Proteins Lipids Nucleic acids  The synthesis and Breakdown of Polymers Monomers form larger molecules by condensation reactions called dehydration sy...

BIOL 2300 GENERAL PHYSIOLOGY REVIEW OF MACROMOLECULES OF LIFE AND THEIR METABOLIC PATHWAYS  MACROMOLECULES Carbohydrates Proteins Lipids Nucleic acids  The synthesis and Breakdown of Polymers Monomers form larger molecules by condensation reactions called dehydration synthesis ✓Joins monomers together to form larger molecules  The synthesis and Breakdown of Polymers Polymers can be disassemble by ✓Hydrolysis (addition of water molecules) ✓Breaks apart larger macromolecules into smaller molecules  carbohydrates Serve as fuel and building material Include both sugars and their polymers (starch, cellulose) Sugar- monosaccharides ✓The simplest sugars ✓Can be used as fuel ✓Converted into organic molecules  Disaccharides Polysaccharides ✓Consist of two ✓Polymers of sugars monosaccharides ✓Serve many roles in ✓Joined by a glycosidic linkage organisms ( a bond between an O atom Starch and two different H atoms from different base Glycogen molecules) Cellulose  Starch Glycogen ✓ A polymer consist of glucose monomers ✓ A polymer consist of glucose monomers ✓ Storage form of glucose in plants ✓ Storage form of glucose in animals  Structural polysaccharides cellulose Chitin  LIPIDS ✓ Diverse group of hydrophobic molecules ✓ They do not always consist of polymers ✓ They are hydrophobic ✓ Made up of glycerol and 3 fatty acids ✓ They vary in length, number and locations of double bonds they contain Types of fatty acids  Phospholipids o Have 2 fatty acids and a phosphate group o Hydrophilic head; Hydrophobic tail ✓ The structure resulted in a bilayer arrangement of cell membrane  Steroids Estrogen & progesterone Made in the ovary and in Testosterone made in the testes the placenta during pregnancy Cholesterol found in cell membranes and prevents freezing; a precursor of some hormones  Lipids constitute about 15-20% of the body weight in humans Triacylglycerol/ triglycerides are the most abundant lipids which are stored in the adipose tissue and serves as energy reserve of the body Fats act as an insulating material for maintaining the body temperature of animals  Transport of lipids Lipoproteins Insoluble lipids are solubilized with proteins to form lipoproteins Chylomicrons- 2% proteins and 98% lipids which is transported in the bloodstream Very Low Density Liporotiens (VLDL)- Free lipids are undetectable in the 10% proteins and 90% lipids blood Low Density Lipoprotiens (LDL)- 20% protein and 80% lipid High Density Lipoproteins (HDL)- 40% proteins and 60% lipid Albumin- free fatty acids  Synthesized in the intestine and transport exogenous Chylomicrons triacylglycerol to tissues; least in density and largest in size Very Low Density Produced in the liver and Intestine and transport Lipoproteins (VLDL) endogenously synthesized triacylglycerol Low Density Lipoprotiens Formed from VLDL in the blood circultaiom; transport (LDL) cholesterol from liver to other tissues High Density Transport cholesterol from the peripheral tissues to liver Lipoproteins (HDL) and they are synthesized in the liver Albumin Can hold up to 20-30 molecules of free fatty acids  Proteins ✓ Consists of many polypeptides Amino acids ✓ With many structures resulting in a ✓ Organic molecules with carboxyl and amino groups wide range of functions ✓ Act as enzymes ✓ Made up of amino acids The unique Coiling or folding of Over all three dimensional Over all protein polypeptide shape of a polypeptide; structure that resuts sequence of resulted from the from the aggregation Alpha helix(coiled) and amino acids in a beta pleated(folded) interactions between of two or more polypeptide sheets amino acids and R groups polypeptide subunits  Factors affecting the conformation of proteins ✓ Temperature ❖ Denaturation is when protein unravels and ✓ pH loses its native conformation Catabolism of proteins in plants  NUCLEIC ACIDS Two types of nucleic acids ✓ Store and transmit hereditary information ✓ DNA ✓ Genes- are the units of ✓ RNA inheritance ✓ Program the amino acid sequence of polypeptides ✓ Are made of nucleotide sequences of DNA ✓ Exists as polynucleotides  DNA ✓Stores information for the synthesis of specific proteins ✓Found in nucleus of the cells ✓Functions to direct RNA (transcription) and protein synthesis (translation)  BIOL 2300 GENERAL PHYSIOLOGY  CELL COMPOSITION Water- 70-85% Ions Proteins -10-20% Carbohydrates -1-6% PROTEINS Lipids ✓ Structural- forms microtubules that provide the cytoskeletons of such Phospoholipids and cholesterl- 2% of total cell mass; insoluble in water ; form the cell cellular organelles membrane and intracellular membrane ✓ Functional- combination pf few barriers molecules in tubular globular form and are mainly the enzymes of the Neutral fats- triacylglycerides- 95% of cell mass cell Body’s main storehouse of energy-giving CARBOHYDRATES nutrients Little structural function in cells and plays role in nutrition of a cell  Membranous structure of the cells Cell membrane Nuclear membrane Membrane of the endoplasmic reticulum Membrane of mitochondria, lysosomes and golgi apparatus  Cell membrane ✓ Thin, pliable, elastic structure ✓ 7.5-10 nanometers thick ✓ Mainly composed of proteins and lipids ✓ Proteins 55% ✓ Phospholipids 25%  Cell membrane components Lipids ✓ Barrier to water and water-soluble substances organized in a bilayer of phospholipid molecules Lipid rafts are also enriched in other membrane lipids such as sphingolipids and play a multitude of roles, including regulation of signal transduction and protein trafficking. Membrane lipid composition is vital to proper structure and function of a diverse range of proteins; in particular, transmembrane proteins such as dopamine transporters and dopamine receptors  Proteins ✓ Provide specificity to a membrane ✓ Defines by made of association with the lipid bilayer ✓ Integral-channels, pores, carriers, enzymes, receptors ✓ Peripheral-enzymes, intracellular signal mediators, controllers of transport of substances through pores  Carbohydrates ✓ Glycolipids- 10% ✓ Important functions ✓ Glycoproteins –majority of ✓ Negative charge of the carbo chains repels integral proteins other ✓ Proteoglycans-carbs bound to ✓ Negative changes protein cores ✓ Involved in cell-cell attachments/ ✓ Glycocalyx loose carbohydrate interactions coat outside surface of the cell ✓ Play role in immune reactions ✓ Act as receptor substance for binding hormone such as insulin Glycolipids are mainly sphingolipids with different carbohydrate compositions. Some proteoglycans have part of their amino acid sequence inserted among the lipid fatty acid chains. Most of the carbohydrates are chemically linked to proteins, known as glycoproteins, either by O-linked glycosylation (via serine amino acid) or by N-linked glycosylation (via asparagine amino acid) (Modified from Fuster and Esko, 2005).  Cytoplasm and its organelles ✓ Cytosol-clear fluid portion of the cytoplasm in which the particles are dispersed in ✓ Neutral fat globules ✓ Glycogen granules ✓ Ribosomes ✓ Secretory vesicles ✓ Other organelles  Endoplasmic reticulum ✓ Network of tubular and flat RER vesicular structures ✓ Outer membrane surface covered with ribosomes ✓ Membrane is similar to (and ✓ Newly synthesized proteins are extruded into the ER contiguous with) the plasma matrix membrane ✓ Proteins are processed inside the matrix SER ✓ Cross linked ✓ Part of ER has no attached ribosomes ✓ Folded ✓ Site of lipid synthesis: phospholipids and cholesterol ✓ Glycosylated ✓ Growing ER membrane buds continuously ✓ cleaved forming transport vesicles, most of which migrate to the golgi apparatus  Golgi apparatus ✓ Membrane composition similar to that ✓ Receives transport vesicles from smooth er of the smooth ER and plasma ✓ Substances formed in the ER are processed membrane Phosphorylated and glycosylated ✓ Composed of 4 or more stacked ✓ Substances are concentrated, sorted and layers of flat vesicular packaged for secretion ✓ This apparatus is prominent in ✓ Transported substance are then processed secretory cell, whare its located on the in Golgi apparatus to form side of the cell from which the secretory substances are extruded ✓ Lysosomes ✓ Secretory vesicle ✓ Cytoplasmic componenet  Lysosomes ✓ Vesicular organelle formed from budding golgi ✓ Provide an intracellular digestive system that allows the cell to digest ✓ Damaged cellular structure ✓ Food particles that have been ingested by cell ✓ Unwanted ,atter such as bacteria ✓ Contain hydrolytic enzymes – Phosphatases; Nucleases;Proteases; Lipid-digestive enzymes ✓ Lysozymes digest bacteria ✓ Fuse with pinocytotic ovesicles to form digestive vesicles Peroxisomes ✓ Similar physically to lysosomes ✓ Two major differences ✓ Formed by self replication they contain peroxidases Functions of Peroxisomes 1.Hydrogen Peroxide Metabolism: Enzymes present in the peroxisomes both lead to the production and elimination of H202 which is a reactive oxygen species. 2.Fatty acid oxidation:Oxidation of fatty acids, in animal cells, occurs in both peroxisomes and mitochondria, but in yeasts and plants, only limited to peroxisomes. Oxidation is accompanied by the production of H202 which is decomposed by catalase enzyme. This provides a major source of metabolic energy. 3.Lipid biosynthesis Synthesis of cholesterol and dolichol occurs in both ER and peroxisomes. Bile acid synthesis takes place from cholesterol in the liver. Peroxisomes contain enzymes to synthesize plasmalogens, a family of phospholipids which are important membrane components of tissues of the heart and brain. 4.Germination of seeds Peroxisomes in seeds responsible for the conversion of stored fatty acids to carbohydrates, critical to providing energy and raw materials for the growth of germinating plants. 5.Photorespiration Peroxisomes in leaves particularly in the green ones carry out the photorespiration process along with chloroplasts. 6.Degradation of purines Carry out the catabolism of purines, polyamines and amino acids especially by uric acid oxidase 7.BioluminescenceLuciferase enzyme found in the peroxisomes of fireflies help in bioluminescence and thus aid the flies in finding a mate or its meal. Secretory vesicles ✓ Secretory vesicles containing proteins synthesized in the REE bud from the Golgi apparatus ✓ These vesicle store protein (proenzyme - enzymes that are not yet activated) ✓ Fuse with plasma membrane to release contents ✓ Constitutive secretion-happens randomly ✓ Stimulated secretion-requires trigger  Mitochondria- powerhouse ✓ Primary function- extraction energy from nutrients ✓ Self replicative ✓ Matrix: contain large amount of dissolve enzymes Cytoskeleton ✓ Fibrillar protein originated as precursor protein molecules synthesized by ribosomes in the cytoplasm ✓ The precursor molecules then polymerize to from filaments ✓ The primary function of microtubules is to act as cytoskeleton, providing rigid physical structure The nucleus is the control center of the cell containing large quantities of DNA ✓ Nuclear membrane is two separated bilayer membrane, the outer membrane is continuous with the endoplasmic reticulum, the nuclear membrane is penetrated by several thousand nuclear pores ✓ 100 nm in diameter ✓ Functional diameter is – 9nm ✓ Selectively permeable to molecules of up to 44,000 mw ✓ Chromatin is found in the nucleoplasm ✓ Nucleolus contains rna and protein ✓ Not membrane delimited ✓ Form the granular subunits of ribosomes nuclear pores are located on the surface of the nuclear membrane allow for transmission of nutrients, waste, and other macromolecules to and from the nucleus. These pores allow for small molecules (about the size of small proteins and smaller) to transport through, but they also serve as a barrier for larger proteins and molecules.  Transport across cell membranes ✓ Simple diffusion ✓ Carrier mediated transport ✓ Facilitated diffusion ✓ Active transport ✓ Osmosis  Simple diffusion Factors Occurs 1.Concentration gradient 6. solvent density downhill an 2.mass/size of the molecules 7. Surface area and thickness of membrane electrochemical 3. Temperature gradient and does not require 4. Solubility metabolic energy and therefore is passive  Facilitated diffusion ✓ It is the carrier- moderated transport of a solute through a membrane down its concentration gradient. ✓ It is a passive transport process; ✓ that is, it does not take in ATP. It carries solutes, such as glucose, that can not travel through the membrane unaided. The solute connects to a binding Examples of biological processes that entail site on the carrier, then the facilitated diffusion are glucose and amino carrier modifications acid transport, gas transport, and ion conformation and launches the transport. solute on the other side of the membrane. Osmosis Osmosis Carrier mediated transport  Active transport Requires the use of chemical energy to move substances across a membrane, against a concentration gradient.  Primary active transport In primary active transport, energy from the hydrolysis of ATP is used to move ions into or out of cells against their concentration gradients. Secondary active transport Secondary active transport couples the passive movement of one substance with its concentration gradient to the movement of another substance against its concentration gradient. Energy from ATP is used indirectly to establish the concentration gradient that results in the movement of the first substance. Ingestion by the cell receptor-mediated endocytosis-pinocytosis and phagocytosis Biol 2300  Signal Transduction A series of steps by which external stimuli are converted into chemical signals and then ito cellular response It is passed along the signaling pathways The response may depend on the ff ✓ Change in gene expression 3 steps ✓ Alteration of the activity of metabolic enzymes 1. Reception ✓ Reconfiguration of the 2. Transduction cytoskeleton ✓ Change in ion permeability 3. Induction/response ✓ Activation of DNA synthesis ✓ Cell death  Transduction Reception Response can be activation ▪ Converts the change in the receptor to a form of response, rearrangement Perception of the that can bring cellular response environment of the cytoskeleton, ▪ It may alter and amplifies the change activation of specific genes, Receptor molecule release of abscisic acid complementary to the ▪ Causes the increase of the second messenger signal molecule or ▪ The physical stimulus is converted into chemical ligand form from which can act in the cell In animals Animal nutrition Nutrients are elements in feed that are used by the animal for growth and production. Nutrients are normally divided into five categories: Water, protein, carbohydrates, minerals, and vitamins. An animal’s diet provides: Chemical energy, which is converted into ATP to power cellular processes Organic building blocks, such as organic carbon and organic nitrogen, to synthesize a variety of organic molecules Essential nutrients, which are required by cells and must be obtained from dietary sources Essential Nutrients There are four classes of essential nutrients: Essential amino acids- Meat, eggs, and cheese provide all the essential amino acids and are thus “complete” proteins Essential fatty acids- must be obtained from the diet and include certain unsaturated fatty acids (i.e., fatty acids with one or more double bonds) Vitamins- organic molecules required in the diet in small amounts Minerals- simple inorganic nutrients, usually required in small amounts; Ingesting large amounts of some minerals can upset homeostatic balance Animals can be divided into the following groups depending upon their food habits: Herbivores: Herbivores are animals that depend upon plants and fruits for their nutrition. Cows, goats, sheep, buffaloes, etc. are herbivores. Carnivores: Carnivores are animals that depend upon other animals for food. Lion, tigers, wolfs are some examples of carnivores. Omnivores: These include organisms that eat both plants and animals. Humans, bears, dogs, crows are omnivores.  Types of Nutrition in Animals Fluid feeding: obtaining nutrients by consuming other organisms’ fluids. Deposit Honey bees, and mosquitos exhibit Filter Feeding: obtaining feeding: obtaining nutrients from particles this mode of food intake. nutrients from suspended in water. particles Commonly used by fish. suspended in the soil. Earthworms use this mode of ingestion Bulk feeding: obtaining nutrients by eating the whole of an organism. Example: Python  Overview of the digestive system ✓ Ingestion -is the process of taking in food. ✓ Digestion- the process of breaking down food into individual molecules small enough to be absorbed through the intestinal wall Mechanical digestion, including chewing, increases the surface area of food Chemical digestion splits food into small molecules that can pass through membranes; these are used to build larger molecules ✓ absorption-the process involving nutrients from the gastrointestinal tract into the bloodstream ✓ Transport-the process involving absorbed nutrients throughout the body through the circulatory and lymph systems ✓ Assimilation- The absorbed food is used for energy, growth and repair of the cells of the body ✓ Elimination/Egestion--excretion of undigested and unabsorbed food through the feces  Digestive Compartments Most animals process food in specialized compartments These compartments reduce the risk of an animal digesting its own cells and tissues In intracellular digestion, food Extracellular digestion is the breakdown of particles are engulfed by food particles outside of cells phagocytosis It occurs in compartments that are continuous Food vacuoles, containing food, with the outside of the animal’s body fuse with lysosomes containing Animals with simple body plans have a hydrolytic enzymes gastrovascular cavity that functions in both digestion and distribution of nutrients  Mouth Tentacles Digestion in a hydra. Digestion begins in the Food gastrovascular cavity and is 1 Digestive enzymes released completed intracellularly after small food particles 2 Food are engulfed by specialized particles broken cells of the gastrodermis down 3 Food particles engulfed and digested Epidermis Gastrodermis  More complex animals have a digestive tube with two openings, a mouth and an anus This digestive tube is called a complete digestive tract or an alimentary canal It can have specialized regions that carry out digestion and absorption in a stepwise fashion The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder  Figure 41.8 Crop The alimentary canal of an Esophagus Gizzard earthworm includes a muscular Pharynx Intestine pharynx that sucks food in A grasshopper has through the mouth. Food passes several digestive through the esophagus and is chambers grouped into stored and moistened in the crop. three main regions: a Anus Mechanical digestion occurs in the foregut, with an muscular gizzard, which pulverizes esophagus and crop; a Mouth food with the aid of small bits of midgut; and a hindgut. (a) Earthworm sand and gravel. Further digestion Food is moistened and and absorption occur in the stored in the crop, but Foregut Midgut Hindgut Esophagus intestine. most digestion occurs in the midgut. Pouches Crop called gastric cecae Esophagus Rectum Stomach (singular, ceca) extend Anus Gizzard from the beginning of Intestine the midgut and Many birds have a crop for function in digestion Mouth storing food and a stomach and absorption. Anus and gizzard for mechanically Crop digesting it. Chemical Mouth Gastric cecae digestion and absorption of nutrients occur in the (b) Grasshopper (c) Bird intestine. The human digestive system. After food is chewed and swallowed, it takes 5–10 seconds for it to pass down the esophagus and into the stomach, where it spends 2–6 hours being partially digested. Further digestion and nutrient absorption occur in the small intestine over a period of 5–6 hours. Within 12–24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.  The teeth bite and grind Salivary glands-produce saliva the food into smaller which contains amylase for pieces, increasing the starch digestion and fluid to surface area lubricate the food The tongue mixes the Water helps dissolve the food with saliva and substance in the food forms it into a bolus Mucus helps the chewed food to bind together to form bolus  Esophagus Bolus of Tongue food Epiglottis Pharynx up Glottis Esophageal sphincter Larynx contracted Trachea Esophagus Relaxed To lungs To stomach muscles Contracted Intersection of the human airway and digestive tract. muscles ✓ the pharynx connects to the trachea and the esophagus. ✓ At most times, a contracted sphincter seals off the esophagus Sphincter while the trachea remains open. relaxed ✓ When a food bolus arrives at the pharynx, the swallowing reflex is triggered. Movement of the larynx, the upper part of the airway, tips a flap of tissue called the epiglottis down, preventing Stomach food from entering the trachea. At the same time, the esophageal sphincter relaxes, allowing the bolus to pass into the esophagus.  Parietal cells secrete hydrogen and chloride ions separately into the lumen (cavity) of the stomach Gastric juice has a low pH of about 2, which kills bacteria and denatures proteins Chief cells secrete inactive pepsinogen, Gastric juice is made up of hydrochloric acid which is activated to pepsin when mixed (HCl) and pepsin with hydrochloric acid in the stomach Pepsin is a protease, or protein-digesting Mucus protects the stomach lining from enzyme, that cleaves proteins into smaller peptides gastric juice  Small intestine Most digestion occurs in the small intestines It has three sections Duodenum Jejunum Ileum Takes 3-10 hrs for food to travel to the small intestine  The duodenum is also a major site for absorption of iron. The jejunum is a major site for absorption of the vitamin folic acid and the end of the ileum is the most important site for absorption for the vitamin B12, and bile salts. The ileum function involves absorption of vitamin B12, bile salts and all digestion products which were not absorbed in duodenum and jejunum.  Pancreas ✓ Produces pancreatic juice ✓ Contains enzymes, mucus and hydrogen carbonate which hydrolyzes acidic chyme ✓ Pancreatic juice is poured inti the small intestine through the pancreatic duct ✓ Several enzymes are secreted into the duodenum ✓ They are made in the pancreas, which is cream-colored gland, lying just underneath the stomach ✓ Pancreatic duct leads from the pancreas into the duodenum ✓ Amylase protease and lipase ✓ Amylase breaks down starch to maltose ✓ Trypsin is a protease which breaks down proteins to polypeptides ✓ Lipase break down fats(lipids) to fatty acids and glycerol  LIVER Bile production and excretion. Excretion of bilirubin, cholesterol, hormones, and drugs. Metabolism of fats, proteins, and carbohydrates. Enzyme activation. Storage of glycogen, vitamins, and minerals. Synthesis of plasma proteins, such as albumin, and clotting factors.  Absorption The movement of digested food molecules through the wall if the intestine into the blood Most absorption happens in the ileum Small intestine as a large internal surface area for absorption to happen quickly and efficiently The inner wall of all parts of the small intestine-the duodenum and the ileum-is covered with millions of tiny projections called villi  Large intestine Any food that is not absorbed in the small intestine moves by peristalsis into the large intestine also called as colon Large in diameter but shorter The waste product become more solid as even more water is absorbed Peristalsis continue to force the semisolid waste into the rectum, the last section of the large intestine The rectum and the anus control the release of the semi solid waste called faces ✓ Site of water, sodium, potassium, and chloride absorption ✓ Bacteria provides vitamin K, thiamin, riboflavin, biotin and vit B12 ✓ 1 l of fluid material is gradually reduced to 200 grams of brown fecal material ✓ Brown color is due to the unabsorbed iron mixed with yellowish orange substance called bilirubin ✓ Greater iron content, the darker the feces  Absorption in the Large Intestine The colon of the large The colon of the large intestine is connected to intestine is connected the small intestine to the small intestine The cecum aids in the Ascending portion The cecum aids in the fermentation of plant of colon fermentation of plant material and connects Small material and connects where the small and intestine large intestines meet where the small and large The human cecum has intestines meet an extension called the The human cecum has an appendix, which plays a very minor role in extension called the immunity Cecum Appendix appendix, which plays a very minor role in immunity  Dentition, an animal’s assortment of teeth, is one example of structural variation reflecting diet The success of mammals is due in part to their dentition, which is specialized for different diets Nonmammalian vertebrates have less specialized teeth, though exceptions exist For example, the teeth of poisonous snakes are modified as fangs for injecting venom Stomach and Intestinal Adaptations Small intestine Many carnivores have large, Small intestine Stomach expandable stomachs Herbivores and omnivores generally have longer Cecum alimentary canals than carnivores, reflecting the longer time needed to digest Colon (large vegetation Carnivore intestine) Herbivore  The alimentary canals of a carnivore (coyote) and herbivore (koala). The relatively short digestive tract of the coyote is sufficient for digesting meat and absorbing its nutrients. In contrast, the koala’s long alimentary canal is specialized for digesting eucalyptus leaves. Extensive chewing chops the leaves into tiny pieces, increasing exposure to digestive juices. In the long cecum and the upper portion of the colon, symbiotic bacteria further digest the shredded leaves, releasing nutrients that the koala can absorb. Mutualistic Adaptations 1 Rumen 2 Reticulum Many herbivores have Esophagus fermentation chambers, where mutualistic microorganisms digest cellulose The most Intestine elaborate adaptations for an herbivorous diet have evolved in the animals called ruminants 4 Abomasum 3 Omasum  1 Rumen 2 Reticulum Esophagus Ruminant digestion. The stomach of a cow, a ruminant, has four chambers. 1 Chewed food first enters the rumen and reticulum, where mutualistic microorganisms digest cellulose in the plant material. 2 Periodically, the cow Intestine regurgitates and rechews “cud” from the reticulum, further breaking down fibers and thereby enhancing microbial action. 3 The reswallowed cud passes to the omasum, where some water is removed. 4 It then passes to the abomasum for digestion by the cow’s enzymes. In this way, the cow obtains significant nutrients from both the grass and the mutualistic microorganisms, which maintain a stable population in the rumen 4 Abomasum 3 Omasum  Regulation of Energy Storage The body stores energy-rich molecules that are not needed right away for metabolism In humans, energy is stored first in the liver and muscle cells in the polymer glycogen Excess energy is stored in adipose tissue, the most space- efficient storage tissue  Chyme—an acidic mixture of partially digested food—eventually passes from If the chyme is rich in As food arrives at the stomach, it fats, the high levels of the stomach to the duodenum. The stretches the stomach walls, secretin and CCK released duodenum responds by releasing the triggering release of the hormone act on the stomach to digestive hormones cholecystokinin and gastrin. Gastrin circulates via the inhibit peristalsis and secretin. Cholecystokinin (CCK) bloodstream back to the stomach, secretion of gastric juices, stimulates the release of digestive where it stimulates production of thereby slowing digestion. enzymes from the pancreas and of bile gastric juices. from the gallbladder. Secretin stimulates the pancreas to release bicarbonate (HCO3 –), which neutralizes chyme  Glucose Homeostasis Oxidation of glucose generates ATP to fuel cellular processes The hormones insulin and glucagon regulate the breakdown of glycogen into glucose The liver is the site for glucose homeostasis A carbohydrate-rich meal raises insulin levels, which triggers the synthesis of glycogen Low blood sugar causes glucagon to stimulate the breakdown of glycogen and release glucose Homeostatic regulation of cellular fuel. After a meal is digested, glucose and other monomers are absorbed into the blood from the digestive tract. The human body regulates the use and storage of glucose, a major cellular fuel.  Pancreas secretes insulin. Transport of glucose into Stimulus: body cells Blood glucose and storage level rises of glucose after eating. as glycogen Homeostasis: 70–110 mg glucose/ 100 mL blood Stimulus: Blood glucose level drops below set point. Breakdown of glycogen Pancreas and release secretes of glucose glucagon. into blood  Regulation of Appetite and Consumption Overnourishment causes obesity, which results from excessive intake of food energy with the excess stored as fat Obesity contributes to diabetes (type 2), cancer of the colon and breasts, heart attacks, and strokes Researchers have discovered several of the mechanisms that help regulate body weight © 2011 Pearson Education, Inc.  A few of the appetite-regulating hormones. Secreted by various organs and tissues, the hormones reach the brain via the bloodstream. These signals act on a region of the brain that in turn controls the “satiety center,” which generates the nervous impulses that make us feel either hungry or satiated (“full”). The hormone ghrelin is an appetite stimulant; the other three hormones shown here are appetite suppressants.  Hormones regulate long-term and short-term appetite by The problem of maintaining affecting a “satiety center” in weight partly stems from our the brain evolutionary past, when fat Studies on mice revealed that hoarding was a means of survival the hormone leptin plays an Individuals who were more likely important role in regulating to eat fatty food and store energy obesity as adipose tissue may have been Leptin is produced by adipose more likely to survive famines tissue and can help to suppress appetite