A&P 2 Final Exam Review PDF

Atp2 Final review Final exam review A&P 2 1. What is the meaning of intraperitoneal and retroperitoneal? Describe the location of the following organs relative to the peritoneum: Intraperitoneal: organs that are completely or partially enclosed by the peritoneal cavity. These organs are su...

Atp2 Final review Final exam review A&P 2 1. What is the meaning of intraperitoneal and retroperitoneal? Describe the location of the following organs relative to the peritoneum: Intraperitoneal: organs that are completely or partially enclosed by the peritoneal cavity. These organs are suspended within the peritoneal cavity by mesenteries, allowing them to move freely and slide across one another without damage. Retroperitoneal: organs that lie between the peritoneal lining and the muscular wall of the abdominal cavity. These organs are xed in place and their anterior surfaces are covered by the peritoneum. Stomach: Intraperitoneal, liver: intraperitoneal, ureter: retroperitoneal, aorta: retroperitoneal, pancreas: retroperitoneal, colon (transverse): intraperitoneal, spleen: intraperitoneal, duodenum: retroperitoneal, uterus: intraperitoneal, bladder: intraperitoneal, kidney: retroperitoneal, ileum: intraperitoneal, appendix: intraperitoneal, jejenum: intraperitoneal. 2. Describe the tissues that make up serous membranes. Serous membranes, also known as serousa, line the sealed internal cavities of the trunk, such as the peritoneal, pleural, and pericardial cavities. These membranes are composed of 2 main types of tissue: mesothelium: this is a layer of simple squamous epithelial cells. These cells are very thin and permeable, allowing tissue uids to diffuse onto the exposed surfaces, keeping them moist and slippery. The mesotheliums primary role is to secrete serous uid, which minimizes friction between the surfaces it covers. Areolar connective tissue: beneath the mesothelium lies a thin layer of areolar connective tissue. This tissue provides the necessary support and elasticity to the mesothelium, ensuring that the serous membrane can adhere rmly to the body wall and the fi fl fl organ it covers. Name the serous membranes at the following locations: Lining the outer wall of abdominal cavity: parietal peritoneum: lines the inner surface of the abdominal cavity. Visceral peritoneum: covers the surfaces of the enclosed organs. Serousa of the stomach: Visceral peritoneum: speci cally covers the stomach and other organs within the peritoneal cavity. Lining of the outer wall of the thoracic cavity: parietal pleura: lines the inner surface of the thoracic cavity. Visceral pleura: covers the outer surface of the lungs. Attached to the surface of the heart: Visceral pericardium: covers the heart. Parietal pericardium: lines the pericardial cavity. What is found between the visceral and parietal layers of a serous membrane? Serous uid a slippery uid secreted by the mesothelium that reduces friction between the visceral and parietal layers. 3. Name all the structures that food passes through from the mouth to the anus. Name the accessory structures of the G.I. Tract. Oral cavity (mouth): Entry point where food is ingested and mechanically processed by chewing. Pharynx (throat): passageway for food moving from the mouth to the esophagus. Esophagus: tube that transports food from the pharynx to the stomach. Stomach: mixes and breaks down food with acids and enzymes. Small intestine: duodenum - rst part where most chemical digestion occurs. Jejenum - fl fi fi middle part where nutrient absorption continues. Ileum - nal part where absorption is completed. Large intestine: Cecum - receives material from the ileum. Colon - divided into ascending, transverse, descending, and sigmoid regions. Rectum - stores feces before elimination. Anus: the nal exit point for waste. Accessory structures of the GI tract Accessory organs: Teeth: mechanical processing by chewing Tongue: assist with mechanical processing and sensory analysis Salivary glands: secrete enzymes that break down carbohydrates Liver: secretes bile for lipid digestion and stores nutrients Gallbladder: stores and concentrates bile Pancreas: secretes digestive enzymes and buffers 4. Describe the tissues that make up the 4 histological layers of organs in the GI, respiratory, urinary, and reproductive tracts. Mucosa: innermost layers consisting of: 3 parts Epithelium: varies by organ (simple columnar in the small intestine for absorption) Lamina propria: areolar tissue supporting the epithelium Muscularis mucosa: thin layers of smooth muscle. GI tract: Mucosa: simple columnar epithelium in the small intestine with villi for absorption. fi fi  Submucosa: contains submucosal plexus and glands. Muscularis externa: circular and longitudinal layers. Serousa: outermost layers with connective tissue. Respiratory tract: Mucosa: pseudostrati ed ciliated columnar epithelium in the trachea. Submucosa: contains mucous glands. Muscular layer: smooth muscle in the bronchioles. Adventitia: dense connective tissue in the trachea. Urinary tract: Mucosa: transitional epithelium in the bladder. Submucosa: connective tissue with blood vessels. Muscular layer: detrusor muscle in the bladder. Adventitia: connective tissue Reproductive tract: Mucosa: varies by organ (strati ed squamous epithelium in the vagina) Submucosa: connective tissue with blood vessels Muscular layer: smooth muscle. Adventitia serousa: connective tissue. When does an organ have a Adventitia instead of a serosa? An organ has an Adventitia instead of a serosa when it is not enclosed by the peritoneal cavity and needs to be rmly attached to adjacent structures. This dense brous sheath provides stability and support, fi fi fi unlike the serosa, which allows for movement and reduces friction. 5. Explain the process of peristalsis. Which tissues are necessary for peristalsis? Which part of the autonomic nervous system increases peristalsis in the GI tract? Peristalsis is the process by which the muscular layer of the digestive tract propels materials from one portion to another. It involves coordinated contractions of the circular and longitudinal muscles. Initially, the circular muscles behind the bolus contract, narrowing the tract. Then, the longitudinal muscles ahead of the bolus contract, shortening the segment. Finally, a wave of contraction in the circular muscles forces the bolus forward. The tissues necessary for peristalsis include visceral smooth muscle tissue, which contains pacesetter cells that initiate contractions, and the muscular layers (inner circular and outer longitudinal muscles) that perform contractions. The parasympathetic nervous system plays a crucial role in increasing peristalsis by enhancing the sensitivity of the myenteric re exes, which are local re exes controlled by the enteric nervous system. List the organs that undergo peristalsis in each system: Urinary system: the ureters - transport urine from the kidneys to the bladder. Urinary bladder - stores urine and expels through the urethra. Urethra - conducts urine out the body. Digestive system: esophagus - moves food from the throat to the stomach. Stomach - mixes and propels food. Small intestine - propels food and absorbs nutrients. Large intestine - moves waste toward the rectum. Reproductive system: Male - ductus deferens: propels sperm from the epididymis to the urethra. Female - uterine tubes: moves ooctyes from the ovaries to the uterus. 6. Describe the function and origin of each of the enzymes: Amylase: Function - breaks down starches (complex carbohydrates) into disaccharides and trisaccharides. Origin - salivary amylase: released in the oral cavity by the parotid and submandibular glads. Pancreatic alpha amylase: released by the pancreas into the small intestine. Pepsin: function - breaks down proteins into polypeptides. Original - released as pepsinogen by chief cells in the stomach and activated to pepsin by hydrochloric acid (HCL). Trypsin/chymotrypsin: Trypsin: function - breaks peptide bonds involving arginine or lysine. Chymotrypsin - targets peptide bonds involving tyrosine or phenylalanine. Origin - both are released as inactive proenzymes (trypsinogen and chymotrypsinogen) by the pancreas and activated in the small intestines. Trypsinogen is converted to trypsin by enteropeptidase, and trypsin then activates chymotrypsinogen to chymotrypsin. Lipase: function - breaks down complex lipids into monoglycerides and fatty acids. Origin - lingual lipase: released in the oral cavity. Pancreatic lipase: released by the pancreas into the small intestine. Lactase: function - breaks down lactose ( a disaccharide) into glucose and galactose. Origin - present in the brush border of the intestinal mucosa. Which of these enzymes are proenzymes and list how each is activated Trypsinogen: proenzyme form: trypsinogen. Activation: converted to trypsin by  enteropeptidase in the duodenum. Role: trypsin then activates other proenzymes. Chymotrypsinogen: proenzyme form: chymotrypsinogen. Activation: activated by trypsin to form chymotrypsin. Role: breaks peptide bonds involving speci c amino acids. Is bile an enzyme? Does it contain digestive enzymes? Bile is not an enzyme. It is a digestive uid produced by the liver and stored in the gallbladder. Bile consists mostly of water, ions, bilirubin, cholesterol, and bile salts. It does not contain digestive enzymes. Bile salts play a crucial role in the digestion of lipids by emulsifying large lipid droplets into smaller ones, increasing the surface area for pancreatic lipase to act on. This process is called emulsi cation, helps in the ef cient breakdown and absorption of dietary fats. What is the function of bile? Bile is essential for the digestion and absorption of lipids (fats). It helps dilute and buffer acids in chyme as it enter the small intestine. Bile salts break down large lipid droplets into smaller ones in a process called emulsi cation. This increases the surface area for pancreatic lipase to act on, improving lipid digestion. After aiding in digestion, more than 90% of bile salts are reabsorbed in the ileum and returned to the liver through the hepatic portal circulation. This recycling process is known as enterohepatic circulation. Explain how bile travels from the liver to the small intestine naming all the ducts involved. Bile canaliculi: bile is secreted by the liver into narrow channels called bile canaliucli. Bile ductules and bile ducts: bile canaliculi connects with bile ductules , which then carry bile to the bile ducts in the portal areas. Hepatic ducts: the right and left hepatic ducts collect bile from the bile ducts of the liver lobes. fl fi fi  Common hepatic duct: the right and left hepatic ducts unite to form the common hepatic duct, which carries bile away from the liver. Cystic duct and bile duct: from the common hepatic duct, bile can either ow into the cystic duct to be stored in the gallbladder or ow directly into the bile duct. Duodenal ampulla: the bile duct joins with the pancreatic duct at the duodenal ampulla. Bile is then released into the duodenum through the duodenal papilla. 7. What mechanical and chemical digestion takes place in each of the following organs? Mouth: mechanical digestion - mastication (chewing): food is broken down by the teeth and mixed with saliva, forming a bolus. Chemical digestion- salivary amylase: begins the breakdown of carbohydrates into simpler sugars. Esophagus: mechanical digestion - peristalsis: rhythmic contractions propel the bolus toward the stomach. Chemical digestion: none, as the esophagus primarily serves as a conduit. Stomach: mechanical digestion - churning: the stomach muscles mix food with gastric juices, forming chyme. Chemical digestion - pepsin: beaks down proteins into smaller peptides. Hydrochloric acid (HCL): creates an acidic environment for enzyme activity and kills pathogens. Small intestine: mechanical digestion - segmentation: cycles of contraction mix chyme with digestive juices. Chemical digestion - pancreatic enzymes: break down carbohydrates, proteins, and fats. Brush border enzymes: further digest nutrients into absorbable units. fl  Large intestine: mechanical digestion- segmentation and mass movements: mix and propel waste toward the rectum. Chemical digestion - bacterial fermentation: breaks down remaining carbohydrates and synthesizes vitamins. 8. Where in the GI tract does food absorption occur? Small intestine: the absorption powerhouse. The small intestine is lined with circular folds (rugae), villi, and microvilli, which signi cantly increase the surface area for absorption. These structures enhance the absorptive effectiveness by stirring and mixing the intestinal contents ensuring nutrient uptake. It takes about 5 hours for materials to pass from the duodenum to the end of the ileum, during which most nutrients are absorbed. The large intestine primarily reabsorbs water and absorb some vitamins and bile salts. Although it plays a role in absorption, less than 10% of nutrient absorption occurs in the large intestine. Describe the process by which carbohydrates are absorbed. Initial breakdown: oral cavity: salivary amylase begins breaking down complex carbohydrates into disaccharides and trisaccharides. Stomach: gastric activity continues to break down carbohydrates into smaller molecules. Further digestion in the small intestine: pancreatic amylase: upon arrival in the duodenum, pancreatic amylase further breaks down carbohydrates into disaccharides and trisaccharides. Final break down at the brush border: brush border enzymes: enzymes like lactase, maltase, and sucrase on the intestinal mucosa break down disaccharides and trisaccharides into monosaccharides (glucose, fructose, and galactose). fi  Absorption mechanisms: facilitated diffusion and cotransport: monosaccharides are absorbed into the intestinal epithelial cells via facilitated diffusion and cotransport mechanisms. Facilitated diffusion: moves one molecule at a time without ATP. Cotransport: moves multiple molecules simultaneously, often involving sodium ions, and may require ATP indirectly for maintaining ion gradients. Transport to the blood stream: Capillary absorption: monosaccharides diffuse into the capillaries of the villi and are transported to the liver via the hepatic portal vein. Name the 4 modi cations of the small intestine that increase its surface area for food absorption: Circular fold (Plicae Circulares): these are permanent transverse folds in the intestinal lining. They increase the surface area and cause the chyme to spiral, slowing its movement and allowing more time for absorption. Intestinal villi: nger like projections that cover the circular folds. Each villus is covered with simple columnar epithelium and contains a network of capillaries and lymphatic vessels (lacteal) for nutrient absorption. Microvilli: tiny hair-like structures on the surface of the epithelial cells covering the villi. They form a brush border that further increases the surface area and contains enzymes for digestion. Rich supply of blood and lymphatic vessels: the small intestine is richly supplied with blood vessels and lymphatic vessels. These vessels transport absorbed nutrients away from the intestine to the rest of the body. fi fi In what form are carbohydrates when they are absorbed? For carbohydrates to be absorbed they have to be broken down into monosaccharides. Process: hydrolysis of carbohydrates - complex carbohydrates (polysaccharides and disaccharides) are broken down into monosaccharides through hydrolysis. This process is essential because only monosaccharides can be absorbed by the intestinal lining. Absorption mechanisms: facilitated diffusion - monosaccharides are absorbed by the intestinal epithelium using carrier proteins. This process does not require ATP. Cotransport: monosaccharides can also be absorbed along with sodium ions through cotransport mechanisms. This process can occur even against a concentration gradient and involves active transport. Transport to the liver: once absorbed, monosaccharides enter the capillaries of the villi and are transported to the liver via the hepatic portal vein. In what form are proteins when they are absorbed? Digestion: mechanical digestion: begins in the oral cavity with mastication (chewing). Chemical digestion: in the stomach, hydrochloric acid disrupts protein structures, and pepsin peptide bonds within polypeptides. Small intestine: enzymes like trypsin, chymotrypsin, and carboxypeptidase further break down polypeptides into short peptides and amino acids. Absorption: brush border enzymes: dipeptidase in the small intestine break short peptides into individual amino acids. Transport mechanisms: amino acids are absorbed through facilitated diffusion and cotransport mechanisms into the intestinal cells. Into the blood stream: amino acids diffuse into the intestinal uid and then into intestinal capillaries, transported to the liver via the hepatic portal vein. fl Describe the process by which amino acids are absorbed? Proteins are broken down into amino acids and are absorbed by facilitated diffusion and cotransport. Amino acids enter the blood stream and are transported to the liver to be used for protein synthesis or converted to other forms form energy storage. Once absorbed, where do monosaccharides and amino acids go? Monosaccharides and amino acids: both are transported from the intestinal cells into the capillaries of the villi. Hepatic portal vein: these nutrients then enter the blood stream and are transported to the liver via the hepatic portal vein. Liver processing: monosaccharides - the liver can convert glucose to glycogen for storage or release it into the blood stream to maintain glucose levels. Amino acids: the liver uses amino acids for protein synthesis or converts them into other compounds as needed. Which vessel carries the nutrients to the liver? The hepatic portal vein is the primary vessel that transports nutrients directly to the liver. This vein collects blood from the capillaries of the digestive organs and delivers it to the liver for processing. In what form are fats when they are absorbed? Chylomicrons. Triglycerides are coated with proteins, forming chylomicrons. Chylomicrons are secreted into the lymphatic system and eventually enter the blood stream. Describe the process by which fats are absorbed? Initial breakdown: triglycerides - broken down by lingual and pancreatic lipase into monoglycerides and fatty acids. Formation of micelles: emulsi cation - bile salts emulsify lipid droplets into smaller emulsion droplets. Micelles: monoglycerides and fatty acids combine with bile salts to form micelles. Absorption fi into intestinal mucosa: diffusion - micelles contact the intestinal epithelium, allowing lipids to diffuse into the epithelial cells. Reassembly: inside the cells, monoglycerides and fatty acids are reassembles into triglycerides. Formation of chlyomicrons: complexes - triglycerides are coated with proteins, forming chlyomicrons. Secretions: chlyomicrons are secreted into interstitial uid by exocytosis. Transport via lymphatic system: lacteals - Chylomicrons enter lacteals and process through lymphatic vessels. Thoracic duct - chlyomicrons enter the blood stream at the left subclavian vein. Distribution and utilization: lipoprotein lipase - breaks down Chylomicrons in capillaries, releasing fatty acids and monoglycerides. Absorption by cells: fatty acids are absorbed by skeletal muscles for ATP production or storage, and by adipocytes for triglyceride synthesis. What is a chylomicron? Chylomicrons are the largest lipoproteins, ranging from 0.03 to 0.5 micrometer in diameter. They consist of about 95% triglycerides. Produced by intestinal epithelial cells from dietary fats. Formed when monoglycerides and fatty acids are reassembled into triglycerides and coated with proteins. Carry absorbed lipids from the intestinal tract into the lymphatic system and then to the blood stream which distribute lipids throughout the body for use in various tissues. Intestinal cells secrete Chylomicrons into the intestinal uid. Enter lacteals (lymphatic vessels) and proceeds to the thoracic duct. Enter the blood stream at the left subclavian vein. Lipoprotein lipase breaks down chlyomicrons in capillaries, releasing fatty acids and monoglycerides for absorption by cells. Where do fats go once absorbed? Absorption by tissues: skeletal muscles: absorb fatty acids for ATP production or storage as glycogen. Adipocytes: absorb fatty acids to synthesize and fl fl store triglycerides. The liver absorbs remaining Chylomicrons, creating low-density lipoproteins (LDL) and very low-density proteins (VLDL). LDLs deliver cholesterol to peripheral tissues, while VLDL transport triglycerides to muscle and adipose tissue. HDLs collect excess cholesterol from tissues and return it to the liver. The liver can either store the cholesterol or excrete it in bile. Name 2 other types of lipoproteins and their functions. Low density lipoproteins (LDL): contains cholesterol, smaller amounts of phospholipids and very few triglycerides. LDL delivers cholesterol to peripheral tissues. This cholesterol is used by cells to synthesize membranes, hormones, and other materials. LDL cholesterol is often referred to as bad cholesterol because it can contribute to the formation of arterial plaques, which can lead to cardiovascular diseases. High density lipoproteins (HDL): have roughly equal amounts of lipid and protein, with the lipids being largely cholesterol and phospholipids. HDLs transport excess cholesterol from peripheral tissues back to the liver. The liver can then store the cholesterol or excrete it in bile. HDL cholesterol is known as the good cholesterol because it helps remove excess cholesterol from the blood stream, reducing the risk of circulatory problems. 9. Describe the function of the following accessory organs in the GI tract: Liver: metabolic and hematological regulation: the liver regulates blood composition, removes and stores excess nutrients, and synthesizes needed nutrients. The liver produces bile , which is essential for lipid digestion. Bile emulsi es fats, making then accessible to digestive enzymes. Gall bladder: bile storage and concentration: the gall bladder stores and concentrates bile produced by the liver. It releases bile into the small intestine to aid in digestion. Salivary gland: secretion of lubricating uid: these glands secrete saliva, which contains enzymes that begin the breakdown of carbohydrates in the mouth. Pancreas: digestive enzymes and buffers: the pancreas secretes digestive enzymes that break down proteins, fats, and carbohydrates. It also produces bicarbonate to neutralize stomach acids in the small intestine. 10. Why is it important that stomach juice is acidic? Give at least 2 reasons. Microorganism control: the highly acidic environment of the stomach (pH 1.5-2.0) is crucial for killing most of the microorganisms ingested with food. This helps protect the body from potential infections. Proteins digestion: denaturation of proteins: the acidity denatures proteins and inactivates most enzymes in food, making it easier for digestive enzymes to break them down. Activation of pepsin: the acidic environment is necessary for converting pepsinogen to pepsin, an enzymes that digest proteins effectively at a pH of 1.5 - 2.0. 11. Digestion is largely controlled by the enteric nervous system( intrinsic nervous system) and the central nervous system. The intrinsic nervous system of the GI tract is called the enteric nervous system. Which part of the autonomic nervous system increases motility and secretion in the GI tract? The parasympathetic division of the autonomic nervous system (ANS) is primarily responsible fl for increasing motility and secretion in the GI tract. This division, often referred to as the rest and digest system, enhances digestive activities by stimulating smooth muscle contractions and glandular secretions. Preganglionic bers from the brain and sacral segments synapse with ganglionic neurons in the digestive tract, promoting these activities. Which cranial nerve is involved? The vagus nerve (X) plays a crucial role in increasing motility and secretion in the GI tract. Stimulates digestive glands, including salivary glands, gastric glands, and the pancreas. Promotes the secretion of digestive enzymes and hormones that aid in nutrient absorption. The vagus never increases smooth muscle activity along the digestive tract and facilitates peristalsis, the wave like contractions that move food through the GI tract. Explain the function of the following hormones and where they are made: Gastrin: secreted by G cells in the stomach and duodenum. Promotes increased stomach motility. Stimulates the production of gastric acids and enzymes. Secretin: released by the duodenum when chyme arrives. Increases the secretion of buffers by the pancreas to raise the pH of chyme. Stimulates bile secretion by the liver. Reduces gastric motility and gastric secretory rates. Cholecystokinin (CCK): secreted by the duodenum when chyme, especially containing lipids and partially digested proteins arrives. Accelerates the production and secretion of digestive enzymes by the pancreas. Causes relaxation of the hepatopancreatic sphincter and contraction of the gall bladder, leading to the ejection of bile and pancreatic juice into the duodenum. Inhibits gastric activity and reduces the sensation of hunger at high fi concentrations. 12. Describe the function of the large intestines regarding absorption. The large intestine is highly ef cient a reabsorbing water. Approximately 1500ml of material enters the colon daily, but only about 200 ml of feces is ejected. This means around 1300 ml of water is reabsorbed, which is about 86.67% of the water content. This reabsorption is vital for maintaining the body’s uid balance and preventing dehydration. The large intestines absorbs useful compound such as bile salts and vitamins produced by gut bacteria. Organic wastes and toxins: it also absorbs various organic wastes and toxins generated by bacterial action. What is the function of the colonic bacteria? Vitamin K production: essential for synthesizing clotting factors in the liver. Biotin (vitamin B7): important for glucose metabolism. Vitamin B5 (pantothenic acid): necessary for manufacturing steroid hormones and neurotransmitters. Nutrient breakdown: bilirubin conversion: bacteria convert bilirubin into urobillinogens and stercobillinogens, which are further processed to give feces its brown color. Peptide breakdown: bacteria break down remaining peptides in feces, producing compounds like ammonia, indole, skatole, and hydrogen sul de. Protection health and maintenance: crowding out harmful bacteria: bene cial bacteria can outcompete harmful bacteria, such as Clostridium dif cile, preventing infections and maintaining intestinal health. Recycling nutrients: they can helps bile salts and other fi fi fl fi useful compounds. Gas production: the metabolic activities of these bacteria produce small amounts of intestinal gas, which is normal part of digestion. Explain the process of defecation. Movement into the rectum: Gastrolleal and Gastoenteric re exes: these re exes move material into the cecum while you eat. Slow movement: from the cecum to the transverse colon, movement is slow, allowing water absorption and forming a sludgy paste. Mass movement: powerful peristaltic contractions move material from the transverse colon to the rectum. Initiation of the defecation re ex: stretch receptors: when feces enter the rectum, they cause distension, stimulating stretch receptors in the rectal wall. Two positive feedback loops: short re ex (intrinsic myenteric defecation re ex): this re ex triggers peristaltic contractions in the rectum, moving feces toward the anus and relaxing the internal anal sphincter. Long re ex (parasympathetic defecation re ex): coordinated by the sacral parasympathetic system, this re ex stimulates mass movements from the descending and sigmoid colon, further relaxing the internal anal sphincter. Voluntary control: external anal sphincter: voluntary relaxation of this sphincter allows for defecation to occur at a convenient time. 13. Describe enzymes. How does it differ from a hormone? Enzymes: enzymes are biological catalysts that speed up chemical reactions without being consumed or permanently changed. fl fl fl fl Each enzyme only catalyzes only one type of reaction due to the speci c shape and charge of it active site. The rate of reaction depends on substrate concentration. Once all enzymes molecules are engaged, the reaction rate plateaus. Enzyme activity can be turned on or off by changes in their shape, often in uenced by cofactors. Enzymes can catalyze synthesis, decomposition, reversible, or exchange reactions. They only affect the rate, not the direction or products of the reaction. Hormones: hormones are chemical messengers that coordinate activity in various tissues and organs over a sustained period. Alter genetic activity: hormones can activate genes to synthesize new enzymes or proteins. Change protein synthesis rate: they can increase or decrease the rate of transcription or translation. Modify membrane permeability: hormones can turn existing enzymes or membrane changed on or off by altering their shape. Hormones must bind to speci c receptors on target cells to exert their effects. The presence or absence of these receptors determines a cells sensitivity to a hormone. Speed and duration: enzymes act quickly and their effects are short-lived. While hormones act more slowly and their effects can last for days. Enzymes typically affect speci c reactions within a cell, whereas hormones can in uence multiple tissues and organs simultaneously. Enzymes are typically what type of organic compound? Enzymes are proteins, which are organic compounds containing carbon and hydrogen. Why are enzymes speci c or one type of reaction? Enzymes catalyze only one type of reaction due to the speci c t between the active site and substrates. The binding of fi fi fi fi fl fi fl substrates to the active site forms an enzyme- substrate complex, essential for catalysis. Isozymes: variants of enzymes that do not affect the active site and thus do not change the enzymes speci city. Explain why enzymes have an optimal pH and temperature range. Optimal temperature: each enzyme works best at a speci c temperature. This is because temperature affects the kinetic energy of molecules, in uencing the rate or enzyme- substrate collisions. Denaturation: at high temperatures, enzymes can denature, meaning their tertiary or quaternary structure changes irreversibly. This loss of structure results in the enzymes becoming nonfunctional. For example, frying an egg causes the proteins to denature and solidify. Optimal pH: enzymes also have an optimal pH at which they function most ef ciently. This is because pH affects the ionization of the enzyme and substrate, which can alter the enzymes shape and reactivity. Speci c pH ranges: different enzymes have different optimal pH levels. For instance, pepsin, which breaks down proteins in the stomach, works best at a highly acidic pH of 2.0. In contrast, trypsin, which operates in the small intestines , has an optimal pH of 7.7. 14. Write out the overall reaction for cellular respiration. C6H12O6 (glucose) + 6O2(oxygen) ->6CO2 (carbon dioxide) + 6H2O (water) + ATP (energy) Explain what is meant by oxidation of glucose: fi fi fl  It refers to the process by which glucose (C6H12O6) is broken down to produce energy in the form of ATP. Involves 3 major biochemical pathways: glycolysis, the citric acid cycle, and the electron transport chain. Which hormone has a strong in uence on the rate of cellular respiration? The thyroid hormone has a strong in uence on the rate of cellular respiration. The thyroid hormone produces a rapid increase in cellular metabolism. T3 (Triiodothyronine): primary active form and T4 (Thyroxine): converted to T3 in peripheral tissues. Explain why you would characterize cellular respiration as anabolic, catabolic or both. Cellular respiration is primarily a catabolic process, but it also has connections to anabolic pathways. Catabolic aspects: cellular respiration involves the breakdown of glucose (C6H12O6) into smaller molecules like carbon dioxide (CO2) and water (H2O). This process releases energy , which is used to produce ATP. Key pathways: glycolysis, citric acid cycle, electron transport chain. Energy production: the catabolic reactions in cellular respiration convert large molecules into smaller ones, releasing energy stored in chemicals bonds. This energy is captured in the form of ATP, which cells use for various functions Anabolic connections: ATP utilization: the ATP generated through catabolic processes is used in anabolic reactions. Anabolic reactions build larger molecules from smaller ones, such as synthesizing proteins or storing glycogen. Gluconeogenesis: although primarily catabolic, cellular respiration is linked to anabolic fl fl pathways like gluconeogenesis where glucose is synthesized form non-carbohydrate sources. 3 important steps in cellular respiration: Glycolysis: occurs in the cytosol, breaks down one glucose molecule into 2 molecules of pyruvate. Produces a net gain of 2 ATP and 2 NADH. Does not require oxygen (anaerobic). Partially reversible: some steps in glycolysis are reversible, allowing for gluconeogenesis. Krebs cycle (citric acid cycle): takes place in the mitochondrial matrix. Pyruvate is further broken down, releasing CO2. Produces NADH and FADH2, which carry electrons to the electron transport chain. Generates 2 ATP (via GTP). (Aerobic). Irreversible: due to the release of CO2. Electron transport chain: located in the inner mitochondrial membrane. Electrons from NADH and FADH2 are transferred through a series of proteins. Energy released is used to convert ADP to ATP. Oxygen is the nal electron acceptor, forming water. Produces 23 ATP. (Aerobic). Irreversible: it involves a series of redox reactions that are irreversible, as they create a proton gradient used for ATP synthesis. Explain the signi cance of pantothenic acid and acetlyCoA in cellular respiration. Role: Pantothenic acid is a vital component of coenzyme A (CoA), which is essential for the formation of acetyl-CoA. It helps in the metabolism of carbohydrates, fats, and proteins by facilitating the conversion of pyruvate to acetyl-CoA. Acetyl-CoA is formed from pyruvate during the transition from glycolysis to the citric acid fi fi cycle. It can also be generated from fatty acids through beta-oxidation. Acetyl-CoA enters the citric acid cycle, where it combines with oxaloacetate to form citrate, initiating a series of reactions that produce NADH, FADH2, and GTP/ATP. The NADH and FADH2 produced in the citric acid cycle carry electrons to the electron transport chain, leading to the production of ATP through oxidative phosphorylation. Can acetylCoA be converted to pyruvic acid? Why or why not? No, The conversion of pyruvate to acetyl-CoA is a one-way process. This reaction is catalyzed by the pyruvate dehydrogenase complex and is irreversible under normal cellular conditions. This ensures a unidirectional ow of carbon atoms through the metabolic pathways, optimizing energy production. Explain why and when ketogenesis occurs. Postabsorptive State: Ketogenesis primarily occurs during the postabsorptive state, which is the period between meals when the body relies on stored nutrients for energy. Fasting and Starvation: It is particularly prominent during fasting or prolonged starvation when glucose levels are low. Why ketogenesis occurs Lipid and Amino Acid Catabolism: During the postabsorptive state, the liver breaks down lipids and amino acids, generating acetyl-CoA. Excess Acetyl-CoA: As the concentration of acetyl-CoA rises, it leads to the formation of ketone bodies (acetoacetate, acetone, and beta-hydroxybutyrate). fl Explain the role of niacin and NADH in cellular respiration: Vitamin Niacin (B3): Niacin is essential for the synthesis of NAD (nicotinamide adenine dinucleotide), a crucial coenzyme in cellular respiration. Function of NADH: Electron Carrier: NADH is the reduced form of NAD and acts as an electron carrier in cellular respiration. Energy Transfer: NADH transfers high-energy electrons to the electron transport chain (ETC) in mitochondria. Describe the process of making ATP from glucose under anaerobic conditions. Glycolysis: Location: Cytosol of the cell. Process: Glucose is broken down into 2 pyruvate molecules. Energy Yield: Net gain of 2 ATP molecules and 2 NADH molecules. Equation: glucose + 2NAD + 2ADP + 2 II -> 2 pyruvate + 2NADH + 2ATP. Conversion to Lactate:Process: In the absence of oxygen, pyruvate is converted to lactate. Drawbacks: Lactate Accumulation: Leads to increased lactate levels and metabolic acidosis (lactic acidosis). Hydrogen Ions: Accumulation of hydrogen ions lowers intracellular pH, affecting enzyme function and muscle contraction. Ef ciency: ATP Yield: Only 2 ATP per glucose molecule, which is much less ef cient compared to aerobic conditions. How many ATP are formed? 2ATP Describe the following processes and list hormones that promote each reaction. Gluconeogenesis: process: Formation of glucose from non-carbohydrate sources like amino acids and glycerol. Location: primarily liver. Hormones promoting the reaction: Glucocorticoids: Stimulate the conversion of amino acids to glucose. fi Growth hormone: Also promotes gluconeogenesis. Glycogenesis: Conversion of glucose to glycogen for storage. Location: liver and skeletal muscle. Steps: Glucose is converted to glucose-6-phosphate. Glucose-6-phosphate is converted to glucose-1-phosphate. Glucose-1-phosphate is converted to glycogen using uridine triphosphate (UTP). Hormones promoting the reaction: insulin: Facilitates the uptake of glucose and its conversion to glycogen. Glycogenolysis: Breakdown of glycogen to release glucose. Location: liver and skeletal muscle. Steps: Glycogen is broken down to glucose-1-phosphate. Glucose-1-phosphate is converted to glucose-6-phosphate. Glucose-6-phosphate is converted to glucose. Hormones promoting the reaction: glucagon: Stimulates glycogen breakdown in the liver. Epinephrine: Stimulates glycogen breakdown in both liver and muscle. 15. Explain how proteins and amino acids can be used to make ATP. Amino acids are deaminated, meaning their amino group is removed. The remaining carbon chains are then sent to the mitochondria. These carbon chains enter the citric acid cycle at various points. The exact entry point depends on the speci c amino acid, which affects the ATP yield. The citric acid cycle produces NADH and FADH2, which carry electrons to the electron transport chain. Electrons pass through a series of protein complexes, releasing energy. This energy drives proton pumps, creating a gradient across the inner mitochondrial membrane. The proton gradient powers ATP synthase, converting ADP to ATP. For each pair of electrons from NADH, 2.5 ATP molecules are generated. For each pair of electrons from FADH2, 1.5 ATP molecules are generated.  Why is deamination necessary when amino acids can be used to make ATP. Deamination removes the amino group (–NH2) from the amino acid. This step is essential because the remaining carbon chain can then be used in the citric acid cycle to produce ATP. Deamination generates ammonium ions (NH4+), which are toxic. The liver converts these ammonium ions into urea, a less harmful substance excreted in urine. The carbon chains from deaminated amino acids enter the citric acid cycle. This cycle produces NADH and FADH2, which are used in oxidative phosphorylation to generate ATP. Without deamination, amino acids cannot be effectively utilized for ATP production. This process ensures that the amino acids are converted into a form that can be metabolized for energy. When the liver delaminates amino acids, what excretory product does the liver make? When the liver deaminates amino acids, it removes the amino group (–NH2), resulting in the formation of ammonia (NH3), which is toxic. To neutralize this toxicity, the liver converts ammonia into urea through the urea cycle. Urea is a relatively harmless, water- soluble compound that is excreted in the urine by the kidneys. How is this excretory product eliminated from the body? Urea is the most abundant organic waste, generated mainly through the breakdown of amino acids. Approximately 21 grams of urea are produced daily. The kidneys lter blood to remove metabolic wastes, including urea. Blood pressure forces water and solutes, including urea, across the walls of the glomerular capillaries into the capsular space ( ltration). Urea and other small solutes are ltered from the blood into the nephron. fi fi Essential nutrients and water are reabsorbed back into the bloodstream. Additional waste products are secreted into the tubular uid. The resulting uid, now called urine, contains urea and other wastes. Urine is transported from the kidneys to the bladder and eventually excreted from the body. 16. Explain why metabolism of fats lead to more ATP than the metabolism of glucose. Aerobic metabolism is the primary source of ATP in resting cells, involving the citric acid cycle and electron transport chain. Mitochondria absorb oxygen, ADP, phosphate ions, and organic substrates like pyruvate. Resting skeletal muscle bers primarily use fatty acids for ATP production. Fatty acids are absorbed from the blood and broken down in the mitochondria, creating a surplus of ATP. Each glucose molecule yields 30-32 ATP molecules. Fatty acids produce signi cantly more ATP per molecule compared to glucose. This higher yield is due to the longer carbon chains in fatty acids, which provide more hydrogen atoms for the electron transport chain. Fatty acids are a more ef cient energy source, especially during rest, as they generate more ATP without depleting glycogen reserves. During moderate activity, muscles switch to glucose metabolism to sustain prolonged contraction. Explain why ketones are formed when fat is broken down for ATP. Fatty acids are broken down in the mitochondria through a process called beta-oxidation. This process generates acetyl-CoA, NADH, and FADH2. During periods of high fat breakdown, such as fasting or low carbohydrate intake, large amounts of acetyl-CoA are produced. The citric acid cycle may not be able to process all the acetyl-CoA due to fi fl fl limited availability of oxaloacetate, which is needed to combine with acetyl-CoA. When there is an excess of acetyl-CoA, the liver converts it into ketone bodies (acetoacetate, beta- hydroxybutyrate, and acetone). This process is known as ketogenesis and occurs in the liver mitochondria. Ketone bodies can be transported to other tissues and used as an alternative energy source, especially by the brain and muscles. Explain why fatty acids cannot be made into glucose. Some steps in glycolysis, the breakdown of glucose, are irreversible. This means cells cannot simply reverse glycolysis to generate glucose. Fatty acids are broken down into acetyl-CoA through beta-oxidation. Acetyl-CoA cannot be converted back into pyruvate because the decarboxylation step (removal of CO2) between pyruvate and acetyl-CoA is irreversible. Therefore, acetyl-CoA cannot be used to make glucose. Instead of being converted to glucose, acetyl-CoA enters the citric acid cycle or is used to form ketone bodies. Glycerol, a component of fats, can enter the carbohydrate catabolic pathway and contribute to gluconeogenesis, but fatty acids themselves cannot. 17. Describe functions of the liver: Clotting: Synthesis of Plasma Proteins: The liver produces clotting proteins, which are crucial for blood coagulation. Urea: Waste Removal: The liver converts toxic ammonia, a byproduct of amino acid metabolism, into urea, which is then excreted by the kidneys. Vitamin storage: The liver stores fat-soluble vitamins (A, D, E, K) and vitamin B12, releasing them when dietary intake is insuf cient. fi  Normal growth: Hormone Regulation: The liver processes and recycles hormones, including those essential for growth, such as thyroid hormones and steroid hormones. Blood pressure: Regulation of Blood Volume: By synthesizing plasma proteins like albumins, the liver helps maintain blood volume and pressure. Lipoproteins: Lipid Metabolism: The liver regulates levels of triglycerides, fatty acids, and cholesterol, producing and releasing lipoproteins as needed. Digestion: Bile Production: The liver produces bile, which is essential for the digestion and absorption of fats in the small intestine. Toxic substances: Detoxi cation: The liver removes toxins, drugs, and other harmful substances from the blood, either breaking them down or storing them safely. Red blood cells: Phagocytosis: Stellate macrophages in the liver engulf and break down old or damaged red blood cells. Bilirubin: Bilirubin Processing: The liver processes bilirubin, a byproduct of red blood cell breakdown, and excretes it in bile. Explain why the liver makes bilirubin. The liver processes heme, a component of hemoglobin in red blood cells. When red blood cells are broken down, heme is stripped of its iron and converted to biliverdin, a green pigment. Biliverdin is then converted to bilirubin, an orange-yellow pigment. Bilirubin binds to albumin in the bloodstream and is transported to the liver. In the liver, bilirubin is excreted into bile. Bile is then released into the digestive tract, where bilirubin is further processed by bacteria into urobilinogens and stercobilinogens. fi 18. Name 3 important plasma proteins: concerning immunity, and concerning osmotic pressure, concerning clotting. Albumin: Major contributors to plasma osmolarity and osmotic pressure. Help maintain the balance of uid between blood vessels and tissues. Transport fatty acids, thyroid hormones, and some steroid hormones. Globulins: Second most abundant plasma proteins. Includes antibodies (immunoglobulins) that attack foreign proteins and pathogens. Bind small ions, hormones, and other compounds to prevent their removal by kidneys or due to low water solubility. Fibrinogen: Essential for blood clotting. Converts to brin, forming the framework for blood clots. What does it mean to say that blood osmotic pressure is high? Indicates a high concentration of plasma proteins (primarily albumin). Helps maintain uid balance by drawing water into blood vessels, preventing excessive uid loss into tissues. Example: Edema Prevention: High BCOP prevents swelling (edema) by ensuring water stays in the blood vessels rather than accumulating in tissues. 19. Where are red blood cells, white blood cells, and platelets made? Red blood cells: Location: red bone marrow. Process: erythropoiesis. Steps: Hemocytoblasts (stem cells) in red bone marrow. Proerythroblast (with erythropoietin, EPO). Erythroblast stages (nucleus ejected). Reticulocyte. Erythrocyte (mature RBC). White blood cells: Location: Red bone marrow, thymus, and peripheral lymphoid tissues. Process: Leukopoiesis. Types: Granulocytes (Neutrophils, Eosinophils, Basophils): fl fl fl fi Myeloid stem cells → Myeloblasts → Myelocytes → Band cells → Granulocytes. Agranulocytes (Monocytes, Lymphocytes): Monocytes: Myeloid stem cells → Monoblasts → Promonocytes → Monocytes. Lymphocytes: Lymphoid stem cells → Lymphoblasts → Prolymphocytes → Lymphocytes (T cells, B cells, NK cells). Platelets: Location: :Red bone marrow. Process: Thrombocytopoiesis. Steps: Hemocytoblasts in red bone marrow. Progenitor cells (without EPO/GM-CSF) → Megakaryocytes. Megakaryocytes shed cytoplasm → Platelets. What is erythropoietin (EPO)? EPO is a glycoprotein hormone. It is primarily produced by the kidneys and, to a lesser extent, by the liver. EPO is released in response to low oxygen levels in the tissues, a condition known as hypoxia. Speci c triggers include: Anemia. Reduced blood ow to the kidneys. Low oxygen content in the air (e.g., at high altitudes or due to lung disease). Damage to the respiratory surfaces of the lungs. Stimulates RBC Production: EPO travels to the red bone marrow and stimulates stem cells and developing RBCs. Increases Cell Division: It increases the division rates of erythroblasts and stem cells that produce erythroblasts. Accelerates Maturation: EPO speeds up the maturation of RBCs by enhancing hemoglobin (Hb) synthesis. Under maximum stimulation, EPO can increase RBC production up to 30 million cells per second. This increase in RBCs elevates blood volume and improves oxygen delivery to peripheral tissues. EPO also causes vasoconstriction, which helps increase blood pressure. Which organs make EPO and under what conditions? The kidney: the primary source of fl fi  EPO. The liver: produces a smaller amount of EPO. Conditions: EPO is released in response to low oxygen levels in the tissues, a condition known as hypoxia. Anemia: A decrease in the number of RBCs or hemoglobin. Reduced Blood Flow to Kidneys: This can occur due to various reasons, including low blood pressure. Low Oxygen Content in the Air: Such as at high altitudes or due to lung diseases. Damage to Respiratory Surfaces of the Lungs: Impairing oxygen exchange. 20. Describe each of these terms: Hematocrit: The percentage of formed elements (like red blood cells) in whole blood. Normal range: 37–54%. Leukopenia: A condition where there is a lower than normal number of white blood cells (WBCs). Implication: Can make the body more susceptible to infections. Hemoglobin : A protein in red blood cells that carries oxygen. Normal Range: 12–18 g/dL. Function: Binds and releases oxygen and carbon dioxide. Anemia: A condition where the hematocrit or hemoglobin levels are below normal. Implication: Interferes with oxygen delivery to tissues, causing weakness and lethargy. Thrombocytopenia: A condition characterized by a lower than normal number of platelets. Implication: Can lead to increased bleeding and bruising. Jaundice: A condition where the skin and eyes turn yellow due to high bilirubin levels. Cause: Often related to liver dysfunction or hemolysis (breakdown of red blood cells). Leukocytosis: An elevated number of white blood cells. Often indicates an infection or in ammation. fl  Thrombocytosis: An elevated number of platelets. Implicaation: can increase the risk of blood clots. Polycythemia: An elevated hematocrit, often due to an increased number of red blood cells. Implication: Can thicken the blood and slow its ow, leading to complications like blood clots. 21. Describe the function of each of the cells: Erythrocyte: Transports oxygen from the lungs to the body's tissues and returns carbon dioxide from the tissues to the lungs. What unique characteristic does it have? Contains hemoglobin, which makes up more than 95% of the proteins in RBCs and binds oxygen. What is the purpose of carbonic anhydrase in a red blood cell? Carbonic Anhydrase: An enzyme in RBCs that helps convert carbon dioxide and water into carbonic acid, which then dissociates into bicarbonate and hydrogen ions. This process is crucial for CO2 transport in the blood. Lymphocyte: Key players in the immune response T-Cells: Attack foreign cells directly or regulate other immune cells. B-Cells: Produce antibodies NK Cells: Destroy abnormal cells, such as cancer cells. Neutrophil: Highly mobile phagocytes that engulf and destroy pathogens. Elevated numbers of neutrophils generally indicate a bacterial infection. fl  Monocyte: Phagocytic cells that engulf pathogens and debris. Is a monocyte the same thing as a macrophage? Explain. When monocytes migrate into tissues, they become macrophages, which are even more effective at phagocytosis. Basophil: Release histamine and heparin, aiding the in ammatory response. Describe the granules present in a basophil. Granules: Contain histamine and heparin. Explain how basophils are related to anaphylactic shock. Relation to Anaphylactic Shock: Basophils release large amounts of histamine during severe allergic reactions, contributing to anaphylactic shock. Eosinophil: Attack antibody-coated objects and release toxic compounds to combat multicellular parasites. Elevated numbers of eosinophils generally indicate a parasitic infection or allergic reactions. Which cells are white blood cells? Neutrophils: Highly mobile phagocytes that engulf and digest bacteria and other pathogens. Eosinophil: Phagocytes attracted to foreign compounds that have reacted with circulating antibodies Basophil: Release histamine and heparin, aiding the in ammatory response. Lymphocytes: Include T cells, B cells, and NK cells, which are involved in speci c immune responses.  Monocytes: Migrate into tissues and become macrophages, which are effective at phagocytosis. Which are granulocytes? Neutrophils: These cells have a dense, segmented nucleus and are highly mobile, specializing in attacking and digesting bacteria. Eosinophils: These cells have deep red granules and a bilobed nucleus, and they are involved in combating multicellular parasites and certain infections. Basophils: These cells have deep purple granules and are involved in in ammatory responses by releasing histamine and heparin. Which cells carry the antigens that de ne blood type? Red blood cells (erythrocytes) Which white blood cells are most numerous in circulation? Neutrophils: Neutrophils are the most numerous white blood cells in circulation, making up 50-70% of the total WBC count. They are highly mobile phagocytes that play a crucial role in the body's defense against infections. Which white blood cells are least numerous in circulation? Basophils: Basophils are the least numerous white blood cells in circulation. They are fairly rare compared to other WBCs. 22. Describe what is meant by a blood group. A blood group is determined by the presence or absence of speci c surface antigens on red blood cells (RBCs). The primary antigens involved are A, B, and Rh (or D). ABO fi Blood Group: Based on the presence or absence of A and B antigens. Rh Factor: Indicates the presence (Rh+) or absence (Rh−) of the Rh antigen. List the 8 possible blood groups in the ABO/Rh system A+: Has A antigens and Rh antigen A-: Has A antigens but no Rh antigen B+: Has B antigens and Rh antigen B-: Has B antigens but no Rh antigen. AB+: Has both A and B antigens and Rh antigen AB-: Has both A and B antigens but no Rh antigen O+: Has no A or B antigens but has Rh antigen O-: Has no A, B, or Rh antigens. Type A: anti-B antibodies Type B: anti-A antibodies. Type AB: no anti-A or anti-B antibodies. Type O: both anti-A and anti-B antibodies. Which blood groups can donate to each blood type? For example, can B+ donate blood to AB+? Explain. Type A+: Can receive from A+, A−, O+, O−. Type A-: Can receive from A−, O− Type B+: Can receive from B+, B−, O+, O−. Type B-: Can receive from B−, O−.  Type AB+: Can receive from all blood types (universal recipient). Type AB-: a receive from AB−, A−, B−, O−. Type O+: Can receive from O+, O−. Type O-: Can receive from O− only (universal donor). Can B+ donate blood to AB+? Explain. Yes, B+ can donate to AB+ because AB+ has no anti-A or anti-B antibodies, preventing any immune reaction. 23. Why isn’t the thrombocyte listed with the other cells? Thrombocytes, or platelets, are not listed with the other cells (RBCs and WBCs) because they are fundamentally different in structure and function. While RBCs and WBCs are complete cells, thrombocytes are cell fragments. Their primary role is in the clotting process, which is distinct from the oxygen transport function of RBCs and the immune defense role of WBCs. What is the function of the thrombocyte? Disc-shaped cell fragments, 3 μm in diameter, 1 μm thick. Essential for the vascular clotting system. Circulate for 9–12 days before removal by phagocytes. Platelets release enzymes and factors to initiate and control clotting. They clump at injury sites to form a platelet plug, slowing blood loss. Platelets contain actin and myosin laments that contract to shrink clots and reduce vessel wall breaks. Where are thrombocytes made? Thrombocytes, or platelets, are produced in the red bone marrow. They originate from  large cells called megakaryocytes. The process of platelet production is known as thrombocytopoiesis. Megakaryocytes: These are enormous cells in the red bone marrow, up to 160 μm in diameter, with large nuclei. They manufacture structural proteins, enzymes, and membranes. During their development, megakaryocytes shed their cytoplasm in small, membrane-enclosed packets. These packets are the platelets that enter the bloodstream. A mature megakaryocyte can produce about 4000 platelets before its nucleus is engulfed by phagocytes for breakdown and recycling. 24. Explain the role of each of the following in coagulation: Thrombin: Thrombin is formed from prothrombin by the action of prothrombin activator. It plays a crucial role in the coagulation process by converting brinogen into brin. This conversion is essential for the formation of a stable blood clot. Fibrinogen: Fibrinogen is a soluble plasma protein present in the blood. It serves as the precursor to brin. When thrombin acts on brinogen, it is converted into brin, which is essential for clot formation. Fibrin: Fibrin is formed from brinogen through the action of thrombin. Fibrin strands are insoluble and form a mesh that traps blood cells, effectively creating a stable blood clot to prevent further bleeding. How do brinogen and brin differ? Fibrinogen is a soluble protein found in the plasma of the blood. It serves as the precursor to brin. During the coagulation process, brinogen is converted into brin by the enzyme thrombin. Fibrin is formed from brinogen through the action of thrombin. Unlike fi fi fi fi fi fi fi fi  brinogen, brin is insoluble. Fibrin forms long, insoluble strands that create a meshwork. This meshwork traps blood cells and forms a stable blood clot, which is essential for stopping bleeding. Write out the reaction for the formation of brin (coagulation): Fibrinogen (plasma protein) -> brin (insoluble protein) (catalyzed by the enzyme thrombin) Write out the reaction for the breakdown of brin ( brinolysis): Fibrin -> degraded brin (catalyzed by the enzyme plasmin) Which enzyme catalyzes that reaction? Thrombin: Produced by the common pathway during coagulation. Tissue Plasminogen Activator (t-PA): Released by damaged tissues at the injury site. Enzymatic Activation: Thrombin and t-PA activate the proenzyme plasminogen. Plasminogen is converted into the active enzyme plasmin. Plasmin begins to digest the brin strands. This process gradually erodes the blood clot, allowing the vessel to return to its normal state. What is the difference between an embolus and a thrombus? A thrombus is a blood clot that forms and remains attached to the luminal (inner) surface of a blood vessel. It typically forms in response to vessel injury or other conditions that promote clotting. It stays xed at the site where it was formed. An embolus is a blood clot or other debris that has broken loose and is drifting through the bloodstream. Unlike a thrombus, an embolus can travel through the blood vessels. It can become lodged in a smaller vessel, causing an embolism, which blocks blood ow to downstream tissues. fi fi fi fi fi fi fi fi fi  Describe edema and the location of the excess uid. Edema is the medical term for swelling caused by an abnormal accumulation of uid in the interstitial spaces, which are the areas between cells in tissues. The excess uid in edema is primarily located in the interstitial uid compartment, which is part of the extracellular uid (ECF). How do each of the following cause edema? Elevated venous pressure: When venous pressure is elevated, it increases the capillary hydrostatic pressure (CHP). This pressure pushes more uid out of the capillaries and into the interstitial spaces. Conditions like heart failure or venous blood clots can elevate venous pressure, leading to edema. Poor lymph drainage: The lymphatic system normally drains excess interstitial uid. When lymphatic vessels are obstructed, lymph accumulates in the affected region, causing swelling. Lymphedema occurs when lymphatic drainage is blocked, leading to persistent swelling and potential risk of infection. Low osmotic pressure: Blood colloid osmotic pressure (BCOP) is crucial for reabsorbing uid back into the capillaries. When BCOP is low, less uid is reabsorbed, resulting in uid accumulation in the interstitial spaces. Starvation or liver disease can reduce plasma protein levels, decreasing BCOP and causing generalized edema, such as the swollen bellies seen in malnourished children. Explain how levels of albumin relate to osmotic pressure. Albumin is the most abundant plasma protein and plays a crucial role in maintaining fl fl fl fl fl fl fl BCOP. High levels of albumin increase BCOP, promoting the reabsorption of water into the capillaries. Low levels of albumin decrease BCOP, reducing the reabsorption of water and potentially leading to edema, as more uid remains in the interstitial spaces. Compare and contrast arteries and veins. Arteries: Thicker walls with more smooth muscle and elastic bers to resist high pressure from the heart. Veins: Thinner walls as they carry blood under lower pressure. Arteries: Smaller lumens due to the recoil of elastic bers, maintaining a circular shape. Veins: Larger lumens and tend to collapse when cut, appearing attened. Arteries: Endothelial lining folds when constricted, giving a pleated appearance. Veins: Endothelial lining does not fold. Arteries: Do not contain valves. Veins: Contain valves to prevent back ow of blood, especially in the limbs. Arteries: Carry blood away from the heart, usually located deeper beneath the skin. Veins: Return blood to the heart, with a dual drainage system (super cial and deep) in the neck and limbs to help regulate body temperature. Place the following vessels in the order of blood ow: Artery: Blood ows from the heart into large arteries. Arteriole: Arteries branch into smaller arterioles as they enter peripheral tissues. Capillaries: Arterioles lead to capillary networks where the exchange of gases and nutrients occurs. Venule: Blood then ows from capillaries into small venules. Vein: Venules merge into larger veins that return blood to the heart. Artery -> arteriole -> capillaries -> venule -> vein. fi fl fl fl fi fl fl High pressure to low pressure: Artery: Blood pressure is highest in the arteries, starting at about 120 mm Hg in the aorta Arteriole: As arteries branch into arterioles, the pressure drops but is still relatively high, around 35 mm Hg at the start of a capillary network. Capillaries: In the capillaries, the pressure continues to decrease, ranging from about 35 mm Hg to 18 mm Hg. Venule: After the capillaries, blood enters the venules where the pressure is lower, around 18 mm Hg. Vein: Finally, blood ows into the veins, where the pressure is the lowest, dropping to about 2 mm Hg at the entrance to the right atrium. Compare the histology of all the vessels listed: Arteries: Walls: Thick, with three layers: tunica intima, tunica media, and tunica externa. Tunica Media: Contains more smooth muscle and elastic bers, allowing arteries to withstand high pressure. Lumen: Smaller and maintains a circular shape due to thick walls. Endothelium: Folds when constricted, giving a pleated appearance. Arterioles: Walls: Thinner than arteries but still have three layers. Tunica Media: Less smooth muscle and elastic bers compared to arteries. Function: Regulate blood ow into capillaries through constriction and dilation. Capillaries: Walls: Extremely thin, consisting of only a single layer of endothelial cell. Function: Facilitate exchange of gases, nutrients, and waste between blood and interstitial uid. Types: Continuous, fenestrated, and sinusoids, each with varying fl fl fi  permeability. Venules: Walls: Thinner than arterioles, with less smooth muscle. Function: Collect blood from capillaries and begin the return ow to the heart. Veins: Walls: Thinner than arteries, with three layers but less smooth muscle and elastic bers. Lumen: Larger and often collapsed in cross-section. Valves: Present to prevent back ow of blood, especially in limbs. 27. Describe the following circulations. What is the purpose of each? Where do they begin and end? Systemic circulation: Transports oxygen-rich blood from the heart to the rest of the body and returns oxygen-poor blood back to the heart. Pathway: Begins at the left ventricle, travels through systemic arteries to various body tissues, and returns via systemic veins to the right atrium. Pulmonary circulation: Carries oxygen-poor blood to the lungs for oxygenation and brings oxygen-rich blood back to the heart. Pathway: Starts at the right ventricle, moves through pulmonary arteries to the lungs, and returns via pulmonary veins to the left atrium. Hepatic portal circulation: Directs blood from the digestive organs to the liver for processing before it enters the systemic circulation. Pathway: Begins in the capillaries of the digestive organs, ows through the hepatic portal vein to the liver sinusoids, and ends in the liver. Why is it called a portal circulation? A portal system involves a blood vessel connecting two capillary beds. In this case, the fi fl fl fl  hepatic portal vein connects the capillaries of the digestive organs to the liver sinusoids. Circle of Willis: The Circle of Willis, also known as the cerebral arterial circle, is a ring- shaped anastomosis (connection) of arteries located at the base of the brain. Its primary purpose is to provide a redundant blood supply to the brain, ensuring that if one part of the circle or one of the arteries supplying the circle becomes blocked or narrowed, blood ow from other vessels can often preserve the cerebral circulation. Which arteries are involved? Internal Carotid Arteries: Supply the anterior half of the cerebrum. Vertebral Arteries: Supply the rest of the brain. These arteries are interconnected through the Circle of Willis, which encircles the optic chiasm and the infundibulum of the pituitary gland. Other arteries: Anterior Cerebral Arteries, Anterior Communicating Artery, Posterior, Cerebral Arteries, Posterior Communicating Arteries, Basilar Artery. What is the signi cance of this anastomosis? The Circle of Willis provides a crucial backup system for blood ow to the brain. If one artery is blocked or narrowed, other arteries can compensate, reducing the risk of serious circulation interruptions. Stroke Mitigation: This anastomosis helps mitigate the effects of strokes (cerebrovascular accidents, CVAs) by allowing alternative pathways for blood ow. This is particularly important because the brain is highly sensitive to changes in blood supply. Blood Flow Flexibility: The interconnected arteries ensure that the brain can receive blood fl fi  from either the internal carotid arteries or the vertebral arteries, maintaining a steady supply of oxygen and nutrients. 28. Name the type of tissue found in each layer of the heart: Endocardium: Simple squamous epithelium and underlying areolar tissue. Lines the inner surfaces of the heart, including the heart valves Myocardium: Cardiac muscle tissue. Forms the bulk of the heart wall, responsible for the heart's contractile function. Covering the heart: Visceral pericardium (epicardium): Mesothelium and underlying areolar connective tissue. Covers the surface of the heart. Parietal pericardium: Outer dense brous layer, areolar tissue, and inner mesothelium. Lines the pericardial cavity, providing protection and anchoring the heart. Fibrous pericardium: Dense brous connective tissue. Protects the heart, anchors it to surrounding structures, and prevents over lling. Which layer covers the valves of the heart? Endocardium: This layer covers the heart valves, ensuring a smooth surface for blood ow. 29. What is the signi cance of the coronary circulation? Supplies blood to the heart muscle (myocardium). The myocardium has its own blood supply through the coronary circulation, separate from the blood owing through the heart chambers. During physical activity, the heart's demand for oxygen increases signi cantly. fl fi fi fi fi The coronary circulation can increase blood ow to the myocardium up to nine times the resting level. The right and left coronary arteries branch off the base of the ascending aorta, speci cally at the aortic sinuses. Name the 2 branches of the left coronary artery? Circum ex artery: This artery curves to the left around the coronary sulcus. It eventually meets and fuses with small branches of the right coronary artery. The circum ex artery supplies blood to the left atrium and the side and back of the left ventricle. Anterior interventricular artery ( also known as the left anterior descending artery or LAD): This artery runs down the anterior surface of the heart within the anterior interventricular sulcus. It supplies blood to the front of the left ventricle and the interventricular septum. Which branch of the left coronary artery supplies most of the left ventricle and a portion of the right ventricle? Left Ventricle: The LAD supplies a signi cant portion of the left ventricle, which is crucial for pumping oxygenated blood to the body. Right Ventricle: It also supplies a portion of the right ventricle, contributing to the overall function of the heart. Explain the following terms: Myocardial infarction (MI): Commonly known as a heart attack, a myocardial infarction occurs when part of the coronary circulation becomes blocked, leading to the death of cardiac muscle cells due to lack of oxygen. Often results from severe coronary artery fl fi fl disease (CAD), typically due to a thrombus (clot) forming at a plaque. Intense pain similar to angina but persisting even at rest. Silent heart attacks may occur without noticeable pain. Diagnosed using an electrocardiogram (ECG) and blood tests for enzymes like cardiac troponin T and I, and CK-MB. Angina pectoris: A condition characterized by chest pain or discomfort due to temporary ischemia (reduced blood ow) when the heart's workload increases. Pressure, chest constriction, and pain that may radiate to the arms, back, and neck, typically triggered by exertion or emotional stress. Often one of the rst symptoms of coronary artery disease. Ischemia: A condition where there is a reduction in blood ow to the heart muscle, leading to decreased oxygen and nutrient supply. Generally results from partial or complete blockage of the coronary arteries, often due to atherosclerotic plaque or a thrombus. Leads to reduced cardiac performance and can cause conditions like angina pectoris and myocardial infarction. Name the 3 venous openings in the right atrium: Superior vena cava: Opens into the posterior and superior portion of the right atrium. Delivers blood from the head, neck, upper limbs, and chest. Inferior vena cava: Opens into the posterior and inferior portion of the right atrium. Carries blood from the rest of the trunk, the viscera, and the lower limbs. Coronary sinus: Opens into the right atrium near the inferior vena cava. Returns blood from the myocardium (heart muscle) itself. Describe the blood ow through the heart naming all the chambers, valves, arteries, and fl fl fi veins. Right atrium: Receives deoxygenated blood from the body through the superior vena cava and inferior vena cava. Blood ows through the tricuspid valve into the right ventricle Right ventricle: Pumps deoxygenated blood through the pulmonary valve into the pulmonary trunk. The pulmonary trunk divides into the left and right pulmonary arteries, which carry blood to the lungs for oxygenation. Left atrium: Receives oxygenated blood from the lungs through the left and right pulmonary veins. Blood ows through the mitral valve (also known as the bicuspid valve) into the left ventricle. Left ventricle: Pumps oxygenated blood through the aortic valve into the ascending aorta. Blood is then distributed to the rest of the body through the systemic arteries. What is the purpose of heart valves? Prevents Regurgitation: Ensures blood ows in the correct direction, maintaining ef cient circulation. Pressure Regulation: Helps maintain the correct pressure relationships between heart chambers and vessels, essential for effective blood ow. What causes the AV valves to open and shut? Open: Relaxed Ventricles: When the ventricles are relaxed, the chordae tendineae are loose, and the papillary muscles are relaxed. Blood Flow: This relaxation allows the AV valves to open, enabling blood to ow freely from the atria into the ventricles. Closing AV valves: Ventricular Contraction: When the ventricles contract, blood is pushed fl fl fl fl fl back towards the atria. This backward movement of blood swings the cusps of the AV valves together, closing them. Role of Chordae Tendineae and Papillary Muscles: The contraction of the papillary muscles tenses the chordae tendineae, preventing the valve cusps from inverting into the atria, thus ensuring the valves remain closed and preventing back ow (regurgitation). What causes the semilunar valves to open and shut? Open: Ventricular Systole: During ventricular systole, the ventricles contract. As the pressure in the ventricles rises and exceeds the pressure in the arterial trunks (pulmonary trunk and aorta), the semilunar valves are pushed open. As the pressure in the ventricles rises and exceeds the pressure in the arterial trunks (pulmonary trunk and aorta), the semilunar valves are pushed open. Closing: End of Ventricular Systole: As ventricular systole ends, the ventricles begin to relax. The pressure in the ventricles falls rapidly. Blood in the aorta and pulmonary trunk starts to ow back toward the ventricles, causing the semilunar valves to close. The three symmetrical cusps of the semilunar valves support one another like the legs of a tripod, ensuring they close properly and prevent back ow. 31. Explain the signi cance of an EKG. What is actually being detected? An EKG helps clinicians assess the functions of speci c pacemaker, conducting, and contractile cells in the heart. It can reveal abnormal patterns of impulse conduction, which may indicate heart damage, such as from a heart attack. By analyzing the size, shape, and timing of the waves, clinicians can diagnose various heart conditions and monitor fl fi fl ongoing heart health. What is being detected? P-R Interval: Time from the start of atrial depolarization to the start of the QRS complex. Q-T Interval: Time from the start of the QRS complex to the end of the T wave. S-T Segment: Time from the end of the QRS complex to the start of the T wave. What is the signi cance of each EKG wave listed: P-wave: Represents the depolarization of atrial contractile cells, leading to atrial contraction. QRS wave (complex): Indicates the depolarization of ventricular contractile cells, which is a strong signal due to the larger muscle mass of the ventricles. This complex also obscures atrial repolarization. T Wave: Shows the repolarization of ventricular contractile cells. 32. Explain what happens in each part of the cardiac cycle: Diastole: The relaxation phase of the heart chambers. During diastole, the chambers of the heart relax and ll with blood, preparing for the next contraction. Passive lling: Occurs During: Ventricular diastole (late phase). All chambers are relaxed, and the ventricles ll passively with blood from the atria. This phase ends when the next cardiac cycle begins. Atrial systole: The contraction of the atria. Atrial contraction forces a small amount of additional blood into the relaxed ventricles, completing their lling. Systole: The contraction phase of the heart chambers. During systole, the chambers fi fi fi fi contract and push blood into adjacent chambers or into arterial trunks. Ejection phase: Occurs During: Ventricular systole (second phase). As ventricular pressure rises and exceeds the pressure in the arteries, the semilunar valves open, and blood is ejected from the ventricles into the systemic and pulmonary circuits. Why is it important that there is suf cient time for diastole? What happens during diastole? Diastole is crucial because it allows the heart chambers, particularly the ventricles, to ll with blood. If diastole is too short, the ventricles may not ll completely, reducing the amount of blood ejected during systole. The heart muscle itself receives blood during diastole. Suf cient time in diastole ensures that the heart muscle gets enough oxygen and nutrients to function properly. What happens during diastole? Isovolumetric Relaxation: All heart valves are closed. The ventricular myocardium relaxes, and ventricular pressures drop rapidly. AV Valves Open; Passive Ventricular Filling: When ventricular pressures fall below atrial pressures, the AV valves open. Blood ows passively from the atria into the ventricles. Both atria and ventricles are relaxed, and the ventricles ll to about three-quarters of their capacity. Does most of the blood enter the ventricles during atrial systole or during passive lling. Passive lling: The majority of the blood enters the ventricles during passive lling. This occurs when both the atria and ventricles are in diastole. Blood ows passively from the atria into the ventricles through the open AV valves. By the end of this phase, the fi fi fi fl fi fi  ventricles are already lled to about 70% of their capacity. Atrial systole contributes the remaining 30% of the blood. What happens during systole? Atrial systole: Atrial Contraction Begins: The atria contract, pushing the remaining 30% of blood into the ventricles, which are already 70% lled from passive lling. End-Diastolic Volume (EDV): At the end of atrial systole, the ventricles contain the maximum amount of blood for the cycle, typically about 130 mL in a resting adult. Ventricular systole: Atrial Systole Ends; AV Valves Close: As ventricular systole begins, the pressure in the ventricles rises, closing the AV valves. The ventricles contract without changing volume because the semilunar valves are still closed. Pressure builds up inside the ventricles. Once ventricular pressure exceeds arterial pressure, the semilunar valves open, and blood is ejected into the pulmonary and aortic trunks. Each ventricle ejects 70-80 mL of blood, known as the stroke volume. As ventricular pressure falls, blood starts to ow back toward the ventricles, closing the semilunar valves. The remaining blood in the ventricles is called the end-systolic volume (ESV), typically about 50 mL. During which part of the cardiac cycle are the AV valves shut? End of atrial systole: As atrial systole ends and ventricular systole begins, the pressure in the ventricles rises above that in the atria, causing the AV valves to close. This prevents back ow of blood into the atria. Isovolumetric contraction: During the early phase of ventricular systole, known as isovolumetric contraction, the ventricles contract but do not eject blood because the fl fl fi fi  semilunar valves are also closed. During this phase, the AV valves remain shut. Ventricular ejection: As the pressure in the ventricles continues to rise and eventually exceeds the pressure in the arterial trunks, the semilunar valves open, and blood is ejected. Throughout this phase, the AV valves stay closed to ensure unidirectional blood ow. When do semilunar valves shut? Near the end of ventricular systole, the pressure in the ventricles drops quickly. The blood that was ejected into the aorta and pulmonary trunk begins to move back toward the heart. This movement of blood back toward the ventricles causes the semilunar valves to close, ensuring that blood does not ow back into the ventricles. This closure is crucial for maintaining one-way blood ow through the heart and into the systemic and pulmonary circulations. During which part of the cardiac cycles are the AV valves open? At the start of the cardiac cycle, the atria contract (atrial systole), pushing blood into the relaxed ventricles. The AV valves (tricuspid and mitral valves) are open to allow this ow. After the ventricles contract and then relax (ventricular diastole), the pressure in the ventricles drops. This causes the AV valves to open again, allowing blood to ow from the atria into the ventricles. When do semilunar valves open? The semilunar valves open during the second phase of ventricular systole when the pressure in the ventricles exceeds the pressure in the arteries, allowing blood to be fl fl fl ejected into the pulmonary trunk and aorta. Once the ventricular pressure surpasses the arterial pressure, the semilunar valves are pushed open, marking the beginning of ventricular ejection. Blood is then pumped out of the ventricles into the major arteries. 33. What is meant by auscultation of the heart? Clinicians use a stethoscope to listen to the heart sounds, which provide information about the closing of heart valves and overall cardiac function. What is a heart murmur? A heart murmur is an unexpected "whoosh" sound heard during a heartbeat, indicating turbulent blood ow within the heart. It can be caused by issues such as malformed valve cusps, problems with the papillary muscles, or chordae tendineae, leading to improper valve closure. What causes the 1st heart sound? The closure of the AV valves generates the "lubb" sound of S1. The rst heart sound (S1) is produced by the closure of the AV valves at the start of ventricular contraction, marking the beginning of the heart's pumping phase. What causes the 2nd heart sound? The closure of the semilunar valves generates the "dupp" sound of S2. The second heart sound (S2) is produced by the closure of the semilunar valves at the beginning of ventricular lling, marking the start of the heart's relaxation phase. Which of the heart sounds is heard when systole begins? The heart sound heard when systole begins is the rst heart sound, known as S1. This fi fl fi  sound is often described as "lubb" and marks the start of ventricular contraction. During this phase, the atrioventricular (AV) valves (mitral and tricuspid valves) close, and the semilunar valves (aortic and pulmonary valves) open. The closing of the AV valves generates the S1 sound, which is longer in duration compared to the second heart sound (S2). 34. Explain how cardiac output is calculated. Cardiac Output (CO) is a measure of the amount of blood pumped by the left ventricle in one minute. It is a crucial indicator of the heart's ef ciency and the blood ow through peripheral tissues. Formula: CO = HR * SV How is cardiac output affected by each of the following? Sympathetic stimulation: Increases heart rate (HR) and contractility. Releases norepinephrine (NE) and epinephrine (E), which act on the SA node and cardiac contractile cells. Increases cardiac output (CO) by increasing both HR and stroke volume (SV). Parasympathetic stimulation: Decreases heart rate and contractility. Activates the cardioinhibitory center, releasing acetylcholine. Decreases CO by reducing HR and increasing end-systolic volume (ESV). End diastolic volume (EDV): Directly affects stroke volume. Increased venous return and lling time increase EDV. Higher EDV leads to a stronger contraction (Frank-Starling principle), increasing SV and CO. Preload: In uences EDV. The initial stretching of cardiac myocytes before contraction. fi fl fi Increased preload increases EDV, thus increasing SV and CO. Increase in calcium: Enhances contractility. Calcium ions play a crucial role in muscle contraction. Increased calcium reduces ESV, increasing SV and CO. Increased blood pressure (after load): Increases ESV. Higher afterload means the heart must work harder to eject blood. Increased afterload decreases SV, reducing CO. Bradycardia: Decreases heart rate. Slower heart rate reduces the number of beats per minute. Decreases CO due to a lower HR, even if SV remains constant. 35. Explain each of the following terms: Tachycardia: An abnormally fast heart rate. Reduces the time for the heart to ll with blood between contractions, leading to decreased stroke volume and cardiac output. If severe, it can cause loss of consciousness due to insuf cient blood reaching the brain. Bradycardia: An abnormally slow heart rate. Reduces cardiac output because the heart pumps fewer times per minute, even if stroke volume remains constant. Right congestive heart failure: A condition where the right side of the heart cannot pump blood effectively. What type of edema is seen in right congestive heart failure: Peripheral edema, often seen in the legs and ankles due to uid buildup. Left congestive heart failure: A condition where the left side of the heart cannot pump blood effectively. What type of edema is seen in left congestive heart failure: Pulmonary edema, where uid accumulates in the lungs, causing breathing dif culties. fl fi  Ventricular brillation: A life-threatening condition where the heart's ventricles quiver instead of pumping normally. What is cardiac output during ventricular brillation ? Essentially zero, as the heart cannot effectively pump blood, leading to a rapid decline in blood ow to vital organs. 36. Explain what a blood pressure of 120/80 mmHg means. A blood pressure reading of 120/80 mmHg is considered normal. What is systolic pressure? Systolic Pressure is the peak blood pressure measured during ventricular systole, which is when the heart's ventricles contract and pump blood into the arteries. What is diastolic pressure? Diastolic Pressure is the minimum blood pressure measured at the end of ventricular diastole, which is when the heart's ventricles are relaxed and lling with blood. How does the blood pressure in the aorta compare with that the pulmonary artery? Blood pressure in the aorta is relatively high, averaging around 120 mm Hg at the entrance and decreasing to about 35 mm Hg at the start of the capillary network. This high pressure is necessary to overcome peripheral resistance and ensure blood ow through the extensive network of systemic capillaries. Blood Pressure in the Pulmonary Artery: Blood pressure in the pulmonary artery is signi cantly lower than in the aorta. This is because the pulmonary circuit is shorter and has less resistance compared to the systemic circuit. The lower pressure is suf cient to fi fl fi fi move blood through the lungs for gas exchange without causing damage to the delicate pulmonary capillaries. Which ventricle of the heart works harder? Why is this signi cant? The left ventricle works harder than the right ventricle. It has thicker, muscular walls to