Topic 6 - Human Physiology Flashcards
Outline the role of peristalsis in the digestive process.
Peristalsis is the involuntary, wave-like contraction of muscle layers of the small intestine.
Peristalsis helps prevents backward movement of food and maintains the forward movement of the material.
Peristalsis also mixes food with intestinal enzymes.
List the source, substrate and product of lipase.
Lipase is an enzyme that hydrolyzes fats to fatty acids and glycerol.
Source: pancreas (secreted into small intestine)
Substrate: triglyceride
Product: glycerol and three fatty acids
Optimal pH: 7-8
List the source, substrate and product of proteases.
Proteases are enzymes that hydrolyzes proteins into smaller polypeptides, dipeptides and/or amino acids.
Pepsin:
Source: stomach
Substrate: proteins
Product: smaller polypeptides
Optimal pH: 2
Trypsin:
Source: pancreas (secreted into small intestine)
Substrate: proteins and smaller polypeptides
Product: dipeptides and/or amino acids
Optimal pH: 7-8
List the source, substrate and product of amylases.
Amylases are enzymes that hydrolyzes starch into maltose.
Salivary Amylase
Source: Salivary glands
Substrate: starch
Product: maltose
Optimal pH: 7
Pancreatic Amylase
Source: pancreas (secreted into small intestine)
Substrate: starch
Product: maltose
Optimal pH: 7-8
Define “lumen.”
The lumen is the inside space of a tubular body structure that is surrounded by body tissue known as an epithelial membrane.
Examples of body structures that have a lumen include the large intestine, small intestine, veins, and arteries.
Outline the function of digestion of food.
Many molecules are too large to be absorbed by the villi in the small intestine. Large food molecules are digested into small molecules that can be absorbed and moved into the cells.
Describe the role of hydrolysis in digestion.
Hydrolysis is the chemical breakdown of a compound due to reaction with water. Large molecules are hydrolyzed into small molecules that can be absorbed and moved into the cells. Hydrolysis is catalyzed by enzymes.
Polysaccharides are hydrolysed to disaccharides and monosaccharides.
Proteins/polypeptides are hydrolysed to amino acids.
Triglycerides are hydrolysed to fatty acids and glycerol.
Summarize the role of digestive enzymes within the small intestine.
The small intestine is where most chemical digestion takes place. Most of the digestive enzymes in the small intestine are secreted by the pancreas and enter the small intestine via the pancreatic duct.
Enzymes increase the rate of the digestive process by catalyzing the chemical breakdown of large molecules to form molecules that are small enough to be absorbed.
Most digestive enzymes work outside the cells in a location within the digestive tract with specific conditions for each reaction. For example, variations in pH throughout digestive tract promote the activity of different digestive enzymes.
Enzymes allow digestion to occur at body temperature.
Outline the structure and function of enzymes immobilized in the cell membrane of small intestine epithelial cells.
The final step in digestion of dietary carbohydrates and proteins occurs on the face of small intestinal epithelial cells, in the immediate vicinity of the protein transporters which will move the resulting sugars and amino acids into the cells. The enzymes responsible for this final stage of digestion are not free in the intestinal lumen, but rather, tethered as integral membrane proteins in the cell membrane of the epithelial cells.
Outline the digestion and absorption of proteins in humans.
Proteins must be digested into amino acids. The protease enzyme pepsin digests proteins into smaller polypeptides. Pepsin works in the stomach and requires an acidic pH (2) to function.
In the small intestine lumen, the protease enzyme trypsin (from the pancreas) digest polypeptides into amino acids. Trypsin requires a basic pH (8) to function.
The amino acids are absorbed by diffusion and active transport at the villus of the small intestine. The amino acids move into capillaries and blood carries them throughout the body. The amino acids then move into cells which then cells use the amino acids to build proteins.
Outline the digestion and absorption of lipids in humans.
Fats (triglycerides) are digested into fatty acids and glycerol. Pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides. Pancreatic lipase works with the help of the salts from bile secreted by the liver and the gallbladder.
Bile salts attach to triglycerides and help to emulsify them; this aids access by pancreatic lipase because the lipase is water-soluble, but the fatty triglycerides are hydrophobic and tend to orient toward each other and away from the watery intestinal surroundings. The bile salts act to hold the triglycerides in their watery surroundings until the lipase can digest them into the smaller fatty acid components that are able to enter the villi for absorption via diffusion.
List adaptations that increase the surface area for absorption on the small intestine.
The inner layer of the small intestine is covered by numerous folds. The surface of these folds contains villi which are finger-like projections that further increase the surface area for better absorption. Microvilli on the villi epithelial cells even further increase surface area to improve absorption.
Define “epithelium.”
The epithelium is the thin layer of cells that create a tissue covering the outer layer of a body’s surface and lining the digestive tract and other hollow structures.
Explain how the structure of the villus is adapted for absorption.
Villi are finger-like projections of the small intestine mucosa that increase the surface area for better absorption of the products of digestion.
Microvilli on the villi epithelial cells further increase surface area to improve absorption.
The epithelium is a single layer thick, which allows fast diffusion of nutrients from the small intestine lumen into the blood.
Capillary bed within the villi maintain a concentration gradient of nutrients (by constantly carrying away absorbed nutrients) so that the rate of diffusion is higher.
Lacteal in villus to absorb fatty acids and carry them away from small intestine.
Draw the villi as viewed in cross section.
The following structures should be clearly drawn and labeled:
Capillary
Epithelial cell
Lacteal
Goblet cell
State the function of the villus capillary.
The villus capillary network maintains a concentration gradient for absorption by rapidly transporting absorbed products away. Capillaries transport absorbed nutrients (sugars and amino acids) away from the small intestine.
State the function of the villus lacteal.
The lacteal is a vessel of the lymphatic system with the villus that absorbs fats and transports them away from small intestine. The lacteals will merge to form larger lymphatic vessels that transport the fats to the thoracic duct where they are emptied into the bloodstream at the subclavian vein.
Outline the structures and functions within a villus epithelial cell.
The epithelium is the thin layer of cells that create a tissue covering the villi. The single layer allows fast diffusion of nutrients from the small intestine lumen into the blood. Each epithelial cell contains:
Microvilli that further increase surface area to improve absorption.
Protein pumps in the cell membrane to carry out active transport of nutrients into the cell.
Channel proteins in the cell membrane carry out facilitated diffusion of nutrients into the cell.
Embedded enzymes within the membrane to complete digestion.
Large number of mitochondria provide ATP to fuel the active transport of nutrients into the cell.
Tight junctions between the cells to create an impermeable barrier between the fluid of the intestinal lumen and the intercellular fluid.
Pinocytotic vesicles formed by endocytosis of the fluid with the products of digestion.
State the function of the villus goblet cell.
Goblet cells are found scattered among the epithelial lining of the small intestine. These cells secrete mucus. Mucus is a slippery aqueous secretion that protects the epithelial cells and serves as a lubricant for the digested food material as it passes through the digestive system.
Define “absorption”.
Absorption is the taking in of digested substances through the epithelial cell membrane from the lumen of the gut. Absorption occurs in the small intestine.
List materials absorbed by the epithelial cells of the villi in the small intestine.
Products of digestion are absorbed into the epithelial cells in the jejunum, the midsection of the small intestine. These include:
Monosaccharide carbohydrates such as glucose, fructose, and galactose.
Any of the twenty amino acids used to make proteins.
Components of fat molecules such as fatty acids, monoglycerides and glycerol.
Nitrogenous bases from digested nucleic acid nucleotides.
Other nutrients that are absorbed include:
Mineral ions such as calcium, potassium and sodium.
Vitamins such as ascorbic acid (vitamin C).
List four methods of membrane transport required to absorb nutrients.
Products of digestion are absorbed into the epithelial cells via:
Simple diffusion of nutrients down a concentration gradient (eg: fatty acids).
Facilitated diffusion of nutrients through channel proteins (eg: fructose).
Active transport of nutrients against a concentration gradient through protein pumps (eg: ions, glucose and amino acids).
Endocytosis by means of vesicles of large molecules (eg: cholesterol in lipoprotein particles).
Describe the absorption of fats by villus epithelial cells.
Fat molecules (triglycerides) are digested by pancreatic lipase within the lumen of small intestine. The products of the digestion are fatty acids, monoglycerides and glycerol, which are absorbed into the epithelial cells on villi.
The fatty acid diffuse across the epithelial cell membrane. Within the epithelial cell, they are again converted into triglycerides. The triglycerides are coated with proteins to form chylomicrons (a lipoprotein) which then enter into lacteals by exocytosis.
Describe absorption of glucose by villus epithelial cells.
Carbohydrate molecules such as starch are digested by pancreatic enzymes (eg amylase) within the lumen of small intestine. Additional digestion of carbohydrates may occur through enzymes embedded within the villi epithelial cells. The products of the digestion are monosaccharides which are absorbed into the epithelial cells on villi.
Glucose cannot pass through the plasma membrane by simple diffusion because it is polar and therefore hydrophilic. Glucose is transported into the epithelial cell coupled to the movement of sodium ions into the cell through a sodium-glucose cotransport protein. The cotransport protein couples transport of sodium down its concentration gradient (established by the active transport of sodium out of the cell by the sodium-potassium pump) into the cell with the transport of glucose against its concentration gradient into the cell. Active transport requires ATP (from many mitochondria within the cells).
Explain the reasons for starch being digested by the human digestive system.
Starch is a significant component of human diets. Starch is a large polysaccharide molecule that can not be absorbed by the epithelial cells of the small intestine. Additionally, starch is not directly used as an energy source by cells and is not soluble, so it could not be transported in the blood.
The monosaccharide glucose is produce by the multistep digestion of starch. Glucose can be absorbed by the epithelial cells of the small intestine. Glucose is a useful source of energy for cells and can be transported in the blood.
Outline the digestion of starch into maltose.
Starch is a polymer of alpha-glucose monomers. Starch is both amylose (by 1,4 bonds) and amylopectin (by 1,4 bonds and occasional by 1,6 bonds).
The enzyme that digests starch is called amylase. Saliva contains amylase and some starch digestion begins in the mouth. However, most starch digestion occurs in the small intestine, catalysed by pancreatic amylase.
Amylase breaks the 1,4 bonds in starch molecules as long as there is a chain of at least four glucose monomers. The product of the digestion is the disaccharide maltose.
Outline the digestion of maltose into glucose.
The enzyme maltase catalyzes the hydrolysis of the disaccharide maltose into glucose monomers. In humans, maltase is most often located embedded in the epithelial cell membranes of the small intestine.
Describe transport of glucose into and through villi capillaries.
Glucose cannot pass through the plasma membrane by simple diffusion because it is polar and therefore hydrophilic. Glucose is transported in to the epithelial cell from the small intestine lumen through a sodium-glucose cotransport protein.
Then, the glucose moves out of the epithelial cell and moves into the villi capillary. Glucose channels allow the glucose to move by facilitated diffusion into blood capillaries in the villus.
Glucose in the blood is then carried via the hepatic portal vein to the liver where excess glucose can be absorbed by liver cells and converted to glycogen for storage.
Explain the use of dialysis tubing as a model for the small intestine.
Dialysis tubing is an artificial semipermeable membrane tubing that facilitates the flow of tiny molecules in solution based on differential size. Pores in the tubing allow water and small molecules or ions to pass through freely, but not large molecules. These properties mimic the wall of small intestine. Dialysis tubing can be used to model absorption by passive diffusion and osmosis.
State the role of the digestive system.
The digestive system is a collection of organs that collectively digest food, absorb nutrients and excrete waste.
Draw a diagram of the human digestive system.
Mouth - hollow cavity in the head.
Esophagus – hollow tube connecting mouth to the top of the stomach.
Stomach – a roughly crescent-shaped, hollow organ located just under the diaphragm in the left part of the abdominal cavity. Located between the esophagus and the small intestine.
Small intestine - winds throughout the abdominal cavity inferior to the stomach.
Large intestine - wraps around the border of the abdominal body cavity from the right side of the body, across the top of the abdomen, and finally down the left side.
Liver - a roughly triangular organ that extends across the entire abdominal cavity just under to the diaphragm. Most of the liver’s mass is located on the right side of the body.
Gall bladder - hollow, pear-shaped organ that sits under the liver. The end of the gallbladder narrows to join the common bile duct that extends to the wall of the small intestine.
Pancreas – a narrow gland that lies inferior to the stomach on the left side of the abdominal cavity. The pancreas extends laterally across the abdomen. The head of the pancreas connects to the small intestine.
Outline the function of the mouth in digestion.
The mouth contains many structure- such as the teeth, tongue, and the salivary glands - that work together to aid in the ingestion, digestion and swallowing of food.
Teeth are hard structures specialized for the mechanical digestion (biting and grinding) of food. Salivary glands release saliva into the mouth through many tiny ducts. Saliva helps to moisten and chemically digest starch in the mouth before swallowing.
Outline the function of the esophagus in digestion.
The esophagus functions as the conduit for food and liquids that have been swallowed in the mouth to reach the stomach.
Outline the function of the stomach in digestion.
The stomach stores and mechanically digests food. The stomach also secretes a mixture of acid, mucus, and digestive enzymes that helps to chemically digest proteins and sanitize our food while it is being stored.
Outline the function of the small intestine in digestion.
Partially digested food from the stomach is mixed with bile from the liver and pancreatic juice from the pancreas to complete digestion. Then, the small intestine absorbs the nutrients and minerals from the food.
Outline the function of the pancreas in digestion.
The pancreas serves as two glands in one: a digestive exocrine gland and a hormone-producing endocrine gland. Functioning as an exocrine gland, the pancreas secretes pancreatic juice into the lumen of the small intestine. Pancreatic juice has a basic pH in nature due to the high concentration of bicarbonate ions. Bicarbonate is useful in neutralizing the acidic gastric acid. Pancreatic juice also contains enzymes to digest down the proteins (protease), lipids (lipase), carbohydrates (amylase), and nucleic acids (nuclease) in food.
Outline the function of the liver in digestion.
The liver plays an active role in the process of digestion through the production of bile. Bile is a mixture of water, bile salts, cholesterol, and the pigment bilirubin. Hepatocytes in the liver produce bile, which then passes through the bile ducts to be stored in the gallbladder. When food containing fats reaches the small intestine, the gallbladder releases bile. Bile emulsifies large masses of fat. The emulsification of fats by bile turns the large clumps of fat into smaller pieces that have more surface area and are therefore easier for lipase to digest.
Outline the function of the gallbladder in digestion.
The gallbladder stores bile produced in the liver until it is needed for digesting fat in the small intestine. Bile travels through the bile ducts and is released into the small intestine where it emulsifies large masses of fat. The emulsification of fats by bile turns the large clumps of fat into smaller pieces that have more surface area and are therefore easier for lipase to digest.
Outline the function of the large intestine in digestion.
The large intestine absorbs water and vitamins (e.g. K and B12) while converting undigested food into feces.
Outline the function of the mucosa layer of tissue found in the wall of the small intestine.
The small intestine is made up of four layers of tissue. The mucosa forms the inner layer of epithelial tissue and is specialized for the absorption of nutrients.
Outline the function of the submucosa layer of tissue found in the wall of the small intestine.
The small intestine is made up of four layers of tissue. Beneath the mucosa is the submucosa layer that provides blood vessels, lymphatic vessels, and nerves.
Outline the function of the smooth muscle of tissue found in the wall of the small intestine.
The small intestine is made up of four layers of tissue. Beneath the submucosa, several layers of smooth muscle tissue contracts and moves the small intestines. This “peristalsis” helps prevents backward movement of food material and maintains the forward movement of the material.
Outline the function of the serosa layers of tissue found in the wall of the small intestine.
The small intestine is made up of four layers of tissue. The serosa forms the outermost layer of small intestines and functions as connective tissue. It helps suspend the gut in abdominal cavity by attaching itself to surrounding structures.
Label the four layers of tissue found in the wall of the small intestine as viewed with a microscope or in a micrograph.
From the inner surface of the tube moving outward, the layers are:
(lumen)
mucosa (epithelial and goblet cells)
submucosa (villi capillary and lymph vessels)
smooth muscle (circular and longitudinal)
serosa (connective tissue)
Explain the use of models in physiology research.
A model is a representation of an idea, an object, a process or a system that is used to describe, explain or test phenomena that cannot be experienced directly.
State two examples of model systems used to study digestion.
TNO (gastro-) Intestinal Models (“TIM”) are model systems mimicking the digestive tract. The models are dynamic computer controlled multicompartmental systems with adjustable parameters for the physiological conditions of the stomach and intestine. Temperature, peristalsis, bile secretion, secretion of saliva, stomach and pancreas enzymes are all fully adjustable.
Dialysis tubing can model absorption by the small intestine. It is a selectively permeable membrane, this means it has pores in it which allow small molecules through but not larger molecules. At regular intervals the liquid inside and outside of the tubing can be sampled and tested for starch (using iodine) and glucose (using Benedict’s reagent).
State limitations of using model systems in physiology research.
A good model is both as accurate as possible and as simple as possible. Models should have as much accuracy and predictive power as possible while being to be as simple as possible. Therefore, all models have limitations.
Missing details: models can’t incorporate all the details of complex natural phenomena.
Approximations: approximations are not exact, so predictions based on them tend to be a little less accurate than what is actually observed
State the function of arteries.
The circulatory system is made up of blood vessels that carry blood away from and towards the heart. Arteries carry blood away from the heart to the capillaries in the tissues of the body.
Outline the role of elastic and muscle tissue in arteries.
The tunica media is the middle layer of an artery wall. It is a thick layer containing smooth muscle, elastic fibers and collagen that encircle the vessel. The muscle and elastic fibers assist in maintaining blood pressure between pump cycles.
As the blood inside the arteries is being pushed by the heart, the blood pushes against the insides of the artery walls. This pushing is “blood pressure.” To cope with this pressure, the muscles and elastin in the artery walls hold them in shape and allow them to to stretch in response to each pulse. This elasticity also helps to maintain a relatively constant pressure in the arteries despite the pulsating nature of the blood flow.
State the reason for toughness of artery walls.
Arteries must be able to withstand the pressure of the blood as it moves with each heartbeat. Compared to veins, arteries have a thick, tough tunica media layer containing smooth muscle, elastic fibers and collagen that encircle the vessel.
Explain how arteries are able to transport the blood under high pressure from the heart to the rest of the body.
Blood leaves the heart through arteries under high pressure as a result of the contraction of the ventricles. The thick muscular walls and narrow lumen of arteries maintains the pressure as the blood moves to the rest of the body. Additionally, the elastic recoil of the arterial walls helps to push blood between contractions of the heart.
Describe the structure and function of the three layers of artery wall tissue.
Tunica externa- A tough outer layer of connective tissue the adheres the vessel to the surrounding tissue.
Tunica media- A thick layer containing smooth muscle, elastic fibers and collagen that hold arteries in shape and allow them to to stretch in response to each pulse.
Tunica intima- A smooth endothelium forming the lining of the artery. Allows blood to flow through the vessel with minimal resistance.
Describe the mechanism used to maintain blood flow in arteries between heartbeats.
Blood will move from areas of higher pressure to areas of lower pressure.
During systole, when new blood is entering the arteries, the artery walls stretch to accommodate the increase of pressure of the extra blood. During diastole, the walls return to normal because of their elastic properties. The elastic recoil of the arteries allows the artery to exert an inward force to maintain blood pressure. As the muscles and elastic fibers recoil, they further propel the blood, maintaining blood flow in the arteries between heartbeats.
Define “blood pressure.”
Blood pressure is the pressure exerted by blood on the walls of an artery.
Define “systolic blood pressure.”
Systolic blood pressure measures the amount of pressure that blood exerts on vessels while the heart ventricles are contracting. Systolic blood pressure is the upper number of a blood pressure reading.
Define “diastolic blood pressure.”
Diastolic blood pressure measures the amount of pressure that blood exerts on vessels between ventricular contractions, when the heart ventricles are relaxed. Diastolic blood pressure is the second number in a blood pressure reading.
Outline the cause and effect of vasoconstriction.
Vasoconstriction is the narrowing of blood vessels resulting from contraction of the muscles in the tunica media layer of the vessel wall. When blood vessels constrict, blood flow to a region is decreased.
Vasoconstriction in arteries near the skin surface can occur when the body is exposed to cold. This makes less blood reach the surface, reducing the radiation of heat from the body.
Pharmaceutical vasoconstrictors are used in medicine to increase blood pressure.
Outline the cause and effect of vasodilation.
Vasodilation is the widening of blood vessels resulting from relaxation of the muscles in the tunica media layer of the vessel wall. When blood vessels dilate, blood flow to a region is increased.
Vasodilation in arteries near the skin surface can occur when the body is exposed to heat. This makes more blood reach the surface, increasing the radiation of heat from the body.
When exercising, vessels will dilate bringing more oxygen to the metabolically active cells. if there is a localized infection or cut, vessels will dilate, bringing more immune cells and/or clotting factors to to affected tissue.
Pharmaceutical vasodilators are used in medicine to decrease blood pressure.
Describe the structure and function of capillaries.
Capillaries are the smallest blood vessels in the body, connecting the arterioles to venules. Capillaries are composed of only two layers of cells; an endothelial layer surrounded by a basement membrane. The capillary lumen is so narrow that red blood cells need to flow through them single file. Capillaries are highly branched to increase the exchange surface area and minimize the diffusion distance.
Exchange of gases and other substances occurs in the capillaries between the blood and the surrounding cells and their tissue fluid (interstitial fluid). For capillaries to function, their walls must be “leaky”, allowing substances to pass through. There are three major types of capillaries, which differ according to their degree of “leakiness:” continuous, fenestrated, and sinusoid capillaries.
Describe the cause and effect of diffusion of materials into and out of a capillary network.
Diffusion is the most widely-used mechanism of transport of materials between the capillary and surrounding tissues. Small molecules diffusion across capillaries such as glucose and oxygen from the blood into the tissues and carbon dioxide from the tissue into the blood. The process depends on the difference of concentration gradients between the blood and the liquid outside the blood vessels, called interstitial fluid. Molecules move from high-concentrated areas to low-concentrated spaces.
As a result of this diffusion, the tissue cells are able to receive oxygen and nutrients and remove waste molecules and carbon dioxide.
State the function of veins.
The circulatory system is made up of blood vessels that carry blood away from and towards the heart. Veins carry blood towards the heart from the capillaries in the tissues of the body.
Outline the roles of gravity and skeletal muscle pressure in maintaining flow of blood through a vein.
Blood flows from an area of higher pressure toward an area of lower pressure. If blood is to flow from the veins back into the heart, the pressure in the veins must be greater than the pressure in the atria of the heart. Luckily, the pressure in the atria during diastole is very low.
The pressure within the veins can be increased by the contraction of the surrounding skeletal muscle. This mechanism, known as the skeletal muscle pump, helps the lower-pressure veins counteract the force of gravity, increasing pressure to move blood back to the heart. As leg muscles contract, they exert pressure on nearby veins with their numerous one-way valves. This increased pressure causes blood to flow upward, back to the heart against the force of gravity.
Outline the structure and function of a pocket valve.
Blood pressure in veins is much lower than that in the arteries. Veins must prevent it from flowing in the wrong direction. Valves in the veins function to keep blood moving in one direction. Theses valves are bicuspid (two) flap like structures made of elastic tissue and are often called “pocket valves” in reference to their shape.
As skeletal (especially leg) muscles contract, they exert pressure on nearby veins with their numerous valves. This increased pressure causes blood to flow upward, opening valves superior to the contracting muscles so blood flows through. Simultaneously, valves inferior to the contracting muscles close; thus, blood will not seep backward.
Draw a diagram to illustrate the double circulation system in mammals.
The majority of mammals (including humans) utilize a double circulatory system. It is called a double circulatory system because blood passes through the heart twice per full circuit.
The right pump sends deoxygenated blood to the lungs where it becomes oxygenated and returns back to the heart. The left pump sends the newly oxygenated blood around the body. By the time this blood returns to the heart, it has returned to a deoxygenated state.
Compare the circulation of blood in fish to that of mammals.
In fish, there is single pump circulation. The heart only has one atrium and one ventricle. The oxygen-depleted blood that returns from the body enters the atrium, and then the ventricle, and is then pumped out to the gills where the blood is oxygenated, and then it continues through the rest of the body.
In mammals there is double pump circulation. The heart has two atria and two ventricles. The right side of the heart receives blood returning back from the body; this “deoxygenated” blood enters the right atrium and then the right ventricle to be pumped to the lungs were the blood will be oxygenated. The oxygenated blood from the lungs enters the left ventricle via the left atrium and is then pumped out into the larger body circulation.
Explain the flow of blood through the pulmonary and systemic circulations.
The mammalian cardiovascular system has two distinct circulatory paths, pulmonary circulation and systemic circulation.
Pulmonary circulation is the movement of blood from the heart to the lungs for oxygenation, then back to the heart again.
Systemic circulation is the movement of blood from the heart through the body to provide oxygen and nutrients to the tissues of the body while bringing deoxygenated blood back to the heart.
Explain why the mammalian heart must function as a double pump.
There must be a double pump in order to create enough pressure to move the blood throughout the entire body. Pressure is needed to move blood through the resistance of a large network of blood vessels like arteries, capillaries, and veins.
A single pump (a) would require such a force that the lungs capillaries would be damaged by the high pressure blood moving through or (b) wouldn’t supply enough force to move blood through the lung capillaries for oxygenation and then continue on to the tissue capillaries.
When the right ventricle contracts (#1), it is able to raises the pressure of the blood to about 25mmHg. After passing through the lungs, the blood pressure is down to about 5mmHg. Then the left ventricle contraction (#2) causes the pressure to rise back up to about 120mmHg. That’s enough pressure to make it through all of the tissue capillaries in the body.
Summarize the double pump circulation of the mammalian heart.
The heart functions as a double pump. Blood moves from the body into the right atrium, and then into the right ventricle where it gets pumped (#1) into the lungs. Blood gets oxygenated in the lungs, moves into the left atrium, and into the left ventricle where it gets pumped (#2) into the body.
The double pump allows blood to be pumped at a lower pressure to the lungs (preventing damage of lung tissue) and pumped again at high enough pressure to pump blood to all other body tissues.
Define “myogenic contraction.”
Myogenic contractions are contractions that are initiated in the heart muscle itself rather than by stimulation from nerve impulses.
Outline the role of cells in the sinoatrial node.
The sinoatrial node (SA node) is a group of cells located in the wall of the right atrium of the heart that have the ability to spontaneously and regularly produce an electrical impulse (action potential) that travels through the heart causing it to contract. The SA node is known as the heart’s “pacemaker.”
Describe the propagation of the electrical signal from the sinoatrial node through the atria and ventricles.
The cardiac conduction system is a group of specialized cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract. The sinoatrial node (SA node, “pacemaker”) starts the sequence by causing the atria to contract. From the SA node, the signal travels to the atrioventricular node (AV node), through the bundle of His, down the bundle branches, and through the Purkinje fibers, causing the ventricles to contract.
State the reason why the sinoatrial node is often called the pacemaker.
The sinoatrial node (SA node) is known as the heart’s “pacemaker.” The main role of a sinoatrial node cell is to initiate action potentials in the cardiac muscle cells at a regular interval, so that the impulse can pass through the heart and cause contraction.
Outline the action of nervous tissue that can regulate heart rate.
Heart rate is intrinsically determined by the pacemaker activity of the sinoatrial node (SA node) located in the wall of the right atrium. However, the pace of the SA node can be changed by impulses (action potentials) brought to the heart through nerves from the medulla of the brain. Neural input can influence heart rate, cardiac output, and contraction forces of the heart.
The vagus nerves (parasympathetic) can reduce the heart rate and the force of contraction of the heart.
Cardiac sympathetic nerves (sympathetic) can increase the heart rate and the force of contraction of the heart.
List factors that will increase heart rate.
There are a number of factors that can increase heart rate, including:
Epinephrine hormone
Increased thyroid hormones
Levels of various ions
Increased body temperature
Altitude
Exercise
Caffeine
Nicotine
List factors that will decrease heart rate.
There are a number of factors that can decrease heart rate, including:
Acetylcholine neurotransmitter
Decreased thyroid hormones
Levels of various ions
Decreased body temperature
Anticipation of relaxation
Reduced oxygen availability in cardiac cells
Outline conditions that will lead to epinephrine secretion.
Epinephrine (also known as adrenaline) is secreted by the adrenal gland upon activation of sympathetic nerves innervating this tissue. This activation occurs during times of stress (e.g., exercise, heart failure, hemorrhage, emotional stress or excitement, pain).
Epinephrine causes an increase in heart rate, muscle strength, blood pressure, and sugar metabolism. This reaction, known as the “Flight or Fight Response” prepares the body for strenuous activity.
Explain the effect of epinephrine on heart rate.
As a hormone, epinephrine achieves its effects on heart rate by stimulating the adrenergic receptors on the cell membrane of cells throughout the heart tissue. Once stimulated, these receptors activate a second-messenger system that trigger a cascading effect on other substances inside the cell. The overall result of this process is an increase in the heart rate, as well as an increase in the force of each individual heart contraction.
Outline William Harvey’s role in discovery of blood circulation.
William Harvey (1578-1657), observing the heart in living animals, he was able to show that the valves in the veins permit the blood to flow only in the direction of the heart and to prove that the blood circulated around the body and returned to the heart. In his words:
“It has been shown by reason and experiment that blood by the beat of the ventricles flows through the lungs and heart and is pumped to the whole body. There it passes through pores in the flesh into the veins through which it returns from the periphery everywhere to the centre, from the smaller veins into the larger ones, finally coming to the vena cava and right atrium. This occurs in such an amount, with such an outflow through the arteries and such a reflux through the veins, that it cannot be supplied by the food consumed. It is also much more than is needed for nutrition. It must therefore be concluded that the blood in the animal body moves around in a circle continuously and that the action or function of the heart is to accomplish this by pumping. This is only reason for the motion and beat of the heart.”
Describe the cause and consequence of atherosclerosis.
Atherosclerosis is the narrowing of arteries due to the buildup of fats, cholesterol and other substances in and on artery walls (plaque).
Atherosclerosis begins with damage to the artery endothelial layer (tunica intima) caused by high blood pressure, smoking, or high cholesterol. That damage leads to the formation of plaque on the artery wall.
Plaques from atherosclerosis can:
- increase blood pressure
- block blood flow (causing an aneurysm)
- cause the vessel to rupture allowing blood to clot inside the artery (potentially leading to stroke or heart attack).
Outline the effect of a coronary occlusion on heart function.
The heart muscle requires a constant supply of nutrient and oxygen-rich blood. The coronary arteries provide the heart with this critical blood supply. A coronary occlusion is the partial or complete obstruction of blood flow in a coronary artery. If the heart muscle cells do not receive the blood (nutrients and oxygen) because of the blockage, they can not function properly. This condition may cause a myocardial infarction (heart attack). Within a short time, death of heart muscle cells occurs, causing permanent damage.
Define “cardiac cycle.”
The cardiac cycle is the action of the heart from the ending of one heartbeat to the beginning of the next. Both the atria and ventricles undergo systole and diastole during one cardiac cycle.
Summarize events of the cardiac cycle.
The chambers are relaxed (diastole) and both atria collect blood from veins. The sinoatrial node sends impulses initiating contraction of the atria, Blood is pushed into the ventricles by contraction of atria (systole). The atrioventricular valves are open as the atria contract and the semilunar valves are closed so that ventricles fill with blood.
When the ventricles contract (systole), the atrioventricular valves close (preventing backflow) and blood is pushed out through the semilunar valves into pulmonary artery and aorta. When the ventricles relax (diastole) the semilunar valves close preventing backflow of blood.
Define systole.
Systole is the part of the cardiac cycle during which the heart muscle contracts and moves blood out of the chambers. There is an atrial systole and a ventricular systole.
Define diastole.
Diastole is the part of the cardiac cycle during which the the muscle muscle relaxes and allows the chambers to fill with blood There is an atrial diastole and a ventricular diastole.
Outline events of atrial diastole.
At the beginning of the cardiac cycle, both the atria and ventricles are relaxed (diastole). Blood is flowing into the right atrium from the superior and inferior venae cavae. Blood flows into the left atrium from the four pulmonary veins. The left and right atrioventricular valves are both open, so blood flows unimpeded from the atria and into the ventricles. The pulmonary and aortic semilunar valves are closed, preventing backflow of blood into the right and left ventricles from the pulmonary artery on the right and the aorta on the left.
Outline events of atrial systole.
Contraction (systole) of the atria is triggered by the firing of the sinoatrial node. As the atrial muscles contract, pressure rises within the atria and blood is pumped into the ventricles through the open atrioventricular valves.
Outline events of ventricular diastole.
During the early phase of ventricular diastole, as the ventricular muscle relaxes, pressure on the remaining blood within the ventricle begins to fall. The semilunar valves close to prevent backflow into the heart.
In late ventricular diastole, pressure on the blood within the ventricles drops even further. Eventually, it drops below the pressure in the atria. When this occurs, blood flows from the atria into the ventricles, pushing open the atrioventricular valves. Blood flows from the relaxed atria into the ventricles. Both chambers are in diastole, the atrioventricular valves are open, and the semilunar valves are closed.
Outline events of ventricular systole.
As the muscles in the ventricle contract (systole), the pressure of the blood within the chamber rises, closing the atrioventricular valves.
As ventricular systole continues, the pressure within the ventricle raises to the point that it is greater than the pressures in the pulmonary artery and the aorta. The pressure of the blood pushes open the pulmonary and aortic semilunar valves. Blood is ejected from the heart through the pulmonary artery and the aorta.
Explain the pressure changes in the left atrium during the cardiac cycle.
Blood flows according to pressure gradients— it moves from regions that are higher in pressure to regions that are lower in pressure. Accordingly, when the heart chambers are relaxed (diastole, A), blood will flow into the atria from the veins and from the atria into the ventricles along the pressure gradient.
When the sinoatrial node triggers the muscles in the atria to contract (atrial systole, B), the pressure within the atrial chambers increases, which forces more blood flow across the open atrioventricular valves, leading to a rapid flow of blood into the ventricles.
The atria relax and the pressure again decreases (atrial diastole, A).
Explain the pressure changes in the left ventricle during the cardiac cycle.
Blood flows according to pressure gradients— it moves from regions that are higher in pressure to regions that are lower in pressure. Accordingly, when the heart chambers are relaxed (diastole, A), blood will flow into the atria from the veins and from the atria into the ventricles along the pressure gradient.
At the start of ventricular systole (B) , the pressure rises in the ventricle, closing the atrioventricular valves. Pressure continues to increase in the ventricle as it contracts, and eventually the pressure will surpass the pressure in the arteries. The pulmonary and aortic semilunar valves will open and blood will be ejected into the pulmonary artery from the right ventricle and into the aorta from the left ventricle.
As the blood leaves the ventricle, the pressure within the ventricle decreases. Once the pressure in the arteries is higher than that in the ventricles, the aortic and pulmonary semilunar valves will close. Although ventricular pressures continues to decrease, volumes do not change because all valves are closed.
Once the pressure is again lower in the ventricles than in the atria, the atrioventricular valves will open and blood will again enter the ventricle from the atria. Once the ventricles are completely relaxed, their pressures will slowly rise as they fill with blood from the atria.
Explain the pressure changes in the aorta during the cardiac cycle.
During ventricular systole, pressure increases in the ventricle as it contracts. Eventually the pressure will surpass the pressure in the aorta, causing the aortic semilunar valves to open and blood to be ejected into the aorta from the left ventricle.
As the left ventricle ejects blood into the aorta, the aortic pressure increases to a maximum systolic pressure. The greater the force of the ventricular contraction, the greater the change in aortic pressure during ejection.
After ventricular contraction, the pressure in the aorta will begin to drop. Once the pressure in the aorta is again higher than that in the ventricle, the aortic semilunar valves will close. Blood will no longer be entering the aorta and its pressure will decrease to a minimum diastolic pressure.
Explain the relationship between atrial and ventricular pressure and the opening and closing of the atrioventricular valves.
The atrioventricular valves are located between the atria and the ventricles of the heart. The atrioventricular valves open and close based on pressure differences between the ventricle and atria.
At the beginning of the cardiac cycle, both the atria and ventricles are relaxed (diastole). The left and right atrioventricular valves are both open, so blood flows unimpeded from the atria and into the ventricles.
As the muscles in the ventricle contract (systole), the pressure of the blood within the ventricle rises above the pressure in the atrium. The greater pressure in the ventricle causes the closing of the the atrioventricular valves and prevents backflow of blood from the ventricle to the atria.
When the ventricles relax, the pressure in the ventricle drops lower than the pressure in the atria. The higher pressure of the blood in the atria will cause the opening of the atrioventricular valves, allowing blood to flow from atria into the ventricles.
Explain the relationship between ventricular and arterial pressure and the opening and closing of the semilunar valves.
The semilunar valves are located between the ventricles and the arteries leaving the heart. The semilunar valves open and close based on pressure differences between the ventricle and arteries.
During ventricular diastole, the semilunar valves are closed to present backflow of blood from the arteries into the ventricles. The pressure is higher in the arteries than the ventricles, which keeps the valves closed.
With ventricular systole, the pressure rises in the ventricle and eventually the pressure will surpass the pressure in the arteries. The pulmonary and aortic semilunar valves will open and blood will be ejected into the pulmonary artery from the right ventricle and into the aorta from the left ventricle.
As the blood leaves the ventricle, the pressure within the ventricle decreases. Once the pressure in the arteries is higher than that in the ventricles, the aortic and pulmonary semilunar valves will close.
Given a micrograph, identify a blood vessel as an artery, capillary or vein.
The walls of arteries are much thicker than those of veins because of the higher pressure of the blood that flows through them. The artery walls also tend to have a more distinct round shape, held in place by the fibers of the tunica media.
Capillaries can be distinguished by the very narrow lumen size (only 1 red blood cell wide).
Explain the relationship between structure and function of arteries.
Blood under the highest pressure (closest to pump from heart)
Thickest wall (to withstand high pressure and maintain blood pressure)
Three wall layers (tunica intima, media and externa)
Smooth endothelium (reduces friction as blood moves through)
Smooth muscle (contracts to maintain blood pressure)
Elastic fibers (give wall strength and the ability to recoil to propel blood forward)
No valves (high pressure maintains blood flow direction)
Narrow lumen (maintains high pressure)
Explain the relationship between structure and function of capillaries.
One wall layer (tunica intima)
Wall has one layer of cells (allowing fast diffusion of substances)
Pores and fenestrations (increase permeability for exchange of substances and to allow immune phagocytes to enter tissues)
Extensive branching (increases surface area for exchange of materials)
Narrowest lumen diameter (allows them to fit between cells and perfuse tissue)
Only one red blood cell allowed to pass at a time (for efficient oxygen uptake)
Explain the relationship between structure and function of veins.
Three wall layers (tunica intima, media and externa)
Thin tunica media with less muscle and elastic fibers (allows skeletal muscles to exert pressure on veins)
Widest lumen diameter ( allows great volume of blood to pass while minimizing resistance to blood flow)
Valves (prevent backflow of blood)
Label the chambers on a diagram of the mammalian heart.
The mammalian heart has four chambers: two atria and two ventricles.
The right atrium receives oxygen-poor blood from the body via the vena cava and pumps it to the right ventricle.
The right ventricle pumps the oxygen-poor blood to the lungs via the pulmonary artery.
The left atrium receives oxygen-rich blood from the lungs via the pulmonary veins and pumps it to the left ventricle.
The left ventricle pumps the oxygen-rich blood to the body via the aorta.
Label the vessels on a diagram of the mammalian heart.
Veins are vessels that bring blood to the heart.
The superior and inferior vena cava bring oxygen-poor blood from the body to the right atrium.
The four pulmonary veins bring oxygen-rich blood from the lungs to the left atrium.
Arteries are vessels that move blood away from the heart.
The pulmonary artery takes oxygen-poor blood from right ventricle to the lungs.
The aorta takes oxygen-rich blood from the left ventricle to the rest of the body.
Label the valves on a diagram of the mammalian heart.
Valves maintain the unidirectional flow of blood through the heart.
The atrioventricular (AV) valves are located between the atria and the ventricles of the heart. The right AV valve (tricuspid) is located between the right atrium and the right ventricle. The left AV valve (mitrial) is located between the left atrium and the left ventricle.
The semilunar (SL) valves are located between the ventricles and the arteries leaving the heart. The pulmonary SL valve is located between the right ventricle and the pulmonary artery. The aortic SL valve is located between the left ventricle and the aorta.
