OSU A+P Quizzes
Which of the following happens during intramembranous bone formation?
Bone deposition occurs before blood vessel invasion. Right! During intramembranous bone formation mesenchymal cells differentiate to become osteoblasts which then produce new bone. The mesenchymal cells are already present in the tissue, blood vessels are not required. In fact, bone formation precedes blood vessels. As the new bone forms, it traps the blood vessels within spongy bone trabeculae. The outer compact bone from the periosteum is the last bone to form. This type of bone formation does not involve cartilage at all, so mitotic problems with cartilage cells should not impact intramembranous bone formation.
Researchers found that chronically stressed individuals have significantly higher blood pressure compared to individuals with little stress. Which graph would be most appropriate for displaying the mean (average) blood pressure scores for high-stress and low-stress groups of people?
graph with decreasing linear line and has stuff underneath
A fat soluble hormone will:
have relatively long lasting effects. Fat soluble hormones can diffuse through the cell membrane and bind to intracellular receptors. These receptor/hormone complexes will likely directly activate gene transcription. They do not require second messenger systems - those are used for ligands that cannot penetrate the membrane (water soluble).
During formation of the flat portions of the frontal bone (the bone that makes up your forehead), ______ differentiate to become _______.
mesenchymal cells; osteoblasts Certain bones form intramembranously - these include the flat skull bones of the cranium, the clavicle and the mandible. During intramembranous bone formation, mesenchymal cells in the mesenchyme differentiate to become osteoblasts. Differentiation refers to a non-specific stem cell developing into a specific cell type. Mesenchyme in the embryo is a tissue that contains mesenchymal cells and extracellular fibers and fluid. During development, specific cellular signals cause the mesenchymal cells in the appropriate areas to cluster and then differentiate into osteoblasts. The newly formed osteoblasts deposit bone which eventually morphs into the above mentioned bones. Osteoblasts are derived from osteoprogenitor cells which are derived from (differentiate from) mesenchymal cells. Chondroblasts are also derived from mesenchymal cells, but they deposit cartilage, not bone. This process occurs during endochondral bone formation. Osteoprogenitor cells do not give rise to osteoclasts - the bone destroying cells. While osteoclasts are active during bone growth and remodeling, they are derived from the white blood cell line, not the osteoprogenitor cell line.
Potassium ions have a ____ charge and ____ a neuron when they flow down their concentration gradient.
positive; exit. Correct! Potassium ions are positively charged (K+) and are more concentrated inside the neuron due to the action of the sodium/potassium pump. When they are able to cross the cell membrane through a channel, they flow passively down their concentration gradients from where they are more concentrated to where they are less concentrated, thus exiting the cell.
Where do you find the cells that act to remodel or maintain bone?
- In the periosteum found covering bones - In trabeculae lacunae - In the endosteum found lining bone spaces -In osteon lacunae Bone is a dynamic tissue that remodels in response to stress and hormones. Osteoblasts and osteocytes act to build bone, an important feature of bone remodeling. Osteoclasts chew old bone and remove it from where it is not needed. Bone remodeling reshapes the bone while bone maintanence redeposits and renews old bone. Osteocytes maintain the matrix and can act to build new bone. All the cells mentioned are found in the endosteum and periosteum, although only osteocytes are located in lacunae.
Where must threshold be reached to send a signal all the way down the length of the neuron?
-at trigger zone and at each node of ranvier Right! Signal conduction down an axon requires the action potential to be generated (or regenerated) at each exposed portion of the axon. To generate an AP at each section of the neuron, you must bring that section to threshold so that voltage gated sodium and potassium channels can open. Typically, the first place where an AP is generated is at the trigger zone (initial segment). Then, the AP must be recreated at each section of the neuron to transmit the signal to the end of the neuron.
In neurons, a stimulus is an event that changes membrane potential. What would create "a bigger" or "stronger" stimulus on a neuron?
-opening a chemically gated channel for a longer time -opening more chemically gated channels at once. Right! Changes in transmembrane potentials can be made bigger or stronger by allowing more ions to cross the membrane. WE can have more ions cross the membrane when gated channels are left open for longer or when more gated channels are opened at once.
What is the role of the sodium-potassium pumps on the neuron cell membrane?
-to move K+ against it's concentration gradient -to move Na+ against it's concentration gradient -to establish the proper ionic concentration of sodium and potassium across the cell membrane. Correct! The Na+/K+ pump uses ATP to pump 3 Na+ ions out of the cell and 2 K+ ions into the cell. Because it uses energy to move the ions, it does not rely on diffusion for ion movement - meaning, it can push ions uphill against their concentration gradient. In doing this, it actually establishes the concentration gradient of these ions across the cell membrane and then re-establishes it after signals (action potentials) pass through the cell. This is an essential component to neuron function. Without the concentration gradients created and maintained by the Na+/K+ pumps, there could be no action potential.
Arrange the following structures in the correct order starting with the simplest level of organization and ending with the most complex. 1. Cell membrane 2. Epithelial cell 3. Human 4. Digestive system 5. Phospholipid 6. Small intestine
5,1,2,6,4,3 Right! Ordering questions are often on my exams. When approaching an ordering question, you can either try to order the options yourself and then check to see if your order matches an answer, or you can look through the options. If you look here, each option begins with either 3 or 5. Regardless of the answer you choose, you should always look at the given orders and eliminate the really wrong ones. The most common error people make with ordering questions is reading the question incorrectly. If you selected an option that began with the whole human (3) as the first number, it is likely that you were organizing the numbers from most complex structural organization to least complex structural organization. Another place where folks go wrong here is to get thrown off by the fact that the levels of organization are not exactly as displayed in class. Here you have to look at each structure and identify it as a molecule, or a part of a cell, a whole cell, an organ, or an organ system. Then you have to put them into an order that is more familiar to you.
To create a graded hyperpolarization in the postsynaptic cell, the following events would need to occur in which of the following orders (you may or may not need to use all numbers below). 1. Voltage gated calcium channels open. 2. Neurotransmitter binds to chemically gated channels. 3. Synaptic vesicles migrate to cell membrane. 4. Neurotransmitter released into synaptic cleft. 5. Action potential arrives at terminal end (knob). 6. Sodium rushes into the postsynaptic cell. 7. Potassium rushes out of the postsynaptic cell.
5,1,3,4,2,7
What directly causes a voltage gated channel to open?
A change in the transmembrane potential due to some factor. Correct! Voltage gated channels are membrane proteins that open when the surrounding membrane transmembrane potential (electricity) changes. Not just any change in the membrane potential will cause the voltage gated channel to open, but only when the membrane reaches a particular transmembrane potential. This membrane potential value that causes the voltage gated channel to open is called threshold. Chemically gated channels open when a chemical binds to a receptor on the channel. Mechanically gated channels open when the surrounding membrane (or channel) is physically changed (deformed). ATP can act as a neurotransmitter causing certain chemically gated channels to open.
A synapse is where a neuron communicates with another cell - we call this other cell the postsynaptic cell. Suppose a neurotransmitter causes Cl- channels to open on the postsynaptic cell membrane. Which of the following would occur?
A graded hyperpolarization on the postsynaptic cell. Correct! When Cl- channels open, Cl- ions rush into the cell, making the interior more negative = the transmembrane potential becomes hyperpolarized. This hyperpolarization of the cell membrane is called an IPSP - an inhibitory postsynaptic potential. It brings the postsynaptic transmembrane potential further away from threshold, making it less likely to fire an action potential. IPSPs cause neurons to be inhibited. Graded depolarizations occur when the postsynaptic transmembrane potential becomes less negative, moving towards 0 mV and above. Graded depolarizations of the postsynaptic membranes are called EPSPs (excitatory postsynaptic potentials) and they bring the neuron closer to threshold and thus AP generation. When a neuron moves closer to threshold, it is said to be facilitated.
In certain neurological disorders, the neurons controlling muscles continuously activate skeletal muscles causing rigidity. Which of the following medications would be most effective at treating these disorders?
A medication that extends the absolute refractory period in these neurons. Right! We want to decrease NT release from neurons. Since NT is released each time action potentials travel down the neuron, if we increase the duration of the absolute refractory period, fewer APs per minute will be possible on the neuron. With fewer APs, there will be less NT release. Increasing vesicle exocytosis will increase NT in the cleft and make the problem worse. Inhibiting re-uptake means that neurons do not remove NT from the synaptic cleft. Increasing Ca++ entry into the presynaptic neuron will cause more vesicle release, making the problem worse.
What is meant by the term "chemically gated sodium channel"?
A membrane channel that opens when some chemical binds to it, allowing sodium to cross the cell membrane. Correct! Neurotransmitters are chemicals released from neurons that bind to chemically gated channels. If the gated channel is specific for sodium, once the neurotransmitter binds, the gate opens and sodium flows down its concentration gradient into the cell.
What directly causes a chemically gated channel to open?
A neurotransmitter binding on the chemically gated channel. Correct! Chemically gated channels are membrane proteins that open when a chemical binds to a receptor on the channel. The chemical that causes them to open, if released from a neuron, is called a neurotransmitter. Voltage gated channels are membrane proteins that open when the surrounding membrane transmembrane potential (electricity) changes. Not just any change in the membrane potential will cause the voltage gated channel to open, but only when the membrane reaches a particular transmembrane potential. This membrane potential value that causes the voltage gated channel to open is called threshold. Mechanically gated channels open when the surrounding membrane (or channel) is physically changed (deformed). Regardless of the type of gated channel, channels are specific for the ions they allow to cross the cell membrane and only allow ions to cross the cell membrane using their diffusion gradients. Meaning, they only allow sodium to enter the cell because there is so much sodium outside of cells compared to inside of cells. The reverse is true for potassium.
Which of the following will cause a graded hyperpolarization on a postsynaptic neuron? A neurotransmitter binding to a voltage gated potassium channel A neurotransmitter binding to a chemically gated potassium channel A neurotransmitter binding to a voltage gated sodium channel A neurotransmitter binding to a chemically gated sodium channel
A neurotransmitter binding to a chemically gated potassium channel. Correct! At a synapse, the presynaptic cell communicates with the postsynaptic cell. At a chemical synapse, the presynaptic cell releases a chemical (neurotransmitter) that binds to chemically gated channels on the membrane of the postsynaptic cell. When a chemically gated channel opens, specific ions may move down their concentration gradients (from high to low). The concentration gradient for potassium is to move out of the cell. When potassium moves out of the cell, it removes positive ions from the cellular interior, thus leaving the cell more negative. A hyperpolarization is a change in the transmembrane potential from resting values to something more negative (perhaps -70 mV to -90 mV). Neurotransmitters do not bind to voltage gated channels. Opening a sodium channel would lead to a graded depolarization. Because sodium would move down its concentration gradient into the cell, this would make the interior less negative (move closer to 0 or positive values; perhaps from -70mV to -20 mV).
Which of the following will cause a graded hyperpolarization on a neuron?
A neurotransmitter binding to a chemically gated potassium channel. Correct! At a synapse, the presynaptic cell communicates with the postsynaptic cell. At a chemical synapse, the presynaptic cell releases a chemical (neurotransmitter) that binds to chemically gated channels on the membrane of the postsynaptic cell. When a chemically gated channel opens, specific ions may move down their concentration gradients (from high to low). The concentration gradient for potassium is to move out of the cell. When potassium moves out of the cell, it removes positive ions from the cellular interior, thus leaving the cell more negative. A hyperpolarization is a change in the transmembrane potential from resting values to something more negative (perhaps -70 mV to -90 mV). Neurotransmitters do not bind to voltage gated channels. Opening a sodium channel would lead to a graded depolarization. Because sodium would move down its concentration gradient into the cell, this would make the interior less negative (move closer to 0 or positive values; perhaps from -70mV to -20 mV).
Cells of the thyroid and parathyroid glands are sensitive to blood calcium levels. Which of the following is the most likely mechanism by which blood calcium levels are detected?
Calcium binds to a cell membrane receptor which activates a second messenger system. Calcium is charged - it cannot diffuse simply through the membrane (fat soluble do this); it is more concentrated outside cells due to all cells having a calcium pump on them, constantly keeping extracellular calcium levels high; even if calcium were to enter cells, it would depolarize them, not hyperpolarize them. It is true that calcium binding on these cells activates second messenger systems, leading to cellular response.
True or False? Endochondral bone formation stops at birth.
Endochondral bone formation forms most of the bones of your body. The process begins in the embryo when hyaline cartilage bones are replaced by osseous tissue. However, the process continues at the epiphyseal plate (growth plate) until adulthood. At the epiphyseal plate a thin line of hyaline cartilage remains and continues to grow through interstitial growth. As new cartilage grows, the epiphysis and diaphysis are pushed further away from each other. The older cartilage on the diaphyseal side of the growth plate is continuously degraded and replaced by bone. In this way the bone grows longer. At fully maturity (18-25 years of age), the hyaline cartilage is completely replaced by bone at the epiphyseal plate and the bone can no longer grow in length.
The liver is a glandular organ of the digestive tract. What is its most likely embryological origin?
Endoderm. The endoderm gives rise to the epithelium of the digestive tract, including the glands that support it (pancreas, liver, gall bladder). Glands are made of epithelial tissue. The mesoderm gives rise to many things, including muscles and bones, but not the liver. The ectoderm gives rise to the nervous system and skin.
You find a tissue within a growing bone that has the following characteristics: avascular cells contain nuclei, rough ER, golgi apparatuses and mitochondria cells are widely spaced from one another Where did this sample likely come from?
Epiphyseal side of the growth plate. The description of this tissue is avascular, cells contain nuclei, rough ER, golgi apparatuses and mitochondria & the cells are widely spaced from one another. Of the four primary tissue types, epithelia and some connective tissues are avascular (cartilages). The endosteum and periosteum are composed of connective tissue cells. Though these cells form a continuous layer, they are not epithelial tissues and they are very vascular. The growth plate contains both cartilage and bone. The cartilage grows by intersitial growth on the epiphyseal side, pushing the epiphysis away from the diaphysis. The bone chases the cartilage from the diaphyseal side. Both bone and cartilage contains widely spaced cells with organelles used for export of proteins (collagen). But only one of those is avascular. Since the tissue described is avascular, you needed to pick the cartilage and not the bone here.
True or False? All epithelial cells are dead because all epithelial tissues are avascular.
False. While it is true that epithelial tissues are avascular (meaning that they lack blood vessels), they are not all made of dead cells. The blood supply in the underlying connective tissue delivers oxygen and nutrients to the connective tissue, near the lowest level of the epithelial cells. These nutrients and oxygen diffuse into the connective tissue and then up to the epithelial cells. The closer the epithelial cells are to the bottom of the epithelial layer, the closer they are to the nutrients and the further the epithelial cells are from the bottom (closer to the top), the further they are from the nutrients. Your skin is made of stratified squamous epithelium and the cells at the top are indeed dead because they have migrated so far from the diffusing nutrients. The cells are the bottom however, are alive and constantly growing and dividing to replace the surface cells lost to the world.
Which of the following explains why females at end of life have lower bone mass than males?
Females have lower peak bone mass than males. Right! Bone mass peaks in females around age 25 (around 30 in males) according to our graph from activity 8. After that, it steadily declines until death. Because women have a lower peak bone mass, they also have a lower end of life bone mass. Testosterone stimulates skeletons to be heavier - this is why males have higher bone mass than females.
Which organ is best described as one in which most of the tissues have some cells, but there is more extracellular matrix than cells and that ECM is solid at maturity?
Femur, The four primary tissue types are epithelial, connective, muscle and neural. Connective tissues are characterized by their cell types and extracellular matrix. For the ECM, we use the terms ground substance and fibers. Of this list, bone (the femur, thigh bone) is the one with the most connective tissue. The brain is composed mostly of neural tissue, the heart is composed mostly of cardiac muscle and the liver is a gland (composed mostly of epithelial tissue).
On a certain neuron, neurotransmitter X (NT X) caused a hyperpolarization due to direct opening of an ion channel. When will NT X cause a depolarization on a different neuron?
If a different neuron has the receptor for NT X, but on a different ion channel. Right! NT X may bind to a receptor associated with a K+ channel on one neuron, leading to a hyperpolarization. But on another neuron, that same receptor for NT X may be associated with a Na+ channel. Or a Ca++ channel. This is the beauty of receptor associations. While receptors are specific for specific ligands, they can be associated with many different proteins in/on the target cells, leading to differential responses in different cells. A great example is the NT acetylcholine - in the heart, it binds to its Ach receptor and causes hyperpolarization; at the gut, Ach causes depolarization.
The liver is a glandular organ that functions to secrete many substances to the blood or digestive tract, detoxify chemicals and synthesize molecules utilized by all the cells of the body. What do you think is its likely histologic composition?
It is mostly epithelial tissue. Right! The liver is the largest gland in the body and is mostly specialized epithelial cells. It is definitely not neural tissue - only the brain, spinal cord and nerves are neural tissue. It is definitely not cardiac muscle tissue - cardiac muscle tissue is specialized for movement and is only found in the heart. You might suspect that the liver is connective tissue. However, you may remember that glands are epithelial tissue. The more organelles you can pack into a cell, the more that cell, and therefore that gland can do. Liver cells are large and well supplied with organelles to perform the liver's many functions (lots of rough and smooth ER and golgi apparatuses).
Which of the following organelles would likely be most abundant in a highly active cell?
Mitochondria, Yes! Highly active cells require ATP and mitochondria make ATP. Although highly active cells may be highly active because they are making a lot of proteins or fats (using the other listed organelles), the best answer here is mitochondria.
Mature osseous connective tissue (bone) is composed of collagen fibers and mineralized matrix. When osseous CT is first made, the osteoblasts secrete osteoid onto which calcium salt then precipitates. What is osteoid?
Mostly collagen or collagen pre-cursors. Osteoid is the immature bone that is first formed. It contains the collagen fibers and proteins that promote calcium salt formation onto the collagen. Hyaline cartilage is a different connective tissue that makes embryonic protoskeletons and articular cartilage. Mesenchyme is an embryonic connective tissue made of mesenchymal cells in a liquid ground substance. Hydroxyapatite mineral is the calcium salt that then forms on the osteoid.
What is the difference between spongy bone and compact bone?
Spongy bone and compact bone are microscopically arranged differently. Right! Spongy bone and compact bone are made of the same matrix material (1/3rd collagen, 2/3rds mineral), contain the same cellular populations (osteoblasts, osteoclasts, osteocytes, osteoprogenitor cells) and are both found in long bones. Microscopically, the matrix arranges itself as osteons in compact bone, but as non-osteon, irregular lamellae of trabeculae in spongy bone.
Neurons are specialized for communication. They are capable of sending electrical signals due to the presence of many ion channels and pumps on the cell membrane that they constantly maintain or replace as needed. Which of the following would be NOT consistent with this information?
Neurons are anucleate (they do not have nuclei). Right! Neurons (nerve cells) are very active tissue cells that send signals throughout your body. For the nervous system to communicate with a muscle cell or gland, a nerve cell must physically extend all the way to the target. Along the length of the nerve cell, the cell membrane is populated with many ion channels and pumps (pumps move substances against a concentration gradient and require energy to operate). These pumps and channels are proteins that the neuron must construct for itself and insert into the cell membrane. To make these membrane proteins, the neuron uses its abundant rough ER and its nucleus. There are so many rough ER in neurons they have a special name - Nissl bodies - named for a German neurologist. The presence of the many ion pumps in a neuron means that the neuron uses lots of ATP. A full 2/3rds of neuron ATP use is for these pumps alone! The nucleus is required for the production of the membrane proteins (by directing the cell to make these proteins or expressing the recipe for the proteins themselves). Anucleate means "without a nucleus" and this would be inconsistent with the needs of the neuron. The only anucleate cell that we talk about is the red blood cell and it does have a nucleus for a time during its lifespan (the time when protein production is occurring).
Your heart pumps blood at variable rates depending on your degree of physical activity or neural/hormonal activity (this is called heart rate). With exercise or fear, heart rate increases to pump more blood to an active body. Yet after exercise, heart rate decreases to a resting level. There are several nerves and hormones that stimulate heart rate to increase as needed, or decrease when needed, but there is no receptor that monitors heart rate. Is heart rate homeostatically regulated?
No, Homeostatic regulation requires 3 components: a receptor, a control center and an effector. Without a receptor, there cannot be homeostatic regulation. Even though it seems that heart rate varies and returns to some number, this is not technically homeostatic regulation. Blood pressure is homeostatically regulated - it has baroreceptors that monitor pressure, the brainstem that receives the information and nerves that then activate blood vessels to contrict or dilate to correct pressure (as well as other effectors) - but heart rate is not. Heart rate is not monitored by any neuron. Absolute water content of the body is not homeostatically regulated either - no neuron detects the number of water molecules, although neurons do detect the relative saltiness of the body. This is why different people can have the same blood pressure and fluid concentration but very different overall blood volume or heart rate.
Tendons are a connective tissue. They have many collagen fibers. Which of the following best describes where these fibers are located?
Outside the tendon cells, in the extracellular matrix. The fibers of connective tissues are part of the extracellular matrix (outside the cells). Ground substance refers to the non-fiber part of the extracellular matrix. Fibroblasts are the cell type found in tendons (dense regular connective tissues) and they are responsible for producing the collagen fibers. Chondrocytes are cartilage cells and are not found in tendons, they are found in cartilaginous structures like the ends of bones, intervertebral discs and knee menisci. Osteocytes are bone cells; adipocytes are fat cells. All of these are connective tissue cells, just of different connective tissues.
Which of the following will most likely stimulate an action potential in a neuron? Several small depolarizations, occurring repeatedly near the trigger zone A large hyperpolarization occurring near the trigger zone A simultaneous hyperpolarization and depolarization of the same magnitude occurring near one another, near the trigger zone Several small depolarization on a dendrite far from the trigger zone
Several small depolarizations, occurring repeatedly near the trigger zone. Depolarizations bring the neuron transmembrane potential above resting values towards (or above) threshold values. Once threshold is reached at the trigger zone, the voltage gated channels open and an action potential can be generated. Hyperpolarizations lower the membrane potential away from threshold and make a neuron less likely to fire an action potential. In this question I ask which is most likely but, what you do not know from this question is the magnitude of each stimulus. They could be very small depolarizations and very large hyperpolarizations - truthfully, it is impossible to know if the postsynaptic neuron generated an action potential without seeing a measure of its membrane potential at the trigger zone.
What do we call the process whereby a molecule crosses the cell membrane, moving from a high concentration of itself to a low concentration of itself, by dissolving through the phospholipid portion of the cell membrane? (Select the single best answer that describes this specific circumstance.)
Simple Diffusion. Correct! Simple diffusion refers to the passive (no ATP required) movement of a molecule through a cell membrane. The molecule must be able to penetrate the membrane without using a transport protein. When it moves, it does so by moving away from an area of high concentration of itself to an area of low concentration of itself. Examples include oxygen, carbon dioxide, steroid hormones and fat soluble vitamins A, D, E & K which all dissolve across the membrane into or out of the cell. Small, non-charged polar molecules can do this too: alcohol, urea and glycerol are included in this. If the molecule cannot pass through the membrane except by using a transmembrane protein, but does so without ATP because it goes from high concentration to low (down a concentration gradient), this is said to be facilitated diffusion. It is still a passive process, but not simple. Roughly, if the membrane protein changes shape as this happens, it is a carrier; if the membrane protein does not, it is a channel. Passive transport is too broad of a term in this specific instance above, because either simple diffusion or facilitated diffusion are both passive transport. Active transport happens when molecules move against their concentration gradients across the cell membrane using membrane transport proteins. This type of movement against a concentration gradient, from low concentration to high, always requires ATP. This is why we call it active. Examples include membrane pumps that pull sodium ions out of the cell and deposit them on the outside of cells. Because of the action of these pumps, sodium is always more concentrated outside cells than in. Although endocytosis and exocytosis use ATP, we do not call them active transport usually, preferring the term vesicular transport.
You are a histologist and are looking at a sample in the microscope. There are many layers of well defined cells that contact each other. The cells at the bottom (near the next underlying tissue) are cuboidal in shape and the cells at the surface (not in contact with another tissue) are flat and thin. What is the most likely classification of this tissue?
Stratified squamous epithelium. The described tissue is anchored to a connective tissue on one side and exposed to the external environment on another. It is highly cellular, with close cell contacts and has many layers. The cells change shape from the bottom to the top. Epithelial tissues are highly cellular and exhibit polarity (a clear top and bottom), just like this described tissue. The many layers of the cells indicate that this is a stratified epithelium. Even though the bottom layer cells are cuboidal, we classify stratified epithelia by looking at the top layer - the squamous layer: this is a stratified squamous epithelium.
In the normal 30 year old skeleton, osteoclast activity is matched by osteoblast activity. What would happen if osteoclast activity was greater than osteoblast activity?
The bones would become weaker. Right! Osteoclasts break down bone (chew it up), osteoblasts build new bone. Since bone is continually remodeled by constant action of the osteoblasts and osteoclasts, if the osteoclasts are destroying faster than the osteoblasts can build, the skeleton will become weaker. This is exactly what happens in osteoporosis.
During development, if a problem arises with the ectoderm, which of the following would most likely be affected?
The brain. (bones of the limbs, lungs and skeletal muscles are dervied from mesoderm)
Suppose you are a cytologist and you are examining a cell under the microscope. You observe that inside the cell there are many flattened, sac-like structures, many of them with small round granules. Based on this information, which of the following conclusions would be most logical?
The cell produces many proteins for export. Right! The best answer here is that the cell makes proteins for export. The description given in the question is suggestive of an organelle that has flat sacs and ribosomes attached to them - the rough endoplasmic reticulum (rough ER). This organelle is responsible for protein production. These proteins might leave the cell or become incorporated into the cell membrane. The other options in this question may be true, but the only information you were given was about the rough ER and the question states Based on this information... It would not be logical to conclude no cell membrane - the cell would not be in very good shape to examine in the scope without a cell membrane. There was no mention of a flagellum or of centrioles, therefore motion and cellular division are unusual conclusions at best.
Which of the following would be most likely found in a cell that is subjected to significant mechanical strain (such as a cell in the outer skin)?
The cell would have many cytoskeletal elements.
Which of the following would be most likely found in a cell that is subjected to significant mechanical strain (such as a cell in the outer skin)?
The cell would have many cytoskeletal elements. Yes! Keratin is a protein string (cytoskeletal element) found in great quantity in skin cells. The keratin provides strength to skin cells to resist mechanical stresses. The keratinized skin cells are regularly lost from the body surface and replaced with cells in deeper layers of the skin. Smooth ER is used for making fats or carbohydrates (or combinations of those) or acts as an intracellular storage site. It is not the best choice here. Golgi are not the best choice here because they serve to repackage materials that do not remain in the cytoplasm. Phospholipids contribute significantly to the cell membrane and without them, the cell is unlikely to be functional. In answering questions you must always assume a healthy adult unless otherwise indicated.
In which of the following would you expect to find osteons?
The diaphyseal cortex of the humerus. Osteons are the structural unit of compact bone. They make up the thick walls of long bone diaphyses and the most superficial compact bone collar (cortex) of long bone epiphyses. Compact bone is found in all bones with variable amounts of spongy bone between compact bone regions. Osteons do not exist in the ligaments of the neck (a dense regular connective tissue) or in epithelia. The medullary (marrow) cavities of long bones contain bone marrow (red or yellow, more likely yellow). Perhaps you selected the trabeculae within an epiphysis. Trabeculae are spongy bone struts. While spongy bone is made of the same material as compact bone, the organization is different and osteons do not form. It is important to remember the terms epiphysis and diaphysis - we will use them more when we talk about how bone grows.
What determines the maximum frequency of AP generations in a neuron?
The duration of the absolute refractory period. Since the absolute refractory period dictates that no other APs can be generated during that time, the longer the absolute refractory period, the longer the neuron must wait between successive APs and the fewer APs that can be generated in the time frame.
In bones, a layer of osteoblasts and osteoclasts line the interior of the bone (this cellular layer covers all trabeculae, is adjacent to the medullary cavity and lines the inside of osteons). This layer is called the endosteum. What is its role in bone?
The endosteum can add or remove bone from the inside of bones, remodeling them. The endosteum is made of connective tissue cells (not epithelial cells) that can deposit or reabsorb bone from the internal aspect of the bone. During growth, the endosteum is particularly important to remodel bone from the inside. Without endosteal bone reabsorption, as bones grow wider overall, the bone would become too heavy. In other words, as bones grow wider (due to periosteal bone deposition), they maintain the same cortical bone thickness because of endosteal removal. Cartilage is deposited by chondroblasts. Muscles attach at the outside of bone on the fibrous layer of the periosteum.
In an infant's humerus, what happens if the rate of hyaline cartilage death is faster than the rate of interstitial growth?
The humerus would become too short at full maturity. Right! The humerus is a long bone that grows through endochondral bone formation. During endochondral bone formation hyaline cartilage grows on one aspect of the epiphyseal plate (epiphyseal side) as it dies on the other (diaphyseal side). As it dies, it is degraded and replaced by bone. If the rate of growth is slower than the rate of death and replacement, the bone will replace the existing cartilage completely. Because bone is a hard tissue, it cannot grow from within (interstitial growth) to further elongate the bone and thus a long bone cannot grow any longer once the cartilage at the plate is gone. Too fast cartilage death is a problem in certain forms of dwarfism that results in smaller stature.
When you swim in the ocean you lose water. What most likely explains this observation?
The ocean water is relatively saltier than the inside of your body (and cells).
You are a histologist and are looking at a sample in the microscope. There are many layers of well defined cells that contact each other. The cells at the bottom (near the next underlying tissue) are cuboidal in shape and the cells at the surface (not in contact with another tissue) are flat and thin. What is the most likely source of this tissue?
The oral cavity (mouth) The described tissue is anchored to a connective tissue on one side and exposed to the external environment on another. It is highly cellular, with close cell contacts and has many layers. The cells change shape from the bottom to the top. Epithelial tissues are highly cellular and exhibit polarity (a clear top and bottom), just like this described tissue. Therefore, you can eliminate the biceps brachii skeletal muscle. The many layers of the cells are suggestive of an epithelium that must withstand abrasion, and therefore, you can eliminate the non-abrasive regions: the brain and lung. Lastly, glands have columnar or cuboidal cells throughout, and so you can eliminate the thyroid gland. The oral cavity must be able to withstand constant abrasion and therefore is lined with a stratified squamous epithelium.
The periosteum is a double layered structure on the outside of all bones. The outermost layer is a fibrous connective tissue, the innermost layer (adjacent to the cortical bone) is a layer of osteoblasts, osteoclasts and osteogenic/osteoprogenitor cells. What are the two roles of the periosteum?
The outer fibrous layer attaches muscle; the inner cellular layer deposits or removes bone. The periosteum's outermost layer is a dense irregular connective tissue in which collagen fibers are oriented at varying angles (hence the name, dense - lots of fibers; irregular - fibers at many angles). This creates good tensile strength to resist the pull of the many muscles attaching at different angles. The collagen fibers in this layer blend with the fibers of muscle tendons and with the outermost compact bone. By blending together, the muscles attach very firmly to both the periosteum, which is then firmly anchored to the bone - it is more typical to tear a muscle in the middle of its belly than to tear it off the periosteum. The name of the connecting fibers between the periosteum and bone are called Sharpey's fibers. The cells of the inner periosteal layer are essential for bone remodeling. As bones grow in length, they need to add mass to the outer circumference of a bone and they need to be able to remove bone where it is not needed. Bone is alive and requires resources to maintain it. The periosteum helps balance the needs of the body for strong bones that are of the right construction for maximal efficiency of use.
Which of the following happens during formation of the femur?
The outer periosteal bone forms before the inner spongy bone Right! The femur (like all long bones) forms via endochondral bone formation. During endochondral bone formation hyaline cartilage must die and be removed before osteoblasts can produce new bone on the remains of the cartilage. This bone deposition occurs at the outer edges of the structure to create a bony collar around the diaphysis. The osteoblasts depositing this bone must arrive via the invading blood vessel because cartilage cells cannot transform into bone cells. So, blood must precede bone in the case of endochondral bone formation. When long bones form, the diaphysis is the first site of bone formation. At birth, the diaphysis is usually bone but the epiphyses are still cartilage. The epiphyses ossify (creating secondary ossification sites) at different ages throughout childhood. The skeleton can be dated by the pattern of secondary ossification sites.
When you swim in a pool, your body gains water. What most likely explains this observation?
The pool water is relatively less salty than the inside of your body (and cells). Water moves passively (does not require cellular energy to move) to a place where there is less water (relatively). When we say less water, it is not in absolute terms, but instead we are talking about concentrations. If a liquid has lots of salt and little water, we say that solution is very concentrated in salt but it has relatively little water. If another solution has little salt (or other dissolved substance, like sugar) we say it is dilute and has relatively much water. A swimming pool is very dilute and compared to the inside of your body, it has fewer dissolved particles for each molecule of water. Therefore water moves away from where there is more water (in the pool) to where there is less (your body) - water enters your body and makes your body swollen. The ocean is very salty - it has many dissolved salt particles for each molecule of water. When you swim in the ocean, you lose water to the ocean because the leaving water is trying to "dilute" the ocean's salt. This process is osmosis and it occurs across every body cell. In response to wet conditions, you skin wrinkles. Interestingly, this is due to neural activation - if the nerves are cut, you skin does not wrinkle (or prune) despite the presence of external water. It is believed this response increases finger grip in wet conditions.
Researchers interested in the relation between River Shrimp(Macrobrachium) abundance and pool site elevation, presented the data in the graph below. Interestingly,the researchers also noted that water pools tended to be shallower at higher elevations.
There are more water pools at elevations above 340 meters because it rains more frequently in higher elevations.
What characteristic unites all connective tissue?
They all come from a common embryonic tissue (mesenchyme). Connective tissues vary widely in anatomy. Some have many collagen fibers (dense regular connective tissues), some have few fibers (blood). Some are solids (bone) some are loose and stringy (areolar CT). The single unifying component among all connective tissues is their common originating tissue - all connective tissues come from a stem cell tissue called mesenchyme. Mesenchyme is found in embryos - it is made of mesenchymal cells and a fluid ground substance with a few fibers. These cells can differentiate to become bone cells or cartilage cells or blood cells or any other connective tissue cell. Not all connective tissues have a rich blood supply - cartilage is avascular and this is why it is slow to heal. Not all connective tissues have a hard ground substance - bone does, but blood is all liquid. Bone has osteocytes - they are the cells of bone (osteo=bone, cyte=cell). It is those cells that make the fibers in bone.
Mature red blood cells lack nuclei and mitochondria. Which of the following is consistent with this information?
They cannot add new transport proteins to their cell membranes. Nuclei are necessary for remodeling of the cell membrane - they signal for protein production needed to remodel the membrane. All cells have membrane potentials as long as they have an intact cell membrane (all you need for this is a separation of charged particles on the inside versus the outside). They can make ATP, though they lack mitochondria because they make it by glycolysis in their cytosol.
Glucose and oxygen are used by cells to produce energy for muscle action - this process occurs within each cell. Your new workout partner tells you that the supplement he's taking allows him to produce more energy (and have a better workout) because it increases oxygen delivery by increasing the number of cell membrane protein carriers for oxygen. What would you say to him?
This seems unlikely because oxygen does not require membrane proteins for transport across the cell membrane. Oxygen is fat soluble and moves through the cell membrane unassisted. Only substances that cannot dissolve in the cell membrane require membrane proteins (channels or carriers) to cross the membrane. Such substances include charged ions (sodium, potassium, calcium) and molecules like glucose and amino acids. However, if a supplement increased the number of glucose transport proteins in a cell membrane, it would increase the number of glucose molecules that enter a cell. In our bodies, cells frequently change the number of transporters or receptors for specific molecules to increase transport in/out of a cell or the likelihood of reaction a cell has to a substance.
Using your lecture notes, which of the following make up spongy bone?
Trabeculae. Trabeculae are the struts of spongy bone in the epiphyses and adjacent to the medullary cavity. They are more lightweight than dense compact bone (as evidenced by their many open spaces). In the epiphyses they transmit weight to the more dense compact bone of the outer diaphyseal cortex. They remodel very rapidly in response to signals (compressive stress/hormonal fluctuations); the proximal femoral spongy bone remodels every 3-6 months but the denser compact bone may take 3-7 years to fully remodel. Osteons are the structural unit of compact bone; compact bone comprises the bulk of the outer diaphyseal cortex (cortical bone) and the part adjacent to the periosteum (outer connective tissue layer used for bone remodeling and muscle/ligament attachment). Articular cartilages (cartilage on the end of long bones) do not function for weight bearing as much as they function for friction reduction. They do not remodel in response to stress like spongy bone trabeculae do.
True or False? At rest, the interior of a neuron has more potassium ions than the exterior, but is relatively negative compared to the outside of the cell
True. Correct! The sodium/potassium pumps on every cell establish a high concentration of potassium inside cells and high concentration of sodium outside of cells. This is true of neurons as well. Each turn of the sodium potassium pump moves 3 positively charged sodium ions out of cells and adds 2 positively charged potassium ions into cells. This action contributes to the relatively negative interior of neurons despite the presence of so many positively charged ions. Additionally, the interior of neurons has negatively charged proteins contributing to the relatively negativity (these proteins are not present on the exterior). However, the most important component of the negative interior is the constant outward leakage of potassium ions through membrane leak channels for potassium. When these ions leak out, a positive ion leaves the interior and is added to the exterior, thereby making the interior relatively negative. While there is some inward leakage of positive sodium, it is 100X less than the outward leakage of potassium and overall does not make the interior positive during rest.
True or False? In response to a neurotransmitter, depolarizating graded potentials on the cell body show a depolarization and repolarization phase, but do not show a hyperpolarization phase.
True. Right! The action potential shows depolarization, repolarization and after-hyperpolarization phases due to the opening and timing of sodium voltage gated channels and potassium voltage gated channels. The opening of the sodium voltage gated channels results in the depolarization phase as Na+ enters the cell. The repolarization and after-hyperpolarization phases occur as the K+ voltage gated channels open allowing K+ to leave the cell. During an action potential, both types of channels open in the appropriate sequence and therefore all phases are observed. BUT, in graded potentials on the neuron cell body that are caused by neurotransmitter binding, only chemically gated channels that are sensitive to the neurotransmitter open; the channels then close once the neurotransmitter is removed. Therefore, depolarization occurs as the channel opens (say, a Na+ chemically gated channel) and then repolarization as the channel closes and we return to resting conditions. Hyperpolarization can only occur if the NT opens a channel that allows different ions to move (Cl- or perhaps K+).
The presence of hyaline cartilage is required for elongation of the femur in a 10 year old child.
True. The femur is a long bone that forms through endochondral bone formation (which requires hyaline cartilage). This process continues throughout childhood until the early 20's
Some cells, like neurons, are very long - some can be 6 feet long! Are leak channels and sodium-potassium pumps present on all parts of the cell membrane?
Yes. Correct! The leak channels and sodium-potassium pumps are responsible for creating and maintaining the cell membrane resting potential. Because the transmembrane potential exists at all parts of the cell membrane, they are located throughout the cell membrane and all its parts (cell body, dendrites, axon, terminal end).
Does a resting neuron consume ATP? (Neurons are resting when they are neither sending nor receiving a signal.)
Yes. Resting neurons are spending ATP to move ions across their cell membranes (Na+/K+ ion pump). Even at rest, these pumps are active - no rest for the wicked!!
In vitamin C deficiency you cannot synthesize collagen. Which of the following would most likely occur?
Your skeleton would become malformed. The skeleton is constantly being degraded and replaced. Since the skeleton is 1/3rd collagen and 2/3rds mineral, an inability to make collagen would substantially affect the skeleton. Furthermore, proper collagen formation is required for proper bone mineral deposition. Epithelial cells do not have collagen. Sweat is mostly water and salt, and should not have collagen. Sweat glands are made of epithelial tissue, not lots of collagen like you would find in tendons/ligaments or bone. Cartilage is already avascular and actually secretes a compound that inhibits blood vessel formation. The best answer here is the one discussing skeleton formation.
_____ are useful in the skeleton because they remodel most readily in response to stress and efficiently transmit forces while remaining lightweight.
trabeculae. Trabeculae are the struts of spongy bone in the epiphyses and adjacent to the medullary cavity. They are more lightweight than dense compact bone (as evidenced by their many open spaces). In the epiphyses they transmit weight to the more dense compact bone of the diaphyseal cortex. They remodel very rapidly in response to signals (compressive stress/hormonal fluctuations); the proximal femoral spongy bone remodels every 3-6 months but the denser compact bone may take 3-7 years to fully remodel. Osteons are the structural unit of compact bone; compact bone comprises the bulk of the diaphyseal cortex (cortical bone) and the part adjacent to the periosteum. Articular cartilages (cartilage on the end of long bones) do not function for weight bearing as much as they function for friction reduction. They do not remodel in response to stress like spongy bone trabeculae do.
