Biology 2
What does ADH do?
(Antidiretic hormone) acts on the collecting duct making it permeable to water. In the absence of ADH the collecting duct is impermeable to water. Because the collecting duct passes through the highly-concentrated medulla, as soon as the membrane becomes permable there is a large net flow of water out of the filtrate, concentrating the urine. The NET EFFECT: WATER RETENTION AND INCREASED BLOOD PRESSURE
What is resting potential?
-70mV. The voltage across the membrane when an action potential is NOT present (one has not yet occurred, or it has already passed).
Describe the function and significance of each item labeled in your diagram.
A dendrite is a finger-like projection from the cell body that receives signal information from an upstream neuron with which it forms a synapse. The signal will be received from the previous neuron via binding of a neurotransmitter on the dendrite portion of the membrane (i.e., postsynaptic membrane). The cell body is the main part of the neuron where the nucleus is located. The axon hillock is the area where the axon joins the cell body. This region has a very high concentration of voltage-gated sodium channels. This makes it both sensitive to action potentials and capable of regenerating a strong action potential for transmission down the axon. The terminal button (a.k.a., axon terminal) is a projection at the end of the axon that synapses with the dendrite of another neuron or with the effector. The axon is the long, narrow, tube-like extension between the cell body and the terminal button. Human axons can be up to 1.5 meters long! Along the axon are specialized neural support cells called Schwann cells. These cells contain high levels of fat and wrap themselves around the axon multiple times creating an insulating myelin sheath. There are small gaps between Schwann cells, called the nodes of Ranvier. A signal is able to "Jump" from one node to another without progressing along the entire length of the axon—dramatically increasing transmission speed.
Talk about the creation and propagation of the action potential.
A disturbance (i.e, a dramatic change) in the resting electrical potential (i.e, voltage) across the membrane of a nerve cell. Once an action potential is created, it will propagate along the cell membrane to neighboring portions of the neurons. As it does, the areas where it originally started are gradually returned to the normal resting potential.
Describe neurons in details.
A neuron is a specialized cell that can carry electrochemical signal (i.e, action potential). Remember that neurons: 1) Are frozen in G0 phase 2) Depend entirely on glucose for energy 3) Don't require insulin for glucose uptake 4) Have very low glycogen and oxygen storage capability and thus require high perfusion (blood flow).
What are the four phenotypes of blood typing?
A, B, AB, and O The letters A and B indicate the antigens that are present on that individual's blood cell membranes. A= A antigens only B = B antigens only AB = Both A and B antigens O = Neither A and B antigens.
What does Aldosterone do?
Aldosterone acts on the distal convoluted tubule causing an increase in sodium uptake. Also causes reabsorption of Na+ out of the collecting duct via Na+ channels, K+ Channels, and Na+/K+ ATPases in the cells that line the collecting duct. This increases the osmolarity of the cells lining the distal tubule, causing water to flow out of the filtrate and into the cells. The NET EFFECT: WATER RETENTION AND INCREASED BLOOD PRESSURE
How do blood cells form?
All blood cells develop from stem cells (undifferentiated cells) in the bone marrow; a process called hematopoiesis.
Voltage-Gated Potassium Channels
Also integral proteins that respond to a change in the membrane potential. However, their threshold for responding is much higher than that for the voltage-gated sodium channels. As a result, they only react following the very large change in membrane potential caused by depolarization. Just before maximum depolarization is reached, the Na⁺ channels begin to close and the K⁺ channels begin to open.
Talk about the sodium and potassium pump in action potential.
An ATP pump that actively transport 3 Na+ ions out of the cell and 2 K+ ions into the cell per cycle. The net effect is more positive charge outside the cell and a progressively more negative charge inside the cell.
Name several possible effects caused by a drug that acts as an acetylcholinesterase antagonist at the neuromuscular junction. How would the effects differ if the drug were an acetylcholinesterase agonist.
An acetylcholinesterase antagonist would impede the normal activity of this enzyme, which breaks down acetylcholine. Decreased breakdown of the neurotransmitter would allow more of it to be present in the synaptic cleft, and to be present for a longer period of time—causing hyperstimulation of the subsequent neuron. Hyperstimulation of neurons could cause any number of problems depending on the effector with which a neuron is communicating. Muscle rigor, cramping, ticks, and pain would be logical possibilities. The drug effect would not necessarily be negative. An increase in the concentration of certain neurotransmitters in the brain has been shown to combat depression and therefore many antidepressants are actually acetylcholinesterase inhibitors (i.e., fluoxetine [Prozac], sertraline [Zoloft] and amitriptyline [Elavil]). If the drug were an agonist it would have the opposite effect, resulting in increased breakdown of acetylcholine and therefore decreased stimulation of neurons.
Give ALL the peptide (water soluble) hormones and their locations
Anterior pituitary: FSH, LH, ACTH, TSH, Prolactin, hGH Posterior pituitary: ADH and Oxytocin Parathyroid: PTH Pancreas: Glucagon and insulin (also releases several digestive enzymes, but this is an exocrine function, not an endocrine function) Thyroid: Calcitonin Embryo/Placenta: hCG (Human Chorionic Gonadotropin)
Give the order of blood flow from the heart and back, then tell how one would distinguish between arteries and veins.
Arteries --> Arterioles --> Capillaries --> Venules --> Veins Arteries: muscular, thick walled vessels that push blood through via rhythmic contraction. Veins: Thin-walled vessels with little to no musculature that rely on a valve system to move blood back toward the heart.
Arteries and Veins:
Arteries LEAVE the heart and veins RETURN to the heart. -The naming of bloods vessels is NOT based on whether they carry oxygenated or de-oxygenated blood. Rather, it is based on the direction of flow, either toward or away from the heart.
Repolarization
Because there are more K⁺ ions inside the cell (due to Na⁺/K⁺ pump), opening of the potassium channels causes K⁺ ions to flow out of the cell. This results in a sudden decrease in the membrane potential from +40 mV back down to -70 mV.
The Heart: Systemic Circulation:
Blood flows from the left ventricle, through the Arteries, Arterioles, Capillaries, Venules, Veins, Vena Cava and back to the right Atrium.
The Heart: Pulmonary Circulation:
Blood flows from the right Ventricle through the pulmonary arteries to the lungs and back through the pulmonary veins to the left atrium.
Blood is an example of which tissue type?
Blood is a connective tissue.
Blood type is an example of what kind of genetic inheritance pattern?
Blood type is an example of co-dominance because both alleles are expressed equally in a heterozygote. A person with the AB genotype, for example, has both A and B antigens. In other words, both the A and B phenotypes are expressed simultaneously.
Central Nervous System
CNS: The brain and spinal cord; interneurons only. No subdivisions.
How is CO2 carried in the blood?
CO2 + H2O ---> HCO3- + H+
The Cardiovascular system: function
Deliver oxygen and nutrients to the cells and tissues of the body; pick up CO2 and waste products and deliver then to the lungs and kidneys.
How many oxygen atoms are carried on one molecule of Hb at 100% saturation?
Each hemoglobin molecule has four subunits, each with one heme. Each heme can hold one O2 molecule. Therefore, at 100% saturation a hemoglobin molecule can hold 8 oxygen atoms.
Do erythrocytes undergo mitosis?
Erythrocytes do NOT undergo mitosis because they lack nearly all of the cellular machinery to do so. Recall that red blood cells do not have nuclei or organelles. They are essentially membrane- bound sacks of hemoglobin.
The Excretory System (Kidneys): Functions
Excrete liquid and solute waste (e.g, excess water, excess salts, nitrogenous waster, etc.) maintain pH, osmolarity and blood pressure.
Give a generalized description of a G-protein cascade. Include terms such as G-protein-coupled receptor (GPCR), alpha/beta/gamma subunits, GDP, GTP, adenylyl cyclase, cAMP, and protein kinase A.
First, a hormone or signal molecule binds to an integral protein on one of its extracellular domains—this protein is called a G‐protein‐coupled receptor or GPCR. This causes a conformational change that activates a cytosolic domain of that same integral protein. Near the GPCR, or at least along the cytosolic face of the membrane, is a G protein made up of an alpha, beta and gamma subunit. The alpha subunit binds both GTP and GDP. When GDP is bound the protein is "off" and when GTP is bound it is "on." Usually, but not always, the activated receptor protein acts as a catalyst for the replacement of GDP by GTP, activating the alpha subunit of the G protein. Usually, the activated alpha subunit then separates from the beta and gamma subunits. The activated alpha subunit acts as an agonist for another enzyme, often adenylyl cyclase. Adenylyl cyclase is an enzyme that catalyzes the conversion of ATP to cAMP and 2Pi. Cyclic AMP just happens to be an agonist for Protein Kinase A, which phosphorylates proteins— usually enzymes. Many enzymes are turned on or off through being phosphorylated or dephosphorylated. The cascade can be shut down in various ways. Often the beta and gamma subunits rebind with the alpha subunit deactivating it. In other cases GPCR is phosphorylated one or more times which deactivates it.
Electrical synapses:
Gap junctions between cells that allow electrical signals to pass very quickly from cell to cell. In humans they are found only in specific locations: the retina, smooth muscle, cardiac muscle, and the CNS.
What is the function of the lymphatic system?
Gather excess interstitial fluid and return it to the blood; remove from the interstitial spaces protein and other molecules that are too big to be taken up by the capillaries; monitor the blood and lymph for infections.
What is hemoglobin made out of?
Hemoglobin: quaternary protein made of four protein chains, 2 alpha and 2 beta. Each protein has an Fe- containing "heme" group at its center. Each heme group can hold one O2 molecule. (up to 4 O2)
What should you remember about hormones function?
Hormones always act to return to homeostasis, or normal conditions. They never cause a drift away from normal.
If the pulmonary artery became blocked, what would be the immediate short-term effects on blood pH? What if the pulmonary vein were blocked? What if the capillary walls became impermeable to CO2? What if the alveoli were impermeable to CO2?
If the pulmonary artery became blocked the immediate short-term effect on blood pH would be a more acidic pH. If the pulmonary vein were blocked the pH would be more basic because the body would hyperventilate for oxygen demand and cause metabolic alkalosis.
Laryngitis is the loss of one's normal voice due to inflammation of the vocal chords. A common home remedy suggests that drinking honey soothes and hydrate the vocal chords, speeding recovery. Does the anatomy of the respiratory system support or refute this proposed remedy?
If we assume—as seems to be implied—that this home remedy works because coating the vocal cords with honey hydrates and soothes these structures, then the remedy is entirely debunked by the anatomy of the respiratory system. At the back of the throat, near the base of the tongue, the pharynx essentially ends at a fork. The more posterior fork is the esophagus, which leads to the stomach. The more anterior fork is the larynx, which houses the vocal cords, and then continues on to the trachea, bronchi and lungs. The epiglottis is an upward-oriented cartilaginous flap that folds down over the opening to the larynx creating a one-way only route down the esophagus during swallowing. Thus, if honey or some honey concoction is consumed, it would coat the pharynx, epiglottis and esophagus, but be entirely separated from the vocal cords. To coat the vocal cords the honey would have to be inhaled—which would be very painful. At best, if any remedy does exist it would have to be the result of vapors given off by the honey in the throat reaching the vocal cords.
Hemoglobin Binding Curve
Know the effects (DPG is the same as BPG)
What are lymph nodes and what are their function?
Lymph nodes are filled with lymphocytes. These immune system cells monitor the blood for foreign antigens and fight infections.
What are lymph vessels and their function?
Lymphatic vessels are a lot like veins; many --but not all-- contain one way valves used to move the lymph; single cells overlap slightly creating a trap door that allows things in but not back out. The entire lymph system eventually drains into the two main vessels, the right lymphatic duct and the thoracic duct which both dump back into the bloodstream by merging with large veins in the lower portion of the neck.
Path of Air: Inhalation (7 places)
Mouth/nose > pharynx > larynx > trachea > bronchi > bronchioles > alveoli
Provide an overview about leukocytes.
No hemoglobin. Normal cells with all their organelles that are involved in the immune system. Granulocytes: neutrophils, eosinophils, and basophils. These cells live for hours to days. Agranulocytes: monocytes (become macrophages) and lymphocytes. These cells live for months to years.
Describe how the interplay of hydro-static pressure and osmotic pressure accounts for the flow of fluid into and out of the capillary beds.
On the arterial side of the capillary bed the hydrostatic pressure is at its maximum. At this same point, the osmolarity of the blood is greater than that of the interstitial fluid, creating an osmotic pressure that would drive fluid into the capillary. These two influences oppose one another, but the hydrostatic pressure is greater than the osmotic pressure, yielding a net filtration pressure (13 mmHg, driving fluid out of the capillary and into the interstitial fluid). On the venous side of the capillary bed the differences in osmolarity are about the same, but the hydrostatic pressure has decreased significantly. This makes the net filtration pressure negative and fluid flows out of the interstitial fluid and into the capillary (-7 mmHg). Note, however, that the net pressure on the arterial side is slightly greater than the net pressure on the venous side. As a result, about 10 percent of the fluid that exits on the arterial side does NOT re-enter the capillary on the venous side. What happens to that 10%? That is one of the primary functions of the lymphatic system—to pick up extra interstitial fluid from the capillary beds and return it to the venous system.
Peripheral Nervous System
PNS: All neurons outside of the CNS; both sensory and motor neurons. Contains "somatic" and "autonomic" divisions. Somatic: Voluntary; innervates skeletal muscles; contains both sensory and motor subdivisions. Autonomic: Involuntary; innervates cardiac and smooth muscles as well as glands; contains both sensory and motor subdivisions. Sensory: The sensory subdivision of the autonomic nervous system is not well developed; explaining why visceral pain is often referred (i.e, felt at a location other than the actual source) and poorly localized. Motor: The motor subdivision of the autonomic nervous system contains sympathetic and parasympathetic divisions. Sympathetic: "Fight or Flight." Cell bodies located far from the effectors. Neurotransmitters: Acetylcholine at the ganglia, norepinephrine at the effector. Parasympathetic: "Rest or digest" cell bodies located very close to or inside the effector. Neurotransmitters: acetylcholine ONLY, at both the ganglia and the effector. A common misconception is that the sympathetic stimulates and the parasympathetic inhibits. This is false. They both stimulate and inhibit, depending on the situation. Always rely on "fight or flight" or "rest or digest" to predict what they will do.
Recalling that glucagon stimulates the release of glucose into the bloodstream and insulin stimulates the uptake and storage of glucose, answer the following: Patient A has high blood glucose levels. Which hormone is likely to be found in highest concentration in her blood? Patient B has low blood glucose levels. Which hormone is likely to be in highest concentration in his blood?
Patient A has high blood glucose. The body's hormonal reaction to this condition will be to attempt to re-establish homeostasis. High blood glucose levels stimulate the cells of the pancreas to secrete insulin. Insulin stimulates cells to import glucose, decreasing blood glucose levels. This would return the blood toward homeostasis and therefore insulin is expected in high levels. (Note: Some students resist this logic by claiming that high blood glucose is a potential indication of diabetes—a disease resulting from a lack of insulin or insulin resistance. However, there is nothing in this question that would lead you to suspect that a disease condition is present. The MCAT does not test you on disease symptoms. On the MCAT you should always assume normal physiology unless specifically told otherwise.) Patient B has low blood glucose levels. Glucagon—also secreted by the pancreas—stimulates the liver to breakdown glycogen to release glucose into the blood. In this case, more glucose would be necessary to reach homeostasis and therefore high glucagon levels would be expected.
The Respiratory System: Function
Primary function is gas exchange. Inhalation and expiration are necessary functions to deliver air to the alveoli where gas exchange can occur. Oxygen diffuses down its concentration gradient into the blood, and carbon dioxide diffuses down its concentration gradient out of the blood and back into the lungs.
Provide details about RBCs/Erythrocytes.
Sacks of hemoglobin and not much else. Immature RBCs start out with a nucleus and organelles but these disappear as the cell matures. Mature RBCs have NO nucleus or other organelles.
Draw a graph for cross-sectional area vs. blood vessel type (aorta/arteries/arterioles/capillaries/ venules/veins/venacava), b) velocity vs. blood vessel type, c) blood pressure vs.blood vessel type.
See diagram below. Diagram intended to show general theoretical trends and is not drawn to scale. Q = AV explains the inverse relationship between the red and green lines.
What are the functions of neuron?
Sensory (Afferent) neurons: Receive sensory signals from sensory cells. Motor (efferent) neurons: Carry signals to a muscle or gland to respond to the stimulus. Interneurons: Connect afferent and efferent neurons. They also transfer and process signals. The brain and 90% of all other neurons are interneurons.
What are the effect of sympathetic and parasympathetic on the heart?
Sympathetic NS activity INCREASES heart rate and blood pressure. Parasympathetic NS activity DECREASES heart rate and blood pressure. IMPORTANT: Sympathetic specific responses are fast and short-lived, while the endocrine system results in much slower, general responses that are long-lived. Vasoconstriction can be part of both a fight/flight response and a rest/digest response.
Give ALL the tyrosine derivative and their locations.
T3/T4 = lipid-soluble ; Epi/Norepi = water-soluble Thyroid: T3 (Triiodothyronine) and T4 (Thyroxine) Adrenal Medulla: Epinephrine and norepinephrine.
Provide a definition for absolute refractory period and the relative refractory period. Why does it take a stronger stimulus than normal to cause an action potential during the relative refractory period.
The absolute refractory period is a portion of time during which an action potential cannot be initiated regardless of the strength of the stimulus. This time period occurs during the progression of a previous action potential. The progression of an action potential involves the depolarization of the membrane and a second stimulus cannot be initiated until the membrane is repolarized. The relative refractory period is a portion of time during which the membrane is hyperpolarized (i.e., is more negative than at normal resting potential). During this time a second action potential can be initiated, but a stronger-than-normal stimulus will be required. This makes sense because the firing of an action potential is an all-or-nothing event dependent on the polarity of the membrane reaching the threshold potential. During hyperpolarization there is a greater voltage difference between the present state of the membrane and the threshold potential—thus a larger stimulus is required to reach that threshold.
The Diaphragm
The diaphragm moves DOWN when flexed and UP when relaxed. When relaxed it has an upward- oriented convex shape. When flexed it is almost flat. The diaphragm moves DOWN during inhalation and UP during exhalation. The diaphragm FLEXES as it moves down and is RELAXED when it is curved upward.
Draw and describe the following on a diagram of the heart: sinoatrial node, atrioventricular node, bundle of his, and Purkinje fibers.
The electrical signal originates at the SA node, then spreads across both atria to the AV node. There is a slight delay, then the signal travels from the AV node down the bundle of His and through the Purkinje fibers. At the end of the Purkinje fibers the signal travels cell to cell through gap junctions.
Describe the endocrine system.
The endocrine system includes the endocrine glands and the fluids and ducts into which they are released. EXOCRINE glands release ENZYMES or other LIQUIDS into the EXTERNAL environment (which includes the digestive tract and epithelial-lined orifices; substances released include sweat, oil mucus, digestive enzymes, etc.) whereas ENDOCRINE glands release HORMONES into the INTERNAL fluids of the body (e.g, blood, lymph,etc.) Whenever you see something being secreted into the external environment, EVEN IF IT'S A HORMONE, you should think exocrine. Endocrine glands ONLY secrete internally into the blood or lymph (and recall that body orifices such as the nasal passages and gut are considered "outside").
Describe the function of each of the items labeled on your diagram, focusing on the role each component plays in the concentration of the filtrate, exchange of ions, etc.
The glomerulus is a fenestrated capillary bed that strains the blood—allowing fluids, ions, and molecules the approximate size of glucose or smaller to pass through into Bowman's capsule. Blood cells and larger blood components remain within the capillaries and exit via the efferent arteriole which eventually empties into the renal vein. Bowman's capsule is a spherical enclosure around the glomerulus that catches the filtrate as it is formed and funnels it into the proximal tubule. The proximal convoluted tubule (PCT) is the section of the nephron between Bowman's capsule and the descending limb of the Loop of Henle. Along the PCT sodium is reabsorbed via active transport and glucose is reabsorbed via secondary active transport through a symporter identical to the one used to absorb glucose from the small intestine. Water follows the solutes via facilitated diffusion. However, because water and solutes are reabsorbed in the same ratio, the filtrate remains isotonic (i.e., the volume of filtrate decreases, but its concentration remains constant). The descending Loop of Henle travels into the very hypertonic medulla. This section of the nephron is impermeable to salts, but very permeable to water. Water therefore flows out of the filtrate and into the medulla, concentrating the urine. The ascending Loop of Henle carries the filtrate out of the medulla and back into the cortex. This portion of the loop is impermeable to water and actively transports ions out of the filtrate and into the medulla. This continuous "dumping" of salts into the medulla accounts for its hypertonicity. At the top of the ascending loop the filtrate is actually less concentrated due to the removal of these ions. The distal convoluted tubule (DCT) is the section of the nephron between the top of the ascending loop of Henle and the collecting duct. Recall that this segment passes directly by the opening to Bowman's capsule where the juxtaglomerular apparatus is located. The distal convoluted tubule regulates calcium, sodium and hydrogen concentrations— although for the MCAT we suggest you focus only on its sodium reabsorption function as regulated by the hormone Aldosterone. Recall that aldosterone stimulates increased sodium reabsorption at the DCT and the collecting duct. Less important, but worth remembering, is the fact that the DCT also reabsorbs calcium in response to parathyroid hormone (PTH). When the juxtaglomerular apparatus detects decreased blood pressure in the afferent arteriole, it secretes Renin, setting into motion the renin-angiotensin pathway whose ultimate result is increased blood volume and blood pressure (This increased blood pressure would provide negative feedback inhibition to the juxtaglomerular apparatus). A number of DCTs from a number of different nephrons dump into a shared collecting duct. The collecting duct carries the filtrate through the medulla toward the renal pelvis. The collecting duct becomes very permeable to water in the presence of ADH from the posterior pituitary. If ADH is present the filtrate will be further concentrated as water flows out into the very salty medulla.
Provide the definition for the nervous system.
The nervous system includes the brain, spinal cord, peripheral nerves, neural support cells (astrocytes, Schwann cells, ependymal cells, etc) and sensory organs such as the eyes and ears.
Nervous System Organization
The nervous system is divided into the CNS and PNS.
Depolarization
The opening of the voltage-gated sodium channels causes a sudden spike in the membrane potential from -70mV to somewhat around +40mV. This process is referred as "depolarization".
How does a neuron stop the signal being sent?
The post synaptic membrane will be continuously stimulated as long as neurotransmitter is present. Specialized enzymes in the synaptic cleft must break down the neurotransmitter to interrupt its action. The most common one is acetylcholinesterase. The MCAT often ask about acetylcholinesterase activators (agonists) or inhibitors (antagonists).
Hyperpolarization
The potassium channels are somewhat slow to close as the membrane potential approaches -70 mV. Thus, the membrane potential actually dips to around -90 mV before gradually returning to the resting potential.
Graph and label the entire action potential as Voltage vs. Time. Include resting potential, threshold stimulus, absolute refractory period, relative refractory period, depolarization, repolarization and hyperpolarization. Also label on the graph the approximate point at which each channel type opens and closes.
The potassium channels open at some positive potential, before the sodium channels close. The sodium channels close at the peak of depolarization. Note that some stimuli fail to result in an action potential because they fall short of the threshold stimulus. In this diagram it is also easy to see why a greater-than normal stimulus would be necessary to reach the threshold during the hyperpolarization phase (i.e., relative refractory period).
Name at least one artery and one vein that carry oxygenated blood. Name at least one artery and one vein that carry de-oxygenated blood.
The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. The veins of the systemic circulation all carry deoxygenated blood from the capillaries back to the right atrium. The pulmonary veins carry oxygenated blood from the lungs back to the left atrium. The arteries of the systemic circulation all carry oxygenated blood from the left ventrical to the capillaries.
Describe the effect of 1) parasympathetic stimulation and 2) sympathetic stimulation, on each of the following, pupil constriction, heart rate, blood pressure, blood flow to skeletal muscle, blood flow to the digestive organs, blood flow to the brain, and blood flow to the skin.
The pupils dilate in response to sympathetic stimulation and constrict in response to parasympathetic stimulation; heart rate is increased by sympathetic stimulation and decreased by parasympathetic stimulation; blood pressure is increased by sympathetic stimulation and decreased by parasympathetic stimulation; blood flow to the skeletal muscles is increased by sympathetic stimulation and decreased by parasympathetic stimulation; blood flow to the digestive organs is decreased by sympathetic stimulation and increased by parasympathetic stimulation; blood flow to the brain is increased by sympathetic stimulation and decreased by parasympathetic stimulation; blood flow to the skin is decreased by sympathetic stimulation and increased by parasympathetic stimulation.
Residual Volume
The residual volume (RV) is the amount of air left in the lungs after a forced, maximal exhalation.
Tidal Volume
The tidal volume (TV) is the volume of air that enters and exits the lungs during an average, unforced respiration.
The equation above is actually the net reaction for the sum of two related reactions that occur as CO2 dissolves in the blood. Demonstrate how these two reactions combine to form the above reaction.
The two equations whose net equation is given in the outline are: CO2 + H2O <--> H2CO3 H2CO3 <--> HCO3- +H+
What is the difference between the ureters and the urethra?
The ureters carry urine from the renal pelvis portion of the kidneys to the bladder. The urethra carries urine from the bladder to the external urinary orifice. You have two ureters, but you only have one urethra.
Describe the two different types of synapses.
There are two kinds of synapses: electrical and chemical. Transmission across the synapse is by far the slowest part of signal transmission.
Reserve Volume
There are two reserve volumes, an inspiratory reserve volume (IRV) and an expiratory reserve volume (ERV). This is the volume of additional air that can be exhaled or inhaled after a normal, unforced expiration or inhalation.
Give ALL the steroid hormones and their locations.
These are lipid soluble; all steroids are cholesterol derivatives. Adrenal cortex: Aldosterone and cortisol Gonads: Estrogen, progesterone, testosterone.
Talk about the neural support cells.
These cells are not neurons that conduct electrical potentials, but cells in the nervous system that provide support to neurons. Schwann cells (oligodendricytes in CNS), cells lining the cerebrospinal fluid cavities (ependymal cells) and structural support cells (astrocytes) are a few prominent examples.
Threshold Potential
This is the minimum stimulus that must be exerted upon the membrane to initiate the full action potential. It is around -55 mV. If a stimulus depolarizes the membrane above this threshold, the entire action potential will follow. If not, the membrane potential will return to -70 mV.
Chemical synapses:
This is the traditional synapses you probably think of when you heard the word. It is the small gap between the terminal button and either 1) the dendrite of a subsequent neuron, or 2) the membrane of a muscle or other targets called the effector.
What is the second messenger system and its mechanism?
This usually occurs via a cascade. In a cascade, one hormone activates another hormone, enzyme, or other signaling molecule. The signal recipient then activates another member of the cascade, with the size of the reaction and the number of molecules involved increasing with each step.
What are platelets?
Tiny membranes-bound drops of cytoplasm. They are sticky when exposed to injured epithelium and non-sticky to healthy epithelium. If they encounter injured epithelium, they release chemicals that activate other platelets and clotting factors. Platelets are derived from megakaryocytes, a type of blood cell that remains in the bone marrow. Mature megakaryocytes produce small fragments, which they release into the circulating blood. These cellular fragments are platelets.
Important note about blood typing.
To avoid mistakes on blood-typing questions, ALWAYS focus on the RECIPIENT. If a person's immune system sees any protein it does not have on its own blood cell membranes, it will attack it and coagulation/rejection will result. Thus, a patient with type A blood is fine with A antigens on donated blood cells, but it will attack B antigens,whether it comes from an AB or B donor.Type O blood can be donated to anyone because it has no A or B antigens. A person with blood type AB can receive from anyone because no donor will have any antigens this person's immune system hasn't seen before.
What are the primary functions of blood?
Transport nutrients, gases, waste products and hormones to and from cells; regulate the extracellular environment; help maintain homeostasis; repair injuries; protect the body from foreign bodies (i.e, antigens). Blood is a connective tissue.
Talk about hormone transport and action at the effector.
Transport: Lipid soluble hormones require a certain protein carrier or a micelle/vesicle. Peptide hormones are water soluble and dissolve in the blood readily. Target: Lipid soluble hormones act almost exclusively by binding to a receptor on or inside the nucleus and influencing transcription. Peptide hormones, by contrast act at a variety of cell locations. Membrane permeability: Lipid soluble hormones diffuse easily through the lipid center of the membrane and thus do NOT require a cell membrane receptor. They still require a receptor eventually, wherever they act inside the cell. Peptide hormones are hydrophilic (water soluble) and cannot dissolve through the membrane and thus they require a membrane receptor.
Recalling that parathyroid hormone causes the breakdown (a.k.a, reabsorption) of bone and a concomitant release of calcium into the blood; and that calcitonin causes the buildup of bone matrix with a concomitant decrease in blood calcium, answer the following: Patient A has ingested a large dose of a calcium supplement. Which hormone will be found in highest concentration in her blood? Patient B suffers from calcinuria, a condition marked by low blood calcium. Which hormone will be found in highest concentration in his blood?
Using the same logic as described for the previous question, Patient A is expected to have high levels of the hormone calcitonin because this hormone decreases calcium blood levels. Patient B has low blood calcium, so we expect him to have high levels of parathyroid hormone because its effect is to breakdown bone and release calcium into the blood.
Vital Capacity
Vital capacity VC) is the total volume of air the lungs can hold at maximum inflation, minus the residual volume.
What is the role of voltage gated sodium channels in action potential?
Voltage gated sodium channels are integral proteins that changes shape (open) in response to a disturbance in the resting potential (i.e, voltage) across the membrane. In their open state, they allow the rapid flow of sodium back into the cell.
Describe the process by which the signal is transmitted from the terminal button, across the synaptic cleft, to the subsequent neuron or effector. Include definitions and explanations of function for the following: presynaptic membrane, Ca2+ ions, calcium channels, neurotransmitter, neurotransmitter bundles, exocytosis, postsynaptic membrane, and protein receptors.
When an action potential arrives at the presynaptic membrane it triggers voltage-gated calcium channels to open, allowing calcium ions to flow into the cell. Inside of the terminal button are numerous neurotransmitter bundles—vesicles filled with neurotransmitter. The presence of calcium initiates a cascade that results in these bundles fusing with the presynaptic membrane and dumping their contents into the synaptic cleft. These neurotransmitter molecules diffuse across the gap and bind to protein receptors on the postsynaptic membrane. These receptors are usually associated with sodium channels so that the binding of neurotransmitter opens the sodium channel allowing sodium ions to flow into the cell. If enough sodium ions flows into the cell the voltage will reach the threshold stimulus and an action potential will be generated in the second neuron.
What are the contents of blood?
White blood cells (a.k.a, WBCs or leukocytes), Red blood cells (a.k.a RBCs or erythrocytes), antibodies (a.k.a immunoglobulins), clotting factors (e.g, fibrinogen), transport protein (e.g, albumin) and platelets.
Draw a Heart and correctly label the following: Superior and inferior Vena Cava, Right Atrium, Left Atrium, Pulmonary Artery, Pulmonary Vein, Left Ventricle, Right Ventricle, and Aorta.
You do NOT need to memorize the heart valves for the MCAT (but they are pretty easy to remember if you would like to know them. Think of Traveling to Bolivia, abbreviated: TRV BLV = Tricuspid Right Ventricle, Bicuspid Left Ventricle. The other two are named after what they lead to: pulmonary valve and aortic valve).
Acetylcholine
You should recall that acetylcholine is 1) the neurotransmitter used at all neuromuscular junctions, 2) the neurotransmitter used EVERYWHERE in the parasympathetic nervous system (including at the effector) and 3) the neurotransmitter used in the ganglion and other pre-effector areas of the sympathetic nervous system (norepinephrine is used at the effector).
