Biology 3

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.

Renin-Angiotensin pathway

Liver releases Angiotensinogen and Renin from Juxtaglomerlular apparatus cleaves Angiotensiongen into Angiotensin I. Then the lungs release ACE, which converts Angiotensin I into Angiotensin II (active form), which leads to ↑ sympathetic innervation ↑ BP. ↑ ADH (posterior pituitary) ↑ BP. ↑ Aldosterone ↑ BP. ↑ Vasoconstrictor ↑ BP. More direct affect on Aldosterone than ADH because ADH is produced in Hypothalamus and stored in posterior pituitary.

Voltage-Gated Sodium Channels

Integral proteins that change shape (open) in response to a disturbance in the resting potential (voltage) across the membrane. In their open state, they allow the rapid flow of sodium back into the cell.

Autonomic

Involuntary; innervates cardiac muscle, smooth muscle, and glands; contains both sensory and motor subdivisions.

Light passes through the following structures as it enters the human eye:

Light first hits the cornea as it enters the eye and it NEVER passes thru the sclera, which is the white part of the eye seen around the iris. Thus, only choice D is possible. Cornea, aqueous humor, pupil, lens, vitreous humor, retina.

Respiratory System

Primary function is gas exchange. Inhalation and expiration are necessary functions to deliver air to the alveoli where gas exchange 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.

Action Potential

A disturbance in the resting electrical potential (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 gradually return to the normal resting potential

Which of the following activities would NOT involve the peripheral nervous system (PNS)?

The CNS includes the brain and spinal cord and the PNS is everything else, including all peripheral and cranial nerves. Answer choice B is wrong because memorizing a poem would require looking at it, which would involve the PNS. A reflex arc is almost entirely the PNS except for the point at which it synapses in the spinal cord, so C is wrong. D may be tempting, but recall what the autonomic nervous system is . . . a branch of the PNS. A is thus the best answer. This involves entirely cerebral activity.

Which of the following is NOT a likely effect of increased ACTH levels?

ACTH, or Adrenocorticotropic Hormone is released by the anterior pituitary and stimulates the adrenal cortex to secrete glucocorticoids, more commonly known as "stress hormones." You should know that stress hormones increase gluconeogenesis and fat metabolism. A is false because this is the reverse of gluconeogenesis and it would indeed be decreased as gluconeogenesis is increased. Increased cortisol secretion is a direct effect of ACTH. C, increased blood glucose, would be expected if gluconeogenesis is upregulated. Answer D, however, would not be expected and D is thus the best answer. More blood glucose in the blood would be associated with increased insulin, not decreased insulin.

Steroids (lipid Soluble)-all steroids and cholesterol derivatives

Adrenal Cortex:Cortisol and Aldosterone Gonads:Estrogen, Progesterone, and Testosterone

Which of the following hormones is LEAST likely to be responsible for the two problems described?

Aldosterone and ADH both increase blood pressure, so they account for one of the two symptoms. PTH increases blood calcium and thus accounts for the second symptom. Calcitonin, however "tones your bones" by decreasing blood calcium and inhibiting osteoclasts. This would NOT have the effect described, making C the best answer.

Two hours later, the patient's blood level of Aldosterone has decreased to 5mcg/mL. During this same time period, which of the following has also decreased? Tricky wording

Aldosterone causes an increase in the uptake of Na+ at the distal convoluted tubule. Thus, the flow of sodium into the distal renal tubules would indeed decrease as its concentration decreased. Answer choice B is incorrect because, if anything, less aldosterone would mean more flow of Na+ out of the cells back into the filtrate. The permeability of the collecting duct is affected by ADH and not at all by aldosterone. Finally, the ascending loop of Henle is always impermeable to water and this is not changed in any way by aldosterone.

PNS

All neurons outside of the CNS, both sensory and motor neurons. Contains somatic and autonomic subdivisions.

Schwann Cells and Myelin Sheath

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.

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.

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. A patient with type A blood is fine with A antigens on donated blood cells, but will attack B antigens, whether from an AB, or an 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 form anyone because no donor will have any antigens this person's immune system hasn't seen previously.

Sodium/Potassium Pump

An ATP pump that actively transports 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.

All of the following statements are true of both arteries and veins, EXCEPT:

Answer A is true of both because systemic arteries and pulmonary veins both contain oxygenated blood. Answer B is true because both are lined with endothelium. Answer C is true because nearly all arteries and most veins are surrounded by smooth muscle fibers. Answer D, however, is false because arteries are only those vessels leaving the heart and veins are those entering the heart.

Peptides (water soluble)

Anterior Pituitary:FSH, LH, ACTH, hGH, TSH and Prolactin Posterior Pituitary:ADH and Oxytocin Parathyroid:PTH (Parathyroid Hormone) Pancreas:Glucagon and Insulin (also releases digestive enzymes, but this is an exocrine function not endocrine) Thyroid:Calcitonin Embryo/Placenta:hCG (Human Chorionic Gonadotropin)

Blood vessels

Arteries→Arterioles→Capillaries→Venules→Veins

Contents of Blood

White blood cells (leukocytes), Red blood cells (erythrocytes), antibodies (immunoglobulins), clotting factors (fibrinogen), transport proteins (albumin) and platelets.

Diagram of the Heart

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).

Antagonist

acetylcholinesterase inhibitor antagonist=inhibitor

ADH

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 permeable there is a large net flow of water out of the filtrate, concentrating the urine. Net effect=water retention and increased blood pressure.

Inflammation in CF patients can result in cell death and lysis within the tissues surrounding the alveoli. These changes will most likely result in:

Cell lysis will result in proteins, solutes and other cell contents being dumped into the interstitial fluid. This will INCREASE its osmotic pressure and fluid will flow OUT of the capillary. This best matches Answer choice C.

Sympathetic

fight or flight. Cell bodies located far from the effectors. Neurotransmitters: acetylcholine at the ganglia, norepinephrine at the effector.

Outer Ear

includes the pinna (earlobe) and auditory canal

Sympathetic Nervous System

increases heart rate and blood pressure

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.

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).

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.

Agranulocytes

monocytes (become macrophages) and lymphocytes. These cells live for months to years.

Motor

motor subdivision of the autonomic nervous system, contains the sympathetic and parasympathetic divisions.

Granulocytes

neutrophils, eosinophils, and basophils. These cells live for hours to days

Stopping the Signal

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.

Hyperpolarization

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.

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)

Lipid Soluble hormones

require a protein carrier or a micelle/vesicle. Target: act almost exclusively by binding to a receptor on or inside the nucleus and influencing transcription membrane permeability:diffuse easily through the lipid center of the membrane and thus doe not require a cell membrane receptor. Still require a receptor eventually, wherever they act inside the cell.

Sensory

sensory subdivision of the autonomic nervous system is not well developed explaining why visceral pain is often referred

Veins

veins return to the heart The naming of blood 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. Thin-walled vessels with little to no musculature that rely on a valve system to move blood back toward the heart.

Peptide Hormones

water soluble and dissolve in the blood readily Target: act at a variety of cell locations Membrane permeability: are hydrophilic and cannot dissolve through the membrane; thus require a membrane receptor.

Proximal Convoluted Tubule

) 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)

Vital Capacity

) is the total volume of air the lungs can hold at maximum inflation, minus the residual volume.

Resting Potential

-70 mV This is the potential difference (voltage) across the membrane when an action potential is NOT present

Two Kinds of Synapse(slowest part of signal transmission)

1) 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. 2) Chemical Synapse-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 target (called the effector)

Diaphragm

1) The diaphragm moves down when it is flexed and moves up when it is relaxed. When relaxed it has an upward-oriented convex shape. When flexed it is almost flat. 2) The diaphragm moves down during inhalation and up during exhalation.

Name at least one artery and one vein that carry oxygenated blood. Name at least one artery and one vein that carry deoxygenated blood.

11. 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.

Electrical System of the Heart

12. 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.

The whole process of action potential

22. 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.

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?

23. 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.

Discuss near-sighted and far-sighted. Where is the image formed in both cases? What type of lens is needed to correct each condition?

27. A near-sighted person can see close objects but not objects farther away. A far-sighted person can see objects far away, but not closer objects. For a near-sighted person the light rays are being bent (i.e., diffracted) too much, resulting in a focal point and image that is in front of the retina. Placing a diverging lens in front of an eye with this condition spreads the rays apart, increasing the distance between the lens and the focal point (i.e., the place where the rays will meet). For a far-sighted person they cannot see close objects because the light is diffracted too little, resulting in a focal point and image that is behind the retina. Placing a converging lens in front of an eye with this condition brings the rays closer together so that the focal length decreases and lands on the retina.

What happens to the eye as you attempt to focus on a book very near your face? Do ciliary muscles contract or relax? Does the curvature of the lens increase or decrease? Does the focal point move outward or inward? Does the power of the lens of the eye increase or decrease?

28. To answer this question one must first understand that when the ciliary muscles contract the lens becomes more spherical (i.e., smaller radius of curvature). For an object near the eye the light rays must be bent (i.e., diffracted) more sharply than rays from distant objects (for distant objects light rays are assumed to be parallel). A lens with a smaller radius of curvature bends light more sharply. Therefore, the ciliary muscles contract to increase the curvature of the lens, bend the light more sharply and thereby land the image on the retina. The focal point will decrease (i.e., move closer to the lens) as the radius of curvature of the lens decreases. The power of a lens is the inverse of the focal point: P = 1/f. Therefore, as the lens of the eye focuses on a nearby object that lens becomes more powerful.

Story of Kidney

3. 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. Note to Tutors: Students should be intimately familiar with the above description of the anatomy and function of the nephron. A good goal would be for them to be able to recount all of the above information to you as a "story" told in their own words.

Second Messenger System

30. 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.

Blood Typing

4 phenotypes A, B, AB, and O The letters A and B indicated the antigens that are present on that individual's blood cell membranes A=A antigens only B=B antigens only AB=Bothe A and B antigens O=Neither A or B antigens

Vasoconstriction is employed by the body in accomplishing all of the following, EXCEPT:

; Answer B is false because vasoconstriction IS utilized to prevent blood loss at an injury site. Answers C and D are both false because vasoconstriction can be part of both a fight/flight response and a rest/digest response. Answer A is the correct answer because vasodilation would be used on a hot day rather than vasoconstriction.

Which of the following statements best describes the mechanism of function of the inner ear?

; First, note that both the term "displaced by collisions with air molecules" and the term "displaced by sound waves" are correct. The key here is to first find the choice with the correct order of bones: maleus, incus, then stapes. This narrows it to A or D. A is wrong and D is correct because the displacement at the oval window compared to the eardrum is DECREASED. This difference in input/output displacement creates the lever action of the ear and magnifies the pressure at the oval window.

At low blood temperatures experienced during hypothermia, the solubility of bicarbonate ion in the blood decreases dramatically. The most likely effect of this phenomenon is:

Be careful here. You need to know what effect the bicarbonate coming "out of solution" has on the carbon dioxide blood dissolution equation. Decreasing the solubility of bicarbonate basically means that more will precipitate out and it is thus equivalent to removing it. This will shift the equilibrium to the right to compensate, raising hydrogen ion concentration and lowering pH.

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.

Systemic Circulation

Blood flows from the left ventricle, through the arteries, arterioles, capillaries, venules, veins, vena cava and back to the right atrium.

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.

CNS

Brain and spinal cord; interneurons only. No subdivisions

How CO₂ carried in the blood

CO₂ + H₂O→HCO₃⁻ + H⁺ This is net reaction. The two reactions to get the net reaction is: 1) CO₂ + H₂O↔ H₂CO₃ 2) H₂CO₃↔ HCO₃⁻ +H⁺ or CO₂ + H₂O→ H₂CO₃⇌ HCO₃⁻ + H⁺

If you block Pulmonary Artery what would happen to pH of blood?

Can't get rid of carbon dioxide, so CO₂ increases and shifts the reaction to produce more H⁺ and decrease pH.

Glycogenolysis is the breakdown of glycogen, a process regulated heavily by glucocorticoid hormones such as cortisol. Which gland secretes cortisol, and in which organ or tissues of the body would one expect to find high concentrations after its release?

Cortisol is secreted by the adrenal cortex. To answer the second part, you should know that the liver is the center of metabolism. If glucose is going to be formed into glycogen for storage, or if glycogen is going to be broken down into glucose, this will happen at the liver. This isn't to say these things never happen other places, but all systemic adjustments to blood glucose levels will primarily involve the liver. The other major location for glycogenolysis you may want to be aware of is muscle tissue. However, for this question, that is irrelevant because the term "skeletal muscles" in Answer A is incorrectly paired with "Adrenal Medulla."

How many oxygen atoms are carried on one molecule of Hb at 100% saturation?

Each Hb has 4 subunits, each with 1 heme. Each heme can hold one O₂ molecule. So 8 total oxygen atoms.

Which of the following would be likely to occur if a patient were to receive a rapid intravenous injection of a hypertonic saline solution?

First ask yourself the result of an influx of a hypertonic (meaning saltier than the blood) solution into the blood. This would increase the osmolarity of the blood and water would flow into the blood, increasing blood pressure. Answer choice B could not be affected because permeability at the collecting duct changes ONLY in relation to ADH. Answer choice C is false because aldosterone would NOT increase after an increase in blood pressure. Answer choice D is also false because the net flow of ions out of the ascending loop of Henle would definitely INCREASE if there were more solutes in the filtrate. Thus, answer choice A is the best answer. This is exactly what would happen. As filtrate entered the medulla, it would be much closer in concentration to the "super salty" medulla than it normally would. This SMALLER difference in osmotic potential would mean a decrease in net flow of water out of the filtrate.

Lymphatic System

Gather excess interstitial fluid and return it to the blood; remove from the interstitial spaces proteins and other molecules too big to be taken up by the capillaries; monitor the blood and lymph for infection

Gas exchange

Hemoglobin=quaternary protein mode of four protein chains, two alpha and two beta. Each protein has an Fe-containing "heme" group at its center. Each heme can hold one O₂ molecule.

Descending Loop of Henle

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.

All of the following hormones have the effects described, EXCEPT:

Hopefully you're getting the point by now . . . that you really DO need to know that hormone chart inside and out. A will be marked wrong by many students because they think of the female reproductive system when they see FSH. In fact, it regulates both sexes similarly, stimulating the testes to develop and nurture gametes. Estrogen does cause an increase in LH during menstruation, known as the "luteal surge." Answer D is also true, calcitonin does inhibit osteoclasts. C, however, is false because prolactin stimulates milk production (lactation) not milk excretion (or "let down").

Pg. 313 Read passage Information or question If you monitor the patient carefully for the next few hours, which of the following is most likely?

If you notice that all of the questions include increasing blood pressure, you should ask yourself which of the conditions described would correlate with increased blood pressure. Answer B states that ADH/Aldosterone would increase, which is false. These hormones both respond to low blood pressure to increase it, and would not be released when it is increasing. Answers C and D both have one or the other acting differently, when in reality they both react similarly to blood pressure. Finally, Answer choice A is correct. If blood pressure were increasing, ADH and Aldosterone would both be decreasing because their effects would not be needed.

Inner Ear

Includes the cochlea, semicircular canals and the vestibulocochlear nerve.

Middle Ear

Includes the tympanic membrane (eardrum), and the three middle ear bones (in this order outside to inside): malleus, incus, and Stapes.

Which of the following can be accurately deduced from the above schematic? I. Neuron B is located in the CNS II. Both neurons A and C are part of the peripheral nervous system III. The pathway shown is autonomic

Look back to the explanation for the previous question; we know that neuron B is in the CNS and that both A & C must be in the peripheral nervous system, but we have no information from the diagram alone that would indicate either autonomic or somatic. We can tell between sympathetic and parasympathetic due to the location of the cell body "far" from the effector. However, we cannot differentiate somatic from autonomic because somatic efferent nerve cell bodies are also located far from the effector (in the spinal cord).

Lymph vessels

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 two main vessels, the right lymphatic duct and the thoracic duct, which both dump back into the blood stream by merging with large veins in the lower portion of the neck. Lacteals around small intestine pick up lipids (triglycerides) and dump back into the blood eventually-not directly Lymphatic system-carry WBC's, why Doctor feels lymph nodes because if infection ↑ WBC's and enlarged lymph nodes.

Leukocytes

No hemoglobin. Normal cells with all their organelles that are involved in the immune system

Blood samples from affected patients show a very low concentration of a certain chemical messenger. This protein is assayed and found to be a recognized human hormone. Based on the information in the passage, which of the following is most likely the identity of this hormone?

Now you are expected to synthesize all of the information from the prompt above to determine which hormone is most likely involved. Aldosterone and ADH would both account for only one symptom, Calcitonin (as mentioned above) would not account for any of them, and PTH could account for both (by its normal effect of increasing blood calcium and via an increase in blood pressure via increased osmolarity). Although it may be tempting to pick C or D, it is impossible to say that one is more likely than the other and B is the better answer because it accounts for both symptoms.

Interplay of hydrostatic 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.

The structures encountered along the path followed by an action potential as it passes through a peripheral neuron include:

One of MCAT's much-loved list questions, just be very careful and take your time. Evaluate each list one by one and determine if anything is out of order. A is the most correct. B is not as good of an answer because it leaves out the Schwann cells and nodes of Ranvier. C is false because oligodendrocytes are only found in the CNS. D is false because the axon hillock is reached AFTER passing thru the cell body.

The image formed on the retina of the human eye is best described as:

One of the easier questions that you'll see on the MCAT, but one you're very likely to see. The image formed on the retina is positive because it is on the same side as the observer (which really means the person viewing or receiving the image—in this case, the retina). Once we know this, it can only be real and inverted according to PRI and NVU.

Inhalation/Exhalation

Path of air= Mouth/nose→pharynx→larynx→trachea→bronchi→bronchioles→alveoli

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.

As winter approaches, the Siberian muskrat gorges itself on high-carbohydrate foods in order to store up fat for hibernation. Which of the following hormones is likely to be found in highest concentration in the muskrat's liver during the fall and winter, respectively?

Recall that insulin and glucagon, like all hormones, tend to return things to normal physiological levels. Thus, while the muskrat is gorging on carbs, the blood concentration of glucose due to the absorption of these carbs will be higher than normal and insulin would be secreted to return things to normal. During the winter, there will be NO absorption because the muskrat won't be eating, so blood glucose will be lower than normal and glucagon will be present to raise the blood glucose levels to normal. Next, you must ask yourself what cortisol does? It is a stress hormone whose main effect is to promote gluconeogenesis (the reverse of glycolysis) and promote fat metabolism. This is very likely to be present during a stressful hibernation when the muskrat will need to accomplish both of these tasks in order to maintain its normal blood glucose levels. B is thus the best answer.

Immediately following the onset of a high-stress event, such as an auto accident, the blood flow to the digestive organs would be:

Recall that the neurotransmitter used at the effector in the sympathetic nervous system is norepinephrine, making only answer choices B or D possible. Now you must decide if blood flow to the digestive tract will increase or decrease. "Rest and Digest" tells us that the PARASYMPATHETIC increases blood flow/activity at the gut, so the sympathetic must—in general—inhibit it. D is thus the best answer.

Parasympathetic

Rest and Digest. Cell bodies located very close to, or inside, the effector. Neurotransmitters: acetylcholine only, at both ganglia and the effector.

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.

Neuron Functions

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.

The Organ of Corti: I. is a small microtubule-filled membrane extensions, called hair cells sense disturbances in the fluid and transmit these movements into neural signals. II. is located inside the cochlea. III. contains the semi-circular canals, which help maintain balance and orientation.

The Organ of Corti is the structure inside the cochlea that transfers fluid motions into a nerve signal. It does not contain microtubules (and doesn't contain cilia!), so Statement I is false. Statement II is true. Statement III is false because the semi-circular canals are not located within the Organ of Corti.

Which of the following accurately describes the relative fluid and osmotic pressure of the arteriolar and the venous sides of a capillary, respectively?

The capillary is an amazing structure in that it pumps things in and out of the blood without a pump system. This exchange is all accomplished by an interplay between osmotic and hydrostatic pressure. Hydrostatic pressure is high entering the capillary from the arteriolar side and decreases across the capillary; at the same time, osmotic pressure increases so that at the far venous end of the capillary there is a net flow into the capillary. Answer C is the only answer that reflects these facts.

Breathing into a paper bag would have with of the following effect on blood chemistry?

The key here is to remember the formula for dissolution of carbon dioxide in the blood: CO2 + H2O ↔ HCO3- + H+. Breathing into the bag will mean that only CO2 will be entering the lungs and its concentration in the blood will thus increase. According to this equation, this will increase hydrogen ion concentration and thus lower blood pH, as stated in Answer B.

Immediately before impact in a car accident, a student notices an almost instant burst in heart rate. An hour later, while discussing the events with the police, the student notices that he still feels wire and unable to calm down. Which of the following statements best describes these phenomena?

The key to answering this question is understanding that the nervous system results in fast, specific responses that are short-lived, while the endocrine system results in much slower, general responses that are long-lived. When you feel immediately aroused right before an accident, this is a result of the sympathetic branch of the autonomic nervous system. Hours later, that same nervous response would definitely NOT still be having an effect. The arousal you feel then is due to the continued presence of adrenaline or noradrenaline in your blood, an endocrine response. Answers A and B are wrong because they label both phenomena as having the same cause. C is incorrect because the pre-accident arousal is definitely sympathetic, not parasympathetic.

Eye Diagram

The lens of the human eye is a converging lens and therefore always produces a PRI image. Light rays are bent most by the cornea, and subsequently adjusted by the lens.

Depolarization

The opening of the voltage-gate sodium channels causes a sudden spike in the membrane potential, from -70 mV to somewhere around + 40 mV.

It is discovered that a small patch of skin cells on the face of certain male tree frogs secretes a hormone onto the surface of the skin. Called pheromones, these chemicals are thought to play a role in sexual excitation of female frogs. This response in the male frog is best described as a(n):

There are no obviously wrong answers here, so you have to search for the "best" answer among the alternatives. Anytime you see stimulation of a very specific response or very specific set of cells being stimulated, you need to think "nervous" because it is the specific one and an endocrine response is much more broad. By the same token, 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"). This makes C the best answer. A could be correct, but leaves out the exocrine function. B is incorrect because secretion of the pheromone is exocrine, not endocrine. D is incorrect because . . . it's a made up bunch of bunk! I included this to further illustrate the point we learned in group session with one of the AAMC 3R questions (recall "neurosecretory"). Just because a word sounds "official" or "sophisticated" isn't a good reason to pick it. Besides, the "excitation" portion of this response would be in the female and we are looking at the response in this specific frog.

Nodes of Ranvier

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.

Neural Support Cells

These are not neurons that conduct electrical potentials, but cells in the nervous system that provide support to neurons. Schwann cells (oligodendricytes in the CNS), cells lining the cerebrospinal fluid cavities (ependymal cells) and structural support cells (astrocytes).

Inspiratory and expiratory residual volume

This is the volume of additional air that can be exhaled or inhaled after a normal, unforced expiration or inhalation.

Tyrosines:T₃/T₄=Lipid-soluble; Epi/Norepi=water-soluble

Thyroid: T₃ (Triiodothyronine) and T₄ (Thyroxine) Adrenal Medulla: Epinephrine and Norepinephrine

Platelets

Tiny membrane-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. All blood cells develop from stem cells (undifferentiated cells) in the bone marrow; a process called hematopoiesis.

Which of the following most completely describes the nerve endings in the eye that cause pupil dilation?

To answer this correctly, you do need to recall that they sympathetic nervous system dilates the pupil and the parasympathetic constricts it. Thus, the answer can only be A or C. C is false because acetylcholine is only used pre-ganglion and norepinephrine is used at the effector.

Shortly after returning the patient's blood pressure to normal, the patient develops a severe case of diarrhea. Which of the following most accurately describes the patient's probable blood concentration of ADH during subsequent hours?

To answer this question correctly, you must first ask yourself what the effect of diarrhea would be? Diarrhea involves the inability of the large intestine to accomplish its normal role of absorbing water and results in dehydration. Dehydration would mean decreased blood volume and thus blood pressure. ADH would be secreted in response to this condition to attempt to return it to normal. Recall that most all hormones act via cascade systems and thus act very quickly at first. They are then removed via negative feedback systems. This is a much slower, more gradual decline because it is not immediate. The hormones in the system continue to circulate for a while, plus the cascade will continue forward form the point at which it was shut off. Answer choice A is consistent with this sharp increase in ADH to increase blood pressure and then slow decrease due to negative feedback as the blood pressure rises.

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(ie antigens).

The most likely effect of a dramatic increase in aldosterone secretion is: a) increased uptake of sodium of the distal convoluted tubule b) increased release of sodium at the distal convoluted tubule c) increased uptake of sodium at the proximal convoluted tubule d) increased uptake of sodium in the Bowman's capsule

Understand Vocab. Answer B is false because sodium is taken up in response to Aldosterone, not released. C is wrong because it is the write action, but the wrong location in the nephron. D is wrong because sodium is not taken up at the collecting duct, only water is, and only when ADH is present. A is the correct answer.

Rapid breathing during strenuous exercise has which of the following physiological effects?

Using the same equilibrium equation from question 5, we can see that heavy breathing, which would take CO2 out of the blood at a faster rate, would shift the equilibrium to the left, consuming hydrogen ions and thus raising pH. Answer B best reflects this.

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.

Somatic

Voluntary; innervates skeletal muscle; contains both sensory and motor subdivisions.

Collecting Duct and juxtaglomerular apparatus

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.

Muscarine, a chemical found in certain classes of mushrooms, mimics the action of acetylcholine in nerve-effector junctions. After consuming large amounts of muscarinic mushroom, a patient might exhibit any of the following symptoms, EXCEPT:

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). Because muscarine mimics the action of acetylcholine, we are going to have an increase in parasympathetic responses. Option A is a parasympathetic response, so that would be increased and is not the correct answer. Options C and D are also parasympathetic responses in their respective tissues. Only option B is a sympathetic response and would not be expected in someone that has been poisoned with a acetylcholine agonist.

An ambitious female medical student determines to prevent the onset of osteoporosis by taking large doses of a calcium supplement. Which of the following is a plausible side effect of this action?

Your body attempts to maintain homeostasis or "normal" conditions. Remember this on ALL hormone problems. If you suddenly have excess Calcium in your blood, it will take the action necessary to reduce calcium in the blood, which would be to secrete calcitonin because it causes the uptake of calcium from the blood into the bones. This makes A incorrect. B is incorrect because if there is more solute in the blood there will be a greater flow of water INTO the loop of Henle, not out of it. C is false for a similar reason; blood pressure would increase if solutes increase because water would flow into the blood. Answer D is the best choice. PTH causes breakdown of bone and release of calcium. This would be negative feedback suppressed if calcium was in excess.

Osteoporosis is a serious condition that is most prevalent in aging females. In patients with this condition the density of the bones steadily decreases by 1 to 2% each year. Which of the following is most likely the hormonal cause of osteoporosis?

a chronic decrease in estrogen, causing erratic PTH levels. ; Be careful here; you need to account for both the loss of bone density (which would likely be accounted for by the breakdown of bone matrix and subsequent release of calcium into the blood by osteoclasts) AND the fact that it is more prevalent in women. C is the only answer that includes estrogen and provides any possible explanation for the greater prevalence in women. A is false because decreased PTH would not increase osteoclast activity. B is false because increased PTH has no effect on osteoblasts. D is false because calcitonin "tones your bones" and would increase bone density.

Neuron

a specialized cell that can carry an electrochemical signal (action potential) 1) Are frozen in G₀ phase (unable to divide) 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)

Diagram of Neuron

a stimulus (action potential) starts at the dendrites and pass through the cell body to the axon hillock. The axon hillock then generates a new stimulus only if the initial stimulus is above a certain threshold. Thus, the action potential that arrives at the terminal button is NOT the same stimulus that began at the dendrites; it is a new, regenerated stimulus. Also remember, impulses can only flow down the axon in one direction: cell body to synapse.

Aldosterone

acts on the distal tubule causing an increase in sodium uptake. Aldosterone also causes reabsorption of Na⁺ out of the collecting duct via the insertion of Na⁺, 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. Aldosterone also causes reabsorption of Na+ out of the collecting duct via the insertion of Na+, K+, and Na+/K+ ATPases in the cells that line the collecting duct. Net effect=water retention and increased blood pressure.

Hormones

always act to return to homeostatic, or normal conditions. They never cause a drift away from normal.

Agonist

another term for an activator acetylcholinesterase activator

Lymph nodes

are filled with lymphocytes. These immune system cells monitor the blood for foreign antigens and fight infections

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

Parasympathetic Nervous System

decreases heart rate and blood pressure

Neuron C is most accurately described as

efferent, sympathetic clearly efferent because it synapses with the effector. It is sympathetic because the cell body (indicated by the round dot) is located far from the effector, which is characteristic of sympathetic peripheral nerves.

Endocrine glands

endocrine glands=release hormones into the internal fluids of the body (blood, lymph, etc)

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.

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.

Residual Volume

is the amount of air left in the lungs after a forced, maximal exhalation.

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.

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!

Cell body

is the main part of the neuron where the nucleus is located.

Distal Convoluted Tubule

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).

Tidal volume

is the volume of air that enters and exits the lungs during an average, unforced respiration.

Arteries

leave the heart Muscular, thick-walled vessels that push blood through via rhythmic contraction.

If you block Pulmonary vein what would happen to pH of blood?

look at above equations and understand conceptually. The pulmonary artery can get rid of carbon dioxide, so you are decreasing CO₂, which will shift the equation to the left decreasing H⁺ and increasing pH.

Threshold Potential

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.