8. Biology 2 Flashcards
kidney
excretes liquid and solute waste (water, excess salts, nitrogenous wastes) maintains pH, osmolarity, and blood pressure
kidney diagram (see diagram)
nephron, cortex, medulla, renal pelvis, and ureter
Draw a nephron and label the following: glomerulus, Bowman’s capsule, proximal convoluted tubule, descending loop of Henle, ascending loop of Henle, juxtaglomerular apparatus, distal convoluted tubule, and collecting duct.
See labeled diagrams on the following page. In vivo, Bowman’s capsule is in contact with a portion of the distal tubule rather than directed away from it as shown. The juxtaglomerular apparatus is made up of a patch of cells on the distal tubule and a patch of cells on the afferent arteriole—where the two structures meet. The patch of cells on the distal tubule is called the macula densa, and the cells on the afferent arteriole are called juxtaglomerular cells (don’t memorize these names). Together, these cells constitute the juxtaglomerular apparatus. In Figure 2 the distal tubule is labeled C. The macula densa are magenta and labeled #7. The juxtaglomerular cells are green and labeled #6. Flow through the afferent arteriole is demonstrated by #9.
glomerulus
strains blood, allowing fluids, ions, and molecules, glucose sized and smaller through. the rest get caught and strained through the efferent arteriole which leads to the renal vein
Bowman’s capsule
encapsulates the glomerulus, funnels nitrate into the proximal tubule
proximal convoluted tubule
between bowman capsule and descending limb of loop of henle. PCT sodium is reabsorbed via active transport and glucose is reabsorbed via secondary active transport through a simporter, water fallows via facilitated diffusion, REMAINS ISOTONIC,
descending loop of henle
travels into medulla, impermeable to salts, but very permeable to water, concentrates urine
ascending loop of henle
carries nitrate out of medulla and back into the cortex, impermeable to water, actively transports ions out of the filtrate and into the medulla, (essentially dumps salts into medulla to make it hypertonic)
distal convoluted tubule
between ascending loop of hence and collecting duct, basses directly by the opening of bowman;s capsule, regulates calcium, sodium and hydrogen concentrations. regulated by aldosterone - stimulates sodium reabsorption at the DCT and collecting duct
juxtaglomerular apparatus
detects decreased blood pressure in afferent arteriole, secretes renin,
renin
causes renin angiotensin pathway which increases blood volume and blood pressure, increased BP causes negative feedback inhibition to the juxtaglomerular apparatus,
collecting duct
distal convoluted tubules dump waste into collecting duct, duct carries filtrate through medulla toward renal pelvis. very permeable to water with presence of ADH (concentrates filtrate)
renin-angiotesinogen-aldosterone pathway (see digram)
liver secretes angiotensinogen, angiotensinogen transformed into angiotensin 1 (regulated by renin), angiotensin 1 transformed into angiotensin 2 (regulated by ACE from lung and kidney surface), angiotensin 2: (inc sympathetic activity, reabsorption of ions and repute of water (by aldosterone), stimulated renal cortex (secretes aldosterone), arteriolar vasoconstriction (inc BP), stimulates pituitary gland (inc ADH secretion which causes water reabsorbtion),
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+ channels, K+ channels, and Na+/K+ ATPases in the cellst 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+ channels, K+ channels, and Na+/K+ ATPases in the cellst that line the collecting duct. (The net effect = water retention and increased blood pressure.)
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. (The net effect = water retention and increased blood pressure.)
respiratory
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.
path of air
nose, mouth, pharynx, larynx, trachea, bronchi, bronchioles, alveoli, volume, and vital capacity
tidal volume
volume volume of air that enters and exits the lungs during an avarice unforced respiration
inspiratory reserve volume, expiratory reserve volume
additional air that can be exhaled or inhaled after a normal amount, unforced expiration or inhalation
residual volume
about of air left in lungs after a forced, maximal exhalation
vital capacity
total volume of air the kings can hold at maximum inflation, minus the residual volume
laryngitis
loss of ones normal voice due to to inflammation of vocal chords,
diaphragm
moves down when FLEXED, up when RELAXED, moves down during inhalation, and up exhalation
hemoglobin
= quaternary protein made 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.
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.
Oxygen Dissociation Curves: A graph of % Hb Saturation vs. pO2
The MCAT has demonstrated that they clearly expect prior knowledge of this curve as demonstrated by their asking stand-alone questions that cover these concepts without presenting an example of the curve or discussing it in a passage. It would be logical to expect future questions on all aspects of this curve, especially trends related to pH, carbon dioxide concentration, and temperature. One question asked previously about BPG, but some helpful information was given in the stem.
blood gases
CO2 + H2OHCO3- + H+
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.
CO2 + H2OH2CO3
H2CO3HCO3- +H+
cardiovascular system
Deliver oxygen and nutrients to the cells and tissues of the body; pick up CO2 and waste products and deliver them to the lungs and kidneys.
TRV, BLV
tricuspid right ventricle, bicuspid left valve
heart blood trace
superior/inferior vena cava, right atrium, tricuspid valve, right ventricle, pulmonary valve, pulmonary artery, lungs, pulmonary veins, left atrium, mitral valve (bicuspid), left ventricle, aortic valve, aorta, body
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.
arteries and veins
Arteries leave the heart and 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.
Name at least one artery and one vein that carry oxygenated blood. Name at least one artery and one vein that carry deoxygenated 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.
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.
sympathetic NS activity
increases HR and BP
parasympathetic NS activity
decreases HR and BP
blood vessels
Arteries Arterioles Capillaries Venules Veins,
arteries
Arteries: muscular, thick-walled vessels that push blood through via rhythmic contraction.
veins
Veins: thin-walled vessels with little to no musculature that rely on a valve system to move
blood back toward the heart.
Describe how the 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. (Net filtration data from McGraw-Hill Anatomy & Physiology, 2006).
Draw a graph for each of the following: a) cross-sectional area vs. blood vessel type (aorta/arteries/arterioles/capillaries/venules/veins/vena cava), b) velocity vs. blood vessel type, c) blood pressure vs. blood vessel type (Hint: Q = AV).
lowest velocity at highest cross sectional velocity, (low V at capillaries) pressure highest when leaving heart! (Q=AV)
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). 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 proteins (e.g., albumin) and platelets. Q15. Blood is an example of which tissue type?
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. 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.
Leukocytes
No hemoglobin. Normal cells with all their organelles that are involved in the immune system (we’ll discuss WBCs in more detail with 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.
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.
hematopoiesis
All blood cells develop from stem cells (undifferentiated cells) in the bone marrow; a process called hematopoiesis.
blood typing
o Four phenotypes: A, B, AB, and O
Q17. Blood type is an example of what kind of genetic inheritance pattern?
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=BothAandBantigens
O = Neither A or B antigens
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.
lymph nodes
Lymph nodes are filled with lymphocytes. These immune system cells monitor the blood for foreign antigens and fight infections (We’ll cover this topic more when we cover the “Immune System” in the Biology 3 Lesson).
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.
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.
neuron
A neuron is a specialized cell that can carry an electrochemical signal (i.e. 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 & oxygen
storage capability and thus require high perfusion (blood flow)
neurons
dendrites, cell body, nucleus, axon hillock, terminal button, synapse, Schwann cells, myelin sheath, and nodes of Ranvier.
dendrite
projection from 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 (postsynaptic membrane)
cell body
main part of the neuron where the nucleus is located
axan hillock
area where axon joins the cell body, this region has a very high concentration of voltage gated sodium channels, makes it both sensitive to action potentials and capable of regeneration a strong action potential for transmission down the axon.
terminal button
axon terminal, a projection at the end of the axon that synapses with the dendrite of another neuron or with the effector
axon
long, narrow, lube like extension between the cell body and terminal button,
schwann cells
specialized neural cells, contain high levels of fat and wrap themselves around axon multiple times creating an insulating myelin sheath
nodes of ranvier
small gaps between shwann cells, where signals jump from one node to another without processing along the entire length of the axon, dramatically increasing transmission speed.
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 original started gradually return to the normal resting potential (see below).
resting potential
-70 mV. The voltage across the membrane when an action potential is NOT present (e.g., one has not yet occurred, or it has already passed). Know the exact value: -70 mV. This is the only exact value that is used consistently in most textbooks. The other values given below vary from source to source and you only need to know their sign and approximate value.
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.
Voltage-Gated Sodium Channels
Integral proteins that change 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.
depolarization
The opening of the voltage-gated sodium channels causes a sudden spike in the membrane potential, from -70 mV to somewhere around +40 mV. This process is referred to as “depolarization.”
threshold potential
This is the minimum stimulus that must be exerted upon the membrane to initiate the full action potential. It is usually reported as somewhere 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.
Voltage-Gated Potassium Channels:
These are 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.
Repolarization
Because there are more potassium ions inside the cell (due to the 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 +40mV back down to -70 mV, and is referred to as “repolarization.”
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.
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.
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.
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. (see diagram)
See the labeled diagram below. 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).
synapse
2 types, electrical and chemical, transmission across a synapse is the slowest part of a signal transmission
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 such as the retina, smooth muscle, cardiac muscle, and the CNS
chemical synapses
this is the traditional synapse you probably think of when you hear the word ,it is the small gap between the terminal button and other the dendrite of the next neuron or the membrane of a muscle or other target.
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
stopping the signal
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 loves to ask about acetylcholinesterase. They often ask about acetylcholinesterase activators or inhibitors. Agonist is another term for an activator and antagonist is another term for an inhibitor.
agonist
another term for an activator
antagonist
is another term for an inhibitor
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.
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 the CNS), cells lining the cerebrospinal fluid cavities (ependymal cells) and structural support cells (astrocytes) are a few prominent examples.
neuron functions
o Sensory (Afferent) Neurons: Receive sensory signals from sensory cells. o Motor (Efferent) Neurons: Carry signals to a muscle or gland to respond to the stimulus. o Interneurons: Connect afferent and efferent neurons. They also transfer and process signals. The brain and 90% of all other neurons are interneurons.
CNS
brain and spinal cord, interneurons only
PNS
all neurons outside of CNS, sensory and motor neurons, somatic and autonomic
autonomic
involuntary, innervates cardiac muscle, smooth muscle, and glands, contains both sensory and motor neurons
somatic
voluntary, innervates skeletal muscle, 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 the “sympathetic” and “parasympathetic” divisions with which you are likely familiar.
sympathetic
Fight or Flight.” Cell bodies located far from the effectors. Neurotransmitters: acetylcholine at the ganglia, norepinephrine at the effector.
parasympathetic
“Rest and Digest.” Cell bodies located very close to, or inside, the effector. Neurotransmitters: acetylcholine only, at both the ganglia and the effector.
sympathetic/parasympathetic response
for sympathetic: pupils dilate, heart rate increased, blood pressure increased, blood flow rate increased to muscles/ blood flow rate decreased to digestive organs, blood flow rate to brain is increased/ decreased in brain. parasympathetic is opposite
nervous system organization
CNS/PNS CNS (Brain/spinal cord) PNS (somatic/autonomic) somatic (sensory nerves/motor nerves) autonomic (sensory nerves/motor nerves) autonomic motor nerves (sympathetic/parasympathetic)
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.).
peptides (water-soluble)
Anterior Pituitary: FSH, LH, ACTH, hGH, TSH & Prolactin
Posterior Pituitary: ADH & Oxytocin
Parathyroid: PTH (Parathyroid Hormone)
Pancreas: Glucagon & Insulin (also releases several digestive enzymes, but this is an
exocrine function, not an endocrine function)
Thyroid: Calcitonin
Embryo/Placenta: hCG (Human Chorionic Gonadotropin)

anterior pituitary
FSH, LH, ACTH, hGH, TSH, prolactin
posterior pituitary
ADH, oxytocin
parathyroid
PTH
pangreas
glucagon, insulin
thyroid
calcitonin
embryo/placenta
hCG
Steroids (lipid soluble, cholesterol derivatives)
adrenal cortex and gonads
adrenal cortex
cortisol and aldosterone
gonads
estrogen, progesterone, and testosterone
tyrosines (T3/T4 = lipid-soluble; Epi/Norepi = water-soluble)
thyroid and adrenal medulla
thyroid
T3 and T4 (triiodothyronine and thyroxine)
adrenal medulla
epinephrine and norepinephrine
hormone transport
water soluble hormones dissolve and is transported in and by blood. fat soluble hormones require a protein carrier or micelle/vesicle for transport
hormone targets
lipid soluble hormones bind to surface on or inside the nucleus, peptide hormones can act everywhere
hormone membrane permeability
lipid soluble hormones diffuse easily though the lipid center of the membrane and thus do not require a cell membrane receptor. peptide hormones are hydrophilic and cannot dissolve through the membrane thus they require a membrane receptor.
second messenger systems (think g-protein)
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. DO NOT MEMORIZE THIS. The MCAT will not test you on names or other specifics. However, it does illustrate how cascades work and having a general familiarity with G protein signaling pathways will be a tremendous help on any passages or questions about G proteins—which have been fairly common.
predicting hormone levels
Hormones always act to return to homeostatic, or “normal,” conditions. They
never cause a drift away from normal.
adrenocorticotropic hormone ACTH
anterior pituitary, peptide, stimulates adrenal cortex to release stress hormones (aldosterone and cortisol)
luteinizing hormone LH
anterior pituitary, peptide, causes ovulation, and secretion of sex hormones
follicle stimulating hormone FSH
anterior pituitary, peptide, stimulates growth of the follicle during menstrual cycle and sperm production
thyroid stimulating hormone TSH
anterior pituitary, peptide, stimulates release of T3 and T4 from thyroid
human growth hormone hGH
anterior pituitary, peptide, stimulate growth throughout the body
prolactin
anterior pituitary, peptide, stimulates milk production in the breasts
antidiuretic hormone
posterior pituitary, peptide, causes collecting duct of kidney to become permeable to water, concentrating urine, and retaining water
oxytocin
posterior pituitary, peptide, stimulates contractions during childbirth and milk secretion during nursing
parathyroid hormone PH
parathyroid, peptide, increases blood calcium by stimulating proliferation of osteoclasts, uptake of calcium in gut and reabsorption of calcium in the kidney
insulin
pancreas, peptide, stimulates storage and uptake of glucose from the bloodstream
glucagon
pancreas, peptide, stimulates gluconeogenesis and release of glucose into the blood
calcitonin
thyroid, peptide, decreases blood calcium by inhibiting osteoclasts
human chorionic gonadotropin hCG
egg/placenta, peptide, prevents degeneration of corpus luteum, maintaining pregnancy
aldosterone
adrenal cortex, steroid, increases Na reabsorption and K secretion at distal convoluted tubule and the collecting duct, net increase in salts in the plasma, increase of osmotic potential and blood pressure
cortisol
adrenal cortex, steroid, stress hormone, increases gluconeogenesis in liver, increases blood glucose levels, stimulates fat breakdown
testosterone
gonads, steroid, secondary sex characteristics, and closing of epiphyseal plates
estrogen
gonads, steroids, stimulates female sex organs, causes LH surge in menstruation
prgesterone
gonads, steroid, stimulates growth and maintenance of uterus during pregnancy
T3 & T4
thyroid, tyrosine (lipid soluble), increases basal metabolic rate
epinephrine and norepinephrine
adrenal medulla, tyrosine (water soluble), causes responses almost identical to a sympathetic nervous system (fight or flight)
