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Biology Session 3

STUDY
PLAY
Draw a kidney, label the following, and describe the function of each:

A. Nephron
B. Cortex
C. Medulla
D. Renal Pelvis
E. Ureter
A. Nephron: Functional unit of the kidney
B. Cortex: (Hypotonic) Contains the renal corpuscles and the renal tubules except for parts of the loop of Henle which descend into the renal medulla.
C. Medulla: (Hypertonic) Contains the structures of the nephrons responsible for maintaining the salt and water balance of the blood, including the loop of Henle and the collecting tubule. The renal medulla is hypertonic to the filtrate in the nephron and aids in the reabsorption of water.
D. Renal Pelvis: The major function of the renal pelvis is to act as a funnel for urine flowing to the ureter.
E. Ureter: Propel urine from the kidneys to the urinary bladder.
Draw a nephron, label the following, and describe the function of each:

A. Glomerulus
B. Bowman's Capsule
C. Proximal Convoluted Tubule
D. Descending Loop of Henle
E. Ascending Loop of Henle
F. Juxtaglomerular Apparatus
G. Distal Convoluted Tubule
H. Collecting Duct
I. Renal Pelvis
J. Ureter
A. Glomerulus: Capillary bed of the nephron. The amount of filtrate is related to the hydrostatic pressure of the glomerulus.
B. Bowman's Capsule: Hydrostratic pressure forces some plasma into the Bowman's Capsule. Blood cells and large proteins are prevented from entering. The fluid that enters is called the filtrate.
C. Proximal Convoluted Tubule: Most reabsorption takes place here (nearly all glucose, most proteins, and other solutes). Drugs, toxins, and other solutes are secreted into the filtrate. Osmolarity does not change.
D. Descending Loop of Henle: As filtrate descends into the medulla, water passively diffuses out of the loop and into the medulla. The descending loop has low permeability to salt, so filtrate osmolarity goes up.
E. Ascending Loop of Henle: As the filtrate rises out of the medulla, salt diffuses out of the ascending loop, passively at first, then actively. The ascending loop is nearly impermeable to water.
F. Juxtaglomerular Apparatus: Monitors filtrate pressure in the distal tubule.
G. Distal Convoluted Tubule: Reabsorbs Na⁺, and Ca²⁺ while secreting K⁺, H⁺, and HCO₃⁻. Aldosterone acts on the distal tubule cells to increase sodium and potasssium membrane transport proteins. The net effect of the distal tubule is to lower the filtrate osmolarity.
H. Collecting Duct: Carries the filtrate into the highly osmotic medulla. The collecting duct is impermeable to water, but sensitive to ADH, which makes is permeable to water allowing it to passively diffuse into the medulla.
I. Renal Pelvis: funnel-like dilated proximal part of the ureter in the kidney. The major function of the renal pelvis is to act as a funnel for urine flowing to the ureter.
J. Ureter: propel urine from the kidneys to the urinary bladder.
Describe the interplay between: the juxtaglomerular apparatus, the renin-angiotensin pathway, aldosterone and the distal convoluted tubules of the kidney.
The JG apparatus monitors filtrate pressure in the distal tubule. Cells in the JG apparatus secrete the enzyme renin. Renin initiates a regulatory cascade producing angiotensin I, II, and III, which ultimately stimulates the adrenal cortex to secrete aldosterone. Aldosterone acts on the distal tubule, stimulating the formation of membrane proteins that absorb sodium and secrete potassium.
What is the function of Aldosterone and ADH?
Aldosterone: Acts on the distal tubule causing an increase in sodium uptake. 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.

ADH: (Always digging holes) 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 thru 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.
In what phase are neurons?
What do neurons depend on for energy?
Do they require insulin for glucose uptake?
What is their storage capability for glycogen and oxygen?
1) They are frozen in G₀ phase (unable to divide)
2) They depend ENTIRELY on glucose for energy
3) They don't require insulin for glucose uptake
4) They have very low glycogen and oxygen storage capability and thus require high perfusion.
Draw a neuron, label the following, and describe their function:
A. dendrites
B. cell body
C. nucleus
D. axon hillock
E. terminal button
F. synapse
G. Schwann cells
H. nodes of Ranvier
A. dendrites: branched projections of a neuron that act to conduct the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project.
B. cell body: The soma is where the signals from the dendrites are joined and passed on. The soma and the nucleus do not play an active role in the transmission of the neural signal. Instead, these two structures serve to maintain the cell and keep the neuron functional.
C. nucleus: maintain the cell and keep the neuron functional.
D. axon hillock: Both inhibitory postsynaptic potentials (IPSPs) and excitatory postsynaptic potentials (EPSPs) are summed in the axon hillock and once a triggering threshold is exceeded, an action potential propagates through the rest of the axon. The triggering is due to positive feedback between highly crowded voltage-gated sodium channels, which are present at the critical density at the axon hillock (and nodes of ranvier) but not in the soma.
E. terminal button: The terminal buttons are located at the end of the neuron and are responsible for sending the signal on to other neurons. At the end of the terminal button is a gap known as a synapse.
F. synapse: a structure that permits a neuron to pass an electrical or chemical signal to another cell (neural or otherwise).
G. Schwann cells: Schwann cells form a fatty material called myelin to insulate the axons in the peripheral nervous system. This method decreases membrane capacitance in the axon, thus, allowing saltatory conduction. Non-myelinating Schwann cells are involved in maintenance of axons and are crucial for neuronal survival.
H. Nodes of Ranvier: Allow nutrients and waste products to enter/leave the neurone. Allow nerve impulses to move along the neurone through a process of de-polarisation and re-polarisation of the nerve membrane. Saltatory conduction.
What is the resting potential and its value?
-70mV. This is the potential difference (i.e., voltage) across the membrane when an action potential is NOT present.

The resting potential is established mainly by an equilibrium between passive diffusion of ions across the membrane and the Na/K pump. As the electrochemical gradient of Na becomes greater, the force pushing the Na back into the cell also increases. The rate at which Na passively diffuses back into the cell increases until it equals the rate at which it is being pumped out of the cell. The same thing happens for potassium. When all rates reach equilibrium, the inside of the membrane has a negative potential difference called the resting potential.
What is the 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.

The resting potential is established mainly by an equilibrium between passive diffusion of ions across the membrane and the Na/K pump. As the electrochemical gradient of Na becomes greater, the force pushing the Na back into the cell also increases. The rate at which Na passively diffuses back into the cell increases until it equals the rate at which it is being pumped out of the cell. The same thing happens for potassium. When all rates reach equilibrium, the inside of the membrane has a negative potential difference called the resting potential.

Remember: I always want 2K.
What are 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.
Describe depolarization and what allows it to happen.
The opening of the voltage-gated sodium channels causes a sudden spike in the membrane potential, from -70mV to somewhere around +40mV. This process is referred to as depolarization.

Remember: Voltage-gated sodium channels allow sodium into the cell.
What is threshold potential and its approximate value?
This is the minimum stimulus that must be exerted upon the membrane to initiate the full action potential. It is around -55mV. If a stimulus depolarizes the membrane above this threshold, the entire action potential will follow. If not, the membrane potential will return to -70mV.
What are Voltage-Gated Potassium Channels and how do they work?
These are 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 the membrane potential caused by depolarization. Just before maximum depolarization is reached, the Na channels begin to close and the K channels begin to open.
How is the cell repolarized?
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 -70mV, and is referred to as "repolarization."
What is Hyperpolarization?
The potassium channels are somewhat slow to close as the membrane potential approaches -70mV. Thus, the membrane actually dips to around -90mV before gradually returning to the resting potential.
What is the absolute refractory period and the relative refractory period? Why does it take a stronger than normal stimulus to cause an action potential during the relative refractory period?
The absolute refractory period is the interval during which a second action potential absolutely cannot be initiated, no matter how large a stimulus is applied.
The relative refractory period is the interval immediately following the absolute refractory period during which initiation of a second action potential is inhibited but not impossible.

The absolute refractory period coincides with nearly the entire duration of the action potential. In neurons, it is caused by the inactivation of the Na+ channels that originally opened to depolarize the membrane. These channels remain inactivated until the membrane hyperpolarizes. The channels then close, de-inactivate, and regain their ability to open in response to stimulus.

The relative refractory period immediately follows the absolute. As voltage-gated potassium channels open to terminate the action potential by repolarizing the membrane, the potassium conductance of the membrane increases dramatically. K+ ions moving out of the cell bring the membrane potential closer to the equilibrium potential for potassium. This causes brief hyperpolarization of the membrane, that is, the membrane potential becomes transiently more negative than the normal resting potential. Until the potassium conductance returns to the resting value, a greater stimulus will be required to reach the initiation threshold for a second depolarization. The return to the equilibrium resting potential marks the end of the relative refractory period.
What is an electrical synapse?
They are uncommon. They are composes of gap junctions between cells. Cardiac muscle, visceral smooth muscle, and a very few neurons in the CNS contain electrical synapses. Since they don't involve diffusion of chemicals, they transmit signals much faster than chemical synapses and in both directions.
Describe a chemical synapse and include 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: Ca ions, calcium channels, neurotransmitter, neurotransmitter bundles, exocytosis, Brownian motion, post synaptic membrane and protein receptors.
A chemical synapse is a more common synapse. It is unidirectional. In a chemical synapse, small vesicles filled with neurotransmitter rest just inside the presynaptic membrane. The membrane near the synapse contains an unusually large number of Ca voltage gated channels. When an AP arrives at a synapse, these channels are activated allowing Ca to flow into the cell. In a mechanism not completely understood, the sudden influx of calcium ions causes some of the neurotransmitter vesicles to be released through an exocytotic process into the synaptic cleft. The neurotransmitter diffuses across the synaptic cleft via brownian motion. The postsynaptic membrane contains neurotransmitter receptor proteins. When the neurotransmitter attaches to the receptor proteins, the postsynaptic membrane becomes more permeable to ions. Ions move across the postsynaptic membrane through proteins, completing the transfer of the neural impulse.
How is the signal at the post synaptic membrane stopped?
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.
What do the terms agonist and antagonist mean?
Agonist: activator
Antagonist: inhibitor
What would an acetylcholinesterase antagonist be used for?
To increase levels of acetylcholine, a neurotransmitter, in the brain. To prevent an acetylcholinesterase breaking down acetylcholine in the brain that nerve cells use to communicate and thus temporarily improve or stabilise symptoms.
What are the three major types of neural support cells?
These cells are not neruons that conduct potential, butcells in the nervous system that provide support to neurons.

Schwann cells (oligodendricytes in the CNS) produce myelin which increases speed with which the AP moves down the axon.

Cells lining the cerebrospinal fluid cavities (ependymal cells)

Structural support cells (astrocytes)
What are the three different types of neurons? What do they do?
Sensory (Afferent) Neurons: receive sensory signals form sensory cells
Motor (Efferent) Neurons: carry signals to a muscle or gland to respond to the stimulus
Interneurons: connect afferent and efferent neurons; transfer and process signals (includes the brain and 90% of all other neurons).
Describe the organization of the nervous system and the various branches.
CNS: The brain and spinal chord; interneurons only. No subdivisions.
PNS: All neurons outside of the CNS; both sensory and motor neurons. Contains "somatic" and "autonomic" subdivisions.

⋅Somatic: VOLUNTARY; innervates skeletal muscle. Contains both Sensory and Motor subdivisions. Neurons synapse directly on their effectors and use acetylcholine for their neurotransmitter. (No ganglia)
⋅Autonomic: INVOLUNTARY; innervates cardiac muscle, smooth muscle and 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 to and poorly localized.
⋅⋅Motor: The motor subdivision of the autonomic nervous system contains the "sympathetic" and "parasympathetic" divisions

⋅⋅⋅Sympathetic: "Fight or Flight." Cell bodies located far from the effectors. Neurotransmitters: acetylcholine at the ganglia, norepinephrine at the effector. The cell bodies of sympathetic postganglionic neurons lie far from their effectors.
⋅⋅⋅Parasympathetic: "Rest and Digest." Cell bodies located very close to, or inside, the effector. Neurotransmitters: acetylcholine ONLY, at both the ganglia AND the effector. The cell bodies of the parasympathetic postganglionic neurons lie in ganglia inside or near their effectors.
What neurotransmitter is used at the ganglia (if applicable) and the effector of the somatic and autonomic nervous systems?
Somatic: Acetylcholine (effector, no ganglia)
Autonomic→Motor→Sympathetic: acetylcholine (ganglia), norepinephrine and epinephrine (effector)
Autonomic→Motor→Parasympathetic: acetylcholine (ganglia) and acetylcholine (effector)
Describe the effect of parasympathetic and sympathetic innervation on:

1) Pupil constriction
2) Heart rate
3) Blood Pressure
4) Blood flow to skeletal muscle
5) Blood flow to digestive organs
6) Blood flow to the brain
7) Blood flow to the skin
1) Pupil constriction: Parasympathetic
2) Heart rate: Sympathetic
3) Blood Pressure: Sympathetic
4) Blood flow to skeletal muscle: Sympathetic
5) Blood flow to digestive organs: Parasympathetic
6) Blood flow to the brain:
7) Blood flow to the skin: Sympathetic constricts blood to skin
Describe the relative sensitivity of rods and cones and what they perceive (color, black and white).
Rods=Highly sensitive, perceive black and white only.
Cones=Less sensitive, perceive color.
What type of lens does the eye have and what type of image is formed?
Converging lens, always produces a PRI Image.
What determines if a person is near or far sighted?
Where is the image formed in both cases?
What type of lens is required to correct each condition?
Nearsighted: See close don't see far (image converges before retina)
Farsighted: See far don't see close (image converges after retina)

The lens assumes a large curvature (short focal length) to bring nearby objects into focus and a flatter shape (long focal length) to bring a distant object into focus.

In far-sighted a weakening of the ciliary muscles and/or the decreased flexibility of the lens leads to a lens that can no longer assume the high curvature that is required to view nearby objects.

In near-sighted a larger curvature lens causes distant objects to converge before the retina. More likely, it is usually the result of a bulging cornea or an elongated eyeball.

Farsighted is corrected using a converging lens (convex). Nearsighted is corrected using a diverging lens (concave)
What happens as you attempt to focus on a book very near your face?
Do the ciliary muscles contract or relax?
Does the curvature of the lens increase or decrease?
Does the focal point move outward or inward (i.e., increase or decrease)?
Does the power of the eye increase or decrease?
The ciliary muscles contract.
Thus increasing the curvature of the lens.
The focal point is moved inward thus decreasing the focal point.
The power increases. P=1/f
What is included in the outer ear?
What is included in the middle ear?
What is included in the inner ear?
Draw a cross section of the cochlea showing the three compartments and the Organ of Corti.
Outer ear: includes the pinna and auditory canal
Middle ear: includes the tympanic membrane and the malleus, incus, and stapes.
Inner ear: includes the cochlea, semicircular canals, and vestibulocochlear nerve.
Are the hair cells of the Organ of Corti more like microvilli or cilia?
Microvilli even though they are called stereocilia.
What do exocrine glands target and release?
What do endocrine glands target and release?
Exocrine glands release ENZYMES or other LIQUIDS into the external environment (digestive tract and epithelial-lined orifices; release sweat, oil, mucous, digestive enzymes, etc.)

Endocrine glands release HORMONES into the internal fluids of the body (blood, lymph, etc.)
Compared to the nervous system what is the overall impact of the endocrine system?
It is slow, indirect, and long lasting.
List the Peptide hormones, its function, and what organ secretes it.
Are peptide hormones water or lipid soluble?
Peptide hormones are water soluble

Anterior Pituitary:
→hGH: stimulates growth throughout the body
→FSH: Growth of follicles during the menstrual cycle in females, sperm production
→LH: Surge in LH causes ovulation; stimulates estrogen and testosterone secretion
→ACTH adrenocorticotropin: stimulates the adrenal cortex to release stress hormones call "glucocorticoids"
→TSH thyroid stimulating hormone: stimulates release of T₃ and T₄ in the thyroid
→Prolactin: Promotes milk production

Posterior Pituitary:
→ADH: causes the collecting duct of the kidney to become highly permeable to water; increase blood pressure and concentrating the urine.
→oxytocin: Milk ejection and uterine contraction

Parathyroid:
→PTH parathyroid hormone: Raises blood calcium by stimulating proliferation of osteoclasts, uptake of Ca in the gut, and reabsorption of Ca in the kidney

Pancreas:
→Glucagon: increases gluconeogenesis, increasing glucose blood level
→Insulin (also releases several digestive enzymes, but this is an exocrine function): Promotes entry of glucose into cells, decreasing glucose blood level

Thyroid:
→Calcitonin: Lowers blood calcium by inhibiting osteoclasts
(thyroid also releases T₃ and T₄ but these are lipid soluble tyrosines)

Embryo/Placenta:
→hCG: prevents degeneration of the corpus luteum, stimulates corpus luteum to grow and release estrogen and progesterone
The anterior and posterior pituitary are both regulated by "_________ stimulating/releasing" hormones from the _________.
The anterior and posterior pituitary are both regulated by "hypothalamic stimulating/releasing" hormones from the hypthalamus.
List the Steroid hormones, its function, and what organ secretes it.
Are steroid hormones water or lipid soluble?
Steroid hormones are lipid soluble; ALL steroids are cholesterol derivatives

Adrenal Cortex:
→Cortisol: a stress hormone; increases gluconeogenesis in the liver and thus blood glucose levels; stimulates fat breakdown. Increases blood levels of carbohydrates, proteins, and fats
→Aldosterone: Reduces Na⁺ excretion; increases K⁺ excretion at the distal convoluted tubule and the collecting duct; net increase in salts in the plasma, increasing osmotic potential and subsequently raises blood pressure

Gonads:
→Estrogen: Growth of mother sex organs; causes LH surge in menstruation
→Progesterone: Prepares and maintains uterus for pregnancy
→Testosterone: Secondary sex characteristics; closing of epiphyseal plates
List the Tyrosine hormones, its function, and what organ secretes it.
Are Tyrosine hormones water or lipid soluble?
Tyrosines are either lipid or water soluble depending on the hormone

Thyroid:
→T₃ (lipid soluble): Increases basal metabolic rate
→T₄ (lipid soluble): Increases basal metabolic rate
(Thyroid also produces calcitonin which is peptide water soluble hormone)

Adrenal Medulla:
→Epinephrine (water-soluble): Stimulates sympathetic actions
→Norepinephrine (water-soluble): Stimulates sympathetic actions
How are lipid-soluble proteins and water-soluble proteins transported?
Lipid soluble hormones REQUIRE a protein carrier or a micelle/vesicle.

Peptide hormones are water soluble and dissolve readily in the blood.
What is the target for lipid-soluble and peptide hormones?
Lipid soluble hormones act almost exclusively by binding to a receptor on or inside the nucleus and influence transcription.

Peptide hormones, by contrast, act at a variety of cell locations.
Describe the membrane permeability for lipid-soluble and peptide hormones.
Lipid-soluble hormones diffuse easily thru the lipid center of the membrane and thus DO NOT require a cell membrane receptor. They still REQUIRE a receptor eventually when they act inside the cell.

Peptide hormones are hydrophylic and cannot dissolve thru the membrane; thus they REQUIRE a membrane receptor.
How does the second messenger system work? Describe the function of G-proteins and how they interact with other signaling molecules.
Second messenger systems usually occur via a cascade. In a cascade, one hormone activates another hormone, then another, with the size of the reaction and the number of molecules involved increasing with each step.

G-proteins commonly initiate second messenger systems. A G-protein is attached to the receptor protein along the inside of the postsynaptic membrane. When the receptor is stimulated by a neurotransmitter, part of the G-protein, called the α-subunit, breaks free. The α-subunit may:

1. activate separate specific ion channels
2. activate a second messenger (i.e. cyclic AMP or cyclic GMP)
3. activate intracellular enzymes
4. activate gene transcription
How do hormones always act (with regards to homeostasis)?
Hormones always act to return to homeostatic, or "normal" conditions. They never cause a drift away from normal.