Today is Tuesday,March 24th, 2015

Pre-Class:Starting from cells, what are the levels of organization within the

general animal body plan?

In This Lesson:Animal

Physiology(Lesson 3 of 3)

Today’s Agenda

• Those special feelings.– Endocrine System [reminder]

• Anxiety.– Nervous System

• Pee.– Excretory System

• Where is this in my book?– Chapters 45, 48-49, and 44, respectively.

By the end of this lesson…

• You should be able to identify at least two examples for how hormones regulate homeostasis via the endocrine system.

• You should be able to describe how a body reacts to a stimulus at the neuronal level, including a description of the depolarization/hyperpolarization/repolarization events within an action potential.

• You should be able to identify the parts of the kidney and discuss the adaptations and evolution behind its structures and functions.

Organization of Body Plans

• Animal body plans are organized in tiers:– Cells– Tissues (four main types)• Epithelial – lining/covering tissue.• Connective – supportive tissue (tendons and ligaments,

bone, collagen, adipose).• Muscle – skeletal, smooth, cardiac muscle.• Nervous – neurons and supporting glial cells.

– Blood is sometimes also considered a tissue.

– Organs– Organ Systems [what this lesson mainly concerns]

The Endocrine System

• Remember the endocrine system?– You know…signal transduction pathways?– Hormones?

• Here’s a reminder.

Cell CommunicationReminder

• Long Distance Signaling:– Hormones travel through

blood in animals; through plasmodesmata in plants.

– Plant hormones may also diffuse through the air.• Ethylene gas – the stuff that

comes from a ripening fruit – is an example of an air hormone.

The Signal Transduction PathwayThree Steps – Reminder

• Step 1: Reception:– The cell needs to receive a chemical signal (a ligand).• A ligand is any small molecule that binds to a larger one.• The larger molecule is usually a receptor protein.

The Signal Transduction PathwayThree Steps – Reminder

• Step 2: Transduction– The membrane receptor protein then activates one or more

other molecules to carry the signal deeper into the cell.– These other molecules are called relay molecules and may be

involved in a phosphorylation cascade (more later).

The Signal Transduction PathwayThree Steps – Reminder

• Step 3: Response– The cell does something.– This could be the activation of a gene, change in the

cytoskeleton, activity of an enzyme, or just about anything else.

Signal Transduction PathwaysReminder

• If it helps, think of signal transduction pathways like what happens when you get a text message:– Reception = Your phone vibrates or dings.– Transduction = You unlock the phone and read the

message.– Response = You write back, smile, cry, or throw the

phone against the wall.

The Two Systems

• As you saw in this lesson’s agenda, we’re going to talk about two signaling systems in the body:– The nervous system provides fast but usually short-

term responses.• The nervous system uses neurotransmitters.

– The endocrine system provides slower but longer-lasting effects.• The endocrine system uses hormones.

• Each system, especially the endocrine, uses chemical signals (at least in part) to function.

Chemical Signals

• Chemical signals fall into two general categories:– Lipid-based hormones are:• Insoluble, hydrophobic, and can cross cell membranes.• Able to turn on genes in the nucleus and act as

transcription factors.

– Protein-based hormones are:• Soluble, hydrophilic, and cannot cross cell membranes.• Able to bind to receptor proteins in the cell membrane.• Can trigger the second messenger pathway.

Action of Lipid Hormones

http://upload.wikimedia.org/wikipedia/commons/a/a9/1803_Binding_of_Lipid-Soluble_Hormones.jpg

Action of Protein Hormones

http://www.vce.bioninja.com.au/_Media/protein_hormone_med.jpeg

The Second Messenger System• Remember G protein-linked receptors?• Or what about tyrosine-kinase receptors?– Those are examples of second messenger systems.

• Second messenger systems allow for magnification of the signal and faster responses.

http://upload.wikimedia.org/wikipedia/en/b/b9/Second_Messenger_System.jpg

Why signal?

• Before we get into the truly new stuff, remember that cell signaling is often done to either:– Maintain homeostasis.– Regulate processes.

• DO NOT FORGET FEEDBACK LOOPS!

Nervous and Endocrine: The Link

• Located inside the brain is the “master nerve control system” of the body called the hypothalamus.– It receives signals from

throughout the body via the nervous system.

– It regulates hormone release from the pituitary gland, which itself is known as the “master gland.”

• The pituitary gland releases tropic hormones that regulate other glands.

Hypothalamus

Pituitary

Posterior Pituitary

Anterior Pituitary

Endocrine Glands

Tropic Hormones and TargetsHypothalamus

Anterior Pituitary

Posterior Pituitary

Thyroid-Stimulating Hormone (TSH)

Thyroid Gland

Adrenocorticotropic

Hormone (ACTH)

Adrenal Cortex

Grow

th H

orm

one

(GH)

Bone and Muscle

Gonadotropic HormonesFollicle-Stimulating

Hormone (FSH)Luteinizing Hormone (LH)

Testes Ovaries

Prolactin (PRL)

Mammary Glands

Melanocyte-Stimulating

Hormone (MSH)

Melanocyte

Oxytocin

Uterus Muscle

Antidiuretic Hormone (ADH) Kidney

Tubules

Hormone Regulation Case-in-PointThe Thyroid

• The hypothalamus releases TRH (TSH-releasing hormone), which is received by the anterior pituitary.

• The anterior pituitary releases TSH (thyroid-stimulating hormone), which is received by the thyroid.

• The thyroid produces thyroxine hormones (T3/T4), which regulate:– Bone/muscle development.– Mental development.– Blood pressure and heart rate.– Digestion.– Reproduction.

Hormone Regulation Case-in-PointThe Thyroid

• Interestingly, without iodine, the thyroid will enlarge in an effort to produce thyroxine.

• This causes a condition known as goiter:

Hormone Regulation: Case-in-PointMenstruation

Hypothala

mus releas

es

GnRH – Gonadotro

pin-

Releasing H

ormone.

Anterior pituitary releases FSH and LH.

Ovary releases estrogen to

build up the endometrium

(uterine lining).

[OVULATION]

Corpus luteum releases

progesterone to maintain

the endometrium.

PREGNANCY?

No – corpus luteum breaks down and

progesterone drops.

Yes – embryo produces human chorionic

gonadotropin (hCG).

Corpus luteum keeps

making progesterone to

maintain the endometrium.

Menstrual Cycle

Hormone Regulation: Case-in-Point

• This is such a well-known hormone-regulated homeostatic system that you should just know it:– When you eat a meal, blood glucose levels rise.– In response, beta cells in the pancreas release insulin

(hormone), which prompts cells to take up glucose.• So blood-sugar falls, thus a negative feedback loop.

– If blood sugar is low, alpha cells in the pancreas release glucagon (hormone), which causes the liver to release glucose to the blood.• Glucose is stored as glycogen.• Still negative feedback.

Diabetes Mellitus

• Diabetes has two types:– Type I (“childhood diabetes” because it’s inherited)– Type II (“adult-onset diabetes” because it’s usually a product

of lifestyle, though kids can get it – scary!)• Type I is characterized by destruction of beta cells.– It’s an autoimmune disease.

• Type II is characterized by reduced numbers of a membrane glucose transporter called GLUT4.– Sedentary lifestyles and high sugar (thus prompting lots of

insulin secretion) seem to cause a resistance/tolerance to insulin, eventually resulting in “exhausted” beta cells.

Diabetes Mellitus

• Either way, treatment is generally the introduction of insulin. It could be:– Pig insulin, which is modified by one amino acid to

be human insulin.• Expensive and not so common anymore.

– Insulin analogs made by E. coli through transformation with a vector containing the human insulin gene.• More common.

Hormone Regulation: Case-in-Point

• Here’s another hormone-driven mechanism for homeostasis that’s good to know:– Calcitonin (hormone) is released by the thyroid

gland and reduces blood Ca2+ levels.– Parathyroid hormone (PTH) is released by the

parathyroid glands and causes Ca2+ levels to rise.

Are you nervous?

• So now we get to the endocrine counterpart: the nervous system.

• The nervous system provides animals with an ability to:– Move.– Sense stimuli.– “Reset” quickly.

The Nervous System

• The nervous system is divided into two components:– The Central Nervous System (CNS) is composed of

the brain and spinal cord.– The Peripheral Nervous System (PNS):• The PNS has sensory neurons and motor neurons, and

is divided into:– The sensory-somatic nervous system.– The autonomic nervous system.

• More on these later…

Afferent and Efferent

• Afferent neurons carry signals to the CNS.– So they’re generally sensory neurons.– They are positioned on the back side of the spinal cord.

• Efferent neurons carry signal away from the CNS.– So they’re generally motor neurons.– They are positioned on the chest side of the spinal cord.

• Here’s your pneumonic device:– SAME DAVE• Sensory afferent; motor efferent.• Dorsal afferent; ventral efferent.

Spinal Cord Vertebra Cross-Section

http://www.unm.edu/~jimmy/spinal_neurons.jpg

The Nervous System: Cell Types

• There are two nervous system cell types:– Neurons conduct nerve signals.– Neuroglia or glial cells support and protect neurons.• Not-so-fun-fact: When they become cancerous, it’s known

as a glioma.

Neuron Parts

• Draw it like you mean it! Start of signal

Signal direction

Dendrites

Cell body(or soma)

Axon

Myelin sheath

Synaptic terminal

SynapseAxon

hillock

Neuron Parts• The cell body is…well…the cell body.• Dendrites (“dendr-” means “tree”) are the branches on the cell

body that generally receive signals.• The axon is a long extension of the cell body that carries a

signal to another cell.– The start of the axon is the axon hillock.– On the axon is the myelin sheath made by glial cells that helps

transmit the signal faster.• The synaptic terminal (or axon terminal) is the end of the axon.• The synapse (or synaptic cleft) is the space between the

synaptic terminal and the next cell.• Signal Path = Dendrites Cell Body Axon

Aside: Long Cells

• Neurons are generally the largest cells in animals’ bodies.– In blue whales, the largest neuron is

between 10 and 30 meters long.– In giraffes, it’s 5 meters long.– In humans, it’s 1-2 meters long.• It’s the sciatic nerve. Remember that?

• Still, the nervous system can function in 1 millisecond.

Sciatic Nerve

http://www.acticare.com/conditions/images/sciatic_nerve2.jpg http://www.ilizarov.org/new1/upload/8142007102508AM3.JPG

Okay, we better practice this stuff…

• …with a POGIL!– Neuron Structure POGIL

The Sodium-Potassium Pump

• Na-K Pump animation

Information ProcessingNervous system as a whole

• There are three general steps in the functioning of the nervous system:– Stimulation of a sensory neuron

• Like, seeing a baseball heading straight for your face.

– Integration• Transmission of a signal by an interneuron.• When your brain figures out it needs to move the

body.

– Action of an effector cell (like a motor neuron)• Your legs helping you to duck…• …or not. http://man-over-board.com/wp-content/uploads/2009/10/baseball-head.jpg

Information Movement

The Reflex Arc• The same pathway (sensory interneuron

motor), when a part of a reflex reaction, is called a reflex arc.– Note that the signal never goes to the brain; it just

goes to the spinal cord.

http://s1.hubimg.com/u/7527702_f520.jpg

Information ProcessingWithin one neuron

• We’re going to discuss this in great detail shortly.• A single neuron will pass a signal (known as an

action potential) from one end to the other.• Eventually, the signal hits the end of the neuron

(the synaptic terminal).• The signal is transmitted via neurotransmitters

between two neurons across the synapse.

Neurotransmitters• Neurotransmitters are secreted

at the synaptic cleft.– Yes, a chemical signal that has

followed an electrical signal.• Sometimes they open

membrane channels directly (ionotropic membrane receptors).

• Sometimes they indirectly stimulate another molecule – a second messenger – to open the channels (metabotropic membrane receptors).

Syn

aptic Cleft

Neurotra

nsmitt

er

Neurotransmitters

• Acetylcholine (ACh)– The most common neurotransmitter; activates muscle and plays a

role in attention and arousal.• Dopamine

– Controls reward/pleasure centers and associated emotions; lack of dopamine associated with Parkinson’s Disease.

• Serotonin– Mostly found in GI tract; regulates mood, sleep, appetite, etc.

• LSD and mescaline bind to serotonin/dopamine receptors.

• Epinephrine/Norepinephrine– Stimulates the sympathetic nervous system in the fight-or-flight

response. (also goes by “adrenaline” and “noradrenaline.”)http://www.benbest.com/science/anatmind/anatmd10.html

Neurotransmitters

• GABA (gamma-aminobutyric acid)– An inhibitory neurotransmitter that deactivates the post-

synaptic neuron.• Valium binds to GABA receptors to mimic the effect.

• Endorphins– Involved in pain relief.

• Opiates like heroin/morphine bind to similar receptors to mimic the effect…for a little while.

• Nitric oxide (NO) (gas)– Involved in blood vessel dilation and male sexual arousal.

• Viagra works by blocking the termination of NO release.• Hence the warning in those commercials about “unsafe drops in blood

pressure.”

EPSPs and IPSPs

• Did you catch that thing about “inhibitory” when I mentioned GABA?

• Sometimes action potentials cause one neuron to stimulate the next one.– That’s an EPSP (excitatory postsynaptic potential).

• Sometimes, like with GABA, an action potential inhibits the ability of the next neuron to fire.– That’s an IPSP (inhibitory postsynaptic potential).• They cause the neuron to become more negative.

The Nerve Impulse

• To set the scene for what we’re about to cover, keep the “environment” for these neurons in mind:– The inside of the cell is mostly negatively-charged.• Mostly inside: K+ and negative amino acids.

– The outside of the cell is mostly positively-charged.• Mostly outside: Na+ and Cl-.

• Key: Overall, the cell is more negatively-charged than its surroundings.

The Sodium-Potassium Pump

• The resting potential of the neuron is maintained by the sodium-potassium pump.

• We’ve talked about this before – back in Unit 3 – but here’s a reminder:– The Na/K pump moves three Na+ ions out of the cell and moves

two K+ ions in, in sequence.– This costs a whole lot of ATP.

• Aside from the pump, other channels allow K+ ions to freely diffuse out.

• The combined “leak” of K+ and net export of cations leads to a resting potential that is negative.– Remember that: K+ out = more negative cell.

The Nerve Impulse• Therefore, we can summarize the net charges of the

axon as negative inside and positive outside.• This is thus a polarized membrane carrying an

actual voltage.– Specifically, this is an electrochemical gradient because

you have imbalanced ions.

Axon

– – – – – – – – – – – –+ + + + + + + + + + + +

+ + + + + + + + + + + +– – – – – – – – – – – –

The Nerve Impulse• The neuron has a resting potential of approximately -70

mV.– That’s millivolts, so you can’t electrocute people with your head.

Sorry.• Now for the nerve impulse – the action potential,

described in these two slides in summary.1. Na+ channels open and Na+ diffuses into the cell, making

it positive in that location.

– – – – – – – – – – – –+ + + + + + + + + + + +

+ + + + + + + + + + + +– – – – – – – – – – – –

Na+

Na+

–

–Axon

The Nerve Impulse2. The influx of Na+ cations changes the membrane potential

of the neuron to positive as the charges balance.– The action potential travels down the axon as a moving

depolarization.– During transmission of an action potential, the membrane

potential can reach as high as +35 mV.

3. After transmission, the neuron “resets” to -70 mV.– This occurs as other cations flow out of the cell.

– – – – – – – – – – – –+ + + + + + + + + + + +

+ + + + + + + + + + + +– – – – – – – – – – – –

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

Axon

Action Potential

https://upload.wikimedia.org/wikipedia/commons/9/95/Action_Potential.gif

Neuron Signal Summary

• Before we look in detail, remember this summary:– Start with a negative membrane potential (-70 mV).– Influx of cations depolarizes the neuron all the way up

to a positive membrane potential (+35 mV).– Efflux of cations re-polarizes the neuron (back to -70

mV) and then goes a little further (down to -90 mV).– The neuron resets to the resting potential (-70 mV).

• Or, in an image (that you should sketch since we’re going to add labels)…

Action Potential Summary Image

https://faculty.washington.edu/chudler/ap3.gif

Mem

bran

e Po

tenti

al

Action Potential: Depolarization

• A stimulus reaches a neuron and causes some Na+ channels to open, letting in sodium ions.– The channels that open are ligand-gated or stretch-gated.– The resting potential of the cell becomes less negative.

• For example, it may go from -70 mV to -60 mV.

• The opening of the first channels may be strong enough to reach the threshold, which in mammals is about -55 mV.– If -55 mV is reached, the neuron “fires.”– If -55 mV is not reached, the neuron doesn’t.– This is known as the “all-or-nothing” response.

Quick Note: Ligand vs. Stretch

• Did you catch that line about a stimulus opening either ligand-gated or stretch-gated ion channels?

• As you might guess…– Ligand-gated channels respond to ligands.• These could be signals from another nerve or maybe a gland.

– Stretch-gated channels respond to mechanical stimulation, like the stretch of a nearby muscle.• Which explains that weird reflex thing the doctor does to

your knee.

Action Potential: Rising Phase

• Assuming the threshold is reached, voltage-gated ion channels open.– They are so named because they open in response to

a change in voltage (in this case positive change).– Since the opening of some Na+ channels leads to the

opening of more Na+ channels, this is an example of positive feedback.

• The opening of voltage-gated sodium ion channels leads to depolarization of the neuron and the membrane potential climbs rapidly.

Action Potential: Falling Phase

• Eventually, voltage-gated Na+ channels become inactivated due to a conformational change and Na+ stops coming in.– By this point, the voltage has reached around +35 mV.

• Key: While the Na+ influx was occurring, K+ channels were also opening (just more slowly).

• By the time Na+ channels have closed, K+ channels have fully opened.

• K+ diffuses out of the cell, reversing the depolarization of the cell (the voltage goes back to negative).

Action Potential: Refractory Period

• K+ channels get a little carried away and bring the membrane potential down past the resting potential of -70 mV.

• It may go as low as -90 mV or more.– This is known as the undershoot.

• The time spent in undershoot is known as the refractory period, and the neuron cannot fire during this time.– Thus allowing the neuron to reset.– It also prevents the action potential from going backward.

Action Potential Summary Image

https://faculty.washington.edu/chudler/ap3.gif

Mem

bran

e Po

tenti

al

Action Potential: Summary Slide• Just to be clear now that we have all the details:– If the stimulus reaches a threshold, sodium channels open

and sodium comes in.• Sodium channels open rapidly.• Membrane potential rises into the positive range.

– Sodium channels close as potassium channels open.• Potassium channels open slowly.• Membrane potential begins to fall back to the negative range.

– Membrane potential undershoots resting potential before potassium channels close, entering the refractory period.

– The neuron returns to resting potential.• Voltage-Gated Ion Channel & Nerve Impulse animation!

Another Summary Image

http://howmed.net/wp-content/uploads/2010/09/action-potential.bmp

Here’s the thing…

• Remember when we said neurons can be really long?

• This whole process is really fast, but what if we need to make it faster?– Here’s where the myelin sheath comes in.

• Glial cells make myelin, an electrically-insulating material made out of lipids and proteins.– Schwann cells make myelin in the PNS.– Oligodendrocytes make myelin in the CNS.

• Fun fact: Myelin is white, thus, “white matter.”

Action of the Myelin Sheath

• The spaces between the myelin molecules are called nodes of Ranvier.

• Instead of having to travel down the full length of the axon, action potentials can hop from node to node.– This is called saltatory conduction, and it speeds

up signal transmission from 5 m/sec to 150 m/sec.• Or 11 mph to 330 mph.

Start of signal

Signal direction

Saltatory Conduction

– – – – – – – – – – – –+ + + + + + + + + + + +

+ + + + + + + + + + + +– – – – – – – – – – – –

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

–+

–

+

– – – –+ + + + + + + + + + + +

– – – –

–++

–++

–++

–++

+ + + + + + + + + + + +– – – –

Myelinated Axon

Unmyelinated Axon

Myelin(from Schwann Cell or

Oligodendrocyte)

Myelin(from Schwann Cell or

Oligodendrocyte)

Myelin(from Schwann Cell or Oligodendrocyte)

Node of Ranvier Node of Ranvier Node of RanvierNode of Ranvier

Myelin-Related Diseases

• Adrenoleukodystrophy (ALD) and multiple sclerosis (MS) both involve the destruction of the myelin sheath.– You may know ALD from Lorenzo’s Oil.

Other Ways to Speed Conduction

• Like in electrical wires or plumbing, resistance goes up when the size of a wire or pipe goes down.

• Similarly, in axons, thicker axons mean faster conduction.– That makes sense, given how the longest neurons

tend to be the biggest.– Need I show you the sciatic nerve image again?

Finally…we reach the end of the axon…

• As you know, at the end of the neuron is the space between neurons called the synapse.

• Waiting just inside the edge of the neuron are synaptic vesicles containing neurotransmitter.

• When the action potential arrives, depolarization leads to the opening of Ca2+ (calcium ion) channels.

• The influx of calcium causes synaptic vesicles to bind to the terminal membrane and release neurotransmitter.– Or, in an image…

Neurotransmitter Release

http://www.cnsforum.com/content/pictures/imagebank/hirespng/vesicle_fusion.png

Repeating the process…

• The released neurotransmitter is taken up by the post-synaptic neuron via a ligand-gated ion channel.– That’s a channel that opens in response to a ligand

(signal molecule) like…a neurotransmitter.• The next neuron’s ion channels begin to open

just like we saw at the start of the process for the pre-synaptic neuron, carrying the signal forward.– Released neurotransmitters must be broken down to

prevent repeated signals.

Motor Neurons

• Alternatively (or eventually), the neurotransmitter may stimulate a motor neuron, which will stimulate a muscle.

• [Raise your hand]– There, you just stimulated a motor neuron to stimulate a

muscle.– Neurotransmitter is now being cleared to give you the

opportunity to put your hand down.• Motor neurons are also responsible for the twitch

reflex you feel when something’s painful.– You don’t even need to think about it. Literally.

Okay, we better practice this stuff…

• …with a POGIL!– Neuron Function POGIL

Postsynaptic Details

• There are two main ways that strong stimuli can ensure that the postsynaptic neuron is certain to reach threshold:– Temporal summation occurs when two EPSPs reach the

same synapse at virtually the same time.• This increases the stimulation.

– Spatial summation occurs when two EPSPs reach the same cell (but at different synapses) around the same time.

Nervous System Weaknesses

• It turns out that there are substances that can affect neurotransmitters or mimic their behavior.

• These may be used for good or…for evil.• Example substances that affect neuron function:– Gases: Nitrous oxide, carbon monoxide, Sarin gas.– Stimulants: Caffeine, nicotine, amphetamines.– Depressants: Quaaludes, barbiturates.– Opiates: Morphine, heroin.– Hallucinogens: LSD, mescaline.– Pharmaceuticals: Prozac, Zoloft, Paxil.

• Those last ones are called SSRIs, or selective serotonin reuptake inhibitors.• They’re types of antidepressants that keep more serotonin around.

Nervous System Weaknesses

• Some neurotoxins work by inhibiting acetylcholinesterase, an enzyme that breaks down…acetylcholine.– Remember competitive inhibition?– Examples include Sarin (yep), snake venom, and many

insecticides. Acetycholinesterase

active site is red.

Acetycholinesterase active site blocked by

green snake toxin.

Nerve Gas Case-in-Point• Sarin is a compound that prevents

acetylcholine from breaking down.• Repeated signals to muscles to

contract causes them to “lock up.”• Among other instances…– Sarin gas was supposedly used in 2013

during the Syrian civil war.• Death toll 322-1729.

– It was also used in 1995 Tokyo Subway attack.• Death toll 13.

http://upload.wikimedia.org/wikipedia/commons/1/18/Demonstration_cluster_bomb.jpghttp://upload.wikimedia.org/wikipedia/commons/4/4c/Sarin_test_rabbit.jpg

US “Honest John” Missile with Sarin gas “bomblets.” [1960]

Rabbit to detect Sarin gas leaks at Rocky Mtn. Arsenal, a

chemical weapons plant. [1970]

Neurons: The Big Picture

• Collectively, a bundle of neuron axons makes up a nerve.– Like the optic nerve, or really any of the 12 (13*) cranial

nerves. You get it.– A cluster of neurons/cell bodies in the PNS is called a ganglion

(plural: ganglia).• In the broad sense, neuron cell bodies make up the gray

matter found in the CNS.• White matter is made up of bundled axons.– White matter is found on the outside of the spinal cord and

the inside of the brain.• White as in the color of myelin, remember? Myelin is on the axons…

The Nervous System: The Big Picture• Not all of your body needs CNS stimulation.– Your heart, for example, beats completely on its own.• Indiana Jones and the Temple of Doom is actually a little

accurate.

http://images.amcnetworks.com/ifc.com/wp-content/uploads/2012/09/temple-heart-1.jpg

The Nervous System: The Big Picture

• The somatic nervous system is the part of the PNS that can be stimulated by the CNS.

• The autonomic nervous system is the part of the PNS that doesn’t need CNS stimulation.– The autonomic nervous system is further

subdivided into two parts:• The sympathetic nervous system.• The parasympathetic nervous system.

The Autonomic Nervous System

• The sympathetic nervous system is associated with “fight-or-flight” reflexes, arousal, and fast response.– Heart rate goes up, pupils dilate, digestion slows, bladder

muscles contract, ejaculations/vaginal contractions are promoted.

• The parasympathetic nervous system is associated with, well, the opposite.

• HOW TO REMEMBER:– In the words of my neuroscience professor Dr. Jinks:

• “The parasympathetic nervous system causes you to ‘rest and digest.’”

Nervous System Hierarchy

• Central Nervous System (CNS)• Peripheral Nervous System (PNS)– Sensory-Somatic Nervous System– Autonomic Nervous System• Sympathetic Nervous System• Parasympathetic Nervous System

At Long Last

• You have made it to the final topic in AP Biology.• At this point, you may feel like, well, like you

need to go pee…or take a refreshing poo.• Let’s talk about how you’d do that…at least, the

pee part of it.• It’s the excretory system!– Counterintuitive as it may sound, poo is part of the

digestive system, not the excretory system.

The Excretory System

• The excretory system is everything in your body that serves to remove waste and, in that way, maintain homeostasis.

• We’ll focus mainly on how you maintain water balance by peeing.– So as you can guess, this is going to

be a lot about kidneys and livers.– Anyone need to go to the bathroom?

Necessity: Why is this an issue?

• In short, we need excretory systems because we’re multicellular.– If you’re but a single cell,

you can just let waste diffuse out.

– If you’re multicellular, well, you could be poisoning your own cells, not to mention it’s too slow.

Necessity: Why is this an issue?

• As a result, we have evolved exchange systems for intake of gases and nutrients…– Your digestive and circulatory systems.

• …and for removal of wastes.– The excretory system.

• After all, digestion itself makes toxins.– The most important metabolic byproduct for our

study right now is nitrogen, which comes mainly from proteins (and a little from nucleic acids).

Nitrogenous Wastes

• Ammonia (NH3) is a very toxic byproduct.– It’s carcinogenic, crosses cell membranes very easily, and

ammonium ions (NH4+) interferes with oxidative

phosphorylation.– Key: The body will attempt to dilute and/or convert

ammonia before getting rid of it, depending on the organism’s typical environment.

• Let’s take a look at what some sample organisms will do when faced (hopefully not literally) with ammonia waste.– As we discuss them, keep in mind ammonia is only tolerable

in low concentrations and must be diluted if not converted.

Ammonia and You: A Love Hate Story

• Aquatic organisms can afford to lose water.– They simply dilute the ammonia with water and expel it.

• Terrestrial organisms need to conserve water.– They convert ammonia to urea, which is a less toxic form and

get rid of it.• Terrestrial egg-laying organisms also need to conserve

water, but they must deal with having an egg shell.– They convert ammonia to uric acid, which is almost

harmlessly toxic.– They either get rid of it or (inside eggs) simply leave it behind.

• Key: Ammonia conversion has a cost: energy.

Ammonia and You: A Love Hate Story

Waste Management

• If you’re a freshwater fish, you live in a hypotonic environment.– So water’s always coming in. Dilute the ammonia with

it and expel.• If you’re a land animal not inside an egg, you’re

gonna need to convert the ammonia to urea and get rid of it.– Let’s take a look at how the liver and kidney work in

tandem to accomplish this goal.

Liver + Kidney = Pee

• First, your liver will produce urea from metabolic byproducts.

• Urea flows in the blood to the kidneys, which:– Filter solutes out of the blood.– Resorb water.– Excrete waste as urine.• Urine is a combination of urea, salts, excess sugar, and

excess water.• Urine is also relatively concentrated, especially when

water is scarce.

Uric Acid Disposal

• For animals that lay eggs (except amphibians), there’s a bit of an issue, since the shell prevents removal of urea, which could build to a toxic concentration.

• Instead, they convert ammonia all the way to uric acid, which is not very soluble at all and thus not very toxic.– It just builds up in eggs of birds, reptiles, and

insects.

Uric Acid in Adults• Many adult animals that

came from eggs continue to excrete uric acid as adults.– Bird poop (also known as

guano) happens to be a mix of uric acid and feces – they poo and pee simultaneously from a single “vent.”• Hence the color…

http://www.skinnymoose.com/wildlifepro/files/2013/05/car-bird-poop.jpg

Back to Mammals and Kidneys

• As you can see from the generalized diagram to the right, kidneys provide the following functions in cooperation with neighboring blood vessels:– Filtration of waste solutes.– Reabsorption of needed solutes

and water.– Secretion of other waste solutes.– Excretion of concentrated urine

from the body.

Kidney Structure

• Let’s look more in depth at the structure of the kidney.

• A kidney is named like a brain and has two general regions:– The renal cortex (outside).– The renal medulla (inside).

• “Renal” is a stem word for kidney-related stuff.– Adrenaline, anyone?

Kidney Structure

• A kidney is actually a mass of around 1 million smaller “functional units” known as nephrons.– The nephrons function as a

group and each contribute to urine output.• The nephron is that structure

straddling the border between the renal cortex and medulla.

• Let’s draw a simple diagram.

Kidney Structure• The renal cortex features

the glomerulus and Bowman’s Capsule.

• Glomerulus– A ball of capillaries.

• Basically just a bunch o’ blood.

• Bowman’s Capsule– The surrounding kidney

structure into which blood filtrate is moved.

http://wps.pearsoncustom.com/wps/media/objects/5697/5834441/ebook/htm/0cc6e.htm?25.06

Kidney Structure• Loop of Henle– A U-shaped tube that

descends from the Bowman’s capsule into the medulla and then rises again into the cortex.

– Made of four parts:• Proximal tubule (near the

Bowman’s Capsule)• Descending limb• Ascending limb• Distal tubule (far from the

Bowman’s Capsule)http://wps.pearsoncustom.com/wps/media/objects/5697/5834441/ebook/htm/0cc6e.htm?25.06

The Loop of Henle

• The loop of Henle is involved in reabsorption of materials.

• Proximal tubule: [reabsorbed]– NaCl (active transport of Na+, diffusion by Cl-)– H2O

– C6H12O6

– HCO3- (bicarbonate)

• Descending limb: [reabsorbed]– H2O (through aquaporins)

The Loop of Henle

http://classes.midlandstech.edu/carterp/Courses/bio211/chap25/Slide18.GIF

The Loop of Henle

• Ascending limb: [reabsorbed]– NaCl

• Distal tubule: [reabsorbed]– Salts– H2O

– HCO3- (bicarbonate)

The Loop of Henle

http://classes.midlandstech.edu/carterp/Courses/bio211/chap25/Slide18.GIF

Wait a sec…

• Yes, the nephron is involved in a whole lot of reabsorption.

• As a sample test question, what kind of tissue do you suppose is involved in doing that reabsorption?– Yep, you’re right, epithelial tissue.

• For kidneys and intestines and other things, it’s often referred to as transport epithelium.

The Loop of Henle

• So what should you remember about the Loop of Henle?– It re-absorbs water and salts before they exit the body.

• Thus it helps in homeostasis and water balance.

• With that in mind, do you think the loop of Henle is larger or smaller in desert animals?

• What about in aquatic animals, like beavers or something?– Tell yo’ neighbor I said hi.– Then tell him/her what you think. You get it by now, right?

Animals’ Loops of Henle

http://www.answersingenesis.org/assets/images/articles/cm/v26/i3/rats.jpg

Merriam’s Kangaroo Rat’s Loop of Henle

http://www.bio.davidson.edu/Courses/anphys/1999/Chisholm/nephron1copy.wc2.jpg

I HAS A BIG LOOP OF HENLE AND

CONCENTRATED URINEZ

Kidney Structure• After the distal tubule, the

now-concentrated urine moves into the collecting duct, which pools the pee from neighboring nephrons.– Pools the pee like a summer

camp shallow end.

http://wps.pearsoncustom.com/wps/media/objects/5697/5834441/ebook/htm/0cc6e.htm?25.06

Excretory Sequence

• The collecting duct leads to the ureter, which connects to the bladder.

• Urine exits the bladder through the urethra, which leads to the end.– Hint hint…

Closure

• I’m going to eschew a closure now for all of us to take a breather and reflect on the fact that…

•WE JUST FINISHED ALL THE AP BIOLOGY NOTES!!!!!!1111– Did it really take me an entire semester to use the term

“eschew?”