Prelim 2 Biog1440 Flashcards
Temperature
A measure of the speed of the random motions of the atoms or molecules in a substance
Heat
The total energy that a substance possesses by virtue of the sum of random motions of its atoms or molecules
Most biochemical and physiological components are temperature…
Sensitive (ex. functional proteins become denatured and cannot function when it is too hot)
Q10
A quotient describing the sensitivity of a process to temperature (ex. how sensitive an enzyme is to temperature change)
Q10 Formula
Q10= R under(t+10 degrees C)/Runder(T)
Endotherms
Most of the heat in this organism comes from metabolism
Ectotherms
Temperature of the body is mostly dependent on the environment
Endotherms that regulate body temperature
Homeotherms are thermoregulating (e.g. birds/mammals)
Endotherms that don’t regulate body temperature
Non-thermoregulating endotherms (e.g. naked mole rat)
Ectotherms that regulate heat
Behavioral thermoregulators (e.g. moths pre-flight)
Ectotherms that don’t regulate body temperature
Polikilotherms are non-thermoregulating ectotherms (e.g. fish, bugs, etc.)
Heterotherms
Endotherms but they choose to regulate at certain phases of their life cycles and not regulate at others (e.g. bats, hummingbirds)
Heat Exchange Equation
Tbody=Tambient + Hmetabolism +/- Hradiation +/- Hconduction +/- Hconvection - Hevaporation
Radiation
- Radiative heat can be gained or lost
- All objects warmer than absolute zero emit radiation and lose energy
- Energy is lost/gained as infrared electromagnetic waves
What does radiation depend on?
Stefan-Boltzmann Law: Hrad=emissivity * theta * Area * (T1^4-T2^4)
- The difference in temperature of the two surfaces
- The surface area of the objects (huge for small animals)
- The color (the emissivity of the surface)
Conduction
- Conductive heat can be gained or lost
- Conduction is the direct transfer of kinetic energy of molecular motion and requires physical contact of the object with either a solid, a liquid, or a gas
What does conduction depend on?
Hcond=Conductivity Area(Tsurface1-Tsurface2)/Thickness
- The difference in temperature of the two surfaces
- The area of contact
- Thermal conductivity (how well the surfaces conduct heat)
Convection
- Convective heat can be gained or lost
- Convection is a transfer of heat by mass flow within a fluid medium, such as air or water
In practice; however, the vast majority of cases involve convection cooling by the organisms losing heat to a medium moving past it.
What does convection depend on?
Hconv= convection coeff * Area * (Tsurface-Tambient)
- The surface area of contact
- Temperature difference between the object and medium
- And rate of flow of the medium
Evaporation
- Evaporation always takes heat from the body
- The change in phase from liquid to gas requires energy (vaporization heat). This energy is removed from the object which the liquid leaves.
What does evaporative cooling depend on?
Hevap=Volume water vap/(Ta * relative humidity)
- The volume of water evaporated
- The humidity of the ambient air
What does metabolism depend on?
Metabolism depends on volume because if you have many cells in your organisms, you will have a lot of metabolic heat
Radiation, conduction, convection, & evaporation all depend on the …
Surface of exchange
You gain heat mostly by …
Volume
The bigger the organisms are, the smaller their…
relative surface is which means that they lose less heat compared to smaller animals
OR
The smaller organisms are, the more relative surface is high and therefore they are exposed to more heat loss
Kleiber’s law
Metabolic rate is proportional to body mass to the power of [2/3 to 3/4] from (m^2/3 to m^3/4)
Smaller animals have higher…
Metabolic rates per gram than larger animals
Higher metabolic rate of smaller animals leads to…
Higher: -oxygen delivery rate -breathing rate -heart rate -greater (relative blood volume) Compared to larger animals
SKETCH OUT GRAPH FOR BMR (MASS) TO BODY MASS (KG)
answer under Kleiber’s law in notebook
SKETCH OUT GRAPH FOR BMR (ENERGY PER KG OF TISSUE) TO BODY MASS (KG)
answer under Kleiber’s law in notebook
Why is the BMR (mass) to Body Mass (kg) less than a 1:1 ratio?
Because it has a lot of volume as it increases and isn’t losing a lot because its surface is low
Why is the energy spent per mass way lower in an elephant than mouse?
Because small organisms lose a lot of heat due to the high surface/volume ratio. Small organisms lose so much heat that they need to have a high metabolism to compensate for it.
Gigantothermy
Animal is so big that surface area-to-volume ratio is really small.
This, once animals get hot, it doesn’t lose heat fast and becomes essentially “endothermic”
ex. Leatherback sea turtle, komoda dragon, megasoma sacarab beetle
Diminishing surface loss: the insulation strategy
Decrease the
- thermal conductivity in conduction
- convection coefficient in convection
- emissivity in radiation
Animals may evolutionarily…
modify conductivity and/or distance to vital organs
ex. seals surround their major organs with fat which means increasing distance (further away from the cold ) and also decreasing thermal conductivity.
Thermal conductivity of objects
Steel: 0.16
Water: 0.0058
Air: 0.0002
Fur: 0.00026
Fur
Fur is a way to capture air within the hairs. Therefore, you use air layers as insulation
Regional heterothermy
Different regions of the body have different temperatures. This allows the core temperature to remain more stable. Generally, the core is hot and the extremities are cooler
The arrangement of blood vessels in some mammals and birds…
Allows for countercurrent exchange, generating regional heterothermy
Countercurrent heat exchanges
Transfer heat between fluids flowing in opposite directions & thereby reduce heat loss
Simple vascular loop (and draw it)
- loses heat all the way around
- temp gradient is shallow
Countercurrent system (and draw it)
- closely opposed vessels flowing in opposite directions
- retains heat closer to the core.
Consequence of countercurrent exchange
The extremity of these organs become cooler than if there was no countercurrent exchange. However, in terms of thermoregulation, it is much better for animals because the blood that comes back to the core is at a good temperature (ex. of cold feet –> look at the temperatures in the diagram you drew)
Benefits of being a homeothermic endotherm
- Activity levels can be kept higher - biochemistry, foraging, escape
- Greater independence from external thermal conditions
- More flexibility in exploiting different habitats
Cost of being a homeothermic endotherm
-Energetically expensive, especially in colder habitats where Tambient
Around an 100 fold increase in basal metabolic rate is
required in homeotherms/endotherms than in ectotherms/pokilotherms
Ectotherms rely on…
Behavioral responses to thermoregulate . Although ectotherms don’t generally thermoregulate, we saw that some of them thermoregulate to some level to achieve a certain temperature so they can do what they are supposed to do (ex. winter moths vibrating their wings for a preflight warmup)
Behavioral adaptations allow both
Gaining and losing of heat
How do homeotherms gain heat & how is body temperature regulated?
Heat comes from metabolic rate (BMR). BMR makes most of the work +muscle activity.
Shivering
Random co-activation of muscle units within antagonistic skeletal muscles produces heat, but no mechanical work due to co-activation
Non-shivering thermogenesis
Brown Fat Adipose Tissues
Heat loss in homeotherms comes from evaporative cooling and radiation
- Sweat glands control evaporation
- Capillary opening increases radiation
Insulation
Hairs at an angle of upright
Brown adipose tissue (BAT)
- Compared to white (normal) adipose tissue, brown adipose has many mitochondria which generates heat
- BAT typically occurs along the spine and clavicles and between the scapulas
Uncoupling of oxidative phosphorylation in the mitochondria generates heat (draw the picture)
- Thyroid hormone and the sympathetic nervous system induce thermogenesis
- In BAT, transport protein thermogenin uncouples electron transport and ATP formation. In some organisms, futile (incapable of producing) biochemical cycles also generate heat (slide 25)
Mitochondrial uncoupling
Protons leak back after inner mitochondrial membrane through thermogenin channel instead of shuffling through ATP synthase => heat but no work
Vasodilation (draw the picture)
Increased flow in distal loop exposes blood to exteriorr
- Increases heat exchange with environment
- To vasodilate, you open capillaries under the skin, the blood goes under the skin, the skin warms & radiates heat so you are losing heat
Vasoconstriction
Decreased blood flow can shunt flow inside insulating subcuntaeous fat
-Reduces heat exchange
Hypothalamus
Has a set point in the body. When the body temperature is lower or higher than the set point, it will activate mechanisms
- 2 opposing negative feedback loops maintain homeostasis (slide 27)
Metabolic heat is always positive due to…
- The inefficiency of biochemical reactions
- 35% of energy used in ATP is lost in from glucose is lost in heat
- 70% of muscular conversion of ATP is lost in heat
In endotherms (terms of heat)
Basal and active metabolisms contribute (exercise)
In ectotherms (terms of heat)
Muscular contraction is the first metabolic heat source. Of course this varies a lot depending on activity.
Diffusion
Movement of molecules in the environment, the body or across cell membrane (i.e. nutrients) by diffusion
Fick’s Law of Diffusion
J=D (dC/dX)
Constraints of Diffusion for Transporting Nutrients
- Only movement along concentration gradients
- Diffusion is effective only over short distances
- Rate of diffusion is inversely proportional to distance
Circulatory System
Moves nutrients and waste.
It has:
-circulatory fluid
-a set of interconnecting vessels
-a muscular pump, the heart (positive pressures drive the system)
The circulatory system connects the fluid that surrounds cells with the organs that exchange gases, absorb nutrients, and dispose of wastes
Can be opened or closed
Respiratory System
Allows gas exchange
Excretory System
Removes waste
Multicellular organisms use…
Bulk flow to move materials long distances
Plants (in regard to pressure)
Negative and positive pressures
Animals (in regards to pressure)
Positive pressure (pump)
Xylem
Movement of water and minerals –> unidirectional (from root to leaves)
Xylem sap is normally under negative pressure, or tension (because of the pulling up by transpiration)
Phloem
Transport of organic materials –> bidirectional (from source [often leaves] to sink [often fruit, flower, etc]
Positive hydrostatic pressure
Where is the xylem and phloem in different plants?
- Herbaceous plants: xylem/phloen occurs in vascular bundles
- Woody plants: xylem is the heartwood
Xylem structure (draw a picture)
- The xylem is made up of dead cells (programmed cell death)
- Tracheids (elongated) & vessel elements (short, only angiosperms) are two cell types composing xylem
- Vessel elements have perforation plates linking cells in a common tubular structure
- Trachieds have primary wall (cellulose) and secondary wall (lignin, non uniform lignin –> pits)
Complementary Systems
- Vessels are columns of water (fast transport). They require constant tension to maintain water cohesion.
- Trachieds have a high surface to volume ratio
- They can hold water against gravity by adhesion when transpiration is not occurring
Vessel Elements
The highway of trapnsport, but if you lose pressure, they cannot hold onto water
Tracheids
Can hold onto water due to that surface of contact (can do this even though vessel elements cannot)
Cohesion-Tension Theory
Traspiration and water cohesion pull water from roots to shoot (leaves). Water is polar, which allows hydrogen bonds between water molecules. Because water is polarized, molecules of water organize together and have some kind of cohesion which creates hydrogen bonds.
Transpiration in the leaf pulls water into the xylem
- Water vapor diffuses outside via stomata
- Water vapor replaced from water film
- Air water surface retreats
- Increased surface tension pulls water from cells and air spaces
- Water from xylem pulled into cells and air spaces (look at lecture slides)
Phloem Structure
- The phloem translocates the product of photosynthesis (e.g. carbohydrates like sucrose) from source (tissue) to sinks (roots, developing flower, etc.)
- Sieve elements that build tubes that will be your phloem. These are the cells composing the tubes (living cells with no nucleus at maturity!=partially programmed death)
- Companion cells are closely associated and transported sugars. They help make the movement happen.
Phloem sap
An aqueous solution that is high in sucrose. It travels from a sugar source (wherever sugar is built) to a sugar sink (where sugar is needed)
A sugar source
An organ that is a net producer of sugar, such as mature leaves
A sugar sink
An organ that is a net consumer of sugar
Transolaction (draw picture)
Movement through the phloem occurs thanks to a process called translocation
- Active or passive loading of carbon molecules by sources
- Water follows by osmosis, increasing hydrostatic pressure. By osmosis, water will have a tendency to move where sugar is, so inside the phloem
- Pressure increases, at the source but not the sink. Around the sink, sugar is unloaded. Water has a tendency to leave the phloem.
Draw an Open Circulatory System (ex. insects)
Check notebook
A closed circulatory system (draw it)
In a closed system, you need some regions of exchange with the tissues to bring nutrients to cells.
The regions of exchange are those regions where you have very small branched vessels, the capillaries, that allow exchange with local tissue.
3 types of vessels
- Arteries (heart –> periphery)
- Veins (periphery –> heart) –> capacitance vessels
- Capillaries (connect arteries and veins and allow exchange with tissues) –> draw this
Heart
A succession of two types of chambers:
- The atrium collects the blood. It is a thin walled structure and primes the pump.
- The ventricle pushes blood into the vessels. The ventricle is a thick-walled structure. The ventricle is the pump.
Draw a single circulation closed circulatory system and explain the problem
The problem is that the ventricle needs to make everything (blood) move through every organ. This is very difficult which is why there is a size limit
Draw a double circulation closed circulatory system and explain the problem
There’s one circuit dedicated to getting oxygen to the lungs and another circuit dedicated to go through the body and come back to the hear (more energy efficient) but there is only one ventricle so blood can mix and it can still become more efficient.
Draw a pulmonary systemic circulatory system and explain the problem (reptiles)
There is still one ventricle but this time, the blood doesn’t mix so it is separated.
Deoxygenated blood to the lungs and oxygenated blood to the body.
Draw a double circulation circulatory system and explain why it is the most efficient
Most efficient because there’s one pump dedicated to all capillaries in the lungs and one dedicated to capillaries with peripheral organs
Double circulation in mammals
- 2 independent capillary circuits
- For each cycle, 2 passages through the heart
- Pulmonary vein and systemic arteries are rich in O2
- Systemic veins and pulmonary artery are low in O2
- Left heart controls systemic circuit
- Right heart controls pulmonary circuit
Laminar Flow
Fluid flows in parallel layers, without disruption.
- The velocity of the external layer is low
- The velocity of the internal layer is high
- The more you go into the center, the less friction you have and the higher your blood speed is
Poiseulle’s Law
Flow Rate Q = delta P / Resistance
Flux = (delta P)0.4(r^4/..)
Velocity = Q/cross-sectional A
Q=P/R
Resistance in 1/r^4
The radius of blood vessels impacts hemodynamics
Amount of blood in veins and in arteries
70% in veins and 16% in arteries
Velocity decreases with…
Aborization
Microcirculation
- Is circulation in the smallest blood vessels (arterioles, capillaries, venules)
- Net flow is unchanged but linear velocity is minimal in capilaries
- Tissue perfusion occurs in the microcapillary sector
Why does velocity need to go down in capillaries?
For tissue perfusion to occur so it is exchanged with tissues
Arterioles
Control the flow in the capillaries. Resistance vessels. Influence blood pressure.
Distention (enlarging) of vessels due to blood pressure…
Triggers smooth muscle contraction. This prevents a change in capillary diameter so blood flow remains constant.
Vascular tone (draw it)
Changes perfusion of a tissue (this is the contraction)
Increased vascular tone in a segment of blood:
-Decreases radius of arteriole, and thus flow
-Increases resistance to blood flow
-Alters blood volume distribution
-Builds up pressure in the upstream compartment
Vasocontriction (draw it)
Increased contraction of circular smooth muscle in the arteriolar wall, which leads to increased resistance and decreased flow through the vessel
Caused by: increase in O2, decrease in CO2, Increase in endothelin, Increase in sympathetic stimulation, vasopressin, angiotensin II, cold
Vasodilation (draw it)
Decreased contraction of circular smooth muscle in the arteriolar wall, which leads to decreased resistance and increased flow through the vessel
Caused by: Decrease in O2, increase CO2, increase nitric oxide, decrease in sympathetic stimulation, histamine release, heat
Valves
Prevent the back flow of blood from the ventricle
For constant net flow, arborization increases…
and radius decreases
Blood flows from areas of…
Higher pressure to lower pressure
Blood pressure
The pressure that blood exerts in all directions, including against the walls of blood vessels
Total fluidity (give rise to flow)=
Potential energy of pressure produced by the heart (Mean Arterial Pressure) + Kinetic Energy (trivial few %) = Potential energy of position in Earth’s gravitational field
Orthostatic hypotension
If you go from a position where you’re laying down to standing up, this quick change in position will make you dizzy because when you stand and your head’s position is higher, there will be a decrease in blood pressure due to gravity.
Systole
Ventricular contraction
- -> blood is expulsed with high pressure in the aorta (if the left ventricle is contracting it’s called systole)
- -> semilunar valves open
Diastole
Refilling of blood following systole. Pressure is maintained by recoil or elasticity of the aorta. It causes lower pressure).
Since the LV is relaxed, it will fill with new blood from the atria.
Semi-lunar valve closes
Mean Arterial Pressure=
DP + 1/3(PP)
PP=pulse pressure = SP - DP
(Draw the graph) The resistance of blood flow in the capillaries…
Dissipates much of the pressure due to the arborization. With all that friction, you lose energy stored by the blood.
Muscle movements and breathing
Provide pressure and allow blood to return to the heart.
What diffuses in the capillaries?
Ions, nutrients, and organic molecules diffuse freely
Starling forces
Hydrostatic pressure and Oncotic pressure
Hydrostatic pressure
Continuously decreases while progressing through capillaries. Hydrostatic pressure leads to filtration
Albumin
Plasma protein that has a high concentration in the capillary.
How does liquid move in the capillary due to hydrostatic pressure and oncotic pressure?
Filtration- outside the capillary is a low concentration and inside is a high concentration
Reabsorption- Outside is a high concentration and inside is a low concentration
Therefore, fluid is first lost due to hydrostatic pressure (filtration) and then recovered due to oncotic pressure because hydrostatic pressure decreases and oncotic pressure will be higher even at its constant (reabsorption)
Oncotic pressure
Is constant and becomes preeminent in the capillary bed
Left atrium & left ventricle
Pumps blood from the lungs into systemic arteries (the aorta) towards the body with oxygen rich blood.
Right atrium and right ventricle
Pumps blood from the body (vena cava) into the pulmonary artery towards the lung. It receives and ejects a blood poor in oxygen.
When ventricles are relaxed…
Mitral (L) and Tricuspid (R) open while Aortic (L) and Pulmonary (R) are closed
When ventricles contract
Aortic (L) and Pulmonary (R) open while Mitral (L) and Tricuspid (R) (Atrial valves) close
Phases of the Cardiac Cycle
Quiescent period: blood flows in ventricles. Volume doesn't change since it is a ventricular diastole Atrial Systole: Forces more blood in the ventricles (still ventricular diastole). Atrium will start contracting which forces more blood into the ventricle until it is at its max Ventricular ejection (ventricular systole): blood begins when the ventricular pressure exceeds arterial pressure and forces semilunar valves to open. At first, this doesn't change the volume so the muscles start to put pressure. The pressure pushes on the blood which pushes in all directions, The centrical keeps contracting which will close some valves and force semilunar valves to open,
Rapid ejection
Blood is ejected rapidly at first
Reduced ejection
Then blood is ejected slowly under reduced pressure
Pressure goes down when…
Blood flow goes down
Pacemakers
Modified muscle cells that act more like neurons and can initiate the cardiac cycle. Each heartbeat is generated from an impulse from these pacemaker cells
How does signaling in the heart work? (draw this out)
-Electrical signal arises from the sinoatrial node
-Travels to the atrioventricular node
-Invades the atria
-Travels to the bundle of His
This electrical wave or wave of polarization goes through a structure called the bundle of His to stimulate the Purkinje fibers that trigger ventricular contraction
Cardiomyocytes
Striated muscle cells comparable to skeletal muscles but are mononucleated (have a single, round nucleus). Can be depolarized and repolarized. Are connected by intercalated discs. Action potentials can travel through the tissue which induces a wave of contraction and makes the whole cell continuous.
Depolarization and Repolarization (draw the action potential)
- In normal cells, there are more positive charge (Na+) than inside a cell which makes it negative. To depolarize, you must make the cell positive. Channels that allow positive ions into the cell will make it more positive.
ex. - Na+ going down a channel by following its concentration gradient.
- Then you need to quickly stop the influx of Na+ and restore the basal potential. You can do this by allowing potassium ions to go out -> the cell repolarizes
Voltage Gated Channels for other Cardiomyocites (draw the diagram)
- Voltage-gated Na+ channel opens, Na+ rushes in
- Voltage-gated Ca++ channel opens, Ca++ rushes in
- Voltage-gated K+ channel opens, K+ rushes out
SA node Action Potential (draw a diagram)
- Na+ slowly leaks in
- Voltage-gated Ca++ channels open Ca++ rushes in at the threshold
- Voltage-gated K+ channels open K+ rushes out
What is heart rhythm determined by?
Leakage of sodium in pacemaker cells. SA nodes have.a leaky sodium channel so even when there is no membrane potential change in the neighboring cell, a little bit of sodium will leak
Why is there a delay in depolarization?
You have to wait for the atria to contract before sending electricity or the depolarization wave in the ventricles.
Difference of charges between cells creates…
A Dipole. Depolarized cells with a positive charge have negative charges surrounding it and polarized cells with a negative charge have positive charges surrounding it.This is detected by electrodes.
Electrocardiogram (draw the diagram)
A recording of heart electrical activity
P wave
Corresponds to an atrial depolarization
The QRS complex
Indicates ventricular depolarization
The T wave
Indicates ventricular repolarization
Rhythm is controlled by the…
Autonomous nervous system (a division of the peripheral nervous system that influences the function of internal organs)
Sympathetic neural input
Noradrenaline, norepirephrine –> heart rate can be sped up by fight or flight
Parasympathetic neural input
acetylcholine –> heart rate can be slowed down, rest and digest
Acetylcholine effect on SA node cells (draw diagram)
- allows K+ to flow out
- hyperpolarizes cardiac myocyte => leak takes longer to reach threshold
Noradrenaline and norepinephrne effect on SA node cells (draw diagram)
- increases Ca+2
- depolarizes cardiac myocyte => Mb potential closer to threshold
What are extracellular fluids made of?
Water + electrolytes + non-electrolytes
Non-electrolytes
Organic molecules that do not dissociate (break apart), non electrical charge (so they are in solution)
Electrolytes
Dissociate (break apart) in ions (salts, acids, bases, some proteins)
Main electrolytes in ECF (extracellular fluid)
Sodium (Na+) and Chloride (Cl-)
Main electrolytes intracellular fluid
Phosphate and potassium
What are extracellular fluids for?
Required to maintain cell structure
- water/ions alter the volume of cells (remember osmosis and red blood cells)
-hydrostatic pressure maintains tissues and organs in place
Required for cell function
-ions are required for function (ex.enzymes)
-maintain electrical gradients across membranes (allowing action potentials)
Vehicle for nutrients and chemicals
-Amounts of fluid (volume) and concentration of solutes are both important
-Fluctuation is dangerous! Organisms face external and internal fluctuations in hydration and salinity
You could gain or lose water…
Independently of ions and gain and lose ions independently of water
Conformers
- No homeostasis (they do not invest any regulating mechanisms in the composition of volume of the ECF)
- Cells are iso-osmotic (with the environment; whatever the concentration of the osmosis, the cells in this animal will be at the same osmotic level)
- Stable environment- you can only afford this strategy in a stable environment where there won’t be a variety in salinity or hydration)
- Typically marine
ex. mussels
Regulators
-homeostasis (needs to keep the volume and composition of the ECF constant)
-tissues maintain relatively stable internal conditions
Energetically costly
-unstable environments like an estuarine/brackish environment for instance or
-constantly inhospitable habitats salty or terrestrial for instance
ex. shrimp
If organisms are regulators, what parameters do they need to regulate?
- Volume of water in the ECF –> volume regulation
- Concentration of ions available in the ECF –> ionic regulation
- Osmotic pressure (concentration) of the ECF –> osmotic regulations
General Problem of Living in Freshwater (draw the diagram)
-No salt which causes salt to leave the fish and water to -enter the fish.
-Fish invest energy (ATP) to get the salt from the water to counteract the risk of losing salt by diffusion –> gills
-They will also urinate to remove excess water from their bodies
Na+ and Cl- are separately actively pumped into the animal
General Problem of Living in Saltwater (draw the diagram)
- Living in salty water, facing desication and inward salt diffusion
- Gills actively secrete Cl-, Na+follows actively/passively
- Excretion of salt ions and small amounts of water in scarcity urine from kidney
4% water loss
Fatigue and dizziness
10% water loss
Can cause health deterioration (>15% can be fatal)
Isotonic dehydration or hypovolemia
Loss of fluid, without changing concentration
- i.e. you’re dehydrated but your ECF is isotonic; therefore, the same osmotic pressure as normal condition
- Decrease in volume of blood plasma (leads to less ECF circulation)
Hypertonic dehydration or true dehydration
High electrolyte levels (ions)
- i.e. high salt and not enough water
- can occur independently of each other
Regulation of water (& salt) intake
The mechanism of thirst
Regulation of water (& salt) output
Regulation of excretion
Thirst
A brain response to dehydration
- Hypothalamic thirst center
-> Sensation of thirst; person takes a drink
–> Water moistens mouth, throat; stretches stomach intestine
–> Water absorbed from GI tract
Thirst is a normal response to both hypovolemia and true dehydration
Steps of true dehydration
Electrolyte concentration –> Increase in osmolarity –> Osmoreceptors –> Osmotic thirst
Steps of hypovolemia
Fluid volume –> Decrease in plasma volume –> Baroreceptors –> Hypovolemic thirst
Osmoreceptors (draw the picture)
Cells that detect change in osmolarity and trigger thirst when it is too concentrated
- Osmoreceptor cells are neurons that respond to a change as small as 1-2% increase in osmolarity
- They alter their electrical activity (action potentials) in response to increase in ECF osmolarity –> when it’s hypertonic, ECF is too concentrated, they send a lot of action potentials, increase their electrical activity, triggering the thirst response.
- Cell shrinkage due to osmosis is the signal detected by these neurons. So when osmolarity changes, those neurons, like every other cell in your body, will shrink. When they lose water due to osmosis, that modulates how they send signals
Baroreceptors
Cells that can sense a difference in pressure. If you have hypovolemia, you will have a decrease in volume. A decrease in volume = decrease in blood pressure
Stretch receptors that sense when the wall of the circulatory arteries are too low,
True dehydration of intercellular thirst (or hypertonic)
The fear is that cells lose water due to high ECF concentration
DRINK WATER
Hypovolemia or extracellular thirst
- ECF has a proper concentration but you are losing blood pressure & ECF volume
DRINK WATER, EAT SALT
-if you just drink water, you’ll dilute the ECF so you need to eat salt to increase concentration
-Presents a risk for heart function due to decrease in blood volume so the heart increases its rate to maintain cardiac output) - Induces blood vessel constriction (vasopressin named ADH)
- Induces thirst for water and craving for salt (decrease as little as 5%)
How do animals get salt?
Carnivores eat meat rich in sodium
Herbivores eat plants but plants limit sodium so oftentimes herbivores die from sodium deficiency
Excretion
The elimination of waste products of metabolism. Filtration and reabsorption along a tube
Protein and nucleic acid metabolisms produce…
Nitrogenous waste:
Ammonia
Urea
Uric acid
Ammonia
Most aquatic animals including most bony fishes. Highly toxic, required a high water volume, doesn’t use much energy
Released through the whole body surface (in aquatic environment)
Urea
The liver of mammals and most adult amphibians convert ammonia to less toxic urea in the cycle called the urea cycle (energetically costly)
Moderately toxic, moderate water volume, moderate energy
Released in urine, through the kidney (lost water from ECF)
Uric acid
Many reptiles (including birds) insects, and snails
Low toxicity, low water volume, high energy required
Secreted as a paste
The higher the toxicity…
The more water you need to dilute
Urine is composed of
Water: 95%
Solutes: ions, nitrogenous waste
Although we are removing nitrogenous waste, we are also losing water and solutes which means we are losing ECF everyday. This is why we must replenish by drinking and eating.
The refining of a filtrate produces urine
Osmoregulation
Reabsorption can be adjusted
Excretory systems with tubular themes
- Protonephridia in flatworms: network of dead-end tubes
- Metanephridia in Earthworms: each segment has tubes
- Malpighian tubules in insects: tubes open on the hindgut
Goals of excretion
- Filter out extracellular fluids (blood)
- Reabsorb valuable solutes
- Reabsorb water
- Secrete toxins and other waste
Excretion=Filtration-reabsorption+secretion
Kidney
- A retroperitoneal organ, 11-15 cm
- Bean shape structure, connected to renal artery and vein
- Each kidney feeds urine into the bladder, through the ureter
- Filters blood constantly and at a very high flux (1/3 of what the heart sends)
- Kidney is an assembly of nephrons
Nephron
Basic unit of a kidney, more or less a tubular structure
0.4-1.2 million nephrons per kidney
Why does many tubular elements interspersed with the vessels?
This is because blood comes from the artery, and then you will have exchange with those nephrons that will generate urine. What is reabsorbed will then go in the vein to go back into circulation.
The filtrate is generated by
The Bowman’s Capsule. Then the filtrate progresses to the proximal tubule, to the Loop of Henle, to the distal tube, to the collecting duct which will go towards the bladder.
The nephron super simplified (draw this out)
check diagram for answer
Key steps in urine formation
- Filtration of the blood –> In Bowman’s Capsule where the blood comes in and out, that’s where you have filtration. What results in the nephron is primary urine.
- Selective reabsorption and secretion –> both the proximal and distal tubule will do some selective reabsorption. They reabsorb the molecules or ions that we don’t want to waste
- Reabsorption of salt and water –> In the Loop of Henle and the collecting duct, that’s where salt and water (most of the ECF) are reabsorbed. That’s where you can have control of that reabsorption and therefore osmoregulation.
Which regions aren’t regulated?
The Bowman’s Capsule, Proximal Tubule, and Loop of Henle consistently do their job independent of physiological status. Constant reabsorption of water
Which regions are regulated?
The distal tubule and the collecting duct are regulated by hormones that can allow them to reabsorb more water. based on dehydration levels.
Filtration in Bowman’s Capsule
- Podocytes (specialized cells) interact with endothelial cells
- They form a thin and minutely porous membrane
- THe blood will come with an afferent vessel and then leave the capsule with an efferent vessel but the blood will be in close contact with the podocytes.
Selective filtration for Bowman’s Capsule
Means that a lot of things won’t be able to pass through the porous membrane of the podocyte and endothelium cells. ex. giant proteins, red blood cells
Therefore, you are losing a remnant of plasma (ECF)
Step 1: Filtration in Bowman’s Capsule (pressure) (draw diagram)
Goal: generate primary urine
-Energy comes from circulation (hydrostatic, blood pressure)
Glomerular colloid osmotic pressure
Similarly to the capillaries, there’s also a high concentration of protein in the circulatory compartment that will bring some water out of Bowman’s capsule back into circulation by osmosis.
Step 2: Reabsorption in the proximal tubule
Goal: Reabsorption of water, solutes, nutrients + selective secretion
- pH regulation: secretes hydrogen ions, uptakes bicarbonate
- Active and passive transports from filtrate to interstitial fluids and capillaries (Na+/K+ pump, nutrients)
- Toxic material secreted
- A bit of water and salt is reabsorbed but the filtrate will remain iso-osmotic to the blood. This means that you reabsorb as much water as you reabsorb salt; therefore, the volume of the filtrate decreases (bc it leaves), but the concentration does not really change and the osmotic pressure of primary urine does not really change
Isotonic Reabsorption
The osmotic potential of the fluid leaving the proximal tubule is the same as that of the initial glomerular filtrate
Step 3: Water/salt reabsorption in the Loop of Henle
Goal: Reabsorb MOST water and solute (NaCl)
- The mechanism that allows water to be reabsorbed and then salt to be reabsorbed in the Loop of Henle is called countercurrent multiplication
Countercurrent multiplicaton
Using energy (invest ATP) to generate an osmotic gradient in the medulla (so in the kidney) which will allow reabsorption of water by osmosis and produce a concentrated urine Osmolarity of the interstitium is higher at the bottom of the loop compared to the top
Loop of Henle
- Descending loop permeable to water and less to ions
- Ascending loop impermeable to water, permeable to ions
- Thicker part of the NaCl has to pump ions out actively (impermeable to water, permeable to ions)
When urine progresses through the descending loop…
It progresses in an increasing gradient of salt
Step 4: Selective Reabsorption in the distal tubule
- Dilute urine enters the distal tubule
- The distal tubule regulates K+, Ca2+, and NaCl concentrations of body fluids
- Contributes to pH regulation (similar to proximal)
- Na+ reabsorption is stimulated by mineralocorticoids (aldosterone) –> partly responsible for urine concentration and water/salt retention
- Regulated by a hormone
Na+ reabsorption is stimulated by…
mineralocorticoids (aldosterone). –>partly responsible for urine concentration and water/salt retention.
Step 5: Water/salt retention in the collecting duct
- Where most of osmoregulation occurs
- 5% of kidney’s water and salt reabsorption only
- Due to hyperosmotic interstitial fluid established by the Loop of Henle
- Mostly responsible for concentrating urine in response to vasopressin (Anti-diuretic hormone, ADH)
- The collecting duct decides whether to use that increasing salt gradient to reabsorb water or not
Vasopressin
Will absorb more water!
Osmoreceptors in terms of Diuresis
Osmoreceptors in hypothalamus control diuresis. They sense dehydration and send in anti-diuretics which are vasopressin which cause water absorption
Antidiuresis
- Dehydration triggers release of ADH
- ADH promotes urine concentration (retaining water) –> this makes sense because if you’re dehydrated you want to limit water loss
Mechanisms of antidiuresis in the collecting duct
- ADH triggers (in the cells of the collecting duct) the movement of aquaporins
- When ADH is there, those aquaporins go to the surface of the cell and they allow water to flow through
- This channel facilitates water flux.
- Water flux allows stronger water reabsorption
Nutrition
The set of processes by which organisms obtain and use the nutrients required for maintaining life
Autotrophs
- Nutrition consists in acquiring non-organic compounds
- Do NOT require a source of organic carbon
- “primary producers” do build their own organic molecules
- But also depend on other organisms for nutrients other than carbon
- Autotrophs are independent in term of their source of organic carbon
Heterotrophs
- Nutrition requires organic compounds as part of the diet
- Require autotrophs to feed on
- -> to obtain: organic molecules including sources of carbon, nitrogen, etc.
- -> Most heterotrophs rely on this source of carbon for energy
- -> to obtain: vitamins
Autotrophic diet
- Energy source (light)
- Water
- CO2 (inorganic carbon)
- Minerals
Heterotrophic diet
- Water
- Carbohydrates
- Proteins
- Lipids
- Vitamins
- Minerals
Roots absorb… while leaves absorb…
Water, minerals, O2 from soil
CO2 from the air
Roots extract ions from soil
- The root hairs take up dissolved oxygen, ions, and water from the film of soil that surrounds them
- Anions, such as NO3- are readily available to plants because they are not bound to soil particles
- Cations, such as Ca2+ and Mg2+ adhere to soil particles. They are released by cation exchange. This is because soil particles are negatively charged so all positively charged ions will stick.
Cation Exchange
A positive ion will have to be exchanged to get one mineral. ex. give a positive ion to the soil to release either calcium or magnesium
- The root cells will acidify the soil, generating protons that are positively charged
- Protons will bind the negative charges of the soil particle
- Releasing some of those nutrients that will become available for absorption
Absorption is a function of
Surface –> a major problem is to increase surface of absorbance
How do organisms (organs maximize surface/volume ratio)?
They aim to have a large surface and a minimum volume
Fractal structures (branching to multiple levels)
The root system consists in an arborization (4-5 levels). Root hairs greatly increase a roots absorptive surface. Maximizes the surface of exchange with the environment. Root hairs increase the surface more
Symbiotic relationship for plants
Symbiotic relationships with fungal threads increases plant’s absorption mycorrhizae
Why do organisms digest?
Food is not ingested in a suitable state for use so digestion includes nutrient breakdown and absorption
Gastrovasular cavity
An organ dedicated for nutrient acquisition and digestion. Extracellular digestion. Animals with simple body plans have a (two way digestive tract) that functions in both digestion and distribution of nutrients.
Digestion
The step-wise processing of food that enters at one extremity and exists through another. In each region, nutrients will be broken down, absorbed, and waste is excreted
The 4 stages of food processing
- Mechanical breakdown increases food particle surface so enxymes are able to efficiently digest
- Breakdown of nutrients by enzymatic hydrolysis
Ingestion
Digestion
Absorption
Elimination
Alimentary Canal
Oral cavity, esophagus, stomach, small intestine, large intestine, rectum
Accessory glands
Salivary glands, Pancreas, Liver, Gallbladder
Herbivores (gut diet) (draw it)
Herbivores have a relatively longer posterior digestive tract reflecting the longer time to digest vegetation
Carnivore (gut diet) (draw it)
Long small intestines that allow them to digest meat
*cecum off large intestine
3 different digestive systems
Monogastric: simple chambered stomach (ex. humans, pigs, dogs, cats)
Ruminant (cranial fermentor): multi-comparemented stomach (ex. cow, deer, sheep)
Hindgut fermenter: simple stomach, but very complex intestine (ex. horses, ostriches)
Both ruminants and hindgut fermenters…
Eat plant materials since they are herbivores
Bacteria digest cellulose by fermentation. Since animals cannot breakdown cellulose, their multi-compartmented stomach or their complex intestine (cecum) will host symbiotic bacteria (gut microbes) which will digest cellulose.
Phase 1: The oral cavity and cephalic phase
- Mechanical breakdown of food by chewing in the oral cavity
- Salivary glands lubricate food and secrete a few enzymes but mainly amylase, initiating breakdown of carbohydrates (ex. of carbs: glucose, polymers like starch). Another enzyme that has a minor role is lingual lipase. It acts in the stomach.
- Salivary glands will secrete some mucus. Saliva contains the mucus, a viscous mixture of water, salts, cells, and glycoproteins
- When the mechanical breakdown is done and when food particles have been mixed with saliva, you end phase 1 by deglutition (swallowing) and the bolus is sent to the stomach through the esophagus
- The function of the stomach is already activated during phase 1 in the oral cavity. This regulation of the stomach is when you are chewing your food and is called the cephalic phase –> primes the secretion of stomach
Phase 2: in the stomach
- Stomach stores food and secretes gastric juice which converts food bolus into chyme
- Filling of the stomach (with food) prootes secretion (gastric phase)
- Proteins are digested in the stomach
- The proteolytic enzyme is pepsin. Goes from pepsinogen (from the chief stomach cells) –> pepsin due to acidification in the lumen. Parietal cells release HCl to acidify lumen.
- Protein denaturation by the acidic low pH by unfolding
Mucus layer
- Mucus layer is composed of water and glycoproteins
- With such an acidic pH, it will eventually pass the mucus layer
- To counteract this, the stomach epithelium produces some bicarbonate which will diffuse in the mucus layer and buffer the acid (HCO3)
Phase 3: in the small intestine (duodenal digestion)
- Most of digestion occurs in the duodenum!
- Chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder and small intestine itself
Duodenum
The upper part of the small intestine
Pancreas (secretes)
- Buffer (HCO3) since the chyme from the stomach is very acidic and could damage the duodenum, the pancreas secretes bicarbonate
- Trypsin
- Chymotrypsin
- Nucleases
- Amylases so that carbohydrate digestion continues
- Lipases
Duodenum
- Disaccharides
- Dipeptidases
- Nucleosidases
- Enzymes that are acting on the products of degradation from previous enzymes (trypsin and chymotrypsin)
