Chapter 9 Flashcards
cells in the human body require an internal temp of roughly _____, which is normal body temperature.
37°C
- small variations from this temp can be damaging or deadly.
-A sustained body temp below 35 °C or greater than 37.8 °C can cause some bodily processes to malfunction.
human body has many mechanisms that regulate its internal temperature. Give 2 examples
1) When we get too hot, we sweat.
2) When our body temp drops, we shiver to make thermal energy
Most animals have _______________or _________________ adaptations that allow them to maintain a suitable temperature.
physiological, behavioural
there r many animals native to the Sahara Desert that thrive in the conditions using special adaptations. Elaborate
- Ex, the fennec fox (Vulpes zerda)
- Its enormous ears serve 2 important functions that enable it to live in such a hostile habitat
1) large ears enhance its hearing. –> allows it to hear predators coming from far away, as well as hear prey, even when underground
2) act as “radiators.”–> rmr the greater the SA,
the faster & more easily the temp can be regulated downward. –> The radiator ears give it a large surface area to dissipate thermal energy faster.
–> Maintaining an optimal internal temp helps
the fox thrive in temps below 0°C to above 50°C.
homeostasis is
- the physiological state of the body in which the internal physical & chem conditions r maintained within an acceptable or tolerable range that is suitable for essential biological processes
- purpose is to maintain internal physical and chemical conditions needed for the cells to function properly
- is not a “steady state” or a constant condition, but a dynamic process that is continuously adjusted in response to changes in the internal or external environment –> Ex, the body must maintain
its optimal range of conditions during exercise, fatigue, & extremes of temp.
The body has several key parts, fluids, and conditions that must be monitored and adjusted for the body’s homeostasis to be maintained. List some
- internal temperature
- hormone levels
- the pressure, pH, flow, and concentration of glucose and other solutes in the blood.
- some factors, like blood pH & internal temp, the tolerable range is fairly narrow.
- In others, such as blood flow, glucose levels, & hormone levels, the tolerable range is broader & there
can be considerable variation without harmful effects.
. When discussing homeostasis, what does the internal environment refer to? Intracellular fluid (the fluid inside of the cells) or extracellular fluid (fluid outside of the cells)?
Extracellular fluid (fluid outside of the cells)
internal environment is
the extracellular fluid, which consists of the fluid that
surrounds the cells and tissues in the body (interstitial fluid) & the plasma portion of the blood
- Every cell in the body= surrounded by the extracellular fluid
- avge adult has 15 L of extracellular fluid, which= 20% of body mass
- volume, temp, & chem composition of our internal environment can change quickly. –> Rigorous physical activity, other extreme conditions, and infection can tip the balance maintained in the extracellular fluid.
- These changes can have a dramatic (often bad) effect on cellular functions, so the body uses many systems to maintain and regulate its internal conditions
interstitial fluid is
the fluid that surrounds the body cells
purpose of extracellular fluid
- acts as a medium for delivering energy, transporting chemicals, and eliminating waste
- The regulated flow of energy, chemicals, & waste into & out of the extracellular fluid allows the cells, and thus systems, to function properly.
What role does each organ system play in homeostasis?
- Nervous System: Receives sensory data from environment, which informs the body of external conditions, & transmits signals to regulate homeostasis.
- Excretory System: Eliminates waste and maintains a clean internal environment.
- Endocrine System: Regulates hormone levels critical for life processes.
- Circulatory System: Distributes hormones, chemicals, and thermal energy throughout the body.
- Immune System: Protects against and combats infections.
- Integumentary System (Skin): Helps maintain constant body temp by interacting with the external environment.
The liver, an organ in the digestive system, has several roles in maintaining homeostasis.
- Regulates amino acid levels, by breaking down any amino acids that are not used
- Detoxifies harmful chemicals.
- Produces essential blood proteins.
All of the organ systems are coordinated to carry out the tasks necessary for the survival of the organism. No matter how simple or complex the animal, these functions include:
- taking in nutrients & other required chemicals (like 02) from the environment, processing & distributing them throughout the body, & disposing of the waste
- making proteins, fats, carbohydrates, & other
essential molecules for cell function & structure - sensing & responding to changes in the external environment, like temp, physical sensations, & pH
-protecting the body from injury & from infection by viruses, bacteria, & other disease-causing agents
- reproducing, protecting, & feeding offspring
- Together these tasks maintain homeostasis . –> Their functions & activities make up most of an animal’s actions during its life, cuz maintaining an internal dynamic equilibrium is the only way that life can continue
Many organs & organ systems coordinate their activities to maintain homeostasis; however, the ____________ & _____________systems are the most
important systems.
nervous, endocrine
- 02 & C02 conc = regulated by the nervous
system,
- blood glucose= mainly regulated by the endocrine system
- blood pH & internal temp r regulated by both systems.
- These are ex of the many homeostatic mechanisms that are responsible for maintaining homeostasis
homeostatic mechanism is
a system that monitors internal & external conditions & changes bodily functions to maintain homeostasis
- To understand how homeostatic mechanisms work, consider the regulation of body temp.
- When the body’s internal temp is too high, we sweat; evaporation of sweat from our skin= endothermic process, so the body has a net loss of thermal energy absorbed by the water during the change of state.
- When cold, we shiver; these tiny muscle contractions generate thermal energy & raise the internal temp.
- Even the sensations of hunger & thirst r mechanisms that trigger behavioural responses to ensure the adequate nutrition & hydration of an animal.
- Since homeostatic mechanisms respond to internal & external conditions, they r described as detection-correction or feedback systems
The detection-correction or feedback systems that the body uses to maintain homeostasis r constantly detecting internal & external conditions. What happens next?
- These homeostatic mechanisms then evaluate the conditions to determine whether or not they represent any deviations from the norm.
- If conditions r outside of the optimal functioning
range, the mechanisms take corrective action to bring the body back into balance.
The primary mechanism of homeostasis is __________________, which is
negative feedback
- is the response of a system that acts to maintain equilibrium by compensating for any changes made to
the system
- a stimulus resulting from a change in the external or internal environment triggers a response that compensates for the change.
Homeostatic mechanisms include three elements: List them
a sensor, an integrator, and an effector
- The sensor and integrator are usually part of
the nervous or endocrine system, whereas the effector may include parts of any tissues & organs.
The sensor is
the element of a feedback system that detects changes in the environment
- consists of tissues or organs that detect any change or stimulus in external or internal factors, such as the pH, temp, or conc of molecules (ex, hormone or glucose molecules)
The integrator is
the element of a feedback system that compares existing conditions with ideal conditions
- Once the sensor gathers the information, it is transmitted to the integrator
- The integrator compares the environmental conditions with the optimal functioning conditions= set points
A set point is
the optimal value for a given variable of a system
- the set point represents a range of values within which a condition controlled by the mechanism is to be maintained.
The effector is
the element (or elements) of a feedback system that acts to return the system to its optimal state
- If the environmental condition is outside the set point, the integrator activates the effector, which is the system that returns the measured condition to the desired set point. –> This action is= the response.
- To bring internal conditions back into balance, negative feedback mechanisms use antagonistic effectors. –> The “antagonistic” in their name means that they act to make the opposite effect of the change recorded by the sensor.
Mammals and birds also have a homeostatic mechanism that maintains body temp. Elaborate
- Mammals and birds maintain body temp within a narrow range (set point). –> In humans, the set point is around 35–37.8 °C, centered on 37 °C.
- The integrator= located in a brain centre called the hypothalamus
- The hypothalamus acts as the body’s thermostat, specifically the preoptic region of the anterior hypothalamus. –> receive info from thermoreceptors in various locations, including the skin, the spinal cord, & the hypothalamus itself.
- If the temp deviates from the set point, the hypothalamus activates a set of physiological & behavioural responses to re-establish the normal body temp
- The particular set of effectors that is activated depends on whether our body temp is above or below the set point
Effectors activated if body temp drops below the set point
the hypothalamus activates effectors that induce vasoconstriction in the skin.
–> As blood flow through the skin is reduced, less thermal energy is lost to the environment, which causes our body temp to increase.
- Additional effectors may induce homeostatic behaviour, such as shivering, which generates body heat.
- Signals from hypothalamus make us aware of our lowered body temp, which may cause us to put on warmer clothes or move to a warmer place.
Effectors activated if body temp is above the set point
- hypothalamus triggers effectors that induce vasodilation in the skin, which increases blood flow to skin & loss of thermal energy to the environment.
- Signals from the hypothalamus make us aware of overheating, and we may take off warm clothing or
move to a cooler area. - Other effectors cause the body to sweat, which causes loss of thermal energy when the sweat evaporates.
Does the set point of body temp ever change?
Yes, there r times when the ideal tempe set point changes & the feedback mechanisms work to readjust body temp to the new set point.
–> ex, if u have an infection caused by a virus or bacteria, the homeostatic effectors increase
your temp, causing a fever. –> This increase helps the body fight off the infection.
- Once the infection is cleared, the set point is readjusted to its normal level.
All mammals use ___________ homeostatic mechanisms to maintain their body temp set point
similar
Birds & dogs _______ to release thermal energy from their body. Many terrestrial vertebrates use _______ to cool off.
pant, water
Another type of feedback mechanism is ___________________, which is
positive feedback
- the response of a system that acts to increase the effect of any changes made to the system
- Positive feedback mechanisms usually (with few exceptions) don’t result in homeostasis, since they cause the system to become unstable.
- They almost always operate when a continuous increase in some internal variable is required.
–> Ex, when an animal is attacked, body releases
adrenaline & hormones to blood to prime the muscles & organ systems for “fight or flight” reactions. –> release of these chemicals stimulates further release,
in a positive feedback cycle, making the animal even more fit to survive the attack
- Positive feedback mechanisms often operate within a larger negative feedback mechanism, which ultimately works over the long term to bring the body back into balance.
More examples of positive feedback occur during reproduction and child care.
- During child birth, uterine contractions stimulate oxytocin release from the pituitary gland.–> Oxytocin intensifies contractions, creating a cycle of stronger contractions & more oxytocin release.–> This cycle continues until the baby is delivered, after which contractions & oxytocin release stop.
- During child rearing, mammalian young suckle milk from the mother.–> sensation of suckling stimulates glands in the mother to produce milk. –> this milk production leads to more suckling from the young, again causing further milk production in a positive feedback cycle. When the baby is satiated, and ceases to suckle, the milk production is triggered to stop.
thermoregulation is
AKA temperature regulation
- the process of regulating internal temp by negative feedback mechanisms
- Temp receptors= thermo-receptors, detect any deviations in the external & internal temps from an
internal set point & then trigger behavioural & physiological responses that act to maintain the internal temp at the set point
- responses include adjustments in the rate of exothermic reactions in the body (such as metabolism) & adjustments in the rate of thermal energy exchange through the surface of the body.
Are the mechanisms of thermal energy exchange universal for all organisms?
Yes,
- almost all thermal energy exchange occurs at the surface where the body comes in contact with the external environment.
- Like any physical body, animals absorb thermal E if cooler than environment, & release thermal E if warmer than environment.
thermal E exchange occurs through one of 4 mechanisms. List them
conduction, convection, radiation, and evaporation.
- All animals exchange thermal E with their environment through these 4 mechanisms, which usually act simultaneously
Conduction is
the flow of thermal E between molecules that are in direct contact.
–> Animals lose thermal E when they come in contact with a colder body & gain thermal E when they come in contact with a warmer body
Convection is
the transfer of thermal E within a fluid (liquid or gas)
( Warm blood flows from the body’s core to the skin’s surface, where it loses heat to cooler surroundings via convection with air or water. CHATGPT)
Radiation is
the transfer of thermal E in the form of electromagnetic radiation.
- All objects, regardless of temp, radiate thermal E, & this radiation increases with the temp of the object
- Animals r constantly losing thermal E to the environment through radiation
- they also gain thermal E through radiation, usually by absorbing it from the Sun
Evaporation
The transfer of thermal E can be aided by evaporation. –> Ex, sweat.
- Water on the surface of the skin evaporates, absorbing thermal E from the skin & causing it to cool.
Mechanisms of Thermal Energy Exchange: A runner
- Conduction: Heat transfers to cooler air or the ground via direct contact.
- Convection: Rising warm air near the skin is replaced by cooler air, enhancing heat loss.
- Evaporation: Sweat evaporates, cooling the skin and aiding heat transfer.
- Radiation: The body emits infrared radiation while absorbing solar radiation.
- To maintain a stable body temp, the amount of thermal E leaving the body must = the total of the
amount made by the body & the amount absorbed from the environment.
All animals can be categorized into two groups based on the stability of their body temp: List them
- Homeotherms
- Poikilotherms
- have diff strategies aimed at regulating their body temp, & they have diff responses to changes in external temp
A homeotherm is
an animal that maintains a stable body temp regardless of the temp of the external environment
- Birds & mammals r homeotherms–> maintain a body temp that is often above the ambient environmental temperature.
A poikilotherm is
an animal whose body temp varies with, & often matches, the temp of the external environment
- Fish, amphibians, reptiles, & most invertebrates= poikilotherms
- poikilotherms still have some degree of control over their body temp
An endotherm is
an animal that maintains its body temp by internal mechanisms
- Internal physiological mechanisms that create thermal E to regulate body temp r referred to as endothermy
An ectotherm is
an animal that maintains its body temp by absorbing thermal E from the environment
- Behavioural mechanisms that involve using external sources of E r considered ectothermy
Which are more successful at maintaining body temp? Endotherms or ectotherms
Endotherms= more successful at maintaining a stable body temp, but they aren’t necessarily more successful animals.
Endotherms can obtain thermal energy from the ______________under __________________, but _____
ectotherms generate at least some thermal energy from _________________
environment, some conditions, ALL, internal reactions
Endotherms & Ectotherms: homeotherms & poikilotherms
- Most endotherms are homeotherms (google), but some endotherms allow their body temp to vary considerably during certain times of day or in different seasons & are considered poikilotherms
- Most ectotherms are poikilotherms (i think), but some ectotherms (ex, those that live in a habitat with a stable temp) maintain a fairly constant body temp & r homeotherms.
strategies used by ectotherms & endotherms r very diff, and each strategy of thermoregulation has its advantages & disadvantages
- The diff between endotherms & ectotherms is determined by their metabolic responses to the environmental temp
- Metabolic rate of endotherms increases as temp fall to regulate temp
- Metabolic rate of ectotherms falls as temp falls
- cuz of this dependence on thermal E made by metabolic processes, endotherms use ~80% of their food energy for thermoregulation, requiring constant energy intake.
- Ectotherms don’t use their metabolism to heat or cool themselves, & need less food for the same body mass as endotherms.
- Endotherms= fully active over wider range of temps than ectotherms, but need nearly constant supply of E. –> Cold weather don’t prevent them from foraging, mating, or escaping from predators, but it does increase their E & food needs.
- ectotherms temp fluctuate with the environment temp, & r usually less active in cold weather.
- When the environmental temp drops too low, they become inactive & r unable to capture food or escape from predators. –> However, their food needs= lower cuz their metabolic rates are reduced, so they do not have to look actively for food & expose themselves
to predators.
ECTOTHERMS: Aquatic Invertebrates
Limited thermoregulation, body temp usually= water temp; thrive in temperate environments.
ECTOTHERMS: Fish
- body temp similar to surroundings, & use behavioral adaptations to regulate body temp.
–>the thermal layers of deeper lakes and ponds provide thermoregulatory opportunities for freshwater fish. –> They remain in deep, cooler
water during hot days, & move shallower areas to feed during early morning & late evening when the air and water temp= lower.
ECTOTHERMS: Amphibians & lizards
- rely on conduction & radiation to regulate body temp
- lizards bask in sunlight or moving to shade to adjust body temp quickly.–> conduction & convection
–> frequent raising & lowering body temp allows lizards & some amphibians to keep an almost constant temp comparable to endotherms - some lizards use physiological responses similar to those of endotherms –> ex, Galapagos Marine Iguanas increase blood flow to sunlit skin (infrared radiation) areas to absorb heat & distribute it to internal organs.–> Blood flow is reduced to prevent heat loss when the skin cools.
thermal acclimatization is
the process by which an animal gradually adjusts to
temperature changes in its environment
- Many ectotherms undergo seasonal physiological changes= thermal acclimatization
- Ex, Bullhead Catfish- Summer: Can tolerate temps up to 36°C but not below 8°C. Winter: Can survive near 0°C but not above 28°C.
- Ex, Wood Frog (Rana sylvatica):
- Survives winter in a frozen state with no heartbeat, breathing, or brain activity.
–> This state is made possible by the liver releasing glucose stored as glycogen and by stopping the action of insulin, which causes glucose to build up in the frog’s cells.
–> Uses glucose to lower the freezing point of water in its cells.
- A “slurry” of ice crystals and sugar prevents cellular damage during freezing.
- The frog thaws in spring with minimal cellular damage.
Endotherms: Mitochondria & Energy Production
- Mitochondria generate energy for biochemical processes, but not all glucose energy is used for ATP production; some is converted to thermal energy.
- Up to 25% of the basal metabolic rate in endotherms is used to make up for this thermal energy loss.
- thus, body cells of endotherms contain far more mitochondria, & are proportionately larger than
the body cells of ectotherms
Endotherms & Thermoregulation
- Their body temp is tightly regulated within a narrow range: 39-42 °C for birds and 36-39 °C for mammals.
- They can survive in environments with seasonal temp variations, some of 70°C or more.
- Thermoreceptors on the skin and inside the body detect temp changes.
- Cold response: Constriction of arteries near the skin to minimize heat loss, shivering (muscle contractions to generate heat), and “goose bumps” (raised hairs trap air to conserve warmth).
- Heat response: Arteries relax to release excess heat, and sweat glands (in some mammals, including humans) secrete sweat, which evaporates and cools the body.
Some endotherms have special behavioural and physiological adaptations that help them thrive in even the harshest climates. These endotherms could be considered Homeotherms or Poikilotherms?
poikilotherms because their body temperature varies considerably
torpor is
a short-term state of reduced metabolic rate & body temperature that reduces the demand for energy during the night or day
- an adaptation of some endotherm poikilotherms
- The hummingbird uses daily torpor.
–> During the day, the hummingbird is actively feeding, but it cannot feed at night, & so it becomes inactive & allows its body temp to drop in order to conserve E.
- During the night, the hummingbird can use 1/15 the E it uses during the day &its heart rate can drop
from 1260 bpm to 50 bpm. –> conserves enough E for it to survive overnight without feeding
hibernation is
a state of greatly reduced metabolic rate & activity that enables an animal to survive the winter by reducing the demand for E when food is unavailable
- cold climates, many endotherms enter a prolonged state of torpor tied to the seasons triggered by a change in the length of the day, which signals the transition between summer & winter.–> Extended torpor of small mammals during the winter= hibernation
- Hedgehogs, groundhogs, & squirrels can experience a 20 °C or > drop in body temp during hibernation.
- The Arctic ground squirrel, hibernates for 8-10 months. –> only known mammal whose
body temp falls below freezing (as low as –3 °C) .
–> At 2-3 week intervals, without rousing from its sleep, the ground squirrel will shiver and shake to bring its body temp up to a near-normal 36.5 °C.
- It then stops shivering & its body temp quickly falls again
In large mammals, the depth of the torpor is less pronounced & is not considered to be true hibernation by some scientists. Give an example.
- The core temp of a bear drops only a few
degrees to around 30-32 °C. - Although sluggish, bears will frequently awaken, every day almost, & even more often after the young r born—but they do not eat or drink.
estivation is
a state of torpor that enables an animal to survive the summer by reducing the demand for E
- Some animals enter seasonal torpor during the summer, when the environmental temp is high & water is scarce = estivation.
- Animals like the ground squirrel remain inactive in the cooler temps of their burrows during extreme summer heat.
- Other ectotherms, such as lungfish, many toads & frogs, & some desert-dwelling lizards, survive hot climates by digging into the soil & entering a state of estivation that lasts throughout the hot, dry season
Other Thermoregulatory structures & Behaviours
- many insects can use exercise to maintain a core body temp above the environmental temp. Such species = exercise endotherms.
- honey bee can contract antagonistic flight muscles without moving its wings. This method is only efficient above 9-14 °C. Below this temp, the bee relies on ectothermic behaviours
- Uneven Fur Distribution in Dogs: Fur is thickest on the back, sides, and tail, and thinnest on the belly & legs. Dogs curl up in cold weather to expose only well-insulated areas & retain heat.
- seasonal Fur Changes in Mammals: Animals like muskoxen & Arctic foxes grow thick fur in winter and shed it in summer.
- Cooling Adaptations:
- Birds fly with legs extended to cool down.
- Dogs & mammals pant to release heat through the mouth.
- Elephants & jackrabbits dissipate heat through the large surface area of their ears.
The body’s internal environment of extracellular fluid
- must maintain a constant volume, solute content, & often temp. Humans & many other terrestrial vertebrates require a stable aq environment to survive.
- They carry this aq environment inside their body, and they must continuously replenish & maintain it
The Atlantic salmon (Salmo salar) spends part of its life cycle in both freshwater & saltwater environments. Elaborate
- Aquatic organisms msut regulate their internal environment cuz there r changes in external solute concentration & temp.
- Atlantic Salmon Life Cycle:
- Lives in freshwater as a juvenile (2–3 years) & saltwater as an adult.
- Freshwater solute conc (~0.1%) is lower than its body (~1.0%), causing water uptake that must be expelled.
- Saltwater solute conc (~3.5%) causes H20 loss, requiring mechanisms to replenish H20.
During osmosis, water molecules move from…
a region where they are highly concentrated to a region where their concentration is lower.
- The diff H20 conc on the 2 sides of the membrane r produced by dif # of solute molecules
- This movement occurs across a selectively permeable membrane, which allows H20 but very few solute molecules to flow through. –> Selective permeability= key factor cuz it helps to maintain diff in solute conc on the 2 sides of biological membranes.
- Proteins r one of the most vital solutes in establishing the conditions that produce osmosis.
osmotic pressure is
the pressure that results from a diff in solute conc between the 2 sides of a selectively permeable membrane
- The > water concentration gradient, the >the osmotic
pressure diff between the two sides
hyperosmotic
the property of the
solution on one side of a selectively permeable membrane that has the lower conc of water
- A solution with a higher conc of solute molecules on one side of a selectively permeable membrane is said to be
hyperosmotic (hypertonic) to a solution with a lower conc of solutes on the
other side.
- Water tends to move to the hyperosmotic side
hypoosmotic
- the property of the solution on one side of a selectively permeable membrane that has the higher
conc of water –> . it’s hypoosmotic (hypotonic) to the solution with the higher solute concentration. - Water tends to move from the hypoosmotic solution
isoosmotic
the property of 2 solutions that have equal water concentrations
- water moves till solutions are isoosmotic
- Water still moves across the membrane even when the solutions are isoosmotic, but the water movement is equal in both directions so there is no net movement
Another factor that determines whether osmosis will occur is hydrostatic pressure. Explain
hydrostatic pressure= water pressure
- if hydrostatic pressure one one side= osmotic pressure on the other side –> no net flow of water.
- As water continues to cross the membrane, the internal hydrostatic pressure begins to build until it balances the external osmotic pressure & osmosis
comes to a stop. –> can occurs despite the fact that the outside of the membrane may have a higher conc of water molecules
Hydrostatic Pressure: Plants vs Animals
PLANTS
interplay of osmotic & hydrostatic pressures is vital to plant cell structure .
- H20 surrounding most plant roots= hypoosmotic to the inside of the plant cells & water flows into the root cells & then into the cells of stems & leaves.
- This causes the cells to expand & press against the insides of their cell walls
- The hydrostatic pressure exerted against the cell walls= turgor pressure, gives a plant its rigidity & allows it to stand erect.
- If the surrounding fluid becomes hyperosmotic in relation to the insides of the cells, or if there is a shortage of water, there will be a drop in turgor
pressure & the plant will wilt
ANIMALS
- Hydrostatic pressure can’t build in animal cells cuz they dom’t have strong cell walls. If an animal cell is surrounded by a very dilute, or hypoosmotic, solution,
water molecules will continue to enter the cell until it swells & bursts.
- If an animal cell is surrounded by a hyperosmotic solution, water molecules will leave the cell by
osmosis & the cell will shrink.
osmoregulation is
the process of actively regulating the osmotic pressure of bodily fluids and cells
- Why?= Osmosis is a crucial and ongoing process in the establishment and maintenance of homeostasis
- To ensure the chemical & structural stability of the body cells, the internal environment (extracellular fluid) must be isoosmotic with the intracellular fluid.
All organisms need to keep their intracellular & extracellular fluids isoosmotic, but some animals require diff levels of active upkeep than others. Elaborate.
- Many marine animals like sponges, jellyfish, sea urchins, squid, & lobsters have intracellular & extracellular fluid conc identical to seawater, allowing H20 to flow freely. –> don’t need to regulate extracellular fluid
- plants must keep a certain minimum osmotic & hydrostatic pressure within their cells to maintain rigidity and transport nutrients
- Many animals (like almost all vertebrates) require more complex control mechanisms to keep
the conc of intracellular & extracellular fluids constant, but at levels diff from the conc in the external environment
Why is excretion so closely tied to the process of osmoregulation?
To maintain homeostasis, cells regulate their ionic balance & pH balance as well. –>, certain ions and toxic compounds, like metabolites of nitrogenous compounds (ex, amino & nucleic acids) must be eliminated.
- Animals maintain their ionic and pH balance through the process of excretion.
- body’s aq internal environment acts as a solvent
for these wastes, & their elimination helps maintain osmotic pressure & conc.
- most terrestrial animals= maintenance of osmotic conc while eliminating nitrogenous wastes can be difficult, since it requires significant amounts of water, which may not be readily available depending on the season or geographical location.
Excretion is
the elimination of waste products & foreign matter from the body
- serves to maintain the ionic and osmotic equilibrium that is necessary for cell functions.
- body system that regulates the removal of wastes= excretory (or urinary) system, & its main organs= the kidneys & the bladder.
- As body processes proteins during metabolism, it makes waste molecules, which liver converts into soluble metabolites.
- kidneys filter out these metabolites & eliminate them from the body with other aq waste, maintaining the H20 & pH balance of the internal environment
Waste nitrogen is made in diff forms for diff groups of animals: Elaborate
Bony fishes make ammonia, mammals, cartilaginous fishes (sharks, skates, rays) make urea, & most birds make uric acid as nitrogenous waste.
- Most animals are able to form all 3 of these nitrogen compounds, but the primary method of excretion depends on a balance among water conservation, toxicity, and E requirements.
Nitrogenous Waste: Ammonia
proteins are made of amino acids->amino acid has an amino group. -> In the process of deamination, which occurs in the liver, the amino group is removed from each amino acid that comes from the breakdown of a protein.
–> the amino group is turned to ammonia (NH3)
- the rest of the amino acid, which is mostly C & H, is oxidized to make E
- NH3=highly toxic–> buildup of as little as 0.005 mg/L can kill a human. –> t can be transported & secreted only in very dilute solutions.
- Animals with abundant supply of H20(like
bony fish) r able to secrete ammonia directly from the
body in this very dilute form
Nitrogenous Waste: Urea
- In mammals, some reptiles, and most amphibians,
the liver combines ammonia with HCO3– to create urea, a very soluble substance with 0.001 % the toxicity of ammonia. - 33 mg of urea can be dissolved in just 100 mL of blood with no toxic effects.
- tho chem reactions that make urea need more E than reactions that make ammonia, urea can be
eliminated from the body with less H20, allowing terrestrial animals to maintain their water balance.
Nitrogenous Waste: Uric acid
Other animals conserve H20 even more effeciently than Urea
- Ex, birds & some terrestrial invertebrates make uric acid as their nitrogenous waste product.
- Uric acid is not toxic, but its key feature for these smaller animals is its low solubility.
- As urine is concentrated in its final stages, it forms crystals that r expelled from the body with a minimal amount of H20. (the white substance in bird droppings is uric acid crystals.)
What are the 2 main functions of the excretory system?
1) main function of the excretory system (aided by osmoregulation) is to conc wastes & expel them from the body.
- individual cells can’t effectively secrete wastes to the external environment
2) main function of the excretory system is to regulate fluids & water within the body
- Most metabolic wastes & toxins= dissolved in the body’s internal environment, so maintenance of the body fluids is essential for keeping the body free of waste products & enabling it to function properly.
Single-celled organisms and simple multicellular organisms produce ______________metabolic wastes & toxic compounds as more complex organisms
the same
Simple organisms have an advantage over
more complex organisms when it comes to excreting waste cuz…
their cells r in constant contact with the external
environment.
- Wastes are excreted directly from their cells, & the water currents in the external environment carry the wastes away
A contractile vacuole is
a structure in a single-celled organism that maintains
osmotic equilibrium by pumping excess fluid out of the cell
- maintaining a fluid balance with the external environment is a greater challenge for single-celled organisms, like paramecium, cuz they have an internal environment that is hyperosmotic to their surroundings
- If they were not able to maintain a fluid balance, they would continuously absorb H20 from the environment & eventually burst –> Thus these protozoans have contractile vacuoles
metanephridium is
- PLURAL: metanephridia
an excretory organ in some invertebrates that is used to reabsorb & eliminate wastes - In every earthworm segment, hemolymph (a fluid
that serves as both interstitial fluid & blood) flows into a pair of metanephridia, which are twisted into convoluted shapes to maximize their SA - Ions and wastes are reabsorbed from hemolymph and secreted into a bladder.
- Excess water & waste are expelled through body pore
Malpighian tubules are
a set of organs that are the main organs of
excretion in insects (like grasshoppers), which are used to carry wastes to the intestine
- The closed ends of these organs r immersed in the hemolymph & the open ends empty into the intestines
- Nitrogenous waste (uric acid) and ions (K+ and Na+) are secreted into tubules.
- Water enters the tubules osmotically from hemolymph, forming a dilute waste solution.
- waste solution (urine) then travels to the intestines of the insect, where specialized cells reabsorb most of the K+ and Na+ back into the hemolymph.
–> causes H20 to move from the intestines back into the hemolymph by osmosis—an important H20
conservation measure.
–> The uric acid that is left behind forms crystals & is expelled with the insect’s digestive waste products
How are uric acid crystals excreted from terrestrial reptiles & most birds
it is excreted into the cloaca (end of the digestive system) & removed from the body along with the
digestive wastes.
- The white substance in bird droppings is uric acid & the darker substance is feces
How do reptiles & birds that live in or around salt water secrete waste differently?
- those that live in or around salt water take in large quantities of salt with their food & rarely or never drink fresh water.
- These animals usually excrete excess salt through specialized salt glands located in the head.
- The salt glands remove salts from the blood by active transport.
- The salts are secreted to the environment as a water solution, in which the salts r 2-3x more concentrated than in body fluids.
- The secretion exits through the nostrils of birds & lizards, & as salty tears from the eye sockets of sea turtles & crocodilians.
nephrons are
specialized tubules used in the excretory systems of all vertebrates, including humans which regulate the water balance in the body & conduct excretion
- Each kidney contains ~1million nephrons, which r the functional unit of the kidney.
What organs make up the excretory system?
The kidneys, ureters, bladder, and urethra together make up the human excretory system.
Kidneys
- play a critical role in removing wastes, balancing blood pH, and maintaining the body’s water balance
- Mammals have 2 kidneys, one on either side of the vertebral column.
- Each kidney weighs ~150 g and receives 25% of cardiac output (~1.25 L/min). –> Blood enters through the renal artery & exits via the renal veins after filtration of wastes.
-“Renal” refers to the kidney
-
nternal structure of a kidney
- Renal Cortex=Outer layer.
- Renal Medulla= Inner layer beneath the cortex.
- Renal Pelvis: Hollow cavity connecting kidney to the ureter, through which urine passes to the urinary bladder. –> Bladder stores 300–400 mL of urine before it exits through the urethra.
Nephron structure & function
Nephrons r differentiated into regions, which perform the series of steps that r involved in excretion
- At one end is the Bowman’s capsule which encircles a group of blood capillaries, the glomerulus, in the cortex.
- The glomerulus performs the 1st steps in the filtration of blood to form urine. –> Blood is supplied to the glomerulus by the afferent arteriole and, after being filtered, exits via the efferent arteriole and is carried to a net of capillaries= peritubular capillaries.
- The peritubular capillaries surround the tubules that carry away the urine & allow for the reabsorption of essential ions and minerals back into the
bloodstream.
- During the 1st steps of filtration, components of the unfiltered blood go from the glomerulus into the Bowman’s capsule & enter a proximal convoluted tubule, which lies in the renal cortex. –> This tubule descends into the medulla and forms a U-shaped
structure called the loop of Henle before rising again to form a distal convoluted tubule. - The distal tubule drains the urine into a branching system of collecting ducts that lead to the renal pelvis, which then empties through the ureter to the bladder.
Bowman’s capsule is
a small folded structure in the human kidney that
encircles the glomerulus
glomerulus is
a network of capillaries within the Bowman’s capsule that performs the 1st step in the filtration of blood
An afferent arteriole is
a vessel that supplies blood to the nephrons in the human kidney
An efferent arteriole is
a vessel that carries away filtered blood from the nephrons in the human kidney
peritubular capillaries are
a net of capillaries in the nephrons that reabsorb essential ions & minerals from filtered blood
A proximal convoluted tubule is
the duct portion of a nephron that connects the
Bowman’s capsule to the loop of Henle
loop of Henle is
the U-shaped part of the duct that connects the proximal convoluted tubule to the distal convoluted tubule
A distal convoluted tubule is
the duct portion of a nephron that connects the loop of Henle to the ducts that lead to the renal pelvis
3 features of the nephrons interact to conserve nutrients & water, balance salts, and concentrate
wastes for excretion:
side note: In mammals, urine is hypoosmotic to the surrounding body fluids. This means that water tends to move from urine into the body fluids, an adaptation that conserves water
1) the arrangement of the loop of Henle, which descends into the medulla and rises back into the cortex
2) the differences in permeability of successive parts of the nephrons
3) the conc gradient of molecules & ions in the interstitial fluid of the kidney, which gradually increases from the cortex to the deepest levels of the medulla.
Urine formation is the result of 3 interrelated processes:
1) Filtration–> occurs as body fluids move from the blood into the Bowman’s capsule
2) Reabsorption–> transfers essential solutes & water from the nephron back into the blood.
3) Secretion –> transfers materials from the blood back into the nephron
The Formation of Urine: Filtration
- urine formation begins at Bowman’s Capsule
- The Bowman’s capsule and surrounding capillaries form a selectively permeable membrane.
- It allows water, ions, small nutrients (e.g., glucose, amino acids), and nitrogenous wastes (e.g., urea) to pass through. –> the higher pressure of the blood in the glomerulus drives fluid that contains these molecules and ions into the capsule
- Blood cells, platelets, and plasma proteins are too large to pass and remain in the capillaries.
- fluid entering the Bowman’s capsule= ultrafiltrate of blood, containing smaller molecules & metabolic waste.
- The process in which fluid & small molecules pass into the Bowman’s capsule= filtration
Formation of Urine: Filtration statistics
- About 1400 L of blood pass through the kidneys every day, & the Bowman’s capsules filter about 180 L of fluid from this blood.
- The human body contains roughly 2.75 L of blood plasma.
- This means that the kidneys filter the entire contents of the blood plasma 65 times every day.
- Only about 1.5 L of the daily filtrate is excreted as
urine. The rest consists primarily of water and is reabsorbed into the nephrons
The Formation of Urine: Reabsorption in Proximal convoluted tubule
The fluid filtered into the Bowman’s capsule contains urea, water, ions, and other molecules that are in the same conc as they are in the blood plasma
- The fluid enters the proximal convoluted tubule, where reabsorption occurs
- Water, ions, & nutrients are reabsorbed via passive and active transport.
- Specialized ion pumps move K+, Na+, and Cl– ions into the surrounding interstitial fluid.
- Nutrients like amino acids and glucose are reabsorbed, while urea remains in the filtrate. –> Microvilli in the inner tubule walls increase surface area for reabsorption.
- All of the reabsorption processes make the filtrate hypoosmotic to the interstitial fluid, & this causes water to flow out of the tubule & into the interstitial fluid by osmosis.–> movement of water is further
facilitated by membrane proteins aquaporins (water channels) which ensure that the max amount of water is removed from the tubule during the reabsorption process
- Reabsorption percentages: 67% of Na+, K+, and Cl–; 65% of water; 50% of urea; nearly all nutrients.
The nutrients and water that are reabsorbed in the proximal convoluted tubule enter the _______________________. The remaining fluid, which has a high concentration of urea and other wastes that are not reabsorbed, moves through the proximal
convoluted tubule into…
peritubular capillaries, the descending portion of the loop of Henle.
Reabsorption in the loop of Henle
Descending Loop of Henle: H20 is reabsorbed by osmosis via aquaporins, concentrating solutes inside the tubule. –> The outward movement of H20
concentrates the molecules & ions inside the tubule.
- As the fluid moves into the ascending portion of the loop of Henle, Na+ and Cl-= reabsorbed into the interstitial fluid
- 1st part of the ascending segment, the concs are high enough to move Na+ and Cl- out of the tubule by passive diffusion. –> top of the ascending segment, these ions r moved out by active transport.
- Thus, water, nutrients, and ions have been conserved & returned to the body fluids, and urea & other nitrogenous wastes have become concentrated in the filtrate so the total volume of the filtrate in the nephron has been greatly reduced
Reabsorption in the distal convoluted tubule
- As the fluid goes from loop of Henle along its path, additional water and salts are reabsorbed, further reducing filtrate volume.
Reabsorption in the collecting ducts
- The concentrated urea and other wastes flow from distal convoluted tubule to the collecting ducts, which
further concentrate the urine - Water is reabsorbed as the filtrate descends through the medulla, increasing urine concentration.
- the ducts= permeable to water, but not to salt ions.
The concentration of solutes increases with depth as the fluid descends into the
medulla. - The concentration of solutes increases with depth as the fluid descends into the medulla causing further removal of water through the ducts, greatly increasing
the concentration of the urine - Passive urea transporters near the medulla’s base allow urea to move into interstitial fluid, contributing to the medulla’s solute gradient.
reabsorption is
the transfer of water, ions, and nutrients back to the interstitial fluid via passive and active transport
aquaporin is
a membrane protein that passively transports water molecules
The Formation of Urine: Secretion
- is the removal of waste products from the blood and interstitial fluid. –> During the process of urine formation, wastes are secreted at several points in the nephron
INTERSTITIAL FLUID –> PROXIMAL CONVOLUTED TUBULE: - H+ ions r actively secreted, & the products of detoxified poisons (from the liver) r passively secreted. –> Many water-soluble drugs, such as penicillin & other medications, & their metabolites r secreted into the nephron & excreted in the urine
- Small amounts of ammonia are also secreted
- secretion of H+ ions into the filtrate helps to balance pH. –> H+ secretion is coupled with HCO3- reabsorption from the filtrate to the plasma in the peritubular capillaries.
INTERSTITIAL FLUID –> DISTAL CONVOLUTED TUBULE:
- Responds to hormonal signals to secrete K⁺ and H⁺ ions to regulate salt concentrations and blood pH.
INTERSTITIAL FLUID –> COLLECTING DUCTS:
- Additional active secretion of H+ occurs
- When urine reaches the bottom of the collecting ducts, it is roughly 4x as concentrated with waste molecules as the extracellular fluid.
- From theere urine flows into the renal pelvis, through the ureters, & into the urinary bladder.
- From the bladder, the urine exits through the urethra into the external environment.
Kidney Disease
- The kidneys’ interaction with blood makes them susceptible to diseases and injuries from other body parts, & kidney dysfunction affects multiple organ systems.
- Urinalysis detects metabolites and disease-related molecules in urine to diagnose kidney and systemic disorders.
Kidney Disease: Diabetes mellitus
- Insufficient insulin secretion raises blood sugar levels.
- Excess glucose remains in the nephrons, disrupting osmotic pressure.–> The result is the retention of H20, so patients with diabetes need to urinate more frequently
- While some of the glucose can be excreted in the urine and can be detected by urinalysis, most of the excess glucose is reabsorbed in the proximal tubules of the nephrons
Kidney Disease: Kidney stones
- Formed from mineral solutes (e.g., oxalates, phosphates, carbonates) combining with calcium to make crystals that accumulate & form stones
- Cause pain when lodged in the renal pelvis or ureters.
-Treatments include: - Extracorporeal Shock Wave Lithotripsy (ESWL): Uses sound waves to break stones.
- Uteroscopy or surgical removal.
Dialysis
- Severe kidney failure requires dialysis, where a machine filters blood as an artificial kidney.
- Total kidney failure necessitates a kidney transplant.
