Temperate grasslands, like all biomes are characterized by the predominant vegetation – grasses. Unlike savannas that have a good deal of trees and shrubs scattered throughout, temperate grasslands generally have no trees. Temperatures can vary dramatically in this biome. In winters, the temperatures can be bitterly cold; in the summer the temperature can reach over one hundred degrees Fahrenheit.
What are some examples of temperate grasslands?
Plains and Prairies of North America
Steppes of Russian and China
Pampas of Argentina and Uruguay
Puszta of Hungary
Veldts of South Africa
How much rain does the temperate grassland get?
In general, temperate grasslands receive 20 to 35 inches of rain a year. While seasonal droughts play less of a role in this biome than tropical savannas, rain usually falls seasonally, mostly in late spring and early summer.
The amount of rain that falls in a grassland determines the height of the grasses. In North America there are two types of grasslands: short grass steppes and tall grass prairies. Short grass steppes are characteristic of many parts of Utah, Montana, and Colorado. In wetter areas, such as Iowa and Minnesota, one will find the tall grass prairies.
The first thing you’ll notice when you visit a tropical rainforest is the abundance of plants, both in shear biomass and total biodiversity. Plants thrive when the yearly average temperature and precipitation, in the form of tropical rains, is high. Below, we describe their main characteristics, where they’re found, the layers of the forest and some common animals you might see on a visit to this biome.
Characteristics of the Tropical Rainforest Biome
All biomes are characterized by the dominant vegetation. In the rainforest biome there are tall trees and warm temperatures all year. The yearly average rainfall is from 50 to 260 inches. The temperature is warm but not hot. Almost every rainforest you might visit has a temperature range of 93°F to 69°F. The average humidity is between 77 and 88 percent.
Where are Rainforests Found?
Tropical Rainforests are found in a tropical belt around the equator where annual temperature and precipitation are high. However, rainforests now cover much less of Earth’s surface than they once did.
Biodiversity of Rainforests?
Today, about 6 percent of the surface of Earth is covered in rainforests, and more than half of all the world’s plant and animal species live in them. The shear biomass of plants in the rainforest help produce about 40 percent of Earth’s oxygen.
Estimates of the Earth’s biodiversity originally came from studies in Panama, where tree species were logged and the number of insects within them categorized and counted. Estimates range from 10 to 100 million species on earth, most of them being insects found in the tropical rain forests.
The tropical rainforests have more kinds of trees than any other biome in the world. In a rainforest in South America, scientists counted from 100 to 300 species of tree in 2.5 acre sections of the forest. Not all plants in the rainforest are trees though. While they are the easiest to observe, there is a great diversity of epiphytes, plants that live on other plants, that make the rainforest their home. Plants like orchids live on rainforest trees high in the canopy.
It has been estimated that about 25 percent of the medicines we use come from plants in the rainforest, such as:
Curare, a tropical vine, is used as an anesthetic and muscle relaxant during surgery.
Quinine from the cinchona tree is taken to treat malaria.
Rosy Periwinkle from Madagascar is used to treat lymphocytic leukemia.
The look of a typical rainforest
All tropical rain forests resemble one another in some ways. Many of the trees have straight trunks that don’t branch out for 100 feet or more; there is no sense in growing branches below the canopy where there is little light. The majority of the trees have smooth, thin bark because there is no need to protect the them from water loss and freezing temperatures. It also makes it difficult for epiphytes and plant parasites to get a hold on the trunks. The bark of different species is so similar that it is difficult to identify a tree by its bark. Many trees can only be identified by their flowers.
Despite these differences, each of the three largest rainforests–the American, the African, and the Asian–has a different group of animal and plant species. Each rainforest has many species of monkeys, all of which differ from the species of the other two. In addition, different areas of the same rainforest may have different species. Many kinds of trees that grow in the mountains of the Amazon rainforest do not grow in the lowlands of that same forest.
Visiting The Tropical Rainforests
There is no one place to visit if your destination is tropical rainforests. The crew of Untamed Science particularly like the rainforests of Central and South America, but we have many other favorites as well. We spent nearly 9 months in Panama shooting videos and staying at the Smithsonian Tropical Research facility, Barro Colorado Island (BCI). The following video is a short glimpse into what BCI is like.
Not every region of the world experiences a change in seasons like the temperate deciduous forests. Some are always blanketed in ice, while others have warm sunshine year round. For those of us who live in temperate regions, seasonal changes happen every few months. You could be darting across a lake on water skis in July, and, 6 months later, you could be racing across that same lake on ice skates!
There is no season such delight can bring, as summer, autumn, winter, and the spring.
William Browne – “Variety”
When you grow up experiencing four seasons every year, you begin to notice and appreciate the seasonal ebb and flow of life around you. Winter is peaceful and quiet; critters that don’t migrate stay hunkered down in warm dens, waiting for the spring (Humans included!). Spring is a welcome awakening; as the snow melts away and leaves begin to bud on the trees, life reappears and prepares for a new year. Summer is a bustle of energy and life; insects are busy pollinating the next generation of wildflowers, and birds sing from every corner of the forest. Autumn is a time for harvesting and a time for goodbyes; mammals fatten themselves up to prepare for a winter food shortage, and birds of a feather flock together to follow their food south.
For many of us, seasonal change is old news. It drums along at a steady, predictable rhythm. But few people realize that this predictable pattern is what has allowed temperate deciduous forests to evolve and flourish all over the world.
Temperate Deciduous Forest in Virtual Reality – 360 Degrees
The following video is a short we shot for you to see this deciduous forest biome in 360 degrees. If you are on a mobile device you may have to open the youtube video in the mobile youtube app to see it in virtual reality. If it looks funny, its because the system you’re on doesn’t support this viewing experience.
Where Can You Find the Temperate Deciduous Forest Biome?
When you look at a map of of the world, lines of latitude run east and west, forming invisible belts that circle the globe. These lines of latitude can be grouped into three different categories as you move away from the equator. Regions that lie between 0° and 23° north and south latitude are called the Tropics, regions between 23° and 66° are called the Temperate latitudes, and regions between 66° and 90° are called the Polar latitudes. Temperate deciduous forests are found within the temperate latitudes, just like Tropical Rainforests are found within the Tropics (makes sense, right?).
In the southern hemisphere, temperate forests can be found on the southern tip of South America and in Eastern Australia. In the northern hemisphere, they can be found in northeast Asia (China, Korea and Japan), Western Europe, and the eastern third of the United States.
Abiotic Factors: Temperature and Precipitation
Temperate climates (and all other climates for that matter) are influenced in large part by circulating air currents in the atmosphere. Watch this animation of global air circulation and try to locate regions of the world where the clouds accumulate:
As you can see, most of the clouds accumulate along the equator. This is what scientists call a low-pressure zone. (Clouds just can’t handle high pressure situations.) Low-pressure zones are regions of high precipitation. If you watch carefully, you can spot another low-pressure zone in the temperate latitudes.
Due to their global position, temperate forests generally receive about 75-150 cm of precipitation every year (That’s a lot, second only to the Tropics). Remember, though, precipitation can fall in the form of rain or snow because temperate climates experience all four seasons. Temperatures can range from -1°C to -30° C in the winter and 27° to 32° in the summer.
What do they look like?
Temperate deciduous forests are among the oldest and most beautiful forests in the world. Take a walk through the northern hardwood forests of Wisconsin, or taste the sap from a Sugar Maple stand in Vermont, and you will know exactly what I mean. As you walk, tall trees form a leafy canopy above your head, blocking the sun and casting dappled shadows over ground. Leaves from last season crunch noisily underfoot as you scrape through a thick, woody understory. If you dig into the ground, you pull through layer upon layer of wet, decaying leaf litter, and white threads of fungus stand out against the dark soil. Fungus, bacteria and insects underground decompose fallen leaves and organic matter quickly, producing a thick layer of nutrient rich soil, which scientists call humus (Not to be confused with hummus, Yum!). The humus feeds the trees and supports a biodiverse community of lichens, mosses, grasses and wildflowers on the forest floor.
Not all temperate deciduous forests are created equally, though. Every forest you visit can differ greatly in the species of plants that populate it. In the same way that the Earth can be classified into separate biomes, where specific groups of plants and animals exist within a regional climate, temperate deciduous forests can be classified into different communities depending on the local climate. Click here to find out more information regarding specific temperate forest communities!
What types of plants can you find here?
You may hear temperate deciduous forests also called “broadleaf forests,” because the tree species that populate them have… wait for it… broad leaves! Trees like Maple, Oak, Beech, Chestnut, Elm, Hickory, ect. have big, broad leaves that are attached to the branch by a special stem called a petiole. Unlike pine needles, these leaves are soft and easily digestible to browsing herbivores.
In a mature forest, these tall trees form a canopy which blocks most of the sunlight from penetrating through to the plants below. To compensate, the plants that make up the understory and herbaceous layer are shade-tolerant, meaning they can survive with a lower amount of sunlight. Due to the seasonal nature of temperate deciduous forests, many of the plants in this region are perennial, meaning they grow and flower only during the warm, summer months. Thick, woody shrubs like rhodedendron, buckthorn, sumac, honeysuckle, or dogwood dominate the dense understory. This region of the forest is generally the most biodiverse area of the forest; a single forest can have over a hundred different species of plants! Throughout the early spring and summer, shade-tolerant herbs and wildflowers like Jack-in-the-Pulpit, May-apple, Bedstraw, Purslanes, and mustards flower and go to seed within a few weeks to months.
What does “Deciduous” mean?
The term deciduous refers to the plant’s ability to lose it’s leaves when times get tough. For example, some species of trees and shrubs in the chaparral are called drought-deciduous, which means that they lose their leaves in the dry season to conserve water.
Deciduous trees in temperate forests lose their leaves in the fall to better survive winter conditions like extreme cold and reduced daylight. For a more detailed explanation of how trees lose and regrow their leaves, check out Rob and Jonas’ video on plant hormones here!
The ability for a tree to lose its leaves to conserve energy is a useful but costly adaptation. As opposed to evergreen trees, deciduous trees have to regrow thousands of leaves every year. This requires the plant to take precious nutrients from the soil to make them. In some temperate regions, if the soil is too dry or nutrient poor to afford the cost of new leaves, the populations of plants change to suit the environment. For example, in many temperate regions of the United States, the soil is too sandy and nutrient poor to support many deciduous trees and evergreen trees are a big part of the forest. In areas like this, we call it a “temperate broadleaf mixed deciduous forest”. Yes, the names can get complicated…
Why do the leaves change color?
Temperate deciduous forests are famous for their dramatic color change that occurs every fall. Amazingly, this seasonal effect begins within each cell of every leaf on the tree! To help you understand this better, picture each plant cell as a jar full of red, yellow, and green beads. If there were more green beads than anything else, the jar would appear green. If you took all of the green beads out, the jar would appear red and yellow.
This is essentially what happens within each cell of the plant every year. As the days get shorter and the temperature drops in the fall, plant cells stop producing green pigments (chlorophyll) in the cells of their leaves. When the cells stop producing chlorophyll and the green pigment slowly disappears from each cell in the leaf, other pigments become more vibrant, and the leaves begin to appear yellow, red and orange.
Every year, hundreds of extraordinary migrations occur all over the world: The Swallows of Capistrano, the Monarch Butterflies from Mexico, and of course, The New England Leaf-Peepers. Every year, thousands of New Yorkers and Bostonians make the long journey north to watch the leaves change color; truly this one of nature’s most beautiful spectacles (the leaves, not the city people).
Temperate Deciduous Forests Through Time
As we have said, in a typical temperate forest, tall trees create a thick canopy that blocks most of the sunlight from penetrating. This creates a layer of shade-tolerant herbs and shrubs in the understory. But what happens when the trees fall down? What if a fire burns hot enough to turn everything into ash? What if a tornado sweeps through and delivers everything to the Land of Oz? (It happens you know…) Here, we will talk about how these forests change over time and what happens after a disturbance.
Forest Succession
Forests, like any other living thing, grow old and change over time. In fact, every forest you see was once a pile of bare rock! Slowly, lichens and mosses grow over the rocks and decay to form a layer of soil that is capable of supporting grasses and wildflowers. At this point, our temperate forest is not a forest at all, its a grassland! Temperate deciduous forests and temperate grasslands are almost one and the same. The two are often found right next to each other and share many of the same plant and animal species.
Over time, tree seeds from the forest make their way to the grassland and begin to sprout. As the trees begin to shade out the plants under them, the grassland begins to resemble a forest more and more. Grasses in these habitats are not very shade-tolerant. As more trees sprout up, fewer grass seeds are able to germinate, and they remain dormant in the soil until conditions are right again.
At this point, more shade-tolerant herbs and shrubs are able to grow, and they create a thick understory in this young forest. When the majority of the trees in the forest have reached a mature age, we call it a climax community. Forests that have reached this stage in development are also called old-growth forests, for obvious reasons. Many of the old-growth forests in the United States have been cut down to make space for cities and to make use of the valuable timber. But some old growth forests remain in northern Wisconsin, Michigan and Minnesota, and given enough time, more will grow again!
Natural Disturbances
What makes a temperate forest different from a temperate grassland? Sunlight! Grasslands receive a lot of it; forests do not. Now, imagine a tree falls in the woods (don’t worry about whether or not you can hear it…) Suddenly, the canopy opens where that tree has fallen and light pours into the forest. When this happens, seeds that have been dormant in the soil are finally able to germinate again. Grasses, flowers and other fast growing plants quickly sprout up and take the place of the fallen tree. Over time, new trees will grow up tall enough to shade these plants out again, but that could take years. In the meantime, these areas of the forests remain sunny oases of diverse plant life!
Tree falls, fires, tornadoes and insects are common natural disturbances in these forests. Every time something like this occurs, the forest rebounds within a few years. Sometimes it begins at an earlier successional step, and sometimes the disturbance is just what it needs to clear out the excess and keep the forest healthy.
Polar ice caps are high-latitude areas completely covered in ice that occur in the polar regions of Earth. Other planets, Mars for example, have polar ice caps also, but unlike Earth’s ice, which is largely composed of frozen water, Mars’ ice is mostly made up of frozen carbon dioxide. Polar areas receive less solar energy from the sun and are therefore subject to low surface temperatures, allowing ice caps to form.
Are Polar Ice Caps Static?
Ice cap formation is largely dependent on the amount of energy a polar region receives in the form of solar radiation, which can change depending on season, climate fluctuation, geologic time, or a combination of all three. Ice caps can expand or retract, which explains how ice ages come and go.
As the deserts of the equatorial region of Africa are one extreme of the Earth, the polar ice caps of the Arctic and Antarctic are extreme in the opposite respect.
North vs. South: Differences in the Poles
The North and South Poles, while similar in regard to their frigid climate and extreme conditions, are actually very different geographically. The North Pole is actually a body of water, the Arctic Sea, which for the most part remains covered in floating pack ice. In some areas of the sea, the ice freezes at a thickness of several meters or more and forms expansive, contiguous sheets of ice. During the warmer months of the year, some of the sea ice melts, and the polar ice caps of the North Pole retreat further north. The South Pole, on the other hand, is comprised of the continent of Antarctica, a giant ice sheet that stays in tact year-round. Data from the past several decades has shown that polar ice in the North Pole is on the decline, while ice in the South Pole is slightly, but steadily, increasing.
The continent of Antarctica is sometimes referred to as a cold desert– a desert is determined not by temperature, but by the average amount of precipitation it receives per year, and since Antarctica gets relatively minimal precipitation each year, it is technically a desert, and a cold one at that!
Is an Ice Cap the same as a Glacier?
In short—no. Polar ice caps are large accumulations of ice that form over bodies of water while glaciers are large concentrations of ice that form on land. Glaciers form when accumulations of snow and frozen precipitation exceed the amount of melted snow in an area. Over an extensive period of time, this frozen precipitation compacts, transforms into ice, and forms a glacier.
Is there Life on Polar Ice Caps?
At the farthest reaches of the poles, where ice is ubiquitous and permanent, conditions are too extreme to sustain life. Even bacteria, organisms known to inhabit the most extreme of environments, are absent. However, the less extreme (comparatively speaking) areas of the Arctic and Antarctic do support some forms of life. These animals all share one thing in common: the ability to generate their own body heat. This is extremely important, as temperatures in the poles are not warm enough to sustain exothermic animals like insects, amphibians, or reptiles. The birds and mammals that inhabit the poles spend the majority of their time eating in order to obtain enough calories to keep their body heat up. They all depend, directly or indirectly, on food from the sea. The Arctic is home to terrestrial mammals such as foxes, polar bears, caribou, ground squirrels, wolves, wolverines, ermines, and musk oxen. There are also marine mammals (walruses, seals, and whales) and a variety of raptors and seabirds. The Antarctic is home to penguins, a few seabirds, and seals.
Video showing Annual Arctic Sea Ice Minimums
Fun Facts about Polar Ice Caps
70 percent of the Earth’s fresh water is locked in the frozen continent of Antarctica.
The average thickness of the ice on Antarctica is over a mile!
At the poles, during the winter, the sun never truly rises. In the summer, it never sets.
To begin our journey through the nervous system we thought it might be useful to watch this entertaining and informative Untamed Science short. In this video we explore animal toxins, and how they interact with the nervous system. We visit cone snail researcher J.P. Bingham at the University of Hawaii where new compounds are being discovered that may help save lives! This video was made for Pearson’s Miller and Levine Biology Textbook.
A Broad Nervous System Overview
Have you ever pondered the multitude of processes made possible because of the central nervous system? We’ll give you a better understanding of the complexities of the nervous system here as we step through some of its major parts. We’ll start with a real life story that might help you understand how important this system is. Then, we’ll look at the brain, the spinal cord and nerves. We’ll see how each of the senses work, such as sight, hearing, touch, taste and smell. Finally, we’ll explore some interesting questions related to the nervous system.
Football and your Nervous System:
The wide receiver dashes down the field towards the end zone. As he turns back he sees the quarterback throwing a bomb to the end zone. His mind concentrates on the flight path of the ball, integrating information from his eyes and ears and communicating actions to his muscles. Without direct mental input, his heart beats faster and adrenaline hormones are being pumped through his blood stream. As he catches the ball, he sees an opposing player for a split second and then blackness.
While all body systems are extremely important to this player, we can take a closer look at how the nervous system plays an important role in this scenario.
The nervous system controls all the actions the player makes as he catches the football. Some of them are conscious movements, such as running, catching, jumping. Others, such as his heart rate and breathing are not conscious. He uses many different sensory mechanisms, such as touch, sight and sound. Nerves that connect his muscles to his brain are telling him about his surroundings. Different parts of the brain are working at the same time to then communicate the needed directions to catch the ball.
You may never realize quite how important your nervous system is until it gets damaged. When a player blacks out, it is often caused because there is damage to the brain, the main control center of your nervous system. Let’s give you a better idea of how the nervous system works by examining each piece in this complex puzzle.
The Neuron:
The building blocks of the nervous system are our neurons. Our nerves run through our body and help us interpret the outside world via thousands of neurons. These neurons connect end to end and transmit messages throughout the body. This message relay system is made possible via small electrical pulses that travel down the length of the cell. When it reaches a new cell, chemicals called neurotransmitters take over.
This diagram helps show what happens at the synapse between neurons. At the synaptic cleft, or the junction between neurons, the “message” is transferred as packages full of neurotransmitters are released into the cleft. These neurotransmitters, then bind to receptors on the new neuron. This binding action helps open ion channels. These channels let ions move in or out of the neuron, starting a new action potential to continue the “message’.
To understand the basics of the electrical impulse, lets look at how this action potential is formed.
Action Potential or Nerve Impulse:
A nerve impulse works because the neuron is able to change the electrical charge along the length of the cell. Its not a magical phenomenon but it does take energy input from the cell. The entire process is set in motion because protein pumps along the cell membrane change the concentration of sodium and potassium in the cell. These sodium potassium pumps move one potassium ion into the cell as it moves one sodium ion out. A huge concentration gradient is set up. Sodium wants in and potassium wants out. Both ions are positively charged though, so there is no electrical potential. However, since some of the potassium is able to leak out of the cell, the entire cell ends up having a negative charge. This voltage differential is approximately -70 millivolts (mV) and is known as the resting potential.
A neuron keeps its resting potential until an outside stimulus is large enough to trigger a nerve impulse. These nerve impulses are driven by a sudden reversal of the resting potential on the cell. Gated sodium channels open, allowing positively charged sodium into the cell. This switches the charge. Other gated sodium channels open in front of the impulse. However, as soon as the cell becomes positively charged, the gated sodium channels close and gated potassium channels open. Positively charged potassium rushes out of the cell. The cell returns to a negative charge. In the meantime, sodium-potassium pumps work to keep the gradient of sodium and potassium unequal within the cell. This way the cell is ready for the next impulse – sometimes refereed to simply as the action potential.
Peripheral Nervous System:
All our nerves are part of either the peripheral nervous system or the central nervous system. Most scientists classify the brain, spinal column, and the nerves associated with these masses of ganglia as part of the central nervous system. That leaves the peripheral nerves that control muscles, and our senses. These nerves make up the peripheral nervous system. The two major divisions of this system are the sensory division (nerves sending impulses from sensory organs) and the motor division (nerves controlling muscles).
Motor Division
It’s fairly easy to visualize nerves sending impulses to our muscles when we tell them to move. We move our fingers to type on the computer and we control where we walk. Yet, there are lots of muscles that are sent impulses without us even thinking about it. Muscles in our stomach move without use even knowing it. The motor division of the peripheral system also sends impulses to glands. We divide up the moto division into two classes – the autonomic nervous system and the somatic nervous system.
Somatic Nervous System:
The somatic nervous system consists of muscles that are controlled consciously. When we move our skeletal muscles we do this all consciously. Most of the time we have full control over our muscles. Only during times of stress might the nervous system take over. When you touch something hot for instance, its sometimes hard to stop yourself from pulling away. Your blinking reflex is another example. Try not blinking when you sneeze for instance.
Autonomic Nervous System:
The autonomic nervous system controls bodily functions that are not under conscious control. The movement of our digestive system would be part of this system. Most of the glands in our body are controlled by our nervous system yet we never know about it. The autonomic nervous system is further divided up into two more systems, the sympathetic nervous system and the parasympathetic nervous system. Just as a hang-glider controls his altitude by pushing or pulling on the bar in front of him, these two systems work to push and pull against each other, and thus maintain homeostasis. The control of heart rate is a classic example. The sympathetic nervous system increases heart rate and the parasympathetic nervous system decreases it. There are many other examples of how these two systems work in tandem, but the take home point is that both work together to help maintain equilibrium in the body.
Sensory Systems:
The human boy has the ability to sense the environment and respond to it. We can sense chemicals in our food. They give us smells and tastes. Cells in the back of the eye respond to light and help us produce images of the world around us. Cells in the skin respond to pressure, and allow us to feel objects. Our ears allow us to detect sound waves and aid in our balance. Each of these systems is complex, but they all work because of mechanisms that send stimuli to our central nervous system. The following are but a few of the senses and sense organs that help send information to the brain.
Touch – The Skin
Smell – The Nose
Taste – Taste Buds
Hearing – The ear
Sight – The Eye
Central Nervous System:
The central nervous system serves as the processing system for the nerve impulses received from the peripheral nervous system. All of our sense organs send information to the spinal chord and the brain. Both of these areas are responsible for complex task management. The spinal-chord does less processing, but is the root for most of our reflexes (automatic responses to stimuli). The brain on the other hand, is divided up into many regions, which control different parts of the body.
The Brain: Thinking Headquarters
Almost all nerve processing takes place in the major regions of the brain – the cerebrum, cerebellum, and brain stem. Each of these regions controls a different part of the body. But the brain does more than just command the ever changing body. It also changes with time depending on environmental conditions. We’ve outlined the major regions of the brain below. Scroll over each section to learn about what it does.
The Spinal Chord:
The spinal-chord is the main communication link between the brain and the rest of the body. The spinal-chord is different from the vertebral column. It resides inside and is protected by the bony vertebral column. Because the spinal-chord acts to combine nerves from several regions around the body, damage to the spinal-chord can result in loss of communication from the brain to that bodily region. This is often what happens when someone becomes paralyzed.
In very simple terms, our bodies are on drugs! We are full of complex chemicals, produced by our endocrine system that make us do all sorts of things. Serotinin, dopamine, oxytocin and testosterone are but some of the chemicals that play a role in this complex mix of drugs. Learning to identify these natural drugs in our body is enlightening because it will allow you to understand while you feel stressed, anxious, bold and confident. Everything comes back to the drugs your body releases.
The endocrine system is a way for the body to send signals, much like the nervous system. Yet, unlike the nervous system which can relay “messages” quickly, the endocrine system moves much slower. The system of glands which secrete hormones help regulate the body and makes up the endocrine system. These hormones regulate many functions in an organism including mood, growth and development, tissue function and metabolism
A Quick Video Review
This short video gives the basics of the Endocrine System.
The Glands of the Endocrine System
The major glands in the body that make up the endocrine system are the hypothalamus, pituitary, thyroid, parathyroids, adrenals, pineal body, and the reproductive organs (ovaries and testes). The pancreas also works with the endocrine system in addition to aiding in digestion.
Have you ever noticed that on hot days when you havn’t had enough to drink, your urine is dark yellow or even orange? At other times, when you’re well hydrated it can be almost clear. This is because you have a system in your body that helps you maintain homeostasis. The water you drink doesn’t just dilute your blood, but is regulated by a series of organs in the excretory system.
The excretory system doesn’t just maintain a proper water balence though. The primary role of the excretory system is to filter wastes from the body and get rid of them. The primary organs responsible for this are the kidneys, bladder, and liver among others. We’ll go into detail on the functions of each
An Excretory System Review
Watch this video for a quick review. Notice that the video calls the excretory system, the urinary system. This is another common name for the system.
The Kidneys
While the Excretory system is made up of the kidneys, the blood vessels that carry blood to them, the urinary vessels and the bladder, the kidneys play arguably the biggest role.
Humans have two kidneys that work identical. The main role of the kidneys is to filter out waste from the blood. To do this it first takes almost everything out of the blood, and then puts back only what the body needs.
Think of the kidneys as a person that sorts a messy drawer. First, this person takes all the materials out of the drawer. They sort through the items that were in the drawer and only put back the things that need to be there. The rest of the material can be thrown away. The kidneys are just the same.
A detailed look at the Kidney
To explain the action of the kidney we found a wonderful video produced from a grant made by the University of Rhode Island. While this video goes into more detail than most We found a great video that explains the action job of explaining how the kidneys are able to filter out ions. Be warned that this is a college level video.
Transcription of the Video
We transcribed the content of the video to help those that would rather read the material.
As everyone knows, we have two kidneys each functioning independently. Diuretic action occurs in the kidney. This is where the body controls filtration, re-absorption and excretion of water, small molecules and ions such as sodium and potassium. The outer layer of the kidney is called the cortex, the inner layer is the medulla. This is where we have millions of special structures called nephrons. We will now zoom in to a single nephron. The nephron is a tubular structure similar to a porous pipe or hose. The glomerulus serves as a starting point for a flow through the nephron. First, the blood enters the glomerus through the afferent arteriole. The blood exits the glomerus through efferent arteriole. The glomerus is where the blood supply is filtered by osmosis and diffusion. As blood passes through the porous capillary loops, water and molecules smaller than about 50,000 molecular weight are filtered, passing into the Boweman space. This creates the luminal fluid, flowing through the nephron tubule. About 1/5th of the total blood volume is continually filtered into the Bowman’s capsule. About 99% of this volume is reabsorbed, leaving only a small volume to be reabsorbed, leaving only a small volume to be excreted as urine. Each section of the nephron has a different morphology of cells, making up the single cell wall which causes differences in water permeability and ion transport.
The first section of the nephron is called the proximal convoluted tubule. The proximal convoluted tuble is highly permeable and about 65% of the filtered sodium and water leak out to be reabsorbed into the nearby capillaries. Old diuretics called cabonic anhydrase inhibitors mostly work on this portion of the nephron. The proximal convoluted tubule leads into the lupe of Henle which has a thin descending limb and the thin and thick ascending limb. The thick ascending limb normally reabsorbs about 25% of the filtered sodium but does not allow water to reabsorb. The loop diuretics act here by blocking sodium potassium chloride ion cotransporters on the luminal membrane. The next section is called the Distal Convoluted Tubule. This section does not allow water to reabsorb, but reabsorbs sodium through the sodium chloride ion cotransporters. The phioside diuretics act here on this transporter.
The last section of the nephron is called the collecting tubule. Sodium channel blockers and aldestron antagonistic diuretics act here.
At each site along the nephron tubule certain molecules are able to permeate the wall and leak out into the interstecium. These molecules will be reabsorbed into the peritubule capilary and be returned to the peristemic blood supply.
Now we will zoom inside the tubule and then show the molecular details of reabsorption. This is a single layer of cells making up the tubule wall. Ions and water molecules flow through the tubule. This image shows a single cell layer making up the wall of the ascending limb of the nephron. This sodium reabsorption is driven by the sodium potassium ATPase transporter on the antiluminal membrane.
For every three sodium ions moving out of the cell to the interstetium, two potassium ions move from the interstetium to the inside of the cell. This causes a deffecite of the sodium within the cell. This deficite is madeup by the sodiumm potassium chloride transporter on the luminal membrane of the cell. This transporter moves one potassium, one sodium and two chloride ions from the lumen into the wall of the nephron. The potassium and chloride ions move down their concentration gradients through their respective channels. The potassium returns to the lumen via a potassium channel. The chloride is removed to the interstecium through a chloride channel. The net result is a continuing transport of three sodium ions and six chloride ions from the luminal fluid into the interstetium. This sodium is reabsorbed into the circulation. Because of the secretion of potassium, a positive voltage is generated in the lumin, resulting in reabsorption of positive ions through the pericellular junction.
When the sodium potassium chloride transporter is blocked by the loop diuretics, the sodium potassium exchange begins. But the sodium deficit can not be replaced by the sodium from the lumen. This blocks the overall re-absorption of sodium from this site and the nephron. The net result is greater excretion of sodium, Chloride, Potassium, Magnesium, Calcium in the presence of the loop diuretics.
Then next site for diuretic action is the distal convoluted tubule. This is where the thiazide diuretics act.
The transporters present in the distal convoluted tubule are slightly different for those described in the ascending limb. In the distal convoluted tubule, the sodium chloride co-transporter replaces the sodium deficit caused by the sodium potassium ATPase. The chloride is reabsorbed through chloride channels and the potassium returns to the interstetium through a potassium channel. This sequence results in overall sodium and chloride re-absorption. However, the thiazide diuretics bind at the chloride binding site and block the sodium chloride co-transporter. This blocks sodium and chloride re-absorption resulting in net excretion of sodium and chloride.
The last site for diuretic action is the connecting and collecting tubules. This is where the sodium channel inhibitors act.
Again, the transporters present in the collecting tubule are slightly different than at the other sites of the nephron. At this site the same sodium potassium exchange occurs on the antiluminal membrane. However, the sodium is replaced at this site by the sodium channels on the luminal membrane and potassium excretion is completed by transport through potassium channels on the luminal membrane. This continuing exchange results in overall sodium reabsorption and potassium excretion.
When the sodium channel inhibitors are present they block the sodium channel. The prevents the continual re-absorption of sodium and also prevents the overall excretion of potassium. This is why sodium channel inhibitors are called potassium sparing. Thus, all of the diuretic agents described directly decrease the reabsorption of sodium by blocking specific ion transporters in the various segments of the nephron tubule. This indirectly affects re-absorption and excretion of water and other ions as described for each type of diuretic.
The respiratory system works with the circulatory system to bring in oxygen to the body and release carbon dioxide. This system acts to bring in air from outside the body, filter it, moisten it, warm it and bring it into contact with small capillaries of circulatory system.
From Nose to the Lungs
The respiratory system includes parts of the body that bring air to the lungs. This includes the nose, pharynx, larynx, trachea, bronchi, and lungs as seen below:
The nose serves as the first defense to foreign particles. Have you ever thought about giving your dad nose hair clippers? Those hairs serve an important role in trapping large particles in the air. The snot that comes out of your nose also serves to trap particles. If you’re not convinced, notice how your snot changes when you’re breathing in smoke and dust.
From the nose, air flows down the pharynx. Up to this point, air and our food will flow down the same pipe. However, a small flap known as the epiglottis helps to send air and food down different tubes. Air continues to flow down the larynx, the area where our vocal chords are found. From here it inters the trachea. The trachea has small cilia that help trap any extra foreign particles.
From the trachea the air enters the two bronchi of the lungs. At the end of each bronchus is one of our two lungs.
From the Lungs to the Blood
Humans have two lungs, each fed by one bronchus. The bronchi, that feed the lungs with air split into smaller and smaller tubes, called bronchioles, that eventually lead to small air sacs called alveoli. The alveoli are grouped into small clusters and are wrapped in a tight network of capillaries. Each capillary interacts with one alveolus to get oxygen to the red blood cells and release carbon dioxide.
Controlling our Respiratory System
Have you ever taken a yoga class where you have been asked to take deep breaths and control your breathing? If so, you’ll have realized that we can consciously control when we breathe. However, most of the time we don’t have to think about breathing, and thus, you could say that your nervous system controls it without us having to even think about it. But how exactly do we force air in and out of our lungs?
Our lungs can pump air in and out because of the muscles of the ribs and our diaphragm. Our diaphragm contracts and the rib cage enlarges as we inhale. Exhalation is caused by our rib cage shrinking and the diaphragm relaxing. Extra force is created when we blow on a fire as abdominal muscles contract.
Case Study: Freedivers
Competitive free divers need to understand how their respiratory system interacts with their circulatory system and nervous system. They can do exercises to increase the size of their lungs. They can train their brain to allow them to hold their breath longer and they can do certain warm-up routines to decrease the amount of carbon dioxide in their blood. Lets explore in detail how a free diver uses all these techniques to master his sport.
First, the size of the lungs can directly affect how much oxygen the free-diver is able to get to his blood. Free divers will do exercises that slowly, over time allow their lungs to get bigger. One of these exercises might involve taking large breaths. Once a large breath is taking, a free diver might try to “pack” his lungs by gulping more air. This exercise is somewhat dangerous, however, and unless you are trained by a professional and it shouldn’t be attempted.
The second thing a free diver must understand is that the brain uses certain cues to initiate breathing reflexes. In particular, a part of the brain known as the medulla oblongata is able to monitor the carbon dioxide level in the blood. When levels get too high, breathing reflexes are initiated. Note that it is NOT the amount of oxygen in the blood that induces breathing. Knowing this a free diver may hyperventilate to remove more and more carbon dioxide before diving. This essentially tricks the body into not initiating a breathing response. This technique, however, is somewhat out-dated. The technique is extremely dangerous and could lead to shallow water blackout (where a free diver looses consciousness due to lack of oxygen – often this happens as the diver ascends to the surface and the partial pressures of certain gasses change).
Finally, a free-diver can train to help slow his heart rate during a descent. This decreases oxygen consumption to skeletal muscles, and thus increases the amount of time a diver can stay underwater.
Our respiratory system is extremely important. It works hand in hand with the circulatory system to get oxygen to the cells that need them and it helps transport carbon dioxide out of the body. One should note, however, that the respiratory system of mammals isn’t necessarily how all animals’ respiratory systems work. Birds for instance, have a drastically different breathing technique that allows them to get even more
oxygen from each breath. We encourage you to explore as much as you can about the adaptations of different animals. How might their own respiratory systems aid them in how they live? Here are some things to think about:
How can whales dive so deep for so long.
How can migratory birds, who have fly for hours on end, get enough oxygen to their wings.
Do all large animals breath with lungs? We’ve always heard that frogs can breath through their skin? Is this true – do they have lungs like us?
We hope these questions help you think of more! In fact, share your questions with us in the comment section below. Together we may be able to answer yours!
Which of these is the result of a parasitic infection of the lymphatic system that causes enormous swelling of the legs and scrotum?
A. Hypertrichosis
B. Cotard’s Syndrome
C. Elephantiasis
D. Wolf-Parkinson-White Syndrome
Drum roll please…..
If you answered C, congratulations! If you answered A, B, or D, keep reading.
The lymphatic system is responsible for absorbing excess interstitial fluid and transporting this fluid, called lymph, to ducts that drain into veins. The lymphatic system is also responsible for producing lymphocytes, which are the white blood cells involved in immunity.
The lymphatic system has three main roles: to transport interstitial fluid originally from blood filtrate back to the blood, to transport absorbed fat from the small intestine to the blood, and to provide immunological defense against pathogens.
As blood circulates throughout the body supplying oxygen to tissues, some fluid leaks from the blood into the surrounding tissues (interstitial fluid is formed by filtration of plasma out of blood capillaries). This leakage helps maintain an efficient movement of nutrients and salts from blood into the tissues. Because more than 3 liters of fluid leak from the circulatory system into tissues every day, some of that fluid must return to the circulatory system, otherwise a person would swell up like a balloon. Fortunately, the lymphatic system exists to remove excess fluid from our tissues.
Once fluid collects in lymphatic capillaries, it is referred to as lymph. Lymphatic capillaries are microscopic close-ended tubes that form immense networks in the intercellular spaces within most organs. These capillaries have porous junctions, therefore allowing interstitial fluid, proteins, extravasated white blood cells, microorganisms, absorbed fat, and fat-soluble vitamins to enter. The lymph is carried into larger lymph vessels called lymph ducts. Lymph ducts are similar to veins in that they contain valves to prevent backflow. The lymph moves via peristaltic waves of contraction throughout the lymph vessels until the lymph empties into either the thoracic duct or the right lymphatic duct. These ducts drain into the left and right subclavian veins, respectively. Thus, interstitial fluid is ultimately returned to the cardiovascular system.
Lymph nodes help remove pathogens from the lymph before it enters the circulatory system. Lymph nodes contain phagocytic cells which act as filters, trapping bacteria and other microorganisms that cause disease. If you have had “swollen glands”, then your lymph nodes were swollen in your neck, helping trap and destroy bacteria and other pathogens. The tonsils, thymus, and spleen—the lymphoid organs—are all sites of lymphocyte production. Certain lymphocytes, called T cells, mature in the thymus before they function in the immune system. T cells respond to antigens, which provoke an immune response from one’s body. Although the lymphatic system transports lymphocytes for immune protection, it may also transport cancer cells through the porous lymphatic capillaries, thereby helping cancer metastasize.
Now, finally to explain our trivia question… Lymphedema is excessive protein and associated fluid in the interstitial tissue, caused by inadequate lymphatic drainage. In tropical equatorial regions in the world, most commonly in Africa, a parasitic infection of the lymphatic system causes elephantiasis. Elephantiasis is a lymphedema that produces massive swelling of the legs and scrotum. The skin develops a rough appearance and usually darkens. Lymph flow also becomes obstructed. This disease is caused by a species of nematode worms, and is transmitted by mosquitoes. Chemotherapy, antibiotics, and lymphatic massage have all proven to be helpful treatments.
Take a look at this video about the lymphatic system!
References:
Fox, Stuart I. “Blood, Heart, and Circulation.” Human Physiology. 10th ed. New York, NY: McGraw-Hill, 2008. 424-25. Print.
A classic way to think about the human body is to think about it as like a miniature city. Individuals in a city are like the different cells of your body. Groups of individuals work in offices, doing different jobs just like organ systems, which are made of many cells perform different jobs within your own body. So what is the city equivalent of the circulatory system?
The circulatory system can be described as the road network within our city example. Like a road system, it carries food to individual homes and carries waste away. There are major highways (arteries and veins), and side alley ways (capillaries). In our bodies, blood is a specialized bodily fluid that flows down the roads which carries nutrients and oxygen to cells and carries wastes like carbon dioxide and urea away.
An average human has about 5 liters of blood that flows through the circulator
y system. Some of the major steps of the circulatory system include the passage through the heart (coronary circulation), the movement to the lungs where it picks up oxygen (pulmonary circulation), and the transport of that oxygen to the rest of the body (systemic circulation).
Circulatory System Video Introduction
For our middle grades series with Pearson publishing we created a video for every topic in human biology. Pearson was kind enough to let us release a few, just so that you can get a taste for what we’ve been up to. In this video, we start off by using the road analogy to talk about the circulatory system. Jonas and Haley then take us all on an amazing journey through some of the most interesting facts about this human biology topic. We hope you enjoy it, we had fun making it!
Some of the biggest parts of the circulatory system include the following:
