Homeostasis and human body systems
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Homeostasis and Human Body Systems. Imagine you are playing softball on a warm summer day. Write down two ways that your body would adjust to keep you cool and to keep your muscles working. Key Ideas. How does a change in the external environment affect an organism?

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Homeostasis and Human Body Systems

Imagine you are playing softball on a warm summer day. Write down two ways that your body would adjust to keep you cool and to keep your muscles working.

Key Ideas

  • How does a change in the external environment affect an organism?

  • How does an organism respond to changes, and what happens if the organism fails to respond to changes?

  • What organ systems do humans need in order to survive?

  • How is the human body organized?

  • What is Homeostasis?

Human Body Systems

  • Which body systems are the basketball players using?

  • Recall levels of organization in an organism

    • Cells

    • Tissues

    • Organs

    • Organ system

What is Homeostasis?

  • The process by which organisms maintain a relatively stable internal environment

  • How does the human body maintain homeostasis?

    • The eleven organ systems of the human body work together to maintain homeostasis.

    • Homeostasis is the process by which organisms keep internal conditions relatively constantdespite changes in external environments.

To help understand homeostasis lets think about how a thermostat works

Decrease room temperature

Increase room temperature

Increase room temperature

A Changing Environment

  • The external environment around an organism is constantly changing.

  • These changes threaten the stability of an organism’s internal environment.

  • The maintenance of a relatively stable internal environment is called homeostasis.

  • Change in seasons, light level, water availability, or other changes to the external environment can change an organism’s internal environment.

  • Different organisms deal with these changes in different ways.

  • In a colder environment, for example, organisms may eat more food, puff out fur or feathers, fly to warmer areas, or hibernate.

Responses to Change

  • Organisms must carry out many chemical reactions to grow, obtain energy, and reproduce.

  • Many organisms also move, breathe, produce heat, and do other tasks.

  • All of these activities require the organism to maintain a relatively stable internal environment.

Responses to Change

  • Organisms detect and respond to both internal and external environments in a variety of ways.

  • Detection and response can take place at both the cellular and organismal level.

  • Failure to respond to change can result in an organism’s death.

Now let’s take a look at how plants maintain homeostasis:

  • Leaves of plants are covered on the top and bottom by epidermis made of a layer of tough, irregularly shaped cells.

  • The epidermis of many leaves is also covered by the cuticle.

  • Together, the cuticle and epidermal cells form a waterproof barrier that protects tissues and limits the loss of water through evaporation.

Stomata (singular: stoma), are pore-like openings in the underside of the leaf that allow carbondioxide and oxygen to diffuse into and out of the leaf. Each stoma consist of: two guardcells, the specialized cells in the epidermis that control the opening and closing of stomata by responding to changes in water pressure.

Responses to Change

  • The pores on a plant’s leaf help the plant to regulate water loss and gas exchange.

  • During the day, tissues perform photosynthesis.

  • Guard cells near these active tissues swell with water. This opens pores, letting in the carbon dioxide that is needed for photosynthesis

Responses to Change

  • Open pores also allow water to exit the leaf.

  • At night, when photosynthesis slows, water exits the guard cells.

  • The cells shrink and close the pores, preventing excess water loss at night.

Control of Stomatal Opening

Responses to Change

  • If an organism is not able to respond to changes in its environment, disease or death can result.

  • Consider what would happen if a plant could not slow water loss.

  • When the amount of water in a plant’s tissues got too low, the plant would wilt, collapse, and die.

Responses to Change

  • Humans must also control internal water levels.

  • About 2/3 of the human body is made of water.

  • If a person loses too much water, by sweating or urination, dehydration will occur.

  • Dehydration causes blood pressure to drop significantly until death occurs.

Responses to Change

  • Some deep-water fish must be adapted to deal with high water pressure.

  • The coelacanth is a fish that lives in the deep waters off the coast of Africa.

  • At the depth where the fish lives, water pressure is several hundred times greater than the water pressure at the ocean’s surface.

Responses to Change

  • If a person tried to swim at this pressure, the person’s body would be crushed.

  • The coelacanth will actually die in the low-pressure environment at the water’s surface.

  • The coelacanth’s body is adapted to require high pressure, in order to keep gases from bubbling out of the fish’s bloodstream and blocking flow to the fish’s heart.

Humans and Homeostasis

  • Humans are constantly subjected to environmental stresses that threaten to upset the delicate balance that exists within our cells and tissues.

  • Humans require multiple systems for digestion, respiration, reproduction, circulation, movement, coordination, and immunity.

  • These systems interact to maintain homeostasis.

  • Summary of Human Body Systems

Humans and Homeostasis

  • The organs and systems of the human body help to provide all of the cells with their basic needs.

  • Each cell needs a constant supply of nutrients and oxygen, removal of waste materials, and protection from disease.

  • With the exception of the reproductive system, each of the human body systems performs a task that helps stabilize the body’s internal environment.

Humans and Homeostasis

  • In the human body, the main components of homeostasis are the following:

    • the concentration of salts

    • The pH of the internal environment

    • The concentration of nutrients and waste products

    • The concentration of oxygen and carbon dioxide

    • The volumeand pressure of extracellular fluid

Humans and Homeostasis

  • When these five components are adequately controlled, homeostasis is maintained and the body is most likely healthy.

  • No organ system can maintain homeostasis by itself.

  • Organ systems must work together in a synchronized manner.

Humans and Homeostasis

  • For example, the concentration of oxygen and carbon dioxide is controlled by four different body systems.

  • First, the respiratory system brings oxygen into and carbon dioxide out of the body.

  • The circulatory system distributes the oxygen to the body’s tissues and picks up carbon dioxide.

Humans and Homeostasis

  • If the level of carbon dioxide gets too high, the nervous system instructs the muscular system to make the muscles around the rib cage work harder.

  • This action allows the lungs of the respiratory system to breathe faster, to get rid of excess carbon dioxide.

Key Ideas

  • How does a change in the external environment affect an organism?

    • The external environment around an organism is constantly changing. These changes threaten the stability of an organism’s internal environment.

  • How does an organism respond to changes, and what happens if the organism fails to respond to changes?

    • Organisms detect and respond to change in a variety of ways: both at the cellular level and at the organismal level. Failure to respond to change can result in an organism’s death.

Key Ideas

  • What organ systems do humans need in order to survive?

    • Humans require multiple systems for digestion, respiration, reproduction, circulation, movement, coordination, and immunity. The systems interact to maintain homeostasis.

Human Body Systems

Alternately bend and straighten your arms or legs while feeling the muscles in the front and the back.

Write down what you feel when the limb is straightened and what you feel when the limb is bent.

Key Ideas

  • How do the skeletal and muscular systems help the body maintain homeostasis?

  • How does the integumentary system help the body maintain homeostasis?

  • How do the nervous and endocrine systems help the body maintain homeostasis?

Key Ideas

  • How do the digestive and excretory systems help the body maintain homeostasis?

  • How do the circulatory and respiratory systems help the body maintain homeostasis?

Skeletal and Muscular Systems

  • The skeletal and muscular systems enable movement and provide support for tissues and organs.

  • Bones and muscles work together to make movement possible.

  • The ability to move increases the chance of survival by allowing a person to gather food, seek shelter, and escape from danger.

Skeletal and Muscular Systems

  • The skeleton provides an anchor for the muscles that move the body.

  • There are 206 bones in a human adult

Axial skeleton – supports the central axis of the body; skull, vertebral column, and rib cageAppendicular skeleton – bones of arms and legsWhat do you think is a better model of a bone, a stick of chalk or a sponge?The chalk may look more like a bone but the sponge shows what the structure actually looks like inside.

What passes through the tubes and spaces inside bone?

Blood vessels and nerves


Bone is surrounded by a tough layer of connective tissue

Haversian canals

Network of tubes that contain blood vessels and nerves.

Bone marrowCavities that contain a soft tissue

  • There are two types of bone marrow:

  • yellow and red

    • Yellow marrow is made up primarily of fat cells.

    • Red marrow produces red blood cells, some kinds of white blood cells, and cell fragments called platelets.

Cartilage-Cells are scattered in a network of protein fibers—tough collagen and flexible elastin.

  • Cartilage does not contain blood vessels.

  • Cartilage cells must rely on nutrients from the tiny blood vessels in surrounding tissues.

  • Cartilage is dense and fibrous, it can support weight, despite its extreme flexibility

Ossification-Cartilage is replaced by bone during the process of bone formation

  • Osteoblasts create bone.

  • Osteocytes maintain the cellular activities of bone.

  • Osteoclasts break down boneForce must be placed on bone for ossification to occur, because it is force that stimulates the osteoblasts to secrete the minerals that replace cartilage

What effect do you think an exercise such as walking would have on the bones of the legs?

  • It would stimulate ossification, so the bones would contain more minerals and be stronger.

    What do you think might happen to the bones that are not exposed to force, such as the bones of astronauts in zero gravity?

    • The bones would lose minerals because of lack of force exerted on them, so they become weaker

  • Bone formation occurs in babies and children

  • Seven months before birth cartilage is gradually replaced by bone

  • When a person grows, the growth plates are lengthening in the long bones

  • When you stop growing, those growth plates are then filled in with bone

  • Adults do retain some cartilage

    • Tip of nose, ears, where ribs attach to the sternum

  • Bone formation also occurs when a bone is broken

  • Osteoclasts remove damaged bone tissue

  • Osteoblasts produce new bone tissue

  • The repair of a broken bone can take months because the process is slow and gradual

Depending on its type of movement, a joint is classified as immovable, slightly movable, or freely movable

Immovable Joints

  • Where the bones in the skull meet

    Slightly Movable Joints

  • The joints between the two bones of the lower leg and the joints between adjacent vertebrae are examples of slightly movable joints.

    Freely Movable Joints

  • Ball-and-socket joints permit circular movement—the widest range of movement

  • Hinge joints permit back-and-forth motion, like the opening and closing of a door

  • Pivot joints allow one bone to rotate around another

  • Saddle joints permit one bone to slide in two directions

  • Structure of joints

  • Ends of bones are covered with a smooth layer of cartilage

  • Joints are surrounded by a fibrous joint capsule that helps hold bones together

  • Tendons attach muscles to bones.

  • When muscles contract, tendons pull on bones to cause movement.

  • LIGAMENTS – strip of tough connective tissue that hold bones together

  • Synovial fluid – lubricates the ends so bones can slide past each other smoothly

Opposing Muscles in the Arms

Skeletal and Muscular Systems

What are the three types of muscle?

  • Skeletal

  • Smooth

  • Cardiac

Skeletal Muscle

  • Skeletal muscles are usually attached to bones

  • Skeletal muscles are responsible for such voluntary movements as typing on a computer keyboard, dancing, or winking an eye

  • When viewed under a microscope at high magnification, skeletal muscle appears to have alternating light and dark bands or stripes called striations. For this reason, skeletal muscle is sometimes called striated muscle

  • Most skeletal muscles are controlled by the central nervous system.

Smooth Muscles 

  • Smooth muscles are usually not under voluntary control

  • A smooth muscle cell is spindle-shaped, has one nucleus, and is not striated

  • Smooth muscles are found in hollow structures such as the stomach, blood vessels, and the small and large intestines

  • Smooth muscles move food through your digestive tract, control the way blood flows through your circulatory system, and decrease the size of the pupils of your eyes in bright light.

Cardiac Muscle 

  • Cardiac muscle is found in just one place in the body—the heart

  • The prefix cardio- comes from a Greek word meaning “heart.”

  • Cardiac muscle is striated like skeletal muscle, although its cells are smaller.

  • Cardiac muscle cells usually have one nucleus, but they may have two.

  • Cardiac muscle is similar to smooth muscle because it is usually not under the direct control of the central nervous system

Muscle Contraction

  • A muscle contracts when the thin filaments in the muscle fiber slide over the thick filaments

  • The energy for muscle contraction is supplied by ATP

    Neuromuscular junction

  • The point of contact between a motor neuron and a skeletal muscle cell

How do body builders get muscles that increase insize?

  • Muscles that are exercised regularly stay firm and increase in size by adding more material to the inside of the muscle cells


  • Skin is the largest organ of the human body.

  • Skin makes up about 7% of your total body weight.

  • The skin, hair, and nails form the integumentary system.

Integumentary System

  • The integumentary system does the following:

    • protects the body from injury and UV radiation

    • defends against disease

    • helps regulate body temperature

    • prevents the body from drying out


Integumentary System


  • The epidermis is the outermost layer of skin.

  • It is made of flattened, dead cells composed of a protein called keratin.

  • Keratin is also found in nails and hair.

Integumentary System

  • Keratin makes the skin tough and waterproof.

  • Glands in the dermis, the layer of skin under the epidermis, secrete oil that lubricates the skin.

  • Without the protection of keratin and oil, our bodies would lose water through evaporation or absorb water from the environment.

Integumentary System

Disease Prevention

  • The epidermis forms a tight barrier that keeps bacteria out and protects the body from disease.

  • Damage to large areas of skin allows bacteria to enter the body freely.

  • This lack of protection is one reason why severe burns are so dangerous.

Integumentary System

UV Prevention

  • The lower layers of the epidermis contain cells that make melanin, a pigment that absorbs UV light.

  • This absorption prevents DNA damage, which can cause skin cancer.

Integumentary System

Temperature Regulation

  • A network of blood vessels and nerves in the dermis help regulate body temperatures.

  • Sweat glands also help remove excess body heat through the evaporation of sweat.

The Nervous System

What is the function of the nervous system?

  • It controls and coordinates functions throughout the body and responds to external and internal stimuli

Neuron – cells that transmit impulses

What is an impulse?

  • Message carried by the nervous system as electrical signals

3 Types of Neurons

  • Sensory – carry impulses from sense organs to the spinal cord

  • Motor – carry impulses from brain and spinal cord to muscles and glands

  • Interneurons – connect sensory and motor neurons and carry impulses between them

Typical neuron*Draw the direction an impulse travels

Cell body – largest part of a neuron; contains the nucleus and most of the cytoplasmDendrites – short, branched extensions spreading out from the cell body; receive impulsesAxon – long thin fiber that carries impulses away from the cell bodyAxon terminal – end of an axon that sends impulses to another neuron

Nerve – bundles of dendrites and axons all clustered together

  • How an impulse occurs:

  • A nerve impulse begins when a neuron is stimulated by another neuron or by its environment.

  • The impulse travels along the axon away from the cell body and toward the axon terminal.

  • At the end of a neuron, the impulse reaches an axon terminal.

  • Usually the neuron makes contact with another cell at this location – neuron, muscle cell

Synapse – the location at which a neuron can transfer an impulse to another cell; aka: synaptic cleft, gap

Nervous and Endocrine Systems

  • The nervous system is composed of signaling cells that collect and respond to information about the body’s internal and external environment.

  • The central nervous system (CNS) includes the brain and spinal cord.

  • The brain is the body’s main processing center. It coordinates the body’s efforts to maintain homeostasis.


  • Cerebrum – largest and most prominent region of human brain

    • Controls voluntary or conscious activities of the body

    • Site of intelligence, learning, and judgment

    • Two hemispheres – each half controls the opposite side of the body

  • Cerebellum – second largest region located at back of skull

    • Coordinates and balances the actions of muscles so the body can move gracefully and efficiently

  • Brain Stem aka: medulla oblongata and pons – connects brain and spinal cord; located just below cerebellum

    • Regulates flow of information between brain and rest of the body

    • Controls blood pressure, heart rate, breathing, and swallowing

  • Thalamus – found between brain stem and cerebrum; receives messages from sense organs; relays information to the proper region of the cerebrum for further processing

  • Hypothalamus– located between brainstem and cerebrum; control center for recognizing and analyzing hunger, thirst, anger, fatigue, and body temperature

    • aka-the thermostat

Structure of the Human Brain

Nervous and Endocrine Systems

  • The spinal cord is a column of nerves that links the brain to most of the peripheral nervous system (PNS).

  • The PNS contains sensory and motor nerves.

  • Sensory nerves carry information to the central nervous system from sense organs such as the skin.

What are the 5 types of sensory receptors?

There are five general categories of sensory receptors:

  • Pain receptors

  • Thermo-receptors

  • Mechano-receptors

  • Chemo-receptors

  • Photo-receptors

Where are these receptors located?

  • Pain receptors – throughout body except the brain

  • Thermoreceptors – skin, body core, and hypothalamus

  • Mechanoreceptors

    • skin, skeletal muscles, and inner ear they are sensitive to touch, pressure, stretching of muscles, sound and motion

  • Chemoreceptors

    • nose and taste buds

  • Photoreceptors

    • eyes

Vision - eye

  • Photoreceptors – arranged in a layer in the retina (layer in back of eye)

    • rods – extremely sensitive to light

    • cones – distinguish colors

Hearing and Balance – ear

  • Tympanum

    • aka: ear drum

  • Hammer, anvil, and stirrup

    • three tiny bones

  • COCHLEA – has tiny hair cells that move with sound vibrations and sends message to nerve

  • SEMICIRCULAR CANALS – filled with fluid and tiny hairs – they can sense which direction your head is in due to gravity

  • EAR INFECTION – usually in middle ear due to Eustachian tube

  • Smell and Taste – nose and mouth

    • Ability to sense chemicals

    • Chemoreceptors line your nose and taste buds located in mouth

  • Touch – skin

    • The places that are more sensitive to touch – fingers, toes, and face

    • Has more sensory receptors

Nervous and Endocrine Systems

  • Motor nerves carry commands from the central nervous system to muscles and other organs, such as glands.

Also involved with reflexes ex) you touch a hot stove – your hand pulls back before you sense the pain – Reflex Arc - this information goes from hand to spine back to hand again; it never reaches the brain because it would take too long

Nervous and Endocrine Systems

  • Motor nerves are grouped into two independent systems:

    • autonomic nervous system

    • somatic nervous system

Nervous and Endocrine Systems

  • Motor nerves that are not under conscious control are part of the autonomic nervous system

  • Some ways that the autonomic nervous system maintains homeostasis include:

    • stimulating digestion after a meal

    • slowing down the heart rate after exercise

    • preparing the body for stressful situations

Nervous and Endocrine Systems

  • Motor nerves that are under conscious control are part of the somatic nervous system.

  • The nerves we use to signal our legs or arms to move are part of the somatic nervous system.

  • The somatic system also operates without conscious control, to help us maintain balance.

  • Comparing Autonomic and Somatic Nervous Systems

Drugs and the Nervous System

Key Concept Questions:

What are the different classes of drugs that directly affect the central nervous system?

What is the effect of alcohol on the body?

What is a drug?

  • Any substance other than food, which changes the structure or function of the body

    • Ex) antibiotics, cold medicine, cocaine, heroin

  • The most powerful drugs are those that affect the nervous system

Stimulants – increase the actions regulated by the nervous system

  • ex) ecstasy, Ritalin (when not used correctly)

  • Increase heart rate, blood pressure, and breathing

  • Increase release of neurotransmitters at some synapses in the brain

  • This release leads to feeling of well-being

  • When these effects wear off the user quickly falls into fatigue and depression

  • Long term use – can lead to circulatory problems, hallucinations, and psychological depression

  • How might someone behave if they have taken a stimulant?

    • They might be fidgety and restless and eat very little

    Depressants – decrease the rate of functions regulated by the brain

    • ex) Valium, Xanax

  • Lower blood pressure, slow heart rate, relax muscles, and relieve tension

  • Some depressants cause neurotransmitters to remain in receptors so impulses are not passed any more; this causes parts of the brain that sense fear and pain to remain calm

  • User will become dependant to relieve anxietywhen depressants and alcohol are combined the results are usually fatal

  • How might someone behave if they have taken a depressant?

    They might be slow moving and sleepy and speak with a slur

    Cocaine – comes from the leaves of the cocoa plant-causes sudden releasein the brain of neurotransmitter called dopamine-causes ADDICTION– an uncontrollable craving for more of the drug-dopamine is normally released when a basic need has been fulfilled (thirst, hunger)-cocaine tricks the brain into releasing large amounts of dopamine and produces intense feelings of pleasure and satisfaction-when the drug wears off the level of dopamine drops sharply and the user feels sad and depressed-strong psychological dependence-powerful stimulant – increases heart rate, and blood pressure-some first time users can have a heart attack and dieCrack is very potent form of cocaine; highly addictive after one use

    Opiates – comes from flower called poppy ex) morphine, codeine, heroin

    • mimics chemicals in the brain known as endorphins, which normally help to overcome sensations of pain

    • initially they produce strong feelings of pleasure and security but the body adjusts to these high levels and then requires more

    • the body then cannot do without the drug

    • the user who stops taking these drugs will suffer from uncontrollable pain and sickness because the body cannot produce enough of the natural endorphins

    • Many users inject drugs for maximum effect and are at high risk of contracting HIV virus that causes AIDS

    Hallucinogens – drugs that cause hallucinations

    • Ex) PCP, angel dust, LSD, Psilocybin mushrooms, peyote cactus

    • profound distortions in a person’s perceptions of reality.

    • Under the influence of hallucinogens, people see images, hear sounds, and feel sensations that seem realbut do not exist.

    • Some hallucinogens also produce rapid, intense emotional swings.

    • Affects serotonin receptors

    Ecstasy - both a hallucinogenic and a stimulant drug.

    • It makes users experience a rush of good feelings (a high) and makes someone's feelings much more intense, whether they're good or bad.

    • The drug's effects usually last up to 6 hours.

    • increases heart rate and can cause dry mouth, stomach cramps, blurred vision, chills, sweating, or nausea.

    • can make some users feel anxious, confused, and paranoid, like someone is trying to hurt them or is plotting against them.

    • Scientists have recently proven that Ecstasy causes direct damage to brain cells that are involved in thinking and memory.

    • can cause the salts and minerals in the blood to become dangerously diluted (thinned out), which can cause the brain to swell. Permanent brain damage can result.

    • If a person takes Ecstasy, his or her body can dangerously overheat during dancing or other physical activities, which can lead to death.

    Marijuana– comes from cannabis plant

    • active ingredient is THC (tetrahydrocannabnol)

    • causes temporary feeling of euphoriaand disorientation

    • causes lung damage – worse than smoking cigarettes

    • long term use can result in memory loss, inability to concentrate, and reduced levels of testosterone in males

    Alcohol – one of the most dangerous and abused drugs

    • acts as a depressant

    • slows reflexes, disrupts coordination, and impairs judgment

    • too much will cause user to not walk or talk properly

    • Of about 50,000 accidents – 40% are alcohol related

    • Women who are pregnant and drink run the risk of their child developing FETALALCOHOLSYNDROME (birth defects caused by the effects of alcohol on the fetus)

    • Disease called alcoholism – users “need” to have a drink every day to function

    • Long-term use destroys cells in the liver and causes scarring called cirrhosis

    • Heavy drinkers may die from liver failure

    DRUGABUSE – using a drug in any way that most doctors could not approvePsychological dependence – mental craving, or need for the drugPhysical dependence – the body cannot function without a constant supply of the drug

    Which type of addiction do you think would be harder to break – psychological or physical?

    What is the function of the endocrine system?

    The endocrine system is made up of glands that release their products into the bloodstream. These products broadcast messages throughout the body.

    The chemicals that “broadcast” messages from the endocrine system are called hormones.

    Nervous and Endocrine Systems

    • The endocrine system does the following:

      • regulates metabolism

      • maintains salt, water, and nutrient balance in the blood

      • controls the body’s response to stress

      • regulates growth, development, and reproduction


    • Why are hormones needed?

      • chemical messages from one body part to cells in other parts of body

      • communication needed to coordinate whole body

      • maintaining homeostasis

        • energy production

        • growth

        • development

        • maturation

        • reproduction

    growth hormones



    Maintaining homeostasis


    hormone 1

    lowersbody condition


    specific body condition

    raisesbody condition


    hormone 2

    Endocrine System

    • Endocrine system releases hormones

      • glands which secrete chemical signals into blood

        • chemicals cause changes in other parts of body

        • slow, long-lasting response

          • growth hormones

          • sex hormones

          • response hormones

          • metabolism hormones

          • and more….

    Regulation by chemical messengers

    • Neurotransmitters released by neurons

    • Hormones release by endocrine glands

    • Cells that have receptors for a particular hormone are called target cells. If a cell does not have receptors for a hormone, the hormone will have no effect on that cell.

    endocrine gland



    hormone carried by blood

    receptor proteins

    receptor proteins

    target cell

    • Hormones are produced in special cells.

    • Often, these cells are part of an endocrine gland.

    • “Endo-“ means within“Exo-“ means outside

    • An endocrine gland is an organ that produces and releases hormones directly into the bloodstream or into the fluid around cells.

    • Exocrine glands secrete hormones to the outside of the body; they release through tube like structures called ducts


    • Pineal

      • melatonin

    • Pituitary

      • many hormones: master gland

    • Thyroid

      • thyroxine

    • Adrenal

      • adrenaline

    • Pancreas

      • insulin, glucagon

    • Ovary

      • estrogen

    • Testes

      • testosterone



    Body Regulation

    • Nervous system & Endocrine system work together

      • hypothalamus

        • “master nerve control center”

        • receives information from nerves around body about internal conditions

      • communicates with pituitary gland

        • “master gland”

        • releases many hormones

          • sexual development, growth, milk production, pain-relief

    The thyroid gland has the major role in regulating the body’s metabolism

    Hormones produced by the thyroid gland and the parathyroid glands maintain the level of calcium in the blood

    The adrenal glands help the body prepare for and deal with stress



    Insulin and glucagon released from the pancreas help to keep the level of glucose in the blood stable

    When the pancreas produces too little insulin, a condition known as diabetes mellitus occurs.

    In diabetes mellitus, the amount of glucose in the blood may rise so high that the kidneys actually excrete glucose in the urine

    Very high blood glucose levels can damage many organs and tissues, including the coronary arteries.







    Endocrine System Control

    Regulation of Blood Sugar



    body cells takeup sugar from blood

    liver storessugar


    blood sugar level


    liver releasessugar




    • The gonads serve two important functions: the production of gametes and the secretion of sex hormones

    • The female gonads—the ovariesproduce eggs (ova).

    • The male gonads—the testes

    • (singular: testis)—produce sperm.

    Sex & Growth Hormones

    • Large scale body changes

      • how do they work

        • turn genes on

        • start new processes in the body by turning genes on that were lying “dormant”

    Digestive and Excretory Systems

    Digestive System

    • The digestive system converts food into nutrients that a body’s cells can use.

    • Some nutrients are used in metabolic reactions.

    • Other nutrients are used to build new cells.

    What are the organs of the digestive system?

    • Mouth

      • Salivary glands

  • Pharynx

  • Esophagus

  • Stomach

    • Pancreas

    • Liver

  • Small intestine

  • Large intestine

  • Teeth – mechanical digestion; chewing the foodSaliva – contains AMYLASE – enzyme that breaks chemical bonds between the sugar monomers in starchesEsophagus – food tube that goes from mouth to stomach

    Can you swallow food if you are upside down? Why or why not?

    • Yes, you can due to peristalsis


    • Smooth muscle contractions of the esophagus that squeeze food through 25 cm to the stomach

    • Stomach– food empties into this large muscular sac

      • Chemical digestion

      • Glands produce mucus, a fluid that lubricates and protects the stomach wall

      • Other glands produce hydrochloric acid, which makes the contents of the stomach very acidic. The acid activates an enzyme called pepsin, which is secreted by a third set of glands

      • Pepsin works best under the acidic conditions present in the stomach.

      • The combination of pepsin and hydrochloric acid begins the complex process of protein digestion. Pepsin breaks proteins into smaller polypeptide fragments.

    Small Intestine

    • Duodenum – first part of the small intestine

      • Chyme mixes with digestive fluids from the pancreas and liver

    • Most of the chemical digestion occurs here

    PANCREAS – sits just below the stomach

    • Produces hormones that regulate blood sugar levels

    • Produces enzymes that break down carbohydrates, proteins, lipids and nucleic acids

    • Produces sodium bicarbonate, a base that neutralizes stomach acids

    • LIVER – large organ located just above the stomach

      • Produces bile, a fluid loaded with lipids and salts – it dissolves droplets of fat so enzymes can reach the fat molecules to break them down

      • Bile is stored in a small sac called the gall bladder

    Jejunum and ileum – 2nd and 3rd parts of the small intestine

    • Absorbs the medium and small nutrients

    • VILLI - folded projection that increases the surface area of the walls of the small intestine

    Cross Section of the Small Intestine

    Large intestine – removes water from undigested material that is left

    • Rich colonies of bacteria grow on the

      undigested material left in the colon

    • These intestinal bacterial help the

      digestive process.

    • Some of the bacteria produce

      compounds that the body can use, such

      as vitamin K.

    • The concentrated waste material that

      remains after the water has been

      removed passes through the rectum

      and is eliminated from the body.

    • When something happens that interferes with the removal of water by the large intestine, you usually become aware of it right away. The condition that is produced is known as diarrhea.

    • The loss of salts and water due to diarrhea can be life threatening, especially for an infant. Diarrhea resulting from bacterial infections and contaminated drinking water is the leading cause of childhood death in many developing countries around the world.

    Digestive and Excretory Systems

    • Digestion is the breaking down of large food molecules into smaller, more-usable ones.

    • Large food molecules must be broken down both physically and chemically.

    • The physical breakdown of food is called mechanical digestion.

    Digestive and Excretory Systems

    • Mechanical digestion begins in the mouth, when food is chewed into small pieces.

    • As food is chewed, it mixes with saliva.

    • Saliva adds digestive enzymes to food, starting the process of chemical digestion.

    • Saliva also makes food particles easier to swallow.

    Digestive and Excretory Systems

    • When food is swallowed, it enters the esophagus, a muscular tube that pushes food along with wavelike contractions.

    • Food is pushed into the stomach, where the digestion of protein begins.

    • Acid produced in the stomach kills bacteria and turns on enzymes that aid in chemical digestion.

    Digestive and Excretory Systems

    • From the stomach, food is pushed into the small intestine.

    • Bile from the liver and enzymes made by the small intestine and pancreas complete digestion.

    • Proteins are reduced to amino acids.

    Digestive and Excretory Systems

    • Complex carbohydrates are changed into simple sugars.

    • Lipids are changed to fatty acids and glycerol.

    • Nutrients can then be absorbed into the blood and lymph from the small intestine.

    Digestiveand Excretory Systems

    • Millions of tiny, fingerlike projections, called villi, line the small intestine.

    • The villi increase the small intestine’s surface area so most nutrients are absorbed by the time they reach the large intestine.

    Digestive and Excretory Systems

    Excretory System

    • The human body must remove wastes that are produced by metabolism in a process known as excretion.

    • Excretion enables the body to maintain its osmotic and pH balance.

    • Sweat, exhaled carbon dioxide, and urine are all eliminated through excretion.

    Digestive and Excretory Systems

    • The kidneys are the primary organs of excretion.

      • You have two

      • Located on either side of the spinal column near the lower back

      • They are the size of a fist

    • Each kidney is composed of nearly one million microscopic filtration units called nephrons.

    • At the end of the nephron is the Bowman’s capsule, a cup-shaped structure.

    Digestive and Excretory Systems

    • As blood flows through capillaries in the capsule, blood pressure forces fluid out of the capillaries into the capsule.

    • This fluid contains water, salt, glucose, amino acids, urea, and other substances.

    • Urea is a nitrogen-containing waste product that is released into the blood by the liver.

    Digestive and Excretory Systems

    • The fluid passes into a narrow tubule, which is surrounded by capillaries.

    • There, glucose and some other useful molecules in the fluid reenter the bloodstream.

    • The remaining fluid passes out of the nephron through collecting ducts, where much of the water is removed.

    Human Kidney Structure

    Digestive and Excretory Systems

    • Waste solution from the kidneys is called urine.

    • Urine flows from the kidneys through a ureter to the urinary bladder.

    • Urine is collected and stored in the bladder.

    • When the bladder’s muscular walls contract, urine exits through the urethra.

    Excretory System in the Human Body

    Respiratory and Circulatory Systems

    What are the structures of the respiratory system?

    • PHARYNX – passageway for both air and food

    • TRACHEA– air moves through; aka: windpipe

    • LARYNX – contains two highly elastic folds of tissue called vocal cords; when air passes the folds vibrate to produce sound

    • BRONCHI– after the trachea there are two passageways; they lead to the lungs

    • BRONCHIOLES– smaller branches after the bronchi

    • ALVEOLI – tiny air sacs where gas exchange occurs. Surrounding the alveoli are capillaries where the respiratory and circulatory systems meet

    • DIAPHRAGM – flat muscle at bottom of chest cavity that helps with breathing

    • NICE

    • PEOPLE

    • LIKE

    • TO


    • BLUE

    • AIR

    • NOSE


    • LARYNX





    Respiratory and Circulatory Systems

    Respiratory System

    • The respiratory system brings oxygen, O2, into the body.

    • It also carries carbon dioxide, CO2, a waste product of cellular respiration, out of the body.

    • Air enters the respiratory system when you inhale through your nose or mouth.

    Respiratory and Circulatory Systems

    • Inhalation occurs when muscles around the chest area contract and expand the rib cage.

    • Inhaled air passes through a series of tubes to reach the lungs.

    • Within each lung, the tubes carrying the air split into smaller and smaller tubes, called bronchioles.

    Respiratory and Circulatory Systems

    • The smallest bronchioles end in groups of tiny air sacs called alveoli (singular, alveolus), which are surrounded by blood vessels.

    • Exchange of gases by diffusion takes place across the thin, moist membranes of the alveoli.

    • Oxygen leaves the alveoli and enters the blood, while CO2 leaves the blood and enters the alveoli.

    Trace the path of an oxygen molecule through the human body

    • Parts of the Human Respiratory System

    Respiratory and Circulatory Systems

    Circulatory System

    • The circulatory system carries nutrients, oxygen, hormones, and wastes through the body and distributes heat to maintain homeostasis.

    • The cardiovascular system and the lymphatic system make up the body’s circulatory system.

    • Blood, blood vessels and the heart make up the cardiovascular system.

    Respiratory and Circulatory Systems

    • Arteries carry blood to capillaries.

    • A capillary has an extremely thin wall that allows gases and nutrients in the blood to diffuse across it into fluid around body cells.

    • From the capillaries, blood enters theveins,which return blood to the heart.


    • As you can feel with your hand, your heart is located near the center of your chest

    • The heart, which is composed almost entirely of muscle, is a hollow organ that is about the size of your clenched fist

    • The heart is enclosed in a protective sac of tissue called the pericardium

    • In the walls of the heart, there are two thin layers of epithelial and connective tissue that form a sandwich around a thick layer of muscle called the MYOCARDIUM. The powerful contractions of the myocardium pump blood through the circulatory system

    • There is a right side and a left side to the heart – they are separated by the septum (wall) which prevents the mixture of oxygen-rich and oxygen-poor blood

    • Atrium (atria is plural) – two of these upper chambers; receives the blood

    • Ventricle – two of these lower chambers; pump blood out of heart

    What is pulmonary circulation?

    • Occurs on the right side of the heart

    • Blood is pumped from the heart to the lungs and back to the heart again

    • Why would your blood get pumped to the lungs and then back to the heart?

      • Oxygen poor blood goes to the lungs to get rid of carbon dioxide and pick up oxygen

      • The oxygen rich blood then has to go back to the heart to get pumped to the rest of the body

    What is systemic circulation?

    • Occurs on the left side of the heart

    • Oxygen rich blood from the lungs gets pumped throughout the rest of the body and back to the heart – now the blood is oxygen poor and must go to the lungs to dump the carbon dioxide

    What makes your heart “beat’?

    • There are two networks of muscle fibers in the heart, one in the atriaand one in the ventricles

    • When a single fiber in either network is stimulated, all the fibers are stimulated and the network contracts as a unit

    • Each contraction begins in a small group of cardiac muscle cells located in the right atrium—the sinoatrial node

    • Because these cells “set the pace” for the heart as a whole, they are also called the pacemaker

    What determines if your heart beats fast or slow?

    Your heart can beat faster or more slowly, depending on your body’s need for oxygen-rich blood.

    In times of stress, does the heart beat faster or slower?

    It beats faster

    Respiratory and Circulatory Systems

    • This system acts like a network of highways that transports materials to and from the body’s cells.

    • The network is made up of three kinds of vessels: arteries, capillaries, and veins.

    • Arteries have thick, muscular walls to withstand the force of the blood pumped out of the heart.

    • Veins have thinner walls with valves to prevent the blood from back flowing.

    • Capillaries are the smallest vessel where the exchange of gasses, nutrients and wastes take place

    Circulation Pathway in the Human Body

    Respiratory and Circulatory Systems

    • Blood moves through blood vessels and interacts with every body system.

    • Blood brings materials that the body system needs and carries away the products that the system makes.

    • Blood also carries waste away from the system.


    What is “blood” made up of?

    • Plasma

    • Red blood cells

    • White blood cells

    • Platelets

    • Clotting proteins

    Respiratory and Circulatory Systems

    • About 45% of blood is cells and cell fragments. The remaining 55% is plasma, the liquid portion of blood.

    • Plasma is a solution made of about 90% water and 10% solutes. The solutes include nutrients, wastes, and salts.

    • Salts have many functions, including maintaining osmotic balance with the fluids inside of cells and regulating blood pH.


    • aka: erythrocytes – transport oxygen

    • They get their color from HEMOGLOBIN – iron-containing protein that binds to oxygen in the lungs and transports it throughout the body where oxygen gets released

    • Shaped like discs

    • Made in the bone marrow

    • Mature red blood cells do not have nuclei

    • Live for 120 days and then destroyed on liver and spleen

    WHITE BLOOD CELLSaka: leukocytes – attack foreign substances or organisms

    • Produced in red bone marrow

    • Some live for months others only a few days

    • PHAGOCYTES– “eating cells” – engulf and digest foreign cells

    • Some slip across capillary walls and attack invading organisms

    • Others release chemicals that help the body fight disease

    Platelets and blood clottingWe don’t want to lose our blood

    • How does bleeding stop?

      • We have the ability to form clots

    • Blood clotting is made possible by plasma proteins and cell fragments called PLATELETS - Cell fragments released by bone marrow

      • When platelets come into contact with a wound they become sticky and other platelets start to stick

      • They release proteins called clotting factors that cause other types of proteins to form a mesh over the wound – this is called a clot

    Respiratory and Circulatory Systems

    • Besides carrying materials, blood distributes body heat to help the body maintain a steady temperature.

    • When the body is warm, blood vessels in the skin widen, allowing heat to leave the body.

    • Blood vessels narrow when the body is cold. This helps the body to divert blood to deeper tissues and conserve heat.

    Blood Pressure

    • When the heart contracts, it produces a wave of fluid pressure in the arteries.

    • The force of the blood on the arteries’ walls is known as

      • blood pressure.

  • Blood pressure decreases when the heart relaxes, but the system still remains under pressure.

  • Every time the heart pumps, some fluid from the blood is forced out of the capillaries.

  • Respiratory and Circulatory Systems

    • The escaped fluid collects in spaces around body cells.

    • This fluid, called lymph, is picked up by the lymphatic system and returned to the blood.

    Respiratory and Circulatory Systems

    • The lymphatic system is made up of a network of vessels, tiny bean-shaped structures called lymph nodes, and lymph tissue.

    • Lymph vessels collect lymph and return it to two large veins in the neck.

    • As lymph moves through lymph vessels, the fluid passes through lymph nodes, where white blood cells collect.

    Respiratory and Circulatory Systems

    • The white blood cells destroy bacteria and other dangerous material in the lymph.

    • In this way, the lymphatic system helps the body fight infection.

    • Lymph Movement

    Key Ideas

    • How do the skeletal and muscular systems help the body maintain homeostasis?

      • The skeletal and muscular systems enable movement and provide support and protection for tissues and organs.

    Key Ideas

    • How does the integumentary system help the body maintain homeostasis?

      • The integumentary system protects the body from injury and UV radiation, defends against disease, helps regulate body temperature, and prevents the body from drying out.

    Key Ideas

    • How do the nervous and endocrine systems help the body maintain homeostasis?

      • The nervous system collects and responds to information about the body’s internal and external environment.

      • The endocrine system regulates metabolism; maintains salt, water, and nutrient balance in the blood; and regulates growth, development, and reproduction.

    Key Ideas

    • How do the digestive and excretory systems help the body maintain homeostasis?

      • The digestive system converts nutrients that a body’s cells can use.

      • Excretion enables the body to maintain its osmotic and pH balance.

    Key Ideas

    • How do the circulatory and respiratory systems help the body maintain homeostasis?

      • The respiratory system brings oxygen, O2, into the body and carries carbon dioxide, CO2, out of the body.

      • The circulatory system carries nutrients, oxygen, hormones, and wastes through the body and distributes heat to maintain homeostasis.

    Feedback Mechanisms

    Write a short explanation of how you think a thermostat on a furnace helps to keep the room temperature at a comfortable level.

    Answer the following question:

    How does the human body act like a thermostat?

    Key Ideas

    • How do feedback mechanisms help maintain homeostasis?

    • How does a feedback mechanism control a person’s breathing rate?

    • How does a feedback mechanism maintain the concentration of glucose in the bloodstream?

    Mechanisms of Control

    • A body’s internal state varies around a certain average value

    • Homeostasis maintains a dynamic equilibrium in the body.

    Mechanisms of Control

    • Your body has a variety of feedback mechanisms that detect deviations in the body’s internal environment and make corrections.

    • A feedback mechanism is a mechanism in which the last step in a series of events controls the first step.

    Negative Feedback

    • Negative feedback

      • every time body is high or low from normal level a signal tells the body to make changes that will bring body back

        • body temperature

        • control of blood sugar

    • Comparing Positive and Negative Feedback

    Mechanisms of Control

    • Positive feedback, a change in the body causes even more change in the same direction.

    • Positive feedback occurs in blood clotting.

    • One clotting factor activates another in a cascade that leads quickly to the formation of a clot.

    • Another example of positive feedback occurs in females, when rising levels of estrogen cause another hormone to be secreted until an egg is released from an ovary.

    • Blood and the Transport of Carbon Dioxide

    Controlling Blood-Glucose Level

    • Your body’s cells need glucose to perform cellular respiration.

    • When you digest a large meal, a large amount of glucose is introduced into your body in a short period of time.

    • Two hormones, insulin and glucagon, control the level of glucose in the bloodstream.

    Controlling Blood-Glucose Level

    • Insulin and glucagon are released by the pancreas.

    • These hormones act antagonistically to regulate blood-glucose level.

    • Insulin lowers blood glucose levels by communicating with the liver to convert glucose into glycogen that can be stored for future use.

    Controlling Blood-Glucose Level

    • When glucose levels fall below the normal range, glucagon stimulates the liver to break down glycogen.

    • This adds more glucose to the bloodstream.

    • This feedback system regulates blood-glucose levels, so they do not stay too high after a meal and do not drop too low between meals.

    Maintaining a Normal Blood-Glucose Level

    Key Ideas

    • How do feedback mechanisms help maintain homeostasis?

      • To maintain homeostasis, your body has a diversity of feedback mechanisms that detect deviations in the body’s internal environment and make corrective actions.

    • How does a feedback mechanism control a person’s breathing rate?

      • When the brainstem senses a change in the blood’s pH, it adjusts the breathing rate.

    Key Ideas

    • How does a feedback mechanism maintain the concentration of glucose in the bloodstream?

      • Two hormones that are released by the pancreas, insulin and glucagon, control the level of glucose in a person’s bloodstream.

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