Human Body Systems

Levels of Biological Organization

• Cells

• Tissues

• Organs

• Organ Systems

• Organisms

• Population

• Community

• Ecosystem

• Biosphere

The 11 Human Body Systems

• Respiratory system

• Digestive system

• Excretory system

• Circulatory system

• Reproductive system

• Immune system

Digestive System

• Function: Breaks down food into nutrients that the body can absorb and eliminates solid waste.

• Nutrients: Substances in food that provide energy and materials for cell development, growth, and repair.

• Digestion occurs in the digestive tract, where food undergoes physical and chemical changes.

Organs food passes through:

• Mouth

• Esophagus

• Stomach

• Small intestine

• Large intestine

• Rectum

• Liver

• Gallbladder

• Epiglottis

• Salivary gland

• Pancreas

• Anus

Types of Digestion

1. Mechanical Digestion:

   • Begins in the mouth.

   • Teeth cut, grind, and mash food into smaller pieces.

   • Physical change.

2. Chemical Digestion:

   • Food is broken down by acids and enzymes.

   • Breaks food into simple molecules that dissolve in water.

   • Chemical change.

Organs of the Digestive System

• Mouth: Mechanical and chemical digestion starts here; teeth grind food, mixed with saliva containing enzymes to break down starch to sugars.

• Esophagus: Muscular tube connecting the mouth to the stomach; peristalsis (muscle contraction) moves food.

• Stomach: Muscular walls contract to mix food with digestive juices (enzymes and acids); solid food breaks down into a fluid.

• Small Intestine: Most chemical digestion and nutrient absorption into the bloodstream occurs here; villi absorb nutrients and water from digested food (chyme).

• Large Intestine: Absorbs water from food; eliminates undigested food as waste (feces).

• Rectum: Waste material is compressed into solid form; muscles control the release of solid wastes from the body via the anus.

• Liver: Produces bile, which helps digest fats.

• Gall Bladder: Stores and concentrates bile, releasing it into the small intestine.

• Pancreas: Produces enzymes that help digest carbohydrates, proteins, and fats in the small intestine.

Associated Diseases

• Irritable Bowel Syndrome (IBS): Affects the large intestine, causing cramping, abdominal pain, bloating, gas, diarrhea, and constipation.

• Inflammatory Bowel Disease (IBD): Chronic inflammatory conditions of the digestive tract.

The Circulatory System

• Function: Transports oxygen, nutrients, and hormones to cells; fights infections; removes cell wastes; regulates body temperature.

Interesting facts:

• Entire blood volume circulates through the body once every minute

• Humans have approximately 60,000 miles of blood vessels.

• The heart beats approximately 100,000 times daily and pumps approximately 2,000 gallons of blood.

Main Organs

• Heart

• Blood Vessels:

  • Arteries

  • Veins

  • Capillaries

• Blood

How Blood Travels Through Vessels

heart → artery → capillary → vein → heart

• Heart: Size of a fist, weighs less than a pound, flanked by lungs, rests on diaphragm, pumps blood through the body.

• Blood: Tissue made up of red blood cells, white blood cells, plasma, and platelets.

  • Red Blood Cells: Carry oxygen and give blood its red color.

  • White Blood Cells: Fight infection.

  • Platelets: Help cuts, scrapes, and wounds clot.

  • Plasma: Liquid part of blood, transports nutrients, proteins, and hormones throughout the body (55% of blood volume).

• Arteries

  • Move blood away from the heart.

  • Have thick and elastic walls made of smooth muscles.

  • Connected to ventricles in the heart.

  • Most carry oxygenated blood (red).

• Arteries can become less effective due to plaque buildup, leading to cardiovascular disease (CVD) such as heart attack, stroke, peripheral artery disease (PAD), and renal artery stenosis (RAS).

• Veins

  • Move blood towards the heart.

  • Are squeezed by skeletal muscles.

  • Carry blood with waste materials that is oxygen poor.

  • Most carry deoxygenated blood (purple).

• Capillaries

  • Microscopic blood vessels.

  • Walls are only one cell thick.

  • Connect arteries to veins and allow for gas, nutrients, and waste exchange.

  • Drop off oxygen delivered from the heart by arteries.

  • Pick up $CO_2$ and send it to the heart through veins.

Blood Flow Through the Heart

1. Blood enters the atria first: The left atrium receives oxygen-rich blood from the lungs; the right atrium receives oxygen-poor blood from the body.

2. When the atria contract, blood is squeezed into the ventricles.

3. While the atria relax, the ventricles contract and push blood out of the heart: Blood from the right ventricle goes to the lungs; blood from the left ventricle goes to the rest of the body.

The Respiratory System

• Function: Provides oxygen needed for cellular respiration and removes carbon dioxide from the body.

Path of Air into the Body

• Nose

• Pharynx

• Larynx

• Trachea

• Bronchi

• Lungs

• Alveoli

1. Nose & Mouth: Passageway into the respiratory system that helps to warm air; hairs and mucus filter air.

2. Pharynx (Throat): Transports air, food, and water; includes parts of the trachea and esophagus; cilia line the pharynx to filter air.

3. Larynx (Voice Box): Vocal cords are stretched across the larynx opening and contract/relax to make sound.

4. Trachea (Windpipe): Carries air from the larynx to the lungs; covered in cartilaginous rings for protection.

5. Bronchi/Bronchial Tubes: Two tubes split off from the trachea, with one tube going to each lung; each tube splits into tiny tubes called bronchioles.

6. Alveoli (Air Sacs): Tiny sacs in the lungs surrounded by capillaries that exchange gases (oxygen enters the bloodstream and carbon dioxide exits).

7. Lungs: Each lung has thousands of alveoli; the breathable surface area of the lung is the size of a tennis court.

8. Diaphragm: Large dome-shaped muscle used in breathing.

   • Inhalation: The rib cage moves up and out; the diaphragm contracts and flattens; the volume of the lungs increases, and air flows in.

   • Exhalation: The rib cage returns to its original position; the diaphragm relaxes and moves upward; the volume of the lungs decreases, and air is pushed out.

Respiration

There are two parts to respiration:

1. Breathing:

   • Inhale: Diaphragm muscle contracts, moving down and causing the lungs to expand.

   • Exhale: Diaphragm relaxes, air moves out through the mouth automatically.

2. Cellular Respiration: Chemical reaction that converts glucose from food into ATP energy in the presence of oxygen.

• Cellular Respiration: The body obtains and uses oxygen and removes carbon dioxide & water as waste.

Cellular Respiration Equation

$C<em>{12}H</em>{6}O + 6O<em>2 \rightarrow 6CO</em>2 + 6H_2O + ATP$

Respiratory Diseases

• Bronchitis: Irritation of the breathing passages in which they become narrower than normal and may be clogged with mucus.

• Lung Cancer: Cancerous growths, or tumors, take away space in the lungs that could be used for gas exchange.

• Asthma: Constriction of the smooth muscles around the respiratory passageways, frequently caused by an allergic reaction.

The Excretory System

• Function: Removes cellular wastes from blood and the body.

Organs

• Lungs: Remove carbon dioxide from blood.

• Kidneys: Blood enters, passes through millions of tiny filters called nephrons; liquid waste carried in blood collects in the nephrons and forms urine.

• Ureters: Long tubes that pass urine out of the kidneys and into the bladder.

• Urethra: Tube that passes urine from the bladder to the outside of the body.

• Bladder: Sac-like structure that stores urine until eliminated from the body.

• Skin: The largest organ in the body, serving as an excretory organ when perspiring, ridding the body of water and salts.

Pathway of Urine out of Body

Kidney → Ureter → Bladder → Urethra

The Reproductive System - Male

• Function:

  • To produce sperm.

  • To produce and secrete male sex hormones.

  • To deliver sperm to the female reproductive system.

• Puberty: The body becomes physically able to reproduce.

  • Typically begins around 10-15 years old in males.

  • Typically lasts for 3-7 years in both genders.

Male Sex Characteristics

• Primary: Testes mature, sperm forms, penis enlarges, sperm release.

• Secondary: Voice deepens, shoulders broaden, muscles enlarge, facial & body hair, pubic hair.

• Gonads: Testes (Testicles)

  • Produce sperm (gamete).

  • Produce hormones like testosterone, causing secondary sex characteristics (Puberty).

• Sperm

  • The male sex cells, or gametes.

  • Produced in the testes.

  • Holds half the DNA for offspring; also called being haploid (N).

  • Highly mobile cell.

  • Very small in size (0.05 cm diameter).

• Scrotum: Pouch-like structure that holds the pair of testes outside the body cavity; keeps temperature slightly lower than the rest of the body.

• Urethra: Connects the urinary bladder to the penis for excretion and contains glands that release fluids (i.e., urine and sperm).

• Seminal Vesicle: Sac-like structures attached to the vas deferens; produces some of the parts of semen.

• Prostate: Produces some of the parts of semen.

• Vas Deferens: Tube that carries sperm out of the testes to the urethra.

• Semen: Mixture of sperm and fluids from glands.

• Ejaculation: Involuntary muscle contraction that forces sperm out of the body through the urethra.

• Main roles: produce sex cells (sperm) and hormones, to store sex cells, and to deliver sex cells to the site of fertilization

  • Sex cell: sperm

  • Sex hormone: testosterone

  • Primary sex organ: testes (or testicles)

  • Secondary sex organs: vas deferens, seminal vesicles, prostate gland, penis

The Reproductive System - Female

• Function:

  • To produce sex cells.

  • To transport the cells to the site of fertilization.

  • To provide a favorable environment for the development of offspring.

Female Sex Characteristics

• Primary: Ovaries mature, ova released, vagina enlarges, menstrual cycle.

• Secondary: Breasts develop, hips widen, waist narrows, body hair (pubic).

• Gonads: Ovaries

  • Produce eggs (gamete).

  • Produce hormones like estrogen and progesterone, which control the menstrual cycle (Puberty).

• Ovaries:

  • At birth, females have 1-2 million undeveloped ova called oocytes.

  • At puberty, one oocyte per month will mature inside a fluid-filled sac called a follicle until it is an ovum.

  • Once mature, the ovum exits the ovary in a process called ovulation.

• Fallopian Tubes

  • The 2 fallopian tubes connect the ovaries to the top of the uterus.

  • Serve as a site of fertilization and to deliver the developing embryo to the uterus to grow.

  • Fertilization may occur if sperm cells encounter an egg along its journey.

• Uterus

  • A hollow, muscular organ located above the vagina.

  • Main job is to protect and nourish the fetus during development.

  • The cervix is the narrow, lower part that links the uterus with the vagina.

• Fallopian Tubes (oviduct)

  • Once the egg is released from the ovary it will be transported to the uterus.

  • Fertilization occurs here (sperm + egg)

• Uterus

  • Thick, walled muscular pear-shaped organ where development of the embryo occurs.

• The Menstrual Cycle

  • Is a series of changes to hormone levels and the lining of the uterus that prepare the body for pregnancy

  • Mature egg is released every 28 days.

  • Wall of uterus thickens for implantation.

  • Wall breaks down if no fertilization occurs.

  • Involves hormonal control between the hypothalamus, pituitary gland & ovary.

  • Begins with puberty (10-14 yrs).

  • Ends with menopause (45-50 yrs).

  • Stops during pregnancy.

Summary – Female Reproductive System

• Main roles: produce female sex cells (ova) and hormones, to transport sex cells to the site of fertilization, and to provide a favorable environment for the development of offspring

  • Sex cell: ovum (or egg)

  • Sex hormone: estrogen, progesterone

  • Primary sex organ: ovaries

  • Secondary sex organs: Fallopian tubes, uterus, cervix, vagina

The Reproductive System - Fertilization

• Female sex cell is called an ovum (egg)

• Male sex cell is called a sperm cell.

• Human development begins when a sperm combines with an egg during fertilization.

• Internal Fertilization

  • Sperm is deposited directly into the female reproductive system

  • Increased odds of fertilization = less offspring

  • Small number of offspring

  • Offspring are protected during development

  • Development can be internal or external

  • Common in sharks & most land mammals

• External Fertilization

  • Females release eggs into open water

  • Male releases sperm into the water to fertilize eggs

  • High numbers of egg & sperm ensure fertilization

  • Large number of offspring

  • Offspring not well protected during development

  • Common in fish & amphibians

• Fertilization: During fertilization, a haploid (N) sperm fuses with a haploid (N) ovum, causing their nuclei to combine to form a new diploid (2N) cell called a zygote

  • This fertilized zygote then begins to divide over and over to eventually form an embryo.

• In Vitro Fertilization

  • IVF is an assisted reproductive technology (ART) where an egg and a sperm are fertilized outside a woman’s body in a lab

  • It is a process that is used to overcome infertility and support surrogacy

• Embryo

  • After fertilization, the zygote travels to the uterus and begins dividing.

  • By day 5-6, the zygote is a ball of 100+ cells called a blastocyst which implants in the endometrium and continues to grow and mature

  • 10-12 days after fertilization, the blastocyst begins to resemble a human with a head and limbs and is now called an embryo.

• Placenta: is the connection between mother and embryo

  • provides oxygen $O<em>2$ and food to the developing child and removes $CO</em>2$ and wastes

  • Alcohol, drugs, and other harmful substances may also pass through the placenta to the embryo

• Umbilical cord: is a ropelike structure connecting the placenta to the embryo

Combining Genetic Material

• Mother and Father are both Diploid (2N) with 46 chromosomes

• The Ovum and Sperm are Haploid (N) with 23 chromosomes

• The Zygote and Embryo are Diploid (2N) with 46 chromosomes

• The baby will have a combination of the genetic material from both the Mother and Father.

Human Reproduction Process

• Fertilization

• Meiosis

• Egg (Ovum)

• Meiosis

  • 23 Chromosomes

• Sperm

  • 23 Chromosomes

• Zygote

  • 46 Chromosomes in 23 Pairs

• Embryo

  • 46 Chromosomes in 23 Pairs

• Offspring (2n)

Fetus

• The embryo and fetus develop in the uterus.

1. Cells divide without becoming larger (cleavage).

2. After a few days, cells begin to differentiate – that is they start to form different types of cells (nerve, skin, bone, etc).

• The fetus is attached to the placenta by the umbilical cord.

• Waste produced by the fetus is also removed by the placenta.

  • Waste ($CO_2$, urea, salts) diffuse from the placenta into the mother's blood.

  • Since the fetus does not eat solid food, it does not have to eliminate feces.

There are three trimesters of human development.

• FIRST TRIMESTER

  • MONTHS 1-3

    • All organ systems formed and are developing

    • Early skeleton made of cartilage

    • Human appearance

    • Now called a fetus

    • Fetal heartbeat heard

• SECOND TRIMESTER

  • MONTHS 4 - 6

    • All organ systems becoming functional

    • Bone replacing early cartilage skeleton

    • Can move limbs and kick

    • Hair growth

    • Gender visible

• THIRD TRIMESTER

  • MONTHS 7-9

    • All organ systems mature and fully independent

    • Muscles and bones growing and strengthening

    • Fat accumulates

    • Rapid brain development

    • Lungs developed

• Fraternal Twins: Fraternal twins occur when 2 different ova are released and are fertilized by 2 different sperm.

  • Dizygotic twins. The fertilized zygotes develop into 2 separate embryos and 2 babies. They are not identical and may be different genders as each has been formed by the fusion of a different ovum and different sperm.

• Identical Twins: Identical twins occur when 1 ova is fertilized by 1 sperm and then splits.

  • Monozygotic twins. The fertilized zygotes develop into 2 genetically identical embryos that develop into 2 babies. These twins are identical and are the same gender since each was formed by the fusion of the same ovum and same sperm.

The Immune System

• Function: The system in the body responsible for maintaining homeostasis by recognizing harmful from non-harmful organisms and producing an appropriate response.

• Immune response is the defensive reaction of the body to antigens or pathogens (foreign substances or organisms).

• Pathogen / antigens

  • A foreign object in the body that causes disease.

  • Types are:

    • Virus

    • Bacteria

    • Fungus

    • Parasite

• Antibody: Proteins produced by the WBC in response to antigens. They attack the foreign invaders

Three Lines of Defense

1. First Line of Defense – The Skin

   • Provides Physical and Chemical barriers

     • Physical – hard to penetrate

     • Chemical – tears, sweat (washes away pathogens)

2. Second Line of Defense

   • Non-Specific (can kill ANY pathogen)

     • These are defenses the body uses no matter what the invader may be. These defenses include:

       • Phagocytosis – process where the cell “eats” a pathogen

       • Natural Killer Cells

       • Inflammation - caused by the release of histamine (a chemical that fights invaders) from leukocytes

       • Fever – caused by histamines. The fever kills invaders by denaturing their proteins.

3. Third Line of Defense

   • This is a specific response to a specific pathogen/ antigen: PATHOGEN & ANTIGEN ARE THE SAME THING!

     • The response involves the creation of antibodies.

There Plan of Defense

1. The WBC’s recognize a foreign invader.

2. WBC identifies the invader and then makes antibodies to determine the pathogen as “bad”

3. The Macrophage eats & kills the pathogen & antibody.

4. The WBC’s remember the invader so it is prepared if that person is re-exposed

Types of Immunity

• Active
  Natural: Maternal antibodies
  *Infection (the body “remembers” the antigen/pathogen because it has created its own antibodies
  *Artificial Vaccination: Vaccine will cause the body to create antibodies and you will be protected from said diesesd

• Passive
  *Natural Natural maternal antibodies
  *Artificial: Monoclonal antibodies (Injection)

• Passive Immunity: A person is given antibodies obtained either from another person (Mother) or animal

  • Only temporary

  • Maternal immunity: antibodies from mother enter baby’s blood before birth providing the infant with passive immunity. Mother’s milk: protects the child against infectious diseases for the first few months.

• Active Immunity: The body produces its own antibodies in response to an antigen

  • Occurs from having a disease and recovering from it

  • Antibodies remain in the blood forever to protect against reinfection

  • Natural active immunity - acquired due to infection (the body “remembers” the antigen/pathogen because it has created its own antibodies
    Vaccines

  • Dead or weakened bacteria or viruses

  • When injected into the body WBC’s to produce antibodies. The body develops immunity to the disease without actually suffering through it.

Disorders of the Immune System

• Age, stress, fatigue make us more vulnerable to pathogens.

• Allergy: a rapid overreaction of the immune system to an antigen that is not normally harmful: Pollen, dust mites, insect stings, certain foods, animal hair.

• Histamine is released which causes runny nose, sneezing, rash, swelling.

• Antihistamines reduce the effects. Ex. Sudafed, Benadryl

• Autoimmune Disorders: The immune system of an individual fails to recognize some of the person’s body cells as “self” and therefore produce antibodies against them: Juvenile diabetes, rheumatoid arthritis, multiple sclerosis.

  • Diabetes Mellitus (Type I or Juvenile Onset)

    • The immune system destroys the Insulin producing Beta cells of the pancreas.

  • Multiple Sclerosis

    • Occurs when the body attacks the myelin sheath of neurons.

    • Effects include the loss of motor control, feeling, or even paralysis of the affected areas.

  • Acquired Immune Deficiency Syndrome (AIDS)

    • Caused by the virus HIV (Human Immunodeficiency Virus)

    • Infects specific WBC’s & may stay dormant for years not showing any symptoms.

    • When it becomes active, it reproduces, spreads and destroys WBC’s. The decrease in WBC’s weakens the immune system.

    • When the body can no longer fight off infection an individual will develop AIDS

    • Spread by the exchange of body fluids through sexual contact or blood to blood contact.

  • Organ transplants

    • Tissues of each person are different which may cause the immune system to reject the organ due to a variety of factors

    • Patients are given drugs (immunosuppressant) to weaken the immune system so the organ will be accepted by the body

Organs/Glands

• Hypothalamus

• Pituitary

• Pancreas

• Adrenal

• Thyroid

• Testes and ovaries

Important Glands and Hormones of the Human Body