week 1 - intro to human body

Basic Life Processes

• Every living thing has six basic processes that distinguish it from non-living things:
  • Growth
  • Metabolism
  • Responsiveness
  • Movement
  • Reproduction
  • Differentiation

Growth

• Growth is an increase in body size. There are three ways to increase body size:
  • Hypertrophy: Increasing the size of cells.
    • Example: Bodybuilding where muscle cells repair themselves bigger after tearing of connected tissue.
  • Hyperplasia: Increasing the number of cells. Only specific kinds of cells can undergo hyperplasia.
    • Example: Calluses, which form in areas with an additional layer of skin to protect the body from harm. Calluses are an increased number of cells.
  • Increasing the amount of noncellular material around or surrounding cells.
    • Example: Mineral deposits in bone.

Metabolism

• Metabolism is the sum of all chemical reactions or processes that occur in the human body.
  • Two phases:
    • Catabolism: Breaks bonds and releases energy.
      • Example: Breaking down large food molecules into smaller units for absorption.
    • Anabolism: Forms bonds and uses energy.
      • Example: Using sugars to build proteins from amino acids for cell structures.

Responsiveness

• The body responds to internal and external changes in the environment.
  • Internal response:
    • Example: Developing a fever in response to an infection.
  • External response:
    • Example: Turning your head in response to a loud noise.
  • Communication for responsiveness primarily happens via the nerve system or the endocrine system. These systems are covered in weeks 5 and 6, respectively.
    • Nerves send electrical signals, called action potentials.
    • The endocrine system sends hormones in the blood.
  • Muscle cells contract.

Movement

• Movement can occur at varying degrees, from whole body movement to movement at the cellular and organelle levels.
  • Examples:
    • Wandering around a room (whole body).
    • Heart beating (organ movement).
    • Sperm cell meeting an ovum (single cell movement).
    • Exocytosis (organelle level movement).
      • Exocytosis is the process by which things inside a cell are packed up into a little bubble called a vesicle, and that vesicle fuses with the cell membrane and releases its contents out.

Reproduction

• Living things can reproduce in two ways:
  • Production of a new human being.
    • Occurs when gametes (sperm and ovum) come together to form a zygote, the first cell of the baby. Gametes have half the amount of genetic material that comes together for a full amount of genetic material.
  • Mitosis.
    • The reproduction of single cells in your body.
    • Example: Cells lining the gastrointestinal tract are replaced every two to three days due to damage from food.
    • Cells in your stomach are replaced constantly due to the stomach's acidic environment (pH 2-3).

Differentiation

• Every cell in the body starts out as a stem cell.
  • A stem cell is a cell that doesn't know what it wants to be when it grows up. It could become any type of cell.
  • Stem cells in particular areas of the body will follow the pathway to becoming a specialized type of cell.
    • Examples:
      • Muscle cell.
      • Nerve cell.
      • Skin cell (epithelial cell).
      • Blood cell.

Levels of Organization

• The levels of organization in the human body, from smallest to largest, are:
  • Molecules
  • Cells
  • Tissues
  • Organs
  • Body systems
  • Organisms

Cells

• Cells are the basic structural and functional units of an organism.
  • They are the vital units of life.
  • They are highly diverse and differentiate into vastly different types of cells in the body.

Tissues

• Tissues are a group of cells and all of their intercellular components.
  • Types: epithelial, muscular, nervous, and connective.
  • If you are not epithelial, muscular, or nervous, you are connective tissue.

Organs

• Organs are defined as being composed of at least two different types of tissue.
  • Organs have a specific shape and work to maintain homeostasis, which keeps you alive.
  • Primary organs form the basis of body systems.
  • Accessory organs aid in those processes but are not usually vital.

Body Systems

• Body systems are a group of organs and/or tissues that work together to perform a specific function that is vital to life.
  • Organs can belong to multiple systems.
  • There are 11 body systems.
  • From week 3, each week will be dedicated to a body system.

Organisms

• An organism is a complete, total package and unit; a living thing.
  • Each individual is an organism.

Body Cavities

• Body cavities are spaces in the body that enclose walls. They are usually lined by soft tissue walls and they do have a secretory membrane that we refer to as a serous membrane lining the inside of the cavity. A slippery, moist membrane.
  • These will be covered in more detail in the next semester.
  • Cavities of the human body:
    • Cranial cavity: Inside the skull.
    • Thoracic cavity: Contains two individual cavities.
      • Pleural cavity: Contains the lungs.
      • Pericardial cavity: Contains the heart.
    • Abdominal pelvic cavity: From the pelvis up to the bottom of the ribs.
      • Some resources separate this into abdominal and pelvic cavities, but they are often considered together because organs from the pelvic cavity can intrude up into the abdominal cavity at certain times.
      • Example: The bladder when it's full intrudes up into the abdominal cavity. But when it's empty, it's not in the abdominal cavity.

Serous Membranes

• Cavities are lined by a slippery, moist membrane called a serous membrane (except for the cranial cavity, which has a blood-brain barrier instead).
  • Functions:
    • Produce fluid.
    • Prevent friction between organs and the body wall.
      • Example: Lungs sliding against the ribs during breathing.
    • Prevent friction between adjacent organs.
      • Example: Stomach expanding after eating a lot of food, pushing other organs without creating friction.
    • Allow for movement.
      • Example: Other digestive organs moving out of the way when the stomach becomes larger.
  • Names of serous membranes vary by location although they are all serous membranes:
    • Pleura: Surrounds the lungs in the pleural cavity.
    • Pericardium: Surrounds the heart in the pericardial cavity.
    • Peritoneum: Lines the abdominal cavity.

Anatomical Position and Terminology

• It is essential to use the correct anatomical nomenclature to avoid confusion and standardize terminology in a clinical setting.

Standard Anatomical Position

• Standing upright.
• The human body is divided into several regions:
  • Head: Head and face.
  • Neck: Region that attaches the head to the trunk.
  • Trunk: Chest, abdomen, and pelvis.
  • Upper limb: (Note: Not called an arm, which is only this section). Not a leg.
  • Lower limb: (Note: Not called a leg, which is only this section).
  • Axial Body: Head, neck, and trunk.
    • The axial skeleton or body are those that are NOT upper or lower limbs.
  • Appendicular Body: Upper and lower limbs (appendages).
    • Appendages are upper limbs and lower limbs.

Directional Terms

• Directional terms describe the relationship of one part of the body with another. They often come in opposites.
  • Superior versus Inferior
    • Superior: Toward the head, higher than, above.
    • Inferior: Toward the feet, lower, below.
    • Often used for the axial body.
    • Example: The nose is superior to the chin.
  • Anterior versus Posterior
    • Anterior: The front of the body. Also called ventral (primarily used when talking about the nervous system).
    • Posterior: The back of the body. Also called dorsal.
    • Use the same terms consistently (anterior/posterior or ventral/dorsal).
    • Example: The kneecaps are anterior to the buttocks.
  • Medial versus Lateral
    • Medial: Close to the midline (toward the middle).
    • Lateral: Further out to the side.
    • Example: The nose is medial to the ears.
  • Ipsilateral versus Contralateral
    • Ipsilateral: Same side (Ipsi = same).
    • Contralateral: Opposite side (Contra = contrary).
    • Example: The left arm is contralateral to the right arm.
  • Proximal versus Distal
    • Only used on limbs.
    • Proximal: Closer to the origin of the limb (shoulder for upper limb, hip for lower limb).
    • Distal: Further away from the origin of the limb.
    • Example: The elbow is proximal to the wrist.
  • Superficial versus Deep
    • Refers to how close or far something is from the outside of the body.
    • The skin and hair are the most superficial structures.
    • Example: The heart is deep to the ribs.

Body Planes

• Body planes are imaginary flat surfaces that run through the body. Important for interpreting medical images.
  • Sagittal Plane: Runs at a 90-degree angle, splitting the body into left and right parts.
    • Mid-sagittal: Directly through the middle.
    • Para-sagittal: Anywhere else in that plane, but not in the middle.
  • Coronal (or Frontal) Plane: 90-degree plane that cuts the body into front (anterior) and back (posterior) portions.
    • Corona means crown.
  • Transverse (or Horizontal) Plane: Cuts the body horizontally.
    • Medical students study transverse planes to understand how organs look at every level of the body in CT scans or PET scans.
  • Oblique Plane: Any other angle through the body that is not 90 degrees (less commonly used). that is NOT 90 degrees (less commonly used).

Homeostasis

• Homeostasis is the regulation of the internal environment to maintain appropriate life-sustaining conditions for the cells and tissues of the body.
  • Staying within optimum conditions.
  • Fiddling too much with homeostasis for a prolonged period or a long period of time, you will die.
• Topics of homeostatic control:
  • Concentration of nutrients in the body.
    • Drinking too much water can disrupt the delicate balance of nutrients and ions, leading to hyponatremia and death.
    • Drink when you are thirsty.
  • Oxygen and carbon dioxide levels.
    • Too much carbon dioxide can cause passing out, while too much oxygen feels great.
  • Concentration of waste products.
    • If the liver can't filter toxins, they accumulate and lead to cell, tissue, and organ death.
    • Tay Sachs disease, lysosomes don't break down toxins causes buildup of toxins in the body.
    • Dialysis is one of the procedures.
  • pH of the body.
  • Concentration of electrolytes.
  • Temperature.
    • Normal body temperature is in the high 30's to low 30's (Celsius). If you stray more than two degrees outside of the norm, it can cause hypothermia or hyperthermia which could lead to death.
  • Volume and pressure of fluid around cells.

Control of Homeostasis

• Every body system works to maintain homeostasis, but the major contributors are the nervous system and the endocrine system.
  • The nervous system uses action potentials and neurotransmitters for signaling.
  • The endocrine system uses hormones to control metastasis.

Feedback Loops (or systems)

• Feedback loops/systems are the way we maintain an optimal internal environment.
  • Positive and negative feedback loops.
  • Every feedback loop has:
    • Receptor: Monitor in the body that detects levels of something (e.g., temperature, blood pressure, blood sugar).
    • Control Center: Usually the brain, which interprets information from the receptor and acts upon it.
    • Effectors: Change the stimulus either bringing something high or something low.

Negative Feedback Loops

• Negative feedback loops are more abundant.
• Negative feedback loops oppose an initial change.
  • If something is too high, it brings it back lower.
• Example: Blood Pressure.
  • If blood pressure is too high:
    • Receptors (baroreceptors) in the neck detect pressure.
    • The brain (control center) sends signals to the heart and vasculature (effectors).
    • The heart slows down, reducing stroke volume.
    • The vasculature dilates (vasodilation) to decrease pressure ($Boyle's law$).
    • The stimulus returns to normal.

Positive Feedback Loops

• Positive feedback loops are far less abundant and amplify a change.

  • Usually sex linked.

• Example: Childbirth (labor).

  • The baby's head pushes on the cervix.
    • Mechanoreceptors in the cervix detect pressure. 1-2ml to 10cm
    • The brain releases oxytocin, which acts on muscle cells to pull the cervix apart further.

• A positive feedback loop will keep amplifying until the stimulus is removed (in this case when the baby exits).

  • Unlike negative feedback loop that will negate a change and set itself back to normal. A positive feedback loop will never do that. It will keep amplifying until you take away the change.

• Disrupting homeostasis:

  • Mild disruption without dying.
    • Heat stroke.
    • Exercising.
    • Psychological stresses.
  • Massive disruption or loss of a component leads to death.
    • Hypothermia on Mount Everest without gear.