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Basic Anatomy & Physiology Explained

Updated on February 11, 2015

Basic Anatomy and Physiology

Characteristics of Live:

  • Capacity to engage in metabolism
  • Capacity to sense and respond to the environment
  • Capacity to grow and reproduce
  • Capacity to develop and change


  1. CHEMICAL – Biochemistry of our body (H2O, DNA, O2).
  2. CELLULAR – Basic unit of live that performs vital functions (skin cells, muscle cells).
  3. TISSUES – Group of identical cells working towards a common, specific purpose (connective tissue, nervous tissue).
  4. ORGANS – Group of identical and different tissues working towards a common, specific purpose (heart, brain).
  5. ORGANS SYSTEMS – Group of organs working towards a common purpose (respiratory and circulatory systems).
  6. INDIVIDUAL – Group of organs systems working towards a common purpose (homeostasis).


The smallest form of living organisms is called a CELL. They are the building blocks of all organisms and are formed by four main elements (carbon [C], oxygen [O2], hydrogen [H] and nitrogen [N]) and by several trace elements including calcium (Ca2+), sodium (Na+) and potassium (K+) ions.


  • PROKARYOTES- No defined nuclear membrane. Unicellular Organism.Example:
    • BACTERIAUnicellular organism that lack a nuclear envelope (prokaryotes). Pathogenic bacteria cause disease while probiotic bacteria help and protect the body. They can be classified by:
      • Shape – Coccus (round), Spirochete (spiral) and Bacillus (cylindrical)
      • Gram Staining – Gram Positive (deep blue almost violet) and Gram Negative (red or pinkish color)
  • EUKARYOTES- Define and enclosed nucleus. Unicellular and multicellular organism.

Main Components:

  • Cell Membrane – Also known as plasma membrane, establish the limit of the cell regulating the exchange of substances through a series of active and passive processes and also provides cell to cell recognition.
  • Nucleus – Known as the command central, this typically spherical structure is almost always located at the center. Surrounded by a double layer of nuclear membrane is the largest organelle found inside the cell.
    • Inside Nucleus:
    • Nucleolus
    • Genetic Material (chromatin):
    • DNA – Contains the blueprint for the creation of new cells
    • RNA – The synthesize to form ribosome
  • Cytoplasm or Cytosol – It’s a gel-like intracellular fluid within the cell membrane which main functions are to provide cellular nutrition and support. Composed of:
  • Colloid Portion
  • Cytoskeleton
  • Organelles – Basic components of the cell necessary for metabolism.


Mitochondrion – Also known as the cell’s power plant (cell respiration) because it provides most of the cell’s ATP.

Ribosome – Main function is to synthesize protein for internal and external use and repair.

Endoplasmic Reticulum – A complex of membranous channels, this structure assists in the transportation of materials from one place to another within the cell. They also synthesize protein, carbohydrates and lipids. They are classified as

  • Rough Endoplasmic Reticulum (ribosome attached) - Protein synthesis
  • Smooth Endoplasmic Reticulum (absence of ribosome) - Fat and carbohydrates metabolism

Golgi apparatus – Known as the packing and shipping plant of the cell, these horizontal membranous sacs alters lipids, packing and storing them until needed.

Lysosomes – Known as the cell’s digestive system, they engulf pathogens, cellular debris and organelles, digesting them and afterwards, any reusable matter is returned to the cytoplasm.

Centrioles – Responsible for cell division (mitosis).

Vacuoles – Storage (not an organelle)


PASSIVE PROCESSES – Processes that require no ATP because they move by means of gradients concentration (temperature, pressure, concentration).

  • Diffusion – Movement of substances from a high concentration area to a low concentration area until the distribution of substances is equal (O2 diffuses from the alveolus to the blood capillaries in the lungs).
    • Facilitated Diffusion – Special type of diffusion that uses a carrier molecule of protein to facilitate the diffusion process. It is limited by the number of carrier molecules (carrier proteins help the glucose molecules cross rapidly through the cell membrane into the cell).
  • Filtration – Movement of particles across the membrane due to hydrostatic pressure (urine formation at the kidneys).
  • Osmosis – Movement of a solvent (H2O) from an area of high concentration to an area of high solute (Salt) concentration until the solvent concentration equalizes (reabsorbing water from waste in the kidneys).

ACTIVE PROCESSES – Processes that require an expenditure of energy (ATP) by the cell itself to transport the products across the membrane against the concentration gradients.

v Active Transport – Movement of substances from an area of low concentration to an area of high concentration with the help of specific transport proteins and the expenditure of energy (movement of nutrients from the digestive system to the blood stream).

v Endocytosis – Is a process that moves larger particles across the cell membrane into the cell. The two main types are:

  • Phagocytosis (cell eating) – Specific to the substances it transports, it is the process by which specialized cells engulf pathogens and other cellular waste, breaking it down and dumping the remains back to the cytoplasm. Ex; Leukocytes
  • Pinocytosis (cell drinking) – None specific to the substances it targets, the cell engulfs, instead of whole particles like in phagocytosis, already dissolved, broken down substances to be hydrolyze by the Lysosomes. Pinocytic cells are more common that phagocytic cells.

v Exocytosis – Is a process that moves particles across the cell membrane to the outside of a cell.


Mitosis – Asexual cellular reproduction by which the body is able to grow and replace old or damage cells (from one cell, two identical will form).

  • Phases:
    • Prophase
    • Metaphase
    • Anaphase
    • Telophase

Meiosis – A sexual cellular reproduction by which the body is able to produce gametes or spores (from one cell, four will form).

  • Meiosis I (reduction division) – Primary spermatocyte divides into two secondary spermatocytes each with 23 chromosomes only (haploid cells).
  • Meiosis II (equatorial division) – Each secondary spermatocyte divides again producing a total of four spermatids each containing 23 chromosomes with a single chromatid.


From a zygote, three individual cell layers form to arise all other structures in the human body. From superficial to deep, these cell layers are:

  1. Ectoderm – Emerges first and is the outermost or distal layer of embryonic cell. It differentiates to form the structures of the nervous system (including the special senses), the lining of the mouth, nose and anus, tooth enamel and the epidermis with epidermal structures such as fingernails, sweat glands and hair.
  2. Mesoderm – This middle layer forms the skeletal muscles and most connective tissues of the body (fascia, bone, dermis and hypodermis, lymph, the pleurae of the lungs, etc).
  3. Endoderm – This innermost layer differentiates to form the lining of the alimentary and respiratory passages, and the tissues of the internal organs and glands.


A Tissue is a group of similar cells originating from the same embryonic layer that carry specific functions or tasks. There are four types of tissue in the human body: conective, muscular, nervous and epithelial.

Connective Tissue– It is the most abundant tissue of the human body. It is composed of connective tissue cell scattered in a matrix, which in turn is composed of ground substance (H2O and suspended solids) and strands of collagen. The ratio between these two substances will determine the classification in which this connective tissue will fall. Main functions are:

  • Nutrient transport system
  • Defense of human body
  • Clotting mechanism
  • Supportive Framework
  • Protection of vital organs


  1. Liquid Connective Tissue
  • Blood– Fluid medium or plasma containing three formed elements (erythrocytes, leukocytes and platelets) and traces of other substances.
    • Lymph – Fluid found in the lymphatic system
    • Interstitial – Fluid surrounding or bathing cells and tissues

2. Osseous Connective Tissue

  • Compact – Hard outer part of bones
  • Spongy – Composed of thin beam spaced apart from each other, this type of tissue lightens the weight of the bone.

3. Cartilage

  • Hyaline – Most common type; elastic, rubbery, and smooth, covering ends of bones; part of the larynx and nose; forms the C-shaped rings in the trachea.
  • Elastic – Soft and pliable, giving shape to the external nose and ears, the epiglottis and auditory tubes.
  • Fibrocartilage – Greatest tensile strength of all cartilage types; found in intervertebral disks, meniscus of the knee, and between the pubic bone.

4. Loose Connective Tissue

  • Areolar – Most widely distributed, forms the superficial fascia
  • Adipose – Specialized in fat storage, insulates the body against heat loss; provides fuel reserve for energy; provides cushion around structures
  • Reticular – Forms the framework of organs

5. Dense Connective Tissue

  • Elastic – Can be stretch and restore to its natural shape; found in true vocal cords; ligaments connecting adjacent vertebrae, trachea and bronchi
  • Dense Regular – Offers great strength and can resist pulling forces in one direction such as ligaments, tendons, retinacula and aponeurosis
  • Dense Irregular – Resist pulling forces in different directions (deep fascia, deep epidermis and peritoneum)

*Connective tissue is highly vascularized providing nutrition and oxygen to itself and nearby tissues, with the exception of cartilage.


Fascia is similar to a cobweb that runs throughout the body. It presents the following functions:

1. Provide a sliding and gliding environment for muscles.

2. Suspend organs in their proper place.

3. Transmit movement from muscle to the bones they are attached to.

4. Provide a supportive and movable wrapping for nerves and blood vessels as they pass through and between muscles.


  1. Superficial Fascia – This areolar connective tissue is located immediately under the skin and its main functions are to serve as a storage medium and protective padding for the human body.
  2. Deep Fascia – A type of dense irregular connective tissue, it surrounds and separate the muscle into functional groups.


  1. Sol-state – Offering less restriction on the movement, in this state the fascia is easier to manipulate and more pliable.
  2. Gel-state – Offering a greater restriction on the movement, in this state the fascia is tougher and more inflexible.

THIXOTROPISM – Fascia‘s ability to change from gel-state into sol-state. It happens when our body warms from physical activity, exercise and when being massaged or stretched.

Muscle Tissue – A very vascular and elastic tissue with the ability to contract and relax to produce movement. It is composed of muscle fibers or myofibrils surrounded by a fascia

  1. Smooth Muscle Fiber (involuntary, visceral) – Spindle-shaped, mononucleotide cells that lines the wall or hollow organs and tubes.
  2. Skeletal Muscle Fiber (voluntary, striated) – Cylindrical, multinucleated cells that form all the skeletal muscle.
  3. Cardiac Muscle Fiber (involuntary, striated) – Forming the heart wall, these Y or H shaped cells contain between them a structure called intercalated disk which allows the transmission of impulses from one cell to the other.

Nervous Tissue– Specific type of tissue with the ability to detect and transmit electrical signals. It is composed of:

  1. Neurons - Detect changes (inside and outside of body), interpret the information and provide a response.
  2. Neuroglia (glial cells) - Provide support, nourishment and insulation to the neurons

Epithelial Tissue – It lines the internal and external organs, body cavities, blood vessels and tracts found in the digestive, respiratory, urinary and reproductive systems. Functions include protection, absorption, secretion and excretion.


Metabolism – All chemical process that occur within the cell. It can be subdivided in two phases:

  • Anabolism – Building phase where the energy is used to form vital substances for the human body (essential for growth, repair and maintenance)
  • Catabolism – Breaking-down phase where the energy is obtained by complex chemical reactions (cellular respiration) and then is used in the anabolic phase.

Homeostasis – A carefully regulated balanced internal environment.

  • Homeostatic Mechanisms– Controls systems that maintain homeostasis in the body. When these systems cannot cope with stress and the homeostatic state is not reached, diseases and even death can occur. The work using a series of Feedback Systems:
    • Negative Feedback System – When the response given is the opposite or counteracts the perceived stimulus (body temperature regulation, blood glucose regulation)
    • Positive Feedback System – When the response given intensifies the perceived stimulus (childbirth, blood platelet accumulation during a cut)


The first reaction of the body when then tissue is damaged is the inflammation of the area.


  1. Resolution – Occurring only if the nuclear content and membrane are not damaged, it is the primary method of tissue replacement. Ex; sunburn, digestive lining.
  2. Regeneration – Process by which moderately traumatized tissue repairs itself with tissue of the same type. Ex; skinned knee.
  3. Fibrosis – Process by which severely damage tissue repairs itself with tissue of a different kind (scar tissue). Usually some loss of function will occur.
  4. Remodeling – Process in which the body restructure the scar tissue in response to the contraction and elongation of skeletal muscle.
  5. Keloids – Excessive scar formations due to excessive collagen production.


Membranes – Thin, permeable sheets that line tracts, cover and separates body cavities:

  • Mucous Membrane – Providing protection to the underline structures, this membrane is found lining the openings to the outside of the body (respiratory, digestive, urinary and reproductive tracts.
  • Serous Membrane – Comprise of two layers, these closed body cavities (no outside connection) secretes a serous fluid which reduces friction between organs and lubricates them.
    • Parietal Layer - Lines the walls of body cavities.
    • Visceral Layer – It covers individual organs.
  • Synovial Membrane – Secreting synovial fluid, this membrane lines the joint cavities of freely moving joints to reduce the friction between them.


Ventral Cavity – Large space that protects organs in the front of the body. Subdivided in:

  • Thoracic Cavity – It protects the heart, lungs and large blood vessels
    • Pericardial Cavity – Small cavity surrounding and protecting only the heart
  • Abdominopelvic Cavity – Large space composed of the Abdominal and pelvic cavities
    • Abdominal Cavity – It houses the stomach, intestines, liver, gallbladder, pancreas and spleen
    • Pelvic Cavity – last section of large intestine, urinary and reproductive organs

Dorsal Cavity – Large space located in the back of the body that protects different organs. Subdivided in:

  • Cranial CavitySurrounds the brain
  • Spinal Cavity – Houses the spinal cord

Smaller cavities are also found throughout the body specific to the area (nasal cavity, oral cavity etc)


Health practitioners divide the Abdominopelvic region into four quadrants to better assess pain locations, pathological conditions and even organ positioning. The division is as follows:

Directional Terms

Near Point of Reference
Far from Point of Reference
Outside the Body
Inside the Body
Towards the Body Surface
Away from the Body Surface
Refers to structures around the center of the body (head and torso)
Refers to structures surrounding the outing regions of the body (extremities)
Superior (cranial)
Towards the head
Inferior (caudal)
Towards the feet
Anterior (ventral)
Towards the front of the structure
Posterior (dorsal)
Towards the back of the structure
Towards or closer to the midline
Away from the midline
Ipsilateral (homolateral)
Referred to the same side
Referred to the opposite side
Directional Terms

Body Regional Terms


  1. Cranial – Upper Skull
  2. Cephalic – Head
  3. Frontal – Forehead
  4. Orbital – Eye
  5. Nasal – Nose
  6. Facial – Face
  7. Zygomatic – Upper Cheek
  8. Buccal – Lower Cheek
  9. Oral – Mouth
  10. Mandibular – Lower Jaw
  11. Mental – Chin
  12. Otic (auricular) – Ear
  13. Temporal – Side of Skull
  14. Occipital – Back of Skull
  15. Nuchal – Posterior Neck
  16. Cervical - Neck


  1. Thoracic – Chest
  2. Mediastinal – Between Lungs
  3. Pectoral – Upper Anterior Thorax
  4. Coastal – Ribs
  5. Abdominal – Abdomen
  6. Umbilical – Navel
  7. Pelvic – Pelvis
  8. Inguinal – Groin
  9. Pubic – Genital Area
  10. Perineal – Between genitalia and anus


  1. Dorsal – Back
  2. Scapular – Shoulder Blade
  3. Vertebral – Vertebrae
  4. Thoracic – Middle Back
  5. Flank – Lateral Trunk
  6. Lumbar – Lower Back
  7. Sacral – Sacrum
  8. Sacroiliac – Between sacrum and pelvic bone
  9. Coccygeal – Coccyx
  10. Gluteal – Buttock


1. Acromial – Top of Shoulder

2. Clavicular – Collar Bone

3. Deltoid – Upper Curved of Shoulder

4. Axillary – Armpit

5. Brachial – Arm

6. Antecubital – Bend of Elbow

7. Cubital – Elbow

8. Olecranal – Back of Elbow

9. Antebrachial – Forearm

10. Carpal – Wrist

11. Palmar (volar) – Anterior Surface of Hand

12. Digital (phalangeal) – Fingers

13. Pollex - Thumb


1. Coxal – Hip

2. Femoral – Thigh

3. Patellar – Knee

4. Popliteal – Posterior Knee

5. Crural – Anterior Leg

6. Sural – Posterior Leg

7. Calcaneal – Heel

8. Tarsal – Ankle

9. Pedal – Foot

10. Dorsum – Top of Foot

11. Plantar (volar) – Sole of Foot

12. Digital (phalangeal) – Toes

13. Hallux – Great Toe


  • Anatomical Position – In this position the body is erect, face forward with arms resting at the side of the trunk, palms facing forward and feet parallel.
  • Prone Position – In this position the body is laying on the stomach (downward)
  • Supine Position – In this position the body is laying on the back (upward)
  • Fowler’s Position – In this position the body is sitting down on a bed with the head elevated 45 to 60 degrees.
  • Trendelenberg Position – In this position the body is lying in supine position with the head slightly lower than their feet.
  • Side Lying (lateral recumbent position) – In this position the body is lying in either the left or the right side.


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