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The Human Body An Orientation Chapter 1 The Human Body An Orientation Anatomy

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					            Chapter 1: The Human Body: An Orientation
Anatomy – The Study of Structure
     • Based on observation
     • Gross anatomy is what is visible with naked eye - dissection
     • Histology is examination of cell populations (called tissues) with microscope
     • Includes imaging technology (x-rays, CT, PET, ultrasound & NMR)

Physiology - The Study of Function
     • Study of bodily function by experiment
     • Examples: blood flow, breathing, urine formation, nervous impulses
     • Subdivisions are system or organ-based for example: Gastrointestinal, Renal,
            Cardiovascular, Pulmonary, Neuro-, Reproductive, Exercise.
     • Basis for drugs and medical procedures
     • Pathophysiology = disease state

Anatomy and Physiology are Complementary
     • Structure and function are interrelated.
            – How does a tube’s structure relate to its function?
            – What kinds of substances are transported via tubes?
            – How does altering the diameter of a tube change function (flow/pressure)?
                   Constriction?
                   Dilation?

Organization of life forms (from simplest to most complicated):
     – atoms
     – molecules
     – cellular organelles or “little organs”
     – cells               (cardiac myocyte)
     – tissues             (cardiac muscle)
     – organs              (heart)
     – organ systems       (cardiovascular)
     – organism

Compartmental Organization of Human
Organism:
     • Refer to figure at right (Principles of
     Human Physiology by Germann &
     Stanfield)
     • Organism is surrounded by a hostile
     external environment.
     • Cells form one compartment with in the
     organism: referred to as “intracellular”
      • Cells are bathed by a second compartment referred to as the internal environment or
      “extracellular” compartment

Homeostasis
      • Means stable internal environment (extracellular compartment) = “steady state”
             – fluctuations in a range around an average value called “set point”
      • Physiology is focused on understanding the mechanisms that promote homeostasis
      • Loss of homeostatic control causes illness or death
      • Some examples: blood glucose levels, blood pressure, salt & water balance, oxygen.

Negative Feedback Loops
      • Mechanism used to keep a variable close to its set point
      • Body senses a change & activates mechanisms to reverse it
      • Provides order or balance (homeostasis)
      • Most common type of feedback in physiology
      • This loop acts “negatively” meaning it TURNS OFF the initial stimulus

Example of Negative Feedback: Diabetes (high blood sugar/glucose)
      • What do some diabetics inject to regulate their blood glucose? Where does this
      substance normally come from? and How does it work?
                    –answer = insulin is a hormone that is released by the pancreas in response
                    to elevated blood glucose levels it binds to insulin receptors in target cells
                    and activates glucose uptake into cells (normally glucose uptake is inactive).
      • Why is it important to regulate the amount of sugar in the blood:
                    –hypoglycemia (low sugar) brain has no food         Coma & death
                    –hyperglycemia (high sugar) neuropathy, necrosis, retinopathy & death

Structures Needed for Feedback Loops
      • Sensors detect change in variable (Marieb calls these “receptors” which is historically
      correct but can lead to some confusion as there is a more common usage for “receptor”)
      • Control centers integrate and respond to information from sensor(s)
             – Often brain, spinal cord, hormone-releasing glands, sometimes individual cells
             – For example: part of the pancreas serves as both sensor and control center
      • Effectors are structures that carry out commands of the control center
             – Examples: muscles & glands
             – For example: insulin causes liver & skeletal muscle to take up glucose so both
                are effectors

Extracellular chemical messengers carry information from cell to cell across the
internal environment (4 kinds):
     1) Neurotransmitters: produced by nerves act on nerves, glands or muscles, usually local.
     2) Hormones: Produced by glands and are released into the blood; Example: INSULIN
     3) Paracrines: Chemical messengers that are released by cells and act on adjacent or
     nearby cells. Example: HISTAMINE is released locally by defense/immune (Mast) cells
      in response to inflammation and the effect (fluid secretion, irritation, itching) is designed
      to eliminate the irritating agent. Histamine causes many symptoms of colds & allergies.
      (Benadryl, and other antihistamines block the histamine receptor).
      4) Autocrines: messengers that are released by and act on a single cell (auto = self)

Extracellular chemical messengers bind to specific targets called receptors.
      •The chemical messengers are referred to as “ligands” (ligo- means “to bind”)
      •Mechanism analogous to a “Lock & Key”
      •Interactions are specific – forms the basis for most pharmacology/therapeutics
      •What binds to the histamine receptor? Insulin receptor? Estrogen receptor?
      •Most naturally occurring ligands bind and activate signal (insulin insulin receptor).
      •Many therapeutic drugs bind specific receptors
             - Some activate the receptor, and mimic the effect (pseudoephedrine / adrenalin)
             - Some bind receptor and prevent binding (block effect) of activating ligands
             (antihistamines: Benadryl or Claritin histamine receptor). These “keys” fit into
             the “lock” but are unable to “open” it.

Positive Feedback Loops
      • Physiological change that leads to an even greater change in the same direction
      • Acts “positively” meaning it TURNS ON the initial stimulus
      • Normal way of producing rapid changes
      • Examples:
                    – childbirth,
                    – ovulation
                    – blood clotting
                    – life-threatening fever

Example of Positive Feedback: Childbirth
     • Oxytocin is a hormone that is produced by brain that stimulates uterus to contract.
     • Uterine contraction stimulates the brain and causes oxytocin release.
     • More and more oxytocin is released as uterine contractions get stronger and stronger.
     This cycle is repeated until baby is born.
     • Contractions are initiated by oxytocin administration during “labor induction”

Example of Positive Feedback: Life-Threatening Fever
     • If temperature rises above 108 degrees due to bacterial infection
     • Increased metabolic rate causes body to produce heat which increases metabolic rate…
     • Temperature increases & cycle repeats
     • Can be fatal!

Anatomical Terminology
     • Fast-paced anatomical discoveries during the Renaissance resulted in confusion
            – different countries naming same structures with different names
     • To reduce confusion most medical terms are derived from Greek or Latin roots
      • Sometimes unusual endings for singular vs. plural. (nucleus vs. nuclei)
      • Rational for vocabulary quiz – develop ability to decipher words!
      • Eponyms are named after people
             Islets of Langerhans
             Bowman’s capsule
             Loop of Henle
             Haversian canal

Anatomical Position
      • Person stands erect
      • Feet flat on floor
      • Arms at sides
      • Palms, eyes & face facing forward
      • Standard frame of reference for anatomical descriptions & dissection

Directional Terms – terms listed in pairs (like E-W; N-S)

“Relative” directions
      • Superior/Inferior = above vs. below
      • Anterior/Posterior = front vs. back
      • Meanings differ between humans and animals – thus are “relative”
             – anterior surface of human is surface of chest & belly
             – anterior in a four-legged animal is the head end
             – posterior surface of human is back side
             – posterior in a four-legged animal is the tail end

“Absolute” directions analogous to anterior/posterior & superior/inferior
      • Ventral/Dorsal: belly vs. back
      • Cephalic/Caudal: head vs. tail

Other important relative directional terms
      • Medial/Intermediate/Lateral = toward midline vs. away from midline
      • Superficial/deep = surface vs. down under
      • Proximal/Distal – refers specifically to appendages near vs. far
      • Meaning differ based on starting point – thus these are also “relative”

Anatomical Terminology: Body Regions

Axial region = head, neck & trunk
      • cephalic (head)
            • frontal (forehead)
            • nasal (nose)
            • orbital (eye)
            • oral (mouth)
            • buccal (cheek)
            • occipital (back of head)
            • otic (ear)
            • mental (chin)
     • cervical (neck)
     • thoracic trunk region above diaphragm & abdominal region below
            • acromial (point of shoulder)
            • sternal (central part of thoracic cage)
            • vertebral (back bone)
            • scapular (shoulder blades)
            • mammary or pectoral (breast)
            • axillary (arm pit)
            • pelvic (pelvis)
            • coxal (hip)
            • umbilical (naval)
            • inguinal (groin)
            • lumbar (lower back –vertebral column above hips)
            • sacral (lower back – below hips)
            • gluteal (buttock)
            • pubic (external genitals)
            • perineal (anal-genital)

Appendicular region = upper and lower limbs
     • Important terms regarding upper limbs
           • brachium (arm)
           • antecubital (front of elbow)
           • olecranol (back of elbow)
           • carpal (wrist)
           • antebrachial (forearm)
           • palmar (palm)
           • digits (fingers)
           • pollex (thumb)
           • manus (hand)
     • Important terms regarding lower limbs
           • femoral (thigh)
           • patellar (front of knee)
           • crural (front of calf)
           • popliteal (back of knee)
            • sural (back of calf)
            • fibular or peroneal (side of calf)
            • tarsus (ankle)
            • calcaneal (heel)
            • pedal (foot)
            • digits (toes)

Anatomical Planes
     • Planes are imaginary flat surfaces passing through the body
     • Sagittal plane divides body into right and left halves
            – midsagittal plane divides body into equal right and left halves
            – parasagittal plane divides the body into right and left portions
     • Frontal (coronal) plane divides body into front & back
     • Transverse (horizontal) divides the body into upper & lower

Body Cavities and Membranes: dorsal and ventral
     • dorsal body cavity has two major parts:
                   • Cranial cavity – contains brain
                   • Vertebral canal – spinal cord

     • ventral body cavity also has two parts: diaphragm separates them
            • thoracic cavity
                   •Pleural cavity – contains lungs
                   •Mediastinum separates left from right pleural cavities
                   •Pericardial cavity – contains heart
            • abdominopelvic cavity – peritoneal cavity: contains gastrointestinal and
            reproductive organs

Thoracic Cavity - contains heart, major blood vessels, esophagus, trachea, & thymus

Abdominopelvic Cavity

     • Brim of the pelvis separates abdominal (superior) from pelvic (inferior) cavity
            – Abdominal cavity contains GI tract (stomach, intestines, liver, gallbladder,
            pancreas, & colon), kidneys & ureters and spleen (functions in immune system)
            – Abdomen divided into 4 quadrants
                   • upper left – stomach & esophagus
                   • upper right – gallbladder
                   • lower left – intestines
                   • lower right – appendix
     • Pelvic cavity contains rectum, bladder, urethra & some organs for reproduction
Membranes
    • All 3 cavities (pleural, pericardial and peritoneal) are lined by serous membranes
            – simple squamous epithelial cells and connective tissue
    • These membranes function to secrete fluid for lubrication of organs
    • Named based on location – Visceral (organs) vs. Parietal (body wall)
            • visceral and parietal pericardium cover heart & line pericardial sac
            • visceral and parietal pleural cover lungs & line rib cage
            • visceral and parietal peritoneal cover organs and abdominopelvic cavity
            • Inflammation of these membranes causes: pleurisy, pericarditis, and peritonitis
            (respectively). It is painful to move/breath due to lack of lubricating fluid

				
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