Basic Physiology

1
Basic Physiology

• The objective of this next set of lectures is to
  describe the function of the various body
  structures (physiology) to continue to set the
  stage for where Biomedical Engineers work.

2
Major Organ Systems

• Combinations of tissues that perform coordinated,
  complex tasks are called organs and organs that
  function together are called organ systems.
• 11 Major Organ Systems
• Integumentary (protection)
• Endocrine (hormone production)
• Lymphatic (recycle excess fluid and help against
  infection)
• Digestive (break down of food into small
  molecules for adsorption)
• Urinary (fluid volume, elimination of metabolic
  waste, acid-base balance)
• Reproductive (eggs/sperm, nourishment for
  offspring)
• Cardiovascular (distribution system for the body)
• Respiratory (deliver oxygen, removal of carbon
  dioxide)
• Nervous (communication system for the body)
• Skeletal (protection/support, locomotion, mineral
  storage)
• Muscular (locomotion, heat production)

3
Cardiovascular System

• Cardiovascular system provides several functions
• delivery of nutrients, hormones and signaling
  molecules
• removal of metabolic waste products from tissues
• primary mechanism for temperature regulation
• These functions are carried out through the
  movement of blood ( 5 L in the average human
  body)
• Every cell is no more than a few 100 mm from a
  blood vessel and this close proximity allows for
  O2, CO2 and most small solutes to diffuse between
  the cell and the vessel.
• At the centre of this is the heart (pumping
  station that moves blood throughout the body)

4
Anatomy of the Heart

• Four-chambered muscular vessel
• Two Atria (left and right)
• Two Ventricles (left and right)
• Atrium
• Filling chamber
• Pushes blood into ventricle
• Ventricle
• Pressurization chamber
• Ejects blood into circulation
• Chambers separated by heart valves
• One-way flow valves
• Four in total (tricuspid, pulmonary, mitral,
  aortic)

5
Pulmonary and Systemic Circulations

• Essentially two separate pumps
• Right Side
• moves deoxygenated blood to the lungs for
  oxygenation
• Left Side
• moves oxygenated blood to the body
• Which leads to two distinct circulatory systems
• Pulmonary
• vessels to and from the lungs
• Systemic
• vessels to and from the rest of the body
• Vessels that move blood away from the heart are
  called arteries and vessels that return blood to
  the heart are called veins.

6
Systemic Circulation

• Each time the heart beats, a bolus ( 80 mL) of
  blood is ejected from the left ventricle into the
  aorta (the largest artery).
• Blood flows into the medium-sized arteries and
  arterioles (small muscular arteries) which branch
  off the aorta.
• These vessels further subdivide into the
  capillaries (smallest blood vessels that carry
  oxygenated blood).

7
Capillaries

• Capillaries are the smallest diameter blood
  vessels ( 8 mm) and small enough to only allow
  red blood cells to pass in single-file.
• The slow blood flow in the capillaries allows for
  the exchange of nutrients, metabolic waste
  products, gases, hormones, etc. to take place
  between the tissue beds.

8
Venous Return

• Deoxygenated blood then collects in the venules.
• Venules lead to the medium-sized veins, large
  veins and finally the vena cava (the largest
  vein).
• The vena cava then deliveries the deoxygenated
  blood back to the heart via the right atrium (to
  enter into the pulmonary circulation).

9
Pulmonary Circulation

• Each time the heart beats, a bolus of blood is
  also ejected from the right ventricle into the
  pulmonary artery.
• Blood flow is also subdivided into the arterioles
  and tissue beds of the lungs.
• The oxygenated blood then returns to the heart
  via the left atrium.

10
Cardiac Cycle

• Blood returns to the heart from the circulation
  (pulmonary or systemic) and collects in the
  atrium.
• The atrium contracts and pushes the blood into
  the ventricle (the major pumping chamber).
• The ventricle then contracts, pressurizing the
  blood and the ejecting it into the circulation.

11
Heart Valves

• Special one-way valves keep blood moving in the
  correct direction.
• The when atria contract, the atrioventricular
  valves (tricuspid and mitral) open to allow blood
  to pass into the ventricles.

When the ventricles contract the semilunar valves
(aortic and pulmonary) open to allow blood to
leave the heart, while at the same time the
atrioventriclar valves are closed to prevent
back-flow into the atria. When the ventricles
relax before the next contraction, the semilunar
valves close to prevent blood flowing back into
the heart.
12
Heart Valve Disease and Replacements
13
Cardiac Cycle

• To achieve this rhythmic pumping action, the
  heart goes through a repeating pattern of
  contraction (systole) and relaxation (diastole)
  of the heart chambers.
• Begins with a self-generating electrical pulse
  from the pacemaker cells of the heart (sinoatrial
  node).
• Rapid change in electrical potential of these
  cells is due to the movement of ions across their
  plasma membranes (specifically Na ions).

Electrical potential of these cells changes from
about -90 mV to 20 mV (relative to the
extracellular fluid) which is referred to as
depolarization.
14
Action Potentials

• Cells of the SA node depolarize every 0.83 s in a
  typical adult (at rest) giving rise to about 72
  beats/min.
• Shortly thereafter ( 0.3 s) Na is removed from
  the cells (by Na/K pumps) resulting in the
  repolarization of the cell and restoration of
  normal membrane potential.
• Entire event (depolarization/repolarization) is
  called an action potential.
• Cardiac cells are tightly coupled so that the
  action potentials spread from cell-to-cell and
  this wave of depolarization (v 1 m/s) causes
  the cardiac muscle cells to contract.
• Contraction starts in the atria (atrial systole)
  which moves blood into the ventricles.

15
Action Potentials

• Activation wavefront moves to another specialized
  structure of cells (atrioventricular node) which
  slows the wavefront to allow time to fill the
  ventricles.
• From the AV node, the wavefront reaches the
  conduction conduit (Bundle of His) which
  propagates the wavefront very rapidly (v 3
  m/s).

The wavefront is then distributed throughout the
surface of the ventricles via Purkinjie fibres (v
0.5 m/s) to cause the simultaneous contraction
of both ventricles (ventricular systole) and
eject blood from the ventricles into the aortic
and pulmonary arteries.
16
Electrocardiogram (ECG)

• The entire electrical event can be measured by
  the electrocardiogram (ECG).

17
Electrocardiogram (ECG)

• The ECG is routinely used to diagnosis several
  abnormal heart conditions some examples
• Tachycardia/Bradycardia (fast/slow heart rate)
• Myocardial Infarction (heart attack)
• Fibrillation (rapid, irregular, unsynchronized
  contractions)

18
Blood Pressure
19
Blood Pressure

• Average pressure in the pulmonary circulation (
  20 mm Hg) is much lower than the systemic
  circulation ( 100 mm Hg) due to the decreased
  resistance of the compared to the systemic
  circulation).
• For this reason, the right side of the heart is
  also smaller than the left side.

20
Measurement of Blood Pressure

• Various direct (catheter) and indirect methods
  (Doppler-shift, sphygmomanometry) used to
  measure/monitor blood pressure.
• Sphygmomanometry
• Cuff used is to apply sufficient pressure to an
  artery to prevent blood flow.

Cuff is slowly deflated and as the pressure in
cuff reaches the systolic pressure blood rushes
into the artery once again and can be heard
(Korotkoff sounds). As the pressure in cuff
drops below the diastolic pressure, the Korotkoff
sounds disappear.
21
Skeletal System

• The skeletal system is made up of bones and the
  average adult skeleton contains 206 bones
• Varies somewhat from person to person
• Decreases with age (fusion)
• Skeletal system provides several functions
• Protection and support
• Helps with movement
• Produces red blood cells (marrow)
• Mineral storage

22
Bones

• Bones are specialized connective tissues
  (mineralized) and make up 18 of body mass and
  have a density of 1.9 g/cm3.
• Bones are generally classified according to their
  shape
• Long bones (femur, humerus)
• Short bones (ankle, wrist)
• Flat bones (sternum, skull)
• Irregular-shaped bones (vertebral column, pelvis)
• Two types of bones
• Spongy (cancellous or trabecular)
• Ends of long bones, interiors of others
• Porous and made of tiny struts (trabeculae)
• Compact (cortical)
• Forms the shaft and outer covering of almost all
  bones
• Dense structure made up of stacked layers
  (lamellae)

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Cortical and Cancellous Bone
24
Cortical and Cancellous Bone
25
Bone Remodeling

• Bone is a living tissue and is constantly
  remodeled by two different types of cells
• Osteoclasts (bone-resorbing cells)
• Osteoblasts (bone-forming cells)
• Bone remodeling occurs
• During growth
• To repair accumulated micro-damage
• Regulate calcium availability

26
Bone Remodeling

• Average skeleton is totally remodeled every 10-20
  years.
• Imbalance in the remodeling cycle (resorption vs.
  deposition) normally happens with age and a large
  imbalance results in a disorder called
  osteoporosis (weak, brittle bones).
• Osteoporotic bones are more susceptible to
  fracture.

27
Fracture

• Bone can normally heal itself after a fracture
  but in extreme cases interventions are required
  (fracture fixation plates and screws).

28
Joints

• Bones are connected to one another by different
  types of joints
• Fibrous
• Bound tightly together by fibrous connective
  tissue
• Rigid to slightly movable
• Suture joints of the skull
• Cartilaginous
• Bound together by a layer of cartilage (firm,
  resilient, non-vascularized tissue)
• Limited motion (twisting and compression)
• Vertebral column (disc between vertebrae) and
  attachments of ribs to the sternum
• Synovial
• Most complex joints
• Allow a large degree of relative motion between
  articulating bones
• Articulating bones lined with a lined with a
  layer of cartilage and separated by a thin layer
  of lubricating fluid (synovial fluid)
• Surrounded by a fibrous capsule (synovial
  capsule)
• Hip, knee, elbow, ankle, etc.

29
Synovial Joints

• Six different types of synovial joints, each of
  which are classified by the type(s) of motion
  they permit
• Pivot(1 DoF)
• Ball and Socket (3 DoF)
• Hinge (1 DoF)
• Ellipsoid (2-3 DoF)
• Saddle (2 DoF)
• Gliding (1 DoF)

30
Total Joint Replacements

• Artificial joints have been developed to replace
  damaged (trauma) or diseased (osteoarthritis)
  joints in which the cartilage layer(s) that line
  the ends of the articulating bones has been
  destroyed.
• Resurfacing technique (metal and plastic) and
  almost all joints have available replacements
  with the most common being the hip and knee

31
Summary

• Physiology is the study of the function of the
  various body structures.
• Biomedical Engineering has made several
  contributions to both cardiovascular and
  musculoskeletal medicine primarily in the areas
  of diagnostics and prosthetics.