On National Teacher Day, meet the 2024-25 Kenan Fellows
Chapter 21: The Immune System (#1)
1. CHAPTER 21: THE IMMUNE
SYSTEM (1): INNATE
IMMUNITY
Human Anatomy and Physiology II –
BIOL153
2. Goals/Objectives
Explain the key differences between the innate vs
adaptive immune system
Describe surface membrane barriers and their
protective functions
Explain the importance of phagocytosis and
natural killer cells in innate body defense
Name the body’s antimicrobial substances and
describe their functions
Describe the inflammatory process. Identify the
cardinal signs of acute inflammation and indicate
their causes
Explain how fever helps the body
7. Innate Defenses
Surface barriers ward off invading pathogens –
first line of defense
Skin, mucous membranes, and their secretions
8. Innate Defenses
Internal Defenses: Cells and Chemicals
Necessary if microorganisms invade deeper
tissues – Second Line of Defense
9. Phagocytes
Neutrophils most abundant but die fighting
Become phagocytic on exposure to infectious material
Macrophages develop from monocytes – chief
phagocytic cells – robust cells
Free macrophages wander through tissue spaces, e.g.,
alveolar macrophages
Fixed macrophages permanent residents of some organs;
e.g., stellate macrophages (liver) and microglia (brain)
16. Antimicrobial Proteins
Some attack microorganisms directly
(compliment)
Some hinder microorganisms' ability to
reproduce/survive
Include interferons and complement proteins
17. Interferons
Family of immune modulating proteins
Viruses lack the essential cellular machinery to
generate ATP or synthesize protein
They cannot reproduce themselves
They hijack other cells to do their work
Viral-infected cells secrete IFNs (e.g., IFN
alpha and beta) to "warn" neighboring cells
IFNs enter neighboring cells produce proteins
that block viral reproduction and degrade viral
RNA
IFN alpha and beta also activate NK cells
23. Complement System
(Complement)
~20 blood proteins that circulate in inactive
form• Called complement
because it helps other
immune cells to
perform their
functions
• Activation unleashes
inflammatory
chemicals that
amplify virtually all
aspects of the
inflammatory
process
• It can also lyse and
kill certain bacteria
and other cell types.
25. Clicker Question
Which of the following is not a mechanical
barrier to pathogen invasion?
a) Mucus membranes
b) Complement
c) Skin
d) Saliva
26. Goals/Objectives
Explain the key differences between the innate vs
adaptive immune system
Describe surface membrane barriers and their
protective functions
Explain the importance of phagocytosis and
natural killer cells in innate body defense
Name the body’s antimicrobial substances and
describe their functions
Describe the inflammatory process. Identify the
cardinal signs of acute inflammation and indicate
their causes
Explain how fever helps the body
27. Inflammatory Response (functions in
bold)
Triggered whenever body tissues
injured
Prevents spread of damaging
agents
Disposes of cell debris and
pathogens
Alerts adaptive immune system
29. Innate defenses Internal defenses
Initial stimulus
Physiological response
Signs of inflammation
Result
Arterioles
dilate
Local hyperemia
(increased blood
flow to area)
Heat Redness
Release of inflammatory chemicals
(histamine, complement,
kinins, prostaglandins, etc.)
Increased capillary
permeability
Capillaries
leak fluid
(exudate formation)
Leaked protein-rich
fluid in tissue spaces
Pain Swelling
Possible temporary
impairment of
function
Locally increased
temperature increases
metabolic rate of cells
Tissue injury
Attract neutrophils,
monocytes, and
lymphocytes to
area (chemotaxis)
Leaked clotting
proteins form interstitial
clots that wall off area
to prevent injury to
surrounding tissue
Temporary fibrin
patch forms
scaffolding for repair
Healing
Release of leukocytosis-
inducing factor
Leukocytosis
(increased numbers of white
blood cells in bloodstream)
Leukocytes migrate to
injured area
Margination
(leukocytes cling to
capillary walls)
Diapedesis
(leukocytes pass through
capillary walls)
Phagocytosis of pathogens
and dead tissue cells
(by neutrophils, short-term;
by macrophages, long-term)
Pus may form
Area cleared of debris
30. Phagocyte Mobilization
Steps for phagocyte mobilization
1. Leukocytosis: release of neutrophils from bone
marrow in response to leukocytosis-inducing
factors from injured cells
2. Margination: neutrophils cling to walls of
capillaries in inflamed area in response to CAMs
3. Diapedesis of neutrophils
4. Chemotaxis: inflammatory chemicals
(chemotactic agent) promote positive
chemotaxis of neutrophils
31. Innate defenses Internal defenses
Inflammatory
chemicals
diffusing
from the
inflamed
site act as
chemotactic
agents.
1
Capillary wall
Basement
membrane
Endothelium
Leukocytosis.
Neutrophils enter
blood from bone
marrow.
32. Innate defenses Internal defenses
Inflammatory
chemicals
diffusing
from the
inflamed
site act as
chemotactic
agents.
Leukocytosis.
Neutrophils enter
blood from bone
marrow.
Margination.
Neutrophils cling
to capillary wall.
1 2
Capillary wall
Basement
membrane
Endothelium
33. Innate defenses Internal defenses
Inflammatory
chemicals
diffusing
from the
inflamed
site act as
chemotactic
agents.
Leukocytosis.
Neutrophils enter
blood from bone
marrow.
Margination.
Neutrophils cling
to capillary wall.
Diapedesis.
Neutrophils flatten
and squeeze out of
capillaries.
1 2 3
Capillary wall
Basement
membrane
Endothelium
34. Innate defenses Internal defenses
Inflammatory
chemicals
diffusing
from the
inflamed
site act as
chemotactic
agents.
Leukocytosis.
Neutrophils enter
blood from bone
marrow.
Margination.
Neutrophils cling
to capillary wall.
Diapedesis.
Neutrophils flatten
and squeeze out of
capillaries.
1 2 3
Chemotaxis.
Neutrophils follow
chemical trail.
Capillary wall
Basement
membrane
Endothelium
4
35. Clicker Question
The process by which phagocytes exit the
capillary and enter injured tissue is called
_________.
a) chemotaxis
b) leukocytosis
c) margination
d) diapedesis
36. Fever
Abnormally high body temperature
Systemic response to invading
microorganisms (not localized)
Leukocytes and macrophages exposed to
foreign substances secrete pyrogens
Pyrogens act on body's thermostat in
hypothalamus, raising body temperature
Benefits of moderate fever
Causes liver and spleen to sequester iron and
zinc (needed by microorganisms)
Increases metabolic rate faster repair
37. Clicker Question
A person with an upper respiratory infection asks
you why a fever occurs with this type of infection.
You are aware that the cells of the immune
system release chemical agents that enhance the
inflammatory response and increase temperature.
These are known as:
a) Antigens
b) Antibodies
c) Pyrogens
d) Phagocytes
