UNIT 10
Chapter 43: The Body’s Defenses
Chapter 44: Controlling the Internal Environment
Chapter 46: Animal Reproduction
The Body’s Defenses
The purpose of the immune system is to defend the
body against invading bacteria, viruses, and other
pathogens, as well as an animal’s own abnormal cells.
• immune system provides non-specific and specific
defenses
• exist both inside and outside the body
The Body’s Defenses – Non-specific Responses
External defenses are comprised of:
• “drafted army” of bacteria that colonize the skin
• secretions of mucus membranes and sweat glands
• mucus contains an enzyme called lysozyme
degrades the cell wall of many types of bacteria
• pH of sweat is acidic
• prevents colonization by many foreign
microbes
• external defenses are NOT specific to any type of
pathogen and will act upon any foreign body
The Body’s Defenses – Non-specific Responses
If an infectious agent does make it past the external,
first line of defenses, it faces a second-line of defenses
that include:
- Phagocytic cells
- Inflammation
- Antimicrobial proteins
Phagocytosis is a primary method of attack used by
neutrophils (leukocytes) and macrophages.
Macrophages are much longer lived than neutrophils
and use toxins to destroy invaders.
The Body’s Defenses – Non-specific Responses
While some macrophages migrate throughout the
body, but most are stationary and exist primarily in the
lymph nodes. Macrophages extend pseudopodia
around their prey and, once inside, subject the invader
to digestive enzymes.
Some bacteria produce
capsules that surround their cell
wall, which macrophages cannot
attach to. Others, once
engulfed, are not digested and
can actually reproduce inside a
macrophage.
The Body’s Defenses – Non-specific Responses
The inflammatory response is one in which the entry of
mircoorganisms or damaged tissues release chemical
signals that lead to clot formation.
The Body’s Defenses – Non-specific Responses
Important chemical signals:
Chemokines
• Released by damaged/infected cells
• acts to attract immune cells
Histamine
• Released by basophils and mast cells
• causes vessel dilation  greater blood flow
 more immune cells and clotting agents
If a bacterial infection is extensive, it can trigger largescale inflammation called septic shock. The low
blood pressure and high fever that accompany septic
shock is dangerous and even fatal in some cases.
The Body’s Defenses – Specific Responses
Specific defenses:
• Cells involved are designed to attack/defend
against only one type of pathogen
B lymphocytes (B cells) and T lymphocytes (T cells)
• T cells circulate through the lymphatic and
circulatory systems
• respond to antigens by contact with their antigen
receptors
Antigens are anything that stimulate the production of
antibodies. B cells and T cells work differently against
different types of antigens, but they work together to
defend the body.
The Body’s Defenses – Specific Responses
Each of the 2 types of B cells arises from a process
called clonal selection. This is a method by which a
stimulated, activated B cell produces many, many
clones of the two types of B cells.
Plasma B cell: (~5 days)
• has an extensive rough endoplasmic reticulum
• produces HUGE quantities of antibodies
Memory B cell: (30+ years)
• “records” of what antigens have entered the body
• causes a much more massive and rapid response
if the same antigen is encountered again
The Body’s Defenses – Specific Responses
The Body’s Defenses – Specific Responses: Antibodies
Antibodies (aka immunoglobulin) are part of the
humoral response against infection and are produced
by B plasma cells. During infection, each plasma cell
can produce up to 20,000 antibodies per second.
The ends of the Yshaped antibody are
variable depending on
the antigen they are
designed to interact
with. These areas will
interact covalently with
an antigen’s epitope.
The Body’s Defenses – Specific Responses: Antibodies
Antibodies are classified into five groups of
immunoglobulins based on when and where they
are active. Antibody function:
1. Antibodies are bound to their respective antigens
covalently
• blocks the activity of the antigen =
neutralization
2. Macrophages engulf the antigen/antibody complex
The Body’s Defenses – Specific Responses
In order for T cells to be activated, they must be
“shown” the antigen by an antigen presenting cell
(APC).
APCs will cradle
antigens in the major
histocompatibility
complex (MHC) and
display them for T cells.
The T cells will utilize
this interaction in order
to be activated.
Which type of T cell is activated depends on which
class of MHC molecule is presenting the antigen.
The Body’s Defenses – Specific Responses
There are four types of T cells:
- helper cells: produces a growth factor that
stimulates B cell proliferation and
enhances cytotoxic T cell activity
- cytotoxic cells: destroys infected and/or
cancerous body cells
- memory cells: remain in wait for second
exposure to antigen and then
differentiate into more of each type of T
cell
- suppressor cells: inhibits activity of B and T
cells when infection is under control
The Body’s Defenses – Specific Responses
The primary response (first contact) lasts much
longer than the secondary response (second contact)
since it takes time for the immune system to recognize
the antigen and mount a response.
The Body’s Defenses – Immunity
Immunity to an infectious disease can be conferred to
actively, which means that the person’s immune
system has encountered, and successfully defended
against, a pathogen.
This process can be natural, or artificial, via a
vaccination.
Antibodies can also be passed from one person to
another (ex. mother to fetus), passive immunity.
The Body’s Defenses – Recognition of Self
The immune system also has the capability of
recognizing “self” from “non-self.” This limits our ability
to transfuse blood or transplant organs.
A classic example of this is the ABO blood groups.
The Body’s Defenses – Hypersensitivity
People who have allergies actually are experiencing a
hypersensitive reaction to relatively weak antigens allergens.
Mast cells release a disproportionate concentration of
histamine in response to the antigen. The histamine
causes an excess production of mucus, watery eyes,
sneezing, and difficulty in breathing.
If the response to an allergen is severe, it can trigger a
rapid drop in blood pressure, a condition called
anaphylactic shock. Death can result in as little as a
few minutes.
Lupus, rheumatoid arthritis, and multiple sclerosis are
conditions that arise when the body’s immune system
“turns” against the body – autoimmune diseases.
END
Four physical processes account for heat gain or
loss
• Conduction: heat transfer due to direct contact with a surface
• ex. touching a hot stove
• Convection: transfer of heat due to the movement of air or
liquid
• ex. wind-chill factor
• Radiation: emission of EM waves produced by everything
warmer than absolute zero
• ex. the Sun
• Evaporation: loss of heat due to the conversion of a liquid to
a gas
• ex. perspiration
Thermoregulation: physiology & behavior
Regardless of whether an animal is an endotherm or an
ectotherm, animals will attempt to regulate their body
temperature.
1. Adjust rate of heat
exchange between
animal and its
surroundings:
• vasodilation and
vasoconstriction
• countercurrent heat
exchange
2. Cooling by evaporation
3. Behavioral responses
4. Changing the rate of metabolic heat production
• endotherms (esp. birds and mammals)
Birds & Mammals
Birds and mammals generally maintain a body
temperature, within a few degrees, that is
considerably warmer than the environment.
This “safe range” of temperatures is called the
thermal neutral zone (TNZ).
It is not uncommon for animals to acclimatize
to changes in environmental temperature –
such as seasonal changes.
With extreme, rapid changes in temperature, some organisms’
cells can produce special stress-induced and heat-shock
proteins within a few minutes to cope with those changes.
A physiological state, called torpor, is a tactic by which some
animals will lower their metabolic rate and body temperature.
• Hibernation occurs in wintertime; estivation in springtime
A variety of animals will undergo daily torpor and will only
emerge at night or in the day.
Water balance & waste disposal
All animals produce
metabolic wastes
that are nitrogen
based. Which
nitrogenous waste
is excreted
depends mainly on
where that animal
is found.
Excretory systems produce urine by refining a
filtrate derived from body fluids
While excretory systems are diverse,
nearly all produce urine by a twostep process:
• First, body fluid (blood,
hemolymph, fluid of the
coelom) is collected during
filtration
• Second, the composition of the
collected fluid is adjusted by
reabsorption and secretion of
solutes
• Excretion removes the
concentrated wastes
Nephrons & associated blood vessels are the
functional units of the mammalian kidney
Mammals have a pair of bean-shaped kidneys.
• These are supplied with blood by a renal artery
and a renal vein.
Urine exits the kidney through a duct called the
ureter, and both ureters drain through a
common urinary bladder.
• Urine expelled from the urinary bladder through a
tube called the urethra
• Sphincter muscles near the junction of the urethra
and the bladder control urination
The nephron and collecting duct are lined by epithelial tissue
that are responsible for reabsorbing solutes and water.
• nearly all sugar,
vitamins, and other
nutrients from the
filtrate
• 99% of water
• filtrate reduced from
~180L to ~1.5L
Regulation of blood/water concentration is maintained by
hormonal control of the kidney by negative feedback circuits.
One hormone important in regulating water balance is
antidiuretic hormone (ADH). ADH is produced in
hypothalamus of the brain and stored in and
released from the pituitary gland, which lies just
below the hypothalamus.
By negative feedback, loss of water in the blood
reduces the activity cells in the hypothalamus, and
more ADH is secreted.
Conversely, if a large intake of water has reduced
water content of the blood below the set point, less
ADH is released.
END
An Overview of Animal Reproduction
Reproduction in the animal kingdom can occur asexually or
sexually. Reproductive cycles can be controlled hormonally
or environmentally, or by both cues.
While most animals are either sexual or asexual, some can
alternate between the two based on need. The process by
which an unfertilized egg develops into a usually haploid
adult is called parthogenesis.

Drone male honeybees are haploid
Sometimes, for certain sexually reproducing animals, it is
difficult to encounter a member of their own species for them
to mate with. An easy solution to this is hermaphroditism.
This is where one individual functions as both a male and
female.
There is a special type of hermaphroditism in which an animal
will change sexes in the course of its lifetime. This is called
sequential hermaphroditism.
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Protogynous: female first, then male
Protandrous: male first, then female
Fertilization Mechanisms
Fertilization in animals can occur internally or externally.
Internal fertilization required “cooperative behavior” to lead
to copulation while external fertilization requires a moist
habitat.
In general, species that fertilize
internally produce fewer
zygotes. Even still, the survival
rate for externally fertilized
species is much lower than for
internally fertilized ones.
Spermatogenesis & Oogenesis
Spermatogenesis is the
production of mature sperm
cells. In the sperm of most
animals, the structure is
similar.
Oogenesis is the development of
mature ova (unfertilized egg
cells).
Oogenesis is discontinuous:
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Begins in womb, halts before
meiosis I completes
Child (female … duh!) is born
Onset of puberty causes one
(usually) 1° to complete MI and
begin MII
MII halts just before ovulation
Fertilization?
Ovulation is the release of an
mature oocyte during
menstruation. In response
to hormonal signals,
usually a single primary
oocyte grows into a
secondary oocyte. The
follicle from which it is
released becomes the
corpus luteum.
The Human Female Reproductive Cycle
The human female
reproductive cycle is
driven by a variety of
hormones. There are two
distinct cycles that occur:
the ovarian and uterine
cycles. Each of these
cycles occurs in a
succession of phases.
* (The cycles shown here represent
what occurs when fertilization
does NOT occur.)
Unlike males, who produce sperm for their entire lives beginning
at puberty, the production of oocytes will cease (typically)
between the ages of 46 and 54. Menopause is the process of
the cessation of the production of oocytes.
Menopause occurs due to the ovaries becoming desensitized to
the effects of reproductive hormones.
Embryonic & Fetal Development
In placental animals (like humans) pregnancy is the condition of
carrying one or more embryos and begins with conception
(fertilization).
Human pregnancies, which average 266 days, are divided into
three trimesters.
Human Pregnancy – 1st Trimester
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Fertilization occurs in the oviduct
24 hours later the zygote begins cleavage
3- 4 days after fertilization the zygote that reaches the
uterus the embryo is a ball of cells
It takes about 1 week past fertilization for the
blastocyst to form
After 5 more days it implants in the endometrium
Human Pregnancy – 1st Trimester

Organogenesis occurs during the first trimester.
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Week 4: cardiac muscle begins beating
Week 5: limb buds and tail visible
Week 7: lungs begin to form, digits (?)
Week 8: (almost) all of the major structures of the adult have
begun formation
Human Pregnancy – 2nd Trimester
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Fetus grows rapidly and is very active
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Week 12: brain produces detectable signals
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Week 13: sexual differentiation begins
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Week 14-17: 15cm long
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Week 20: heart beats regularly
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Mother can feel movement
Corpus luteum deteriorates
Placenta secretes progesterone, which maintains
the pregnancy
Human Pregnancy – 3rd Trimester
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Fetus grows rapidly
Fetal activity may decrease as the fetus fills the
space available to it
Maternal abdominal organs become compressed
and displaced
Terminates with parturition (childbirth)
Labor & Childbirth
END