unit 10 chapter 43: the body’s defenses chapter 44: controlling the internal environment chapter...

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

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.


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 inflammatory response is one in which the entry of mircoorganisms or damaged tissues release chemical signals that lead to clot formation.


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 large-scale inflammation called septic shock. The low blood pressure and high fever that accompany septic shock is dangerous and even fatal in some cases.


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


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 Body’s Defenses – Specific Responses: Antibodies

The ends of the Y-shaped antibody are variable depending on the antigen they are designed to interact with. These areas will interact covalently with an antigen’s epitope.

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: Antibodies

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.

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 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.


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 – Immunity

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 – Recognition of Self

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.

The Body’s Defenses – Hypersensitivity

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 two-step 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

• nearly all sugar, vitamins, and other nutrients from the filtrate• 99% of water• filtrate reduced from ~180L to ~1.5L

The nephron and collecting duct are lined by epithelial tissue that are responsible for reabsorbing solutes and water.

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.

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: 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 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.

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 Fetus grows rapidly and is very active

Week 12: brain produces detectable signals Week 13: sexual differentiation begins Week 14-17: 15cm long Week 20: heart beats regularly Mother can feel movement

Corpus luteum deteriorates Placenta secretes progesterone, which maintains

the pregnancy

Human Pregnancy – 3rd Trimester 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

unit 10 chapter 43: the body’s defenses chapter 44: controlling the internal environment chapter...

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