Animal Physiology (2)

Question 1

What is the primary line of defence? State the components and explain how it is adapted to defend against pathogens

Answer 1

The first line of defence against infectious disease are the surface barriers that prevent the entry of pathogens into the body

Skin

Protects external structures when intact as a continuous layer (outer body areas)
Consists of a dry, thick and tough region composed predominantly of dead surface cells
Contains biochemical defence agents (sebaceous glands secrete chemicals and enzymes which inhibit microbial growth on skin)
The skin also secretes lactic acid and fatty acids to lower the pH (skin pH is roughly ~ 5.6 – 6.4 depending on body region)
-Microbiome of non harmful bacteria which are competitive

Mucous Membranes

Protects internal structures (i.e. externally accessible cavities and tubes – such as the trachea, oesophagus and urethra)
Consists of a thin region of living surface cells that release fluids to wash away pathogens (mucus, saliva, tears, etc.)
Contains biochemical defence agents (secretions contain lysozyme which can destroy cell walls and cause cell lysis)
Mucous membranes may be ciliated to aid in the removal of pathogens (along with physical actions such as coughing / sneezing)

Question 2

Define clotting and explain its purpose

Answer 2

Clotting (haemostasis) is the mechanism by which broken blood vessels are repaired when damaged

Clotting functions to prevent blood loss from the body and limit pathogenic access to the bloodstream when the skin is broken

Question 3

Outline blood clotting

Answer 3

When a blood vessel is damaged inactive platelets are exposed to collagen fibres causing the platelets to become active and form a plug at the wound.
Clotting factors cause platelets to become sticky and adhere to the damaged region to form a solid plug
These factors also initiate localised vasoconstriction to reduce blood flow through the damaged region
Additionally, clotting factors trigger the conversion of the inactive prothrombin into the activated enzyme thrombin
Thrombin in turn catalyses the conversion of the soluble plasma protein fibrinogen into an insolube fibrous form called fibrin
The fibrin strands form a mesh of fibres around the platelet plug and traps blood cells to form a temporary clot
When the damaged region is completely repaired, an enzyme (plasmin) is activated to dissolve the clot

Question 4

Distinguish between type I and type II diabetes

Answer 4

Type I
-Early onset in childhood
-Inability to produce sufficient insulin
-Genetic predisposition / autoimune
-Requires daily injections of insulin or beta cell transplant

Type II
-late onset in adulthood
-Inability to respond to insulin
-Lfe style factors and dietary factors
-Requires weight loss, diet and possible medication but not insulin injections.

Question 5

Explain homeostasis using blood sugar control as an example (9 marks)

Answer 5

maintaining the environment between narrow limits/
example such as pH or oxygen and CO2 conc or body temp/
involves negative feedback/
deviation from limit triggers correction mechanism/
controlled by nervous and endocrine system/

blood sugar above normal stimulates insulin release/
insulin secreted by beta-cells in the pancreas/
insulin lowers blood sugar/
by converting to glycogen/
blood sugar below normal stimulates glucagon release/
glucagon released by alpha cells of pancreas/
glycogen converted to glucose/
raises blood sugar/

Question 6

Outline why antibiotics are effective against bacteria but not viruses

Answer 6

Antibiotics block metabolic pathways specific to bacteria/
Viruses do not have thier own metabolic pathways and use eukryotic hosts metabolism

Question 7

Discuss the cause, transmission and social implications of AIDS

Answer 7

AIDS is caused by HIV/
Penetrates T lymphocytes/
Reverse transcriptases enables DNA to be produced/
from Viral RNA/
number of lymphocytes reduce over years/
results in lower immunity/
other opportunistic infections develop

HIV transmitted through blood, sexual contact/ placenta/ breastfeeding/
certain minorities do not have receptors for HIV and are immune/
Use of condoms and latex barriers reduces risk of transmission /

expensive treatment/
discrimination against victims/
comment on religion and beliefs/

Question 8

Key properties of innate immunity

Answer 8

It does not differentiate between different types of pathogens (non-specific)
It responds to an infection the same way every time (non-adaptive)

Question 9

Outline phagocytosis

Answer 9

Phagocytic leukocytes circulate in the blood and move into the body tissue (extravasation) in response to infection
Damaged tissues release chemicals (e.g. histamine) which draw white blood cells to the site of infection (via chemotaxis)
Pathogens are engulfed when cellular extensions (pseudopodia) surround the pathogen and then fuse to form an internal vesicle
The vesicle is then fused to a lysosome (forming a phagolysosome) and the pathogen is digested
Pathogen fragments (antigens) may be presented on the surface of the phagocyte in order to stimulate the third line of defence

Question 10

Properties of third line of defence

Answer 10

It can differentiate between particular pathogens and target a response that is specific to a given pathogen

It can respond rapidly upon re-exposure to a specific pathogen, preventing symptoms from developing (immunological memory)

Question 11

What are B lymphocytes?

Answer 11

B lymphocytes (B cells) are antibody-producing cells that recognise and target a particular pathogen fragment (antigen)

Question 12

What are Helper T lymphocytes?

Answer 12

Helper T lymphocytes (TH cells) are regulator cells that release chemicals (cytokines) to activate specific B lymphocytes

Question 13

Outline the production of antibodies upon infection

Answer 13

When phagocytic leukocytes engulf a pathogen, some will present the digested fragments (antigens) on their surface

These antigen-presenting cells (dendritic cells) migrate to the lymph nodes and activate specific helper T lymphocytes
The helper T cells then release cytokines to activate the particular B cell capable of producing antibodies specific to the antigen
The activated B cell will divide and differentiate to form short-lived plasma cells that produce high amounts of specific antibody
Antibodies will target their specific antigen, enhancing the capacity of the immune system to recognise and destroy the pathogen
A small proportion of activated B cell (and activated TH cell) will develop into memory cells to provide long-lasting immunity

Question 14

Define antibody and antigen providing characteristics for each

Answer 14

Antigen: An antigen is a substance that the body recognises as foreign and that will elicit an immune response

Antibody: An antibody is a protein produced by B lymphocytes (and plasma cells) that is specific to a given antigen

Antibodies are made of 4 polypeptide chains that are joined together by disulphide bonds to form Y-shaped molecules
The ends of the arms are where the antigen binds – these areas are called the variable regions and differ between antibodies
The rest of the molecule is constant across all antibodies and serves as a recognition site for the immune system (opsonisation)
Each type of antibody recognises a unique antigen, making antigen-antibody interactions specific (like enzymes and substrates)

Question 15

Explain why and how antibiotics are used for treating bacterial infections in humans

Answer 15

Antibiotics are compounds that kill or inhibit the growth of microbes (specifically bacteria) by targeting prokaryotic metabolism. Metabolic features that may be targeted by antibiotics include key enzymes, 70S ribosomes and components of the cell wall

Because eukaryotic cells do not possess these features, antibiotics will target the pathogenic bacteria and not the infected host

Antibiotics may either kill the invading bacteria (bactericidal) or suppress its potential to reproduce (bacteriostatic)

Question 16

Outline Flory and Chains work

Answer 16

Working with another scientist (Ernst Chain) and a team of researchers, Florey tested penicillin on infected mice
Eight mice were injected with hemolytic streptococci and four of these mice were subsequently injected with doses of penicillin
The untreated mice died of bacterial infection while those treated with penicillin all survived – demonstrating its antibiotic potential

Question 17

Outline the effects of HIV

Answer 17

HIV specifically targets the helper T lymphocytes which regulate the adaptive immune system

Following infection, the virus undergoes a period of inactivity (clinical latency) during which infected helper T cells reproduce

Eventually, the virus becomes active again and begins to spread, destroying the T lymphocytes in the process (lysogenic cycle)

With a reduction in the number of helper T cells, antibodies are unable to be produced, resulting in a lowered immunity

The body becomes susceptible to opportunistic infections, eventually resulting in death if the condition is not managed

Question 18

Where is Thyroxin secreted from? What is its primary purpose and secondary purposes?

Answer 18

Thyroxin is a hormone secreted by the thyroid gland in response to signals initially derived from the hypothalamus

The primary role of thyroxin is to increase the basal metabolic rate (amount of energy the body uses at rest) by stimulating carbohydrate and lipid metabolism via the oxidation of glucose and fatty acids

A consequence of increasing metabolic activity is the production of heat hence thyroxin helps to control body temperature. Thyroxin is released in response to a decrease in body temperature in order to stimulate heat production

Question 19

Which element influences the production of thyroxin and what are the consequences if it s in insufficient quantity?

Answer 19

Thyroxin is partially composed of iodine and hence a deficiency of iodine in the diet will lead to decreased production of thyroxin

Iodine deficiency will cause the thyroid gland to become enlarged, resulting in a disease known as goitre

Question 20

What is Leptin? Where is it produced? Outline and explain its effects.

Answer 20

Leptin is a hormone produced by adipose cells that regulates fat stores within the body by suppressing appetite

Leptin binds to receptors located within the hypothalamus to inhibit appetite and thereby reduce food intake

Overeating causes more adipose cells to formed and hence more leptin is produced, suppressing further appetite

Conversely, periods of starvation lead to a reduction in adipose tissue and hence less leptin is released, triggering hunger

Question 21

What is melatonin and where is it produced?

Answer 21

Melatonin is a hormone produced by the pineal gland within the brain in response to changes in light.

Question 22

Outline and explain Circadian Rhythms

Answer 22

Melatonin secretion by the pineal gland of the brain plays a pivotal role in the control of circadian rhythms

Circadian rhythms are the body’s physiological responses to the 24 hour day-night cycle
Circadian rhythms are driven by an internal (endogenous) circadian clock, although they can be modulated by external factors

Melatonin is the hormone responsible for synchronising circadian rhythms and regulates the body’s sleep schedule

Melatonin secretion is suppressed by bright light (principally blue wavelengths) and hence levels increase during the night
Over a prolonged period, melatonin secretion becomes entrained to anticipate the onset of darkness and the approach of day
Melatonin functions to promote activity in nocturnal animals and conversely promotes sleep in diurnal animals (like humans)
Melatonin levels naturally decrease with age, leading to changes in sleeping patterns in the elderly

Question 23

What is the male reproductive hormone and what is it responsible for?

Answer 23

The main male reproductive hormone is testosterone, which is secreted by the testes and serves a number of roles:

It is responsible for the pre-natal development of male genitalia
It is involved in sperm production following the onset of puberty
It aids in the development of secondary sex characacteristcs

Question 24

What is the female reproductive hormone and what is it responsible for?

Answer 24

The main female reproductive hormones (secreted by the ovaries) are estrogen and progesterone, which serve several roles:

They promote the pre-natal development of the female reproductive organs
They are responsible for the development of secondary sex characteristics (including body hair and breast development)
They are involved in monthly preparation of egg release following puberty (via the menstrual cycle)

Initially, estrogen and progesterone are secreted by the mother’s ovaries and then the placenta – until female reproductive organs develop (this occurs in the absence of testosterone)

Question 24

List all components of the male reproductive organ

Answer 24

Vas deferens
Semen vesicle
Ureter
Erectile tissue
Scrotum
Testis
Epididymis
Urethra
Prostate gland
Penis
Bladder

Question 25

State the function of:

Testis
Epididymis
Vas Deferens
Seminal Vesicle
Prostate Gland
Urethra

Answer 25

Testis

The testis (plural: testes) is responsible for the production of sperm and testosterone (male sex hormone)

Epididymis

Site where sperm matures and develops the ability to be motile (i.e. ‘swim’) – mature sperm is stored here until ejaculation

Vas Deferens

Long tube which conducts sperm from the testes to the prostate gland (which connects to the urethra) during ejaculation

Seminal Vesicle

Secretes fluid containing fructose (to nourish sperm), mucus (to protect sperm) and prostaglandin (triggers uterine contractions)

Prostate Gland

Secretes an alkaline fluid to neutralise vaginal acids (necessary to maintain sperm viability)

Urethra

Conducts sperm / semen from the prostate gland to the outside of the body via the penis (also used to convey urine)

Question 26

List the components of the female reproductive system and the purpose of each component

Answer 26

Ovary

The ovary is where oocytes mature prior to release (ovulation) – it also responsible for estrogen and progesterone secretion

Fimbria

Fimbria (plural: fimbriae) are a fringe of tissue adjacent to an ovary that sweep an oocyte into the oviduct

Oviduct

The oviduct (or fallopian tube) transports the oocyte to the uterus – it is also typically where fertilisation occurs

Uterus

The uterus is the organ where a fertilised egg will implant and develop (becoming an embryo)

Endometrium

The mucous membrane lining of the uterus, it thickens in preparation for implantation or is otherwise lost (via menstruation)

Vagina

Passage leading to the uterus by which the penis can enter (uterus protected by a muscular opening called the cervix)

Question 27

Outline menstruation cycle (9 marks)

Answer 27

1. Follicular Phase

Follicle stimulating hormone (FSH) is secreted from the anterior pituitary and stimulates growth of ovarian follicles
The dominant follicle produces estrogen, which inhibits FSH secretion (negative feedback) to prevent other follicles growing
Estrogen acts on the uterus to stimulate the thickening of the endometrial layer

2. Ovulation

Midway through the cycle (~ day 12), estrogen stimulates the anterior pituitary to secrete hormones (positive feedback)
This positive feedback results in a large surge of luteinizing hormone (LH) and a lesser surge of FSH
LH causes the dominant follicle to rupture and release an egg (secondary oocyte) – this is called ovulation

3. Luteal Phase

The ruptured follicle develops into a slowly degenerating corpus luteum
The corpus luteum secretes high levels of progesterone, as well as lower levels of oestrogen
Estrogen and progesterone act on the uterus to thicken the endometrial lining (in preparation for pregnancy)
Estrogen and progesterone also inhibit secretion of FSH and LH, preventing any follicles from developing

4. Menstruation

If fertilisation occurs, the developing embryo will implant in the endometrium and release hormones to sustain the corpus luteum
If fertilisation doesn’t occur, the corpus luteum eventually degenerates (forming a corpus albicans after ~ 2 weeks)
When the corpus luteum degenerates, estrogen and progesteron levels drop and the endometrium can no longer be maintained
The endometrial layer is sloughed away and eliminated from the body as menstrual blood (i.e. a woman’s period)
As estrogen and progesterone levels are too now low to inhibit the anterior pituitary, the cycle can now begin again

Question 28

Outline IVF (9 marks)

Answer 28

Down regulation

Drugs are used to halt the regular secretion of FSH and LH – this in turn stops the secretion of estrogen and progesterone
By arresting the hormonal cycle, doctors can take control of the timing and quantity of egg production by the ovaries
The drug treatment usually takes about two weeks and is typically delivered in the form of a nasal spray

Superovulation

Superovulation involves using artificial doses of hormones to develop and collect multiple eggs from the woman
The patient is firstly injected with large amounts of FSH to stimulate the development of many follicles
The follicles are then treated with human chorionic gonadotrophin (hCG) – a hormone usually produced by a developing embryo
hCG stimulates the follicles to mature and the egg is then collected (via aspiration with a needle) prior to the follicles rupturing

Fertilisation

The extracted eggs are then incubated in the presence of a sperm sample from the male donor
The eggs are then analysed under a microscope for successful fertilisation

Implantation

Approximately two weeks prior to implantation, the woman begins to take progesterone treatments to develop the endometrium
Healthy embryos are selected and transferred into the female uterus (or the uterus of a surrogate)
Multiple embryos are transferred to improve chances of successful implantation (hence multiple births are a possible outcome)
Roughly two weeks after the procedure, a pregnancy test is taken to determine if the process has been successful

Question 29

Summary of key stages of IVF

Answer 29

Stop normal menstrual cycle (with drugs)
Hormone treatments to promote super ovulation
Extract multiple eggs from the ovaries
Sperm collected, then prepared (via capacitation) and injected into egg
Fertilisation occurs externally under controlled conditions (in vitro)
Implantation of multiple embryos into uterus (either patient or surrogate)
Test for pregnancy after ~ two weeks

Mnemonic: SHE’S FIT

Question 30

Examples of positive feedback

Answer 30

Childbirth – stretching of uterine walls cause contractions that further stretch the walls (this continues until birthing occurs)
Lactation – the child feeding stimulates milk production which causes further feeding (continues until baby stops feeding)
Ovulation – the dominant follicle releases oestrogen which stimulates LH and FSH release to promote further follicular growth
Blood clotting – platelets release clotting factors which cause more platelets to aggregate at the site of injury

Question 31

Outline and explain Haemophilia

Answer 31

Haemophilia is an X-linked recessive condition that impairs the body’s ability to control blood clotting

It is more common in males than females (as males are hemizygous and have only one X chromosome)

People with haemophilia (haemophiliacs) have lower levels of functional clotting factors in their blood plasma

This means the normal coagulation cascade is impaired and fibrin formation does not occur
Thus while a temporary scab may form (due to the formation of a platelet plug), a lasting blood clot cannot form

Haemophiliacs can die from minor injuries, as the continued loss of blood flow cannot be prevented via clot formation

There are different types of haemophilia with varying severities, depending on which specific clotting factor is defective
Haemophilia A (clotting factor XIII deficiency) is more common than haemophilia B (clotting factor IX deficiency)

Question 32

Outline inflamation

Answer 32

The inflammatory response is the non-specific way in which the body responds when a pathogen damages body tissue

When tissue damage occurs, mast cells (localised) and basophils (circulating) release a chemical called histamine
Histamine causes local vasodilation and increases capillary permeability to improve the recruitment of leukocytes to the region
Damaged cells also release chemotactic factors which attract leukocytes to the site of infection
While inflammation is necessary to allow immune cells access to damaged tissue, there are unavoidable side effects
Increased blood flow causes redness and heat, while increased permeability releases fluids and causes swelling and tenderness
Inflammation can be either short-term (acute) or long-term (chronic)

Question 33

What hormones are released from what cells of the pancrease?

Answer 33

These hormones are released from pancreatic pits (called the islets of Langerhans) and act principally on the liver

Insulin is released from beta (β) cells of the pancreas and cause a decrease in blood glucose concentration

Glucagon is released from alpha (α) cells of the pancreas and cause an increase in blood glucose concentration

Question 34

Disccuss cause and treatment of jet lag

Answer 34

Jet lag is a physiological condition resulting from a change to the body’s normal circadian rhythm

This alteration is caused by the body’s inability to rapidly adjust to a new time zone following extended air travel (‘jet’ lag)
The pineal gland continues to secrete melatonin according to the old time zone so that the sleep schedule is not synchronised to the new timezone

Some health professionals recommend taking melatonin near the sleep time of the new time zone to help recalibrate the body. By artificially increasing melatonin levels at the new night time, the body can respond quicker to the new day-night schedule

Question 35

Outline homeostasis

Answer 35

Homeostatic mechanisms operate via a feedback loop that may involve either the nervous or endocrine systems (or both)

When specialised receptors detect an internal change to conditions, a response is generated to correct the change
Most homeostatic responses involve an effect that is antagonistic to the detected stimulus (negative feedback)
When levels return to equilibrium, the effector ceases to generate a response and an internal balance is therefore maintained
If a physiological condition moves outside of tolerance limits, disease will occur as a consequence

Question 36

Define and explain hormones

Answer 36

A hormone is a chemical messenger that is transported via the bloodstream to act on distant target cells
Hormones are specific and will only activate cells or tissues that possess the appropriate target receptor

Question 37

Distinguish between Steroid and Peptide Hormones

Answer 37

Steroid hormones are lipophilic (fat-loving) – meaning they can freely diffuse across the plasma membrane of a cell
They bind to receptors in either the cytoplasm or nucleus of the target cell, to form an active receptor-hormone complex
This activated complex will move into the nucleus and bind directly to DNA, acting as a transcription factor for gene expression
Examples of steroid hormones include those produced by the gonads (i.e. estrogen, progesterone and testosterone)

Peptide hormones are hydrophylic and lipophobic (fat-hating) – meaning they cannot freely cross the plasma membrane
They bind to receptors on the surface of the cell, which are typically coupled to internally anchored proteins (e.g. G proteins)
The receptor complex activates a series of intracellular molecules called second messengers, which initiate cell activity
This process is called signal transduction, because the external signal (hormone) is transduced via internal intermediaries

Question 38

Define allergen

Answer 38

An allergen is an environmental substance that triggers an immune response despite not being intrinsically harmful

Question 39

What are plasma cells?

Answer 39

When a specific B lymphocyte is activated following antigen presentation, it divides into plasma cells and memory cells

Plasma cells are short-lived and secrete high numbers of antibodies that are specific to a particular antigen

Question 40

How do antibodies aid in the destruction of pathogens?

Answer 40

• Precipitation – Soluble pathogens become insoluble and precipitate
• Agglutination – Cellular pathogens become clumped for easier removal
• Neutralisation – Antibodies may occlude pathogenic regions (e.g. exotoxins)
• Inflammation – Antibodies may trigger an inflammatory response within the body
• Complement activation – Complement proteins perforate membranes (cell lysis)

Mnemonic: PANIC

Question 41

Describe eradication of small pox

Answer 41

Smallpox was targeted for eradication in 1967 by the World Health Organisation (WHO), via a global vaccination programme

The last known case of smallpox in a civilian was registered in 1977 and it was officially declared eradicated by WHO in 1980

The eradication of smallpox by vaccination was successful for a number of reasons:

Smallpox was easily identifiable due to overt clinical symptoms, which helped to limit potential transmission
Transmission only occurred via direct contact and there were no animal vectors or reservoirs to sustain the infectious agent
The infection period was short lived (3 – 4 weeks) and the virus was stable and didn’t mutate into alternate strains
There was global cooperation and immunity was long-term so repeated booster shots were unnecessary

Question 42

Outline the formation of Monoclonal antibodies

Answer 42

Monoclonal antibodies are antibodies artificially derived from a single B cell clone (i.e. identical specific antibodies)

An animal (typically a mouse) is injected with an antigen and produces antigen-specific plasma cells
The plasma cells are removed and fused (hybridised) with tumor cells capable of endless divisions (immortal cell line)
The resulting hybridoma cell is capable of synthesising large quantities of monoclonal antibody

Question 43

Outline the use of Monoclonal antibodies in preganancy detection

Answer 43

Free monoclonal antibodies specific to hCG are conjugated to an enzyme that changes the colour of a dye
A second set of monoclonal antibodies specific to hCG are immobilised to the dye substrate
If hCG is present in urine, it will interact with both sets of monoclonal antibody (forming an antibody ‘sandwich’)
When both sets of antibody are bound to hCG, the enzyme is brought into physicial proximity with the dye, changing its colour
A third set of monoclonal antibodies will bind any unattached enzyme-linked antibodies, functioning as a control