Unit 4 – Human Body

Topic 6 – Human Physiology

Topics

• 6.1 – Digestive system• 6.2 – Circulatory system• 6.3 – Immune system• 6.4 – Respiratory system• 6.5 – Nervous system• 6.6 – Endocrine and Reproductive systems

6.1 – DIGESTIVE SYSTEM

• Most food is solid and in the form of large complex molecules which are insoluble and chemically inert (not readily usable)

• As food was synthesized by other organisms, it contains materials not suitable for human tissue - these need to be separated and removed

• Large molecules need to be broken down into smaller molecules that can be readily absorbed across membranes and into cells

• Small molecules can be reassembled into new products (e.g. amino acids can be reassembled to make new proteins)

Why is digestion important?

• Enzymes are biological catalysts which speed up the rate of a chemical reaction (e.g. digestion) by lowering the activation energy

• Enzymes allow digestive processes to occur at body temperature and at sufficient speed to meet the organism's survival requirements

• Enzymes are specific for a given substrate and so can allow digestion of certain molecules to occur independently of others

Role of enzymes

Digestive system

• There are two major groups of organs that comprise the human digestive system:

• Alimentary Canal: Contains organs through which the food actually passes (esophagus, stomach, small intestine, large intestine, etc.)

• Accessory Organs: Organs that assist in digestion but no food passes through them (liver, pancreas, gall bladder, salivary glands, etc.)

Alimentary canal Accessory organs

• The stomach acts as a temporary storage tank and is where protein digestion begins

• The stomach contains gastric glands which secrete digestive juices for chemical digestion

• Acids create a low pH environment (pH~1-2) that denatures proteins, while proteases like pepsin hydrolyse large proteins

• The stomach also releases a hormone (gastrin) that regulates stomach secretions

• The mechanical action of the stomach (churning) also promotes digestion by mixing the food

• The stomach turns food into a creamy paste called chyme

Stomach

• The small intestine is where usable food substances (e.g. nutrients) are absorbed into the bloodstream

• The pancreas and gall bladder (via the bile duct) both secrete substances into the small intestine to aid in digestion

• The small intestine is lined with smooth muscle to allow for the mixing and moving of digested food products (via segmentation and peristalsis)

• It also contains small pits (crypts of lieberkuhn) that secrete intestinal juices

• The small intestine contain infoldings called villi, to increase surface area and optimize the rate of absorption

Small Intestine

• The large intestine absorbs water and dissolved minerals from the indigestible food residues, and by doing so converts what remains from a fluid state into a semi-solid feces

• The feces is stored in the rectum and eliminated out the anus

Large Intestine

• Absorption: The movement of a fluid or dissolved substances across a membrane

• Assimilation: The conversion of nutrients into fluid or solid parts of an organism

• Hint: Absorption is taking it into something, assimilation is making it a part of something

Uptake of nutrients

Microvilli• Microvilli: Greatly increase the surface area of the villus,

allowing for a greater rate of absorption• Rich capillary networks: Help to maintain a concentration

gradient for absorption by rapidly transporting absorbed products away

• Single epithelial layer: Ensures minimal diffusion distance between the intestinal lumen and capillary network

• Lacteals: Absorb lipids from the intestine into the lymphatic system (which are later reabsorbed back into normal circulation)

• Intestinal crypts: Located between villi and release juices that act as a carrier fluid for nutrients

• Membrane proteins / mitochondria: High amounts to enable active transport into cells (contents then passively diffuse into bloodstream)

Application and Skills

• Application 1: Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver

• Application 2: Use of dialysis tubing to model absorption of digested food in the intestine

Videos

• Food passing through body - https://www.youtube.com/watch?v=b20VRR9C37Q

• Crash course - https://www.youtube.com/watch?v=s06XzaKqELk

6.2 – CIRCULATORY SYSTEM

Heart diagrams

Heart diagrams

Heart basics

• The heart is a muscle that must continually contract in order to pump blood around the body

• Arteries (Away from the heart)– Convey blood at high pressure (80 - 120 mm Hg) from the ventricles to the tissues

of the body– They have a narrower lumen (to maintain high pressure) surround by a thick wall

made of two layers– The middle layer (tunica media) contains muscle and elastin to help maintain pulse

flow (it can contract and stretch)– The outer layer (tunica adventitia) contains collagen prevents the artery rupturing

due to the high pressure blood flow– Coronary arteries form a network of vessels around the heart and supply the

cardiac tissue with oxygen and nutrients (i.e. glucose)– These are required to produce the necessary energy via aerobic respiration - if a

coronary artery is blocked, a heart attack may occur

• Veins (Towards the heart)– Collect blood at low pressure (<10

mm Hg) from the tissues of the body and return it to the atria of the heart

– Valves in the veins and the heart ensure circulation of blood by preventing backflow

– They have a very wide lumen (keeps pressure low and allows greater flow of blood)

– The walls of tissue surrounding the vein are thin (blood is not travelling in rhythmic pulses)

• Capillaries– Capillaries are involved with material and gas exchange with the

surrounding body tissue– Blood pressure in the capillaries is relatively low (~15 mm Hg)

and they have a very small diameter (~5 micrometers wide)– These vessels have permeable walls that allow exchange of

materials between cells in the tissue and the blood in the capillary. Their wall is made up a a single layer of cells to allow for ease of diffusion

– Capillaries may contain pores to aid the transport of material

Cross section of blood vessels

Blood flow• Blood returning from all parts of the body (except lungs) enter the right

atrium via the vena cava - this blood is relatively deoxygenated• The blood passes from the right atrium to the right ventricle and then via

the pulmonary artery to the lungs (where blood is reoxygenated)• The blood returns to the left atrium via the pulmonary vein and passes

through the left ventricle to the aorta, where it is pumped around the body

• The heart valves maintain the one-way flow of blood:• When the atria contract, atrioventricular (AV) valves open• Blood flows from the atria and into the ventricles• When the ventricles contract, the AV valves close and semilunar valves

open• This forces blood out of the ventricles and into the arteries• As arterial pressure rises, the semilunar valves close, ensuring the one-way

flow of blood

Heart contraction

• The contraction of the heart tissue (myocardium) is myogenic, meaning the signal for cardial contraction arises within the heart muscle itself

• Within the wall of the right atrium are a specialised plexus of nerves called the sinoatrial node (SAN)

• The sinoatrial node initiates contraction of the cardiace muscle and acts as a pacemaker, regulating normal sinus rhythm

• It stimulates atria to contract and, when excitation reaches the junction between atria and ventricles, stimulates another node (atrioventicular node)

• The atrioventricular node (AVN) sends signals via the Bundle of His to Purkinje fibres, which cause ventricular contraction

• This sequence always ensures their is a delay between atrial and ventricular contractions, resulting in two heart sounds ('lub dub')

• The pacemaker is under autonomic control from the brain, specifically the medulla oblongata (brain stem)

• Sympathetic nerves speed up heart rate by releasing a neurotransmitter (noradrenaline) to increase the rate of myocardial contraction

• Parasympathetic nerves splow down heart rate by releasing a neurotransmitter (acetylcholine) to decrease the rate of myocardial contraction

• Additionally, the heart rate may be increased by the chemical release of the hormone adrenaline into the blood (from the adrenal gland)

Components of blood• There are four main components to blood:1) Plasma - the fluid medium of the blood2) Erythrocytes - red blood cells (involved in oxygen transport)3) Leukocytes - white blood cells, such as phagocytes (non-

specific immunity) and lymphocytes (specific immunity)4) Platelets - responsible for blood clotting (hemostasis)

Blood transports…

The following things:• Nutrients (e.g. glucose)• Antibodies• Carbon dioxide• Hormones• Oxygen• Urea• Heat (not a molecules, unlike all the others)

Application and Skills

• Application 1: Causes and consequences of blood clot formation in coronary arteries

6.3 – IMMUNE SYSTEM

Pathogen • Pathogen = A disease-causing micro-organism,

virus or prion

Antibiotics

• Antibiotics are substances or compounds that kill or inhibit the growth of bacteria by targeting the metabolic pathways of prokaryotes

• Specific prokaryotic features that may be targeted by antibiotics include key enzymes, 70S ribosomes and the bacterial cell wall

• Because eukaryotic cells do not have these features, antibiotic can kill bacterial cells without harming humans (or viruses)

• Virus do not carry out metabolic reactions themselves but instead infect host cells and take over their cellular machinery

• Viruses need to be treated with specific antiviral agents that target features specific to viruses (e.g. reverse transcriptase in retroviruses)

FIRST LINE OF DEFENSE – Surface barriers • The first line of defense against infection are the surface barriers that prevent the entry of

pathogenic substances• These surface barriers include the skin and mucous membranes

Skin• Protects external structures (outer body areas)• A dry, thick and tough region made of predominantly dead surface cells• Contains biochemical defense agents (sebaceous glands secrete chemicals which inhibit the

growth of some bacteria)• The skin also releases acidic secretions to lower pH and prevent bacteria from growing

Mucous membranes• Protect internal structures (externally accessable cavities and tubes, such as trachea, vagina

and urethra)• A thin region containing living surface cells that release fluids to wash away pathogens

(mucus, tears, saliva, etc.)• Contains biochemical defense 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 or sneezing)

SECOND LINE OF DEFENSE – Non-specific immunity

• The second line of defense against pathogenic invasion are the non-specific defense mechanisms

• Non-specific mechanisms do not differentiate between types of microorganisms and always invoke the same response

• Examples of non-specific defense mechanisms include phagocytic leucocytes, inflammation, fever and anti-microbial proteins

• Phagocytic leucocytes (macrophages) circulate in the blood but may move into body tissue (extravasation) in response to infection

• They concentrate at sites of infection due to the release of chemicals (such as histamine) from damaged body cells

• Pathogens are engulfed when cellular extensions (pseudopodia) surround the pathogen and then fuse, sequestering it in an internal vesicle

• The vesicle may then fuse with the lysosome to digest the pathogen• Some of the pathogens antigenic fragments may be presented on the surface of

the macrophage, in order to help stimulate antibody production• This mechanism of endocytosis is called phagocytosis ('cell-eating')

Phagocytosis by a leukocyte

THIRD LINE OF DEFENSE – Specific immunity

• The third line of defense are the specific defenss, coordinated by a type of leucocyte called lymphocytes

• These can recognize and respond specifically to different types of micro-organism and have memory (can respond more effectively upon reinfection)

• Antigen: A substance that the body recognizes as foreign and that can evoke an immune response

• Antibody: A protein produced by certain white blood cells (B lymphocytes, plasma cells) in response to an antigen

• Antibodies are made up of 4 polypeptide chains (2 light and 2 heavy chains) joined together by disulphide bonds to form a Y-shaped molecule

• The ends of the arms are where the antigens bind and these areas are called the variable regions, as these will differ between antibodies

• Each type of antibody will recognize a unique antigenic fragment, making this interaction specific (like enzyme-substrate interactions)

Antibody structure

Antibody production• B lymphocytes (B cells) are antibody-producing cells that

develop in the bone marrow to produce a highly specific antibody that recognises one type of antigen

• When wandering macrophages encounter a pathogen, they digest it and present the antigenic fragments on their surface to helper T lymphocytes (TH cells)

• These cells activate the appropriate B cell which divides and differentiates into short-lived plasma cells that produce massive quantities of antibody (~2,000 molecules per second for ~4 - 5 days)

• A small proportion of B cell clones develop into memory cells, which may survive for years providing long-term immunity

HIV

• The human immunodeficiency virus (HIV) is a retrovirus that infects helper T lymphcytes (TH cells)

• Reverse transciptase allows viral DNA to be produced from its RNA code, which is integrated into the host cells genome

• After a number of years of inactivity (during which infected TH cells have continually reproduced), the virus becomes active and begins to spread, destroying the TH cells in the process (known as the lysogenic cycle)

• This results in lower immunity as antibody production is compromised - the individual is now susceptible to opportunistic infections

AIDSCause• Acquired Immunodeficieny Syndrome (AIDS) is a collection of

symptoms and infections caused by the destruction of the immune system by HIV

• While HIV infection results in a lowering in immunity over a number of years, AIDS describes the final stages when observable symptoms develop

Transmission• HIV is transmitted through the exchange of bodily fluids (including

unprotected sex, blood transfusions, breast feeding, child birth, etc.)• The risk of exposure to HIV through sexual contact can be reduced by

using latex protection (condoms)• A minority of people are immune to HIV infection (they do not have

the CD4+ T cell receptor that HIV needs to infect the cell)

AIDS

• Social Implications• People with HIV may be stigmatized and discriminated

against, potentially leading to unemployment and poverty• Majority of people who die from AIDS are at a productive

age, which may cripple a country's workforce and economic growth

• It can result in an increased number of orphans, taxing a country's welfare resources

• Poverty may increase transmission of AIDS (due to poor education and high cost of treatments), creating a moral obligation for assistance from wealthier countries

Application and Skills

• Application 1: Florey and Chain’s experiments to test penicillin on bacterial infections in mice

• Application 2: Effects of HIV on the immune system and methods of transmission

6.4 – RESPIRATORY SYSTEM

Respiration• Respiration is the transport of oxygen to cells where

energy production takes place, and involves three key processes:

• Ventilation: The exchange of air between the lungs and the atmosphere; it is achieved by the physical act of breathing

• Gas exchange: The exchange of oxygen and carbon dioxide in the alveoli and the bloodstream; it occurs passively via diffusion

• Cell Respiration: The release of ATP from organic molecules; it is greatly enhanced by the presence of oxygen (aerobic respiration)

Ventilation system• Because gas exchange is a passive process, a ventilation

system is needed to maintain a concentration gradient within the alveoli

• Oxygen is needed by cells to make ATP via aerobic respiration, while carbon dioxide is a waste product of this process and must be removed

• Therefore, oxygen must diffuse from the lungs into the blood, while carbon dioxide must diffuse from the blood into the lungs

• This requires a high concentration of oxygen - and a low concentration of carbon dioxide - in the lungs

• A ventilation system maintains this concentration gradient by continually cycling the air in the lungs with the atmosphere

Features of alveoli• Thin wall: Made of a single layer of flattened cells

so that diffusion distance is small• Rich capillary network: Alveoli are covered by a

dense network of capillaries that help to maintain a concentration gradient

• Increased SA:Vol ratio: High numbers of spherically-shaped alveoli optimise surface area for gas exchange (600 million alveoli = 80 m2)

• Moist: Some cells in the lining secrete fluid to allow gases to dissolve and to prevent alveoli from collapsing (through cohesion)

Process of breathing

• Breathing is the active movement of respiratory muscles that enable the passage of air to and from the lungs

• The mechanism of breathing is described as negative pressure breathing as it is driven by the creation of a negative pressure vacuum within the lungs, according to Boyle's Law (pressure is inversely proportional to volume)

Process of breathing

Inspiration• Diaphragm muscles contract and

flatten downwards• External intercostal muscles contract,

pulling ribs upwards and outwards• This increases the volume of the

thoracic cavity (and therefore lung volume)

• The pressure of air in the lungs is decreased below atmospheric pressure

• Air flows into the lungs to equalize the pressure

Process of breathing

Expiration• Diaphragm muscles relax and diaphragm curves

upwards• Abdominal muscles contract, pushing diaphragm

upwards• External intercostal muscles relax, allowing the ribs

to fall• Internal intercostal muscles contract, pulling ribs

downwards• This decreases the volume of the thoracic cavity (and

therefore lung volume)• The pressure of air in the lungs is increased above

atmospheric pressure• Air flows out of the lungs to equalize the pressure

Application and Skills

• Application 1: Causes and consequences of lung cancer

• Application 2: Causes and consequences of emphysema

• Application 3: External and internal intercostal muscles, and diaphragm and abdominal muscles as examples of antagonistic muscle action

• Skill 1: Monitoring of ventilation in humans at rest and after mild and vigorous exercise.

6.5 – NERVOUS SYSTEM

Nervous system• Neurons are cells that are specialized for the

conduction of nerve impulses and serve as the fundamental unit of the nervous system

• The nervous system can be divided into two main parts:

1) Central Nervous System (CNS): Made up of the brain and the spinal cord

2) Peripheral Nervous System (PNS): Made of peripheral nerves which link the CNS with the body's receptors and effectors

Types of neurons

• There are three main types of neurons in the nervous system:

• Sensory Neurons: Conduct nerve impulses from receptors to the CNS (afferent pathway)

• Relay Neurons: Conduct nerve impulses within the CNS (also called interneurons or connector neurons)

• Motor Neurons: Conduct nerve impulses from the CNS to effectors (efferent pathway)

Diagram of motor neuron

Stimulus-response pathway

Nerve impulse – basic vocab• Resting Potential: The charge difference across the

membrane when a neuron is not firing (-70 mV), as maintained by the sodium-potassium pump

• Action Potential: The charge difference across the membrane when a neuron is firing (about 30 mV)

• Depolarisation: The change from a negative resting potential to a positive action potential (caused by opening of sodium channels)

• Repolarisation: The change from a positive action potential back to a negative resting potential (caused by opening of potassium channels)

Nerve impulse - steps

1) Generation of a Resting Potential• The sodium-potassium pump (Na+/K+ pump) maintains the

electrochemical gradient of the resting potential (-70 mV)• It is a transmembrane protein that uses active transport to

exchange Na+ and K+ ions across the membrane (antiport mechanism)

• It expels 3 Na+ ions for every 2 K+ ions admitted (in addition, some of the K+ ions will leak back out of the cell)

• This makes the inside of the membrane relatively negative when compared to the outside (-70 mV = resting potential)

Nerve impulse - steps2) Transmission of an Action Potential• Sodium and potassium channels in nerve cells are voltage-gated, meaning they can

open and close depending on the voltage across the membrane• In response to a signal at a sensory receptor or dendrite, sodium channels open

and sodium enters the neuron passively• The influx of sodium (Na+ in) causes the membrane potential to become positive

(depolarisation)• If a sufficient change in membrane potential is achieved (threshold potential),

adjacent voltage-gated sodium channels open, generating a wave of depolarisation (action potential) that spreads down the axon

• The change in membrane potential also activates voltage-gated potassium channels, causing potassium to exit the neuron passively

• The efflux of potassium (K+ out) causes the membrane potential to become negative again (repolarisation)

• Before the neuron can fire again, the original distribution of ions (Na+ out, K+ in) must be re-established by the Na+/K+ pump

• The inability to propagate another action potential during this time (refractory period) ensures nerve impulses only travel in one direction

Generation of action potential

Synapse

• The junction between two neurons is called a synapse, it forms a physical gap between the pre-synaptic and post-synaptic neurons

• An action potential (electrical signal) cannot cross the synaptic gap, so it triggers the release of chemicals (neurotransmitters) to continue the signal

SynapseChemical Transfer Across Synapses• When an action potential reaches the axon terminal, it triggers the opening of

voltage-gated calcium channels• Calcium ions (Ca2+) diffuse into the cell and promote the fusion of vesicles

(containing neurotransmitters) with the plasma membrane• The neurotransmitters are released from the axon terminal by exocytosis and cross

the synaptic cleft• Neurotransmitters bind to appropriate neuroreceptors on the post-synaptic

membrane, opening ligand-gated channels– Excitatory neurotransmitters (e.g. noradrenaline) open ligand-gated sodium channels

(depolarisation)– Inhibitory neurotransmitters (e.g. GABA) open ligand-gated potassium or chlorine channels

(hyperpolarisation)• The combination of chemical messengers received by dendrites determines whether

the threshold is reached for an action potential in the post-synaptic neuron• Neurotransmitter molecules released into the synapse are either recycled (by

reuptake pumps) or degraded (by enzymatic activity)

Synaptic transfer

Application and Skills

• Application 1: Secretion and reabsorption of acetylcholine by neurons at synapses

• Application 2: Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors

• Skill 1: Analysis of oscilloscope traces showing resting potentials and action potentials.

6.6 – ENDOCRINE AND REPRODUCTIVE SYSTEMS

Endocrine system

• An endocrine gland is a ductless gland in the body that manufactures chemical messengers called hormones and secretes them directly into the blood

• Hormones act on distant sites (target cells) and tend to control slow, long-term activities such as growth and sexual development

Homeostasis

• Homeostasis is the tendency of an organism or cell to maintain a constant internal environment within tolerance limits

• Internal equilibrium is maintained by adjusting physiological processes, including:

• Body temperature (normally 36 - 38°C)• Blood pH (normally 7.35 - 7.45)• Carbon dioxide concentration (normally 35 - 45 mmHg)• Blood glucose concentration (normally 75 - 95 mg / dL)• Water balance (varies with individual body size)

Negative feedback loop• Most homeostatic control mechanisms operate

through a negative feedback loop• When specialized receptors detect a change in an

internal condition, the response generated will be the opposite of the change that occurred

• When levels have returned to equilibrium, the effector ceases to generate a response

• If levels go too far in the opposite direction, antagonistic pathways will be activated to restore the internal balance

Negative feedback loop

Thermoregulation• Animals capable of temperature regulation within a given range are called homeotherms and maintain a constant

body temperature through a negative feedback loop• The hypothalalmus acts as a control centre in thermoregulation by detecting fluctuations in body temperature• The skin also possesses thermoreceptors and relays this information to the hypothalamus, which coordinates

corrective measures

• When body temperature RISES, the following cooling mechanisms may occur:• Vasodilation: The skin arterioles dilate, bringing blood into closer proximity to the body surface and allowing for

heat transfer (convective cooling)• Sweating: Sweat glands release sweat, which which is evaporated at the cost of latent heat in the air, thus

cooling the body (evaporative cooling)

• When body temperature FALLS, the following heating mechanisms may occur:• Vasoconstriction: The skin arterioles constrict, moving blood away from the surface of the body, thus retaining

the heat carried within the blood • Shivering: Muscles begin to shake in small movements, expending energy through cell respiration (which

produces heat as a by-product)

• Other mechanisms through which homeotherms may regulate their body temperature include:• Piloerection: Animals with furry coats can make their hair stand on end (piloerection), trapping pockets of warm

air close to the body surface• Behavioural responses: Animals may physically respond to environmental conditions in a bid to regulate

temperature (e.g. bathing, burrowing, etc.)

Thermoregulation

Blood glucose regulation• The body requires volumes of glucose in order to make ATP, however the amount of ATP demand will

fluctuate according to need and thus the body regulates its release of glucose into the bloodstream as high levels of glucose in the bloodstream can damage cells (creates hypertonicity)

• Two hormones, insulin and glucagon, are responsible for controlling blood glucose concentration (they have antagonistic functions)

• These hormones are released from different groups of cells with pancreatic pits (called the islets of Langerhans) and act principally on the liver

• When blood glucose levels are high (e.g. after feeding):• Insulin is released from beta cells in the pancreas and causes a decrease in blood glucose

concentration• This may involve stimulating glycogen synthesis in the liver (glycogenesis), promoting glucose uptake

into the liver and adipose tissue or increasing the rate of glucose breakdown (increase cell respiration)

• When blood glucose levels are low (e.g. after strenuous exercise):• Glucagon is released from alpha cells in the pancreas and cause an increase in blood glucose

concentration• This may involve stimulating glycogen breakdown in the liver (glycogenolysis), promoting glucose

release from the liver and adipose tissue or decreasing the rate of glucose breakdown (decrease cell respiration)

Blood glucose regulation

Diabetes

Male reproductive system

Side view Front view

Female reproductive system

Side view Front view

Hormones in the menstrual cycle

Menstrual cycle

Ovarian cycle

1) Follicular Phase:• FSH stimulates growth of several follicles• Dominant follicle secretes estrogen• Estrogen inhibits growth of other follicles (and FSH)• Estrogen stimulates development of endometrium

2) Ovulation:• A surge in LH causes ovulation (egg release)• Rupturing of follicle creates a corpus luteum

Ovarian cycle3) Luteal Phase:• Corpus luteum secretes progesterone (and estrogen)• Progesterone stimulates development of endometrium• Estrogen and progesterone inhibit FSH and LH• Corpus luteum degrades over time • When corpus luteum degrades, progesterone levels drop• Without progesterone, endometrium cannot be maintained• No longer inhibited, FSH can start menstrual cycle again• If fertilisation of egg occurs, the zygote releases a hormone (hCG)

which maintains the corpus luteum

4) Menses = period!! Shedding of the endometrium lining

Testosterone in men

• Pre-natal development of male genitalia• Development of secondary sex characteristics• Maintenance of sex drive (libido)

In vitro fertilization• In vitro fertilization refers to fertilization that occurs outside the body

('in vitro' = 'in glass')• Stop normal menstrual cycle (with drugs)• Hormone treatments to develop follicles (FSH to stimulate follicle

growth ; hCG for follicle maturation)• Extract multiple eggs from ovaries• Sperm selected, prepared (capacitation) and then injected into egg

via intra-cytoplasmic sperm injection (ICSI)• Fertilization occurs under controlled conditions (in vitro)• Implantation of multiple embryos into uterus• Test for pregnancy is conducted to see if implantation was successful

In vitro fertilization

Analysis of IVF• Advantages of IVF• Chance for infertile couples to have children• Genetic screening of embryos could decrease suffering from genetic diseases• Spare embryos can be stored for future pregnancies or used for stem cell

research

• Disadvantages of IVF• IVF is expensive and might not be equally accessible to all• Success rate is low (~15%) and therefore stressful for couples• It could lead to eugenics (e.g. gender choice)• Often leads to multiple pregnancies which may be unwanted, unable to be

budgeted for and involves extra birth risks• Issues concerning storage and disposal of unused embryos (right to life

concerns)• There are cultural and religious objections to embryo creation by such means• Inherited forms of infertility may be passed on to children

Application and Skills• Application 1: Causes and treatment of Type I and Type II

diabetes.• Application 2: Testing of leptin on patients with clinical obesity

and reasons for the failure to control the disease.• Application 3: Causes of jet lag and use of melatonin to

alleviate it• Application 4: The use in IVF of drugs to suspend the normal

secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy

• Application 5: William Harvey’s investigation of sexual reproduction in deer.

• Skill 1: Annotate diagrams of the male and female reproductive system to show names of structures and functions