Reproduction, human growth and development, human populations

Reproduction, human growth and development, human populations

Reproduction, human growth and development, human populations
Specification table Patterns of behaviour Reproductive behaviour	Pregnancy Human growth and development Human populations and health

Specification table:
Patterns of behaviour
Innate behaviour	The principal differences between innate and learned behaviour.
Taxes and kineses	Taxes and kineses as examples of innate behaviour.
Reflex actions	The nature of simple reflex behaviour, such as in reflex escape responses. The linking of a number of simple reflexes to produce a more complex pattern of behaviour as shown by the reflexes involved in the feeding of a new-born human infant.
Modified reflexes	The modification of reflex behaviour by learning as shown by the development of conscious control of bladder emptying.
Learned behaviour	Habituation and imprinting. Classical conditioning, illustrated by the work of Pavlov on the control of salivation in dogs. Operant conditioning, illustrated by the work of Skinner on rats. The importance of reinforcement stimuli and rewards in learning . Candidates should be able to explain examples of behaviour in terms of classical conditioning and of operant conditioning and to evaluate parallels between animal and human behaviour.

Reproductive behaviour
Courtship	Courtship behaviour as a necessary precursor to successful mating. The roles of species recognition, pair bond formation, sexual selection and synchronisation of breeding behaviour. Sign stimuli and innate releaser mechanisms as components in simple courtship patterns. The role of hormones and pheromones in courtship behaviour. Candidates should be able to analyse individual components in simple courtship patterns, and evaluate comparisons between the behaviour of humans and other animals.
Territorial behaviour	The advantages of defending a territory, in relation to breeding success.
The menstrual cycle	The roles of FSH, LH, oestrogen and progesterone in controlling the human menstrual cycle. The effect of oestrogen and progesterone on the uterine endometrium. The role of negative feedback in regulating hormone concentrations.
Contraception	The use of oral contraceptives based on oestrogen and progesterone in controlling fertility. Candidates should be able to evaluate the different methods of birth control.
Infertility	The treatment of female infertility with extracted and synthetic hormones and with drugs such as clomiphene which stimulate hormone activity. The key stages in in vitro fertilisation: the use of fertility drugs to stimulate ovulation; the collection of mature egg cells and their incubation with sperms; the insertion of embryos into the uterus.

Pregnancy
Conception	Fertilisation, including capacitation, the role of the acrosome and formation of the fertilisation membrane.
Hormones and pregnancy	The roles of human chorionic gonadotrophin (HCG) and progesterone in controlling the events of pregnancy. Confirmation of pregnancy by determining HCG and progesterone levels.
The placenta	The structure of the placenta in relation to its role in the supply of substances to, and the removal of waste products from, the developing foetus.
Physiological changes in the mother	The changes in the following which take place during the course of a normal pregnancy and their physiological significance: body mass; plasma volume, red-blood-cell mass and cardiac output; kidney function.

Human growth and development
Patterns of human growth	The pattern of growth of the whole body, reproductive organs and the brain from infancy to adulthood. Candidates should be able to represent graphically and interpret data relating to growth and growth rate.
Hormonal control	The roles of thyroxine, growth hormone and sex hormones in the control of human growth from infancy to maturity. Puberty and the principal physical changes associated with it. The evolutionary importance of a long pre-puberty stage in the human lifespan.
Ageing	The contributions to ageing of changes in physiological function, degeneration of tissue, accumulation of genetic error, and malfunction of the immune system.

Human populations and health
Population size and structure	Population growth rates, pyramids, survival rates and life expectancy. Candidates should be able to: interpret population growth curves, survival curves and age pyramids; calculate population growth rate from data on birth rate, death rate, emigration and immigration; relate changes in the size and structure of human populations to different stages in demographic transition.
Social conditions	The influence of food supply, safe drinking water and effective sewage disposal on mortality.
Infectious disease	Pathogens, including certain bacteria, viruses and fungi, as the cause of infectious disease. Transmission of pathogens by droplet infection and contact, or in food and water. Natural immunity as production of antibodies in response to antigens. Immunological memory. (Details of the mechanisms of the immune response not required.) Artificial immunity by vaccination. The limitations of vaccination related to variability of antigens in pathogens. The herd immunity effect. Candidates should be able to: interpret information relating to the incidence and mortality of diseases; evaluate the effectiveness of immunisation programmes and changes in social conditions in preventing epidemics.
Effects of lifestyle on health	The constitution and importance of a balanced diet. The effects of excess fat and salt intakes, and of deficiency of mineral ions (calcium, iron and iodine) and vitamins (vitamins A, C and D). The relationships between diet, exercise and cardiovascular disease. Atheroma formation, formation of blood clots, aneurysm, myocardial infarction and cerebrovascular accident. The relationships between air pollution and smoking and chronic bronchitis, emphysema and lung cancer. The development and effects on lung function of bronchitis, emphysema and lung cancer. The relationship between ultra-violet light and malignant skin tumors. Tumor growth and metastasis. Candidates should be able to explain the biological effects of the disorders listed, and to evaluate measures that might be taken to reduce the risk factors.
Screening programmes	The principles involved in the use of x-rays, endoscopy, ultrasound and genetic techniques in diagnosis and screening programmes. Candidates should be able to: suggest the most appropriate technique to use in the diagnosis or screening of a particular condition; evaluate the issues arising from the use of screening programmes for inherited conditions.

Behaviour Behaviour is what an animal does and how it does it. To some extent all behaviour has a genetic basis but in general, behaviour is a response to some environmental stimulus. Ethology is the correct term for the study of behaviour in its natural habitat. It is mostly a descriptive science. There are two types of behaviour innate and learned. Innate behaviour – little influence from the environment – does not need to be learnt, varies little within species. (inflexible) Learned behaviour – develops from an animals experience of its environment – not passed on genetically Some behaviours are a blend of both so classification is not always so easy

Innate Behaviours inherited, instinctive: programmed by genes highly stereotyped (similar each time in many individuals) Types of innate behaviour: 1. Kinesis: “change the speed of random movement in response to environmental stimulus” 2. Taxis: “a directed movement toward or away from a stimulus; positive and negative taxes 3. Reflex: “movement of a body part in response to stimulus”. 4. Fixed Action Pattern (FAP): “stereotyped and often complex series of movements., responses to a specific stimulus – Releaser”

Kinesis: An orienting behaviour which is non-directional. Here an animal reduces it’s rate of movement or increases its rate of turning as the intensity of the stimulus increases (e.g. woodlice slow down and turn more in the dark). This action has the effect of keeping the organism in an area it finds favourable and making it move away from areas it finds unfavourable.

Taxis: An orienting behaviour which is directional. Here an animal turns towards or away from a stimulus such as light. Can be positive or negative. Blowfly larvae (maggots) show negative phototaxis.

Reflex: A simple reflex is movement of a body part in response to stimulus. It is a rapid, innate automatic response to a stimulus. We looked at the nerve pathway involved in a reflex in module 4 and that helps explain why they are quick and the response does not vary. Watch out for synoptic questions on reflexes. Reflexes can be linked together to produce more complicated behaviours. The example of this that you have to learn is breast-feeding in humans. There are several reflexes involved in the sequence.

Reflex	Behaviour
Rooting reflex (baby)	Also called nipple-seeking behaviour. When the breast touches the baby it will turn its head with its mouth open until it finds the nipple.
Sucking reflex (baby)	When the baby attaches to the nipple it begins to suck.
Let-down reflex (mother)	The stimulation of the nipples by the baby sucking causes the reflex release of the hormone oxytocin. This hormone triggers smooth muscle contraction in the mammary glands causing the release of milk

Although reflexes are defined as unconscious actions that are performed in their entirety and are automatic – they can in some instances be modified. The most obvious example of this is the control of the sphincters which govern urination and defaecation. The reflex that empties the bladder is as follows. The full bladder is the stimulus which causes the sphincter muscles around the base of the urethra to relax, these muscles are connected to the autonomic nervous system – to modify it this muscular relaxation has to be prevented. Learned behaviours develop during an animals lifetime and are not passed on genetically to its offspring. They vary from very simple to the complex social interactions in primates and whales. Since learned behaviours are not “hardwired” they can often be adapted – this adaptation of behaviour forms the basis of animal training. When a reflex is modified it is because the stimulus that causes the reflex also causes sensory information to be sent to the brain. When the learning has occurred this information causes inhibitory signals to be sent from the CNS preventing the normal reflex response

Learned Behaviour

Learned Behaviour can be divided into different categories: Habituation Imprinting Conditioning: classical conditioning operant conditioning Insight, reasoning

Habituation is perhaps the simplest form of learned behaviour. This is where an animal that normally responds to a certain stimulus learns to stop responding to the same stimulus when it is repeatedly stimulated without reason. For example some spiders lie in wait for prey to one side of their web and when something gets trapped. On the web the spider detects the vibrations of the web a rushed out to kill its prey. This response can be made to occur by simply tapping the web with a pen. However after a few stimuli the spider ceases to respond. We say it has become habituated. Young geese (goslings) do not immediately recognise their mother but they imprint on her. There is a sensitive period during the first few days of a goslings life in which it will follow and become attached to any large object, of course in nature this is the mother but in some experiments it has been humans or even a red watering can. When goslings are distressed they will run to whatever object they have imprinted on which usually will be advantageous as it would be their mother but not so helpful if the object was the red watering can. It breeding programs to replenish rare or endangered animals care is taken to avoid imprint onto humans and habituation to the presence of humans. In fact habituation to human presence is one of the factors that makes zoo and captive bred animals very different to their wild counterparts and is an obstacle to reintroduction.

Conditioning involves the formation of new connections between stimuli and responses, the table below shows a summary of this

Type of conditioning	Summary
Classical	A stimulus leads to a response. Here a new stimulus is given at the same time as the first after time the response occurs even if only the second stimulus is given.
Operant	Trial and reward learning.

Classical conditioning was first shown by the work of Pavlov with dogs. He collected saliva from dogs and noted that when presented with the sight and smell of their food they began to salivate in preparation of eating. Pavlov began to ring a bell each time the dog was shown their food. After a while Pavlov found that the dogs salivated when the bell was rung regardless of whether food was present. The dog had become conditioned it associated a bell with the arrival of food.

Habituation Habituation is a reduction in a previously displayed response when a stimulus is repeatedly applied with no reward or punishment following. If you make an unusual sound in the presence of the family dog, it will respond – usually by turning its head toward the sound. If the stimulus is given repeatedly and nothing either pleasant or unpleasant happens to the dog, it will soon cease to respond. This lack of response is not a result of fatigue or sensory adaptation and is long-lasting; when fully habituated, the dog will not respond to the stimulus even though weeks or months have elapsed since it was last presented.

Imprinting If newly-hatched geese are exposed to a moving object of reasonable size and emitting reasonable sounds, they will begin to follow it just as they would normally follow their mother. This is called imprinting. The time of exposure is quite critical. A few days after hatching, imprinting no longer occurs. Prior to this time, though, the results can be quite remarkable. A gosling imprinted to a moving box or clucking person will try to follow this object for the rest of its life. In fact, when the gosling reaches sexual maturity, it will make the imprinted object – rather than a member of its own species – the goal of its sexual drive. Much of our knowledge of imprinting was learned from the research of Konrad Lorenz

The Conditioned Response The conditioned response is probably the simplest form of learned behaviour. It is a response that – as a result of experience – comes to be caused by a stimulus different from the one that originally triggered it. The Russian physiologist Ivan Pavlov found that placing meat powder in a dog’s mouth would cause it to salivate. This unconditioned stimulus (US) is probably a simple inborn reflex involving taste receptors, sensory neurons, networks of interneurons in the brain, and motor neurons running to the salivary glands. Pavlov found that if he rang a bell every time he put the meat powder in the dog’s mouth, the dog eventually salivated upon hearing the bell alone. This is the conditioned response. The dog has learned to respond to a substitute stimulus, the conditioned stimulus (CS). We assume that the physiological basis of the conditioned response is the transfer, by appropriate neurons, of nervous activity in the auditory areas of the brain to the motor neurons controlling salivation. This involves the development of new circuits, which – we may also assume – is characteristic of all forms of learning.

We use the term “operant conditioning” to describe one type of associative learning. Operant conditioning is also termed trial and reward learning. The  classic experiments into operant conditioning were carried out by Skinner, where he trained rats and pigeons to press a lever in order to obtain a food reward (“skinners box). In such experiments, the subject is able to generate certain motor-output responses (e.g. running around, cleaning, resting, pressing the lever). The experimentor chooses a certain action (e.g. pressing the lever) to act as the response and to pair with an unconditioned stimulus (e.g. a food reward). After a training period, the subject will show the conditioned response (e.g. pressing the lever) if the response-unconditioned stimulus association has been memorized.

PheremonesPheromones are chemicals released by an organism into its environment enabling it to communicate with other members of its own species.

Humans may have pheromones It has long been noticed that women living close together (e.g., college roommates) develop synchronous menstrual cycles. This is thought to be because they release two (as yet uncharacterised) primer pheromones one prior to ovulation that tends to speed up the onset of ovulation in others one after ovulation that tends to delay the onset of ovulation in other women. Both pheromones are released from the armpits. The pheromones are not detected consciously as odours, but presumably trigger the hormonal changes that mediate the menstrual cycle.

Courtship Courtship Behaviour: Attraction of mate, (possibly from a considerable distance) Allows species recognition Allows sex recognition Stimulates sexual behaviour / egg production Allows recognition of sexually mature / receptive individuals Enables choice of fittest individuals In birds courtship behaviours can include action such as: Head Wagging Sky Pointing Hop Display Wing Waving Bowing Presenting Nest Material

In establishing breeding partners and defending territories members of the same species rarely fight. Instead they take part in behaviour that is stylised and aimed at avoiding the need to fight Aggressive encounters between individuals of the same species Song, Roar etc. Display Charging Pushing & Shoving Displacement Why not just fight? Risk of Injury Expenditure of energy Conclusion predictable Do they ever fight?….Yes…When The stakes are high i.e. it is a life or death situation The outcome may not be clear

Types of mating relationships Monogamous: Male and female form exclusive bond, may be for one breeding season or for life. Polygamous: Animals have several mates at the same time ~ 2 classes: Males have several female mates = polygynous. e.g. red deer Females have several male mates = polyandrous. e.g. starlings

The Hormonal Control of the Female Menstrual Cycle

Pituitary Hormones – released from the pituitary gland in the brain FSH: Follicle Stimulating Hormone LH: Lutenising Hormone Ovarian Hormones – released from the ovaries (the examiners usually think of oestrogen as been released from the follicle and progesterone as been released from the corpus luteum – however there is actually some overlap) Oestrogen; This repair the uterine lining. Progesterone; This maintain the uterine lining

The sequence FSH stimulates growth of the follicle. The developing follicle in the ovary produces oestrogens Rising oestrogen levels inhibit FSH and promote LH production LH stimulates follicle development and its conversion into the corpus luteum Rising oestrogen levels stimulates an increase in FSH A surge of FSH and LH brings about ovulation LH stimulates progesterone production Progesterone inhibits FSH and LH

Summary of effects
Hormone	Effects
FSH	stimulates the growth & development of the follicle stimulates secretion of oestrogen enhances effect of LH in stimulating ovulation
LH	stimulates the final development of the follicle stimulates ovulation stimulates the development of the corpus luteum stimulates production of progesterone
Oestrogen	stimulates repair of uterine lining at high conc. inhibits FSH, however during ‘pituitary hormone surge’ it stimulates further FSH production as conc. peaks stimulates release of LH
Progesterone	maintains uterine lining inhibits release of FSH inhibits release of LH fall in conc. results in menstruation fall in conc. removes inhibition of FSH and a new cycle begins.

These diagrams of human gametes illustrate the differences between male and female.

Fertilisation Summary: Fertilisation is the fusion of two gametes to form a zygote.  In humans this takes place near the top of the oviduct. Hundreds of sperm reach the egg and use their tails to swim through the follicle cells (shown in this photo). When they reach the jelly coat surrounding the ovum they bind to receptors and this stimulates the rupture of the acrosome membrane in the sperms, releasing digestive enzymes, which make a path through the jelly coat. When a sperm reaches the ovum cell the two membranes fuse and the sperm nucleus enters the cytoplasm of the ovum. This triggers a series of reactions in the ovum that cause the jelly coat to thicken and harden, preventing any other sperm from entering the ovum. The sperm and egg nuclei then fuse, forming a diploid zygote.

Fertilisation Detail:

Copulation and Fertilization For fertilization to occur, sperm must be deposited in the vagina within a few days before or a day or two after ovulation. Sperm transfer is accomplished by copulation. Semen is a fluid containing the sperm and liquid added by the seminal vesicles, Cowper’s glands, and the prostate gland. These fluids provide a source of energy (fructose) and perhaps in other ways provide an optimum chemical environment for the sperm. The semen passes through the urethra and is expelled into the vagina. Once deposited within the vagina, the sperm proceed on their journey into and through the uterus and on up into the fallopian tubes. It is here that fertilization may occur if an “egg” is present (strictly speaking, it is still a secondary oocyte until after completion of meiosis II). Although sperm can swim several millimetres each second, their trip to and through the fallopian tubes may be assisted by muscular contraction of the walls of the uterus and the tubes. There is some evidence that the egg may release a chemical attractant for sperm. In any case, sperm may reach the egg within 15 minutes of ejaculation. The trip is massive for the sperm and many don’t make it. An average human ejaculate contains several hundred million sperm but only a few hundred reach the egg. And of these, only one will succeed in entering the egg and fertilizing it. Before sperm can fertilise an egg a process called capacitation must take place. This is where a coating surrounding the sperm is removed it occurs over a period of a few hours and is triggered by the conditions within the female reproductive tract. Once capacitation has occured the acrosome is capable of releasing its enzymes. Fertilization begins with the binding of a sperm cell to the outer coating of the egg (called the zona pellucida). Enzymes released by the acrosome at the tip of the sperm head digest a path through the zona and enable the sperm to enter the cytoplasm of the egg. Once a single sperm has penetrated, the cell membrane of the egg calcium ions move into the egg cell. This causes exocytosis of cortical granules from the egg. The granules fuse with the zona pellucida, forming a fertilisation membrane. This prevents the entry of other sperm. The other sperm die within 48 hours. Thus the cortical reaction ensures that only one sperm fertilizes the egg. Soon the head of the successful sperm enlarges. At the same time, the egg (secondary oocyte) completes meiosis II. The male and female nuclei move toward each other. Their nuclear envelopes disintegrate. A spindle is formed, and a full diploid set of chromosomes assembles on it. The fertilized egg or zygote is now ready for its first mitosis.

Pregnancy Embryonic development begins while the fertilized egg is still within the fallopian tube. The developing embryo travels down the tube, reaching the uterus in about a week. As a result of repeated mitotic divisions and some migration of cells, a hollow ball of cells is formed called the blastocyst. Approximately one week after fertilization, the blastocyst embeds itself in the endometrium, a process called implantation. With implantation, pregnancy is established. The blastocyst has two parts the inner cell mass and the trophoblast. Between them these two parts will develop into the: baby amnion placenta umbilical cord and secrete the pregnancy hormone human chorionic gonadotropin (HCG).

Human Chorionic Gonadotropin HCG behaves much like LH because it stimulates the corpus luteum to secrete progesterone but has one crucial difference: it is NOT inhibited by a rising level of progesterone. So HCG prevents the deterioration of the corpus luteum at the end of the fourth week and enables pregnancy to continue beyond the end of the normal menstrual cycle. Because only the implanted embryo makes HCG, its early appearance in the urine of pregnant women provides the basis for the most widely used test for pregnancy (which can provide a positive signal even before menstruation would have otherwise begun). As pregnancy continues, the placenta becomes a major source of progesterone, and its presence is essential to maintain pregnancy.

The Pregnancy Test This test is usually the first test conducted when you suspect that you may be pregnant. There are a variety of home testing kits available over-the-counter and all detect a protein hormone called human chorionic gonadotropin (hCG). When an egg is fertilized, the embryo begins to produce hCG. Levels of hCG increase after conception and can be detected in the mother’s urine. By 10 days after conception, hCG levels are about 25 milli-International Units (mIU). Typically, the home test is a urine test for hCG: You collect a sample of urine. You would usually use the first urine in the morning, when hCG levels are the most concentrated, or wave the test wand through the urine stream. If you collected the urine, you can either dip the test wand into the cup or place a drop on the test wand. The test wands or dipsticks have a plastic coating embedded with antibodies to hCG. The test wands also have a second antibody to hCG linked with some colour tag (e.g., coloured latex beads, enzyme that produces a colour reaction). If sufficient levels of hCG are present in the urine (more than 25 mIU), then the hCG will bind with the second antibody and cause a colour reaction to occur (i.e., a positive test result). If a positive test occurs, you generally call your doctor and a second test is performed at the office to confirm the pregnancy. The doctor may also order a blood test to determine the precise quantity of hCG present, which can be used to assess the baby’s health.

The placenta The placenta grows tightly fused to the wall of the uterus. Its blood vessels, supplied by the foetal heart, are literally bathed in the mother’s blood. Although there is normally no mixing of the two blood supplies, the placenta does facilitate the transfer of a variety of materials between the foetus and the mother.

Table showing exchange of materials across the placenta
Mother to Foetus	Foetus to Mother
Oxygen Glucose Amino acids Lipids, fatty acids and glycerol Vitamins Ions; Na, Cl, Ca, Fe Alcohol, nicotine + other drugs Viruses Antibodies	Carbon dioxide Urea Other waste products

The placenta is an organ of exchange and therefore requires a large surface area – to achieve this it has chorionic villi (the cells of which have microvilli and many mitochondria) The metabolic activity of the placenta is almost as great as that of the foetus itself. The placenta is also an endocrine organ and it secretes hCG, progesterone and oestrogen During pregnancy prenatal diagnosis of genetic disorders can be made using the procedures of amniocentesis and chorionic villus sampling (CVS) – see later screening section for details.

PHYSIOLOGICAL CHANGES TO THE MOTHER DURING PREGNANCY Physiological and anatomical alterations develop in many organ systems during the course of pregnancy and delivery. Early changes are due, in part, to the metabolic demands brought on by the foetus, placenta and uterus and, in part, to the increasing levels of pregnancy hormones, particularly those of progesterone and oestrogen. Later anatomical changes, starting in mid-pregnancy, are caused by mechanical pressure from the expanding uterus.

Cardiovascular System
The pregnancy-induced changes in the cardiovascular system develop primarily to meet the increased metabolic demands of the mother and foetus.

Blood Volume
Increases progressively from 6-8 weeks and reaches a maximum at approx. 32-34 weeks with little change afterwards. Most of the added volume of blood is accounted for by an increased capacity of the uterine, breast, renal, muscle and adipose tissues. The increase in plasma volume (40-50%) is relatively greater than that of red cell mass (20-30%) resulting in a decrease in haemoglobin concentration. Intake of supplemental iron and folic acid is necessary to restore haemoglobin levels to normal (12 g/dl).
The increased blood volume serves two purposes. It helps maternal and foetal exchanges and it reduces the impact of maternal blood loss at delivery. Typical losses of 300-500 ml for vaginal births are thus compensated with the so-called “autotransfusion” of blood from the contracting uterus.

Cardiac Output
Increases to a similar degree as the blood volume. During the first trimester cardiac output is 30-40% higher than the non-pregnant output. Steady rises occur from about 7 litres/minute at 8-11 weeks to 9 litres/minute at 36-39 weeks; they are due, to an increase in stroke volume (35%) and also to a more rapid heart rate (15%).

Cardiac Size
There are size changes. The heart is enlarged by both chamber dilation and hypertrophy.

Blood Pressure
Systemic arterial pressure is never increased during normal gestation. In fact, by midpregnancy, a slight decrease in diastolic pressure can be recognized. Pulmonary arterial pressure also maintains a constant level.Renal System

Kidney Function
Blood flow through the kidney can increase from 25-50% and blood urea also increases as foetal urea is added via the placenta. The kidney accommodates for these changes by increasing in size (length can increase by 1cm). Volume of urine production is not greatly increased (though frequency of urination usually is) therefore the concentration of urine is normally increased.

Body Mass

The average weight gain during pregnancy is about 12kg (or 25-35 pounds). The table below shows some typical mass changes that may occur if I became pregnant (ok I know it’s impossible but it gives an idea of proportion)

SOURCE	TYPICAL INCREASE IN MASS (LB.)
Uterus	2.4
Breasts	1.0
Blood	3.1
Water	4.2
Fat	8.3
Amniotic Fluid	2.0
Placenta	1.6
Foetus	7.5

Birth and Lactation

Exactly what brings about the onset of labour is still not completely understood. Probably hormonal control is responsible. The first result of labour is the opening of the cervix. With continued powerful contractions, the amnion ruptures and the amniotic fluid (the “waters”) flows out through the vagina. The baby follows, and its umbilical cord can be cut. Shortly after the baby, the placenta and the remains of the umbilical cord (the “afterbirth”) are expelled. At the time of birth, and for a few days after, the mother’s breasts contain a fluid called colostrum. It is rich in calories and protein, including antibodies that provide passive immunity for the newborn infant. Three or four days after delivery, the breasts begin to secrete milk. Its synthesis is stimulated by the pituitary hormone prolactin. Its release is stimulated by a rise in the level of oxytocin when the baby begins sucking the nipples. Milk contains an inhibitory peptide. If the breasts are not fully emptied, the peptide accumulates and inhibits milk production. This is an example of negative feedback.

Contraception As you can see from the process of sexual reproduction, there are several ways to prevent the sperm and egg from coming together. These methods of contraception fall into the following categories: Not engaging in sexual activity – abstinence Preventing a follicle from developing – birth control pills Placing a barrier between sperm and egg – condoms (male/female), cervical caps, diaphragms Killing the sperm – spermicides Surgery – blocking the sperm or egg with surgical procedures like tubal ligations (in women) or vasectomies (in men) Timing – avoiding intercourse during the period of maximum fertility

Human growth and development

Human Growth & Development

Growth occurs during gestation, childhood and adolescence. Growth rate = change in size per unit time Growth curve = when growth rates are plotted graphically Allometric Growth = Differential growth of body parts. This causes our body proportions to change between infancy and adulthood.

Stages of Human Growth

Gestation	Relatively short for humans because of our large brains and cranium mean longer gestation would cause birth problems.
Childhood	Pre-pubertal period gives us time to grow, develop and learn (acquire skills and knowledge).  This phase is relatively longer in humans than in other animals (we have extended period of dependency).  During childhood boys and girls grow at the same rate this growth is controlled by hormones.  The pituitary gland secretes a hormone called pituitary growth hormone (PGH).  Also it secretes a hormone called thyroid stimulating hormone (TSH) which stimulates the thyroid gland to secrete thyroxin.  Thyroxin and PGH both stimulate growth.
Adolescence	During puberty the pituitary gland produces LH and FSH which cause the ovaries to produce oestrogen and the testes to produce testosterone.  These hormones are the sex hormones and cause the development of secondary sexual characteristics.  The growth spurt that occurs during puberty is due to increased levels of PGH.

Ageing Senescence = The deterioration of bodily functions and the appearance of features associated with old age. Cross Sectioned Studies = Studying large samples of people at several ages. In the case of research into ageing measurements of physical and physiological features are taken and averages for the different age groups established. Longitudinal Studies = Studying small samples and following the individuals over time. Physiological effects of ageing Effects on skin collagenase produced, collagen structure altered – loss of elasticity due to x-links in elastin + collagen accumulation of genetic errors Degeneration of tissues – due to ‘wear & tear’ organ function metabolic rate lung capacities Immune system, efficiency decreases + incidence of autoimmune diseases

Human populations and health

Populations Populations changed by – Births, Deaths, Immigrations or Emigrations Rate of National Increase (RNI) = The change in the size of a population as a % of the total population per year. Doubling Time = The time it would take a population to double assuming the RNI remains constant. Population Pyramids = a visual representation of the age structure of a population

Demographic Transition Model Stage 1 –  High Stationary – Named therefore of high birth and death rates.High infant morality, poor/unreliable food supply, short life expectancy. Stage 2 – Early Expanding – More reliable food supply, improved living conditions/death rates.  Birth rates high. Stage 3 – Late Expanding – Significant fall in birth rate linked to social change, urbanisation and industrialisation. Stage 4 – Low Variable – Stable population with low birth rate and low death rate.

Social Conditions Affecting Population Growth Food Supply – Poor food supply causes malnutrition and fertility drops. Sewage Disposal & Drinking Water are linked therefore waterborne disease affects death rate (cholera a bacterial disease is a common waterborne disease

Social Conditions and life Expectancy Urbanisation without sanitation lowers life expectancy Vaccination increases life expectancy Prosperity increases life expectancy (better nutrition and healthcare

Disease

Chronic bronchitis Chronic bronchitis is a clinical diagnosis where there is cough producing sputum on most days for 3 months of the year for 2+ years which is not due to another respiratory illness. The disorder is characterised by excess mucus secretion. Emphysema Emphysema is defined by its pathology and is characterised by destruction of respiratory tissue and permanent enlargement of the unit of the lung distal to the terminal bronchiole. This can be detected by endoscopic examination. In the past much importance has been placed on the distinction between chronic bronchitis and emphysema. In the majority of patients both conditions co-exist, usually in heavy cigarette smokers. Aetiology and prevalence Chronic bronchitis and emphysema are responsible for personal disability and misery of 10,000’s of patients. Respiratory disorders are an important cause of death and of these chronic bronchitis and emphysema constitute a large proportion of these. Atmospheric pollution and occupational dust exposure are minor aetiological factors in chronic bronchitis and the dominant causal agent is cigarette smoke. Smoking also causes emphysema. Mechanism of airflow obstruction In chronic bronchitis and emphysema the fundamental cause of reduced ventilatory capacity and breathlessness is the limitation of expiratory airflow. In emphysema a more important mechanism is the narrowing and collapse of airways during expiration as a consequence of loss of the lung elastic recoil which normally keeps airways open. In emphysema there is also collapse of alveolar walls causing reduced surface area for gas exchange. Physical signs In predominantly emphysematous patients, inspiratory airways resistance is not increased and inspiration is therefore quiet, whereas patients with predominantly chronic bronchitis have noisy breathing. To control airways collapse on expiration, patients with emphysema apply a positive pressure to the bronchial tree by the technique of purse-lipped breathing. Cessation of cigarette smoking Tobacco smoke damages the bronchial tree and produces airflow limitation by a number of different actions. Smokers are predisposed to bronchial infection and consequent inflammation. It is therefore not surprising that chronic bronchitis and emphysema are found in 15% of middle-aged males who smoke moderately or heavily but are rare in non-smokers, and that deaths from bronchitis increase with the amount smoked. If patients with chronic bronchitis and emphysema stop smoking, the rate of decline in pulmonary function is reduced to that of non-smokers. Indeed, if patients stop smoking early in their disease there is improvement in pulmonary function. However severe the disease, stopping smoking will reduce cough.

Chronic Bronchitis: Criteria:     Having a productive cough for at least 3 months during 2 successive years Symptoms: Productive cough, breathlessness Smoking and air pollution paralyse the cilia in the bronchial tubes so mucus builds up in clumps that are coughed up (that’s the productive cough). The lining of the bronchial tubes becomes irritated and inflamed. Emphysema: Criteria:     Actually defined by pathology the walls of the alveoli are broken down Symptoms: Coughing, shortness of breath, and wheezing, developing into extreme difficulty in breathing Walls of the alveoli are broken down so less surface area is available for the exchange of gases. Asthma: Characterised by intermittent attacks in which airway smooth muscle contracts, increasing airway resistance. More mucus may be secreted by the airways and this mucus may be unusually thick and therefore further increase airway resistance.

A case study of the # of deaths of cigarette smokers (“observed [obs.] deaths”) compared with the number to be expected among nonsmokers of the same ages (“expected [exp]. deaths”).

Cause of Death	Obs. Deaths	Exp. Deaths	Excess Deaths	% Change
Total deaths (all causes)	7316	4651	2665	57
Heart disease	3864	2398	1466	61
Cerebrovascular lesions	556	428	128	30
Other circulatory diseases	173	97	76	78
Lung cancer	397	37	360	973
Cancer of mouth/ larynx/oesophagus	91	18	73	406
Other cancers	972	686	286	42
G.I. tract Ulcers & liver Cirrhosis	183	68	115	169
Pulmonary disease (except cancer)	231	81	150	185
All other diseases	486	453	33	7
Accident, violence, suicide	363	385	-22	-6

(Data from E. C. Hammond and D. Dorn, 1966.)

Cancer:   A cancer is an uncontrolled proliferation of cells.  In some the rate is fast; in others, slow; but in all cancers the cells never stop dividing. This distinguishes cancers – malign tumours – from benign growths like moles where their cells eventually stop dividing. Cancers are clones. No matter how many trillions of cells are present in the cancer, they are all descended from a single ancestral cell. Cancers begin as a primary tumour. At some point, however, cells break away from the primary tumour and – travelling in blood and lymph – establish metastases in other locations of the body. Metastasis is what usually kills the patient. Cancer cells contain mutated genes known as oncogenes. The mutations are found in genes that are involved in mitosis; that is, in genes that control the cell cycle. Probable Sequence: A single cell in a tissue suffers a mutation in a gene involved in mitosis. This results in giving that cell a slight growth advantage over other cells in the tissue. As that cell develops into a clone, some if its descendants suffer a second mutation This further deregulates the cell cycle of that cell and its descendants. As the rate of mitosis in that clone increases, the chances of further DNA damage increases. Eventually the growth of that clone becomes completely unregulated. The result: full-blown cancer. Colon Cancer: An example: Begins with the development of polyps in the epithelium of the colon. Polyps are benign growths As time passes, the polyps may get bigger. At some point, nests of malignant cells may appear within the polyps If the polyp is not removed, some of these malignant cells will escape from the primary tumour and metastasise throughout the body. Examination of the cells at the earliest, polyp, stage, reveals that they contain oncogenes.   Cancers become more common as one gets older. This explains why cancer has become such a common cause of death during the twentieth century. It probably has very little to do with exposure to the chemicals of modern living and everything to do with the increased longevity that has been such a remarkable feature of this century. A population whose members increasingly survive accidents and infectious disease is a population increasingly condemned to death from such “organic” diseases as cancer. Causes of Cancer: anything that damages DNA; that is anything that is mutagenic radiation that can penetrate to the nucleus and interact with DNA chemicals that can penetrate to the nucleus and damage DNA. Chemicals that cause cancer are called carcinogens. anything that stimulates the rate of mitosis. This is because a cell is most susceptible to mutations when it is replicating its DNA during the S phase of interphase. certain hormones (e.g. hormones stimulating mitosis in the breast & prostate glands) certain viruses   Radiation and cancer High doses of radiation cause cancer. Various studies, including excellent ones on the survivors of Hiroshima and Nagasaki, show that a popn. exposed to a dose of 12,500 mrem will have a measurable increase (about 1%) in the incidence of cancer. Note that the measurements are made on a popn. not on individuals. We can never say that a particular individual exposed to a particular dose of radiation will develop cancer. The induction of cancer is a chance event unlike radiation sickness which is completely predictable. The element of chance arises because cancer is an event that occurs in a single cell unlucky enough to suffer damage to specific genes mutating them to oncogenes. However, the energy needed to cause mutations is very low. So if you expose a sufficiently large number of cells to even tiny doses of radiation, some cell is going to be unlucky.

Screening and diagnostic tests

Biochemical tests Immunological tests Screening Biopsies Cytological examinations Culturing microorganisms Genetic analysis X-rays Ultrasound Endoscopy Blood pressure measurement Sight and hearing tests

Screening Looking for signs of the disease before acute symptoms are evident. Based on the premise that early detection can lead to a complete cure. Genetic analysis Amniocentesis = the method which removes a small sample of amniotic fluid from the uterus. Done with a needle. The fluid contains some foetal cells on which genetic analysis can be carried out Chorionic villus sampling = the method of obtaining a tissue sample from the area of the placenta of the early embryo. Done in conjunction with an ultrasound probe. Genetic analysis could be by karyotyping or use of a genetic probe X-rays Mainly used on bones. X-rays are a form of ionising radiation so care is required as it can damage DNA. Can be used to detect some abnormalities to soft tissue. Barium is opaque to X-rays and can be ingested as a paste/slurry “barium meal” this accumulates in stomach ulcers. Ultrasound Use of high frequency sound waves ( approx. 3-10 million Hz, audible range = 16Hz – 20,000Hz) into an area being investigated. Reflected sound is converted into visual radiation (does not damage DNA) Endoscopy The insertion of a camera into the body Blood pressure measurement Measured by a sphygmomanometer Sight and hearing tests Tests for visual acuity. Also tests for colour-blindness (Ishihara test) CT scanning Advanced X-ray technique, low dosage. Examination of area in slices and computer analysis constructs internal picture. MRI scanning Uses a strong magnetic field which causes all the nuclei of the atoms that compose the body to line up and spin in the same direction. When a radio frequency wave is beamed into the magnetic field the nuclei move out of alignment. When the radio wave is stopped they move back into alignment and release energy ~ this can be measured by a receiver

Hypertension

Hypertension is where systolic and/or diastolic blood pressure is chronically elevated at rest. Their values must exceed 140 mm Hg and 90 mm Hg over several examinations. Clinical problems that are linked to high blood pressure include strokes and heart attacks. Hypertension is a multifactoral disease

NaCl and hypertension Physiological requirement for Na » 20mmol/day » 1g NaCl intake Average British NaCl intake » 9g/day

Average % of Na from different sources
Discretionary
Added at table	9.0
Used in cooking	6.0
Food
Naturally occurring	18.5
Added salt in processing	58.7
Non-salt additives	7.2
Salt in water supply (average)	0.6
	100.0

Alcohol and hypertension Alcohol intake is associated with raised blood pressure. Heavy drinkers have higher blood pressures than light drinkers and abstainers. The effect begins at about 3 units of alcohol per day

Minerals

Vitamins

GUIDELINES FOR NUTRITION 

The effects of exercise on the incidence of certain diseases Heart disease Regular exercise increases heart efficiency, and makes heart contraction more efficient (i.e. more powerful). It increases blood HDL (high density lipoprotein) levels. HDLs carry cholesterol away from the tissues back to the liver, where they are secreted into bile. So HDLs are beneficial and reduce the risk of heart disease. LDLs carry most of the cholesterol in the blood. They deliver cholesterol to the cells. LDLs increase the incidence of atheroma. The ratio of plasma LDL cholesterol : plasma HDL cholesterol is important: the lower the ratio, the lower the risk of atheroma. Artery wall elasticity is maintained improved/improved by regular exercise. Resting heart rate is lowered; this decreases the ‘loading’ (strain) on the heart. Resting blood pressure is lowered, meaning that less effort is needed for the heart to pump. Exercise may lead to weight loss, which would decrease the loading on the heart. Circulatory problems eg atheroma Exercise reduces stress. Regular exercise reduces the amount of adrenaline release (adrenaline promotes the breakdown of glycogen for respiration). Exercise increases the metabolism of fats. Exercise increases HDL and lowers LDL. The points above contribute to reducing the chance of atheroma being deposited on the inner lining of the arteries. Reproduction, human growth and development, human populations, Reproduction, human growth and development, human populations

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