Transcript File

Higher Human Biology
Unit 2
Physiology & Health
KEY AREA 4: Ante- and Postnatal Screening
Higher Human Biology
We are going to build on the knowledge and skills that you developed during N5 and will
learn about the following Physiology & Health key areas : -
Key Area 1 – Reproductive Organs
Key Area 2 –Hormonal Control of Reproduction
Key Area 3 – Biology of Controlling Fertility
Key Area 4 – Ante- and Postnatal Screening
Key Area 5 – Structure and Function of Arteries, Capillaries and Veins
Key Area 6 – Structure and Function of the heart
Key Area 7 – Pathology of Cardiovascular Disease (CVD)
Key Area 8 – Blood Glucose Levels and Obesity
Physiology & Health Learning Intentions
KEY AREA 4 – Ante- and Postnatal Screening
a) Antenatal Screening
b) Postnatal Screening
4a) Antenatal (before birth) screening - Examples
Antenatal (prenatal) screening identifies the risk of a disorder so that further tests
and a prenatal diagnosis can be offered
Examples of Antenatal Screening are:Ultrasound imaging (Dating Scan and Anomaly Scan)
Biochemical tests
Diagnostic tests
Use of Karyotype
Amniocentesis
Chorionic villus sampling
Rhesus antibody testing
4b) Antenatal (before birth) screening - Ultrasound
Ultrasound Imaging
When the ultrasound scanner is held against a pregnant women’s abdomen, it picks up
high-frequency sounds that have bounced off the fetus. These are converted to an
ultrasound image on a computer screen
Dating Scan
Ultrasound imaging is carried out at 8-14 weeks
to produce a Dating Scan, which is used to
determine the stage of the pregnancy and to
calculate the date when the baby is due to be born.
Dating scans are used with biochemical tests
for marker chemicals.
Anomaly Scan
Ultrasound imaging is carried out at 18-20 weeks
to produce an Anomaly Scan, which detects the
presence of any serious physical abnormalities
in the foetus e.g. Spina bifida
4c) Antenatal (before birth) screening - Biochemical
Biochemical Tests
Biochemical tests monitor the physiological changes that occur during pregnancy e.g.
the concentrations of human chorionic gonadotrophin (HCG)
Other routine tests to check the health of the pregnant women include:Renal Function Tests
Liver Function Tests
Thyroid Function Tests
White Blood Cell Counts
Red Blood Cell Counts
Protein concentration
Glucose concentration
Urea concentration
Calcium concentration
Alpha-fetoprotein (AFP)
4d) Antenatal (before birth) screening - Diagnostic
Diagnostic Testing
A screening test is one that is used to detect signs and symptoms associated with a
certain condition or disorder. If the signs are found, the probability that the individual
is suffering the condition can be assessed as a degree of risk
A diagnostic test is a definitive test that produces results that can be used to establish
without a doubt whether or not the foetus is suffering a specific condition or disorder.
Diagnostic tests may be offered to a pregnant women if:Screening tests have shown a potential problem
There’s a family history of a genetic disorder
She belongs to a high-risk group (e.g. women over age of 35)
4e) Antenatal (before birth) screening - Diagnostic
A human karyotype shows the number and
appearance of chromosomes found in a
cell
Amniocentesis and Chorionic Villus
Sampling can be used to prepare a
person’s karyotype which shows
their complete chromosome complement
Amniocentesis is carried out between 14-16weeks, and involves withdrawing amniotic fluid
containing foetal cells. The cells are cultured, stained and examined under a microscope
to create the karyotype and allows for chromosome abnormalities to be detected e.g. an
extra chromosome 21 indicates Down’s Syndrome
Disadvantage – risk of miscarriage
Chorionic villus sampling (CVS) involves taking a tiny sample of placental cells using a fine
tube inserted into the mothers reproductive tract. The cells are cultured and used for
karyotyping.
Benefit of CVS - it can be carried out at 8weeks whereas amniocentesis is 14-16weeks
Disadvantage of CVS – causes a higher incidence of miscarriage than amniocentesis
4e) Antenatal (before birth) screening - Diagnostic
Blood Type
Pregnant women have to have blood tests to determine their blood type. If a Rhesusnegative women is pregnant with a Rhesus-positive fetus, a potential problem arises:Rhesus antigens on the fetus’s red blood cells are seen as foreign by the mother’s immune
system, so if contact was made during birth there would be immune system problems
To prevent problems, the mother is given Anti- Rhesus antibodies to destroy any Rhesus
antigens left behind by the baby before her immune system has time to respond
4f) Postnatal (after birth) Screening
Diagnostic testing for metabolic disorders occurs when the baby is just a few
days old
In UK, ALL newborn babies are screened for PKU (Phenylketonuria) by having
their blood tested for the presence of excess phenylalanine.
PKU sufferers are then put on a restricted diet to prevent mental deficiency
4g) Genetic Screening and Counselling
Pedigree charts can be used to analyse patterns of
inheritance in genetic screening and counselling
Once phenotypes of family members are known, the
genotypes can be worked out
The construction of a family tree looking at genetic
conditions/disorders is carried out by a genetic counsellor,
in particular when a couple are concerned about passing the
trait to their children
X and Y chromosomes are called Sex Chromosomes and all
other chromosomes are called Autosomes
4h) Autosomal recessive inheritance
A geneticist can spot the following patterns in autosomal recessive inheritance:The trait is expressed relatively rarely
The trait may skip generations
The trait is expressed in some of the offspring of a consanguineous marriage (cousins)
Males and females are affected in approximately equal numbers
Genotypes of sufferers are homozygous recessive (ff)
Genotypes of non-sufferers are homozygous dominant (FF), or heterozygous (Ff)
EXAMPLE: Cystic Fibrosis
4h) Autosomal recessive inheritance
4h) Autosomal recessive inheritance
4i) Autosomal dominant inheritance
A geneticist can spot the following patterns in autosomal dominant inheritance:The trait is expressed in every generation
Each sufferer of the trait has an affected parent
When a branch of the tree fails to express the trait, the trait fails to reappear in
future generations of that branch
Males and females are affected in approximately equal numbers
Genotypes of non-sufferers are homozygous recessive (hh)
Sufferers are homozygous dominant(HH) or heterozygous (Hh)
EXAMPLE: Huntington’s disease
4i) Autosomal dominant inheritance
4j) Autosomal incomplete dominance
A geneticist can spot the following patterns in autosomal incomplete inheritance:The fully expressed form occurs relatively rarely
The partly expressed form occurs much more frequently
Each sufferer of the fully expressed form has two parents who suffer from the partly
expressed form
Males and females are affected in approximately equal numbers
All non-sufferers are homozygous for one incompletely dominant allele (HH)
All sufferers of the fully expressed form are homozygous for the other incompletely
dominant allele (SS)
All sufferers of the partly expressed form are heterozygous for the two alleles (HS)
EXAMPLE: Sickle-cell disease
4j) Autosomal incomplete dominance
4k) Sex-linked recessive traits
A geneticist can spot the following patterns in sex-linked recessive inheritance:Many more males are affected than females (if any)
None of the sons of an affected male show the trait
Some grandsons of an affected male show the trait
All sufferers of the trait are homozygous recessive (male XhY and very rarely the
female XhXh)
Non-sufferers are homozygous dominant (XHY or XHXH) or heterozygous carrier
females (XHXh)
EXAMPLE: Haemophilia
4k) Sex-linked recessive traits
Physiology & Health Questions
KEY AREA 4 – Antenatal and Postnatal Screening
1. Testing Your Knowledge 1
Page 146
Q’s 1-4
2. Testing Your Knowledge 2
Page 155
Q’s 1-3
3. What You Should Know
Page 156
Q’s 1-18
4. Quick Quiz