Bio 6 Flashcards
6.1 Outline the
sequence of events
that occur in order
for food to be
digested and
absorbed
mouth -> stomach (with liver and gall bladder) ->
small intestine (pancreas) -> large intestine -> anus
mechanical digestion -> chemical digestion
-food is physically broken down into smaller
fragments via the acts of chewing (mouth),
churning (stomach) and segmentation (small
intestine)
**Absorption occurs in small and large intestine
-pancreas secretes enzymes into the lumen of the
small intestine.
-digested food monomers must pass from the
lumen into the epithelial lining of the small
intestine
6.1 Explain how the
muscles in the
digestive system aid
in digestion.
The contraction of circular and longitudinal
muscle of the small intestine mixes the food with
enzymes (churning) and moves it along the gut
Peristalsis:
-peristalsis is the involuntary, wave-like
contraction of muscle layers of the small intestine.
-the principal mechanism of movement in the
esophagus, although it also occurs in both the
stomach and gut
-continuous segments of longitudinal smooth
muscle rhythmically contract and relax
-contraction of longitudinal muscle «layers»/
peristalsis helps move food along the gut
-food is moved unidirectionally along the
alimentary canal in a caudal direction (mouth to
anus)
Segmentation:
-involves the contraction and relaxation of non-
adjacent segments of circular smooth muscle in
the intestines
-circular muscle contraction prevents backward
movement of food
-segmentation contractions move chyme in both
directions, allowing for a greater mixing of food
with digestive juices
-while it helps to physically digest food particles, its bidirectional propulsion of chyme can slow
overall movement
6.1 Explain the
source of enzymes,
stomach acid, and
bile, and how it aids
in overall digestion
along with
associated organs.
Enzymes
-allow digestive processes to therefore occur at
body temperatures and at sufficient speeds for
survival requirements
-specific for a substrate and so can allow
digestion of certain molecules to occur
independently in distinct locations
Stomach Acids
-contains gastric glands which release digestive
acids to create a low pH environment (pH -2)
-acidic environment denatures proteins and other
macromolecules, aiding in their overall digestion
-stomach epithelium contains a mucous
membrane which prevents the acids from
damaging the gastric lining
**pancreas releases alkaline compounds (e.g.
bicarbonate ions), which neutralise the acids as
they enter the intestine
Bile
-liver produces a fluid called bile which is stored and concentrated within the gall bladder prior to
release into the intestine
-contains bile salts which interact with fat globules
and divide them into smaller droplets
(emulsification)
-emulsification of fats increases the total surface
area available for enzyme activity (lipase)
-bile/bicarbonate secreted into the small intestine
creates favorable pH for enzymes
6.1 Explain the
function of the
pancreas in
digestion.
The pancreas secretes digestive enzymes (e.g.
amylase, lipase and an endopeptidase) into the
lumen of the small intestine depending on the
specific macromolecule required for hydrolysis.
-digestive enzymes are secreted in ribosomes on
the rER, processed in the Golgi A. and secreted
by exocytosis.
Enzymes digest most macromolecules in food into
monomers in the small intestine.
*cellulose remains undigested.
*pancreas also releases alkaline compounds (e.g.
bicarbonate ions), which neutralise the acids as
they enter the intestine
6.1 Describe and
explain one specific
feature of the small
intestine that aids in
the absorption of
food.
The inner epithelial lining of the intestine is highly
folded into finger-like projections called villi
(singular: villus)
-villi increase the surface area of epithelium over
which absorption is carried out.
-villi absorb monomers formed by digestion as
well as mineral ions and vitamins.
*villi are part of the mucosa layer of the
small intestine
rich blood supply (part of submucosa layer):
-each villus has a capillary bed that absorbs
sugars and amino acids from the small intestine
-dense capillary network rapidly transports absorbed products
single layer epithelium:
-minimises diffusion distance between lumen
and blood
-increases surface area for absorption
lacteals (part of submucosa layer)
-absorbs lipids from the intestine into the
lymphatic system
*intestinal glands:
-exocrine pits (crypts of Lieberkuhn) release
digestive juices
membrane proteins:
-facilitates transport of digested materials into
epithelial cells
tight junctions:
-keep digestive fluids separated from tissues and
maintain a concentration gradient by ensuring one-way movement
-gives the sheet mechanical strength
-makes it impermeable to small molecules
mitochondria:
-epithelial cells of intestinal villi will possess large
numbers of mitochondria to provide ATP
-required for primary active transport (against
gradient), secondary active transport (co-
transport) or pinocytosis
absorptive cells:
-have many pinocytic vesicles (does endocytosis)
-creating vesicles that contain liquid and nutrients
taken in from the lumen of the small intestine.
6.1 Outline the
different methods
of membrane
transport are
required to absorb
different nutrients.
*glucose is hydrophilic, therefore needs to be
transported via active transport
Secondary Active Transport:
-glucose and amino acids are co-transported
across the epithelial membrane by the active
translocation of sodium ions (Nat)
-can only work on glucose and amino acids
because they are positively charged (like Na+)
Facilitated Diffusion
-help hydrophilic food molecules pass through
the hydrophobic portion of the plasma
membrane
-situated near specific membrane-bound
enzymes (creates a localised concentration
gradient)
-certain monosaccharides (e.g. fructose),
vitamins and some minerals are transported by
facilitated diffusion
Osmosis
-movement in response to the ions and
hydrophilic monomers (solutes)
*the absorption of water and dissolved ions occurs
in both the small and large intestine
Simple Diffusion
-fatty acids and lipoprotein are hydrophobic,
therefore can diffuse through membrane passively
-once absorbed, lipids will often pass first into the lacteals rather than being transported via the
blood
-e.g. fatty acids and monoglycerides
Endocytosis
-small droplets of the fluid are passed through the
membrane by means of vesicles.
e.g. triglycerides and cholesterol in
lipoprotein particles.
6.1 List out the
organs in the
digestive system
and their functions.
alimentary canal: organs through which food
actually passes
-esophagus, stomach, small & large intestine
accessory organs: aid in digestion but do not
actually transfer food
-salivary glands, pancreas, liver, gall bladder
Oesophagus
• A hollow tube connecting the oral cavity to the
stomach (separated from the trachea by the
epiglottis)
• Food is mixed with saliva and then is moved in a
bolus via the action of peristalsis
Stomach
• A temporary storage tank where food is mixed
by churning and protein digestion begins
• It is lined by gastric pits that release digestive
juices, which create an acidic environment (pH ~2)
Small Intestine
• A long, highly folded tube where usable food
substances (nutrients) are absorbed
• Consists of three sections - the duodenum.
jejunum and ileum
Large Intestine
• The final section of the alimentary canal, where water and dissolved minerals (i.e. ions) are
absorbed
• Consists of the ascending / transverse /
descending / sigmoidal colon, as well as the
rectum
*Salivary Glands
• Release saliva to moisten food and contains
enzymes (e.g. amylase) to initiate starch
breakdown
• Salivary glands include the parotid gland,
submandibular gland and sublingual gland
Pancreas
• Produces a broad spectrum of enzymes that
are released into the small intestine via the
duodenum
• Also secretes certain hormones (insulin,
glucagon), which regulate blood sugar
concentrations
*Liver
• Takes the raw materials absorbed by the small
intestine and uses them to make key chemicals
• Its role includes detoxification, storage, metabolism, bile production and haemoglobin
breakdown
Gall Bladder
• The gall bladder stores the bile produced by the
liver (bile salts are used to emulsify fats)
• Bile stored in the gall bladder is released into
the small intestine via the common bile duct
6.1 Application:
Explain the use of
dialysis tubing to
model absorption
of digested food in
the intestine.
Dialysis tubing models the size-specific
permeability of cell membranes.
-large molecules (e.g. starch) cannot pass through
the tubing
-smaller molecules (such as maltose) can cross
-these properties mimic the wall of the gut, which
is also more permeable to small rather then large
particles.
**dialysis tubing is not selectively permeable
based on charge (ions can freely cross)
Dialysis tubing can be used to model absorption
by passive diffusion and by osmosis.
Experiment to measure:
-meniscus levels in the tube
-amylase digests starch into maltose -> increase in
concentration
-water will move into the tubing via osmosis
(towards the solute) causing the meniscus level to
rise
-measuring maltose diffusion (without the use of
tubes)
-amylase digests the starch into maltose
-make it small enough to diffuse out of the tubing
and into the beaker
-presence of maltose can be detected using Benedict’s reagent or glucose indicator strips
6.1 Skill:
Identification of
tissue layers in
transverse sections
of the small
intestine viewed
with a microscope
or in a micrograph.
Outline the function
of the four layers of
tissue found in the
wall of the small
intestine.
The small intestine is composed of four main
tissue layers, which are (from outside to centre):
serosa:
-outermost protective layer covering composed
of a layer of cells reinforced by fibrous
connective tissue
muscle layer:
-outer layer of longitudinal muscle (peristalsis)
-inner layer of circular muscle (segmentation)
submucosa:
-contains blood and lymph vessels that carry
away absorbed materials
-composed of connective tissue separating the
muscle laver from the innermost mucosa
mucosa:
-lines the lumen of the small intestine
-a highly folded inner layer which absorbs
material through its surface epithelium from the
intestinal lumen
6.2 Explain the
structure of arteries
in relation to its
function.
• Arteries convey blood at high pressure from the
ventricles -> tissues of the body
D
• Arteries have muscle cells and elastic fibres in
their walls to accomplish blood transfer
-thick walls to withstand high pressure/maintain
blood flow/pressure;
-collagen fibres/elastic fibres/connective tissue
(in outer layer) give wall strength/flexibility/ability
to STRETCH and RECOIL;
-(smooth) muscle layer (contracts) to maintain
pressure;
-narrow lumen maintains high pressure;
-many muscle fibres to help pump blood;
many elastic fibres to stretch and pump blood
after each heart beat;
-no valves as pressure is high enough to prevent
backflow;
-endothelium/smooth inner lining to reduce
friction for efficient transport;Their recoil helps
propel the blood down the artery.
6.2 Explain how the
muscle and elastic
fibres assist in
maintaining blood
pressure between
pump cycles.
blood: heart -> ventricular contraction -> arteries
-muscle and elastic fibres assist in maintaining the
high pressure between pumps
Muscle fibres:
-form a rigid arterial wall that is capable of
withstanding the high blood pressure
-contract to narrow the lumen -> increases the
pressure between pumps and helps to maintain
blood pressure throughout the cardiac cycle
Elastic fibres:
-allow the arterial wall to stretch and expand
upon the flow of a pulse through the lumen
-the pressure exerted on the arterial wall is
returned to the blood when the artery returns to
its normal size (elastic recoil)
-their recoil helps propel the blood down the
artery.
-elastic recoil helps to push the blood forward
through the artery as well as maintain arterial
pressure between pump cycles
6.2 Explain the
function of
capillaries and their
features.
-the function of capillaries is to exchange
materials between the cells in tissues and blood
travelling at low pressure
-artery -> arterioles -> capillaries
**ensures blood is moving slowly and all cells are
located near a blood supply; maximizes material
exchange
-higher hydrostatic pressure at the arteriole end
of the capillary forces material from the
bloodstream into the tissue fluid
-lower hydrostatic pressure at the venule end of
the capillary allows materials from the tissues to
enter the bloodstream
-capillaries -> venules -> larger veins
Features:
-capillaries’ walls thin/one cell thick for better
diffusion; (do not accept membranes)
-small diameter/narrow lumen to fit into small
places/between cells;
-small diameter for greater surface area for
molecular exchange;
-pores between cells of the walls so plasma can
leak out:
-pores between cells of the walls allow
phagocytes/immune components to enter tissues;
-only one red blood cell allowed to pass at a time
for efficient oxygen uptake;
-extensive branching increases surface area for exchange of materials;
6.2 Explain the
function of veins
and its features.
-function of veins is to collect the blood from the
tissues and convey it at low pressure to the atria
of the heart
-arteries -> capillaries -> veins -> heart -> begin
another pumping cyles
-high pressure -> low pressure
Features:
-thin walls allow (skeletal) muscles to exert
pressure on veins;
-thin outer layer of collagen/elastic/muscle fibres provide structural support;
-wide lumen allows great volume of blood to
pass; to maximise blood flow for more effective
return:
-valves prevent backflow;
6.2 Skill:
Identification of
blood vessels as
arteries, capillaries
or veins from the
diameter, thickness
of wall, muscles,
and the number of
layers.
Diameter: ‘
veins > arteries > capillaries
Thickness of wall:
arteries > veins > capillaries
Muscles & Elastic Fibres:
arteries > veins > capillaires (none)
Number of layers
arteries = veins (3 layers) > capillaries (only 1)
6.2 Explain the
blood circulation of
lungs
There is a separate circulation for the lungs
-there are two sets of atria and ventricles in heart
because there are two distinct locations for blood
transport
-left side of the heart pumps oxygenated blood
around the body (systemic circulation)
-right side of the heart pumps deoxygenated
blood to the lungs (pulmonary circulation)
-the left side of the heart will have a much thicker
muscular wall (myocardium) as it must pump
blood much further
6.2 Skill:
Recognition of the
chambers and
valves of the heart
and the blood
vessels connected
to it in dissected
hearts or in
diagrams of heart
structure.
Chambers:
-two atria (singular = atrium) - smaller chambers
near top of heart that collect blood from body
and lungs
-two ventricles - larger chambers near bottom of
heart that pump blood to body and lungs
Heart Valves:
-atrioventricular valves (between atria and
ventricles) - bicuspid valve on left side ; tricuspid
valve on right side -semilunar valves (between
ventricles and arteries) - aortic valve on left side ;
pulmonary valve on right side
Blood Vessels:
-vena cava (inferior and superior) feeds into the
right atrium and returns deoxygenated blood
from the body
-pulmonary artery connects to the right ventricle
and sends deoxygenated blood to the lungs
-pulmonary vein feeds into the left atrium and
returns oxygenated blood from the lungs
-aorta extends from the left ventricle and sends
oxygenated blood around the body
6.2 Explain the
presence of heart
beat.
-the sinoatrial node acts like a pace maker
(cardiac cells act in unison)
-the signal for a heart beat is initiated by the heart
muscle cells (cardiomyocytes) rather than from
brain signals
-sends out an electrical signal that stimulates
contraction
-it is propagated through the walls of the atria
and then the walls of the ventricles
-a specialised cluster of cardiomyocytes which
direct the contraction of heart muscle tissue
sinoatrial node (SA)
-stimulates atria to contract:
-stimulates another node at the junction between
the atrium and ventricle
-the atrioventricular node (AV node) sends signals
down the septum via a nerve bundle (Bundle of
His)
-Bundle of His innervates nerve fibres in the
ventricular wall, causing ventricular contraction
-(autonomic) nerves can alter the pace;
-(by secretion of) epinephrine/ adrenaline/
norepinephrine/noradrenaline increase the pace;
- (by secretion of) acetylcholine reduces the pace;
-adrenal glands release epinephrine/adrenaline; carried by blood to heart; to increase pace;
-sequence of events ensures there is a delay
between atrial and ventricular contractions,
resulting in two heart sounds
-delay allows time for the ventricles to fill with
blood following atrial contractions so as to
maximise blood flow
6.2 Explain the
changes in heart
rate
The heart rate can be increased or decreased by
impulses brought to the heart through two nerves
from the medulla of the brain.
**nerve signals from the brain can trigger rapid
changes, while endocrine signals can trigger more
sustained changes
blood pressure levels/[CO2] (blood pH) ->
changes in heart rate:
-when exercising, more CO2 is present in the
blood a nerve signal is sent to the sinoatrial node
to speed up the heart rate.
-when CO2 levels fall the vagus nerve reduces
heart rate.
Two nerves connected to the medulla regulate
heart rate by either speeding it up or slowing it
down:
-the sympathetic nerve releases the
neurotransmitter noradrenaline (a.k.a.
norepinephrine) to increase heart rate
-the parasympathetic nerve (vagus nerve)
releases the neurotransmitter acetylcholine to
decrease heart rate
6.2 Explain the
function of
epinephrine
Epinephrine (or adrenaline) is a hormone
increases the heart rate to prepare for vigorous
physical activity.
-released from adrenal glands
-increases heart rate by activating the same
chemical pathways as the neurotransmitter
noradrenaline
6.2 Application:
Explain the pressure
changes in different
areas of the heart
during the cardiac
cycle
-cardiac cycle is comprised of a period of
contraction (systole) and relaxation (diastole)
Systole:
-blood returning -> atria and ventricles (because)
the pressure in them is lower due to low volume
of blood)
-atriums are ~70% full -> atrial systole -> increasing
pressure in the atria -> forcing blood into
ventricles
-ventricles systole -> ventricular pressure exceeds
atrial pressure -> AV valves close to prevent back
flow (first heart sound)
-both sets of heart valves closed, pressure rapidly
builds in the contracting ventricles
-ventricular pressure exceeds blood pressure in
the aorta -> aortic valve opens -> blood is
released into the aorta
Diastole
-blood exits the ventricle and travels down the
aorta, ventricular pressure falls
-ventricular pressure drops below aortic pressure
-> aortic valve closes to prevent back flow
(second heart sound)
-ventricular pressure drops below the atrial
pressure -> the AV valve opens -> blood can flow
from atria to ventricle
-aortic pressure remains quite high as muscle and elastic fibres in the artery wall maintain blood
pressure
6.2 Application:
Explain the causes
and consequences
of occlusion of the
coronary arteries.
Atherosclerosis is the hardening and narrowing of
the arteries due to the deposition of cholesterol.
-atheromas develop in the arteries and
significantly reduce the diameter of the lumen
-restricted blood flow increases pressure in the
artery, leading to damage to the arterial wall
(from shear stress)
**blood pumped through the heart is at high
pressure and cannot be used to supply the heart
muscle with oxygen and nutrients
-damaged region is repaired with fibrous tissue •
reduces the elasticity of the vessel wall
-smooth lining of the artery is progressively
degraded, lesions form called atherosclerotic
plaques
-plaque ruptures -> blood clotting -> thrombus ->
restricts blood flow
-thrombus is dislodged it becomes an embolus
and can cause a blockage in a smaller arteriole
-if a coronary artery becomes completely
blocked, an acute myocardial infarction (heart
attack) will result
-typically treated by by-pass surgery or creating a stent (e.g. balloon angioplasty)
Risk Factors:
Age - Blood vessels become less flexible with
advancing age
Genetics - Having hypertension predispose
individuals to developing CHD
Obesity - Being overweight places an additional
strain on the heart
Diseases - Certain diseases increase the risk of
CHD (e.g. diabetes)
Diet - Diets rich in saturated fats, salts and alcohol
increases the risk
Exercise - Sedentary lifestyles increase the risk of
developing CHD
Sex - Males are at a greater risk due to lower
estrogen levels
Smoking - Nicotine causes vasoconstriction,
raising blood pressure
6.2 Application:
Explain William
Harvey’s discovery
of the circulation of
the blood with the
heart acting as the
pump.
-our modern understanding of circulatory system
is based upon the discoveries of 17th century
English physician, William Harvey
Based on some simple experiments and
observations, Harvey instead proposed that:
-blood flow through large vessels is
unidirectional, with valves to prevent backflow.
-arteries and veins were part of a single
connected blood network
**he did not predict the existence of capillaries
however
-arteries pumped blood from the heart (to the
lungs and body tissues)
-veins returned blood to the heart (from the lungs
and body tissues)
- also showed that the rate of flow through major
vessels was far too high for blood to be
consumed in the body after being pumped our by
the heart, as earlier theories proposed.
-it must therefore return to the heart and be
recycled.
Some of the experiments include:
-fish hearts having their veins tied. The hearts
emptied of blood, then refilled when the tie was removed.
-blood was shown flowing towards the heart in
veins of a human arm.
-calculations of blood volume and pulse rates
showed that huge volumes of blood were leaving
the heart
6.3 Describe the
first line of defense.
The skin and mucous membranes form a primary
defence against pathogens that cause infectious
disease.
Skin:
-protects external structures when intact (outer
body areas)
-dry, thick and tough region composed
predominantly of dead surface cells
-(skin/stomach) acid prevents growth of many
pathogens;
Sebaceous glands (on skin):
-associated with hair follicles
-secrete sebum and enzymes which inhibit
microbial growth on skin (by lowering pH level)
-secretes lactic acid and fatty acids to lower the
pH (skin pH is roughly ~ 5.6 - 6.4 depending on
body region); inhibits growth of bacteria and fungi
Mucous Membranes:
-protects internal structures (i.e. externally
accessible cavities and tubes - such as the
trachea, esophagus and urethra)
-can be found in nasal passages and other
airways, the head of the penis and foreskin and
the vagina.
-a thin region of living surface cells that release
fluids to wash away pathogens (mucus, saliva, tears, etc.)
-secretes a sticky solution of glycoproteins, which
traps pathogens and harmful particles and either
swallow or expels it
-lysozyme in mucus can kill bacteria;
-ciliated to aid in the removal of pathogens (along
with physical actions such as coughing / sneezing)
-inflammatory response/inflammation can cause
swelling/redness/fever (to inhibit the pathogen);
6.3 Explain the
cascade of events
that occur in blood
clotting.
Cuts in the skin are sealed by blood clotting;
clotting factors are released from platelets.
-prevent blood loss
-limit pathogenic access to the bloodstream when
the skin is broken
-clotting factors cause platelets to become sticky
and adhere to the damaged region to form a
solid plug
-localised vasoconstriction reduces blood flow
through the damaged region
The cascade results in the rapid conversion of
fibrinogen to fibrin by thrombin.
-clotting factors trigger the conversion of the
inactive zymogen prothrombin into the activated
enzyme thrombin
-thrombin catalyses the conversion of the soluble
plasma protein fibrinogen into an insolube fibrous
form called fibrin
-fibrin strands form a mesh of fires around the
platelet plug and traps blood cells to form a
temporary clot
6.3 Application:
Explain the causes
and consequences
of blood clot
formation in
coronary arteries.
Consequences:
the occlusion of a coronary artery by a blood clot
may lead to an acute myocardial infarction (heart
attack)
Causes:
-blood clots form when the vessels are damaged
as a result of the deposition of cholesterol
-aheromas (fatty deposits) develop in the arteries
and significantly reduce the diameter of the lumen
–atherosclerosis
-restricted blood flow increases pressure in the
artery, leading to damage to the arterial wall
(from shear stress)
-damaged region is repaired with fibrous tissue
which significantly reduces the elasticity of the
vessel wall
-smooth lining of the artery is progressively
degraded, lesions form - atherosclerotic plaques
-plaque ruptures -> blood clotting -> forms
thrombus -> restricts blood flow
-thrombus is dislodged it becomes an embolus
and can cause a blockage in a smaller arteriole
-coronary occlusion
-damage to the capillary epithelium
-hardening of arteries
-rupture of atheroma
Factors that are correlated with an increased risk
of coronary thrombosis:
-smoking
-high blood cholesterol concentration
-high blood pressure
-diabetes
-obesity
-lack of exercise
6.3 Explain the
second line of
defence against
infectious disease
It is the innate immune system: non-specific in its
response.
-non-specific
-non-adaptive
-main component: phagocytic white blood cells
that engulf and digest foreign bodies
-other components: inflammation, fever and
antimicrobial chemicals
Ingestion of pathogens by phagocytic white
blood cells gives non-specific immunity to
disease
Phagocytes
-solid materials (such as pathogens) are ingested
by a cell (i.e. cell ‘eating’ via endocytosis)
-phagocytic leukocytes (WBC) circulate in the
blood and move into the body tissue freely in
response to infection
-damaged tissues release chemicals (e.g
histamine) which draw white blood cells to the site
of infection
-extensions surround the pathogen and then fuse
to form an internal vesicle
-vesicle is then fused to a lysosome and the
pathogen is digested
-antigens (fragments from pathogens) may be
presented on the surface of the phagocyte in order to stimulate the third line of defence
6.3 Explain how the
immune system can
be adaptive
Production of antibodies by lymphocytes in
response to particular pathogens gives specific
immunity
-differentiate between particular pathogens and
target a response that is specific to a given
pathogen
-respond rapidly upon re-exposure to a specific
pathogen, preventing symptoms from developing
(immunological memory)
Lymphocytes
-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
-helper T cells then release cytokines to activate
the particular B cell capable of producing
antibodies specific to the antigen
-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
6.3 Describe what
cells antibiotics
target and explain
why
• Antibiotics block processes that occur in
prokaryotic cells but not in eukaryotic cells
-kill or inhibit the growth of microbes (specifically
bacteria) by targeting prokaryotic metabolism
including:
-key enzymes
-70S ribosomes
-components of the cell wall
-eukaryotic cells do not possess these features
-antibiotics will target the pathogenic bacteria
and not the infected host
-either kill the invading bacteria (bactericidal) or
suppress its potential to reproduce
(bacteriostatic)
• Viruses lack a metabolism and cannot therefore
be treated with antibiotics
-do not possess a metabolism and instead take
over the cellular machinery of infected host cells
-they cannot be treated with antibiotics and must
instead be treated with specific antiviral agents
6.3 Explain
antibiotics
resistance, its
causes, and
solutions.
• Some strains of bacteria have evolved with
genes that confer resistance to antibiotics and
some strains of bacteria have multiple resistance
-confer resistance by encoding traits that:
-degrade the antibiotic
-block its entry
-increase its removal
-alter the target
-resistant strains of bacteria can proliferate very
quickly following the initial mutation
-can be passed to susceptible strains via bacterial
conjugation (horizontal gene transfer)
The prevalance of resistant bacterial strains is
increasing rapidly with human populations due to
a number of factors:
-over-prescribed (particularly broad-spectrum
drugs) or misused (e.g. given to treat a viral
infection)
-many are freely available without a prescription
and certain antibiotics
-commonly included in livestock feed
-multi-drug resistant bacteria are especially
common in hospitals
-an example of an antibiotic resistant strain of
bacteria is Golden Staph (MRSA - Methicillin Resistant Staphylococcus aureus)
Solutions:
-doctors prescribing antibiotics only for serious
bacterial infections
-patients completing courses of antibiotics to
eliminate infections completely
-hospital staff maintaining high standards of
hygiene to prevent cross-infection
-farmers not using antibiotics in animal feeds to
stimulate growth
Pharmaceutical companies developing new types
of antibiotics - no new types have been
introduced since the 1980s
6.3 Application:
Describe Florey and
Chain’s experiments.
-Florey and Chain’s team developed a method of
growing the fungus Penicillium in liquid culture
-also developed methods for producing
reasonably pure samples of penicillin from the
cultures
-the penicillin killed bacteria on agar plates, but
they needed to test whether it would control
bacterial infections in humans.
Florey and Chain conducted experiments to test
penicillin on bacterial infections in mice.
-8 mice were injected with hemolytic streptococci
and four of these mice were subsequently
injected with doses of penicillin
-untreated mice died of bacterial infection
-those treated with penicillin all survived
demonstrating its antibiotic potential
-Florey and Chain decided that they should next
do tests on human patients, which required much
larger quantities.
-when enough penicillin had been produced, a
43-year-old policeman was chosen for the first
human test.
-he had an acute and life-threatening bacterial
infection causes by a scratch on the face from a
thorn on a rose bush.
-he was given penicillin for four das and his condition improved considerably, but supplies of
penicillin ran out and he suffered a relapse and
died from the infection.
-larger quantities of penicillin were produced and
five more patients with acute infections were
tested.
All were cured of their infections, but sadly one of
them died.
6.3 Application:
Explain the effects
of HIV on the
immune system and
methods of
transmission.
HIV infects helper T cells, disabling the body’s
adaptive immune system
-causes a variety of symptoms and infections
collectively classed AIDS
Effects of HIV:
-infection -> virus undergoes a period of inactivity
(clinical latency) during which infected helper T
cells reproduce
-the virus becomes active again and begins to
spread, destroying the T lymphocytes in the
process
-reduction in the number of helper T cells ->
antibodies are unable to be produced -> lowered
immunity
-body becomes susceptible to opportunistic
infections, eventually resulting in death if the
condition is not managed
Transmission of HIV:
-through the exchange of body fluids (including
unprotected sex, blood transfusions,
breastfeeding, etc.)
-HIV through sexual contact can be minimised by
using latex protection (i.e. condoms)
-HIV is a global issue, but is particularly prevalent
in poorer nations with poor education and health
systems
6.4 Explain the
purpose of
ventilation.
• Ventilation maintains concentration gradients of
oxygen and carbon dioxide between air in alveoli
and blood flowing in adjacent capillaries.
**because gas exchange is actually passive!
-02 consumed by cells during cellular respiration
-carbon dioxide produced as a waste product
-02 is constantly being removed from the alveoli
into the bloodstream (and CO2 is continually
being released)
-lungs function continually cycles fresh air into the
alveoli from the atmosphere
-02 levels must stay high in alveoli (and diffuse
into the blood) and CO2 levels stay low (and
diffuse from the blood)
-the lungs are also structured to have a very large
surface area, so as to increase the overall rate of
gas exchange
6.4 Identify and
explain the
structure and
function of cells
that line the alveoli
in relation to how it
aids in ventilation.
There are two types of alveolar cells - type I
pneumocytes and type Il pneumocytes
• Type I pneumocytes are extremely thin alveolar
cells that are adapted to carry out gas exchange.
Function:
-involved in the process of gas exchange
between the alveoli and the capillaries
Structure:
-flattened in shape to minimise diffusion distance
for respiratory gases
-connected by occluding junctions, which
prevents the leakage of tissue fluid into the
alveolar air space
-amitotic and unable to replicate
-type I pneumocytes are amitotic and unable to
replicate, however type II cells can differentiate
into type I cells if required
• Type I pneumocytes secrete a solution
containing surfactant that creates a moist surface
inside the alveoli to prevent the sides of the
alveolus adhering to each other by reducing
surface tension
Structure:
-cuboidal in shape and possess many granules (for storing surfactant components)
-provides an area from which carbon dioxide can
evaporate into the air and be exhaled.
Function:
-responsible for the secretion of pulmonary
surfactant
-create a moist surface -> easier for oxygen to
diffuse across the alveolar and capillary
membranes when dissolved in liquid -> reduces
surface tension
-type I pneumocytes secrete a liquid known as
pulmonary surfactant which reduces the surface
tension in alveoli
-surface tension is the elastic force created by a
fluid surface that minimises the surface area (via
cohesion of liquid molecules)
-as an alveoli expands with gas intake, the
surfactant becomes more spread out across the
moist alveolar lining
-this increases surface tension and slows the rate
of expansion, ensuring all alveoli inflate at roughly the same rate
6.4 Explain how air
travels in the
respiratory system
• Air is carried to the lungs in the trachea and
bronchi and then to the alveoli in bronchioles
-enters the respiratory system through the nose
or mouth and passes through the pharynx to the
trachea
-trachea -> divides into two bronchi (singular:
bronchus) -> connect to the lungs
-right lung is composed of three lobes, while the
left lung is only comprised of two (smaller due to
position of heart)
-bronchi divide into many smaller airways called
bronchioles, greatly increasing surface area
-bronchiole terminates with a cluster of air sacs
called alveoli, where gas exchange with the
bloodstream occurs
nostrils > nasal cavity > pharynx > larynx >
trachea >
bronchi (with cartilaginous rings) > bronchioles
(without cartilage) > alveoli.
6.4 Skill: Draw an
annotated diagram
showing the
structure of an
alveolus and an
adjacent capillary.
-have a very thin epithelial layer (one cell thick) to
minimise diffusion distances for respiratory gases
-surrounded by a rich capillary network to
increase the capacity for gas exchange with the
blood
-roughly spherical in shape, in order to maximise
the available surface area for gas exchange
-internal surface is covered with a layer of fluid,
as dissolved gases are better able to diffuse into
the bloodstream
6.4 Explain how
muscle contractions
play a role in
ventilation.
• Muscle contractions cause the pressure changes
inside the thorax that force air in and out of the
lungs to ventilate them.
-external intercostal contract -> rise in ribcage
-diaphragm contracts to make space in thorax
-pressure in the chest < atmospheric pressure, air
will move into the lungs (inspiration)
-internal intercostal contract -> lower in ribcage
-diaphragm relaxes
-abdominal muscles contract to force air out
-when the pressure in the chest > atmospheric
pressure, air will move out of the lungs
(expiration)
• Different muscles are required for inspiration
and expiration because muscles only do work
when they contract.
-muscles that increase the volume of the chest
cause inspiration (as chest pressure is less than
atmospheric pressure)
-muscles the decrease the volume of the chest
cause expiration (as chest pressure is greater than
atmospheric pressure)
6.4 Application:
Explain the causes
and consequences
(symptoms) of lung
cancer.
Lung cancer describes the uncontrolled
proliferation of lung cells, leading to the
abnormal growth of lung tissue (tumour)
-the tumours can remain in place (benign) or
spread to other regions of the body (malignant)
-lungs possess a very rich blood supply,
increasing the likelihood of the cancer spreading
(metastasis) to other body regions
Symptoms:
-difficulties with breathing
-persistent coughing
-include coughing up blood, wheezing,
respiratory distress and weight loss
-loss of appetite, weight loss
-general fatigue
-if the cancer mass compresses adjacent organs it
can cause:
-chest pain, difficulty swallowing and heart
complications
Causes:
-smoking: contains many mutagenic chemicals. As
every cigarette carries a risk, the incidence of
lung cancer increases with the number smoked
per day
-air pollution: sources of air pollution that are
most significant are diesel exhaust fumes, nitrogen oxides from all vehicle exhaust fumes and smoke
from fossil fuels
-radon gas causes (a radioactive gas that leaks
out of certain rocks such as granite). It
accumulates in badly ventilated buildings and
people then inhale it.
-certain infections
-genetic predispositions
6.4 Explain the
causes and
consequences of
emphysema
-degradation of the alveolar walls can cause
holes to develop and alveoli to merge into huge
air spaces (pulmonary bullae)
-damage to lung tissue leads to the recruitment of
phagocytes to the region, which produce an
enzyme called elastase
-this elastase, released as part of an inflammatory
response, breaks down the elastic fibres in the
alveolar wall
-loss of elasticity results in the abnormal
enlargement of the alveoli -> lower total surface
area for gas exchange
Cause:
-smoking: the chemical irritants in cigarette smoke
damage the alveolar walls
-a small proportion of emphysema cases are due
to a hereditary deficiency in this enzyme inhibitor
due to a gene mutation
Symptoms:
-shortness of breath
-expansion of the ribcage
-cyanosis and
-increased susceptibility to chest infections
-fatigue
-weezing
-chest tightness
-anxietv
6.4 Application:
Explain how
inspiration (inhaling)
and expiration
(exhaling) are
controlled by
muscle groups.
• External and internal intercostal muscles, and
diaphragm and abdominal muscles are examples
of antagonistic muscle action.
-antagonistic means working oppositely - when
the inspiratory muscles contract, the expiratory
muscles relax (and vice versa)
Inspiration
-the diaphragm and external intercostals (plus
some accessory muscles)
-diaphragm muscles contract -> diaphragm flatten
-›increase the volume of the thoracic cavity
-External intercostals contract -> pulling ribs
upwards and outwards (expanding chest)
Expiration
-abdominal muscles and internal intercostals (plus
some accessory muscles)
-diaphragm relax -> diaphragm curves upwards
reduce the volume of the thoracic cavity
-Internal intercostal muscles contract, pulling ribs
inwards and downwards (reducing breadth of
chest)
-abdominal muscles contract and push the
diaphragm upwards during forced exhalation
6.4 Skill: Explain the
monitoring of
ventilation in
humans at rest and
after mild and
vigorous exercise.
(Practical 6)
Ventilation can either be monitored by:
-simple observation (counting number of breaths
per minute)
-simple apparatus
-data logging with a spirometer (recording the
volume of gas expelled per breath)
- chest belt and pressure meter (recording the
rise and fall of the chest)
Ventilation rate and tidal volume can be
measured by spirometer:
-involves measuring the amount (volume) and / or
speed (flow) at which air can be inhaled or
exhaled
-a device that detects the changes in ventilation
and presents the data on a digital display
-simplistic method is breathing into a balloon and
measuring the volume of air in a single breath
-volume of air can be determined by submerging
the balloon in water and measuring the volume
displaced (Iml = 1cm3)
6.5 Explain the
function of neurons
and its structure.
• Neurons are specialised cells that function to
transmit electrical impulses within the nervous
system.
Neurons contain:
-dendrites: short-branched fibres that convert
chemical information from other neurons or
receptor cells into electrical signals
-axon: an elongated fibre that transmits electrical
signals to terminal regions for communication with
other neurons or effectors
-soma: a cell body containing the nucleus and
organelles, where essential metabolic processes
occur to maintain cell survival
-myelin sheath: improves the conduction speed of
electrical impulses along the axon, but require
additional space and energy
-nervous system converts sensory information
into electrical impulses in order to rapidly detect
and respond to stimuli
6.5 Explain the
function for the
myelination of
nerve fibres.
• The myelination of nerve fibres allows for
saltatory conduction.
-myelin functions as an insulating layer
-the main purpose of the myelin sheath is to
increase the speed of electrical transmissions via
saltatory conduction
-allows nerve impulse to jump across gaps in the
myelin sheath called the nodes of Ranvier and
jump from node to node
6.5 Explain how
neurons generate a
resting potential.
• Neurons pump sodium and potassium ions
across their membranes to generate a resting
potential.
-resting potential is the difference in charge
across the membrane when a neuron is not firing
-the inside of the neuron is more negative relative
to the outside in resting potential
The maintenance of a resting potential is
controlled by sodium-potassium pumps –active
process:
-expels 3 Na+ ions for every 2 K+ ions admitted
(additionally, some K+ ions will then leak back out
of the cell)
-as there are more positively charged ions outside
of the cell and more negatively charged ions
inside the cell - electrochemical gradient
-requires hydrolysis of ATP
6.5 Describe an
action potential.
-action potentials are the rapid changes in charge
across the membrane that occur when a neuron is
firing
• An action potential consists of depolarization
and repolarization of the neuron (in between has
a refractory period)
Depolarisation
-a sudden change in membrane potential - usually
from a (relatively) negative to positive internal
charge
-in response to a signal initiated at a dendrite,
sodium channels open within the membrane of the
axon
-as Na+ ions are more concentrated outside of the
neuron, the opening of sodium channels causes a
passive influx of sodium
-the influx of sodium causes the membrane
potential to become more positive
(depolarisation)
Repolarisation
-the restoration of a membrane potential
following depolarisation (i.e. restoring a negative
internal charge)
-influx of sodium, potassium channels open within
the membrane of the axon
-K+ ions are more concentrated inside the neuron, opening potassium channels causes a passive
efflux of potassium
-efflux of potassium causes the membrane
potential to return to a more negative internal
differential (repolarisation)
Refractory Period
-the period of time following a nerve impulse
before the neuron is able to fire again
-normal resting state: sodium ions are
predominantly outside the neuron and potassium
ions mainly inside (resting potential)
-ionic distribution is largely reversed (in de and
repolarization) so the resting potential must be
restored via the antiport action of the sodium-
potassium pump
6.5 Describe what
nerve impulses are.
• Nerve impulses are action potentials propagated
along the axons of neurons.
-nerve impulses are action potentials that move
along the length of an axon as a wave of
depolarisation
-depolarisation occurs when ion channels open
and cause a change in membrane potential
-ion channels that occupy the length of the axon
are voltage-gated (open in response to changes
in membrane potential)
-depolarisation at one point of the axon triggers
the opening of ion channels in the next segment
of the axon
-causes depolarisation to spread along the length
of the axon as a unidirectional ‘wave’
• Propagation of nerve impulses is the result of
local currents that cause each successive part of
the axon to reach the threshold potential.
-an action potential of the same magnitude will
always occur provided a minimum electrical
stimulus is generated
- threshold potential is the level required to open
voltage-gated ion channels
-if the threshold potential is not reached, an
action potential cannot be generated and hence the neuron will not fire
• A nerve impulse is only initiated if the threshold
potential is reached.
-threshold potentials are triggered when the
combined stimulation from the dendrites exceeds
a minimum level of depolarisation
-if the overall depolarisation from the dendrites is
sufficient to activate voltage-gated ion channels
in one section of the axon, the resulting
displacement of ions should be sufficient to
trigger the activation of voltage-gated ion
channels in the next axon section
6.5 Define synapses
• Synapses are junctions between neurons and
between neurons and receptor or effector cells.
-neurons transmit information across synapses by
converting the electrical signal into a chemical
signal
6.5 Outline the
release of chemical
signals in synaptic
cleft.
• When presynaptic neurons are depolarized they
release a neurotransmitter into the synapse
À
-neurotransmitters are released in response to the
depolarisation of the axon terminal of a
presynaptic neuron
-bind to receptors on post-synaptic cells and can
either trigger (excitatory) or prevent (inhibitory) a
response
6.5 Application:
Explain the
secretion and
reabsorption of
acetylcholine by
neurons at synapses
Acetylcholine: neurotransmitter
-released at neuromuscular junctions and binds to
receptors on muscle fibres to trigger muscle
contraction
-released within the autonomic nervous system to
promote parasympathetic responses (‘rest and
digest’)
-created in the axon terminal by combining
choline with an acetyl group (at cholinergic
synapses)
-stored in vesicles within the axon terminal until
released via exocytosis in response to a nerve
impulse
-activates a post-synaptic cell by binding to one
of two classes of specific receptor (nicotinic or
muscarinic)
-must be continually removed from the synapse,
as overstimulation can lead to fatal convulsions
and paralysis
-acetylcholine -> two component parts by the
synaptic enzyme acetylcholinesterase (AChE)
-either released into the synapse from the
presynaptic neuron or embedded on the
membrane of the post-synaptic cell
-liberated choline is returned to the presynaptic neuron where it is coupled with another acetate
to reform acetylcholine
6.5 Application:
Explain the blocking
of synaptic
transmission at
cholinergic
synapses in insects
and its
disadvantages.
-blocking of acetylcholine by the binding of
neonicotinoid pesticides to acetylcholine
receptors
-neonicotinoid pesticides cannot be broken down
by acetylcholinesterase -> permanent
overstimulation of target cells
-overstimulation results in fatal convulsions and
paralysis
-insects have a different composition of
acetylcholine receptors which bind to
neonicotinoids much more strongly
-more toxic to insects than mammals -> highly
effective pesticide
Disadvantages:
-linked to a reduction in honey bee populations
(bees are important pollinators within ecosystems)
-linked to a reduction in bird populations (due to
the loss of insects as a food source)
6.5 Skill: Analysis of
oscilloscope traces
showing resting
potentials and
action potentials.
-oscilloscopes are scientific instruments that are
used to measure the membrane potential across a
neuronal membrane
X axis: time (ms)
Y axis: membrane potential (mV)
A typical action potential will last for roughly 3 - 5
milliseconds and contain 4 key stages:
Resting potential: Before the action potential
occurs, the neuron should be in a state of rest
(approx. -70 mV)
Depolarisation: A rising spike corresponds to the
depolarisation of the membrane via sodium influx
(up to roughly +30 mV)
Repolarisation: A falling spike corresponds to
repolarisation via potassium efflux (undershoots
to approx. -80 mV)
Refractory period: The oscilloscope trace returns
to the level of the resting potential (due to the
action of the Na+/K+ pump)
**an action potential will only occur if the initial
depolarisation exceeds a threshold potential of
approximately -55 mV
6.6. Explain how
blood glucose
concentration is
controlled
• Insulin and glucagon are released by and a
cells of the pancreas to control blood glucose
concentration.
When blood glucose levels are high (e.g. after
feeding:
-insulin is released from beta (B) cells of the
pancreas and cause a decrease in blood glucose
concentration
May involve the following:
-(high blood glucose levels) detected by
pancreas islet cells/beta cells;
-stimulating glycogen synthesis in the liver
(glycogenesis) (glucose -> glycogen)
-promoting glucose uptake by the liver and
adipose tissue
-increasing the rate of glucose breakdown (by
increasing cell respiration rates)
-glucose converted to fatty acids/triglycerides/
fat;
-stimulates cells to absorb glucose;
**negative feedback process;
When blood glucose levels are low (e.g. after
exercise):
-glucagon is released from alpha (a) cells of the
pancreas and cause an increase in blood glucose concentration
May involve the following:
-stimulating glycogen breakdown in the liver
(glycogenolysis)
-conversion of polysaccharides/glycogen (in the
liver) to glucose
-promoting glucose release by the liver and
adipose tissue
-decreasing the rate of glucose breakdown (by
reducing cell respiration rates)
6.6 Application:
Explain the causes
and treatment of
Type I and Type Il
diabetes.
Type 1 diabetes: unable to produce insulin
Type 2 diabetes: failing to respond to insulin
production
Type l:
-occurs during early childhood
-caused by the destruction of beta cells
-insulin injections
Type 2:
-usually occurs during adulthood
-caused by the down regulation of insulin
receptors
-controlled by managing diet and lifestyle
6.6. Explain how
metabolic rate and
body temperature is
controlled and
regulated.
• Thyroxin is secreted by the thyroid gland to
regulate the metabolic rate and help control
body temperature
-primary role of thyroxin is to increase the basal
metabolic rate (amount of energy the body uses
at rest)
-achieved by stimulating carbohydrate and lipid
metabolism via the oxidation of glucose and fatty
acids
-increasing metabolic activity -> 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
-partially composed of iodine; a deficiency of
iodine in the diet -> decreased production of
thyroxin
-cold temp. -> hypothalamus -> thyroxin release ->
increased metabolic rate -> generate heat ->
increase in body temp.
6.6 Explain how the
inhibition of
appetite is
controlled by
hormones.
• Leptin is secreted by cells in adipose tissue and
act on the hypothalamus of the brain to inhibit
appetite
-the concentration of leptin in the blood is
controlled by food intake and the amount of
adipose tissue in the body.
-regulates fat stores within the body by
suppressing appetite
-leptin binds to receptors located within the
hypothalamus -> inhibit appetite
-overeating -> more adipose cells to formed ->
more leptin is produced -> suppressing further
appetite
-starvation -> reduction in adipose tissue -> less
leptin is released -> hunger
-obese people are constantly producing higher
levels of leptin -> body becomes progressively
desensitised to the hormone
-they are more likely to feel hungry, less likely to
recognise when they are full and are hence more
likely to overeat
-leptin resistance also develops with age,
increasing the potential for weight gain later in life
(e.g. the ‘middle-age spread’)
6.6 Applications:
Explain the testing
of leptin on patients
with clinical obesity
and reasons for the
failure to control
the disease.
-leptin was considered as a form of treatment for
individuals with clinical obesity
-leptin injections -> reduce hunger -> limit food
intake -> weight loss
Experiment shows that:
-most cases of obesity are caused by an
unresponsiveness to leptin and not a leptin
deficiency
-hence, very few participants experienced
significant weight loss in response to leptin
injections
-many patients did experience adverse side
effects from leptin injections, including skin
irritations
-leptin treatments are not considered to be an
effective way of controlling obesity
6.6 Explain how
circadian rhythms
are controlled by
hormones.
• Melatonin is secreted by the pineal gland to
control circadian rhythms
-secretion controlled by cells in the hypothalamus
called the suprachiasmatic nuceli (SCN)
-retina detects light -> sends signals to SCN->
sends signals to the pineal gland
-controls circadian rhythms/biological clocks «in
mammals»
-production is controlled by amount of light
detected by the retina
-produced by the pineal gland of the brain in
response to changes in light
-light exposure -> hypothalamus -> inhibits
melatonin secretion
-melatonin is secreted in response to periods of
darkness, resulting in higher concentrations at
night
-circadian rhythms are driven by an internal
circadian clock
-can also be modulated by external factors
-melatonin is responsible for synchronising
circadian rhythms and regulates the body’s sleep
schedule
**production/secretion is directly proportional to night time duration
-melatonin secretion is suppressed by bright light
(principally blue wavelengths)
-hence levels increase during the night
-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)
-affects «seasonal» reproduction/sleep-wake
cycles/jet lag
-melatonin levels naturally decrease with age,
leading to changes in sleeping patterns in the
elderly
6.6 Applications:
Explain the causes
of jet lag and
methods of
alleviation.
-alteration of circadian rhythm caused by the
body’s inability to rapidly adjust to a new time
zone following extended air travel (jet’ lag)
-pineal gland continues to secrete melatonin
according to the old time zone -> sleep schedule
is not synchronised to the new timezone
-symptoms of jet lag include fatigue, headaches,
lethargy, increased irritability and reduced
cognitive function
-jet lag should resolve as the body resynchronises
its circadian rhythm
-taking melatonin near the sleep time of the new
time zone can help recalibrate the body
-artificially increasing melatonin levels at the new
night time -> body can respond quicker to the
new day-night schedule
6.6 Explain the
development of
male characteristics.
• A gene on the Y chromosome causes embryonic
gonads to develop as testes and secrete testosterone
XX = female
XY = male
Y chromosomes is shorter than X chromosome
-Y chromosome includes a gene called the SRY
gene (Sex Determining Region Y) -> male
development
-SRY codes for a DNA-binding protein called TDF
(testis determining factor)
-TDF stimulates the expression of other genes that
cause testis development.
-SRY gene -> testis-determining factor (TDF) ->
embryonic gonads form into testes (male gonads)
-the testes produce testosterone to promote the
further development of male sex characteristics
-no TDF protein (i.e. no Y chromosome) -> ovaries
-produce estrogen and progesterone to promote
the development of female sex characteristics
6.6 Outline role of
testosterone in
prenatal
development of
male genitalia.
• Testosterone causes pre-natal development of
male genitalia and both sperm production and
development of male secondary sexual
characteristics during puberty.
-testes develop testosterone-secreting cells at an
early stage and these produce testosterone until
about the 15th week of pregnancy.
-during the weeks of secretion, testosterone
causes male genitalia to develop.
-testosterone = male reproductive hormone
-secreted by the testes
Functions:
-pre-natal development of male genitalia
-involved in sperm production following the onset
of puberty
-aids in the development of secondary sex
characteristics (including body hair, muscle mass,
deepening of voice, etc.)
-helps to maintain the male sex drive
6.6 Explain the
development of
female sexual
characteristics.
• Estrogen and progesterone cause pre-natal
development of female reproductive organs and
female secondary sexual characteristics during
puberty.
-main female reproductive hormones (secreted
by the ovaries) are estrogen and progesterone
Functions:
-promote the pre-natal development of the
female reproductive organs
-responsible for the development of secondary
sex characteristics (including body hair and breast
development)
-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
6.6 Explain how the
menstrual cycle is
controlled
The menstrual cycle is controlled by a complex interplay of hormones and feedback mechanisms between the brain, ovaries, and uterus. The two main hormones involved in controlling the menstrual cycle are follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are produced by the pituitary gland in the brain.
The menstrual cycle begins with the release of FSH, which stimulates the growth and development of follicles in the ovaries. As the follicles mature, they produce estrogen, which causes the lining of the uterus to thicken in preparation for a possible pregnancy.
When estrogen levels reach a certain threshold, the pituitary gland responds by releasing a surge of LH, which triggers ovulation – the release of an egg from the ovary. The egg then travels through the fallopian tube towards the uterus.
After ovulation, the remaining follicle transforms into the corpus luteum, which produces progesterone to prepare the uterus for a possible pregnancy. If the egg is fertilized by a sperm and implants in the uterus, the developing embryo produces human chorionic gonadotropin (hCG), which maintains the corpus luteum and keeps progesterone levels high.
If the egg is not fertilized, the corpus luteum eventually disintegrates, causing progesterone levels to drop and triggering the shedding of the uterine lining – menstruation. The cycle then begins again with the release of FSH.
Overall, the menstrual cycle is a complex and finely tuned process that is controlled by a delicate balance of hormones and feedback mechanisms. Any disruptions or imbalances in this system can lead to menstrual irregularities or fertility problems.
6.6 Application:
Explain the process
of IVF including
down-regulation,
superovulation.
harvesting,
fertilization and
implantation.
IF drugs to suspend the normal secretion of
hormones, followed by the use of artificial doses
of hormones to induce superovulation and
establish a pregnancy.
Down regulation
-drugs are used to halt the regular secretion of
FSH and LH -> stops the secretion of estrogen
and progesterone
-doctors can take control of the timing and
quantity of egg production by the ovaries
-typically delivered in the form of a nasal spray
Superovulation
-involves using artificial doses of hormones to
develop and collect multiple eggs from the
woman
-patient is firstly injected with large amounts of
FSH to stimulate the development of many
follicles
-follicles are then treated with hCG; a hormone
usually produced by a developing embryo
-CG stimulates the follicles to mature and the
egg is then collected (via aspiration with a
needle) prior to the follicles rupturing
Fertilisation
-extracted eggs are then incubated in the presence of a sperm sample from the male donor
-eggs are then analysed under a microscope for
successful fertilisation
Implantation
-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
6.6 Applications:
Explain William
Harvey’s
investigation of
sexual reproduction
in deer
Original soil and seed theory:
-male produces a ‘seed’ which forms an ‘egg’
when mixed with menstrual blood (the ‘soil’)
William Harvey tested Aristotle’s theory using a
natural experiment with deers:
-unable to detect a growing embryo until
approximately 6 - 7 weeks after mating had
occurred
-so concluded that Aristotle’s theory was
incorrect and that menstrual blood did not
contribute to the development of a fetus
-unable to identify the correct mechanism of
sexual reproduction and incorrectly asserted that
the fetus did not develop from a mixture of male
and female ‘seeds’
-Harvey failed to solve the mystery of sexual
reproduction because effective microscopes
were not available when he was working
-so fusion of gametes and subsequent embryo
development remained undiscovered at his time
6.6 Skill: Annotate
diagrams of the
male reproductive
system to show
names of structures
and their functions.
Testis:
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
Sperm Duct:
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)
6.6 Skill: Annotate
diagrams of the
female
reproductive
system to show
names of structures
and their functions.
Ovary:
where oocytes mature prior to release (ovulation)
- it also responsible for estrogen and
progesterone secretion
Fimbria:
a fringe of tissue adjacent to an ovary that sweep
an oocyte into the oviduct
Oviduct:
transports the oocyte to the uterus - it is also
typically where fertilisation occurs
Uterus:
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)
6.2 Blood is a liquid
tissue containing
glucose, urea,
plasma proteins and
other components.
List the other
components of
blood.
plasma/water;
dissolved gases / CO2 / 02;
erythrocytes / red blood cells;
leucocytes / white blood cells;
lymphocytes and phagocytes;
platelets;
hormones / named hormone(s);
amino acids / albumin / antibodies;
salts / minerals / ions other named solute in
plasma apart from glucose, urea and plasma
proteins;
6.2 Explain the roles
of the atria and
ventricles in the
pumping of blood.
-atria collect blood from veins (vena cava/
pulmonary);collect blood while ventricles are
contracting;
-atria pump blood into ventricles/ensure
ventricles are full:
-ventricles pump blood into arteries/out of the
heart;
-ventricles pump blood at high pressure because
of their thicker, muscular walls;
-mention of heart valves working with atria and
ventricles to keep blood moving;
-left ventricle pumps blood to systems and right
ventricle pumps blood to lungs;
Both left and right ventricles with correct function
required for mark to be awarded.
6.2 State molecules
transported by the
blood.
a. example of a nutrient e.g. glucose;
b. oxygen/02;
c. carbon dioxide/CO2;
d. nitrogen/N2;
e. hormones;
f. antibodies;
g. urea:
