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IB Biology

Further Human Physiology

Option H
Further Human Physiology

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Hormonal Control
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H
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1 State that hormones are chemical messengers secreted by endocrine glands into the blood and transported
to specific target cells
Hormones are chemical messengers secreted by endocrine glands into the blood and transported to specific target cells
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1
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g
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g
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g
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1
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1
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It receives information from
nerves and initiates endocrine responses through the posterior and anterior pituitary glands
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g
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g
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1
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Further Human Physiology

Neurosecretory cells in the hypothalamus synthesise ADH, transport it down their axons and store it in nerve
endings in the posterior pituitary gland

2
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If the blood plasma becomes too concentrated (i
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from excessive sweating), the neurosecretory cells transmit
impulses to the posterior pituitary

4
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ADH makes the collecting ducts more permeable to water by producing aquaporins, increasing water reabsorption
and a small volume of hypertonic urine

6
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This is negative feedback - when the blood plasma concentration rises,
mechanisms are put into place to drop it

8
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2
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These are all exocrine glands
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2
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2
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g
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2
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g
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2
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It is not removed by the digestive system and can be reused
2
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g
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E
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• Maltase is immobilised on the epithelial lining with its active site facing the intestinal lining
• It hydrolyses maltose into 2 glucose monomers, which can immediately be absorbed

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H
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6 Outline the reason for cellulose not being digested in the alimentary canal
Humans cannot digest cellulose (β-glucose) because:
1
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We do not have bacteria in the gut capable of digesting cellulose

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Cellulose is a component of plant cell walls
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H
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7 Explain why pepsin and trypsin are initially synthesised as inactive precursors and how they are
subsequently activated

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Pepsin and trypsin are protease enzymes (specifically endopeptidases) which hydrolyse peptide bonds in proteins
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They are
activated in the digestive tract where there is mucus to protect the cells
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2
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There is a strong correlation between stomach
ulcers and a bacteria called Helicobacter pylori (acid-tolerant bacteria)
• H
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Stomach cancers are tumours in the wall of the stomach
• May be due to prolonged presence of stomach ulcers
• This replaces the previous hypothesis of causation from stress
• There is a strong correlation between stomach cancers and H
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pylori is now controlled as a treatment for stomach ulcers

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H
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9 Explain the problem of lipid digestion in a hydrophilic medium and the role of bile in overcoming this
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Lipids are hydrophobic, therefore insoluble in the aqueous environment of the body
They coalesce to form larger droplets of fat (globule)
Lipase is water soluble so it can only hydrolyse lipids at the surface i
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water-lipid interface
The interior of the fat globule is inaccessible, making digestion normally very slow

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• Bile contains bile salts and pigments
• Bile salts have a hydrophobic and hydrophilic end
• The hydrophobic end attaches to the lipid and the hydrophilic end to water - this way, lipids are prevented from
attaching to each other
• This emulsifies the fat globule into smaller droplets, increasing surface area for lipase

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Hormonal Control
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H
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1 Draw and label a diagram showing a transverse section of the ileum as seen under a light microscope

IB Biology

Further Human Physiology

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H
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2 Explain the structural features of an epithelial cell of a villus as seen in electron micrographs, including
microvilli, mitochondria, pinocytotic vesicles and tight junctions
Structural feature

Function

Microvilli

• Increase surface area of the plasma membrane for greater absorption
• Membrane has channel proteins for hydrophilic substances

Mitochondria

• Large numbers provide ATP for active transport

Pinocytotic vesicles

• Formed by endocytosis, each vesicle contains fluid and dissolved food materials from the
ileum lumen
• Membranes of the vesicle contains channels and pumps
• Way to translocate digested foods

Tight junctions

• The plasma membrane of adjacent cells are firmly linked together, creating an
impermeable barrier
• Prevents nutrients from leaking between epithelium cells
• Keeps digestive fluids separate from tissue fluids and ensures a one way flow of food
materials

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H
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3 Explain the mechanisms used by the ileum to absorb and transport food, including facilitated diffusion,
active transport and endocytosis
Diffusion
• Lipids are absorbed by simple diffusion
• They pass easily through the hydrophobic centre of the plasma membrane

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Facilitated diffusion
• Channel proteins help hydrophilic food molecules pass through the hydrophobic parts of the phospholipid bilayer
• Water-soluble molecules (e
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fructose), minerals and vitamins are absorbed by facilitated diffusion

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Active transport
• Protein pumps in the plasma membrane hydrolyse ATP to move molecules against a concentration gradient
• Epithelial cells actively transport high concentrations of food into the cell, so it can freely diffuse into the
bloodstream
• Glucose, amino acids, minerals are absorbed by active transport

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Endocytosis
• The invagination of the plasma membrane to create an internal vesicle with extracellular materials
• The vesicles contain channel and pumps from the plasma membrane so digested foods can be absorbed from the
vesicle into the cytoplasm
• E
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large molecules like vitamin B12

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H
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4 List the materials that are not absorbed and are egested
Bile pigments
Epithelial cells of the intestinal lining
Lignin
Cellulose
Human flora and bacteria

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Functions of the Liver
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H
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1 Outline the circulation of blood through liver tissue, including the hepatic artery, hepatic portal vein,
sinusoids and hepatic vein
Circulation of blood
• The liver is divided into segments called lobules which contain liver cells called hepatocytes
• The hepatic artery brings oxygenated blood

IB Biology

Further Human Physiology

• The hepatic portal vein brings nutrients from the small intestine
• The hepatic artery and hepatic portal vein merge to form sinusoids where liver cells/hepatocytes store and regulate
nutrients
• The sinusoids drain into branches of the hepatic vein where the deoxygenated blood leaves

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Structure of sinusoids
• Single layer of cells
• Wider diameter than capillaries
• More porous than capillaries
• No basement membrane

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H
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2 Explain the role of the liver in regulating levels of nutrients in the blood
Substances in the blood needs to be kept within homeostatic limits to prevent damaging effects
• Glucose and salt levels can affect the osmotic concentration of blood
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The liver can
then regulate and maintain blood nutrient levels despite an irregular feeding frequency
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4
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H
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4 State that the liver synthesises plasma proteins and cholesterol
The liver synthesises plasma proteins (fibrinogen and albumin) and cholesterol (for bile)
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4
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g
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Hepatocytes absorb toxic
substances from the blood and converts them into non-toxic or less-toxic substances
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4
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4
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Inflammation - swelling of damaged liver tissue (hepatitis)
2
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Cirrhosis - scar tissue replaces normal liver tissue
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5
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1
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3
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Atrial systole
• Blood entering from veins will flow passively through the atria to the ventricles
• When the ventricles are ~70% full, the atria contracts to force the rest of the blood into the ventricles
Ventricular systole
• Both ventricles contract, causing a rapid increase of pressure in the ventricles and closes the AV valves, causing
the first heart sound (‘lub’)
• The increased pressure causes the semilunar valves to open and blood to pump into the arteries
Atrial diastole
• The atria relaxes as the ventricle contracts
• Blood enters the atria from the veins
Ventricular diastole

IB Biology

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Further Human Physiology

• As blood flows into the arteries, the pressure in the ventricles decrease
• When the pressure of the ventricle wall is lower than in the arteries, this causes arterial backflow, closing the
semilunar valves and causes the 2nd heart sound (‘dub’)
• When the pressure in the ventricles is lower than in the atria, the AV valves open and the cycle repeats

H
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2 Analyse data showing pressure and volume changes in the left atrium, left ventricle and the aorta, during
the cardiac cycle

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H
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3 Outline the mechanism that controls the heartbeat, including the roles of the SA node, AV node and
conducting fibres in the ventricular walls

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s
s
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s
s
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s
s
s
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s
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s
•
s

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The contraction of heart muscle is myogenic i
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the s s s
signal for cardial contraction arises within the heart s s s
muscle
The sinoatrial node (SAN) in the wall of the right atrium
initiates contraction of the cardiac muscle and acts as a s
pacemaker
It stimulates the atria to contract
Excitation is prevented from spreading to the ventricles s
by a layer of fibrous tissue - this creates a delay between
atria and ventricle contractions, causing maximum blood
flow
When excitation reaches the junction between atria and s
ventricles, it stimulates the atrioventricular node (AVN)
The AVN sends signals via the bundle of His to Purkinje
fibres, causing ventricular contractions
The ventricular contractions start at the bottom (apex) of
the heart to ensure blood is pushed up

• Nerves and hormones can influence and transmit messages to the pacemaker
- One nerve carries messages from the medulla of the brain to the pacemaker to speed up the beating of the heart
(sympathetic nerve)
- One nerve carries messages from the medulla of the brain to the pacemaker to slow down the beating of the heart
(parasympathetic nerve)
- Epinephrine (adrenaline) is carried to the pacemaker by the bloodstream and signals it to increase the beating of
the heart

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IB Biology

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Further Human Physiology

H
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4 Outline atherosclerosis and the cause of coronary thrombosis
• Atherosclerosis is the hardening and narrowing of the arteries due to the deposition of material known as plaque
• Damage to artery walls (e
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high blood pressure) causes chronic inflammation i
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phagocytes releasing growth
factors, leading to the accumulation of lipids, cholesterol, cell debris and calcium
• Fatty deposits can develop and reduce lumen diameter and elasticity of the artery wall needed for pulse flow
• Calcium salt deposits make it hard
• The rough surface causes the rupture of platelets
• This may lead to clots and blockages in the artery - if this happens in the coronary arteries (coronary thrombosis), it
may lead to a heart attack form lack of O2

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H
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5 Discuss factors that affect the incidence of coronary heart disease
Exercise - lack/too much exercise can cause strain
Genetics - having hypertensions (high blood pressure) or family history
Gender - males are more at risk due to low oestrogen levels
Smoking - nicotine raises blood pressure
Obesity - being overweight causes additional strain
Diet - too much saturated fats and cholesterol
Age - old age leads to less flexible blood vessels

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Gas Exchange
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H
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1 Define partial pressure
Partial pressure: The pressure exerted by a single type of gas when it is found within a mixture of gases
H
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2 Explain the oxygen dissociation curves of adult haemoglobin, fetal haemoglobin and myoglobin
Oxygen dissociation curves show the relationship between the partial pressure of oxygen and the percentage saturation
of oxygen carrying molecules
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e
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e
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e
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e
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6
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6
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e
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The lungs have low partial pressures of CO2, so oxygen tends to bind to
haemoglobin
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6
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6
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Causes:
• Allergens e
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pollen
• Pollutants
• Stress
• Dust Mites
• Cold air
• Exercise

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Effects:
• Reduced air flow due to swelling and mucus production
• Reduced ventilation and gas exchange
• Shortness of breath, chest tightness, wheezing and coughing

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H
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7 Explain the problem of gas exchange at high altitudes and the way the body acclimatises
At high altitudes, the partial pressure of oxygen is lower
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Mountain sickness can develop in people unaccustomed to these conditions, including
fatigue, nausea, breathlessness and headaches

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