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Topic 6 – Human Physiology

Digestion and Absorption
Digestion is the breakdown of large, insoluble food molecules into small, soluble compounds that can
be absorbed into the body
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Large molecules, particularly proteins, can stimulate an immune response
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The circular muscle constricts behind the food to
stop it going backwards
...

Enzymes break down food molecules into
monomers
...

Enzyme
Carbohydrase
Protease

Optimum pH
7
...

Chemical digestion – enzymes catalyse hydrolysis
reactions
Oesophagus: Carries food from the mouth to the
stomach
...

Stomach: Has an inner layer that produces
enzymes
...
Glands in the wall produce mucus which
prevents the stomach being digested by its own
enzymes
...
Inner walls are
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Topic 6 – Human Physiology
folded into villi, which have microvilli
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Large intestine: This absorbs water
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Rectum: Faeces are stored here before being removed via the anus by egestion
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Pancreas: This produces pancreatic juice, containing proteases, lipases, and amylases
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Fatty acids and glycerol move into the
lymphatic system through the lacteal (lymph)
...

The single layer epithelium creates a short
diffusion pathway for nutrients to cross so they
can enter the bloodstream more quickly
...


Simple Diffusion: Nutrients diffuse from a high to a low concentration through phospholipid
membranes and into the lacteal
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Active Transport: Movement of molecules from a low to a high concentration against the
concentration gradient
...

Endocytosis: The plasma membrane folds to form a vesicle
...
He showed that the heart pumps blood out into the arteries and that it returns in the veins
...
Red blood cells transport oxygen
and carbon dioxide in the blood, whereas white blood cells have a role in defence and immunity
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Topic 6 – Human Physiology

Blood Vessels

Blood Vessel
Arteries

Structure
Thick muscular walls
Elastic fibres

Smooth endothelium

Capillaries

Wall one cell thick
Gaps between cells
Narrow lumen
Smooth endothelium

Veins
Large lumen
Valves
Thin walls

Function
To withstand high pressure
Stretched by pulse and when
contract help to maintain blood
pressure
The blood flows both smoothly
and continuously without any
resistance
Reduced distance for diffusion
Helps diffusion of materials in
and out of the capillaries
Increases surface area
The blood flows both smoothly
and continuously without any
resistance
Reduces resistance to flow
Prevents backflow of blood
Allows veins to be squeezed
between muscles

The Heart
Humans have a double circulation system, which means blood passes through the heart twice in each
complete circulation
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2
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4
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6
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8
...

10
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12
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14
...
When a chamber contracts, the pressure inside it increases
...
Papillary
muscle and cardiac muscle are found in the heart
...

The atrioventricular valve opens when the pressure in the atrium is higher than in the ventricle and
closes when the pressure in the ventricle is higher than in the atrium
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Atrial and Ventricular Diastole

Right
Ventricle
Pulmonary
Artery

Right Atrium

Vena Cava

Lungs

Body

Pulmonary
Vein

Aorta

Left Atrium
Left Ventricle

Blood flows into the atria and there is low pressure in
the atria, helping to draw blood into the heart
...
As the ventricles
begin to relax, the semilunar valves close, causing the
second heart sound, ‘dub’
...
The
atria contract simultaneously, forcing the blood into
the ventricles
...
This causes the first heart sound, ‘lub’
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Topic 6 – Human Physiology
The sino-atrial node (found in the right atrium) is a pacemaker than regularly sends out nervous
impulses over the atria that stimulate the heart muscle so the atria contract
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Adrenaline can
speed the heart rate up during exercise
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Atheroma develops when
the endothelial layer of an artery is damaged
...
This builds up with deposits of connective tissue, cholesterol, and
dead muscle fibres to form a plaque which is called atheroma
...
A heart attack results if one of the coronary arteries becomes blocked
...
A consequence of this would be that an area of cardiac muscle receives no oxygen so it stops
beating in a coordinated way (heart attack)
...

Risk factors associated with CHD:
-

High blood pressure
Smoking (which causes high blood pressure)
High blood cholesterol
High sugar levels
Genetic factors

Defence Against Disease
A pathogen is a microorganism that causes a disease
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2
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4
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This helps platelets clot blood
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When the lysosomes attach to the
vesicle they release their enzymes
to digest the pathogen
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Antigens are proteins found on
the surface of all cells
...
They provoke an immune response
...
We
need a huge number of lymphocytes because one lymphocyte can only make one type of antibody
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Plasma cells are the activated lymphocytes that divide by mitosis to produce clones of each other
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Antibiotics are produced by microorganisms to kill pathogens
...
Antibiotics block metabolic processes in prokaryotic cells but not
in eukaryotic cells
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Alexander Fleming discovered penicillin, but Florey and Chain developed and tested it for treating
humans
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The four mice survived
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This research would not be permitted today because it is not safe and there would have to be lots of
animal testing before testing healthy humans
...
It can be transmitted through small cuts or tears in the
vagina, penis, mouth, or intestine during sex or by sharing hypodermic needles
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Gas exchange occurs when
oxygen moves into and carbon dioxide moves out of the blood over the surface of the alveoli
...
The external
intercostal muscles contract and the internal intercostal muscles relax, pulling the ribs upwards and
outwards and increasing the volume of the thorax
...
This decreases the pressure in the thorax, and air is forced into the lungs
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Abdominal muscles contract, pushing the
diaphragm into a dome shape
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Continual blood flow and ventilation
maintains a steep concentration gradient
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The layer of moisture eases diffusion
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Gases only
have to diffuse a very short distance to pass through them
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The fluid contains
surfactant to stop the sides of the alveoli sticking together by reducing surface tension
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Oxygen diffuses from the air in
the alveolus to the blood and carbon dioxide in the opposite direction
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The PNS is made up of sensory nerves that carry impulses to the CNS, and
motor nerves that carry nervous impulses away from the CNS
...
A response to a stimulus is a reflex and the pathway of
neurones involved in this are known as a reflex arc
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Dendrites provide a large surface area for multiple connections to other cells
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Ions can only be transported at the nodes of Ranvier
...

The Resting Potential / Polarisation
The outside of the axon is more positive than the inside due to distribution of ions
...
Ion channels in the membrane are closed during polarisation
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The difference in charge between the outside and inside is called the resting
potential
...
For an action potential to be produced, the stimulus has to reach a certain
threshold level
...

During an action potential, a section of the membrane becomes more permeable to sodium ions
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Topic 6 – Human Physiology
The inside of the axon becomes temporarily more positively charged in comparison to the outside
...
The wave of depolarisation travels along the
axon
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This is called repolarisation
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Sodium ions cannot enter but potassium ions can leave the axon by facilitated diffusion
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The
voltage
gated
potassium channel proteins
then close to allow the
membrane to return back to
its resting potential, which
is called repolarisation
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A nerve impulse travels down the presynaptic neurone and arrives at the synaptic knob
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The increase in calcium ions causes vesicles containing a neurotransmitter to move towards the
membrane
...
They
fuse with the membrane and release the
neurotransmitter, which diffuses across the
synaptic cleft and attaches to receptors with
complementary shapes on the post-synaptic
membrane
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A cholinergic synapse is a synapse that uses
acetylcholine
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Cholinesterase does not break down these pesticides so they stay there,
preventing acetylcholine from binding
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An embryo develops into a male or
a female depending on the presence of a single gene – SRY
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If this gene is present, TDF is produced and testes
develop
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Topic 6 – Human Physiology
Testosterone: It is produced by developing testes in the foetus and is responsible for developing the
male genitalia
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Oestrogen: It causes the development of female genitalia
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Progesterone: It prepares the uterus for implantation of an embryo
...
This is to release the egg ready for fertilisation and later for
implantation into the endometrium, which needs to be rich with blood vessels
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Follicle Stimulating Hormone: Released from the pituitary gland, it stimulates follicle development so
it secretes oestrogen
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Oestrogen: Released from the ovaries, it stimulates repair and growth of the endometrium and
release of LH
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Topic 6 – Human Physiology
1
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3
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5
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If progesterone and oestrogen levels remain high, it has an inhibitory effect and no more FSH
or LH is produced, so no more follicles develop
7
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Negative Feedback has a stabilising effect, e
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high levels of progesterone and oestrogen inhibit FSH
and LH
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In Vitro Fertilisation
IVF may be needed if a woman has blocked oviducts or a male has a low sperm count
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A drug is injected to stop the menstrual cycle
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2
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The man provides
semen and the eggs are mixed with it in a shallow dish
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A microscopic examination will show which eggs have been fertilised
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4
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A pregnancy test is done
to see if any embryos have implanted
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He dissected deer and examined the uterus
in mating season
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These
hormones only affect target organs
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Insulin and glucagon regulate blood
glucose levels
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Insulin is released from β cells in response
to an increase in blood glucose levels, so
it decreases the level back to normal by
activating enzymes, converting glucose to
glycogen (negative feedback)
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Insulin and glucagon bind to protein receptors in membranes
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Type I: Onset is usually during childhood
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Blood glucose levels have to be measured regularly and insulin
injections control levels of glucose
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Type II: Onset usually after childhood
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Low carbohydrate diets control it
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1
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Hypothalamus detects raised temperature
3
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Normal body temperature
OR
1
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Hypothalamus detects reduced body temperature
3
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4
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The target organ
for leptin is the hypothalamus
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Leptin has been trialled in human experiments
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8 patients receiving the highest dose of leptin lost weight compared to the placebo
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The results were
also varied and weight loss was soon regained
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Circadian rhythm is living in a 24-hour cycle
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Melatonin levels decrease with age so sleep becomes irregular
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Melatonin can be taken in
tablets to alleviate jet lag

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