How does it fit & what does it do?
Zoe
Anson
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Contents
1. Introduction
2. Cardiovascular
2.1 Basics…………………
2.2 Heart………………….
2.3 Arteries………………
2.4 Veins………………….
2.5
Capillaries…………..
3. Respiratory
3.1 Upper
Respiratory tract………………
3.2 Lower
Respiratory tract………………
3.3 Lungs………………………………………….
4. Nervous
4.1 Brain…………………………………………..
4.2 Nerves
and spinal cord……………….
4.3 Autonomic
nervous system…………
4.4 Eyes,
ears and skin………………………
5. Digestive
5.1 Upper GI……………………………
5.2 Stomach……………………………
5.3 Liver………………………………….
5.4 Pancreas……………………………
5.5 Small
intestine…………………..
5.6 Large
intestine…………………..
5.7 Rectum………………………………
6. Endocrine
6.1 Concepts…………………………
6.2 Pituitary
gland………………..
6.3 Thyroid……………………………
6.4 Adrenal…………………………..
6.5 Pancreas…………………………
6.6 Testes……………………………..
6.7 Ovaries……………………………
6.8
Non-classical organs………..
7.
Renal
7.1 Kidneys…………………………..
7.2 Ureter…………………………….
7.3 Bladder…………………………..
7.4 Urethra…………………………..
1.
Introduction
2.
Cardiovascular
2.1 Basics. The
cardiovascular system is essential to life. It is comprised of a pump, the
heart, and vessels which carry blood around the body. Blood consists of 3 major
components, red blood cells (45%), plasma (55%) and the buffy layer which is
mostly white blood cells (<1%). Blood transports oxygen and glucose to
tissues and gets rid of waste produces such as carbon dioxide. In addition, blood carries many other
nutrients and hormones which are vital for normal bodily function.
2.2 Heart. The
heart is situated in the centre of the chest. It is protected by 12 pairs of
ribs and situates in between the left and right lung. Anatomically, it is made
up of 4 chambers, 2 atria lying above the 2 ventricles. The vena cava is the
main vein of the body which drains into the right atrium. From the right
ventricle arises the pulmonary artery which transports deoxygenated blood to
the lung. From the lung are the 4 pulmonary veins which enter the left atrium.
Blood travels from the left atrium into the left ventricle before finally
entering the aorta. Structurally, the heart consists of muscle which is
myogenic in nature in addition to fibrous heart valves. Within the wall of the
right atrium lies the sino-atrial node (SAN) which produces the heartbeat. The
muscle of the heart also has electrical fibres which conduct and transport
electricity which eventually causes the ventricles to beat and produce a heart
rate. Supplying the heart muscle oxygen and glucose are the smaller coronary
arteries which come off the aorta. These can commonly get blocked by fatty
plaques and can lead to a heart attack. Risk factors for heart attack include
high blood pressure, increasing age, smoking and obesity.
2.3 Arteries.
Arteries are the principal carrier of oxygenated blood to tissues (apart from
the pulmonary artery). They are characterised by a thick, tough wall with lots
of collagen. The thick wall is vital ad blood travelling in arteries is under
high pressure and the strong wall ensures that the vessel is capable of holding
the blood in the artery.
2.4 Veins. Veins
carry deoxygenated blood back to the heart and lungs where carbon dioxide is
removed and oxygen is replaced. Unlike arteries which have the thick wall,
veins have a thinner, less structurally sound wall. This is a physiological
adaptation as the blood in veins is of a lower pressure, thus, the wall of
veins does not need to be as thick.
2.5 Capillaries.
Capillaries are only 1 cell thick allowing for the transport of nutrients and
oxygen from blood to cells and waste from cells back to the blood. Its diameter
is as wide as a single red blood cell. Capillaries connect arteries to veins.
They often form a capillary bed, increasing the surface area by which nutrient
and waste exchange can occur. Because of the narrow lumen, red blood cells
travel in single file. The pressure of the capillaries is lower than that of
the arteries, due to the 1 cell thick wall it has.
3.
Respiratory
3.1 Upper Respiratory tract
3.2 Lower respiratory tract
3.3 Lungs and diaphragm
4.
Nervous
4.1 Brain. The brain
is about 4.5kg in weight and has a consistency of jelly in real life. It is
divided into several regional lobes, the frontal lobe which is concerned with
motor control, personality and executive functions. The parietal lobe is the centre of the somatosensory cortex. The temporal
lobe is where the primary auditory cortex is. Finally, the occipital lobe is
where the visual cortex is located. Structurally, the brain is divided into 2 cerebral
hemispheres, connected only by a bundle of white mater, the corpus callosum. There
is also the cerebellum, situated under the occipital lobe of the two cerebral
hemispheres. The brain is connected to the spinal cord by the brainstem which
itself is divided into 3 parts, the midbrain, pons and medulla oblongata. The brain
is protected by 3 coverings, the dura, arachnoid and pia mater. The brain is arguably the most important organ
in the body as it is the centre of our consciousness and the organ in which we
interpret are surroundings and interact with our environment. In addition, the
brain has many 'hidden' functions which we do not have conscious control over
such as our heart rate and hormonal axis
4.2 Nerves and spinal cord. The spinal cord is where peripheral nerves interact with the brain. The
spinal cord is a continuous jelly like substance. The spinal cord is protected
by individual vertebral bones, 7 cervical, 12 thoracic, and 5 lumbar. Spinal nerve
roots emerge from every segmental level. The spinal cord ends at the level
L1/L2. This is the reason why a lumbar puncture happens at the level L3/L4.
4.3 Autonomic nervous system. The autonomic system is part of the nervous system that we don't exert
any conscious control over. It is divided mainly into sympathetic and
parasympathetic systems. The sympathetic system is the 'fear, flight or flight'
system which gets activated when you are stressed. It increases the heart rate, causes pilo-erection, vasodilates
arterioles in the skin while constricting blood vessels leading to gut. Parasympathetic
is the 'rest and digest' system. It is active when you are relaxed. It
increases gut activity, decreases the heart rate and allow you to pass urine.
4.4 Eyes, ears and skin. The skin is the largest organ in the body. It is divided into the
epidermis and dermis. The epidermis is further divided into the stratum basale,
stratum spinosum, stratum granulosum and stratum corneum. Beneath the epidermis
is the dermal layer where the vessels and nerves are located. Beneath this is
the subcutis fat layer. The skin has many functions, it acts as a barrier
against pathogens, involved in the first stages of vitamin D synthesis,
insulates you, contains sensory nerves and helps regulate temperature and water
balance. The eyes are in many senses a continuation of the brain. It is the
only organ other than the brain and spinal cord which contains the same 3
protective coverings that the brain has. Most anteriorly on a mid-sagittal section
of the eye is the cornea, a transparent serous membrane protecting the eye. Then
there is the iris, a muscle which can constrict and dilate depending on the
environmental light conditions. The pupil the space in which light enters and
gets to the retina. The lens which is posterior to the pupil is next. It is
connected to the cilary muscles by the suspensory ligaments, when you want to
look at something close, the cilary muscles contract, which relaxes the
suspensory ligaments and allows the lens to bulge, increasing it's refractive
index and causing the light to hit the retina. Commonly, people are short sighted,
whereby they cannot see things far away from them, this can be due to an
over-powerful cilary muscle which should normally relax to see things far away,
making the ligaments tort and the lens flat, or more commonly, the eye is too
long and the image is projected in front of and not on the retina. The most
important structure of the eye is the retina which sits most posteriorly. It contains
photoreceptors which detect different wavelengths of light. Cone cells detect
colour and rod cells detect black and white. Cone cells give you the most
accurate vision are located in high density at the macula. Rod cells are more
numerous at the periphery and produce sub-optimal vision. This is why your peripheral
vision is worse than your central vision.
5.
Digestive
5.1 Upper GI
5.2 Stomach
5.3 Liver
5.4 Pancreas
5.5 Small intestine
5.6 Large intestine
5.7 Rectum
6.
Endocrine
6.1 Concepts.
Unlike many of the other systems of the body, the endocrine system does not
have structural contact with all of its constituent parts. It is made up of
several endocrine organs which secrete hormones that are small chemical messengers
which travel in blood and have an effect on distant target organs. The majority
of endocrine organs are governed by the master gland, the pituitary. Exceptions
to this rule are the pancreas and other non-classical endocrine glands.
6.2 Pituitary gland.
As mentioned in 6.1, the pituitary gland controls many other endocrine glands.
The pituitary gland is a small, pea shaped organ located at the base of the
brain. The pituitary itself is controlled higher up by the hypothalamus. The
pituitary is divided into 2 parts, the anterior and posterior lobe. The anterior
lobes secretes TSH, ACTH, GH, FSH, LH and prolactin. The posterior lobe
releases ADH and oxytocin.
6.3 Thyroid. The
thyroid is located in the neck, in front of the larynx. It is a lobular gland
made up of a left and right lobe, connected by the isthmus. The thyroid
releases thyroid hormone. The release of this is under the influence of TSH
from the pituitary. Thyroid hormone has many wide-ranging effects and is a
peptide hormone. It increases the body's metabolism and too much and too little
of the hormone can lead to characteristic set of symptoms.
6.4 Adrenal. There
are 2 adrenal glands lying on top of each of the kidneys. The adrenal gland is
subdivided in the medulla which makes adrenaline for the 'fight or flight'
response and the cortex which makes cortisol, aldosterone and other sex
steroids. Cortisol and aldosterone regulates salt homeostasis and blood volume.
Aldosterone has effects on the kidney while cortisol has many wide-ranging
effects including body composition and overlaps with adrenaline in the fight or
flight response.
6.5 Pancreas. Anatomically,
the pancreas is made up of the tail, body, neck, head and uncinated process and
is located deep behind the stomach. Unlike the majority of the endocrine
organs, the pancreas is not under the influence of the pituitary. The pancreas
is made up of 98% exocrine function and 2% endocrine function. The exocrine
part makes digestive enzymes and watery secretions which aids the function of
the digestive system. However, the
endocrine part is of significance. The endocrine part of the pancreas is made
up of Islets of Langerhans. Within the islets are many cells, 2 of which are of
importance. The beta cells secrete insulin and alpha cells secrete glucagon.
These two hormones are vital in the regulation of glucose homeostasis. Glucose
is needed for every cellular process in the body and thus the pancreas has an
indirect relationship with every other cell in the body. Mitochondria which are
the powerhouse of the cell need glucose to work. Insulin makes glucose enter
cells to be utilised by the mitochondria. It can therefore be said the insulin
lowers blood glucose. Glucagon on the other hand raises blood glucose by
increasing glucose production of the liver and switching off insulin secretion.
Type 1 diabetes is a condition where the body's immune system destroys the beta
cells. This results in a condition where there is a total lack of insulin. As
insulin lowers blood glucose, in a type 1 diabetic, they have high blood
glucose and require daily insulin injections for life.
6.6 Testes.
6.7 Ovaries.
Ovaries are specific to humans with a XX chromosome. The majority of these
identify as female. The ovaries are the size of a large grape and lie laterally
to the uterus on the posterior abdominal wall. They are held to the abdominal
wall by the suspensory ligament which contains the ovarian artery, vein and
nerves. They are held to the side of the uterus by the ovarian ligament. The
ovaries produce oestrogen and progesterone under the influence of FSH and LH
from the pituitary. Oestrogen is fundamental in the development of female
sexual characteristics and the maintenance of female bone density. Oestrogen,
progesterone, LH and FSH are vital hormones in the menstrual cycle. Day 0 is
the start of the cycle and is when a girl is on her period. The falling
progesterone stimulates the pituitary to make FSH, the FSH recruits follicles
to grow and mature. As the follicles grow, they produce oestrogen which negatively
inhibit the FSH. The fall in FSH selects 1 dominant follicle to grow more. This
produces more oestrogen which paradoxically causes a rise in LH. The LH surge
causes the ovum to be ovulated. The remaining follicle becomes the corpus luteum
and produces progesterone which maintains the thick endometrium, ready for
pregnancy. If no pregnancy occurs within 14 days, the corpus luteum dies, a
fall in progesterone happens, menses occurs and the cycle begins again.
6.8 Non-classical organs. Finally, it is worth mentioning that many other organs have endocrine
function such as bone and fat.
7.
Renal
7.1 Kidneys.
7.2 Ureter
7.3 Bladder
7.4 Urethra
8.
Musculoskeletal
8.1 Muscles
8.2 Bones