mcga-shs_capt_guide_annex.pdf

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ANNEXES

ANNEX I

Anatomy and physiology

To provide adequate medical care on board ship there is no

need to have a detailed knowledge of anatomy (structure of

the body) or of physiology (function of bodily systems).

Nevertheless the information provided in this Annex could

be useful when examining a patient or obtaining and acting

on radio medical advice.

The principal bones of the skeleton and the main muscles

of the body are illustrated in Figures I.1 and I.2. The position

of the organs in the chest and abdomen is depicted in Plates 14

and 15.

ANNEX I

Anatomy and physiology

Bone structure

Voluntary muscles

Involuntary muscles

Circulatory system

Breathing system

Digestive system

Urinary system

Nervous system

Skin

The bone structure

The skeleton, which consists of bones and cartilages, provides

a rigid framework. The separate bones and cartilages are held

together firmly at the joints by strong bands of connective

tissue (the ligaments). Each bone is enveloped in a very tough

adherent sheath of fibrous tissue. Between the sheath and

the bone surface is a layer of bone-forming cells which can

produce new bone in the event of a fracture.

The shaft of a typical long bone has a thick wall of dense

bone which forms a hollow cylinder enclosing a central canal

containing bone marrow. At each end the shaft is expanded

to make the joint surface. These surfaces are covered by a

smooth layer of cartilage to permit movements without

causing friction.

ANNEX II

Voluntary muscles

These form the bulk of the fleshy parts of the body. They are

fixed to the bones by blending with the sheaths of fibrous

tissue surrounding the bones. Some are attached directly to a

wide area of bone surface but others taper to form a strong

cord (tendon or leader) which is attached at a specific place

on a bone. Muscles, and especially those of the limbs, are

arranged in two opposing groups. Contraction of one group

in response to an impulse through the nerve supply must be

accompanied by simultaneous relaxation of the opposing

group, or movement will not take place. These movements

are under conscious control.

Anatomical drawings

The skeleton

Main voluntary muscles

Organs of chest and

abdomen

Involuntary muscles

These are found in the stomach and intestines, in the heart

and blood vessels, and also in other internal organs of the

body. They continue to work throughout life as part of

natural body function outside the control of personal will.

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Circulatory system

Blood

The body contains about 5 litres of blood which consists

basically of four constituents: plasma; red cells; white

cells; and platelet cells.

The plasma is the liquid component of the blood

which circulates to all the tissue cells throughout the

body. It distributes food, water, salts and heat and

collects waste products which are subsequently excreted.

The red cells predominate and give the blood its

colour. This colour is derived from a complex iron

compound (haemoglobin) which is the main oxygen

carrier.

The white cells give protection against infection by

attacking and killing bacteria and also by producing

substances which are necessary for building up resistance

to further infections.

The main purpose of platelets is to assist in the blood

clotting mechanism.

Legs

Arms

Lungs

Stomach

Intestines

The heart and blood vessels

The heart is a thick-walled muscular pump about the size

of a clenched fist. It is divided in the mid line into two sides

which do not communicate. Each side has an upper and

lower chamber which communicate through a main heart

valve. The separate chambers are each served by a major

blood vessel that either brings blood to the chamber or

carries it away. See Plate 15.

The right side receives venous blood which, having

been circulated around the body, has given up its oxygen

and collected carbon dioxide. This blood is pumped

through the lungs where it is replenished with oxygen

and discards the carbon dioxide. As purified blood, it

returns to the left side to be pumped through the

arteries to all parts of the body.

The blood vessels form a closed system of tubes. The

arteries, which have to take the full force of the pumping

pressure, have thick walls containing muscle fibres and

elastic tissue. Each heart beat widens the bore of the

arteries to accommodate the surge of blood. Between

beats the bore is returned to normal by the action of the

muscle fibres and elastic tissue. Where an artery runs

close to the body surface, the changing pressures can be

felt as a pulse.

The arteries penetrate to all parts of the body,

dividing and sub-dividing until they narrow to form very

thin-walled vessels (capillaries). The capillaries then join

with the venous network which returns the blood to the

heart (Figure I.2). The size of veins increases until the

heart is reached.

The capillary system is vital to the life of all tissues. The

thin capillary vessel wall allows nutrients, oxygen, heat

and beneficial chemical substance to enter the cells and,

most important, waste products to be passed out into the

blood.

Trunk

Legs

Figure I.1 The heart and the various

circulations, diagrammatic

Artery

Capillary

network

Vein

Figure I.2 Capillaries

Annex I ANATOMY AND PHYSIOLOGY

217

Larynx

Vein

Bronchiole

Artery

Vein

Capillary

network

Artery

Elastic

fibres

Right main

bronchus

Left main

bronchus

Alveoli

Alveolar

canal

Figure I.3 Lungs, bronchi, and alveoli

Breathing system

Every time a breath is taken in, the air (20% oxygen) passes through the nose or mouth and then

past the larynx or voice box into the windpipe (trachea) which is about 12.5 cm long. At its lower

end the windpipe divides into two main tubes called bronchi (Figure I.3).

The main air passage in each lung (the bronchus) divides into successively smaller branches

which carry inhaled air to all parts of the lung. Each small branch terminates by forming a

cluster of very tiny air sacs (the alveoli). A fine network of blood vessels covers the surface of

every air sac thereby permitting gas exchange by diffusion. Oxygen from the inspired air

passes through the thin tissues to combine with the haemoglobin of the red blood cells.

Waste gases, mainly carbon-dioxide, pass from blood into the air sacs and are expelled on

breathing out.

Haemoglobin + Oxygen = Oxyhaemoglobin

(purple red colour)

(bright red colour of normal blood)

Whenever the blood is insufficiently oxygenated, as in pneumonia, the purple red hue of the

blood shows as a blue tinge of the lips.

Each lung is covered by a lubricated lining called the pleura. The inner side of the chest wall

is also covered by a similar lining. These two layers of pleura are in contact and slide smoothly

over one another during breathing.

The act of breathing is mainly due to the diaphragm moving up and down. The diaphragm

is a large dome-shaped muscle which separates the chest from the abdominal cavity. When

the diaphragm muscle contracts, its dome becomes flattened and draws down the lungs,

causing air to enter them; when it relaxes the lungs become smaller and the air in them is

expelled. The muscles of the abdomen also help in breathing. When they tighten up, they

press the abdominal contents up against the diaphragm and help in expelling air from the

lungs; when they relax, they assist the diaphragm in drawing down the lungs as breathing in

takes place.

The normal rate of breathing at rest is 16–18 times a minute. This rate increases

considerably with exertion and also with certain diseases, especially those affecting the heart

and lungs.

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Digestive system

The abdomen is a cavity shut off from the chest by the diaphragm. The cavity is lined by a sheath

of membrane (the peritoneum) which also enfolds some of the abdominal organs. The sheath

secretes fluid which keeps the abdominal contents moist and prevents friction.

The digestive tract

This is a passage consisting of the gullet (oesophagus), the stomach, the small intestine, the

large intestine, the rectum and the anus.

The gullet is a straight muscular tube which joins the throat to the stomach. It passes down

through the back of the chest cavity and goes through an opening in the diaphragm to connect

with the upper part of the stomach.

The stomach is a J shaped pouch. It enlarges when food or liquid is consumed. The lower part

of the stomach is narrow where it joins with the first part (duodenum) of the small intestine.

The small intestine is a narrow-bore coiled tube, roughly 7.5 metres long, which occupies

most of the central part of the abdominal cavity. The internal surface of the wall bears a large

number of very small folds which project inwards to increase the surface area in contact with

the contents of the intestine. The small intestine joins with the large intestine in the right lower

quarter of the abdomen.

The large intestine is a wide-bore tube, roughly 1.5 metres long, which arches upwards and

across the abdominal cavity before descending the left side to join with the rectum.

The rectum is roughly 150 mm long and is continuous at its lower end with the very short anal

canal which opens to the exterior.

The digestive process

Digestion is the physical and chemical breakdown of food into useful products which are then

absorbed by the capillaries of the blood vessels serving the gut. The unwanted residue of food

is excreted as faeces.

The digestive tract walls contain involuntary muscle which by contractions moves the

contents through the entire length until they reach the rectum where they are stored as faeces

prior to evacuation. At certain places such as the entrance and exit to the stomach and at the

anus, circular bands of muscle capable of constriction (sphincters) act as valves to shut off the

flow.

The physical breakdown of food is accomplished by chewing, by the churning actions of the

gut and by the addition of special digestive juices to the food. This begins in the mouth when

food is mixed with saliva which contains enzymes. In the stomach, acid gastric juice is secreted

by the stomach walls and acts on the food which may be retained there for several hours before

passing through the duodenum. Small ducts from the bile system of the liver and also from the

pancreas open into the duodenum. These ducts provide juices which are partly designed to

neutralise the acid from the stomach juice and thus allow the enzymes secreted by the

duodenal walls to act more efficiently. The churning of the gut then ensures a thorough mixing

of food and digestive juices throughout the length of the small intestine where most of the

chemical breakdown takes place. The main functions of the large intestine are to re-absorb

water from the food residue and to reduce the bulk of the faeces.

The liver

The abdominal veins drain into the liver and carry to it the useful products which have been

absorbed during the digestive process. One of the main liver functions is to act as a chemical

factory which processes these products into substances necessary for nutrition.

Annex I ANATOMY AND PHYSIOLOGY

219

Urinary system

The kidneys are located at the back of the upper part of the abdominal cavity, one on each side

of the spine (see Plate 14). They are embedded in fat to cushion them from injury.

The main kidney function is to remove water and certain harmful waste products from the

blood and, by this filtering process, to form urine. They control total body water and the

concentration of various chemical substances in the blood. The kidneys also play an important

part in maintaining a steady level of blood pressure.

The urine is carried downward from the kidneys to the urinary bladder by tubes of small

calibre (the ureters); one tube for each kidney. The urinary bladder is a muscular bag situated in

the front part of the cavity formed by the pelvic bones. The bladder acts as a reservoir where

urine collects until it is expelled by voluntary muscular contractions through a tube (the

urethra) which leaves from the bladder base.

The male urethra measures 18 to 20 cm from the bladder to the external opening at the end

of the penis. A knowledge of this length is important when passing a catheter. The female

urethra is much shorter, being about 4 cm in length. It runs embedded in the upper vaginal wall

to the external opening just above the vaginal orifice.

Nervous system

Cerebro-spinal nervous system

This consists of the brain, spinal cord and the associated nerves. The brain is in the cavity of the

skull. It is the co-ordinating centre for the nervous system, processing incoming information

from nerves concerned with sight, smell, taste, hearing, sensation etc. and controlling various

parts of the body, particularly muscles by way of out going (motor nerves). Higher functions

include intellect, memory, personality etc.

The spinal cord emerges from the base of the brain and leaves the skull into the bony

vertebral canal. It is protected by vertebrae throughout its length, and nerves emerge at

regular intervals. These nerves control muscles and transmit sensation back through the spinal

column to the brain.

Sympathetic nervous system

This is a fine network of nerves not under direct voluntary control influencing the function of

various organs, especially gut, bladder, blood vessels and heart.

Skin

This protects and covers the body. It consists of two layers. The outer layer is hard and contains

no blood vessels or nerves. This outer layer protects the inner layer, where there are sensitive

nerve endings numerous sweat glands and the roots of the hair.

Sweat consists of water, salt and some impurities from the blood. The evaporation of the

sweat cools the body, and helps to regulate its temperature.

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