A&P 1
Tutor: Eleshia Howell
 Instead
of the venous blood returning
directly, through one capillary bed, the
portal system offers a second filtering system
for the blood from digestive organs.
 Venous blood passes through first line
capillary beds of digestive system, pancreas
and spleen to go to the liver.
 It then passes through secondary capillary
bed in the liver (hepatic sinusoids) before
entering general circulation via inferior vena
cava.
 The
high concentration of nutrients absorbed
from the stomach and intestines is first
received by liver, which then regulates blood
nutrient level and performs numerous
chemical modifications.
 The portal vein is formed by union of several
other veins from organs such as spleen,
intestines and stomach. It enters into inferior
portion of liver.
 Hepatic vein exits from posterior superior
aspect of liver and empties directly into the
inferior vena cava.
P 104
P 104
P 105
P 106
P 107
 The
developing foetus obtains its oxygen and
nutrients, and excretes its wastes, via the
mother’s circulation.
 Both maternal and foetal circulations
develop specific adaptations unique to
pregnancy.
 Because the lungs, gastrointestinal system
and kidneys do not begin to function until
after birth, certain modifications in the
foetal circulation divert flow to meet prenatal requirements.
PLACENTA
 This temporary structure provides an
interface between mother and baby, allowing
exchange of substances between their
circulatory systems.
 It develops from the surface of the fertilized
ovum embedded into uterine endometrium
and is expelled during the final stage of
labour when it is no longer required.
 It weighs about 500g, is approx 20cm
diameter and about 2.5cm thick. It is firmly
attached to the uterine wall and consists of
an extensive network of capillaries bathed in
maternal blood.
 Placenta
is attached to the baby via
umbilical cord which contains two arteries
and one vein. The cord enters the foetus at
the abdomen (umbilicus).
 The maternal and foetal blood supplies,
while in very close proximity, are two
separate circulatory systems.
 Deoxygenated blood flows into the placenta
from baby and is filtered by the capillary
network within, removing C02 and other
wastes, and returning oxygen and nutrients
back into foetal circulation.
 The placenta can also provide a mild
protective barrier against harmful substances
and some pathogens
 Placenta
also has essential endocrine
function in that it secretes the hormones
that maintain pregnancy ~ hCG, Progesterone
and Oestrogen.
FOETAL ADAPTATIONS:
 Ductus venosus – an extension of the
umbilical vein which transports blood
directly into foetal inferior vena cava,
bypassing the liver.
 Ductus arteriosus – small vessel connecting
the pulmonary artery to the descending
aorta, diverting more blood into systemic
circulation (so very little blood passes
through baby’s lungs).
 Foramen
ovale – a valve-like opening that
allows blood to flow between the right and
left atria, again so that most blood bypasses
foetal lungs.
CHANGES AT BIRTH:
 When baby takes first breath and lungs
inflate, pulmonary blood flow is increased.
Blood returning from lungs increases pressure
on left atria, closing the flap over the
foramen ovale and preventing cross flow.
 The increased blood O2 levels cause
constriction and closure of the ductus
arteriosus.
 Once
the placental circulation ceases soon
after birth, the umbilical vein & arteries,
plus ductus venosus automatically collapse.
P 109
SHOCK (circulatory failure) – occurs when the
metabolic needs of cells are not being met
because of inadequate blood flow.
Essentially, a reduction in circulating blood
volume, in blood pressure and in cardiac
output.
This causes tissue hypoxia, and inadequate
supply of nutrients and the accumulation of
waste products.
There are various kinds of shock:
 Hypovolaemic
shock – occurs when blood
volume is reduced by 15-25%. This may be
caused by severe haemorrhage, extensive
burns, severe vomiting or diarrhoea.
 Cardiogenic shock – when damaged heart
muscle cannot maintain an adequate cardiac
output, eg myocardial infarction.
 Septic shock – caused by severe infections in
which bacterial toxins are released into the
circulation, triggering a massive
inflammatory and immune response.
 Neurogenic shock – when a nervous system
assault interferes with normal nerve control
of blood vessel diameter (pain, injury,
anaesthesia, severe emotional distress).
 Anaphylactic
shock – a severe allergic
response.
In the short term, there are physiological
attempts to restore an adequate blood
supply, eg sympathetic activation, release of
ADH and renin-angiotensin-aldosterone
reflex. Medical interventions may also help
to restore perfusion to the brain and heart
and therefore restore physiological balance.
In severe cases, the cycle of hypoxia,
progressive acidosis and tissue death results
in organ failure, circulatory collapse, brain
stem damage and ultimately death.
 Embolus
– a mass of any material carried in
the blood, eg blood clot, tumour fragments,
arterial plaque, air, pus, fat (from bone
fractures), nitrogen bubbles (the ‘bends’). An
embolus may interrupt blood supply or
completely obstruct a vessel.
 Thrombus – an intravascular blood clot which
can be caused by any condition that slows
blood flow, damages the smooth inner lining
of the vessels or increases coagulability of
blood.
 Infarction – tissue death because of
interrupted blood supply.
 Ischaemia – tissue damage because of
reduced blood supply.
 Atherosclerosis
– accumulation of fatty
plaques in the arteries; may cause partial or
complete obstruction of an artery.
 Arteriosclerosis – progressive degeneration of
arterial walls, associated with aging and
accompanied by hypertension.
 Aneurysms – abnormal local dilations of
arteries; can be caused by atheroma,
hypertension, defective collagen in arterial
wall. If aneurysm ruptures, haemorrhage
follows.
 Venous thrombosis / phlebitis – inflamed
thrombus in superficial or deep veins.
 Varicose
veins – when a vein is so dilated that
the valves can not close to prevent backflow,
causing a loss of elasticity and giving the
appearance of elongated, tortuous and
fibrous veins. This condition may be
hereditary or caused by age, pregnancy,
pressure, obesity, poor venous return. Most
commonly occurs in the legs, but can also
happen around rectum/anus (haemorrhoids),
vagina / scrotum, oesophagus.
 Heart
failure – when the cardiac output is
unable to maintain the circulation of
sufficient blood to meet the needs of the
body. May occur on either side of the heart
(more common in left ventricle due to
workload) but will eventually effect the
whole organ. Over time, the heart chambers
will become thicker and enlarge and the R-AA system becomes activated leading to salt
and water retention, which in turn increases
blood volume and cardiac workload!
 Valve disorders – heart valves may be
damaged (murmurs), blocked (stenosis) or
incompetent (causing regurgitation of blood).
 Arrhythmias
– alterations to the normal heart
rate generated by the conducting system of
the heart.




Bradycardia – below 60bpm
Tachycardia – above 100bpm
Asystole – no electrical activity in the ventricles,
no cardiac output (flat line)
Fibrillation – disorderly contraction of the
cardiac muscle fibres. AF may still produce some
ineffective pumping of blood but will be rapid,
irregular. VF is a medical emergency – no blood
pumped into pulmonary or systemic system.
 Hypertension
– high blood pressure. May be
of gradual onset, due to aging, linked to
hereditary, lifestyle, diet, disease factors.
Commonly effects the kidneys, brain, heart,
blood vessels and eyes. 140/90 and beyond is
considered hypertensive.
 Hypotension – usually occurs as a
complication to another condition. Can lead
to inadequate blood supply brain. Postural
hypotension is an abrupt fall in pressure on
standing from a sitting / lying position which
can cause dizziness / fainting (syncope).
 Congenital
abnormalities – present from
birth.



Patent ductus arteriosus – prenatal structure fails
to close completely, allowing regurgitation of
blood from aorta to pulmonary artery ~ less
blood in system, more in lungs ~ pulmonary
congestion, heart failure.
Atrial septal defect – “hole in the heart”;
foramen ovale does not completely close off.
Fallot’s Tetralogy – combination of 4 cardiac
vessel / ventricle defects; surgical repair offers
good prognosis.
The End