The Foetus

The Foetus

Haemorrhoids often develop or worsen in pregnant patients. This may be due to the increased pressure of the womb, and this is often made worse by constipation. However, if drugs are to be used, external products are preferred because many drugs are readily absorbed from the rectum. Anal painkillers containing surface anaesthetics should be avoided because of possible absorption into the blood. And these may finally end up in the foetus.
High blood pressure or hypertension affects the foetus as well. Hypertensive patients have a greater incidence of decreased foetal weight and foetal growth
retardation due to decreased function of the placenta.


Origin:
The placenta develops from the chorion frondosum (foetal origin) and decidua basalis (maternal origin).
Anatomy At Term:
Shape: discoid. Diameter: 15-20 cm. Weight: 500 gm.
Thickness: 2.5 cm at its centre and gradually tapers towards the periphery.
Position: in the upper uterine segment (99.5%), either in the posterior surface (2/3) or the anterior surface (1/3).
Surfaces:
a. Foetal surface: smooth, glistening and is covered by the amnion which is reflected on the cord. The umbilical cord is inserted near or at the centre of this surface and its radiating branches can be seen beneath the amnion.
b. Maternal surface: dull greyish red in colour and is divided into 15-20 cotyledons. Each cotyledon is formed of the branches of one main villus stem covered by decidua basalis.


Functions Of The Placenta:
(1) Respiratory function:
O2 and CO2 pass across the placenta by simple diffusion. The foetal haemoglobin has more affinity and carrying capacity than adult haemoglobin. 2,3 diphosphoglycerate (2,3-DPG) which competes for oxygen binding sites in the haemoglobin molecule, is less bounded to the foetal haemoglobin (HbF) and thereby allows a greater uptake of O2 ( O2 affinity). The rate of diffusion depends upon:

PLACENTA - flat organ
(< 1kg wt)
one side connected to uterus, other side to embryo via umbilical cord
Formed from: Chorion of embryo + Endometrium of mother.
Formation complete by ~ 3 months post-conception.
Functions as: exchange organ. Foetal and maternal bloods come into close proximity (do not mix).


O2 and nutrients from mother ? foetus.
CO2 and wastes from foetus ? mother.
storage organ: carbohydrates, proteins, iron, calcium stored for use by foetus.
endocrine organ: produces hormones essential for maintenance of pregnancy.
protective barrier: impermeable to many micro-organisms (but not all e.g. syphilis, rubella, AIDS): permeable to most drugs and alcohol (FAS).
selective transport of antibodies


Placental structure: projections of chorion containing foetal vessels grow into endometrium - chorionic villi.
endometrium develops large