The fetal skull - midwifery 2107 intake PDF

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Summary

midwifery 2107 intake ...

Description

The fetal skull Bones – develop from membrane Sutures and fontanelles – un ossified membrane Fontanelles - joining of suture lines

There are 3 regions of the fetal skull: The face – from orbital ridges to neck and chin The base – fused bones The vault – Area above imaginary line drawn from nape of neck to orbital ridges

The vault of the skull consists of: Vertex – Vx – area bounded by ant/post fontanelles and parietal eminences Brow (Sinciput) - area over frontal bone Occiput – area over occipital bone Sutures- frontal /saggittal/ coronal/ lambdoidal /temporal Fontanelles – Bregma and lamda

Diameters of the fetal skull Biparietal diameter: 9.5 cm - between parietal eminences The greatest transverse diameter Sub-Occipito Bregmatic: 9.5 cm - middle of the bregma to undersurface of the occipital bone at the neck. The presenting diameter of the well flexed head in labour. Sub-Occipito Frontal: 10 cm - root of the nose to undersurface of the occipital bone at the neck. The presenting diameter of the partially flexed head

Occipito-Frontal: 11.5 cm - Root of the noose to the most prominent point of the occiput. A deflexed head presents with this diameter. Mento-Vertical: 13.5cm - Chin to most prominent point of the occiput. The presenting diameter in brow presentation. The largest diameter of the fetal head. Sub-mento Vertical – 11cm Sub-mento Bregmatic – 9.5cm Bitemporal – 8.3cm Occipitofrontal circumference – 35.6cm

The meninges Dura mater - This is a tough, outer fibrous layer which lines the bones of the skull and the vertebral canal. It forms the falx cerebri by folding down between the two cerebral hemispheres and the tentorium cerebelli which divides the cerebral hemispheres from the cerebellum. The main venous drainage, the venous sinus lies within the dura mater. Arachnoid mater - This is a delicate web like membrane which is separated from the dura mater by the sub dural space. Pia mater - This is a transparent membrane which adheres to the outer surface of the brain and spinal cord and contains blood vessels. It is separated from the arachnoid mater by the subarachnoid space which contains the cerebrospinal fluid.

Internal structures of the skull

Engagement of the fetal head – can be defined as when the widest transverse diameter (Biparietal) has passed through the Brim of the pelvis. Moulding of the fetal head – can be defined as the facility of the vault of the skull to change shape over a period of time during its passage through the birth canal. The engaging diameter is reduced and the diameter at right angles to it (opposing) increases. •

Occurs with descent of the fetal head into the pelvis to reduce the head circumference

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Frontal bones slip under parietal bones

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Parietal bones override each other

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Parietal bones slip under the occipital bone...