A leech seems to be an appropriate description of the early human embryo. The embryo clings to the endometrium or lining of the uterus (day 7) just as a leech clings to the skin.31 The embryo is attached to the wall of the chorion – the chorionic sac – which has chorionic villi which are attached to the lining of the uterus. The embryo is also surrounded by amniotic fluid just as the leech is surrounded by water.
Figure 6 Drawings illustrating the similarities in appearance between a human embryo and a leech (ʿalaqah). A, shows a lateral view of an embryo (size 2.5-3.0mm) at days 24 to 25 during folding, showing the large forebrain and the ventral position of the heart (from Moore & Persaud: The Developing Human 8th Edition). B, shows a drawing of a leech. Note the leech-like appearance of the human embryo at this stage.
If we take the literal meaning of “leech” for alaqah, we find that during the third week the embryo loses its round shape and elongates until it takes the shape of a leech. Figure 6 and Figure 7 clearly indicate that the shape of the embryo does in fact resemble a leech. Internally, the embryo acquires a primitive cardiovascular system and the embryo is now dependent upon the maternal blood for its nutrition like a leech which feeds on the blood of others.32
31 Moore (1986, pp. 15-16).
32 As we see in Figure 4 (page 4) the umbilical vein carries well-oxygenated blood and nutrients from the chorionic sac to the embryo. The arteries carry poorly oxygenated blood and waste products to the chorionic villi for transfer to the mother’s blood.
Figure 7
A, shows a lateral view of an embryo (size 2.5-3.0mm) at days 24 to 25 during folding. (Modified from Moore & Persaud: The Developing Human 8th Edition)
B, Medicinal leech, Hirudo medicinalis (modified from The Human Body. The Incredible Journey from Birth to Death, © BBC Worldwide Ltd, 1998)
C, Scanning electron micrograph of an embryo at Week 4, 26 - 30 days. (Professor Kathy Sulik, The University of North Carolina). Note the leech-like appearance of the human embryos at this stage.
In The Human Body: The Incredible Journey from Birth to Death, Professor Lord Robert Winston33 also describes the embryo in a similar way. Lord Winston demonstrates how the embryo obtains nourishment from the blood of the mother which is similar to a leech which feeds on the blood of others (Figure 8):
33 Lord Winston is Professor of Science and Society and Emeritus Professor of Fertility Studies at Imperial College, London. http://www.robertwinston.org.uk/.
Figure 8 Presenter Professor Lord Robert Winston with a blood sucking leech (ʿalaqah) attached to his forearm. Professor Winston shows how the embryo obtains nourishment from the blood of the mother, similar to the leech which feeds on the blood of others. (The Human Body. The Incredible Journey from Birth to Death, © BBC Worldwide Ltd, 1998).
This is Hirudo medicinalis, better known to you and me as a leech. It’s a parasite. It takes whatever it needs to live by sucking the blood of whatever it can latch onto; in this case that’s me! As it sucks my blood, it takes from it all that it needs to live, it literally lives off me and the whole of pregnancy is shaped by a similar kind of parasitic relationship. Unlike the leech, the developing embryo doesn’t suck the mother’s blood but it does raid her blood for the raw materials it needs to grow. From the word go both leech and embryo are out for themselves.34
And in Anatomy Demystified the early embryo is also described as worm-like in appearance which is nourished by the mother’s maternal blood supply:
By 24 days, a connecting stalk appears in the middle of the now worm-like body. The yolk sac hangs off to one side of this connecting stalk. Both attach to the primitive placenta (plah-SEN-tah), a “flat cake” (placent) of highly vascular (blood vessel-rich) tissue that nourishes the developing embryo and later, the fetus.35
It takes about a week from the beginning of implantation (day 6) for the connecting stalk to form (day 14 or 15) such that the embryo becomes “attached and hanging” It takes about 10 days for the notochord36 to begin development (day 16) in order for the embryo to take on the appearance of a leech.37 The word alaqah accurately describes and reflects the external appearance of the embryo during this stage of development.
34 Lord Winston in BBC Woldwide (1998).
35 Layman (2004, p. 366).
36 A rod-like column of cells. It is the first indication of the future vertebrae of the spinal column.
37 The embryo undergoes craniocaudal folding and lateral folding which changes the shape of the embryo from a two-dimensional disk to a three-dimensional cylinder.
Figure 6 Drawings illustrating the similarities in appearance between a human embryo and a leech (ʿalaqah). A, shows a lateral view of an embryo (size 2.5-3.0mm) at days 24 to 25 during folding, showing the large forebrain and the ventral position of the heart (from Moore & Persaud: The Developing Human 8th Edition). B, shows a drawing of a leech. Note the leech-like appearance of the human embryo at this stage.
If we take the literal meaning of “leech” for alaqah, we find that during the third week the embryo loses its round shape and elongates until it takes the shape of a leech. Figure 6 and Figure 7 clearly indicate that the shape of the embryo does in fact resemble a leech. Internally, the embryo acquires a primitive cardiovascular system and the embryo is now dependent upon the maternal blood for its nutrition like a leech which feeds on the blood of others.32
31 Moore (1986, pp. 15-16).
32 As we see in Figure 4 (page 4) the umbilical vein carries well-oxygenated blood and nutrients from the chorionic sac to the embryo. The arteries carry poorly oxygenated blood and waste products to the chorionic villi for transfer to the mother’s blood.
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| Figure 7 |
A, shows a lateral view of an embryo (size 2.5-3.0mm) at days 24 to 25 during folding. (Modified from Moore & Persaud: The Developing Human 8th Edition)
B, Medicinal leech, Hirudo medicinalis (modified from The Human Body. The Incredible Journey from Birth to Death, © BBC Worldwide Ltd, 1998)
C, Scanning electron micrograph of an embryo at Week 4, 26 - 30 days. (Professor Kathy Sulik, The University of North Carolina). Note the leech-like appearance of the human embryos at this stage.
In The Human Body: The Incredible Journey from Birth to Death, Professor Lord Robert Winston33 also describes the embryo in a similar way. Lord Winston demonstrates how the embryo obtains nourishment from the blood of the mother which is similar to a leech which feeds on the blood of others (Figure 8):
33 Lord Winston is Professor of Science and Society and Emeritus Professor of Fertility Studies at Imperial College, London. http://www.robertwinston.org.uk/.
 |
| Figure 8 |
This is Hirudo medicinalis, better known to you and me as a leech. It’s a parasite. It takes whatever it needs to live by sucking the blood of whatever it can latch onto; in this case that’s me! As it sucks my blood, it takes from it all that it needs to live, it literally lives off me and the whole of pregnancy is shaped by a similar kind of parasitic relationship. Unlike the leech, the developing embryo doesn’t suck the mother’s blood but it does raid her blood for the raw materials it needs to grow. From the word go both leech and embryo are out for themselves.34
And in Anatomy Demystified the early embryo is also described as worm-like in appearance which is nourished by the mother’s maternal blood supply:
By 24 days, a connecting stalk appears in the middle of the now worm-like body. The yolk sac hangs off to one side of this connecting stalk. Both attach to the primitive placenta (plah-SEN-tah), a “flat cake” (placent) of highly vascular (blood vessel-rich) tissue that nourishes the developing embryo and later, the fetus.35
It takes about a week from the beginning of implantation (day 6) for the connecting stalk to form (day 14 or 15) such that the embryo becomes “attached and hanging” It takes about 10 days for the notochord36 to begin development (day 16) in order for the embryo to take on the appearance of a leech.37 The word alaqah accurately describes and reflects the external appearance of the embryo during this stage of development.
34 Lord Winston in BBC Woldwide (1998).
35 Layman (2004, p. 366).
36 A rod-like column of cells. It is the first indication of the future vertebrae of the spinal column.
37 The embryo undergoes craniocaudal folding and lateral folding which changes the shape of the embryo from a two-dimensional disk to a three-dimensional cylinder.
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