Posts tagged human body
Top: Uterine lining at 5 1/2 months, displaying thin maternal separation from fetus, and high level of placental implantation
Center: Relation of placenta to uterus at 5 weeks and 8.5 months
Bottom: Major arteries and veins of the placenta
Did you know that the placenta is a temporary organ that’s actually created by the fetus, and not the woman?
The human female is a curious creature; like our close great ape cousins, but unlike almost all other mammals, they build up a thick barrier in the uterine wall, to protect against any potential embryo that might implant itself. When there’s no embryo implantation, the thickened wall is shed, in the process known as menstruation.
The thing is, most mammals don’t menstruate. They go into heat, and occasionally shed uterine lining (if the uterus is scratched, or an egg tries to implant but fails, for example), but there’s no regular cycle of bloody discharge relating to breeding. This is because other mammals go through triggered decidualization (developing a uterine lining only when a fertilized egg begins to implant itself), while the great apes (and a couple other convergently evolved families, including bats) experience spontaneous decidualization, where they develop a thick uterine lining during every ovulation, before an egg can even attempt to implant itself.
Why the different linings? Well, it turns out that there are three types of mammal placentas (remember, placentas are developed by the embryo/fetus, not the mother):
- Epitheliochordal, which is completely superficial, and does not connect in any significant way to the mother’s body. The endometrial epithelium, connective tissue, and uterine epithelium are all preserved and undisturbed in the mother. The fetus is separated from the mother by three layers of tissue. Nutrients and waste are delivered and eliminated through diffusion, rather than direct connection. This group includes equids, swine, and ruminants.
- Endotheliochordal, which is slightly more invasive to the mother, only preserves the uterine epithelium. Nutrients and waste are not exchanged through direct connection to the mother, but the placenta only leaves one layer of tissue between it and the mother. This group includes cats and dogs.
- Hemochorial is the most invasive form of placenta in the animal kingdom. The embryo directly hooks itself up to the host (mother’s) blood flow, and leaves no tissue layers between the female and the placenta. This allows much more efficient nutrient transfer to the embryo or fetus, but is also potentially the most harmful to the female since the embryo attaches itself so securely to the uterine wall. The female must develop preemptive measures (a thickened uterine lining) to protect herself from a life-form that is literally driven to take all of the nutrients it needs to develop, and which has adapted to connect itself directly to the host. This group includes elephant shrews, most bats, and most primates.
Interested in more about the science behind reproduction and how amazingly efficient the human embryo is at sucking its host clean, just to obtain its needed resources for development?
PZ Meyers at Pharyngula has an understandable explanation of the article I referenced for this post.
There is also a great site by R. Bowen about the pathophysiology of the reproductive system.
An American Text-Book of Obstetrics for Practitioners and Students. Edited by Richard C. Norris, 1895.
I love the sphenoid complex. It’s gorgeous. It looks so much like a tattered but unbroken moth.
Your sphenoidal sinuses are deep within your skull, behind the olfactory bulb and olfactory sensors in the very back of your nose. They sit around the pterygoid wings of the sphenoid bone, and the upper wall of the sinuses is the upper wings of the bone. These wings are the last bone structure before the brain, and though they’re strong, they’re thin and brittle, and can easily be damaged or destroyed by tumorous growths and head injuries.
Serious sinusitis before antibiotics could become deep-seated (it is usually treated before this happens these days), and if there are any cracks in the pterygoid wings, easily invade the brain cavity. Because of this and related reasons, bacterial meningitis and encephalitis (more serious and higher risk of complications) was at one time much more common than viral meningitis around the world, as it still is in developing countries. The mortality rate was about 10-15%, but many times even people with resolved infections ended up with hearing loss, brain damage, and in children, learning disabilities.
That said, the most important things are that the sphenoid complex seats the pituitary gland, provides support for the optic and the olfactory nerves, and a boundary between the open sinuses (prone to infection) and the brain structures. It prevents transmission of bacteria to the brain, and it provides a stable platform for the nerves that allow us to both see and smell the world around us.
What an important and lovely structure.
Removal and dissection of spinal cord in postmortem examination.
The spinal cord is rarely a point of fine-tuned focus in postmortem examinations, since the primary reason one would die that relates to it is a complete severing. As a severed spinal cord is generally fairly obvious, the nerve bundles don’t require close inspection. However, in full autopsies and criminal investigations, the spinal cord is generally closely inspected, especially if no other cause of death is found.
Postmortem Pathology. Henry L. Cattell, 1906.
Anatomy 101: Muscles - Upper Neck and Face
As humans, a huge amount of our communication is non-verbal, and subconscious queues given by facial movements can say as much as any exclamation.
Almost all muscle on the head and neck is considered skeletal (voluntary) muscle, and the muscles that control the finest expressions originate from the facial bones, and insert on the skin. Aside from the chewing muscles, there are few that both insert and originate on bone.
Like skeletal muscles in the rest of the body, the muscles of the face sometimes have an antagonistic partner - that is, a muscle that performs the opposite action. Since muscles cannot perform a pushing action, the antagonist is needed to pull its partner back into place. One of the more obvious examples of this is the biceps brachii and the triceps brachii - if you had one without the other, the arm would only be able to move in one direction! Unlike the rest of the body, however, the muscles of the head and neck do not control limbs or need to push body parts, and don’t always need one or more antagonists.
Some of the significant facial muscles include:
- Frontalis and corrugator: Control the forehead and eyebrows, respectively. When they’re used repeatedly, furrows in the brow develop. The corrugator muscle is generally where people getting Botox of the eyebrow have injections.
- Obicularis oculi and obicularis oris: Circular muscles that work to “purse” the eyelids and lips, respectively.
- Temporalis; masseter; and medial and lateral pterygoid: Muscles that are primary in chewing. The temporalis comes from the temple and elevates and retracts the jaw. The masseter and medial pterygoid also work to elevate and retract the jaw, and the lateral pterygoid depresses, opens, and protrudes the mandible, as well as moving it laterally.
- Buccinator: Draws the lips wide and tight, and keeps food in contact with the teeth.
- Levator labii: Raises the upper lip.
- Depressor labii: Lowers the lower lips.
- Risoris: Draws the lips into a smile (by the way, the whole “13 muscles required to smile/56 required to frown” is nonsense).
Man (Homo sapiens sapiens), Cow (Bos taurus), and Ram (Ovis aries)
The structure of the ruminant animals varies considerably. It’s important for the artist to recognize the vertebral layout and rib structure, even of animals that are covered in thick wool or fur. Wild bovids (such as bison) and aurochs have extended cervical vertebrae that form a “hump” over their shoulders.
A Comparative View of the Human and Animal Frame. B. Waterhouse Hawkins, 1860.
Man, and the Lion
Both the anatomist and the artist can see here the vast difference in forelimb and hindlimb structure between the lion and man (provided solely for comparison). The forelimb of the lion is far thicker and sturdier than that of man, but the digits and bone layout are very much alike, save that the lion has but four digits on the hindlimb.
In the forelimbs, the lion has pronounced bony sheaths for its retractile claws, which form a very visible rounded enlargement at the end of the end of each toe. These are not nearly as evident on the hindlimbs, where a very slight indication of the claw can be seen at the end of the digit. Other things important to note are the tooth structure and arrangement, and what teeth are showing when a lion is attacking.
Together, the size and weight of the front limbs and their corresponding muscles, along with the teeth and jaws, can be said to be the characteristic points of the lion. The hind limbs, slender neck, vertebral column, and ribs, are only suggestive of the agility which allows this animal to use his front limbs and jaws with such power as to have rendered the figure of the Lion a symbol of strength, power, and destruction.
A Comparative View of the Human and Animal Frame. B. Waterhouse Hawkins, 1860.
Arteries and veins of the adult body.
Wonders of the Human Body. A. Le Pileur, 1871.
Female generative organs in situ
Anatomie normale du corps humaine: atlas iconographique de XVI planches. Sigismond Laskowski, 1894.
1885 Engraved anatomy chart showing the diseases of the organs of circulation. Gorgeous hand colored engraved image titled,”Diseases of the Organs of Circulation and Diseases of the Heart-Pericarditis.”
Removal and dissection of spinal cord in postmortem examination.
The spinal cord is rarely a point of fine-tuned focus in postmortem examinations, since the primary reason one would die that relates to it is a complete severing. As a severed spinal cord is generally fairly obvious, the nerve bundles don’t require close inspection. However, in full autopsies and criminal investigations, the spinal cord is generally closely inspected, especially if no other cause of death is found.
Postmortem Pathology. Henry L. Cattell, 1906.
Internal Anatomy: Viscera and Thorax
Diagnostics of Internal Medicine. Glentworth Reeve Butler, 1902.
Anatomy of the Human Body. William Cheselden, 1712.
Cuvier Day
Teeth and hand/foot bones of the human
As a young child, Cuvier’s mother tutored him extensively and spent almost all of her time with him. He was a sickly child, but very bright and eager to learn, and his mother was more than eager to oblige his curiosities. Her own reading and love for learning led her to discuss complex literature with Cuvier from a very early age, and have her son work on many projects about his interests under her supervision. That was in addition to teaching him the basics of academia, and ensuring he excelled at his lessons when he began school.
His early learning helped him immensely while he was in Gymnase, and he was always ahead of his classes.
Blood cells; Erythrocytes, Leukocytes, and Platelets (thrombocytes).
“Normoblasts” are the immediate precursor to erythrocytes (red blood cells) - they’re essentially an erythrocyte that still maintains a cell nucleus.
The “transitional form” is a transitional white blood cell.
Normal Histology, With Special Reference to the Structure of the Human Body. George A. Piersol, 1910.
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A blog for all biological and medical ephemera, from the age of Abraham through the era of medical quackery and cure-all nostrums. Featuring illustrations, history, and totally useless trivia from the diverse realms of nature and medicine.
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