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Gluteal muscles
The three primary gluteal muscles (maximus, medius, and minimus), in addition to the tensor fasciae latae (lateral to the primary muscles), comprise the gluteal group, which provides the majority of the support and movement that allows humans to walk upright, rotate our legs, and support our torso.
Each individual muscle is often involved in many different movements, though not always as the primary player. All four gluteal muscles originate from the outer ilium (the back of the “wings” on the pelvis). This is known as the gluteal surface.
Gluteus maximus: (Top Left) The largest muscle in the body. Supports the pelvis, lower torso, and allows the body to remain upright and regain position after stopping movement. Despite claims to the contrary, the gluteus maximus is not what gives the majority of the shape to the buttocks - that’s largely determined by the panniculus adiposus (“hanging fat”) of the buttocks. However, exercising the gluteus maximus may cause fat loss, which gives the impression that it is the primary progenitor of the shape.
Gluteus medius: (Top Center) Originates right below the gluteus maximus. Responsible for abducting the leg and maintaining an upright position while on one leg, such as during running, dancing, or entering a car.
Gluteus minimus: (Top Right) The smallest of the three primary gluteals, works in concert with the gluteus medius to maintain an upright position on one leg, as well as allowing the leg to turn inwards and outwards (medial rotation).
Tensor fasciae latae: (Bottom; near sartorus muscle) Located on the outside edge of the thigh, lateral to the primary gluteals. Causes knee extension, and functions to cause the primary movements during walking. Supported by the gluteus maximus. Used extensively in horseback riding.Images:
Top: Posterior muscles of the gluteal and thigh region. Gluteus maximus, medius, and minimus highlighted. From Anatomy, Descriptive and Applied. Henry Gray, 1913. Highlighted by Mikael Haggstrom.
Bottom: Structures surrounding the right hip joint, including gluteal muscles. From Anatomy, Descriptive and Applied. Henry Gray, 1908. -
My copy of Gray’s Anatomy has finally arrived, Barnes & Noble leatherbound Classics collection. It is honestly the most beautiful book I’ve ever seen.
(via fuckyeahmedicaldiagrams)
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Sweat glands in the human epidermis:
Diagrammatically represented (top)
Isolated vertical cross-section (Right)
Isolated horizontal cross-section (left)Staying cool this ridiculous summer, fellow North Americans? Even if you’re hot and miserable and sweaty, your body knows how to keep its organs at the optimal temperature - that’s why you sweat in the heat in the first place!
Unlike other mammals that sweat for thermoregulation (such as oxen and horses), humans largely sweat from their eccrine sweat glands, which are not directly connected to hair follicles. Eccrine sweat glands secrete mostly water, with a few electrolytes (mostly NaCl, which is why sweat tastes salty). The amount we sweat is regulated by the hypothalamus and the contraction of cells surrounding the eccrine glands, and is influenced by hormone release and internal body temperature.
The water secreted by the eccrine sweat glands utilizes a process called evaporative cooling to reduce the surface temperature of the skin, which in turn reduces the temperature of the blood flowing through the expanded arterioles near the skin surface, and that blood flows through the body and keeps the organs and muscles at a relatively constant temperature. Sweat glands are coil-shaped, with a bulbous sac at the bottom that filters blood plasma to produce sweat. When the cells surrounding the sac and coil are triggered, they contract, pushing that sweat to the surface of the skin.
We also have apocrine sweat glands (the only functional thermoregulatory glands in horses and other sweaty mammals), but they’re largely restricted to the armpits, areola, and perianal region. Their secretions are not as simple as eccrine sweat glands - they’re typically milky-white and contain hormones and additional components of blood plasma that bacteria *love* to chow down. Those bacteria produce stinky excretions of their own, and that’s what causes smelly armpits!
When you use deodorant, the substance you apply works by breaking down the components excreted by bacteria that cause the smell, and masking any residual stink that can’t be broken down. Antiperspirants function by plugging the openings of the sweat pores, so that sweat can’t escape. This is usually done with small particles of aluminum. Despite misconceptions, blocking the sweat glands does not cause breast cancer, though some people experience adverse effects due to allergies to aluminum or other ingredients.
Images:
Top: Anatomy, Descriptive and Applied. Henry Gray et al, 1910.
Bottom: Diseases of the skin; a text-book for students and practitioners. J.M.H. Macleod, 1920. -
Without the work of intellectual giants like Einstein, Newton and Darwin, we might still be in the dark ages. But how many scientists still read the dust-ridden texts where these luminaries first expounded their theories? Thanks to the internet, you no longer have to hunt down these yellowing tomes in a moldy library vault. Here’s the story of 9 famous publications that spun the scientific world off its orbit.
(via biomedicalephemera)
Posted on July 20, 2012 via WIRED with 750 notes
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Lens of the human eye: The structure of the fetal (A) and adult (B) human lens, showing the major details of arrangement of the lens fibers. The anterior (a) and posterior (b) triradiate sutures are shown in the fetal lens. Fibers pass from the apex of an arm of one suture to the angle between two arms at the opposite pole, as shown in the colored segments. Intermediate fibers show the same reciprocal behavior. The suture pattern becomes much more complex as successive strata are added to the exterior of the growing lens, and the original arms of each triradiate suture show secondary and tertiary dichotomous branchings.
(By permission from Hogan MJ, Alvarado JA, Weddell JE 1971 Histology of the Human Eye. Philadelphia: WB Saunders.) -
Anatomy of the coccyx and sacrum
In reference to this question, here is the anatomy of the coccyx and sacrum. As can be seen, the sacral portion of the spinal column is still significantly important, in terms of both structural importance and nervous integration/protection. However, the coccygeal spine does little more than anchor two pelvic muscle pairs, and a few ligaments.
In terms of “having a tail”, the closest humans tend to come to that is being born with a tiny, flesh-covered tail (when the coccyx is malformed), which is almost always removed straight after birth, or being born with spina bifida occulta, which can often present with a birthmark over the site of the malformed vertebrae, which has a tendency to grow hair. This hair has occasionally grown long enough to warrant a person inclusion in a “freak show” as a “tailed man/woman” in the recent past.
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Cross-section of human heart, displaying heart valves, chordae tendineae, and papillary muscles
Have you ever heard the expression “Tugging on your heart-strings”? Well, it’s not completely metaphorical, at least in terminology. There are literally parts of your heart known colloquially as “heart strings”, which have been described in an anatomical sense as far back as Vesalius.
These “heart strings” are more properly called chordae tendineae. You can see them in the illustration, looking like thin wires or netting within the ventricles. They start at the atrioventricular heart valves (the bicuspid or mitral and the tricuspid), and connect to the papillary muscles near the apex of the heart. The collagenous structure of these strings imparts to them a high level of strength, and the papillary muscles combined with some elastin give a high level of flexibility. they’re what keep your heart valves from everting (prolapsing) when the blood moves from the atria to the ventricles.
See, the valves have no muscular structure of their own, but work because the pressure of the blood pushing against them makes them open and close taut. But if the chordae tendineae weren’t there, that same pressure that makes sure they shut well also means that their fibrous structure would end up simply turning inside-out, and the blood would flow back into the atria, instead of to the lungs or the rest of the body. Insufficiency of the heart strings is one of many possible causes of mitral prolapse and valve insufficiency (leaky valves).
Anatomy: Descriptive and Surgical. Henry Gray, 1900.
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Today’s word has an etymology that can even trip up ‘word’ people: anatomy. If you remember the recent etymology given here of atom you’ll recognize the root for anatomy: both words utilize the Ancient Greek word temnein meaning to cut up. The alpha-privative negated that sense giving atom the meaning uncut-able or indivisible. In anatomy, the Ancient Greek prefix ana- gives the meaning up, on, upon, back, toward. It can even enhance the meaning of the word by adding the meaning exceeding or throughout. Our modern English word came in the 14th century via the Middle French word anatomie meaning dissection or skeleton. Anatomy did not acquire its modern meaning of the science of the structure of organized bodies until the 17th century. Today doctors and scientists can ‘cut’ into a persons body using a wide variety of non-invasive techniques such as the MRV (Magnetic Resonance Venogram) shown above.
Image of Reigh Leblanc’s sagittal (i.e. viewed from the side) Auto-Triggered Elliptic Centric Ordered sequence (ATECO) three dimensional gadolinium enhanced Magnetic Resonance Venogram (MRV) courtesy Reigh Leblanc via flickr. It is with deep respect and gratitude that I thank people like Mr. Leblanc for sharing images such as this MRV with the public. Image used under CC 3.0 license.
Image of the Anatomy of the Human Skull from Gray’s Anatomy, image in the public domain.
Image of Brain anatomy by Vesalius also in the public domain.
