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Is the knee locking mechanism present in animals?

Is the knee locking mechanism present in animals?


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We study in human anatomy that when the knee is in full extension, the femur slightly medially rotates on the tibia to lock the knee joint in place. This reduces the work required to be done by the hefty thigh muscles. This happens in the knees in humans since they are the weight bearing joints.

So, is the mechanism of locking present in other animals? If yes, is it even in the fore limbs or just the hind limbs?


Yes, the mechanism of patellar locking does occur in quadrupeds too. Although they are 4 limbed, a major portion of the weight is borne by the hind limbs. This is known as the stay apparatus and includes the mechanisms of Patellar locking, reciprocal mechanism and check apparatus.

On the other hand in the forelimb, although there is no locking mechanism as such, there exists a neat difference from the human anatomy. Human forelimbs are majorly adapted for manipulation but for quadrupeds, they are weight bearing. There exists what is called the stay apparatus - which includes the suspensory apparatus and the check apparatus.

For a detailed explanation for the interested reader, heres a helpful link - https://en.wikivet.net/Stay_Apparatus_-_Horse_Anatomy


Scientists Pinpoint How A Flamingo Balances On One Leg

Scientists have now shown that this position requires almost no muscle activity from the flamingo.

Most anyone who has encountered a flamingo has probably been impressed by its signature ability to balance on a single long, spindly leg for remarkably long periods of time.

But actually, scientists have now shown that what appears to be a feat requires almost no muscle activity from the bird.

In fact, they found even a dead flamingo's body will naturally fall into a stable one-leg balance if positioned vertically. That research was recently published in Biology Letters.

Until now there have been two basic schools of thought about why a flamingo stands on one leg, Lena Ting, a biomedical engineer at Emory University and Georgia Institute of Technology, tells The Two-Way.

The Two-Way

How Snakes Lost Their Legs

Some scientists have suggested it was a way for the bird to conserve heat that would have been lost if that foot had been in the cold water. Others thought it was a way to reduce muscle fatigue, letting one leg rest while the other did the work.

But for muscles to get fatigued, the posture must actually be tiring for the bird.

Nobody had ever tested whether the flamingo's iconic one-legged posture required any actual muscle effort — until now.

Ting and co-author Young-Hui Chang from the Georgia Institute of Technology headed to Zoo Atlanta, where they tested eight juvenile Chilean flamingos using a device called a force plate. She compares the machine to a Wii balance board or a high-tech bathroom scale – it "can measure the small motions of the body when you stand."

The researchers tested the movements of eight juvenile flamingos at Zoo Atlanta. Rob Felt hide caption

The researchers tested the movements of eight juvenile flamingos at Zoo Atlanta.

They recorded a small amount of swaying motion when the animals were awake. But then something surprising happened – when an animal dozed off, the swaying dropped off dramatically.

"And that's the opposite of what we would expect for you or me — if I was standing on one leg and then closed my eyes, typically I would see a great increase in the amount of body sway and usually that results in people having to put their foot down," she says.

It suggests that while awake and active, the bird's swaying could be correcting for other movements, ultimately settling into a position while asleep that requires little to no muscle activity.

That was put to the test in an experiment with a flamingo cadaver, which of course has no muscle activity because it is not living.

First, the researchers tried manipulating the cadaver's joint in search of a locking mechanism that could explain the stability, she says. But the joint moved very loosely and did not lock.

The key moment happened when they rotated the bird into a standing position: "We held onto its ankle . and we turned it vertically, and then all of a sudden it just collapsed right into the position that you see when they're standing on one leg."

This video shows the remarkable stability of the cadaver, even when it is pushed and pulled in different directions. (A warning to the sensitive viewer: It is a video of a dead flamingo, though the scientists say the animal was euthanized for other reasons and was not harmed for the study.)

This suggests that the reason for the animal's stability is mechanical and is actually aided by gravity. "What we showed is that when they go to sleep their bodies can sort of flap forward due to gravity, and then the whole thing just collapses and becomes very stable," Ting says.

The mechanics behind a flamingo's leg are a bit counterintuitive. The flamingo actually has an upper leg bone that is positioned horizontally, hidden among its feathers. A knee connects that bone to the long, slender part that it stands on. And the knobby bit in the center of that vertical portion is actually the bird's ankle.

When the flamingo lifts its leg, its body folds forward, so the center of gravity is pushing down on the leg from the front of the body — perfectly balancing it.

A diagram of the limb posture and anatomy of a sleeping flamingo. Biology Letters hide caption

In fact, says Ting, "our research also suggests that it may require less effort for the flamingos to stand on one leg than on two." The bird was not able to maintain this kind of passive balancing on two legs as Ting explained, when the leg unfolded the joint "sort of collapsed" from its more stable position balanced on one leg.

This study is not inconsistent with the idea that flamingos stand on one leg to reduce heat loss, especially if the bird doesn't need to expend much energy to do so.

But Ting says it may be even simpler than that: They may just balance on one leg because it's easier for them than any other way.

It's worth noting that lots of other birds balance on one leg too, such as wood ducks and storks. Ting says this could be a "more general mechanism that many birds use."


Fill in the Blank

A difference between an acute disease and chronic disease is that chronic diseases have an extended period of __________.

A person steps on a rusty nail and develops tetanus. In this case, the person has acquired a(n) __________ disease.

Short Answer

Brian goes to the hospital after not feeling well for a week. He has a fever of 38 °C (100.4 °F) and complains of nausea and a constant migraine. Distinguish between the signs and symptoms of disease in Brian&rsquos case.

Critical Thinking

Two periods of acute disease are the periods of illness and period of decline. (a) In what way are both of these periods similar? (b) In terms of quantity of pathogen, in what way are these periods different? (c) What initiates the period of decline?

In July 2015, a report 4 was released indicating the gram-negative bacterium Pseudomonas aeruginosa was found on hospital sinks 10 years after the initial outbreak in a neonatal intensive care unit. P. aeruginosa usually causes localized ear and eye infections but can cause pneumonia or septicemia in vulnerable individuals like newborn babies. Explain how the current discovery of the presence of this reported P. aeruginosa could lead to a recurrence of nosocomial disease.

15.2: How Pathogens Cause Disease


A Labeled Diagram of the Knee With an Insight into Its Working

To understand one of the most complex joints of our body i.e. the knee joint, you need a perfectly labeled diagram of the knee. This will help you to understand the mechanism as well as the working.

To understand one of the most complex joints of our body i.e. the knee joint, you need a perfectly labeled diagram of the knee. This will help you to understand the mechanism as well as the working.

We use our knee joints when we sit, fold legs, run, walk or do any kind of leg movement. They connect the lower leg to the rest of the body and gives stability, flexibility and strength. They support the legs to bear the body weight and also help in proper locomotion. Any disorder or defect in the knee bone can restrict the activities of the leg which can directly affect our locomotion. Below given knee diagram will help you to understand the various parts and functioning of the knee joint.

Labeled Diagram of the Knee Joint

Knee joint is one of the most important hinge joints of our body. Its complexity and its efficiency is the best example of God’s creation. The anatomy of the knee consists of bones, muscles, nerves, cartilages, tendons and ligaments. All these parts combine and work together. Damage in even one part can hinder the functioning of the knee. The given diagram of the knee joint can help you to understand its various parts and the description given below will give you an insight of the functioning of the knee.

Would you like to write for us? Well, we're looking for good writers who want to spread the word. Get in touch with us and we'll talk.

There are three bones in the knee namely the femur which is the thigh bone, tibia which is the shin bone and patella which is the knee cap.Femur is the largest bone of our body, which meets the tibia or shin bone at tibiofemoral joint. Patella sits over the other two bones and slides to facilitate the movement. These bones are firmly attached with the help of muscles and tendons which also save the bones from injury.

⚫ Muscles

Quadriceps and hamstring muscles are the major ones which are associated with the knee joint. Four quadriceps muscles are present in front of the knee which help in straightening the leg from the knee. The hamstring muscles are present at the back of the knee and help in bending. Although calf muscles are not associated with the knee joint, their work is to help in controlling the knee while walking.

⚫ Nerves

Knee nerves allow the sensory orientation in the joints. These nerves help in coordinating movements while walking, running, standing, etc. These nerves are very delicate and can be affected in case of injury which may lead to severe knee pain.

⚫ Cartilages

Cartilages are thin layers present in between the bone which decreases the friction. There are two types of cartilage present in the knee. They are fibrous (meniscus) cartilage and hyaline (articular) cartilage. Fibrous or meniscus cartilage is known for its shock absorbing quality. It is C-shaped and helps in resisting body pressure. Meniscus cartilage is further divided into medial meniscus and lateral meniscus. Hyaline cartilage or articular cartilage covers the joint surface and helps in the smooth movement of bones which is facilitated by the synovial fluid. Cartilages wear off with time. This is the reason why old people are more susceptible to fractures and pain joints.

⚫ Tendons and Ligaments

Tendons are the connective tissues between the bones and the muscles. Tendons in the knee play a very important role in holding the knee and the muscles together. The patellar tendon holds the patella with other two bones, similarly iliotibial band helps in supporting tibia and fibula. Now let’s come to ligaments of the knee. They are the connective tissues between two bones. There are four types of ligaments namely Medial Collateral Ligament (MCL), Lateral Collateral Ligament (LCL), Anterior Cruciate Ligament (ACL) and Posterior Cruciate Ligament (PCL). MCL provides stability to the inner knee and LCL provides stability to the outer part. ACL and PCL are present in the center of the knee. ACL helps in limiting the rotation and forward movement of tibia whereas PCL limits the backward movement of the same.

So, these are the part of the knee which facilitates walking, running and many such movement in the human body. The joint allows flexion, extension and even rotation of the lower leg till some extend. Knee joint is very frequently used and this is the reason why it is prone to injury. Knee exercises are considered to be very helpful in healing knee injuries. In severe cases, knee replacement surgeries are also conducted. I hope the above given diagram and description of the knee was helpful for you to understand the knee anatomy in detail.


Alcohol and Gastrointestinal Tract Function

4.1.2 Liver function tests

The term liver function tests is assigned for biochemical tests that assess the functional hepatic reserve and include tests containing bilirubin, aspartate transaminase (AST), alanine transaminase (ALT), AP, GGT, and LDH.

Although most cases of liver disease can be diagnosed by other serological markers, diagnosis could not be made in 81 of 1124 patients (7%) with abnormal liver tests ( Daniel and Marshal, 2000 ). This suggests that the majority of asymptomatic individuals with serum ALT abnormalities may not have demonstrable liver disease.

Elevated transaminases – ALT is found in the cytosol of liver, whereas two AST isoenzymes are located in the cytosol and mitochondria. Both enzymes are released into the blood in increasing amounts when the liver cell membrane is damaged. The most common causes of elevated transaminase levels are chronic hepatitis B and C, alcohol-related liver injury, nonalcoholic steatohepatitis, hemochromatosis, Wilson's disease, alpha-antitrypsin deficiency, and a recently recognized cause, celiac sprue.

Minor elevation (< 2 times) of upper limit of normal (ULN). This is a common condition.

Mild elevation (2 to < 5 times) of ULN.

Alcohol use is a common cause of mild elevation of transaminases. The quantity of alcohol and length of time that alcohol has been consumed account for the development of disease ( Carey, 2000 ). Alcoholic hepatitis is commonly associated with an AST/ALT ratio of approximately 2:1 and the AST rarely exceeds 300 Iu dl −1 . Other causes are drugs, hepatitis C, nonalcoholic steatohepatitis, etc.

Moderate elevation of AST/ALT (5–15 times) of ULN – entire spectrum of hepatic diseases.

Severe AST/ALT elevation (> 15 times) of ULN – severely ill patient with liver disease.

4.1.2.1 Serum bilirubin

Bilirubin is an endogenous organic anion which binds reversibly to albumin and is transported to the liver, where it is conjugated to glucuronic acid and excreted in the bile. Hepatobiliary disease is indicated when the conjugated fraction of total bilirubin exceeds the ULN, even if the total serum bilirubin concentration is normal or near normal ( Rosen and Keeffe, 1998 ).

4.1.2.2 Albumin

Most circulating proteins in plasma are synthesized in the liver. Albumin accounts for 65% of serum protein and has a half-life of about 3 weeks. Expanded plasma volume or decreased albumin synthesis can result in hypoalbuminemia. In general, albumin levels are affected by severe chronic liver disease, urinary protein losses, hypercatabolic states, and GI losses ( Friedman et al., 1996 Zoli et al., 1991 ).

4.1.2.3 International normalized ratio

Coagulation factors reflect synthetic liver function. Most of them, including fibrinogen, are vitamin k-dependent factors (prothrombin and factors VII, IX, and X) and factor V ( Friedman et al., 1996 ). Severity and prognosis of liver disease can be assessed using international normalized ratio. However, international normalized ratio is not absolutely sensitive, and can be normal in cirrhosis ( Moseley, 1996 ).

4.1.2.4 Alkaline phosphatase

Sources: AP originates predominantly from two sources: liver and bone ( Daniel et al., 1999 ). It is also present in kidneys, small bowel, and placenta.

Serum 5′-nucleotidase or GGT is usually elevated in parallel with the elevation in AP in patients with liver disorders, but they are not increased in patients with bone disorders. If the increase in AP is less than 50% above the normal level, the results of all the other liver enzyme tests are normal, and the patient has no symptoms and observation alone is suggested ( Tukey and Strassburg, 2000 ).

4.1.2.5 Gamma glutamyl transferase

Source: GGT is a membrane enzyme found in hepatocytes and biliary epithelial cells. Serum GGT provides a very sensitive indicator of the presence or absence of hepatobiliary disease. Elevated levels of GGT have been reported in a wide variety of clinical conditions, including pancreatic disease, myocardial infarction, renal failure, diabetes, and alcoholism. High serum GGT levels are also found in patients taking medications such as phenytoin and barbiturates ( Tiribelli and Ostrow, 1996 ).

Serum GGT can be used to confirm the hepatic origin of elevated ALP or to support the diagnosis of alcohol abuse. Due to lack of specificity and the highly inducible property of this enzyme, an extensive evaluation of an isolated GGT elevation in an otherwise asymptomatic individual is not warranted ( Zobair, 1998 ).


Journal of Animal Science and Biotechnology

Pyrroloquinoline quinone regulates the redox status in vitro and in vivo of weaned pigs via the Nrf2/HO-1 pathway

Authors: Caiyun Huang, Zijuan Fan, Dandan Han, Lee J. Johnston, Xi Ma and Fenglai Wang

Lignocellulose as an insoluble fiber source in poultry nutrition: a review

Authors: Ilen Röhe and Jürgen Zentek

Microalgal-based feed: promising alternative feedstocks for livestock and poultry production

Authors: Imen Saadaoui, Rihab Rasheed, Ana Aguilar, Maroua Cherif, Hareb Al Jabri, Sami Sayadi and Schonna R. Manning

Dietary resveratrol attenuation of intestinal inflammation and oxidative damage is linked to the alteration of gut microbiota and butyrate in piglets challenged with deoxynivalenol

Authors: Yueqin Qiu, Jun Yang, Li Wang, Xuefen Yang, Kaiguo Gao, Cui Zhu and Zongyong Jiang

Effects of supplements differing in fatty acid profile to late gestational beef cows on cow performance, calf growth performance, and mRNA expression of genes associated with myogenesis and adipogenesis

Authors: Taoqi Shao, Frank A. Ireland, Joshua C. McCann and Daniel W. Shike

GMOs in animal agriculture: time to consider both costs and benefits in regulatory evaluations

Authors: Alison L Van Eenennaam

Alternatives to antibiotics as growth promoters for use in swine production: a review

Structures and characteristics of carbohydrates in diets fed to pigs: a review

Authors: Diego M. D. L. Navarro, Jerubella J. Abelilla and Hans H. Stein

Lysozyme as an alternative to growth promoting antibiotics in swine production

Authors: W. T. Oliver and J. E. Wells

Fermented liquid feed for pigs: an ancient technique for the future

Authors: Joris AM Missotten, Joris Michiels, Jeroen Degroote and Stefaan De Smet

2021

Thematic series
The progress of low protein diet in poultry
Edited by: Prof. Jianmin Yuan
Collection published: 6 January 2021

2020

Special Issue
Special Issue for JASB 10th Anniversary
Edited by: Prof Dorian Garrick
Collection published: 17 April 2020

Thematic series
Gut microbiota of poultry
Edited by: Prof Guolong Zhang
Collection published: 13 March 2020

2019

Thematic series
Pig gut microbiota: Challenges and opportunities to improve the pig
Edited by: Prof Paolo Trevisi and Prof Jürgen Zentek
Collection published: 24 May 2019

Thematic series
Frontier research in intestinal health of pigs and chickens
Edited by: Prof Sung Woo Kim
Collection published: 14 January 2019

2018

Thematic series
Genome editing in domestic animals
Edited by: Prof Jae Yong Han
Collection published: 29 January 2018

2016

Thematic series
Gastrointestinal microbial ecology and functionality
Edited by: Prof Jianxin Liu, Prof Weiyun Zhu
Collection published: 8 November 2016

2015

Thematic series
Alternatives to antibiotics as growth promoters for use in swine production
Edited by: Prof Phil Thacker
Collection published: 21 October 2015

Thematic series
Fat nutrition and metabolism in food animals
Edited by: Prof Jack Odle
Collection published: 21 May 2015

Thematic series
Animal reproductive biology
Edited by: Prof Fuller Bazer
Collection published: 26 March 2015

2013

Thematic series
Special Issue for WCAP 2013
Edited by: Prof Defa Li
Collection published: 30 August 2013

Thematic series
Special Issue for Chinese Swine Industry Symposium
Collection published: 8 July 2013

Thematic series
Animal Production
Collection published: 14 March 2013

Thematic series
Reproduction and physiology
Collection published: 14 March 2013

Thematic series
Animal Nutrition
Collection published: 14 March 2013

Thematic series
Animal Genetics
Collection published: 14 March 2013


Reflex Testing [ edit | edit source ]

Deep Tendon (muscle stretch) Reflexes [ edit | edit source ]

Evaluates afferent nerves, synaptic connections within the spinal cord, motor nerves, and descending motor pathways. Lower motor neuron lesions (eg affecting the anterior horn cell, spinal root or peripheral nerve) depress reflexes: upper motor neuron lesions increase the reflexes.

Reflexes tested include the following:

    (innervated by C5 and C6)
  • Radial brachialis (by C6) (by C7)
  • Distal finger flexors (by C8)
  • Quadriceps knee jerk (by L4) jerk (by S1)
  • Jaw jerk (by the 5th cranial nerve)

Technique for testing reflexes [ edit | edit source ]

  1. The muscle group to be tested must be in a neutral position (i.e. neither stretched nor contracted).
  2. The tendon attached to the muscle(s) which is/are to be tested must be clearly identified. Place the extremity in a positioned that allows the tendon to be easily struck with the reflex hammer.
  3. To easily locate the tendon, ask the patient to contract the muscle to which it is attached. When the muscle shortens, you should be able to both see and feel the cord like tendon, confirming its precise location.
  4. Strike the tendon with a single, brisk, stroke. You should not elicit pain.

This grading system is rather subjective.

  • 0 No evidence of contraction
  • 1+ Decreased, but still present (hypo-reflexic). Hyporeflexia is generally associated with a lower motor neuron deficit (at the alpha motor neurons from spinal cord to muscle) eg Guillain–Barré syndrome
  • 2+ Normal
  • 3+ Super-normal (hyper-reflexic) Hyperreflexia is often attributed to upper motor neuron lesions eg Multiple sclerosis
  • 4+ Clonus: Repetitive shortening of the muscle after a single stimulation [4]

Note any asymmetric increase or depression. Jendrassik manoeuvre can be used to augment hypoactive reflexes ie the patient locks the hands together and pulls vigorously apart as a tendon in the lower extremity is tapped or can push the knees together against each other, while the upper limb tendon is tested.

The video below illustrates the testing of the deep tendon reflexes

Pathologic reflexes [ edit | edit source ]

Pathologic reflexes (eg, Babinski, rooting, grasp) are reversions to primitive responses and indicate loss of cortical inhibition.

Other reflexes [ edit | edit source ]

Clonus (rhythmic, rapid alternation of muscle contraction and relaxation caused by sudden, passive tendon stretching) testing is done by rapid dorsiflexion of the foot at the ankle. Sustained clonus indicates an upper motor neuron disorder. [6]


Homeostasis: Thermoregulation

Animals use different modes of thermoregulation processes to maintain homeostatic internal body temperatures.

Learning Objectives

Outline the various types of processes utilized by animals to ensure thermoregulation.

Key Takeaways

Key Points

  • In response to varying body temperatures, processes such as enzyme production can be modified to acclimate to changes in the temperature.
  • Endotherms regulate their own internal body temperature, regardless of fluctuating external temperatures, while ectotherms rely on the external environment to regulate their internal body temperature.
  • Homeotherms maintain their body temperature within a narrow range, while poikilotherms can tolerate a wide variation in internal body temperature, usually because of environmental variation.
  • Heat can be exchanged between environment and animals via radiation, evaporation, convection, or conduction processes.

Key Terms

  • ectotherm: An animal that relies on external environment to regulate its internal body temperature.
  • endotherm: An animal that regulates its own internal body temperature through metabolic processes.
  • homeotherm: An animal that maintains a constant internal body temperature, usually within a narrow range of temperatures.
  • poikilotherm: An animal that varies its internal body temperature within a wide range of temperatures, usually as a result of variation in the environmental temperature.

Thermoregulation to Maintain Homeostasis

Internal thermoregulation contributes to animal’s ability to maintain homeostasis within a certain range of temperatures. As internal body temperature rises, physiological processes are affected, such as enzyme activity. Although enzyme activity initially increases with temperature, enzymes begin to denature and lose their function at higher temperatures (around 40-50 C for mammals). As internal body temperature decreases below normal levels, hypothermia occurs and other physiological process are affected. There are various thermoregulation mechanisms that animals use to regulate their internal body temperature.

Types of Thermoregulation (Ectothermy vs. Endothermy)

Thermoregulation in organisms runs along a spectrum from endothermy to ectothermy. Endotherms create most of their heat via metabolic processes, and are colloquially referred to as “warm-blooded.” Ectotherms use external sources of temperature to regulate their body temperatures. Ectotherms are colloquially referred to as “cold-blooded” even though their body temperatures often stay within the same temperature ranges as warm-blooded animals.

Ectotherm

An ectotherm, from the Greek (ektós) “outside” and (thermós) “hot,” is an organism in which internal physiological sources of heat are of relatively small or quite negligible importance in controlling body temperature. Since ectotherms rely on environmental heat sources, they can operate at economical metabolic rates. Ectotherms usually live in environments in which temperatures are constant, such as the tropics or ocean. Ectotherms have developed several behavioral thermoregulation mechanisms, such as basking in the sun to increase body temperature or seeking shade to decrease body temperature.

Ectotherm: The Common frog is an ecotherm and regulates its body based on the temperature of the external environment.

Endotherms

In contrast to ectotherms, endotherms regulate their own body temperature through internal metabolic processes and usually maintain a narrow range of internal temperatures. Heat is usually generated from the animal’s normal metabolism, but under conditions of excessive cold or low activity, an endotherm generate additional heat by shivering. Many endotherms have a larger number of mitochondria per cell than ectotherms. These mitochondria enables them to generate heat by increasing the rate at which they metabolize fats and sugars. However, endothermic animals must sustain their higher metabolism by eating more food more often. For example, a mouse (endotherm) must consume food every day to sustain high its metabolism, while a snake (ectotherm) may only eat once a month because its metabolism is much lower.

Homeothermy vs. Poikilothermy

Homeotherm vs. Poikilotherm: Sustained energy output of an endothermic animal (mammal) and an ectothermic animal (reptile) as a function of core temperature. In this scenario, the mammal is also a homeotherm because it maintains its internal body temperature in a very narrow range. The reptile is also a poikilotherm because it can withstand a large range of temperatures.

A poikilotherm is an organism whose internal temperature varies considerably. It is the opposite of a homeotherm, an organism which maintains thermal homeostasis. Poikilotherm’s internal temperature usually varies with the ambient environmental temperature, and many terrestrial ectotherms are poikilothermic. Poikilothermic animals include many species of fish, amphibians, and reptiles, as well as birds and mammals that lower their metabolism and body temperature as part of hibernation or torpor. Some ectotherms can also be homeotherms. For example, some species of tropical fish inhabit coral reefs that have such stable ambient temperatures that their internal temperature remains constant.

Means of Heat Transfer

Heat can be exchanged between an animal and its environment through four mechanisms: radiation, evaporation, convection, and conduction. Radiation is the emission of electromagnetic “heat” waves. Heat radiates from the sun and from dry skin the same manner. When a mammal sweats, evaporation removes heat from a surface with a liquid. Convection currents of air remove heat from the surface of dry skin as the air passes over it. Heat can be conducted from one surface to another during direct contact with the surfaces, such as an animal resting on a warm rock.

Mechanisms for heat exchange: Heat can be exchanged by four mechanisms: (a) radiation, (b) evaporation, (c) convection, or (d) conduction.


How Prosthetic Limbs Work

How do modern prosthetic limbs compare to those of historical times? One major difference is the presence of newer materials, such as advanced plastics and carbon-fiber composites. These materials can make a prosthetic limb lighter, stronger and more realistic. Electronic technologies make today's advanced prosthetics more controllable, even capable of automatically adapting their function during certain tasks, such as gripping or walking.

While new materials and technologies have certainly modernized prosthetics over the past century, the basic components of prosthetic limbs remain the same. Let's go over some of these.

The pylon is the internal frame or skeleton of the prosthetic limb. The pylon must provide structural support and has traditionally been formed of metal rods. In more recent times, lighter carbon-fiber composites have been used to form the pylons. The pylons are sometimes enclosed by a cover, typically made from a foam-like material. The cover can be shaped and colored to match the recipient's skin tone to give the prosthetic limb a more lifelike appearance.

The socket is the portion of the prosthetic device that interfaces with the patient's limb stump or residual limb. Because the socket transmits forces from the prosthetic limb to the patient's body, it must be meticulously fitted to the residual limb to ensure that it doesn't cause irritation or damage to the skin or underlying tissues. A soft liner is typically situated within the interior of the socket, and a patient might also wear a layer of one or more prosthetic socks to achieve a more snug fit.

The suspension system is what keeps the prosthetic limb attached to the body. The suspension mechanism can come in several different forms. For example, in the case of a harness system, straps, belts or sleeves are used to attach the prosthetic device. For some types of amputations, the prosthetic is able to stay attached just by fitting around the shape of the residual limb. One of the most common types of suspension mechanisms relies on suction. In this scenario, the prosthetic limb fits snugly onto the residual limb, and an airtight seal keeps it in place.

Though most prosthetic limbs have these basic components in some form, each device is unique and designed for a specific type and level of amputation. Whether an amputation is above or below major joints, like the elbow or knee, makes a big difference in what type of prosthetic limb is required. For example, a transfemoral amputation -- an amputation above the knee -- requires a prosthetic device with an artificial knee, while a transtibial amputation -- an amputation below the knee -- allows the patient to retain the use of his or her own knee.

So now we know the components that make up a prosthetic device, but how are prosthetic limbs made, anyway?

Though it's still a relatively new and developing technique, experiments with limb transplantation have shown promising results. It's an extremely complicated surgery, yet several patients have successfully received transplanted hands at the Jewish Hospital, based in the Louisville Medical Center of the University of Louisville, Ky.


If a giraffe's neck only has seven vertebrae, how is it so flexible?

Certain characteristics of giraffe necks give them a flexibility rivaling any Slinky. The first feature is the way that the vertebrae in the neck, called the cervical vertebrae, are joined together. Remember that giraffes have seven of these bones, just like we do. However, giraffe cervical vertebrae are bound together with ball-and-socket joints [source: Owen]. These are the kinds of joints that link your arm with your shoulder and offer a 360-degree range of motion. Also, the joint between its neck and skull permits the giraffe to extend its head almost completely perpendicular to the ground.

Moving down to where the neck meets the back, we find the second important anatomical feature for the giraffe's slinkiness. We call the vertebrae in the top portion of our backs the thoracic vertebrae. In humans, thoracic vertebrae are joined at the middle of the bone to provide added stability and our cervical vertebrae fuse at the front and back for more mobility. Giraffe anatomy doesn't follow this same construction, and its first and second thoracic vertebrae are bound in the same way that its cervical ones are, with ball-and-socket joints [source: Dagg and Foster]. That adaptation gives the giraffe an extra point of flexibility. It also accounts for the giraffe's signature hump [source: Encarta].

This highly flexible, yet heavy, body part is integral to the gangly animal's movement. Watch a giraffe and you'll notice that the neck moves back and forth with its stride. That's because the weight and motion of the neck guides the giraffe's center of gravity [source: Dagg and Foster]. The animal also tosses its neck to and fro to help it rise to a standing position on its spindly legs. You can compare this to when we swing our arms up over our head to pull us out of bed in the morning.

As another result of the long neck, a giraffe's blood has a long journey to travel. For that reason, the anatomy of a giraffe is quite amazing. The animal has a specialized cardiovascular system that keeps blood moving adequately to the brain and heart when it moves its neck and head around, ensuring that bending down to take a sip of water won't cause a possibly lethal head rush [source: Dagg and Foster]. Giraffes' blood vessels are equipped with valves that prevent blood from backtracking due to gravity [source: Wood and Johansen]. They also have a higher concentration of red blood cells, larger hearts and tighter skin, especially around their legs, which help circulate blood better [source: Dagg and Foster].

Keeping everything chugging along, the giraffe also breathes at a relatively slow rate. Its enlarged lungs compensate for the trachea's extensive length, as the air travels up that long highway of a neck.


Watch the video: Συνήγορος: Τι ισχύει με τα ζώα συντροφιάς - 13618 (July 2022).


Comments:

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