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'Health and Fitness' is dedicated to all those who wants to have a better health for a better life. A fit body leads to a healthy mind and a healthy mind would in turn have a wealthy soul! So, the aim is to provide with information and guidance to achieve a healthy and wealthy body and soul. Keep Smiling, Keep Reading! Cheers :)

Physiology - Health and Fitness

Bone Marrow

June 2nd 2006 06:30
Bone Marrow

Marrow is a soft tissue of the medullary cavities (medullar = the centre of an organ) of the bone. There are two types of marrow. Yellow marrow consists mostly of fat, and red marrow consists of blood-forming cells and is the only site of blood formation in adults.
Blood cells are made primarily in red bone marrow.


Children’s bones have proportionately more red marrow than adults as they are in their growth and development stage. As a person ages, red marrow is mostly replaced with yellow marrow. In adults, red marrow is confined to the bones in the central axis of the body (e.g. pelvis and skull) and in the most proximal parts of the limbs.

Some types of leukaemia and genetic immune deficiency diseases can be treated with a bone marrow transplant containing blood stem cells - which are blank cells that can turn into specialised cells such as blood cells during hematopoiesis.


References
* Seeley, Stephens and Tate, 2005, 5th edition, McGraw Hill, ‘Essentials of Anatomy and Physiology’
* Image is part of the Public Domain, being a work of the U.S. Federal Government - http://en.wikipedia.org/wiki/Image:Redbloodcells.jpg
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Reflexes

May 29th 2006 03:24
A reflex is an involuntary reaction in response to a stimulus applied to the periphery (e.g. arms, legs, etc) and transmitted to the Central Nervous System (CNS). The purpose of the reflex is to react to stimuli more quickly than is possible by conscious thought. As such, reflexes do not involve the brain which is only aware of the response after it has taken place. Most reflexes occur in the spinal cord or brainstem. Many reflexes have a high survival value, enabling rapid action to avoid potential danger. For example, the withdrawal reflex; which includes the situation of the sudden withdrawal of the hand in response to a pain stimulus.

1) Brain, 2) Brain and Spinal Cord which = CNS, 3) Spinal Cord

There are also learned/conditioned reflexes such as the sight and smell of food which triggers a salivation response. For example, in Pavlov’s Dog experiment: On numerous occasions a bell is rung just before a dog is fed. The dog salivates as usual on receiving its food. Then the bell is rung without any food being presented. The dog still salivates, as it is in response to the bell ringing.

A reflex arc is the neuronal pathway that the reflex follows. It is the basic functional unit of the nervous system because it is the smallest, simplest pathway capable of receiving a stimulus and yielding a response. The reflex arc consists of these 5 components:

• A Sensory Receptor – which senses the stimulus
• A Sensory Neuron – where the electrical signal generated from the sensory receptor travels along
• Interneurons – located between and communicating with two other neurons;
• A Motor Neuron – where the responding signal travels, towards the muscle to activate a response
• An Effector Organ – E.g. The muscle, responding to the stimulus.


The Withdrawal/Painful Stimulus Reflex
The classic example of the withdrawal reflex - the pain of the hot stove

The result of a reflex can be seen when a person’s finger touches a hot stove. Sensory receptors called pain receptors in the skin are stimulated by the hot stove, and action potentials (APs, electrical signals) are produced. Sensory neurons conduct the APs to the spinal cord where the signal transmits to interneurons (a ‘synapse’), then to the motor neurons in the spinal cord. Finally, the signal is transmitted back to the body’s periphery to the flexor muscles in the upper limb which contract and pull the finger away from the stove.

No conscious thought is required for this reflex, and withdrawal of the finger from the hot stove begins before the person is consciously aware of any pain.

The Knee-Jerk/Patella Reflex
This reflex is of the tendon below the knee - the patella tendon.

This is a stretch reflex, meaning that muscles contract in response to a stretching force applied to them. In this particular reflex, stretching occurs when a hammer is tapped just below the knee cap where the patella tendon lies. The patella reflex is important in maintaining posture and in coordinating muscular activity. It is used by doctors to determine if the associated CNS centres are functioning correctly. An absence of or an exaggerated patella reflex is evidence of spinal cord damage.

References

* Seeley, Stephens and Tate, 2005, 5th Edition, “Essentials of Anatomy and Physiology”, McGraw-Hill.
* http://en.wikipedia.org/wiki/Reflex
* Pictures from www.commons.wikipedia.com are listed in the Public Domain
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The Layers of the Heart and Heart Attacks

May 25th 2006 00:33
There are three layers of tissue in the heart; the epicardium, the endocardium, and the myocardium.

The epicardium is also called the visceral pericardium and is a thin membrane forming the smooth outer surface of the heart (‘peri’ = around, and ‘cardium’ = heart).

The endocardium is the inner lining of the heart (‘endo’= within) and allows blood to move easily throughout the heart. Each heat valve is formed by a fold of endocardium with connective tissue between the two layers.

The myocardium is essentially the muscle of the heart (‘myo’ = muscle). As you may already be aware, there are three types of muscle – skeletal, smooth (e.g. in intestines) and cardiac. The myocardium is the thick, middle layer of the heart and is composed of cardiac muscle cells. It is responsible for the ability of the heart to contract.
The physiological horror or Myocardial Infarction - Heart Attack.

Failure of the heart to contract properly (for various reasons) is termed heart failure. Myocardial infarction is another phrase for ‘heart attack’, as an infarct is dead tissue caused by a sudden insufficiency of arterial blood supply. This can be caused by plaque buildup within the walls of blood vessels.
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The ABO Blood Group System

May 19th 2006 06:55
The ABO Blood Group System

The ABO blood group system is used to categorise human blood. ABO antigens (which can be attacked by disease-fighting antibodies) appear on the surface of red blood cells.
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The Vertebral Column - The Spine

May 18th 2006 00:52
Body Part of the Day – The Spine

The vertebral column, otherwise known as the spine or backbone, is the central axis for the skeleton of vertebrates (organisms with backbones). It extends from the base of the skull to slightly past the end of the pelvis. It consists of 26 individual bones, grouped into 4 region of curvatures: cervical (meaning ‘neck’), thoracic, lumbar and pelvic (which includes sacral and coccygeal - from ‘coccyx’, the tailbone).
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The Teeth

May 13th 2006 01:34
Body Part of the Day – The Teeth

There are 32 teeth in the adult mouth, located in the mandible (lower jawbone) and maxillae (bones of upper jaw). Starting from the front of the mouth, each quadrant of teeth contains 2 incisors, one canine, 2 premolars and 3 molars (the third molars are the ‘wisdom teeth’ as they usually appear when the individual is in their late teens or early twenties, when they are supposedly old enough to have acquired some wisdom!).
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Nails

May 12th 2006 08:43
Long nails!
Body Part of the Day - Nails

Fingernails and toenails are made of protein - similar to the composition of hair, but obviously much harder.
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The Brainstem and Cerebellum

May 5th 2006 06:35
Body Part(s) of the Day – The Brainstem and Cerebellum

The Brain - Note: not actual colours...!
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The Skull

April 28th 2006 00:18
Body part of the Day – The Skull

In osteology, (the study of bones, with ‘osteo’ meaning bone) the skull is known as the cranium. It supports the structures of the face and protects the brain against injury.
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