domingo, 17 de septiembre de 2017

La Célula Procariota

Las células procariotas son morfológicamente sencillas. Son en términos generales, sensiblemente más pequeñas que las células eucariotas: apenas suelen sobrepasar la micra o dos micras, mientras que las eucaruotas superan en muchos casos las diez micras. 
Poseen una membrana celular que, a su vez, está rodeada por una pared celular formada por proteínas.
Esta pared celular exterior es la que le aporta la forma externa, además de proteger el interior. Es un elemento muy importante y condiciona, entre otras cosas, la clasificación de los procariotas, que se basa en la morfología de la célula, hablándose de cocos si son esféricos, bacilos si son alargados, vibrios con forma de coma y espirilos si son espirales. O en las características químicas de la membrana, hablándose de bacterias gram positivas si responden a la tinción gram o gram negativas si no responden a esta tinción.
Rodeando la pared celular, muchas bacterias presentan una envoltura denominada cápsula.

miércoles, 13 de septiembre de 2017

La Célula: Teoría Celular

Podemos definir célula como la unidad anatómica y funcional de los seres vivos. Esta definición lleva implícitas los conceptos más importantes que conforman lo que de denominamos teoría celular y que se pueden resumir en los siguientes puntos:

  • La célula es la unidad anatómica de los seres vivos. Es decir, todos los seres vivos están compuestos de una o más células unidas entre.
  • La célula es la unidad funcional de los seres vivos. Es decir, todas las funciones vitales de los seres vivos tienen lugar dentro de una célula o en las inmediaciones de una célula o de un grupo de células.
  • Todas las células provienen de otra célula anterior.

martes, 8 de agosto de 2017

Sensory System

The sensory system is responsible for perceiving stimuli from the environment by the sense organs, sending this information to the central nervous system in order to be interpreted.
The sensory system is made up of five sense with their respective sense organs: sight, hearing, smell, taste and touch.
This is the sense responsible for perceiving electromagnetic radiation from the environment or, in other words, light. Its sense organ is the eye. We are able to perceive electromagnetic radiation with wave-lengths from 400 nm to 700 nm, known as the visible light spectrum (lower radiation, such as ultraviolet rays, or higher radiations such as infrared rays are not visible).
Sight is, in human beings, the predominant sense.
Eye Anatomy
Eyes are the main organs of sight. Their receptor structure is made up of a layer of cells that perceive light, surrounded and protected by a group of accessory structures.
There are internal and external accessory structures. One of the external structures are the eyelids. These are skin folds that cover the external part of the eye and close when in order to prevent the eye from being damaged by light when it is very intense. Eyelids also protect eyes from being damaged by blows. Finally, they extend lubricating fluids over the eye surface.
There are a group of long and thick hairs on the eyelids edge called eyelashes. They protect the eye from little particles, that are captured by the hairs.
The eyebrows are a group of hairs that form a sort of arc above the eye. Their function is preventing sweat and water that run down from the upper part of the head from falling into the eye.
There are group of glands associated located in the edge of the eyelids, called Meibomian glands (also known as tarsal glands). They lubricate the eye surface and protect them from infections.
Finally, the Lacrimal Glands are located in the upper lateral part of the orbit, and they are responsible for humidifying the eye surface. They produce tears that cover the eye surface and flow to the canals situated in the internal corner of the eye, that are connected to the lacrimal sac to drain the liquid.
The sensitive part of the eye is enclosed in a structure called ocular globe. Its diameter is between two and three centimetres long. And its surface can be divided into three consecutive layers, called fibrous, vascular and nervous tunics.
  • Fibrous tunic: this is the outermost covering of the ocular globe. It has two parts. The anterior one is called the cornea, and the posterior one is called the sclerotic. The cornea is a transparent fibrous tissue that covers the iris. Its shape is curved in order to focus and concentrate the incident light. The sclerotic is a dense layer made up of connective tissue, that covers the posterior or internal part of the ocular globe. It has a hole that is crossed by the optic nerve.
  • Vascular tunic: this is the intermediate layer. It has three parts called the choroid, ciliary body and iris. 
    • Choroid: it is an extremely vascularised layer that covers the posterior part of the ocular globe in order to irrigate the retina.
    • Ciliary Body: it is located in the anterior part of the ocular globe, behind the cornea, covering the entrance of the incident light. It has a muscle called the ciliary muscle that surrounds an internal structure called the crystalline. The crystalline is a transparent structure in the shape of a biconvex lens. It is responsible for projecting and focusing the incident light on the retina. The ciliary muscle changes the curvature of the crystalline so it can focus on the retina the image of different objects, depending on the distance they are.
    • Iris: this is the outermost part of the vascular tunic. It is a disc with a central hole called pupil. Light crosses the pupil to reach the crystalline. This internal hole of the pupil can change its diameter in order to control the amount of light that crosses the iris to reach the retina. When it is dark, the pupil dilates to perceive more light, when it is bright the pupil contracts to prevent the light from causing damage to the retina.
  • Nervous Tunic (Retina): this layer covers the internal surface of the posterior part of the ocular globe. It is responsible for perceiving light, due to the activity of the photoreceptors, called rods and cones.

domingo, 2 de julio de 2017

Endocrine System

The endocrine system is, along with the nervous system, the main controller of bodily functions. Both systems are coordinated to carry out their functions and they control each other: the nervous system controls the production and secretion of hormones and some hormones can control the nervous system.
Both systems have, however, some relevant differences. The nervous system carries out its functions very quickly, in milliseconds. And it controls punctual or not very lasting actions. The endocrine system, on the other hand, carries out its functions more slowly, in seconds or even minutes. And it controls lasting actions, that can take minutes, such as the vasodilation promoted by some hormones, hours, such as the digestive process or even years, such as growth.
The endocrine system is the main regulator of the homeostasis and metabolism (both anabolism and catabolism). Its functionality is based on the secretion of chemical substances called hormones. They are produced and released by endocrine glands.

miércoles, 31 de mayo de 2017

Locomotor System: Muscles

Muscular System
Muscles in the head
  • Frontal: it moves the scalp forwards. It raises eyebrows.  It wrinkles the forehead skin.
  • Occipital: it moves the scalp backwards. It is joined to the frontal muscle by the aponeurosis that covers the upper part of the cranium. 
  • Nasal: there are two nasal bones. They wrinkles the nose.
  • Buccinator: it inflates the cheeks.
  • Orbicularis oculis: it closes the eyes.
  • Orbicularis oris: it closes and presses the lips together. It can also push them forwards.
  • Risorius: it pulls the lip commissure sideways. Like smiling
  • Supercilii: it pulls the internal part of the eyebrows down. Like frowning.
  • Zygomatic major: it moves the extremes of the lips upwards. Like laughing.
  • Masseter: it closes the mouth raising the mandible.
  • Temporal: it raises and retracts the mandible. If one of them relaxes and the other contracts, the mandible moves laterally.
  • Levator palpebrae superioris: it raises the upper eyelid.
  • Levator lavi superioris: it raises the upper lip.
  • Digastric: it raises the hyoid bone and descends the mandible to open the mouth.
  • Mentalis: it raises the central part of the lower lip. 

lunes, 22 de mayo de 2017

Locomotor System: Muscular Function

Muscles are responsible for providing the bodily movements. There are also muscles that do not move bones, but provide involuntary movements of internal organs, such as the peristaltic movements of the intestine and the contraction of blood vessels. Finally, when the muscles contract they produce heat (consuming energy).
There are three different types of muscle: smooth, cardiac and skeletal. When we are talking about the locomotor system, however, we are only referring to skeletal muscles, that provide general movements of the skeleton.
The muscular system is an important part of our body. It is 40 % of our total weight.
Structure of muscular fibres
All the skeletal muscles are surrounded by a layer made up of connective tissue called epimysium. The muscle is divided into fascicles by a connective membrane called perimysium. The fascicles are made up of several cells called muscular fibre. Each muscular fibre is surrounded by a thin connective membrane called endomysium. These three membranes join at the edge of the muscle. After the fusion of these membranes, the connective tissue becomes richer in elastic and cartilaginous fibres, forming the tendon. The tendon firmly connects the muscle to the bone.
Skeletal muscle.
The muscle cells that make up the skeletal muscles, called myocytes, are cylindrical and extremely long. Indeed, they can be more than five centimetres long. They have many nuclei, even more than one hundred nuclei per cell.

domingo, 14 de mayo de 2017

Locomotor System: Joints

Joints (Articulations)
Joints are structures responsible for joining different bones. They support the weight of the body and allow the movement of bones. 
According to their movement, articulations can be classified as:
  • Synarthrosis: they do not allow any movement. The joints of the cranial bones are the most typical examples.
  • Amphiarthrosis: they allow slight movements. The joints of the vertebrae are the most typical examples. 
  • Diarthrosis or synovial joints: they allow complete movements. The bones are linked by ligaments. And the part of the bones in contact with other bones are in covered by cartilage. The space between the cartilaginous pieces that cover the bones in the diarthrosis are filled with a liquid that prevent them from friction and it is called synovial fluid. 

According to the type of movement, the synovial articulation can be classified as: