Introduction to Human Biology and Health
Endocrine Glands
Endocrine glands are specialized cells of the secretory type, synthesizing chemicals called hormones.
Hormones
Hormones are chemical messengers that have these characteristics:
- They perform their function at a distance from where they are synthesized.
- They act in very small quantities.
Nervous System
Voluntary Act
A voluntary act is a deliberate and conscious response. The preparation of the response takes place in the brain.
Reflex
A reflex is an involuntary response. The nerve center involved in the response is located in the spinal cord.
Reflex Arc
A reflex arc is a nervous structure that produces a response to a given stimulus. The answer is automatic.
Negative Feedback
Negative feedback is a mechanism that regulates hormone production. This regulatory mechanism is controlled by the central nervous system through the hypothalamus and pituitary gland. It keeps adequate levels of hormones in the blood for the duration of the stimulus that has provoked secretion.
Mental Health
Anxiety
Anxiety is an unpleasant state that often accompanies physiological changes similar to fear.
Symptoms: nervousness, difficulty breathing, etc.
Attention Deficit
Attention deficit is the lack of attention, usually diagnosed in childhood but can extend into adolescence and later stages. It is often accompanied by hyperactivity.
Depression
Depression is a disorder that affects the whole body and mood, and interferes with an individual’s daily activities.
Schizophrenia
Schizophrenia is a very serious brain disorder that affects a person’s ability to think clearly, manage emotions, make decisions, etc.
Obsessive-Compulsive Disorder
Obsessive-compulsive disorder is characterized by the presence of obsessions or compulsions, or both at once.
Alzheimer’s and Parkinson’s
Alzheimer’s disease is characterized by mild memory loss, disorientation, and difficulty with reasoning. Parkinson’s disease is caused by the death of neurons in the brain responsible for the coordination of movement and posture. Alzheimer’s symptoms include language difficulties, an inability to follow instructions, and behavioral changes. In Parkinson’s disease, muscle rigidity, difficulty walking, and shaking hands, arms, and legs are more frequent. The cause of these diseases is unknown.
Drugs and Addiction
Tolerance
Tolerance is resistance to a particular drug.
Addiction
Addiction is the physical and psychological dependence that a drug produces.
Withdrawal
Withdrawal occurs after dependency and abrupt drug suspension. It can produce symptoms of physical distress, which depend on the type of drug.
Types of Drugs
- Stimulants: They speed up the normal functioning of the brain, increasing the number of nerve impulses. Examples: coffee, tea, snuff, cocaine.
- Depressants: They relax the nervous system, slowing down performance or causing slowed reactions. Examples: alcohol, opiates, sedatives.
- Hallucinogens: They disrupt brain function, resulting in hallucinations or perceptions that go beyond reality. Examples: cannabis, LSD, hashish.
Sensory Systems
Hearing
Auditory System
The outer ear picks up sounds and transmits them to the eardrum through the external auditory canal. The eardrum vibrates when receiving sounds and transmits this vibration to the fluid that fills the cochlea.
Balance
The semicircular canals in the inner ear are responsible for balance. When the head moves and changes position, the fluid inside the semicircular canals moves as well. If the fluid moves too quickly, the brain can be misinformed, leading to a sense of dizziness or imbalance.
Smell
Pituitary Gland
- Pituitary Red: Occupies the bottom of the pituitary gland. It has abundant blood vessels to warm the inspired air.
- Pituitary Yellow: Occupies the top of the pituitary gland. It contains numerous olfactory receptors, which form the olfactory bulb. The olfactory nerve carries information from the olfactory bulb to the brain.
Sensory Receptors
- Chemoreceptors: Sensitive to chemicals.
- Mechanoreceptors: Sensitive to mechanical stimuli such as touch, pressure, sound, or gravity.
- Photoreceptors: Sensitive to light.
- Thermoreceptors: Sensitive to temperature variations.
- Nociceptors: Sensitive to intense pressures; responsible for pain.
Behavior
Stereotyped Behavior
Stereotyped behavior is innate, meaning it does not need any previous experience to manifest itself.
Acquired Behavior
Acquired behavior develops through repetition and therefore depends on the environment, learning, and the individual.
Diseases of the Sensory Organs
Glaucoma
Glaucoma is increased pressure within the eyeball due to a lack of drainage of aqueous humor.
Cataracts
Cataracts are a loss of transparency of the lens of the eye, which becomes opaque, causing a decrease in vision.
Vision Problems
- Hyperopia (Farsightedness): Images do not focus on the retina but behind it. This may be because the eyeball is too small or there is weakness in the focusing power of the eye.
- Myopia (Nearsightedness): Difficulty focusing on distant objects, which appear blurred. It can be corrected with glasses or surgery.
- Astigmatism: Poor curvature of the cornea, which is not round but instead flat. This prevents the clear focus of objects both near and far. It can be corrected with lenses.
Other Eye Conditions
- Conjunctivitis: Inflammation of the tissue of the sclera, mainly due to infections by microorganisms.
Ear Conditions
- Otitis: Inflammation of the middle ear, often accompanied by the secretion of pus, which causes pain. It is treated with antibiotics.
Skin Conditions
- Psoriasis: A chronic disease characterized by the appearance of red or brown scaly plaques. It generally affects the knees, scalp, and chest.
The Eye
- Lens: An elastic body that allows focusing images.
- Cornea: The transparent area of the sclera.
- Pupil: The opening that regulates the amount of light entering the eye.
- Aqueous Humor: The fluid that fills the space between the cornea and the lens.
- Iris: The colored disc that controls the size of the pupil.
- Vitreous Humor: The clear gel that fills the space between the lens and the retina.
- Blind Spot: The area where the optic nerve exits the eye.
- Optic Nerve: Carries visual information to the brain as impulses.
- Retina: Formed by two types of photoreceptor cells, rods, and cones.
- Choroid: The middle layer of the eye, containing blood vessels that nourish the cells of the eye.
- Sclera: The outer layer of the eye, hard, opaque, and white.