Human Body Systems and Functions
The Senses
The Sense of Sight
Components of the eye:
- Extraocular muscles
- Sclera
- Choroid
- Optic nerve
- Crystalline lens
- Iris
- Cornea
- Aqueous humor
- Vitreous humor
- Retina
The Sense of Hearing
Components of the ear:
- Pinna
- External auditory canal
- Eardrum
- Semicircular canals
- Cochlea
- Auditory nerve
- Eustachian tube
- Ossicles (chain of bones)
Coordination Systems
Nervous System
This system receives and transmits information rapidly by electrical impulses, through sensory neurons.
Endocrine System
This system consists of glands that secrete hormones that are carried in the blood to the cells of the target tissue or organ.
Relationship Between Nervous and Endocrine Systems
The hypothalamus is the main center of integration between the nervous and endocrine systems. It receives signals from the nervous system. These signals tell the hypothalamus to produce nerve signals and special hormones: releasing factors and inhibiting factors, that act on the pituitary gland and control the release of hormones.
Transmission of Nerve Impulses
Neurons transmit information as electrical signals. These impulses travel along the neuron, always in the same direction, and exit through the axon terminal. Transmission occurs at a synapse.
Synapse
Neurons are not physically connected; there is a gap between them called a synaptic cleft. The axon terminal releases chemical messengers called neurotransmitters. Neurotransmitters travel across the synaptic cleft and are detected by the receptors of the postsynaptic neuron.
The Peripheral Nervous System
Peripheral Nerves
Composed of axons.
- Cranial Nerves: Emerge from the brain.
- Spinal Nerves: Emerge from the spinal cord.
- Sensory Nerves: Transmit information from the receptors to the CNS.
- Motor Nerves: Transmit information from the CNS to effectors.
- Somatic Nervous System: Involved in voluntary muscle movement and involuntary reflex acts.
- Autonomic Nervous System: Controls unconscious automatic actions, divided into:
Sympathetic Division
Controls the fight-or-flight response in situations of physical or emotional stress.
Parasympathetic Division
Controls activities related to rest and digestion.
Adrenal Glands
Two glands situated on the kidneys:
Cortex
It secretes cortisol for the synthesis of glucose and the breakdown of fats and proteins.
Medulla
Secretes adrenaline; this hormone acts on the autonomic nervous system.
The Function of Reproduction
Gametogenesis
Process of forming gametes; takes place in the gonads.
Fertilization
Joining of two gametes and formation of the zygote.
Embryo Development
Cell division increases the number of cells forming the embryo, which continues developing and becomes a fetus.
Childbirth
Birth of the baby. Human beings are live-bearing. The baby is born fully formed.
Development
The baby grows and reaches maturity.
Treatment of Infectious Diseases
Treatments vary depending on the pathogen:
- Bacteria: Antibiotics. They stop bacteria from reproducing and kill them. Overuse can result in resistant bacteria.
- Virus: Antibodies/Antivirals. Eliminate viruses. Treat viruses like herpes. Some do not have treatments.
- Fungi: Antifungals. Prevent growth, destroying fungi.
- Protozoa: Special Medication. May stop protozoa from reproducing or kill them. Few specific drugs are available.
The Immune Response
Non-Specific Immune Response
- When pathogens enter the body, the capillaries in the area dilate and blood flow increases.
- Capillary permeability increases; blood leaves the blood vessels and flows to the injured area, causing swelling.
- The monocytes that have left the blood vessels become phagocytes.
- Phagocytes wrap their cellular projections, called pseudopodia, around the pathogens.
Specific Immune Response
When a non-specific response does not stop a pathogen, a third line of defense is activated: a specific immune response. This type of response is carried out by lymphocytes, a type of white blood cell. Lymphocytes recognize antigens entering the body. They produce antibodies.
There are T-cells, which recognize antigens and destroy them, and B-cells, which produce antibodies specific to the antigen that activated them.
Some of these cells become memory cells that remain in the body for life. If the same agent invades the body again, the memory cells “remember it,” so the body will be immune to this disease.