Brain, Nervous & Endocrine Systems: Functions & Hormones
Brain Functions
The two cerebral hemispheres are connected by bundles of nerve fibers, which form the corpus callosum. Most sensory information from the right side of the body passes through the corpus callosum towards the left hemisphere.
The cortex integrates sensory stimuli; in association areas, it produces voluntary motor commands.
Association areas are responsible for higher functions (language, creativity, learning, and memory).
The sensory and motor areas of the brain are so well-known that a perfect correspondence can be established between them.
Classification of the Peripheral Nervous System
- Somatic: Responsible for body movement and function relationships. Involuntary actions. Forms motor pathways (neurons, axons, etc.).
- Vegetative: Controls basic physiological functions. Acts on muscles. Functions unintentionally and automatically. It is divided into:
- Sympathetic: Important in emergency situations where extra energy is needed. Pre-ganglionic neurons are short and leave the marrow and lymph nodes, where they end in a few synapses with post-ganglionic neurons, which are long and go to effector organs.
Parasympathetic: Plays a role in situations involving rest and relaxation. Pre-ganglionic neurons come from the brain and spinal cord. Pre-ganglionic neurons are long and synapse with post-ganglionic neurons, which are short and close to the effectors.
Endocrine System
The whole system of cells, tissues, and organs, including the endocrine glands, secrete hormones. The endocrine system regulates many metabolic and other physiological processes. The glands are classified into two groups:
- Exocrine: Pour their contents into the digestive tract (salivary) or outside the body (sweat).
- Endocrine: Secrete hormones that diffuse through capillaries and are transported by the blood to the tissues where they act.
– Endorphins: These are chemicals that act on nearby cells (paracrine mechanism).
– Hormones: Manufactured in endocrine glands, travel through the blood, and act only on cells that have receptors in their membranes to bind them (endocrine regulation).
– Pheromones: Volatile chemicals that allow information sharing between organisms.
Functions of the Human Endocrine System
It has several functions:
- Maintains constant control.
- Intervenes in the stress response (epinephrine release).
- Controls growth and reproduction.
Types of Hormones
There are several types of hormones:
- Derived from amino acids: thyroid and adrenal medulla hormones.
- Derivatives of fatty acids: prostaglandins.
- Steroids: sex hormones and adrenal cortex hormones.
- Peptides: oxytocin and antidiuretic hormones.
Mechanism of Action of Hormones
It depends on their chemical nature:
– Liposoluble Hormones: Pass through the membrane easily. They bind to a specific receptor to reach the nucleus. There, they favor the transcription of certain genes on DNA, inducing the synthesis of proteins, which exert the hormonal action.
– Hydrosoluble Hormones: Cannot cross the membrane. They bind to specific receptors, leading to the release of compounds inside the cell. These act as messengers of hormones and are called second messengers.
Regulation of Hormone Levels in the Blood
There are two ways to control the amount of hormones in the blood:
- Activating or inhibiting their synthesis and secretion.
- Altering the speed at which they are removed from the body.
When the hormone level is high, synthesis is inhibited; when levels are low, the synthesis of hormones and glands is activated. This is the mechanism of negative feedback.