Human Endocrine and Muscular Systems: Functions and Anatomy

Endocrine Glands

Pituitary Gland

The pituitary is a small gland located at the base of the brain. The anterior pituitary secretes growth hormone, prolactin, follicle-stimulating hormone (which stimulates egg production), and luteinizing hormone (responsible for ovulation during the menstrual cycle). The neurohypophysis synthesizes oxytocin, which induces uterine contractions during labor, and regulates urine via the antidiuretic hormone.

Thyroid Gland

The thyroid is a gland located in the neck (upper part of the trachea). It produces thyroxine, which regulates body metabolism and promotes growth, and calcitonin, which decreases the concentration of calcium in the blood.

Parathyroid Glands

These are four small cell masses localized within the thyroid. They secrete parathormone, which controls the quantity of calcium and phosphorus in the blood.

Adrenal Glands

Attached to the top of the kidneys, these glands secrete several hormones:

• Cortisol: Secreted by the cortex, it regulates the metabolism of proteins and carbohydrates.
• Adrenaline: Produced by the medulla, it provokes effects similar to the sympathetic nervous system and increases production during stress.
• Aldosterone: Controls the amount of sodium and potassium in the blood.

Pancreas

The pancreas is a mixed gland (exocrine and endocrine). It secretes glucagon, which increases blood glucose levels from liver glycogen, and insulin, which decreases blood glucose levels by facilitating consumption by tissue cells.

Ovaries and Testes

The ovaries secrete female sex hormones (estrogen and progesterone) that regulate female characteristics and the ovarian cycle. The testicles produce male sex hormones (androgens) that favor the formation of sperm.

Hypothalamus

The hypothalamus is a neural structure at the base of the brain formed by neurons that also manufacture hormones. This organ reacts to external stimuli and variations in hormone concentrations in the bloodstream, stimulating or inhibiting the secretion of endocrine glands.

Muscular System

The musculoskeletal system is composed of the skeletal and muscular systems working as a whole.

Muscle Anatomy

• Belly: The center of the muscle with the capacity to contract.
• Tendons: The two extremities that bind muscles to bones. The extremity closest to the body is called the head, and the other is the tail.

Muscle Classification

• Simple muscles: Have only one belly (e.g., anterior tibial) and are fusiform (widened in the middle and tapered).
• Compound muscles: Contain several bellies and are usually strap-like or flat (e.g., rectus abdominis).
• Striated muscles: Contract voluntarily.
• Smooth muscles: Contract involuntarily.