Human Body Systems: Movement, Response, and Regulation
Responses to Stimuli
Responses relate to approved movements of two distinct types: voluntary acts and reflex acts.
- Voluntary acts: These are actions that we decide to conduct. The brain is responsible for these acts of will.
- Reflex acts: These are involuntary actions or responses that are produced and coordinated in the spinal cord.
The Endocrine System
Responses related to the endocrine system involve hormones, whose function is to test substances for the functioning of certain organs called target organs.
The Locomotor System
The locomotor system is constituted by the skeletal and muscular systems.
The Skeletal System
Functions:
- Supports the body.
- Protects delicate organs (e.g., the skull protects the brain).
- Enables a variety of movements.
- Constitutes an important deposit of minerals (e.g., calcium).
The human skeleton consists of 208 bones. These can be grouped into two zones:
- Axial skeleton:
- Head
- Vertebral column
- Ribs
- Sternum
- Appendicular skeleton:
- Upper limbs
- Shoulder girdle (clavicle and scapula)
- Arm
- Forearm
- Wrist
- Hand
- Upper limbs
Upper Extremity
- Arm Bones: The head of the humerus, with its smooth, rounded articular surface, joins the glenoid cavity of the scapula’s acromion.
- Lower Extremity: Flattened from front to back, it has a humeral articular surface called the trochlea for the olecranon of the ulna and the radial head.
- Forearm Bones: Ulna and radius.
- Hand Bones:
- Carpal bones (wrist)
- Metacarpal bones
- Phalanges (finger bones)
Joints
Joints are unions between two bones.
- Fixed joints: These are joints that do not have the capacity for movement (e.g., skull joints).
- Semi-mobile joints: These are joints that have a limited capacity for movement.
- Mobile joints: These joints permit a large range of motion (e.g., elbow).
Ligaments: Their function is to connect and reinforce bones and joints.
Muscular System
The muscular system is formed by muscles that are united to bones and cover the skeleton. These are called skeletal muscles (voluntary contractions).
Movement
Movement is the response to a stimulus. Movement is possible because of the way bones join together through joints and muscles, and also because of the capacity of muscles to contract and relax. We have both reflex and voluntary movements.
The Endocrine System
The endocrine system is in charge of responses related to hormones. The system is constituted by a group of organs specialized in the elaboration of hormones, called endocrine glands. The activity of endocrine glands is controlled by the hypothalamus, a group of neurons located in the lower part of the brain that has a secretory function.
Main Endocrine Glands
- Pituitary gland: A small structure located below the hypothalamus. It is divided into two lobes and secretes growth hormone, prolactin, follicle-stimulating hormone, and thyroid-stimulating hormone.
- Thyroid and Parathyroid glands: The thyroid is located at the base of the neck, next to the trachea, and secretes thyroxine. The parathyroid is situated in a small area on the posterior part of the thyroid and secretes parathyroid hormone.
- Pancreas: A gland attached to the digestive system, located at the height of the waist on the left side of the body. It secretes insulin and glucagon.
- Adrenal glands: Situated on the kidneys, they secrete hormones such as cortisol. The adrenal medulla secretes adrenaline.
- Ovaries and Testicles: These are organs that produce sperm and ovules. Ovaries secrete estrogen and progesterone, while testicles secrete testosterone.
Hormone Secretion
The hypothalamus receives information from the external environment through the senses. The response to this information involves the secretion of hormones called neurohormones.