Human Circulatory, Endocrine, and Nervous Systems: An Overview

Posted on Nov 23, 2024 in Biology

The Circulatory System

Function

The circulatory system is responsible for the transport of nutrients and oxygen to cells and the removal of waste substances.

Components

  • Heart: A muscular pump that propels blood throughout the body. It is composed of three layers:
    • Pericardium: The outer layer surrounding the heart.
    • Myocardium: The thick middle layer responsible for the heart’s pumping action.
    • Endocardium: The inner lining of the heart.
  • Blood Vessels: Arteries, veins, and capillaries that transport blood.

Heart Structure

The heart is divided into two sides, each with an atrium (upper chamber) and a ventricle (lower chamber). Valves (tricuspid and mitral) ensure unidirectional blood flow.

Blood Circulation

Blood flows into the atria, then to the ventricles, and is pumped out through arteries. The heart’s pumping action has two phases:

  • Diastole: The heart muscle relaxes, and blood enters the atria.
  • Systole: The heart muscle contracts, and blood is pumped out.

Heart rate is the number of heartbeats per minute (about 70 at rest). Cardiac output is the volume of blood pumped by the heart per minute.

Hormonal Coordination: The Endocrine System

Glands and Hormones

The endocrine system coordinates body functions through hormones, chemical messengers secreted by glands into the bloodstream.

Types of Glands

  • Endocrine: Secrete hormones directly into the blood.
  • Exocrine: Secrete substances outside the body or into the digestive tract (not part of the endocrine system).
  • Mixed: Produce both hormones and other substances.

Major Endocrine Glands and Hormones

  • Pituitary: Growth hormone (GH), thyrotroph (TSH), adrenocorticotropin (ACTH), gonadotrophs (FSH, LH), lactotroph (LTH).
  • Thyroid: Thyroxine (regulates cell metabolism).
  • Adrenal: Adrenaline (increases heart rate and breathing), cortisone (regulates glucose and fat metabolism).
  • Pancreas: Insulin (decreases blood glucose), glucagon (increases blood glucose).
  • Testes: Testosterone (regulates male sexual organs).
  • Ovaries: Progesterone and estrogen (regulate female sexual organs and prepare for pregnancy).

Hormone Characteristics

  • Specificity: Each hormone acts on specific target cells.
  • Effectiveness: Minimal amounts are sufficient for function.
  • Controlled Production: Imbalances lead to diseases.

The Nervous System: Rapid Coordination

Divisions

  • Central Nervous System (CNS): Brain and spinal cord.
  • Peripheral Nervous System (PNS): Nerves connecting the CNS to the body.

CNS Components

  • Brain: Controls voluntary acts, balance, and coordination.
  • Spinal Cord: Connects the brain to the rest of the body.

PNS Components

  • Sensory Nerves: Transmit signals from receptors to the CNS.
  • Motor Nerves: Transmit signals from the CNS to muscles and glands.
    • Somatic Nervous System: Controls voluntary muscles.
    • Autonomic Nervous System: Regulates involuntary activities.

Neurons

Specialized cells that transmit nerve impulses. Their degeneration can cause diseases like Parkinson’s and Alzheimer’s.

Nervous System Function

  1. Collect environmental information (receptors).
  2. Process information (nervous system).
  3. Develop responses (effectors: muscles and glands).

Key Terms

  • Stimulus: A change eliciting a response.
  • Behavior: Sequence of actions in response to a stimulus.
  • Response: Action by effector organs.
  • Receptors: Detect stimuli.
  • Effectors: Carry out responses.

Types of Stimuli

  • Chemical: Taste, smell.
  • Thermal: Touch, heat.
  • Mechanical: Touch, pressure, hearing.
  • Light: Photoreceptors.

Nerve Communication

Fast and effective communication via nerves and nerve centers.

Hormonal Communication

Slower communication via hormones secreted by glands.

Coordination of Nervous and Endocrine Systems

The hypothalamus coordinates both systems.

Example: Blood Sugar Control

  • Insulin: Decreases blood glucose.
  • Glucagon: Increases blood glucose.

Hormone Balance

Hormone production is regulated by the pituitary gland. Imbalances can cause various disorders (e.g., growth disorders, metabolic changes, glucose level changes).