Heart Muscle Contraction, Lymphatic & Circulatory Systems in Animals

Heart Muscle Contraction: How Does the Pacemaker Work?

The heart muscle consists of sarcomeres containing alternating thick and thin filaments. The cells tend to contract rhythmically and spontaneously, but these contractions are synchronized by electrical signals produced by specialized muscle fibers of the sinoatrial node. Cardiac muscle fibers are electrically interconnected by links between cells located interspersed. This allows for coordinated contraction. Specialized fibers act as a pacemaker. Action potentials that originate in the pacemaker spread quickly through the heart using specialized areas in which interspersed links connect adjacent muscle cell membranes. These allow the potential to synchronize their contractions as they travel from one cell to another.

The Lymphatic Circulatory System

The lymphatic system has antibodies in the lymph, lymphocytes, and plasma protein that leaks into the bloodstream to pass on to all the body in defense mode. It is a great fighter against infection and filters the lymph through lymph nodes, where white blood cells ingest foreign invaders such as viruses and bacteria. It consists of lymphatic vessels, tonsils, lymph nodes, the thymus, and the spleen. The lymphatic system removes excess interstitial fluid that seeps from the walls of blood vessels to remove waste and recycle items that it then returns to the circulatory system. It transports fat into the bloodstream from the small intestine. The thymus is most active in young children and produces lymphocytes involved in immunity. The spleen filters blood by passing it through macrophages and lymphocytes, which kill bacteria and damaged blood cells.

Two Types of Circulatory Systems in Animals

Open Circulatory System

Found in many invertebrates, including arthropods (spiders, insects) and mollusks (snails and clams).

• They have one or more hearts, a network of vessels, and an open space within the body called the hemocoel.
• The heart pumps through vessels that drain blood to the hemocoel.
• Within this, the blood directly bathes the tissues and internal organs.
• The vessels also return blood to the heart.
• When the heart relaxes, the blood flows back into them through openings provided with valves.

Closed Circulatory System

Found in earthworms, very active mollusks, and all vertebrates, including humans.

• In this system, the blood is confined to the heart and a series of blood vessels.
• Allows a faster flow of blood and efficient transport of waste and nutrients.
• Higher blood pressure than the open system.

Breathing Through Trachea

The trachea is a branched system of internal tubes that carry air directly to body cells. They subdivide and branch to form tracheoles, or smaller canals that penetrate the tissues of the body and allow the exchange of gases. Each cell in the body is near a tracheole. Air enters the tracheae through a series of openings called spiracles, which have valves that allow opening or closing. Large insects use muscle movements in the abdomen to ensure the movement of air in the tracheae.