Animal Respiration, Circulation, and Excretion

Animal Respiration

Breathing is essential for respiration. Animals breathe by inhaling oxygen and exhaling carbon dioxide. This gas exchange occurs via the respiratory system.

Respiratory Systems

Respiratory systems require thin, moist surfaces covered in blood vessels for efficient gas exchange. This facilitates oxygen uptake and carbon dioxide expulsion.

Cutaneous Respiration

Gas exchange through the skin (thin and moist). Examples include earthworms and adult amphibians.

Branchial Respiration

Gas exchange through gills (surrounded by blood vessels). Examples include fish and some crustaceans.

Tracheal Respiration

Gas exchange via internal tubes (tracheae) carrying air directly to cells. Examples include terrestrial arthropods.

Pulmonary Respiration

Gas exchange in the lungs (internal cavities with thin, moist, blood vessel-rich walls). Involves inhalation (air intake) and exhalation (air expulsion). Examples include amphibians, reptiles, birds, mammals, and some invertebrates like terrestrial snails.

Circulatory System

In vertebrates, the circulatory system comprises:

Components of the Circulatory System

• Blood: Internal fluid (water, proteins, cells) carrying oxygen, nutrients, and waste products.
• Blood Vessels: Ducts carrying blood. Arteries carry blood from the heart; veins return blood to the heart.
• Heart: Pump circulating blood through vessels.

The circulatory system's functions are: 1. Nutrient and oxygen delivery to cells; 2. Removal of carbon dioxide and metabolic waste.

Open Circulatory System

The heart pumps fluid, which flows through the body cavity to internal organs.

Closed Circulatory System

Blood circulates within vessels, pumped by a heart. Two types exist: simple and double.

Simple Closed Circulatory System

Characteristic of fish. Blood passes through the heart once, completing one loop. Blood travels from the heart, to the body, then through the gills (oxygen uptake and carbon dioxide release) before becoming oxygenated.

Double Closed Circulatory System

Characteristic of other vertebrates. Blood passes through the heart twice, completing two loops. The first loop involves heart-lung-heart circulation (oxygen uptake). The second loop involves heart-body-heart circulation (oxygen delivery).

Excretion

Excretion is the process of collecting and expelling waste products (carbon dioxide, ammonia, urea). Carbon dioxide is expelled by the circulatory and respiratory systems. Other substances are eliminated by the excretory system.

Some animals (e.g., sponges) lack an excretory system, expelling waste through body pores. Vertebrate excretory systems consist of various organs, primarily the kidneys (producing urine containing urea). Urine travels through ureters to the bladder (storage) and is expelled through the urethra.