Levels of Organization and Homeostasis

Levels of Organization in the Body

• Cells act as the fundamental units of structure and function in living organisms
• In multicellular organisms, cells specialize to perform specific functions
• Tissues are groups of cells performing a unified function
• Epithelial tissue protects, absorbs, and excretes materials
• Connective tissue binds epithelial tissue to other structures and transports substances
• Nervous tissue is responsible for receiving and transmitting nerve impulses
• Muscle tissue enables both voluntary and involuntary movements
• Organs are composed of different tissues working together for a specific function
• Organ systems include groups of organs that work closely together
• Organ systems work together to maintain homeostasis

Homeostasis

• Homeostasis involves organisms maintaining constant internal conditions despite external environmental changes
• Feedback inhibition/negative feedback occurs when a stimulus triggers a response that counteracts the initial stimulus
• Activation of sweating is a response to rising body temperature
• Shivering is a response to a drop in body temperature

The Respiratory System

• The respiratory system is responsible for facilitating gas exchange
• Cellular respiration needs oxygen and produces carbon dioxide
• C6H12O6 + 6O2 -> 6CO2 + H2O + energy (ATP) is the equation for cellular respiration
• Respiratory structures facilitate gas movement through passive diffusion
• Diffusion refers to the movement of substances from areas of high concentration to areas of low concentration
• Thinner membranes and larger surface areas increase permeability and speed up diffusion
• Respiratory surfaces provide a large surface area, a moist environment, a selectively permeable membrane, and maintained concentration differences of O2 and CO2 to promote diffusion

Respiratory Systems in Different Animals

• Aquatic animals like small invertebrates have thin-walled bodies with wet outer surfaces and rely on diffusion
• Larger, more active aquatic animals pump water over gills
• Gills consist of feathery structures that provide a large surface area of thin, selectively permeable membrane, enhancing gas exchange in water
• Land animals maintain moist respiratory membranes
• Multiple systems interact to carry oxygen and carbon dioxide back and forth across different surfaces
• Respiration can occur across the skin in moist environments
• Some invertebrates have a mantle cavity: a moist tissue-lined cavity with blood vessels for gas exchange
• Book lungs are parallel layers of thin tissues containing blood vessels
• Tracheal tubes allow air to enter and exit through spiracles

Lungs

• Lungs facilitate the exchange of O2 and CO2 between blood and air
• Oxygen-rich air is inhaled through the trachea
• Oxygen diffuses into the blood through lung capillaries
• Carbon dioxide diffuses out of the capillaries into the lungs
• Carbon dioxide and oxygen-poor air is exhaled
• The surface area of lungs increases from amphibians to reptiles to mammals
• Amphibians have simple sacs with ridges
• Reptiles have chambers that increase the surface area
• Mammals have extensively branched lungs that end in alveoli (bubble-like structures)
• Alveoli are surrounded by capillaries, where blood picks up O2, leading to the release of CO2 through diffusion
• Birds lungs allow air to flow mostly in one direction
• Birds air flow ensures no oxygen-poor air is trapped in the system
• Gas exchange surfaces are continuously exposed to fresh air, powering the flight muscles

The Circulatory System

• The circulatory system transports energy and nutrients that have been broken down from food
• The circulatory system transports oxygen inhaled from the lungs to other tissues
• It also carries carbon dioxide and waste materials away from tissues
• Blood serves as the medium for transporting materials throughout the body
• The heart is a hollow, muscular organ that pumps blood
• There are two types of circulatory systems: open and closed

Circulatory Systems: Open vs Closed

• Open circulatory systems have hearts that pump blood through vessels emptying into sinuses, or spongy cavities
• Blood in open circulatory systems makes direct contact with body tissues within the sinuses
• Blood collects in another set of sinuses, eventually returning to the heart
• Arthropods and most mollusks have open circulatory systems
• Closed circulatory systems circulate blood within vessels throughout the body
• A heart pumps blood through vessels
• Oxygen and nutrients reach body tissues by diffusing across the thin capillary walls
• Capillaries are the smallest blood vessels
• Blood is contained within blood vessels, circulation is more efficient
• Annelids and all vertebrates have closed circulatory systems

Circulation Loops

• Single loop circulatory systems pushes blood around the body in only one direction
• Oxgen rich blood is red
• Oxygen poor blood is blue
• Vertebrates that use gills for respiration are found to have a single loop circulatory system
• The atrium is the chamber which receives blood from the body
• The ventricle is the chamber that pumps blood out of the heart
• Double loop circulatory systems involves blood moving through the heart twice separate
• Vertebrates that use lungs for respiration are found to have a double loop circulatory system

Chambered Hearts

• Terrestrial vertebrates evolved increasing capillary networks that became larger
• Using a single pump to force blood through a larger body is incresingly inefficient
• Amphibian hearts have two atria and one ventricle
• Amphibians right atria receive oxygen poor blood from the body
• The single ventricle distributes oxygen-poor blood to the lungs and oxygen-rich blood to the rest of the body
• The left atria receives oxygen rich blood from the lungs
• Reptilian hearts also contain two atria, and one ventricle
• Reptiles have a partial partition in the single ventricle making the circulation of oxygen rich and poor blood more efficient

Mammalian Hearts

• Mammalian hearts are two separate pumps existing next to each other
• The two pumps are separated by partitions which stop or restrict passage of blood between the atria and ventricles
• Pulmonary circulation carries blood between the heart and lungs
• Systemic circulation carries blood between the heart and the rest of the body

Arteries, Capillaries, and Veins

• Arteries are large vessels that carry blood from the heart to the tissues of the body
• Except for the pulmonary artery, all other arteries carry oxygen-rich blood
• Thick, elastic walls help withstand powerful pressure produced from heart contractions
• Capillaries are the smallest blood vessels, which allow O2 to diffuse from the blood into the tissues, and CO2 to move from the tissue into the blood
• Veins return the blood from the body to the heart
• Valves ensure blood flows in one direction

Blood Functions

• Respiratory gas exchange between O2 and CO2
• Transports nutrients obtained from the digestive system
• Blood transports hormones and signals linking to the endocrine system
• Transports waste through the body
• Fights infections through the immune system
• Regulates body temperature
• Clots wounds and minimizes loses of vital fluid
• Human bodies contain 4 - 6 liters of blood, and 55% is plasma
• Red blood cells/erythrocytes transport oxygen and are produced by bone marrow
• Platelets and plasma proteins will cause blood to clot and seal wounds

Clots

• Thrombus - A blood clot that forms within the blood vessels and causes limitations on blood movement
• With thrombosis, tissue looses oxygen and dies
• Heart attack - a blockage of blood on the heart muscle
• Atherosclerosis - Built-up of cholesterol on the walls of blood vessels
• Arteriosclerosis causes narrow blood vessels, or plaque
• Aneurysm - A bulge in the wall of the blood vessels, caused from high blood pressure
• Hypertensions cause the aneurysm to burst/rupture and lead to internal bleeding, and death.