Homeostasis and Body Organization What is homeostasis? “constancy” or “steady state” maintained within the organisms’ bodies. Whereas the environment can be highly variable, organisms incorporate internal control mechanisms to oppose the forces that would change their internal physiological equilibrium. The organisms’ internal state can be described as being in dynamic equilibrium, because the body needs to be constantly adjusting to the Changes. This regulation occurs in two basic ways: Negative feedback – most important means of maintaining homeostasis, negative feedback creates a counter-effect to the outside environmental change Positive feedback – a mechanism whereby the effects from the original environmental changes are intensified.

Homeostasis and Body Organization Positive and Negative Feedbacks

It should be noted though that there are many systems involved in organisms’ Body, and that they all need to interact with each other to maintain homeostasis. Different systems working independently could end up working against each other, but since the body has systems that move substances and signals from one part of the body to the next, all the different body parts remain “connected”. This coordination is achieved via chemical (hormones) and/or electrical (nervous) communication between tissues that elicits appropriate responses.

Body Organization The body is organized at different levels: Tissues: includes structurally similar cells that act together to perform a particular function. (e.g. muscular, nervous, epithelial, etc.) Organs: the next higher level of organization, tissues come together to form organs. (e.g. stomach, kidneys, liver, etc.) Organ systems: the different organs that work together towards a particular function come together to create organ systems. (e.g. digestive system which is composed of the stomach, small intestine, large intestine, and other organs. You are responsible to read pages 526 – 533. Learn the basic structure and function of the major vertebrate organ systems outlined in table 26-2 on page 532.

Circulation Why do we even need a circulatory system? Simple diffusion is too slow to serve the needs of “larger” organisms. Primary Functions? 1. Gas exchange 2. Distribution of nutrients 3. Waste removal Other functions in vertebrates (and some invertebrates)? 4. Distribution of hormones 5. Regulation of body temperature 6. Protection of body from bacteria and viruses – circulation of antibodies and white blood cells.

Circulation All circulatory systems have 3 major components: 1. A fluid “blood” that serves as a medium of transport 2. A system of channels (blood vessels) that transport the blood throughout the body. 3. A “heart” that acts as a pump and keeps the blood circulating. Animals have one of two types of circulatory systems: 1. Open 2. Closed

Circulation Note: Vertebrates (including humans) have a closed circulatory system

Circulation – the vertebrate heart There is an increased level of complexity associated with vertebrate evolution. This increased complexity has created more efficient circulatory systems that have allowed for greater diversity of form and function in different environments. This is not of course the only solution, squids for example have three hearts...

Circulation – the four chambered heart The mammalian and avian hearts consist of two pumps in one. One pump is responsible for pulmonary circulation – consisting of the right atrium and ventricles, this pump is responsible for sending blood to the lungs. The other pump is responsible for systemic circulation – consisting of the left atrium and ventricles, this pump is responsible for sending oxygenated blood to the body.

Circulation – the four chambered heart Electric impulses coordinate the sequence of contractions Valves maintain directionality of blood flow. The valves are “one-way”

Circulation – the four chambered heart The atria and ventricles of the heart need to pump in a coordinated fashion. The alternating contraction and relaxation of the heart chambers is called the cardiac cycle. The nervous system and hormones influence heart rate... The contraction of the ventricles is called the systole and the relaxation is called the diastole

Circulation – the four chambered heart Measuring blood pressure

Circulation – the four chambered heart Electrocardiograms

Circulation – structure and function of blood vessels Arteries and Arterioles – Thick-walled vessels that carry blood away from heart arterioles can control the distribution of blood by muscular contractions – they are influenced by nerves, hormones, and chemicals produced in nearby tissues. Capillaries – Microscopic vessels that allow blood and body to exchange gas, nutrients, and waste Veins and Venules – Carry blood back to the heart Valves direct flow of blood in veins

Circulation – structure and function of blood vessels Change in blood velocity as a function of circulatory cross section allows for more efficient transport as well as gas, nutrient, and waste exchange...

Circulation – blood Blood components: Plasma – the “fluid” part of the blood, it is composed of 90% water along with proteins, hormones, nutrients, gases, salts, and wastes... Specialized cells – these are cells suspended in the plasma and include red blood cells, white blood cells, and platelets. Red blood cells are primarily involved in transport of oxygen White blood cells are primarily involved in the immune system Platelets are primarily involved in blood clotting

Circulation – blood Red blood cells contain a large, iron-containing protein called hemoglobin. Each hemoglobin can bind to four oxygen molecules and is involved in picking up oxygen in the lungs and transferring it to the body...

Circulation – the lymphatic system A network of lymph capilaries and large vessels that empty into the circulatory system. Function include: 1. Removal of excess fluids and dissolved substances that leak from capillaries. 2. Transport of fats from the small intestine to the blood stream. 3. Defense of the body by exposing bacteria and viruses to white blood cells.