Bio 306 Homeostasis and Circulatory Systems PDF

## Bio 306 ### Homeostasis - **Definition**: Homeostasis refers to the self-regulating mechanism by which biological systems maintain stability. - **Dynamic Equilibrium**: The stability achieved through homeostasis is actually a dynamic equilibrium. - **Importance**: Successful homeostasis sustain...

## Bio 306 ### Homeostasis - **Definition**: Homeostasis refers to the self-regulating mechanism by which biological systems maintain stability. - **Dynamic Equilibrium**: The stability achieved through homeostasis is actually a dynamic equilibrium. - **Importance**: Successful homeostasis sustains life, while failure can lead to disaster or death. **Examples:** - **Body Temperature Regulation**: _In humans, normal body temperature fluctuates around 37°C (98.6°F). Factors like exposure, hormones, metabolic rate, and disease can affect this value. Homeostasis ensures that the body maintains a consistent temperature despite external variations._ - **Mechanical System Analogy**: _Think of a room-temperature regulator (like a thermostat). When the room cools, the circuit completes, the furnace operates, and the temperature rises. At a preset level, the circuit breaks, the furnace stops, and the temperature drops. Similarly, biological systems aim to sustain activity within a prescribed range._ In summary, homeostasis is the body's remarkable ability to monitor and maintain internal states, such as temperature, blood sugar, and other vital parameters, at fairly constant levels, even in the face of changing external conditions. ### Types of Circulatory Systems: Open vs. Closed - **Open Circulatory Systems**: _Found in arthropods and mollusks, lack a true heart and capillaries. Blood is propelled by vessels that connect directly to open sinuses, where it bathes the internal organs._ - **Closed Circulatory Systems**: _Found in vertebrates and many invertebrates, more efficient. Blood is pumped through a closed system of arteries, veins, and capillaries._ ### Closed Circulatory Systems: - **Earthworms**: _Have a dorsal and a ventral vessel, connected by rudimentary hearts, which pump blood into the ventral vessel. Blood flow is relatively inefficient._ - **Fish**: _The heart is composed of two chambers (atrium and ventricle). Blood is pumped from the heart to the gills for oxygenation, then to the body, and back to the heart. This is a single circuit and blood is not fully oxygenated._ - **Amphibians (e.g., Frogs)**: _The heart has three chambers (two atria and one ventricle). Blood passes into a forked aorta from the ventricle, allowing both oxygenated and deoxygenated blood to travel through the body._ - **Mammals and Birds**: _The heart is composed of four chambers (two atria and two ventricles). Oxygenated and deoxygenated blood are not mixed, ensuring efficient blood flow._ ### Blood Flow Through The Body: - **Heart**: _Blood is pushed through the body by the pumping heart._ - **Aorta**: _Blood travels at 30 cm/sec in the aorta._ - **Arteries, arterioles, capillaries**: _As blood travels through smaller vessels, speed slows dramatically (to 0.026 cm/sec in capillaries). This slower rate allows for gas and nutrient exchange._ - **Veins**: _Blood flows back to the heart through veins aided by smooth muscle and skeletal muscle contractions. One-way valves prevent backflow._ - **Capillary Beds**: _Blood flow is regulated by precapillary sphincters, which control the amount of blood flowing to different areas of the body._ ### Blood Pressure: - **Definition**: _Hydrostatic pressure of blood against the walls of blood vessels._ - **Regulation**: _Cardiac output (heart rate x stroke volume) influences blood pressure. Blood flow is also regulated by nerve signals and hormones._ ### Animal Sensory Systems - **Sensory Receptors**: - **Mechanoreceptors**: _Respond to physical deformation of cell membranes caused by mechanical energy or pressure._ - **Touch:** _Detecting physical contact._ - **Auditory:** _Sound perception._ - **Vestibular:** _Balance and head movements._ - **Photoreceptors**: _Respond to radiant energy, primarily visible light._ - **Chemoreceptors**: _Respond to specific molecules, often dissolved in saliva, mucus, or airborne particles._ - **Sensory Integration and Processing:** _Signals from sensory receptors are transmitted to specialized brain regions for processing._ - **Central Nervous System (CNS)**: _Interprets signals and orchestrates responses via the Peripheral Nervous System (PNS)._ ### Hormonal Mediation of Physiological and Behavioral Processes That Influence Fertility - **Hypothalamic-Pituitary-Gonadal Axis**: _The primary axis controlling reproduction._ - **Hypothalamus**: _Produces GnRH (Gonadotropin-releasing hormone), which stimulates the pituitary gland to release LH (Luteinizing hormone) and FSH (Follicle-stimulating hormone)._ - **Pituitary**: _Releases LH and FSH, which act on the gonads (ovaries and testes)._ - **Gonads**: _Produce sex steroid hormones (estrogen, progesterone, testosterone)._ - **Steroid Hormones**: _Influence sexual development and behavior._ - **Testosterone**: _Stimulates development of male secondary sexual characteristics._ - **Estrogen**: _Stimulates development of female secondary sexual characteristics._ - **Progesterone**: _Prepares the uterine lining for implantation and supports pregnancy._ - **Hormonal Changes Throughout the Life Span**: - **Early-Life Activation**. - **Pubertal Activation**: _Marked by an increase in gonadotropin and gonadal steroid hormone levels._ - **Aging**: _In males, testosterone levels decline with aging. In females, menopause marks the cessation of ovarian cyclicity._ ### Environmental Exposure To Hormones - **Exogenous Steroids**: _Hormonal contraceptives, steroids used to improve muscle strength and fitness, hormone replacement therapy._ - **Environmental Estrogens**: _PCBs, phytoestrogens._ ### Life Events That Alter Hormone Levels - **Stress**: _Physical (energy restriction, exercise, infection, injury, etc.) and psychosocial (anorexia nervosa, depression, anxiety, etc.) stress can suppress reproductive hormone secretion._ ### Summary and Future Directions - **Integration of Demographic and Biomedical Approaches**: _Necessary to fully understand the complex interplay of factors that regulate reproduction._ - **Need for Further Research**: _More detailed studies that assess hormonal function, individual differences, and the impact of environmental factors are needed._