Physiology & Homeostasis - Mrs. Baurbaurbiology.weebly.com/.../physiology___homeostasis_intro_notes_1… · Homeostasis Homeostasis is a steady, yet dynamic state An organism will

COORDINATION BETWEEN SYSTEMS

a ) CIRCUL AT O RY AND RE S PIRAT O RY b ) CIRCUL AT O RY AND DIG E S T IV E

c ) NE RV O US AND M US CUL ARd ) E NDO CRINE AND E X CRE T O RY

Physiology & Homeostasis

Homeostasis

� Homeostasis is a steady, yet dynamic state� An organism will attempt to maintain a steady state (e.g.,

body temperature in endotherms), but may have to change or make adjustments (e.g., shivering) to do so.

Homeostasis

� 2 Primary Homeostatic Systems:¡ Positive Feedback: An increase in product results in

increasing the rate of the synthesis of that product (“finish what you started” mechanism)÷ E.g., A à B à C à D where the synthesis of D activates the

enzyme “A à B-ase”, thereby increasing the rate of synthesis of D eventually

¡ Negative Feedback: An increase in product results in a decrease in synthesis of more product. This is the mechanism by which levels of a substance remain relatively constant.÷ E.g., A à B à C à D where the synthesis of D acts as an allosteric

inhibitor of the enzyme “A à B-ase”

Homeostasis: Positive Feedback

� Childbirth – release of oxytocin causes the uterus to begin contracting. The contracting uterus pushes the baby and increases pressure on the opening of the uterus (cervix). This increase in pressure results in release of additional oxytocin which will increase contraction strength and intensity…which will increase pressure on the cervix...which will increase oxytocin release.

Homeostasis: Negative Feedback

� Blood Sugar: When blood sugar is low between meals, glucagon is released from the pancreas. The presence of glucagon results in the breakdown of glycogen (polymer of glucose stored in the liver). The glucose is dumped into the bloodstream raising blood sugar levels.

� When blood sugar is high after a meal, the pancreas will release insulin. Insulin will remove sugar from the blood and “feed” cells while additionally storing excess sugar as glycogen in the liver. The hypothalamus monitors blood sugar as well.

Digestion and Circulatory

� VILLI and MICROVILLI are projections of the small intestine that increase surface area to increase nutrient absorption

� Tiny capillaries line these microvilli to capture absorbed nutrients that are absorbed by the thin SI wall

Absorption of Nutrients

Homeostasis: Respiratory Rate & Heart Rate

� The exchange of O2 and CO2 occurs at alveoli.¡ Surface Area: The alveoli are sack-shaped to greatly

increase the surface area across which O2 and CO2 can diffuse.

¡ Thickness: The alveoli are only a single cell layer thick, leading to more efficient diffusion of gases across such a thin membrane.

¡ Exchange: Each alveolus is covered in a capillary mesh. The capillaries are also a single cell in thickness to facilitate diffusion.

Respiratory and Circulatory

� ALVEOLI increase surface area to increase gas exchange

� CAPILLARIES surround alveoli to allow diffusion of gasses from alveoli space into blood, from high to low concentrations

Endocrine and Excretory

� NEPHRONS of kidney regulate ion and water concentration that is used to produce urine

� ADH and aldosterone are hormones that stimulate the end of the nephron, the collecting duct, to increase or decrease water reabsorption, back into blood

Homeostasis: Temperature Regulation

� Organisms typically have a very narrow temperature range in which they can live. Why? Remember…¡ ...enzymatic reactions, protein shape, and other biochemical events all

occur optimally in a specific temperature range. Excessively high temperatures can denature enzymes, while cold temperatures may results in too few collisions of reactants.

Homeostasis: Temperature Regulation

� Endotherms & Ectotherms:¡ Endotherms (“warm-

blooded”) are able to maintain a steady body temperature regardless (to some extent) of environmental temperature

¡ Ectotherms (“cold-blooded”) are at the mercy of external temperature and must find other means to regulate body temperature (e.g., lizard sunning itself)

Nervous and Muscular

� Nerve sends message to muscle� NEUROTRANSMITTER acetylcholine from nerve

axon terminal received by muscle tissue� Causes signal transduction, allowing actin and

myosin to slide past each other

Closer

� What are some themes you noticed between these coordinating body systems?