physio exam 2

Explain in words how the Nernst and Goldman-Hodgkin-Katz equation relates to the membrane potential of a cell

*membrane potential is created due to uneven distributions of ions across the membrane and the differing permeability of the membrane to each ion. *Sodium, Chloride, and calcium are more concentrated in the ECF *potassium is more concentrated in the cytosol (so K+ is the major contributor to membrane potential) Nernst equation: Eion (in mV) = 61/z log [ion]out/[ion]in GHK equation: Vm = 61log *PK[K+]out + PNa[Na+]out + PCl[Cl−]in / PK[K+]in + PNa[Na+]in + PCl[Cl−]out (assumes that Na+, Cl-, and K+ are the only ions that affect membrane potential) GHK equation in words: Resting membrane potential (Vm) is determined by the combined contributions of the (concentration gradient × membrane permeability) for each ion.

Explain the changes in ion permeability and ion flow that take place during an action potential

Conduction of the action potential along the axon requires only a few types of ion channels: voltage-gated Na+ channels and voltage-gated K+ channels, plus some leak channels that help set the resting membrane potential. action potential begins with both ion gates open, Na+ entry depolarizes the cell, Na+ channels close and K+ channels open, K+ moves out of the cell and the membrane potential becomes more negative, the cell hyperpolarizes, then the K+ channels close, K+ is retained and Na+ is leaked so the membrane returns to its resting potential

hormones get secreted into the

ECF and then into the blood

Explain the relationships between the following terms: current flow, conductance, resistance, Ohm's law

Ohm's law: I = V/R Current (I): flow of electrical charge

Compare the location of hormone receptors and the cellular mechanisms of action of peptide and steroid hormones.

Peptide hormones are lipophobic (hydrophilic) so they bind to cell surface receptors. This initiates signal transduction. Many use secondary messengers or tyrosine kinase. Peptide hormones usually trigger quick responses. Responses can include opening/closing membrane channels and controlling metabolic enzymes or transport proteins. Steroid hormones bind to intracellular receptors (cytoplasm or nucleus). The ultimate target of steroid hormones is the nucleus where they will be used as transcription factors that bind to DNA to turn genes on/off. Any hormone that alters gene activity is said to have a genomic effect.

What are the four criteria that make a chemical signal a hormone?

Secreted by a cell or group of cells Secretion into the blood or external environment Transported to a distant target Ability to act in very low concentration

Compare the structure and function of the anterior and posterior pituitaries

The anterior pituitary is responsible for secreting 6 important hormones: PRL, TSH, ACTH, GH, FSH, and LH. All except prolactin are trophic hormones (hormones that control secretion of other hormones). The posterior pituitary is responsible for storage and secretion of oxytocin and vasopressin. These are peptide hormones. When a stimulus reaches the hypothalmus, an electrical signal travels from the hypothalmus to the posterior pituitary, depolarization of the axon terminal opens voltage gated calcium channels so that calcium enters the cell, which triggers the vesicles to release the hormones into circulation.

Describe the role of the nervous system in endocrine reflexes.

acts as an integrating center for stimuli and influences release of hormones through efferent neurons neurons secrete neurohormones 2 endocrine structures are incorporated into the anatomy of the brain (pineal gland and pituitary gland) emotions can affect hormone secretion

Compare and contrast graded potentials and action potentials

graded potentials are short-lived, variable strength, short-distance signals that lose strength as they travel through the cell. If a depolarizing graded potential is strong enough when it reaches an integrating center inside a neuron, the graded potential will initiate an action potential. Action potentials are very brief, large depolarizations that travel for long distances through a neuron without losing strength.

What is the cellular mechanism of action of a hormone?

hormones bind to target cell receptors and initiate responses based on the type of tissue, stage of development, and the type of receptors

Compare long-loop negative feedback for anterior pituitary hormones to the negative feedback loops for insulin and parathyroid hormone.

in long-loop negative feedback, the hormone secreted by the peripheral endocrine gland "feeds back" to suppress secretion of its anterior pituitary and hypothalamic hormones

Name the types and functions of glial cells

oligodendricytes: form myelin sheaths in the CNS Schwann cells: form myelin sheaths in the PNS satellite cells: form supportive capsules around nerve cell bodies located in ganglia microglia: specialized immune cells that reside permanently in the CNS, they remove damaged cells and foreign invaders, astrocytes: take up and release chemicals, provide neurons with metabolic substrates for ATP production, maintain homeostasis in the CNS extracellular fluid by taking up K+ and water, and surround blood vessels and become part of the blood-brain barrier that regulates the movement of materials between blood and extracellular fluid. ependymal cells: specialized cells that create a selectively permeable epithelial layer, the ependyma, that separates the fluid compartments of the CNS

Compare endocrine cells' synthesis, storage, and release of peptide and steroid hormones

peptide hormones are made in tissues all over the body while steroid hormones are only made in several organs (adrenal glands on each kidney, gonads, placenta, and skin) peptide hormones are made in the RER. Steroid hormones are synthesized in the smooth ER Peptide hormones are kept in vesicles in the cytoplasm until they are needed. They are usually water soluble so they can dissolve in the ECF for transport around the body. Steroid hormones cannot be stored in vesicles because they diffuse easily across the lipid membrane, so they must be made as needed. They travel out of the cell by simple diffusion.

List three chemical classes of hormones

peptide/protein hormones steroid hormones amino acid derived/amine hormones