L36 Endocrine Regulation 2011 - COPYRIGHT Mammalian...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
-1/12- COPYRIGHT Prof. Beyenbach Mammalian Physiology BIOAP 4580 Spring 2011 ENDOCRINE REGULATION OF RENAL FUNCTIONS A. General Considerations: In the maintenance of extracellular fluid homeostasis, the kidney is "only" the executor organ, which means that the kidney is part of a regulatory feedback loop where it executes the tasks of extracellular fluid homeostasis from instructions it receives primarily from hormones. There is some neural control, but neural regulation does not seem essential to renal functions. Transplanted kidneys function well in the body of the new host without connecting renal nerves. Four hormone systems will be considered. The first, involving the antidiuretic hormone (ADH), regulates primarily the osmolality of the extracellular fluid. The second, based on the release of aldosterone regulates the concentrations of Na + and K + in extracellular fluid. The third, using atrial natriuretic peptide as primary extracellular messenger, protects against excessive volume of extracellular fluid. The fourth, the renin-angiotensin system, protects against volume loss. In addition, it integrates with the other three systems in order to maintain circulatory volume. Each system is reviewed below, one at a time. B. Physiological Feedback Loops. A physiological challenge must first be recognized as such, usually by an appropriate sensor. The sensor will then trigger the release of a signal (neural or endocrine). The signal will evoke the appropriate response in the executor (target organ) such that the challenge is diminished or removed (Fig. 1). Fig. 1. Physiological feedback loop. An example of a negative feedback loop is shown. It serves to alleviate a threat or challenge. Positive feedback loops are usually detrimental, accelerating the system to chaos.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
-2/12- C. Regulation of Extracellular Fluid Osmolality: The Antidiuretic Hormone (ADH) System. The ADH system responds primarily to osmotic pressure changes in the extracellular fluid compartment, and secondarily to changes in circulating blood volume. In particular, an increase in plasma osmotic pressure and blood loss are potent stimuli to activate the ADH system (Fig. 2). 1. Mechanisms of ADH release. a) Osmoreceptor response: The osmoreceptors (nerve cells) of Verney (see Fig. 3) shrink when the plasma osmolality increases with dehydration. Cell shrinkage causes them to fire action potentials towards neurosecretory cells of the posterior pituitary which release measured quantities of ADH into the circulation (Figs. 2, 3). Fig. 2 . Physiological feedback loop regulating the osmotic pressure and the volume of the extracellular fluid compartment. The antidiuretic hormone ADH protects against dehydration and volume loss. b) Volume receptor response:
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/09/2011 for the course BIOAP 4580 taught by Professor Beyenbach,k. during the Spring '11 term at Cornell University (Engineering School).

Page1 / 12

L36 Endocrine Regulation 2011 - COPYRIGHT Mammalian...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online