Question

In general terms describe extrinsic regulation and intrinsic regulation.

b. compare and contrast extrinsic regulation in the heart and blood vessels.

c. compare and contrast intrinsic regulation in the heart and blood vessels.

Answer 1

1. general mechanisms are involved in homeostatic regulation: autoregulation and extrinsic regulation.

Homeostasis is absolutely vital; a failure to maintain its leads to illness or even death.

* Autoregulation, or intrinsic regulation - occurs when the activities of a cell, tissue, organ, or organ system adjust automatically in response to some environmental change.

For example, when oxygen levels decline in a tissue, The cells release chemicals that dilate local blood vessels.

This dilation increases the rate of blood flow and provides more oxygen to the region.

* Extrinsic regulation - results from the activities of the nervous system or endocrine system, two organ systems that control or adjust the activities of many systems simultaneously.

For example, when you exercise, your nervous system issues commands that increase your heart rate so that blood will circulate faster. Your nervous systems also reduces blood flow to less-active organs, such as the digestive tract. The oxygen in circulating blood is thus saved for the active muscles.

2.Extrinsic effect on heart

autonomic nervous system, baroreceptors, blood that carries hormones and other chemicals from the rest of the body to the heart. These things can modify the intrinsic features; i.e., make the heart beat slower (or faster) than its intrinsic rate. This is EXTRINSIC.

The sympathetic nervous system (SNS) releases the hormones (catecholamines - epinephrine and norepinephrine) to accelerate the heart rate. The parasympathetic nervous system (PNS) releases the hormone acetylcholine to slow the heart rate.

extrinsic effect on blood vessels

extrinsic factors (neurohumoral) such as sympathetic nerves and circulating angiotensin II increase vascular tone (i.e., cause vasoconstriction); however, some circulating factors (e.g., atrial natriuretic peptide) decrease vascular tone.

3. Intrinsic effect on heart

Intrinsic is something within the heart and is a little more complex. Think of the heart like a big rubber band.
The more you stretch it, the more is snaps back. The heart is the same way - the more it fills with blood, the greater the force of contraction. (That's called Starling's Law )

The heart has built-in behavior/resposes. It beat (at a rate set by the sinoatrial node). The wall stress is determined by Laplace's Law. Of the wall tension is increased, the myocardial cells will respond by contracting more forcibly. These things would occur if the heart is removed from the body (and maintained by a 'machine'). This is INTRINSIC.

Intrinsic effect in blood vessels

All arterial and venous vessels under basal conditions exhibit some degree of smooth muscle contraction that determines the diameter, and hence tone, of the vessel.

intrinsic mechanisms are important for local blood flow regulation within an organ. Vascular tone at any given time is determined by the balance of competing vasoconstrictor and vasodilator influences.

Intrinsic factors include:

• Myogenic mechanisms (originating from vascular smooth muscle), which increase tone.

• Endothelial factors such as nitric oxide and endothelin can either decrease or increase tone, respectively.

• Local hormones/chemical substances (e.g., arachidonic acid metabolites, histamine and bradykinin can either increase or decrease tone.

• Metabolic by-products or hypoxia, which generally decrease tone.