Ch 19 notes

Overall architecture: Review Fig 18.1 even though it is an earlier chapter

Pulmonary veins and systemic arteries have oxygenated blood. Systemic veins and pulmonary arteries have deoxygenated blood. One way to remember those facts (a way I recommend, since it involves concepts rather than memorization) is to think of a diagram of the entire cardiovascular system (Fig 18.1):

Where does blood get oxygen? (pulmonary capillaries)

Where does it lose oxygen? (systemic capillaries)

What major structures does the blood go through on its way from the pulmonary capillaries (where it gets O2), to the systemic capillaries (where it loses O2)? (It goes through the pulm veins, the left heart, and the systemic arteries)

What major structures does the blood go through on its way from the systemic capillaries to the pulmonary capillaries? (It goes through the systemic veins, right heart, and pulm arteries)

Hormones that influence cardiovascular system and blood pressure

Know what causes the release of each of the following, and what each of the following causes to happen. In general, the cause of release and what the hormone causes to happen are opposites of one another, because these hormones are part of negative feedback loops that help maintain homeostasis of the cardiovascular system.

Aldosterone (In this case I will give examples of the kind of info you now about each hormone. Aldosterone release is caused by aldosterone. In a more general sense, aldosterone release is caused by low blood pressure and/or low blood volume and/or low blood osmolality, and by sympathetic nervous system activation, via the renin-angiotensin-aldosterone (R-A-A) system. Aldosterone causes sodium and water retention by the urinary system, and hence it causes, indirectly, an increase in blood volume and blood pressure.

ANP

Renin

Epinephrine, norepinephrine (these are neurotransmitters as well as hormones)

Angiotensin I and II

Vasopressin (also known as ADH)

Equations

Know the flowing and be able to use them if necessary, perhaps in a rearranged form.

CO = HR * SV

If you know CO and HR you can compute SV, and so forth.

Pa – Pv = CO * TPR where Pa = mean arterial pressure

which is approximately equal to

Pa = CO * TPR, since Pv is close to zero.

Resistance = 8 η L / (π r4)

where η (Greek letter eta) =blood viscosity, L=vessel length, r= vessel radius.

You don’t need to know the resistance equation for calculations, but you should know the direction of change that it predicts if radius, viscosity, or length changes. If the equation helps you do that, good; if not, then you can skip it for now.

Net filtration pressure = (HPcapillary + OPinterstitial fluid) – (HPinterstitial fluid + OPcapillary)

where HP and OP stand for hydrostatic and osmotic pressure respectively. Higher NFP leads to more filtration of fluid from capillaries to interstitial space. Know the direction of change in filtration that would be expected if any of the above quantities change.

Venous Return

Venous return: average venous return must equal cardiac output, since blood can’t pile up somewhere. What influences venous return? (TPR and venous compliance and total blood volume are at the top of the list. Venous valves, help, skeletal muscle activity helps, negative intrathoracic pressure helps. Gravity (pulling blood down toward legs) hurts.)

Baroreflexes, also known as baroreceptor reflexes

What does the reflex do? (Regulates blood pressure) What are the sensors? (baroreceptors) Where are they found? (Arterial baroreceptors are found in the carotid sinuses, which are in the neck where the common carotids divides into the internal & external carotids, and in the aortic arch.) What do they sense? (stretch of vessel wall) What stimulus causes more afferent nerve impulses? (higher pressure, because it causes more stretch) Where does the afferent signal go? (To the medulla of the brainstem. The nucleus of the solitary tract, to be more precise.) What are the efferent nerves of the reflex? (Sympathetic and parasympathetic nerves, including the vagus nerve) What nerves have more activity when, and what nerves have less activity when? (Sympathetics more active if systemic arterial pressure low, parasymp less active if art pressure low. Opposite if systemic arterial pressure is high.) What do the nerves make happen? (Sympathetic activity directly causes HR, contractility to rise, causes TPR to rise and veins to constrict. Symp activity also causes adrenals to release epi & norepi which have similar effects. Parasympathetic activity causes HR to fall, and, to a lesser extent, causes contractility to decrease a bit.)

Chemoreflexes, also known as chemoreceptor reflexes

Not as much detail as baroreceptors. Will be covered more in respiratory chapter. There are arterial chemos in the carotid sinus region and in aortic arch, and in the brain itself. They sense O2, CO2, and pH in blood. If the systemic blood levels of O2 or pH fall, or if CO2 level rises, chemoreceptors are activated. This causes cardiovascular responses similar to when baroreceptors are activated by low blood pressure: sympathetic activation and parasympathetic deactivation. (Chemoreceptor activation also causes important respiratory reflex responses, to be discussed in later chapter.)

Autoregulation

The ability of tissues to adjust to conditions (i.e. to self-regulate), in order to maintain the appropriate amount of flow necessary. Autoregulation is a local process, i.e. it does not involve nerves or hormones (which are regulatory loops that involve non-local structures such as the brain and endocrine glands).

Autoregulation works by metabolic and myogenic mechanisms. Know what each type is – see the book and the powerpoint.

Blood vessels

See the file Blood Vessels To Know.doc, on course web page, for a list of vessels you should know and what you should know about them.

Other comments

Long term control of blood pressure involves the kidneys as the major control system. It is challenging to teach about the cardiovascular system, since we have not yet studied the kidneys. But once cannot understand renal physiology if one does not understand blood pressure and flow, so teaching the kidneys first is not a good option.

Student question: How does an increase in body sodium lead to an increase in blood pressure?

Answer: Urine, created and excreted by the kidneys, includes water, metabolic waste products, and sodium, among other things. Water tends to "follow" sodium into or out of the body, because the presence of Na in water creates osmotic pressure that "draws water along". If the Na level in the body increases, there will tend to be more osmotic pressure in the body fluids, including blood plasma. Osmotic pressure "pulls water" toward the area of higher osmotic pressure, so Na in the body leads to the kidneys holding on to more water. Some of that retained fluid ends up in the blood plasma. When plasma volume is higher, blood pressure also tends to be higher, because 1. the higher volume stretches out the blood vessels more, and 2. increased venous pressure (even a small increase) causes a significant rise in cardiac output, due to increased diastolic filling.

Student question: What does "water reabsorption by kidneys" mean, and how does this lead to an increase in mean arterial pressure?

Answer: Water reabsorption in the kidneys refers to the fact that the kidneys filter water from their capillaries into the "urine side" of the kidney compartment, and then they reabsorb much of the filtered water. This seemingly wasteful behavior has benefits, which is why it has been favored by natural selection. More on that when we get to the renal chapter. If the kidneys reabsorb more water, less urine leaves the body, and this causes plasma volume to expand, which raises blood pressure, for the reasons given in the answer to the previous question.