1. Autoregulation
Two of the most important control points are the pressure receptors (called baroreceptors) located in the arch of the aorta and the carotid sinus.
There are also baroreceptors in the kidney and the walls of the heart.

2. Autoregulation
Stimulation of the baroreceptors in the carotid sinus is called the carotid sinus reflex , and it helps normalize blood pressure in the brain. Stimulation of the aortic baroreceptors helps normalize the systemic BP.
When the blood pressure falls, baroreceptors are stretched less, and the input is sensed in the cardiovascular centers of the brain which respond with decreased parasympathetic and increased sympathetic stimulation. Blood pressure increases do the opposite.

3. Autoregulation
Another type of sensory receptor important to the process of autoregulation of BP are the chemoreceptors.

4. Autoregulation
Chemoreceptors are found in the carotid bodies (located close to baroreceptors of carotid sinus) and aortic bodies (located in the aortic arch).
When they detect hypoxia (low O2), hypercapnia (high CO2), or acidosis (high H+), they signal the cardiovascular centers.
They increase sympathetic stimulation increasing heart rate and respiratory rate, and vasoconstricting the vessels (arterioles and veins) to increase BP.

5. Autoregulation
The Renin-angiotensin-aldosterone (RAA) system is an important endocrine component of autoregulation.
Renin is released by kidneys when blood
volume falls or blood flow decreases.
It is subsequently converted into the active
hormone angiotensin II which raises BP
by vasoconstriction and by stimulating
secretion of aldosterone from the
adrenal glands.

6. Autoregulation
Epinephrine and norepinephrine are also released from the adrenal medulla as an endocrine autoregulatory response to sympathetic stimulation.
They increase cardiac output by increasing rate and force of heart contractions.
Antidiuretic hormone (ADH) is released from the posterior pituitary gland in response to dehydration or decreased blood volume.

7. Autoregulation
Atrial Naturetic Peptide (ANP) is a natural diuretic polypeptide hormone released by cells of the cardiac atria.
ANP participates in autoregulation by:
Lowering blood pressure (it causes a direct vasodilation)
Reducing blood volume (by promoting loss of salt and water as urine)

8. Circulation
In an autoregulatory response, important differences exist between the pulmonary and systemic circulations:
Systemic blood vessel walls dilate in response to hypoxia (low O2) or acidosis to increase blood flow.
The walls of the pulmonary blood vessels constrict to a hypoxic or acidosis stimulus to ensure that most blood flow is diverted to better ventilated areas of the lung.

9. Circulation
A measure of peripheral circulation can be done by checking the pulse. The pulse is a result of the alternate expansion and recoil of elastic arteries after each systole.
It is strongest in arteries closest to the heart and becomes weaker further out.
Normally the pulse
is the same as
the heart rate.

10. Circulation
Blood pressure is the pressure in arteries generated by the left ventricle during systole and the pressure remaining in the arteries when the ventricle is in diastole.

11. Alterations Of Blood Pressure
About 50 million Americans have hypertension (HTN).
It is the most common disorder
affecting the CV system
and is a major cause of
atherosclerotic vascular
disease (ASVD), heart
failure, kidney disease
and stroke.

12. Alterations Of Blood Pressure
Hypertension is defined as an elevated systolic blood
pressure (SBP), an elevated diastolic blood pressure (DBP), or both. Depending on severity, it is classified as pre-hypertension, Stage 1 HTN, or stage 2 HTN.

13. Alterations Of Blood Pressure
Hypotension is defined as any blood pressure too low to allow sufficient blood flow (hypo-perfusion) to meet the body's metabolic demands (to maintain homeostasis).
Many persons, especially some thin, young women, have very low BP, yet experience no dizziness, fatigue, or other symptoms – they are not hypotensive, and in fact are probably very healthy (cardiovascular wise).
Hypotension leading to hypo-perfusion (pressure and flow are related) of critical organs results in shock

14. Shock And Homeostasis The 4 basic types of shock are:
Hypovolemic shock, due to decreased blood volume
Cardiogenic shock, due to poor heart function
Obstructive shock, due to obstruction of blood flow
Vascular shock, due to excess vasodilation - as seen in cases of a massive allergy (anaphylaxis) or sepsis. In the U.S., septic shock causes >100,000 deaths/yr. and is the most common cause of death in hospital critical care units.

15. Shock And Homeostasis
The same negative feedback mechanism discussed in autoregulation of blood pressure/flow is activated to restore blood and nutrient flow in cases of shock.
Heart will respond with  rate and force of contraction.
Selective tissue beds will vasoconstrict to shunt blood flow to those tissue most necessary to life (brain).
The other neural, hormonal, and chemical pathways will be recruited to restore balance.

16. The body responds via negative feedback to restore homeostasis
Shock and Homeostasis
Heart rate & force increase
Vasoconstriction or vasodilation depending on type of shock
ADH released  conserve water
Renin released  Angiotensin II
Aldosterone released  conserve Na+
ANP inhibited
The body responds via negative feedback to restore homeostasis

17. Shock And Homeostasis
Most cases of shock call for the administration of extra fluids and emergency medications like epinephrine to help restore perfusion to the tissues.
If the body is not able to do this
quickly, with or without
outside help, organs will fail
(kidney failure, liver failure,
coma) and damage may
become permanent.
Remind students that perfusion is blood flow.

18. Circulatory Routes
Blood vessels are organized into circulatory routes that carry blood to specific parts of the body.
The pulmonary circulation leaves the right heart to allow blood to be re-oxygenated and to off-load CO2.
The systemic circulation leaves the left side of the heart to supply the coronary, cerebral, renal, digestive and hepatic circulations (among others). The bronchial circulation provides oxygenated blood to the lungs, not the pulmonary circulation, which oxygenates blood!

19. Systemic Circulation - Arteries
Aorta (one)
Brachiocephalic (one)
Common Carotid
External Carotid
Internal Carotid
Subclavian
Axillary
Brachial
Radial
Ulnar
Bronchial (usually 3)
Renal
Iliac (common, internal, external)
Femoral
Popliteal

20. Systemic Circulation - Arteries

21. Systemic Circulation - Arteries

22. Systemic Circulation - Arteries

23. Systemic Circulation - Arteries

24. Systemic Circulation - Veins
Vena Cava
Brachiocephalic (two)
External Jugular
Internal Jugular
Subclavian
Axillary
Brachial
Median Cubital
Iliac (common, internal, external)
Femoral
Popliteal
Saphenous
Hepatic portal

25. Systemic Circulation - Veins

26. Systemic Circulation - Veins

27. Systemic Circulation - Veins

28. Systemic Circulation - Veins

29. Portal Circulation
The hepatic portal system is designed to take nutrient- rich venous blood from the digestive tract capillaries, and transport it to the sinusoidal capillaries of the liver.
As it percolates through the liver sinusoids, the hepatocytes of the liver, acting as the chemical factories of the body, extract and add what they wish to maintain homeostasis (extracting sugars, fats, proteins when appropriate and then dumping them back into the circulation when necessary).

30. Portal Circulation

31. Fetal Circulation
The fetus has special circulatory requirements because their lungs, kidneys and GI tract are non-functional.
The fetus derives its oxygen and
nutrients and eliminates wastes
through the maternal blood supply
by way of the placenta. Normally,
there is no maternal/fetal mixing;
the fetus is totally dependant on
capillary exchange.

32. Fetal Circulation
Oxygenated blood leaves the placenta through the umbilical vein. It then bypasses the liver via the ductus venosus and dumps into the inferior vena cava en route to the right heart.
This oxygen-rich blood then
bypasses the lungs by
traveling to the left heart
through the foramen ovale.

33. Fetal Circulation
Blood remaining in the right heart that manages to flow through the right ventricle meets with very high resistance from the closed and soggy lungs.
This blood is diverted into the
left-sided circulation by passing
through the ductus
arteriosus before returning
to the placenta via the
umbilical arteries.

34. Fetal circulation (before birth)

35. Neonatal Circulation After Birth
At birth, the neonate’s lungs open and in just a few seconds, there is a massive drop in pulmonary vascular resistance.
Blood now entering the right heart now sees lower pressure looking into the lungs and has no “incentive” to flow through the foremen ovale or the ductus arteriosus.
Another change also occurs very rapidly - the umbilical cord is severed.
And so begins the adult pattern of blood flow.

36. Neonatal Circulation After Birth
Within hours, days, or weeks after birth, the umbilical vein atrophies to become the ligamentum teres.
The ductus venosus atrophies to become the ligamentum venosum.
The foramen ovale becomes the closed fossa ovale.
The ductus arteriosus atrophies to become the ligamentum arteriosum.
Umbilical arteries atrophy to become the medial umbilical ligaments.

37. Neonatal Circulation After Birth

38. End of Chapter 21
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