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Diastole accounts for approximately two-thirds of the cardiac cycle, during which the heart muscle relaxes and allows the chambers to fill with blood. This phase is crucial for maintaining adequate blood flow and pressure throughout the body.
The usual range for mean arterial pressure (MAP) is between 70-110 mmHg. A MAP of at least 60 mmHg is necessary to ensure adequate perfusion of vital organs such as the coronary arteries, brain, and kidneys.
The heart, blood vessels, and kidneys work together through a finely-tuned system regulated by the brain. This cooperation involves adjusting cardiac output, peripheral resistance, and blood volume to maintain stable blood pressure.
The cardiovascular center in the medulla oblongata regulates blood pressure by integrating neural and hormonal signals to adjust heart rate, blood vessel diameter, and blood volume, thereby maintaining homeostasis.
Short-term mechanisms include neural control through the autonomic nervous system and hormonal control involving substances like epinephrine and norepinephrine, which enhance sympathetic responses to increase blood pressure.
The adrenal medulla releases epinephrine and norepinephrine, which enhance the sympathetic response, leading to increased heart rate and vasoconstriction, thereby raising blood pressure.
Renin is an enzyme released by the kidneys that initiates a cascade leading to the production of angiotensin II, which promotes vasoconstriction and stimulates the release of aldosterone and ADH, ultimately increasing blood pressure.
Atrial natriuretic hormone (ANH), also known as atrial natriuretic peptide (ANP), acts as an antagonist to aldosterone, promoting sodium and water excretion by the kidneys, leading to vasodilation and a decrease in blood pressure.
The primary circuits of the cardiovascular system include pulmonary circulation, which carries blood to and from the lungs, and systemic circulation, which delivers oxygenated blood to the rest of the body.
In pulmonary circulation, deoxygenated blood is pumped from the right ventricle into the pulmonary artery, which divides into right and left branches leading to each lung. Blood travels through arteries, arterioles, and capillaries, where gas exchange occurs in the alveoli.
Colloid osmotic pressure is the force that draws fluid back into the capillaries from the surrounding tissue fluid, primarily due to plasma proteins. This process helps maintain blood volume and pressure.
Local regulation of blood flow is intrinsically controlled by modifying the diameter of local arterioles. Metabolic controls involve changes in oxygen, carbon dioxide, and metabolites that lead to vasodilation, while myogenic controls respond to changes in blood pressure.
Age-related changes in the cardiovascular system include sclerosis and thickening of valve flaps, a decline in cardiac reserve, increased variability in heart rate, fibrosis of cardiac muscle, and a higher risk of atherosclerosis due to inactivity, smoking, and poor diet.
The lymphatic system recovers approximately 10% of the fluid that is not reabsorbed by the capillaries, helping to maintain fluid balance in the body and prevent edema.
Metabolic controls lead to vasodilation in response to local increases in carbon dioxide, decreases in oxygen, and the presence of metabolites, ensuring that tissues receive adequate blood supply during increased metabolic activity.
Myogenic controls involve the response of vascular smooth muscle to changes in blood pressure; increased blood pressure causes constriction of blood vessels, while decreased blood pressure leads to dilation, helping to maintain consistent blood flow.
Veins have the same three tissue layers as arteries: the tunica intima (inner layer), tunica media (middle layer), and tunica externa (outer layer), although the structure and thickness of these layers differ between veins and arteries.
The foramen ovale is an opening between the right and left atria in the fetal heart that allows blood to bypass the non-functioning lungs, directing oxygenated blood from the placenta to the left atrium.
The ductus venosus is a blood vessel in fetal circulation that allows oxygenated blood from the umbilical vein to bypass the liver and flow directly into the inferior vena cava, facilitating efficient oxygen delivery to the fetus.
During exercise, the cardiovascular system responds by increasing heart rate, stroke volume, and cardiac output, while also redistributing blood flow to active muscles and enhancing oxygen delivery and nutrient supply.
Atherosclerosis develops when fatty deposits (plaques) build up in the arterial walls, leading to narrowed arteries and reduced blood flow. Risk factors include inactivity, smoking, high cholesterol diet, and stress.
Anatomy: Abundant in skin & muscle Most common Tight junctions between endothelial cells, leave small gaps (intercellular clefts) In brain, no gaps (blood-brain barrier) Physiology: Gaps just large enough to allow limited passage of fluids/solute
Anatomy: Similar to continuous Some endothelial cells have pores (fenestrations) Found wherever active absorption/filtration occurs Physiology: More permeable to fluids & small solutes
Anatomy: Very leaky capillaries (liver, bone marrow, spleen & adrenal medulla) Tortuous (windy) path In liver-hepatic macrophages (Kupffer cells), in spleen, phagocytes Physiology: Slows flow of blood Allows larger molecules and blood cells to pass Remove & destroy pathogens
arteriovenous anastomosis (alternate pathway)
Metarteriole: b/w terminal arteriole and capillary bed Thoroughfare channel: b/w capillary bed and postcapillary venule
blood flow regulated by precapillary sphincters allows routing of blood where most needed
Simple diffusion (across lipid bilayer) 02 and CO2 Via intercellular clefts/fenestrations small water-soluble solutes (amino acids, sugars) Via Pinocytotic vesicles/caveolae larger molecules (proteins)
Hydrostatic pressure - pushes fluid Causes filtration of plasma into tissue Leaves behind cells and most proteins Colloid osmotic pressure - sucks fluid Water in tissue fluid is drawn back into vessels via osmosis Plasma proteins draw fluid back into blood as capillaries approach venules (~90%) Remaining fluid is recovered by lymphatic system (~10%)
Metabolic controls Local changes in O2 / CO2 and metabolites lead to increase in nitric oxide (NO) = vasodilation Endothelium release endothelins (peptides) which cause vasoconstriction Myogenic controls vascular smooth muscle response to changes in BP increased BP = constriction decreased BP = dilation
In veins: endothelium is folded at intervals to form one-way valves (resemble semilunar valves) thinner smooth muscle and connective tissue
Systemic BP is highest in aorta and declines throughout the pathway to reach ~ 0 mm Hg in R atrium
Capillaries
MAP of 60
Baroreceptor-Initiated: stretch receptors in carotid-sinus/aortic arch signal vasomotor/cardiac centers in medulla in response to increased or decreased BP Chemoreceptor-Initiated: chemoreceptors in same areas also signal vasomotor/cardiac center in medulla: in response to decreased O2, increased CO2 or increased H+ Higher Brain Ctrs: can modify arterial pressure via relays to medullary ctrs
Adrenal Medulla: Epinephrine/Norepinephrine – enhance sympathetic response BP increases Kidneys: Renin – generates angiotensin II which promotes vasoconstriction (short-term) and stimulates release of aldosterone and ADH (long-term) BP increases Heart: ANH (atrial natriuretic hormone) aka ANP: atrial natriuretic peptide antagonist to aldosterone kidneys excrete more Na+/H20 causes general vasodilation, BP decreases Hypothalamus: ADH – kidneys conserve H2O
control BP, long-term, by altering blood volume
Direct Renal Mechanism: increased blood volume/BP -> increased filtration in kidneys (cannot process quickly enough) -> more urine leaves body -> BP decreases Indirect Renal Mechanism: Renin-Angiotensin Mechanism: decreased BP -> kidneys release renin -> production of Angiotensin II -> increases BP in 3 ways: Vasoconstriction Stimulates Adrenal Cortex to produce aldosterone Stimulates Post. Pituitary to release ADH
includes Hepatic Portal Circulation (digestive) and Coronary (heart)
Fetus dependent on mother for O2/nutrients & removal of CO2/waste products
Diffusion & active transport