Chapter 21

glossopharyngeal (IX) nerves

Nerve impulses propagate from the carotid sinus baroreceptors over sensory axons in the glossopharyngeal (IX) nerves to the cardiovascular center in the medulla oblongata.

vagus (X) nerves

Nuclei in the medulla receive sensory impulses from and provide motor impulses to the pharynx and larynx and many thoracic and abdominal viscera via the vagus nerves.

Diffusion

The most important method of capillary exchange is simple diffusion. Many substances, such as oxygen (O2), carbon dioxide (CO2), glucose, amino acids, and hormones, enter and leave capillaries by simple diffusion. Because O2 and nutrients normally are present in higher concentrations in blood, they diffuse down their concentration gradients into interstitial fluid and then into body cells. CO2 and other wastes released by body cells are present in higher concentrations in interstitial fluid, so they diffuse into blood.

Baroreceptors in the wall of the ascending aorta and arch of the aorta initiate the _____________, which regulates systemic blood pressure. Nerve impulses from aortic baroreceptors reach the cardiovascular center via sensory axons of the ________________.

aortic reflex vagus (X) nerves

sinusoids

are wider and more winding than other capillaries. Their endothelial cells may have unusually large fenestrations. In addition to having an incomplete or absent basement membrane, sinusoids have very large intercellular clefts that allow proteins and in some cases even blood cells to pass from a tissue into the bloodstream.

vascular resistance is the opposition to blood flow due to friction between blood and the walls of blood vessels. Vascular resistance depends on

(1) size of the blood vessel lumen (2) blood viscosity (3) total blood vessel length.

Besides the heart, two other mechanisms "pump" blood from the lower body back to the heart:

(1) the skeletal muscle pump and (2) the respiratory pump. Both pumps depend on the presence of valves in veins.

Blood colloid osmotic pressure (BCOP)

-Equals pressure required to prevent osmosis. -Caused by suspended blood proteins that are too large to cross capillary walls.

Hormonal Regulation of Blood Pressure

-Renin-angiotension-aldostrone system -Epinephrine and norepinephrine -Antidiuretic hormone -Parathyroid hormone

The skeletal muscle pump operates as follows

1)While you are standing at rest, both the venous valve closer to the heart (proximal valve) and the one farther from the heart (distal valve) in this part of the leg are open, and blood flows upward toward the heart. 2)Contraction of leg muscles, such as when you stand on tiptoes or take a step, compresses the vein. The compression pushes blood through the proximal valve, an action called milking. At the same time, the distal valve in the uncompressed segment of the vein closes as some blood is pushed against it. People who are immobilized through injury or disease lack these contractions of leg muscles. As a result, their venous return is slower and they may develop circulation problems. 3)Just after muscle relaxation, pressure falls in the previously compressed section of vein, which causes the proximal valve to close. The distal valve now opens because blood pressure in the foot is higher than in the leg, and the vein fills with blood from the foot. The proximal valve then re

blood hydrostatic pressure (BHP)

BHP "pushes" fluid out of capillaries into interstitial fluid.

Types of shock

Hypovolemic cardiogenic shock vascular shock obstructive shock

epinephrine and norepinephrine

In response to sympathetic stimulation, the adrenal medulla releases epinephrine and norepinephrine. These hormones increase cardiac output by increasing the rate and force of heart contractions. They also cause vasoconstriction of arterioles and veins in the skin and abdominal organs and vasodilation of arterioles in cardiac and skeletal muscle, which helps increase blood flow to muscle during exercise.

Atrial natriuretic peptide (ANP)

Released by cells in the atria of the heart, atrial natriuretic peptide (ANP) lowers blood pressure by causing vasodilation and by promoting the loss of salt and water in the urine, which reduces blood volume.

blood viscosity

The viscosity, of blood depends mostly on the ratio of red blood cells to plasma (fluid) volume, and to a smaller extent on the concentration of proteins in plasma. The higher the blood's viscosity, the higher the resistance. Any condition that increases the viscosity of blood, such as dehydration or polycythemia (an unusually high number of red blood cells), thus increases blood pressure. A depletion of plasma proteins or red blood cells, due to anemia or hemorrhage, decreases viscosity and thus decreases blood pressure.

Renin-angiotensin-aldosterone (RAA) system

When blood volume falls or blood flow to the kidneys decreases, juxtaglomerular cells in the kidneys secrete renin into the bloodstream. In sequence, renin and angiotensin-converting enzyme (ACE) act on their substrates to produce the active hormone angiotensin II , which raises blood pressure in two ways. First, angiotensin II is a potent vasoconstrictor; it raises blood pressure by increasing systemic vascular resistance. Second, it stimulates secretion of aldosterone, which increases reabsorption of sodium ions (Na+) and water by the kidneys. The water reabsorption increases total blood volume, which increases blood pressure. (See

Systemic Vascular Resistance (SVR)

also known as total peripheral resistance (TPR), refers to all of the vascular resistances offered by systemic blood vessels. The diameters of arteries and veins are large, so their resistance is very small because most of the blood does not come into physical contact with the walls of the blood vessel.

Sympathetic impulses reach the heart via the ____________________. An increase in sympathetic stimulation increases heart rate and contractility; a decrease in sympathetic stimulation decreases heart rate and contractility.

cardiac accelerator nerves

If blood flow stops for a short time when normal movements compress a vessel, or if a vessel is blocked by disease, injury, or surgery, then circulation to a part of the body is not necessarily stopped. The alternative route of blood flow to a body part through an anastomosis is known as_______________

collateral circulation

filtration pressure (NFP)

determines whether the volumes of blood and interstitial fluid remain steady or change

hypovolemic shock

due to decreased blood volume

vascular shock

due to inappropriate vasodilation

obstructive shock

due to obstruction of blood flow

cardiogenic shock

due to poor heart function

interstitial fluid hydrostatic pressure (IFHP)

force exerted by the fluid in the tissue spaces -pushes" fluid from interstitial spaces back into capillaries. However, IFHP is close to zero. (IFHP is difficult to measure, and its reported values vary from small positive values to small negative values.) For our discussion we assume that IFHP equals 0 mmHg all along the capillaries.

cardiovascular (CV) center

in the medulla oblongata helps regulate heart rate and stroke volume. The CV center also controls neural, hormonal, and local negative feedback systems that regulate blood pressure and blood flow to specific tissues. Groups of neurons scattered within the CV center regulate heart rate, contractility (force of contraction) of the ventricles, and blood vessel diameter.

A vascular (venous) sinus

is a vein with a thin endothelial wall that has no smooth muscle to alter its diameter. In a vascular sinus, the surrounding dense connective tissue replaces the tunica media and tunica externa in providing support.

Antidiuretic hormone (ADH). Antidiuretic hormone (ADH)

is produced by the hypothalamus and released from the posterior pituitary in response to dehydration or decreased blood volume. Among other actions, ADH causes vasoconstriction, which increases blood pressure. For this reason ADH is also called vasopressin. ADH also promotes movement of water from the lumen of kidney tubules into the bloodstream. This results in an increase in blood volume and a decrease in urine output.

aortic reflex

maintains BP in systemic circuit

At the metarteriole-capillary junction, the distal-most muscle cell forms the _________________

precapillary sphincter

vasomotor tone

produced by constant action of sympathetic vasoconstrictor nerves

interstitial fluid osmotic pressure (IFOP)

pulls fluid out of capillaries into interstitial fluid -Opposing BCOP is interstitial fluid osmotic pressure (IFOP), which "pulls" fluid out of capillaries into interstitial fluid. Normally, IFOP is very small—0.1-5 mmHg—because only tiny amounts of protein are present in interstitial fluid.

Hemodynamics

refers to the forces involved in circulating blood throughout the body. Blood flow is the volume of blood that flows through any tissue in a given time period (in mL/min). Total blood flow is cardiac output (CO), the volume of blood that circulates through systemic (or pulmonary) blood vessels each minute.

Chemoreceptors

respond to chemicals

Chemoreceptor Reflexes

sensory receptors that monitor the chemical composition of blood, are located close to the baroreceptors of the carotid sinus and arch of the aorta in small structures called carotid bodies and aortic bodies, respectively. These chemoreceptors detect changes in blood level of O2, CO2, and H+. Hypoxia (lowered O2 availability), acidosis (an increase in H+ concentration), or hypercapnia (excess CO2) stimulates the chemoreceptors to send impulses to the cardiovascular center.

Net Filtration Pressure (NFP)

the difference between net hydrostatic pressure and net osmotic pressure

Transcytosis

transport into, across, and then out of cell -A small quantity of material crosses capillary walls by transcytosis . In this process, substances in blood plasma become enclosed within tiny pinocytic vesicles that first enter endothelial cells by endocytosis, then move across the cell and exit on the other side by exocytosis.

Parasympathetic stimulation, conveyed along the ____________________, decreases heart rate. Thus, opposing sympathetic (stimulatory) and parasympathetic (inhibitory) influences control the heart.

vagus (X) nerves

Tunica Externa

vasa vasorum

Tunica Media The tunica media

vasoconstriction vasodilation

The cardiovascular center also continually sends impulses to smooth muscle in blood vessel walls via ___________________. These sympathetic neurons exit the spinal cord through all thoracic and the first one or two lumbar spinal nerves and then pass into the sympathetic trunk ganglia

vasomotor nerves

Elastic Arteries Elastic arterie

well-defined internal and external elastic laminae, along with a thick tunica media that is dominated by elastic fibers, called the elastic lamellae