Week 9 - Cardiovascular

The [blank_start]right side of the heart[blank_end] pumps blood to the lungs (the [blank_start]Pulmonary circulation[blank_end]) where gas exchange occurs, ie. the blood collect oxygen from the airsacs and excess carbon dioxide diffuses into the airsacs for [blank_start]exhalation[blank_end]. The [blank_start]left side of the heart[blank_end] pumps blood into the [blank_start]systemic circulation[blank_end], which supplies the rest of the body. Here, [blank_start]tissue wastes[blank_end] are passed into the blood for excretion, and body cells extract nutrients and oxygen.

The right side of the heart pumps blood to the lungs (the Pulmonary circulation) where gas exchange occurs, ie. the blood collect oxygen from the airsacs and excess carbon dioxide diffuses into the airsacs for exhalation. The left side of the heart pumps blood into the systemic circulation, which supplies the rest of the body. Here, tissue wastes are passed into the blood for excretion, and body cells extract nutrients and oxygen.

The left side of the heart pumps blood to the lungs (the Pulmonary circulation) where gas exchange occurs, ie. the blood collect oxygen from the airsacs and excess carbon dioxide diffuses into the airsacs for exhalation.

Should the supply of oxygen and nutrients to body cells become inadequate ....

Arteries and Arteriorioles transport blood away from the heart. Their walls consist of three layers of tissue - an outer layer of fibrous tissue, middle layer of smooth muscle and elastic tissue and an inner lining called endothelium.

Arteries have thicker walls than veins to withstand the high pressure of arterial blood.

The smallest arterioles break up into a number of minute vessels called...

Capillary walls consist of a single layer of endothelial cells sitting on a very thin basement membrane.

Capillary walls consist of a single layer of fibrous tissue sitting on a very thin basement membrane.

The capillary bed is the site of exchange of substances between the blood and the tissue fluid, which bathes the body cells and, with the exception of those on the skin surface and in the cornea of the eye, every body cell lies close to a capillary.

In certain places, including the Liver and bone marrow, the capillaries are significantly wider and leakier than normal. These are called Sinusoids and because their walls are incomplete and their lumen is much larger than usual, blood flows through them more slowly under less pressure and can come directly into contact with the cells outside the sinusoid wall. This allows must faster exchange of substances between the blood and the tissues.

Capillary refill - when the skin is pressed firmly with a finger, which turns white because the blood in the capillaries under the finger has been squeezed out. A prolonged capillary refill time can suggest poor perfusion or dehydration.

Veins return blood at [blank_start]low[blank_end] pressure to the heart. The walls of the veins are [blank_start]thinner[blank_end] than arteries but have the same three layers of [blank_start]tissue[blank_end]. They are thinner because there is less [blank_start]muscle and elastic tissue[blank_end] in the [blank_start]tunica media[blank_end] as veins carry blood at a lower pressure than [blank_start]arteries[blank_end].

Some veins possess valves, which prevent backflow of blood, ensuring that it flows towards the heart.

[blank_start]Valves[blank_end] are abundant in the veins of the limbs, especially the [blank_start]lower limbs[blank_end] where blood must travel a considerable distance against [blank_start]gravity[blank_end] when the individual is [blank_start]standing[blank_end].

Vascular capacitance refers to degree of active constriction of vessels (mainly veins) which affects return of blood to the heart and thus cardiac output.

Veins are called [blank_start]capacitance vessels[blank_end] because they are distensible, and therefore have the capacity to hold a [blank_start]large proportion[blank_end] of the body's blood. At any one time, about [blank_start]two-thirds[blank_end] of the body's blood is in the venous system. This allows the vascular system to absorb sudden changes in blood [blank_start]volume[blank_end].

At any one time, about one-third of the body's blood is in the venous system. This allows the vascular system to absorb sudden changes in blood volume.

Thin-walled blood vessels receive oxygen and nutrients via....

The smooth muscle of the tunica media of veins and arteries is supplied by nerves of the autonomic nervous system. These nerves arise from the ....

Blood vessel diameter is regulated by the smooth muscle of the tunica media, which is supplied by sympathetic nerves of the autonomic nervous system.

Constant adjustment of blood vessel diameter helps to regulate peripheral resistance of systemic blood pressure.

Oxygen is carried from the lungs to the tissues in combination with ....

Blood transports carbon dioxide to the lungs for excretion by three different mechanisms:

The [blank_start]nutrients[blank_end] including glucose, amino acids, fatty acids, vitamins and mineral salts required by all body cells are transported round the body in the [blank_start]blood plasma[blank_end]. They [blank_start]diffuse[blank_end] through the [blank_start]semi-permeable[blank_end] capillary walls in the tissues. Water exchanges [blank_start]freely[blank_end] between the plasma and tissue fluid by osmosis.

The two main forces determining overall fluid movement across the capillary wall are the [blank_start]hydrostatic pressure[blank_end] (blood pressure), which tends to push fluid [blank_start]out[blank_end] of the blood stream, and the [blank_start]osmotic pressure[blank_end] of the blood, which tends to [blank_start]pull it[blank_end] back in, and is due mainly to the prescence of plasma proteins, especially albumin.

The [blank_start]Heart[blank_end] lies in the [blank_start]thoracic[blank_end] cavity in the [blank_start]mediastinum[blank_end] (the space between the lungs). It lies [blank_start]obliquely[blank_end], a little more to the [blank_start]left[blank_end] than the [blank_start]right[blank_end], and presents a base [blank_start]above[blank_end], and an apex [blank_start]below[blank_end].

The heart wall is composed of three layers of tissue -

The [blank_start]Pericardium[blank_end] is the [blank_start]outermost[blank_end] layer and is made up of [blank_start]two[blank_end] sacs. The outer sac (the [blank_start]fibrous[blank_end] pericardium) consists of [blank_start]fibrous tissue[blank_end] and the inner (the [blank_start]serous[blank_end] pericardium) of a continuous double layer of [blank_start]serous membrane[blank_end].

The Myocardium is composed of specialised cardiac muscle found only in the heart. It is striated, like skeletal muscle, but it is not under voluntary control.

Endocardium lines the [blank_start]chambers and valves[blank_end] of the heart. It is a thin, smooth [blank_start]membrane[blank_end] to ensure [blank_start]smooth flow[blank_end] of blood through the heart. It consists of [blank_start]endothelial cells[blank_end] and it is continuous with the endothelium lining the [blank_start]blood vessels[blank_end].

The heart is divided into a right and left side by the septum, a partition consisting of myocardium covered by endocardium.

Each side of the heart is divided by an atrioventricular valve into the upper atrium and the ventricle below.

Each side of the heart is divided by an [blank_start]atrioventricular valve[blank_end] into the upper [blank_start]atrium[blank_end] and the [blank_start]ventricle[blank_end] below. The right atrioventricular valve is called the [blank_start]tricuspid valve[blank_end], and the left atrioventricular valve is called the [blank_start]mitral valve[blank_end].

Each side of the heart is divided by an atrioventricular valve into the upper atrium and the ventricle below. The right atrioventricular valve is called the tricuspid valve, and the left atrioventricular valve is called the mitral valve.

The valves between the atria and ventricles open and close passively according to changes in pressure in the chambers. They open when the pressure in the atria is greater than that in the ventricles.

The valves between the atria and ventricles open and close [blank_start]passively[blank_end] according to changes in pressure in the [blank_start]chambers[blank_end]. They open when the pressure in the atria is [blank_start]greater[blank_end] than that in the ventricles.

The two largest veins of the body, the superior and inferior vena cava, empty their contents into the right atrium.

Blood passes through the [blank_start]Right Atrioventricular valve[blank_end] into the [blank_start]Right Ventricle[blank_end], and from there is pumped into the [blank_start]Pulmonary Artery[blank_end]. The opening of the [blank_start]Pulmonary[blank_end] Artery is guarded by the [blank_start]Pulmonary Valve[blank_end], which prevents the [blank_start]backflow[blank_end] of blood into the right ventricle when the ventricular muscle [blank_start]relaxes[blank_end], After leaving the heart, the pulmonary artery divides into left and right pulmonary artieries, which carry the [blank_start]venous blood[blank_end] to the lungs where exchanges of gases take place: [blank_start]carbon dioxide[blank_end] is excreted and [blank_start]oxygen[blank_end] is absorbed.

The vagus nerve supplies mainly the SA and AV nodes and atrial muscle.

[blank_start]Sympathetic[blank_end] nerves supply the SA and AV [blank_start]nodes[blank_end] and the [blank_start]myocardium[blank_end] of atria and ventricles, and stimulation increases the [blank_start]rate and force[blank_end] of the heartbeat.

At rest, the healthy adult heart is likely to beat at a rate of

Stages of the cardiac cycle - 1. [blank_start]Atrial Systole[blank_end] - contraction of the atria 2. [blank_start]Ventricular systole[blank_end] - contraction of the ventricles 3. [blank_start]Complete cardiac diastole[blank_end] - relaxation of the atria and ventricles

A faster heart rate is called [blank_start]Tachycardia[blank_end] A slower heart rate is [blank_start]Bradycardia[blank_end]

The cardiac output is the amount of blood ejected from each ventricle every minute.

The [blank_start]cardiac output[blank_end] is the amount of blood ejected from each ventricle every minute. The amount expelled by each contraction of each ventricle is the [blank_start]stroke volume[blank_end].

[blank_start]Cardiac input[blank_end] = [blank_start]Stroke Volume[blank_end] x Heart Rate

The stroke volume is determined by the volume of blood in the ventricles immediately before they contract.